1

Chapter-1

INTRODUCTION

1.1 AN OVERVIEW OF R.S.E.B.

“Rajasthan State Electricity Board” started working form 1 July, 1957. When India

becomes independent its overall installed capacity was hardly 1900 mw. During first year

plan (1951-1956) this capacity was only 2300 MW. The contribution of Rajasthan state

was negligible during 1 & 2 year plans the emphasis was on industrialization for that end it

was considered to make the system of the country reliable. Therefore Rajasthan

state electricity board came into existence in July 1957.

In 1957 RSEB (Rajasthan State Electric Board) is comes in to existence and it satisfactorily

work from 1 July 1957 at that time energy level in Rajasthan is very low . The 1st survey for

energy capacity in Rajasthan is held in 1989 at that time the total electric energy capacity of

Rajasthan is 20116 MW. At that time the main aim of RSEB is to supply electricity to entire

Rajasthan in the most economical way.

The aim of RSEB is to supply electricity to entire Rajasthan state in the most economical

way. Government of Rajasthan on 19th July 2000, issued a gazette notification unbundling

Rajasthan State Electricity Board into Rajasthan Rajya Vidyut Utpadan Nigam Ltd

(RRVUNL), the generation Company; Rajasthan Rajya Vidyut Prasaran Nigam Ltd,

(RRVPNL), the transmission Company and the three regional distribution companies namely

Jaipur Vidyut Vitran Nigam Ltd, (JVVNL) Ajmer Vidyut Vitran Nigam Ltd (AVVNL) and

Jodhpur Vidyut Vitran Nigam Ltd (JVVNL)

The Generation Company owns and operates the thermal power stations at Kota and

Suratgarh, Gas based power station at Ramgarh, Hydel power station at Mahi and mini hydel

stations in the State

The Transmission Company operates all the 400KV, 220 KV, 132 KV and 33KV electricity

lines and system in the State.

The three distribution Companies operate and maintain the electricity system below 66KV in

the State in their respective areas

Rajasthan State Electricity Board has been divided in five main parts are:-

-> Electricity production authority - RRVUNL

-> Electricity transmission authority - RRVPNL

-> Distribution authority for Jaipur - JVVNL

2

-> Distribution authority for Jodhpur - JVVNL

-> Distribution authority for Ajmer - AVVNL

Power obtain from these stations is transmitted all over Rajasthan with the help of grid

stations. Depending on the purpose, substations may be classified as:-

1. Step up substation

2. Primary grid substation

3. Secondary substation

4. Distribution substation

5. Bulky supply and industrial substation

6. Mining substation

7. Mobile substation

8. Cinematograph substation

Depending on constructional feature substation are classified as:-

1. Outdoor type

2. Indoor type

3. Basement or Underground type

4. Pole mounting open or kilos type

3

Chapter-2

GRID SUBSTATION

A substation is a part of an electrical generation, transmission, and distribution system. A

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

energy from one form to another say from one voltage level to another level. Hence a

substation is an intermediate link between the generating station and consumer.

Fig. 2.1: 132 KV GSS Sitapura, Jaipur

Fig. 2.2: 132 KV GSS Sitapura, Jaipur

4

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

generated voltage for transmission and step down transmitted voltage for distribution. For

this purpose substations are installed. The normal voltages for transmission are 400KV,

220KV, 132KV and for distribution 33KV, 11KV etc.

2.1 CONSTRUCTIONAL FEATURES OF 132KV GSS SITAPURA, JAIPUR

In this substation the power is coming from two lines namely

1. 220 KV INDIRA GANDHI NAGAR

2. 220 KV SANGANER

Outgoing feeders are

1. 33 KV NRI 2. 33 KV SITAPURA 3. 33 KV PRATAP NAGAR

4. 33 KV MICO 5. 33 KV TIJARIA

6. 33 KV STONE MART 7. 33 KV SEZ I 8. 33 KV SEZ II

9. 33 KV RAMCHANDRAPURA

10. 33 KV GONER

11. 33 KV PRATAP APARTMENT

In this substation there are two yards

1. 132 KV Yard

Fig.2.3 132 KV yard

5

2. 33 KV Yard

Fig.2.4 33 KV yard

There are two bus bars in 132 KV yard and also two bus-bars in 33KV yard. The incoming

feeders are connected to bus-bar through circuit breakers, Isolators, LIGHTNING arrestors,

current-transformers etc. The bus-bars are to have an arrangement of auxiliary bus So that

when some repairing work is to be done an main bus the whole load can be transferred to the

auxiliary bus through bus-coupler.

In this 132 KV GSS the incoming 132 KV supply is stepped down to 33 KV with the help of

transformers which is further supplied to different sub-station according to the load.

132 KV GSS has a large layout consisting of 2 Nos of 40/50 MVA transformers having

voltage ratio respectively 132/33 KV in addition to these transformers. And a 250KVA,

33KV/415V Station Transformer gives the supply to the control room and electrical

equipment of GSS.

6

Fig. 2.5 Single Line Diagram of GSS, Sitapura

7

Chapter-3

EQUIPMENTS USED IN G.S.S.

Some equipments are used in the GSS for successful operational breaker & a half scheme two

buses, they are:

1. LIGHTNING ARRESTER

2. CVT

3. LINE ISOLATOR

4. WAVE TRAP

5. CIRCUIT BREAKER

6. POTENTIAL TRANSFORMER

7. CURRENT TRANSFORMER

8. BUS BARS

9. POWER TRANSFORMER

10. CONTROL AND RELAY PANEL

11. BATTERY CHARGER

8

Chapter-4

LIGHTNING ARRESTER

Lightning arrestor is a device, which protects the overhead lines and other electrical apparatus

viz transformer from overhead voltages and Lightning. An electric discharge between cloud

and earth, between cloud and the charge centers of the same cloud is known as lightning. The

earthing screens and the ground wires can well protect the electrical system against direct

lightening strokes but they fail to provide protection against travelling waves which may

reach the terminal apparatus. The lightening arrestors or the surge diverters provide

protection against such surges.

Every instrument must be protected from the damage of Lightning stroke. The three

protection sin a substation is essential:-

Protection for transmission line from direct strokes

Protections of power station or substation from direct strokes

Protection of electrical apparatus against traveling waves

Effective protection of equipment against direct strokes requires a shield to prevent Lightning

from striking the electrical conductor together with adequate drainage facilities over insulated

structure.

Description

The Thyrite Alugard Lightning arrester consists of a stack of one or more units connected in

series depending on the voltage and the operating condition of the circuit three single pole

arresters are required for 3-phase installation. The arresters are single pole design and they

are suitable for indoor and out-door service.

Each arrester unit consists essentially of permanently sealed Porcelain housing equipped with

pressure relief and containing a number of thyrite value-element discs and exclusive locate

gaps shunted by Thyrite resistors metal fitting cemented of the housing provide means for

bolting arrester units into a stack. Each arrester unit is shipped assembled. No charging or

testing operation is required before placing them in service.

Installation Location

Install arrester electrically as close as possible to the apparatus being protected Line and

ground connections should be short and direct

Grounding

The arrester ground should be connected to the apparatus grounds and the main station

ground utilizing a reliable common ground network of low resistance. The efficient operation

of the Lightning arrester requires permanent low resistance grounds Station class arresters

should be provided with a ground of a value not exceeding five ohms.

9

Clearances

These are given on the drawings. These are the maximum recommended. The term

‘clearance’ means the actual distance between any part of the arrester or disconnecting device

at line potential, and any object at ground potential or other phase potential.

Arrester voltage

The thyrite station-class arrester is designed to limit the surge voltages to a safe value by

discharging the surge current to ground; and to interrupt the small power frequency follow

current before the first current zero. The arrester rating is a define limit of its ability to

interrupt power follow current. It is important, therefore, to assure that the system power

frequency voltage from line to ground under any condition switching, fault, overvoltage

never exceeds the arrester’s rating.

LIGHTENING ARRESTER

It consist of a isolator in series and connected in such a way that long isolator is in upward

and short isolator is in downward so that initially large potential up to earth is decreased to

zero. An ideal arrestor must therefore have the following properties:

1. It should be able to drain the surge energy from the line in a minimum time.

2. Should offer high resistance to the flow of power current.

3. Performance of the arresters should be such that no system disturbances are

introduced by its operation.

4. Should be always in perfect from to perform the function assigned to it

5. After allowing the surge to pass, it should close up so as not to permit power current

to flow to ground.

Fig 4.1: L.A. IN SITAPURA G.S.S.

10

WORKING

Lightning, is a form of visible discharge of electricity between rain clouds or between a rain

cloud and the earth The electric discharge is seen in the form of a brilliant arc, sometimes

several kilometers long, stretching between the discharge points How thunderclouds become

charged is not fully understood, but most thunderclouds are negatively charged at the base

and positively charged at the top However formed, the negative charge at the base of the

cloud induces a positive charge on the earth beneath it, which acts as the second plate of a

huge capacitor.

When the electrical potential between two clouds or between a cloud and the earth reaches a

sufficiently high value (about 10,000 V per cm or about 25,000 V per in), the air becomes

ionized along a narrow path and a Lightning flash results.

Many meteorologists believe that this is how a negative charge is carried to the ground and

the total negative charge of the surface of the Earth is maintained.

The possibility of discharge is high on tall trees and buildings rather than to ground

Buildings are protected from Lightning by metallic Lightning rods extending to the ground

from a point above the highest part of the roof The conductor has a pointed edge on one side

and the other side is connected to a long thick copper strip which runs down the building The

lower end of the strip is properly earthed When Lightning strikes it hits the rod and current

flows down through the copper strip These rods form a low-resistance path for the Lightning

discharge and prevent it from travelling through the structure itself.

11

Chapter-5

CAPACITIVE VOLTAGE TRANSFORMER (C.V.T.)

CVTs are special king of PTs using capacitors to step down the voltage. A capacitor voltage

transformer (CVT), or capacitance coupled voltage transformer (CCVT) is a transformer used

in power systems to step down extra high voltage signals and provide a low voltage signal,

for measurement or to operate a protective relay In its most basic form the device consists of

three parts: two capacitors across which the transmission line signal is split, an inductive

element to tune the device to the line frequency, and a transformer to isolate and further step

down the voltage for the instrumentation or protective relay The device has at least four

terminals: a terminal for connection to the high voltage signal, a ground terminal, and two

secondary terminals which connect 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, capacitor C1 is

often constructed as a stack of smaller capacitors connected in series This provides a large

voltage drop across C1 and a relatively small voltage drop across C2.

The CVT is also useful in communication systems CVTs in combination with wave traps are

used for filtering high frequency communication signals from power frequency This forms a

carrier communication network throughout the transmission network .

Fig.5.1: capacitor voltage transformer

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Application:

1) Capacitive voltage transformer can be effectively as potential sources for measuring,

metering protection, carrier communication and other vital functions of an electrical network.

2) Capacitive voltage transformers are constructed in single or multi-unit porcelain

housing with their associated magnetic units. For EHV system.

3) In the case of EHV CVTs the multi-unit construction offers a number of advantages easy

of transport and storing, Convenience in handling and erection etc.

Description:

1) The capacitive voltage transformer comprises of a capacitor divider with its associated

Electro-magnetic unit. The divider provides an accurate proportioned voltage, while the

magnetic unit transformers this voltage, both in magnitude and to convenient levels suitable

for measuring phase metering, protection etc. all W.S.I.capacitor units has metallic bellows to

compensate the volumetric expansion of oil inside the porcelain. In the multiunit stack, all the

potential point are electrically tied and suitably shielded to overcome the effects of corona,

RIV etc.

2) Capacitive voltage transformers are available for system voltage of 33KV to 420KV.

3) Packing and transportation:

3.1) all the capacitor units of capacitive voltage X-mer are securely packed in woolen crates.

The electro-magnetic unit form an integral part with the capacitor unit is hermetically

associated with the electromagnetic unit; the wooden crate for this is exclusive and is sized

heavier taller than for the capacitor unit alone.

3.2) each woolen crate is identified with the corresponding serial number of the unit.

3.3) each capacitor unit has one nameplate designing the rating of the unit Position of the unit

in the complete assembly is also indicated in the nameplate by a suffix T or M

RATINGS OF CVT:-

Insulation Level : 460KV

Rated Voltage factor : 1.2/cont.

Time : 1.5/30 sec

Highest system Voltage : 145KV

Primary Voltage : 132/1.732KV

Secondary Voltage : 33/1.732KV

Weight : 850Kg.

13

Chapter-6

POTENTIAL TRANSFORMER

Potential Transformer is designed for monitoring single-phase and three-phase power line

voltages in power metering applications.

The primary terminals can be connected either in line-to-line or in line-to-neutral

configuration. Fused transformer models are designated by a suffix of "F" for one fuse or

"FF" for two fuses. A Potential Transformer is a special type of transformer that allows

meters to take readings from electrical service connections with higher voltage (potential)

than the meter is normally capable of handling without at potential transformer.

6.1 Potential Transformer

Potential transformers are instrument transformers. They have a large number of primary

turns and a few number of secondary turns. It is used to control the large value of voltage.

Potential Transformer is designed for monitoring single-phase and three-phase power line

voltages in power metering applications.

The primary terminals can be connected either in line-to-line or in line-to-neutral

configuration Fused transformer models are designated by a suffix of "F" for one fuse or "FF" for two

fuses.

14

Chapter-7

ISOLATOR

Fig.7.1 Isolator

An isolator switch is part of an electrical circuit and is most often found in industrial

applications. They are commonly fitted to domestic extractor fans when used in bathrooms in

the UK. The switch electrically isolates the circuit or circuits that are connected to it. Such a

switch is not used normally as an instrument to turn on/off the circuit in the way that a light

switch does. Either the switch isolates circuits that are continually powered or is a key

element which enables an electrical engineer to safely work on the protected circuit.

15

Isolator switches may be fitted with the ability for the switch to padlock such that inadvertent

operation is not possible (see: Lock).In some designs the isolator switch has the additional

ability to earth the isolated circuit thereby providing additional safety. Such an arrangement

would apply to circuits which inter-connect power distribution systems where both end of the

circuit need to be isolated. The major difference between an isolator and a circuit breaker is

that an isolator is an off-load device, whereas a circuit breaker is an on-load device.

When to carry out inspection or repair in the substation installation a disconnection switch is

used called isolator. Its work is to disconnect the unit or section from all other line parts on

installation in order to insure the complete safety of staff working. The isolator works at no

load condition. They do not have any making or breaking capacity.

On fundamental basis the isolating switches can broadly divided into following categories: -

1. Bus isolator

2. Line isolator cum earthling switch

3. Transformer isolating switch.

OPERATION: -

The operation of an isolator may be hand operated without using any supply or may be power

operated which uses externally supplied energy switch which is in the form of electrical

energy or energy stored in spring or counter weight.

In a horizontal break, center rotating double break isolator, 3 strokes are found. Poles are

provided on each phase. The two strokes on side are fixed and center one is rotating. The

center position can rotate about its vertical axis at an angle of 90. In closed position, the

isolating stroke mounts on galvanized steel rolled frame. The three poles corresponding to 3

phases are connected by means of steel shaft.

Isolators are of two types -

1. Single pole isolator

2. Three pole isolator

Construction of Isolator:

Isolator for three-phase we provided in such a manner that for each phase one frame of

isolator. These three isolator must be operated all together. In each frame, line is connected to

terminal stud. Terminal stud is coupled with contact. Contact arm are supported by isolators.

Contacts are made or broken by motor operated mechanism. When contact is to be open then

both arms are rotated in opposite direction, so that contact is broken. Same time earthing pole

moves upward to make contact with a female contact situated adjoined to terminal stud.

Hence, that terminal gets earthen. On these criteria isolator can be carried out manually but

for quick operation motor is used.

16

Chapter-8

WAVE TRAP

To communicate between two G.S.S. we use power line itself. Power line carrying 50Hz

power supply also carries communication signals at high frequency. Wave Trap is a device

used for this purpose. It traps the frequency of desired level for communication and sends it

to P.L.C.C. department. 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.

Transmitter:-

The transmitter consists of an oscillator and an amplifier. The oscillator generates a frequency

signal within 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.

17

Figure-8.1 Wave Trap

18

Chapter-9

CIRCUIT BREAKER

A circuit breaker is an automatically operated electrical switch designed to protect an

electrical circuit from damage caused by overload or short circuit Its basic function is to

detect a fault condition and, by interrupting continuity, to immediately discontinue electrical

flow Unlike a fuse, which operates once and then has to be replaced, a circuit breaker can be

reset (either manually or automatically) to resume normal operation Circuit breakers are

made in varying sizes, from small devices that protect an individual household appliance up

to large switchgear designed to protect high voltage circuits feeding an entire city.

In any circuit, carrying a large amount of current, if a contact is opened then normally a spark

is produced due to fact that current traverses its path through air gap Arcing is harmful as it

can damage precious equipment media are provided between contacts. This is one of the

important equipment in power system It protects the system by isolating the faulty section

while the healthy one is keep on working Every system is susceptible to fault or damages

while can be caused due to overloading, short-circuiting, earth fault etc. thus to protect the

system and isolate the faulty section C B are required Apart from breaking and making

contacts, a C B should be capable of doing

1. Continuously carry the maximum current at point of installation

2. Make and break the circuit under abnormal and normal condition

3. Close or open the faulty section only where fault exists

There are different arc quenching media:-

1) Air blast

2) Oil

3) SF6 gas

4) Vacuum

In 132 KV GSS, SF6 gas circuit breaker are used, as for greater capacity GSS SF6 type

breakers are very efficient.

9.1 AIR BLAST CIRCUIT BREAKER

Air blast circuit breakers are normally only used at low voltage levels but are available with

high current ratings up to 6000 A and short circuit ratings up to 100 kA at 500V.The air blast

circuit breakers according to type of flow of blast of compressed air around the contacts are

three namely (i) Axial (ii) Radial (iii) cross flow of blast air type.

19

Construction & working:

The physical size of such units, which contain large arc chutes, quickly makes them

uneconomic as voltages increase above 3.6KV. Their simplicity stems from the fact that they

use ambient air as the arc quenching medium. As the circuit breaker contacts open the arc is

formed and encouraged by strong thermal convection effects and electromagnetic forces to

stretch across splitter plates. The elongation assists cooling and deionization of the air/contact

metallic vapor mixture. The long arc resistance also improves the arc power factor and

therefore aids arc extinction at current zero as current and circuit breaker voltage are more in

phase. Transient recovery voltage oscillations are also damped thus reducing over voltages.

Arc products must be carefully vented away from the main contact area and out of the

switchgear enclosure. As we know many MCB and MCCB low-voltage current limiting

devices are only designed to have a limited ability to repeatedly interrupt short circuit

currents. Care must therefore be taken when specifying such devices. Air circuit breaker with

fully repeatable high short circuit capability as typically found in a primary substation

auxiliary supply switchboard.

9.2 OIL CIRCUIT BREAKER

Mineral oil has good dielectric strength and thermal conductive properties. Its insulation level

is, however, dependent upon the level of impurities. Therefore regular checks on oil quality

are necessary in order to ensure satisfactory circuit breaker or oil-immersed switch

performance. Carbon deposits form in the oil (especially after heavy short circuit interrupting

duties) as a result of decomposition under the arcing process. Oil oxygen instability,

characterized by the formation of acids and sludge, must be minimized if cooling properties

are to be maintained. Insulation strength is particularly dependent upon oil moisture content.

The oil should be carefully dried and filtered before use. Oil has a coefficient of expansion of

about 0.0008per°C and care must be taken to ensure correct equipment oil levels.

The oil can be moved into arc zone after the current reaches zero by the following actions.

(i)By the pressure caused by the natural head of the oil,

(ii) By the pressure generated by the action of the arc itself (iii) by the pressure caused by

external means.

Thus the oil circuit breakers may be classified as:

(i)Plain break oil circuit breakers.

(ii) Self blast or self-generated or arc control oil circuit oil circuit breakers.

(iii) Externally generated pressure oil circuit breakers of forced blast oil circuit breakers or

impulse oil circuit breakers.

Oil, as an arc quenching medium, has the following advantages and dis-advantages.

Advantage:-

(i)arc energy is absorbed in decomposing of oil (ii)The gas formed, which is mainly hydrogen

have a high diffusion rate and high head absorption in changing from the diatomic to

monotonic state and thus provides good cooling properties. (iii)Surrounding oil presents the

20

cooling surface in close proximity to the arc.(iv)The oil used such as transformer oil is a very

good insulator and allows smaller cleaner between live conductors and earth

components.(v)The oil has ability to flow into the arc space after current is zero.

Disadvantage:-

(i)There is a risk of formation of explosive mixture with air(ii)Oil is easily in flammable and

may causes fire hazards(iii)Owing to formation of carbon particles in the oil due to heat, the

oil is to be kept clean and thus requires periodical replacement.

9.3 SF6 BREAKER

The outstanding physical and chemical properties of SF6 gas makes it an ideal dielectric

media for use in power switchgear. These properties of SF6 gas makes it an ideal dielectric

media for use in power switchgear, these properties are included:

1) High dielectric strength

2) Unique arc quenching ability

3) Excellent thermal stability

4) Good thermal conductivity

In addition, at normal temperature SF6 is chemically inert, inflammable, noncorrosive and

non-condensable at low temperatures.

Working of circuit breaker:

Interrupter unit fixed contacts that are connected through a moving contact. Fixed contacts

are of rod shape. There contacts are known as male contacts.

In closed position, fixed contacts are joined by a moving contact known as female contact.

This female contact is of hollow cylindrical shape. Main parts of female contacts are blast

cylinder, contact tube and guide tube. In closed position female contact overlaps male

contacts.

Contact tube shorts two made contacts and current completes its path from one male contact

to another through contact. Counteracting piston moves towards contact compressing the SF6

present in blast cylinder. When it is required to open the contacts then piston is forced to

move vertically download by hydraulic or pneumatic pressure.

This piston pulls operating rod pulls blast cylinder using bell and crank mechanism. Contact

tube moves away from contact. Counteracting piston moves towards contact compressing the

SF6 present in blast cylinder. When contact between male and female contacts is just going to

break. Then counteracting piston reaches its extreme position performing maximum

compression of SF6 gas .when arc is produced, SF6 at very high pressure quenches the arc.

21

Fig.9.1 SF6 Circuit Breaker

Rating of SF6 breaker:

Type: pneumatic operated

Make: ABB

Rated Voltage 145KV

22

Rated normal current 2000A

Rated Lightning withstand impulse voltage: 650KV

Rated short circuit breaking current: 31.5KA

Rated short time withstand current and duration: 31.5KA, 3 sec.

Rated line charging, breaking current: 50A

Rated SF6 gas pressure at 200c (abs.): 7.0bar

Closing and opening device supply voltage: 110Vdc

Auxiliary circuit supply voltage: 240Vac

Rated air pressure: 22bar

Rated frequency: 50Hz

Maximum weight: 1750Kg.

9.4 Vacuum Circuit Breaker

Vacuum interrupter tubes or ‘bottles’ with ceramic and metal casings are evacuated to

pressures of some 10-6 to 10-9 bar to achieve high dielectric strength. The contact separation

required at such low pressures is only some 0 to 20mm and low energy mechanisms may be

used to operate the contacts through expandable bellows. Below figure shows a cut away

view of such a device. The engineering technology required to make a reliable vacuum

interrupter revolves around the contact design. Interruption of a short circuit current.

Figure 9.2 vacuum circuit breaker

23

Chapter-10

CURRENT TRANSFORMER

When current in a circuit is too high to directly apply to measuring instruments, a current

transformer produces a reduced current accurately proportional to the current in the circuit,

which can be conveniently connected to measuring and recording instruments. A current

transformer also isolates the measuring instruments from what may be very high. Current

transformer is an instrument transformer which is mainly used for measuring currents where

very high currents are flowing.

According to the construction of the current transformer the primary winding of transformer

is in series with high current carrying line & measuring instrument is connected to the

secondary.

Figure 10.1 CURRENT TRANSFORMER

24

The current transformer is mounted one of the power transformer leads; it can be associated

with an Lv or Hv lead; depending on voltage and current consideration. A section of the lead

is demountable locally to enable the current transformer to removed, should the necessity

arise, without disturbing the main connection. The secondary of CT is connected to the

heating coil directly located under the main cover in the oil. On the larger transformers the

various connections may be brought up to terminals in the main the cover for external

linkage.

RATINGS OF CT:-

Frequency : 50 Hz

Highest System Voltage : 145 KV

Short Time Current : 40KA

Rated Current : 600A

Current ratio : 600-300-150/1

Min. Knee Potential Voltage : 850 V at 150/1

Max. Exciting Current : 100MA at 150/1

Max. Sec. Winding Resistance: 2.5 ohm at 150/1

25

Chapter-11

BUS BAR SYSTEM

The conductors used

(i) For 400KV line : Taran Tulla and Marculla conductor.

(ii) For 132KV line : Zebra conductor is used composite of Aluminium strands and Steel

wires.

(iii) For 132KV line : Panther conductor is used composite of Aluminium strands and

Steel wires.

The material used in these conductors is generally Aluminium Conductor Steel Reinforced

(ACSR). The conductors run over the towers cross arms of sufficient height with the

consideration to keep safe clearance of sagged conductors from ground level and from the

objects (trees, buildings etc.) either side also.

Figure 11.1 Bus bar

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 132 KV GSS there are two bus running parallel

to the each other, one is main and another is auxiliary bus is only for standby, in case of

failure of one we can keep the supply continues.

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

breaker which is connected to the bus bar. This remaining all the feeders will be in running

position .if we want to work with any human damage. In this case all the feeders will be on

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

& features and it is cheap.

26

Chapter-12

POWER TRANSFORMER

A transformer is a device that transfers electrical energy from one circuit to another through

inductively coupled conductor -the transformer's coils. A varying current in the first or

primary winding creates a varying magnetic flux in the transformer's core and thus a varying

magnetic field through the secondary winding. This varying magnetic field induces a varying

electro-motive force, or voltage in the secondary winding this effect is called mutual

induction

If a load is connected to the secondary, an electric current will flow in the secondary winding

and electrical energy will be transferred from the primary circuit through the transformer to

the load. By appropriate selection of the ratio of turns, a transformer thus allows an

alternating current voltage to be "stepped up" by making Ns greater than Np, or "stepped

down" by making Ns less than Np

Fig.12.1: POWER TRANSFORMER

Very high cost of transformers is due to three parts:-

1) CORE

2) WINDING

3) OIL

Now we describe the three major parts of transformer

27

CORE

Core is the main part of the transformer It is subjected to magnetic flux For efficient

operation, it is essential that the core of transformer must be constructed from laminated

magnetic material of low hysteresis loss and high permeability Transformers for use at

power or audio frequencies typically have cores made of high permeability silicon The steel

has permeability many times that of space and the core thus serves to greatly reduce the

magnetizing current, and confine the flux to a path which closely couples the windings Early

transformer developers soon realized that cores constructed from solid iron resulted in

prohibitive eddy-current losses, and their designs mitigated this effect with cores consisting

of bundles of insulated iron wires Later designs constructed the core by stacking layers of

thin steel laminations, a principle that has remained in use Each lamination is insulated from

its neighbors by a thin non-conducting layer of insulation The universal transformer equation

indicates a minimum cross-sectional area for the core to avoid saturation

The effect of laminations is to confine eddy currents to highly elliptical paths that enclose

little flux, and so reduce their magnitude Thinner laminations reduce losses, but are more

laborious and expensive to construct Thin laminations are generally used on high frequency

transformers, with some types of very thin steel laminations able to operate up to 10 kHz.

A steel core's remanence means that it retains a static magnetic field when power is

removed When power is then reapplied, the residual field will cause a high inrush current

until the effect of the remaining magnetism is reduced, usually after a few cycles of the

applied alternating current Overcurrent protection devices such as fuses must be selected to

allow this harmless inrush to passion transformers connected to long, overhead power

transmission lines, induced currents due to geomagnetic disturbances during solar storms can

cause saturation of the core and operation of transformer protection devices.

WINDING:-

Core type transformers use concentric type of winding Each limb is wound with a group of

coil consisting of both primary and secondary winding, which are concentric to each other

Low voltage winding is placed near to the core (which is at earth potential) and high voltage

winding is placed outside, however L T and H T windings are inter-leaved to reduce the

leakage reactance.

It is found that the magnetic properties of transformer sheet steel vary in accordance with the

direction of the grain oriented by rolling, sheet are cut as far as possible along the grain which

is the direction in which the material has a higher permeability It must be made In building

the core, considerable pressure is used to minimize air gaps between the plates, which would

constitute avoiding loosed of area and might contribute to noisy operation The reduction of

core sectional area due to presence of insulating material is of the order of 10%.

The winding is layered type and used either rectangular or round conductors. In a cylindrical

winding. Using rectangular conductor, the conductors are wound on the flat side with three-

28

layer side parallel to the core axis. The winding using rectangular conductors may be

simultaneously wound from or more parallel conductors.

The layered winding may have conductors wound in one, two or more layers and is therefore

accordingly called one, two or multi- layer winding. The windings using rectangular

conductors are usually two layered because this case it is easier to secure the lead out ends.

The windings designed for heavy currents are wound with a number of conductors connected

in parallel located side by side in one layer. The parallel conductors have the same length and

are located in the magnetic field or almost the same flux density and hence it is not necessary

to make any transposition of conductors. A wedged shaped packing is used at each of two

entrance ends of winding in order to level it, the packing is made of press bar strips.

Cylindrical winding using circular conductors are multi layered. They are wound on a solid

paper Bakelite cylinder.

TRANSFOMER OIL:

Oil in transformers construction, serves the double purpose of cooling and insulating. For use

in transformer tank, oil has to fulfil certain specifications and must be carefully selected. All

type of oils are good insulators. Animal oil are good insulator but they are too viscous that

they tend to form fatty acids, which attack fibrous materials (e.g. Cotton) and therefore are

undesirable for transformers. Vegetable oils are opt to be inconsistent in quality and like

animal oils, tend to form to form destructive fatty acids. Mineral oils are suitable for electric

purpose; some have a bituminous and other have a paraffin base. The crude oil as tapped, is

distilling producing a range of volatile spirits and oils ranging from the very light to the

heavy paraffin wax or bitumen.

Viscosity:

Insulating properties:

Flash point:

Fire point:

Slugging

TRANSFORMER- ACCESSORIES

WINDING TEMPERATURE INDICATOR

Winding temperature indicator consists essentially of a current transformer and a thermal unit

comprising a heating coil and a thermometric device. The thermal unit, which is designed to

have a thermal performance similar to that of the win windings of the power X-mer, is

influenced by two factors:

(1) The temperature of the surrounding oil, and

(2) The current flowing through the heater coil, which will raise the temperature of the unit

above that of the surrounding oil.

29

The CT secondary current is chosen to the max ‘hot spot’ winding gradient occurring in

either Hv or Lv windings of the power transformer. Thus the thermal unit’s capable of

simulating the hottest-spot temperature of the transformer windings under al conditions.

THERMAL DEVICE

The bulb of a capillary type dial thermometer is screwed into a blind pocket, which is fitted

inside the heating coil. This type of pocket enables the dial thermometer to be removed from

the transformer without having to lower the oil level.

The heating coil with its blind type pocket fitted inside is supported independently under the

cover of the transformer; hence it is always in the hottest oil. The dial thermometer is

provided with one or more sets of contacts for alarm/ or trip circuit and at time for controlling

cooking equipment when forced cooling is called for.

OIL TEMPERATURE INDICATOR

An oil temperature indicator has been provided for measuring the transformer top oil

temperature. The heat sensitive device of the thermometer is placed in an oil pocket mounted

at the transformer cover, the thermometer has two adjustable mercury contacts and a

maximum reading pointer. The contact may be used to close circuit for alarm and tripping

device. The mercury switches are accessible by removing the top cover of the instrument and

are adjustable for different temperature ratings by location of the mount a repeater dial is for

remote indication of the oil temperature in the control room. The thermometer is housed in

the marshalling box.

OIL SURGE REALY FOR OLTC GEAR

An oil- operated relay having one set of contracts is designed to trip the transformer between

the oil conservator. The relay is designed to trip the transformer on the occurrence of violent

oil surges arising out of any malfunction in the OLTC operation. The conservator for the

OLTC gear is separate from the main transformer conservator forms the conservator forms

the conservator for the OLTC the terminals from the relay are wired to the terminal block

located in the marshalling box.

MARSHALLING BOX

The marshalling box is of sheet steel, weatherproof construction, mounted on the side of the

transformer. It is provided with a hinged door and pad lock, and housed the following

instrument and terminal block:-

(a) Winding temperature indicator

(b) Oil temperature indicator

30

(c) Terminal block for alarm and contacts of buchholz relay

(d) Terminal block for oil level alarm and contacts of Magnetic oil level Gauge.

(f) Heater with switch

(g) Magnetic oil gauge

The oil level gauge is mounted on the flat end of the con servitor. The indicator reads the oil

level inside the conservator and initiates an alarm by closing the mercury contacts switch

when the oil level is below the predetermined minimum. The contacts from the oil level

gauge are wired to the terminal block located in the marshaling box.

(h) Cooling equipment

The transformer having mixed cooling ONAF and ONAF is provided with detachable

radiators foxed to the tank wall through valves. The ONAF cooling equipment comprises of

four 457 mm dia fans, each blowing 3600 cu.ft. Of air per minute on the radiator element

directed in such a way that the no longer effective they turn pink. At the bottom of the

breather a cup containing the transformer oil is screwed this oil acts as a seal, preventing the

crystals from absorbing moisture except when breathing is taking place.

COOLING PLANT

Oil cooling is normally achieved by heat exchange to the surrounding air. Sometimes a water

jacket acts as the secondary cooling medium. Fans may be mounted directly onto the

radiators and it is customary to use a number of separate fans rather than one or two large

fans. Oil pumps for OFAF cooling are mounted in the return pipe at the bottom of the

radiators. The motors driving the pumps often use the transformer oil as their cooling

medium.

With ODAF cooling, the oil-to-air coolers tend to be compact and use relatively large fan

blowers. With this arrangement the cooling effectiveness is very dependent on proper

operation of the fans and oil pumps since the small amount of

Cooling surface area gives relatively poor cooling by natural convection alone. Water cooling

(ODWF) has similar characteristics to the ODAF cooling described above and is sometimes

found in power station situations where ample and well-maintained supplies of cooling water

are available. Cooling effectiveness is dependent upon the flow of cooling water and

therefore on proper operation of the water pumps. Natural cooling with the out-of-service

water pumps is very limited. Operational experience has not always been good, with

corrosion and leakage problems, and the complexity of water pumps, pipes, valves and flow

monitoring equipment. The ODAF arrangement is probably favorable as a replacement for

the ODWF designs. Double wall cooler pipes give added protection against water leakage.

The inner tube carries the water and any leakage into the outer tube is detected and causes an

alarm. This more secure arrangement is at the expense of slightly reduced heat transfer for a

given pipe size. Normal practice with cooling plant is to duplicate systems so that a failure of

one need not directly affect operation of the transformer. Two separate radiators or radiator

31

banks and duplicate oil pumps may be specified. In the larger ODAF cooling designs there

may be four independent unit coolers giving a degree of redundancy. The transformer may be

rated for full output with three out of the four coolers in service. Dry type transformers will

normally be naturally air-cooled (classification AN) or incorporate fans (classification AF).

TAPPINGS AND TAP CHANGER

The transformer has an on load tap changer to cater for a variation of +5% to -15% in the HV

voltage in 14 equal steps of 1.43% each for a constant power output. The tappings from the

HV tapping winding are connected to a 15 position ‘66’KV Crompton greaves make high-

speed resistor transition on load tap-changer. The tap-changer may be either manually

operated or motor driven.

The motor driving mechanism is also described in the leaflet and is arranged for the

following types of control.

Local electrical independent

Remote electrical independent

Remote electrical group parallel control

Tap changer is used to change the HV voltage. We use tap changer in HV side only because

in HV side current is less hence it is easy to handle lower amount of current. Tap changers

are of two types.

1) No Load Tap changer

2) On Load tap changer

No Load Tap changer in this type tap changer, we have to cut off load before changing the

taps. These kinds of tap changer are used in small transformers only.

On Load tap changer

In this type tap changer load remains connected to transformer while changing the taps. This

kind of tap changer requires special construction. Tapping winding is placed over HV

winding. Generally, tapping winding is divided in 6 parts by the combination of these 6

winding and HV winding 17 different tap positions are used.

32

Chapter-13

RELAY

A relay is an electrically operated switch Current flowing through the coil of the relay

creates a magnetic field which attracts a lever and changes the switch contacts The coil

current can be on or off so relays have two switch positions and they are double throw

(changeover) switches

Relays allow one circuit to switch a second circuit which can be completely separate

from the first For example a low voltage battery circuit can use a relay to switch a 230V AC

mains circuit There is no electrical connection inside the relay between the two circuits, the

link is magnetic and mechanical.

The coil of a relay passes a relatively large current, typically 30mA for a 12V relay,

but it can be as much as 100mA for relays designed to operate from lower voltages. Most

ICs (chips) cannot provide this current and a transistor is usually used to amplify the small IC

current to the larger value required for the relay coil The maximum output current for the

popular 555 timer IC is 200mA so these devices can supply relay coils directly without

amplification.

Relays are usually SPDT or DPDT but they can have many more sets of switch

contacts, for example relays with 4 sets of changeover contacts are readily available.

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

1. Over voltage relays

2. Over current relays

3. I D M T fault relay

4. Earth fault relay

5. Buchholz’s relay

6. Differential relay

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.

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

33

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.

DIRECTIONAL RELAY: - It allows flowing 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:-

i. Electromagnetic Induction type

ii. Permanent magnetic moving coil type

iii. 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 we can say that this relay works as circuit breaker .

34

Chapter-14

INSULATORS

In order to avoid current leakage to the Earth, through the supporting structure provide to the

conductor of overhead transmission lines, insulators are used. The conductors are secured to

the supporting structures by means of insulating feature, which do not allow current to flow

through these support and hence finally to the earth . Bus support insulators are porcelain or

fiberglass insulators that serve to the bus bar switches and other support structures and to

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

similar in function to other insulator used in substations and transmission poles and towers.

An Insulator should have following characteristic:-

High Insulation resistance.

1. High mechanical strength

2. No internal impurity or crack Disc

Generally Porcelain or glass is used as material for insulators. Porcelain because of its low

cost.is more common. Insulators can be classified in following ways:-

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

the cross arm of a pole. As the name suggests, the pin type insulator is mounted on a

pin on the cross-arm on the pole. There is a groove on the upper end of the insulator.

The conductor passes through this groove and is tied to the insulator with annealed

wire of the same material as the conductor. Pin type insulators are used for

transmission and distribution of electric power at voltages up to 33 kV. Beyond

operating voltage of 33 kV, the pin type insulators become too bulky and hence

uneconomical.

Figure-14.1 Pin Type Insulator

35

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

string. For voltages greater than 33 kV, it is a usual practice to use suspension type

insulators shown in Figure. Consist of a number of porcelain discs connected in series

by metal links in the form of a string. The conductor is suspended at the bottom end of

this string while the other end of the string is secured to the cross-arm of the tower.

The number of disc units used depends on the voltage.

Figure-14.2 Suspension Type Insulator

3. Strain insulator - A dead end or anchor pole or tower is used where a straight section

of line ends, or angles off in another direction. These poles must withstand the lateral

(horizontal) tension of the long straight section of wire. In order to support this lateral

load, strain insulators are used. For low voltage lines (less than 11 kV), shackle

insulators are used as strain insulators. However, for high voltage transmission lines,

strings of cap-and-pin (disc) insulators are used, attached to the cross arm in a

horizontal direction. When the tension load in lines is exceedingly high, such as at

long river spans, two or more strings are used in parallel.

Figure-14.3 Strain Type Insulator

4. Shackle insulator - In early days, the shackle insulators were used as strain

insulators. But now a day, they are frequently used for low voltage distribution lines.

Such insulators can be used either in a horizontal position or in a vertical position.

They can be directly fixed to the pole with a bolt or to the cross arm.

36

Figure-14.4 Shackle Type Insulator

37

Chapter-15

POWER LINE CARRIER COMMUNICATION

15.1 INTRODUCTION

Power line communication or power line carrier (PLC), also known as Power line Digital

Subscriber Line (PDSL), mains communication, power line telecom (PLT), or power line

networking (PLN), is a system for carrying data on a conductor also used for electric power

transmission. Broadband over Power Lines (BPL) uses PLC by sending and receiving

information bearing signals over power lines.

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.

All power line communications systems operate by impressing a modulated carrier signal on

the wiring system. Different types of power line communications use different frequency

bands, depending on the signal transmission characteristics of the power wiring used. Since

the power wiring system was originally intended for transmission of AC power, in

conventional use, the power wire circuits have only a limited ability to carry higher

frequencies. The propagation problem is a limiting factor for each type of power line

communications. A new discovery called E-Line that allows a single power conductor on an

overhead power line to operate as a waveguide to provide low attenuation propagation of RF

through microwave energy lines while providing information rate of multiple Gbps is an

exception to this limitation.

15.2 MAJOR SYSTEM COMPONENTS EQUIPMENT

The major components of a PLC channel are shown in Figure. The problem associated with

the PLC channel is the requirement to put the carrier signal onto the high voltage line without

damaging the carrier equipment. Once the signal is on the power line it must be directed in

the proper direction in order for it to be received at the remote line terminal.

15.3 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.

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.

38

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.

15.4 LINE TRAPS OR WAVE TRAPS:-

The carrier energy on the transmission line must be directed toward the remote line terminal

and not toward the station bus, and it must be isolated from bus impedance variations. This

task is performed by the line trap. The line trap is usually a form of a parallel resonant circuit

which is tuned to the carrier energy frequency. A parallel resonant circuit has high impedance

at its tuned frequency, and it then causes most of the carrier energy to flow toward the remote

line terminal. The coil of the line trap provides a low impedance path for the flow of the

power frequency energy. Since the power flow is rather large at times, the coil used in a line

trap must be large in terms of physical size.

Once the carrier energy is on the power line, any control of the signal has been given over to

nature until it reaches the other end. During the process of traveling to the other end the

signal is attenuated, and also noise from the environment is added to the signal. At the

receiving terminal the signal is decoupled from the power line in much the same way that it

was coupled at the transmitting terminal. The signal is then sent to the receivers in the control

house via the coaxial cable.

15.5 COUPLING CAPACITORS:-

The coupling capacitor is used as part of the tuning circuit. The coupling capacitor is the

device which provides a low.

Impedance path for the carrier energy to the high voltage line and at the same time, it blocks

the power frequency current by being a high impedance path at those frequencies. It can

perform its function of dropping line voltage across its capacitance if the low voltage end is at

ground potential. Since it is desirable to connect the line tuner output to this low voltage point

a device must be used to provide a high impedance path to ground for the carrier signal and a

low impedance path for the power frequency current. This device is an inductor and is called

a drain coil.

It is desirable to have the coupling capacitor value as large as possible in order to lower the

loss of carrier energy and keep the bandwidth of the coupling system as wide as possible.

However, due to the high voltage that must be handled and financial budget limitations, the

coupling capacitor values are not as high as one might desire. Technology has enabled

suppliers to continually increase the capacitance of the coupling capacitor for the same price

thus improving performance.

39

15.6 DRAINAGE COILS:-

The drainage coil has a pondered iron core that serves to ground the power frequency

charging to appear in the output of the unit. The coarse voltage arrester consists of an air gap,

which sparks over at about 2 KV and protects the matching unit against line surges. The

grounding switch is kept open during normal operation and is closed if anything is to be done

on the communication equipment without interruption to power flow on the line. The

matching transformer is isolated for 7 to 10 KV between the two winding and former two

functions. Firstly it isolates the communication equipment for the power line. Secondly it

serves to match the characteristic impedance of the power line 400-600 ohms to that of the

co-axial vacuum arrester (which sparks) is over at about 250 V is provided for giving

additional protection to the communication equipment.

15.7 ADVANTAGES & DISADVANTAGES OF PLCC

ADVANTAGES

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

themselves carry power as well as the 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 condition

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 area resulting in very low resisntanc3 per unit

length. Consequently the carrier signal suffers lesser attenuation than when travel on

usual telephone lines of equal lengths.

5. Power lines are well insulated to provide 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 voltage and currents on the line.

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

attenuation and create other problems.

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

Sub-station equipments adversely affect the carrier currents.

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

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

processes.

40

Chapter-16

CONTROL ROOM

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

located at a suitable point remote from immediate vicinity of CB’s and other equipments.

In GSS the separate control room provided for remote protection of 132KV switch yards

transformer incoming feeder, outing feeders. Bus bar has their own control plant in their

control rooms. The control panel carrier the appropriate relays. Necessary meters indicating

lamp control switches and fuses. There are meters for reading purpose. A circuit concerning

the panel is shown on the panel with standard colour.

On each panel a control switch is provided for remote operation of circuit breaker. There are

two indicators which show that weather circuit breaker is closed or open. A control switch for

each insulator is also provided. The position indicator of isolator is also done with the help of

single lamp and indicator. The colour of signal lamps are as follows:-

Red:- for circuit breaker or isolator is close option

Green - for circuit breaker is in open position.

Amber - indicates abnormal condition requiring action.

In addition to used indication an alarm is also providing for indicating abnormal condition

when any protective relay or tripping relay has operated. Its constants energies on auxiliary

alarm. Relay which on operation completes the alarm belt circuit.

Synchronizing:-

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

any incoming feeders to the bus bar. It just be synchronized with switches. When the

synchronous copy shows zero we close the circuit breaker.

Synchronoscope is used to determine the correct instant of closing the switch which connect

the new supply to bus bar. The correct instant of synchronizing when bus bar incoming

voltage.

1. Are in phase

2. Are equal in magnitude

3. Are in some phase sequence

4. Having same frequency

5. The voltage can be checked by voltmeter the function of synchronoscope is to

indicate the difference in phase and frequency.

41

Fig.16.1: panel of control room

ENERGY METER: - These are fitted on different panel to record transmitted energy

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

WATT METER: - This is mounted on each feeder panel to record import or export

power.

FREQUENCY METER: - Provided to each feeder to measure frequency which

analog or digital.

VOLT METER: - Provided on each panel or the purpose of indication of voltage.

AMMETER: - These are used to indication the line current.

MVAR METER: - Provided for indicating power factor of import and export.

MAXIMUM INDICATOR DEMAND: - Chief requirement of these indicators to

record the minimum power factor taken by feeder during a particular period. This

record the average power successive predetermined period.

42

Chapter-17

BATTERY ROOM

In a GSS, Separate dc supply is maintained for signaling remote position control, alarm

circuit etc. There is a battery room which has 55 batteries of 2 volt. Therefore D.C. power

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

battery. Various parts of lead acid batteries:-

Fig.17.1: a view of battery room

1. Plates

2. Separators

3. Electrolyte

4. Container

5. Terminal port

6. Vent plugs

43

CHARGING OF BATTERIES:-

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

“lead peroxide”, whereas the –ve plates will converted to spongy lead. Also in a fully

charged battery the electrolyte specific gravity will be at its highest venue of 1.2.

DISCHARGING:-

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

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

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

gravity of the electrolyte also decreases the value around 1.00 and the terminal

voltage also decreases from its initial to a lower value which may be around 1.85 or

1.8.

44

Chapter-18

CAPACITOR BANK

Capacitor banks are used to improve the quality of the electrical supply and the efficient

operation of the power system. Studies show that a flat voltage profile on the system can

significantly reduce line losses. Capacitor banks are relatively inexpensive and can be easily

installed anywhere on the network.

Fig.18.1:- CAPACITOR BANK

The capacitor unit is made up of individual capacitor elements, arranged in parallel/ series

connected groups, within a steel enclosure. The internal discharge device is a resistor that

reduces the unit residual voltage to 50V or less in 5 min. Capacitor units are available in a

variety of voltage ratings (240 V to 24940V) and sizes (2.5 KVAR to about 1000

KVAR).capacitor bank used for 33 KV at GSS has 2 units of 7.2 MVAR.

45

Chapter-19

CONCLUSION

It was a very good experience of taking vocational training at 132KV GSS Sitapura, Jaipur.

All the Employees working there were very helpful and were always ready to guide us. They

gave their best to make us understand.

The Assistant Engineer, Junior Engineer & Technicians gave us the detailed theory. Training

at 132KV GSS Sitapura, 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, Isolator, Control Room, and Battery Room etc.

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

electrical power transmission and distribution. Protection of various apparatus was a great

thing. Maintenance of transformer, circuit breaker, isolator, insulator, bus bar etc. was

observable.

I had a chance to see the remote control of the equipments from control room itself, which

was very interesting. All in all the training at 132KV GSS Sitapura, Jaipur was a memorable

experience.

46

Chapter-20

REFERENCES

1. Electrical Technology By B.L.Theraja & A.K.Theraja

2. Power System Protection And Switchgear By Badri Ram & D N Vishwakarma

3. Power System By J.B.Gupta

4. http://electricalpowerengineering.blogspot.in

5. http://www.electrical4u.com/

6. http://en.wikipedia.org/wiki/Insulator_(electricity)

7. http://www.engineersgarage.com/articles/plcc-power-line-carrier-communication\

8. Electrical Machine By P.S.bhimbra