REPORT ON INDUSTRIAL TRAININGVENUE: - GLADNI (NARWAL)

SUBMITTED TO: - SUBMITTED BY:-

V.K.KAUL RASLEEN K SUDAN

H.O.D ELECTRICAL ROLL NO:- 146/06

ELECTRICAL- 7th SEM

LIST OF CONTENTS

CHAPTER 1 INTRODUCTION

1.1 Location of Gladni Grid Station

1.2 Description of single line diagram

1.3 Substations

1.3.1 Design of substations

1.3.2 Location of Substations

CHAPTER 2 EQUIPMENTS&SWITCH GEAR

INSTALLATIONS IN GLADNI GRID

STATIONS

2.1 Incoming lines

2.2 Busbars

2.2.1 Single bus bar

2.2.2 Double bus bar

2.3 Insulator

2.3.1 Pin type insulator

2.3.2 Suspension type insulator 2.3.3 Post type insulator

2.4 Isolating switches

2.5 Circuit breaker

2.5.1 Classification of circuit breaker

2.5.1.1 MOCB

2.5.1.2 . Sulphur Hexafluoride

2.5.1. Vacuum Circuit breaker

2.5.2 Applications

2.6 Lightening arrester

CHAPTER 3 RELAY

3.1 Protective relay

3.2 Types of relay

3.2.1 IDMTL

3.2.2 Buchol’z relay

3.3 Earthing

3.3.1 Neutral grounding

CHAPTER 4

4.1 Power transformer

4.2 Instrument transformer

4.2.1 Current transformer

4.2.2 Potential transformer

4.3 Metering and indicating instruments

4.4 Power line carrier communication system

CHAPTER 5 TRANSFORMERS

5.1 Introduction

5.2 Main circuits in transformers

5.2.1 Magnetic Circuit

5.2.2 Electric Circuit

5.2.3 Dielectric Circuit

5.2.4 Thermal Circuit

5.2.5 Structural Circuits

5.3 Transformer Cooling

5.4 Structural Circuits

5.4.1 Conservator

5.4.2 Breather

5.4.3 Temperature Indicator

5.4.4 Buchholz’s Relay

5.4.5 Bushings

5.4.6 Tap Changes

LIST OF ABBERVIATIONS

S.No. ABBERVIATIONS FULL NAME

1. ac Alternating current

2. dc Direct current

3. kV Kilo Volts

4. PT Potential transformer

5. CT Current transformer

6. HT High terminal

7. MOCB Minimum Oil Circuit Breaker

INTRODUCTION

In the beginning of the electrical age, electricity was generated, transmitted and distributed in the form of direct current and voltages were low. With the development of transfer, ac system has become predominant. The present day large power systems has been possible only due to adoption of ac system.

The present day electrical power generator system is ac. The electrical power is

produced at power stations which are located at favorable places quite away from consumers. It

delivers to consumers through large network of transmission and distribution. For the further

distribution of electrical supply grid station plays an important role.

Sometimes it becomes necessary to use dc, at the time, ac can be converted to dc by the

use of rectifiers. In the short ac is of utmost importance.

INTRODUCTION (GLANDI ,JAMMU)

Location:- Narwal, Gladni ,Jammu (J&k)

In Gladni Grid Station there is provision for three incoming transmission lines:-

1) 220KV Salal-12) 220KV Salal-23) 220KV Hiranagar-1

The outgoing/incoming line is one that is: 1) 22Okv Jammu-Hiranagar/saran/Hiranagar-2

There are two numbers 220/132KV two transformer banks with capacity:-

3 x 133.33MVA = 400MVA

1 x 160 MVA = 160MVA

Total = 560MVA

Again there are two transformers banks 132/33KV with capacity,

2 x 50MVA = 100MVA

There is provision following 132 KV line outgoing feeders,

1) 132 KV Miran Sahib Line2) 132 KV Kalakote Line3) 132 KV Hiranagar-14) 132 KV Hiranagar-25) 132 KV Sidhra-16) 132 KV Sidhra-27) 132 KV Bari-Brahamana

There is also provision for following 33 KV lines,

1) 33KV G-1,It is used by power station itself2) 33KV G-2, Trikuta-Nagar and Railway complex3) 33KV G-3,Ghandi-Nagar and shastri-Nagar4) 33 KV G-4,Old city and panjthrithe5) 33 KV G-5,Bahu fort …6) 33KV G-6, channi

SINGLE LINE DIAGRAM

DESCRIPTION ABOUT SINGLE LINE DIAGRAM

Figure attached shows key diagram of a typical 220/132/33 KV Gladni Grid Station. The diagram of this grid station is explained as under:-

1) There are three 220 KV in coming lines connected to the bus bars. Each incoming lines is capable of suppling the sub station load. All these lines can be loaded simultaneously to share the grid station load the three lines arrangement increases the reliability of the system. In case there is a break down of one incoming line, the continuity of supply can be maintain by the other line.

2) The grid station has double bus bar system, one main bus bar and the other spare bus bar. The incoming can be connected either bus bar with the help of an arrangement of circuit breaker and isolators. The advantage of double bus bar system is that if repair is to be carried on one bus bar, the supply need not to be interrupted as the entire load can be transferred to the other bus.

3) There is an arrangement in gladni grid station to step down the incoming 220 KV supply to 132 KV by two transformer banks with capacity, 3 x 133.33 MVA = 400 MVA 1 x 160 MVA = 160 MVA Total = 560 MVA

4) All the three incoming and out going lines are connected through circuit breaker having isolators on there either ends. Whenever repair is to be carried over the line towers, the lines first off and then earthed.

5) The P.T and C.T are suitably located for supply to metering and indicated instruments and relay circuit. The P.T is right on the point where the line is terminated. The C.T are connected at the terminals of each circuit breaker.

6) The lighting arresters are connected near the transformers terminals to protect those lighting strokes.

7) Against there is provision for further step down 132 KV supply to 33 KV by two transformers with capacity:-

2 x 50 MVA = 100 MVA

8) There are other auxiliary components in the grid station such as wave trapper, capacitor bank for power factor improvement, each connections, local supply connections, and D.C supply connections.

GRID STATION

Gridstation are the important part of power system. serve as a source of energy supply for the local areas of distribution in which these are located. Their main functions are to receive energy transmitted at high voltage from generating stations, reduce the voltage to a value appropriate for local distribution and provide facilities for switching. Some substation are simply switching where different connections between various transmission lines are made, others are converting substations which convert AC into DC or vise-versa or convert frequency from higher to lower or vise-versa, substation have some additional functions. They provide points where safety devices may installed to disconnect equipment or circuit in the event of faulty. Voltage on the out going feeder can be regulated at the substation. A substation is convenient place for installing synchronous condensers at the end of the transmission line for purpose of improving power factor and make measurements to check the operation of the various part of the power system . Thus gridstations may be defined as the assembly of apparatus, which transfer energy to another; e.g. from AC to DC or to the voltages from 66kv, 110kv, or 220kv.however 500kv will used for the national grid system in future. The consumer do not use such high voltage and so they must be transformed to low voltage levels by means of substations, thus a substation may be called as link between the generating stations and consumer.

DESIGN OF GRIDSTATION

When a station is to be designed, the following procedure should be adapted:- Prepare a single line diagram of main electrical connections

showing bus bar arrangements, circuit breaker and transformers. Decide the layout of the switchgear keeping views capacity of substations,

methods of control and number of feeders,reliability, safety, flexibility, space needed and construction.

The layout should be such that it should be possible to isolate any section during fault, without affecting the service of the healthy section.

It should be possible to have an easy and safe access for maintenance and inspection for different equipments.

An arrangement should be made to extinguish fire. The earth conductor should of sufficient cross-sectional area to carry the fault

current in severe conditions. A proper and sufficient automotive electrical protective gear should be used.

Power cables should be separate from control cable. Allow reasonable amount of expansions for substation.

LOCATION OF GRIDSTATION

The following points should be taken mainly into consideration in choosing the location of gridstation:-

Location stations as close to the load center as possible. Locate stations at such points that all the perspective loads may be conveniently

reached without under voltage regulation. Allow access to the incoming transmission line and outgoing distribution line. Choose the site where municipal restriction of property laws should permit the type of

building necessary for substation. Keep load on substations with in such limits that an undue large area or number of

consumers will not be affected in case the station shut down occurs.

The location of station should be indoor, outdoor, and underground or pole mounted. The last two are for small size of distributions stations and the rural electrification may be considered only in large crowded cities, with space limitations. The indoor type of station, which is common used, all the equipments. In case of outdoor types of station, which is common used, all the equipments are arranged outdoors and should with stand weather conditions. The advantage of outdoor type is that they do not need any buildings. In case of outdoor the cost of transformers and switchgear equipments is less than that indoor type.

In case of stations at the generating stations, to step up generations voltage to transmission voltage, they are located in the outstation yard. So in the transmission stations also control and protective equipments are located inside the buildings near the station yard.

EQUIPMENTS AND SWITCH GEAR INSTALLATION IN THE GLADNI GRID STATION

There are the various electrical equipments installed at the substations. These are:

1) INCOMING LINES

These lines supply powers to the substations from source of generations or from transmission lines at high voltages.

2) BUS BARS

When a number of lines operate at the same voltage have to be directly connected electrically, bus bars are used as the common electrical components. Bus bars copper or aluminum bars (generally rectangular x – section) and operate at constant voltage. The incoming and outgoing lines in a substation are connected to the bus bars. The outdoor bus bars is either of the rigid type or the strain type. In rigid type pipes are used for bus bars and also for making the connections among the various equipments wherever required. The strain type bus bars are the overhead system of wires string between the two supporting structures and supported by the strain type insulators.

There are numerous variations of bus bars arrangements. The choice of a particular arrangement depends on various factors, system voltage and position of the substation in the system flexibility, reliability of supply and cost:-

Simplicity is the keynote of dependable system. Maintenance should be possible without interruption of supply or danger to the

operating personal. Alternative arrangements should be available in the event of an outage of any of the

apparatus. The installation should be as economical as possible keeping in view the requirements

and continuity of supply.

The most commonly used bus bars arrangements in substations are:

a) Single line bus bar arrangement

It consists of single (three phase) bus bars to which the various feeders are connected. In case of fault or maintenance of bus bar the entire bus bar has to be de energized and total shut down results. The equipment connections are very simple and it is very easy to operate. It is not popular used for 33KV and above, except where the relative importance of the substation is less or the position of the substation does not justified elaborate schemes. This arrangement is simplest and cheapest. However it suffers from two major defects:- maintenance without interruption of supply is not possible and extension of substation without a shutdown is not possible.

b) Double bus bar arrangement

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

The scheme used two identical bus bars so that

Each load may be fed from either bus. The load circuits may be divided into two separate groups if needed from the

operational considerations. Either bus bar may be taken out for the maintenance and cleaning of

insulators

This arrangement has been used quite frequently adopted where the load and continuity of supply justify additional cost. This type of bus is used in GLADNI are main bus bar(bus 1) & reserve bus bar( bus 2) .

3) INSULATORS

The insulator used in connection with over head systems employing bar conductors are composed almost invariably of glazed porcelain, although some moulded materials are used for low voltage, and glass material are also used. The insulator serves two purposes. The most usually material for manufacture of insulators is porcelain. The porcelain should be ivory white, sound free from defects and thoroughly vitrified so that the glaze is not dependent upon insulation. This through vitrification of the porcelain is of paramount importance, since the presence of pores or other air- spaces will lower the dielectric strength, and it therefore follows that porcelain for electrical purposes must be both thoroughly air- free and impervious to the entrance of gases and liquids. Toughened glass is also sometime used for insulators but its use is limited to about 33KV. The design of the insulator is such that the stress due to contraction and expansion in an par of insulator does not to any defect. It is desirable not allow porcelain to come in direct wit a hard metal screw thread. Normally cement is used between metal and porcelain.

Types of insulators

a) Pin type insulator

As the name suggests the pin- type insulator is attached to steel bolt or pin, which is secured to a cross arm on the transmission pole. This type of insulator consists of single or multiple shells ( petticoats or rain sheds) adopted to be mounted on a spindle to a fixed to the cross arm of the supporting structures. Multiple shells are provided in order to obtain sufficient length of leakage path so that the flash over voltage between the power conductors and pin of the insulator is increased. The design of the shells is such that if upper most shell is wet due to rain the lower shells are dry and provided sufficient leakage resistance. The insulator and its pin, or other support, should be sufficiently strong mechanically to withstand the resultant force due to

the combined effects of wind pressure and weight of span. The pin type insulators are normally

used up to 33KV. It is not desirable to use them beyond 50KV as a cost of such insulators then

increase much faster then the voltage.

b) Suspension type insulator

For high voltage rating these insulators are used. These insulators consists of one or more insulator units flexibly connected together and adopted to the hung for the cross on of the supporting structure and to carry a power conductor at its lowest extremity. Such composite units are known as string insulators. each insulator is a single disc shape piece of porcelain grooved on the under surface to increase the leakage path between the metal cap at the top and the metal pin at the bottom of the insulator. Suspension insulators being free to swing, the clearance required between the power conductor and the supporting structures are more as compared to pin type insulators. Each insulator is design for 11KV and hence for any operating voltage a string of insulators can be used.

Several important advantages follow from this system

Each insulator is designed for a comparatively low working voltage, usually about 11,000 volts, and the insulation for any required line voltage can be obtained by using a ‘string’ of a suitable number of such insulators.

In the event of a failure of an insulator, one unit- instead of the whole string- has to be replaced.

The mechanical stress are reduced, since the line is suspended flexibly with pin type insulators, the grid nature of the attachment results in fatigue and ultimate brittleness of the wire, due to the alternating nature of the stresses. Also string is free to swing; there is an equalization of the tensions in the conductors of successive spans.

In the event of an increase in the operating voltage of the line, this can be met by adding the requisite number of units to each string, instead of replacing all insulators, as would be necessary with pin-type.

c) Post type insulator

Post insulators have metal bolt down base as opposed to threads. Many early multipart lines are spotted with line post insulators as replacements. Post insulators are also used in substations to insulate high voltage switching gear and transformers. There is no hobby numbering system for post insulators yet. Most insulators are used for bus bars. Post insulators consist of porcelain body, cast iron cap and flanged cast iron base. The hole in the cap is the threaded so that the bus bars can be directly to cap.

4) ISOLATING SWITCHES

In substation, it is often desired to disconnect part of the system of the general maintenance and repairs. The isolating switch or isolator accomplishes this. It may be defined as a device used to open or close a circuit either when negligible current is interrupted or when no significant change in the voltage across the terminals of each pole of the isolator will result from the operation. An isolator is essentially a knife switch and is designed to open the circuit under no load. In other words, isolator’s switches are operated only when the lines in which they are connected carry low current. Isolators are not fitted control device and function only for instantaneous changes of switching circuit’s arrangements and for providing a visible break in a circuit. So as to make certain operation that can be performed on

an isolated section without running a risk. Isolators are handling manually as well as automatic.

5) CIRCUIT BREAKER

A circuit breaker is equipment which can be open are closed a circuit under a normal as well as fault condition. It is so desired that it can be operated manually or by remote control under normal condition and automatically under fault condition. For the latter operation a relay is used in the circuit breaker. A circuit breaker essentially consists of fixed and moving contacts, called electrodes. Under normal operating condition, these contacts remain closed and will not open automatically until and unless the system becomes fault. The contacts can be opened manually or by remote control whenever desired. When a fault occurs on any part of the system, the trip coils of the circuit breaker get energized and moving contacts are pulled apart by some mechanism, thus opening the circuit. the basic construction of any circuit breaker requires the separation of the contacts in any insulating fluid, when serves two function:-

It extinguishes the arc drawn between the contacts when the circuit breaker open. It provides adequate insulation between the contacts and from each contacts to earth.

Many insulating fluids are used for arc extinction and the fluid chosen depend upon the rating and type of the circuit breaker.

The insulating fluids commonly used are :- Air at atmospheric pressure Compressed air Ultra high vacuum Oil which produces hydrogen for arc extinction Sulphur hexafluoride (SF6)

In GLADNI grid station there different types of circuit breakers are used. In 220 KV line minimum oil circuit breaker (MOCB) is used where as in 132KV line MOCB and SF6 are used and for 33KV line MOCB and vacuum circuit breaker is used.

TYPES OF CIRCUIT BREAKER :-

1. MINIMUM OIL CIRCUIT BREAKER (MOCB)

One of the important development in

the design of oil circuit breaker has been to reduce

the amount of oil needed. The other advantages

are reduction in tank size , reduction in total

weight and reduction in cost . It used minimum

amount of oil and is only used for arc

extinguishing the current conducting parts are

insulated by porcelain or organic insulated

material. Low oil circuit breaker employees solid

materials for insulations purpose and uses a small

qty.of oil which is just sufficient for arc extinguishing .By using suitable arc control devices,

the arc extinguishing can be further facilitated in low circuit breaker. venting.

2. SULPHUR HEXAFLURIOD(SF6 )

In such circuit breaker sulphur hexafluoride gas is used as arc quenching medium. The

SF6 is electronegative gas and has a strong tendency to absorb free electrons. The contacts of

the breaker an opened in a high pressure flow of SF6 gas and an arc is struck between them.

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

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

insulating strength.The SF6 circuit breaker has been found to be very effect able for high

power and high voltage services.SF6 has excellent insulating strength because of its affinity for

electrons i.e whenever a free electrons collides with the neutral gas molecules to form

negatives ions, the electrons is absorbed by the neutral gas molecules may occur in two ways

SF6 + e -> SF6

SF6 + e -> SF5 + F

The negative ion formed are relatively heavier as compared to free electrons and therefore

under a given electric field the ions do not attain sufficient energy to lead cumulative ionization

in the gas.

(SF6 CIRCUIT BREAKER TYPE FXT14F

RATED VOLTAGE-245KV

NORMAL CURRENT-2500A

FREQUENCY-50HZ

DURATION OF SHORT CIRCUIT CURRENT-3SEC)

WORKING

In closed position of the breaker, the contacts remains surrounded by SF6 gas at a pressure of about 6KG/sq.cm. When the breaker operates, the moving contact is pulled apart and arc is structure between the contacts. The movement of the moving contacts is synchronized with the opening of the valve, which permits SF6 gas at 15Kg/sq.cm pressures from the reservoir to the arc interruption chamber. The high- pressure flow of SF6 rapidly absorbs the electrons in the arc path to form immobile negative ions, which ineffective as charge carriers. Thus, medium between the contacts quickly built up high dielectric strength and cause the extinction of the arc, after the breaker operates.

III. VACCUM C IRCUIT BREAKER:

In such breakers (degree f

vacuum being from 10-7 to 10-5 tore) is

used as arc quenching medium. Since vacuum offers the high insulating strength, it has

superior quenching properties then any other medium e.g when contacts of the breaker are

opened n vacuum , the interruption occurred first current zero with dielectric strength between

the contacts building at a rate of 1000th of times higher then that obtained with other circuit

breaker . Thus a vacuum arc is different from the general class of low & high pressure arc . In

the vacuum arc the neutral atoms, ions and electrons do not come from the medium in which

the arc is drawn but they are obtained from the electrodes themselves by evaporating its surface

material , because of the large mean free path for the electrons , the dielectric strength of the

vacuum is a 1000 times more than when the gas is used as the interrupting medium .

LIGHTENING ARRESTERS :

It is protective device which conducts the high voltage surges on the power system to the

ground.

Surge voltages are abnormal voltage that may cause break down of insulation of electrical equipment. These voltages may result from switching disturbance in the electrical installation circuit or from lightning stroke.

In Gladni grid station valve type arrester is used. It consists of two assemblies:

Series spark gaps and non-linear resistor discs. These both are connected in series under normal conditions; the normal system voltage is insufficient to cause the break down of air gap assembly. On the occurrence over voltage, the break down of series spark gap take place and the surge current is conducted to earth via the non-linear resistor. They provide effective protection.

Requirement of lightning Arrester

It should not pass any current at normal or at abnormal (normally 5% more than normal voltage) power frequency voltage.

It should break down as quickly as possible after abnormal high frequency voltage is arrived.

It should not only protect the equipment for which it is used but should discharge the surge current without damaging it self.

It should interrupt the power frequency follow current after the surge is discharged to ground.

BUS COUPLER

Breakers are used as bus couplers. They provide the coupling between the two bus bars of the zone e.g. the provide the coupling between the zone A and B. when ever there is a fault in the main bus couple the load of the main bus bars to there serve bus bar and vice versa.

CONTROL CABLES

The control cables and conduit system is required for affecting automatic controls. For laying these cables generally ducts are run from control room basement to centrally located junction box from where the conduits are run to be required.

POWER TRANSFORMERS :

A power transformer is used in a sub station for step down the voltage. Expect at the power station, all the subsequent sub station used step down transformer to gradually reduce the voltage of electrical supply and finally delivered it at the utilization voltage. The modern practice is to used 3 phase transformer in the sub station, although 3 single phase bank of transformer can also be used. The use of three phase transformer (instead of 3 phase bank of transformer) permits two advantages. Firstly, only one 3 phase load tap changing mechanism can be used. Secondly its installation is much similar then single phase transformer. The power transformers are generally installed upon length of rails fixed on concrete slabs having foundation 1 to 1.5 m deep. In gladni sub station two rating of transformers are installed 220/132/33 KV.

ACCESSORIES AND AUXILIARIES USED IN TRANSFORMER

Tank Radiators Cooling fans, oil pump, oil to water heat exchangers Bushings Buchholz Relay/ Oil surge Relay Temperature Indicator – WTI , OTI. Oil level Indicators Pressure Relief device Marshalling Box/ Control Cubicle Oil preservation systems : Conservators and Breathers

TRANSFORMER OIL

One of the most important factors, which determine the life, satisfactory operations of the transformer are the oil in which it is immersed

The transformer oil has two prime functions:-

To create the acceptable level of insulation in conjunction with insulated conductors and coils.

To provide a cooling medium capable of extracting quantities of heat without deterioration as an insulating medium.

Transformers oil is a mineral oil obtained by fractional distillation of crude petroleum. Vegetables and animal oils are not used in transformers. Some of the important characteristics necessary in transformer oil are its dielectric, strength, resistance, to emulsion viscosity, purity, and flash point and sludge formations.

TRANSFORMER COOLING

Transformer is a static device that converts energy at one level to another voltage level. During this process of energy transfer, losses occur in the windings and core of the transformer. These losses appeared as heat. This heat is dissipated to the surroundings. The coolants used in the transformers arre:-

Air OIL

The transformers using air as coolant are called dry type transformers while transformers using oil as coolant are known as oil immersed transformers. In dry type transformers the heat generated is conducted across the core and windings to be dissipated from the Outer surface of the windings to the surrounding air through convection. In case of oil immersed transformers, the heat produced inside the core and the windings are connected across them to their surfaces.

The heat is transferred from oil to the walls of the tank through convection. Finally, the heat is transferred from the tank walls of the surrounding air by radiation and convection.

Method of cooling

The cooling methods used for dry type transformers are

Air natural (AN)

The natural circulation of surrounding air is utilized to carry the heat generated by natural convection.

Air Base (AB)

Air blast is employed in order to keep the temperature rise within the limits. The forced air circulation improves the heat dissipation.

The cooling method used for oil- immersed transformers are:-

Oil Natural (ON)

The cooling by air is not so effective and proves insufficient for transformers of medium sizes. Oil coolant has two advantages:

It is better conductor of heat then air. It has high coefficient of volume expansion with temperature.

Oil natural air forced (ONAF)

In this method the oil circulating under natural head transformer heat to the tank walls. The transformer tank is made hollow and air is blown through the hollow space to cool the transformer. The heat is removed from the inner tank walls can be increased to five or six times that dissipated by natural means.

Oil natural water forced (ONWF)

In this method copper cooling coils are mounted on the transformers core but below the surface of the oil. Water is circulated through the cooling coils to cool the transformer.

Forced circulation of oil

In large transformer the natural circulation of oil is insufficient for cooling the transformer and forced circulation is employed. Oil is circulated by a motor driven pump from the top of a tank to a external cooling plant (heat exchanger) where the oil cooled. The cold oil enters the transformer at the bottom of the tank.The methods of cooling oil in the heat transformers by forced circulation of oil areas classified accordingly as:-

Oil forced air natural (OFAN)

In this method oil is circulated to the transformer with the help of a pump and cooled in heat exchanger by natural circulation of air. This method is not commonly used.

Oil forced air forced(OFAF)

The oil is cooled by external heat exchangers using air blast produced by fans. The arrangement results in higher efficiency for the system.

Oil forced water forced(OFWF)

The heated oil is cooled in a water heat exchanger. In this method the pressure of oil is kept higher than that of water and therefore leakage occurs in from oil to water.

INSTRUMENT TRANSFORMERS :

The lines I sub station operate at high voltage and carry current of 1000 of amperes. The measuring instruments and protective devices are designed for low voltages ( for generally 110 volts ) and currents ( about 5 A ) .Therefore, they not work satisfactory if mounted directly on the lines this difficulty is overcomes by installing instrument transformers on the power lines. The function of his instrument transformers is to transfer voltage or current in the power lines to values which are convenient for the operation of measuring instrument and relays. There are two types of instrument transformers viz ;

CURRENT TRANSFORMERS :

C.T is essentially a transformer which steps down current to a known ratio. The primary winding of this transformer consists of one or more turns of thick wire connected in series with the line. The secondary consists of large number of turns of fine wire and provides for the measuring instruments & relays a current which is a constant fraction of the current in the line . Suppose current transformer rated at 100/5 A is connected in the line to measure current in primary the current in primary the current in the line 100 A , then secondary of C.T will be 5 A .Similarly , if current in the line is 50 A , then secondary of C.T will have current of 2.3 A .Thus C.T under consideration will step down the line current by a factor of 20 .

POTENTIAL TRANSFORMER :

It is essentially a step down transformer & step downs the voltage to known ratio. The primary of this transformer consists of large number of turns of fine wire connected across the line instrument relays a voltage a known fraction of the line voltage. Suppose a potential transformer rated at 66kv/ 110v is connected to a power line .If line voltage is 66kv, then the voltage across secondary will be 110 kv.

METERING & INDICATING INSTRUMENTS

There are several metering & indicating (e.g ammeter, voltmeter, energy meter etc) installed in a sub station to maintain watch over the ckt quantities .The instrument transformer are invariably used with them for satisfactory operation.

POWER LINE CARRIER COMMUNICATION SYSTEM

Whenever some breakdown occurs in the transmission network at any place, the message to rectify the fault must be sent to all sub station. Quickness is the first priority .The ordinary telephone network cannot be used as it already overloads and remains engaged. Therefore, the same power lines, which carry energy, are used for this purpose. The signal is modulated by HF carrier and is send as radio waves through the power lines. This system is known as power line carrier communication system.

PROTECTIVE RELAY AND EARTHING

PROTECTIVE RELAYS :

It is a device that defect the faults and initiates the operation of the ckt breaker to isolate the defective element from the rest of the system .The relay ensures the safety of the ckt equipment from any damage which might be otherwise caused by the fault.

THE TYPES OF RELAYS INSTALLED AT GLADNI

IDMLT type relay (Directional & non directional) Primary relays such as buchhol’z Restricted earth fault etc.

IDMTL (INVERSE DEFINITE MINIMUM TIME OVER CURRENT RELAY) :

IDMTL is one in which the operating time approx inversely proportional to the fault current near pick up value and becomes substantially constant slightly above the pick up value of the relay. This is achieved by using a core of the electromagnet which gets saturated for currents slightly greater than pick up current. It has two types:-

( a ) Non – directional relay

( b ) Directional relay

( a ) Non directional ( over current or earth leakage ) relay :-

This types of relay will not be able to discriminate when used on transmission lines, whether the fault has been taken place in the section where the relay is located or it has taken place in the adjoining section. under the condition of high power factor or leading power factor , the impedance seen by relay is a very low or even negative.

( b ) Directional (Over current or earth fault ) relay :- The non directional relay can operate for fault flow in either direction. In order to achieve operation for the fault flowing in a specific direction, it is necessary to add a directional element to the non directional element. Such a relay which responds to fault flow in a particular directional is called a directional relay .

3.2.2 BUCHHOL’Z RELAY :-

Buchhol’z relay is a gas actuated relay used for protecting oil immersed transformer against all types of internal fault and makes use of the fact that fault decompose oil thus generating gases. The device relies on the fact that an electrical fault inside the transformer

tank is accompanied by generation of gas , and if the fault current is high enough by a surge of oil from the tank to the conservator.

EARTHING

Connecting of an electrical equipment or apparatus to the earth with the help of a connecting wire of negligible resistance is known as “ear thing” or “grounding”.

In an electric installation, if a metallic part of an electric appliance comes in direct contact with a bare or livewire, the neutral being a good conductor of electricity is charged static charge on it will accumulate. Now if any person comes in contact with this charged metal part, he will get a severe shock. But if the metallic parts of the equipment or apparatus are earthed, the charge will be given to earth immediately as the metallic part comes in direct contact with a bare or live wire or breakdown occurs. And as the discharge takes place to the earth, the impedance of the path of the current is low, heavy current flows to earth, the instant the current exceeds the limiting value the protective device (usually a fuse) operates and isolates the appliance or equipment form the supply. Thus to provide safety to the users as well as for the operating and maintenance personals it is essential to provide ear thing.

(1 ) SYSTEM EARTHING :-

It is required to provide low fault impedance to the ground fault currents for proper operation of the protective relays and for meeting the system requirement by effectively earthed system.

( 2) SAFETY EARTHING :-

It is required to provide protection to the operating staff working in the yard and sub station from any injury during fault condition by keeping the voltage gradient with

in safe limits. The above two parts have common earth mat from which flat iron risers are taken out to connect all the non-current carrying metal parts of the equipment. At the same

time the earth mat conductor rise to voltage, which is equal to the resistance of the earth mat multiplied by ground fault current. This difference of potential results in voltage gradients.

NEUTRAL GROUNDING :

In practice, the neutral of a three- phase system is earthed at sub station. This is known as neutral earthling or grounding .An earthed neutral system has the following advantages :-

A ) It provides a better protection against earth faults.

B ) It ensures nearly constant voltage of healthy phases because neutral point is not shifted.

C ) This system provides a better reliability of service .

D ) It is safer for personal and equipment.

E ) It requires lesser maintenance expense as compared to the unearthed neural (isolated system.

F ) In the system, transient voltages produced are very small.

G ) Ground fault relaying is simple . The earth may be utilized to operate protective relays to isolate the fault.

H ) Persistent arcing ground can be eliminated by employing protective gear.

In addition to above, there are following equipments in a sub station :-

A ) Fuses

B ) Carrier-current Equipment

C ) Substation Auxiliary Supplies.

FUSES :

Fuse is a essentially a short piece of metal ( or a fusible material ) inserted in a circuit which melts when a predetermined value of current flows through it and thus breaks the circuits .The protective element of the fuse is a fuse-link inserted in series with the circuit being protected . The most generally material used for fuse element is a low melting point material such as tin, lead or zinc .Fuses may be low voltage type or high voltage type : low voltage can be further divided into two classes namely semi- enclosed rewire able fuse and the cartridge type fuse.

SUBSTATION AUXILIARY SUPPLY :

In small –unattended substations only small amount of power for electric lightening during regular periods of inspection, maintenance and repair is required. In regional substation the electric power is required for the auxiliaries- the lightening circuits, air blast fans of power transformers, battery changing sets, compressor units in case of air blast circuit breakers, ventilating fans of the substation buildings etc. In large substation it is wide practice to connect two transformers to the main bars supply of the auxiliaries.

TRANSFORMERS

INTRODUCTION :-

As in well known transformers is a piece of apparatus without continuously moving parts,

which by electromagnetic induction transformers alternating voltage and current in one or

move windings usually of different values of voltage and current and at same frequency.

Transformers is heart of power system and is most important and costliest in power system

.It is estimated that one MW of additional power earning capacity requires about 7 to 8 MVA

transformers’ capacity .The diamond for transformer is expected to grow at a lipid pace, since

the the generating station conventionally Hydroelectric ,thermal are situated geographically

for a part from load centers and since these are linked by transformer.

MAIN CIRCUITS IN TRANSFORMERS

1 . MAGNETIC CIRCUITS :

Cold rolled grain oriented silicon (CRGOS) Steel (with lower specific losses to the folw of

magnetic flux along the diection of grain orientation;s is universally utilized.

With the advent of computer controlled machines for cutting the laminations

precisely ,step lap lamination joints are economically used to achieve low no- load losses.

2 .ELECTRIC CIRCUIT :

It consists of primary and secondary winding which are costliest and which have to meet

stringent requirement of Dielectric , thermal and mechanical stresses expected during testing as

well as service conditions. ANNEALED rectangular shaped copes conductor s most

commonly used and for Distribution transformer and high voltage testing transformers and

conductor are also used. In order to minimize the stay losses in the winding, continuously

transposed conductor (CTC) are used type of winding normally include Helical, continuous

Disc, Multilayer and inter laved Disc winding.

3 .DIELECTRIC CIRCUIT :

It comprises of insulation:

- Minor insulation between lure to lure on within the layers o same winding.

- Major insulation between winding and between winding earth.

- Oil serves as an insulation as well as coolant paper oil combination has been

established as effective insulation system even up to HV transformers.

4 .THERMAL CIRCUIT :

The losses produced in transformer should be dissipated in order to limit the temperature rise

of oil and winding working at 98mof winding temperature, over weighted ambient of 32 ,

transformers have continuous healthy life during its entire service span and every 6 rise ova

98 reduces the life to half .By providing additional cooling through radiators ,fans .etc heat

can be dissipated and capacity of transformer can be updated.

5 .STRUCTURAL CIRCUITS :

This is essential to house the transformer oil, flitting and accessories such as terminal

arrangements, conservator, Breather, safety device etc. The structural design should also

withstand seismic forces.

( a ) CONSERVATOR :

Conservator with valiation of temperature there is corresponding variation in oil volume. To

account for this, an expansion vessel

called conservator is added to hemp

with a connecting pipe to main tank.

In smaller transformers this vessel is

open to atmosphere through

dehydrating breathers in large

transformer, an air bag is mounted

inside the conservator with inside

bag open atmosphere through

breathers and outside surface of bag

in contact with oil surface.

( b ) BRAETHER ;

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

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

this will find its way finally into paper insulation and causes reduction insulation strength of

transformer to minimize this the conservator is allowed to breath only through silica gel

colomin ,which absorb the moisture in air before it enters the conservator air surface.

PREASURE RELIEF DEVICE / EXPANSION VENT.

Transformers tank is a pressure vessel as the inside pressure can group steeply whenever there

is a fault in the windings and the surrounding oil is suddenly vaporized. TANKS as such are

tested for a pressure with stand capacity of 0.35 kg /cm.To prevent bursting of the tank , these

tanks are in addition provide with expansion vents with a thin diaphragm made of Bakelite

/Copper / glass at the end . In present day transformer, pressure relief device are replacing

expansion vents. These are similar to safety valves on boilers.

BUSHINGS :

Transformer are connected to HV

lines and therefore care is to taken to

prevent flash-over from high voltage

connections to earthed

tank .Connections from cables are

made in cable boxes , but overhead

connections are to be brought through

bushing specially designed for

different classes of voltages.

TAP CHANGER

It is very essential to maintain system voltage within prescribed limits for better health of

electrical equipments voltage of system can be varied by changing the true ration of

transformer .The device tap changer is used for adding a cutting out turns of primary or

secondary winding of transformer .It is of basically two types :

1 .Off-Circuit tap changer

2 .On-Load tap changer (OLTC )

OFF-CIRCUIT TAP CHANGER

The cheapest method of changing turn ratio of transformer is use of off-circuit tap changer. It is

essential to de-energise the transformer before changing tap.

ON – LOAD TAPCHANGE

On-load tap changers are employed

to change the turn ratio of the

transformer to regulate system

voltage while transformer is

delivering normal load. With the

introduction of on-load tap

changer, operating efficiency of

electrical system has considerably

improved.

133.3 MVA TRANSFORMER (SINGLE PHASE)

160 MVA POWER Transformer (3 Phase)

TYPE OF COOLING

OFAF ONAF ONAN

Rating HV&IV(MVA)

160 128 96

Rating LV (MVA) 53.33 42.67 32No load HV(KV) 220 220 220No load IV(IV) 132 132 132No load LV(KV) 11 11 11Line current HV(A) 419.8 335.91 251.94 IV(A) 699.8 559.8 419.8 LV(A) 2799.27 2239.42 1679.5

50MVA EMCO Transformer

TYPE OF COOLING ONAN ONAMRated power HV KVA 40000 50000 LV 40000 50000 IVRated voltage at no load HV(KV)

132 132

IV 33 33 LVRated line current HV(A) 174.95 218.69 LV 699.8 874.7

50 MVA CGL Transformer

TYPE OF COOLING ONAN ONAFNo load voltage HV(KV) 132.8 LV 33Current HV 218.7

160 MVA Transformer Control panel

ACKNOWLEDGEMENT

I avail this opportunity to express my profound sense of sincere and deep gratitude to Mr. V. K. Suri,

chief executive engineer, GLADNI Narwal Jammu for giving me the opportunity to carry out my one

month training in this organization.

I am blissful to express my deep sense of gratitude to employees, GLADNI Narwal who helped me a

lot in giving minute details of Design and Constructional Features of Grid Station and enlightened me

with the knowledge of Grid Station and Its working.

Last, but not the least, I must express my immense gratitude to all the members of the GLADNI

NARWAL JAMMU , from whom I got all necessary help whenever required.

CONCLUSION

It is itself is a feeling of gratitude to have visited one of the chief Electrical installation of the Jammu. Though the period of one month was not that much to have explored such a wonderful

sight.

I am sure that the technical knowledge which I have gained at GLADNI Narwal Jammu would serve great in future.

Still I am pleased to have learnt a lot about the work culture and the ethics of industries.

CAPACITOR BANK

REFRENCE

WEBSITE:i)WWW.GOOGLE.COM

ii)WWW.WEKIPIDIA.COM

BOOKS: NAME OF THE BOOK : PRINCIPLE OF POWER SYSTEM

AUTHOR :V.K.Mehta & Rohit Mehta

PUBLISHER :S.CHAND

CHAPTER :i)CIRCUIT BREAKERS

ii)SUBSTATIONS

iii)PROTECTIVE RELAY`S