ATRAINING REPORT

ON

PLCC“132KV GSS Hawa sarak, Jaipur (Raj.)”

Submitted In partial fulfillment of the Requirements for Award of of the Requirements for Award of

the Degree ofthe Degree of

BACHELOR OF TECHNOLOGYBACHELOR OF TECHNOLOGYININ

ELECTRONICS&COMMUNICATIONELECTRONICS&COMMUNICATION

From Rajasthan Technical University From Rajasthan Technical University

Submitted ToSubmitted To Submitted BySubmitted By Mr.NITIN GUPTA Mr.NITIN GUPTA ANTIMA GARG ANTIMA GARG (HOD of EC deptt.) (HOD of EC deptt.) 4 4thth year E.C year E.C R.C.E.W R.C.E.W

DEPARTMENT OF ELECTONICS&COMMUNICATIONDEPARTMENT OF ELECTONICS&COMMUNICATIONRAJASTHAN COLLEGE OF ENGINEERING FOR WOMENRAJASTHAN COLLEGE OF ENGINEERING FOR WOMEN

BHANKROTA, JAIPUR – 302 005BHANKROTA, JAIPUR – 302 005Session 2008Session 2008 – 2012 – 2012

1

OFFICE OF ASSISTANT ENGINEER (PLCC)

RAJASTHAN RAJYA VIDYUT PRASARAN NIGAM LIMITED

132KV G.S.S CHAMBAL POWER HOUSE

JAIPUR

TO WHOM SO EVER IT MAY CONCERN

This is certify that ANTIMA GARG student of B.TECH 3rd year of Electronics &

communication from RAJASTHAN COLLEGE OF ENGINEERING FOR

WOMEN,BHANKROTA,JAIPUR has attended practical training program from

29-06-2011 to 29-07-2011 (30 working days) in this organization connected

with power line carrier communication (PLCC).

Her performance during the practical training period remained good/ very

good/excellent and completed his training with full devotion.

Date:-29-07-2011 (MOHD. FAROOQ NIRWAN)

2

PREFACE

Summer Training is an important part of our Engineering Curriculum. The B. Tech. course

helps a student in getting acquainted with the manner in which his/her knowledge is being

practically used at a large scale. Hence, when the student switched from the process of

learning to that of implementing his/her knowledge, he/she finds an abrupt change. This is

exactly why summer training during the B. Tech. curriculum becomes all the more

important. Summer Training is prescribed for the student of Technical College as a part of

the four-year degree course of Engineering by the AICTE.

We are required to do training and it has to be completed within a particular period of time

before completion of the 3rd year ending VI semester. This training report describes each

and every detail of the work we performed to make a successful completion of project. This

report also give us a brief idea of how we move ahead step by step reaching to specific

height and ultimately completing the goal.

ANTIMA GARG

B.Tech.VII Semester

RCEW

3

ACKNOWLEDGEMENT

We are over helmed in all humbleness and gratefulness to acknowledge our depth to

all those who have helped us to put these ideas, well above the level of simplicity

and into concrete something.

We are very thankful to all the instructors of PLCC, Jaipur for their valuable help.

With the help of their valuable suggestions, guidance and encouragement.

I would also like to thank to our institution RAJASTHAN COLLEGE OF ENGINEERING

FOR WOMEN, BHANKROTA,JAIPUR and faculty members of the department, who

often helped and gave me valuable guidence to prepare my presentation. Last but

not the least, I would like to thank my parents who helped me a lot in gathering

different information, collecting data and guiding me from time to time in making this

project .despite of their busy schedules ,they gave me different ideas in making this

project unique.

ANTIMA GARG

B.Tech.7THSemester

RCEW / ECE

4

TABLE OF CONTENTS

1. Company profile

2. Introduction

3. Coupling devices

4. The yard

5. Lightning arrester

6. Circuit breaker

7. Isolater

8. Relays

9. Battery charger

10. Precautions and Maintenance

11. Advantages and Disadvantages

5

COMPANY PROFILE

INTRODUCTION OF RSEB

"Rajasthan state electricity board" started working from Ist July, 1957. This is the body of big organization and is to function under provision electricity act, like public limited companies. The board does not have article and memorandum of association.

In order to carry out its function, its rules & regulation and his mad other necessary administrative arrangement. After the acting of RSEB six dimensions along with 64 offices & about 300 employees were transferred to its control by the state Govt.

The aim of RSEB is to supply electricity to entire Rajasthan State in the most economical way. There are no possibilities of staking or electricity so the target of board is to distribute the energy in the new area as possible. The board has to carry the business on profit without losses.

After an efficient starting, for the better service privatization of RSEB has been done recently, it has been divided in five main parts, they are:

1. Electricity production authority: RRVUNL

2. Electricity transmission authority: RRVPNL

3. Distribution authority for Jaipur: JVVNL

4. Distribution authority for Jodhpur: JDVVNL

5. Distribution authority for Ajmer: AVVNL

6

CHAPTER-1

INTRODUCTION

POWER LINE CARRIER COMMUNICATION (PLCC)

voltage transmission lines, distributed over medium voltage, and used inside buildings at

lower voltages. Power line communications can be applied at each stage. Most PLC

technologies limit themselves Electrical power is transmitted over high to one set of wires

(for example, premises wiring), but some can cross between two levels (for example, both

the distribution network and premises wiring). Typically the transformer prevents

propagating the signal so multiple PLC technologies are bridged to form very large

networks.

Electrical power is transmitted over high voltage transmission lines, distributed over

medium voltage, and used inside buildings at lower voltages. Power line communications

can be applied at each stage. Most PLC technologies limit themselves to one set of wires

(for example, premises wiring), but some can cross between two levels (for example, both

the distribution network and premises wiring). Typically the transformer prevents

propagating the signal so multiple PLC technologies are bridged to form very large

networks

BASIC PRINCIPLE OF PLCC

In PLCC the higher mechanical strength and insulation level of high voltage power lines

result in increased reliability of communication and lower attenuation over long distances.

7

Since telephone communication system cannot be directly connected to the high voltage

lines, suitably designed coupling devices have therefore to be employed. These usually

consist of high voltage capacitors or capacitor with potential devices used in conjunction

with suitable line matching units (LMU’s) for matching the impedance of line to that of the

coaxial cable connecting the unit to the PLC transmit-receive equipment.

Also the carrier currents used for communication have to be prevented from entering the

power equipment used in G.S.S as this would result in high attenuation or even complete

loss of communication signals when earthed at isolator.. Wave traps usually have one or

more suitably designed capacitors connected in parallel with the choke coils so as to

resonate at carrier frequencies and thus offers even high impedance to the flow of RF

currents.

8

PLCC technology is used for the following these places which are given

below:-

1. point to point communication (hot line comm.)

2. Data telemetry purpose

3. Tele protection purpose

Point to point communication :- point to point communication states that the

communication in between two particular stations now the question is arises that why we go

towards that communication when mobile and telephone are available . two problems are

arises in mobile communication.

First is when we are using mobile that the networking problems may arises.

Second thing is someone at any stations may busy talking with another person while

/when you are try to call him.

Data telemetry :- PLCC terminals can be used for sending and receiving data signal for

telemetry etc. The input for this channel will be in 2000-3000Hz.

Tele Protection :- Protection coupler Equipment can be used along with PLCC terminals

telemetry purpose.

During line fault other fault occurring between sub station trip

Signals can be transmitted or received by a protection coupler

through PLCC terminal for activation distance protection Relaying Equipment.

9

In PLCC the higher mechanical strength and insulation level of high voltage power line

communication and lower attenuation over long distance. The idea is to use the power line

as a transmission line for communication purpose

CHAPTER-2

COUPLING DEVICES

Earliest coupling devices used were antenna as similar to these used in radio work. This

was because capacitors capable of withstanding the high voltages used in transmission of

electrical power were not available at that time. The antennas used for coupling the PLC

equipment to the transmission lines were usually erected below the line and parallel to it.

They were usually more then 300 ft long and were tuned to the carrier frequency employed.

These were rather inefficient and the systems were affected but interference from nearby

long wave radio transmitters.

By about 1930, suitably paper and oil capacitors were developed which could withstand the

high voltage and serve as affectidive coupling units to PLC equipments.

A modern coupling capacitor consists of stack of flat would elements of pure cellulose

paper and aluminium coils held between insulating roads under optimum pressure to

minimize capacitance the changes with time and temperature. The interconnection is

designed to obtain.

Highest possible range withstands capacity and highest cut-off frequency. The entire stack

assembly as placed in a suitable pro claim insulating shall fill with insulation coils and

hemetically sealed by metallic flanges and gaskets of synthetic rubber with a dry nitrogen

gas cushion. The mechanical strength of the shell and flanges are carefully matched.

Coupling capacitors are designed for outdoors use and withstand normal atmospheric

phenomenon such as temperature and humidity rain, shown etc. The capacitor's used in

modern PLCC systems have a capacity between 2000 and 8000 ft. The usual value is

10

between 3000 and 5000 ft. The units are designed to have a very low (<0.5dB). There are

usually mounted on pedestals below the line conductors.

In many cases the capacitive voltage dividers are used for communication system and

voltage is used for synchronizing purpose or voltage measurement.

Coupling is necessary because, if power of power line is flow through the communication

line it cause the burning of PLCC equipment. So overcome this problem a coupling

capacitor is used to block the flow of power into the carrier signal line.

TYPE OF COUPLING

(A)Phase To Ground Coupling

(B)phase to phase coupling

(C)inter circuit coupling

(A)Phase To Ground Coupling

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As can be seen from the figure, the wave traps and coupling capacitors are all connected to

one conductor of the power line. The remaining two conductors, though not directly

connected to the.

Line carry a portion of the returning carrier current because these two conductors do not

have wave traps, a portion of the carrier energy is 1 lost. Also radiation losses are goes

high as earth forms a part of the circuit and the noise pickup is correspondingly higher. The

method of connecting is inefficient and the connection at the receiving and can not be made

to match the line perfectly. This is because the impedance of the line can not be calculated

correctly as it depends partly on the soil conductivity enrote the line which varies from place

to place and time to time and parity on station switching condition.

b)Phase To Phase Coupling

This type of coupling was formally being used to improve the reliability of communication

case of breakage of one of the coupled conductors the system used double the number of

wave traps and coupling capacitors used in phase to ground and hence is costlier. This

coupling capacitor at each and have the line are connected in parallel to the LMUs as

shown in this sketch figure-

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Through this type coupling increase the reliability of communication, the attenuation,

interference from radio transmission and monitoring possibilities are all-higher than those of

phase to ground coupling. Hence this type of coupling has been discontinued and super

sided by the phase to phase coupling system.

(C)Inter Circuit Coupling

This type is coupling uses the same number of wave traps and the capacitor as two

phase coupling but the capacitance are not connected in parallel as in the case of that type

of coupling. The two power conductors used in this case may be considered as metallic go

and return lines for the carrier currents. The conductor has no appreciable influences on the

carrier currents. The third has no appreciable influence on the carrier current transmission.

Hence the switching conditions attention is less because two conductors are used instead

of one conductor and earth. This type of coupling is more reliable over longer distance and

is generally used load dispatch work, though is lightly costlier than the two phase system.

13

COMPARISON OF PHASE TO PHASE AND PHASE TO GROUND

COUPLING

The phase-to-ground coupling has the advantage of requiring only half the number of wave

traps and coupling capacitors in comparison to phase-to-phase coupling. But it is inferior to

many respects as would be evident from the following points:

1. The phase-to-ground coupling has higher attenuation and unlike phase-to-phase

coupling, the attenuation varies with station switching conditions.

2. The variation of attenuation function with changes in weather condition is greater in

phase-to-ground coupling.

3. Reflection and echoes due to mismatch difficulties are much greater in phase-to-

ground coupling.

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4. Signal-to-noise ratio is poorer due to longitudinal noise voltages induced in the line.

In phase-to-phase coupling thee noise voltages tend to cancel themselves as equal

voltages are induced in the coupled conductors, which oppose each other in the

circuit.

5. Radiation from phase-to-ground case is about double than that in the other case.

6. A break or fault of some other kind will hamper the transmission in phase-to-ground

coupling much more seriously than in phase-to-phase coupling.

Hence, phase-to-ground coupling is used due to its cheapness, especially when frequency

used and distances to be covered are suitable, and radiation not particularly objectionable,

as may be the situation in sparsely populated areas.

15

CHAPTER-3

THE YARD

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

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

. PLCC equipment including coupling capacitance

Lighting Arrester

Wave Trap

Circuit Breaker

Isolater

Bus Bars

Insulator

Static earthling system

PLCC equipment including coupling capacitance

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Switch Yard

Switch yard

THE YARD

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 auxiliary 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

17

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 supply which is coming from different higher order GSS.

PROPERTIES

COPPER ALUMINIUM 

1. Electricity resistively at 0.0172410.00403 

2. Temp coff. of resistively 0.0041 0.00403 

3. Softening tem.200

4. Thermal conductivity.932.503 

5. Meting point1083657 

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CHAPTER-4

LIGHTENING ARRESTER

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

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

waves reaching the terminal equipment .so some protective device is necessary to produce

power station, sub-station and transmission lines against the high voltage wave reaching 

here.This is connected between line and earth it acts as a safty value.

  Through the surge impedance of line limits the amplitude of the line to earth over voltage

to a value which wills safe guard the insulation of the protected 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 than 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 series with a completely light porcelain

condition humidity etc.

SPARK GAPE:-

They include a number of identical elements connected in series .Each element consist

of with pre ionization device between each grounding resistance of high ohmic value

connected in parallel. 

19

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.    

20

Lightning arrester

21

CHAPTER-5

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 series 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 receive 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 transformers 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 .

22

 

Figure-4.1 Line Matching Filter & Protective Equipments

Transmitter

The transmitter consists of an oscillator and a amplifier. The oscillator generates 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 capable 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 transmitting. 

23

CHAPTER-6

CIRCUIT BREKER

Breakers are switching and current interrupting devices. Basically a circuit 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 circuit 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. 

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.

24

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 immediately re-

opening to clear the fault from system

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.

Types of Circuit Breaker

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

Bulk oil circuit breaker:-

Bulk oil circuit breakers are enclosed in metal-grounded waterproof tanks that are referred

to as dead tanks. The tank type circuit breakers had 3 separate tanks for 72.5 KV and

above (Fig. 12a). For 36 KV and below, single tank construction, phase barriers were

provided between phase.

25

Figure 19      Schematic diagram of bulk oil circuit

breaker

       The contact separation takes place in steel tanks filled with oil. The gases formed, due

to the heat of the arc, expand and set the turbulent flow in the oil. The arc was drawn

directly inside of the container tank without any additional arc extinguishing but the one

provided by the gas bubble surrounding the arc. Plain break breakers were superseded by

arc controlled oil breakers.

To assist arc extinction process, arc control devices were fitted to the contact assembly.

These were semi-enclosed chamber of dielectric materials.The purpose of the arc control

devices is to improve operating capacity, speed up the extinction of arc, and decrease

pressure on the tank. The performance of oil circuit breaker depended on the effectiveness

of the arc control devices.

26

The breakers incorporate arc control are called arc control circuit

breakers.

These are two types of such breakers:

1. Self blast oil circuit breakers – In which arc control is provided by internal

means i.e. are itself facilitates its own extinction efficiency. 

There are three types of pot:-

Plain explosion pot

Cross jet explosion pot

Self compensated explosion pot

2. Forced blast oil circuit breakers - in which arc control is provided by

mechanical means external to the circuit breaker.

       In this type of circuit breaker there is a piston attached to a moving contact. When fault

occurs the moving contact moves and hence the piston associated with it also moves

producing pressure inside the oil chamber. So the oil gets movement or turbulates and

quenching the arc.

The arc control devices can be classified into two groups: cross-blast and axial blast

interrupters.

27

Figure 16  Classification of arc control devices

Figure content:-

1. Fixed contact assembly    

2. Arc    

3. Moving contact with tungsten-copper tip  

4. Fiber reinforced tube

5. Gas evolved by decomposition of oil   

6. Dielectric oil

7. Outer enclosure (Porcelain or Fiber Reinforced Epoxy )

The major disadvantages of tank type circuit breakers are ;

1. Large quantity of oil is necessary in oil circuit breakers though only a small quantity

is necessary for arc extinction.

2. The entire oil in the tank is likely to get deteriorated due to sludge formation in

proximity of the arc. Then the entire oil needs replacement. 

3. The tanks are too big, at 36 KV and above, and the tank type oil circuit breaker loses

its simplicity.

28

Minimum oil circuit breaker

  This type is also known as poor oil or small oil circuit breaker. In the bulk oil circuit

breakers, the oil serves as both arcs extinguishing medium and main insulation. The

minimum oil circuit breakers were developed to reduce the oil volume only to amount

needed for extinguishing the arc - about 10% of bulk oil amount. The arc control for the

minimum oil breakers is based on the same principle as the arc control devices of the bulk

oil breakers. To improve breaker performance, oil is injected into the arc.

       In MOCB, The current interruption takes place inside "interrupter". The enclosure of the

interrupter is made of insulating material, like porcelain. Hence, the clearance between the

line and the enclosure can be reduced and lesser quantity of oil would be required for

internal insulation. 

       The interrupter containers of the minimum oil circuit breakers are insulated from the

ground. This is usually referred to as live tank construction. For high voltage (above 132

KV), The interrupter are arranged in series. It essential to ensure that each interrupter

carries its share of the duty. Care must be taken that all breaks occur simultaneously, and

that the restriking voltage is divided equally across the breaks during the interrupting

process. The thermal voltage division depends on stray capacitances between the contacas

and the ground, and therefore is in very uneven. This is corrected by connecting

capacitances or resistors in parallel with the interrupting heads. Figure 20 shows a three

phase minimum oil circuit breaker along with cross-section through a single phase. 

29

Minimum oil circuit breaker

Figure content:-

1    Vent valve                           

2    Terminal pad                                        

3    Oil level indicator                                 

4    Moving contact                                   

5    lower fixed contact

6 Separating piston

7 Terminal pad

8 Upper drain value

Air blast circuit breaker

1 Introduction

        Air blast circuit breakers are used today from 11 to 1100 KV, for various application.

They offer several advantages such as faster operations, suitability for related operation,

auto-reclosure, unit type multi-break construction, simple, assembly, modest maintenance,

etc. A compressor plant is necessary to maintain high air pressure in the receiver. Air-blast

30

circuit breakers operates repeatedly. Air-blast circuit breakers are used for interconnected

lines and important lines when rapid operation is desired.

Construction of   Air-Blast Circuit-Breaker

       In air blast circuit breaker (also called compressed air circuit breaker) high pressure air

is forced on the arc through a nozzle at the instant of contact separation. The ionized

medium between the contacts is blown away by the blast of the air. After the arc extinction

the chamber is filled with high pressure air, which prevents restrike. In some low capacity

circuit breakers, the isolator is an integral part of the circuit breaker. The circuit breaker

opens and immediately after that the isolator opens, to provide addition gap. 

        In EHV circuit of today, isolators are generally independently mounted.

31

Schematic diagram of air blast circuit breaker

32

Principle

Description

High pressure air between 20 to kgf/cm2 , is stored in the air reservoir (item 1 in Fig. 7). Air

is taken from compressed air system. Three hollow insulator columns (item 2) are mounted

on the resrvoir with valves (6) at their base. The double arc extinguishing chambers (3) are

mounted on the top of the hollow insulator chambers. The current carrying parts (7) connect

the three arc extinction chambers to each other in series and the pole to the neighboring

equipment. since there exist a very high voltage between the conductor and the air

reservoir, the entire arc extinction chamber assembly is mounted on insulators. 

Sulphur Hexafluoride (SF6) Circuit Breaker and SF6 Insulated

Metalclad switchgear

33

Introduction

       Sulpher hexafluoride (SF6) is an inert, heavy gas having good dielectric and arc

extinguishing properties. The dielectric strength of the gas increases with pressure and is

more than that of dielectric oil at pressure of 3 kgf/cm2 . This gas is now being very widely

used in electrical equipment like high voltage metal enclosed cables; high voltage metal

clad switchgear, capacitors, circuit breakers, current transformers, bushings, etc. This gas

liquefies at certain low temperatures, the liquefaction temperature increases with pressure.

This gas is commercially manufactured in many countries and is now being extensively

used by electrical industry in Europe, U.S.A. and Japan.

       Several types of SF6 circuit breakers have been developed by various manufacturers

in the world, for rated voltage from 3.6 to 760 KV. However, at present they are generally

preferred for voltages above 72.5 KV. 

       Sulphur hexafluoride gas is prepared by burning coarsely crushed roll sulphur in the

fluorine gas, in a steel box, provided with staggered horizontal shelves, each bearing about

4 kg of sulphur. The steel box is made gas-tight. The gas thus obtained contains other

fluoride such as S2F10 , SF4 and must be purified further. SF6 gas is generally supplied by

chemical firms. The cost of gas is low if manufactured on a large scale.

34

       The gas is transported in liquid from in cylinders. Before filling the gas, the circuit

breaker is evacuated to the pressure of about 4 mm of mercury so as to remove the

moisture and air. The gas is then filled in the circuit breaker. The gas can be reclaimed by

the gas-handling unit.

       There are tow types of SF6 circuit breakers:

1.   Single pressure puffer type SF6 circuit  

       In which the entire circuit breaker is filled with SF6 gas at single pressure ( 4 to 6

kgf/cm2) . The pressure and gas flow, required for arc extinction, is obtained by piston

action.

2.   Double pressure type SF6 circuit breaker

       In which the gas from high pressure system is released into low pressure system over

the arc during the  arc quenching process. This type has been superseded by puffer type.

Properties of SF6 Gas

       Sulphur hexafluoride (SF6) gas has good dielectric and arc extinguishing properties.

The dielectric strength of the gas increase with pressure and is more than that of the

35

dielectric oil at high pressures. SF6 is now very widely used in electrical equipments like

high voltage metal enclosed cables, high voltage metal clad switchgear, capacitors, circuit

breakers, current transformers, high voltage bushing, etc.

       Sulphur hexafluoride gas is of low cost if manufactured on a large scale. It is

transported in liquid from cylinders. Before filling the gas, the circuit breaker is evacuated to

the pressure of about 4mm of mercury so as to remove the moisture and air. The gas is

then filled in the C.B.

Physical properties of SF6 gas  

Colorless.

Odorless.

Nontoxic. Pure SF6 gas is not harmful to health. However, impure SF6 gas contains

toxic impurities.

Inflammable.

Stat: gas at normal temperature and pressure.

Density : heavy gas with density 5 times that of air at 20 ° C and atmospheric

pressure.  

Chemical properties of SF6 Gas

1. Stable up to 500 ° C.

2. Inert. The chemical inertness of this gas is advantageous in switchgear. The life of

metallic part, contacts is longer in SF6 gas. The components do not get oxidized or

deteriorated. Hence the maintenance requirements are reduced. Moisture is very

harmful to the properties of the gas. In the presence of moisture, hydrogen fluoride is

formed during arcing which can attack the metallic and insulating parts in the circuit

breaker.

3. Electronegative gas.

4. Does not react with structural material up to 500 ° C.

5. Products of decomposition. During arc extinction process SF6 is broken down to

some extent intoSF4, SF2. The products of decomposition recombine upon cooling to

form the original gas. The remainder is removed by filters containing activated

alumina ( AL2O3) Loss factor is small. The products of decomposition are toxic and

attack certain structural materials.

36

6. The metallic fluorides are good dielectric materials hence are safe for electrical

equipment.

7. Moisture content in the gas, due to influx from outside, present a various problems in

SF6 circuit breakers. Several failures have been reported recently due to this cause.

Dielectric properties of SF6 Gas

1. Dielectric strength of SF6 gas atmospheric pressure is 2.35 times that of air, it is

30% less than of dielectric oil used in oil circuit breakers.

2. At higher pressure the dielectric strength of the gas increases. At pressure about 3

kgf/cm2 the dielectric strength of SF6 gas is more than that of dielectric oil. This

property permits smaller clearance and small size of equipments for the same KV.

3. The breakdown voltage in SF6 gas depends on several aspects such as electrode

configuration, roughness of electrodes, distribution of electric field, vicinity of

insulating supports, moisture, wave shape etc. Other parameters remaining

constant, the breakdown voltage in SF6 increases with pressure. The gas follows

paschen's law which states that "in uniformly distributed electric field, the breakdown

voltage (Vb ) in a gas is directly proportional to the product of gas pressure (p) and

electrod gap (d)"

Vb∝pd

4. With the non uniform field, the breakdown voltage versus pressure curve does not

follow the paschent's law strictly. The breakdown voltage increases with pressure.

However after about 2.5  kgf/cm2 it starts reducing and then rises again. The

pressure at which the breakdown voltage starts reducing is called 'Critical pressure'.

The dielectric strength at pressure between 2-3 kgf/cm2 is high. Hence this pressure

range preferred in SF6 insulated metal enclosed switchgear. However, in circuit

breaker compartment, the pressure of the order of is kgf/cm2 preferred for arc

quenching process.

5. Rough electrode surface reduces the breakdown voltage with rough surface the

ionization starts earlier near the sharp points on conductors. Hence conductor

surfaces should be smooth

6. Thew conductor in SF6 insulating equipment are supported on epoxy or porcelain

insulators. The flashover invariably takes place along the surface of the support

insulators. The breakdown can occur at extremely low values if the insulators

37

supports are covered by moisture and conducting dust. Hence the insulators should

be extremely clean and should have anti-tracking properties.

7. The breakdown is initiated at sharp edges of conducting parts and parts having

maximum stress concentration. The limiting value of breakdown stress is of the order

of 20 P KV/cm for pure SF6 and P is pressure of gas in kgf/cm2 . Good stress

distribution is very important in SF6 insulated equipment.

8. The breakdown value depends on the wave-shape characterized by peak value,

wave front, wave-tall, polarity in case of impulse wave. Voltage withstand value

reduces with increase in steepness and increase in duration of the wave. Negative

polarity is generally more severe than positive.

9. SF6 gas maintain high dielectric strength even when diluted by air (Nitrogen).

30% SF6 + 70 % of air, by volume, has a dielectric strength twice that of air

( at the same pressure). Below 30% by volume, the dielectric strength

reduces quickly.

Vacuum circuit breaker

In this breaker, vacuum is being used as the arc quenching medium. Vacuum offers highest

insulating strength, it has far superior arc quenching properties than any other medium.

When contacts of a breaker are opened in vacuum, the interruption occurs at first current

zero with dielectric strength between the contacts building up at a rate thousands of times

that obtained with other circuit breakers.

Principal:- When the contacts of the breaker are opened in vacuum (10 -7 to 10 -5 torr),

an arc is produced between the contacts by the ionization of metal vapours of contacts. The

arc is quickly extinguished because the metallic vapours, electrons, and ions produced

during arc condense quickly on the surfaces of the circuit breaker contacts, resulting in

quick recovery of dielectric strength. As soon as the arc is produced in vacuum, it is quickly

extinguished due to the fast rate of recovery of dielectric strength in vacuum.

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Working :- When the breaker operates the moving contacts separates from the fixed

contacts and an arc is struck between the contacts. The production of arc is due to the

ionization of metal ions and depends very much upon the material of contacts. The arc is

quickly extinguished because the metallic vapours, electrons and ions produced during arc

are diffused in short time and seized by the surfaces of moving and fixed members and

shields. Since vacuum has very fast rate of recovery of dielectric strength, the arc extinction

in a vacuum breaker occurs with a short contact separation.

39

CHAPTER-7

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 terminal of each pole of

the isolator, will result from the operation.

Broadly speaking isolator are the switches which’s operate under "No current”

condition. Thus, isolator is an apparatus which makes a visible and reliable 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, heerapura 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

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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 construction.

Isolator

MOUNTING: -

The central post rotates in gun metal bushing and tapered roller bearing provided with

grease nipples for lubrication required to be alone at regular’s intervals during routine check

up. 

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 heerapura at are three post

types. Each isolator has three insulators post per phase mounted on a phase of steal

construction.

41

CHAPTER-8

RELAYS

Introduction: -

In order to generate the electric power and transmit it to consumer millions of rupees must

be spent on power system equipment. These equipment are to work under specified normal

conditions. However, a short circuit may occur due to failure of insulation called by:

Over voltage due to switching.

Over voltage due to direct and indirect lightning strokes.

Briding of conductors by birds.

Break damage of insulation due to decrease of it’s di-electric strength.

Mechanical damage of the equipment. The fault takes place in following properties.

VARIOUS FAULTS:-

Phase to phase 20-25%

Single phase short circuit 50-60%

Double phase S.S. 3-5% 20-25%

Three phase short circuit 3-5%

Phase to Phase and Phase to guard 10-15%

Fault may be defined as the rise of current in the several times to normal current, resulting

the high temperature rise which can damage the equipment.

It reduces the voltage immediately and considerably.

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Basic Requirement of protective relays are as follows:

Speed

Protective relaying should do’s connect a faulty element as quickly as possible.

Selectivity

The ability of the protective relay to determine the point of which have the fault occurs and

select the nearest circuit breaker tripping of which will lead the clearing of fault with min-or

so damage to the system.

Sensitivity

It is the capacity of the relaying to operate relay under the actual condition that produces

the last operating condition tendency.

Depending upon the method of element connected primary relay (series element connect

directly on the circuit of protective element) and secondary relay 9sensing element

connected through a current and voltage transformer.

Types of Relays

These are called normally opened, normally closed in GSS control room there is panel in

which the relays are set and there are many types of relays.

Over voltage relays

Over current relays

I.D.M.T. fault relay

Earth fault relay

Bucheloz’s relay

Differential relay

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Over voltage relay – This protection is required to avoid damage of system in case line

becomes open circuited at one end. These fault would trip the local circuit breaker thus

block the local and remote ends. This relay is operated i.e., energized by CVT connected to

lines.

Fig 3. Relays on panel

Over Current relay – This relay has the upper electromagnet of non-directional relay

connected in series with lower non-directional electromagnet. When the fault current flow

through relay current coil which produces flux in lower magnet of directional element. Thus

the directional relay has the winding over the electromagnets of non-directional element

and produces a flux in lower magnet and thus over current operates.

Earth fault relay: - when a conductor breaks due to some reason and it is earthen then

earth fault occurs. The fault current is very high thus, there is need to of over current relay.

This relay has minimum operating time.

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Directional relay: - It allows to flow the current only in one direction then only this relay

operates. It has a winding connected through the voltage coil of relay to lower magnet

winding called current coil. Which is energized by C.T. if fault occurs. This relay operates

when v/I is less than theoretical value. The v/I is normally constant.

Differential relay:- This relay operates when phase difference of two electrical

quantities exceeds the predetermined value. It has always two electrical quantities; hence

in 400kv GSS for transformer differential relay is used.

Inverse time characteristics relay:- The relay using here having the inverse time

characteristics having the time delays dependent upon current value. This characteristic is

being available in relay of special design. There are:-

Electromagnetic Induction type

Permanent magnetic moving coil type

Static type

Buchholz’s relay : - It is the protective device of the transformer. When any fault occurs

in the transformer then it indicates about fault and we disconnect the transformer from the

circuit. It is used in the power transformer. It is connected between the tank and

conservator. It has two floats on which two mercury switch are attached. One float is used

for the bell indication and other float is used for the tripping. In the normal position the relay

is filled with the oil and contacts of the mercury switch are opened. When the earth fault

occurs in the transformer then it increases the temperature of oil and oil flows into the

conservator through relay. On the way it makes the contacts of the tripping circuit short. So

in the we can say that this relay works as circuit breaker.

Buchholz’s relay

45

CHAPTER-9

BATTERY CHARGER

PLCC (Power Line Carrier Communication) works on rectified AC or main when supply

goes off. We make use of a device for proper functioning of PLCC, called BATTERY

CHARGER. this is the device that provides supply to the PLCC equipment for uninterrupted

working. It provides DC to the panel by battery of 48 V. In this type 24 batteries are

connected in series and individually per battery has approximately 2 V capacities.

1. General Description

Battery charger mainly consists of 4 sections -

1. Float charger

2. Boost charger section

3. Control section

4. Alarm section

All the four sections are situated in mounted sheet steel. The sides and tops of the frame

are provided with removable panels suitable recess has been provided in front panel to

prevent the compenent from projecting out. All meters indicating lamps, push buttons have

been mounted on front panel.

2. Technical Specifications

- Normal Input - 415 V AC 3 phase

- Input variation- +/20% of voltage

Float charger -

DC output - 50 V +/-1%

Output current - 20 to 40 ampere

Line regulation & load regulation - +/-1% individual

Ripple - 0.6 Vpp (peak to peak)

Efficiency - > 70%

Boost charger -

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DC output - 43.2 to 67.2 V

Output current - 25-70 Amps.

Over load - 10%

Efficiency - > 80%

1. Float Charger -

The float charger is basically static type 3-phase charger with stabilized output dc voltage.

The charger output dc voltage is constantly compared with standard dc reference voltage

and error voltage is again amplified. This amplified voltage control the triggering signals of

all the 3 phase bridge control rectifier, as the output voltage tends to decrease than it's

selected value, it makes the triggering signals of each thyristor of all 3 phase, to advance

for firing them, so that the output voltage remains within the specified accuracy. If the output

voltage tends to increase more than the selected value, the triggering pulses of these

thyristors of all 3 phase are delayed in firing operations in such a way so that the output dc

voltage is again brought back to its stabilized voltage.

Circuit Description -

The 3-phase AC input is applied through the 3 poles 2 way switch (RS-I) and fuse F-18 to

F-20 to the float input contractor (CON-1).

The AC voltage is applied after CON-1 to the float transformer TX-1. The pilot lamp LED 4

To LED 6 indicates 'ON' condition of the float charger. The secondary of the TX -1 is

connected to the 3-phase full wave half controlled bridge rectifier, which consists of silicon

diodes D-2 to D-4, and SCR-1 to SCR-3, D-1 is the free wheeling diodes. HRC fuses F1 to

F7 protect all diodes and SCR's, Special surge circuits have also been provided to protect

SCR's.

The rectified output is filtered by the choke XL-1 and KL-2 and the capacitor bank C-1 and

C-2, which are protected by the HRC fuse F-8. The filtered DC output is protected by the

HRC fuses F-9 and LK-1. BR-1 is the bleeder is the resister for the capacitor bank.

Control Circuit of Float Charger - 47

The output of the charger is controlled through the electronic controller. Using phase control

of the SCR's feedback control the output. The control circuit has plug in type cards with

hard type connectors for external connections. The control circuit consists of following

functional circuits:

1. Power supply

2. UOT firing for SCR phase control

3. Amplifier

4. DC under voltage/over voltage sensing

Power Supply :

This card provides regulated power supplies of +/-12% and u unregulated24 V used for ICs

and relays respectively, regulated output is 200 (maximum)., Auxiliary transformer TR-5

gets supply from main transformer's phase and neutral points. The two identical secondary

circuits consisting of bridge rectifier, filter and IC regulator provide +/- 12V stabilized output

and 24V unregulated DC output. The output of the bridge is filtered using L-C filter

comprising of filter Choke CH-1 and capacitor bank consisting of capacitor C-1. The

capacitor is protected by HRC fuses. BR-1 is bleeder resistance dummy load connected

across the DC output; the filtered output is then connected to the load circuit or to the

battery through a rotary switch. Shunt SH-1 is used for current limit control, which is also

used for measuring output current on ammeter. A DC volt- meter indicates the DC output

voltage. An indicating lamp indicates DC 'ON' condition. Blocking diodes are used to

prevent reverse current flowing from the battery to the charger when the charger voltage

goes below the battery voltage or charger is 'OFF'. The DC voltmeter V-2 reads voltage

across the load bus.

UOT Firing Card:

There are three (3) identical firing cards, each for triggering one SCR in the main bridge.

Zener diodes DZ-1 to DZ- 6 and resistance R-15, R-16, R-17 connected to the secondary of

the TX-2, TX-2 and TX-4 clamp the positive half of the input sine wave to the Zenor voltage.

RV-1 and RV-2 are adjusted to equalize the conduction angle of the SCR's resulting in law

ripple. All SCR's at the same conduction angle +/-10% input and output adjusted to 5V. RV-

2 again adjusted in full load to keep conduction angle of the SCR's equal.

C-1 beings charging at the start of the cycle, through current supplied by the R-2, RV-2 and

TR-1. When voltage across C-1 reaches the threshold value, UOT fires and C-1 discharge

through the pulse transformer. This pulse fires the main SCR via auxiliary transistor.48

Output voltage control is obtained by varying the base ammeter bias of TR-1. An

increase/decrease in charging current leads to a decrease/increase in firing andgle and a

corresponding increase/decrease in the output voltage. Senor DZ-1 limits the gate voltage

of the main SCR to the Zenor voltage.

Amplifier Card:

This card consists of two operational amplifiers IC-1 and IC-2 reference Zenor diodes DZ-1,

emitter follower TR-1 and buffer amplifier TR-3 and TR-4; IC-1 is the error detector

amplifier.

A negative reference by a Zenar diode DZ-1 and voltage sensing singles are given to the

inverting input of operational amplifier IC-1 the output is taken through a diode D-1 to the

base of transistor TR-1 from whose emitter the output is taken to the UOT driver cards.

Ratio of R-4 and R-5 determine the voltage gain of the operational amplifier and Rv-1 is

used for offset nulling.

The voltage sensing input is supplied to the OPAM IC-2 through an 'OR' gate formed by

diode D-2 & D-15. Whichever signal in higher the amplifier will respond to that signal. D-2

accepts the battery current signal while D-15 accepts the float or voltage limit signal at any

time only one of the above signals will be commanding the amplifier.

The overall working of the feedback control can be explained as follows :-

If the inverting input tends to rise or increase in loading during current limit, the output of the

operational amplifier IC-1 decrease which in turns makes the emitter voltage or TR 1 lower.

This reduces the bias on transistor TR 1 on firing cards so that charging current supplied by

them to the capacitor are reduced. Hence the triggering pulses are retarded and make the

output lower. Thus the negative feedback is complete so that the increase in output voltage

will reduce or if the unit is in load limit condition. The increase in output current will also be

reduced to bring the current to the original condition.

49

Resistance R-3, capacitor C-2 and also resistance R-2, capacitor C-1 are incorporated to

remove the instabilities like hunting. Operational amplifier IC-2 l liner amplifier the mv drop

across shunt. The ratio of R-14/R-15 determine the gain of the amplifier and RV-2 on sub

assemble sets the charging current. When charging current increases the mv drop across

pin No. 2 & 3 of IC-2 will increased. This voltage is applied to the base of TR-3 and TR-3

through R-11. Transistor TR-4 will be the base current of TR-3 and TR-3 will increase the

voltage from D-2 will control in DC output voltage to keep the battery current at set level,

which can be adjusted by potentiometer RV-2.

It is desired that output of the rectifier attain its steady state value slowly rather than by

step.

Fuse Fail Alarm:

Fuse Fail alarm is also available in float charger. In the event of any HRC fuse failure.

Corresponding types fuse blows and trip the corresponding relay.

2. Boost Charger Section

The battery can be charged by using the two rotatory switches provided on front panel for

coarse and fine control and that charging current can be read by ammeter A-3 provided on

the front panel. The operator must ensure that the rotatory switches are in minimum

position before switching on the boost charger.

50

PRECAUTIONS AND MAINTENANCE

In normal rooms the ETI equipment generally erected on an open rack on a frame of

freestanding cabinet.

The rooms for the erection of the equipment should have a dust free floor, which is

washable. The room should be well ventilated and of normal temperature & humidity and

where necessary provided with a ventilator fan having a dust filters.

The cabinets should be checked for damage before mounting.

Caution - before opening the hinged frame, make sure that the cabinet cannot tip forward.

Fault Analysis, Test Equipment And Test Procedure

(1)Test Equipments

(A) Test Oscillator

Test oscillator enables the commissioning of the PLC link without aid of external signals,

pressing the CALL button initiate a test tone of 1 KHZ which is fed to the voice amplifier and

passes through all transmit stages of the PLC equipment with the exception of the

telephone adapter. It is possible to check at any test point the DBR value printed in the front

side of the equipment is against the measured dB reading. It simplifies also the setting of

the transmitting (Tx) output power, which is measured by T (HF) on the transmitting level

test point.

(B) Dummy Load And Hf Loop Test

Faultfinding is much simplified when the HF output is connected to a definite resistive load

in place of the more or less ill defined characteristics of the power line. The ohmic load with

additional isolates the line, takes the form of a 50 ohms artificial load, which insert in place

of P3EO at the time of testing. Connecting back-to-back transmitter and receiver can test

the complete PLC equipment. This is achieved by to feeding a reduced transmitting voltage.

The dummy load automatically adjusts the receiver to accept the transmitter frequency.

51

(C) Audio Test

For a quick and simple check of the equipment and audio test circuit is provided. The audio

test (voice amplifier) is to patch on the front side of the equipment to any desired signal

path and the received signal will be heard in the handset of the service telephone via

amplifier.

The following signals can be checked in the AF section of the equipment:

Speech,Tele operation/data dialing.

(2) Fault Analysis

In fault analysis the faulty devices are checked in this serial or manner:

- Telephone or Tele operation signals

- Cabling-low frequency circuits or DC power supplies

- PLC equipments

- HF transmission path

Comparisons with the transmission levels and working voltages measured under health

conditions are valuable aids to fault analysis. The back-to-back testing of the equipment

using the dummy load is also a very useful aid.The presence of AF signals in the various

stages of the equipment can be checked using the telephone handset and test load

connected between the associated measuring point and audio testing.

52

ADVANTGES & DISADVANTAGES OF PLCC

Advantages -

1. No separate wires are needed for communication purposes, as the power

lines themselves carry power as well as communication signals. Hence the

cost of constructing separate telephone lines is saved.

2. When compared with ordinary lines the power lines have appreciably higher

mechanical strength. They would normally remain unaffected under the

conditions, which might seriously damage telephone lines.

3. Power lines usually provide the shortest route between the power stations.

4. Power lines have large cross-sectional areas resulting in very low resistance

per unit length. Consequently the carrier signals suffer much less attenuation

then when they travel on usual telephone lines of equal lengths.

5. Power lines are well insulated to provide only negligible leakage between

conductors and ground even in adverse weather conditions.

6. Largest spacing between conductors reduces capacitance, which results in

smaller attenuation at high frequencies. The large spacing also reduces the

cross talk to a considerable extent.

Disadvantages -

1. Proper care has to be taken to guard carrier equipment and persons using them

against high voltages and currents on the lines.

2. Reflections are produced on spur lines connected to high voltage lines. This

increases attenuation and creates other problems.

3. High voltage lines have transformer connections, attenuate carrier currents. Sub-

station equipments adversely affect the carrier currents.

4. Noise introduced by power lines is far more than in case of telephone lines. This

is due to the noise generated by discharge across insulators, corona and

switching processes.

53

CONCLUSION

The Practical training has proved to be knowledge buster for me and I have acquired a

good practical knowledge of the field which can’t be gained nearly by reading books. As

PLCC is the power line carrier communication that is used to transmit the signal with power

line network for such large distances, the power line themselves provides a very good

medium of transmission of information. So the power line carrier communication (PLCC) is

mostly used. The training has proved me with a good knowledge of working of PLCC and

base for relating the theoretical knowledge with the practical one. It was a very exciting

adventurous and exhaustive training which has raised my practical skills to a great extent.

54

BIBLIOGRAPHY

The reference of the books and author I have referred to complete my training report are as follows:

1). www.google .com

2). www.wikipedia .org

3). Help from executive engineer of plcc.

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