Proceedings of National Seminar on Etdg-12

Proceedings of National Seminar on

EMERGING TRENDS IN DISTRIBUTED GENERATION

ETDG – 2012 13th October 2012

Organized by: Northern India Engineering College

(Babu Banarasi Das Group of Educational Institution) Department of Electrical & Electronics Engineering

FC-26 Shastri Park, New Delhi – 53 Ph: 011 – 22854321, 22854633

NBA Accredited & AICTE approved

Affiliated to GGSIP University, New Delhi. ISO 9001:2008 & EN ISO 14001:2004 Certified Institute

Declaration

“All data, views, opinion etc, being published are the sole responsibility of the authors and neither

the publisher nor the organizer of the Seminar is anyway responsible for them”

Proceeding of National Seminar on Emerging Trends in Distributed Generation

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Organizing Committee

Chief Patron

Dr. Akhilesh Das Gupta (Chairman) Mrs Alka Das Gupta, (Vice Chairperson)

Patron

Mr. S.N.Garg, CEO, NIEC

Seminar Chairperson Prof. (Dr.) S.C. Gupta, Director, NIEC

Seminar Convener

Mrs. Anuradha Tomar, Department Electrical & Electronics, NIEC

Seminar Co-convener

Mr. Deepak Thakur, EEE, NIEC

Technical Committee Mr. Ajit Sharma, HOD (EEE), Member

Mrs. Trina Som, Member Mr. Rahul Pathak, Member Mrs. Monika Dubey, Member Mr. Manas Taneja, Member

Mr. Vikasdeep, Member Mrs. Shweta Singh, Member Mr. Mohit Katiyar, Member Ms. Vandana Arora, Member Ms. Monika Gupta, Member

Editorial Board Prof. (Dr.) S.C.Gupta Mrs. Anuradha Tomar Mr. Deepak Thakur


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Speakers

Prof. (Dr.) D. K. Jain Electrical Engineering Department, Deenbandhu Chhotu Ram University,

Murthal (Sonipat), India.

Dr. Yog Raj Sood Professor (Electrical Engineering) &

Dean R & C (Research and Consultancy) National Institute of Technology,

Hamirpur (H.P), India.

Prof. (Dr.) Narendra Kumar, Head of Electrical Engineering Department,

Delhi Technical University, New Delhi, India.

Prof. (Dr.) Tanmey Dev Head of Electrical Engineering Department,

KIIT, Gurgaon, India.


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Editorial Board We are pleased to present proceeding of one day’s National Seminar on Emerging Trends in Distributed Generation. The objective of the seminar is to bring together leading researchers and developers from electrical power system for discussion on distributed generation. It also aims to promote the research and practice of new strategies, tools, techniques and technologies for the design, development and implementation of distributed generation. This seminar identifies issues that must be addressed to design the controls for such inertial less sources and suggests how these issues can be solved. Distributed generation could have a large role to play in the future of electricity systems in terms of both supply and use. The seminar covered the basics of interconnected distributed generation technologies that provide the exchange of ideas and its related research areas that all the participants are involved is gained. The researchers may interact and create new ideas concerning future work. Common research programmes can be created based on the complement work of the participants. The present volume is the compilation of some good papers selected by technical committee. We are of the view that this seminar would highlight many new frontiers of knowledge and provide ideas of research. We wish to thanks to the management to the management Authority and various faculty members of Northern India Engineering College, New Delhi, and to those who have directly or indirectly helped us to prepare case studies in various new emerging technologies. We look forward to suggestions from all sections of researchers, practioners, student and delegates to make this endeavor fruitful for all. Mrs. Anuradha Tomar Mr. Deepak Thakur Prof. (Dr.) S. C. Gupta Convener Co-convener Chairperson


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Message form Hon'ble Chairman, BBDGEI Desk The maturity of a technical college is reflected in the seminars, Seminars, publications and other such academic events conducted by the institution. I am happy to see the maturing of our institute's academic and research environment, with the National Seminar “ETDG - 2012” on 'Emerging Trends on Distributed Generation”, adding more rich colors to our institute's vibrant academic canvas. NIEC has a rich tradition of perusing academic excellence, value based education and providing a conductive environment foe overall personality development of the student. I hope that this national seminar offers an excellent opportunity to the participants to deliberate on this important theme, which would no doubt help in extending the opportunities offered by Distributed Generation for the benefit of mankind. I congratulate the C.E.O, Director, Head of EEE department and their entire team for making the event a resounding success. Dr. Akhilesh Das Gupta Chairman BBDGEI


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Message from the Hon'ble Vice Chairperson Desk

The organization of such a high level National Seminar by Northern India Engineering College, New Delhi, is a huge achievement and is taking place at a very appropriate time. Moreover the subjects being taken up in the National Seminar are of great current interest and relevance. It reflects the intense commitment of NIEC to constantly update the intense environment and engineering skills of its students and faculty. Distributed generation (or DG) generally refers to small-scale (typically 1 kW – 50 MW) electric power generators that produce electricity at a site close to customers or that are tied to an electric distribution system. Distributed generators include, but are not limited to synchronous generators, induction generators, reciprocating engines, microturbines (combustion turbines that run on high-energy fossil fuels such as oil, propane, natural gas, gasoline or diesel), combustion gas turbines, fuel cells, solar photovoltaics, and wind turbines. The papers being presented reflect the interest of the scholars in Distributed Generation and various technologies involved at all levels. Some of the research topics that are being taken up in the seminar are the net metering, wavelet technique, power delivering system and information & communication technology in distributed generation. I extend my heartiest congratulations to the organizers and wish the Seminar a great success. Mrs. Alka Das Vice Chairperson BBDGEI


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Message from Chief Executive Officer, NIEC Desk

Distributed Generation is the one of the latest research area in the technological world today. The national Seminar on such an enticing topic, organized by Northern India Engineering College, New Delhi is an enlightening and revolutionary endeavor by the organization. The national Seminar will serve a step in the progress and advancement of Power Distribution and Generation. Distributed energy resources (distributed power) refers to a variety of small modular power generating technologies that can be combined with energy management and storage systems and used to improve the operations of the electricity delivery systems, whether or not these technologies are connected to an electric grid. Distributed energy resources support and strengthen the central-station model of electricity generation, transmission and distribution. Distributed power can assume a variety of forms. It can be as simple as installing a small electricity generator to provide back-up power at an electricity consumer site. On the other hand it can be a more complex system highly integrated with the electricity grid and comprising electricity generation, energy storage and power management systems. The national Seminar is rightly intended to provide opportunity to the participants and delegates to upgrade their knowledge in Emerging Trends in Distributed Generation. This ETDG – 2012 bring into light all major issues of latest technology. We thank Babu Banarasi Das Educational Society for its immense support. We appreciate co-operation of students and faculty for their efforts to make this national Seminar a success. Sh. S N Garg CEO Northern India Engineering College

Proceedings of National Seminar on Emerging Trends in Distributed Generation

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Message from Director, NIEC Desk

It gives me great pleasure to announce that Northern India Engineering College, New Delhi is organizing a National Seminar on the topic of “Emerging Trends in Distributed Generation” on October 13th, 2012 in NIEC Campus. The Seminar is organized by the department of Electrical & Electronics Engineering to boost the benefits of Distributed Generation. The Seminar objectives is to bring eminent academicians, scholars, scientists, researchers, industrialists and experts from different technical domains to update their knowledge and explore new horizons in the field of information and network technology. It is heartening to note that Seminar is not only meeting the above objectives successfully but also putting forward research papers of different topics of Distributed Generation. I am sure the contributions in the form of research papers will enrich knowledge of all, who are participating in the Seminar and motivate every one of us to adapt to new challenges and applications areas for the development of new technology so that society, industry and the nation as a whole are benefitted. I congratulate the Seminar organizing team for their hard work and wish this National Seminar a great success and best of luck for their future endeavours. I am grateful to the Chief Patrons of the College for the financial support and cooperation extended to us for the successful conduction of the Seminar. Prof. (Dr.) S. C. Gupta Seminar Chair person and Director, NIEC, New Delhi.


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Message from Convener

At a time when Distributed Generation is capturing enormous interest from researchers and the industry itself, this national Seminar should be an essential part of your educational & professional development plans. The ETDG – 2012 Seminar takes a highly applied and practical focus. Due to increasing demand of Electricity and high transmission and distribution losses and cost, Distributed power generation is getting importance. It is thereby necessary to keep up with the latest trends, techniques and technologies for the design, development and implementation of Distributed generation. I would like to thank the patron, Hon’ble Dr. Akhilesh Das, Chairman, Hon’ble Alka Das, Chairperson, Northern India Engineering College, All India council of Technical Education for their support in organizing the national Seminar. I would also like to take this opportunity to congratulate the technical committee for having taken all the trouble to edit and accumulate the proceedings, along with their devoted team and brought out the same in such a short time. Delegates, themselves experts in their Power System fields, will contribute to debate and discussion along with our impressive array of national speakers. I shall also like to convey my deep appreciation to all the participants for their applause worthy efforts and quality papers. I wish the ETDG - 2012 team success in all future accomplishments.

Mrs. Anuradha Tomar Convener Northern India Engineering College


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Address by Chief Guest

In Conventional power system, the delivery of electricity to the customer is becoming a very difficult task because of increased demand. For this the power system has renewed interest in small scale electricity generation namely Distributed Generation. Nowadays, there is a strong focus on delivering power to the consumer in a reliable efficient and environment friendly manner, which is predicted to lead to increasing attention towards Distributed Generation Technologies, and gradual obsolescence of conventional power system. The transition of electric power industry from a regulated monopoly to a deregulated industry is in full swing. Properly plant and operated Distributed Generation can provide consumers and society with a wide variety of benefits, including economic savings, improved environmental performance and greater reliability. The upcoming technologies deal with challenges in both efficient and clean power generation and effective power delivery. Various renewable and non- conventional energy resources are promising candidates for efficient and clean power generation; while micro grid and smart grids are promising potential solution to the challenges of effective consumer friendly delivering of power. At last I want to say that Distributed Generation unlike traditional generation aims to generate part of required electrical energy on small scale. So, keeping the above issues in mind, let us make a small step in search of better power generation & distribution options for future, through this seminar.

Prof. H. C. Rai Director (Academics) GGSIP University


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Contents

LECTURES

S.No. Lecture Title Page No.

1 Role of Green Energy as Distributed Generation in Deregulated Power Sector

By - Dr. Y. R. Sood

1 - 9

TECHNICAL PAPERS

Paper Title

1 Damping Torsional Electromechanical oscillations in a Series Compensated Power System

By - Narendra Kumar, S.K. Agarwal, Upma Singh

10 - 19

2 Biomass Based Distributed Power Generation Current Status and Future Challenges.

By - Tanmoy Deb

20 – 26

3 Economic and Environmental Analysis of an Autonomous Power Delivery System Utilizing Hybrid Solar - Diesel - Electrochemical Generation

By - Trina Som, Shweta Singh, Akhil Sharma, Kushagar

27 – 33

4 A Topology Survey of Doubly-Fed Induction Generators for Wind Turbines

By –Rishu Goel, Amit Patel, Kamal Singh

34 – 40

5 Modelling and Simulation of Single Shaft Micro Turbine in Distributed Generation System

By - Ajit Kumar Sharma, Deepak Kumar Thakur

41 – 53


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6 A Review on Modelling& Analysis of Hybrid Fuel Cell Stack Model for Distributed Power Generation

By - Anjali Sharma, Nidhi Joshi, Yamini Vashishth, Amit Yadav

54 – 57

7 Applications of Wavelet Technique in Distributed Generation By - Rahul Pathak, Mohit Kumar Katiyar, Priya Banga

58 – 66

8 A Review on Distributed Generation By –Sharique Asir, Schrutir Jain, Majid Hussain

67 – 74

9 Distributed Generation in Rural India By - Devesh Singh

75 – 83

10 Review Paper on Basics of Net-Metering and Ideas to Promote Renewable Resources

By - Gaurav Gupta, Apurva Rajput, Amit Kumar

84 – 88

11 A Survey on Smart Grid By - Kritika Sharma, Swati Singh, Amit Kumar Yadav

89 – 93

12 Authentication Protocol for Distributed Sensor Network By - Amit Kumar, Sunil Gupta, Rashmi Sharma

94 – 102

13 Effects of Net Metering On The Use Of Small Scale Renewable Energy Sources Systems In Today’s World

By -Yagdeep Sharma

103 -107

14 A Detailed Review on Energy and Economic Aspects in Developing Smart GridTechnologies

By - Monika Dubey, Vandana Arora

108 – 115

15 Cost-effective Smart Metering for Home/Building using LDR Single-Channel Narrow-Band Power Line Communication

By – Ayush Sagar, Sumit Joshi

116 – 119


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16 Reactive Power Compensation Using Interline Power Flow Controller (IPFC) with 48 Voltage Source Converter

By - Neeru Devi, Vinesh Agarwal, Chandra Prakash Jain, Vinod Yadav

120 – 128

17 Review Paper on Smart Grid: Introduction, Technology used Merits and Demerits

By – Chandan Jayaswal, Rajat Gupta

129 – 135

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Distributed Generation: Issue and Approaches By – Anuradha Tomar, Sunil Gupta

136 – 140

19 Study of Distributed Generation Effectiveness in Power Grid Stability. By - Balwinder Singh Surjan

141 – 145

20 Information and Communication Technology in Distributed Generation Solutions By - Sunil Gupta, Anuradha Tomar

146 – 149

21 Series and Shunt FACTS Controllers in Power System: A Review By - Avinash, Sanjiv Kumar, Dushyant Gaur

150 – 155

22 Emerging Trends in Distributed Generation System By - Renu Sharma

156 – 158

23 Study and Characterization of reactive power in wind farm operation using MATLAB Simulink By – Tilak Thakur, Priya Sharma

159 - 162

24 Potential Benefits of Self-excited induction generator (SEIG) in Distribution Generation

By - Ahmed Riyaz, S P Singh, S K Singh

163 - 172


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Role of Green Energy as Distributed Generation in Deregulated Power Sector

Lecture by

Dr. Yog Raj Sood Professor, Department of Electrical Engineering

National Institute of Technology (N.I.T.) Hamirpur (HP)-177005, India Recent Power Trends

The energy is the prime mover of theeconomical and social growth as it is vital formaintaining

and developing a moderneconomy and society. Economical, social andenvironmental

sustainability are the mostimportant variables in the energy scenario ofthe 21stcentury. For socio-

economic developments, recentlymany large power plants are being installed inhilly/rural/remote

areas because of geographicalproblems.The deregulated powermarkets are bringing about the

uncertainevents and increasing the degree of uncertaintyin a power system. In addition to that,

theamount of loads such as heaters, airconditionersand industry load suddenly increase.The

challenge of supplying the nation with reliable, high quality electrical energy at a reasonable cost

is at the heart of a nation's economy. The electric power system is one of the oldest

infrastructures.

However, the demographics of power generation, transmission, and distribution are changing

dramatically in both the operating and business sector of the electric utility industry due to

deregulation of power industry.The Indian power sector is presently going through a processof

reform and restructuring as is the trend in many other partsof the world. Under reform,

independent regulatorycommissions are set up at center as well as state wise andvertically

integrated utilities are being unbundled intocorporate entities.The developments of the global

electricity industries are facing with many challenges. Thepower enterprises of the developed

and developing countries including India are alsofacing with massive challenges with the

increasing grid scale, grade and more complexstructure, along with the risk of safe and reliable

operation of power systems.In the India, the Distributed generation (DG) technologies are getting


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highly importance to solve the toughest energy crisis.At present India is fifth largest country

inthe world in electricity generation, having aggregate capacityof 203 GWs out of which 66% is

from thermal, 20% fromhydro, 2% from nuclear and the rest about 12% is fromrenewable energy

sources and one of the largest in the world.

Presently power industries are moving rapidly towards restructuring from fully regulated

conventional set up. In the modern restructured power industry, the role played by generation,

transmission and distribution in power sector are independent. In India, traditional integrated

power systems moving towards modern deregulated power system such as shown in figure 1.The

main objective of the deregulated power sector market is to decrease the cost of electricity

through competition. The market environment typically consists of a pool and privately

negotiated contracts. The performance of a market is measured by its social welfare, also called

social benefit. Social benefit is the difference of society’s willingness to pay for energy and its

cost.

Figure 1 Traditional integrated power systems moving towards modern deregulated power system

The need for more efficiency in power production and delivery has led to a restructuring

of the power sectors in several countries traditionally under control of federal and state

governments. Developed countries like India as well as other developing countries are also

considering the restructuring of their electricity power sector so as to introduce more competition

among producers and to offer more choices for customers.There is still a larger population in the

rural communities in India without access to proper lighting, clean water, and health care. India,


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total grid-connected renewable/green power generationcapacity of 23,129.40 MW has been

achieved till 31 January2012, which is about 12% of the total installed powergenerating capacity

in the country. It includes wind power of16,179.0 MW, small hydropower of 3,300.1 MW,

biomasspower of around 1,142.6 MW, and around 481.4 MW SolarPower as shown in figure 2.

Among the several renewable energy technologies available have the potential to meet the

electricity needs of rural communities in developing countries in view of the dispersed nature of

solar resource which makes PV and other systems adaptable to distributed power generation.

Renewable as green generation reduces system CO2 emissions, but the emissions of reserve

unitsrequired by lower renewable capacity factors must be included. The reductions in CO2

emissions are a complex calculation that includes generation characteristics (ramp ratesand cost

functions), transmission congestion, and the number of fossil-fired generatorsonline as reserve

units. Conventional control of energy storage to minimize operatingcosts tends to increase CO2

emission because storage is charged by high-carbon coal offpeakand offsets lower-carbon natural

gas as it discharges on-peak.In addition. CO2 reductions are sensitive to a number of other

factors,including congestion, load level and fuel price. Depending on natural gas and coal

prices,it may require a very high CO2 price to reduce CO2 emissions in existing systems

byswitching from coal-fired generation to gas-fired generation

Figure 2 Green energy statuses in India

0 5000 10000 15000 20000

Wind Energy

Small hydro Power

Biomass Power

Bagasse Cogeneration

Waste to power (Urban & Industrial)

Solar Power

Capacity (MW)

Cumulative achievement up to 31.01.2012

Total achievement during 2011-12


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Role of Distributed generation:

Distributed generation (DG) is an emerging concept in electricity market which

represents good alternative forelectricity supply instead of traditional central generation concept.

The electricity Market place is undergoingtremendous transformation as it moves towards a more

competitive environment. The growing impact of transformation-price instability, an ageing

infrastructure, changing regulatory environment are causing both energy users as well as electric

utilities to take another look at benefits of distributed generation. The growing pressure toreduce

emissions of carbondioxide has fueled global interestin new efficient and renewableenergy

technologies and createdsubstantial commitment to thedevelopment and deployment ofthese

systems. Investment inthese areas is leading to a growingnumber of installations ofdistributed

generation (e.g., windturbine generators, combinedheat and power plants, solarsystems, fuel

cells, and energystorage) and promoting increasedopportunities for effectivedemand

management schemesand energy efficiency initiatives.

The combination of utility restructuring, technology evolutions, recent environment

policies provide the basis for DG to progress as an important energy option in the near future.

The open energy market favors small modular technologies that can be installedquickly based on

the response of market signal. In liberalized competitive electricity markets, it is important to

adapt to the changing economic environment in a more flexible way and DG is expected to play

key role in future competitive markets due to their economic viability, small sizes, and the short

construction lead times.

Over the last century, be it developed nation or developing nation, on account of rapid

industrialization causing high rate of growth in the demand for electricity, everyone resorted to

establishment of large scale centralized generation facility. The plants concerned were based on

use of fossil-fuel (solid, liquid as well as gas), hydro, nuclear elements. Due to the economy of

scale with large unit size, it became possible to have big centralized power stations near the

sources to deliver power to load centers through the medium of high voltage transmission lines

over a long distance. From environment point of view as well due to limitation of natural

resources, it is in fact advantageous too to have the plants away from populated areas.

Increasing power system reliability expectations have evolved into the growth of

distributed generation. The main drivers of that growth can be divided into three categories,


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which are environmental concerns, commercial policies and energy policies. These factors have

been contributing to the high interest and penetration of distributed generation utilisation. Issues

related to the operation and interconnection of distributed generation into power system

networks, such as power quality, reliability, stability and protections have been the focus of

stakeholders, including power operators, designers, policy makers, engineers and consumers.

However, in spite of triggering these issues, distributed generation also offers several

advantages.

As mentioned above, basic tangible advantages that may bederived out of such sort of distributed

or dispersed ordecentralized generation are the following.

Easy and quicker installation on account of prefabricated standardized components.

Lowering of cost by avoiding long distance high voltage transmission.

Environment friendly where renewable sources are used.

Running cost more or less constant over the period of time with the use of renewable

sources.

Possibility of user-operator participation due to lesser complexity.

More dependability with simple construction, andconsequent easy operation and

maintenance.

Renewable energy sources (RES), including wind power plants, have high priority of

promotion in the energypolicy of the India as well as all over world. An increasing share of RES

and distributed generation, should, as has been assumed, provide improvement in reliability of

electricity delivery to the customers. Currently available DG technologies in the 5 kW to 5 MW

size range, including their history and current status, operation, emission control technologies,

potential applications, representative manufacturers, and important issues surrounding their

development. The indices and the new model can reflect the environmentalbenefits correctly and

will eventually accelerate thedevelopment of DG in India.The DG has been seen as one of the

enabling technologiesthat can facilitate more efficiently and rapidly the integrationof renewables

in distribution networks. The application of thistechnology has many potential benefits which

should beexplored and quantified to enable proper assessments andanalysis.These DG

technologies include:


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RECIPROCATING ENGINES- This DG technology was developed more than a century ago,

and is still widely utilized in a broad array of applications. The engines range in size from less

than 5 to over 5,000 kW, and use diesel, natural gas, or waste gas as their fuel source.

Development efforts remain focused on improving efficiency and on reducing emission levels.

Reciprocating engines are being used primarily for backup power, peaking power, and in

cogeneration applications.

MICRO TURBINES- Microturbine is a promising technology which has the unique ability to

produce electricity and heat simultaneously. These very small turbines contain essentially one

moving part and use either air or oil for lubrication.A new and emerging technology, micro

turbines are currently only available from a few manufacturers. Other manufacturers are looking

to enter this emerging market, with models ranging from 30 to 200 kW. Micro turbines promise

low emission levels, but the units are currently relatively expensive. Obtaining reasonable costs

and demonstrating reliability will be major hurdles for manufacturers. Micro turbines are just

entering the marketplace, and most installations are for the purpose of testing the technology.

Unit sales are expected to increase in 2001 and beyond.

INDUSTRIAL COMBUSTION TURBINES- A mature technology, combustion turbines range

from 1 MW to over 5 MW. They have low capital cost, low emission levels, but also usually low

electric efficiency ratings. Development efforts are focused on increasing efficiency levels for

this widely available technology. Industrial combustion turbines are being used primarily for

peaking power and in cogeneration applications.

PHOTOVOLTAIC’S- Commonly known as solar panels, photovoltaic (PV) panels are widely

available for both commercial and domestic use. Panels range from less than 5 kW and units can

be combined to form a system of any size. They produce no emissions, and require minimal

maintenance. However, they can be quite costly. Less expensive components and advancements

in the manufacturing process are required to eliminate the economic barriers now impeding

wide-spread use of PV systems. Photovoltaics are currently being used primarily in remote

locations without grid connections and also to generate green power.


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WIND TURBINE SYSTEMS - Wind turbines are currently available from many manufacturers

and range in size from less than 5 to over 1,000 kW. They provide a relatively inexpensive

(compared to other renewables) way to produce electricity, but as they rely upon the variable and

somewhat unpredictable wind, are unsuitable for continuous power needs. Development efforts

look to pair wind turbines with battery storage systems that can provide power in those times

when the turbine is not turning. Wind turbines are being used primarily in remote locations not

connected to the grid and by energy companies to provide green power. DG technologies are

currently being used for the niche applications described later in this report. Many reports and

studies predict that the market for DG technologies will continue to grow as their price and

performance improves and energy markets deregulate.

COMBINED HEAT AND POWER- Combined Heat and Power (CHP), or co-generation as

it’s sometimes called, is the process of capturing and then utilizing the heat produced by

generating electricity. Conventional electricity generation by power stations is only around 37%

efficient, which means a huge potential source of energy is simply released into the atmosphere

as a byproduct. CHP can harness this power. By recovering most of this otherwise wasted heat,

CHP can bring overall energy savings of up to 40 per cent. Additionally, CHP has been widely

recognized as a key measure in helping to reduce harmful emissions of CO2. Many DG

technologies, such as Reciprocating engines, Micro-turbines and Fuel Cells can be used as CHP

plants.

Role of DG in Indian power sector

At the time of independence in 1947 India was having a meager generation of above 1,360

MW, that too in a highly decentralized manner in and around urban areas to meet the load of

latter. It followed decades of development in powersector, aiming at optimum utilization of

geographically dispersed resources, economy of scale, harnessing of hydro-energy in far flung

areas as well as thermal energy at mine-mouth power stations. Technological innovations,

marketing through competitive unit pricing at different point of time through power and energy

trading are encouraging Distributed Generation to a large extent, requiring of course a good

amount of coordination of stake-holders side by side. Governments of India policies as well as


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initiatives in respect of Rural Electrification vis-à-vis Distributed Generation are quite

encouraging.

The concept of DG has been taken as decentralized generation and distribution of power

especially in the rural areas. In India, the deregulation of the power sector has not made much

headway but the problem of T & D (Transmission & Distribution) losses, the unreliability of the

grid and the problem of remote and inaccessible regions have provoked the debate on the subject.

The DG technologies in India relate to turbines,micro turbines, wind turbines, biomass,

andgasification of biomass, solar photovoltaic cells andhybrid systems. However, most of the

decentralizedplants are based on wind power, hydro power andbiomass, and biomass

gasification. The technologyof Solar Photo Voltaic (SPV) cells is costly and fuelcells are yet to

be commercialized.

Ministry of New and Renewable Energy, however, feels that there exist challenges for

Renewable Energy based Distributed Generation, some of which are universal and some local,

like,

Inherent intermittent nature of renewable energy sources leading to relatively lower

capacity utilization factors

Instances of inadequate load needing to couple rural industrial load

Relatively high capital costs when compared to conventional power systems which in

turn require incentives and financial arrangement

For capacity building, promotion and development of energy

Requirement of servicing companies for local program implementation

Need for adequate mobilization for payment of user charges involving perhaps Non-

Government Organizations and local bodies

Lack of O&M services providers is an issue that needs attention

Need for developing sustainable revenue / business models

Assistance for project preparation

Establishment of sustainable fuel linkages includingFuel Service Agreement

India is on right track to pursue development of Distributed Generation with the unbundling

of power sector utilizing captive and co-generation, besides putting all out effort in harnessing

various forms of new and renewable energy. Collective participation of industries, private


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entrepreneurs, giant Corporations hitherto engaged in conventional power development is the

essence of such venture. Liberalization of Government policy vis-à-vis support as well as

regulatory mechanism in place is helping to create conducive atmosphere to achieve target set in

this direction. However, there are challenges that are being attended to with utmost sincerity after

being identified during the course of journey in having electricity for all by 2020.


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Damping Torsional Electromechanical Oscillations in aSeries Compensated Power System

Narendra Kumar1, S.K. Agarwal2 Upma Singh3

Professor, DTU, Delhi YMCA, Faridabad M.Tech, DCRUST

Abstract— This paper is concerned with the application of SVS control technique to examine the efficacy of auxiliary control signal for reactive power modulation of a midpoint located static Var System (SVS) in damping the electromechanical oscillations in the turbine generator unit of the power system and to enhance the power transfer capability of long transmission line. A new auxiliary signal designated combined voltage angle and reactive power (CVARP) is proposed along with induction machine damping unit (IMDU) that is coupled with IP turbine to enhance the effect of SVS in damping out the torsional electromechanical oscillations. The proposed control strategy has been validated using IEEE first benchmark model. Dynamic study using eigenvalue analysis has been performed and optimal parameters of controller have been obtained using extensive study of root locus. The damping torque results are correlated with those obtained from eigenvalue analysis. Index Terms— Static VAR system (SVS), combined voltage angle and reactive power (CVARP), Torsional electromechanical oscillations, sub synchronous resonance (SSR), Transient performance, IMDU. I. INTRODUCTION Power systems are among the largest and most complex systems made by human beings. Efforts are always done to enhance power transfer capability of the existing transmission system. Series compensation is used to enhance power transfer capability but gives rise to dynamic instability problem. Various modes of oscillation occur due to interactions among system components. One of the most significant oscillations is caused by synchronous generator rotors swinging against each other, giving typical frequency ranges from 0.1 to 2 Hz [2].. Power system stabilizers (PSSs) are used to add

damping to generator rotor oscillations by controlling the excitation using auxiliary stabilizing signals where the speed deviation is usually used as an input signal. [3] In recent years, due to the rapid progress of power electronics i.e. flexible AC transmission system (FACTS) Controllers, much research work has been reported addressing oscillation damping enhancement. Static var system is a FACTS device, which is used primarily for the purpose of reactive power support and voltage control. In principle, a thyristor-controlled series capacitor (TCSC) and a static-var system (SVS) could provide rapid control of active power through a transmission line. Static Var System (SVS) is known to extend the stability limit and improve system damping when connected at the midpoint of a long transmission line [4,7]. While an SVS with pure voltage control may not adequately contribute to system damping, a significant enhancement in the same is achieved when SVS reactive power is modulated in response to auxiliary control signal superimposed over its voltage control loop [11]. A new auxiliary control signal designated as combined voltage angle and reactive power (CVARP) is proposed which involves the voltage angle and bus reactive power signals in coordination with induction machine damping unit (IMDU) for damping oscillations due to SSR in a series compensated power system. Eigenvalue analysis is employed for prediction of system stability. The analytical prediction of SVS performance with voltage control based on linearized models is validated using IEEE first benchmark model. A digital simulation study using the non-linear system model and CVARP auxiliary controller in coordination with IMDU exhibits a commendable improvement in the dynamic and transient performance of series compensated power system. The controller is


11

able to stabilize all the torsional modes over wide spread of power transfer and the torsional electromechanical oscillations are damped out considerably and the system transient performance is greatly improved. Proposed controller is robust and can easily be implemented as auxiliary signals are derived locally from the SVS bus. II. MODELING

The study system consists of a steam turbine driven synchronous generator (a six- mass model) supplying bulk power to an infinite bus over a long transmission line (IEEE first benchmark model). An SVS of switched capacitor and thyristor controlled reactor type is considered located at the middle of the transmission line that provides continuously controllable reactive power at its terminals in response to combined voltage angle and reactive power (CVARP) auxiliary control signal. The series compensation is applied at the sending end.

Fig.1.Study system.

GENERATOR In the detailed machine model [7] used here, the stator is represented by a dependent current source parallel with the inductance. The generator model includes the field winding ‘f’ and a damper winding ‘h’ along d-axis and two damper windings ‘g’ and ‘k’ along q-axis. The IEEE type-1 excitation system is used for the generator. In the mechanical model detailed shaft torque dynamics [7, 8] has been

considered for the analysis of torsional modes due to SSR. The rotor flux linkages ‘ψ’ associated with different windings result in rotor equations:

q6h8g7

.

k

q5k6g5

.

g

d3h4f3

.

h

d2f1h2f1

.

f

Ibaa

Ibaa

Ibaa

IbVbaa

Where Vf is field excitation voltage. The above eqns. have been linearized and the state space model is obtained as follows:

[ ] [ ] [ ] [ ] R3R3R2R2R1R1RRR.

UB+UB+UB+XA=X (1) [ ][ ]tQD3R

f2Rt

1R

iΔiΔ=U

,VΔ=U,ωΔδΔ=U

tkghfRX Prefix Δ indicates incremental values and the output equations are

t

Q.

D.

2Rt

QD1R

3R4R2R3R1R2RR2R2R

1R1RR1R1R

IIY,IIYwhere

UDUDUDXCYUDXCY

MECHANICAL SYSTEM

The six spring mass model as used in the IEEE first bench mark model [2] describes the mechanical system as shown in Fig.3. The governing equations and the state and output equations are given as follows

HP

IP LPA LPB GEN EXC

Tm1 Tm2 Tm3 Tm4 Te

1 2 3 4 5 6 D12 D23 D34 D45 D56

K12 K23 K34 K45 K56

D11 D22 D33 D44 D55 D66

Fig.3.6-Spring mass model of mechanical system

i = i, i=1, 2, 3, 4, 5, 6

1M2112

21211211

11

.

T)(KD)DD(

M1

2M1212

3232232212112

22

.

T)(KD)DDD(D

M1


12

4

3

M54453434

5454454434334

44

.

M43342323

4343343323223

33

.

T)(K)(KD)DDD(D

M1

T)(K)(KD)DDD(D

M1

e6556

4545656

5565545445

55

.

T)(K)(KD

)DDD(D

M1

)(K)DD(DM1

5656666565566

6

.

)IiIi(XT DQQD"de

Where 1, 2, 3, 4, 5, 6, are the angular displacements and 1, 2, 3, 4, 5, 6 are the angular velocities of different shaft segments as shown in fig. 3. Linearizing the above equations the state space model is derived as follows:

2M2M1M1MMMM.

UBUBXAX (3) MMM XCY (4)

Where:

Mt

QD2M

tQD1M

tM

Y,iiU

IIU,X

AM, BM1, BM2, and CM, are given in the appendix 2.

EXCITATION SYSTEM The excitation system is represented by the IEEE Type I model. The state and output equation are

fEgEt

rSfE

EEE

EEEEE.

vY,vU,vvvX

whereXCY

UBXAX

NETWORK

The transmission line (fig.3) is represented by lumped parameter T- circuit. The network has been represented by its –axis equivalent circuit, which is identical with the positive sequence network. The governing equations of the -axis, T-network representation are derived as follows

T C R

V3 V4 i V2 i1

V1 I

ia Ra LT1 Cse

R L L R LT2 "

dL

Ix

i2 iCFC

Cn

Fig.3. α – axis representation of the network

RiVV

dtdiLL 122T

4

'da2A VILiRRV

dtdiLL

i-i--idt

dVCn 12

2

-idV Cse 4 dt

Where FCn"d1Ta ccandcLLi

Similarly, the equations can be derived for the

- network. The - network equations are then

transformed to D-Q frame of reference.

t

Q.

D.

1Nt

QD2Nt

Q2D21Nt

QDN

3N3N2N2N1N1NNNN.

IIU,IIU,iiU,XXX

whereUBUBUBXAX

and output equations are

tQ2D23N

tQD2NG1N

N3N3NN2N2N

3N3N2N2N1N1NN1N1N

vvY,iiY,vY

whereXCY;XCY

UDUDUDXCY

STATIC VAR SYSTEM

Fig. 4 shows a small signal model of a general SVS. The terminal voltage perturbation ∆V and the SVS incremental current weighted by the factor KD representing current droop are fed to the reference junction. TM represents the measurement time constant, which for simplicity is assumed to be equal for both


13

voltage and current measurements. The voltage regulator is assumed to be a proportional- integral (PI) controller. Thyristor control action is represented by an average dead time TD and a firing delay time Ts. ∆B is the variation in TCR susceptance. ∆VF represents the incremental auxiliary control signal. The α, β axes currents entering TCR from the network are expressed as:

SK

K ip

sST11

Z3

DST11 B

TCR

G(S)

KD MST1

1

+ Vref

+ Z1

- Z2

VF UC

i2

V2

+

-

Fig.4. SVS control system with auxiliary feedback

2s22

s iR-V dt

diL

222

s dtdi

L iRV s (6)

Where RS,LS represent TCR resistance and inductances respectively. The other equations describing the SVS model are:

Z-V Z 2ref

.

1 FV

2M2D22.

ZT/iKVZ

srefP32P1I

.

3 )/TVK - Z-ZKZ(-KZ (7)

D3

.T/BZB

Where ΔV2 & Δi2 are incremental magnitudes of SVS voltage and current, respectively, obtained by linearizing

2Q2

2D22

2Q2

2D22 iii,VVV (8)

the state and output equations are summarized as

tQ2D2SF3Sref2St

Q2D21S

t321Q2D2S1SSSSS

3S3S2S2S1S1SSSS.

iiYvU,vU,vvU

BZZZiiXwhereUDXCY

UBUBUBXAX

III. DEVELOPMENT OF SVS AUXILIARY CONTROLLER

The auxiliary signal UC is implemented through a first order auxiliary controller transfer function G(s) as shown in fig.5 which is assumed to be: 21BcF sT1/sT1KU/vsG

(9)

Fig.5. General first-order auxiliary controller

This can be equivalently written as

( ) ( ) ( )221B21B sT+1/T/T1K+T/TK=sG (10)

The state and output equations are given by

CCCCC

CCCCC

.

UDXCYUBXAX

(11)

Where Fccc VY,ZX , 2c T/1A ,


14

21Bcc21Bc T/TKD,1C),T/T1(KB (12)

REACTIVE POWER AUXILIARY SIGNAL The auxiliary control signal in this case is the deviation in the line reactive power entering the SVS bus. The reactive power entering the SVS bus can be expressed as:

DQ2QD22 iViVQ (13)

Where iD , iQ and V2D, V2Q are the D-Q axis components of the line current i and the SVS bus voltage V2 respectively. Linearizing eqn. (13) gives the deviation in the reactive power ΔQ2 which is taken as the auxiliary control signal UC1.

Q20DD0Q2D20QQ0D221C ViiVViiVQU (14)

VOLTAGE ANGLE AUXILIARY SIGNAL SVS Bus angle is given by

2

20D2Q2Q2D222C

220D2Q2Q2D22

D2Q21

2

D2Q21

2

V/VVVVU

V/VVVVdt

V/Vtand

V/Vtan

(15)

Linearizing eqn.(15) gives the deviation in bus

voltage angle control signal:

220D20Q2Q20D222C V/VVVVU (16)

‘0’ represents operating point or steady state values. The state and output equations for the VARP auxiliary controller are obtained as follows:

2

1

2

1

2

1

2

1

2.

1

.

00

00

UU

BB

XX

AA

X

X C

C

C

C

C

C

C

C

C

2

121

2

121

C

CCC

C

CCCC U

UDD

XX

CCY (17)

Where the state XC1 and matrices AC1, BC1, CC1 and DC1 correspond to reactive power auxiliary controller and the state XC2 and matrices AC2,BC2,CC2 and DC2 correspond to the active power / voltage angle auxiliary controller. IV. INDUCTION MOTOR DAMPING UNIT (IMDU)

The property of induction machine to act as a generator or motor is utilized to absorb the mechanical power when there is excess and to release when there is a deficiency. Since machine comes into operation during transients only, it is designed for very high short term rating and very small continuous rating. Consequently the machine has low inertia, low power, small size and low cost. Because of its small mass and tight coupling with the intermediate pressure turbine it has been considered as a single mass unit with IP turbine. Electrically it is connected to the generator bus. The per unit torque (Timl) is given by :

INDUCTION MACHINE DAMPING UNIT (IMDU)

The property of induction machine to act as a generator or motor is utilized to absorb the mechanical power when there is excess and to release when there is a deficiency. Since machine comes into operation during transients only, it is designed for very high short-term rating and very small continuous rating. Consequently the machine has low inertia, low power, small size and low cost. Because of its small mass and tight coupling with the intermediate pressure turbine it has been considered as a single mass unit with IP turbine. Electrically it is connected to the generator bus.


15

The per unit torque (Timl) developed by the induction machine is given by:

Timl= ]r/sx1[r.

s32'

2'2

'20

(21)

And slip s = (0-3)/0, where 3 is the angular velocity corresponding to mass 3. Now linearizing eqn. (21)

22'

2'2

'20

2'2

'2

22'2

'2

iml]r/sx1[r.

sr/xs2r/sx13T

(22) At normal operating point s = 0, hence

'20iml r./s3T

Or '2

203iml r./3T

Hence by considering eqn. 23 mechanical system model corresponding to mass 3 becomes

1imM43342323

4343'2

20343323223

33

.

TT)(K)(KD)r./3DDD(D

M1

3 (23) Similarly other mechanical equations can be modified to account for the damping effect of IMDU for its different locations on T-G shaft. The state and output equations of the different constituent subsystems along with the auxiliary controller state and output equations are combined to result in the linearized state equations of overall system as:

TT.

XAX , where tCSNEMRT XXXXXXX (24) The dimension of the system matrix is 35 V. A CASE STUDY

The study system consists of 1110 MVA synchronous generator supplying power to an infinite bus over a 400 kV, 600 km. long series compensated single circuit transmission line.

The system data and torsional spring mass system data are given in Appendix. The SVS rating for the line has been chosen to be 100 MVAR inductive to 300 MVAR capacitive.

40% series compensation is used at the sending end of the transmission line. VI. DYNAMIC PERFORMANCE The eigenvalues have been computed for the system with and without CVARP auxiliary controller incorporated in SVS control system for wide range of power transfer. Table1 presents the eigenvalues for the system at generator power PG=200, 500, 800 MW without any auxiliary controller. When no auxiliary controller is incorporated, four unstable modes 5 , 4 , 1 and 0 are investigated in the system at PG= 800 MW. At PG= 500 and 200 MW, three torsional modes 5, 4 and 3 are unstable. Table 2. shows the system eigenvalues at PG= 200, 500 and 800 MW using CVARP auxiliary controller. The CVARP auxiliary controller stabilizes all the torsional modes at PG=200 MW, 500 MW and 800 MW. The auxiliary controller parameters are selected based on an extensive root locus study and are listed in table 2. Optimized controller parameters KB1, T!, T2 and KB2,T3,T4 are adjusted for wide spread of power transfer using root locus technique. Fig. 6 depicts root loci of subsystem with combined voltage angle and reactive power signal. All the electrical modes and electromechanical modes are found to be stable. The torsional electromechanical modes (0—5) corresponding to mechanical subsystem are highlighted.


16

Pg=200 MW Pg = 500 MW Pg = 800MW

Mode 5 Mode 4 Mode 3 Mode 2 Mode 1 Mode 0

-.0000j298.1006 -.0593±j202.7368 -.0111±j160.5519 .0008±j126.9794 .0167±j98.8784 -.3969±j4.7451

-38.063 -2.4258

-.7529+j0.7922 -28.4922

-25.7111j24.1491 -.7529-j0.7922

-13.1481±j1477.135 -14.9725±j846.9496 -12.7503± j444.7002

-9.564±j189.3292 -54.6373±j74.2791

-548.0913 ± j90.600 -5.8025±j311.4741

. 0.0000±j298.1006 -.0681±j202.7265 .0050±j160.5464

.0017 ± j126.9764 .0090 ±j98.8318 .1985±j5.0264

-.38.4461 -2.8524

-.6020+j0.7966 -32.0219

-.25.6813±j24.2982 -.6020-j.7966

-12.8610±j1148.229 -18.2145± j520.6694 -12.4440±j445.3199 -9.5753±j188.8829 -51.8765±j75.8508

-545.4075±j74.89 53 -6.8082±j311.6204

.0001±j298.1006 -.1118±202.7264 .0089±j160.5241 .0032±j126.9691 .0100±j98.7327 .0153+j4.9871

-39.1137 -3.0092

-.6219+j.8583 -33.3539

-25.7639±j24.3904 -.6219-j.8583

-13.454±j1069.1750 -11.9887±j441.7564 -22.2118±j441.5703 -10.4269±j192.6654 -47.8021±j81.2018 -545.4495±j72.3131 -4.9340±j311.2883

TABLE 1 SYSTEM EIGENVALUES WITHOUT AUXILIARY CONTROLLER

TABLE 3

EIGENVALUES WITH IMDU AND CVARP AUXILIARY CONTROLLER (KB1=-.01, KB2=-.54,T1=.046, T2=.05 ,T3=.39, T4=.2 )

Pg = 200 MW Pg = 500 MW Pg = 800MW

Mode 5 Mode 4 Mode 3 Mode 2 Mode 1 Mode 0

-0.002 ± j 298.10 -0.015 ±j 202.89 -0.015±j160.52 -0.0002±j126.98 -0.018±j98.981 -0.49±j6.66 -13.38 ±j1964.70 -11.11 ±j692.95 -576.88 -466.33 -12.82 ±j 449.35 -7.42 ±j 313.85 -154.26 -9.09 ±j166.60 -25.95±j24.63 -36.564 -33.286 -21.34±j4.28 -5.083 -2.391 -0.389±j0.539

-0.002±j 298.10 -0.001 ±j 202.89 -0.012 ± j160.52 -0.0001±j126.98 -0.0188 ±j98.98 -0.327±j6.81 -13.39 ±j 1964.70 -11.10 ± j692.94 -574.64 -467.93 -12.72 ±j 449.25 -7.29 ±j 316.62 -168.55 -8.066 ±j 166.55 -25.96 ±j24.65 -36.84 -33.308 -25.77 -5.41 ±j1.84 -0.433 ±j 0.60 -2.32

-0.0021±j298.100 -0.015±j202.89 -0.012 ±j160.525 -0.00013±j126.98 -0.019±j98.984 -0.326± j 6.82 -13.39±j1964.71 -11.10±j692.945 -574.643 -467.934 -12.728±j449.253 -7.295±j 316.62 -168.56 -8.073±j166.562 -25.962±j24.653 -36.840 -25.771 -33.308 -5.41±j1.85 -0.433±j0.605 -2.326

Root locus plot for 200MW


17

1.0481.05

1.0521.0541.0561.0581.06

0 5 10 15 20 25

Time,s

Term

inal

Vol

tage

,p.u

.

1.045

1.05

1.055

1.06

1.065

0 5 10 15 20 25

Time,s

Term

inal

Vol

tage

,p.u

.

1.021.031.041.051.061.071.08

0 5 10 15 20 25

Time,s

SV

S Bu

s Vo

ltage

,p,u

,

1.041.0451.05

1.0551.06

1.0651.07

0 5 10 15 20 25

Time,s

SV

S Bu

s Vo

ltage

,p.u

.

-0.8-0.78-0.76-0.74-0.72-0.7

-0.68

0 5 10 15 20 25

Time,s

Pow

er A

ngle

.rad.

-0.75-0.74-0.73-0.72-0.71-0.7

0 5 10 15 20 25

Time,s

Pow

er A

ngle

,rad

00.10.20.30.40.50.6

0 5 10 15 20 25

Time,s

SVS

sus

cept

ance

,p.u

.

00.10.20.30.40.5

0 5 10 15 20 25

Time,s

SVS

Sus

cept

ance

,p.u

.

02468

10

0 5 10 15 20 25

Time,s

T (B

-G),p

.u.

7.67.8

88.28.48.6

0 5 10 15 20 25

Time,s

T(B

-G),p

.u.

00.5

11.5

22.5

3

0 5 10 15 20 25

Time,s

T (H

-I),p

.u.

2.3

2.35

2.4

2.45

2.5

0 5 10 15 20 25

Time,s

T(H

-I),p

.u.

-0.3-0.2-0.1

00.10.20.30.4

0 5 10 15 20 25

Time,s

W-W

o

-0.2

-0.1

0

0.1

0.2

0 5 10 15 20 25Time,s

W-W

o

(a) (b)

SIMULATION RESULTS




18

VII. TIME DOMAIN SIMULATIONS A digital computer simulation study, using a

nonlinear system model, has been carried out to demonstrate the effectiveness of the CVARP auxiliary controller under large disturbance conditions. Applying a pulsed torque of 30% for 0.1 s simulates a disturbance. The simulation study has been carried out at PG=800MW. All the self and mutual damping constants are assumed to be zero. Fig. 7 shows the response curves of the terminal voltage, SVS bus voltage, SVS susceptance, power angle, variation in Torsional torques without and with the CVARP auxiliary controller after the disturbance. It can be seen that there is tendency towards instability when no auxiliary controller is used in the SVS control system. The torsional oscillations are stabilized and the CVARP auxiliary controller attains a significant improvement in the transient performance of the series compensated power system. The control strategy is easily implemental as it utilizes the locally derived signals from the SVS bus.

CONCLUSION

In this paper the effectiveness of combined voltage angle and reactive power (CVARP) SVS auxiliary controller has been evaluated for damping the electromechanical torsional oscillations in a given series compensated power system. The following conclusions can be drawn from the eigenvalues study performed. a. CVARP auxiliary controller is able to

stabilize all the system torsional modes, for all power levels. Damping of torsional mode 0 is good which is responsible for the dynamic interaction of the generator and transmission line.

b. The time domain simulation study demonstrates that the CVARP auxiliary controller improves the damping of the torsional electromechanical oscillations due to sub synchronous resonance (SSR) in the series compensated power system. The control strategy is easily implemental as it

utilizes the locally derived signals from the SVS bus.

ACKNOWLEDGEMENT

The work presented in this paper has been performed under the AICTE R&D Project, “Enhancing the power system performance using FACTS devices” in the Flexible AC Transmission Research Laboratory at Delhi College of Engineering, Delhi (India).

APPENDIX

Generator data: 1110MVA, 22kV, Ra= 0.0036,XL = 0.21 Two

’=6.66, Two’ =0.44, Two

” =0.032,

Two” =0.057s

Ad = 1.933, Ax = 1.743, Ad’ =0.467,

Ax’ = 1.144,

Ad” = 0.312, Ax

” = 0.312 put IEEE type 1 excitation system: TR=0, TA=0.02, TE=1.0, TF=1.0s, KA=400, KE=1.0; KF=0.06 put. VFmax=3.9, Fin=0, Irma=7.3, VR min=-7.3 Transformer data: RT=0, XT=0.15 put. (Generator base) Transmission line data: Voltage 400kV, Length 600km, Resistance R=0.034Ω / km, Reactance X=0.325 Ω / km Susceptance Be=3.7μ mho / km SVS data (Six-pulse operation) TM=2.4, TS=5, TD = 1.667ms, K1= 950, KP = 0.5, KD = 0.01 Torsional spring-mass system data ---------------------------------------------------------- Mass shaft Inertia H (s) Spring

constant ---------------------------------------------------------- HP 0.1033586 HP-IP 25.772 IP 0.1731106 IP-LPA 46.635 LPA 0.9553691 LPA-LPB 69.478 LPB 0.9837909 LPB-GEN 94.605 GEN 0.9663006 GEN-EXC 3.768


19

EXC 0.0380697 ---------------------------------------------------------- IMDU Data: '

2r =3.64x10-4 pu.

REFERENCES

[1] K.R.Padiyar and R.K.Varma,'Concepts of Static VAR system Control for Enhancing Power Transfer in Long Transmission Lines' To appear in Journal of Electric machines and Power Systems', vol. 18, No.4.

[2] Narendra Kumar, M.P. Dave, “Application of Static VAR System auxiliary System Auxiliary Controllers to Improve the Transient Performance of Series Compensated Long Transmission lines,” Electric Power Systems Research 34 (1995) 75-83.

[3] E.Larsen and J. H. Chow, “Application of static var systems for system dynamic performance,” IEEE Tutorial Course 87 THO187-5 PWR, 1987.

[4] Narendra Kumar, M.P. Dave, “Application of Auxiliary Controlled Static Var System for Damping Subsynchronous Resonance in Power Systems”. Electric Power System Research 37 (1996) 189 – 201.

[5] S.K. Gupta, Narendra Kumar et.al., “Controlled Series Compensation in Coordination with Double Order SVS Auxiliary Controller and Induction Machine for repressing the Torsional Oscillations in Power system”. Electric Power System Research 62 (2002) 93-103.

[6] R.S.Ramsaw, K.R.Padiyar, “Generalized System Model for Slip Ring Machines”, IEEE Proc. 120 (6) 1973.

[7] K. R. Padiyar, R.K. Varma, “Damping Torque Analysis of Static Var System Controllers”, IEEE Trans. on Power Systems, 6(2) (1991)458-465.

[8] E. Lerch, D. Povh, and L. Xu, “Advanced SVC control for damping power system oscillation,” IEEE Trans. Power Systems, vol. 6, no. 2, pp. 524–535, May 1991.

[9] A. E. Hammad, “Analysis of power system stability enhancement by static var compensators,” IEEE Trans. Power Systems, vol. PWRS-1, no. 4, pp. 222–227, Nov. 1986. [10]G. D. Galanos et al., “Advanced static

compensator for flexible AC transmission,” IEEE Trans. Power Systems, vol. 8, no. 1, pp. 113–121, Feb. 1993.

[11] J. F. Gronquist et al., “Power oscillation damping control strategies for FACTS devices using locally measurable quantities,” in IEEE 1995 Winter Meeting, Paper no. 95 WM 185-9 PWRS.


20

Biomass Based Distributed Power Generation

Current Status and Future Challenges Tanmoy Deb

KIIT College of Engineering, Gurgaon [email protected]

Abstract- This paper presents an overview of biomass based distributed power generation in India. The paper discusses opportunities available for power generation for rural and off grid application. It explores current technologies and their relative merits and demerits. It discussed the incentives provided by govt. of India for its promotion. It further explores issues, challenges and solutions to make it technically and commercially viable source of power for rural areas. Keywords: Off-grid applications, distributed generation, incentives.

I.INTRODUCTION

70% of country’s population depends on biomass resources in India. About 32% of the total primary energy used in obtained from biomass resources. India generates about 500 million tons of biomass material in agricultural, agro-industrial and forestry operations. Majority of it is used as fuel and fodder. A significant portion of this bio-mass goes waste due to lack of any avenues for productive use. For a power deficient country like India, it spells an excellent opportunity. It can provide a sustainable means of power generation in distributed mode. This will work as a great equalizer for economic upliftment of rural masses. The current biomass potential in India is for power generation is 34,961 MW (2010). The biomass power generation sector attracts Rs. 600 crores of investment every year and generates about 5000 million units of

electricity. The installed capacity of biomass based power generation as of 30th June 2012 is 1182 MW (grid connected) and another 648 MW in off grid mode. About 2.4 billion people rely on biomass mainly for heating and cooking needs. The subsequent sections discusses threadbare the technology of biomass for sustainable power generation especially for villages.

II. BIOMASS MATERIALS

Biomass is a natural substance that stores solar energy by way of photosynthesis. It contains cellulose, hemicelluloses and lignin. The average composition of biomass is C6H10O5. Biomass material is classified as (a) Dry biomass (b) West biomass (c) Municipal solid waste (d) industrial waste (e) Forest Waste and (f) agricultural waste. Dry biomass consists of tree chips, paper, corn, soybean, sorghum, sunflower, Oats, barley, wheat etc. Wet biomass includes animal waste, water plants, bio-diesel etc. Methane is used as gaseous biomass.

III. BIOMASS BASED DISTRIBUTED POWER GENERATION.

Distributed Power generation is a small scale generation of power near load centre. It is also known as on-site power generation or dispersed generation or decentralized generation. The capacity may range from 3 KW to 10 MW. Such systems have


21

numerous advantages and are suited for off-grid and rural areas. A variety of power sources can be used for distributed generation. Some are listed below:

(i) Biomass based generation. (ii) Natural gas fired micro-turbine. (iii) Liquid fuel based IC engines. (iv) Wind Power based generation. (v) Solar PV based generation (vi) Micro & mini -hydel based generation. (vii) Fuel cell based generation.

S.NO. Technology Typical sizes

1. Combined cycle gas

turbine

35-400 MW

2. IC engine 5KW-10MW

3. Micro-turbine 35KW-1MW

4. Small hydro 1-25 MW

5. Micro-hydro 25KW-1MW

6. Wind turbine 200W-

100KW

7. Solar PV 1 MW-10

MW

8. Biomass(Gasification) 100KW-20

MW

9. Fuel Cell (Phos acid) 200 KW-

2MW

10 Fuel Cell (Proton

Exchange)

1 KW-250

KW Table 3.1 -- Capacity range of distributed generation. Distributed generation can integrate both renewable as well as non-renewable sources.

Biomass based distributed power generation possesses following advantages:

(i) Suitable for off grid and stand alone application such as rural area.

(ii) Low cost of power projects due to small size.

(iii) It is carbon neutral (iv) Raw material is cheap and abundantly

available. (v) It results in efficient utilization of

renewable biological resource. (vi) It results in rural economic upliftment. (vii) System has low financial risk. (viii) Reduction in migration of labour to urban

areas. (ix) Boosts rural entrepreneurship.

For biomass based power generation, three methods viz combustion, gasification and anaerobic digestion is used. In recent times, pyrolysis method is gaining acceptance. Compared to other renewable energy generation methods, investment in biomass based power generation is cost competitive. For a 10-100 KW capacity range, the capital investment cost is given in table 3.

S.NO. Type of

Energy

Capital Investment

(Million Rs/MW)

1 Solar PV 300-400

2. Micro-hydel 40-60

3. Wind 40-50

4. Biomass 20-40 Table 3.2 – Comparison of biomass power generation with other renewable energy sources. Table 3.2 shows comparison amongst Solar PV, micro-hydel, wind and biomass. As can be seen , the capital investment required is highest in case of solar PV (300-400 million


22

Rs/MW) followed by Micro-hydel, wind and biomass. So, biomass has lowest investment cost (20-40 million Rs/MW for setting up power generation unit. IV.BIOMASS ENERGY CONVERSION PROCESS

Biomass can be used directly or can be converted into other energy form. There are three processes used for the extraction of bio-energy as described below. (i) Thermal conversion process: The process uses thermal energy to convert biomass into another form. The processes used are combustion, torrefaction, pyrolysis and gasification.

(a) Combustion process: The biomass

material is ignited (200-1400 C) and its results in production of heat, gas or oil. This in turn is used to generate steam for power generation.

(b) Torrefaction: In this process, biomass is heated to a temperature of 200-320 C at atmospheric pressure and in the absence of air. The final product is solid black material called bio-coal.

(c) Pyrolysis: In this method, the biomass is rapidly heated to 450 – 600C in the absence of air . It results in the production of bio-oil. This oil is fired in a boiler to raise steam. The steam thus obtained is used to drive steam turbine.

(d) Gasification: In this method, biomass in a gassifier is used to produce synthesis gas at a temperature of 500-1300 C.

(ii) Chemical Conversion: This technique uses chemical process to convert biomass into a fuel. The fuel so produced is easy to store, transport and use. Examples are production of methanol,

olefins, conversion of waste vegetable oil into bio-fuel.

(iii) Bio-Chemical conversion: This process uses micro-organisms to breakdown biomass. The result is generation of bio-gas or liquid fuel. The processes used are following:- (a) Anaerobic digestion: In this, the biomass

is put in a digester and micro-organisms are used to decompose the biomass in the absence of air. It results in production of methane gas.

(b) Fermentation: It is the process of converting carbohydrates to alcohol and carbon dioxide using yeast or bacteria or both under anaerobic condition. Essentially, the process converts sugar into alcohol using microorganism.

(c) Composting: It is the process of generating biogas through anaerobic digestion in the presence of micro-organisms. A variety of bio-fuels are available for power generation. These are listed in Table 4.1

S.No. Ist Generation IInd Generation

1. Methanol Cellulose ethanol

2. Ethanol Algae fuel

3. Propanol/Butanol Bio-hydrogen

4. Bio-diesel Bio-Methanol

5. Vegetable oils Fischer Tropsch

Diesel

6. Bio-ether Bio-hydrogen diesel

7. Bio-gas Mixed alchol

8. Syn.gas

Table 4.1 Bio-fuels


23

All above mentioned conversion process converts bio-mass into useful form (with higher energy content) which is then used for power generation. The table 4.2 illustrates comparison of different biomass technologies From Table 4.2 it is seen that except pyrolysis all other processes are

commercialized. Anaerobic digestion process is specially suited for high moisture content organic waste. Biomass material needs to be dried in case of gasification and pyrolysis

S.NO Parameter Combustion Anaerobic digestion Gassification Pyrolysis

1. Raw Material Solid biomass Wet biomass Solid

biomass

Solid biomass

2. Technology status Commercial Commercial Commercial Demonstation

3 Temperature ( c) 700-1400 N/A 500-1300 380-530

4. Pressure (MPa) >0.1 - >0.1 0.1-05

5. Drying Not essential but

may help

Not essential Necessary Necessary

6. Advantages - Suitable for high

moisture content

organic matter

High

efficiency 25-

50%

Main product

liquid – Easy to

store and

transport

Table 4.2 comparison of different biomass technologies

V. BIOMASSPOWER GENERATION TECHNOLOGIES

Biomass can be used as direct firing or

can be used as co-firing i.e. in combination with Coal etc. In direct firing, following technologies are used –

(i) Direct biomass combustion: The biomass is used to generate either power or heat or bot. It is economically viable for 6-15MW. The payback period is 6-7 years. This technology is especially suited for plantations / mills for e.g. sugar

cane (Bagasse), rice husk), wood/ paper (wood waste), corn (corn waste), palm oil (shells, empty fruit bunches). The method can also use urban waste to generate power

(ii) Biomass liquification via pyrolysis: The method uses pyrolysis of biomass material. The output of pyrolysis is oil. This oil is fired in a boiler to generate power.

(iii) Gasification of Biomass: The biomass is converted into gaseous form called synthesis gas (or syn gas). This gas can be used in a boiler or in a gas engine to


24

generate power. Syn. Gas composition is H2-20%, CO2-12%, CH4-3%, CO-20% rest N2. The process is suitable for 500 kw – 2MW range.

(iv) Bio Gas from an aerobic digestion: The biomass in a digester is decomposed by microorganism in the absence of air. The biogas so produced is either used in a boiler or in a gas engine. The biogas (mainly methane) so produced is cleaned through scrubber before being fed to gas engine.

VI. CURRENT STATUS FOR

BIOMASS POWER GENERATION IN INDIA

The current availability of biomass is

500 million metric tons per year. According to one estimate by ministry of new and renewable energy, the estimated surplus biomass availability is 120-150 million metric tonnes per year covering agricultural & forestry residue. This corresponds to a power potential of 18,000MW. Apart from this, additional 500MW of power can be generated to bagasse based Co-generation. The power generation potential from biomass (2010) is given in table 6.1

S.N. Biomass Type Potential

(MW)

1. Agro residue 18728

2. Live stock 9332

3. Fruits 660

4. Vegetables 1220

5. Industrial waste 1470

6. Municipal solid

waste

3190

7. Municipal liquid 361

waste

Total 34961 TABLE – 6.1 BIOMASS POTENTIAL IN INDIA

(2010) The power generation potential from biomass is 34961 MW. Table 6.2 gives breakup of biomass consumption by different fuels.

Animal Dung Crop residue Fuel wood 14% 23% 63%

TABLE 6.2 BIOMASS CONSUMPTION BY DIFFERENT FUELS

The majority of biomass consumption is in fuel wood category & it includes power generation, cooking and heating purposes. The total installed capacity of grid interactive biomass power generation is 1182 MW (as on 30th June 2012). The off grid includes 648 MW (waste to energy – urban – 105 MW, biomass non-bagasse cogen-391MW, biomass gassifier – rural – 16 MW and biomass gassifier Industrial – 136 MW. During 2011 alone, 25 rice hursk based gassifier system for industrial generation were installed in 70 remote villages of Bihar. The largest biomass gas plant is at Sirohi, Rajasthan of 20 MW capacity. In 2011, biomass gassifier of 1.2 MW was installed in Gujarat & 0.5 MW in Tamil Nadu. In Kakadpara, Nasik district of Maharashtra, a test project of 10 KW gassifier was commissioned in 16th April 2011 to feed power to 85 households in the village. The power supplied meets the need of domestic lighting, street lighting and other entertainment activities. Power is supplied from 7 PM to 2AM at night. The project was commissioned with financial assistance from ministry of new & renewable energy forces and is running successfully since then. Such role models can be replicated in rural areas


25

which can meet power as well as cooking gas need. VI.ISSUES AND CHALLENGES ION BIOMASS BASED DISTRIBUTED POWER GENERATION

No technology is free from drawbacks. Idea is to remove process bottlenecks, provide financial incentive, raise awareness & provide training to make it a sustainable model to meet power needs of rural folks. Then, this model can be replicated across various states to act as role model, provide rural upliftment both socially & financially. This is important as 70% of total population lives in rural area. Some areas are located from electricity grid & there are no ways of providing electricity due to high cost of laying transmission lines, inaccessibility or are insurgency affected or due to several other reasons. Some of the major issues are listed below:-

(i) Difficulty in ensuring continues supply of feed stock.

(ii) High cost of generated energy. It ranges from 3.43 – 5.46 Rs. / KWH

(iii) Rising cost of feed stock. (iv) Capital cost of large size unit is high (4.5

to 5 Rs. Crore / MW). (v) The unit cost depends upon cost of feed

stock, plant food factor & conversion efficiency.

(vi) Due to low energy density in biomass, the conversion efficiency is poor. For example, the energy content in sugar cane is 2%, corn – 1%, forest residue – 0.8% food plants – less than 0.8%. The maximum theoretical efficiency is 10%.

(vii) Handling of residue is cumbersome. For example, gasification method produces residue such as ash and tarry condensate.

(viii) Power plants below 6 MW are not economically sustainable and above 10 MW face raw material logistic problems.

The life of plant on an average is 20 years which can be extended further by 10 years by major rehabilitation. The average plant load factor varies from 45-55%. The average time required for commissioning is 18 months provided there are no issues related to funding & feed stock collection. Even after due to these reasons, it is still an attractive option. Govt. of India provides financial incentives, these include following:-

(i) 80% deprecation can be claimed in first year for co-generation unit such as back pressure turbine, extraction cum condensing, low inlet pressure small turbine etc.

(ii) There is income tax holiday for 10 years (iii) Concessional customs and excise duty

exemption is granted for machinery and components.

(iv) General sales tax exemption is available in certain states.

Apart from financial incentives extended by central government following needs tobe done by state government – (i) Subsidy need to be given for plant &

machinery to the extent of 80% the rest 20% to be shared by gram panchayat.

(ii) A sustainable means of feedstock generation is required to feed the plant. It can be decided based on availability at site. The restriction s on use of forest produce need to be removed (under forest Act).

(iii) The small scale entrepreneurs need to be encouraged to produces/ fabricate machinery locally.

(iv) Interest free financial assistance need to be provided for overhauling of the system after a prefix period.

(v) State energy development agency can provide help in development of train pool of manpower at site.

(vi) A business model can be develop in the form of energy service companies who


26

would operate on build, operate & maintain bases at a tariff structure decided by state energy regulatory body.

CONCLUSION

From foregoing discussion, it emerges that biomass based distributed power generation holds promise of being a vehicle for rural electrification in India. However, due to some technical and commercial issues, it can be made economically viable by providing thrust in problems area by the state energy agency. With active support of ministry of new & renewable energy sources.

REFERENCES

[1]Nadejda M.Victor,, David G. Victor, “Macro patterns in the use of traditional bio mass fuels” Stanford / TERI workshop on rural energy transition, 5-7 Nov, 2002.

[2] www.bea.doc.gov/bea/dn1.htm. [3] www.bp.com/centres/energy 2002/ [4]IEA (1998), ‘Biomass Energy; Data,

Analysis and Trends, “IEA, Sept, 1988.


27

Economic and Environmental Analysis of an Autonomous Power Delivery System Utilizing Hybrid Solar - Diesel -

Electrochemical Generation

Trina Som1 Shweta Singh2Akhil Sharma3 Kushagar4 NIEC, Delhi NIEC, Delhi NIEC, Delhi NIEC, Delhi [email protected] [email protected]@yahoo.com

Abstract - The growing awareness of power shortage and high demand for reliable power supply the centralized power system is shifting towards decentralized power generating systems or distributed generations. Moreover, the concerns towards global warming and depleting oil/gas reserves have made it inevitable to seek energy from renewable energy resources. Many nations are embarking on introduction of clean/ renewable solar energy for displacement of oil-produced energy. Photovoltaic power generating modules (PV) with diesel generators (DG) and battery energy storage systems (BESS) is an emerging hybrid energy generation technology. It promises great deal of challenges and opportunities for developed and developing countries. The present work depicts the economic analysis and environmental impacts of a decentralized or distributed power delivery system integrated with a hybrid distributed energy resources (DERs). The model for decentralized power delivery system has been developed using MATLAB Simulink considering load demand scenario for a small village in India. Optimal power generation has been made using different sets of distributed energy resources, pertaining to cost estimation and respective environmental impact. The results show a cost effective power delivering network for hybrid DG and BESS, but PV-BESS distributed energy resources represents a beneficial power delivering network from environmental aspect. Keywords: DERs, Economy, Environmental Impact. I. INTRODUCTION

The need for energy-efficient electric power sources in remote locations is a

driving force for research in hybrid energy systems.Power utilities in many countries round the world are diverting their attention toward more effective and renewable electric power sources [1,2]. Reasons for this interest include the possibilities of taxes or other penalties for emissions of greenhouse gases as well as other pollutants with finite supply of fossil fuels. The use of renewable energy sources in remote locations could help reduce the operating cost through the reduction in fuel consumption, increase system efficiency, and reduce noise and emissions. The electricity sector in India though installed capacity of 199.6 Gigawatt (GW) as of March 2012 among which thermal power plants constitute 65% and hydroelectric about 21% and rest being a combination of wind, small hydro, biomass, waste-to-electricity, and nuclear, but still over one third of India's rural population lacked electricity, as did 6% of the urban population and the rest access the electricity with intermittent and unreliable supply [3-6]. Due to this huge gap of shortage between power supply and demand, an Indian load demand scenario has been considered for modeling an autonomous power delivery framework integrated with DERs and consumers. The economic part of the model calculates the fuel consumed per kilowatt-hours for DG and battery energy storage system along with the total initial cost for different DERs, and constructional cost for power delivery network. The environmental part of the model calculates the CO2, particulate matter


28

(PM), and the NOx emitted to the atmosphere [1]. Simulations based on an actual system in the remote village of India were performed for three cases as follows; Case I: Autonomous power delivery system consist of hybrid photovoltaic power generating modules (PV) - diesel generators (DG) - battery energy storage system (BESS) as DERs. Case II: Autonomous power delivery system consists of hybrid diesel generators (DG) - battery energy storage system (BESS) as DERs. Case III: Autonomous power delivery system consisting of hybrid photovoltaic power generating modules (PV) - diesel generators (DG) as DERs. II. PROBLEM FORMULATION

Economic estimation for distributed power system has been analyzed by optimal power generation from different sets of DERs. The power optimization is based on the logic of meeting the required load demands in apportion to the electrical production between the PV [7], DG [8] and battery system.

PHYSICAL DESCRIPTION The stimulant model for case I, as shown in figure.1, contain all 3 power generating resources, namely photovoltaic module, diesel generator and battery bank. Initially the load power required is compared with the power supplied by the pv module. If the generated power is more than the required power then the excess power is used for the charging of battery bank, while if the power generated by the pv module is not enough to feed the load entirely then the pv module supplies as much power during the day time, and the remaining demand is supplied by DG or BESS. This is done by comparing the power delivering capacities of diesel generator and BESS, i.e. if the battery energy storage system is not able to supply the required load then it provides upto its

installed capacity and finally the remaining load requirement is met by the diesel generator. Diesel generators for our experiment purposes have been taken for such a capacity that it fulfills the remaining load requirement, and has been used as a last power generating option in consideration to environmental aspect. The stimulant model for case II, as shown in figure.2, consists of hybrid DG-BESS power generating resources. The optimal power operation is performed by the same logic as used for case I. Here the load power required is compared with the power supplied by DG. If the generated power is less than the required demand then the remaining power is delivered by BESS, or it will charge the BESS. Figure.3 represents the stimulant model for case III. This consists of hybrid PV-DG as distributed energy resources. The optimal power operation is performed by the same logic as used for case I and case II. Here the load power required is compared with the power supplied by PV during day time. If the generated power is less than the required demand then the remaining power is delivered by BESS, or if the power generated is more than demand the excess power is fed to BESS for charging, which further helps in delivery power during peak and night time.

INPUT PARAMETERS The input parameters considered for the simulation are load demand data for a real-time Indian scenario, initial costs for different DERs and annual solar irradiance for India [9]. These three input parameters are shown in figure 4, table 1 and figure 6 respectively.


29

Figure 1. Optimal power generation through hybrid PV-DG-BESS

Figure 2. Optimal power generation through hybrid DG-BESS

Figure 3. Optimal power generation through hybrid PV-DG


30

Figure 4. Load data for an Indian Village

Table 1. Initial Costs for DERs

Figure 5. Annual Solar Irradiance in India

CODES DEVELOPED: Coding used for optimal generation for case I

function P = fcn(Ir) DF=0.8; %derating factor% RC=12; %rated capacity% Sr=1; %standard irradiance% P=(DF*(RC*(Ir/Sr)))'; %solar irradiance varying with month and place% function [Pln,Plp] = fcn(u,j) %u=pv power %v=load power required %Plp=charging power %Pln=remaining requirement if j>u Pln = (j-u); Plp = 0; else Plp = (u-j); Pln = 0; end Coding used for Case II and CaseIII

function y = fcn(c,d) r=10; y=r+c-d; for discharge of BESS a feedback loop is made with the help of another comparison block which compares the available battery power to the required demand. function [y,z] = fcn(u,v) %u=power requirement %v=Available battery power r=0; if u>r if v>u y = v-u; z=0; else y=v; z=u-v; end else y=0; z=0; end

Elements Ratings Initial Cost (Rs)

Running Cost (Rs.)

PV, DG and BESS

PV=12 KW

DG=50 KW

BESS=10 KW

10016099

40.67/gallon

40.67/gallon

PV and DG

PV=12 KW

DG=100 KW

8442068 40.67/gallon

DG and BESS

DG=100 KW

BESS=10 KW

7011264

40.67/gallon


31

Coding for Output functions: function [fc,cost,NOx,PM,Co2] = fcn(u) fc=u; % in pounds cost=u*40.3*3.67; %in rupees NOx=u*0.017*7.1; %in pounds Co2=u*1.7*7.1; %in pounds PM=u*1.91/8; %in grams III. RESULTS

The simulated results for case I in terms of running cost, i.e. fuel consumption cost, NOx emission, carbon-dioxide, and particulate matters emission are presented in figure 6.

Figure 6. Results for case I The first two panes of fig. 6 denote the cost results, while the last 3 panes give us the results for emission of pollutants. The results for case II and case III are portrayed in figure 7 and figure 8 respectively.

Figure 7. Results for case II

Figure 8. Results for case III The comparative results between case I, case II and case III has been presented in table 2 as shown below.


32

CONCLUSION

The present work concludes that a decentralized power delivery system using different hybrid - non-conventional energy resources are very encouraging and effective for future power supply in an Indian scenario. The comparative studies for different power delivery models utilizing different sets of hybrid DERs depict different costs and environmental impacts. It has been observed that though case III provides a cost effective power delivery system, but from environment perspective, it has been obtained as an inferior system in comparison with case I. The power optimization using all the three types of DERs focuses on both economical and environmental aspects. Hence, the simulation models give us various power delivery options leading to more economical, eco-friendly and reliable future power.

REFERENCES

[1]. Ron. A. Jhonson, Ashish N. Agrawal, Tyler J. Chubb, ‘Simulink Model for Economic Analysis and Environmental Impacts of a PV With Diesel-Battery System for Remote Villages’, IEEE Transactions on

power system, Vol. 20, No. 2, May 2005.

[2]W. S. Fyfe, M. A. Powell, B. R. Hart, and B. Ratanasthien, “A globalcrisis: Energy in the future,” Nonrenewable Resources, pp. 187–195,1993.

[3]A report on ‘Power sector at a glance:

All India data’. Ministry of Power,Government of India. October 2011.

[4]A report on ‘World Energy Outlook 2011: Energy for All’. International Energy Agency. October 2011.

[5] ‘Winds of change come to country plagued by power blackouts’ Guardian. 30 december 2008. Retrieved on 2012-01-13.

[6]‘Nuclear Power Corporation of India Limited (NPCIL) Annual Report’, 2010–2011’. [7]Stand-Alone Photovoltaic Systems: A Handbook of Recommended Design Practices (Revised), Sandia National Labs, Albuquerque, 1995

[8]F. P. Dawson and S. B. Dewan, ‘Remote diesel generator with photovoltaic cogeneration,’ in Proc. Solar Conf., Denver, CO, Sep. 1989, pp.269–274.

[9]National solar radiance database http://rredc.nrel.gov/solar/old_data/nsrd

DERs outputs

PV-DG-BESS PV-DG DG-BESS

Total installation cost (Rs)

10016099 8442068 7011264

Fuel Consumption (Gallons)

101.2842 140.5393 352.5071

Total Fuel cost (Rs) 14969.77 20785.903 52136.1525

TotalAnnual Cost(Rs) 10031068.77 8462853 7063400

NOX Emitted (Pounds) 12.2167 16.9630 42.5476

CO2 Emitted (Pounds) 1221.663 1696.30935 4254.7607

PM Emitted (Grams) 24.165 33.905 84.1610


33

[10]G. Kats, ‘The Costs and Financial Benefits of Green Buildings,’ California’s Sustainable Building Task Force, 2003.


34

A Topology Survey of Doubly-Fed Induction Generators for Wind Turbines

Rishu Goel1 Amit Patel2 Kamal Singh3 RGGI,Meerut RGGI,Meerut RGGI,Meerut

[email protected] [email protected] [email protected]

Abstract- By the use of doubly fed induction generator we can efficiently use variable speed wind turbine with proper pitch control. In this paper, we have studied how to minimize the magnetizing losses using power electronics equipment based doubly fed induction generator, on account of which it consumes only a fraction of total power and thereby increases the electrical energy as well. For this we have studied two methods, first- short circuiting stator and transmit all the wind power to the convertor and the second is maintaining connections of stator as Δ-connected at high wind speeds and Y-connected at low wind speed. The dissect of this approach is that we get fairly low rotational speed which can be compensated by using gear box or by pole pair of the generator. This paper deals with the review of the progress made in the area of doubly-fed induction generator (DFIG) for wind turbines till date. I. INTRODUCTION Wind turbines (WTs) can either operate at fixed speed or variable speed. For a fixed speed wind turbine the generator is directly connected to the electrical grid. For a variable speed wind turbine the generator is controlled by power electronic equipment. There are several reasons for using variable-speed operation of wind turbines; among those are possibilities to reduce stresses of the mechanical structure, acoustic noise reduction and the Possibility to control active and reactive power [1]. Most of the major wind turbine manufactures are developing new larger wind turbines in the 3-to-5-MW range [2]. These large wind turbines are all based on variable-speed operation with pitch control using a direct driven synchronous generator without gearbox or a

doubly-fed induction generator (DFIG). Fixed-speed induction generators with stall control are regarded as unfeasible [2] for these large wind turbines. Today, doubly-fed induction generators are commonly used by the wind turbine industry for larger wind turbines. The major advantage of the doubly-fed induction generator, which has made it popular, is that the power electronic equipment only has to handle a fraction (20–30%) of the total system power [3]. This means that the losses in the power electronic equipment can be reduced in comparison to power electronic equipment that has to handle the total system power as for a direct-driven synchronous generator, apart from the cost saving of using a smaller converter. According to the energy production can be increased by 2–6% for a variable-speed wind turbine in comparison to a fixed-speed wind turbine, while in [4] it is stated that the increase in energy can be 39%. In [5] it is shown that the gain in energy generation of the Variable-speed wind turbine compared to the most simple fixed-speed wind turbine can vary between 3–28% depending on the site conditions and design parameters. Factors such as speed control of variable-speed WTs, blade design, what kind of power that should be used as a common basis for comparison, selection of maximum speed of the WT, selected blade profile, missing facts regarding the base assumptions etc, affect the outcome of the investigations. There is thus a need to clarify what kind of energy capture gain there could be when using a DFIG WT, both compared to another variable-speed WT and towards a traditional fixed-speed WT.


35

Today, the DFIG WT will be disconnected from the grid when large voltage sags appear in the grid. After the DFIG WT has been disconnected, it takes some time before the turbine is reconnected to the grid. This means that new WTs have to ride through these voltage sags. The DFIG system, of today, has a crowbar in the rotor circuit, which at large grid disturbances has to short circuit the rotor circuit in order to protect the converter. This leads to that the turbine must be disconnected from the grid, after large voltage sag.

II. THEORY The main theoretical aspect is the analysis of the DFIG for a WT application both during steady-state operation and transient operation. The main contribution is dynamic and steady-state analysis of the DFIG, with details being as follows:

WIND TURBINE SYSTEMS Wind turbines can operate with either fixed speed (actually within a speed range about 1 %) or variable speed. For fixed-speed wind turbines, the generator (induction generator) is directly connected to the grid. Since the speed is almost fixed to the grid frequency, and most certainly not controllable, it is not possible to store the turbulence of the wind in form of rotational energy.

Fig.1. Typical characteristic for a variable-speed wind

turbine. a) Rotor speed as a function of wind speed.

b) Mechanical power as a function of wind speed.

Therefore, for a fixed-speed system the turbulence of the wind will result in power variations, and

thus affect the power quality of the grid [6]. For a variable-speed wind turbine the generator is controlled by power electronic equipment, which makes it possible to control the rotor speed. In this way the power fluctuations caused by wind variations can be more or less absorbed by changing the rotor speed [7] and thus power variations originating from the wind conversion and the drive train can be reduced. Hence, the power quality impact caused by the wind turbine can be improved compared to a fixed-speed turbine [8].The rotational speed of a wind turbine is fairly low and must therefore be adjusted to the electrical frequency. This can be done in two ways: with a gearbox or with the number of pole pairs of the generator. The number of pole pairs sets the mechanical speed of the generator with respect to the electrical frequency and the gearbox adjusts the rotor speed of the turbine to the mechanical speed of the generator. There are four types of wind turbine systems as: 1. Fixed-speed wind turbine with an induction generator. 2. Variable-speed wind turbine equipped with a cage-bar induction generator or synchronous Generator. 3. Variable-speed wind turbine equipped with multiple-pole synchronous generator or Multiple-pole permanent-magnet synchronous generator. 4. Variable-speed wind turbine equipped with a doubly-fed induction generator. There are also other existing wind turbine concepts; a description of some of these systems can be found in [9].

FIXED-SPEED WIND TURBINE For the fixed-speed wind turbine the induction generator is directly connected to the electrical grid according to Fig. 2.4. The rotor speed of the fixed-speed wind turbine is in principle


36

Fig. 2. Fixed-speed wind turbine with an induction generator.

determined by a gearbox and the pole-pair number of the generator. The fixed-speed wind turbine system has often two fixed speeds. This is accomplished by using two generators with different ratings and pole pairs, or it can be a generator with two windings having different ratings and pole pairs. This leads to increased aerodynamic capture as well as reduced magnetizing losses at low wind speeds. This system (one or two-speed) was the “conventional” concept used by many Danish manufacturers in the 1980s and 1990s [9].

VARIABLE-SPEED WIND TURBINE The system presented in Fig.3. consists of a wind turbine equipped with a converter connected to the stator of the generator. The generator could either be a cage-bar induction

Fig.3. Variable-speed wind turbine with a synchronous/induction generator.

generator or a synchronous generator. The gearbox is designed so that maximum rotor speed corresponds to rated speed of the generator. Synchronous generators or permanent- magnet synchronous generators can be designed with multiple poles which imply that there is no need for a gearbox, see Fig.4. Since this “full-power” converter/generator system is commonly used for

other applications, one advantage with this system is its well-developed and robust control [7].

Fig.4. Variable-speed direct-driven (gear-less) wind turbine with a synchronous generator

Fig.5. means that the stator is directly connected to the grid while the rotor winding is connected via slip rings to a converter. This system have recently become very popular as

Fig.5. Variable-speed wind turbine with a doubly-fed induction generator (DFIG).

generators for variable-speed wind turbines. This is mainly due to the fact that the power electronic converter only has to handle a fraction (20–30%) of the total power [9]. Therefore, the losses in the power electronic converter can be reduced, compared to a system where the converter has to handle the total power. In addition, the cost of the converter becomes lower. There exists a variant of the DFIG method that uses controllable external rotor resistances (compare to slip power recovery). Some of the drawbacks of this method are that energy is unnecessary dissipated in the external rotor resistances and that it is not possible to control the reactive power.

DOUBLY-FED INDUCTION GENERATOR SYSTEMS FORWIND TURBINES

For variable-speed systems with limited variable-speed range, e.g. ±30% of synchronous speed, the


37

DFIG can be an interesting solution. As mentioned earlier the reason for this is that power electronic converter only has to handle a fraction (20–30%) of the total power [9]. This means that the losses in the power electronic converter can be reduced compared to a system where the converter has to handle the total power. In addition, the cost of the converter becomes lower. The stator circuit of the DFIG is connected to the grid while the rotor circuit is connected to a converter via slip rings, see Fig.5. Amore detailed picture

Fig.6. Principle of the doubly-fed induction generator

of the DFIG system with a back-to-back converter can be seen in Fig.5. The back-to-back converter consists of two converters, i.e., machine-side converter and grid-side converter, which are connected “back-to-back.” Between the two converters a dc-link capacitor is placed, as energy storage, in order to keep the voltage variations (or ripple) in the dc-link voltage small. EQUIVALENT CIRCUIT OF THE DOUBLY-

FED INDUCTION GENERATOR The equivalent circuit of the doubly-fed induction generator, with inclusion of the magnetizing losses, can be seen in Fig.7. This equivalent circuit is valid for one equivalent Y phase and for steady-state calculations. In the case that the DFIG is Δ-connected the machine can still be represented by this equivalent Y representation. In this section the jω-method is adopted for calculations. Note, that if the rotor voltage, Vr, in Fig.7. is short circuited

Fig.7. Equivalent circuit of the DFIG.

the equivalent circuit for the DFIG becomes the ordinary equivalent circuit for a cage-bar induction machine. Applying Kirchhoff’s voltage law to the circuit in Fig.7., yields.

TABLE I Typical parameter of the induction machine in

P.U

Small Machine 4KW

Medium Machine 100KW

Large Machine 800KW

Stator and Rotor resistance

Rs & Rr

0.04 0.01 0.01

Leakage inductance

Lsλ+Lrλ=Lo

0.2 0.3 0.3

Magnetizing inductance

Lm= L

2.0 3.5 4.0

POWER FLOW In order to investigate the power flow of the DFIG system the apparent power that is fed to the DFIG via the stator and rotor circuit has to be determined. The stator apparent power Ss and rotor apparent power Sr can be found as


38

which can be rewritten, using the expressions in the previous section, as

Now the stator and rotor power can be determined as

where the approximations are because the resistive losses and the magnetizing losses have been neglected. From the above equations the mechanical power produced by the DFIG can be determined as the sum of the stator and rotor power. Then, by dividing Pmech with mechanical rotor speed, ωm=ωr/np, the produced electromechanical torque can be found. Moreover, this means that Ps ≈ Pmech / (1 − s) and Pr ≈ −sPmech / (1 − s). In Fig.8, the power flow of a “lossless” DFIG system can be seen.

Fig.8. Power flow of a “lossless” DFIG system.

The mechanical power divides between the stator and rotor circuits and that it is dependent on the slip. Moreover, the rotor power is approximately minus the stator power times the slip: Pr ≈ −sPs. Therefore, as mentioned earlier, the rotor converter can be rated as a fraction of the rated power of the DFIG if the maximum slip is low. METHODS TO REDUCE THE MAGNETIZING

LOSSES FOR THE DFIG There are two methods to lower the magnetizing losses of the DFIG.

1. Short-circuiting the stator of the induction generator at low wind speeds, and transmitting all the turbine power through the converter. This set-up is referred to as the short-circuited DFIG. 2. Having the stator Δ-connected at high wind speeds and Y-connected at low wind speeds; referred to as the Y-Δ-connected DFIG.

SHORT-CIRCUITED DFIG Fig.8. shows a diagram of the “short-circuited DFIG.” In the figure two switches can be seen. Switch S2 is used to disconnect the turbine from the grid and switch S1 is then used to short-circuit the stator of the DFIG. Now the turbine is operated as a cage-bar induction machine, except that the converter is connected to the rotor circuit instead of the stator circuit. This means, that in this operating condition, the DFIG can be controlled in a similar way as an ordinary cage-bar induction generator. For instance, at low wind speeds the flux level in the generator can be lowered.

Fig.9. Principle of the “short-circuited DFIG.”

Fig.11. presents a set-up of the Y-Δ-connected DFIG. As shown in the figure, a device for changing between Y and Δ connection has been inserted in the stator circuit. Before a change from Y to Δ connection (or vice versa) the power of the turbine is reduced to zero and the switch S1 disconnects the stator circuit from the grid. Then the stator circuit is connected in Δ (or vice versa) and the turbine is synchronized to the grid.


39

Fig.10. Principle of the Y-Δ-connected DFIG.

CONCLUSION

In this paper, it has been found that there is a possibility to gain a few percentage units in energy efficiency for a doubly-fed induction generator system compared to a cage-bar induction generator, controlled by a full-power converter. It was found that the method utilizing a Y-Δ switch in the stator circuit had the largest gain in energy of the two investigated methods. Finally, it was found that the converter losses of the DFIG can be reduced if the available rotor-speed range is made smaller. However, the aerodynamic capture of the wind turbine is reduced with a smaller rotor-speed range. This means that the increased aerodynamic capture that can be achieved by a larger converter has, thus, a greater impact than the increased converter losses. Worth stressing is that the main reason for using a variable-speed turbine instead of a fixed-speed turbine is not the energy efficiency, instead it is the possibility of lowering the mechanical stresses and also improving the power quality. It has been shown that by using grid-flux orientation the stability and the damping of the system is independent of the rotor current, in contrast to stator-flux orientation. This implies that for a grid-flux-oriented system, it is possible to magnetize the DFIG entirely from the rotor circuit without reducing the damping of the system.

Moreover, for the grid-flux-oriented system, it is possible to produce as much reactive power as possible and still have a stable system with the same damping from a stability point of view.

FUTURE WORK

The following topics are proposed for future: • Development of a unified estimator for both stator-flux and grid-flux field orientation. Since the flux dynamics are poorly damped, a desired property would be a relatively good damping of the flux dynamics. • More thorough dynamic, steady-state, and experimental analysis of the voltage sag ride-through systems for the DFIG wind turbine. In addition, it is essential to study the hardware configuration of the voltage sag ride-through systems. • Development of mathematical models of wind turbines with voltage sag ride-through properties. Experimental evaluation of the developed models with commercial wind turbines with voltage sag ride-through properties. • Derivation of analytical expressions for the response of the DFIG to unsymmetrical voltage sags.

REFERENCES [1] T. Burton, D. Sharpe, N. Jenkins, and E.

Bossanyi, Wind Energy Handbook. John Wiley & Sons, Ltd, 2001.

[2] T. Ackermann and L. S¨oder, “An overview of

wind energy-status 2002,” Renew. Sustain. Energy Rev., vol. 6, no. 1–2, pp. 67–128, Feb./Apr. 2002.

[3] L. H. Hansen, L. Helle, F. Blaabjerg, E.

Ritchie, S. Munk-Nielsen, H. Bindner, P. Sørensen, and B. Bak-Jensen, “Conceptual survey of generators and power electronics for wind turbines,” Risø National Laboratory, Roskilde, Denmark, Tech. Rep. Risø-R-1205(EN), ISBN 87- 550-2743-8, Dec. 2001.


40

[4] D. S. Zinger and E. Muljadi, “Annualized

wind energy improvement using Variable speeds,” IEEE Trans. Ind. Applicat., vol. 33, no. 6, pp. 1444 1447, Nov./Dec. 1997.

[5] P. Mutschler and R. Hoffmann, “Comparison

of wind turbines regarding their energy generation,” in Proc. 2002 IEEE 33rd Annual IEEE Power Electronics Specialists Conference, vol. 1, Cairns, Qld., Australia, June, 23–27, 2002, pp. 6–11.

[6] M. P. Papadopoulos, S. A. Papathanassiou, N.

G. Boulaxis, and S. T.Tentzerakis,“Voltage quality change by grid-connected wind turbines,” in European Wind Energy Conference, Nice, France, 1999, pp. 783–785.

[7] T. Petru and T. Thiringer, “Active flicker

reduction from a sea-based 2.5 MW wind park connected to a weak grid,” in

Proc. Nordic Workshop on Power and Industrial Electronics, Aalborg, Denmark, June, 13–16, 2002.

[8] A. Larsson, P. Sørensen, and F. Santjer, “Grid

impact of variable speed wind turbines,”in Proc. of European Wind Energy Conference and Exhibition (EWEC´99), Nice, France, Mar., 1–5, 1999.

[9] L. H. Hansen, L. Helle, F. Blaabjerg, E.

Ritchie, S. Munk-Nielsen, H. Bindner, P. Sørensen, and B. Bak-Jensen, “Conceptual survey of generators and power electronics for wind turbines,” Risø National

Laboratory, Roskilde, Denmark, Tech. Rep. Risø-R-1205(EN), ISBN 87

550-2743-8, Dec. 2001.


41

Modelling and Simulation of Single Shaft Micro Turbine in Distributed Generation System

Ajit Kumar Sharma1 Deepak Kumar Thakur2

NIEC, New Delhi NIEC, New Delhi [email protected] [email protected] Abstract - Distributed generation (DG) is going to become more important in the future generating system. Utility restructuring technology evolution, public environmental policy, and expending power demand are providing the opportunity for micoturbine and fuel cells to become important energy resources. This paper deals with the performance of a microturbine connected to a LV grid during different transient events in the network. The study is based on the dynamic modeling of a microturbine and the simulation of different events in the Matlab/Simulink environment. I.INTRODUCTION

A study by the Electric Power Research Institute (EPRI) indicates that by 2010, 25% of the new generationwill be distributed; a study by the Natural Gas Foundation concluded that this figure could be as highas 30% [1]. The European Renewable Energy Study (TERES), commissioned by the European Union (EU)to examine the feasibility of EU CO2-reduction goalsand the EU renewable energy targets, found thataround 60% of the renewable energy potential that can be utilized until 2010 can be categorized as decentralized power sources [2]. Traditional nonutility-generated power sources, such as emergency and standby power systems, have minimal interaction with the electric power system (EPS). As distributed generation (DG) hardware becomes more reliable and economically feasible, there is an increasing trend to interconnect those DG units with existing utilities to meet various energy needs and

offer more service possibilities to customers and the host EPS. Among these possibilities are: 1. Standby/backup power to improve the

availability and reliability of electric power.

2. Peak load shaving. 3. Combined heat and power. 4. Sales of power back to utilities or other

users. 5. Renewable energy 6. Power quality, such as reactive power

compensation and voltage support 7. Dynamic stability support.

Distributed generation is a new approach in the electricity industry and as the analysis of the relevant literature has shown there is no generally accepted definition of distributed generation[3] For example, Anglo-American countries often use the term ‘embedded generation’, North American countries the term ‘dispersed generation’, and in Europe and parts of Asia, the term ‘decentralized generation’ is applied for the same type of generation.And because of different government regulations, the definition of the rating of each distributed power station also varies between countries;several country-specific strict definitions are available for DG all over the world, depending upon plant rating, generation voltage level, etc. However, the impact of DG on the power system is normally the same irrespective of these different definitions. According to several research studies,


42

Some universally accepted common attributes of DG are as follows: It is not centrally planned by the power

utility, nor centrally dispatched. It is normally smaller than 50 MW. The power sources or distributed

generators are usually connected to the distribution system, which are typically of voltages 230/415 V up to 145 kV.

II.DISTRIBUTED ENERGY

RESOURCES

Renewable or non-conventional electricity generators employed in DG systems or Microgrids are known as distributed energy resources (DERs) or micro sources. The main advantage of Microgrids is to combine all benefits of non-conventional/ renewable low-carbon generation technologies and high-efficiency combined heat and power (CHP) systems the CHP-based DERs facilitate energy efficientpower generation by capturing waste heat while low-carbon DERs help to reduce environmental pollution by generating clean powerProspective DERs range from micro-CHP systems based on Stirling engines, fuel cells and microturbines to renewables like solar photovoltaic (PV) systems, wind energy conversion systems (WECS) and small-scale hydroelectric generation CHP generation systems are most promising as DERs for Micro grid applications. Their main advantage is energy-efficient power generation by judicious utilization of waste heat. One of the main energy producers in CHP system is micro turbine. III.MICROTURBINE

Microturbines are small single staged combustion turbines that generate between 25 kw to 500 kw of power although their size varies.

Microturbine is based on technology as a jet engine but integrates patented air bearing and innovative recuperator technology with state of art electronics. The result is a versatile, reliable, environmentally beneficial solution for generations that is virtually maintenance free. The designs for micro turbine are composed in five parts:

1. TURBINE There is two kinds of turbines, high speed single shaft turbine (fig 1) and split- shaft turbine (fig 2). Single shaft unit is high speed synchronous machine with compressor and turbine mounted on the same shaft. For these machine, the turbine speed range from 50,000 rpm to 120,000 rpm. On the contrary, the split shaft design uses a power turbine rotating at 3,000 rpm and a conventional generator connected via a gearbox for speed multiplication. The single shaft turbine uses permanent magnet synchronous generator (PMSG) or asynchronous generator for power generation.

2. ALTERNATOR OR CONVENTIONAL MACHINE

In the single shaft design, an alternator is directly coupled to single shaft turbine. The rotor is either a two or four pole permanent magnet design, and the stator is a conventional copper wound design. In split shaft design a conventional induction or synchronous machine is mounted on power turbine via a gear box.

Fig 1: Single shaft microturbine


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Fig 2: Split shaft microturbine

3. POWER ELECTRONICS In single shaft design of alternator to generate a very high frequency. Three phase signal ranging from 1500 to 4000 Hz. The high frequency voltage is first rectified and then inverted to a normal 50 Hz voltage. In split phase turbine design power inverters are not needed.

4. RECUPERATOR The recuperator is a heat exchanger which transfers heat from the exhaust gas to the discharge air before it enters the combustor. This reduces the amount of fuel required to raise the discharge air temperature to that required by turbine.

5. CONTROL SYSTEM

Control system is included full control of turbine.

TURBINE MODEL DESCRIPTION Microturbine–generator (MTG) system consisting of a microturbine (MT) coupled with a synchronous generator. The model is then used to perform the load-following analysis of the MTG system in both stand-alone and grid-connected modes. The MTG is analysed for slow dynamic performance of the system and not for transient behaviors. Therefore modeling is based on the following assumptions: (1) System operation is under normal operating conditions. Start-up, shutdown and

fast dynamics (faults, loss of power, etc.) are not included.

Fig3 : Power works microturbine (2) The MT’s electromechanical behavior is of main interest. The recuperatoris not included in the model as it is only a heat exchanger to raise engine efficiency. Also, due to the recuperator’s very slow response time, it has little influence on the timescale of dynamic simulations. (3)The temperature and acceleration controls have been omitted in the turbine model as they have no impact on the normal operating conditions. Temperature control acts as an upper output power limit. At normal operating conditions, the turbine temperature remains steady, and hence, it can be omitted from the model. Acceleration control is used primarily during turbine start-up to limit the rate of the rotor acceleration prior to reaching operating speed. If the operating speed of the system is closer to its rated speed, the acceleration control could be eliminated in the modeling. (4) Governor model has been omitted as the MT does not use any governor. IV. MODELING OF MICROTUBINE


44

Single shaft micro turbine [8] operates in

the thermodynamics cycle known as a Brayten cycle. The produce rotating mechanical power in the turbine turns both the compressor and generator. This generator requires high frequency (about 1.6 kHz). Micro turbine is generally equipped with controls that allow the unit to be operated either in parallel with, or independent of grid. The block diagram of the single shaft gas turbine isshown in Fig. The model includes the temperaturecontrol, fuel system, turbine dynamic, speed governorand acceleration control blocks. The output of the speedcontrol, temperature control, and acceleration control areall inputs of a low value select (LVS) block, whoseoutput is the input of fuel system.

TURBINE MODEL DESCRIPTION

Microturbine–generator (MTG) system consisting of a microturbine (MT) coupled with a synchronous generator. The model is then used to perform the load-following analysis of the MTG system in both stand-alone and grid-connected modes. The MTG is analysed for slow dynamic performance of the system and not for transient behaviors. Therefore modeling is based on the following assumptions: (1) System operation is under normal operating conditions. Start-up, shutdown and fast dynamics (faults, loss of power, etc.) are not include

Fig 5 : Block diagram of speed and acceleration control

As shownabove in Fig, the speed governor controller has been modeled by using the lead-lag transfer function, where W is the controller gain, X (Y) is the governor lead (lag) time constant, and Z is a constant representing the governor droop or isochronous modes. Acceleration control is used during turbine startup to limit the rate of the rotor acceleration. If the operating speed of the system is close to its rated speed, the acceleration control system could be eliminated [5]

FUEL CONTROL The fuel control system scheme is shown in Fig 6. It consists of series blocks of the valve positioner and flow dynamic.

E1 = ܽ

ݏܾ + ܿ ݂d And for the flow dynamic transfer function,

W1 = 1

ݏ݂ܶ + ܧ1


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Fig 6: Block diagram of fuel system

Where, ais the valve positioner gain, band Tfare thevalve positioner and fuel system time constant. cis a constant. fdand E1are the input and output of the valve positioner and Wfis the fuel demand signal in per unit.

COMPRESSOR-TURBINE The gas turbine block diagram is shown in figure 7. The signals to the gas turbine are the fuel flow, Wf(signal from the fuel control) and the speed deviation, ΔN. The output signals are the turbine torque. The gas turbine dynamic transfer function is expressed by

Wf2 = 1

ݏܦܥܶ + 1ܹ݂ Where, TCD is the gas turbine dynamic time constant. The torque characteristic of the single shaft microturbine is the function of the following equation

f2= af2+ bf2.Wf2+ cf2.ΔN

Where, f2is a function whose inputs are fuel flow and turbine speed.

Fig 7: Block diagram of compressor-turbine

TEMPERATURE CONTROL

The temperature controller block diagram is shown in fig 8. The input temperature controller is the fuel flow and turbine speed and the output is temperature control signal to the LVS. The fuel burned in combustor results in turbine torque and in exhaust gas temperature. The exhaust temperature characteristic of the single shaft microturbine equation,

f1= TR − a f 1. (1−Wf 1)+ bf2.ΔN

Where,f1is a function whose inputs are fuel flow and turbine speed. the exhaust temperature is measured using a set of thermocouples incorporating radiation shields. The output of the thermocouple is compared with a reference value. In below fig,K4 and K5are constant in radiation shield transfer function. T3 and T4 are the timeconstant of the radiation shield and thermocouple transfer function respectively. T5 and Ttare the time constant of the temperature control transfer function.When the temperature control output signal becomes lower than the speed controller output, the former value will pass through the LVS to limit the turbine’s output and the turbine operates on temperature control mode.


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Fig 8: Block diagram of temperature control V.PERMANENT MAGNET

SYNCHRONOUSGENERATOR MODEL

The electrical generator is a high speed

permanent magnet synchronous generator (PMSG) and it has been modelled using a 5th order model in the d-q reference frame [6]. The three equations of the electrical part assume sinusoidal flux:

The other two equations of the model are the mechanical equations of a rotating single shaft with the damping (friction factor) neglected:

The parameters of the model are shown in Table 1. They have been obtained from the manufacturer data [7] and from the experimental tests.

Table 1 - PMSG main parameters

VI. POWER ELECTRONIC

INTERFACE

Power Interface unit consist of a rectifier-inverter system with DC link. It is a general configuration of power electronic interface in the MTU. The high frequency electric power of PSMG must be converted to DC, inverted back to 60 or 50 Hz AC and filtered to reduce harmonic distortion. An IGBT based PWM inverter is used with a 2 kHz carrier frequency. The inverter injects AC power from DC link of the MTU to the AC distribution system [9-10]. The MT units are connected in parallel to achieve the required total system capacity and provide a level of redundancy. Grid connected mode (on-grid mode) allows the MTU to operate parallel to the grid, providing base loading and peak shaving and grid support. Stand alone mode (offgrid mode) allows the MTU to operate completely isolated from the grid. In dual mode, the MTU can switch between these two modes automatically. Two different control strategies have been considered [11-12]


47

1. P-Q control strategy for on-grid operation mode

2. V-f control strategy for off-grid operation mode.

Fig 9: Power Electronics Interface

P-Q CONTROL In this controlling mode, the inverter must regulate the DClink voltage at 0.75 kV, and control the active and reactive powers injected into the AC grid, considering theset points, Prefand Qref. These set points can be chosen by the customer or remote power management units. The P-Q control strategy is shown in Fig. phase lock loop (PLL) is used to synchronize the PWM inverter with the grid.

Fig 10. P-Q control

The reference currents are as follows:

The zero-sequence current in the zero coordinatereference is io. The three-phase current references to be fed into the Hysteresis Current Control (HCC) scheme by the following equation:


48

V – F CONTROL In this control mode, MTU should supply AC loads, such as nonlinear and unbalanced loads. Below fig shows the control scheme, which regulates the voltage and frequency of the islanded operation mode. In the design of the V-f controller, the frequency ω is obtained by a Phase Lock Loop (PLL), which measures the AC voltage of the AC distribution network. In this case, theload voltage is regulated at desired voltage amplitude and phase by a PI controller using a − b − c to d − q − 0 and via laplacetransformations. LC filter is used to eliminate switching harmonics. As shown in Fig. the reference voltage calculation box calculates the reference voltages. The load voltages are detected and then transformed into synchronous d − q − 0 references.

Fig 11: V-f Control

The load voltage should be sinusoidal with constantamplitude and frequency. So, the expected load voltages in d − q − 0 reference frame have only one value, The reference voltage is calculated, as follows,


49

Vldqovoltages afterpassing through a PI block are transformed into a − b − c synchronous reference frame, in order to obtain the reference voltage for the PWM voltage control system. VII. CASE STUDIES

Following cases have been simulated in

MATLAB Simulink. Total simulation time for each case is 300 seconds for off- gridmode and 500 seconds for grid-connected mode. The output powers and loads are expressed as per unit (p.u.) with 150 kVA base. The speed responses are also expressed in per unit with reference to a base speed of 3,600 rpm.

OFF GRID MODE Case 1: In this case, the MT unit is initially running with a load of 30 kW (0.2 p.u.) applied to the generator bus up to t = 150 seconds. Another step load of 90 kW (0.6 p.u.) is applied at t = 150 seconds. The load on the MTU is shown in Figure 12.

Figure 12: Load on MTU

Figure13 (a&b) shows the mechanical power output of MT. It is observed that MT power output takes about 90 seconds to match the load demand. MTG speed plotted in Figure shows that MTG system takes almost the same time to reach the new steady-state speed at the new load.

Figure 13(a) MT mechanical power; (b) MTG speed

The electrical power output of the generator is shown in Figure 14.It is seen to closely follow the step change in load demand.


50

Figure 14: Generator electrical power

Case 2 In this case, a speed control has been incorporated in the stand-alone MTG system to maintain the speed constant at 1 p.u. The MTG is running initially at no load. At time t = 50 seconds a load of 0.2 p.u. is applied and at t = 200 seconds another load of 0.6 p.u. is applied. The mechanical power output of the MT shown in Figure 15 indicates that the MT follows the load demand with a time lag of approximately 50 seconds.

Figure 15: MT mechanical power

The generator power output shown in Figure 16. indicates that it closely follows the load as in Case 1. The plot of MTG speed shown in Figure17indicates that speed reaches 1 p.u. and is maintained at that level at the new load.


Figure 17: MTG speed

GRID-CONNECTED MODE

Case 1 In this mode, the MTG system is connected to the utility grid. Initially, both MTGsystem and grid are running separately at no load. At t = 5 seconds, loads of 0.2 p.u. and 160 kW (1.07 p.u.) are applied separately to the MTG and the grid, respectively. At t = 125 seconds another load of 0.6 p.u. is applied to MTG. At t = 250 seconds, the MTG is interconnected with the grid and at


51

t = 375 seconds it is again disconnected from the grid. The MT mechanical power output and the generator electrical power output are shown in Figures 18 & 19,respectively.

Figure 18: MT mechanical power


The responses show that load on MTG reduces to some extent due to grid support when it is grid-connected from t = 250 to 375 seconds. When standalone, theMTGis taking up its entire load of 0.8 p.u

Figure 20: Generator voltage

Figure20, shows that thegenerator voltage dips from 1 p.u. at t = 250 seconds during grid-connection but again settles down to 1 p.u. Again, during grid-disconnection generator voltage momentarily shoots up above 1 p.u. but again settles down to 1 p.u. The variation of MTG speed shown in Figure indicates that speed settles down to 1 p.u. after application of load and after connection and disconnection events. generator voltage dips from 1 p.u. at t = 250 seconds during grid-connection but again settles down to 1 p.u. Again, during grid-disconnection generator voltage momentarily shoots up above 1 p.u. but again settles down to 1 p.u. The variation of MTG speed shown in Figure indicates that speed settles down to 1 p.u. after application of load and after connection and disconnection events. The plot of grid power in Figure 21, shows that when MTG is connected to the grid at t = 250 seconds, it shares a load of about 12 kW (0.08 p.u.) from the MTG. This is also evident from Figures 21 & 22,that show a similar 0.08 p.u. reduction in MT mechanical power and generator electrical power, respectively. The shared load is again transferred to MTG as it is disconnected at t = 375 seconds.


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Figure 21: MTG speed

Figure 22: Grid power

CONCLUSION

The modeling of a single-shaft MTU suitable for off-grid (isolated) and on-grid operation modes is presented in this paper. The simulation of on-grid and off-grid operation modes shows that the presented model is suitable for dynamic studies.

REFERENCES

[1]R.H. Lasseter, Control of distributed resources, in: L H. Fink, C.D. Vournas (Eds.), Proceedings: Bulk Power Systems

Dynamics and Control IV, Restructuring, organised by IREP and National Technical University of Athens, Santorini, Greece, August 23–28, 1998, pp. 323–329.

[2]M. Grubb, Renewable Energy Strategies for Europe-Volume I, Foundations and Context, The Royal Institute of InternationalAffairs, London, UK, 1995.

[3]CIRED, Dispersed Generation; Preliminary Report of CIRED (International Conference on Electricity Distribution), Working Group WG04, Brussels, Belgium, June 1999.

[4]Hydro-Québec, “SimPowerSystems 5 User’s Guide”, 3 Apple Hill Drive, Natick, MA, USA. See also: http://www.mathworks.com/products/simpower/

[5]S. Guda, C. Wang, M. Nehrir, "Modeling of Microturbine Power Generation Systems, Electric Power Components and Systems," Volume 34, Number 9, September 2006,pp. 1027-1041(15).

[6]Casoria S, “VSC-Based HVDC Transmission System”, in Sim Power Systems 5 User’s Guide.

See also: http://www.mathworks.com/products/simpower/

[7]“Capstone Model C30 MicroTurbine Technical reference. Component description”, Ref. 410014-001 Rev B, August2003. See also: http://www.capstoneturbine.com

[8]R.H. Lasseter, Control of distributed resources, Proceedings of the 1998 International Conference on Bulk Power Systems Dynamics and Control IV*/Restructuring, Santorini, Greece,August 1998, pp. 323_/330.

[9]R. Lasseter, "Dynamic Models for Microturbines and Fuel Cells," IEEE PES Summer Meeting, 2001.


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[10] Al-Hinai, A. Feliachi,"Dynamic Model of a Microturbine Used as a Distributed Generator," IEEE Proc. 34-th Southeastern Symposium on System Theory, 2002, pp: 209- 213.

[11]Bertani, C. Bossi, F. Fornari, S. Massucco, S. Spelta, F. Tivegna, "A microturbine generation system for grid connected and islanding operation," Power SystemsConference and Exposition, 2004. IEEE PES, Vol. 1, 10- 13 Oct. 2004, Page(s): 360 - 365.

[12]O. Fethi, L.-A. Dessaint, K. Al-Haddad, "Modeling and simulation of the electric part of a grid connected microturbine," Power Engineering Society General Meeting, 2004. IEEE, Vol.2, 6-10 June 2004 Page(s): 2212 – 2219.

[13]Al-Hinai, A.; Schoder, K.; Feliachi, A., "Control of gridconnectedsplit-shaft microturbine distributed generator,"System Theory, 2003. Proceedings of the 35thSoutheastern Symposium, 16-18 March 2003 Page(s): 84– 88.

[14]L. N. Hannett, Afzal Khan, "Combustion Turbine Dynamic Model Validation from Tests," IEEETransactions on Power Systems, Vol. 8, No. 1, February1993

[15]Ahn, J.B., Jeong, Y.H., Kang, D.H., Park, J.H, "Development of high speed PMSM for distributed generation using microturbine," Industrial Electronics Society, 2004.IECON 2004. 30th Annual Conference of IEEE, Vol. 3, 2-6 Nov. 2004 Volume: 3, on page(s): 2879- 2882

[16]T. E. Hoff, National Renewable Energy Laboratory, IntegratingRenewable Energy Technologies in the Electric Supply Industry: A Risk Management Approach; December 1996, http://wwwleland.stanford.edu/_tomhoff/cv.htmcreports.

[17]H.R. Linden, Distributed Power Generation — The logical Response to Restructuring and Convergence,

Available at: http://www.dpc.org/publications/index.html.

[18]International Energy Agency, Enhancing the Market Deployment of Energy Technology: a Survey of Eight Technologies, Paris, 1997.

[19] J. A. Duffie, W. A. Beckman, Solar Engineering of Thermal Processes, Second, John Wiley & Sons, New York, USA, 1991.

[20]M. Kaltschmitt, T. Stelzer, A. Wiese, GanzheitlicheBilanzierungam BeispieleinerBereitstellungelektrischerEnergieausregenerativenEnergien; in: Zeitschriftfu¨ r Energiewirtschaft, Vol. 20; Heft 2/ 1996; Energiewirtschaftliches Institute an der Universita¨tKo¨ ln, Germany, 1996, pp. 177–178.


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A Review on Modeling & Analysis of Hybrid Fuel Cell Stack Model for Distributed Power

Generation

Anjali Sharma1 Nidhi Joshi2 Yamini Vashishth3 Amit Yadav4 RKGITW, Ghaziabad RKGITW, Ghaziabad RKGITW, Ghaziabad RKGITW, Ghaziabad [email protected] [email protected] [email protected] [email protected]

Abstract - As the world’s energy use continues to grow; the development of clean distributed generation becomes increasingly important. Fuel cells which run on hydrogen, the most abundant element on Earth are an environmentally friendly renewable energy source that can be used in a wide range of applications and are ideal for distributed power applications [5].This paper explains the Role of Fuel Cell in Power system in which stress has been given on the most promising applications such as distributed power generation. In this paper a Hybrid stack model proposed by Xin Kong [2] which is a combination of empirical & an electrical model of fuel cell has been studied simulated by using MATLAB/SIMULINK. The empirical cell model has been used in past to represent the steady-state behavior, whereas, the circuit equivalent of the cell was used for dynamic behavior & Hybrid model gives a very good combination of both the characteristics. Due to low operating temperature (80–1000C), high power density, smaller size & rapid start up, PEM fuel cells are best suited for Residential applications [5], so it is a chosen FC for this paper. Keywords - PEM Fuel Cell, Steady State & Dynamic behavior of Fuel cell. I. INTRODUCTION

The history of fuel cells dates back to 1839

when Sir William Grove, a British Scientist, discovered the technology. However, it was not until the mid 1900’s when fuel cells began to make a name for themselves in the space industry Shortly after that, several private companies became interested in fuel cell technology, but the

economic and technological barriers were difficult to overcome. A fuel cell is a device for directly converting the chemical energy of a fuel into electrical energy in a constant temperature process. In a typical fuel cell, gaseous fuels are fed continuously to the anode (negative electrode) and an oxidant (i.e., oxygen from air) is fed continuously to the cathode (positive electrode); the electrochemical reactions take place at the electrodes to produce an electric current In many ways the fuel cell is analogous to a battery, but a battery which is constantly being recharged with fresh reactants. As well as offering a high theoretical efficiency, especially at low temperatures, fuel cells emit low or zero levels of pollutants. They can run on a wide range of fuels, ranging from gaseous fuels such as hydrogen and natural gas to liquid fuels such as methanol and gasoline [5]. As per the electrolyte used FC’s are classified as, Proton exchange membrane fuel cell (PEMFC)-800C, Alkaline fuel cell (AFC)-1000C, Phosphoric acid fuel cell (PAFC)-2000C, Molten carbonate fuel cell (MCFC)- 6500C, Intermediate temperature solid oxide fuel cell (ITSOFC)- 8000C, Tubular solid oxide fuel cell (TSOFC)- 10000C. Due to low operating temperature (80–1000C), high power density, smaller size & rapid start up, PEM fuel cells are best suited for Residential applications so, FC is chosen for this paper.

II. MODELLING OF PEMFC


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PEMFC mainly consists of three components Fuel processing unit or the reformer, Fuel cell stack, Power conditioning unit [5]. The purpose of this section is to describe the chemical and thermodynamic relations governing fuel cells and how operating conditions affect their performance. Understanding the impacts of variables such as temperature, pressure, and gas constituents on performance allows fuel cell developers to optimize their design of the modular units and it allows process engineers to maximize the performance of systems applications. A logical first step in understanding the operation of a fuel cell is to define its ideal performance. Once the ideal performance is determined, losses arising from non-ideal behavior can be calculated and then deducted from the ideal performance to describe the actual operation. The actual cell potential is decreased from its equilibrium potential because of irreversible losses, as shown in Figure 1. Multiple phenomena contribute to irreversible losses in an actual fuel cell. The losses, which are called polarization, over-potential, or over-voltage, originate primarily from three sources: 1) activation polarization, 2) ohmic polarization, and 3) concentration polarization . These losses result in a cell voltage (V) that is less than its ideal potential

Figure 1 Polarization Curve

An empirical fuel cell model [3] proposed by Junbom Kim was shown to fit the experimental V -i data for PEMFC. The empirical equation is: Vcell″= V″o - R″ I - b″ *log(i) - m″ exp(n″ * i). Where Vcell″, V″o, R″, b″ , m″ ,n″ are empirical

parameters estimated using nonlinear estimation, while j is fuel cell current density. The excellent fit of the experiment data to this empirical equation is demonstrated in [2]. Vcell = Vo - Ri - b * log i - mexp(n * i) Where Vo, b, R, m and n are still empirical parameters and can be represented as: Vo V″o +b″ *log(i); R R″ /Amea (Amea is the active area of the membrane-electrodes assemblies); b b″ n n″ m m″*exp(1/Amea) So for N number of stacks the total stack voltage is given by, Vstack = N*(Vo - Ri - b * log i - mexp(n * i)) J.C. Amphlett proposed an equivalent electrical circuit in [4] which shares the same topology with the one proposed earlier by Larminie and Dicks [6]. The circuit is shown in Figure 2, the open circuit voltage of the fuel cell, Rh models the immediate ohmic voltage drops. Rcl and Ccl represent the “charge double layer” phenomenon.

Figure 2] Electrical circuit model of single fuel cell

III. MODEL WITH COMBINED STEADY STATE

AND DYNAMIC CHARACTERSTICS

Thus it is clear that a fuel cell stack can be expressed using an empirical model and also as a circuit model. Both the stack model has a structure similar to the cell model. However, the empirical model simulates only the steady state behavior whereas the circuit model simulates only the dynamic. So in [2] both the models are combined to get a hybrid model. Subsequently we will simulate proposed hybrid fuel cell stack model and compare the results actual results given in [2]


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IV. SIMULATION OF HYBRID FC STACK MODEL BY USING MATLAB/SIMULINK

In [2] a 1.2kW fuel cell stack from Ballard

Company is used to verify the steady state & dynamic performance of proposed stack model and in this paper this model is verified by using MATLAB/SIMULINK as shown in figure [2]. V. STEADY-STATE PERFORMANCE OF THE PROPOSED FUEL CELL STACK MODEL

Figure [3] gives the steady state response of hybrid stack model given in SIMULINK

X-axis = Stack Current (A) Y-axis = Stack voltage (V)

Figure 3 Steady-state Response of Simulink model VI. DYNAMIC PERFORMANCE OF THE PROPOSED FUEL CELL STACK MODEL

The rest waveforms with different step changes are used to verify the model dynamic characteristics. Good correlation between the experimental results obtained in reference paper [2] & results of SIMULINK model of Hybrid stack model can be seen from the fig. 4 to fig. 6

Figure 4 - 8.1A-17.4A-8.1A

Figure 5 - 16.7A-34A-16.7A

Figure 6 - 18.8A-38A-19.2A

CONCLUSION

The proposed model is a good simulation tool to analyze the fuel cell performance during the system design stage. A good correlation between the experimental data and the simulation results proves the validation of the hybrid model proposed by Xin Kong. Without complicated mathematics, the proposed model is simple in

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evaluating the fuel cell stack steady-state and dynamic performance.

REFERENCES:

[1] M.Y. El-Sharkh, A.Rehman, M.S. Alam , ‘Analysis of Active & Reactive Power Control of a Stand Alone PEM Fuel Cell Power Plant’, IEEE Transaction on Power Systems, Vol. 19, No.4,November 2004.

[2] Xin Kong, Ashwin Khambadkone, ‘A HYBRID Model With Combined Steady State & Dynamic Characteristics of PEMFC Fuel Cell Stack’, IEEE transaction,2005.

[3] Junbom Kim, Seong Min Lee, Supramaniam Shrinivasan, “Modeling of proton exchange memberane fuel cell performance with an emp-irical equation”, Journal of the

Electrochemical Society, vol 142,pp. 2670-2674,1995.

[4] J C Amphlett, R M Baumert, R F Mann, B A Peppley, “A model predicting transient responses of proton exchange membrane fuel cells,” Journal of Power Sources, vol. 142, pp.9-15,1995.

[5] Fuel Cell Handbook (Fifth Edition),EG&G Services, Parsons Inc., DEO of Fossil Energy, National Energy Technology Lab, Oct.2000.

[6] J E Larminie & DICKS, Fuel Cell Systems Explained, John Wiley & Sons Chichester England,2002

Figure 2 Simulink Model of Hybrid FC Stack


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Applications of Wavelet Technique in Distributed Generation

Rahul Pathak1 Mohit Kumar Katiyar2 Priya Banga3 NIEC, New Delhi M.Tech (C&I), DTU, New Delhi M.Tech (C&I), DTU, New Delhi [email protected] [email protected] [email protected]

Abstract - Distributed generation is presently attracting increasing interest in all electrical stakeholders. Economical reasons, environmental concerns, technological advancements and market deregulation have brought distributed generation to forefront. Wavelet Transform is being used to develop new methods to sort out various issues related to economical, efficient and secure operation of distributed generation system. In this article, an attempt has been made to review application of wavelet transform in fault location, island detection and power quality issues in distributed generation.

Keywords—Distributed generation; wavelet transform; fault location; islanding detection; power quality.

I. INTRODUCTION Distributed generation is recent innovation in

power generation sector. Traditional power system characterized by centralized bulk power production is increasingly supported also by energy resources connected to distribution grid [1-3]. Distributed generation (DG) refers to any electric power production technology that is integrated within distribution system close to point of use. Distributed generators are connected to medium or low voltage grid [67]. DG has gain strong interest because of its capability of operating on broad range of renewable energy sources, along with cost effective, efficient, reliable and flexible on-site power alternative [4]. In era of DG integrated power system wavelet technique is proving effective way to address problems like fault location [7], islanding detection [5], power quality issues [6]. Wavelet technique was introduced to power system in 1994 by Robertson & Ribeiro. Since then, wavelet technique has found its way in almost all areas of power system like power quality improvement, transient analysis, load

forecasting, power system measurement, fault detection etc. Wavelet transform has been the evident signal processing development in recent year, as it has numerous applications. There are various types of transforms available; but the attention is subsequently focused on introducing wavelets in any application using the Fourier transform, has been more accurately localized sensual and frequency information (overview of wavelet analysis by HP Laboratories Japan, Daniel T. L. Lec and Akio Yamamoto). Because when a graph of captured signal is plotted in spite of amplitude versus time, information of frequency and phase also required for signal processing, now more significant is to know which type of processing to apply to solve the data-analysis problem. Here the wavelet analysis comes in focus. Wavelet analysis is performed using a prototype function called a wavelet. The history of wavelet analysis is research of several decades, idea of approximation determined as Fourier analysis is not new, and it has existed since 1807 given by Joseph Fourier. However, in wavelet analysis, the fundamental idea is to analyze according to scale i.e. wavelet algorithms process data to different scales and resolutions [8], [9]. The elementary wavelet basis is the Haar basis. The first mention of wavelets appeared in an appendix to the thesis of Alfred Haar (1909) [10]. One property of the Haar wavelet is that it has compact support, which means that it vanishes outside a finite interval. Unfortunately, Haar wavelets are not continuously differentiable which somewhat limits their applications. In 1930 physicist Paul Levy investigated Haar basis function superior to the Fourier basis functions for studying small


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complicated details in the Brownian motion. In 1980, Grossman and Morlet, a physicist and an engineer, broadly defined wavelets in the context of quantum physics. They also proved that with nearly any wave shape they could recover the signal exactly from its transform [8]. In 1985, Stephane Mallat gave wavelets an additional jump-start through his work in digital signal processing. Then Y. Meyer constructed the first non-trivial wavelets. Unlike to Haar wavelets, the Meyer wavelets are continuously differentiable, but not have compact support. After sometime Daubechies construct a set of wavelet orthonormal basis functions, which is used in wavelet applications today [11]. In this article an attempt to review various applications of wavelet technique in DG system is done.

II. WAVELET TECHNIQUE Wavelet multi-resolution analysis has drawn

much consideration for its ability to analyze swiftly changing transient signals in both time and frequency domains. The term wavelet means a small wave. The smallness refers to the condition that this window function is of finite length. The ‘wave’ refers to the condition that this function is oscillatory [12]. There are several types of Wavelet transforms, mainly: Continuous Wavelet transform Discrete Wavelet transform Depending on the application one of these types of Wavelet transform may be selected. The Continuous Wavelet transform (CWT) [13] was developed as an alternative to Short Time Fourier Transform, to overcome the resolution problem and most suitable for signal analysis. The CWT is defined as:

CWTx

Ψ (τ, s) = ΨxΨ (τ, s) = 1/√s ∫ x (t) Ψ*(t- τ /s) dt (1)

Where s>0 and -∞< τ<∞ The transformed signal is function of translational (τ) and scale (s) parameters [14]. The factor 1/√s are used to ensure that each scaled wavelet function has the same energy as the wavelet basis function. It should also satisfy following admissible condition:

-∞ ∫∞ Ψ (t) dt = 0 (2) Ψ (t) is the mother wavelet, in equation (2) the necessary and sufficient condition for wavelets is

that it must be oscillatory, must decay quickly to zero and must have an average value to zero. The mother wavelet is a band-pass filter and Ψ* is the complex conjugate form. The term translational refers to the location of window so is scale parameter is inversely proportional to frequency. In the definition of the wavelet transform, the scaling term is used in the denominator. So scales s<1 dilates the signals whereas scales s>1 compresses the signal as scale is inversely proportional to frequency. In practical applications [19], low scales (high frequencies) do not last for long, but they usually appear from time to time as short bursts. High scales (low frequencies) usually last for the entire duration of the signal. CWT is also continuous in terms of time shifting. During computation, the scaled mother wavelet is shifted smoothly over the full domain of the signal. Accordingly, a one-dimensional signal is translated into a two-dimensional time-frequency representation by the coefficient of CWT.

Figure 1: Daubechies wavelet basis function [8]

Multi-resolution and scaling laws can more be studied through [15], [16]. The smooth transition of the scaled mother wavelet implies that there are many overlaps in the transform making the CWT representation highly redundant [14]. Instead of the highly redundant CWT, DWT is often used as it is more efficient computationally and requires less memory storage. DWT is a digitally implementable counterpart of wavelet. Wavelet transform of sampled waveforms can be obtained


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by implementing the DWT; this digital transform can be studied in detail in [17]. In DWT equation (1) s and τ are replaced by am and nbam respectively n and m being integer variables, n as the total number of samples and m as discrete levels, k denotes translation in time.

(3)

The generated waveforms are analyzed with wavelet multi-resolution analysis [15] to extract sub-band information from the simulated transients. Daubechies wavelets are commonly used in the analysis of traveling waves [18]. Daubechies wavelets are more localized i.e., compactly supported in time and hence are good for short and fast transient analysis and provide almost perfect reconstruction. Actual implementation of the DWT involves successive pairs of high-pass and low-pass filters at each scaling stage of the DWT. DWT follows a certain discrete expansion pattern determined by the selection of a factor a. The most widely used pattern is called dyadic expansion with a = 2 and the expansion is implemented for scales a = am, where m = 1, 2, 3 etc. The information in the high frequency bands as carried by the details Dj, scale j denotes different frequency bands. Similarly, the information in the low frequency band as carried by the approximations Aj are coefficients of DWT with the scaling function.

Figure 2: Fast DWT decomposition [20]

The effectiveness of CWT and DWT is influenced by the choice of mother wavelet and its scaling function. Different types of mother wavelets have different properties [20]. They can be divided into three types according to their orthogonal nature,

namely, redundant wavelets, orthogonal wavelets, and bi-orthogonal wavelets. Here the consideration of orthogonal wavelets in taken into account.

III. FAULT LOCATION Fault location estimation in distribution power

system, has been an area of increasing research interest. Several research works has been done in this field [21-30]. Various methods for fault detection can be broadly grouped in three categories: [assessment of fault location]

Impedance measurement based methods [21-30]

Methods based on analysis of travelling waves [24-27]

Expert systems methods based on Neural network[28-30]

Impedance measurement based methods is mainly concerned with analysis at power-frequency of voltage, current fault signals [21]. These techniques are widely used in fault location in transmission lines. However their applications to distribution networks having multi branch radial topologies may show lack in location accuracy of faults [31]. Presence of distribution generators poses huge challenges of relays and other protective devices becomes unmanageable due to in-feed current from distributed generators [32-34]. Complex signal analysis technique as well as measurement of high frequency components is hallmarks of travelling wave techniques [35, 36]. They rely on analysis of high component of fault originated transients which are rather uninfluenced by fault type and impedance [37]. An aspect of great interest for distribution network is related to number of measurement terminals required by applied methods. Researcher are giving importance to single ended methods, which need measurement from only one terminals, typically installed in primary station . Wavelet technique for fault location detection is an extension of algorithm presented by A. Borghetti [38]. Current or voltage transients have both constant low frequency component of large duration and time varying high frequency components for short duration. A traditional operator like Fast Fourier Transform (FFT) analyzes the signal with constant


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frequency resolution that depends on width of chosen observation time window [39]. Hence it is not appropriate. Wavelet technique however allows good frequency resolution at low frequency [8]. Moreover, WT allows for analysis of high frequency component very close to each other in time and frequency and low frequency component very close to each other in frequency [40]. These properties make WT a suitable candidate to be used as tool for studying transient waveforms produced by these faults [40, 41]. Several researches have demonstrated the accuracy of WT in fault location studies [42, 43]. However choice of mother wavelet has proved to be a determining factor in accuracy of WT for fault location studies [44]. These methods are insensitive to naturally occurring in-feed from distribution generator during a fault. Hybrid methods with expert system like neural networks and fuzzy cluster along with wavelets techniques are being explored to use as fault location methods [45-48]. These methods are proving to be economical and efficient. IV. ISLANDING OPERATION & DETECTION

It is being reported that with installation of DGs in parallel with utility network, the efficiency and stability of supplying power would be improved. However, many technical obstacles are present to achieve more secure and economic operation. Islanding problem becomes an urgent issue since power output of DG system is not under direct control of utility engineer [49-51]. Islanding problem occurs when load of interest is severed off from centralized power unit but the system continues to receive power from connected DGs. This forms so called island giving unexpected outcomes like increased complexity of orderly restoration, poor voltage stability, and worst of all, a raised risk to related maintenance personnel.

Figure 3: Islanding Operation [62]

Several methods have been suggested to detect islanding effect [49], [52-61]. Most of these techniques are based on measurement of system parameters like phase displacement, system impedance, and the rate of change of output power [52-54]. However, there is need to formulate islanding detection technique which can work in power distribution network interfaced with multiple DGs. Wavelet technique is proving to be an effective method to meet this requirement [60]. Wavelet transform-based approach can monitor the parameter variations of interests, where Daubechies wavelet serves as basis [61]. Enhanced by such an approach, it is anticipated that any abrupt change occurred in the acquired signal would be effectively caught, hence increasing the reliability of islanding-detection.

Islanding Detection method [62] Some useful features of this new method are listed below [62]: It helps improve the islanding-detection

capability of protective relays. The safety of utility engineers is, meanwhile, better ensured.

Because the time and frequency information can be simultaneously observed, the robustness of the method can be better realized for the application considered.

With the increased number of installed distributed generators, the proposed method would serve as a potential alternative in addition to existent approaches.

The method is easy to program, facilitating the firmware realization of integrated circuit design for the portable detector applications.

The basic functions in wavelet analysis are localized in frequency making mathematical tools


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such as power spectra (power in a frequency interval) useful at picking out frequencies and calculating power distributions [63, 64]. The most important feature of this transforms is that individual wavelet functions are localized in space .This localization feature, along with wavelets localization of frequency, makes many functions and operators using wavelets “sparse”, when transformed into the wavelet domain. This sparseness, in turn results in a number of useful applications along with islanding detection.

V. POWER QUALITY IEEE defines power quality as a concept of

powering and grounding sensitive equipment in a manner that is suitable to operation of that equipment [65]. From electric point of view the term power quality is supply of electric power as per specified standards, whereas from in user side, it is smooth functioning of electrical equipments without any destruction [66]. Highly sensitive and electronics equipment have brought power quality in limelight [68-70]. Equipments are becoming more and more sensitive to even minor change in supply [67]. Large number of nonlinear loads like power electric based system, like adjustable speed drives, inverters in systems generating electricity from renewable energy sources is source of voltage fluctuation in system. Installation and connection of DG unit might have negative impact on system frequency, since any imbalance between demand and supply of electricity causes system frequency to deviate from rated value of 50 Hz. Introduction of DG units might also change voltage level in system [66]. High voltage due to DG unit, DG unit interfacing with utility system and there interaction with regulating equipment are the major issue of concern affecting power quality of distribution generation. Traditional methods to analyze power quality are based on visual waveform analysis [68]. Power quality engineers have to take daunting task of inspection of huge amount of data. Automatic methods for detecting, identifying, analyzing various power quality disturbances are need of hour [68-70].

DFT is known method to analyze power quality disturbances like voltage fluctuation, voltage swell, voltage sag, voltage variation, frequency variation, waveform distortion [68]. However leakage effect which comes into effect due to variation in flicker level puts accuracy of this method in question [69]. Apart from that short time duration disturbances require Short Time Fourier Transformation. In order to improve this limitation waveform technique is being used [70, 71]. WT can be used for voltage flicker signal extraction [69]. To speed up extraction processing, S-transform [70], which is an extension of ideas of WT is also being taken into consideration. WT along with multiple layer perceptron has better processing time for detection of power quality disturbances [72, 73]. However multiple layer perceptron suffers from drawback of longer training time for hidden layers and nodes [74]. Support vector machine which are known to have strong classification property [73, 75, 76] can also be used along with WT for disturbance classification [x9].

CONCLUSION Distributed generation is known as power

generation paradigm of new era. Distributed generation is expected to be more secure, efficient, environmental friendly approach that will meet our ever increasing demand of electricity. While researchers are trying to develop new methods to address power quality, islanding and fault determination problem wavelet transform has gained wide acceptance and appreciation among research community. Several new methods based on wavelet transform are in developing phase. In future wavelet transform is expected to play key role in distributed generation sector.

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A Review on Distributed Generation

Sharique Asir1 Schrutir Jain2 Majid Hussain3 B.Tech (EEE), NIEC B.Tech (EEE), NIEC B.Tech (EEE), NIEC [email protected] [email protected] [email protected]

Abstract - This paper is review of the different concepts of distributed generation and smart grid. Distributed energy (DG) is believed to be future of the power generation. This paper concerns with the exploitation of various renewable sources of energy and energy storage technique in smart grid.

Keywords:Distributed generation, distributed resources, Distributed energy resources, and embedded generation.

I.INTRODUCTION

The electricity supply came to existence initially by installing generators located according to distribution need.So this way concept of distribution was there from very beginning. [1]Later high electricity demand forced the generation plant to move to primary energy sources (e.g. rivers, coal mines etc) which is then fed to the consumers through complex system of transmission lines. This conception, that has been in existence for more than fifty years, and has been characterized for: big generation plants, generally placed far from where the power demands is, and great transmission networks that carry the generated power to the demand sites. [2]These economies of scale for central plants began to fail in the late 1960s and, by the start of the 21st century, Central Plants could arguably no longer deliver competitively cheap and reliable electricity to more remote customers through the grid, because the plants had come to cost less than the grid and had become so reliable that nearly all power failures

originated in the grid. Thus, the grid had become the main driver of remote customers’ power costs and power quality problems, which became more acute as digital equipment required extremely reliable electricity.[34]Efficiency gains no longer come from increasing generating capacity, but from smaller units located closer to sites of demand. Capital markets have come to realize that right-sized resources, for individual customers, distribution substations, or microgrids, are able to offer important but little-known economic advantages over Central Plants. Smaller units offered greater economies from mass-production than big ones could gain through unit size. These increased value—due to improvements in financial risk, engineering flexibility, security, and environmental quality—of these resources can often more than offset their apparent cost disadvantages [5] In this context, distributed energy resources (DER) -small power generators typically located at users’ sites where the energy they generate is used - have emerged as a promising option to meet growing customer needs for electric power with an emphasis on reliability and power quality. II. DEFINITIONS AND RATINGS FOR DISTRIBUTED GENERATION FROM DIFFERENT INSTITUITIONS:

IEEE The Standard for Interconnecting Distributed Resources with Electric Power


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System of IEEE, define distributed generation like electric generation facilities connected to an area EPS (electrical power system) through a point of common coupling; a subset of distributed resources. Some others definitions are implicit in this. EPS area are facilities that deliver electric power to a load (this can include generation units) that serves Local EPSs. Each Local EPS is contained entirely within a single premises or group of premises. The point where a Local EPS is connected to the Area EPS, receive the name of point of common coupling. Finally IEEE, define distributed resources as sources of electric power that are no directly connected to a bulk power transmission system. And the DR includes generator and energy storage technologies [7]

CALIFORNIA ENERGY COMMISSION: Distributed energy resources are small-scale power generation technologies (typically in the range of 3 to 10,000 kW) located close to where electricity is used (e.g., a home or business) to provide an alternative to or an enhancement of the traditional electric power system [8] In addition, in regards to the rating of distributedgeneration power units, the following different definitions are currently used: 1. The Electric Power Research Institute defines distributed generation as generation from a few kilowatts up to 50 MW [10] 2. According to the Gas Research Institute, distributedgeneration is ‘typically [between] 25 kw and 25 MW[11]. 3. Preston and Rastler define the size as ranging froma few kilowatts to over 100 MW[12] 4. Cardell defines distributed generation as generationbetween 500 kW and 1MW[13] And because of different government regulations, thedefinition of the rating of

each distributed power station also varies between countries, for example: 1. In the English and Welsh market, DG plantswith a capacity of less than 100 MW are notcentrally dispatched and if the capacity is less than50 MW, the power output does not have to betraded via the wholesale market [14]. The term distributed generation is, therefore, predominantlyused for power units with less than 100 MW capacity. [14] 2. Swedish legislation gives special treatmentto small generation with a maximum generationcapacity of up to 1500 kW . Hence,DG in Sweden is often defined as generation with up to 1500 kW. But under Swedish law, a wind farmwith one hundred 1500 kW wind turbinesis still considered DG, as the rating of each wind energy unit, and not the total wind farm rating, isrelevant for the Swedish law. For hydro units, incomparison, it is the total rating of the powerstation that is relevant. Some of the proposed offshore wind farms for Sweden have a maximumcapacity of up to 1000 MW. This would still beconsidered DG as they plan to use 1500 kW windturbines [15]. III. TYPES OF DISTRIBUTION ENERGY RESOURCES

There are several renewable and non-renewable sources in nature which can be effectively used as distribution energy resources. DER technologies include wind turbines, photovoltaic(PV),fuel cells, microturbines, reciprocating engines,combustion turbines, cogeneration, and energy storage systems. MICROTURBINES are small combustion turbines that produce between 25 kW and 500 kW of power. Micro turbines were derived from turbocharger technologies found in large trucks or the turbines in aircraft auxiliary power units (APUs).


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CONVENTIONAL COMBUSTION TURBINE (CT) generators typically range in size from about 500 kW up to 25 MW for DER and up to approximately 250 MW for central power generation. They are fueled by natural gas, oil, or a combination of fuels ("dual fuel"). INTERNAL COMBUTION ENGINESA reciprocating, or internal combustion (IC), engine converts the energy contained in a fuel into mechanical power. This mechanical power is used to turn a shaft in the engine. A generator is attached to the IC engine to convert the rotational motion into power. STIRLING ENGINES are classed as external combustion engines. They are sealed systems with an inert working fluid, usually either helium or hydrogen. They are generally found in small sizes (1-25 kW) and are currently being produced in small quantities for specialized applications in the space and marine industries. FUEL CELL power systems are quiet, clean, highly efficient on-site electrical generators that use an electrochemical process—not combustion—to convert fuel into electricity. In addition to providing power, they can supply a thermal energy source for water and space heating, or absorption cooling. In demonstration projects, fuel cells have been shown to reduce facility energy service costs by 20% to 40% over conventional energy service. ENERGY STORAGE technologies produce no net energy but can provide electric power over short periods of time. They are used to correct voltage sags, flicker, and surges that occur when utilities or customers switch suppliers or loads. They may also be used as an uninterruptible power supply (UPS). As such, energy storage technologies are considered to be a distributed energy resource. PHOTOVOLTAIC (PV) CELLS, or solar cells, convert sunlight directly into electricity. PV cells are assembled into flat plate systems that can be mounted on

rooftops or other sunny areas. They generate electricity with no moving parts, operate quietly with no emissions, and require little maintenance. WIND TURBINES use the wind to produce electrical power. A turbine with fan blades is placed at the top of a tall tower. The tower is tall in order to harness the wind at a greater velocity, free of turbulence caused by interference from obstacles such as trees, hills, and buildings. As the turbine rotates in the wind, a generator produces electrical power. A single wind turbine can range in size from a few kW for residential applications to more than 5 MW. CO-GENERATION (combined heat and power, CHP) All thermal power plants and devices emit a certain amount of heat during electricity generation. This can be released into the natural environment through cooling towers, flue gas, or by other means. By contrast, CHP captures some or all of the by-product heat for heating purposes, either very close to the plant. HYBRID SYSTEMS: Developers and manufacturers of DER are looking for ways to combine technologies to improve performance and efficiency of distributed generation equipment. Several examples of hybrid systems include: 1. Solid oxide fuel cell combined with a gas turbine or micro turbine 2. Stirling engine combined with a solar dish (see the photograph) 3. Wind turbines with battery storage and diesel backup generators 4. Engines (and other prime movers) combined with energy storage devices such as flywheels All the above resources can be used effectively using a system of advanced electric network called smart grid which uses information and communication technology to simplify complex networks.


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IV. SMART GRID

Alternating current power grid evolved in 1896 where the grid was conceived as a centralized unidirectional system of electric power transmission, electricity distribution, and demand-driven control. Eventually power grids transformed into local grids as they grew over time, and were eventually interconnected for economic and reliability reasons. By the 1960s, the electric grids had become very large, mature and highly interconnected, with thousands of 'central' generation power stations delivering power to major load centres via high capacity power lines By the late 1960s and 1970, the demand for electric power increased and this growing demand led to increasing numbers of power stations. These growing demands also led to the problems resulting in poor power quality including blackouts, power cuts, and brownouts. The largest ever blackout on 30-31 july in India in which about 10% of world population went through the power crisis has raised the alarm an sound steps are required to be taken.Some technology sources and USAIDproposed that another widespread outage could be prevented by integrated network ofmicro gridsand distributed generation connected seamlessly with the main grid via a superior smart grid technology which includes automated faultdetection,islanding and self-healingof the network.[16, 17, 18, 19] Smart grid a modernized electric grid is the use of advanced technology to increase the reliability and efficiency of the grid, from transmission to distribution. Its implementation dramatically increases the quantity, quality, connectivity, automation and Coordination between the suppliers, consumers and networks, and use of data available from advanced sensing, computing, and communications hardware and software.

How a smart Grid can help in improving and dealing with the problems faced by the world at present Increasing reliability, efficiency and

safety of the power grid. Enabling decentralized power

generation so homes can be both an energy client and supplier (provide consumers with interactive tool to manage energy usage).

Flexibility of power consumption at the client’s side to allow supplier selection (enables distributed generation, solar, wind, and biomass).

Increase GDP by creating more new, green collar energy jobs related to renewable energy industry manufacturing, plug-in electric vehicles, solar panel, and wind turbine generation, energy conservation and construction.

V. GRID ENERGY STORAGE

Grid energy storage refers to the storage

of electricity at large scale in a grid when the production increases the consumption level. This way production is maintained at a more constant level lowering the effort put in production. This method is very useful when it comes to completely harness the discontinuous sources of energy like wind energy and solar energy. Thus, grid energy storage is one method that the operator of an electrical power grid can use to adapt energy production to energy consumption, both of which can vary over time. This is done to increase efficiency and lower the cost of energy production, or to facilitate the use of intermittent energy sources. As of March 2012, pumped-storage hydroelectricity(PSH) is the largest-capacity form of grid energy storage available; the Electric Power Research Institute(EPRI) reports that PSH accounts for more than 99% of bulk storage capacity worldwide, around 127,000 MW [20] PSH energy efficiency varies in


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practice between 70% to 75%. 2011-03-03. Retrieved 2012-03-11. Several techniques have been devised to store energy at large scale. Some of them are Electric vehicles, Compressed air, Hydrogen, Pumped water, super conducting magnetic energy, Thermal and Batteries

ELECTRIC VEHICLES

Companies are researching the possible use of electric vehicles to meet peak demand. A parked and plugged-in electric vehicle could sell the electricity from the battery during peak loads and charge either during night (at home) or during off-peak.[21]Plug-in hybrid or electric carscould be used[22, 23,24] for their energy storage capabilities. Vehicle togrid technology can be employed, turning each vehicle with its 20 to 50 Kw-h battery packinto a distributed load-balancing device or emergency power source. This represents 2 to 5 days per vehicle of average household requirements of 10 kW-h per day, assuming annual consumption of 3650 kW-h. This quantity of energy is equivalent to between 40 and 300 miles (64 and 480 km) of range in such vehicles consuming 0.5 to 0.16 kW-h per mile. These figures can be achieved even in home-made electric vehicle conversions. Some electric utilities plan to use old plug in vehicle to store electricity[25,26].

COMPRESSED AIR:

Another grid energy storage method is to use off-peak or renewably generated electricity to compress air, which is usually stored in an old mine or some other kind of geological feature. When electricity demand is high, the compressed air is heated with a small amount of natural gas and then goes through turboexpanders to generate electricity.

PUMPED WATER:

In 2008 world pumped storage generating capacity was 104 GW,while other sources claim 127 GW, which comprises the vast majority of all types of grid electric storage - all other types combined are some hundreds of MW.In many places, pumped storage hydroelectricity is used to even out the daily generating load, by pumping water to a high storage reservoir during off-peak hours and weekends, using the excess base-load capacity from coal or nuclear sources. During peak hours, this water can be used for hydroelectric generation, often as a high value rapid-response reserve to cover transient peaks in demand. Pumped storage recovers about 75% of the energy consumed, and is currently the most cost effective form of mass power storage. The chief problem with pumped storage is that it usually requires two nearby reservoirs at considerably different heights, and often requires considerable capital expenditure.[27]Pumped water systems have high dispatchability, meaning they can come on-line very quickly, typically within 15 seconds,[28] which makes these systems very efficient at soaking up variability in electrical demand from consumers. There is over 90 GW of pumped storage in operation around the world, which is about 3% of instantaneous global generation capacity. Pumped water storage systems, such as the Dinorwig storage system, hold five or six hours of generating capacity [28] and are used to smooth out demand variations.

HYDRODEN

Hydrogen can be produced either by reforming natural gas with steam or by the electrolysis of water into hydrogen and oxygen (see hydrogen production). Reforming natural gas produces carbon dioxide as a by-product. High temperature electrolysis and high pressure


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electrolysis are two techniques by which the efficiency of hydrogen production may able to be increased. Hydrogen is then be converted back to electricity in an internal combustion engine, or a fuel cell which convert chemical energy into electricity without combustion, similar to the way the human body burns fuel.

SUPERCONDUCTING MAGNETIC ENERGY

Superconducting magnetic energy storage (SMES) systems store energy in the magnetic field created by the flow of direct current in a superconducting coil which has been cryogenically cooled to a temperature below its superconducting critical temperature. A typical SMES system includes three parts: superconducting coil, power conditioning system and cryogenically cooled refrigerator. Once the superconducting coil is charged, the current will not decay and the magnetic energy can be stored indefinitely. The stored energy can be released back to the network by discharging the coil. The power conditioning system uses an inverter/rectifier totransform alternating current (AC) power to direct current or converts DC back to AC power. The inverter/rectifier accounts for about 2–3% energy loss in each direction. SMES loses the least amount of electricity in the energy storage process compared to other methods of storing energy. SMES systems are highly efficient; the round-trip efficiency is greater than 95%. The high cost of superconductors is the primary limitation for commercial use of this energy storage method. Due to the energy requirements of refrigeration, and the limits in the total energy able to be stored, SMES is currently used for short duration energy storage. Therefore, SMES is most commonly devoted to improving power quality. If SMES were to be used for utilities it would be a diurnal storage

device, charged from base load power at night and meeting peak loads during the day.

BATTERIES The battery enables large amounts of energy from wind or solar power to be stored, managed, controlled and sent into the electricity grid when it is needed. It doesn’t matter whether the wind is blowing or not; the battery makes the electricity output predictable and reliable. Battery systems connected to large solid-state converters have been used to stabilize power distribution networks. For example in Puerto Rico a system with a capacity of 20 megawatts for 15 minutes (5 megawatt hour) is used to stabilize the frequency of electric power produced on the island. A 27 megawatt 15 minute (6.75 megawatt hour) nickel-cadmium battery bank was installed at Fairbanks Alaska in 2003 to stabilize voltage at the end of a long transmission line.[29] Many "off-the-grid" domestic systems rely on battery storage

CONCLUSION

Various definitions from different instituition was briefly described and was found to be to be quite inconsistent in terms of rating as they were from different governing bodies. So the author inclines for a wide open definition which includes the contextual validity of all the other in concepts.Different distribution energy sources were studied of which wind energy, photovoltaic system and fuel cells were found to be very promising in near future.

To use the concepts of distributed generation efficiently smart grid is going to play very crucial role by providing communication technique to simplify and run the grids as stand-alone grids.

Grid energy storage technique using pumped water, batteries and electric vehicles will further boost the distributed


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generation and make the electrical energy even more economical.

REFERENCES

[1]CIGRE, Working Group 37.23. Impact of IncreasingContribution of Dispersed Generation on the PowerSystem, 1999.

[2]Vignolo M, Zeballos R. “Transmission Networks or Embedded Generation?” Proceedings IASTED

[3]DOE;The Potential Benefits of Distributed Generation and Rate-Related Issues that May Impede Their Expansion; 2007.

[4]Lovins; Small Is Profitable: The Hidden Economic Benefits of Making Electrical Resources the Right Size; Rocky Mountain Institute, 2002.

[5]Takahashi, et al; Policy Options to Support Distributed Resources; U. of Del., Ctr. for Energy &Env.Policy; 2005.

[6]Hirsch; 1989; cited in DOE, 2007.7 IEEE P1547/D08. Draft Standard for Interconnecting Distributed Resources with Electric Power Systems http://grouper.ieee.org/groups/scc21/1547/1547_index.html

[7]American Gas Association. “What is Distributed Generation?”.Fullarticleathttp://www.aga.org/Content/ContentGroups/Newsroom/Issue_Focus/Distributed_Generation.htm

[8]California Energy Commission. “Distributed Energy Resources: Guide”.http://www.energy.ca.gov/distgen/index.html

[9]See Electric Power Research Institute web-page (January 1998) http://www.epri.com/gg/newgen/disgen/index.html

[10]Gas Research Institute, Distributed Power Generation: A Strategy for a

Competitive Energy Industry, Gas Research Institute,Chicago, USA 1998

[11]D. Sharma, R. Bartels, Distributed

electricity generation incompetitive energy markets: a case study in Australia, in: The Energy Journal Special issue: Distributed Resources: Toward a New Paradigm of the Electricity Business, The International Association for Energy Economics, Clevland, Ohio, USA, 1998, pp. 17–40.

[12] J. Cardell, R. Tabors, Operation and control in a competitive market: distributed generation in a restructured industry, in: The Energy Journal Special Issue: Distributed Resources: Toward a New Paradigm of the Electricity Business, The International Association for Energy Economics, Clevland, Ohio, USA, 1998,pp. 111–135.

[13]J. Watson, Perspective of Decentralised Energy Systems in aliberalised Market: The UK Perspective, in: RoIfWu¨stenhagen, Thomas Dyllick, St. Gallen, Institute for Wirtschaft undOkologie (IWO) Diskussionsbeitra¨ge Nr. 72: NachhaltigeMarktchancen Dank dezentralerEnergie? EinBlick in dieZukunft der Energiedienstleistung, Switzerland, January 1999, pp. 38–47

[14]T. Wizelius, Series of Offshore Projects Planned; in: Wind PowerMonthly, Vol. 14, No.10, October 1998, pp. 23–24

[15]"Power crisis and grid collapse: Is it time to think different, small and local?". SME Mentor. 3 August 2012. Retrieved 6 August 2012.

[16]"How Power Outages in India May OneDayBeAvoided".technologyreview.com. 31 July2012.Retrieved 9 August 2012.


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[17]"The smart grid vision for India's power sector". USAID India. March 2010. Retrieved 9 August 2012.

[18]"Enabling integrated network of microgrids and distributed power connected to the grid via Smart Grid technology with [self-healing"]. Retrieved 9 August 2012.

[19]"Energy storage -Packing some power". The Economist.

[20]New electric car scheme for California [21]Eberle, Ulrich; von Helmolt, Rittmar

(2010-05-14). "Sustainable transportation based on electric vehicle concepts: a brief overview". Royal Society of Chemistry.Retrieved 2010-06-08.

[22]http://www.newscientist.com/article.ns?id=dn7081

[23]http://www.toshiba.co.jp/about/press/2005_03/pr2901.htm

[24]Woody, Todd. "PG&E's Battery Power Plans Could Jump Start Electric Car Market." (Blog).Green Wombat, 2007-06-12. Retrieved on 2007-08-19

[25]Planet Ark : E.ON UK Plans Giant Battery to Store Wind Power

[26]http://www.doc.ic.ac.uk/~matti/ise2grp/energystorage_report/node6.html

[27]"First Hydro Dinorwig Power Station" [28]Gyuk I, Kulkarni P, Sayer JH, 'et al.'

(2005). "The United States of storage". IEEE Power and Energy Magazine 3 (2):10.1109/MPAE.2005.1405868

[29]Sadoway proposing all-liquid metal battery for grid energy storage [30]Appalacian Power [31]Eric Wesoff, "Sadoway’s MIT Liquid

Metal Battery Startup Adds $15M and Khosla Ventures as Investor", GreentechMedia, May 24, 2012

[32]Conway, E. (2 September 2008) "World's biggest battery switched on in Alaska"Telegraph.co.uk

[34]Wind farm with battery storage in Ireland | Leonardo ENERGY

[35]http://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/30535ag.pdf

[36]Better Batteries Dramatically Boost Wind Energy - The Cutting Edge ... www.thecuttingedgenews.com/index.php?article=428

[37]Batteries to store wind energy | ZDNet www.zdnet.com/blog/emergingtech/batteries-to...wind-energy/1133 www.zdnet.com/blog/emergingtech/batteries-to...wind-energy/1133


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Distributed Generation in Rural India Devesh Singh

Prabha Electronic & Automation, [email protected]

Abstract - In this paper, firstly a brief background of India power sector is presented. Thereafter we have discussed various distributed power generation possibilities in rural area along with a description of present scenario. Different possible options to improve power in rural areas are discussed.

I. INTRODUCTION

Distributed generation, for the moment looselydefined as small-scale electricity generation, is a fairlynew concept in the economics literature about electricitymarkets, but the idea behind it is not new at all. In theearly days of electricity generation, distributed generationwas the rule, not the exception. The first powerplants only supplied electricity to customers in the closeneighborhood of the generation plant. The first gridswere DC based, and therefore, the supply voltage waslimited, as was the distance that could be used betweengenerator and consumer. Balancing demand and supplywas partially done using local storage, i.e. batteries,which could be directly coupled to the DC grid. Alongwith small-scale generation, local storage is also returningto the scene. Later, technological evolutions, such as the emergenceof AC grids, allowed for electricity to be transportedover longer distances, and economies of scale inelectricity generation lead to an increase in the poweroutput of the generation units. All this resulted inincreased convenience and lower per unit costs. Massiveelectricity systems were constructed, consisting of

hugetransmission and distribution grids and large generationplants. Balancing demand and supply was done by theaveraging effect of the combination of large amounts ofinstantaneously varying loads. Security of supply wasincreased as the failure of one power plant wascompensated by the other power plants in the interconnectedsystem. In fact this interconnected highvoltage system made the economy of high-scale in generationpossible. In the last decade, technological innovations and achanging economic and regulatory environment haveresulted in a renewed interest for distributed generation.This is confirmed by the IEA (2002), who lists five majorfactors that contribute to this evolution, i.e. developmentsin distributed generation technologies, constraintson the construction of new transmission lines, increasedcustomer demand for highly reliable electricity, theelectricity market liberalization and concerns aboutclimate change. II.INDIAN POWER SECTOR

India had an installed capacity of 105,000MW(Ministry of Power, 2003a, b) in the centralized powerutilities as on 31st March2003. Of this 74,400MW isaccounted for by thermal power plants, 26,300MW oflarge hydro plants and 2700MW of nuclear power plants. The focusof power planning has been to extend the centralizedgrid throughout the country. However the capacityaddition has not been able to keep pace with theincreasing


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demand for electricity. This is reflected by thepersistent energy and peak shortages in the country. Thetransmission and distribution losses are extremely high(estimated to be more than 25%, this includes theft). India has a plan to add 100 000MW of additionalpower generation capacity by 2012 (MOP, 2001). Thisrequires an average capacity addition of more than10,000MW per year. Centralized generation alone isunlikely to meet this target. In this context DG is likelyto be important. DG also has the advantage ofimproving tail-end voltages, reducing distribution lossesand improving system reliability.The present installed capacity of DG is about13,000MW (10,000MW diesel, 3000MW renewable).The majority of this is accounted for by diesel enginesthat are used for back-up power (in the event of gridfailure) and operate at very low load factors. The shareof the energy generation from DG is marginal (about2–3% of the total generation). Apart from the dieselengines, the DG options that have been promoted inIndia are modern renewable. India is probably the only country with a separateMinistry of Non-conventional Energy Sources (MNES).The renewable energy installed capacity was 205.5MWin 1993 (104.6MW small hydro, 39.9MW Wind). Thisincreased to 2978 MW in 2001 (as on 31st March2001)and accounted for almost 3% of India’s installed powercapacity (MNES, 2001; Annual Reports MNES, 2000,2001, 2002). The growth rate of installed renewablepower capacity during the period 1993–2001 was 39%per year. During the period January 2000–April 2001the installed capacity increased from 1600MW to2978MW (an annual growthrate of 49%).The major contributors are small hydroðo25MWÞ which accounts for 1341MW (45%)

andwind which accounts for 1267MW (42%). The installedcapacity in Biomass based power generation is 308MW(10.3%), with most of it coming from biogas basedcogeneration. Most of the installed capacity availablefrom renewable is accounted for by grid connectedsystems (wind, small hydro and biomass cogeneration). This accounts for about 3% of India’s installed capacitycontribute to about 1–2% of the total generation (due tolow capacity factors on renewable). The growth ratehas been significant (above 30% per year). This has beenfacilitated by an enabling policy environment and asupportive government.Despite the emphasis on extending the centralizedgrid to the rural areas, 78 million rural households(Ministry of Power, 2003b) or 56.5% of rural householdsare still unelectrified. The recently passed ElectricityAct (2003) has made it a statutory obligation tosupply electricity to all areas including villages andhamlets. The act suggests a two pronged approachencompassing grid extension and through standalonesystems. The act provides for enabling mechanisms forservice providers in rural areas and exempts them fromlicensing obligations. MNES has been given theresponsibility of electrification of 18,000 remote villagesthrough renewable. The ministry has set up anambitious target of meeting 10% of the power requirementsof India from renewable by 2012 . In most cases,the areas to be electrified do not have sufficient payingcapacity. Most systems are subsidized by the Governmentor the utility. The power sector has significantlosses and needs to ensure that the DG systems selectedare likely to be cost-effective. This paper examines thecost effectiveness of the different DG options selected.


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III. BRIEF OVERVIEW OF OPTIONS TO ENHANCE RURAL POWER SUPPLY The existing options to increase electricity access focus either on enhancing centralized generation or improving efficiency in the distribution business. This is done through stand-alone distributed generation projects feeding into the grid or establishing an input-based distribution franchisee. But neither of these addresses the basic issue of the unavailability of electricity in rural households. The current mechanisms are based on two fundamental choices: • Centralized generation (status-quo) or localized distributed generation. • Utility managed distribution (status-quo) or private distribution franchises. The feed-in-tariff (FIT) distributed generation model (localized generation that feeds into the grid combined with utility managed distribution), already prevalent in India, could address the rural supply situation provided that locally generated distributed power is earmarked for serving rural areas. But this never happens in practice as the power from distributed sources is diverted to urban markets along with other common pools of resources. Also, the FIT often is more expensive than the current utility power procurement costs, hence, it has substantial impact on its overall power purchase costs and tariffs. In areas where the power situation adequately serves rural areas, rural distribution franchises, which combine centralized generation with private distribution franchisees, could very well improve service and reduce technical and commercial losses. India has already experimented with this model successfully, particularly in the city of Bhiwandi and in the rural areas of Assam, as discussed in

chapter 3. Results from both these markets show great potential for success if the distribution utility can guarantee an adequate power supply. But these individual models do not address all issues facing rural markets, such as high distribution and commercial losses, very low supply hours, deteriorating quality, and unreliable service. A combination of existing models would not only facilitate a strong role for the private sector; it would also increase the supply of electricity to underserved areas. In this case, power from a distributed generation plant is ring-fenced to supply the local rural area first. The improved underlying commercial aspects of the market reduce the subsidy for supporting distributed generation. This would allow private developers to generate and distribute electricity locally by acting as the utility’s franchisees. Such a model would augment generation using local resources and supply power to areas that otherwise may remain power-starved despite having access to the grid. There are three options to enhance electricity supply in rural areas: 1) FIT model: Distributed generation plants sell power to the grid at FIT determined by the regulator, and this power is added to the utility’s centralized pool. 2) Rural distribution franchisee (RDF): An input-based distribution franchisee is appointed by the utility for metering, billing, and collection activities, but is not permitted to source power beyond its contract with the utility. 3)Distributed generation and supply (DG&S): Combined generation and distribution, i.e., in addition to distributing power and collecting revenues, the franchisee also generates power locally and supplies to the franchised area. In the DG&S model, the franchisee also generates power locally and supplies most of the plant’s output (more than 70 percent)


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to rural franchise areas. The surplus power, if any, is fed back into the grid and is paid for by the utility at the appropriate FIT (in case of renewable energy as per power purchase agreement [PPA]). Operational subsidies or additional income is provided to incentivize DG&S operator to first meet local demand before routing power to the grid. The utility significantly reduces its aggregate technical and commercial (AT&C) losses for serving the area. In addition, if the local plant is renewable-based, the capacity is credited against its renewable portfolio obligation (RPO) quota as determined by the State Electricity Regulatory Commission (SERC). This model has the advantages of distribution franchises (reduced AT&C losses and improved customer service) and the following additional benefits to the stakeholders:

CUSTOMERS Increasing reliability and service levels. Increasing electricity availability (as

local generation is captive, the rural areas are guaranteed supply).

Accelerating community development. (While not sufficient by itself, the availability of guaranteed, long-term, reliable electricity from a local source can spur economic growth through energy intensive value-added service industries.)

UTILITY

Contributing to the RPO of the utility if the local plant uses a renewable energy resource. Avoiding transmission charges and losses associated with centralized power sources by using local generation utilities.

Meeting its service obligations.

REGULATORS Meeting the goals of improving

availability, reliability, and quality to rural areas.

Increasing generation capacity by encouraging private distribution franchises to invest in distributed generation.

As part of this study, TERI undertook a field survey across selected rural districts in 2009. Domestic, commercial, and agricultural consumers reported that an improved power supply could have a significant impact on their socioeconomic status. The possibility of establishing new commercial establishments was also emphasized. These could include shops that sell electronic goods and home appliances; flour mills and bakeries; motor service shops; general stores and clothing stores; spice-floor mills; pharmacies; cyber cafés; welding and repair shops, furniture shops; and agricultural industries, including poultry farms and dairies. While such development is a key feature of off-grid plants, this will be significant in the DG&S model also. The pilot program can be implemented in areas where programs to support rural development already exist or can be designed to stimulate economic activities and boost demand.

IV. Distributed Generation in Rural India The Government of India set up a

Commission for Additional Sources of Energy in the Department of Science and Technology on the lines of the Space Commission and the Atomic Energy Commission to promote R & D activities in the area. In 1982, a separate department of Non-Conventional Energy Sources was created in the Small scale industry of Energy. After a decade, the department was


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elevated and converted into a full-fledged Smallscale industry. The mounting burden of subsidy has also lead to the introduction of the new legislation referred to above. There are a number of technologies for distributed generation, the details of which are given below: a. The Internal Combustion Engine. b. Biomass c. Turbines d. Micro-turbines e. Wind Turbines f. Concentrating Solar Power (CSP) g. Photovoltaics h. Fuel Cells i. Small-Hydel. a. The Internal Combustion Engine The most important instrument of the D. G systems around the world has been the Internal Combustion Engine. Hotels, tall buildings, hospitals, all over the world use diesels as a backup. Though the diesel engine is efficient, starts up relatively quickly, it is not environment friendly and has high O & M costs. Consequently its use in the developed world is limited. In India, the diesel engine is used very widely on account of the immediate need for power, especially in rural areas, without much concern either for long-term economics or for environment. b. Biomass Biomass refers to renewable energy resources derived from organic matter, such as forest residues, agricultural crops and wastes, wood, wood wastes that are capable of being converted to energy. This was the only form of energy that was usefully exploited till recently. The extraction of energy from biomass is split into three distinct categories, solid biomass, biogas, and liquid bio-fuels. Solid biomass includes the use of trees, crop residues, household or

industrial residues for direct combustion to provide heat. Animal and human waste is also included in the definition for the sakes of convenience. It undergoes physical processing such as cutting and chipping, but retains its solid form. Biogas is obtained by an aerobically digesting organic material to produce the combustible gas methane There are two common technologies, one of fermentation of human and animal waste in specially designed digesters, the other of capturing methane from municipal waste landfill sites. Liquid bio-fuels, which are used in place of petroleum derived liquid fuels, are obtained by processing plants seeds or fruits of different types like sugarcane, oilseeds or nuts using various chemical or physical processes to produce a combustible liquid fuel. Pressing or fermentation is used to produce oils or ethanol from industrial or commercial residues such as bagasse or from energy crops grown specifically for this purpose. c. Turbines Turbines are a commercialized power technology with sizes ranging between hundreds of kilowatts to several hundred megawatts. These are designed to burn a wide range of liquid and gaseous fuels and are capable of duel fuel operation. Turbines used in distributed generation vary in size between 1-30 MW and their operating efficiency is in the range of 24-35%. Their ability to adjust output to demand and produce high quality waste heat makes them a popular choice in combined heat and power applications. d. Micro-turbines Micro turbines are installed commercially in many applications, especially in landfills where the quality of natural gas is low.These are rugged and long lasting and


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hold promise for Distributed Generation in India. e. Wind-turbines Wind turbines extract energy from moving air and enable an electric generator to produce electricity. These comprise the rotor (blade), the electrical generator, a speed control system and a tower.These can be used in a distributed generation in a hybrid mode with solar or other technologies. Research on adaptation of wind turbines for remote and stand-alone applications is receiving increasingly greater attention and hybrid power systems using 1-50-kilowatt (kW) wind turbines are being developed for generating electricity off the grid system. Wind turbines are also being used as grid connected distributed resources. Wind turbines are commercially available in a variety of sizes and power ratings ranging from one kW to over one MW. These typically require a Small mum 9-mph average wind speed sites.

f. Concentrating Solar Power Various mirror configurations are used to concentrate the heat of the sun to generate electricity for a variety of market applications that range from remote power applications of up to 1- 2kW to grid connected applications of 200MW or more. R & D efforts in the area of distributed generation applications are focused on small, modular, and dish/ design systems. g. Photovoltaic Photovoltaic power cells are solid state semi conductor devices that convert sunlight into direct current electrical power and the amount of power generated is directly related to the intensity of the light PV systems are most commonly used for standalone applications andare commercially available with capacities

ranging between one kW to one MW. The systems are commonly used in India and can contribute a great deal for rural areas, especially remote and inaccessible areas. It can be of great help in grid connected applications where the quality of power provided by the grid is low. This is yet to be proved. High initial cost is a major constraint to large-scale application of SPV systems. R&D work has been undertaken for cost reduction in SPV cells, modules, and systems besides improvements in operational efficiency. h. Fuel Cells Fuel cells produce direct current electricity using an electromechanical process similar to battery as a result of which combustion and the associated environmental side effects are avoided. Natural gas or coal gas is cleaned in a fuel cell and converted to a hydrogen rich fuel by a processor or internal catalyst. The gas and the air then flow over an anode and a cathode separated by an electrolyte and thereby produces a constant supply of DC electricity, which is converted to high quality AC power by a power conditioner. Fuel cells are combined into stacks whose sizes can be varied (from one kW for mobile applications to 100MW plants to add to base load capacity to utility plants) to meet customer needs. However, the technology is not yet ripe for being considered for DG application in India, as it is very expensive, and has not yet been commercially tried on a large scale even in the U. S. A. 4. The technologies referred to above are applied under various schemes for generation of electricity from renewable sources of energy in the country. A bird’s eye view of the schemes would give a good insight into the status of Distributed Generation based on renewable sources of energy.


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BIOMASS BASED SCHEMES This can be considered under three distinct heads, National Project on Biogas Development, National Program me on Bio-Mass Power/Cogeneration and Bio-Mass GasifiedProgram me.

Biogas The gas is piped for use as cooking and lighting fuel in especially designed stoves and lamps respectively and can also be used for replacing diesel oil in fuel engines for generation of motive power and electricity. The Floating Gas Holder Type, that is India or KVIC model andFixed Dome Type which is made of brick masonry structure i.e. Deenabandhu model are among the indigenous designs of biogas plants. A Bag Type Portable Digester made of rubberized nylon fabric, suitable for remote and hilly areas, is being promoted. The recently developed methodology of on sight construction of Deenabandhu model with Ferro cement, which costs about 10 to 15% less as compared to the model constructed with bricks and cement, is getting popular in the Southern States.

The National Project on Biogas

Development was started in 1981-82. About 33.68 lac families have been benefited up to March 2002. The Community and Institutional Biogas Plants Program me was initiated in 1992-93. In order to achieve recycling the cattle dung available in the villages and institutions for the benefit of the weaker sections as well. Biogas is generally used for motive power and generation of electricity under the programme in addition to meet the cooking fuel requirement. A total of 3,901 plants, including 600 night soil based Biogas plants had been installed up to March 2002.

R & D in Biogas :The thrust of the R&D

efforts is on increasing the yield of biogas,

especially at low and high temperatures, development of cost effective design of bio gas plants, development of designs and methodologies forutilization of biomass, other than cattle dung for biogas production,reduction in the cost of biogas plants by using alternative building materialand construction methodology and diversified use of digested slurry forvalue added products.

Wind Energy The programme was initiated in the year 1983-84. Amarket-oriented strategy has been adopted right from the beginning andhence commercial development of the technology has been successfullyachieved. Scientific assessment of wind resources throughout the countryand a series of other systematic steps have facilitated the emergence of acost effective technology.8.1 The wind power potential of the country was initially assessed at 20000 MWand reassessed at 45000 MW subsequently assuming 1% of landavailability for wind power generation in potential areas. The technicalpotential has been assessed at 13000MW assuming 20% grid penetration,which will go up with the augmentation of grid capacity in potential States.The installed capacity in the country is 1628 MW, 63 MW underdemonstration projects and 1565 MW under private sector projects, whichrepresents just 13% of the technical potential. Tamil Nadu alone accountsfor nearly 50% of the installed capacity (857.5 MW) and the States ofTamil Nadu Maharashtra and Gujarat account for 1423.6 MW of the totalinstalled capacity. The Centre for wind energy technology (C- WET) is coordinating the WindResource Assessment Program me with the States and Nodal Agencies.8.3 Wind diesel projects are being taken up in Island


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regions and remoteareas which are dependent on costly diesel for power generation .Twomachines of 50 kW capacity each have been installed in the first phase ofthe project at Sagar Islands in West Bengal. Similar projects are beingconsidered for Lakshadweep and Andaman and Nicobar Islands. Solar Power Program The solar power program me comprises SolarPhotovoltaic Power Programmes and Solar Thermal Power Programmes.27 grid interactive SPVprojects have been installed, with an aggregate capacity of 2.0 MW inAndhra Pradesh, Chandigarh, Karnataka, Punjab, Kerala, Lakshadweep,Madhya Pradesh, Maharashtra, Rajasthan,Tamil Nadu, and UttarPradesh. These are meant for voltage support applications in remotesections of weak grids, peak shaving applications in public buildings inurban centers and for saving diesel use in islands. These are expected togenerate and feed over 2.6 million units of electricity annually to therespective grids. In addition, ten projects of 900 kW capacity, are underdifferent stages of implementation,9.2 The solar photovoltaic systems can be used for a variety of applications,such as rural telecommunications, battery charging, road and railwaysignalling which are non-subsidized. Only 3 MW out of the total aggregatecapacity of 96 MW (9,80,000 systems) is used by the power plants. In so far as rural areas are concerned, the SPV systems can beuseful for the following: i. Village electrification through SPVs: A five KW PV plant can servea village of 50 to 80 households for street lighting, lighting homes/radioTV, and community requirements like post office school primary healthcenter and drinking water supply. More than 2500 villages, mainly in

U.P, Rajasthan, West Bengal and Islands and also in Nyoma town inLadakh. Ninety villages in Bastar district of Madhya Pradesh andfourteen villages in Meghalaya have also been electrified throughSPVs. ii. SPV seem to be one of the best solutions on for the 18000 remoteand inaccessible villages. Solar electrification is more economical intribal areas and the North Eastern Region compared to grid extensionbeyond three kilometers. iii. In Gujarat, SPV systems have been applied at ten rural milkcollection centers of Panchamahal District Dairy Cooperative during2000-2001, ten more were sanctioned in 2001-02. The deployment ofsolar PV systems for this application has a large potential forreplication. iv. SPV water pumping systems for agriculture and related are alsobeing used by farmers. A cumulative total of 4500 SPV water systemshave been installed by March 31, 2002.

CONCLUSION

Our country is having a huge geographical variance and one approach or solution is never an optimized one. For remote regions like Thar in Rajasthan and Saurashtra in Gujarat are most fit for solar zone. Most coastal areas like Okhajaisalmer regions are fit for Wind power grid Likewise Hills areas are known for Hydro-power projects. All metro and capital cities must have Biomass projects. Nuclear power stations may be stationed in low population zones but having waters resources nearby to them. Other rural areas may have mixed /hybrid approaches depending upon resources. It is firmly suggested that transportation cost either in form of transmission lines or inform of fuel must be curtailed and centralized grid must be limited independently region wise in ring topology


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REFERENCES

[1] Ackerman, T., Andersson, G., Sodder, L., 2001. Distributed generation: a definition. Electric Power Systems Research57, 195–204.

[2] Ganesh, A., Banerjee, R., 2001. Biomass pyrolysis for power generation—a potential technology. Renewable Energy 22, 9–14.

[3] Resource Dynamics Corporation, 2001. Assessment of Distributed Generation Technology Applications, Prepared for Maine Public Utilities Commission by Resource Dynamics Corporation, Vienna, VA, USA; available on the web at //www.distributed-generation.-com.

[4] Annual Report. 1999-2000, Ministry of Non-Conventional Energy Sources, Government of India: New Delhi.


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Review Paper on Basics of Net-Metering and Ideas to Promote Renewable Resources

Gaurav Gupta1 Apurva Rajput2 Amit Kumar3 B.Tech (EEE), NIEC, Delhi B.Tech (EEE), NIEC,Delhi B.Tech (EEE), NIEC, Delhi

Abstract-The paper summarizes various methods for compensation to customers by the utility for using renewable resources.It also explains briefly about net-metering and its Indian context. Some ideas to use renewable resources at individual level have also been discussed. I. INTRODUCTION

There are basically three methods to give compensation for the use of renewable energy by the customers:-

(a)Feed in-tariff (FIT) (b)Power PurchaseAgreement (PPA) (c)Net Metering FIT is one of the solutions to compensate the electric bill by selling the produced electricity by any individual. consumer can produce electricity in his/her houses using renewable source of energy like solar source of energy, wind power energy, micro-hydroelectricity (home based hydro generation),biogas and after his/her use some amount of electrical energy can be sold back to grid.

FIT is implemented in different countries in USA and Europe. The first form of feed-in tariff was implemented in the US in 1978 under President Jimmy Carter, who signed the National Energy Act (NEA). This Act included five separate Acts, one of which was the Public Utility Regulatory Policies Act (PURPA). The purpose of the National Energy Act was to

encourage energy conservation and the development of new energy resources, including renewables such as wind, solar and geothermal power. In 1990, Germany adopted its "StromeinspEisungsGesetz" (StrEG), or its "Law on Feeding Electricity into the Grid" The StrEG required utilities to purchase electricity generated from renewable energy sources at prices that were determined as a percentage of the prevailing retail price of electricity. Germany's Feed-in Law underwent a major restructuring in the year 2000, being re-framed as the Act on Granting Priority to Renewable Energy Sources, German Renewable Energy Act.

India inaugurated its most ambitious solar power program to date on 9 January 2010. The Jawaharlal Nehru National Solar Mission (JNNSM) was officially announced by Prime Minister of India on 12 January 2010.This program aims to install 20,000 MW of solar power by 2022. The first phase of this program aims to install 1000 MW by paying a tariff fixed by the Central Electricity Regulatory Commission (CERC) of India. While in spirit this is a feed in tariff, there are several conditions on project size and commissioning date. Tariff for solar PV projects is fixed at Rs. 17.90 (USD 0.397/kWh). Tariff for solar thermal projects is fixed Rs. 15.40 (USD 0.342/kWh). Tariff will be reviewed periodically by the CERC.


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PPAis another option to compensate the problem related to electrical use. There is an entity which is responsible for compensation of electricity production, they use renewable source of energy to produce electrical energy and sell to nearest individuals.A Power Purchase Agreement (PPA) is a legal contract between an electricity generator (provider) and a power purchaser (buyer, typically a utility or large power buyer/trader). Contractual terms may last anywhere between 5 and 20 years, during which time the power purchaser buys energy, and sometimes also capacity and/or auxiliary services from the electricity generator. Key advantage of power purchase agreements is the predictable cost of electricity over the life of a 15 to 25 year contract. This avoids unpredictable price fluctuation from utility rates, which are typically dependent on fossil fuel prices.

Net Metering is a concept based on net consumption of energy. Customer will produce some amount of energy in his/her house and according to this he/she can contribute in generation of electrical energy.

It can be practiced by using some renewable energy sources like solar source of energy, wind energy source, micro-hydroelectricity using water harvesting. In a day there is some period of time when customer needs negligible energy and he/she is generating more energy than he/she consumes, in this case customer can send his/her produced energy back to the grid. A meter is installed which reads net consumption of energy by moving its indicator in forward and reverse direction .When customer consumes energy from grid then meter moves in forward direction and if customer sends produced energy back to the grid then meter moves in reverse direction. The Produced electricity back to the grid and meter moves in reverse direction. Net metering allows for the production of electricity that reduces demand on a strained grid. This practice helps the utility to make the system efficient, reliable and stable. To know the difference that the customer sited DG (such as a PV system) makes to the system the utility installs a costly additional meter at customer’s house and undertake the burden and expense of reading both meters and billing consumer for the result of this process.


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II. NET METERING Net metering originated in the United States,

where small wind turbines and solar panels were connected to the electrical grid, and consumers wanted to be able to use the electricity generated at a different time or date than when it was generated. However, Minnesota passed the first net metering law, in 1983. In 2000 this was amended to compensation "at the average retail utility energy rate". This is the simplest and most general interpretation of net metering, and in addition allows small producers to sell electricity at the retail rate. Utilities in Idaho adopted net metering in 1980 and in Arizona in 1981. Massachusetts adopted net metering in 1982.[3] Two California utilities initially adopted a monthly "net metering" charge, which included a "standby charge" but these charges were banned later. In 2005, all U.S. utilities were required to offer net metering "upon request". As of 2012 43 U.S. states have adopted net metering, as well as utilities in 3 of the remaining states, leaving only 4 states without any established procedures for implementing net metering.[4]Net metering was slow to be adopted in Europe, especially in the United Kingdom, because of confusion over how to address the value added tax (VAT). Only one utility in Great Britain offers net metering. [5] Implementation of Net-Metering Implementation of net-metering basically requires two steps. Interconnection - An interconnection standard includes the technical requirements and the legal procedures whereby a customer-sited generator

interfaces with the electricity grid. Individual states regulate the process whereby renewable energy systems are connected to the electric distribution grid. These policies, commonly known as interconnection procedures, seek to maintain the stability of the grid and the safety of those who use and maintain it. A complete interconnection procedure must address fees, timelines, insurance requirements and indemnification, forms and certain other issues to provide a comprehensive procedure that supports investment in customer-sited Distributed Generation — either by individuals or by project development investors. Net-Metering - Net metering allows customers to offset their electricity consumption with small-scale renewable generation over an entire billing period (or in some instances over an entire year) without considering when the power is consumed or generated. Net metering uses a single bi-directional meter that registers the flow of electricity in both directions. With net metering, either the customer pays for the net electricity consumed over the billing period at the retail rate, or the utility purchases the net electricity generated over the billing period at the lower cost rate. One of the examples of policy (interconnection procedure):- The “Four Pillars” of effective state policy.


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The Four Pillars take into consideration the best practices of net metering and interconnection. Incentives (Pillar 1) and utility rates and revenue policies (Pillar 4) are also crucial components in developing a world-class solar market. While financial incentives are the engine of market development, interconnection and net metering policies are the road. Pitfalls in the Interconnection Procedures After analysing some of the policies, the pitfalls have been identified in the regulatory rule making process. Common pitfalls include: Restricting eligibility to certain classes of

electric customers. Limiting program eligibility based on the

size of individual renewable energy systems. Preventing customers from receiving credit

for excess electricity. Charging discriminatory or unclear fees and

standby charges. Failing to promote the program to eligible

customers.[6] Trends in net meteringNet-metering is presently utilized in many countries as follows[7]: Generally small scale electric customers

have simple bidirectional meters-capable of spinning backwards to record energy flowing from their system to the utility grid. These basic meters are often referred to as "non-time-of-use meters" because they are not capable of recording when electricity was used. They can only record how much energy was used. Some utilities want two meters for net energy metering, one to measure electricity going from the grid to your home or business, and one to measure surplus energy going from your system to the grid.

Time-of-use (TOU) meters are more complex and they record when electricity is used and allowing the utility to charge different rates at different times of the day or week.

A small number of states (including California) allow “virtual” meter aggregation, where certain customers can net meter multiple systems at different facilities on different properties owned by the same customer.

In addition, “community net metering” or “neighbourhood net metering,” which allows for the joint ownership of a solar energy system by different customers, is in effect or under development in a some places, including Massachusetts.

Virtual Net Metering A newer approach to for CommunitySolarprojects to leverage net metering is to establish a "Virtual Net Metering" system. In this model the owner/manager of the solar array would track the energy production per individual share of the system. If the utility is managing the system, they could credit participants' energy bills for their portion of solar production just as they would for individually-metered systems. [8] Benefits of Net-Metering An easily recognizable benefit of net-metering is reduction in the amount of money spent each year on energy. One can even make money from the electric utility if the production is greater than the consumption. Here are a few other benefits of net metering: The most immediate and substantial benefit

of renewable energy based net-metering process is that it provides jobs. The solar industry is generating jobs at a rate 680% faster than the overall economy. For instance, as of August 2011, the American solar industry employed over 100,000 solar workers. And the future for the solar industry is just as bright: almost 50% of the country’s solar companies expect to add jobs,

The system is easy and inexpensive. It enables people to get real value for the energy they produce, without having to install a second meter or an expensive battery storage system.


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It allows homeowners and businesses to produce energy, which takes some of the pressure off the grid, especially during periods of peak consumption. For instance in Australia, the Solar Bonus Scheme pays 44 cents for every excess kilowatt hour of energy fed back into the state electricity grid. This is around three times the current retail price for electricity.

Each home can potentially power two or three other homes. If enough homes in a neighborhood use renewable energy and net metering, the neighborhood could potentially become self-reliant.

By facilitating distributed renewable energy development on-site, net metering accesses the greatest benefits of renewable energy without one of its most significant environmental costs. NET METERING IN INDIAN CONTEXT

Electricity demand in India is expected to rise 5 times over the next four decades. The challenge is to reduce the demand supply gap. As a result the government of India has announced plans to add 100giga watts of new generation capacity of 2017 through an investment of over $102 billion in the generation, transmission and distribution sectors.

In early 2011, India announced a $132 million smart grid pilot project. India does have feed-in tariffs plans in various states for wind power but they are for wind farms. At the home-owner level, there are no feed-in tariffs that exist. Grid characteristics and distribution sector are not fully ready for implementation of Net Metering. Much attention has not been paid to generate and bank electricity locally using solar power. But there are some renewable sources of energy to implement net-metering in India on a large scale.

With an average of 300 sunny days per year, India has vast potential for tapping solar energy. Though Photovoltaic systems are expensive but they are easier to use and to install than wind farms. They are motionless, noiseless and pollution free. They can be a part of the building's roof or facade and thus occupy less space.

CONCLUSION

Net metering promises development of a clean and green environment. It offers to use renewable resources effectively and creation of jobs in solar, wind and otherindustries. It helps the transmission and distribution system to become stable and reliable and at the same time helps customers to reduce their electricity costs.

REFERENCES

[1]http://sgstage.nrel.gov/the_smart_grid#smart_grid [2] Wikipedia.com [3] Current Experience with Net Metering Programs (1998) [4] Net Metering Map [5] SolarNet and Net Metering [6] FreeingTheGrid2009.pdf [7]http://www.gosolarcalifornia.org/solar_basics

/net_metering.php [8]http://nwcommunityenergy.org/solar/intercon

nection [9]http://science.howstuffworks.com/environmental/green-science/net-metering1.htm [10]The_Statewide_Benefits_of_Net-

Metering_In_CA_Weissman_and_Johnson.pdf(http://www.law.berkeley.edu/files/The_Statewide_Benefits_of_NetMetering_in_CA_Weissman_and_Johnson.pdf)


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A Survey on Smart Grid

Kritika Sharma1 Swati Singh2 Amit Kumar Yadav3 B.Tech(EEE), RKGITW, Ghaziabad B.Tech(EEE), RKGITW, Ghaziabad RKGITW, Ghaziabad [email protected] [email protected] [email protected]

Abstract— This paper deals with Smart Grid technology and its implementations to improve the efficiency of power grid. Today’s grid needs to be upgraded because it is aging, inadequate, outdated. Smart grid comprises of digital system capable of identifying surges downed lines. These include advanced meters, sensors, monitors and motors. The paper highlights on various problems and challenges related to electricity grids that are faced everywhere. It is much more practical to consider smart grids in terms of opportunities to improve the operation of the power system that are being exploited. Smart grid can be described as modernization of nation’s electricity transmission and distribution system to achieve a reliable and secure electricity infrastructure that can meet future demand. One of the key features of a smart grid is the ability to utilize information to make better operational decisions. The implementation and operation of the Smart Grid will affect every type of organization across the electricity supply chain, from regulators to consumers.

Keywords- Smart Grid , Two way flow

I. INTRODUCTION Power system consists of generation,

transmission, distribution and utilization of electrical power. The distribution and utilization need to embrace active network management technologies with an interface to the transmission system. A smart grid embrace new technologies i.e. telecommunication, control, self-healing, efficiency, reliability and security of power systems [6]. The need to meet increasing electricity demand, integrate more distributed sustainable resources including renewable energy

sources and advanced storage devices (batteries, compressed air system, fuel cell etc.). The role of the electric grids is becoming very important to balance the energy demand variations with the fluctuating power generation from the irregular sun and wind [8]. Smart grids must provide the electric energy to all consumers with a highly reliable, cost effective power supply, fully utilizing the large centralized generators and smaller distributed power sources. To switch from modern grid to smart grid all the relevant must be involved: government, regulators, consumers, generators, traders, power exchangers, transmission companies, distribution companies, power equipment manufacturers, etc.[3] II. SMART GRID

About hundred years ago, the power engineers crafted an excellent reliable power delivery system from generation to the consumer end through transmission and distribution. At that time power system supported a regulated monopolistic business model, large remote generation sites, less restrictive environmental constraints and system overbuild to account for load growth. In the present scenario, higher reliability is expected, with dramatically different and challenging design criteria. Consumers are more sensitive to outages, low voltage and harmonic issues. Environmental constraints are more restrictive. Efforts to control CO2 emissions is leading to expanded adoption of central station and distributed renewable power and electric energy storage, as well as expanded electric transportation and demand response technologies. The power delivery infrastructure in its current state will not be able to effectively


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accommodate the extent and types of these carbon reduction technologies [1]. There is need for upgrading and evolving the networks design to accommodate all low carbon generation technologies as well as to encourage the demand side to play an active part in supply, efficiently and economically.[1][4] The smart grid is a network of computers and power infrastructures that observe power system parameters and control energy usage. The intelligent electronic devices communicate energy usage to the utility using a modern communication technology. The intelligent electronic device at each consumer premises is called a smart meter. It’s a computerized replacement of the electrical meter attached to the outer walls of many of our homes today. Each smart meter contains a processor, non volatile storage, and communication facilities. Smart meters can track usage as a function of time of day, disconnect a customer via software, or send out alarms in case of problems [2]. The smart meter can also interface directly with consumers, in following way:

i. Consumers receive a “high cost period” pricing signal.

ii. Plug-in hybrid electric vehicles stop charging and pump power onto the grid.

iii. The set points on air conditioning thermostats are raised by two degrees or turn down the air conditioner during peak periods.

iv. The heating coils in cloth dryers turn off. v. One of two heating coils in each storage

electric water heater turns off. vi. The lights at large retail stores are

gradually reduced by 20%. vii. Refrigerator and freezer compressors are

cycled off. viii. Back-up generation at commercial and

industrial facilities comes on-line.

Fig: 1 Future Power System

SMART INFRASTRUCTURE SYSTEM

The smart infrastructure System is the energy, information, and communication infrastructure underlying the SG. It supports two-way flow of electricity and information. Note that it is straight forward to understand the concept of “two-way flow of information.” “Two-way flow of electricity” implies that the electric energy delivery is not unidirectional anymore. For example, in the traditional power grid, the electricity is generated by the generation plant, then moved by the transmission grid, the distribution grid, and finally delivered to users. In an SG, electricity can also be put back into the grid by users. For example, users may be able to generate electricity using solar panels at homes and put it back into the grid, or electric vehicles may provide power to help balance loads by “peak shaving” (sending power back to the grid when demand is high). This backward flow is important.

SMART MANAGEMENT SYSTEM The smart management system is the subsystem in SG that provides advanced management and control services and functionalities. With the development of new management applications and services that can leverage the technology and capability upgrades enabled by this advanced in-frastructure, the grid will keep becoming “smarter.” The smart management system takes advantage of the smart infrastructure to pursue various advanced management objectives. Thus far, most of such objectives are related to energy


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efficiency improvement, supply and demand balance, emission control, operation cost reduction, and utility maximization.

SMART PROTECTION SYSTEM The smart protection system is the subsystem in SG that provides advanced grid reliability analysis, failure protection, and security and privacy protection services. By taking advantage of the smart infrastructure, the SG must not only realize a smarter management system, but also provide a smarter protection system which can more effectively and efficiently support failure protection mechanisms, address cyber security issues, and preserve privacy.

Fig: 2 Smart Grids

III. ENABLING TECHNOLOGY

SMART METERING

Smart metering is the most important mechanism used in the SG for obtaining information from end users’ devices and appliances, while also controlling the behavior of the devices. Automatic metering infrastructure (AMI) systems, which are themselves built upon automatic meter reading (AMR) systems , are widely regarded as a logical strategy to realize SG. Smart meters, which support two-way communications between the

meter and the central system. Smart metering offers a number of potential benefits to consumers. It enables end user to estimate bills and thus manage their energy consumptions to reduce bills.

SMART MONITORING AND

MEASUREMENT An important function in the vision of SG is monitoring and measurement of grid status. a) Sensors- Sensors or sensor networks are used as a monitoring and measurement approach for different purposes and used to detect mechanical failures in power grids such as conductor failures, tower collapses, hot spots, and extreme mechanical conditions. b) Phasor Measurement Unit- Recent developments in the SG have spawned interest in the use of phasor measurement units (PMUs) to help create a reliable power transmission and distribution infrastructure. A PMU measures the electrical waves on an electrical grid to determine the health of the system.

SMART MATERIALS

Smart materials are necessary in the future power grid to give it the ability to self-recover with fast response in milliseconds under outage events or terrorist attacks. To accomplish this level of self-recovery, it is necessary to make each component intelligent. Such local, autonomous control will make the system much more resilient to multiple contingencies. One class of materials known as smart materials and structures (SMSs) has the unique capability to sense and physically respond to changes in the environment—changes in temperature, pH, or magnetic field. For the wires used in the electric power industry, smart materials could be utilized to monitor the condition of conductors, breakers, and transformers to avoid outages. The growing list of smart materials encompasses a number of different physical forms that respond to a wide variety of stimuli. Examples include the following:


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i. Piezoelectric ceramics and polymers are materials, such as lead zirconate titanate ceramics and polyvinylidene fluoride polymers that react to physical pressure. They can be used as either sensors or actuators, depending on their polarity.

ii. Conductive polymers are polymers that undergo dimensional changes upon exposure to an electric field. These versatile materials can be used not only as sensors and actuators, but also as conductors, insulators, and shields against electromagnetic interference.

iii. Electrorheological fluids are materials containing polarized particles in a nonconducting fluid that stiffens when exposed to an electric field. As such, they can be used in advanced actuators.

iv. Fiber optics are fine glass fibers that signal environmental change through analysis of light transmitted through them. Perhaps the most versatile sensor material, optical fibers can indicate changes in force, pressure, density, temperature, radiation, magnetic field, and electric current.

NANOTECHNOLOGY The theme of the development of nanotechnology in energy application technology is geared toward two main directions: nonmaterials for energy storage and nanotechnology for energy saving. Because of the small dimensions (5–20 nm), high specific surface areas, and special optical properties of nonmaterial’s, nanotechnology for energy saving is expected to increase with the contact area of the medium. Nanotechnology is being used to better the performance of rechargeable batteries through the study of molecular electrochemical behavior. Owing to the advantages of high reactivity, large surface area (200–2000 m2/g), self-assembly (~1–3-nm active catalyst), super crystal characteristics (~10–30-nm nanostructures), and special opto-electronic effects of nanomaterials for energy saving, several countries are heavily engaged in the development of energy-related nanomaterials.

IV. SMART GRID Vs TRADITIONAL GRID

In this producer-controlled model, power flows in one direction only. There is no two-way communication that allows interactivity between end users and the grid. The smart grid delivers electricity to consumers using two-way digital technology to enable the more efficient management of consumers’ end uses of electricity as well as the more efficient use of the grid to identify and correct supply demand-imbalances instantaneously and detect faults in a “self-healing” process that improves service quality, enhances reliability, and reduces costs.

Table 1 Smart grid Vs Traditional Grid

Smart Grid Existing Grid Digital Electromechanical

Distributed generation Centralized generation

Tow-way communication One-way communication

Self-monitoring Manual monitoring

Sensors throughout Few sensors

Self-healing Manual restoration

Pervasive control Minimum control

Adaptive and islanding Failures and blackouts

Many customer choices Few customer choices V. BENEFITS OF SMART GRID Benefits and requirements of SG are the following:

i. Improving power reliability and quality. ii. Optimizing facility utilization and averting

construction of back-up (peak load) power plants.

iii. Enhancing capacity and efficiency of existing electric power networks.

iv. Improving resilience to disruption. v. Enabling predictive maintenance and self-

healing responses of system disturbances.


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vi. Facilitating expanded deployment of renewable energy sources.

vii. Accommodating distributed power sources.

viii. Automating maintenance and operation. ix. Reducing greenhouse gas emissions by

enabling electric vehicles and new power sources.

x. Reducing oil consumption by reducing the need for inefficient generation during peak usage periods.

xi. Presenting opportunities to improve grid security.

xii. Enabling transition to plug-in electric vehicles and new energy storage options.

xiii. Increasing consumer choice.

CONCLUSION In near future, electricity demand is expected to continue to grow further, to provide the power quality and to meet the ever rising demand economically, more power generation is needed at centralized level or at distribution level. Due to environmental constraints, more stress has to be given to generate the power from green and clean energy sources. The power generation through green energy sources varies with time, to integrate with these sources; network configuration has to be changed. The plug in hybrid electric vehicles may also play an important role to meet the energy demand during peak demand period and during off peak hours they may be connected for charging. With the help of advanced communication technologies the utility will be able for effective decisions to be made and timely actions propagated to the points at which intelligent electronic devices installed, resulting in the smart

grid benefits that the utility and its consumers expects. Modern communication technology has ability to introduce a new era in electricity generation, distribution,

REFERENCES

[1] I. S. Jacobs and C. P. Bean, “Fine particles, thin films and exchange anisotropy,” in Magnetism, vol. III, G. T. Rado and H. Suhl, Eds. New York: Academic, 1963, pp. 271–350.

[2] K. Elissa, “Title of paper if known,” unpublished.

[3] R. Nicole, “Title of paper with only first word capitalized,” J. Name Stand. Abbrev., in press.

[4] Y. Yorozu, M. Hirano, K. Oka, and Y. Tagawa, “Electron spectroscopy studies on magneto-optical media and plastic substrate interface,” IEEE Transl. J. Magn. Japan, vol. 2, pp. 740–741, August 1987 [Digests 9th Annual Conf. Magnetics Japan, p. 301, 1982].

[5] M. Young, The Technical Writer’s Handbook. Mill Valley, CA: University Science, 1989.

[6] Electronic Publication: Digital Object Identifiers (DOIs): Article in a journal:

[7] D. Kornack and P. Rakic, “Cell Proliferation without Neurogenesis in Adult Primate Neocortex,” Science, vol. 294, Dec. 2001, pp. 2127-2130, doi:10.1126/science.1065467.

[8] H. Goto, Y. Hasegawa, and M. Tanaka, “Efficient Scheduling Focusing on the Duality of MPL Representatives,” Proc. IEEE Symp. Computational Intelligence in Scheduling (SCIS 07), IEEE Press, Dec. 2007, pp. 57-64, doi:10.1109/SCIS.2007.357670.


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Authentication Protocol for Distributed Sensor Network

Amit Kumar1 Sunil Gupta2 Rashmi Sharma2 ABES EC, GZB NIEC, New Delhi ABES EC, GZB [email protected] [email protected] [email protected] Abstract - With the emergence of ubiquitous computing the role of sensor network is becoming more important which demands highest level security and energy efficiency. In this paper we have analysis authentication protocols that resolve the weakness of security & suitable for the application with higher security requirement. We present a survey based on computation & communication cost with their performances. The authentication is a crucial service in distributed WSN because of limitation in computing power, data storage & communication capabilities. Keyword:- Authentication, Wireless Sensor Network, Security.

I. INTRODUCTION

Security allows WSNs to be used with assurance. Without security, the use of WSN is any application area would cause in undesirable consequences. Wireless sensor networks are rapidly gaining regard due to low cost solutions to a variety of real world challenges. The basic idea of sensor network is to disperse tiny sensing devices, which are able for sensing some changes of incidents/parameters and communicating with other devices, over a specific geographic area for some particular purposes like surveillance, environmental monitoring and target tracking. Now a day’s sensors can monitor pressure, temperature, humidity, soil makeup, noise levels, vehicular movement, and lighting

conditions, the presence or absence of certain kinds of objects or substances, mechanical stress levels on attached objects, and other properties [17]. In case of wireless sensor network, the communication among the sensors is done using wireless transceivers. Basically the major challenge for employing any efficient security scheme in wireless sensor networks is created by the size of sensors, as a result the memory, processing power and type of tasks affected from the sensors. To deal with the important security issues in Wireless sensor networks we talk about cryptography, steganography and other basics of network security and their applicability. We investigate various types of threats and attacks against wireless sensor network to save manufacturing cost. A sensor node is usually built as a small device, which has limited memory, a low-end processor, and is powered by a battery. So during the design of any security solution we need to take care of resource constraints like limited energy, limited memory, limited computing power, limited communication bandwidth, limited communication range. The type of security mechanism that can be hosted on a sensor node platform is dependent on the capabilities and constraints of sensor node hardware. After months of operation or a several weeks, some of the nodes in the network may weaken their power because of the irregular distribution of traffic load. so


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new node deployment is needed in this case. Besides the natural loss of sensor nodes, a sensor network is also vulnerable to malicious attacks in unattended and hostile environments. Some of the sensor nodes may be destroyed by opponent, so that the entire network may become useless. So, new sensor nodes have to be deployed. On the other hand, an opponent can also position a malicious node into the network. These malicious nodes may insert false reports and eaves drop messages. Recently many schemes were proposed to defend the sensor networks. It may prevent external attackers from inserting false reports or eavesdropping messages. But, they can hardly protect against internal attacks .In this paper; we evaluate the internal attacks in WSN. We observe that these attacks manipulate existing nodes to introduce malicious ‘‘new’’ nodes, which are indistinguishable from legitimate new nodes under current sensor network security technology. Those introduced ‘‘new’’ nodes could be accepted by other normal nodes as legitimate ones. Based on this observation, we design a protocol for sensor networks to prevent malicious nodes. However, most of previously proposed key pre distribution schemes cannot be easily implemented as a dynamic access control because all the old secret keys and broadcasting messages of existing nodes should be updated once a new node is added [17,18,19,20]. We introduce the node Security time stamp, which is the time when the new node joins the sensor network, into the authentication procedure to differentiate malicious ‘‘new’’ nodes, which are actually old nodes, from legitimate new nodes. Moreover, key establishment is also included in our authentication protocol to help the new node establish shared keys with its neighbors so that it can perform secure communications with them. Com-pared to RSA, ECC can achieve the same level of security with smaller key size. It has been

known that 160-bit ECC provides comparable security to 1024-bit RSA and 224-bit ECC provides comparable security to 2048-bit RSA [21] Hence, under the same security level, smaller key sizes of ECC offer merits of computational efficiency, as well as memory, and bandwidth saving. It is better suited for the resource constrained devices. Owing to the merits of ECC, this Protocol is based on elliptic curve cryptography (ECC). II. WHY NEED SECURITY

The goal of security services in WSNs is to protect the information and resources from attacks and misbehavior. The security requirements in WSNs include:

Node authentication: Ideally, the key management technique should guarantee that the communicating nodes are able to verify each other’s identity in a secure way. This feature helps the network to pinpoint misbehaving nodes, resulting in a higher resistance against the capture of valid nodes and attempts of impersonating them.

Resilience: Refers to the resistance of the scheme against node capture, where an adversary physically attacks a sensor and recovers secret information from its memory. The scheme’s resilience is given by the fraction of the network communications that are exposed to the adversary,[22] excluding the communications in which the compromised node is directly involved.

Node revocation: Upon the discovery of compromised nodes, the key management solution should provide efficient ways to dynamically revoke them from the network. Such mechanisms are useful to prevent an adversary from inserting malicious nodes into the network, even if this adversary obtained access to some secret information (e.g., through node capture).


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Scalability: During the sensor network lifetime, its size may vary dynamically; thus, the key distribution

Scheme must support large networks and, at the same time, allow the introduction of new nodes without loss of security.

III. REVIEW ATTACKS IN WSN

Security Requirements in Wireless Sensor Networks There are several problems with regard to the security of user authentication provided by IEEE 802.15.4 [17]. They cited key management problems.

Secure user authentication in WSNs should include, to the extent possible, methods for addressing application layer issues such as masquerade, replay, and forgery attacks.

Secure user authentication in WSNs should be based on mutual authentication.

A large-scale sensor network consists of thousands of sensor nodes and may be dispersed over a wide area. Typical sensor nodes are small with limited communication and computing capabilities, and are powered by batteries. These small sensor nodes are susceptible to many kinds of attacks. Attacks against wireless sensor networks could be broadly considered from two different levels of views. One is the attack against the security mechanisms and another is against the basic mechanisms. A. Passive Information Gathering: An opponent with powerful assets can collect information from the sensor networks if it is not encrypted [23]. B. Node Subversion: Capture of a node may tell its information including disclosure of cryptographic keys and thus compromise the whole sensor network [23]. C. False Node: A false node involves the addition of a node by an opponent to inject

malicious data, whereby the false node is computationally robust enough to lure other nodes to send data to it [23]. D. Node Malfunction: A malfunctioning node will generate inaccurate data which could put at risk to the integrity of sensor network especially if it is a data aggregating node such as a cluster head [23]. E. Node Outage: Node outage is when a node stops its function. In the case where a cluster head stops functioning, the sensor network protocols should be robust enough to moderate the effects of node outages by providing an alternate route. [23]. F. Message Corruption: Any modification of the content of a message by an attacker compromises its integrity [23]. G. Traffic Analysis: Even when the messages transferred are encrypted, it still leaves a high possibility analysis of the communication patterns and sensor activities can potentially reveal enough information to enable an adversary to cause malicious harm to the sensor network [23]. H. The Sybil attack: In a Sybil attack, a single node presents several identities to other nodes in the network. They pose a significant risk to geographic routing protocols, where location aware routing requires nodes to exchange coordinate information with their neighbors to efficiently route geographically addressed packets. Authentication and encryption techniques can prevent an outsider to launch a Sybil attack on the sensor network. However, an insider cannot be prevented from participating in the network, but it should only be able to do so using the identities of the nodes has compromised. Using globally shared keys allows an insider to masquerade as any node [24, 25]. I. Sinkhole attacks: In a sinkhole attack, the goal of opponent is to tempt nearly all the traffic from a particular area through a compromised node, creating a metaphorical sinkhole with the opponent at the center.


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Sinkhole attacks typically work by making a compromised node look especially attractive to surrounding nodes with respect to the routing algorithm [26]. J. Wormholes: In the wormhole attack, an opponent messages received in one part of the network over a low latency link and replays them in a different part. The simplest instance of this attack is a single node situated between two other nodes forwarding messages between the two of them. on the other hand, wormhole attacks more commonly involve two distant malicious nodes colluding to understate their distance from each other by relaying packets along an out-of-bound channel available only to the Attacker [27]. K. No Protection against Insider Attacks: Nowadays users use a single common password for accessing different applications or servers. The situation is common practice and this is done for their convenience. It relieves the user from having to remember multiple passwords. Nevertheless, if the system manager or a privileged user of the GW-node obtains the common password of Ui, he/she may try to impersonate Ui by accessing other servers where Ui could be a registered user. L. No Provision for Changing/Updating Passwords: The fixed password is definitely suffered from threats than an updating password. It is a widely recommended security policy, for highly secure applications, that users should update or change their passwords frequently. In the scheme [14,15], there is no provision for a user to easily change his/her password. IV. LITERATURE SURVEY ON WSN SECURITY

The following section provides a brief on related work on total access control protocol include authentication and key management. Zhou et al. [1] proposed an access control protocol based on elliptic curve cryptography (ECC) for sensor networks. Their scheme can provide new nodes to join the sensor network dynamically, and key establishment is also included in their access control protocol to help the new node establish shared keys with its neighbors so that it can carry out secure communications among sensor nodes. They included a bootstrap in their access control protocol to provide authentication procedure. And two sensor nodes should have the same bootstrapping time if deployed simultaneously. Their scheme also assumes that each sensor node can sustain a tolerance time interval before it is compromised. Then, it will be not convenient for some practical implementations. ACP is consisted of four phases, Redeployment phase, Node Deployment, node authentication and key establishment. Huang [2] proposed a novel access control protocol (NACP) based on ECC and authentication hash chain to support the practical implementations for sensor networks. NACP is quite adequate for power and resource constrained sensor nodes and could be easily implemented as a dynamic access control because all the old secrets and broadcasting information in existing nodes should not be updated once a new node is added. Huang claimed that her NACP can resist against various known attacks including the replay attack and the forgery attack. NACP is consisted of three phases, i.e. an initialization phase, an authentication and key establishment phase, and a new node addition phase. Compared with Zhou et al.'s [1] scheme, this scheme could reduce large amounts of computations and communications between two nodes. Moreover, this scheme can be easily implemented as a dynamic


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access control because the old secret keys and broadcasting information of existing nodes should not be updated once a new node is added. Kim and Lee [3] proposed an enhanced novel access control protocol (ENACP) by adding a hash chain renewal phase and supporting the mutual authentication, and claimed that ENACP can resist against replay attack, new node masquerading attack and lack of hash chain renewability. Kim and Lee’s enhanced novel access control protocol (ENACP) consists of four phases: initialization phase, authentication and key establishment phase, new node injection phase, and hash chain renewal phase.

J. Shen et al [4] find that there are still some fatal weaknesses in enhanced novel access control protocol ENACP [3] even though it improves the security and flexibility of NACP. In the authentication and key establishment phase, an adversary can easily intercept a random number of base station and hash operation from initialization phase. When node i communicates with node j to do the authentication via the wireless channel. In this case, the adversary can block the correct random number of base station and hash operation), and resubmit the distorted random number and hash function to node j after modifying the value of random number and hash function . Therefore, node i is not able to pass the authentication in node j, and node j considers node i as a illegitimate node because all the verification equations cannot hold. On the other hand, when node j communicates with node i, the adversary is also able to intercept and modify the values of random number and hash function in order to make the authentication of node j fail. Rabia Riaz and Ayesha Naureen [5] have introduced SACK (Storage and Communication optimized keying) framework for wireless sensor networks. In this

framework each sensor node is programmed according to the application requirements before network deployment. At the same time, one unique Key (KNB) of size m bit and one master key (KM) of size M bits is stored in FLASH ROM of each node. The reason for storing KM in FLASH ROM instead of hard coding in ROM is to exploit this information for later purging the keys in corrupted/compromised nodes. Base station (BS) stores the [SNIDj, KNB] pair for each node and uses it to authenticate and establish a pairwise symmetric key for each sensor node at the time of node joining in the network. BS also stores routing keys (KCL) and cluster keys (KCi) in a database for specified period of time

T = Tmax + Smax.

This information is used when a sleep node has to re-join the network on becoming active. Base Station Node Pairwise Key (KNB) is a unique pairwise key of each node with the BS. BS can use this key to propagate any interest directly to that sensor node. Routing Key (KCL) is used by CL’s to communicate with BS and other CL’s. If any CL cannot directly reach BS, then it establishes a route through other CL using this key and hence we call it the routing key. Cluster Key (KCi) is used by CN of ith cluster to communicate with their CL and other members of their cluster. Tanveer Ahmad Zia[ 6] have introduced a secure triple key scheme that covers the aspects of key pre-distribution, key deployment and key establishment. The STKS consists of three keys: a network key, a sensor key and a cluster key. These keys ensure authentication and encryption in communication from the base station to the nodes, from the nodes to cluster leaders, and back to the base station. The STKS achieves confidentiality using RC5 block cipher algorithm and authentication using MAC. Experimental results prove the performance of


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the STKS with negligible security overheads. The STKS also forms the basis of encryption and authentication which has been applied in the other three components of WSNS. Park and Shin [7] propose a dynamic group key management protocol called LiSP. LiSP addresses the vulnerability of key stream ciphers caused by key reuse. It addresses the problem by frequently and synchronously updating the group key. LiSP utilizes broadcast transmission to distribute the group keys and uses one-way key chains to recover lost keys. This scheme is very efficient; LiSP requires the use of static administration keys to perform periodic administrative functions. This leaves those keys vulnerable to disclosure. Carman et al. [8] conducted a comprehensive analysis of various group key schemes. The authors conclude that the group size is the primarily factor that should be considered when choosing a scheme for generating and distributing group keys in a WSN. Wong et al. [9] propose a scalable group key management protocol using key graphs. They utilize keys of multiple granularities to reduce the re-keying overhead associated with membership management. They also investigate multiple approaches for constructing re-keying messages. While efficient, this approach requires a centralized key distribution center. Zhu et al. [10] propose a comprehensive dynamic key management scheme called LEAP that establishes multiple keys for supporting neighborhood as well as global information sharing. Although LEAP includes several promising ideas, it does not adequately address scalability issues concerning the distribution and re-keying of group keys. Perrig et al. [11] introduce SPINS (Security Protocols for Sensor Networks) which is a collection of security protocols (SNEP) and micro-TESLA. SNEP (Secure Network Encryption Protocol) provides data

confidentiality and two-way data authentication with minimal overheads. Micro-TESLA, a micro version of TESLA (Time Efficient Streamed Loss-tolerant Authentication) provides authenticated streaming broadcast. SPINS leaves some questions like security of compromised nodes, DoS issues and network traffic analysis issues unaddressed. Furthermore, this protocol assumes a static network topology ignoring the ad hoc and mobile nature of sensor nodes.

J. Leavy et al. [12] proposes a light-weight security protocol that operates in the base station of sensor communication whereby the base station can detect and remove an aberrant node if it is compromised. This protocol does not specify any security measures in case of a passive attack on a node where an adversary is intercepting the communication

Zhu et al [13] present a LEAP which stands for Localized Encryption and Authentication Protocol is a key management protocol for sensor networks designed for in-network processing. Every node is only engaged with a limited number of its neighboring nodes to build its required keys out of its neighboring nodes; in other words, it does not involve all nodes of the network. The design of the protocol is motivated by the observation that different types of messages exchanged between sensor nodes have different security requirements, and that a single keying mechanism is not suitable for meeting these different security requirements. Hence, LEAP supports the establishment of four types of keys for each sensor node: an individual key shared with the base station, a pair-wise key shared with another sensor node, a cluster key shared with multiple neighboring nodes, and a group key that is shared by all the nodes in the network. The protocol used for establishing and updating these keys is communication and energy efficient, and minimizes the


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involvement of the base station. LEAP also includes an efficient protocol for inter-node traffic authentication based on the use of one-way key chains. A salient feature of the authentication protocol is that it supports source authentication without precluding in network processing and passive participation. M. Sharifi et al [14] present a SKEW is a lightweight protocol for key management in WSNs. It tries to manage keys with minimum communication, key transmission and storage usage. It is a base key management protocol that preserves network security before start up. It approaches in two cases: hierarchical WSNs and distributed WSNs. In the first case, our network is a hierarchical WSN and each sensor node has: A unique ID, A pseudo-random function (F) for generating the next key in sequence, A unique cluster number for each cluster member, and A group key as shared key between all nodes. Author divide node memory to three logical parts: 1) RAM memory section, 2) executive code memory section, and 3) non volatile memory section. Edmond Holohan & Michael [15] have introduced AVCA, “Authentication using Virtual Certificate Authorities”, which is such PKI architecture. It is based on commonly used and well established PKI concepts and designed specifically for resource constrained devices on distributed ad-hoc networks. It provides a mechanism to overcome the difficulties in securing many distributed networks with non tamper-proof devices. AVCA has many benefits including that the basis for initial trust is not stored on any of the sensor devices and that these devices do not require significant memory AVCA supports node authentication and a private key distribution mechanism. It also enhances many WSN design goals including simplicity, scalability, interoperability and control for individual manufacturers.

Manik Lal Das [16] have proposed two-factor user authentication protocol for WSN, provides strong authentication, session key establishment, and achieves efficiency. The protocol is divided into two phases: Registration phase and Authentication phase. The protocol avoids many logged in users with the same login-id and stolen-verifier attacks, which are prominent threats for a password-based system if it maintains verifier table at the GW-node or sensor node. In addition, the protocol resists other attacks in WSN except the denial-of-service and node compromise attacks.

CONCLUSION

In this research we will design a authentication protocol to prevent malicious nodes, which may be directly deployed or just old nodes manipulated by adversaries, from participating in sensor networks. Besides the node identity, we want to introduce the new node novel authentication protocol to differentiate malicious nodes from legitimate new nodes. Unlike the conventional approaches that try to detect malicious nodes after they join sensor networks, our mechanism can prevent malicious nodes from joining sensor networks at the very beginning. In addition, key establishment is also realized in our protocol to help the new node establish shared keys with its neighbors so that it can perform secure communications with them. Compared with the conventional sensor network security solutions, our framework can defend against most of the notorious attacks in sensor networks, and achieve better computation and communication performance due to the usage of the more efficient algorithms based on Elliptic Curve Cryptography than those based on RSA. Hence, it is very suitable for the sensor nodes that are limited in power, computational capacities, and bandwidth.


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REFERENCES

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[3] H. S. Kim and S. W. Lee, “Enhanced Novel Access Control Protocol over Wireless Sensor Networks,” IEEE Trans. on Consumer Electron., vol.55, no. 2, pp. 492-498, May 2009.

[4] J. Shen et al.: COMMENT: “Enhanced Novel Access Control Protocol over Wireless Sensor Networks” 2010 IEEE Trans. on Consumer Electron pp 2019- 2021

[5] Rabia Riaz , Ayesha Naureen , Attiya Akram , Ali Hammad Akbar , Ki-Hyung Kim, and Farooq Ahmed , “A unified security framework with three key management schemes for wireless sensor networks” Computer Communications, July 2008, pp.45-59.

[6] T.A Zia, and A.Y. Zomaya, “A security framework for wireless sensor networks,” in Proceedings of IEEE Sensor Applications Symposium (SAS06), February 7-9 2006, Hoston, Texas, USA,pp.89-97.

[7] T. Park and K. Shin, “LiSP: A lightweight security protocol for wireless sensor networks,” in ACM Transactions on Embedded Computing Systems Vol. 3, No.3, pp.634-660, August 2004.

[8] D. Carman, B. Matt, and G. Cirincione. “Energy-efficient and low-latency key management for MSN networks.” in Proc. of 23rd Army Science Conference, Orlando FL, December 2002.

[9] C K Wong, M Gouda, and S Lam, “Secure group communications using key graphs,” in Proc. IEEE Transactions on

Networking vol 8, no 1, pp. 16-29. February 2000.

[10] S. Zhu, S. Setia, S. Jajodia, “LEAP: efficient security mechanisms for large-scale distributed MSN networks,” in Proc. of the 10th ACM Conference on Computer and Communication Security (CCS), pp. 62-72, Washington DC, October 2003.

[11] Perrig, R. Szewczyk, V. Wen, D. Culler, and J. Tygar, “SPINS: Security protocols for sensor networks,” Wireless Networks, vol. 8, no. 5, pp.521-534. November 2002.

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[13] Joseph Polastre, Robert Szewczyk, Alan Mainwaring, David Culler, and John Anderson. ”Analysis of wireless sensor networks for habitat monitoring.” In Cauligi S. Raghavendra, Krishna M. Sivalingam, and Taieb Znati, editors, Wireless Sensor Networks, 2005.

[14] D. M. Doolin and N. Sitar. “Wireless sensors for wildlife monitoring”. In SPIE Symposium on Smart Structures and Materials, March 2005.

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[16] Ning Xu, Sumit Rangwala, Krishna Kant Chintalapudi, Deepak Ganesan, Alan Broad, Ramesh Govindan, and Deborah Estrin. “A wireless sensor network for structural monitoring”. In SenSys ’04: Proceedings of the 2nd international conference on Embedded networked sensor systems, pages 13–24, New York, NY, USA, 2004. ACM.

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Effects of Net Metering On The Use Of Small Scale Renewable Energy Sources Systems In

Today’s World

Yagdeep Sharma B.Tech(EEE), NIEC, New Delhi [email protected]

Abstract-Factors such as technological advancements, steadily decreasing costs, consumer demand, and state and government policies are combining to make renewable sources of energy, a new potent field for exploration. Net metering, also referred to as net billing, is one particular policy that states are implementing to encourage the use of small renewable energy systems. This paper is an attempt to analyze implementation of netmetering and its effect on use of renewable energy resources in 10 USA states.

I. INTRODUCTION

Net metering is an electricity policy for consumers (generally small renewable energies (such as wind, solar power and home fuel cells)V2G electric vehicles. "Net", in this context, is used in the sense of meaning "what remains after deductions" — in this case, the deduction of any energy outflows frommetered energy inflows. Under net metering, a system owner receives retail credits for at least a portion of the electricity they generate. Most electricity meters accurately record in both directions, allowing a no-cost method of effectively banking excess electricity production for future credit. However, the rules vary significantly by country and possibly state/province: if net metering is available, if and how long you can keep your banked credits, and how much the

credit are worth (retail/wholesale). Most net metering laws involve monthly roll over of kWh credits, a small monthly connection fee, require monthly payment of deficits (i.e. normal electric bill), and annual settlement of any residual credit.

In the U.S.A., as part of the Energy Policy Act of 2005, under Sec. 1251, all public electric utilities are now required to make available upon request net metering to their customers. Thirty-six states of US as shown (figure 1) have adopted some form of net metering law for renewable energy sources facilities (such as wind, solar power or a home fuel cells) or V2G electric vehicles.. The 10 states analyzed here include California, Idaho, Illinois, Iowa, Maine, Minnesota, Nevada, Oregon, Vermont and Washington (figure 2)

Figure 1. Current U.S. Residential Small Wind Incentives


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Figure 2. States Surveyed for Net Metering Programs

II. METHODS OF NETMETERING

TIME OF USE METERING (TOU) NET METERING

TOU Employs a specialized reversible smart(electric) meter that is programmed to determine electricity usage any time during the day. Time-of-use allows utility rates and charges to be assessed based on when the electricity was used (i.e., day/night andseasonal rates). Typically the production cost of electricity is highest during the daytime peak usage period and low during the night, when usage is low. Italy has installed so much photovoltaics that peak prices no longer are during the day, but are instead in the evening, reversing the result - less electricity can be consumed than produced using time of use net metering.

MARKET RATE NET METERING SYSTEMS

Here,the user's energy used and it is priced dynamically according to some function of

wholesale electric prices. The users' meters are programmed remotely to calculate the value and are read remotely. Market rate metering systems will be implemented in California starting in 2006 and under the terms of California's net metering rules will be applicable to qualifying photovoltaic and wind systems. Under California law the payback for surplus electricity sent to the grid must be equal to the (variable, in this case) price charged at that time. It can never be negative, meaning you cannot make money from selling the electricity back. If you generate more electricity than you use then over a period of a month you will be billed zero and in effect you give away your extra energy if you do not use.

III. NET METERING IN MAJOR USA STATES.

CALIFORNIA has the largest number of net-metered customers. They have had the earliest adoption of state incentives, of which the buy-down program started in 1998. A total of 1,416 net metered systems have been approved and 994 net metered systems are pending approval in the territories of Southern California Edison (SCE), San Diego Gas & Electric (SDG&E), and Pacific Gas & Electric (PG&E), which account for all net metered customers, most of these installations are solar.

The CEC reported the total number of small turbines installed under its buy-down program (California financial incentive where the states pays 50 percent of the installed small turbine costs), as shown in figure 3. All these turbines installed under the buy-down also have net metering so we can determine that, at the minimum, 704 kW of wind net metering exists in California.


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Figure 3. California Small Wind Turbine

Installations

MINNESOTA Minnesota’s program began in 1983 with the net excess generation being purchased by the utility company at the average retail electricity rate. Currently, 232 kW of installed capacity is tied to wind net metering programs.In this state Net metering program began so early because of environmentally conscious citizens and because the state is short on domestic energy sources such as coal and natural gas. Currently, the number of small wind installations in Minnesota is decreasing, while the number of small solar installations is increasing.

MAINE The Public Utility Commission (PUC) in Maine administers the state’s net billing program. According to Mitch Tannenbaum of the PUC, Central Maine Power and

Bangor Hydro-Electric have customers participating in the program. Tannenbaum provided a general list of current net billing customers. Gary Cole, with Central Maine Power (CMP), provided a list of current and previous net billing customers, the date the customer started net billing, the type of technology in use, and the rated capacity of each project. These data are shown in figure 5, which illustrates changes in the number of net metering customers from 1981 to 2001.

Figure 4. Minnesota Net Metering

Figure 5. Maine Net Metering

OREGON Although no small wind systems are currently net-metered in Oregon, the state is included here to further illustrate how customers’ concerns about the reliability of the electric system can influence their participation in net metering programs. Figure 6 shows Oregon net metering, which


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has 20 solar installations and one micro hydropower installation. Interestingly, the data shows a dramatic upward trend in the number of solar installations growing from just three installations in 1999 to 20 in 2001. One possible explanation for this is that customers in Oregon who were affected by the power shortage in California wish to generate their own power to protect themselves from future power shortages.

Figure 6. Oregon Net Metering

WASHINGTON About 10 percent of the land in Washington is suitable for small wind systems and the lack of qualified turbine installers may be the reason for the low number of small wind net metered projects. Compared to small wind systems, photovoltaic systems are comparatively easy to install.

Figure 7. Washington Net Metering

VERMONT Although the number of solar and wind system installations are increasing in

Vermont (figure 8), interest in net metering remains comparatively low. There are two possible explanations for this. First, because the program is fairly new, many customers may not yet know of its existence. Second, the permitting process for small wind turbines can be cumbersome and expensive.

Figure 8. Vermont Net Metering

CONCLUSION

For eight of the states surveyed, a total of 1,363 kW of installed small grid-connected wind existed at the end of 2001as shown in figure 9.

Figure 9. Total Installed Capacity of Net Metered,

Small Wind Systems for 8 States (in kW)

Although it is difficult to show specific cause and effect for the data presented, some conclusions can be drawn. The first is that net metering programs alone seem to offer


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minimal incentive for consumers, particularly in light of difficulties with county zoning officials and cumbersome interconnection agreements. Another conclusion is that when consumers are concerned about utility service reliability issues due to storms (like the New England ice storm in 1998), brown outs (like those experienced in California in the summer of 2001), or higher electricity rates, there is an increase in net metering customers. This is particularly true for states and counties where helpful financial incentives exist for home-based renewable energy projects. It also appears that when there are multiple incentives for net-metered systems in addition to education and outreach programs (such as the Million Solar Roofs Program), the number of net-metered installations increases. This suggests that education and outreach programs can influence the number of net-metered customers.To seek out and utilize home-based renewable energy It also appears that when there are multiple incentives for net-metered systems in addition to education and outreach programs (such as the Million Solar Roofs Program), the number of net-metered installations increases. This suggests that education and outreach programs can influence the number of net-metered customers.

REFERENCES

[1]Cory, K., T. Couture, and C. Kreycik. 2009. Feed-in Tariff Policy: Design, Implementation, and RPS Policy Interactions. NREL

[2]Couture, T. and K. Cory. 2009. State Clean Energy Policies Analysis (SCEPA) Project: An Analysis of Renewable Energy Feed-in Tariffs in the United States. NREL: Golden, Co.

[3]Doris, E., J. Mclaren, V. Healey, and S. Hockett. 2009. State of the States 2009:

Renewable Energy Generation and the Role of Policy. NREL: Golden, Co.

[4][DSIRE] Database of Incentives for Renewable Energy and Energy Efficiency. 2009

[5].California: Incentives/Policies for Renewable Energy – Net Metering.

[6] Connecting to the Grid July 29, 2009.

[7]Kroposki, B, R. Margolis, G. Kuswa, J. Torres, W. Bower, T., Key, and D. Ton. 2008. Renewable Systems Interconnection

[8]Network for New Energy Choices. 2008. Freeing the Grid 2008: Best and Worst

[9]National Renewable Energy Laboratory. 2009. OpenPV database


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A Detailed Review on Energy and Economic Aspects in Developing Smart Grid

Technologies

Monika Dubey1 VandanaArora2 NIEC, New Delhi NIEC, New Delhi [email protected] [email protected] Abstract:In recent years, the energy deficiency has been faced in many countries which not only makes adverse impact on economics, society and development of the country, but also results inthe global warming. Energy demand is exponentially increasing worldwide and energysaving has become a dire need of the times. Nowadays, large scale development of RES, e.g., wind and PV power generation are highly demanded due to need for clean and green power. However, integration of RES into existingpower network along with load or consumers in future may bring many technical challenges. In attention towards the above issues smart grid are fast emerging technologies to meet the challenges. I. INTRODUCTION In most of the countries, the electrical and distribution systems were constructed whenenergy production was relatively cheap. The important aspect of the grid reliability wasbased on having excess capacity in the system, with unidirectional electricity flow toconsumers from centrally dispatched power plants. Investments in the electric systemwere made to meet increasing demand and not to change fundamentally the way thesystem works. While innovation and technology have dramatically transformed other industrial

sectors,the electric system has continued to operate in the same way for decades. The lackof investment, combined with an asset life of 40 years or more, has resulted in an inefficientand increasingly unstable electric system [1]. Taking into account above mentioned challenges, the energy community starting to integrate information and communications technology (ICT) with electricity infrastructure. Technology enables the electric system to become ‘smart’. The real-time information allows utilities to manage the entire electricity system as an integrated framework, actively sensing and responding to changes in power demand, supply, costs, qualityand emissions across various locations and devices. The real-time monitoring of grid performance will improve grid reliability and utilization, reduce blackouts and increase financial returns on investments in the grid. These changes on the demand and supply side may require a new, more intelligent smart grid system that can manage the increasingly complex electric grid efficiently.

ECONOMIC STATUS OF CONVENTIONAL POWER DELIVERY

SYSTEM High demands for reliable power set of recent developments are about to change and put the electricity networks under pressure to change. The conventional power delivery systems, i.e. grid generally consist of large


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unit and equipments for power transmission and distribution.This requires an expensive maintenance and control systems. Transmission losses related to conventional grids are large and compensation for these losses requires additional control systems which are also cost – ineffective. Moreover, the conventional power systems generally utilize energy resources like hydro and thermal power plant which results in high installation and maintenance cost. In spite of more expensive power delivery system conventional grids fail to deliver reliable power to the consumers.

ENVIRONMENTAL IMPACT IN CURRENT POWER DEMAND

SCENARIO It has been revealed that electric power causes approximately25% of global greenhouse gas emissions and utilities are rethinking what the electricitysystem of the future should look like. It is hoped that renewable and distributed powergeneration will play a significant role in reducing greenhouse gas emissions.Generation of electrical energy, however, iscurrently the largest single source of carbon dioxide emissions, making a significantcontribution to climate change.

DEMAND FOR SMART GRID The systematic development of electric power networks includes improved communicationsand utilizing modern computer technology providing more intelligent automation devices and improvedoptimized systems. It will enable utilities to meetregulatory requirements and customer demands for reliable power flow from both conventionaland renewable energy sources (RES) [2]. If efficiently developed and managed smart grids are used then it is considered as an important research topic for the inboth academia and industry. Variouskinds of information

technology (IT), such as sensors, digital meters and a communicationsnetworks to the internet or to the dumb wires create smart grid. A smart grid would be able to avoidoutages, save energy and help other green undertakings, such as electric cars and distributedgeneration (DG).

SMART GRID VISION Smart grid gathers the latest technologies to ensure success, while keeping the high chances to get flexible with further developments. This will improves efficiency of supply by increasing power transfers and reducing energy losses,while power electronic technologies will improve the quality of electric supply. Advancesand developments in simulation tools will greatly assist the transfer of innovativetechnologies to practical application for the benefit of both customers and utilities.Developments in communications, metering and business systems will open up new opportunities at every level on the system to enable market signals to drive technical and commercial efficiency. Key elements of the smart grid vision include: - Creating a toolbox of proven technical solutions that can be deployed rapidlyand cost effectively, enabling existing grids to accept power injections from allenergy resources. - Harmonizing regulatory and commercial frameworks to facilitate cross-bordertrading of both power and grid services, ensuring that they will accommodate awide range of operating situations. - Establishing shared technical standards and protocols that will ensure open access,enabling the deployment of equipment from any chosen manufacturer. - Developing information, computing and telecommunication systems that enablebusinesses to utilize innovative service arrangements to improve their


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efficiencyand enhance their services to customers. - Ensuring the successful interfacing of new and old designs of grid equipment toensure interoperability of automation and control arrangements. II. STUDY ON NEWLY DECENTRALIZED POWER SYSTEMS IN DIFFERENT COUNTRIES

SMART GRID DEVELOPMENTS IN INDIA

The growth rate in India has been raised recently as its government implements reformsto encourage foreign investments and improve infrastructure and basic living conditionsfor its 1.1 billion citizens. However, India is losing money in the form of electric gridlosses. As India keeps one of the weakest electric grids in the world, the opportunitiesfor building the smart grid are high. Building a modern and intelligent grid is the keyrequirement to keep economic growth continuously. It is only with a reliable, financiallysecure smart grid that India can provide a stable environment for investments in electricinfrastructure, a prerequisite to fixing the fundamental problems with the grid. Withouthaving it, India will not be able to keep pace with the growing electricity needs of itscornerstone industries and will fail to create an environment for growth of its high-techand telecom sectors.According to statistics given by ministry of power, the T&D losses are among thehighest in the world, averaging 26% of total electricity production, with some states ashigh as 62%. When non-technical losses such as energy theft are included in the total,average losses are as high as 50%. The financial loss has been estimated at 1.5% of thenational GDP and is growing steadily.India’s power sector is still largely dominated by state utilities. Despite several attemptedpartnerships with foreign

investors, few projects have actually been implemented.This lack of foreign investment limits utilities’ ability to raise needed capitalfor basic infrastructure. India’s grid is in need of major improvements. This neglect hasaccumulated in a variety of system failures: - Poorly planned distribution networks - Overloading of system components - Lack of reactive power support and

regulation services - Low metering efficiency and bill collection - Power theft. While the government’s ambitious “Power for All” plan calls for the addition of over 1TW of additional capacity by the year 2012, it faces the challenge of overcoming a history poor PQ, capacity shortfalls and frequent blackouts. The Government of India in cooperation with the state energy board had put forwarda road to improvement when the new Electricity Act of 2003 was announced, aimed atreforming electricity laws and bringing back foreign investment. The act had consideredseveral important measures: - Unbundling the State Electricity Board’s

assets into separate entities for generation,T&D, with the intention of eventual privatization

- Adding capacity in support of a projected energy use growth rate of 12%, coincidingwith a GDP growth rate of roughly 8%

- Improving metering efficiency -Auditing to create transparency and

accountability at the state level - Improved billing and collection -Mandating minimum amounts of electricity from renewable -Requiring preferential tariff rates for renewable -End use efficiency to reduce the cost of

electricity. India has started to put labels on the appliances with energy use to help


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consumers determineoperating costs. Significant efforts have been made to improve energy efficiency,e.g., to increase the average energy efficiency of power plants up from 30 40%, and pushing major industries to reduce energy consumption. Without addressing the problemsof investment and financial stability, India is not able to solve its inadequate gridinfrastructure. Financial stability and concurrent investment only arises from loweringthe enormous problems with power theft in India.Recently, discussion has been raised that using DSM to selectively curtail electricityuse for delinquent customers or neighborhoods, while improving PQ for consistentlypaying customers. It might not sound like a desirable program to most American utilities,however, it may make sense in India’s constrained power grid where high levels ofdelinquency have increased system load without revenue returns. Another motivation tobuild smart grid in India is its trend towards energy efficiency and increased use of renewable.India would greatly benefit from intelligent energy efficiency in the form of DR and grid responsive appliances. [3]

SMART GRID DEVELOPMENTS IN UNITES STATES

The steps toward a fully realized smart grid are being taken now and the potential investmenthas been considered substantial. EPRI estimates the market for smart gridrelatedprojects in the US will be around $13 billion per year over the next 20 years.That comes in addition to an estimated $20 billion per year spent on T&D projects generally.More recently, a Morgan Stanley report analyzing the smart grid market put currentinvestment at $20 billion per year, increasing to over $100 billion per year by 2030.Despite these remarkable forecasts, however, smart grid deployments still represent amajor departure from current

utility practices. For an industry with a time honored focus on reliability and certainty in the application of new technologies, the shift tosmart grid presents a daunting challenge. However, some exciting projects are alreadyunderway.The US is home to several consortia working on smart grid issues. EPRI’s IntelliGridprogram and department of energy (DoE’s) GridWise Alliance are just two examples.Likewise, the nation’s utilities are actively involved with approximately 80% of investor-owned utilities developing some form of smart grid, e.g. by participating in pilotstudies of wide area monitoring systems (WAMS).The energy policy act of 2005 (EPAct) in US introduced mandatory reliability standardsand required state regulators to investigate advanced metering, time-based pricingand DR programs, all of which will rely on smart grid advances. The energy independenceand security act of 2007 (EISA) included an entire title devoted to smart grid thatprovided funding for research and development (R&D) efforts, created a smart grid advisorycommittee and requires state regulators to consider smart grid alternatives beforeapproving investments in traditional technologies. Standards are vital to accelerate theadoption of smart grid technologies across the utility industry. The national institute ofstandards and technology (NIST) is leading the standards effort and, in May 2009, publishedan initial list of standards that will be used in smart grid development. The governmentwill also play a major role in the development of the smart grid through itsmany regulatory agencies, both state and federal. EPAct. e.g., established a mechanismfor creating so called National Interest Electric Transmission Corridors to speed up theapproval process for new transmission lines in heavily congested areas.Recently, the federal energy regulatory commission (FERC) has issued an interim ratepolicy, by


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which investments in smart grid area would be included as recoverable costsin a utility’s regulated rates. To create a smart grid collaborative of regulators at thestate and federal level, FERC has also joined with the national association of regulatoryutility commissioners. These are few examples in the role of advisor, regulator, policymakeror even banker, the government holds tremendous influence over the course ofsmart grid development [4]. The potential economic and environmental advantages of a smart grid cannot beoverlooked. A recent PNNL study provided homeowners with smart grid technologiesto monitor and adjust the energy consumption at their homes. The average householdreduced its annual electric bill by 10%. By deploying this approach widely, the peakloads could be reduced on utility grids up to 15% annually, which equals more than 100GW, or the need to build 100 large coal-fired power plants over the next 20 years in theUS alone. This could save up to $200 billion in capital expenditures on new plant andgrid investments and take the equivalent of 30 million autos off the road [1].

SMART GRID DEVELOPMENTS IN CHINA

Electricity consumption in China has been growing at an unprecedented rate since theyear 2004 due to the rapid growth of industrial sectors. Serious electric supply shortage during year 2005 had affected the operation of many Chinese companies badly. Since then, China has very aggressively invested in electricity supply business in order to fulfill the demand from industries and hence securing continuous economic growth. In additionto increase generation capacity, it is equally important to improve distributionnetworks and utilization. In the last few years, the country has focused to expand T&Dcapacity and

reduce line losses by uplifting transmission voltage and installing highefficiency distribution transformers. In addition to physics-based technological improvements,smart grid offers the possibility to very effectively manage utilization andlead to very substantial energy saving. After US and Europe, China has also announcedan aggressive framework for smart grid deployment.Owing to energy-based nature of the present gross domestic product (GDP) growth,China’s energy demand in the recent years has increased substantially. As a result, China’selectricity industry has been growing at the fastest rate in human history. Installedgeneration capacity has run from 443 GW at end of year 2004 to 793 GW at the end ofyear 2008. Increment in these merely four years is equivalent to approximately onethirdof the total capacity of US, or 1.4 times of the total capacity of Japan. During thesame period of time, power consumption has also raised from 2,197 TWh to 3,426 TWh. Being the medium for delivering electricity to users, this rapidly increasing demandpresents a serious challenge to the capacity, reliability and efficiency of the gridsystem. In parallel to the economic growth aspect, the environmental problems associatedwith heavy industries are well known. China’s heavy industrial sector is one of the biggestsources of CO2 and SO2 in the world [5]. The problem is further aggravated by thefact that generation resources and load centers in the country are located far apart; majorityof hydropower resources are located in west, coal in northwest, but huge loadingsare prevailing in east and south. It has been estimated that 100-200 GW transmissioncapacity will be required to deliver electricity over long distance from west to east andfrom north to south in coming 15 years. The existing grid structure in China (primarilybased on 500 kV AC and


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±500 kV DC backbones) is not sufficient to meet the existingdemand [6]. Furthermore, overall T&D loss consideration is also critical because thenet growth of electricity consumption will be at the magnitude of 2,000-3,000 TWh inthis period of time [7]. To satisfy the needs, it is therefore necessary to establish reliabletransmission circuits that can deliver electric energy across extremely long distanceat low losses and developing an extra efficient distribution system for end customers.After carrying out investigations, it has been revealed that developing and deployingultra high voltage (UHV) technologies are mandatory for the country [7], [8]. Consequently, the government has approved a number of transmission line construction projectsusing UHVAC (refers to 1,000 kV) and UHVDC (refers to ±800 kV) technologies.On the other hand, to improve the overall efficiency of the grid, distribution network isanother critical area that needs to be addressed. Distribution transformer core losses orno-load losses are a major component of the total T&D loss. At present in China, the smart grid is focusing more on the transmission networks rather than the distribution networks. Based on the fact that coal is the main energy source and coal mines are far away from the main load centers, it is the right choice that the power grid development should be focused on the transmission networks. The project is known as the "West-East Electricity Transfer Project," which includes three major westeast transmission corridors construction. The transmission capacity of each corridor will be 20 GW by the year 2020. Through these transmission grids, electricity distributors in China will bond regional power grids in different areas of the country and improve cross-region electricity transmission ability. This will balance the power generation disparities in different regions of the country.

The state grid corporation of China (SGCC) has considered power grid construction as its core business operation at the moment. In developing power grid for transmission network, SGCC has been deploying several technologies such as WAMS and information system integration project etc. WAMS uses the phasor measurement unit (PMU) based on the global positioning system (GPS) to develop the stability of power grids. SGCC is building a WAMS and by year 2012 plans to have PMU sensors at all generators of 300 MW and above and all substations of 500 kV and above. SGCC has been deploying extensive fiber-optic networking throughout China HV substations. This network amounts to over one million kilometres of fiber-optic channels. The main features of smart grid technology implemented so far in China are [9]: -Policy and strategy for smart grid development - Latest T&D upgrades and developments to

improve grid connectivity, capacity and efficiency

- Developing interoperability and standards to improve the connectivity of the grid components

- Preparing the engineering workforce for the emergence of the smart grid technologies

- Developing smart metering and AMI - Management platforms, integration and

security of smart grid technologies -Renewable energy integration and

environmental issues related to it - Large scale EV grid requirements. According to SGCC, China’s smart grid plan can be divided into three stages [10]: (1) Planning and testing (2009–2010) Major tasks at this initial stage are establishing developmental plan, setting up technical and operational standards,


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developing technologies and equipment, performing trial tests. (2) Construction and development (2011–2015) This second stage focuses on accelerating UHV, urban and rural grids construction, establishing the basic framework for smart grid operation control and interaction, achieving the projected advancements in technology and equipment production, mass deployment. (3) Upgrading (2016–2020) This would be the final period of the completion of the whole Strengthened Smart Grid with most advanced technology and equipment. As further details are yet to be announced, however, it is interesting to note that the Chinese smart grid framework could be different from the rest of the world. This is because of the relatively primitive structure at the distribution ends, the extensive development of UHV transmission in recent years and also the unique asset ownership and management structure in China. III. COMPARISON BASED ON TECHNOLOGICAL DEVELOPMENTS The definition of smart grid is global; however, from the operation and control perspective,smart grid technologies are varying from country to country. The actual smart grid deployment plan, however, would likely vary significantly based on the country or the region’s own particular circumstances. It can be explained on the basis thatUS system is more mature and the design orientation focuses more heavily on users andservices integration (metering, renewable, electric transportation, etc.). It could also beaffected by the fact that the US grids are operated by many individual players so it is difficult to enforce unified changes throughout.

In China, both the focal problems andthe asset structure and management are different from US. The smart grid plan design could be different from several perspectives as discussed earlier. The huge geographical mismatch between energy supplies and load centers inChina has led to the decision to deploy a reliable interconnected UHV grid system.While interaction and services integration at user level are desirable, it is at least equallyimportant to have a smart grid plan that can fully realize the potential of UHV transmission.Furthermore, the end-users and distribution networks in China are not as mature asmost developed countries, and the penetration rate of small-scale renewable are relativelylow at the moment. In fact, growth of renewable energy in the country is primarilydriven by large-scale projects that do not directly connected to end-users. Given theseconditions, it is expected that initial stages of the Chinese smart grid plan will focus onthe ability of controlling bulk electricity transfer efficiently, and then moves towardsend-users and services integration in the next stages when the users are becoming more ready. In other words, it will likely start with transmission-centric control that effectivelymanage connectivity and gradually enhance itself by adding discrete control and servicescapabilities at distribution and end-user levels. Hence, the deployment plan andtechnology roadmap for the Chinese Strengthened Smart Grid will likely show considerabledissimilarities in relation to the US Unified Smart Grid. Let us compare Indian grid with one’s in US. The Indian national grid was not designedfor high capacity, long-distance power transfer as is the case in the rest of the world. India needs to interconnect regional grids as has already been practiced in US.Although coal and hydro-electric potential has peaked in many parts of India, there arestill several regions with excess


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capacity. Having large wind potential and increasingwind power capacity in the southern and western parts, the need to improve transmissioninfrastructure has been realized. Unfortunately, the regions are generally sectionalizedwith some asynchronous or high voltage direct current (HVDC) links allowing forminimal power transfer as is the case in US The major difference is that India’s transmissiongrid only reaches 80% of its population, while the transmission grid in the USreaches over 99% of its population.

CONCLUSION

The report presented the vision to develop smart grids in India, US and China. The comparison was carried out on the technological aspects which also include energy and economical aspects. The key points areto reduceenergy deficiency and global warming, to save energy more effectively and economically ,reducing transmission losses, updating ageing grid infrastructures and improving power quality.

REFERENCES [1]Feisst, C., Schlesinger, D. & Frye, W. ”

Smart Grid, The Role of Electricity Infrastructure inReducing Greenhouse Gas Emissions”. Cisco internet business solution group, whitepaper, October 2008.

[2] A Transition from Traditional to Smart Grid. ABB report DEABB 1465 09 E, Germany 2009

[3] Zheng, A. “A Smarter Grid for India”, October 2007 [www.SmartGridNews.com].

[4] ABB Review 1/10, Smart Grids. ISSN: 1013-3119, 2010

[5] Zhang, Y. & Liu, D. "Study on city

heavy modality problems caused by heavy industry”. Journal of Qingdao Technological University, Vol. 28, No. 3, P.118–121, 2007 (In Chinese).

[6] Du, Z. “Study on Strategic Planning of Ultra High Voltage Grid Development in China”, Ph.D Thesis, Shangdong University, 2008 (In Chinese).

[7] The Necessity and Feasibility of Developing UVH Technologies in China. SGCC Journal, Issue 2009-3, P.32–34, 2009.

[8]Shu, Y. “Development and execution of UHV power transmission in China”. China Power,Vol. 38, No. 3, P.12–16, 2005 (In Chinese).

[9] Li, J. “From Strong to Smart: The Chinese Smart Grid and its relation with the Globe”. AsiaEnergy Platform Article 00018602, September 2009.

[10] Completing Strengthened Smart Grid

by 2020. China Business News – June 13, 2009 (InChinese).


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Cost-effective Smart Metering for Home/Building using LDR Single-Channel Narrow-Band Power

Line Communication

Ayush Sagar1 Sumit Joshi2 B.Tech (EEE), NIEC, New Delhi B.Tech (EEE), NIEC, New Delhi

[email protected] [email protected] Abstract - Smart Metering in the distribution side of Smart Grid enables advanced management of energy flow for utility companies and consumers, and currently, various smart metering communication technologies are being considered for standardisation, most of which are not economically viable to the domestic consumers. This paper describes a qualitative model of smart metering approach for home/building using Power Line Communications (PLC). Among the various available PLC methods the proposed model uses Half-Duplex Low Data Rate (LDR) single-channel narrow-band (NB) PLC method which is expected to minimize financial burden on domestic consumers for meeting the new policies of utility companies for adoption of Smart Grid technology on distribution side without compromising on the core benefits of Smart Metering for both consumers and utility companies.

I. INTRODUCTION At present, the main requirement for adoption of

Smart Grid is the ability to monitor the flow of energy in real time. Smart metering uses Advanced Metering Infrastructure (AMI) for allowing the utility companies and the consumers to monitor and control the electrical energy flow. Apart from measuring consumption smart metering measures energy flow in both directions, thus allowing net-metering for distributed generation. The proposed model of smart metering has the following core benefits: (1) Real-time analysis of energy flow and supply quality within consumer premise, (2) Possibility of reading measurements both locally and remotely, (3) Allowing remote control of electrical appliances. In addition to this, the Smart Meters can also read water, gas and heat consumption (in cogeneration), allowing Automatic Meter Reading (AMR) by water supply and gas

supply companies. Also, the communication method is chosen such that the implementation cost for domestic consumers is minimized.

II. MOTIVATION Even though Smart Grid technology has benefits

for utility companies as well as energy consumers the cost of implementation is restrictive to the domestic consumers especially in developing countries. Unfortunately, the cost of modifications in the electrical system inside a home/building has to be beared by the consumer. So we propose a Smart Metering model to minimize the modifications required in the existing electrical system within the consumer premise to enable them to comply with the new requirements for Smart Grid adoption more comfortably.

III. PLCS IN SMART GRIDS PLCs work by adding a high frequency carrier

wave into the AC mains and uses digital modulation techniques to transmit data. Currently two types of PLCs are being considered for use in Smart Grid:

NARROW-BAND PLCS Narrow-band PLCs operate in 3 kHz to 500 kHz

region [6]. There are two types on the basis of data rate:

High Data Rate (HDR): This is a multi-carrier based technology with data rate ranging between tens of kbps and nearly 500kbps [6]. These can carry low latency control signals and are more suitable where response times are more critical, such as fault detection.

Low Data Rate (LDR): This is a single-carrier based technology capable of few kbps [6]. Even though the data rates are low, it can


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provide the core benefits of our proposed smart metering model. Since this is the slowest communication mode it uses lowest frequency.

BROAD-BAND (BB) PLCS BB PLC technology operates in 1.8-250 MHz

region having data rate ranging from few Mbps to few hundreds of Mbps [6]. This can also allow transmission of broadband internet at consumer premise without additional wiring. However, because of higher frequency BB PLC signals attenuate faster with cable distance hence special power cables have to be used. There is no such requirement in case of NB PLC.

It is possible for NB and BB PLCs to coexist on same power line as described in [3] and it will be possible for a domestic consumer to implement BB PLC for broadband internet at any later stage. However, NB PLC should be mandatory for the smart metering to work. A similar application is described in [4] which is a metering system where one master polls many slave units using half-duplex burst mode transmission and achieves a data rate of few hundred bits per second. Unlike wireless solutions like ZigBee and Wi-fi, PLCs have a proven track record of being able to avoid network congestion. Narrow band PLCs have been in use for home automation since 1970s using the popular X10 technology [5]. Each receiver in the system has an address and can be individually commanded by the signals transmitted over the household wiring and decoded at the receiver.

IV. PROPOSED MODEL

Different parts of the model are explained as follows:

SMART METER The Smart Meter has the following functions in our model: 1) It will establish bidirectional communication

between electricity provider through a distribution network and the home/building area network.

2) For PLC to work it will act as a master device and should provide all necessary timing and control signals to enable

bidirectional communication with other slave devices.

3) The Smart Meter should measure energy flow in both directions in real time to allow net-metering.

4) The Smart Meter should be able to allot a power quota for loads which do not communicate (reason explained later in the heading: Non-smart Appliances)

5) In case the smart meter is not able to communicate with the electricity provider for some time, it should have the ability to store measurements and event history.

6) For security purposes, the smart meter should incorporate a filter such that HAN PLC signals do not propagate towards the distribution side.

Figure 1: Proposed smart metering model

HOME/BUILDING AREA NETWORK (HAN) The HAN comprises of the smart meter, electrical

wiring inside the consumer premise and all the loads connected to it. All loads in a house/building can communicate to the Smart Meter using NB PLC on conventional copper wiring. However, some loads that are a potential source of harmonics will be required to conform to certain specifications so that they do not interfere with the PLC signals. All the loads connected in the home/building maybe broadly categorized into 4 categories:


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1) Smart Appliances: These are the appliances that will incorporate built-in PLC modem and logic circuits for communication with the Smart Meter. Heavy consumption appliances such as air conditioners, heaters, geysers and ovens will be required to come into this category. These appliances will be able to send power parameters and an appliance identification code and operation state to the smart meter, and should be able to respond to command signals sent by smart meter. The expected response to command signals may be sending out the power parameters, or changing the operating mode of the appliance. In event of power shortage, utility companies may choose to remotely shut down certain non-necessary appliances to avoid complete blackout. The command signals for smart appliances will be standardized.

2) Electric Vehicle Charging Station: Electric vehicles are going to increase in the future due to limited availability of fossil fuels and it is expected that their charging is going to contribute significantly to the peak demand. In this model, the charging station is simply a wall socket and the plugged in vehicle will communicate to the smart meter similarly to smart appliances using a built in PLC modem.

3) Power Generation Sources: Consumers may use solar panels and other alternative energy sources to supply energy to other home equipment or to the distribution grid. Such power generation sources will also incorporate battery to store energy for later use. The energy supplied to the grid will help the consumer to earn credits by the net-metering feature of the smart meter.

4) Non-smart Appliances: In certain low power loads such as fans and lights it may not be practical to incorporate a PLC modem into them and these may be classified as non-smart appliances. It is possible for certain people to tamper with smart appliances such as air conditioners so that they appear as non-smart appliance to the smart meter in order to restrict the utility companies from shutting it down. To avoid such a possibility the non-smart appliances

category should have a small and reasonable power quota set by the company since this category is intended for low power loads.

HOME/BUILDING ENERGY

MANAGEMENT & AUTOMATION MODULE

This is an optional indoor module that can enable the home/building owner to visualize the energy consumption (and generation) data, see the consumption history of each smart appliance, enforce restrictions on the ability of users to turn on certain smart appliances and to fix monthly target energy bill so that the module can automatically manage loads in a way that the monthly bill does not exceed the prescribed bill amount. Moreover, this module can also allow home automation using PLC signals to switch on or off various smart appliances by a wireless remote and GSM.

V.SECURITY CONCERNS The following are the foreseen security concerns in the given model:

A. Tampering of PLC signals: For the remote shut-off feature to work properly some encryption techniques will have to be used to avoid interception and modification of the signals.

B. Detection of any tampering of the smart metering system should call for heavy penalty, and/or legal action against the consumer.

C. Since PLC signals can propagate to nearby homes (or buildings) on same distribution system, it is desirable to isolate the PLC signals from outside. In traditional home automation system mentioned in [5] this is done by using an owner code for each device. In our model this isolation can be achieved by incorporating a filter inside the smart meter which is a simpler approach.

D. Since the Smart Meter can be monitored remotely by the utility companies, any suspicious tampering activity can be detected by automated algorithms and special staff should be employed by the utility companies to inspect the consumer premise in such case.

E. Privacy of the smart metering data should be ensured at the utility company’s end.


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CONCLUSION A model for cost-effective Smart Metering

model has been proposed to make the Smart Grid adoption attractive for the domestic consumers. The proposed model uses LDR NB PLCs which require little to no modification in existing wiring system. PLCs do not require external wiring or a wireless spectrum to operate thus they are the cheapest available mode of communication. Half-duplex LDR NB PLC modems tend to be cheaper and can be easily implemented into various appliances. Appliances can communicate to the Smart Meter just by plugging them into the wall socket. The Smart Meter will also establish bidirectional communication between the consumer appliances and the utility end. Moreover, an optional Home/Building Energy Management & Automation Module has been described which will help the consumer to maximize the benefits of smart metering.

REFERENCES

[1] R. van Gerwen, S. Jaarsma, and R. Wilhite, “Smart metering,” July 2006. [Online]. Available:http://www.leonardo-energy.org/webfm send/435

[2] Cooper, D.; , "Low-data-rate narrow-band power-line communications on the European Domestic Mains: symbol timing estimation," Power Delivery, IEEE Transactions on , vol.20, no.2, pp. 664- 667, April 2005

[3] Muller, C.; Lewandowski, C.; Wietfeld, C.; Kellerbauer, H.; Hirsch, H.; , "Coexistence analysis of access and indoor powerline communication systems for Smart Grid ICT networks," Power Line Communications and Its Applications (ISPLC), 2012 16th IEEE International Symposium on , vol., no., pp.77-82, 27-30 March 2012

[4] Sheppard, T.J.; , "Mains communication-a practical metering system," Metering Apparatus and Tariffs for Electricity Supply, 1992., Seventh International Conference on , vol., no., pp.223-227, 17-19 Nov 1992

[5] Edward B.Driscoll, Jr.. "The history of X10". [Online] Retrieved 22. July 2011 Available: http://home.planet.nl/~lhendrix/x10_history.htm

[6] Galli, S.; Scaglione, A.; Zhifang Wang; , "Power Line Communications and the Smart Grid," Smart Grid Communications (SmartGridComm), 2010 First IEEE International Conference on , vol., no., pp.303-308, 4-6 Oct. 2010


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Reactive Power Compensation Using Interline Power Flow Controller (IPFC) with 48 Voltage Source Converter

Neeru Devi1 Vinesh Agarwal2 Chandra Prakash Jain3 Vinodyadav4

1,2,3,4ITM, Bhilwara

Abstract—The paper describes the simulation of IPFC for two transmission lines is also done using MATLAB,Simulink where real power flow between the lines is equalized by transferring power demand from overloaded to under loaded line. It also compensate against resistive line voltage drops and the corresponding reactive power demand. In Interline power flow controller is VSC based FACTS controller for series compensation with unique capability of power flow management among multi lines .In this paper 48-Pulse GTO Based Voltage-Sourced Converter is used. The paper designs and models the complete IPFC is able to carry out an overall real and reactive power compensation of the total transmission system. This capability makes it possible to equalize both real and reactive power flow between the lines, transfer power from overloaded line to under-loaded line, compensate against reactive voltage drops and the corresponding reactive line power, and to increase the effectiveness of the compensating system against dynamic disturbances. Key words - flexible ac transmission, static synchronous series compensator Interline Power Flow Controller (IPFC), Power Flow Control,Voltage Source Converter (VSC). I. INTRODUCTION

The concept of Flexible AC Transmission Systems (FACTS) was first defined by N.G. Hingorani, in 1988 [2]. A Flexible Alternating Current Transmission System (FACTS) is a system comprised of static

equipment used for the AC transmission of the electrical energy. It is generally a power electronic-based device. FACTS are defined by the IEEE as “a power electronic based system and other static equipment that provide control of one or more AC transmission system parameters to enhance controllability and increase power transfer capability” [3]. The brief review on the placement ofFACTS devices is presented here. The concept of FACTS and FACTS controllers was first defined by Hingorani, 1988 in [2-3]. FACTS usually refer to the application of high-power semiconductor devices to control different parameters and electrical variables such as voltage, impedance, phase angles, currents, reactive and active power [11-12]. The power controllability of the network can be enhanced and the power transfer capability can be improved by systems used for AC transmission of electrical energy composed of static equipments called Flexible Alternating Current Transmission System (FACTS) [4]. FACTS is described as a power electronic based system and other static equipment that enhances the controllability and increases the power transfer capability by providing control of one or more AC transmission system parameters [2].Some of the several kinds of FACTS devices existing for this use are Static Var Compensator (SVC),Thyristor controlled series Capacitor (TCSC), Static Synchronous series compensator (SSSC), StaticSynchronous Compensator (STATCOM), Unified Power Flow


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Controller (UPFC) and Interline Power Flow Controller (IPFC). Gyugyietal have firstly proposed and discussed The Interline Power Flow Controller, in 1998, targets the problem of compensating a number of transmission lines at a given substation The transmission line parameter of the interconnected systems can be efficiently controlled by the IPFC which is an extension of the UPFC . IPFC employs a number of VSCs linked at the same DC terminal, each of which can provide series compensation for its own line. It can also be regarded as several SSSCs sharing a common DC link. In this way, the power optimization of the overall system can be realized in the form of appropriate power transfer through the common DC link from over-loaded lines to under-loaded lines. In [1,11], the basic principles of the Interline Power Flow Controller were discussed in detail and simulation results were shown to demonstrate the capability of the IPFC to realize power balance between a transmission system with two identical parallel lines..According to analysis, a basic control system for the two-identical-line transmission system with IPFC controller to realize power flow control of real and reactive as reference inputs is presented ..in practice, it is very difficult to find angle, if not impossible. Moreover, different lines with different transmission voltages, impedances and power angles are in operation in practical power system. Thus it is desirable to design a more applicable control system for the IPFC. Xuan Wei et al. have proposed a system with a UPFC, maximum power transfer capability is often achieved when the UPFC is operated at its rated capacity and conventional voltage and line-flow set point regulation is no longer possible. In this injected voltage sources to directly model a UPFC and imposethe rating limits in a NRFL algorithm. A dispatch strategy is proposed for a UPFC operating at rated capacity in which the power circulation

between the shunt and series converters is used as the parameter to optimize the power transfer[5] S.Sankar et al.have proposed an approach,. By injecting active and reactive voltage component series with the transmission line, IPFC a type of FACTS device controls the power flow in transmission line It is proposed to use IPFC for regulation of the receiving end voltage in series compensation and shunt compensation modes. IPFC to perform the voltage regulation at the receiving end of the line which is terminated at a sub-station to feed a distribution network simulated. Simulation results for both types of compensators series and shunt obtained. The author has proposed that IPFC is modeled and simulated to perform the receiving end voltage regulation for lines which terminate at the given sub-station to feed the distribution network. Two options considered are series compensation and shunt compensation modes. [6]. B. Karthik et al.have proposed an idea of identification of a proper place for fixing the IPFC in the transmission system.hybrid technique for identifying the proper place for fixing the IPFC. The proposed hybrid technique utilizes genetic algorithm and neural network to identify the proper place for fixing the IPFC.[9] Two or more SSSC with a common dc-link are present in the IPFC, and a voltage - with controllable magnitude and phase angle - is injected into the line .Juan Dixon, et al. has discussed about Reactive Power Compensation Technologies. The author dicudded an overview of the state of the art in reactive power compensation technologies. The principlesof operation, design characteristics and application examples of VAR compensators implemented with thyristors and selfcommutated converters are presented. Examples obtained from relevant applications describing the use of reactive power compensators implemented with new static VAR technologies are also


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described.[3] Soubhik et al. has discussed the versatile benefits of FACTS in to transmission utilities such as control of power flow, increasing capabilities of lines to their thermal limits ,steady state reducing loopflows, providing greater flexibility [9-10]. D. Gotham et al discussed how to control power flow and minimize power loss with FACTS devices. The reactive power compensation of AC system can be done using fixed series or shunt capacitor however the slow nature of control and limits on frequency are the drawback and can be overcome byusing FACTS controllers [6-8] L. Gyugyi, et al gave a new New Approach to Power Flow Management in Transmission Systems using IPFC. The main objective of this paper is To optimize the utilization of the overall transmission system. The increasing Industrialization, urbanization of life style has lead to increasing dependency on the electrical energy. This has resulted into rapid growth of power systems. This rapid growth has resulted into few uncertainties. Power disruptions and individual power outages are one of the major problems and affect the economy of any country. In contrast to the rapid changes in technologies and the power required by these technologies, transmission systems are being pushed to operate closer to their stability limits and at the same time reaching their thermal limits due to the fact that the delivery of power have been increasing. The major problems faced by power industries in establishing the match between supply and demand are: Transmission & Distribution supply theelectric demand without exceeding the thermal limit. In large power system, stability problems causing power disruptions and blackouts leading to huge losses. FACTS devices can be utilized to control power flow and enhance system stability. Reactive power compensation is provided to

minimize power transmission losses, to maintain power transmission capability and to maintain the supply voltage.

II. CONCEPT OF INTERLINE POWER FLOW CONTROLLER The interline power flow controller

(IPFC) Concept compensates the problem of compensating a number of transmission lines at sub station .the IPFC consists of two or more SSSC with a common dc link ,so,each SSSC contains a VSC that is in series with the transmission line through a coupling transformer and injects a voltage with controllable magnitude and phase angle. IPFC provide independent control of reactive power of each individual line , while active power could be transferred via dc link between compensated lines. An IPFC used to equalize active/reactive power between transmission lines and transfer power from overloaded lines to under loaded lines.[10]

BASIC CHARACTERISTICS OF IPFC The interline power flow controller employs a number of dc to ac inverters each providing series compensation for a different line. and the compensating inverters is shown infig 1.

Fig2.1 .interline power flow controller (ipfc) comprising n converters


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Fig.2.Schematic diagram of two-converter IPFC.

Consider an IPFC scheme consisting of two back to back dc to ac inverters, each compensating a transmission line transmission systems employ self commutated inverters as synchronous voltage sources .the power electronic based voltage sources can internally generate and absorb reactive power without the use of capacitors and inductors .they can facilitate both real and reactive power compensation and can independently control real and reactive power flow.

Fig.2.2 Fig 3.basic two inverter interline power flow controller

Consider an IPFC scheme consisting of two back to back inverters each compensating a transmission line by series voltage injection. The arrangement is shown in Fig 2.2.where two synchronous voltage sources V1pq &V2pq,in series with transmission lines 1 and 2represent to back to back inverters. The common dc link is represented by directional link for real power exchange

between voltage sources. The sending and receiving voltages are assumed to be equal.V1s=V2s=V1r=V2r=1.0p.u. withfixed angles resulting in identical transmission lines with fixed angles δ1= δ2=30.for two systems.[2]

OPERATION OF INTERLINE POWER FLOW CONTROLLER [14] [15] [17] [18]

An Interline Power Flow Controller (IPFC), shown in figure 2.2.1, consists of two series VSCs, whose DC capacitors are coupled, allowing active power to circulate between different power lines. When operating below its rated capacity, the IPFC is in regulation mode, allowing the regulation of the P and Q flows on one line, and the P flow on the other line. In addition, the net active power generation by the two coupled VSCs is zero, neglecting power losses.

Fig. 2.2.1 IPFC Power Circuit Topology

Consider an elementary IPFC scheme consisting of two back to back dc to ac inverters, each compensating a transmission line by series voltage injection. This arrangement is shown functionally in figure 2.2.1, where two synchronous voltage sources, with phasorsV1pqand V2pq in series with transmission Lines 1 and 2, represent the two back-to-back dc to ac inverters. (The common dc link is represented by a bidirectional link (P12 = P1pq = -P2pq) for real power exchange between the two


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voltage sources.) Transmission Line 1, represented by reactance X1, has a sending-end bus with voltage phasor V1S and a receiving-end bus with voltage phasor V1r. The sending-end voltage phasor of Line 2, represented by reactance X2, is V2S and the receiving-end voltage phasor is V2R. For clarity, all the sending-end and receiving-end voltages are assumed to be constant with fixed amplitudes, V1S = V1R = V2S = V2R, and with fixed angles resulting in identical transmission angles, ρ1 = ρ2, for the two systems. The two line impedances, and the rating of the two compensating voltage sources, are also assumed to be identical, i.e., V1pqmax = V2pqmax and X1 = X2, respectively. Although Systems 1 and 2 could be different (i.e., different transmission line voltage, impedance and angle), to make the relationships governing IPFC perspicuous, the above stipulated identity of the two systems is maintained throughout this section. In order to establish the transmission relationships between the two systems, System 1 is arbitrarily selected to be the prime system for which free controllability of both real and reactive line power flow is stipulated. The reason for this stipulation is to derive the constraints the free controllability of System 1 imposes upon the power flow control of System 2.

Fig. 2.2.2 Variation of P & Q with Phase Angle The rotation of phasor V1pq with angle ρ1 modulates both the magnitude and the angle

of phasor VX1 and, therefore, both the transmitted real power, P1R, and the reactive power, Q1R vary with ρ1 in a sinusoidal manner, as illustrated at right in figure 2.5. This process, of course, requires the voltage source representing Inverter 1 (V1pq) to supply and absorb both reactive and real power, Q1pq, and P1pq, which are also sinusoidal functions of angle ρ1.

III. SIMULATION USING SIMULINK

SIMULATION OF INTERLINE POWER FLOW CONTROLLER USING MATLAB

7.5.0 (R2007B) IPFC is a combination of two SSSCs. Coupled with common DC link for two identical transmission lines. So here a VSC based FACTS controller SSSC which is apart of IPFC with a transmission line is modeled. The power control and Receiving end voltage varies with the variation of firing angle is analyzed. A transmission line is modeled as series R,L and it is terminated with a load .the VSC based FACTS controller is modeled and connected to transmission line. the voltage variations are clearly analyzed.

Fig 3.1Model of IPFC in Simulink

Interline Power Flow Controller (IPFC) is used to control the power flow between two transmission systems of voltage rating 500 kV and 230 kV. The IPFC consist of two SSSC one is located at the right end of the


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500 kV, 75-km transmission line 1 between bus B_S_1 and B12, other is located at the right end of the 230 kV, 50-km transmission line 2 between B_S_2 and B22. It is used to control the active and reactive powers flowing through bus B12 and B22. It consists of two 50-MVA, three-level, 48-pulse GTO-based converters, one connected in series between buses B_S_1 and B12 and other connected in series between buses B_S_2 and B22. Both series converters can exchange power through a DC bus. The series converter can inject a maximum of 10% of nominal line-to-ground voltage (i.e. 28.87 kV) in series with transmission line 1 and (13.27 kV) in series with transmission line 2. OPERATION OF SIMULATION MODEL

[20] [21] 3.2 Modes of Operation of IPFC Model

IPFC model is operating in two different modes (when the disconnect switches between the DC buses of the series converters are opened or closed respectively the pair of converters is operating in two different modes) which are:

1. Series converter operating as a Static Synchronous Series Capacitor (SSSC) controlling injected voltage, while keeping injected voltage in quadrature with current of respective transmission line.

2. Interline Power Flow Controller (IPFC) mode, where series converters are interconnected through the DC bus. Real power can be transferred from transmission line one to transmission line two.

The natural power flow for mode IPFC_SE through bus B12, when zero voltage is injected by the series converter (zero voltage on converter side of the four converter transformers) is P1 = +200 MW and Q1 = -

200 MVAR and through bus B22 is P2 = +550 MW and Q2= -100 MVAR. In IPFC_SE mode, both the magnitude and phase angle and the series injected voltage can be varied, thus allowing control of P and Q. The IPFC controllable region is obtained by keeping the injected voltage to its maximum value (0.1 pu.) and varying its phase angle from 0 to 360°. The mode of operation as well as the reference voltage and reference power values can be changed by means of the “IPFC GUI” block IV. RESULTS OF SIMULATION

1. Series voltage injection in SSSC mode

SSSC 1

Fig 4.1 Waveform for Series voltageinjection in SSSC modeSSSC


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Fig 4.2 Waveform for Series voltage injection in SSSC mode SSSC 2

I. Power control in IPFC mode (i.e. IPFC_SE)SSSC 1

Fig 4.3 Waveform for Power control in IPFC

mode (i.e. IPFC_SE)SSSC 1

Fig 4.4 Waveform for Power control in IPFC mode (i.e. IPFC_SE)SSSC 2

CONCLUSION

As the consequence of fast growing

demands on active and reactive power control and the rapid development of power electronic technology FACTS devices are being developed in the field of modern power systems. Of all the FACTS devices, the combined compensators such as the unified power flow controller (UPFC) and the interline power flow controller (IPFC) are regarded as the most powerful and versatile ones. Both the UPFC and IPFC are based on the self-commutated, voltage-sourced switching converters (VSCs) coupled via a common DC voltage link. Unlike the UPFC, the IPFC employs at least two VSCs respectively connected in series with different lines, which can address the problem of compensating multiple transmission lines at a given substation. In the IPFC structure a number of inverters are linked together at their dc terminals. Each inverter can provide series reactive compensation, as an SSSC, for its own line.


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However, the inverters can transfer real power between them via their common dc terminal. This capability allows the IPFC to provide both reactive and real compensation for some of the line and thereby optimize the utilization of the overall transmission system. In particular, the IPFC can equalize both real and reactive power flow in the lines, relieve the overloaded lines from the burden of reactive power flow, compensate against resistive as well as reactive voltage drops, and provide a concerted multi-line counter measure during dynamic disturbances. The IPFC has all the advantages established for the inverter based FACTS controllers: Modular construction from similar building blocks which can be fully decoupled (i.e., operated as independent series compensators) or reconfigured into shunt compensators or UPFC. Also, by the combination of the individual building blocks, the rating of selected individual compensators can be increased. The fact that the IPFC configuration provides an extremely flexible utilization of needed compensation assets, without any significant cost addition, is hoped to make this approach an attractive for utilities (or other transmission system operators) to solve some of difficult transmission problems they face today.

V. FUTURE WORK

There can be compensation requirements for particular multi-line transmission systems which would not be compatible with the basic constraint of the IPFC, because active power transfer function requires the difference of voltage magnitude between both terminal voltages of IPFC but the maximum difference of voltage magnitude in a transmission line seems to be under 10 - 15 % of rated voltage under a normal operation. Hence maximum active power possibly transferred by the IPFC seems to be less than 10 -15 % of power transmission

capacity of the transmission line. This constraint can be circumvented in future work with the maximum power transfer capacity can be increased to any value.

REFERENCES

1. L. Gyugyi, K. K. Sen, C. D. Schauder, “The Interline Power Flow Controller Concept: A New Approach to Power Flow Management in Transmission Systems”, IEEE Transactions on Power Delivery, Vol. 14, No. 3, pp.1115~1123, July 1999.

2. N.G. Hingorani and L.Gyugi , “Understanding FACTS –Concepts and Technology ofFlexible Ac Transmission Systems”, Standard Publishers Distributors, IEEE Press, New York, 2001.

3. Juan Dixon, Luis Morán, José Rodríguez, Ricardo Domke “Reactive Power Compensation Technologies, State-of-the-Art Review”.

4. John J. Paserba, “How FACTS Controllers Benefit AC Transmission Systems”, Mitsubishi Electric Power Products, Inc., Warrendale, Pennsylvania, USA.

5. Xuan Wei, Joe H. Chow, B. Fardanesh, and Abdel-AtyEdris, “A dispatch strategy for ainterline power flow controller operating at rated capacity”, the Electrical, Computer, and Systems Engineering Department, Rensselaer Polytechnic Institute, Troy, NY 12180-3590.

6. S. Sankar, Dr. S. Ramareddy “Simulation of Closed Loop Controller IPFC System”, IJCSNS International journal of computer science and networking security, Vol. 7, No. 6, June 2007.

7. V. Diez-Valencia, U.D. Annakkage, D. Jacobson “Interline power flow controller(IPFC) steady state operation”, Proceedings of the 2002 IEEE Canadian


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Conference on Electrical & Computer Engineering, 0-7803-7514-9/02.

8. Gyugyi L., “A Unified Power Flow Control Concept for Flexible AC Transmission Systems”, IEE Proceedings-C, Vol. 139, No. 4, July 1992

9. B. Karthik, S. Chandrasekar “A Hybrid Technique for Controlling Multi Line Transmission System Using Interline Power Flow Controller” European Journal of Scientific Research ISSN 1450-216X Vol.58 No.1 (2011), pp.59-76

10. M. Noorzian and G. Anderson, “Power flow control by use of controllable series components”, IEEE Transactions on Power Systems, vol. 8, no. 3, pp. 1420-1429, 1993.

11. L.Gyugyi, K.K.Sen, C.D.Schauder, “The Interline Power Flow Controller Concept: A New Approach to Power Flow Management in Transmission Systems”, IEEE/PES Summer Meeting, Paper No. PE- 316-PWRD-0-07-1998, San Diego, July 1998

12. Y. Xia, Y. H. Song, C. C. Lier and Y. X. Sun, “Available Transfer Capability Enhancement using FACTS Devices”, IEEE Transactions on Power Systems, vol. 18, no. 4,pp.305-312, 2003.

13. Gyugyi L., “A Unified Power Flow Control Concept for Flexible AC Transmission Systems”, IEE Proceedings-C, Vol. 139, No. 4, July 1992

14. Juan Dixon, Luis Morán, José Rodríguez, Ricardo Domke “Reactive Power Compensation Technologies, State-of-the-Art Review”.

15. L. Gyugyi, K. K. Sen, C. D. Schauder, “The Interline Power Flow Controller Concept: A New Approach to Power Flow Management in Transmission Systems”, IEEE Transactions on Power Delivery, Vol. 14, No. 3, pp.1115~1123, July 1999.

16. Xuan Wei, Joe H. Chow, B. Fardanesh, and Abdel-AtyEdris, “A dispatch strategy

for an interline power flow controller operating at rated capacity”, the Electrical, Computer, and Systems Engineering Department, Rensselaer Polytechnic Institute, Troy, NY 12180-3590.

17. S. Sankar, Dr. S. Ramareddy “Simulation of Closed Loop Controller IPFC System”, IJCSNS International journal of computer science and networking security, Vol. 7, No. 6, June 2007.

18. V. Diez-Valencia, U.D. Annakkage, D. Jacobson “Interline power flow controller (IPFC) steady state operation”, Proceedings of the 2002 IEEE Canadian Conference on Electrical & Computer Engineering, 0-7803-7514-9/02.

19. MATLAB 7.5.0 (R2007b) help.


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Review Paper on Smart Grid: Introduction, Technology used, Merits and Demerits

ChandanJayaswal1 Rajat Gupta2 NIEC, New Delhi NIEC, New Delhi

Abstract - Smart grid is an approach towards smarter and intelligent power grids. Proper and optimum application of smart grid technology is projected to throw great opportunities and significant financial applications. It has the potential to revolutionize the way we see the energy sector today be its generation or distribution or its end cost. This paper is an attempt to introduce smart grid, its requirement/need, merits and demerits and various smart grid initiatives and implications.

I. INTRODUCTION The power grid of India is considered one of the

weakest in the world as its transmission and distribution losses are highest, averaging around 24% and in some states this figure shoots up to 62% of total electricity production, for improvement from present scenario and also to make its pace with economic growth India needs a modern, intelligent grid. The smart grid ensures uninterrupted power supply to consumers; it also eliminates various losses at plants. This technology is quickly evolving and is becoming nerve centre across globe. Three main factors are driving utility deployments of the smart grid: Unrelenting increases in electricity demand Global warming An upturn trend in unit costs of electricity And the six factors will drive the adoption of the smart grid in India: Supply shortfalls Reduction in energy generation and

transmissionloss Managing the “human element” in system

operations to lower the errors

Peak load management by demand response system

Desire to use renewable energy efficiently[7] Technological leapfrogging[2] The smart grid in itself is an collection of visions. Due to its vast nature, complex technology involved a number of definitions and explanations have been given to explain it.Here is one example: “A smart grid is a modern electricity system .It uses sensors, monitoring, communications,automation and computers to improve the "flexibility, security, reliability, efficiency, and safety of the electricity system.”[3-5] By understanding the above definitions the key themes like communication, integration, economic, security and adaptable, suitable automations are identified. Combining these themes; a shorter definition of smart grid is: A smart grid is a group of information based application electric grid, it uses information and communication technology to gather and act on information in an automated fashion, this technology integration improve the efficiency, reliability, economics, and sustainability of the production and distribution of electricity.

(Reference http://thewmeacblog.org/2012/01/31/a-watershed-moment-living-with-a-smart-grid/ )


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Smart grid workincreases transparency in electricity prices. Transparency will help customers to understand the cost of electricity according to time of day. It also helps in reduction of emissions by 31-114 million metric tons of CO

2equivalent in

2030 as the usage is adjusted by consumers in response of pricing. [6]

II. TECHNOLOGY USED Hard infrastructure Smart net meters Storage devices Distributed generation system Renewable energy Energy efficiency equipments Home area networks configuration Demand response systems Superconductive transmission lines

Soft infrastructure IT and back office computing Security Integrated communications systems

protocols Communication spectrum

HARD INFRASTRUCTURE Advanced Metering Infrastructure (AMI) It is architecture for automated, two-way

communication between a utility’s smart meter with a special address and a utility’s head end systems. The goal of an AMI is to provide utility companies with real-time data about power consumption and allow customers to make informed choices about energy usage based on the price at the time of use.

(Reference-http://southriversource.com/wp-content/uploads/2012/04/smart_meter.jpg) Phasor Measurement Units Popularly referred to as the power system’s “health meter,” Phasor Measurement Units (PMU) sample voltage and current many times a second at a given location, providing just like a MRI scan of power system rather than X-Ray scan which is available from earlier Supervisory Control and Data Acquisition (SCADA) technology. The measurements of SCADA are taken once every 2-4 seconds giving a view toward power system behaviour. With the smart grid technology measurements are time synchronized and taken many times a second (i.e.30 samples/second). This information helps out in wide area situation awareness, work needed to ease out congestions and bottlenecks or even prevent blackouts. Adoption of the Smart Grid will enhance every facet of the electric delivery system, including generation, transmission, distribution and consumption. It will possibly bring the generation closer to its servers which will empower consumers to become active participants in their energy choice to a degree never possible before.

ISLANDING

At the transmission level, large sections of a utility, state, or region may be cut off from other sections in order to preserve the electrical system during major system disturbances and block cascading outages. Such systems have been used for many decades, having been perfected and extensively implemented in Russia before 1990. These protection systems operate veryfast, and keep generation and load in balance; when a generating unit trips, a corresponding block of load is immediately tripped. Within minutes other generators increase their output and when spinning reserve and frequency are strong, the load that was shed is reconnected, usually within minutes. The philosophy behind this is to keep most of the electric system operating so that power can be restored quickly and efficiently. The smart grid can do the same thing at the distribution level, rapidly isolating failed portions


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of the network and restoring service automatically and rapidly.

ADVANCED CAPACITOR CONTROL Capacitor control in the distribution network has a direct and significant effect on customer satisfaction. It also improves utilities’ financial performance by reducing a component of technical losses. If capacitor control is implemented poorly, there will be insufficient capacitor support during periods of high demand and low voltage (peak times), and over-compensation during periods of light load and high voltage (midnight to dawn, and weekends). When integrated into a smart grid, advanced capacitor control by the utility (not the customer) allows the utility to provide the right amount of capacitor injection at the right time. This approach also removes a requirement on customers to install, operate, control, and maintain their own capacitors.

DISTRIBUTED ENERGY STORAGE Optimizing the power supply to reduce losses, power outrage and improved power quality can be done through distributed energy storage system.Local storage will also allow the increased usage of renewable sources and at the same time will increase the stability and reliably of energy supply. The main obstacle for employing additional "exile storage solutions such as batteries, or pumped storage, is their relatively high cost. Electric vehicles provide a fractional solution to this distribution storage problem, but significant result is still many years from now as yet no option for clean storage from ‘plug in’ vehicles have been proved.

HIGH-TEMPERATURE SUPERCONDUCTIVITY

Ithas the potential for achieving a more fundamental change to electric power technologies than has occurred since the use of electricity became widespread nearly a century ago. Just as fibre optics enabled the “information superhighway” by supplanting lower-capacity copper, superconductivity is enabling an “energy

superhighway” by supplanting copper electrical conductors with a ceramic superconducting alternative that has higher capacity while eliminating resistive losses. It will increase grid reliability and security by providing efficient power interconnections with high capacity. Minimal environmental impact also occurs as HTS cables can be readily permitted and installed in dense urban areas and low-impedance design enables dynamic control of alternating current power flow, alleviating grid congestion. This can be used for developing HTS-based electric power equipment such as transmission and distribution cables and fault current limiters and also to develop high-performance, low-cost, second-generation HTS wire at long lengths [8]

(Reference Supercon_Overview_Fact_Sheet_7_14_09)

RENEWABLE ENERGY A very important element of smart grid initiatives is to integrate as much renewable and greener sources of power generation into the grid as possible, these measures leads to less carbon footprint per unit power generation and thus has both societal and environmental benefits. it also helps in bringing the per unit cost of production down, over a longer period of time due to some intrinsic difficulties and discontinuities of power generation from such resources it’s not an easy task to integrate these generation units with the


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conventional grid system but the smart grid system is better equipped for the purpose as it is extensively automated and monitored.Thus to realize the projected benefits of a smart grid project it becomes important to generate and integrate as much green power as possible. Two important and high on potential, sources in India are wind power and solar power. Wind power- The wind power potential on a national level, base data collected from 10 states considering only 1% of land availability, is around 46,092 MW. Solar power- If tropical India were to convert just 1% of the 5,000 trillion kilowatt-hour of solar radiation (or, simply, sunlight) it receives a year into energy, the country will have enough to meet its energy needs. In most parts of India, clear sunny weather is experienced 250 to 300 days a year. The annual global radiation varies from 1600 to 2200 kWh/sq. m. The equivalent energy potential is about 6,000 million GW of energy per year.The highest annual global radiation is received in Rajasthan and northern Gujarat.[9][10].

SOFT INFRASTRUCTURE: Interoperable Communication Standards and protocols One of the lessons of the USA, 2003 blackout, according to ArshadMansoor, a smart grid expert at the Electric Power Research Institute in California, is that “you can’t just look at your system. You have got to look at how your system affects your neighbors and vice versa.”[11]. The risks associated with it are: First, without standards, there is a risk that “the various smart grid technologies that are the objects of these growing investments will become too early outdated; Second, and worse, they could be implemented without adequate security measures. To elaborate on the security point, if the technology is proprietary and only well understood by its proponents, it could contain vulnerabilities to hackers or even terrorists.

Third, a lack of standards may also hamper future innovation and the realization of promising applications Fourth, on a related note, standards enable economies of scale and scope that help tocreate competitive markets. A lack of standards may encourage monopolistic and rent-seeking behavior. There is also a fifth argument: protection of customer privacy.

CYBER SECURITY STANDARDS With the addition of communication capabilities to the grid network various problems regarding its security is also rising. Due to communication grid there are now million of new hack-able points which might be used to sabotage the data or for personal unethical use. Many important services like banking, wireless communications, government networks, etc could be severely affected by these attacks. Therefore a new cyber security standards need to be developed to counter these problems to ensure that hacking attempts can be isolated and dealt with. Even with this realistic approach, utilities will have to determine what actions are appropriate for customers who have attempted to breach security protocols.

GHZ SPECTRUM The critical infrastructure of industry need to be protected and enhance the spectrum resources to ensure that the bandwidth needed in smart grid does not affect any non commercial or commercial services and that too at a reasonable price.

CUSTOMER ENGAGEMENT Lack of awareness of smart grid along with lot of confusion is there in public. A better understanding of the benefits of smart grid is important for customer to make smart grid effective and sustainable. Since the high cost of smart grid implementation will, directly or indirectly, be shared by customers, if they are not convinced by claims regarding current and future benefits, they are likely to resist and challenge those costs over time.Customs must be made aware that the present grid technology and infrastructure is aging, have


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great losses thus need to be replaced for a better upgraded technology for optimization. [12]

II. BENEFITS ANALYSIS OF SMART GRID The step towards a smarter grid will change the

entire business model in the energy sector and the way it’s related with all stakeholders, involving and affecting utilities, regulators, energy service providers, technology and automation vendors, and all consumers of electric power. The smart grid brings upon choice at the doorstep of customer and enables them to control the timing and amount of power they consume based upon the price of the power at a particular moment of time.

Some basic benefits of a smart grid are: Peak load reduction. Smart grids can use time-of-day price signals as communicated from consumer end to reduce peak load – this benefit has particular importance in Indian urban load management. Self-healing. A smart grid system is completely automatic in detection and response to routine problems and quickly recovers if they occur, minimizing downtime and financial loss. Consumer motivation. A smart grid gives all consumers – industrial, commercial, and residential – visibility into real-time pricing, and gives them the ability to choose their consumption and price that best suits their needs. Attack resistance. The Smart Grid will be more resistant to attack and natural disasters. it also brings in energy independence as the power sources outside our control are vulnerable to attacks. Improved power quality. A smart grid provides power free of sags, spikes, harmonics disturbances and interruptions. This makes the power suitable for all sort of industries, improves efficiency of production and thus power economy blooms. Accommodation of all generation and storage options. A smart grid enables integration of different kinds of distributed sources of power and storage (e.g., wind, solar, battery storage).

Enabled markets Greatly improved reliability and efficiency that encourage both investment and innovation. Optimized assets and operating efficiently. A smart grid needs less infrastructure construction per unit production and transmittal of power .Also existing systems are optimised, thereby requiring less cost of operation and maintenance of the grid.

These benefits can be combined under three broad categories: Economic benefits

Followingfive types of economic benefits can be derived from the smart grid.

Cost savings from peak load reduction. Reductions in capacity costs.

Deferred capital spending for generation, transmission, and distribution investments

Reduced operations and maintenance costs.

Reduced industrial consumer costs.

Service benefits Improved reliability Increased efficiency of power delivery Consumption management. Improved system security.

Enhanced business and residential

consumer service.

Environmental benefits According to recent studies, the smart grid can reduce emissions at a lower cost than many of the newest clean energy technologies. The smart grid will reduce emissions in four ways:

Enabling the integration of clean, renewable generation sources.

Reducing electrical losses. Increasing the penetration of distributed

energy resources.


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Increasing energy conservation through

feedback to consumers.

III.RISKS ASSOCIATED WITH SMART GRID Lack of experience in full scale deployment of AMI and dynamic pricing, uncertainties associated with smart grid and costs. Assessing the Impact of a Project’s Scale and Complexity, and the Impact of Resources Constraints Uncertainties brings in financial risks, that the projected benefits might not be achieved by a smart meter plan. A number of AMI projects were not approved in US and Europe as their projections were unclear and there was no suitable plan for the case, which the utility get cash strapped. A large part of the increased price tag is associated with the unanticipated difficulty of the scale and resources required in constructing the system’s fibre network. Hence, it is important to plan in advance for unanticipated resource constraints while budgeting for a smart grid project [1]. The Effect of “Fast Tracking” on Project Schedules and Cost The system planner has a tough job to do as they have to consider the rapid development of both technologies and rate designs and related AMI functionalities. When evaluating project costs, they must determine exactly what the information will do, and who needs it for what purpose, at what time. Systems Integration Effect The largest cost component in a smart grid project is the integration of information technology, and the software’s. The utility recovers this cost partly through smart pricing techniques, which help in peak load management, thus reducing the utility’s cost of generation and service. Accelerated depreciation of technology So far, a utility plant constructed or installed equipment, could be reliably expected to remain in service for its estimated useful life, which ranged from 10 to 40 years, Meters, for example, had useful lives of

10 to 15 years. However, advanced meters and metering systems employ computing technology. Equipments used in the electric utility industry may show different technological and cost curves than computers. If advanced metering systems exhibit technological and cost behaviours that are similar to those of computers, then their useful lives may turn out to be shorter than estimated. Risk of stranded assets It involves equipment that was at the time of installation was according to modern and best technology, but before it completes its life cycle becomes obsolete and outdated. A newer better technology that has lesser cost and losses overshadows it. Utility managers and regulators may have to deal with the unique challenge of cost recovery as some electric utilities take best of high tech industry’s technologies. Deployment of smart grid technology will be slowly and utilities that do not install smart meters will still need to install conventional meters. This clearly establishes the risk of creating stranded assets, as the smart roll-out could make them outmoded before the end of their asset life. Security Involvement of communications technologies also brings in concern of cyber crime. Concerns chiefly centre around the communications technology at the heart of the smart grid. Designed to allow real-time contact between utilities and meters in customers' homes and businesses, there is a very real risk that these capabilities could be exploited for criminal or even terrorist actions. Aside from computer infiltration, there are also concerns that computer malware like Stuxnet, which targeted SCADA systems which are widely used in industry, could be used to attack a smart grid network. [13]

IV.CHALLENGES FOR THE SMART GRID Several challenges present themselves for smart grid development, and may affect the results of a cost-benefit analysis. Financial resources. Government support. Compatible equipment. Speed of technology development.


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Lack of policy and regulation. Capacity to absorb advanced technology. Consumer education. Cost assessment. Rate design. Consumer protection. Cooperation. Lack of empirical evidence.

CONCLUSION

Since 2008 the power market in India has started their operation. Many utilities are coming with a proposed idea to build distribution and renewable energy sources according to Smart Grid. Power markets are generally characterized by the poor demand side response for the lack of proper infra structure. Smart Grid can gracefully address this issue. Few initiatives in India are reported briefly with some details of the future plans also. Proper communication protocols are needed for integration of retail market with consumers. Effective database management, data mining techniques and architecture which provide seamless flow of data from both ends is also required. Few quality aware customers may be able to specify their power quality requirement through Smart Grids. The smart grid model will open new potential towards cleaner, efficient, effective technology. [16]

REFERENCES [1] ‘The smart grid vision for India’s power

sector"- prepared by PA Government Services, Inc for USAID

[2] Y. Pradeep, S. A. Khaparde, R. Kumar, “Intelligent Grid Initiatives inIndia,” IEEE Intl. Conf. on Intelligent Systems Applications to PowerSystems, pp. 1-6, Nov. 2007.

[3]Paul Murphy et. al., Enabling tomorrow’s Electricity System: Report of the Ontario

Smart Grid Forum, http://www.ieso.ca/imoweb/pubs/smart_grid/Smart_Grid_Forum-Report.pdf (September, 2010)

[4]Miles Keogh, the Smart Grid: Frequently Asked Questions for State Commissions, The National Association of Regulatory Utility Commissioners,May 2009, p. 2, http://www.naruc.org/Publications/NARUC%20Smart%20Grid%20Factsheet%205_09.pdf, (June, 2010)

[5]The Smart Grid: An Introduction, U.S. Department of Energy, http://www.oe.energy.gov/DocumentsandMedia/DOE_SG_Book_Single_Pages (1).pdf (September, 2010)

[6][Online]. Available: The Climate Group, http://www.theclimategroup.org,Nov. 2009

[7]http://my.epri.com/portal/server.pt?space=CommunityPage&cached=true&parentname=ObjMgr&parentid=2&control=SetCommunity&CommunityID=405

[8]supercon_overview fact sheet 7-14-09 www.oe.energy.gov

[9][Online]. Available: Indian Energy Exchange Website,www.iexindia.com/, Nov. 2009.

[10][Online]. Available: Ministry of Power, Government of India Website,http://powermin.nic.in, Nov. 2009.

[11]NARUC Briefing on SGIG Consumer Behaviour Study Effort http://www.naruc.org/Policy/FERC/?c=3

[12]http://www.cea.nic.in/reports/regulation/grid_standards_reg.pdf

[13] http://en.wikipedia.org/wiki/Smart_grid [14]www.apdrp.gov.in/ [15][Online]. Available: Bangalore Electricity

Supply Company (BESCOM) Website. http://www.bescom.org/, Nov. 2009. [16] V. S. K. Murthy Balijepalli, R. P. Gupta,

and S. A. Khaparde, “Towards Indian Smart Grids,” in IEEE TENCON

Conference, Singapore, Nov.2009.


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Distributed Generation: Issue and Approaches Anuradha Tomar 1 Sunil Gupta2 NIEC, New Delhi NIEC, New Delhi [email protected] [email protected]

Abstract - Distributed generation (DG) is expected to become more important in the future generation system. The current literature, however, does not use a consistent definition of DG. This paper discusses the relevant issues and aims at providing a general definition for distributed power generation in competitive electricity markets. In general, DG can be defined as electric power generation within distribution networks or on the customer side of the network. In addition, the terms distributed resources; distributed capacity and distributed utility are discussed.

I. INTRODUCTION

Distributed generation (DG) refers to power generation at the point of consumption. Generating power on-site, rather than centrally, eliminates the cost, complexity, interdependencies, and inefficiencies associated with transmission and distribution. Like distributed computing (i.e. the PC) and distributed telephony (i.e. the mobile phone), distributed generation shifts control to the consumer [1].

For a large and dispersed rural country, decentralized power generation systems, where in electricity is generated at consumer end and thereby avoiding transmission and distribution costs, offers a better solution. Gokak Committee had gone into details about the concept of decentralized generation to meet the needs of rural masses. The main recommendations of the Committee are as under:-

1.The concept of Distributed Generation (D.G.) has been taken as decentralized generation and distribution of power especially in the rural areas. In India, the deregulation of the power sector has not made much headway but the problem of T&D losses, the unreliability of the grid and the problem of remote and inaccessible regions have provoked the debate on the subject.

2.The D.G. technologies in India relate to turbines, micro turbines, wind turbines, biomass, and gasification of biomass, solar photovoltaics and hybrid systems. However, most of the decentralized plants are based on wind power, hydel power and biomass and biomass gasification. The technology of solar photovoltaics is costly and fuel cells are yet to be commercialized.

3.In so far as the 18,000 villages in remote and inaccessible areas are concerned, the extension of grid power is not going to be economical. Decentralized plants based on biomass, gasification of biomass, hydel power and solar thermal power and solar photovoltaic’s are the appropriate solution for these areas. A decision with regard to the available options will have to be taken depending on the feature of each site/village.

4.As regards the remaining unelectrified villages, the responsibility should rest primarily with the State Governments. The Govt. of India would, however, act as the facilitator to them.

5.As people in many of the electrified villages are very much dissatisfied with the


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quality of grid power, such villages also encouraged to go ahead with the Distributed Generation Schemes. These should also be the responsibility of the State Governments.

6.Though India has made considerable progress in adopting technologies based on renewable sources of energy these are not yet capable of commercial application on a large scale.

7.Association of Village Panchayat with Village Level Committees is important for the success of the programme. The fact that the Rural Electric Cooperatives which were established in the 80.s for distribution of power supplied by the SEBs incurred losses need not deter us from trying them out again as these did have some positive features[2].

Distributed generation takes place on two-levels: the local level and the end-point level. Local level power generation plants often include renewable energy technologies that are site specific, such as wind turbines, geothermal energy production, solar systems (photovoltaic and combustion), and some hydro-thermal plants shown in fig 1 and fig

Fig 1: Distributed Generation

These plants tend to be smaller and less centralized than the traditional model plants [3]. They also are frequently more energy and cost efficient and more reliable. Since these local level DG producers often take into account the local context, the usually produce less environmentally damaging or disrupting energy than the larger central model plants.

Fig 2: Wind Turbines

II. APPLICATIONS OF DISTRIBUTED GENERATING SYSTEMS There are many reasons a customer may

choose to install a distributed generator. DG can be used to generate a customer’s entire electricity supply; for peak shaving (generating a portion of a customer’s electricity onsite to reduce the amount of electricity purchased during peak price periods); for standby or emergency generation (as a backup to Wires Owner's power supply); as a green power source (using renewable technology); or for increased reliability. In some remote locations, DG can be less costly as it eliminates the need for expensive construction of distribution and/or transmission lines [4].


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III. BENEFITS OF DISTRIBUTED

GENERATING SYSTEMS Distributed Generation:

1. Has a lower capital cost because of the small size of the DG (although the investment cost per kVA of a DG can be much higher than that of a large power plant). 2. May reduce the need for large infrastructure construction or upgrades because the DG can be constructed at the load location. 3. If the DG provides power for local use, it may reduce pressure on distribution and transmission lines. 4. With some technologies, produces zero or near-zero pollutant emissions over its useful life (not taking into consideration pollutant emissions over the entire product lifecycle ie. pollution produced during the manufacturing or after decommissioning of the DG system). 5.With some technologies such as solar or wind, it is a form of renewable energy. can increase power reliability as back-up or stand-by power to customers.Offers customers a choice in meeting their energy needs.

IV. CHALLENGES ASSOCIATED WITH DISTRIBUTED GENERATING SYSTEMS

1. There are no uniform national interconnection standards addressing safety, power quality and reliability for small distributed generation systems. 2. The current process for interconnection is not standardized among provinces. Interconnection may involve communication with several different organizations 3. The environmental regulations and permit process that have been developed for larger distributed generation projects make some DG projects uneconomical.

4. Contractual barriers exist such as liability insurance requirements, fees and charges, and extensive paperwork. V. CHARACTERISTICS OF THE

NEW GENERATION

This multiple, diverse and dispersed generation can provide a number of services to customers and utilities. From the utility side: grid support and avoidance of expensive upgrades. From the customer side: standby generation, peak shaving, stand-alone generation Prime movers for these generation systems include internal combustion engines, combustion or gas turbines, steam turbines, microturbines, wind turbines, solar (photovoltaic and thermal), fuel cells, hydro and ocean (tidal and marine current) [5]. The engine and turbine based prime movers (except wind) are capable of burning a variety of fuels, including natural gas, coal and oil, and alternative fuels such as wood, biomass, black liquor and process gas. All types of fuels (non-renewable and renewable) are used allowing for wind, hydro, ocean. The generation technologies can be classified into renewable and non-renewable. This classification means that DG is not a synonym for Renewable Energy Source. The DG technologies based on renewable are: wind, photovoltaic and solar thermal, ocean (tidal and marine current), hydro (small). The non-renewable DG technologies are: micro turbine, combustion turbine,

steam turbine, combined cycle, Internal combustion engine. Fuel cells can be classified as renewable (using hydrogen) or non-renewable (using natural gas or petrol). A consensus about large hydro should not be part of DG exists but this limit is not clear. When convenient, instead of DG, we must tell renewable (or not renewable) energy. The


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ranges of electrical rating of DG technologies are: Wind A few W to few MW Photovoltaic and solar thermal A few

W to few MW Fuel cell A few tens of kW to few tens

of MW Ocean A few hundred kW to few MW Micro turbine A few tens of kW to few

hundred of kW Combustion turbine A few MW to

hundreds of MW Gas turbine A few hundred kW to few

hundred of MW Steam turbine A few tens of kW to

several hundreds of MW Combined cycle A few tens of MW to

several hundreds of MW Internal combustion engine A few kW

to tens of MW

Electrical power rating is not used consistently to distinguish DG from central generation. If the power output is used only within the local distribution network, Ackermann suggested the term embedded (distributed) generation. For most of the analysed countries there is a wide range of connection voltage, from BT to 132kV. Therefore voltage range cannot be used to characterise a DG. Three types of interface arrangements are used to connect DG to the grid: dc/ac converter, synchronous and asynchronous generator. Transformers are used to connect DG to higher voltage grids.

VI. DISTRIBUTED-GRID(MINI-GRID) SYSTEMS

Distributed-grid or mini-grid systems are decentralized power plants, effectively larger standalone systems, which supply power to isolated groups of householders, communities or even larger groupings. They involve a local grid-network for the supply of power. Connecting the utility grid to remote regions usually requires electricity transportation over long

distances to a dispersed population. For this reason mini-grid systems can provide more cost-effective electrification than grid-extension for such areas. Mini-grid systems can not only provide access to household electric-ity in rural areas, but also contribute to income generation, i.e. small-scale industry, and social needs, i.e. clinics. They can be used for the generation of motive power, heat, and other energy requirements. They may also contribute to changes that benefit the local economics and the environment [6]. A typical village mini-grid system

would provide a village with energy for various applications:

Electricity for lighting and appliances(radio,TV computer,etc), in homes and public buildings such as schools and clinics;

Electrical power (or mechanical power common from hydro-powered systems) for local industries;

Electrical power (or mechanical power common from hydro-powered systems) for agricultural value-adding industries and labour saving activities;

Electricity for lighting and general uses in public spaces, i.e. health centres, and for collective events [7].

CONCLUSION

This paper discusses the relevant issues and aims at providing a general definition for distributed power generation in competitive electricity markets. In general, DG can be defined as electric power generation within distribution networks or on the customer side of the network. In addition, the terms distributed resources; distributed capacity and distributed utility are discussed. Network and connection issues of distributed generation are presented, too.


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REFERENCES

[1] Distributed generation in liberalised electricity market, IEA Publications, 2002

[2] Impact of increasing contribution of dispersed generation on the Power System, CIGRE SC #37, 1998. [3] R.H. Lasseter, Control of

distributed resources, in: L H. Fink. [4] C.D. Vournas (Eds.), Proceedings:

Bulk Power Systems Dynamics and Control IV, Restructuring, organised by IREP and National Technical University of Athens, Santorini, Greece, August 23–28, 1998, pp. 323–329.

[5] M. Grubb, Renewable Energy Strategies for Europe-Volume I, Foundations and Context, The Royal Institute of International Affairs, London, UK, 1995.

[6] D. Sharma, R. Bartels, Distributed electricity generation in competitive energy markets: a case study in Australia, in: The Energy Journal Special issue: Distributed Resources: Toward a New Paradigm of the Electricity Business, The International Association for Energy Economics, Clevland, Ohio, USA, 1998, pp. 17–40.


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Study of Distributed Generation Effectiveness in Power Grid Stability

Balwinder Singh Surjan

Associate Professor, Electrical Engineering Department PEC University of Technology, Chandigarh

[email protected]

Abstract- In the present paper load frequency control of interconnected power systems has been investigated from the small signal stability point of view. The interconnected areas are coupled through tie-lines. The frequencies of respective areas are indicative of the power-load imbalance and the tie-line power indicates the power flow from one area to the other. The load frequency control diagram has been augmented by including the distributed generation, and distributed area demands shared by each area. The results obtained are the indicatives of the effect of load sharing upon the grid stability in maintaining the frequency constant.

I. INTRODUCTION

The global electric power industry is evolving from a financial and engineering model that relies on large centralized power plants owned by the utilities to one that is more diverse – both in sources of generation and ownership of the generation assets. Renewable distributed energy generation (RDEG) technologies represent a growing part of the new model for the electric power industry. Like any emerging industry, new policies and standards must be developed and practiced before the market can mature. Worldwide, utility companies and policy makers are testing programs and business models to support this industry. RDEG stands in contrast to the traditional one-way power supply, as well as the traditional relationship utilities have with their customers. The transition to a more distributed system of power generation will require the evolution of both technologies and business practices.The shift to a distributed generation model will challenge the business model of existing traditional utilities and generators as the demand for centrally generated power falls. These companies

will need to adapt if they are to survive. It will also have social implications that extend beyond the electricity system itself as consumers take control of where and how they generate their electricity. Business Insights appreciate the importance of accurate, up-to-date incisive market and company analysis and their aim therefore is to provide a single, off-the-shelf, objective source of data, analysis and market insight. Business Insights work in association with leading industry experts to produce a range of reports across a wide range of industry sectors. In the influence of market dynamics on the stability of interconnected power systems is analyzed and it is concluded that these dynamics significantly affect the design of control in power systems. With these findings in addition, proper frequency control becomes again very important in today’s power systems. Distributed generation refers to relatively small-scale generators that produce several kilowatts (kW) to tens of megawatts (MW) of power and are generally connected to the grid at the distribution or substation levels. Distributed generation units use a wide range of generation technologies, including gas turbines, diesel engines, solar photovoltaic (PV), wind turbines, fuel cells, biomass, and small hydroelectric generators. Distributed generation can be owned and operated by utilities or their customers and can provide a variety of theoretical benefits to their owners and the broader power system. Renewable DG from wind and solar power also typically is not dispatchable or easily controllable. Improved system reliability results from the ability of DG units to maintain supply to local loads in the event of a broader system outage. This could be done by creating “islands” in which a


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section of a distribution feeder is disconnected from a faulted area. Such an action is called “islanding.” Successful islanded operation requires sufficient generation to serve local loads and also the necessary distributed system control capabilities. 9 Distributed generation capable of providing constant, uninterrupted power can improve power quality by mitigating flicker and other voltage regulation problems. On the other hand, distributed generation connected to the grid via power electronic inverters (e.g., solar PV, fuel cells, and most wind turbines) are widely understood to be sources of voltage waveform distortion. However, if designed and implemented properly, the power electronics could theoretically cancel grid distortions and help regulate voltage. The frequency in power systems represents the balance between generated power and demanded power. In normal operation small load variations occur spontaneously. In addition, more severe power imbalances might occur from power plant outages or line tripping and result in larger frequency deviations. In order to avoid these large deviations and secure a stable electrical grid, a frequency control mechanism must be implemented in power systems. Besides these classical disturbances affecting frequency stability, in more and more deregulated power systems, conditions imposed by market mechanisms affect the system additionally.

In the present paper load frequency control of interconnected power systems has been investigated from the small signal stability point of view. The results obtained are the indicatives of the effect of load sharing upon the grid stability in maintaining the frequency constant.

II. SYSTEM SIMULATION

The load frequency control of power system can help in mitigating the problem of grid failure; also the distributed generation in system can be triggered to supply additional demand with a area, without loading the grid tie-lines. The distributed generation plants can also avoid the total system collapse in the case of system islanding. Therefore, the effect of disturbance in one of the interconnected areas can

travel through tie lines to the other area, resulting in inter-area oscillations to develop. The power system dynamics can be studied through the load frequency control assisted by the distributed generation. The block diagram of the two areas coupled through tie-line is given in the Fig. 1 to Fig. 4 below:

Fig. 1 Block Diagram of Two-Area Interconnected Power System

Fig. 2 Internal Block Diagram of Subsystem for Area 1

Fig. 3 Internal Block Diagram of Subsystem for Area2.


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Fig. 4 Internal Block Diagram of Subsystem for Load Sharing between Two-Areas.

III. SYSTEM DATA

The value of various system parameters are tabulated below in Table I.

Table I System Data Parameters of

Area 1 Parameters of

Area 2 KP 100 KP 100 TP 20 TP 20 Ksg 1 Ksg 1 Tsg 0.4 Tsg 0.4 Kt 1 Kt 1 Tt 0.5 Tt 0.5 R 3 R 3 b 0.425 b 0.425 Ki 0.09 Ki 0.09 a12 1 a12 1

2πT12 0.05 2πT12 0.05

The values of cpfij have been varied to observe the effect of load sharing between areas for disturbance in one of the areas, also its effect transmitted to area Further the effect of distributed generation has been simulated through the tie-line power schedule. The effect of load shared by other power system has also been observed. IV. SYSTEM RESPONSE AND ANALYSIS

The system simulated using Matlab simulink as well as script programming has been tested for load sharing and the response in terms of frequencies and tie-line power has been presented and analyzed.

The response of the system has been obtained for the step load change in area 1 and various graphs has been shown in Fig. 5-10. The graphs of frequency versus time show that there is improvement of the system response as the load sharing between the two areas is considered. The tie-line power as a function of time also represents significant improvement.

Fig. 5. Frequency as a function time

Fig. 6 Tie-Line Power as a function time


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Fig. 7. Frequency as a function time

Fig. 8 Tie-Line Power as a function time

Fig. 9 Frequency as a function time for varing Generation

sharing.

Fig. 10 Tie-Line Power as a function time for increasing

Generation sharing

REFERENCES

[1] P. Chiradeja and R. Ramakumar, “An

Approach to Quantify the Technical Benefits of Distributed Generation,” IEEE Transactions on Energy Conversion 19 (2004): 764–773.

[2] R.H. Lasseter, “Smart Distribution: Coupled Microgrids,” Proceedings of IEEE 99, no. 6 (2011): 1074–1082.

[3] W. P. Poore et al., Connecting Distributed Energy Resources to the Grid: Their Benefits to the DER Owner/Customer, Other Customers, the Utility, and Society (Oak Ridge, TN: Oak Ridge National Laboratory, 2002),http://www.ornl.gov/~webworks/cppr/y2002/rpt/112701.pdf.

[4] P. P. Barker and R. W. De Mello, “Determining the Impact of Distributed Generation on Power Systems,” presented at IEEE Power Engineering Society Summer Meeting, Seattle, WA, July 16–20, 2000.

[5] U. N. Khan, “Distributed Generation and Power Quality” presented at the International Conference on Environment and Electrical Engineering, Karpacz, Poland, May 10–13, 2009.


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[6] P. Kundur, Power System Stability and Control. New York: McGraw-Hill, 1994.

[7] Parameter Uncertainties in Power Systems,” Proceedings of IEEE conference on Power Symposium, pp. 630–635, Sep. 2007.

[8] A. Morinec, and F. Villaseca, “Continuous-Mode Automatic Generation Control of a Three-Area Power System,” The 33rd North American Control Symposium, pp. 63–70, 2001.

[9] M. Kothari, N. Sinha and M. Rafi, “Automatic Generation Control of an Interconnected Power System under Deregulated Environment,” Power Quality, vol. 18, pp. 95–102, Jun. 1998.

[10] V. Donde, M. A. Pai, and I. A. Hiskens, “Simulation and Optimization in an AGC System after Deregulation,” IEEE Transactions on Power Systems, vol. 16, pp. 481–489, Aug. 2001.


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Information and Communication Technology in Distributed Generation Solutions

Sunil Gupta1 Anuradha Tomar2

NIEC, New delhi NIEC, New Delhi [email protected] [email protected]

Abstract: This paper investigates the potentially enable sustainable telephone and Internet connectivity to majority of households in remote locations. We emphasis on ‘affordable telecommunications infrastructure’ and its locally available distributed generation solution’. Several telecommunication technologies are reviewed and one that is affordable and has the lowest power consumption for remote equipment is discussed in detail.

I. INTRODUCTION

Information and Communication Technology (ICT) has long been recognized as a crucial constituent in the social infrastructures to constitute a modern nation. In many developing countries, ICT plays a key role in social development. The evidence has indicated that ICT has potential to empower the quality of lives for people living in poverty. It provides the community with the power to access virtually all kinds of information, knowledge, as well as communications services. In Africa [1] for instance, ICT is being used as a tool to achieve better learning outcomes and enable access to material and resources from international, national and local sources in remote communities. It has also become common understanding that telecom and Internet infrastructure is indispensable for the development of economy. In addition, ICT benefits community businesses in numerous ways, essentially by facilitating access to global

markets, and boosting both domestic and international trade. For example, in Sri Lanka farmers used newly installed telephones to find out the prices of coconut, fruit and other produce in Colombo. Instead of selling them at fifty to sixty percent of the Colombo price, farmers were able to get between eighty and ninety percent [2]. Although the benefits of ICT have long been established, and several attempts have been initiated to integrate ICT into the economy of the developed world, least developed countries are being left behind in their number of telephone and Internet subscribers. II. USAGE OF DISTRIBUTED GENERATION

Despite the immense environmental, technical, and financial promise of renewable energy systems, such generators still constitute a very small percentage of electricity generation capacity in the United States. Throughout the 1970s, some policy experts expected renewable energy systems to be used for much more generation capacity than they have. Dr. Arthur Rosenfeld, one of the five CEC commissioners serving from 2002 until the present, noted that President Carter had told him (during his presidency in the late 1970s) that he expected renewable energy systems to reach 10 percent of national electricity capacity by 1985. However, Carter’s expectation went unfulfilled: excluding large hydroelectric generators,


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renewable energy technologies in 2003 comprised only about 2 percent of the U.S. electricity generation mix. The relatively minor use of renewable energy systems has created a general attitude among energy analysts, scholars, and laboratory directors that the technologies are not viable sources of electricity supply. For example, Rodey Sobin, former Innovative Technology Manager for the Virginia Department of Environmental Quality, argues that “in many ways, renewable energy systems were the technology of the future, and today they still are.” Ralph D. Badinelli, a professor of Business Information Technology at Virginia Tech, explains that renewable energy technologies do not contribute significantly to U.S. generation capacity because “such sources have not yet proven themselves … Until they do, they will be considered scientific experiments as opposed to new technologies.” Similarly, Mark Levine, the Environmental Energy Technologies Division Director at the Lawrence Berkeley National Laboratory, comments that despite all of the hype surrounding renewable energy, such systems are still only “excellent for niche applications, but the niches aren’t large.” DG/CHP technologies have an only slightly better record. In 2004, the Energy Information Administration characterized only 3.1 percent of electricity generation capacity as commercial or industrial combined heat and power (33,217 MW out of 1.49 Terrawatts [TW]). The EIA also estimated that in 2002 only 0.9 Gigawatts (GW) of distributed generation capacity existed in the United States. Similarly, the EIA’s 2005 Annual Energy Outlook projected that CHP systems are not widely used in the electric power sector, amounting to 0.053% of utility generation (197 billion kWh out of 3,700 billion kWh). Tom Casten, the Chair and Chief Executive Officer of Primary Energy, a

manufacturer of fuel processing cogeneration steam plants, notes that even though CHP plants can reduce energy costs for industrial firms by over 40 percent, such plants remain “the exception instead of the rule.” III. DISTRIBUTED GENERATION SOLUTIONS

According to the assessment of four energy sources, it is found that solar energy, biomass (especially rice husks) and natural gas are the potential resources for electricity production in the country. However, since the peak power demand for the proposed telecenters is less than 2 kW, the paper recommends four promising small-distributed power schemes in far-flung remote areas of the country [3]. These include: Solar photovoltaics (PV) with battery

storage Diesel engines with battery storage Gas engines with battery storage Fuel cells fueled by natural gas. IV. THE APPLICABLE TELECOMMUNICATIONS SYSTEMS

This section investigates various last-mile solutions that are applicable to provide ICT connection in rural areas. These are plain old telephone service, optical fiber system, TDMA point-to-multi-point systems and wireless local loop systems, and lastly satellite communication system. Plain Old Telephone Service (POTS) is the most common telecommunications system that presently provides telecom and Internet access to majority of the world’s population. POTS connect end users to public switched telephone network (PSTN) through copper wires. Its popularity stems from the very simple connection and its low cost of entry if copper wire is available in the area. Usually, its distance


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limitation is in order of 2 to 5 km from the PSTN. To connect to the Internet, a user uses a telephone line, with a moderately equipped personal computer and a modem, and dials an Internet service provider (ISP). Then, the ISP connects the user to a router, which in turn is connected to other routers on the Internet V.SYSTEM PLANNING AND

OPERATIONS REQUIREMENTS

The increasing penetration of DG resources heightens the significance of scheduling, dispatching, availability, capacity factor, spinning reserve, and voltage and frequency support. Renewable, solar or wind DG has an additional complexity in that most systems have a higher degree of variability in generation output, requiring more insight into real-time status and generation output. Performing long-term generation planning, substation and distribution system upgrade design and routine load flow analysis requires insight into all available DG resources. This in turn requires that these sources provide real-time information to the utilities that can be fed into the new generation of DMS power flow applications for both planning and system operations. This provides the information that utilities need to plan and operate the grid—safely and reliably[4]. A key enabler for effectively integrating, monitoring and managing DG sources within the smart grid lies with the utility's ability to ingest, route, process and act upon the increased levels of instrumentation data from DG sources and the larger grid. With the increasing deployment of information technology solutions such as enterprise service buses (ESBs) and stream processing tools, the latency between "sensory" and "actionable" information has the ability to be dramatically compressed, consequently reducing the time between grid stimulus and effective utility response.

Distributed generation, and especially renewable based technologies, will continue to gain in popularity due to technology advances, environmental benefits, political support and growing energy awareness. Utilities need to prepare themselves for this increased penetration of renewable DGs through the investigation and application of smart grid solutions such as smart metering, smart communications solutions, distributed monitoring and control, and DMS applications (see table). These solutions have far-reaching value beyond supporting DG. By proactively embracing these changes, utilities can begin to shape the myriad of planning and operating approaches that maximize the potential long term benefits to the utility and its customers VI.THE ASSESSMENT OF ENERGY RESOURCES

Electric power is a prerequisite to the operation of telecommunication and Internet connection. Thus, in order to enable ICT connection and provide electricity to telecenters in remote areas of a country, power requirements of each subsystem must be met by certain generation scheme. In other words, power schemes must be identified to all ICT subsystems (including Telecenters) at the transmitting end, at the repeater station, and on the subscriber premises. These schemes depend very much on the locally available resources, which vary from country to country. Energy resources such as solar energy, wind energy, and agricultural waste are decentralized and can be harnessed to produce electrical energy for remote locations. This section investigates renewable energy resources as well as some fossil fuel options in a target country [5].


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SOLAR ENERGY Due to its location, Bangladesh is ideally located for utilizing solar energy. It is situated between 20.30 – 26.38 degrees north latitude and 88.04-92.44 degrees east. Solar energy has been used in Bangladesh for drying crops and fish since time immemorial. The average solar insolation is between 3 to 6 kWh/m2/day, which is quite good for photovoltaics applications.

WIND ENERGY In Bangladesh, other than in coastal areas, there is very little wind power potential for electricity generation. Wind speeds at most meteorological stations appear to be low with typical annual mean wind speeds of 3-5 km/hour, at heights between 5 to 10 meters above ground level. The shape of frequency distribution curve is generally found to be skewed due to low frequency for high-speed values and high frequency for low speed values. By analyzing wind roses, which were developed for all meteorological stations in the country, it was found that wind blows mainly from two directions, NE and SE, in most stations [14].

BIOMASS ENERGY Biomass is the most important renewable energy sources in Bangladesh since most of the rural people are fully dependent on biomass energy for their daily energy needs. Biomass is estimated to provide as much as 70% of the total final energy requirement in Bangladesh. The main sources of biomass energy are: rice husk (26%), cow dung (19%), and rice straw (16%). At present, there is acute shortage of wood fuel in Bangladesh with the bleak future projection for supply to meet the need. On the other hand, agricultural residues or crop production contribute significantly to the biomass sector of Bangladesh and generates considerable amounts of residues that can be used as energy source.

CONCLUSION

The paper neither considers wind turbine nor biomass plant because (1) there is insufficient wind resource to economically operate wind turbines, and (2) efficient biomass plants in general have capacities in the order of 100’s of kilowatts, which is much higher than the requirement (<2kW). Note that although Bangladesh has to import diesel oil, diesel engines are considered as an alternative due to its popularity and ease of operation by village farmers. The technical and economic data, i.e. heat rate, heating value, investment costs, fuel costs, maintenance costs and service life of these alternatives are summarized next.

REFERENCES

[1]. Acacia New, International Development Research Center, Volume 1, Issue 2, December 2001-February 2002,

[2]. A training document from JRC, Japan, role of rural telecommunications, Mar 2000 from Telephone Organization of Thailand (TOT).

[3]. The Economist, elecommunications, April 6th-12th, 2002, pp. 90.

[4]. Energy Information Administration, U.S. natural gas and diesel prices, 2002,

[5]. International Telecommunication Union (ITU 2002), ICT-Free Statistic Homepage


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Series and Shunt FACTS Controllers in Power System: A Review

Avinash1 Sanjiv Kumar2 Dushyant Gaur3

MIT,Meerut MIT,Meerut MIT,Meerut Abstract—In the last two decades power demand has increased substantially while the expansion of power generation and transmission has been severely limited due to many reasons like limited resources, environmentalrestrictions, complexity among operation and control. The existing networks are mainly mechanically controlled the mechanical switching device are slow in operation and control cannot be initiated frequently in these devices. To overcome the problem related to the system stability and controllability so FACTS controllers are developed. Enhancement of system stability using facts controllers has been investigated. This paper is aimed towards the benefit of utilizing FACTS devices with the purpose of improving the operation of an electrical power system as well as the application of FACTS to power system studies. Keywords— AC, FACTS, IPFC, PSS, SVC, STATCOM, SSSC, TCSC, TCPS, UPFC. I. INTRODUCTION-

The problems faced in maintaining economic and secure operation of large interconnected systems can be eased if sufficient margin (in power transfer) can be maintained but this is not feasible due to the difficulties in the expansion of the

transmission networks caused by economic and environmental reasons. The required safe operating margin can be substantially reduced by the introduction of fast dynamic control over reactive and active power by high power electronic controllers. This can make the ac transmission network flexible to adapt to the changing condition caused by contingencies and load variation then these devices are known as facts devices. FACTS; Flexible alternating current transmission system is defined as a power electronic based system and other static equipment that provide control of one or more ac transmission system parameter and to provide stability to power system. II. CONTROL OF POWER SYSTEM

GENERATION, TRANSMISSION,

DISTRIBUTION In any power system, the creation, transmission, and utilization of electrical power can be separated into three areas, which traditionally determined the way in which electric utility companies had been organized. These are illustrated in Figure 1 and are: • Generation • Transmission • Distribution Although power electronic based equipment is prevalent in each of these three areas,


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such as with static excitation systems for generators and Custom Power equipment in distribution systems, the focus of this paper and accompanying presentation is on transmission, i.e., moving the power from where it is generated to where it is utilized.

CONTROLLABILITY OF POWER SYSTEMS

To illustrate that the power system only has certain variables that can be impacted by control, we have considered here the power-angle curve, shown in Figure 2. Although this is a steady-state curve and the implementation of FACTS is primarily for dynamic issues, this illustration demonstrates the point that there are primarily three main variables that can be directly controlled in the power system to impact its performance. These are: • Voltage • Angle • Impedance We can also infer the point that direct control of power is a fourth variable of controllability in power systems. With the establishment of “what” variables can be controlled in a power system, the next question is “how” these variables can be controlled. The answer is presented in two parts: namely conventional equipment and FACTS controllers. III. Classification

There is different classification for the fact devices;Depending on the types of connection to the network FACTS controllers can be differentiate into four categories; *series connected controllers *shunt connected controllers *combined series – series controllers *combined series – shunt controllers

Depending on the power electronic based devices used in the control The FACTS controllers can be classified as; *Variable impedance type *Voltage source converter based FACTS controllers

SERIES CONNECTED CONTROLLERS

It can consist of variable impedance as a condenser, coil, etc or a variable electronics based source at a fundamental frequency. The principle of operation of all serial controllers is to inject a serial tension to the line. Variable impedance multiplied by the current that flows through it represents the serial tension. While the tension is in phase with the line current the serial controller only consumes reactive power; any other phase angle represents management of active power. A typical controller is Serial Synchronous Static compensator.

SHUNT CONNECTED CONTROLLERS

As it happens with the serial controller, the controller in derivation can consist of variable impedance, variable source or a combination of both. The operation principle of all controllers in derivation is to inject current to the system in the point of connection. Variable impedance connected to the line tension causes variable current flow, representing an injection of current to the line. While the injected current is in phase with the line tension, the controller in derivation only consumes reactive power; any other phase angle represents management of active power. A typical controller is Synchronous Static Compensator (STATCOM).

SERIES-SERIES CONTROLLERS This type of controllers can be a combination of coordinated serial controllers in a multiline transmission system. Or can


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also be a unified controller in which the serial controllers provide serial reactive compensation for each line also transferring active power between lines through the link of power. The active power transmission capacity, that present a unified serial controller or line feed power controller, makes possible the active and reactive power flow balance and makes the use of transmission bigger. In this case, the term “unified” means that the DC terminals of the converters of all the controllers are connected to achieve a transfer of active power between each other. A typical controller is the Interline Power Flow Compensator (IPFC).

SERIES -SHUNT CONTROLLERS This device can be a combination of serial and derivations controllers separated, coordinately controlled or a unified power flow controller with serial and derivation element s. The principle of operation of the serial-derivation controllers is to inject current to the system through the component in derivation of the controller, and serial tension with the line utilizing the serial component. When the serial and derivation controllers are unified, they can have an exchange of active power between them through their link. A typical controller is Unified Power Flow Controller (UPFC), which incorporating function of a filtering and conditioning becomes a Universal Power Line Conditioner (UPLC).

VARIABLE IMPEDANCE TYPE

STATIC VAR COMPENSATOR (SVC)

A static VAR compensator (or SVC) is an electrical device for providing fast -act ing react ive power on high-voltage electricity transmission networks. SVCs are part of the Flexible AC transmission system device family, regulat ing voltage and stabilizing the

system. The term "static" refers to the fact that the SVC has no moving parts (other than circuit breakers and disconnects, which do not move under normal SVC operation). Prior to the invent ion of the SVC, power factor compensat ion was the preserve of large rotating machines such as synchronous condensers. The SVC is an automated impedance matching device, designed to bring the system closer to unity power factor. If the power system's react ive load is capacit ive (leading), the SVC will use reactors (usually in the form of Thyristor-Controlled Reactors) to consume VARs from the system, lowering the system voltage. Under induct ive (lagging) condit ions, the capacitor banks are automat ically switched in, thus providing a higher system voltage. They also may be placed near high and rapidly varying loads, such as arc furnaces, where they can smooth flicker voltage. It is known that the SVCs with an auxiliary inject ion of a suitable signal can considerably improve the dynamic stability performance of a power system. It is observed that SVC controls can significant ly influence nonlinear system behavior especially under high-stress operat ing condit ions and increased SVC gains. THYRISTOR-CONTROLLED SERIES

CAPACITOR (TCSC) TCSC controllers use thyristor-controlled reactor (TCR) in parallel with capacitor segments of series capacitor bank. The combination of TCR and capacitor allow the capacitive reactance to be smoothly controlled over a wide range and switched upon command to a condition where the bi-directional thyristor pairs conduct continuously and insert an inductive reactance into the line. TCSC is an effective


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and economical means of solving problems of transient stability, dynamic stability, steady state stability and voltage stability in long transmission lines. TCSC, the first generation of FACTS, can control the line impedance through the introduction of a thyristor controlled capacitor in series with the transmission line. A TCSC is a series controlled capacitive reactance that can provide continuous control of power on the ac line over a wide range. The functioning of TCSC can be comprehended by analyzing the behavior of a variable inductor connected in series with a fixed capacitor. THYRISTOR-CONTROLLED PHASE

SHIFTER (TCPS) In a TCPS control technique the phase shift angle is determined as a nonlinear function of rotor angle and speed. However, in real-life power system with a large number of generators, the rotor angle of a single generator measured with respect to the system reference will not be very meaningful.

THE VSC BASED FACTS CONTROLLERS

STATIC COMPENSATOR

(STATCOM) The emergence of FACTS devices and in particular GTO thyristor-based STATCOM has enabled such technology to be proposed as serious competitive alternatives to conventional SVC [21] A static synchronous compensator (STATCOM) is a regulating device used on alternating current electricity transmission networks. It is based on a power electronics voltage-source converter and can act as either a source or sink of reactive AC power to an electricity network. If connected to a source of power it can also provide active AC power. It is a member of the FACTS family of devices. Usually a STATCOM is installed to support electricity networks that have a poor power factor and

often poor voltage regulation. There are however, other uses, the most common use is for voltage stability .From the power system dynamic stability viewpoint, the STATCOM provides better damping characteristics than the SVC as it is able to transiently exchange active power with the system.

STATIC SYNCHRONOUS SERIES COMPENSATOR (SSSC)

This device work the same way as the STATCOM. It has a voltage source converter serially connected to a transmission line through a transformer. It is necessary an energy source to provide a continuous voltage through a condenser and to compensate the losses of the VSC. A SSSC is able to exchange active and reactive power with the transmission system. But if our only aim is to balance the reactive power, the energy source could be quite small. The injected voltage can be controlled in phase and magnitude if we have an energy source that is big enough for the purpose. With reactive power compensation only the voltage is controllable, because the voltage vector forms 90º degrees with the line intensity. In this case the serial injected voltage can delay or advanced the line current. This means that the SSSC can be uniformly controlled in any value, in the VSC working slot.

UNIFIED POWER FLOW CONTROLLER (UPFC)

A unified power flow controller (UPFC) is the most promising device in the FACTS concept. It has the ability to adjust the three control parameters, i.e. the bus voltage, transmission line reactance, and phase angle between two buses, either simultaneously or independently. A UPFC performs this through the control of the in-phase voltage, and shunt compensation. The UPFC is the most versatile and complex power electronic equipment that has emerged for the control


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and optimization of power flow in electrical power transmission systems. It offers major potential advantages for the static and dynamic operation of transmission lines. The UPFC was devised for the real-time control and dynamic compensation of ac transmission systems, providing multifunctional flexibility required to solve many of the problems facing the power industry. Within the framework of traditional power transmission concepts, the UPFC is able to control, simultaneously or selectively, all the parameters affecting power flow in the transmission line. Alternatively, it can independently control both the real and reactive power flow in the line unlike all other controllers.

INTERLINE POWER FLOW CONTROLLER (IPFC)

The objective of introducing this controller is to address the problems of compensating a number of transmission lines connected at a substation. While pure series reactive compensation can be used to control or regulate the active power flow in a line, the control of reactive power is not feasible unless active voltage in phase with the line current is not injected. In addition to the facility for independently controllable reactive compensation of each individual line, a capability to directly transfer or exchange real power between compensated lines. This is achieved by coupling the series connected VSCs in an individual line on the dc side, by connecting all the dc capacitors of individual converters in parallel. Since all the series converters are located inside the substation in close proximity this is feasible. IV. BENEFITS DUE TO FACTS

CONTROLLERS 1. FACTS contribute to optimal system operation by reducing power losses and improving voltage profile.

2. The power flow in critical lines can be enhanced as the operating margins can be reduced due to fast controllability. 3. The transient stability limit is increased thereby improving dynamic security of the system and reducing the incidence of blackouts caused by cascading outages. 4. The steady state or small signal stability reason can be increased by providing auxiliary stabilizing controllers to damp low frequency oscillation. 5. The problem of voltage fluctuation and in particular, dynamic over voltage can be overcome by FACTS controllers.

V. FACTS APPLICATIONS TO STEADY STATE POWER SYSTEM PROBLEMS

For the sake of completeness of this review, a brief overview of the FACTS devices applications to different steady state power system problems is presented in this section. Specifically, applications of FACTS in optimal power flow and deregulated electricity market will be reviewed

FACTS APPLICATIONS TO OPTIMAL POWER FLOW

In the last two decades, researchers developed new algorithms for solving the optimal power flow problem incorporating various FACTS devices. Generally in power flow studies, the thyristor controlled FACTS devices, such as SVC and TCSC, are usually modeled as controllable impedance. However, VSC-based FACTS devices, including IPFC and SSSC, shunt devices like STATCOM, and combined devices like UPFC, are more complex and usually modeled as controllable sources. The Interline Power Flow Controller (IPFC) is one of the voltage source convertor (VSC)


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based FACTS Controllers which can effectively manage the power flow via multi-line Transmission System.

FACTS APPLICATIONS TO DEREGULATED ELECTRICITY

MARKET

Nowadays, electricity demand is rapidly increasing without major reinforcement projects to enhance power transmission networks. Also, the electricity market is going toward open market and deregulat ion creat ing an environment for forces of compet it ion and bargaining. FACTS devices can be an alternat ive to reduce the flows in heavily loaded lines, result ing in increased load abilit y, low system loss, improved stability of the network, reduced cost of production, and fulfilled contractual requirements by controlling the power flows in the network. Generally, the changing nature of the electricity supply industry is introducing many new subjects into power system operat ion related to trading in a deregulated compet it ive market. Commercial pressures on obtaining greater returns from exist ing assets suggests an increasingly important role for dynamic network management using FACTS devices and energy storage as an important resource in generat ion, transmission, distribut ion, and customer service. There has been an increased use of the FACTS devices applicat ions in an electricity market having pool and contractual dispatches.

CONCLUSION

To overcome the problems related to stability and controllability of power system FACTS controllers should be used. The

essential features of FACTS controllers and their potential to improve system stability is the prime concern for effective & economic operation of the power system. The location and feedback signals used for design of FACTS-based damping controllers were discussed. The coordination problem among different control schemes was also considered. Performance comparison of different FACTS controllers has been reviewed. The likely future direction of FACTS technology was discussed.

REFERENCES

[1] N. G. Hingorani and L. Gyugyi, Understanding FACTS: Concepts and Technology of Flexible AC Transmission Systems. New York: IEEE Press, 2000.

[2] N. G. Hingorani, “FACTS-Flexible AC Transmission System”, Proceedings of 5th International Conference on AC and DC Power Transmission-IEE Conference Publication 345, 1991, pp. 1–7.

[3] N. G. Hingorani, “Flexible AC Transmission”, IEEE Spectrum, April 1993, pp. 40–45.

[4] N. G. Hingorani, “High Power Electronics and Flexible AC Transmission System”, IEEE Power Engineering Review, July 1988

[5] R. M. Mathur and R. S. Basati, Thyristor- Based FACTS Controllers for Electrical Transmission Systems. IEEE Press Series in Power Engineering, 2002.

[6] Yong Hua Song and Allan T. Johns, Flexible AC Transmission Systems (FACTS). London, UK: IEE Press, 1999.

[7] M. Noroozian and G. Andersson, “Power Flow Control by Use of Controllable Series


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Emerging Trends in Distributed Generation System

Renu Sharma

IET, Alwar, Rajasthan

Abstract - This paper describes model of smart micro grids suitable for limited areas already served by existing networks and remote zones where electricity is not available with technology of Active front end generators which can be used efficiently with renewable sources of energy.

I. INTRODUCTION: As everything around us is dependent on energy so there has been many discussions/researches are ongoing for its preservation and better use for future. In terms of it most famous technology emerging is Renewable sources of energy also called green energies like sun energy, wind energy but in promoting these energies main drawback is that these energies are not stable and could not be stored in greater stock. For an efficient distributed generation system it is necessary that power supply shall be smooth without any distortion/blackouts hence to sort this problem Smart Micro grid system comes in picture. Distributed generation and energy efficiency is the main basis for conception of smart micro grid system.Micro grids are modern, small-scale versions of the centralized electricity system. They achieve specific local goals, such as reliability, carbon emission reduction, diversification of energy sources, and cost reduction, established by the community being served. Like the bulk power grid, smart micro grids generate, distribute, and regulate the flow of electricity to consumers, but do so locally. Smart micro grids are an ideal way to integrate renewable resources on the

community level and allow for customer participation in the electricity enterprise. They form the building blocks of the Perfect Power System.The smart grid can work in parallel to main grid or disconnected from it. In disconnected mode it is called to be in “island mode”. A simple micro grid as shown in fig. 1 represents the main components of smart grid system: local generating stations, loads with their controllers and the power interface to main grid and power management systems. Power equipments shall be of good quality i.e. provide energy with minimum distortion, electrical losses, with reliable and safe duty capable of managing every normal and transient situation without tripping or losing its functionality. Digital technology that allows for two-way communication between the utility and its customers, and the sensing along the transmission lines is what makes the grid smart. Like the Internet, the Smart Grid will consist of controls, computers, automation, and new technologies and equipment working together, but in this case, these technologies will work with the electrical grid to respond digitally to our quickly changing electric demand.


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DESCRIPTION Distributed generation system can be classified on basis of two parameters for design of smart grids: kind of duty they can provide and kind of equipment used by them to deliver energy to grid. The first parameter indicates the power availability provided by generation system i.e. continuous or random. For e.g. Main grid system provide the power continuously while power from renewable sources of energy depend upon climatic condition thus it is random type so these sources can’t be taken as primary source for smart grids so smart grid must be connected to main grid to compensate these random supplies. Proper calculation need to be done to check how much power can be provided from renewable sources and how much power will be required from main grids as back up. The second power represents static type generators or rotating type generators to be used for smart grids. Generally static type generators are being used for renewable sources to store enrgy while rotating type is used in conventional grid system. Thus a

smart micro grid shall have either type of generators. But to reduce the cost and improve functionality of generators to get connected to both static power and to main grid static power converters are used called “Active Front End type converters”. Active Front End Converters: The active front end converter can be seen in its basic hardware elements in fig. 2 &3, where two main cases are illustrated. Fig. 2 provides a link between a dc source to an ac grid, as in case of photovoltaic cells. Fig. 3 is related to method used for connecting a variable speed rotating generator to grid for e.g. in Wind generators using variable speed motors or permanent magnet motors. The frequency and amplitude of variable voltage of rotating generator is converted to dc first, then from the dc voltage the power section connected to grid produces voltage equal to the one of the grid. AFE is provided with some special software features that it can be used as generalized solution for delivering energy to grid from any renewable sources of energy

Following are the features of AFE solution are:


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Production of sinusoidal voltage and control emc emissions: AFE is equipped with special type of “T low-pass” filter in order to suppress any voltage harmonics having an order greater than fundamental frequency. The “T” filter is inserted between the three phase output of the AFE converter and the grid.

Delivering power to grid in parallel with other generators: AFE converters can be used in weak grid system to control active and reactive energy components. Dedicated regulation algorithms are implemented in control system of AFE converter.

Management of grid transients: AFE converter can be equipped with special control functions to manage transient of grid, mainly the short circuit currents. This function provides flexibility to prevent AFE from tripping and contributes the clearing of fault occurred on the grid.In case of fault AFE just changes its mode of operation.

CONCLUSION

This paper introduced basic

understanding for smart micro grid system and special technique of AFE converters which is already running and tested in many industrial applications. The micro grid can be made “smart” with introduction of new features and thus can solve the complex problems of energy loss/blackouts with random production capability and thus reduction in conventional sources of energy in power generation.

REFERENCES

[1]. Marina G. Gatti, 2004 Large Power

PWM IGBT converter for shaft generator systems Vol.5 Page 3444-3450

[2]. Numeroli R. Gatti, Torri. G., Kranenburg R, 1995, Four quadrant, large power, igbt vector controller adjustable speed drive

[3]. AA. VV. Enel. 2007 DK5940 ed 2.2 [4]. Flueck A. Zuyi li, 2008. Destination:

perfection. IEEE power & energy magazine. Nov/Dec. 2008


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Study and Characterization of reactive power in wind farm operation using MATLAB Simulink

Dr. Tilak Thakur1 Priya Sharma2

1,2PEC University of Technology, Chandigarh

Abstract: To harness the wind power efficiently the most reliable system in the present era is grid connected doubly fed induction generator. The DFIG brings the advantage of utilizing the turns ratio of the machine, so the converter does not need to be rated for the machine’s full rated power. The rotor side converter (RSC) usually provides active and reactive power control of the machine while the grid-side converter (GSC) keeps the voltage of the DC-link constant. The GSC can supply the required reactive current very quickly while the RSC passes the current through the machine resulting in a delay. Both converters can be temporarily overloaded, so the DFIG is able to provide a considerable contribution to grid voltage support during short circuit periods. These wind energy conversion systems are connected to the grid through Voltage Source Converters (VSC) to make variable speed operation possible. The studied system here is a variable speed wind generation system based on Doubly Fed Induction Generator (DFIG). The stator of the generator is directly connected to thegrid a fraction of the generator rated power. The convertor as well as the rotor requires reactive power which is either drawn from the grid or is obtained from the reactive power sources like FACTS devices. An attempt has been made to understand the role of reactive power in the wind farm operation.

Keywords: DFIG, Phase locked loop, FACTS, STATCOM

I. INTRODUCTION: Wind turbine consists of induction generator of wound rotor type. The stator is

connected to the grid and the rotor to the turbine. The reactive power is fed to the rotor through a convertor which has sides- grid side and the turbine side. These two are linked to each other with a dc-link which is basically a capacitor. Also because of the large requirement of the reactive power, the wind turbine is generally supported with the reactive power sources like capacitor banks or the unconventional sources like FACTS devices.[1],[2] A case with the STATCOM has been considered to analyze the impact of reactive power in the wind farm operation.

MODEL DESCRIPTION A wind farm consisting of six 1.5-MW wind turbines is connected to a 25-kV distribution system exports power to a 120-kV grid through a 25-km 25-kV feeder. The 9-MW wind farm is simulated by three pairs of 1.5 MW wind-turbines. Wind turbines use squirrel-cage induction generators (IG). The stator winding is connected directly to the 60 Hz grid and the rotor is driven by a variable-pitch wind turbine. The pitch angle is controlled in order to limit the generator output power at its nominal value for winds exceeding the nominal speed (9 m/s). In order to generate power the IG speed must be slightly above the synchronous speed. Speed varies approximately between 1 pu at no load and 1.005 p.u at full load. Each wind turbine has a protection system


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monitoring voltage, current and machine speed. [5],[7]

Reactive power absorbed by the IGs is partly compensated by capacitor banks connected at each wind turbine low voltage bus (400 kvar for each pair of 1.5 MW turbines). The rest of reactive power required to maintain the 25-kV voltage at bus B25 close to 1 pu is provided by a 3-Mvar STATCOM with a 3% droop setting. The 9 MW wind farm considered for the purpose of analysis has been shown in the following figure 1 Figure 1: Model for the 9 MW wind farm The comprehensive model incorporating the wind farm and the STATCOM has been shown below in figure 2. The encircled wind farm has already been discussed above.

Figure 2: Model incorporating 9 MW wind farm &

STATCOM

DEMOSTRATION AND SIMULATION RESULTS

(a)Turbine response to a change

in wind speed

Start simulation and observe the signals on the "Wind Turbines" scope monitoring active and reactive power, generator speed, wind speed and pitch angle for each turbine. For each pair of turbine the generated active power starts increasing smoothly (together with the wind speed) to reach its rated value of 3 MW in approximately 8s. Over that time frame the turbine speed will have increased from 1.0028 pu to 1.0047 pu. Initially, the pitch angle of the turbine blades is zero degree. When the output power exceed 3 MW, the pitch angle is increased from 0 deg to 8 deg in order to bring output power back to its nominal value. We observe that the absorbed reactive power increases as the generated active power increases. At nominal power, each pair of wind turbine absorbs 1.47 Mvar. For a 11m/s wind speed, the total exported power


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measured at the B25 bus is 9 MW and the statcom maintains voltage at 0.984 pu by generating 1.62 Mvar (see "B25 Bus" and "Statcom" scopes). [3] (b) Operation of protection system At t=15 s, a phase to phase fault is applied at wind turbine 2 terminals, causing the turbine to trip at t=15.11 s. If we look inside the "Wind Turbine Protections" block you will see that the trip has been initiated by the AC Undervoltage protection. After turbine 2 has tripped, turbines1 and 3 continue to generate 3 MW each.

(c) Impact of STATCOM

First, opening the "Fault" block menu and disabling the phase to phase fault.Then putting the "STATCOM" out of service by double clicking the "Manual Switch" block connected to the "Trip" input of the "STATCOM". Restart simulation. [4] Observing on "B25 Bus" scope that because of the lack of reactive power support, the voltage at bus "B25" now drops to0.91pu.This low voltage condition results in an overload of the IG of "Wind Turbine 1". "Wind Turbine 1" is tripped at t=13.43 s. Looking inside the "Wind Turbine Protections" block we see that the trip has been initiated by the AC Overcurrent protection.[6]

SIMULATION RESULTS

The simulation output gives the variation of various parameters of wind turbine, STATCOM and the isolated bus.

Figure3. simulation showing variation of turbine

parameters.

Figure4. simulation showing variation of turbine output.


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Figure5. simulation showing variation of connecting terminal parameters.

CONCLUSION Each wind turbine block

represents two 1.5 MW turbines. The turbine mechanical power as function of turbine speed is displayed for wind speeds ranging from 4 m/s to 10 m/s. The nominal wind speed yielding the nominal mechanical power (1pu=3 MW) is 9 m/s. The system has been observed for 20s.The wind speed applied to each turbine is controlled by the "Wind 1" to "Wind 3" blocks. Initially, wind speed is set at 8 m/s, then starting at t=2s for "Wind turbine 1", wind speed is rammed to 11 m/s in 3 seconds. The same gust of wind is applied to Turbine 2 and Turbine 3, respectively with 2 seconds and 4 seconds delays. Then, at t=15s a temporary fault is applied at the low voltage terminals (575 V) of "Wind Turbine 2".

REFERENCES [1] Ancona DF, Goldman PR, Thresher

RW. Wind program technological developments in the United States. Renew Energy 1997;10:253-8.

[2] Bird L, Bolinger M, Gagliano T, Wiser R, Brown M, Parsons B. Policies and market factors driving wind power development in the United States. Energy Pol 2005;33:1397-407.

[3] Ja¨ ger-Waldau A, Ossenbrink H. Progress of electricity from biomass, wind and photovoltaics in the European Union. Renew Sustain Energy Rev 2004;8:157-82.

[4] Georgilakis PS. State-of-the-art of decision support systems for the choice of renewable energy sources for energy supply in isolated regions. Int Distrib Energy Resour 2006;2:129-50.

[5] Stampolidis VL, Katsigiannis YA, Georgilakis PS. A methodology for the economic evaluation of photovoltaic systems. Oper Res An Int J 2006;6:37-54.

[6] Katsigiannis YA, Georgilakis PS. Reliability and economic evaluation of small autonomous power systems containing only renewable energy sources. In: Proceedings of the international conference on electrical machines, Chania, Greece, September 2006.

[7] Lambert T, Gilman P, Lilienthal P. Micropower system modeling with HOMER. In: Farret FA, Simo˜ es MG, editors. Integration of alternative sources of energy. New York: Wiley; 2006 pp. 379-418.


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Potential Benefits of Self-excited induction generator (SEIG) in Distribution Generation

Ahmed Riyaz1 S P Singh2 S K Singh3

RGGI, Meerut IIT, Roorkee RGGI, Meerut [email protected] [email protected] [email protected]

Abstract: Owing to shrinking energy resources facing mankind, have led to exhaustive hunt for environment friendly ways of energy generation. A novel trend in electric power production is the decentralization of power generation and increased use of non-conventional energy sources such as wind energy, bio-gas, solar and hydro potential, etc. Induction generators are increasingly being used in non-conventional energy systems such as wind, micro/mini hydro, etc. The advantages of using an induction generator instead of a synchronous generator are reduced unit cost and size, ruggedness, brushless (in squirrel cage construction), absence of separate dc source, ease of maintenance, self-protection against severe overloads and short circuits, etc. In isolated systems, squirrel cage induction generators with capacitor excitation, known as self-excited induction generators (SEIGs), are very popular. This paper, therefore, reviews the progress made in induction generator particularly, the self-excited induction generator (SEIG) research and its importance with regard to distribution generation. Attempts are made to highlight the current and future issues involved in the development of SEIG technology for its large-scale future applications.

I. INTRODUCTION

A half century ago, electricity was important but not necessary to maintain important functions in the community. Today on the other hand it is almost impossible to live a sophisticated life without electricity. The dependency on electricity has increased the cost of a blackout. Our helplessness to a blackout is increasing as the number of functions in the society depending on electricity is mounting. Following major blackouts all over the world,

in recent years, power supply reliability has become a very important issue [1]. In the last two centuries the world's population and the worldwide total energy consumption have been constantly mounting, at a rate even greater than exponential [2]. By now a situation has been reached in which energy resources are falling short, which for a long time have been treated as though they were almost inexhaustible. The on-going growth of the world's population and a growing demand of energy in developing countries mean that the yearly overall energy consumption will continue to grow, so that it would have doubled by 2035 [2]. The increasing rate of the depletion of conventional energy sources, particularly after the increases in fuel prices during the 1970s has given rise to an increased emphasis on eco-friendly technologies, the use of renewable sources such as small hydro, wind and biomass is being explored [3,4]. Generation of electrical energy mainly so far has been from thermal, nuclear, and hydro plants. They have continuously degraded the environmental conditions. Also, the utilities in many developing countries are finding it difficult to establish and maintain remote rural area electrification. The costs of delivering power to such areas are becoming excessively large due to large investments in transmission lines for locally installed capacities and large transmission line losses. For these reasons, distributed power generation has received attention in recent years. This paper gives an overview on the development of self-excited induction generator research and its importance with regard to distribution generation.


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II. DISTRIBUTED GENERATION

The increasing diffusion of distributed generation is due to many factors. In many Countries various government actions try to incentive the diffusion of renewable energy generation systems connected to electrical distribution networks [5]. Society demands environmental-friendly energy and governments often promotes renewable energy sources. By their nature, renewable energy sources are mostly delocalized with limited production capability and therefore their utilization takes often the form of small to medium scale distributed generation. Our society has become highly dependent on electricity supply. Important industrial sectors and infrastructures are equipped with emergency back-up electricity sources to minimize the risks of damages due to power outages. Private consumers may also be seriously affected by long power outages. Important industries such as paper mills disconnect from the grid and use their own power generation in an island grid during thunderstorms to avoid uncontrolled interruptions in the production. With the deregulation of electric power utilities, advancement in technology, and environmental concerns, optimal distributed generation (DG) will be a focus to the electric utilities to cater the growing need of electric power [6]. Distributed generator is generally connected directly to grid or can operate independently. They are considered to be less than 5MW in capacity [7]. There are different definitions of distributed generation. In general, distributed generation can be defined as electric power generation within distribution networks or on the customer side of the network. DG can be based on renewable technologies such as wind turbine, photovoltaic or non-renewable technologies such as micro-turbine and fuel cell. Distributed generation using micro-turbine generator (MTG) is a practical solution because of its environment friendliness and high energy efficiency. Various applications such as peak shaving, co-generation, remote power and base load power will make its use worldwide.

Dynamic model of MTG system have been suggested in [8, 9].

As per the Government of India, decentralized power production facility is defined as any facility that produces power less than 100 kW and is not connected to central grid. These are stand-alone systems that supply power to a particular commercial/domestic setup. Due to unavailability of grid the management of power produces is more difficult for such systems however there are no grid losses and voltage problems associated with it. These systems are characterized by an energy storage device in form of batteries. The storage also has capacity to run 24 hours of normal operation of the setup. Decentralized electricity has some very fundamental differences compared to centralized electricity production [10].

Advantages of Decentralized over centralized in Indian context:

Considering the unique demographical and geographical position of India and collating it with the current and the predicted future economic scenario of the country, we can say that decentralized electricity possess an edge over centralized electricity for the rural and off-grid electrification in India in the coming years.

Minimal losses Cogeneration Easier Set-up, Maintenance and

Operation Opportunity for SMEs and entrepreneurs

Gas/fossil fuel can be a viable option for energy production, but setting up infrastructure for gas/fossil fuel supply over a wide region will be a huge infrastructure investment that will also take considerable time. Setting up decentralized power production facility can drastically shrink infrastructure investment which can then be transferred for subsidizing renewable energy production which will run on very less operation cost. It will also aid in solving the problem of India’s heavy dependence on imported fossils. Decreasing its fossil fuel import bill and simultaneously increasing rural


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electrification can thus be tackled by decentralized renewable production of electricity [11-13].

Different regions in India are endowed with a wide variety of resources that can be used as fuel. A large portion of coastal regions have a huge wind power potential. Many remote locations in the region of western desert, wind power can be employed to generate electricity and run irrigation pumps. India also possesses the highest potential in the world to harness solar power and thus MNRE has recognised solar power as a major source of energy in future for India and has created ambitious plan in Jawaharlal Nehru National Solar Mission (JNNSM). JNNSM has also been integrated with RGVVY of Ministry of Power and RVE programme of MNRE [14, 15]. Wind and Solar power resources complement each other perfectly in Indian climatic cycle. Wind-solar hybrid systems can be very effective solutions.

Distributed generation may be divided into different groups depending on the type of network interface: induction generators, synchronous generators or power electronic converters. This paper focuses on the first of these groups.

III. INDUCTION GENERATOR

Conventionally, synchronous generators have been used for power generation but induction generators are increasingly being used these days because of their relative advantageous features over conventional synchronous generators. These features are brush less and rugged construction, low operational and maintenance cost, maintenance and operational simplicity, capability to generate power at varying speed, etc. The later feature facilitates the induction generator operation in stand-alone/isolated/island mode to supply far flung and remote areas where extension of grid is not economically viable; in conjunction with the synchronous generator to fulfil the increased local power requirement, and in grid-connected mode to supplement the real power demand of the grid by integrating

power from resources located at different locations [16]. Unlike the synchronous generator, an induction generator does not have an internal magnetization source. However, a voltage may build up in an induction generator as the result of a physical process known as self-excitation. This permits the utilization of an induction generator as a standalone unit operating in island without connection to any other voltage source. It may take place if a sufficient amount of capacitors is connected at the generator terminals. Self-excitation is initiated by the residual flux in the induction generator rotor iron. When the generator is accelerated to a certain speed, the residual flux will induce a voltage in the stator. Under these conditions, the induction generator behaves much like a synchronous generator with permanent magnet rotor [17].

The induction generator’s potential to produce power even at varying speed facilitates its application in various modes such as self-excited stand-alone (isolated) mode; in parallel with synchronous generator to complement the local load, and in grid-connected mode also. There is huge research in progress for the last few decades for the use of induction generator as an alternative to the synchronous generator to utilize the small hydro and wind energy.

IV. SELF-EXCITED INDUCTION GENERATOR

In early 1970s with a sharp rise in oil prices, interest in wind power re-emerged. However by the end of 1990s, wind power became as one of the sustainable energy resource. No other renewable energy based electricity producing technology has attained the same level of maturity as wind power. There are no major technical barriers to large-scale penetration of wind power. It also offers an attractive investment option to the private sector for power generation [18-21]. It is observed that winds carry enormous amount of energy and could meet sufficient energy needs of the world. The regions in which strong winds


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prevail for a sufficient time during the year may use wind energy profitable for different purposes. It has been found that cost of wind generation is comparable to that of hydro and thermal plants. There is a little doubt that while the cost of wind generation would be even lowers in the coming years; the prices of fossil fuels used by thermal plants would definitely go up. In view of high capital constructional cost hydro power would be dearer too. In addition to this wind energy generation provides a clean and pollution free environment. It does not lead to global warming and ozone depletion. No hazardous waste is created. Further a wind turbine generator may be a very worthwhile proposition for an isolated and remote area. Application of induction generators [22-37] is well known to extract the wind energy through turbines. An induction motor connected to constant voltage, constant frequency supply system behaves as a generator if made to run at a speed higher than synchronous speed. In such an operation, the exciting current is provided by the supply system, to which the machine is connected and the frequency of the voltage generated by the induction generator is the same as that of supply system. It was also well established that an induction machine might be run as a generator by connecting suitable capacitors across stator terminals to provide excitation. In such an arrangement, the frequency of the generated voltage is not fixed but beside other factors depends upon the speed of the prime mover. Self-excited induction generators (SEIG) are found to be most suitable for many applications including wind energy conversion systems. Such generators may also be used in the remote areas in the absence of grid. These machines have many advantages such as brush less construction (squirrel-cage rotor), reduced size, and no need of of DC power supply for excitation as in conventional generators, reduced maintenance cost; self-short-circuit protection capability and no synchronizing problem. Steady state equivalent circuit representation and mathematical modelling is required to evaluate the steady state performance of a SEIG feeding a specific load. In order to estimate the performance of a SEIG, researchers have made use of the

conventional equivalent circuit of an induction motor. Steady state modelling of grid connected induction generator using saturated magnetizing reactance has been described in [18]. Power quality effects in case of SEIG are investigated by [19]. Whereas, [20] investigated the stability aspects of wind driven induction generator. Some of the researchers [21, 22] used the impedance model, and a few [23-26] used the admittance-based model for to estimate the performance of these machines. However it has been felt that the old conventional equivalent circuit model, in the absence of an active source, does not effectively correspond to generator operation. Therefore [27] suggested a new circuit model for the representation of induction generator. For windmill drives, the speed of the induction machine depends upon the velocity, volume and the direction of wind. These parameters may vary in wide limits. It is found that such machine exhibits poor performance in terms of voltage and frequency under frequent variations of operating speeds, which is a common feature in wind energy conversion. It is therefore, desirable to investigate the behaviour of a self-excited induction generator suitable for windmill drive under controlled and uncontrolled speed operation. It is realized that such variations in operating speeds may be compensated by proper handling of load and rotor resistance. On the basis of rotor construction, induction generators are two types (i.e., the wound rotor induction generator and squirrel cage induction generator). Depending upon the prime movers used (constant speed or variable speed) and their locations (near to the power network or at isolated places), generating schemes can be broadly classified as under [28, 29]:

i) Constant-speed constant-frequency (CSCF);

ii) Variable-speed constant-frequency (VSCF);

iii) Variable-speed variable-frequency (VSVF).


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V. SELF-EXCITATION AND VOLTAGE BUILD-UP IN SEIG

The principle of self-excitation of an induction motor is well known since the 1930s [30]. Self-excitation phenomenon is still a subject of considerable attention. The interest in this topic is primarily due to the application of SEIG in isolated power systems. Physical background of the self-excitation process has been described in considerable depth in [30]. When an induction machine is disconnected from the supply, and driven by a mechanical source, terminal voltage builds up if its lagging var demand is supplied externally, and sufficient residual magnetism is present in the rotor core. This is known as self-excitation phenomenon in the literature. Shunt compensation capacitors are the most common var supplies for the self-excitation of induction motors. The use of an induction machine as an autonomous generator due to self-excitation phenomenon has been extensively investigated by several researchers, especially for wind power generation [36-41]. In the self-excited mode, the induction generator is excited with three-phase ac capacitors. The frequency, the slip, the air gap voltage and the operating range of the system are affected by the characteristics of the induction generators and the choice of capacitor sizes. The operating slip in a self-excited mode is generally small and the variation of the frequency depends on the operating speed range. When an induction machine is driven at a speed greater than the synchronous speed (negative slip) by means of an external prime mover, the direction of induced torque is reversed and theoretically it starts working as an induction generator. From the circle diagram of the induction machine in the negative slip region [43], it is seen that the machine draws a current, which lags the voltage by more than 90. This means that real power flows out of the machine but the machine needs the reactive power. To build up voltage across the generator terminals, excitations must be provided by some means;

therefore, the induction generator can work in two modes (i.e., grid connected and isolated mode). In case of a grid-connected mode, the induction generator can draw reactive power either from the grid but it will place a burden on the grid or by connecting a capacitor bank across the generator terminals [44–46]. For an isolated mode, there must be a suitable capacitor bank connected across the generator terminals. This phenomenon is known as capacitor self-excitation and the induction generator is called a “SEIG.” The process of voltage build-up in an induction generator is very much similar to that of a dc generator. There must be a suitable value of residual magnetism present in the rotor. In the absence of a proper value of residual magnetism, the voltage will not build up. So it is desirable to maintain a high level of residual magnetism, as it does ease the process of machine excitation. The operating conditions resulting in demagnetization of the rotor (e.g., total collapse of voltage under resistive loads, rapid collapse of voltage due to short circuit, etc. should be avoided [47]). When an induction generator first starts to run, the residual magnetism in the rotor circuit produces a small voltage. This small voltage produces a capacitor current flow, which increases the voltage and so forth until the voltage is fully built up. The no-load terminal voltage of the induction generator is the intersection of the generator’s magnetization curve with capacitor load line [48]. The magnetization curve of the induction generator can be obtained by running the machine as a motor at no load and measuring the armature current as a function of terminal voltage. To achieve a given voltage level in an induction generator, an external capacitor must be able to supply the magnetizing current of that level.

VI. MODELLING AND CONTROL OF SEIG

The induction machine is modelled using the steady-state equivalent circuit. Detail derivation of equations for self-excited induction generator can be found in literature [49, 50]. The stable


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operation of the system can be sustained at any moment when the balance of real power and reactive power can be maintained. The balance of real power is established mainly between the power produced in the rotor and the power consumed from the stator winding through the power converter. The balanced of reactive power is established between the ac capacitors and the air-gap flux condition at any operating condition[51].

Fig. 1: Cross Section of Induction Machine

Fig. 2: Circuit-connection of a wound-rotor Induction Machine.

Fig. 3: A 1.8kW wound-rotor induction machine.

Fig. 4: A 2.2kW squirrel-cage induction machine.

The frequency in a power system is closely related to the generator speed. In synchronous generators the speed is directly tied to the frequency through the number of poles divided by two. In induction generators the frequency also differs from the mechanical speed by the number of poles divided by two, but also by the slip which is in order of a percent. The torque balance in the system given by Eq. 1 directly affects the system frequency.

.elmec TTdtdwJ (1)

A difference between driving mechanical torque, e.g. water in a turbine, and electrical load torque results in a change in frequency. Eq. 1 could be expressed with power as well.


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.elmec PPdtdwJ (2)

If the input mechanical power is higher than the electrical power consumption the frequency increases and if the consumption is higher than the input power the frequency decreases. The rate of change in frequency is proportional to the inverse of the inertia, J. In a big power system J is the total inertia of all connected generators and their turbines. With more generators connected a disturbance has less influence on the frequency. It is thus more difficult to regulate frequency in an isolated mode of operation with only one or a few generators. The same load changes will have greater impact on frequency than at interconnected operation.

The influence between power and frequency is utilized in the turbine control. The frequency decreases and the frequency error are fed back to the turbine governor which opens the gate. The deviation Δf is determined by the gain R in the turbine governor. The gain R is called frequency droop. It is given by

PfR

(3)

and determines the maximum steady-state frequency error when the generator is operating at full load. If R is selected to have the same value in p.u. for different generators this allows parallel operation with equal sharing of the control effort. A change in frequency then results in the same power change in pu for all the generators. While the frequency is the same in the entire grid the voltage is not. The voltage is controlled by each generator individually. In a synchronous generator this is done by changing the excitation. The reactive power to the grid is then changed and the voltage at the connection point is changed accordingly. Another way to control the voltage in a grid is to change the reactive power balance by means of connecting reactors or capacitors. The local change in

voltage may then be approximately calculated from the short circuit capacity of the grid [17].

scSQV

(4)

When the load in the power system is changed it is important to immediately compensate for this by means of changing the mechanical power input to the generators. If this is not done properly the frequency may deviate too much from rated frequency (50 Hz) and in case of a big change in power, caused by for example disconnection of a large production unit, the power system may go unstable. A fast turbine governor is therefore desirable. However all types of power sources do not permit fast control of mechanical power. Among these are hydro power stations which often have long waterways and hence a large inertia in the water that has to be accelerated when an increase in power is required. An additional problem with hydro power is the non-minimum phase characteristic of the system. When opening the gate the power decreases before increasing. This may lead to instability if the electrical power is used as feedback to the governor. Another problem with power feedback is that the voltage control affects the frequency control. Voltage variations may then lead to fluctuations in the water flow which results in torque and power oscillations and further voltage variations. If the gate position is used as feedback signal instead, the system will be more stable. However the relation between gate position and power output is non-linear and thus the feedback is slightly non-linear. In case of an electro-hydraulic turbine governor this may be easily compensated for and causes no problem [17]. Small isolated systems with low inertia tend to lead to higher frequency variations than for large interconnected system. In hydro power plants the water inertia is significant and implies an additional challenge when maintaining as stable frequency as possible. The frequency control with droop described above is insufficient for hydro turbines in island operation. The total inertia is small, the load steps are big in proportion to the generator rating and the mechanical system is slow due to


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long water starting time. This together with the non-minimum phase characteristic puts great demands on the frequency control. If a fast turbine governor is used this will lead to instability. To maintain stability the governor has to be slowed down in order to give time for the water to accelerate. This is achieved by means of transient droop compensation in the governor (Kundur 1994). There is a strong connection between frequency and voltage in an induction generator. This does not cause much problem when the generator is connected to a strong grid due to the fixed frequency. In isolated mode of operation on the other hand there is no fixed frequency, the generator sets both voltage and frequency by itself and the connection between voltage and frequency become obvious.

CONCLUSION

In contrast to conventional generators, self-excited induction generators are found to be most suitable machines for wind energy conversion in remote and windy areas due to many advantages over grid connected machines. However such machines exhibit poor performance in terms of voltage and frequency under frequent variations of operating speeds, which is a common feature in wind energy conversion. In this paper an attempt has been made to give an overview on the development of self-excited induction generator research and its importance with regard to distribution generation.

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