Grid integration issues and solutions

GRID CONNECTIVITY OF RENEWABLE

ENERGY SOURCES ISSUES & SOLUTION

Swathi venugopal

Semester; 8

Electrical & Electronics

RIT, Kottayam

Date; 22/02/13

More than 400 cities

50 million people globally

Major icons went dark

Seminar Series-4,

2013

GRID CONNECTIVITY OF RENEWABLE ENERGY SOURCES ISSUES & SOLUTION

Increasing oil

prizes

Exhaustible sourcesReleases

GH gases

Increasing co2

SO2+NOX+H2O+O2=ACID RAIN

NITROGEN OXIDE + VOC = SMOG

Global warming

Effect Of Combustion Of Fossil Fuels?

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Declining Fossil Fuel Supplies

Environmental Concerns

Increasing Cost of Fossil Fuels

Business Opportunities

Energy Security

Energy independence

Reasons for Renewable Energy in India why and why now??

“1 MW of wind plant in one year can displace 1500 tons of

CO2, 6.5 tons of SO2 and 3.2 tons of NOx. (REPP report,

Washington July 2003)”

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The vision of Indian renewable energy program

“To develop new and renewable energy technologies,

processes, materials, components, sub-systems,

products and services at par with international

specifications, standards and performance parameters

in order to make the country a net foreign exchange

earner in the sector and deploy such indigenously

developed and/or manufactured products and services

in furtherance of the national goal of energy

security”.

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Generating units

Transmission

network

Distribution

network

Consumers

Features And Structures Of Electrical

Power Systems

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Features And Structures Of Electrical

Power Systems

Electricity Demand (Inc. Losses) Is Varying ..

Minimum at night and increasing to a peak during working hours.

During working days and weekends/holidays

seasonal variations

.

Generators Must Be Scheduled To Match These

Variations Throughout The Year

To maintain an AC power system at its nominal

frequency , “Instantaneous Power Supplied = Demand .”

Done by control of generation regulation/ load following Controlled automatically or by a central electricity system operator

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Grid connectivity renewable energy issues and solutions .

Renewable Energy Generation

Characteristics

Grid Connectivity

REIssues And Solutions .

Comparison

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Most RE resources are location specific.

• Renewable-generated electricity may need to be

transported over considerable distances.

• Beneficial combinations of renewable sources may

not always be practicable.

CHALLENGES WITH INTEGRATING INTO

ELECTRICAL POWER SYSTEMS

Lack of flexibility

• Balancing supply and demand

• Uncertainty in predicted out-put.

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Transmission

GeneratorsTransmission Network

Distribution Network

Distribution Generators

Consumers

Transmission

Generators

DISTRIBUTED GENERATORS

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What is an efficient grid connection ?

Respect the power quality of the grid

Respect the grid protection plan

Allow control and clear monitoring

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Lack of standerds

1. Central Electricity Authority

2. Central Electricity Regulatory

Commission

3. State Electricity Regulatory

Commissions

.

Exist only for connecting

voltage levels of 33 kv &

above to the grid

“ Viable standards of grid connectivity to be framed ”

Voltage fluctuation and regulation

Extended under voltage causes “brownouts”

Extended overvoltage decreases the life of

equipment's.

DG systems are not only affected by voltage

fluctuations, but can cause voltage fluctuations

themselves

INTEGRATING INTO ELECTRICAL POWER

SYSTEMS ISSUES & SOLUTIONS

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1. Grid-derived voltage fluctuations

Inverters - ‘voltage-following’

• Avoid this happening, Low Voltage Ride-through Techniques

(LVRT) could be incorporated into inverter design

inject reactive power during voltage sags

Reduce network voltage by drawing reactive power during voltage

rise.

provide current that is out of phase with the grid voltage so provide

power factor correction.

Disconnect DG when the grid voltage moves outside set parameters.

Ensure suitable power quality

Antislanding.

Automatic disconnection will cause overloading of other generators

Inverters -‘voltage-regulating’ mode

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2. Voltage imbalance

Voltage imbalance is when the amplitude of each

phase voltage is different in a three-phase system or

the phase difference is not exactly 120°.

High RE penetrations, the cumulative size of all

systems connected to each phase should be as equal

as possible.

3. Power output fluctuation

Short-term fluctuations

Affect power quality

Continuous tap-changing and capacitor switching

increased number of switching surge

Long-term fluctuations

Require back-up generation to maintain power

supply.

Geographical dispersal

Forecasting

Storage

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4. Voltage rise and reverse power flow

Voltage

max

min

Substa

tion

Overhead line

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Ensuring PV systems are smaller than the daytime load,

Use dynamically controlled inverter (DCI) to gradually reduce PV

output

Use of a minimum import relay (MIR) to disconnect the RE system,

Use of a reverse power relay (RPR) to disconnect the system on

low voltage and reverse power flow

Decreasing the network’s series impedance , to reduce voltage

drop.

Requiring customer loads to operate at improved power factor

Requiring customers with large loads to incorporate some form of

load-shedding scheme,

The use of storage units

To minimize voltage rise and reverse power flow

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Power factor correction

Poor power factor -increases line losses & makes voltage

regulation more difficult.

voltage-following have unity power factor

voltage-regulating mode provide power factor correction.

Grid connectivity renewable energy issues and solutions .

Unintentional islanding

Occurs when DG delivers power to the

network even after circuit breakers have

disconnected from main grid.

grid inverter technology has developed to

include anti-islanding features as per local

regulations and standards

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Unbalanced supply-demand lead to frequency fluctuation

High penetration of intermittent energy make control more

difficult.

DG inverters can provide frequency control in milliseconds,

Only when they can inject power into the network

DG linked to thermal plant are restricted in their ability to

provide frequency regulation because of their thermal loads.

Inverters disconnect from the grid when the frequency moves

outside set limits (as a form of islanding detection),

Ability to provide frequency support may be compromised.

All DG will also disconnect, exacerbating the power imbalance

Leads to complete system shutdown

.“New frequency ride through systems that do not interfere with the anti-

islanding protection systems will need to be developed”

Frequency variation and regulation

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Harmonics

Transformers

• Overheating leads to insulation

failure

• Reverse power flow capability?

Switchgear

• Overheating leads to insulation

failure

Cables• Overheating leads to insulation

failure

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Harmonics

HARMONIC REDUCTION

voltage-source inverters can provide the harmonic

support but do so at an energy cost

There are a variety of harmonic compensators that are

likely to be cheaper.

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1. Very low penetration (typically 5-10% of connected load)

Can be tolerated without significant problems

2. Moderate level penetration (10-20% of connected load)

• Minimizing VAr flows, power factor correction, increased

voltage regulation and careful consideration of protection.

More significant issues arise .

More DG may be accommodated by making changes to

the network

3. High levels of penetration, (Network dependent)

Require significant overall design and communications

infrastructure changes – for coordinated protection and power flow

control.

Under research and development

Generalization

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No market

Utility culture & framework

Lack of expertise

Limited role for private sector

Capital costs vs. variable energy costs

Transmission access & strength of grid

What are the other key barriers ?

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Promote market development

Support utility RE procurement

Encourage private investment

Provide long-term contracts

Value RE attributes

Facilitate access to Electricity grid

Train RE designers and operators

What are the Strategies to overcome

barriers ?

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GUIDE LINES

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1. CONNECTION OF REPS TO THE GRID

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2. SAFETY CONSIDERATIONS

Incorporate an anti islanding function

Install a lockable switch at an easily accessible position –

manually isolate REPS from grid

Update circuit diagram regularly and display at

appropriate locations

Establish a direct communication channel between owner

and utility

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3. EQUIPMENT PROTECTION

Carry out assessments on the new fault levels due

to connection of REPS

Incorporate the following features

auto switching & auto reclosing

facility to isolate REPS from DS when fault occur

protection facilities against transient abnormalities in the grid

stable and fast responding voltage & frequency regulators

Protection facilities to avoid unsynchronized connections

4 pole CB to provide complete isolation from DS when REPS

is not in service.

Automatic reconnection facility after the fault is removed

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3. POWER QUALITY

inverter with power conditioning feature to control THD & PF

Isolation transformer on the output side of inverter to avoid the

injection of DC to DS

Fast responding frequency and voltage regulator.

Design REPS with three phase inverter or three

identical single phase inverter to supply current Which

is balanced over the three phases to the grid –

minimize voltage & current unbalance

Install the following features

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Policy implementation & enforcement

Renewable energy market promotion

Pricing of electricity

Cost sharing

What is the the need for government

involvement?

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Centralized power

YESTERDAY

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Price of non renewable energy source is increasing

day by day , where as the availability is reducing day

by day.

It is mandatory that we have to depend on renewable

energy sources

Centralized power Off grid power

plant

TODAY

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High initial capital costs

Electricity production is dependent on availability of

source

Electricity production may not match when household

requires .

Electricity requiring either batteries to store electricity

(especially if there is no grid connection and/or an

agreement with your electricity retailer to purchase

surplus electricity from you).

TOM0RROW

GRID TIED SYSTEM

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DECENTRALIZED GENERATION / FUTURE

INTEGRATION

Additional energy supply systems (esp using RE)

in the medium and low voltage level is highly visible

Configuration of an intelligent distributed electricity

system as the most important alteration.

In Europe it is called “decentralized generation”.

Aims at generating the energy where it is

required

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Should avoid interferences and overcharge in

circuits

storage facilities

Energy management

Accumulator systems.

capacitors

compressed-air stores

interactions between different electricity levels.

communication,

information, control, metering, services, planning,

optimization

forecast

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4

7

Central GeneratingStation

Step-Up Transformer

DistributionSubstation

ReceivingStation



Commercial

Industrial Commercial

Gas Turbine

DieselEngine

Cogeneration

Cogeneration

Turbine

Fuel cell

Micro-turbine

Wind Power

Residential

Storage

Photovoltaic systems

Control Center

Operators,

Planners & Engineers

2. Communications and Information Infrastructure


CONCLUSION

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Wind energy , tidal energy ,and solar PV are not dispatchable unlike NRE

Integrating this RE to power system is a difficult process Grid tied system is becoming a must New Technologies will need to be developed. Promote off – grid (mainly solar pv ) for sustainable

economyAdvantages of grid tied system is predominating over disadvantages

Save energy save environment

Integration of Renewable Energy into Present and Future Energy Systems-Ralph Sims (New Zealand), Pedro Mercado (Argentina), Wolfram Krewitt †(Germany)

Vergnet S.A. Integration Of A Wind Farm Into The Utility Grid

Eric ANDRIEU, Electric Al Design Département Manager Pierre

PESNEL,Export Manager

Grid integration of renewable energy sources GermanP. Kammer, A. Kober BTU Cottbus Cottbus, y

Renewable Energy Sources (RES) Grid Integration: Key Issues and Challenges Bharat Singh

REFERENCE

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Addressing Grid-interconnection Issues With Variable Renewable Energy Sources Summary Document Report for Asia Pacific Economic Cooperation (APEC)

Renewable Energy Technologies Solutions Grid Connected Systems IRENA Workshop

Grid connection of Renewable Energy CHALMERS ENERGY CONFERENCE 2012 Peter Konings – SEIAPI / APEG

Renewable Energy in India: Progress, Vision and StrategyMinistry of New and Renewable Energy Government of India

Fractional Order Modeling & Control Strategies for Grid-Connected Renewable Energy SourcesMajor Professor : Dr. Chen

Renewable Energy Grid Connection Dave Fleming

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2013


Engineering

Grid integration issues and solutions