Protection Of Generators[1]

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PROTECTION OF GENERATORS

Project report submitted in partial fulfillment of the requirements of the award of the degree of

BACHELOR OF TECHNOLOGY I N

ELECTRICAL AND ELECTRONICS ENGINEERING

By V.Vikrant Reddy P.SeshaNaveen

03881A0258 03C11A0243

Pavan Manilal Savla N.Satish Pavan Kumar 03881A0223 03881A0236

Under the guidance of Prof. K.V.R. Prasad Head of the Department

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

ADAMS COLLEGE OF ENGINEERING PALONCHA

J.N.T. UNIVERSITY, HYDERABAD

Adams College of Engg.

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2006-2007

ANDHRA PRADESH POWER GENERATION CORPORATION LTD.

C E R T I F I C A T E This is to certify that the project report entitled “GENERATOR

PROTECTION” is a bonafide report of strenuous work carried out by V.Vikrant Reddy,

P.SeshaNaveen, Pavan Manilal Savla and N.Satish Pavan Kumar under the guidance of

Mr.K.Sreenivasulu, ADE/MRT/KTPS - Vth Stage, Mr.M.V.Suryanarayana,

AE/MRT/KTPS - Vth Stage and Mr.K.Vasu, AE/MRT/KTPS - Vth Stage, Paloncha

during the period 15.02.2007 to 03-03-007, in partial fulfillment of the requirements for the

award of the degree of Bachelor of Technology in Electrical and Electronics engineering.

Mr.SURYANARAYANA, T.S.N.MURTHY, A.E., D.E., (MRT) (EM& MRT) KTPS V-Stage, Paloncha. KTPS V-Stage, Paloncha.


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DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

ADAM’S ENGINEERING COLLEGE PALONCHA

C E R T I F I C A T E

This is to certify that the project entitled “GENERATOR

PROTECTION” is bonafide work done by V.Vikrant Reddy (03881A0258),

P.SeshaNaveen (03C11A0243), Pavan Manilal Savla (03881A0223) and N.Satish

Pavan Kumar (03881A0236) in partial fulfillment of the requirement for the award of

the degree of Bachelor of Technology in Electrical and Electronics Engineering,

J.N.T.University, Hyderabad during the year 2006-07.

Prof. K.V.R.Prasad Head of the Department, External Examiner EEE Dept.


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ACKNOWLEDGEMENTS

The development of this project through it was an arduous task, has been successfully completed. We are pleased to express our thanks to these people, whose suggestions, comments and critics greatly encouraged us in the betterment of this project. First of all, we thank the Mr.C.RADHAKRISHNA, CE/O&M/KTPS Vth-Stage, for giving us the opportunity to carry our project work. We also thank Mr.T.S.N.Murthy, DE/EM&MRT/KTPS Vth-Stage and Mr.K.Sreenivasulu, ADE/MRT/KTPS V-Stage, who helped us for the completion of this project work. We are grateful to Mr.M.V.Suryanarayana, AE/MRT who guided us in every aspect of the project and provided valuable material with out their motivation and inspiration. It would be impossible for us to complete this project. They helped us a lot to understand the theoretical concepts of our subjects through practical point of view. We also thank our Head of the Department Prof. K.V.R.Prasad for giving us permission to do this project work and also acted as our internal guide for giving us valuable suggestions and proper guidance in the preparation of this work. We take opportunity to thank our Principal Prof.P.Nageshwar Rao for permitting to carry out this project in college.

Finally we thank all the people who helped us complete this project

successfully.

Projectees:

V.Vikrant Reddy P.SeshaNaveen

Pavan Manilal Savla N.Satish Pavan Kumar


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Content

Chapter No. Title Page No 1 Introduction 5 1.1 Need for electric power 6 1.2 Role of thermal plants 8 1.3 About APGENCO 12 1.4 About KTPS V stage 14 1.5 Plant overall Layout 17 2 Power Generation in KTPS V stage 20 2.1 AC Generators 21 2.2 Excitaion Systems 23 2.2.1 General Structure 24 2.2.2 Types of Excitation 25 2.2.3 Excitation in KTPS V stage 26 2.3 Automatic Voltage Regulator 28 2.4 Electrical Layout 29

3 Major Electrical components in Power Systems 30

3.1 Circuit Breakers 31 3.2 Relays 33 3.3 Instrument Transformers 35 3.4 Surge Arrestors 37 3.5 Isolators 37

3.6 Carrier Communication using Coupling Capacitor 38

4 Protection of Alternators 39 4.1 Need for protection 40 4.2 Generator faults and their effects 41 4.3 Essential Qualities of protection 43

4.4 Protection used in HT, LT and 220KV

system 44 4.5 Protection of 250MW Turbo Alternator 51 4.5.1 Nomenclature of relays 54 5 Case Study 78 6 Conclusion 83 7 Bibliography 86


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INTRODUCTION


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1.1 Need for Electric Power Both the historical and the present-day civilization of mankind are closely

interwoven with energy, and there is no reason to doubt but that in the future our

existence will be more and more dependant upon the energy. Electrical energy

occupies the top position in the energy hierarchy. It finds innumerable uses in home,

industry, agriculture and even in transport. Besides its use for domestic, commercial

and industrial purposes it is required for increasing defense and agricultural production.

In agriculture, it is used for pumping water for irrigation and for improving the

methods of production and numerous other operations. Electrical energy is a

convenient form of energy because in can be generated centrally in bulk and

transmitted economically over long distances and is almost pollution free at the

consumer level. Further, it can be adopted conveniently in the domestic, industrial and

agricultural fields. The process of modernization, increase in productivity in industry

and agriculture and improvement in the quality of life of the people depend so much

upon the supply of electrical energy an that the annual per capita consumption of

electrical energy has emerged these days as an accepted yardstick to measure the

prosperity of the nation. Some of the advanced and developed nations of North

America and Europe have a very high annual per capita consumption of electrical

energy; say from 8 to 13 thousand kWh, while in most of Africa, Asia and Latin

America it is too low to be considered. India had an annual per capita consumption of

electrical energy of 15.5 kWh in 1950, 105 kWh in 1975, 131 kWh in 1979, 154 kWh

in 1984, 299 kWh in 1993, 349 kWh in 1997, The annual per capita consumption of

Japan 8,000 kWh, UK 7,200 kWh and USSR 6,000 kWh. The United States has only

6% of world population but accounts for over 30% of electrical consumption of the

world.

The industrial growth of a nation requires increased consumption of energy,

particularly electrical energy. This has led to increase in the generation and


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transmission facilities to meet the increased demand. In U.S.A., till the early seventies,

the demand develops every ten years. In developing countries, like

India, the demand doubles every seven years which requires considerable

investment in electrical power sector.

SUPERIORITY OF ELECTRICAL ENERGY

Electrical energy is considered superior to all other forms (chemical, heat,

light, sound or mechanical) of energy due to the following reasons:-

(i) Cheapness. It is much cheaper than other forms and therefore,

it is economical to use energy in this form for domestic,

commercial, industrial and agricultural purposes.

(ii) Convenient and Efficient Transmission. The Electrical energy

can be transmitted conveniently and efficiently from the

gathering stations, usually located quite away from the

centers of usage, through conductors of suitable size.

(iii) Easy Control. Electrically operated machines have simple and

convenient starting, control and operation. For example, an

electrical motor can be started or stopped by making the

switch on or off and its speed can be conveniently controlled

over a wide range with simple arrangements.

(iv) Cleanliness. Use of electricity (electric drive or electric

heating) does not produce smoke, fumes, dust or poisonous

gases and therefore, its use ensures cleanliness and pollution

free conditions.


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(v) Greater Flexibility. Electrical energy offers greater flexibility

as it can be taken to any corner of the house, factory, street,

hospital, farm, mine etc. through solid, stranded or flexible

conductors.

(vi) Versatile form. Electrical energy is a very convenient form of

energy and it can be easily converted into other forms of

energy—heat, light, mechanical, sound or chemical. For

example electric lamps, especially fluorescent give rise to

pleasant and cheaper light as compared to that produced by

lamps of

Other types and can be located at any desired place where

other lamps cannot be placed due to the danger of the fire or

due to other reasons.

Though at present about three-fourths of the total energy is still used

in non-electrical form (transport, residential heating and industrial heating

and industrial heating use energy mostly in non-electrical form) but because

of numerous advantages, mentioned above, electricity will account for a

greater and greater portion of total energy consumption in the coming years.

It is expected that the electricity demand will continue to go up for more

years to come, even in developed countries.

1.2 Role of Thermal Power Plants in meeting High Load

Demands The fact that the thermal energy is the major source of

power generation itself shows the importance of thermal power generation in India-more

than 70% of electric power is produced by the steam plants in India. This position is

likely to continue due to large pit head plants being setup. Larger sizes of units due to


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overall increase in the demand for power and because of necessity of keeping down the

cost of power generation with increasing fuel prices are the developing trends in large

steam power plants.

USES: The thermal power station can be used as

1. private industrial plant

2. central stations

The use of steam station for privative industrial plants is purely a question of economics.

There are some industries which require steam at lower pressure for process purpose.

Trends: The next era in thermal power generation in India started with commissioning in

1952-53 of 50MW units at Bokaro. The overall thermal efficiency of this unit was 28%

the fact that thermal energy is the major source of power generation itself shows the

importance of thermal power generation in this country. Larger sizes of units due to

overall include in demand for power and because of the necessity of keeping down the

cost of power with increase in fuel process are the Diesel opening trends in large thermal

power station.

STEAM POWER PLANT With the invention of steam engine for obtaining mechanical energy the

so called non conventional methods i.e. wind, tidal, geothermal etc. were abandoned as

the cost involved was high and also there was no flexibility for transportation of this form

of energy. The development of steam turbines and then electric generator completely

replaced the non conventional methods. Fossil fuels became the main source of energy

for quite sometime. The size of the thermal plants grew from a few KW to more than

1000 MW as of today. The concept of generating electrical energy using fossil fuel has


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changed completely the concept of location the power plants near the load centers to

location near the fuel pithead. Super thermal power plants have come into existence. It

has been found more economical in general to generate electrical energy near the pithead

rather than near the load centers even though the energy has to be transported over the

transmission lines, which involves a large percentage of total capital cost and

transmission line losses. On the other hand by installing a plant near pithead saves the

cost of transporting the coal etc. a 400MW capacity plant requires about 5000 to

6000tons of coal every day.


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Thermal plants are major source of power generation

Thermal capacity in India : 80777.45 MW

Thermal capacity in AP : 7058.71 MW


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1.3 About AP GENCO: As a consequence of AP Electricity Reforms ACT enacted by Government of

A.P the erstwhile APSEB (Andhra Pradesh state electricity board) is unbundled in to

APGENCO, APTRANSCO and DISCOMS. APGENCO is entitled to Acquire, Establish,

Construct and Operate Power generating stations.

Andhra Pradesh Power Generation Corporation limited is the power

generating company of Andhra Pradesh. Its installed capacity is 6550.9MW. It is the third

largest power utility in India. It has also achieved highest PLF of 94.5% in the country (in

year 2004-05).

Vision:

To be the best power utility in the country and one of the best in the world.

Mission:

• To generate adequate and reliable power most economically, efficiently and eco-

friendly.

• To spearhead accelerated power development by planning and implementing new

power projects.

• To implement Renovation and Modernization of all existing units and enhance

their performance.

Landmarks and Achievements:

• Unit 3 (210 MW) of Vijayawada Thermal Power Station has established a

National Record of continuous service for 441 days from 14.12.2004 to

28.02.2006

• First in the southern region to commission fully underground power house,

Srisailam left bank HES.


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Types of power plants APGENCO operates :

Source Installed Capacity (MW)

Thermal 2962.5

Hydel 3586.40

Wind 2.00

The top three PLF's achieved by their thermal plants:

KTPS V : 94.5%

RTPP : 91.2%

RTS : 90.6%

The Hon’ble President of India and Hon’ble Union Minister for Power have awarded

gold shields and certificates to RTPP, VTPS and KTPS-V.

1.4 About KTPS V stage: Kothagudem Thermal Power Station, K.T.P.S., a place of pride in the

thermal map of India. It was the first major thermal power station to set up in Andhra

Pradesh State Electricity Board.

TOTAL INSTALLED CAPACITY:

KTPS-A Station : 4*60 = 240 MW

KTPS-B Station : 2*110 = 220 MW

KTPS-C Station : 2*110 = 220 MW


http://www.apgenco.com/inner.asp?frm=viewcontents&filename=HomePgCategory.xml&Tagname=HP_Cat206&subhname=NewsandEvents


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KTPS-V Station : 2*250 = 500 MW

Total installed capacity = 1180 MW

DATE OF COMMISIONING:

KTPS-V Station was commissioned in 1996.

KTPS-V Stage is the one, which is highly technical and have more advantages. Units

9&10 of KTPS-V stage were successfully completed and commissioned in a record of 31

& 28 months after commencement of work. Since when the station has started its

working it was running successfully with out any problem.

Objectives One of the important objectives of K.T.P.S. is to generate thermal power

efficiently and economically. It is also fulfilling the role of social responsibility objective

by encouraging local small-scale industries, providing employment to the people of the

backward and tribal areas. It has crores of rupees controlling pollution by installing

Electrostatic Precipitators.

Locations: The actual site of the station is near Paloncha town, which is about 12 KM from

collieries town Kothagudem. The site of power station is only about 3 Km from the main

Bhadrachalam road. The project authorities to connect the main road with the power

station have constructed feeder road.

Rail head:


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K.T.P.S., is located about 12 KM from the near rail head at Bhadrachalam road

Railway station, which is the terminus for the broad gauge branch line taking off from

Dornakal on the south central railway.

Extent of Land: In site of the power station and its apartment structures as well as the

administration buildings and residential colonies are located.

Ash Pond: The site of the power station has a low laying area to the south of it, where Ash

Pond is formed. The crushed ash dust is hydraulically disposed off in the ash pond.

GENERATOR:

Generator is an electrical synchronous alternator in which the mechanical energy

conveyed by the turbine will be converted into electrical energy. Generator is of 2 pole 3-

ф, Y- connected, lap wound machine of M/s BHEL make. Electrical power will be

generated in the generator at 16.5 KV and will be stepped up to 220 KV through 16.5/220

KV 290 MVA transformer and then connected to the grid through 220 KV SF6 circuit

breaker.

Primary Fuel Supply: KTPS Complex is linked to Singareni Collieries Company limited.

(S.C.C.L.) for supply of coal from Manuguru, Yellandu and Rudrampur mines.

The advantages distance of S.C.C.L. coalmines by rail around 50 KM.

Annual coal requirements are about Lakh tones. Annual coal bill works out to about

RS.700 crores.


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WATER SOURCE: Water requirement for the KTPS complex are provided from Kinnersani

Project. Water is one of the basic raw materials in the production of power in a thermal

power station. It is essential that the supply of water should be available at all times with

complete reliability. The total water requirements for the station 1, 50,000 Tones per day.

The water supply for the power station is drawn from the reservoir built across

Kinnersani River at a distance of 10 KM from the power station is through open concrete

lined channel and the flow is by gravity. The carrying of channel is 110 cases (4 cubic

meters second). The Kinnersani is one of the principal tributaries at the mighty rivers

Godavari flowing on its right side of Warangal and Khammam Districts at A.P.

Kinnerasani Dam was constructed at a cost of RS.5.6 crores and maintained by Irrigation

department up to march 1998. Project was taken over by APSEB/APGENCO on

01.04.1998.Reservoir level is 407 ft.

AWARDS:

Year Shield

1998-99 Silver

1999-00 Gold

2000-01 Gold

2001-02 Gold

YEAR ALL INDIA RANK MU PLF

2002-03 3 4080 93.16

2003-04 2 4040 91.95

2004-05 1 4140 94.53

2005-06 - 3482 79.50

KTPS-V Stage Power Plant has been awarded the ISO 9001:2000 certificate



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1.5 Plant overall view

Although steam power station simply involves the conversation of heat of coal

combustion into electrical energy, yet it embraces many arrangements for the proper

working and efficiency. The schematic arrangement of a modern power station is shown

in figure. The whole arrangement can be divided into the following stages for the sake of

simplicity:

1. Coal and ash handling arrangements

2. Steam generating plant

3. Steam turbine

4. Alternator

5. Feed water

6. Cooling arrangement.


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POWER GENERATION AND

EXCITAION IN KTPS STAGE-V


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2.1 A.C GENERATORS An A.C generator also known as synchronous generator or

alternator, as it is driven at constant speed for it to produce a constant frequency

essential for the power system to be stable works on the principle of Faraday’s law of

dynamically induced emf.

The two pole generator uses direct hydrogen cooling for the rotor

winding and indirect hydrogen cooling for the stator winding. The losses in the

remaining generator components, such as Iron losses, Friction and windage losses and

stray losses are also dissipated through hydrogen.

The generator frame is pressure-resistant and gastight and equipped with

end shields at each end. The hydrogen coolers are arranged horizontally inside the

stator frames.

The generator consists of the following components:

• STATOR Stator frame

Stator core

Stator winding

Hydrogen coolers

• ROTOR Rotor shaft

Rotor winding

Rotor retaining rings

Field connections

• BEARINGS

• SHAFT SEALS The following additional auxiliaries are required for generator operation

• Oil System

• Gas System

• Excitation System


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Principle: The A.C. generator or alternator is based upon the principle of the Electromagnetic

Induction. The stator housed the armature windings. The rotor houses the field

windings; DC voltage is applied to the field windings. When the rotor is rotated, the

lines of the magnetic flux cut through the stator windings. The magnitude of EMF is

given by the following expression.

E=4.44 Ǿ f T volts

Classification of Alternators The A.C generators are of two types,

1) Rotating armature type alternator

2) Revolving field type alternator

a) Salient pole type field structure

b) Smooth cylindrical or Non-salient Pole Type Field Structure

Rotating armature type This type of alternator looks very much like a D.C generator except that

instead of a commutator it consists of 3- slip rings in place of commutator. In such

generators the required magnetic field is produced by DC electromagnets placed on the

stationary member called stator, and the current generated is collected by means of

brushes and slip-rings on the revolving member, called the rotor. Such arrangement is

economical for small low voltage generators. They are built only in small ratings up to

about 200 or 250 Kva because the voltage generated is comparatively low and current

to be collected by the brushes small, no difficulty being experienced in collecting such

a current.

Revolving field type alternator

Practically all medium and large machines are always constructed with

revolving field. The advantages of stationary armature and revolving field system are:


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1. It is easier to insulate stationary armature winding for very high voltage e.g. as

high as 33,000 volts because insulation of stationary armature is not subjected to

mechanical stresses due to centrifugal action and more space is available on the

stator for providing more insulation as the stator is outside the rotor.

2. The load current can be connected directly with the fixed terminals of the stator

without passing through slip-rings and brushes.

3. The armature winding can be more easily braced in a rigid frame to prevent any

deformation which could be developed by the mechanical stresses set up due to

short-circuit currents and the high centrifugal forces brought into play.

4. The armature winding is cooled more readily because the stator core can be made

large enough with many air passages or cooling ducts for forced air circulation.

5. Only two slip rings are required for the supply of the direct current to the rotor

and since the exciting current is to be supplied at low voltage of 125 or 250v there

is no difficulty in insulating them.

6. Since the exciting current is relatively small, therefore, the slip rings and the

brush gear need to be only of light construction.

7. Due to simple, light and robust construction of the rotor higher speed of rotating

DC field is possible. This results in increased output.

2.2 Excitation Systems: The excitation system comprises of an exciter and automatic voltage regulator.

The duty of an exciter is to provide the necessary field current to the rotor winding of

the alternator. Fundamentally simplest excitation system consists of an exciter only.

When the excitation system has also the task of maintaining the terminal voltage of the

alternator constant under varying load conditions, it incorporates voltage regulator.

The D.C excitation needed for the alternator may be supplied from D.C source

or from A.C. source after rectification. There are two schemes for supplying the

excitation. One is the common excitation bus scheme while the other is unit exciter

scheme. Each alternator is fed from its own exciter in unit exciter scheme, while in


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common excitation bus scheme two or more exciters feed a bus bar to which field

systems of all alternators are connected.

The simplest excitation system consists of a shunt wound D.C machine as

exciter. For large alternator, the main exciter is a separately excited D.C machine

supplied by the pilot exciter. As the rating of the alternator continues to increase, it is

getting difficult to supply excitation for the large alternators by D.C exciters due to

commutating troubles and also a large number of brushes are required on the

commentator because of high excitation current at comparatively low voltages. These

difficulties have been overcome with the use of modern excitation schemes namely

STATIC EXCITATION SYSTEM and BRUSHLESS EXCITATION SYSTEM which are finding

more and more use in the present day excitation schemes.

2.2.1 General Structure of Excitation System: We shall now present the physical components used for

excitation system. To give an insight of excitation system, a general structure of

excitation system in the form of block diagram is depicted in FIG…


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The various components present in the general configuration are:

1) Synchronous Generator: Synchronous generator is a machine which generates

a.c. three phase powers. It may be a turbo alternator run by steam turbine at a very

high speed or be a low speed a.c. generator run by water-turbine. The terminal

voltage of the generator is maintained constant during is varying load conditions

with the help of excitation system.

2) Exciter: the purpose of the exciter is to supply field current tot the rotor field of

the synchronous generator. It may be a a.c generator driven by either the steam

turbine or an induction motor. But in the modern systems of excitation, the

exciters are solid state systems consisti9ng of some form of rectifier or thyristor

system from the a.c bus or from an alternator-exciter

3) Voltage Regulator: voltage regulator working in conjunction with the exciter

tries to maintain terminal voltage of alternator constant. In several aspects the

voltage regulator is the heart of the excitation system. Voltage regulators are

generally classified into three categories, namely, rheostat type regulator, non

continuously acting regulator and cautiously acting regulator. In fact voltage

regulator couples the output variables of the synchronous generator to the input of

the exciter through feed back and forwarding elements for the purpose of

regulating the synchronous machine output variables. Thus the regulator may be

assumed to consist of an error detector preamplifier, power amplifier, stabilizers,

compensators, auxiliary inputs and limiters. However all these components may

not be present for each type of regulator. It should be noted that exciter and

regulator constitutes excitation system. Exciter, regulator and synchronous

generator constitute a system known as Excitation control system.

2.2.2 TYPES OF EXCITATION SYSTEMS The excitation systems can be broadly classified into following types.

1. D.C excitation system

2. A.C excitation system

3. Static excitation system


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In D.C excitation system, there are various configurations of rotating exciters. For

example we may have:

a. Self excited exciter with direct acting rheostatic type voltage regulator.

b. Main and pilot exciters with indirect acting rheostatic type voltage regulator.

c. Man exciter, amplidynes and static voltage regulator.

d. Main exciter, magnetic amplifier and static voltage regulator.

The main drawbacks of D.C excitation system are large time constan6ts and

commutation difficulties. In view of this D.C excitation system have been superseded

by a.c excitation system and static systems.

An A.C excitation system consists of an a.c generator and thyristor rectifier bridge

directly connected to the alternator shaft. The advantage of this method of excitation is

that the moving contacts such as slip rings and brushes are completely eliminated thus

offering smooth and maintenance free operation. Such a system is known as brushless

excitation system.

A static excitation system draws the excitation power from the alternator

terminals through step down transformer and a rectifier system using mercury arc

rectifiers of silicon controlled rectifiers.

2.2.3 Excitation system used in KTPS V stage

Brushless excitation system The problem of feeding excitation current from static to the rotating

field of the main alternator persists even in the static excitation system. It means that

constant maintenance of the carbon brushes to feed field current still exists. The

brushless excitation system eliminates the use of commutator, slip rings and brushes

.Such a system is shown in fig by a simplified diagram. The portion enclosed by dashed

lines is the rotating portion of the system. The complete structure of this excitation

system is depicted in the figure.

In this system an alternator exciter with rotating armature and

stationary field is employed as the main exciter. It incorporates a pilot permanent

magnet generator with a permanent magnet field to supply the (stationary) field for


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the (rotating) alternator-exciter. Direct voltages for the generator excitation is obtained

by

rectification through a three-phase full wave rectifier bridge ,which is mounted in the

hollow shaft of the generator .thus the permanent magnet field of permanent magnet

generator, the armature of the main exciter ,the rectifier bridge and the generator field

are rigidly connected on the generator shaft. These elements are labeled “rotating

elements”, in the diagram. Note, however, that since these components are all moving

with the rotor and no slip rings or thyristor type. Draw back of rotating Diode Bridge is

the presence of considerable exciter time constant which affects the rate of change of

voltage.

The voltage regulator measures the out-put or the terminal voltage, compares it a

set of reference and utilizes the error signal, if any, to control the gate pulses of the

thyristor Network .Thus the regulator controls excitation by supplying a buck-boost

control signals which ads algebraically to the base setting. The base excitation is

controlled by an input setting to the thyristor gating circuits. For base excitation, the

control signal is derived from the permanent magnet generator.


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2.4 Automatic Voltage Regulator:


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2.5 Electrical layout:


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MAJOR ELECTRICAL COMPONENTS

IN THE POWER SYSTEM


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3.1 Circuit breakers:

A circuit breaker is a piece of equipment which can

• Make or break a circuit either manually or by remote control under normal

conditions.

• Break a circuit automatically under fault conditions.

• Make a circuit either manually or by remote control under fault conditions.

Operating Principle: A circuit breaker essentially consists of fixed and moving contacts, called

electrodes. Under normal conditions, these contacts remain closed and will not open

automatically until and unless the system becomes faulty. When a fault occurs on any

part of the system, the trip coils of the circuit breaker get energized and the moving

contacts are pulled apart by some mechanisms thus opening the circuit.

When the contacts of a circuit

breaker are separated under fault conditions, an arc is struck between them. The current

is thus able to continue until the discharge ceases. The production of arc not only delays

the current interruption process but it also generates enormous heat which may cause

damage to the system or to the circuit breaker itself. Therefore, the main problem in a

circuit breaker is to extinguish the arc within the shortest possible time so that heat

generated by it may not reach a dangerous value.

Based upon the medium used for arc extinction, the circuit breakers are classified as:

1. Oil Circuit Breakers : The Oil Circuit Breakers employs some insulating oil (e.g.

Transformer oil) for arc extinction. Based upon the quantity of oil used in the circuit

breaker these are classified as:


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a. Bulk Oil Circuit Breaker which uses a large quantity of oil so as the oil

has to serve two purposes. Firstly it extinguishes the arc during opening

of contacts and secondly, it insulates the current conducting parts from

one another and from the earthed tank.

b. Low Oil Circuit Breaker which uses minimum amount of oil. In such

circuit breakers oil is used only for arc extinction, the current conducting

parts are insulated by air or porcelain or organic insulating material.

2. Air – blast Circuit Breakers : The Air-blast Circuit Breakers employs high pressure air-blast for

arc extinction. The contacts are opened in a flow of air-blast established by the

opening of blast valve. The air-blast cools the arc and sweeps away the arcing

products to the atmosphere. Depending upon the direction of air-blast in relation to

the arc, air-blast circuit breakers are classified as:

a. Axial-blast type in which the air-blast is directed along the arc path.

b. Cross-blast type in which the air-blast is directed at right angles to the arc path.

c. Radial-blast type in which the air-blast is directed radially.

3. Sulphur Hexafluoride (SF6) Circuit Breaker : In SF6 Circuit Breakers sulphur hexafluoride gas is used

for arc extinction. The Sulphur Hexafluoride is an electro negative gas and has a

strong tendency to absorb free electrons. The contacts of the breaker are opened in a

high pressure flow of SF6 gas and an arc is struck between them. The conducting

free electrons in the arc are rapidly captured by the gas to form relatively immobile

negative ions. This loss of conducting electrons in the arc quickly builds up enough

insulation strength to extinguish the arc. The SF6 circuit breakers have been found to

be very effective for high power and high voltage service.


33

4. Vacuum Circuit Breakers : In Vacuum Circuit Breakers vacuum (degree of vacuum being in

the range from 10-7 to 10-5 torr) is used as the arc quenching medium. Since

vacuum offers the highest insulating strength; it has far superior arc quenching

properties than any other medium. When contacts of a breaker are opened in vacuum,

the interruption occurs at first current zero with dielectric strength between the

contacts building up at a rate thousands of times higher than that obtained with other

circuit breakers.

To operate the correct circuit breakers so as to disconnect only the faulty

equipment from the system as quickly as possible we need relays.

3.2 Relays : A relay is an automatic device which senses an abnormal condition in an electric

circuit and closes its contacts. These contacts in turn close the circuit breaker trip coil

circuit, thereby it opens the circuit breaker and the faulty part of the electric circuit is

disconnected from the rest of the healthy circuit.

Characteristics of a protective relay: A protective relay is required to satisfy four basic functional characteristics:

1) Reliability: The relay should be reliable is a basic requirement. It must operate

when it is required. There are various components which go into operation before

a relay operates. Therefore, every component and circuit which is involved in the

operation of the relay plays an important role.


34

2) Selectivity: It is the basic requirement of the relay in which it should be

possible to select which part of the system is faulty and which is not and should

isolate the faulty part of the system from the healthy one. Selectivity is achieved

in two ways: (i) Unit system of protection and (ii) non-unit system of protection.

3) Speed: A protective relay must operate at the required speed. It should neither

be too slow which may result in damage to the equipment, nor should it be too

fast which may result in undesired operation during transient faults.

4) Sensitivity: A relay should be sufficiently sensitive so that it should operate

reliably when required under the actual conditions in the system which produces

the least tendency for operation. It is normally expressed in terms of minimum

volt-amperes required for the relay operation.

Types and Operating Principle: Depending upon the operating principle the relays are classified as follows:

1. Electromagnetic Attraction Relays: This type of relays operated based on the electromagnetic attraction

principle. In this type of relays the operation is obtained by virtue of an armature being

attracted to the poles of an electromagnet or a plunger being drawn into a solenoid.

These relays can be operated by both D.C. as well as A.C. Quantities.

2. Electromagnetic Induction Relays: This type of relays operated based on the electromagnetic induction principle.

Therefore, these relays can be used only on a.c. circuits and not on D.C. circuits.


35

3.3 Instrument Transformers : In a.c power systems, large currents, to transmit at very high voltages is a

usual practice. It is a difficult and not economic to design meters to measure such large

currents and voltages directly. To solve this problem, a special type of transformer came

to support ordinary meters, which are useful in measuring large currents and voltages.

Such special transformers are Instrument Transformers. The Instrument Transformers are

used in a.c systems for the measurement of current, voltage, power and energy.

Instrument Transformers are categorized as:

1. Current transformers or simply C.T

2. Potential transformers or voltage transformers or simply P.T

The current transformers steps down currents to the range of ordinary ammeter, while the

Potential transformer steps down voltages to the range of ordinary voltmeters .In other

words, the Instrument Transformers extend the range of ordinary meters.

CURRENT TRANSFORMER (CT) These transformers are used with low range ammeters to measure currents

in high voltage alternating current where it is impractical to connect instruments and

meters directly to the lines. So series transformer is a better substitute to the shunt for

increasing the range of the ammeter. They step down the current from the high voltage

line to a low value. The current transformer has a primary coil of one or a few turns of

thick wire connected in series with a line whose current is to be measured. The secondary

consists of a large no. of turns of fine wire and is connected across the standard 5A or 1A

ammeter.

ERRORS IN CURRENT TRANSFORMER There are two types of errors in a current transformer (CT).They are

the ratio-error and the phase angle error. The ratio error comes from the deviation of the

turn’s ratio from the current ratio. The cause for this error is the exciting current. The


36

current ratio is not constant, as it depends on the load current and its power factor and

hence a considerable error is introduced.

The ratio error is defined as:

Percentage ratio error = (nominal ratio-actual ratio) * 100

Actual ratio

POTENTIAL TRANSFORMER (PT) The theory of a potential transformer is essentially the same as that of

a power transformer .The main point of difference is that the power loading of a P.T is

very small and consequently the exciting current is of the same order as the secondary

winding current while in a power transformer the exciting current is very small fraction

of secondary winding load current.

DIFFERENCES BETWEEN C.T & P.T 1. The P.T may be considered as ‘parallel’ transformer with its secondary winding

operating nearly under open circuit conditions whereas the current transformer

may be thought as a ‘series transformer under virtual short circuit conditions.

Thus the secondary winding of a P.T can be open-circuited without any damage

being caused to the operator or to the transformer.

2. The primary winding current in a C.T is independent of the secondary winding

circuit conditions while the primary winding current in a P.T certainly depends

upon the secondary circuit burden.

3. In a potential transformer, full line voltage is impressed upon its terminals

whereas a C.T carries the full line current.

4. Under normal operation the line voltage is nearly constant and ,therefore the flux

density and hence the exciting current of a potential transformer varies only over

a restricted range whereas the primary winding current and excitation of a C.T

vary over wide limits in normal operation.


37

3.4 Surge Arresters (Lightning Arresters)

Surge Arresters are usually connected between phase and ground in

distribution system; near the terminals of large medium voltage rotating machines

and in HV, EHV, HVDC sub-stations to protect the apparatus insulation from lightning

surges and switching surges.

The resistor blocks in the surge arrester offer low resistance to

high voltage surge and divert the high voltage surge to the ground. Thereby insulation

of protected installation is not subjected to the full surge voltage. The surge arrester

does not create short-circuit like rod gaps and retains the residual voltage across its

terminals.

Surge arrester discharges current impulse surge to earth and dissipates energy

in the form of heat. After discharging the impulse wave to the earth, the resistor blocks

in the surge arrester offers a very high resistance to the normal power frequency voltage

and the arrester acts as open circuit. Surge arrester provides protection against surge

voltage waves.

At present the following types of surge arrester are used:

1. Gapped silicon-carbide Surge arresters

2. Zinc-oxide Gapless Arresters

3.5 Isolators : Isolator (disconnecting switch) operates under no load condition. It does not have

any specified current breaking capacity or current making capacity. Isolator is not even

used for breaking load currents.

Circuit breaker can make and break electric circuit under normal current or short

circuit conditions. Isolators are used in addition to circuit breakers and are provided on

each side of every circuit breaker to provide isolation and enable maintenance.

While opening a circuit, the circuit breaker is opened first, then isolate. While

closing a circuit, the isolator is closed first, then circuit breaker. Isolators are necessary


38

on supply side of circuit breakers in order to ensure isolation of the circuit breaker from

live parts for the purpose of maintenance.

3.6 Carrier Communication using Coupling Capacitor: The term power line carrier is used to represent the

entire process of communication which uses high voltage overhead power lines as the

means of transmission. The power lines offer the following advantages.

i. Lines have thicker cross section of wire and hence attenuation of signals is

not much.

ii. Leakage is negligible even under wet weather conditions as lines are

insulated with high voltage insulators.

iii. Lines are disrupted during foul weather conditions as conductors are strung

on very robust tower structures.

iv. As the phases are separated from each other quite appreciably, cross-talks

between lines is practically avoided.

v. The cost of providing extra lines for the purpose is avoided.

However there are certain difficulties associated with the transmission of

communication signal over the power lines:

i. Since the power is being transmitted at relatively high voltages, the

operation on these lines may prove to be dangerous to human lives and

also to telephone apparatus.

ii. During transient operation of system e.g., switching transients, surge

voltages or corona phenomenon etc. the presence of higher harmonics in

power currents may interfere with the communication signal.


39

These difficulties of course, have been overcome by selecting suitable coupling

capacitor and carrier frequencies. The power line carrier communication finds application

in telemeter, power line protection, tele control etc.

The power lines may have higher harmonics due to switching surges and corona

loss on overhead lines. These frequencies generally lie between 100 Hz to 50 Hz and,

therefore, if carrier frequencies are chosen in this region, noise introduced in carrier

signal would be very large and hence carrier frequency in the range 30 kHz to 500 kHz is

used. In order that these carrier signals do not interfere into the adjoining section of lines

and also that these carrier signals are not lost by being shorted by low impedance of

transformer or generator at the end of the line, line traps are used which offer very high

impedance to carrier frequency and low impedance to power frequency. Similarly the

coupling capacitors are so designed that they offer very high impedance to power

frequency but low to carrier frequencies.


40

PROTECTION OF ALTERNATOR


41

4.1 NEED FOR PROTECTION:

AC power system is covered by several protection zones. Each protective zone

protects one or two components of the system. The neighbour protective zones over lap

so that no part of the system is left unprotected. Each component of the power system

is protected by a protective system consisting of protective transformers, protective

relays, all or nothing rays, auxiliaries, trip circuit, trip coil, etc. During fault conditions

the protective relaying senses the fault and closes the trip circuit of the circuit breaker

open and the faulty part of the system is disconnected from the remaining part of the

system. The various power system elements include generator transformers, bus bars,

transmission lines etc.

The protection of generator is most complex and elaborate.

Generator is large machine and is connected to bus bars. Unit auxiliary transformers,

excitation system, prime over, voltage regulator, cooling systems etc, accompany it. So

it is not single equipment. The protection of generator should be coordinated with

associated equipment. Generator should not be shunt off as far as possible since that

would result in power shortage and emergency.

The generator should be protected against several faults like differential,

restricted earth fault time over current, negative sequence, bearing temperature, bearing

insulation, rotor earth fault, back up over current etc. Several other abnormal

conditions give an alarm and indicate on static protection schemes have been

developed for generator protection.

While selecting the scheme for generator protection, the protection of the

complete unit and stability of the system due to disturbance in generator in addition to

protection of generator it self.


42

4.2 GENERATOR FAULTS AND THEIR EFFECTS All the generator faults can be classified as:

1. Stator faults

2. Rotor faults

3. miscellaneous faults or abnormal operating conditions

Stator faults:

The stator faults include

i. phase to earth faults

ii. phase to phase faults

iii. inter turn faults

Most faults occur in the stator windings, of which majority are earth faults. Phase

faults & inter faults are less common, these usually develop an earth fault. The effect

of earth in the stator is two fold:

1. Arcing to core which welds laminations together causing eddy current hot spots

on subsequent occurrence, repairs to this condition involve considerable

expenditure of time and money.

2. Severe heating in the conductors damaging them & the insulation, with possible

fire risks.

Rotor faults:

Faults in the rotor circuit may be either earth faults or between

turns. But as the rotor field circuit is operated ungrounded a single ground fault does

not affect the operation of generator or cause any damage. However, It increases the

stress to ground in the field when stator transients induce an extra voltage in the field

winding. Thus the probability of occurrence of the second fault is increased. If a

second ground fault occurs a part of the filed winding is by passed, thereby increasing

the current through the remaining portion of the field winding. This causes an

unbalance in the air gap fluxes, leading to severe vibration of the rotor.


43

a) Loss of excitation: Failure of excitation system is one of the serious

abnormal operations of the alternator. It may occur due to the failure or mal

operation of a faulty field breaker. The alternator speeds up slightly & operates

as an induction generator. Round rotor generators don’t have damper windings

& hence they are not suitable for such an operation. The rotor is over heated

quickly due to heavy induced currents in the rotor iron. Stator also gets over

heated due to wattles current drawn by the machine as magnetizing current

drawn from the system but slower then rotor heating. A large machine like a

Turbo alternator may upset the system stability because it draws reactive power

from the system stability because it draws reactive power from the system when

working as n induction generator.

b) Unbalanced three – phase faults: The unbalanced operation of the Alternator may arise due to

Fault in stator winding

An unbalanced external fault, which is not cleared quickly

Open circuiting of a phase

Failure of one contact of the circuit breaker

The unbalanced operation gives rise to negative sequence currents, which rotate

in a direction opposite to that of the rotor and hence produced a flux, which

sweeps through the rotor with twice the rotational speed. Hence spurious

currents of twice the machine frequency are induced in rotor body leading to

overheating of the rotor.

c) Miscellaneous faults or abnormal operating conditions: 1. Unbalanced loading

2. Over loading

3. Over speed

4. Over voltage

5. Fa i lu re of prime mover


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6. Loss of excitation

7. Vibrations

8. Excessive bearing temperature

9. Motoring of generator

4.3 Essential qualities of protection: High grade, high-speed reliable protective devices are the

essential quantities of a power system to minimize the effects of faults and other

abnormalities. Faults should be instantly detected and the faulty section isolated from

the rest of the system in the shortest period. It is obviously not possible to do this

manually, and it must, therefore be accomplished automatically. Faults are detected

automatically by means of relays and the faulty section is isolated by circuit breakers

connected at the boundaries of the section. The combination of relays and circuit

breakers is known as protective system.

The essential qualities of a power system protection are:

Speed: Faults at any point in the system must be detected and isolated in the

shortest time possible. This is of the order of 30-100ms, depending on the fault

level if the section involved.

Sensitivity: Relaying equipment must be sufficiently sensitive to operate reliably

when required under conditions that produce the least operating tendency.

Selectivity: relaying equipment must clearly discriminate between normal and

abnormal system conditions, so that it never operates unnecessarily..

Reliability: Relaying equipment must be found in healthy operating condition

when called upon to act as years might elapse between two consecutive operations

of relays at particular station.

Economy: The most important factor in the choice of a particular protection

scheme is the economic aspect. Sometimes a compromise method has to be

adopted. The protective gear should not cost more than 5% of total cost. However

when the apparatus to be protected is of utmost importance economic

considerations are often subordinated to reliability.


45

Protection relays used in HT, LT and 220 KV systems H.T MOTOR PROTECTION:

The motors driven by the supply of 6.6 KV comes under category of HT motors. The major auxiliary equipment of the station work on 6.6 kv voltage level. The

equipments include PA fans, FD fans, ID fans, Boiler feed pumps, Condensate

extraction pumps, coal mills and step down transformers like unit service transformer,

station service transformers, ESP transformers etc.

H.T. Motors are used for critical applications, & their failures results in stoppage of

system & subsequent loss to generation / production. Hence, failure these H.T. Motors

is a matter of great cancer everybody. Usually, it is noticed that motors are mostly

failing because of the mechanical problems & subsequently resulting in failure of the

H.T. motors are

1. Design lacunas.

2. Operation procedures.

3. Bearing failure.

4. Misalignment.

5. Excessive vibration.

6. Electrical problems.

7. Others.

REMEDIAL MEASURES:

The followings are made to avoid these failures

1) The motor should be selected according to application & operational constraints.

2) The manufacture should be informed in details about application, operation

procedures, environmental conditions etc., so that care is taken at the same time of

design.


46

3) It must be ensured that the manufacturers strict quality control at time of

assembling at every stage. Brazing, tying at overhang portions, lugging etc., should be

very carefully done.

4) No foreign material should be left inside during assembly. Use of bolts magnetic

material for tie rods, which may get loosened in course of time, should be avoided.

5) Timers should be used for those systems where frequent ON/OFF operations take

place. This will avoid over heating of motor.

6) Causes of excessive vibrations, noise, over heating should be immediately

eliminated.

7) Frequent checks of associated auxiliaries, environmental conditions etc., will

increase service life of motor.

8) IR values and delta of H.T. motors should be periodically monitored to take up re

varnishing etc.

9) Manufacturers / Rewinds should be asked not to use graded insulation for those

motors having internal neutral, if they are doing the same. If possible these motors

should be provided with earth fault trip circuit.

10) Care should be taken to check the proper contact between power cable lugs and

motor terminal studs. Otherwise, tapered washers should be provided.

HT motors protection is done using Vacuum circuit breakers

VACCUM CIRCUIT BREAKER:

The VM12 Vacuum circuit breakers are designed to handle all

recognized switching duties. The breakers are extremely reliable in service, require

only a minimum of maintenance and have long life expectancy. Moreover, their small

size and weight, quiet and low vibration levels, the fact that they are not affected by

variation in temperature and freedom from fire hazards enable the breakers to be used

in locations subject to adverse conditions.


47

The three breaker poles, each with its vacuum

interrupter are mounted on a common mechanism housing the energy storing spring

mechanism is motor operated and can be actuated by hand also.

RATINGS AND SPECIFICATIONS

Applicable standards : IS 13118 & IS 3427

Type : VM 12

Rated voltage : 3.6/7.2/12KV

Rated normal current : 630/800/1000/1250/1600/2000/2500A

Rated frequency : 50HZ

Rated short current

Breaking current : 16/20/25/31.5/40KA rms

Rated short circuit

Making current : 40/50/62.5/78.8/100KA peak

Rated short time

With stand current : 16/20/25/31.5/40KArms

Rated duration of short circuits : 1 or 3 seconds

Rated opening time : 60 + 5 ms

Rated break time : 80+5ms

Rated closing time : 75+5ms

Rated operating sequence : 0-0.3 seconds –CO-3min-CO

Rated impulse with stand voltage : 75KV peak

Rated 1-min power frequency

With stand voltage : 28/35 KV rms


48

L.T MOTOR PROTECTION:

The motors driven by the supply of 415 V comes under category of LT motors.

The 415 V systems comprises of 9 Nos. 6.6 KV/415V power transformers fed from

respective 6.6 KV buses and 32 Air Circuit Breakers. The station service transformers

termed as SST-IV A & SST-IV B fed from station transformer bus contain important

loads such as DM plant, control and service air MCC.

The lighting for the entire station is fed from this transformer. Further an

Emergency bus is formed which is fed from SST-IV A or SST-IV B which contain LT

loads which are to be in service even if the entire grid fails. Hence a 250 KVA Diesel

Generator set is also connected to the EMS Bus to meet the emergency.

The protection for these motors are provided in the form of modules .A

module consists of fuses, power contactor ,switch fuse unit ,relays ,circuit breakers

which helps in protecting the motor to a greater extent .

The simple construction of protective system employed for a LT motor in is

described as stated below,


49

The relays generally used for L.T motors are

Thermal over load relay

Ramde relay

PROTECTION OF 220 KV systems

220KV systems are protected by using SF6 circuit breakers

(mainly in switch yard protection).

SF6 CIRCUIT BREAKER:

Type: ELF SL 4-1

Type designation:

E L F SL 4 1

SF6 gas insulation

Generation Outdoor design Extinction chamber type Breaker construction Code BIL rated voltage, 4=245/460/1050KV Number of chambers

CONSTRUCTION:

The high voltage circuit breaker type ELF SL 4-1 comprises of three

breaker poles, a common control cubicle and a pneumatic unit (compressed air plant)

A breaker pole consists of:

1.Support (frame)

2.Pole column


50

3.Pneumatic actuator

The actuator operated with compressed air. A pneumatic unit, an air receiver

and a unit compressor is installed to supply the compressed air. The compressed air

stored in the air receiver is distributed to the three actuators via pipelines. The common

control cubicle which is installed separately contains all control devices and most of the

monitoring instrumentation. (With the exception of the density monitor mounted on the

middle breaker pole). The pressure switches are installed in the control cubicle. All

three pole columns are filled with insulating gas and are interconnected by means of

pipelines. The gas is monitored by a density monitor (temperature compensated

pressure monitor).

SULPHUR HEXAFLOURIDE (SF6) CIRCUIT BREAKER: The SF6 circuit breaker consists of interrupter units each capable of

dealing with currents up to 60 KAmps and voltages in the range of 50-80 KV. A number

of units are developed for voltages 115-230 KV, power ratings 10-20 MVA and

interrupting time less than 3 cycles.

Properties of SF6 gas: I. High dielectric strength.

II. Thermal and chemical stability

III. Non inflammable, non poisonous and odorless.

IV. Pure SF6 gas is inert and thermally stable

V. Arc extinguishing ability: It should have a low dissociation temperature, a

short time constant.

VI. It remains stable up to a temperature of 500º C

VII. It is an electronegative gas.

VIII. It remains in a gaseous state up to a temperature of 9º C and its density is about

5 times that of air and pre heat convention is 1.6 times as much as that of air.


51

Arc extinction in SF6 circuit breaker: During the arcing period, SF6 is blown axially along the arc. The gas

from the compressor is let into the auxiliary high-pressure reservoir at a pressure of

about 14Kg/cm2. The gas is admitted into the arc extinction chamber just before the

contact separation. The gas comes into LP cylinder.

The following are the current carrying parts:

The terminals are connected to the neighboring equipment form the

conductors are taken through bushings. The arc extinction chamber house is made of

dielectric material and the chamber is mounted on the insulator supports.

The moving contacts are pulled apart from the fixed contacts by means

of insulating links. At the same time valves on the high pressure cylinders are opened

and the gas from the high pressure tank flows to the low pressure reservoir through

nozzles. The arc is extinguished by hot air flow.

Data of the Generator Type : THRI 108/44

Apparent Power : 294 MVA

Active power : 250 MW

Current : 10,290A

Voltage : 16.5KV +/-825V

Speed : 3000 R.P.M

Frequency : 50 Hz.

Power Factor : 0.85

Interconnection of

Stator winding : stat-star

Hydrogen Pressure : 3.0 bar

Continuous permitted

Unbalance load : 8%

Rated field current o/p: 2386A D.C

Rated field voltage : 319Volts D.C

No. of rectifier wheels: 2


52

4.5 Protection of 250MW turbo generator

The generators bring the most important and costliest equipment of a power

system it is provided with a vast range of protection schemes as categorized below:

Unit protection can be classified into following three categories

Class - A

Class – B

Class –C

Class – A protection:

1. Turbine and Generator tripped simultaneously due to sevearity of the fault.

2. It covers all types of major electrical faults in the Generator, GT and UATs.

3. It causes over speed of the TG set.

4. Over speed is tolerated in view of the severity of the fault.

5. It is known as simultaneous trip

The faults come under class – A protection is as follows.

1. Negative Phase sequence relay (46 GB) RARIB

2. Loss of excitation relay (40 G) RAGPC

3. Generator stator earth fault relay RAGE A (64 GA) + RXIG 28 (64 GB)

4. Generator stand by earth fault relay (64 GC)

5. Low forward power relay (37 G)

6. Reverse Power relay (32G) RXPE

7. Generator differential relay (87G)

8. GT restricted earth fault relay (87 NT)

Class-A Protection

Turbine Trip

Generator Trip


53

9. UAT – A differential relay (87 UAT-A)

10. UAT – A differential relay (87 UAT-B)

11. Overall differential relay (87-O) RADSB

12. Back up impedance realy (21GB)

13. Over flux relay, stage – II (99 GT)

14. Pole slip relay, stage – II (98 G)

15. Over current in UAT – A (51 UAT – A)

16. Over current in UAT – B (51 UAT – B)

17. Rotor Earth fault relay (7UR 22)

Class – B protection:

1. No immediate danger or damage

2. Turbine trips instantaneously

3. Then the generator trips on low forward power relay interlock

4. Back up is the reverse power relay

5. Faults in UAT & GT which are not severe covered by this protection.

6. No over speed in the TG set.

7. It is also known as sequential trip.

2 sec

2 sec

20 sec

The faults which come under this category are as follows.

1. GT winding temperature high ( 49 GT-W-T)

Class-B Protection Turbine

Trip

Low Forward Power Relay

Reverse Power Relay

Generator Trip

Reverse Power Relay


54

2. GT oil temperature high (49 GT – O-T)

3. GT OLTC buchholz relay (63 GT)

4. UAT- A winding temperature high (49 UAT A –W-T)

5. UAT- B winding temperature high (49 UAT B –W-T)

6. UAT-A oil temperature high (49 UAT- A– O-T)

7. UAT-A oil temperature high (49 UAT –B- O-T)

8. GT oil level low trip

9. UAT - A oil level low trip

10. UAT - B oil level low trip

Class – C protection:

1. Faults in the grid.

2. Only 220 KV circuit breaker will be opened.

3. TG set maintains house load operation

4. Unit can be reconnected to the grid after isolating the fault.

Faults covered in this protection are as follows.

1. Negative phase sequence relay ( 46 A)

2. Back up impedance relay (21 GA)

3. GT over current relay ( 51 GT)

Mechanical protections of the Generator:

1. High cold gas temperature in Generator:

Alarm 45ºC

Trip 50ºc

2. Liquid level in Generator terminal box.

a. Seal oil may enter into the Generator chamber due to more gap at the seals.

b. Hydrogen cooling water may enter the chamber due to hydrogen cooler leak.

c. level detectors are used to find out the liquid level.


55

d. 2/3 logic is used for operation.

3. High hot air temperature in Exciter unit

Alarm 50ºC

Trip 75ºC

Above three faults initiate class – B protection as there is no immediate danger to the

Generator.

RELAYS IN KTPS V STAGE:

The relays used for Generator protection is of static type of make ABB in KTPS

– V stage. Latest trend in the protection of Generator is to use Numerical or Micro

processor based relays.

Nomenclature of relays:

R- Relay

A- Assembly (single parts are assembled)

X- Single piece of device

D- Differential relay

I- Current

F- Frequency

E- Voltage


56

Product overview:


57

1. Overall Differential Protection Relay 87 (RADSB):

Make Type: ABB RADSB

This relay gets inputs from the following C.T cores

1. Core- 1 of 220 KV switchyard CT 1000/1A

2. Core- 4 f 16.5 bus duct in the neutral side of generator CT 12500/5A

3. Core- 3 of UAT - A duct (16.5 KV) CT 12500/5A

4. Core-3of UAT-B duct (16.5 KV) CT 12500/5 A

Relay details

Operating voltage: 100-400V


58

System Details

Sub transient reactance of the generator Xd" = 0.117 p.u

(To be checked at site and any changes has to be incorporated).

Voltage Rating = 16.5 KV

MVA Rating = 294 MVA

CT Ratio =12500/5A

Ret =3 ohms

Rl (loop resistance) = 0.8 ohms (assumed)

Calculations

Full load current = (294 MVA) / (>/3 *16.5KV) = 10287.33.4

Fault Current If =Full Load Current / Xd11 = 58120.52A

Secondary Fault Current Ik = 58120.52*(5/12500) = 23.25

Max Voltage developed across the relay = Ik* (Ret +R1) = 88.35V.

Normally a setting of 110% of this voltage will provide full stability

against external faults.

Relay setting > 1.1 * Max voltage = 100V

Recommended Setting:

RADHA set-to 100V.

2. Generator Stator Earth Fault Relay 64GA & 64GB Make Type: ABB RAGEA

This relay gets input from the Generator Neutral Earthing Transformer secondary

side voltage across the resistor of value 0.52ohms

0-95% E/F relays------------- Over voltage

95-100% E/F relays---------- Under voltage

Stand by earth fault relay---- Over voltage

0-95% Earth fault relay:

An over voltage relay is used for finding the earth fault in 0 – 95% of the

stator winding.


59

95%-100% Earth fault relay:

1. Third harmonic voltage is measured at the neutral of generator.

2. In case of earth fault near the neutral third harmonic voltage falls.

3. So a under voltage relay is provided for detecting the earth faults in

95-100% of the stator winding.

Relay details

95% Element RXIG 28: 5-15V

95-100% Element RXIG 21: 0.15-0.45V

Supervision unit RXEG: 40-120V

Time delay: 20msec - 99sec

System Details

Neutral Grounding Transformer 16.5KV / 240V

3OKVA continuous, 80KVA for 5 minutes.

Neutral Grounding Resistor 0.52ohms, 46.8KW, 330A, 1100V.


60

Trip

High Current

64 GA


61

Calculations

95%Element RXIG 28

For phase to ground fault Vph-n =l 6.5KV / √3 = 9.52KV

Voltage across relay = 240 / Vs = 138.56V

To cover 0 to 95%, setting should be 5%of the above value

=0.05* 138.56 = 6.92V

Lime delay =3sec. 95-100% Element RXIG 21

Normally third harmonic voltage is measured at generator neutral, when the

machine rated voltage is build up and machine is not loaded. Setting of 95-

100% element will be half of the peak value measured. For example Third

harmonic voltage=l% of normal system voltage

=0.01*16.5KV/V3 = 95.26V

Approximately more than 30% appears across neutral = 28.57V

Secondary value = 0.401V

Supervision unit RXEG:

Range available: 40-120V

Recommended setting = 85% of rated voltage = 0.85* 110 = 93.5V

3. Loss of Excitation 40G

Make type: ABB RAGPC

Causes: 1. Accidental tripping of the excitation system

2. Mal operation of field circuit breaker

3. Failure of fuse near PMG

4. Open or short ckt occurs in the DC excitation circuit

Effects:

1. As excitation fails, its terminal voltage reduces observed as dip.

2. Heavy reactive power drawn from the grid, which causes very high

current drawn from the network.

3. Characterized by dip in stator voltage and rise in stator current.


62

4. Generator speed increases, runs above synchronous speed and machine

works as Induction Generator.

5. Results in overheating of the rotor.

6. Instability may occur, if other generator in the power system could not

be supply the required reactive power.

Excitation--- MVAR

Steam Input- MW C.T P.T

MVAR

MW

MVAR

MW

This relay gets input from A. core 4 of PT situated in 16.5KV side of generator duct. The PT ratio

is (16.5AT/V3)/ (110/V3)/ (110/V3)

B. core 3 of CT ratio 12500 / 5A, situated in the generator neutral side 16.5KV

bus duct.

Immediately after the operation of loss of excitation realy, ensure The 220 KV

breaker was tripped otherwise trip the breaker manually.

Relay details

Directional unit: 1-4A

Under voltage RXEG2: 40- 120V

Over current RXIG2: 2.5-7.5A

Lime setting: l-10sec.

Generator Grid

Generator Grid

40G


63

Calculations

Under voltage element RXEG

Setting recommended will be 85% of nominal voltage = 0.85 * 110=93.5V

Recommend settings

Directional unit RXPE = 1.4A

U/V RXEG 21 =93.5V

O/C RXIG21 =5A

Time setting =2sec.

4. Negative Sequence Protection 46G: Make Type: ABB RARIB

It is also knows as unbalance protection

Causes:

1. Unbalanced loads

2. Unbalanced system faults

3. Open circuits

4. Breaker failures

Effects:

1. Negative Phase sequence currents are induced in the stator body.

2. Negative sequence flux rotates in opposite direction to that of the rotor

flux.

3. Relative speed will be equal f – (-f) = 2f.

4. Double frequency (i.e. 100 Hz) currents and voltages are induced in the

rotor.

5. High frequency causes increased iron losses and hence heating of the rotor


64

With negative phase sequence fault in one phase, the frequency becomes

f - (-f) =2=100 Hz

With such high frequency, the magnetic losses i.e. the hysterisis losses increases and

the rotor overheats.

Generally every Generator is capable of carrying negative phase sequence currents

to a certain time. Normally two relays are used against negative sequence protection

46 A realy: It only trips the 220 KV breaker thus isolating from the grid (i.e. class –

C protection).

46 B relay: even then also if the fault exits, then this relay operates and initiates

class – A protection.

System details

This relay gets input from C.T. core 3 (12500/5A) situated in the generator

neutral side of 16.5KV bus duct.


65

Settings:

Alarm : 8% of the rated current.

Time delay : 6 sec

Trip: 10% of the rated current.

Time delay: inverse characteristics.

5. Generator out of step (pole slip relay) 98G

Make Type: ABB RXPE + RXZF21

Causes:

(1) Excessive Load on the Generator.

(2) Insufficient Field.

(3) Generator breaker closed when out of synchronism.

Effects:

1. Generator will draw reverse from the network.

2. Also draws heavy current from the grid.

3. So a reverse power relay in conjunction with over current relay is used

to detect pole slip condition.

System details

This relay gets inputs from

a. C.T. core 3 (12500/5) situated in the generator neutral side of 16.5KV bus

duct.

b. P.Tcore4 (16.5KV/V3)/( HO/ V3 / (110/73) Situated in the Phase

side of the generator bus duct.

Relay details

d= 1, 1.5,2,3,5,6.

Q = 20, 21 ...29.

Is = rated current = 5A


66

6. Low Forward Power Relay (37G) (< 2MW)

Make Type: ABB RXPE40

Generally Generator Circuit Breaker is opened for urgent faults in which

over speed can be tolerated. For non-urgent faults GCB is to be opened only after

falling of Generator power to a low value (which will not cause overspeed) i.e.

after tripping of turbine. For detecting this low power from the generator, low

forward power relay is used. If the low forward power realy fails to operate, then

the machine runs as a motor.

V

I

Turbine Trip

220 KV C.B closed Trip Generator

P.T Fuse healthy

To find whether P.T fuse is healthy, a relay 60 G1 is used. In this process, VT1

and VT4 are compared. If these values are not same, then P.T fuse failure has

occurred.

VT1

VT1=VT4

VT4 PT fuse failure

PT fuse failure

37

37 <2 MW

60 G1


67

System details


a C.T. core 2 (12500/5) situated in the generator neutral side of 16.5 KV

bus duct.

b. P.T.core4 (16.5KV /3) / (110 /3 ) / (110 /V3 ) situated in the phase

side of the generator bus duct.

Relay details

RXPE40 setting: 30 - 120mA

Time setting: 20msec - 99hrs.

Recommended settings

Setting of RXPE40 = 30mA

Time setting for trip = 2sec.

7. Reverse Power (32G)

Make Type: ABB RXPE

I V

This is like a back up protection to the low forward power relay. Incase if

the generator is not tripped by low forward power relay, the machine draw power

from the grid and will acts as a motor. This reverse power is sensed using this

relay. The level of power drawn from the power system depends upon type of

prime mover. The realy used for reverse power detection is as same as that of the

low forward power – difference is only the connections. If the relay doesn’t

32 2sec


68

operate at proper time, the alternator will run as a synchronous motor and over

currents will flow.

Prime mover Motoring power

1. Diesel engine 5% - 25%

2. Gas turbine 10% - 15%

3. Hydraulic turbine 0.2 – 2 %

4. Steam turbine 0.5 – 3.0%

System details


a. C.T core 2 (12500/5) situated in the generator side of 16.5KV Bus duct.

b. P.T. core 4 (16.5KV / V3) / (110 / √3) / (110 / √3) situated in the

Phase side of the generator bus duct.

Relay details

RXPEi setting: 30- 120mA

Time setting: 20msec - 90hrs.

Calculations

Minimum setting of 30mA corresponds to primary current of 75A with 12500 / 5

A C.T ratio. This is 0.77% of full load.

Recommended setting

RXPI< setting = 30mA

With turbine trip = 3 sec.

With out turbine trip = 20 sec.

Time trip = 20sec.

Time delay setting = 1 sec.


69

8. Generator backup impedance 21GA & 21GB

Make Type: ABB RAKZB

1. Operated for the prolonged uncleared faults out side the yard.

2. Phase faults in the unit & switch yard

3. Phase faults in adjacent transmission lines

4. When main protection fails

5. Distance type of relay is used.

6. Distance type of relays will operate when the impedance seen by the relay is

less the set value.

System details


a. C.T core 3 (12500 / 5) situated in the Generator neutral side of 16.5KV bus

duct,

b. P.T. core4 (16.5KV/ V3)/(110/√3)/(110/ 73) situated in the phase side of the

generator bus duct.

Relay details

RAKZB: 5A, 1 10V, characteristic angel = 75deg.

Time setting: l-10sec.

Calculations

Impedance as seen from the Generator terminal is given by

(16.5 * 16.5) / 294 = 0.926ohms.

Usually backup impedance is set to 70% of the terminal impedance

= 0.7 * 0.926 = 0.648ohms.

Secondary value – Zf = 0.648 * (CTR / PTR) = 231 ohms.


70


Time delay = 3sec,

Time setting = 2sec,

A = 20, B = 7.35, D= 1.

9. Over Voltage RXEG (59G)

Make Type: ABB RXEG-21

Causes:

1. Sudden loss of load.

2. Sudden increase in turbine speed.

Effects:

1. Higher voltages may damage the insulation of the stator winding

Stage 1: 18.15 KV, time setting: 3 sec, alarm only

Stage 2: 19.8KV, time setting: 1 sec, trip is provided.

Relay details:

Setting range: 80 - 240 V

Time setting: 20msec - 99sec.

Calculations

Over voltage protection is set to 110%of the rated voltage

Setting of RXEG= 1.1 * 110 = 121V

Time delay

Stage 1 = 2sec

Setting of RBEG = 1.15 * 110= 127V

Stage2 = 0.2sec


71

10. Under Frequency Relay PCX 103 B As the frequency of generation falls, all motors connected runs at lesser speeds which

reduces their rated output.

Make Type: ABB PCX 103 B:

Stage Frequency (Hz) Time setting(sec)

I 48 5

II 47.5 3

III 47 2

All the three stages initiate alarm only. No trip is provided for the Generator.

11. Definite Time Overload Relay RXIG 21 50G

Make Type: ABB RXIG -21

CT ratio 12500/5A

Current setting = 1 *In where In=5A

Time delay 2sec

12. Voltage Balance RXEG 60G Make Type: ABB RXEG -21

Relay Details

RXEG range: 40- 120V

Calculations

The voltage balance scheme is generally set to 70% of the rated voltage

Rated voltage = 110V (on secondary)

Setting of RXEG = 0.72 * 110 = 80V

Recommended setting

RXEG: (2*40)


72

13. Overall Differential RADSB 87 GT

Make Type: ABB RADSB

220 kV side of GT CT's 1000/1 Aux:0.712/2.88A

Gen neutral side CT's 12500/5A Aux: 4.11/5A

16.5kV side of UATs 9A & 9B CT's 12500/5A Aux: 4.1 1/5 A

Restrained operation 0.25 * In

Unrestrained operation 13 * In

14. Generator Transformer REF relay RADHD 87 NT Make Type: ABB RADHD

Phase side CT 1000/1A

Ret = 3 ohms, RI = 2 ohm km Total distance (134 mtrs)

System details

Transformer impedance 14.5%

Calculations

Max through fault current = 1/0.145 = 6.896 pu.

Through fault current in amps on secondary

((290*10A6/(sqrt3*220*10A3))*(6.896*l/1000) = 5.2

Voltage across relay = If(Rct+2RI)

= 5.248(3+2*0.5) = 20.992V

Therefore the setting is 40 volts


73

15. Generator Transformer Over Flux RATUB 99 GT

Make type: ABB RATUB

1. Also known as V/f protection for generating transformer.

Flux = V/f

Causes:

1. In correct voltage regulator action

2. Load throws off.

3. sudden over voltage.

4. Turbine speed is less than the rated speed

Effects:

1. Higher amount of Flux saturates the core.

2. Overheating of the stator.

3. Damage to the insulation of transformer. V

Relay setting

Stage I (alarm):

V/F: - 1.5 -3.5 sec

Stage II (trip):

V/F setting: - 1.5-3.0 V/HZ

Time multiplier K = 1-63 sec.

99 GT


74


PT ratio 16500/110 V

V/F (alarm) 2.5 V/Hz

Time setting 3.5 sec.

V/F trip 2.5 V/Hz

Time setting 1 sec

16. Generator Transformer HV Overload Relay RACID 51 GT Make Type: ABB RACID

CT Ratio = 1000/1A

Relay setting

In- 1A, M=l,Ig = 0.2A,Is>=0.2A

K - 0.8

Is»= blocked

Inverse time characteristics Switch "Normal"position.

17. Generator Transformer E/F Relay on HV side RACID 5 Make Type: ABB RACID

CT ratio = 1000/1A

Relay setting

In 1A, M= 1, Ig = 0.2A, Is >= 0.2A '

K - 0.8

Is»— blocked

Inverse time characteristics. Switch "Normal" position


75

18. Generator Transformer LBB relay RAICA 50 GT

Make type: ABB RAICA

Relay details

RXIB24 Range: 0.2-3A

Timer 0.1 sec — 1 sec

Calculation

The LBB unit is always set as sensitive as the most sensitive

protection for the unit, in this case it is the reverse power protection.

Hence the RXIB24 current unit in RAICA can be ser to 0.02pu

Full load current = 10287.33

Full load current on current transformer secondary side =10287.33/1000= 10.20A

RAICA to be set to 0.02pu. i.e., 0.02 * 10.20 = 0.205 A

Set time +0.2A

Time delay

The time delay should include

RXIB pickup time + Breaker opening time +Reset time of RX1B24+

Margin i.e., the time delay - 4 ms+60ms 12ms+75ms(assuming 3 cycle

breaker)= 150ms

Time setting = 0.2sec

Settings recommended = 200mA

Time delay = 200msec

19. Unit Auxiliary Transformer Differential 87 UAT RADSB

Make type: ABB RADSB

IIV side of CT's 800/5 Aux:4.37/5A

LV side of CT's 2000/5 Aux:4.182/2.88 A


76

Restrained operation 0.25*In

Unrestrained operation 0.25*In

Unrestrained operation 13*In

20. UAT Overload Relay HV side RACID 51 UAT Make type: ABB RACID CTs 800/5

In -5A, M= l,Is>=5A

K 0.5

In 5A, M = 2, Is»=10

Inv time characteristics Switch "Norm" position

21. UAT O/L Relay LV side CAG 37 51 UAT Make type: GEC CAG37

CT ratio 2500/5A

In = 5A, PS = 400%

Time =1sec

22. Rotor Earth fault relay - Siemens relay (7UR22)

Rotor windings are damaged by earth faults. A single ground fault connection

does not cause flow of current since the rotor circuit is ungrounded. When the second


77

ground fault occurs, part of the rotor winding is by passed and the currents in the

remaining portion may increase.

The rotor earth fault relay is used to detect high and low ohmic earth faults in the

excitation circuits of synchronous machines. Any further earth fault in the excitation

circuit results in a double earth fault, which, on the one hand, mechanically endangers the

rotor due to magnetic unbalance, and, on the other hand, thermally endangers the rotor

due to the high fault current. For this reason the single earth fault should be either

alarmed or initiate tripping.

The protection has two stages; gradual deterioration of the insulation initiates an

alarm, a solid earth fault initiates a trip.


78

The same figure can be shown as:

BUCHHOLZ RELAY The incipient faults in transformer tank below oil level actuate Buchholz relay

so as to give an alarm. The arc due to fault causes decomposition of transformer oil. The

product of decomposition contain more than 70% of hydrogen gas, which being light,

rises upwards and tries to go in to the conservator. The Buchholz relay is fitted in the pipe

leading to the conservator. The gas gets collected in the upper portion of the Buchholz

relay, there by the coil level in the Buchholz relay drops down. The float, floating in the

oil in the Buchholz relay tilts down with the lowering oil level. While doing so the

mercury switch attached to the float is closed and the mercury switch closes the alarm

circuit. Thereby the operators know that there is some incipient fault in the transformer.

The transformer is disconnected as early as possible and the gas sample is tested.

The testing of gas gives clue regarding the type of insulation failure. Buchholz relay

gives an alarm so that the transformer can be disconnected before the incipient fault goes

in to a serious one.


79

CASE STUDY


80

Case Study: Generator 10 was tripped in the month of October 2006 with 95% earth fault (64

GA) and standby earth fault (64 GC) relay operated. The same kind of fault occurred

thrice in the total year (twice in 9th plant and once in 10th plant). To know the

healthiness of insulation anywhere in power system, IR values of stator windings is to

be measured.

Finding the IR values here means that we have to calculate the value of resistance. This

is also called Megger test. In this test, a DC voltage is connected to each phase and it is

grounded in one side and the other side is connected to each phase. When the phase is

healthy, only a small current called capacitive current flows through the circuit and

resistance is very high and when an earth fault occurs, a very high current flows

through the circuit so current if very low or approximately zero.

IR values are measured at 5KV with insulation meter and the results are as follows:

R-E : 45 M ohm

Y-E : 50 M ohm

B-E : 0 M ohm

So from the above results it is known that the earth fault is in the B-Phase but it is very

difficult to find out the exact location where the earth fault occurred because of the

large volume of the stator core and winding. Even then the entire stator core and

winding inspected physically for locating the earth fault. But it was not visible. So in

order to find out the exact location of the earth fault, smoke test is to be conducted and

it is as follows:

At around 32V from the 1-phase variac and a current of about 8 amps,

smoke was observed at 27th slot top bar (double layered winding) nearer to end

winding. Immediately voltage switched off. The area where the smoke was observed is

fully cleaned with contact cleaners. It is observed that, the core stamping (laminated

stamping) came outside from the core and it was pierced into 27th topbar which created

earth fault. So the earth fault is at the 27th topbar. Hence 27th topbar is debrazed from

the winding and high voltage test is conducted for rest of the winding and the results

are as follows:


81

HV test:

Voltage applied leakage current

R-> E with Y+B-> E 22.6 KV 2.91 A

Y-> E with R+B-> E 22.9 KV 2.92 A

B-> E with Y+R-> E 23.1 KV 2.87 A

So from the results it can be seen that all the three phases are healthy.

IR values are found again with 5 KV source:

15 sec (in M ohm) 60 sec (in M ohm)

R-E 500 2000

Y-E 500 1750

B-E 350 1950

R-Y 1000 2750

Y-B 1250 4500

B-R 1000 3250

From the above results, it is found that the remaining winding is healthy.

New top bar placed at site, tested for high voltage and IR values are also measured.

HV Test Current

31 KV (for 1 minute) 90 mA

IR values at 5 KV

15 Sec 30 sec 60sec

5 KV 1, 00,000 M ohm 2, 00,000 M ohm 40, 00,000 M ohm


82

Top bar is placed in the 27th slot and brazing was done on both turbine and exciter end

sides. Insulating tapes were wound on the brazed winding. Insulating liquids are also

applied on the brazed positions.

Stator overhang position was kept for heating for 24 hours. Again the test was

conducted and IR values are also measured.

Voltage applied leakage currents

R-> E with Y+B-> E 23.0 KV 2.92 A

Y-> E with R+B-> E 22.7 KV 2.88 A

B-> E with Y+R-> E 23.0 KV 2.93 A

IR values at 5 KV

15 sec 60 sec

R-E 550 2500

Y-E 450 1850

B-E 450 2000

R-Y 1050 3000

Y-B 1300 4000

B-R 1500 3900

It can be observed from the above results that the entire stator winding is healthy.

There was also some special tests were conducted both on stator and rotor.

• ELCID Test (Electromagnetic core imperfection detector test)

It is to find out the healthiness of laminations of stator core. The maximum shootout

current should be less than 100 mA for better operation.

• Wedge deflection test

It is to find out the stiffness of the wedges fixed on the stator winding with hydraulic

jerks. A dial gauge will be placed on the wedge and a pressure of about 100kg/cm sq.

will be applied with the hydraulic jark.The maximum deflection of the dial gauge will

be measured and is found to be normal for the total stator wedges.


83

• RSO Test (Recurrence Surge Oscillogram)

It is done for rotor winding. It is to find out if there are any internal short or earth faults

in the rotor winding.

Modern technique: A new technique is implemented at Rayalseema thermal plant

(RTTP) in stage-2 in which there is negligible chance of vibrations which caused trips

in KTPS V stage thrice last year. In the slots, the insulator is poured at the time of

construction and then conductor is directly poured on that so that, the whole stator is a

single and strong piece and less damage is done to the system during vibrations.


84

CONCLUSION


85

Upcoming trends in protection:

Adaptive Protection Systems

Adaptive protection is as "an online activity that modifies the preferred protective

response to a change in system conditions or requirements. It is usually automatic, but

can include timely human intervention". An adaptive relay is "a relay that can have its

settings, characteristics or logic functions changed online in a timely manner by means

of externally generated signals or control action". In other words, adaptive protection

systems are systems which allow changing relay characteristics/settings due to the

actual system state. For example, the primary zone pickup value of a distance relay can

be changed online according to power in feed from a T-connected generator

There are several adaptive techniques proposed which use online information of the

system to optimise the protection system function. Some examples are:

• Adaptive system impedance modeling (an up-to-date impedance model of the

network that provides input data for a relay).

• Adaptive sequential instantaneous tripping (for faults near the remote station).

• Adaptive multi-terminal distance relay coverage (regarding in feed from T-

connections in the relay settings).

• Adaptive reclosure (prevent unsuccessful reclosure for permanent faults, high-

speed reclosure in case of false trips).


86

Block diagram of adaptive relay coordination software It is proposed to use real-time synchronized phasor measurements of bus voltages and

line currents as a source of information for adaptive relays. The basic requirements for

implementing adaptive relaying concepts:

1. Microprocessor-based relays

2. Appropriate software for relay modelling, relay coordination and communication

3. Appropriate means of communication

A relay coordination software model as shown in figure is introduced which makes real

time changes of relay configurations possible.


87

BIBILOGRAPHY

1 The Manual of Asean Brown Boveri.

2. BHEL – Manual for Alternators KTPS, Paloncha.

3. Switch Gear and Protection

--- Sunil S.Rao

4. Electrical Power Systems

— CL. Wadhwa

5. The Art and Science of Protective Relaying

— Crussel Masan


Documents

Protection Of Generators[1]