63724247 220 Kv Gss Sanganer Report

A PRACTICAL TRAINING SEMINAR REPORT

ON

“RAJASTHAN RAJYA VIDHUT PRASARAN NIGAM

LIMITED

220 KV G.S.S., SANGANER”

SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENT FOR THE

AWARD OF THE DEGREE OF

BACHELOR OF TECHNOLOGY

(ELECTRICAL ENGINEERING)

Session: - 2011-2012

SUBMITTED TO: - SUBMITTED BY:-

Mr. DEVENDRA DODA SURESH KUMAR KHINCHI

LECTURER, ELE. DEPTT. ELECTRICAL ENGG. (7TH SEM)

ROLL NO. - 7EE 96

ENROLLMENT NO.-0105080363

JAIPUR NATIONAL UNIVERSITY, JAIPUR

(A Venture of Seedling Group of Institutions)

A PRACTICAL TRAINING SEMINAR REPORT

ON

“RAJASTHAN RAJYA VIDHUT PRASARAN NIGAM

LIMITED

220 KV G.S.S., SANGANER”

JAIPUR NATIONAL UNIVERSITY, JAIPUR

(A Venture of Seedling Group of Institutions)

SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENT FOR THE

AWARD OF THE DEGREE OF

BACHELOR OF TECHNOLOGY

(ELECTRICAL ENGINEERING)

SUBMITTED BY:

BHAGWAN MEENA

ELECTRICAL ENGG. (7TH SEM)

ROLL NO. – 7EE 20

ENROLLMENT NO.-0105080296

JAIPUR NATIONAL UNIVERSITY, JAIPUR

(A Venture of Seedling Group of Institutions)

CANDIDATE’S DECLARATION

I hereby certify that the work which is being presented in the report entitled “RAJASTHAN

RAJYA VIDHUT PRASARAN NIGAM LIMITED 220 KV G.S.S., SANGANER” by

“BHAGWAN MEENA” in partial fulfillment of requirements for the award of degree of

B.Tech. (4th year, Electrical Engg.) submitted in the Department of Electrical Engg. at Jaipur

National University, Jaipur is an authentic record of my own work carried out during a period

from

13-06-2011 to 28-07-2011 under the supervision of Mr. K.K. MEENA (Executive Engg. of

GSS, Sanganer, Jaipur) and Mr. K.C. YADAV (Asst. Engg. of GSS, Sanganer, Jaipur).

Signature of the Student

The B.Tech (3rd year, Electrical Engg.) seminar presentation of BHAGWAN MEENA has been held on and accepted.

Signature of Internal Examiner 1 Signature of Internal Examiner 2

ACKNOWLEDGEMENT

It is mandatory for all students to undertake a practical training after 3rd year in any of the

relevant electrical companies, generating stations or G.S.S.

First of all I would like to convey my sincere thanks to Mr. DEVENDRA DODA,

Lecturer of Electrical. Deptt. and Mr. VISHWASH KUMAR, Lecturer of Electrical Deptt. for

recommendation to 220 KV , G.S.S. SANGANER training program.

I take this opportunity to express my gratitude towards all those people who helped me

successfully complete this summer training.

I am especially grateful to Mr. K.K.MEENA (Executive Engg.) and Mr. K.C. YADAV (Asst.

Engg) for providing me their elusive guidance during my training.

I would also like to offer my sincere thanks to all those staff officials for their untiring support

and help at various levels.

BHAGWAN MEENA

B.TECH. 7th SEM. (EE)

JNU, JAIPUR

LIST OF FIGURES

Page No.

220 KV GSS SANGANER 1

SINGLE LINE DIAGRAM OF 220KV GSS SANGANER (JAIPUR) 5

LIGHTNING ARRESTER 6

PIN TYPE INSULATOR 11

SUSPENSION TYPE INSULATOR 12

STRAIN TYPE INSULATOR 12

ISOLATOR 13

SF6 CIRCUIT BREAKER 16

AIR BLAST CIRCUIT BREAKER 17

RELAYS 21

POWER TRANSFORMER 23

RADIATOR WITH FAN 24

BUCHHOLZ RELAY 25

WINDING AND OIL TEMPERATURE INDICATOR 26

SILICA GEL BREATHER 26

CONSERVATOR WITH BUCHHOLZ RELAY AND TANK 27

CURRENT TRANSFORMERS 29

POTENTIAL TRANSFORMER 31

CONTROL ROOM IN GSS SANGANER 34

CAPACITOR BANK 36

WAVE TRAP 37

BATTERY ROOM 41

CONTENTS

Page No.

Chapter 1: INTRODUCTION1

1.1: 220 KV GSS, SANGANER 2

1.2: INCOMING FEEDER 3

1.3: OUTGOING FEEDER 3

Chapter 2: LIGHTNING ARRESTER 6

2.1: TYPES OF ARRESTERS 7

2.1.1: ROD/SPHERE GAP 7

2.1.2: EXPULSION TYPE LA 7

2.1.3: VALVE TYPE LA 7

Chapter 3: BUS BARS 8

3.1: TYPES OF BUS BAR ARRANGEMENT 8

3.1.1: SINGLE BUS BAR ARRANGEMENT 9

3.1.2: DOUBLE BUS BAR ARRANGEMENT 9

3.1.3: DOUBLE BUS BAR ARRANGEMENT WITH AUXILIARY BUS 9

Chapter 4: INSULATORS 10

4.1: TYPES OF INSULATORS 10

4.1.1: PIN TYPE 11

4.1.2: SUSPENSION TYPE 12

4.1.3: STRAIN INSULATOR 12

Chapter 5: ISOLATORS 13

Chapter 6: CIRCUIT BREAKER 15

6.1: TYPES OF CIRCUIT BREAKER 16

6.1.1: SF6 CIRCUIT BREAKER 16

6.1.2: AIR BLAST CIRCUIT BREAKER 17

6.1.3: OIL CIRCUIT BREAKER 19

6.1.4: BULK OIL CIRCUIT BREAKER (MOCB) 20

6.1.5: MINIMUM OIL CIRCUIT BREAKER 20

Chapter 7: PROTECTIVE RELAYS 21

7.1: DISTANCE RELAYS 22

7.2: TYPES OF DISTANCE RELAY 22

7.2.1: IMPEDANCE RELAY 22

7.2.2: ADMITTANCE RELAY 22

7.2.3: REACTANCE RELAY 22

Chapter 8: POWER TRANSFORMER 23

8.1: WINDINGS 23

8.2: TANK & FITTINGS 24

8.3: COOLING EQUIPMENTS 24

8.4: TRANSFORMER ACCESSORIES 25

8.4.1: BUCHHOLZ RELAY 25

8.4.2: TEMPERATURE INDICATOR 25

8.4.3: SILICA GEL BREATHER 26

8.4.4: CONSERVATOR 27

Chapter 9: CURRENT TRANSFORMER 29

Chapter 10: POTENTIAL TRANSFORMER 31

Chapter 11: CAPACITIVE VOLTAGE TRNSFORMER 33

Chapter 12: CONTROL ROOM 34

12.1: MEASURING INSTRUMENT USED 35

Chapter 13: CAPACITOR BANK 36

Chapter 14: POWER LINE CARRIER COMMUNICATION 37

14.1: WAVE TRAP 37

Chapter 15: EARTHING OF THE SYSTEM 39

15.1: PROCEDURE OF EARTHING 39

15.2: NEUTRAL EARTHING 40

Chapter 16: BATTERY ROOM 41

Chapter 17: RATTINGS 42

CONCLUSION 45

REFERENCES 46

CHAPTER 1

INTRODUCTION

Electrical power is generated, transmitted in the form of alternating current. The electric

power produced at the power stations is delivered to the consumers through a large network of

transmission & distribution. The transmission network is inevitable long and high power lines

are necessary to maintain a huge block of power source of generation to the load centers to inter

connected. Power house for increased reliability of supply greater.

The assembly of apparatus used to change some characteristics (e.g. voltage, ac to dc,

frequency, power factor etc.) of electric supply keeping the power constant is called a substation.

An electrical substation is a subsidiary station of an electricity generation, transmission

and distribution system where voltage is transformed from high to low or the reverse using

transformers. Electric power may flow through several substations between generating plant and

consumer, and may be changed in voltage in several steps.

Fig.1.1 - 220 KV GSS Sanganer [Ref.-7]

Page-1

Substations have switching, protection and control equipment and one or more

transformers. In a large substation, circuit breaker are used to interrupt any short-circuits or

overload currents that may occur on the network.

Depending on the constructional feature, the high voltage substations may be

further subdivided:

(a) Outdoor substation

(b) Indoor substation

(c) Base or Underground substation

1.1) 220KV Grid Substation, Sanganer:

Its part of RVPN. It is situated 13.4km away from Jaipur. The power mainly comes from 220 KV

K.T.P.S, 220KV Heerapura (400KV) and 220 KV Heerapura (220KV) 132 KV Heerapura

(220KV). The substation is equipped with various equipments and there are various

arrangements for the protection purpose. The equipments in the GSS are listed previously. At

this substation following feeders are established.

1. TIE FEEDERS

2. RADIAL FEEDERS

220KV GSS SANGANER is an outdoor type primary substation and distribution as well it has

not only step down but the distribution work

The electrical work in a substation comprises to:

1. Choice of bus bar arrangement layout.

2. Selection of rating of isolator.

3. Selection of rating of instrument transformer.

4. Selection of rating of C.B.

5. Selection of lighting arrester [LA]

6. Selection of rating of power transformer

7. Selection of protective relaying scheme, control and relay boards.

8. Selection of voltage regulator equipment.

9. Design a layout of earthing grids and protection against lightening stockes.

Page-2

1.2) INCOMING FEEDERS:

The incoming feeders are:

1) 220 KV HEERAPURA-I

2) 220 KV HEERAPURA-II

3) 220 KV K.T.P.S.

1.3) OUTGOING FEEDERS:

The outgoing feeders are:

A) 132 KV:

1) Sitapura

2) Heerapura

3) Mansarovar

4) SMS Stadium

5) Balawala

6) Chaksu

B) 33KV:

1) Durgapura -1

2) Durgapura-2

3) Sanganer

4) Sitapura

5) I.O.C

6) Watika

7) Phagi

8) Malpura gate

9) Mandi

Page-3

C) 11KV:

1) Muhana

2) Tejawala

3) Prem nagar

4) Industrial

Rajasthan Rajya Vidyut Prasaran Nigam Limited (RVPN) a company under the Companies

Act, 1956 and registered with Registrar of Companies as "RAJASTHAN RAJYA VIDYUT

PRASARAN NIGAM LIMITED" vide No. 17-016485 of 2000-2001 with its Registered Office

at VIDYUT BHAWAN, JYOTI NAGAR, JAIPUR-302005 has been established on 19 July,

2000 by Govt. of Rajasthan under the provisions of the Rajasthan Power Sector Reform act

1999 as the successor company of RSEB. The RERC has granted RVPN a license for

transmission and bulk supply vide RERC/Transmission and Bulk Supply License 4/2001 dated

30.

Our aim is to provide reliable electric transmission service to these customers. As a public

utility whose infrastructure serves as the link in transporting electricity to millions of electricity

users, RVPN has following duties and responsibilities:

• Intra state transmission of electricity through Intra-State Transmission System.

• Ensuring development of an efficient, co-ordinated and economical system of intra-state

transmission of electricity from generating stations to Load Centers.

• Non-discriminatory Open Access to its transmission system on payment of transmission

charges

• Complying with the directions of RLDC and SLDC, operating SLDC until any other authority

is established by the State Govt.

• Now RVPN is "An ISO 9001:2000 Certified Company" [Ref.-7]

Page-4

Fig 1.2: Single Line Diagram of 220KV GSS Sanganer(Jaipur) [Ref.-7]

Page-5

CHAPTER 2

LIGHTNING ARRESTER

Fig.2.1- Lightning arrester [Ref.-7]

A lightning arrester (also known as surge diverter) is a device connected between line and

earth i.e. in parallel with the over headline, HV equipments and substation to be protected. It is a

safety valve which limits the magnitude of lightning and switching over voltages at the

substations, over headlines and HV equipments and provides a low resistance path for the surge

current to flow to the ground. The practice is also to install lightning arresters at the incoming

terminals of the line.

Page-6

All the electrical equipments must be protected from the severe damages of lightning strokes.

The techniques can be studied under:-

• Protection of transmission line from direct stroke.

• Protection of power station and sub-station from direct stroke.

• Protection of electrical equipments from travelling waves.

2.1) Types of Arrestors:-

2.1.1) Rod/sphere gap:- It is a very simple protective device i.e. gap is

provided across the stack of Insulators to permit flash-over when undesirable

voltages are impressed of the system.

2.1.2) Expulsion type LA:- It have two electrodes at each end and consists

of a fiber tube capable of producing a gas when is produced. The gas so evolved

blows the arc through the bottom electrode.

2.1.3) Valve type LA:- It consists of a divided spark-gap in series will a non linear resistor. The divided spark gap consists of a no. of similar elements, each of it two electrode across which are connected high resistor.

Page-7

CHAPTER 3

BUS BARS

Bus Bars are the common electrical component through which a large no of feeders

operating at same voltage have to be connected.

If the bus bars are of rigid type (Aluminum types) the structure height are low and

minimum clearance is required. While in case of strain type of bus bars suitable ACSR conductor

are strung/tensioned by tension insulators discs according to system voltages. In the widely used

strain type bus bars stringing tension is about 500-900 Kg depending upon the size of conductor

used.

Here proper clearance would be achieved only if require tension is achieved. Loose bus

bars would effect the clearances when it swings while over tensioning may damage insulators.

Clamps or even effect the supporting structures in low temperature conditions.

The clamping should be proper, as loose clamp would spark under in full load condition

damaging the bus bars itself.

3.1) BUS BAR ARRENGEMENT MAY BE OF FOLLOWING TYPE

WHICH IS BEING ADOPTED BY R.R.V.P.N.L.:-

3.1.1) Single bus bar arrangement

3.1.2) Double bus bar arrangement

a) Main bus with transformer bus

b) Main bus-I with main bus-II

3.1.3) Double bus bar arrangement with auxiliary bus.

Page-8

3.1.1) SINGLE BUS BAR ARRANGEMENT :

This arrangement is simplest and cheapest. It suffers, however, from major defects.

1. Maintenance without interruption is not possible.

2. Extension of the sub station without a shut down is not possible

3.1.2) DOUBLE BUS BAR ARRANGEMENT :

1. Each load may be fed from either bus.

2. The load circuit may be divided in to two separate groups if needed from

operational consideration. Two supplies from different sources can be put on

each bus separately.

3. Either bus bar may be taken out from maintenance of insulators.

The normal bus selection insulators can not be used for breaking load currents.

The arrangement does not permit breaker maintenance without causing stoppage of

supply.

3.1.3) DOUBLE BUS BAR ARRANGEMENTS CONTAINS MAIN BUS

WITH AUXILARY BUS :

The double bus bar arrangement provides facility to change over to either bus to carry out maintenance on the other but provide no facility to carry over breaker maintenance. The main and transfer bus works the other way round. It provides facility for carrying out breaker maintenance but does not permit bus maintenance. Whenever maintenance is required on any breaker the circuit is changed over to the transfer bus and is controlled through bus coupler breaker.

Page-9

CHAPTER 4

INSULATOR

The insulator for the overhead lines provides insulation to the power conductors from the ground

so that currents from conductors do not flow to earth through supports. The insulators are

connected to the cross arm of supporting structure and the power conductor passes through the

clamp of the insulator. The insulators provide necessary insulation between line conductors and

supports and thus prevent any leakage current from conductors to earth. In general, the insulator

should have the following desirable properties:

• High mechanical strength in order to withstand conductor load, wind load etc.

• High electrical resistance of insulator material in order to avoid leakage currents

to earth.

• High relative permittivity of insulator material in order that dielectric strength is

high.

• High ratio of puncture strength to flash over.

These insulators are generally made of glazed porcelain or toughened glass. Poly come type

insulator [solid core] are also being supplied in place of hast insulators if available indigenously.

The design of the insulator is such that the stress due to contraction and expansion in any part of

the insulator does not lead to any defect. It is desirable not to allow porcelain to come in direct

contact with a hard metal screw thread.

4.1) TYPE OF INSULATORS:

4.1.4: Pin type

4.1.5: Suspension type

4.1.6: Strain insulator

Page-10

4.1.1) PIN TYPE: pin type insulator consist of a single or multiple shells

adapted to be mounted on a spindle to be fixed to the cross arm of the supporting

structure. When the upper most shell is wet due to rain the lower shells are dry

and provide sufficient leakage resistance these are used for transmission and

distribution of electric power at voltage up to voltage 33 KV. Beyond operating

voltage of 33 KV the pin type insulators thus become too bulky and hence

uneconomical.

Fig.4.1-Pin type insulator [Ref.-5]

Page-11

4.1.2) SUSPENSION TYPE: suspension type insulators consist of a

number of porcelain disc connected in series by metal links in the form of a string.

Its working voltage is 66KV. Each disc is designed for low voltage for 11KV.

Fig.4.2-Suspension type insulator [Ref.-5]

4.1.3) STRAIN INSULATOR: the strain insulators are exactly identical in

shape with the suspension insulators. These strings are placed in the horizontal

plane rather than the vertical plane. These insulators are used where line is

subjected to greater tension. For low voltage lines (< 11KV) shackle insulator are

used as strain insulator.

Fig.4.3-Strain type insulator [Ref.-5]

Page-12

CHAPTER 5

ISOLATORS

“Isolator" is one, which can break and make an electric circuit in no load condition. These

are normally used in various circuits for the purposes of Isolation of a certain portion when

required for maintenance etc. Isolation of a certain portion when required for maintenance etc.

"Switching Isolators" are capable of

• Interrupting transformer magnetized currents

• Interrupting line charging current

• Load transfer switching

Fig.5.1- Isolators [Ref.-7]

Page-13

Its main application is in connection with transformer feeder as this unit makes it possible to

switch out one transformer, while the other is still on load. The most common type of isolators is

the rotating centre pots type in which each phase has three insulator post, with the outer posts

carrying fixed contacts and connections while the centre post having contact arm which is

arranged to move through 90` on its axis.

The following interlocks are provided with isolator:

a) Bus 1 and2 isolators cannot be closed simultaneously.

b) Isolator cannot operate unless the breaker is open.

c) Only one bay can be taken on bypass bus.

d) No isolator can operate when corresponding earth switch is on breaker.

Page-14

CHAPTER 6

CIRCUIT BREAKER

The function of relays and circuit breakers in the operation of a power system is to

prevent or limit damage during faults or overloads, and to minimize their effect on the remainder

of the system. This is accomplished by dividing the system into protective zones separated by

circuit breakers. During a fault, the zone which includes the faulted apparatus is de-energized

and disconnected from the system. In addition to its protective function, a circuit breaker is also

used for circuit switching under normal conditions.

Each having its protective relays for determining the existence of a fault in that zone and

having circuit breakers for disconnecting that zone from the system. It is desirable to restrict the

amount of system disconnected by a given fault; as for example to a single transformer, line

section, machine, or bus section. However, economic considerations frequently limit the number

of circuit breakers to those required for normal operation and some compromises result in the

relay protection.

Some of the manufacturers are ABB, AREVA, Cutler-Hammer (Eaton), Mitsubishi

Electric, Pennsylvania Breaker, Schneider Electric, Siemens, Toshiba, Končar HVS and others.

Circuit breaker can be classified as "live tank", where the enclosure that contains the

breaking mechanism is at line potential, or dead tank with the enclosure at earth potential. High-

voltage AC circuit breakers are routinely available with ratings up to 765,000 volts.

Page-15

6.1) Various types of circuit breakers:-

6.1.1) SF6 Circuit Breaker

6.1.2) Air Blast Circuit Breaker

6.1.3) Oil Circuit Breaker

6.1.4) Bulk Oil Circuit Breaker (MOCB)

6.1.5) Minimum Oil Circuit Breaker

6.1.1) SF6 CIRCUIT BREAKER:-

Sulphur hexafluoride has proved its-self as an excellent insulating and arc quenching medium. It

has been extensively used during the last 30 years in circuit breakers, gas-insulated switchgear

(GIS), high voltage capacitors, bushings, and gas insulated transmission lines. In SF6 breakers the

contacts are surrounded by low pressure SF6 gas. At the moment the contacts are opened, a small

amount of gas is compressed and forced through the arc to extinguish it.

Fig.6.1-SF6 Circuit Breaker [Ref.-7]

Page-16

6.1.2) AIR BLAST CIRCUIT BREAKER:

The principle of arc interruption in air blast circuit breakers is to direct a blast of air, at

high pressure and velocity, to the arc. Fresh and dry air of the air blast will replace the

ionized hot gases within the arc zone and the arc length is considerably increased.

Consequently the arc may be interrupted at the first natural current zero. In this type of

breaker, the contacts are surrounded by compressed air. When the contacts are opened the

compressed air is released in forced blast through the arc to the atmosphere extinguishing

the arc in the process.

Fig.6.2-Air Blast Circuit Breaker [Ref.-7]

Page-17

Advantages:

An air blast circuit breaker has the following advantages over an oil circuit breaker:

• The risk of fire is eliminated

• The arcing products are completely removed by the blast whereas the oil deteriorates

with successive operations; the expense of regular oil is replacement is avoided

• The growth of dielectric strength is so rapid that final contact gap needed for arc

extinction is very small. this reduces the size of device

• The arcing time is very small due to the rapid build up of dielectric strength between

contacts. Therefore, the arc energy is only a fraction that in oil circuit breakers, thus

resulting in less burning of contacts

• Due to lesser arc energy, air blast circuit breakers are very suitable for conditions where

frequent operation is required

• The energy supplied for arc extinction is obtained from high pressure air and is

independent of the current to be interrupted.

Disadvantages:

Air has relatively inferior arc extinguishing properties.

• Air blast circuit breakers are very sensitive to the variations in the rate of restriking

voltage.

• Considerable maintenance is required for the compressor plant which supplies the air

blast

• Air blast circuit breakers are finding wide applications in high voltage installations.

Majority of circuit breakers for voltages beyond 110 kV are of this type.

Page-18

6.1.3) OIL CIRCUIT BREAKER:

Circuit breaking in oil has been adopted since the early stages of circuit breakers

manufacture. The oil in oil-filled breakers serves the purpose of insulating the live parts from the

earthed ones and provides an excellent medium for arc interruption. Oil circuit breakers of the

various types are used in almost all voltage ranges and ratings. However, they are commonly

used at voltages below 115KV leaving the higher voltages for air blast and SF6 breakers. The

contacts of an oil breaker are submerged in insulating oil, which helps to cool and extinguish the

arc that forms when the contacts are opened. Oil circuit breakers are classified into two main

types namely: bulk oil circuit breakers and minimum oil circuit breakers.

The advantages of using oil as an arc quenching medium are:

1. It absorbs the arc energy to decompose the oil into gases, which have excellent cooling

properties.

2. It acts as an insulator and permits smaller clearance between live conductors and

earthed components.

The disadvantages of oil as an arc quenching medium are:

1. Its inflammable and there is risk of fire

2. It may form an explosive mixture with air.

3. The arcing products remain in the oil and it reduces the quality of oil after several

operations.

This necessitates periodic checking and replacement of oil.

Page-19

6.1.4) BULK OIL CIRCUIT BREAKER:

Bulk oil circuit breakers are widely used in power systems from the lowest voltages up to

115KV. However, they are still used in systems having voltages up to 230KV.The

contacts of bulk oil breakers may be of the plain-break type, where the arc is freely

interrupted in oil, or enclose within arc controllers.

Plain-break circuit breakers consist mainly of a large volume of oil contained in a

metallic tank. Arc interruption depends on the head of oil above the contacts and the

speed of contact separation. The head of oil above the arc should be sufficient to cool the

gases, mainly hydrogen, produced by oil decomposition. A small air cushion at the top of

the oil together with the produced gases will increase the pressure with a subsequent

decrease of the arcing time.

6.1.5) MINIMUM OIL CIRCUIT BREAKER:

Bulk oil circuit breakers have the disadvantage of using large quantity of oil. With frequent breaking

and making heavy currents the oil will deteriorate and may lead to circuit breaker failure. This has

led to the design of minimum oil circuit breakers working on the same principles of arc control as

those used in bulk oil breakers. In this type of breakers the interrupter chamber is separated from the

other parts and arcing is confined to a small volume of oil. The lower chamber contains the operating

mechanism and the upper one contains the moving and fixed contacts together with the control

device. Both chambers are made of an insulating material such as porcelain. The oil in both

chambers is completely separated from each other. By this arrangement the amount of oil needed for

arc interruption and the clearances to earth are roused. However, conditioning or changing the oil in

the interrupter chamber is more frequent than in the bulk oil breakers. This is due to carbonization

and slugging from arcs interrupted chamber is equipped with a discharge vent and silica gel breather

to permit a small gas cushion on top of the oil. Single break minimum oil breakers are available in

the voltage range 13.8 to 34.5 KV.

Page-20

CHAPTER 7

PROTECTIVE RELAYS

Relays must be able to evaluate a wide variety of parameters to establish that corrective

action is required. Obviously, a relay cannot prevent the fault. Its primary purpose is to detect the

fault and take the necessary action to minimize the damage to the equipment or to the system.

The most common parameters which reflect the presence of a fault are the voltages and currents

at the terminals of the protected apparatus or at the appropriate zone boundaries. The

fundamental problem in power system protection is to define the quantities that can differentiate

between normal and abnormal conditions. This problem is compounded by the fact that “normal”

in the present sense means outside the zone of protection. This aspect, which is of the greatest

significance in designing a secure relaying system, dominates the design of all protection

systems.

Fig.7.1-Relays [Ref.-7]

Page-21

7.1) Distance Relays:

Distance relays respond to the voltage and current, i.e., the impedance, at the relay

location. The impedance per mile is fairly constant so these relays respond to the distance

between the relay location and the fault location. As the power systems become more complex

and the fault current varies with changes in generation and system configuration, directional over

current relays become difficult to apply and to set for all contingencies, whereas the distance

relay setting is constant for a wide variety of changes external to the protected line.

7.2) Types of Distance relay:-

7.2.1) Impedance Relay:

The impedance relay has a circular characteristic centred. It is non directional and is used

primarily as a fault detector.

7.2.2) Admittance Relay:

The admittance relay is the most commonly used distance relay. It is the tripping relay in

pilot schemes and as the backup relay in step distance schemes. In the electromechanical

design it is circular, and in the solid state design, it can be shaped to correspond to the

transmission line impedance.

7.2.3) Reactance Relay:

The reactance relay is a straight-line characteristic that responds only to the reactance of

the protected line. It is non directional and is used to supplement the admittance relay as a

tripping relay to make the overall protection independent of resistance. It is particularly

useful on short lines where the fault arc resistance is the same order of magnitude as the

line length.

Page-22

CHAPTER 8

POWER TRANSFORMER

Power transformers are called autotransformers.

8.1) Windings:

Winding shall be of electrolytic grade copper free from scales & burrs. Windings shall be

made in dust proof and conditioned atmosphere. Coils shall be insulated that impulse and

power frequency voltage stresses are minimum. Coils assembly shall be suitably

supported between adjacent sections by insulating spacers and barriers. Bracing and other

insulation used in assembly of the winding shall be arranged to ensure a free circulation

of the oil and to reduce the hot spot of the winding. All windings of the transformers

having voltage less than 66 kV shall be fully insulated. Tapping shall be so arranged as to

preserve the magnetic balance of the transformer at all voltage ratio. All leads from the

windings to the terminal board and bushing shall be rigidly supported to prevent injury

from vibration short circuit stresses.

Fig.8.1-Power Transformer [Ref.-7]

Page-23

8.2) Tanks and fittings:

Tank shall be of welded construction & fabricated from tested quality low carbon steel of

adequate thickness. After completion of welding, all joints shall be subjected to dye

penetration testing.

At least two adequately sized inspection openings one at each end of the tank shall be provided

for easy access to bushing & earth connections. Turrets & other parts surrounding the conductor

of individual phase shall be non-magnetic. The main tank body including tap changing

compartment, radiators shall be capable of withstanding full vacuum.

8.3) Cooling Equipments:

Cooling equipment shall conform to the requirement stipulated below:

(a.) Each radiator bank shall have its own cooling fans, shut off valves at the top and

bottom (80mm size) lifting lugs, top and bottom oil filling valves, air release plug at the

top, a drain and sampling valve and thermometer pocket fitted with captive screw cap on

the inlet and outlet.

(b.) Cooling fans shall not be directly mounted on radiator bank which may cause

undue vibration. These shall be located so as to prevent ingress of rain water. Each fan

shall be suitably protected by galvanized wire guard.

Fig.8.2-Radiator with fan [Ref.-7]

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8.4) Transformer Accessories:

8.4.1) Buchholz Relay:

This has two Floats, one of them with surge catching baffle and gas collecting space at

top. This is mounted in the connecting pipe line between conservator and main tank. This

is the most dependable protection for a given transformer.

Gas evolution at a slow rate that is associated with minor faults inside the

transformers gives rise to the operation or top float whose contacts are wired for alarm.

There is a glass window with marking to read the volume of gas collected in the relay.

Any major fault in transformer creates a surge and the surge element in the relay trips the

transformer. Size of the relay varies with oil volume in the transformer and the mounting

angle also is specified for proper operation of the relay.

Fig.8.3-Buchholz Relay [Ref.-7]

8.4.2) Temperature Indicators:

Most of the transformer (small transformers have only OTI) are provided with indicators

that displace oil temperature and winding temperature. There are thermometers pockets

provided in the tank top cover which hold the sensing bulls in them. Oil temperature

measured is that of the top oil, where as the winding temperature measurement is indirect.

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This is done by adding the temperature rise due to the heat produced in a heater coil

(known as image coil) when a current proportional to that flowing in windings is passed in

it to that or top oil. For proper functioning or OTI & WTI it is essential to keep the

thermometers pocket clean and filled with oil.

Fig.8.4-Winding and oil temperature indicator [Ref.-5]

8.4.3) Silica Gel Breather:

Both transformer oil and cellulosic paper are highly hygroscopic. Paper being more

hygroscopic than the mineral oil The moisture, if not excluded from the oil surface in

conservator, thus will find its way finally into the paper insulation and causes reduction

insulation strength of transformer. To minimize this conservator is allowed to breathe

only through the silica gel column, which absorbs the moisture in air before it enters the

conservator air surface.

Fig.8.5-Silica gel Breather [Ref.-7]

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8.4.4) Conservator:

With the variation of temperature there is corresponding variation in the oil volume. To

account for this, an expansion vessel called conservator is added to the transformer with a

connecting pipe to the main tank. In smaller transformers this vessel is open to

atmosphere through dehydrating breathers (to keep the air dry). In larger transformers, an

air bag is mounted inside the conservator with the inside of bag open to atmosphere

through the breathers and the outside surface of the bag in contact with the oil surface.

Fig.8.6-Conservator with Buchholz relay and tank [ref.-6]

Total No. of transformers = 6 No. of transformers

220/132 KV------------------------------------ 100MVA 2

132/33 KV--------------------------------------20/25MVA 2

132/33KV---------------------------------------40/50MVA 1

132/11 KV---------------------------------------10/12.5 MVA 1

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MAKE Company

220/133 KV, 100MVA X-Mer 1----------------------------------- TELK

220/133KV, 100 MVA X-Mer 2---------------------------------- ALSTOM

132/33 KV, 20/25 MVA X-Mer 1---------------------------------- TELK

132/33 KV, 20/25 MVA X-Mer 2-----------------------------------BBL

132/33 KV, 40/50 MVA X-Mer 3-----------------------------------T&R

132/33 KV, 10/12.5 MVA X-Mer 1---------------------------------EMCO

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CHAPTER 9

CURRENT TRANSFORMER

As you all know this is the device which provides the pre-decoded fraction of the primary

current passing through the line/bus main circuit. Such as primary current 60A, 75A, 150A,

240A, 300A, 400A, to the secondary output of 1A to 5A.

Now a day mostly separate current transformer units are used instead of bushing

mounting CT’s on leveled structure they should be for oil level indication and base should be

earthed properly. Care should be taken so that there should be no strain as the terminals.

When connecting the jumpers, mostly secondary connections is taken to three unction boxes

where star delta formation is connected for three phase and final leads taken to protection

/metering scheme. There should be no chance of secondary circuit remaining opens as it leads to

extremely high voltage which ultimately damages the CT itself

Fig.9.1-Current Transformers [Ref.-7]

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It can be used to supply information for measuring power flows and the electrical inputs for the

operation of protective relays associated with the transmission and distribution circuit or for

power transformer. These current transformers have the primary winding connected in series

with the conductor carrying the current to be measured or controlled. The secondary winding is

thus insulated from the high voltage and can then be connected to low voltage metering circuits.

Current transformers are also used for street lighting circuits. Street lighting requires a

constant current to prevent flickering lights and a current transformer is used to provide that

constant current. In this case the current transformer utilizes a moving secondary coil to vary the

output so that a constant current is obtained.

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CHAPTER 10

POTENTIAL TRANSFORMER

A potential transformer (PT) is used to transform the high voltage of a power line to a

lower value, which is in the range of an ac voltmeter or the potential coil of an ac voltmeter.

Fig.10.1-Potential Transformer [Ref.-7]

The voltage transformers are classified as under:

• Capacitive voltage transformer or capacitive type

• Electromagnetic type.

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Capacitive voltage transformer is being used more and more for voltage measurement in

high voltage transmission network, particularly for systems voltage of 132KV and above where

it becomes increasingly more economical. It enables measurement of the line to earth voltage to

be made with simultaneous provision for carrier frequency coupling, which has reached wide

application in modern high voltage network for tele-metering remote control and telephone

communication purpose.

The capacitance type voltage transformers are of twp type:

• Coupling Capacitor type

• Pushing Type

The performance of CVT is affected by the supply frequency switching transient and

magnitude of connected Burdon. The CVT is more economical than an electromagnetic voltage

transformer when the nominal supply voltage increases above 66KV.

The carrier current equipment can be connected via the capacitor of the CVT. There by

there is no need of separate coupling capacitor. The capacitor connected in series act like

potential dividers, provided, the current taken by burden is negligible compared with current

passing through the series connected capacitor.

CVT as coupling capacitor for carrier current application:

The carrier current equipments is connected to the power line via coupling

capacitor. The coupling CVT combines the function of coupling and voltage transformer.

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CHAPTER 11

CAPACITIVE VOLTAGE TRANSFORMER

A capacitor voltage transformer (CVT) is a transformer used in power systems to step-

down extra high voltage signals and provide low voltage signals either for measurement or to

operate a protective relay. In its most basic form the device consists of three parts: two capacitors

across which the voltage signal is split, an inductive element used to tune the device to the

supply frequency and a transformer used to isolate and further step-down the voltage for the

instrumentation or protective relay. The device has at least four terminals, a high-voltage

terminal for connection to the high voltage signal, a ground terminal and at least one set of

secondary terminals for connection to the instrumentation or protective relay. CVTs are typically

single-phase devices used for measuring voltages in excess of one hundred kilovolts where the

use of voltage transformers would be uneconomical. In practice the first capacitor, C1, is often

replaced by a stack of capacitors connected in series. This results in a large voltage drop across

the stack of capacitors that replaced the first capacitor and a comparatively small voltage drop

across the second capacitor, C2, and hence the secondary terminals.

The porcelain in multi unit stack, all the potentials points are electrically tied and suitably

shielded to overcome the effect of corona RIV etc. Capacitive voltage transformers are available

for system voltage. [Ref.-4]

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CHAPTER 12

CONTROL ROOM

Control panel contain meters, control switches and recorders located in the control

building, also called the dog house. These are used to control the substation equipment to send

power from one circuit to another or to open or to shut down circuits when needed.

Fig.12.1-Control Room in GSS Sanganer [Ref.-7]

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12.1) MEASURING INSTRUMENT USED:

12.1.1) ENERGY METER: To measure the energy transmitted energy meters are fitted to

the panel to different feeders the energy transmitted is recorded after one hour

regularly for it MWHr, meter is provided.

12.1.2) WATTMETERS: It is attached to each feeder to record the power exported from

GSS.

12.1.3) FREQUENCY METER: To measure the frequency at each feeder there is the

provision of analog or digital frequency meter.

12.1.4) VOLTMETER: It is provided to measure the phase to phase voltage .It is also

available in both the analog and digital frequency meter.

12.1.5) AMETER: It is provided to measure the line current. It is also available in both the

forms analog as well as digital.

12.1.6) MAXIMUM DEMAND INDICATOR: There are also mounted the control panel to

record the average power over successive predetermined period.

12.1.7) MVAR METER: It is to measure the reactive power of the circuit.

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CHAPTER 13

CAPACITOR BANK

The capacitor bank provides reactive power at grid substation. The voltage regulation

problem frequently reduces so of circulation of reactive power.

Unlike the active power, reactive power can be produced, transmitted and absorbed of

course with in the certain limit, which have always to be workout. At any point in the system

shunt capacitor are commonly used in all voltage and in all size.

Fig.13.1-Capacitor Bank [Ref.-7]

Benefits of using the capacitor bank are many and the reason is that capacitor reduces the

reactive current flowing in the whole system from generator to the point of installation.

1 .Increased voltage level at the load

2. Reduced system losses

3. Increase power factor of loading current

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CHAPTER 14

POWER LINE CARRIER COMMUNICATION

As electronics plays a vital role in the industrial growth, communication is also a backbone of

any power stations. Communication between various generating and receiving station is very

essential for proper operation of power of power system. This is more in case of large

interconnected system where a control leads dispatch station has to co-ordinate the working of

various unit to see that the system is maintained in the optimum working condition, power line

communication is most economic and reliable method of communication for medium and long

distance in power network.

14.1) Wave Trap:

Line trap also is known as Wave trap. What it does is trapping the high frequency

communication signals sent on the line from the remote substation and diverting them to

the telecom/teleprotection panel in the substation control room (through coupling

capacitor and LMU).

Fig.14.1-Wave Trap [Ref.-7]

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This is relevant in Power Line Carrier Communication (PLCC) systems for communication

among various substations without dependence on the telecom company network. The signals

are primarily teleprotection signals and in addition, voice and data communication signals.

The Line trap OFFERS HIGH IMPEDANCE TO THE HIGH FREQUENCY COMMUNICATION SIGNALS thus obstructs

the flow of these signals in to the substation bus bars. If there were not to be there, then signal

loss is more and communication will be ineffective/probably impossible.

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CHAPTER 15

EARTHING OF THE SYSTEM

The provision of an earthing system for an electric system is necessary by the following reason.

• In the event of over voltage on the system due to lightening discharge or other system

fault. These parts of equipment, which are normally dead, as for as voltage, are concerned

do not attain dangerously high potential.

• In a three phase, circuit the neutral of the system is earthed in order to stabilize the

potential of circuit with respect to earth.

The resistance of earthing system is depending on:

• Shape and material of earth electrode used.

• Depth in the soil.

Specific resistance of soil surrounding in the neighbourhood of system electrodes.

15.1) PROCEDURE OF EARTHING:

Technical consideration the current carrying path should have enough capacity to deal with more

faults current. The resistance of earth and current path should be low enough to prevent voltage

rise between earth and neutral. The earth electrode must be driven in to the ground to a sufficient

depth to as to obtain lower value of earth resistance. To sufficient lowered earth resistance a

number of electrodes are inserted in the earth to a depth, they are connected together to form a

mesh. The resistance of earth should be for the mesh in generally inserted in the earth at 0.5m

depth the several point of mesh then connected to earth electrode or ground conduction. The

earth electrode is metal plate copper is used for earth plate.

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15.2) NEUTRAL EARTHING:

Neutral earthing of power transformer all power system operates with grounded

neutral. Grounding of neutral offers several advantages the neutral point of generator

transformer is connected to earth directly or through a reactance in some cases the neutral

point is earthed through an adjustable reactor of reactance matched with the line.

• The earth fault protection is based on the method of neutral earthing.

• The neutral earthing is associated switchgear.

The neutral earthing is provided for the purpose of protection arcing grounds unbalanced

voltages with respect to protection from lightening and for improvement of the system.

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CHAPTER 16

BATTERY ROOM

In a GSS, separate dc supply is maintained for signalling remote position control, alarm circuit

etc. Direct current can be obtained from 220volt 3 phase ac supply via rectifier and in event of ac

failure, from the fixed batteries, which are kept, charged in normal condition by rectifier supply.

Fig.16.1-Battery Room [Ref.-7]

Battery System:

The batteries used are lead acid type having a solution of sulphuric acid and distilled

water as electrolytes. In charged state, it has a specific gravity of 1.2 at temperature of 30C.In the

battery room batteries are mounted on wooden stand. The cells are installed stand by porcelain.

Following precautions are taken in a battery room:

• The conductor connecting the cells are greased and coated with electrolyte resisting varnish.

• Proper care is taken so that acid vapours do not accumulate in the room to avoid risk of

explosion, smoking, winding etc.

• The windows of battery are of forested glass to avoid the batteries from direct action of

sun light.

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CHAPTER 17

RATINGS

17.1) TRANSFORMER:

Total No. of transformers = 6 No. of transformers

220/132 KV------------------------------------ 100MVA 2

132/33 KV--------------------------------------20/25MVA 2

132/33KV---------------------------------------40/50MVA 1

132/11 KV---------------------------------------10/12.5 MVA 1

MAKE Company

220/133 KV, 100MVA X-Mer 1----------------------------------- TELK

220/133KV, 100 MVA X-Mer 2---------------------------------- ALSTOM

132/33 KV, 20/25 MVA X-Mer 1---------------------------------- TELK

132/33 KV, 20/25 MVA X-Mer 2-----------------------------------BBL

132/33 KV, 40/50 MVA X-Mer 3-----------------------------------T&R

132/33 KV, 10/12.5 MVA X-Mer 1---------------------------------EMCO

17.2) CIRCUIT BREAKER:

No. of 220KV breaker - 6

No. of 132KV breaker - 13

No. of 33KV breaker - 12

No. of Capacitor Bank (33kv)- 4

No. of 11KV breaker - 7

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SF6 CB

BREAKER SERIAL NO. 030228

RATED VOLTAGE 145KV

NORMAL CURRENT 1250A

FREQUENCY 5OHz

LIGHTNING IMPULSE WITHSTAND 650KV (Peak)

FIRST POLE TO CLEAR TO CLEAR FACTOR 1-2

SHORT TIME WITHSTAND CURRENT 31.5KA

DURATION OF SHORT CIRCUIT 3 Sec.

(SHORT CIRCUIT SYM. 31.5KA

BREAKING CURRENT) ASYM. 37.5KA

SHORT TIME MAKING CURRENT 8.0KA

OUT OF PHASE BREAKING CURRENT 7.9KA

OPERATING SEQUENCE 0-0.3-CO-3min-CO

SF6 GAS PRESSURE AT 20C 6.3 Bar

TOTAL MASS OF CB 1300Kg

MASS OF SF6 GAS 8.7Kg

17.3) BATTERY CHARGER:

Battery Charger – 220AH VDC HBL NIFE LTD.

440AH VDC HBL NIFE LTD.

Capacitor BankNo.-1 BHEL 38KV 6.6MVAR

Capacitor BankNo.-2 BHEL 38KV 7.2MVAR

Capacitor BankNo.-1 ABB 38KV 7.2MVAR

Capacitor BankNo.-1 WS 38KV 7.2MVAR

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17.4) CURRENT TRANSFORMER:

FREQUENCY 50Hz

HIGHEST SYSTEM VOLTAGE 245KV

SHORT TIME CURRENT 40KA/15

RATED CURRENT 600A

CURRENT RATIO 600-300-150/1

MIN. KNEE POTENTIAL VOLTAGE 850V at 150/1

MAX. EXCITING CURRENT 100MA at 150/1

MAX. SEC. WINDING RESISTANCE 2.5OHM at 150/1

17.5) CAPACITIVE VOLTAGE TRANSFORMER:

SERIAL NO. 0173537

INSULATION LEVEL 460KV

RATED VOLTAGE FACTOR 1.2/cont

TIME 1.5/30sec.

HIGHEST SYSTEM VOLTAGE 245KV

PRIMARY VOLTAGE 22OKV/1.732

TYPE OUTDOOR Wgt. 850Kg

PHASE SINGLE TBONP.CAT 50C

SECONDARY VOLTAGE 110/1.732 110/1.732

RATED BURDON 220Va 110Va

FREQUENCY 49.5-50.5Hz

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CONCLUSION

Training at 220KV GSS Sanganer, Jaipur gives the insight of the real instruments used. There

are many instruments like transformer, CT, PT, CVT, LA, relay, PLCC, bus bars, capacitor bank,

insulator, isolators, control room, Battery room etc. What is the various problem seen in

substation while handling this instruments. There are various occasion when relay operate and

circuit breaker open, load shedding, shut down, which has been heard previously.

To get insight of the substation, how things operate, how things manage all is learned

there. Practical training as a whole proved to be extremely informative and experience building

and the things learnt at it would definitely help a lot in snapping the future ahead a better way.

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REFERENCES

1. B.R.GUPTA (2005), “POWER SYSTEM ANALYSIS AND DESIGN”

P122, P123, S.Chand & Company Ltd.

2. ASHFAQ HUSSAIN (2005), “ELECTRICAL POWER SYSTEM” P79, P501, P516,

CBS publisher and distributors.

3. V.K.MEHTA (2002), “POWER SYSTEM” P447, P483, P507, P527, P555,

S.chand & company Ltd.

4. http://upload.wikimedia.org/wikipedia/en/6/63/cvt.png

5. http://images.google.co.in/(Equipment’s name)

6. www.browzen.com/relay

7. Manual of G.S.S.

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