Final Iqbal Report on Gss 220kv

“ 220 KV GRID SUBSTATION ALWAR”

A

SUMMER TRANNING REPORT

SUBMITTED

To

Rajasthan Technical University

In partial fulfillment  for the award of the Degree of

BACHELOR OF TECHNOLOGY

In

ELECTRICAL & ELECTRONICS ENGINEERING

ACADEMIC SESSION 2012 – 2013

  Submitted To:                                                                    Submitted By:

  Mr. AMAN MATHUR                                                       IQBAL DEEN

  HOD                                                                   09ECEEX020

  EEE DEPARTMENT                              EEE

                                                                                             B.TECH 7TH SEM 

          DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING

CHACHAN EDUCATION & WELFARE SOCIETY GROUP OF INSTITUTIONS,CHIKANI

Alwar (Rajasthan)-301028

INDEX

S.NO. TOPIC

1. INTRODUCTION

2. THE YARD

3. LIGHTINING ARRESTOR

4. WAVE TRAP

5. ISOLATOR

6. INSTRUMENT TRANSFORMER

7. CURRENT TRANSFORMER

8. POTENTIONAL TRANSFORMER

9. POWER TRANSFORMER

10. INSULATOR

11. CIRCUIT BREAKER

12. EARTHING

13. POWER LINE CARRIER COMMUNICATION

14. PROTECTION RELAY

15. CONTROL ROOM

16.BATTERY ROOM

17. CONCLUSION

ACKNOWLEDGEMENT

I would like express my knowledgement for valuable cooperate ren-

dered by Mr. N. K.  Garg (X En), Mr.  AlokSinha (A En) and Ms. Honny-

Chaudhary (J En), who prided me various facilities and lot of knowledge

about GSS and its different parts during my training session I would like to

express my thanks to staff members, technicians of GSS Alwar, who all

co-operated me for setting the knowledge of various equipments and their

operations And A very special thanks to Mr. AlokSinha Sir, who encour-

aged us in training session .

I would also like to thanks to Mr. Aman

Mathur sir(HOD) and all staff members of CEWS&GI,Chikani,Alwar.

IQBAL DEEN

EEE

PREFACE

This is training of 30 days   my training place was 220 KV ,GSS, Alwar, ra-

jasthan. GSS is the mean of connection between generating station and con-

sumer by providing safety and reliability of system in case of default. 

This sub station step down the incoming  voltage  power transmission to the

required valve and then  is supplied to the consumer feeder or GSS done by

connecting auto transformer operation and requirement of  various equipment

have been include in detail , further in case of report is the bus bar. 

Arrangement of different

feeder level and switch yards  included information of  bus bar arrangement of

different  level  isolator and  growing substation also power transformer circuit

breaker oil, filtration plant, and compression protection control room and place

are leveled.     

CHAPTER-1

INTRODUCTION

     When India becomes independent its overall installed capacity was hardly

1900 mw. During first year plan (1951-1956) this capacity was only 2300 mw.

The contribution of Rajasthan state was negligible during 1&2 year plans the

emphases was on industrialization for that end it was considered to make the

system of the country reliable. Therefore Rajasthan state electricity board came

into existence in July 1957.

In India electrical power  is generated at a voltage of 11KV to 33 KV .

which is taken  stepped up to the transmission level in the range of 66 KV to

400 KV

Member of transmission and switching have to be created. These are

known as “SUB STATION”.

Along these transmission lines secondary substation are created where volt-

age is further stepped down to sub transmission and primary distribution volt-

age.   

    A substation is an assembly of apparatus, which transform the characteristics

of electrical energy from one form to another say from one voltage level to an-

other level. Hence a substation is an intermediate link between the generating

station and consumer.

For economic transmission the voltage should be high so it is necessary to

step up the generated voltage for transmission and step down transmitted volt-

age for distribution. For this purpose substations are installed. The

normal voltages for transmission are 400kv, 220kv, 132kv and for distribution

33kv, 11kv etc.

Electricity boards are setup in all states of India which are responsible for

1. Generation

2. Transmission

3. Distribution

They also construct, install and maintain all the station made for these pur -

pose. In Rajasthan ,R.R.V.P.N.L. is responsible for transmission and distribu-

tion of electrical power all over Rajasthan. It has its own generating station and

it’s also gets power from various other stations also.

Power obtain from these sta -

tions is transmitted all over Rajasthan with the help of grid stations. Depending

on the purpose, substations may be classified as:-

1. Step up substation

2. Primary grid substation

3. Secondary substation

4. Distribution substation

5. Bulky supply and industrial substation

6. Mining substation

7. Mobile substation

8. Cinematograph substation

Depending on constructional feature substation are classified as:-

1. Outdoor type

2. Indoor type

3. Basement or Underground type

4. Pole mounting open or kilos type

Any substation has many types of civil and electrical works. Main components

are:-

Bus bar

Power transformers

Isolators

Circuit breaker

Lightening arrester

Insulators

Instrument transformers

The control room is equipped with protective relays, ammeters, voltmeters,

energy meters and frequency and power factor meters

D.C. supply is heart of GSS batteries are used for this purpose. They have

separate charging circuit also. For communication purpose P.L.C.C. is used

which has its various components.

220 KV GSS,”Alwar” is the part of the transmission system.

.INCOMING FEEDER:

  1 Heerapura ( Jaipur)

  2. MIA (Badarpur )

  3.  Dousa

  4.  Bhiwadi

  5.  Khuskhera

.OUTGOING FEEDER:-

1.         220 KV Kotputli

2.         132 KV GSS Alwar

3.         132 KV Bharatpur

4.         132 KV LCAL

5.         132 KV Kishangarh Bass

6.         132 KV Mundawar

7.         132 KV M.I.A.

8.         132 KV Ramgarh

9.         132 KV Malakhera

10.       132 KV Bansur

CHAPTER-2

THE YARD

The yard is spread in very long area. The yard of 220 KV GSS at Alwar has

various equipment installed at the yard of 220 KV GSS, Alwar are:- 

Lighting Arrester

Wave Trap

Current Transformer

Circuit Breaker

Bus Bars

Power Transformer

Insulator

Potential Transformer

Static earthling system

PLCC equipment including coupling capacitance

Bushing

Isolator

Figure-2.1

BUS BAR SYSTEM

This bus bar arrangement is very useful for working purpose as every GSS.

It is a conductor to which a number of  cut .Are connected in 220 KV GSS there

are two bus running parallel to the each other, one is main and another is auxil-

iary bus is only for stand by, in case  of failure of one we can keep the supply

continues.

   If more loads are coming at the GSS then we can disconnect any feeder

through circuit breaker which is connected to the bus bar. This remaining all the

feeders will be in running position .if we want to work with any human damage.

In this case all the feeders will be on conditions.

According to bus voltage the material is used .Al is used because of the

property & features and it is cheap. 

With the help of bus bar arrangement we can connect all the incoming sup-

ply which is coming from different higher order GSS.        

CHAPTER=3

PROPERTIES

COPPER ALUMINIUM 

1. Electricity resistively at 20 c

0.017241

0.00403 

2. Temp coff. Of resistively

0.00411

0.00403 

3. Softening tem.

200

180 

4. Thermal conductivity

.932

.503 

5. Meting point

1083

657 

LIGHTENING ARRESTER

Lightening arrester is first equipment of GSS. It is protecting all the equip-

ment against the HV. The ground wire or earthing does not provide protection

against the high voltage waves reaching the terminal equipment .so some pro-

tective device is necessary to produce power station ,sub-station and transmis-

sion lines against the high voltage wave reaching  here. Which is connected be-

tween line and earth it acts as a safty valve. . 

Through the surge impedence of line limits the amplitude of the line to

earth over voltage to a value which wills safe guard the insulation of the pro-

tected equipment. 

An ideal L.A should have following characteristics:-

1. It should not take any current under normal condition .i.e. its spark

over voltage must be higher then the system voltage.

2. Any abnormal transient voltage above the break down voltage must

caused it to break as quick as possible in order to provide an alternate path to

earth.

3. It must be able to carry the resultant discharge current without

causing damage to itself.

For high voltage system the thirties type L.A are used .The value type is

also known as non linear diverter .These arrester consist of a spark gape and a

non linear resistance. Both resistance and spark gape are accommodated in se-

ries with a completely light porcelain condition humidity etc.

SPARK GAPE:-

They include a number of identical elements connected in series .Each ele-

ment consist of with pre ionization device between each grounding resistance of

high ohmic value connected in parallel. 

3.3 NON LINEAR RESISTER:-

The resister disc comprises inorganic material having a silicon carbide base

in a clay board. These discs form a block. The ohmic value of which decreases

rapidly when the applied voltage and current increases as soon as the current

wave resulting from the over voltage has been discharged. The resister block

subjected to the sole. Alternating Voltage and resistance assumes great

value .So that the amplitude of the resulting current becomes zero.    

Figure-3.1 Lighting Arresters

CHAPTER=4

WAVE TRAP

It is used to trap the communication signals & send PLCC room through

CVT.  

Rejection filters are known as the line traps consisting of a parallel resonant

circuit ( L and C in parallel) tuned to the carrier frequency are connected in se-

ries at each and of the protected line such a circuit offer high impedance to the

flow of carrier frequency current thus preventing the dissipation. The carrier

current used for PLC Communication have to be prevented from entering the

power equipments such as attenuation or even complete loss of communication

signals. For this purpose wave trap or line trap are used between transmission

line and power station equipment to- 

Avoid carrier power dissipation in the power plant reduce cross talks with

other PLC Circuits connected to the same power station.

Ensure proper operating conditions and signal levels at the PLC transmit re-

ceive equipment irrespective of switching conditions of the power circuit and

equipments in the stations. 

    Line Matching Filter & Protective Equipments

For matching the transmitter and receiver unit to coupling capacitor and power

line matching filters are provided. These flitters normally have air corral trans-

formers with capacitor assumed.

The matching transformer is insulated for 7-10 KV between the two windings

and perform two functions. Firstly, it isolates the communication equipment

from the power line. Secondly, it serves to match .

Figure-4.1 Line Matching Filter & Protective Equipments

Transmitter

The transmitter consists of an oscillator and a amplifier. The oscillator gener-

ates a frequency signal with in 50 to 500 HZ frequency bands the transmitter is

provided so that it modulates the carrier with protective signal. The modulation

process usually involves taking one half cycle of 50 HZ signal and using this to

create block to carrier.    

Receivers 

The receivers usually consist of and alternate matching transformer band

pass filter and amplifier detector.

The amplifier detector converts a small incoming signal in to a signal capa-

ble of operating a relatively intensive carrier receiver relay. The transmitter and

receiver at the two ends of protected each corresponds to local as far as trans-

mitting. 

CHAPTER=5   

 ISOLATOR :-

When carrying out inspection or maintains work in substation ,it is essential

to disconnect reliability the unit of other station on which the work is done from

all other parts on installation in order to ensure full safety of working staff .So

guard against mistake it is desirable that should be done by an apparatus is

called “ISOLATOR”. In other words a device which is used to open or close the

circuit either when negligible current is interrupted or when no significant

change in voltage across the terminal of each pole of the isolator will result

from operation .they must only be opened or closed when current is zero. There

is single ear thing Isolator used .

Isolator is switching device used to open (or close) a circuit either when a

negligible current exists or when no significant change in voltage across the ter-

minal of each pole of the isolator, will result from the operation.

Broadly speaking isolator are the switches which’s operate under "No cur-

rent” condition. Thus, isolator is an apparatus which makes a visible and reli-

able disconnection of the unit or the section after opening the circuit breaker. 

Isolators are file with earthing blades as an integral part of it. They may be

isolators with single ear thing blades or two earthling blades on either side of it.

The isolators used at 220 KV GSS,Alwar have single earthing blades either side

of it.They must only be opened or closed when current is zero. Isolators are

classified into following categories.

1. Bus isolator

2. Line isolator

3. Transformer isolating switch

From constructional point of view the isolator may be classified as-

1.The post- centre post rotating part, double post break type.

2.Two post single type.

3.Base: - Each pipe phase isolator is mounted on a robust base of steal construc-

tion.

Figure- 5.1 Isolator

MOUNTING: -

The central post rotates in gun metal bushing and tapered roller bearing pro-

vided with grease nipples for lubrication required to be alone at regular’s inter-

vals during routine check up. 

EARTH SWITCH :-

(For line side insulation only ) Earthling is achieved by means of an earthed

blade pivoted at the base     steady operation mechanism .the earth contacts are

fixed either at the back or left or right side of main contact and interlocked with

them by mechanism interlock.    

OPERATING MECHANISM:-

1.Hand operated: - It consists of a fulcrums and level system for easy operation

of isolators.

2.The isolators used in G.S.S Alwar at are three post types. Each isolator has

three insulators post per phase mounted on a phase of steal construction.

CHAPTER=6

INSTRUMENT TRANSFORMER:-

The transformers which are used in A.C. system for the measurement of current,

voltage, power and energy are called Instrument transformer. These are also

used in connection with the measurement of power factor, frequency and for in-

dication of synchronism.They are two types namely:

1.Current transformer

2.Potential transformer.

Figure-7.1 POWER X-MER

(1) Core type  

(2) Shell type 

The x-mer used substation is auto-transformer which employed only single

winding per- phase. A part of winding is common to both of sides. In addition

to primary and secondary winding known as tertiary winding is also provided

the power transformer required at substations contain following additional part

–  

1. HV winding bushing

2.  LV winding  bushing

3. Tertiary winding bushing

     4. Jucking plate

Transformer used in conjunction with measuring are ‘INSTRUMENT

TRANSFORMER’. According to the quality   measured. These may be di-

vided as

1.  Current transformer

2   Potential transformer

These instrument transformers are used to step down these current and voltage.

So that they would be metered with instrument of moderate size.     

CHAPTER=7

CURRENT TRANSFORMER:-

The current transformers are kept in the category of the instrument transformer.

The C.T. are used to reduce/ stepping down A.C form high value to lower value 

for  measurement / protection / control.

They are usually installed in the out door switch. The primary conductor at

high voltage with respect to earth. The secondary of  C.T. is just like the ring

type C.T. the primary winding consists of a very few turns , and therefore there

is no. appreciation volt drop across injection . Current is transformed by  C.T.

the current transformer is used with primary winding , connected in series with

the line carrying the current to be measured and therefore primary current is de-

pendent upon load connected in the system.

Measurement of alternating current is one of the most frequent operation not

only because of it’s inheriant but a also because it is necessary in determining

other parameters of electrical circuit. A current transformer value of current is

used for Indication of current kwh and kw meters Telementry Protective relay

etc

A current transformer is intended to operate normally with rated current of

the system flowing through the primary winding which is increased in the series

with the network .Secondary winding of current transformer Connected to mea-

suring instruments and relay supplies currents circulating in the design of cur-

rent transformer.

CHAPTER=8

POTENTIAL TRNASFORMER

Similar to CT it is another  type of instrument type of instrument

transformer .Transformer used for voltage measurements are called voltage

transformer or Potential transformer. it may be of 1 phase or 3

phase                                        

These transformers make the instruments suitable for measurement of high

voltage and isolating then from high voltage. these transformer are connected in

parallel and secondary winding is always open ckt.

 The primary winding of the potential transformer is connected to the main

GSS LINE DIAGRAM. the primary has large no of turn in  secondary,which 

provided step down of voltage , and then the voltmeter is connected  across sec-

ondary terminal  the high voltage line.

Some terms related to PT :-

A. RATED VOLTAGE :-  the capacity voltage  of the PT

which it can stand

B. RATED TRARNSFORMER RATIO:- The ratio of the rated

primary voltage to the rated second voltage.

C. RATED SECONDARY VOLTAGE:- 130 / root (3) = 63.3

VAR.

              Voltage transformer which step down system voltage to sufficient form

high value to low value are necessary in every system for

Induction of d.c supply voltage conduction.

Metering of the supply of energy.

Relaying

Syncronizing.

Design and ranges are selected according to the secondary size of potential

transformer for indicating instruments, meter and relays. But calibration of these

instruments is done according to the primary voltage .   

  CHAPTER=9       `

POWER TRANSFORMER:-

GENERAL:-

The transformers are used to step down or step-up the incoming line voltage

but at grid substation for the purpose of distribution. it is the main & major re-

quirement of GSS for step down the supply voltage .The rating of transformer is

taken according to the load .

There are two power transformers  of 100 MVA . They are used convert 220

KV/132 KV. And  two power transformers  are used of 20/25 MVA .which con-

vert 132KV/33KV. Which transforms e/e energy from one voltage level to an-

other desired level with corresponding change in current value and with out any

change in frequency value.

The physical basis of a transformer is mutual induction between the circuits

linked by a common magnitude pulse voltage supplied to one set of winding

called primary switch builds up a magnitude flux through the iron.

A transformer in simplest form consist of two magnetic coil, which are

electrically separated from each other but magnetically linked through path of

reluctance .

In brief a transformer is a device that

1. Transform electric power from the one circuit to another.

2.  It does not so without a change of frequency.

3.  It accomplishes this by electromagnetic induction.  

The magnetic core is built up of laminations of high –grade section or other

steel which are insulated from each to other by varnish or other insulation mate-

rials.

According to the number of winding placed around the core. The trans-

former are classified as  

     5. Earthing terminals the trank

     6.  Cooling systems

     7.  Pressure relief value

      8. Bush hold relay

       9. Dehydration breather  

      10.  Rollers

     11. Filters

Automatic control:-

The automation required use of automatic voltage control of substation so

that a predetermined bus- bar voltage can maintained. In general a tap changer

is provided on a transformer for a maintaining a pre determine outgoing voltage

where the incoming voltage may be subjected to voltage variations. The output

of P.T. connected to controlled voltage side of the power of transformer is used

to energize the automatic voltage regulating relays. The voltage to be controlled

remains with in prescribed limits.

GAS OPERATED RELAY:-

The relay is located in the pipe between the main tank and conservator. In

case of fault such as insulation was creating impulse failures fall of oil level

produces gases. This rises and accumulated in the upper part of the housing con-

sequently the oil level falls down and the float sinks thereby tilling the mercury

switch. The conducts are closed and alarm circuit is energized. Bachholz protec-

tion is always used in conjunction with some other forms of electricity operated

protective gears as it can unity operate  for truly internal transformer faults and

does not respond to external bushings or cable faults. 

SILICA GEL BREATHER:-

A silica gel breather is employed as a measurement of preveusing moisture

in gress. It is connected to the conservator tank which is filled to transformer to

allow for changes in volume due to temperature variation.

FILTER: - Filter is intended for prolonging like water acid etc from oil. . 

TRANSFORMER OIL:-

In transformer, the insulating oil provides an insulating medium as well as a

heat transferring medium that carry away heat produced in the winding and iron

core.

The life of the transformer depends chiefly upon the quality of the insulat-

ing oil. So high quality insulating oil are used. It should meet the following re-

quirements:-

It should be provide good transfer of heat.

It should provide high electric strength.

It should have low velocity.

Flash point of the oil must be high.

Also fire point should be high.

CHAPTER=10

INSULATORS

In order to avoid current leakage to the Earth, through the supporting struc-

ture provide to the conductor of overhead transmission lines, insulators are

used. The conductors are secured to the supporting structures by means of insu-

lating feature, which do not allow current to flow through these support and

hence finally to the earth . Bus support insulators are porcelain or fiberglass in-

sulators that serve to the bus bar switches and other support structures and to

prevent leakage current from flowing through the structure or to ground. These

insulators are similar in function to other insulator used in substations and trans-

mission poles and towers. 

An Insulator should have following characteristic:-

1. High Insulation resistance.

2. High mechanical strength

3. No internal impurity or crack  Disc

Generally Porcelain or glass is used as material for insulators. Porcelain be-

cause of its low cost. is more common. 

Insulators can be classified in following ways :- 

Pin Type: - These are designed to be mounted on a pin, which in turn is in-

stalled on the cross arm of a pole. 

Figure-8.1 INSULATORS

Suspension Type:-These insulators hang from the cross arm, there by forming

a string. 

The centre post carries the moving contact assembled at the extremities the

moving contact engages the fixed contacts are generally in the form of spring

loaded finger contact.

The insulator consist of following parts - 

1. Contacts :- The contacts are rated for line current and designed to with-

stand electromagnetic strains and prevent charging at rated shortly time current

the contact are made of electrolytic fixed in housing.

2. Switching blade:- The blade is made of electrolytic copper. 

3. Tandom pipe:-All three phases are opened or closed simultaneously with a

tandem pipe this is dipped galvanized and provided with on or off insulators and

pad locking. 

4. Motor operated:-This is meant rotary motion of the linear operating pipe for

either of opening or closing for remote level local operation. Hand operation is

also provides with detectable handle that can be fitted and square.     

CHAPTER-11

CIRCUIT BREAKERS:-

Breakers are switching and current interrupting devices. Basically a cir-

cuit breaker comprises a set of fixed and movable contacts. The contacts can be

separated by means of an operating an arc. The arc is extinguished by a suitable

medium such as dielectric oil vacuum, SF6 gas.

The circuit breakers play an important role in the design and performance

of a power system, in that these are the key pieces of apparatus protecting the

system and thus ensure continuity of supply from consideration of cost, the cir-

cuit breakers represent a major items, and are, next only to the generator and

transformer, since their quantity is greater than that of generators/transformer in

a power system owing to the services required for control of transmission lines,

bus-bar etc. in addition to control of transformers and generator. 

Figure-9.1 CIRCUIT BREAKERS.

FUNCTION OF CIRCUIT BREAKER

The expected functions of a circuit breaker are: -

i. It must be capable of closing on to and carrying full load currents for long

period of time.

ii. Under proscribed condition, it must open automatically to disconnect the

load or some small overload.

iii. It must successfully and rapidly interrupt the heavy current, which flow

when a short circuit has to be cleared from the system.

iv. It must be capable of closing on to a circuit in which a fault exists and im-

mediately re-opening to clear the fault from system

v. It must be capable of carrying current of short circuit magnitude until,

and for such time as, the fault is cleared by another breaker nearer to the pint of

fault.

Circuit Breaker Types

i. Bulk oil Circuit Breakers

ii. Minimum oil Circuit Breakers.

iii. Air blast Circuit Breakers

iv. Sulphur hexafluoride (SF6) Circuit Breakers.

v. Vacuum Circuit Breakers

AIR BLAST CIRCUIT BREAKER

This type of breaker find application operating system from 132 kv and

these are meant for outdoor used and based on the multiple interception. Princi-

pal using compressed air as a medium for quenching the arc. The compressed

air acts as a medium of high dielectric strength which present flashover across

the writers in case of over voltage when the contacts are in open position. The

breaker can be opened or closed pneumatically from the control cabin or by pro-

tective relay or electrically fault occuring the operating pressure used at G.S.S

Alwar is 12 kg/cm. 

AIR BLAST C.B. HAS FOLLOWING ADVANTAGES:-

1. No fire hazards caused by oil.

2. The C.B operates at hogs speeds.

3. The duration of arc is possible.

4. Frequent operation of C.B’s is possible.

5. Almost no maintenance is needed.

6. Facility of high speed recoding.

TYPES OF AIR BLAST C.B’s:-

There are three types of air blast circuit breaker:-

1. Axial blast C.B.

2. Axial blast air C.B. and with side moving contact.

3. Cross blast air circuit breaker.

OPERATION:-

              In the closed position of air blast circuit breaker. There is no com-

pressed air in arc chamber hallow calcium insulator. When fault occurs on the

line CB operates and compressed air quenches the arc into no of section.  

                    VACUUM CIRCUIT BREAKER

    FUNCTION OF SF6 GAS IN SF6 CIRCUIT BREAKERS  

The density of SF6 Gas is about five times that of air and heat dissipation in it

is also much more than in air. 

Air atmospheric pressure dielectric strength of SF6 gas is about 2.4 times

that of air and at about 3-Kg/cm2 it is same as that of oil. Table no. D1 gives

physical properties of SF6 gas. 

There is some decomposition of the gas long periods of arcing. However

such decompositions very little and has no effect upon dielectric strength and

interrupting capability. The solid are product formed by arcing metallic fluoride,

which appears in the form of fine gray powder. This are generated power has

high dielectric strength under dry conditions existing in the breaker. A good

quality absorbent is used so that the level of the gaseous by products is kept

very low. Certain impurities such as air result in the dilution of SF 6 gas in the

field as long as the process recommended is followed. While releasing the arced

gas into atmosphere, international sniffing of gas should be avoided. The rela-

tion between SF6 gas pressure and temperature is given in fig. 4.13, which is a

very useful date at the tie filling of SF6 in circuit breaker.

Figure-9.2 SF6 CIRCUIT BREAKERS

CHAPTER -12

EARTHING

Earthing is the provision of a surface under the sub station, which has a

uniform potential as nearly as zero or equal to Absolute Earth potential. The

provision of an earthing system for an electric system is necessary by the fol-

lowing reason. 

1. In the event of over voltage on the system due to lighting discharge or other

system fault. These parts of equipment which are normally dead as for as volt-

age, are concerned do not attain dangerously high potential.

2. In a three phase, circuit the neutral of the system is earthed in order to stabi-

lize the potential of circuit with respect to earth.

The resistance of earthing system is depending on shape and material of

earth electrode used.

The earthing is of two principal types  :-

Neutral Earthing

Equipment Body Earthing

    Neutral Earthing:-

Neutral Earthing also known as System Neutral Earthing (or Grounding)

means connecting the neutral point i.e. the star point of generator,transformer

etc. to earth. In rotating machines, generator, transformer circuit etc., the neutral

point is always connected to earth either directly or through a reactance. The

neutral point is usually available at every voltage level from generator or trans-

former neutral. If neutral point is not available, then the most common method

used is using a Zigzag transformer. Such a transformer has no secondary. Each

phase of primary has two equal parts. There are 3 limbs and each limb has two

winding, providing flux density under normal condition. Since the fluxes are

opposite, the transformer takes very small magnetizing current under normal

conditions. During fault, the circuit is primary side,

which provides very less impedance to the current. The grounding trans-

formers are short time rating. Their size is almost one tenth as compared to

power transformer. 

Electrical Earthing:-

Electrical Earthing is different from neutral earthing. During fault condi-

tion, the metallic parts of an electrical installation which do not carry current

under normal conditions, may attain high potential with respect to ground. As

human body can tolerate only I=0.165A/T current for a given time t so to ensure

safety we connect such metallic parts to earth by means of Earthing

system ,which comprises of electrical conductor to send fault current to earth.

The conductor used is generally in the form of rods, plates, pipes etc. 

Earthing system ensures safety in following ways :-

1. The potential of earthen body does not reach dangerously high value

about earth, since it is connected to earth.

2.  Earth fault current flows through earthing and readily causes the opera-

tion of fuse or an earth relay.

Connection of Electrical Equipment to Substation:- 

S.NO. Apparatus Path to be connected

1. Supporting of bus insu-

lator

Base plate

2. High voltage circuit

breaker

Operating mechanism

frame

3. Isolator Operating mechanism

frame bed

4. Potential transformer Transformer tank LV

5. Power transformer Core tank

Merits of neutral Earthing:-

1. Arcing grounding is reduced.

2. Voltage of heating with respect to earth remains at harmless value they don't

increase to root 3 times of normal value. 

3. Suitable neutral point.

4. The earth fault relaying is relatively simple useful amount of earth fault cur-

rent is available to operate earth fault relay.

5. The over voltage due to lightening are discharged to earth. 

6. Improved service reliability due to limitation of arcing ground and improved

of unnecessary fringing of CB.

At GSS the neutral point of power transformer is connected solidly to earth gen-

erally the earth connection are provided which leads reliability.

CHAPTER-13

Power Line Carrier Communication :-

Introduction

Power Line Carrier Communication (PLCC) provides for signal transmis-

sion down transmission line conductors or insulated ground wires. Protection

signaling, speech and data transmission for system operation and control, man-

agement information systems etc. are the main needs which are met by PLCC. 

PLCC is the most economical and reliable method of communication be-

cause of the higher mechanical strength and insulation level of high voltage

power line which contribute to the increased reliability of communication and

lower attenuation over the larger distances involves.   

High frequency signals in the range of 50 KHZ to 400 KHZ commonly

known as the carrier signal and to result it with the protected section of line suit-

able coupling apparatus and line traps are employed at both ends of the pro-

tected section. Here in Alwar and also in other sub-station this system is used.

The main application of power line carrier has been from the purpose of super-

visory control telephone communication, telemetering and relaying.  

PLCC Equipment

The essential units of power line carrier equipment consists of :-

a. Wave trap

b. Coupling Capacitor 

c. LMU and protective equipments.

MERITS AND DEMRITS OF PLCC 

Merits  

The severity that a power line can withstand is much more than that odd com-

munication line due to higher mechanical strength of transmission line power

lines generally provide the shortest route between the Power Station and the Re-

ceiving Stations. 

The carrier signals suffer less attenuation, owing to large cross sectional area of

power line

Larger spacing between conductors reduces the capacitances which results in

lesser attenuation of higher frequencies.

Large spacing also reduces the cross talk to a certain extent.

The construction of a separate communication line is avoided. 

Demerits 

Utmost care is required to safeguard the carrier equipment and persons using

them against high voltage and currents on the line. 

Noise introduced by power line is far more than in the case of communication

line. This is due to the discharge across insulators and corona etc. 

Induced voltage surges in the power line may affect the connected carrier equip-

ment.   

CHAPTER-14

PROTECTIVE RELAY

The purpose of protective relay and protective system is to operate the

correct CB‘s as to disconnect only the faulty equipment from the system as

quickly as possible. Thus minimizes the trouble caused by fault by they do oc-

cur. The protective relay does not operate possibility of the fault on the system.

Their active starts only after the faults have occurred. It could be idea led if the

protection could anticipate and peasant faults because it is impossible to except

where original case of fault create some effects which can operate a protective

relay. These are two groups of protective relay.

1. Primary relaying equipments.

2. Back-up relaying equipments.

  Primary relaying is the first line of difference whereas back up protection

relaying works. Only when the primary relaying equipments fails and also back

up relays are slow in motion condition. Another job of back relay is to act as

primary relay in case of where this is out work.

Relay must operate when it is required. Since relay remains ideal. Most of

the time proper maintenance also plays important role in improving reliability.

Relay should select fault region and isolate that section from circuit. It should

also operate required speed. It should neither be slow which may not result in

damage to the equipment nor it should too fast which may result undesired op-

eration during transient faults and should be sensitive to faults. 

OPERATION:-

The protective relay serves for preventing tap changers and transformer

from being damage which is the part of delivering the protective relay as to be

connected in away that transformer immediately switched off captions oil im-

mersed transformer. Transformer break down are always precede by more or

less violent generation of gas. A broking joints produce local arc and vaporize

in the vicinity. As earth faults has the some results sudden short circuit rapidly

increased the temperature of the winding particularly the inner layer and packed

oil in vaporize. Discharge due to insulation weaken i.e. by the dehydration of

the oil produce local heating and generate gas. The generation of oil vapour or

gas in utilize to actuate a relay the relay is arranged between the transformer

tank and the separate oil conservator. The vessel is normally is full of oil. It

contains two floats if the gas bubbles are generated in transformer due to faults.

They will be rise and transfers the conservator and will trap in the upper part of

the relay chamber. Thereby displacing the oil and lowering the faults. This sinks

and eventually closes and external contacts which operates an alarm over other

protection and flashover at the bushing are not at adequately covered by other

protective scheme also unless it improves ground.

The differential scheme detects such faults and also on the leads between

CTs are power transformer provided ct’s are not mounted separately on trans-

former bushing. In service internal faults operate when the relay is energizes.

The protective relay reenergized only by oil flow from the tap changer heat to

the conservator. The oil flow operates the flap value which is trapped into the

“off” position by timing mechanism. Thus the trapping switch is energized the

CB’s are operated the transformer off the line.

                      CHAPTER-15

CONTROL ROOM

        To remote control of power switch gear requires the provision of suitable

control plates located at a suitable point remote from immediate vicinity of

CB’s and other equipments.

At "GSS ALWAR" the separate control room provided for remote protec-

tion of 220KV switch yards transformer incoming feeder, outing feeders. Bus

bar has their own control plant in their control rooms. The control panel carrier

the appropriate relays. Necessary meters indicating lamp control switches and

fuses. There are meters for reading purpose. A circuit concerning the panel is

shown on the panel with standard co lour.

On each panel a control switch is provided for remote operation of circuit

breaker. There are two indicators which show that weather circuit breaker is

closed or open. A control switch for each insulator is also provided. The posi-

tion indicator of isolator is also done with the help of single lamp and indicator.

The colour of signal lamps are as follows :- 

RED:- For circuit breaker or isolator is close option

GREEN:-For CB or isolator in open position.    

In addition to used indication an alarm is also providing for indicating ab-

normal condition when any protective relay or tripping relay has operated. Its

constants energies on auxiliary alarm. Relay which on operation completes the

alarm belt circuit. 

Synchronizing:-

There is a hinged Synchronizing panel mounted at the end of control panel.

Before coupling any incoming feeders to the bus bar. It just be Synchronized

with switches. When the synchronous copy shows zero we close the circuit

breaker. 

Synchronoscope:-

Synchronoscope is used to determine the correct instant of closing the

switch which connect the new supply  to bus bar. The correct instant of syn-

chronizing when bus bar incoming voltage. 

a. Are in phase

b. Are equal in magnitude

c. Are in some phase sequence

d. Having same frequency

e. The voltage can be checked by voltmeter the function of syn-

chronoscope is to indicate the difference in phase and frequency. 

Energy Meter:-

These are fitted on different panel to record transmitted energy and recorded

in energy hours. For this purpose MWH meter have been provided. 

Watt Meter:-

This is mounted on each feeder panel to record import or export power. 

Frequency Power:-

Provided to each feeder to measure frequency which analog or digital. 

Volt Meter :-

Provided on each panel or the purpose of indication of voltage. 

Ammeter:-

These are used to indication the line current. 

MVAR Meter:-

Provided for indicating power factor of import and export. 

Maximum Indicator Demand :-

Chief requirement of these indicators to record the minimum power factor

taken by feeder during a particular period. This record the average power suc-

cessive predetermined period.

CHAPTER-16

BATTERY ROOM

There is a battery sexton or battery room which has 55 batteries of 2 volt

each for 132KV section and 110 batteries for 220KV section. Therefore D.C.

power available is for functioning of the control panels. A battery charger to

charge the battery. 

Various parts of lead acid batteries:-

o Plates

o Separators

o Electrolyte

o Container

o Terminal port

o Vent plugs

Charging of batteries:-

Initial charging-: 

It is the first charging given to batteries by which the   positive plates are

converted to “lead peroxide”, where as the –ve plates will converted to spongy

lead.

       Also in a fully charged battery the electrolyte specific gravity will be at its

highest venue or 1.2 and its terminal voltage will be 24 volts

Discharging:-

When a fully charged battery delivers its energy out by meeting a load the

lead peroxide of the +ve plates slowly gets converted to lead sulphate and the

spongy lead of the –ve plates also gets converted into lead sulphate during this

time the specific gravity of the electrolyte also decreases the value around 1.00

and the terminal voltage also decreases from its initial to a lower value which

may be around 1.85 or 1.8.

CHAPTER-17

CONCLUSION

The training at grid substation was very helpful. It has improved my theoretical

concepts of electrical power transmission and distribution. Protection of various

apparatus was a great thing. Maintenance of transformer, circuit breaker, isola-

tor, insulator, bus bar etc was observable.

I had a chance to see the remote control of the equipments from control

room itself, which was very interesting.

So the training was more than hope to me and helped me to understand

about power system more.