Distribution Substation

7/29/2019 Distribution Substation

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NAME OF TRAINEE: 1. ARIJIT DE; 2. DEBABRATA DEY;

3. KUNAL PAHARI; 4.ROSHNI BAGCHI;NAME OF THE COLLAGE: NARULA INSTITUTE OF TECHNOLOGY...

NAME OF THE TRAINING CENTER: TITAGARH 132KV SUBSTATION

DUREATION OF TRAINING: 27TH JUNE 2005 TO 26TH JULY 2005..

SUBJECT OF TRAINING: CONTROLLING & TRANSMISSION OF HIGH...VOLTAGE POWER SUPPLY

INTRODUCTION:In 20th century electricity is one of the most essential things. Without electric power human civilization sinks into

the darkness. So we can say that invention and development of electricity is comparable to the invention of fire by ancient

people. Now we can generate power by different means, those are

1. Thermal power plant (by burning fossil fuel coal & diesel).

2. Hydroelectric power plant (by using the flow of the water).

3. Nuclear power plant (by using RADIO ACTIVE MATERIAL).

The above given means are called as CONVENTIOAL ENERGY SOURCE. But there are other sources like,

i) Solar power plant (by using energy of sunlight).

ii) Wind power plant (by using flow of wind).iii) Tidal power (by using force of water during tide in river)

iv) Terrestrial heat energy.

Those areNON-CONVENTIONAL ENERGY SOURCE.

Power generated in power plants is of 11KV rating, but to distribute it to the consumers requires two processes,

I. Transmission system.

II. Distribution system.

To transmit the power through conductors we have to increase the voltage step by step from

11KV/66KV/110KV/132KV/220KV/400KV due to minimise the line losses.

It is clear that after generation, power does not directly reach to the consumers. From generating station it goes to

different grade of SUB-STATIONS where the voltage is stepping down to 33KV, 11KV even 3.3KV and send to the

distribution units. In distribution units, voltages again step down to 416volt and send to the consumers.

UnderWEST BENGAL STATE ELECTRICITY BOARD many SUB-STATIONS are there, TITAGARH is oneof them. W.B.S.E.B. was established on 1955 and during 50 years given excellent service. Now though it is a Govt. undertaking sector, it becomes one of the finest service sectors in country.

As we see that power sector is PUBLIC ORGANIZATION, therefore it has to do some duties those are,

a. Must supply power to all who so ever applies for it.

b. Must supply his maximum demand and should be prepared to increase it in future if asked for.

c. Must provide the service line to the consumer that must carry the consumers load safely.

d. Must not discriminate between consumers of same category, i.e. the categories of consumers may be

domestic consumers, industrial consumers and bulk consumers etc.

e. May collect revenue at reasonable rate with reasonable profit.

SUB-STATION:The SUB-STATION is defined as an assembly of equipments, which transform the characteristics (VOLTAGE,

CURRENT and POWER FACTOR) of electrical energy.

CLASSIFICATION OF SUB-STATION:The classification of SUB-STATION depends on some factors. Those are given below,

SERVICE: Static AC; converting AC to DC.

FUNCTION: BHV transmission; Distribution; Industrial; Power factor correction; Frequency changer; DC for light and

power.

CONTROL: Manual; Automatic; Supervisory.

MOUNTING: Indoors; Outdoors; Pole mounting.

COMPONENTS OF SUB-STATION: TOWERS AND TRANSMISSION LINES .

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POWER TRANSFORMER (voltage rating above 200kVA).

CURRENT TRANSFORMER .

PROTECTION DEVICES .

MEASUREMENT DEVICES .

CONTROL PANEL.

SECONDARY POWER SOURCE (AC or DC).

COMUNICATION.

PROPERTIES OF SUB-STATION:Also a power station should have some properties. Those are given below,

a. RELIABILITY.

b. MINIMUM CAPITAL COST.

c. MINIMUM OPERATING COST.

d. SIMPLE IN DESIGN.

e. SHOULD HAVE LABOUR-SAVING EQUIPMENT.

f. EXTENSIBILITY.

LOCATION OF SUB-STATIONS:We know that theoretical considerations are not always used in practice. Therefore, location of SUB-STATION

has theoretical considerations but in practice there are various types of problems occurred. Following points helps to

relocate the SUB-STATIONS,

Theoretically SUB-STATION should be located at the center of load gravity. If commercial locality is at the

center then SUB-STATION should be situated to a more appropriate place.

If the incoming line passes through any of the zones, the SUB-STATION preferably should be located in that

zone.

SOME CONVENTIONS:When new people visit the power station some conventions are there to know information about that SUB-

STATION.

1. HOW CAN YOU recognize WHICH ONE OF THE CONDUCTORS OF THE INCOMING CIRCUIT ISYELLOW phase?In any high voltage transmission line YELLOW phase is always in the middle, like in VIBGYOR yellow colour

stands between red & blue colour. Therefore when we see the transmission line according to INDIAN ELECTRICAL

CONVENTION the three phases are RYB, the topmost is RED, then YELLOW, then the lower one is BLUE.2. HOW CAN you recognize the incoming circuit if multi-circuit incoming is there?

If there are two or more circuits as incoming, we have to stand by facing towards the source then the extreme

right is CIRCUIT 1, next in left is CIRCUIT 2 and go on.

3. HOW CAN YOU RECOGNIZE THE PHASES ENTERING INTO THE TRANSFORMER?If we stand infront of Power Transformer in the primary side then from right to left the RYB phases are arranged,

but from secondary side the RYB phases are arranged from left to right.

TITAGARH SUB-STATION:TITAGARH SUB-STATION is one of the oldest SUB-STATIONS whose age is near about 45. It is situated in

the sub-urban area in south-west portion of north 24 parganas. It was built to supply the power to BARRACKPORE

industrial zone. Now its primary task is to supply RAILWAYS. The infrastructure has been successively developing time

to time.

This SUB-STATION is 132/33/25KV SUB-STATION. This SUB-STATION has two bas system in incomingside.

MAIN BUS.

TRANSFER BUS.

In two-bus system every bay has three isolators, three C.T.s, one three-pole circuit breaker, one lightning

arrester. Normal width of 132KV bay is 12.2m and Normal length of it is 56m. All the structures are of galvanized steel.

BUS COUPLER: The bay which couples the main & transfer bus is called BUS COUPLER. But in two-bus

system it should be called bus transfer. This bay is used when there is a fault in

SUB-STATION equipment and has to cut off for maintenance then the main bus supply is transferred to bus coupler bay

or bus transfer bay.

SALIENT FEATURES:

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Double circuit 132KV incoming source only 28/30 k.m. from 132KV DHARAMPURSUB-STATION, Nadiawhere DHARAMPUR132KV bus is energized by triple circuits from B.T.P.S. and double circuit from

JEERAT 400/220/132KV SUB-STATION, Eastern grid SUB-STATION in India.

132KV tied up gas pressure cable line from nearby C.E.S.C. TITAGARH generating station. Import & exportof132KV power supply facility in both the ends when it needed.

Highest ever 25KV single phase power supply capacity from two 132/25KV 20MVA transformers to EasternRail, Sealdha Division.

Air-conditioned control room with modern parameters, high sensitive relays and tripping devices in control &operational system.

Newly designed SUB-STATION earthing network for safety of the system and equipments. Meets up consumers` supply with many bulk power drawers for heavy industry, civic need of vast area with the

capacity or two 132/33KV 50MVA power transformers in parallel operation.

Very stable D.C. source with new set of YKP-11 125Amp-hour capacity EXCIDE make STORGE Cell keep theSUB-STATION alive.

Two 33/0.4KV 100KVA earthing cum station auxiliary transformers with an extra 415volt auxiliary supply fromC.E.S.C. line.

Under Frequency relay device now set at 48.3Hz feeders under imposition or exemption is controlled by C.L.D.Howrah.

100% metering system in every stage for line or transformer and further A.T.C. loss calculation. Routine patrolling of incoming transmission line pre-puja and winter maintenance and pre-arranged energy shut

down to keep the lines steady and to avoid any interruption.

Load diversion facility of most of the 33KV feeders.TRANSMISSION TOWERS & LINE CONDUCTORS:

An overhead line comprises mainly of conductors, supports, insulators and pole fittings. The function of overhead

lines is to transmit electrical energy and the important characteristics which the line-conductors must have are:1) HIGH ELECTRICAL CONDUCTIVITY.

2) HIGH TENSILE STRENGTH.

3) LOW DENCITY.

4) LOW COST.

The metals which posses the above properties are copper, aluminium and steel, which are either alone or in

combination.

Transmission line design does not complete without mentioning the line supports. So these should have some

minimum allowable properties,

They must be mechanically strong with factor of safety of 2.5 to3.

They must be light in weight without the loss strength.

They must have least number of parts. They must be cheap.

They must have longer life.

They must have pleasing shape.

Their maintenance cost should be least.

Now the design of the tower depends on some factors. Those are,

I. Length of insulator.

II. Minimum clearance to be maintained between conductors and tower.III. Location of the conductors with respect to outermost conductors.

IV. The midspan clearance required from consideration of dynamic behaviour of conductor and lightning protection

of line.

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V.

Ground clearance i.e. clearance between the bottom conductors and ground level. According to I.E. rules the

minimum clearance are as follows,

VOLTAGE (KV) CLEARANCE (m)

66KV 5.49m

132KV 6.10m

220KV 7.01m400KV 8.84m

Here in TITAGARH steel tower is used having square base. Generally lattice towers are used, which are

mechanically strong and depending upon the angle of deviation the tower design is done. Further vibrationDampers,

Jumpers & Arching Horns are also used.

As we mentioned earlier that this SUB-STATION developing successively, conductors used here in earlier daysare ACSR(Aluminium Conductor Steel Reinforced) type in which the core of the conductor is made of Steel wires and

the periphery is made of Aluminium wires. But we know that steel is used here only to strengthen conductor, it does not

help in transmission. Therefore, it is not economically allowable. Now these conductors are changed to AAAC (All

Aluminium Alloy Conductor) which is made of Aluminium alloy gives the strength more then Aluminium conductor and

also the whole conductor transmit the power which save the amount of conductor needed for certain amount of power

transmission. Though the conducting capacity of alloy is lower than Aluminium but overall this is economically sound.

Different types of conductor are there, depending upon its voltage and current rating.

MOUSE 400KV SYSTEM, 800Amps.

ZEBRA 220KV SYSTEM, 700Amps.

PANTHER .132KV SYSTEM, 400Amps.

Busbar:132 KV bay has two parallel busbars one is main bus other is transfer bus. The provision of another parallel

busbar makes the scheme expensive but its advantages out merit the extra cost. The main advantage consists in fact that

whole of the load is transferred to the auxiliary busbar when maintenance or repairs are being done on the main busbar.

Normally, however, the main busbar is used and the auxiliary busbars serve the purpose of a reserve busbar. In testing of

the circuit breaker on the various feeders and commissioning of the new feeders can be easily undertaken by running them

on the auxiliary busbar without tempering with the main busbar. It involves the use of double isolating switches for one

breaker.The advantage & disadvantage of the system are:

ADVANTAGES:1. It ensures supply in case of bus fault, incase of any fault in one of the bus, the circuit can be transferred to the

transfer bus.

2. The circuit breaker can be maintained with uninterrupted supply as the load can be transferred to the other bus

through the bus coupler circuit breaker. However, the relaying will be scarified as the relaying system is not

transferable.

3. It is easy to connect the circuit from either bus.

4. The maintenance cost of substation decreases.

5. The bus potential can be used for relays.

DISADVANTAGE:The bus is maintained or expanded by transferring all of the circuits to the transfer or auxiliary bus depending

upon the remote back up relays and breakers for eliminating faults of the bus would shut down the entire station.

SECTIONALIZED BUSBAR:Under the scheme duplicate busbar are used with main busbar in sections connected through a bus coupler. In this

method of connection, any section of the busbar can be isolated for maintenance while any section may be synchronized

with any other auxiliary busbars. It will be noted that the auxiliary busbar is not sectionalized because this is not necessary

and is expensive. The main busbar is sectionalized by high voltage isolator.

FEEDERS:

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There are two types of feeders in SUB-STATION, import & export. Import or incoming feeder is double circuit

feeder is coming from DHARAMPUR. These two feeders consist of lightning arrestors, transfer bus isolator that are

generally kept open. The export or outgoing feeders also consists of isolators, C.B.s, lightning arrestors, C.T.s.

Five feeders are going out

AGARPARA-I

AGARPARA-II

OLD CALCUTTA-I

OLD CALCUTTA-II

BARRACKPUR

These feeders have the supply 33KV for the connecting substations. There are other four feeders from traction

transformer supplied 25KV single phase for railways. Also there is a tie up line with C.E.S.C. Through which power can

be taken from generating station or given to the C.E.S.C. grid.

INSULATOR:In power sectorINSULATORis one of the most wanted things. For high voltage transmission insulator is must

to prevent shock hazard, short circuit, and leakage of power.

Mainly it separate line conductors from each other & from supporting structures. For using insulator in high

voltage purpose it should have some considerations. Those are,1) The insulator should have high permittivity so that it can tolerate high electrical stresses i.e. the dielectric strength

of insulating material is high. The insulator should be able to with stand the lightning & switching surge.

2) It should possess high mechanical strength in order to withstand conductor load even in worst condition like in

hail storm, high velocity wind etc.

3) It needs to have a high resistance to temperature changes to reduce damages from power flash over i.e. insulatorshould have high ratio ofPUNCTURE STRENGTH to flash over.

4) The electrical resistance of insulating material should be high to prevent the leakage of current to earth to keep

corona loss and ratio interference within reasonable limits.

5) The insulating material should not be porous and should be impervious to gases in atmosphere and should be free

from impurity and cracks which may lower the permittivity.

Here in TITAGARH three types of insulators are used,

PIN TYPE OR STACK INSULATOR. SUSPENTION TYPE INSULATOR.

STRAIN TYPE INSULATOR.

PIN types are used for holding solid G.I. pipes act as conductor. SUSPENSION types are used for holding and

separating the incoming & outgoing feeders from horizontal towers and from each other. STRAIN types are used in the

lattice tower to hold the conductors, busbars etc. with certain calculated amount of strain to make sure that the conductorssuspended in air with perfectSAGand height from earth. Different grade of insulator is used depending upon the supply

voltage & the span of conductor.

SUSPENTION TYPES FOR 70KN TENTION.

STRAIN TYPES FOR 90KN TENTION.

STRAIN TYPES FOR 120KN TENTION.

Pin type insulators are mainly used for


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WINDINGS:LV windings are next to the core over which HV tapping and HV main windings are placed. Tapping windings

with same no of turns are placed after HV main winding depending on impedance. Windings are arranged in concentric

formation with lowest voltage winding next to core to avoid insulation. In case, tertiary winding is arranged then this

winding be placed next to core.

Various types of windings used for making coils are

i) Tertiary winding: - Spiral/Helical/Disc.ii) Low voltage: - Helical/Disc.

iii) High voltage: - Partially inter leaved disk/layers winding/ disc winding.

iv) Tapping winding: - Inter wound spiral or helical coil/ Interleaved disc or ordinary disc.

BUSHING:Transformers are connected to H.V lines & therefore care must be taken to prevent flash over from H.V

connection to earthed bank. Connections for cables are made in cable boxes but overhead connections should be brought

through bushing. The simplest bushing is molded, high quality glazed porcelain insulator with a condenser through center.

The conductor is in the axis of porcelain cylinder. The spaced between this two is filled by oil. The active part of bushingconsists of an oil impregnated paper (OIP) condenser core manufactured from superior grade craft paper, wound on metal

tube. The bushings are voltage graded by suitably interposed Aluminum foils forming condenser layer.

TANK:The core & windings of transformer are placed in main tank. Each tank is generally equipped with the following

valves:

i) One drains & lower filter valve (at L.V side).

ii) One filter valve (on the top of the tank).

iii) One filter valve (on the bottom of tank on the L.V side).

iv) One relief valve.

This is made from mild steel plate.

CONSERVATOR:Transformers are not totally filled with oil & some space is left between oil level & tank. This space is filled by

air. As the temperature of oil is increases or decreases during operation there is a corresponding rise & fall in volume. To

account for this an expansion vessel called conservator is connected to the transformer tank. It is provided with a magnetic

oil level indicator on one of the end covers that has a low level alarm.

BREATHER:A dehydrating breather is used to dry air that enters the transformer as the displacement of air due to the change of

oil volume because of fall in temperature. It contains calcium chloride or silica gel to dehydrate. Air entering the breather

is first drawn through an oil seal then passedthrough silica gelcrystals to the connecting pipe at the top. During thisupward passing of air any moisture presents is absorbed by dry silica gel & it becomes white or pinkish.

TRANSFORMER OIL:Transformer oil is used as an insulating &cooling medium in power transformer .The mineral oil which have a

paraffin base are used as transformer oil. The characteristic of transformer oil is as follows,

SL. NO. CHARACTERISTICS UNIT REQUIRMENTS

1. Appearance ------------Oil shall be clear, transpar

free from suspended ma

2. Density gm/cc 0.89

3. Kinematics viscosity at 27 oc cst 27

4. Interfacial tension N/m 0.04

5. Flash point (min) C 140

6. Pour point (max) C -6

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7. Neutralization value of total acidity mg/KOH/g 0.03

8. Corrosive sulphur ----------- Non corrosive

9.Breakdown voltage

1. Untreated oil

2. Filtered

KV (rms) 30(if


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In TITAGHARSubstation both of the transformers are there. They distribute power in local areas at the rate of

416volts.

There are 7 transformers in the substation.

1. T1 (20 MVA)(FOR RAILWAYS)

2. T2 (20 MVA)(FOR RAILWAYS)

3. T3 (50 MVA)(FOR TRANSMISSION 33KV POWER)

4. T4 (50 MVA)(FOR TRANSMISSION 33KV POWER)

5. T5 (33/0.416KV)(FOR DISTRIBUTION)

6. E1 (33/ 0.4KV)(STATION TRANSFORMER)

7. E2 (33/0.4KV)(EARTHING TRANSFORMER)

COOLING OF TRANSFORMER WINDING:The temperature of the winding increases due to some reasons as follows,

1. Due to overloading.

2. Due to leakage current in winding.

3. Due to higher ambient temperature.

4. Due to any sparking in the transformer tank.

Here in TITAGHARlarge transformers like T1, T2, T3, and T4 have the cooling arrangement for their windings. The

methods are

i) ONAN (OIL NATURAL AIR NATURAL)

ii) ONAF (OIL NATURAL AIR FORCED)iii) OFAF (OIL FORCED AIR FORCED)

ONAN (OIL NATURAL AIR NATURAL): The transformer is immersed in oil and the heat generated incores and windings is passed on to oil by conduction. Oil in contact with the heated parts rises and its place is taken by

cool oil from the bottom. The heated oil transfers its heat to the tank walls from where it is taken away to the ambient air.

The heated oil there by gets cooler and falls to the bottom. Therefore, a natural thermal head is created which transfers

heat from the heated parts to the tank walls from where it is dissipated to surrounding air. The tank surface is the best

dissipater of heat but in large rating of transformers the transformer tank will have to be excessively large, if used without

any auxiliary means of heat dissipation.

ONAF (OIL NATURAL AIR FORCED): In this method, the oil circulating under natural head transfers heatto the tank walls. The transformer tank is made hollow and air is blown through the hollow space to cool the transformer.

The heat removed from the inner tank walls can be increased to five or six times that dissipated by natural means and

therefore very large transformers can be cooled by this method. However, the normal way of cooling the transformers byair blast is to use radiator banks of corrugated or elliptical tubes separated from the transformer tanks and cooled by air

blast produced by fan.

OFAF (OIL FORCED AIR FORCED): The oil is cooled in external heat exchangers using air blastproduced by fan. It is interesting to note that the oil pump and fans may not be used all the time. At low loads, the losses

are small and therefore natural circulation of oil with an ONAN condition may be sufficient to cool the transformer. At

higher loads, the pump and the fans may be switched on by temperature sensing elements. Therefore mixed cooling

conditions are used, the transformer working with ONAN conditions up to 50% of rating and OFAF conditions at higher

loads. This arrangement results in higher efficiency for the system.

Here in TITAGHARthe large transformers have radiator that originally helps to cool the hot oil. Oil passes

through the radiator channels, which are little bit elliptical in shape, due to which the surface area is much wider,

helps to radiate heat to air.

For small transformers like T5, E1, and E2 also have cooling arrangement but as those transformers ratings are very lowonly OIL NATURAL COOLINGorAIR NATURAL COOLINGis used.

DIFFERENT TYPES OF TRANSFORMER PROTECTION

RELAY ALARM TRIP

1. OVER CURRENT

2. EARTH FAULT

3. RESTRICTED EARTH FAULT

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IN OVER CURRENT

4. BUCHOLZ

5. DIFFERENTIAL

6. a) TEMPARATURE OILb) WINDING

7. PRESSURE RELEASE VALVE(P.R.V)

8. MAGNETIC OIL BREAK

(M.O.B)

I. OVER CURRENT RELAY:Over current protection is one so devised that it comes into action when the current in the circuit it protects rises

above some pre set value. The minimum value of current in the winding at which the relay will operate is called pick up

current.

II. EARTH FAULT RELAY:Another vital shortcoming consisting in its relatively low sensitivity to the currents that appear in the

event of single-phase fault to earth. The protection employs an over current relay & three current transformer,with the secondaries of the latter arranged so that all the like terminals are connected to each other. When

overloads, three phase & phase-to-phase short circuit occurs a unbalanced current flows through circuit & relay

coil, that is why relay operate.

III. RESTRICTED EARTH FAULT RELAY :This is same as earth fault relay except it is highly sensitive. If any short circuit occurs between

transformer-turns then it is used. So, its working range is also small.

IV. BUCHOLZ RELAY :An oil-immersed transformer is not completely protected unless it is protected with a gas-actuated relay.

The relay is particularly effective forA. Short circuit of core lamination

B. Broken down core bolt insulationC. Over heating of some parts of winding

D. Bad contacts

E. Short circuit between phases & turns

A. Earth fault

F. Puncture bushing insulation inside tank

G. Relay can develop conditions leading to a fault to transformer e.g. falling oil level owing to leaks,

ingress of air etc.

V. DIFFERENTIAL RELAY :

SPECIFICATION OF

GASCONCLUSION

Gas yellow in colour Surface leakage in material like wood

Gas grayish white with pungent odour Overheated or faulty condition

Gas colourless & odourless Gas is air trapped in the oil or insulation

Gas dark grayFlash over or excessive heating of oil caused by

fault in windings or coil.

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A differential scheme is one of the most widely used forms of quick acting protection against interphase short

circuit, in system with an isolated neutral, against single phase fault to earth etc. This type of protection mostly achieved

by using current transformer.

VI. OIL TEMPATURE INDICATOR:This is a distance thermometer operating on the principle of liquid expansion. It provides local indication of the

top oil temperature at the marshalling box. The connection between thermometer bulb & dial indicator is made by flexible

steel capillary tube. The bulb is enclosed in a pocket is fixed on the transformer at the hottest oil region. The pocket is

filled with transformer oil.VII. WINDING TEMPARATURE INDICATOR :

The indicator operating on the principle of liquid expansion. The winding hot spot to top oil differential is

simulated by means of a heater coil fitted around the operating levels. This is done by feeding a current proportional to

load current to the heater coil.

VIII. PRESSURE RELIEF VALVE :In case of severe fault in the transformer the internal pressure may built up to a very high level that may result in

an expansion of tank. To avoid such a contingency a P.R.V is fitted on transformer.

SPECIFICATION OF POWER TRAMSFORMER T3 ( 50 MVA)

SPECIFICATION OF POWER TRANSFORMER T4 ( 50 MVA)

Type of cooling ONAN ONAF OFAF

Rating- H.V.

L.V.

132KV

33KV

Line current-H.V.

L.V.

2180.95A

875.81A

Temp rise of oil: 40C

Temp rise of winding 55C 55C 55C

% Impedance (N.T) 12.5%

Phase 3

Frequency 50Hz

Connection Ynd1

Insulation level (HV) 550KVP

TYPE OF COOLING ONAN ONAF OFAF

RATED POWER (HV) 25 32.5 50RATED POWER (LV) MVA 25 32.5 50

RATED VOLTAGE (KV)- H.V.

L.V.

132

33

RATED LINE CURRENT (A)- H.V.

L.V.

109.3 142.2 218.7

437.4 568.6 874.8

NUMBER OF PHASES 3

MAX TEMP. RISE (OVER AN AMBIENT OF 45oC)- TOP

OIL

AVG WINDING:

45

55 55 60

IMPEDANCE VOLT.AT MVA BASE (HV-LV) TAP1 TAP9 TAP17

12.33 11.591 11.338

TYPE DOUBLE WOUND

VECTOR GROUP YNd1

TOTAL WEIGHT 97000kg

MAKER GEC ALSTHOM, NAINITAL, INDIA

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(LV) 170KVP

Maker BHEL

SEPCIFICATION OF TRACTION TRANSFORMER ( 25 KV)

Type of cooling ONAN ONAF

MVA (nominal) 12.5 18.75MVA (as per I.S) 13.5 20

KV (no load)-H.V.

L.V.132

27

KV (full load at .8 power factor lagging) 25

Line current- (H.V.)

(L.V.)102 151.5

500 750

Phase Single

Frequency 50Hz

SPECIFICATION OF TRANSFORMER FOR LOCAL SUPPLY

KVA: 100

VOLTS (H.V) 33KV

AT NO LOAD (L.V): 400V

AMPERE (H.V.):

(L.V.):1.75

144.3

PHASE (H.V&L.V): 3

TYPE OF COOLING: ON

FREQUENCY 50Hz

PERCENTAGE IMPEDENCE: 6.01

VECTOR GROUP Dy11

TEMP.RISE IN OIL 32C

TOTAL WT 1.44 TONNES

TRANSFORMER EARTHING:According to the I.E rule the two neutral points are earthed separately. In each earth connection there are two

separate electrodes. There are two separate earthing connections in the transformer tank also.

There are 3 types of earthing arrangements in transformer

1. Core earthing;

2. Tank to tank cover earthing;

3. Earthing of tank;

Apart from 4 power transformers there are 2 earthing transformers at the 33KV side in TITAGARH substation. One isused for earthing cum station service transformer & other is used as neutral earthing transformer. Their nameplate ratings

are given below.

EARTHING TRANSFORMER:Some times it is essential to create an artificial neutral when the access to the existing neutral is not possible or the

system is in delta formation. Earthing transformers are used for the same. It is core type of transformer having three limbs

built up in the same manner as that of power transformer. Each limb accommodates two equally spaced windings. It will

be seen that the current in two halves of the winding on each limb is in opposite direction. These opposite directionalcurrents will not allow the undesirable harmonics prevail in the circuit and thereby the stresses on the insulation of the

transformer are considerably reduced.

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The impedance of the earthing transformer is quite low, therefore the fault current will be quit high. The

magnitude of the fault current is limited by inserting resistance either in the neutral circuit or in the windings of the

earthing transformer.

The terminals of the earthing transformer for obtaining solid connection between them. The capacity of earthing

transformer is denoted by the fault current it is capable of handling,

Under normal condition, only iron losses will be continuously occurring but at the time of fault due to heavy fault currentthere will also be copper losses in the earthing transformer. As the duration of the fault is usually between 30-60 seconds,

therefore the copper losses will occur only for a short interval.

EARTHING TRANSFORMER I(With 200A combine fuse switch)

KVA: 100

VOLTS (H.V) 33KV


AMPERE (H.V.):

(L.V.):1.75

144.3

PHASE (H.V&L.V): 3

TYPE OF COOLING: ONAN

FREQUENCY 50Hz

ZERO SEQUENCE IMPEDENCE: 115

VECTOR GROUP ZNYN11

%IMPEDENCE AT 70: 3

OIL QUANTITY: 800Lts

RATED SHORT TIME CURRENT & DURATION: 500A FOR 30 sec

EARTHING TRANSFORMER II(With 200A combine fuse switch)

KVA: 100

VOLTS (H.V) 33KV


AMPERE (H.V.):

(L.V.):1.75144.3

PHASE (H.V&L.V): 3

TYPE OF COOLING: ONAN

FREQUENCY 50Hz

ZERO SEQUENCE IMPEDENCE: 114

VECTOR GROUP Znyn11

TRANSFORMER TESTING & COMMISSIONING:Before start the transformer some of the testing has to be done. These are as follows,

1. Oil test

2. Insulation resistance test

3. Ratio, Polarity tests.

PROTECTION DEVICES:Protection for the transformer & other transmission lines is provided by a set of Circuit breaker & Relays. The circuit

breakers are activated by relays whose main control is done from the panel.

CIRCUIT BREAKER: The circuit breaker is one of the most important units in the electrical power system. ThePROTECTION, STABILITY & CONTINUITYof the system depends on the circuit breakers ability to switch line load

and exciting currents and to interrupt fault currents.

There are different types of circuit breaker, but in TITAGARH two types of circuit breakers are installed, such as

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1. MINIMUM OIL CIRCUIT BREAKER.

2. GAS CIRCUIT BREAKER OF SF6CIRCUIT BREAKER.

MINIMUM OIL CIRCUIT BREAKER: In minimum oil circuit breaker the oil serves only for arc extinction. The current carrying parts are insulated air

and porcelain and organic materials.

They can be used for voltage up to 72 KV.

They have a line tank.

They are less bulky than Bulk Oil Circuit Breakers.As we say earlier that, it is one of the oldest substations and now developing successively so they replace the M.O.C.B.sin to gas circuit breaker.

GAS CIRCUIT BREAKER or SF6 CIRCUIT BREAKER: The SF6 gas breaker assures the high levelof performance required for the electrical system by making full use of the exceptionally good electrical insulating

characteristic and excellent arc quenching properties of SF6 gas.

The reliability of the system is further increased by the use of a SF 6 gas insulating the system.

OPERATING MECHANISM:CLOSING SPRING DISCHARED, TRIPPING SPRING DISCHARED. (BREAKER OPEN)

At the initial state of the breaker both the Closing spring and Tripping spring remain discharged. Now control

circuit is connected to power supply and motor starts running. Due to the presence of eccentric crankshaft the motion of

pawls is reciprocating. Thereby, theRatchetwheel rotates in counter clockwise direction. As the crank lever is fixed with

cam-shaft as well as withRatchetwheel, it rotates and charges the closing spring.

CLOSING SPRING CHARGED, TRIPPING SPRING DISCHARGED. (BREAKER OPEN)

When closing spring is fully charged the limit switch cut-off the power supply to stop motor. The moment when

spring charge completed crank lever gives slight rotating force. But, since the closing spring release latch supports the

stop roller provided at the ratchet wheel, the closing spring remains charged.

CLOSING SPRING DISCHARGED, TRIPPING SPRING CHARGED. (BREAKER CLOSED)

Under closing signal the closing coil pulled up the plunger & the hook is lifted. Thereby, the closing trigger

disengaged. The closing latch losing the support of the closing trigger rotates and the cam makes half turn in counter

clockwise direction.

In the mean time, due to the movement of cam roller the main operating lever rotates in the clockwise direction,

which closes the breakers contacts through connecting rod, shaft seal and inner lever. On the other hand the tripping

spring is charged and gives the main operation lever a rotating force in counter clockwise direction. As the roller is caught

by the tripping latch the force sustained & the closed state is maintained.

Due to support given by the tripping trigger, the tripping latch cant move and the main operating lever is

maintained in the closed state. When closing spring discharged, the limit switch turns on again; the motor starts to charge

it again.

CLOSING SPRING CHARGED, TRIPPING SPRING CHARGED. (BREAKER CLOSED)

The charging of closing spring is completed. This is the most common state of the breaker in service. After

getting tripping signal, the tripping trigger pulls up the plunger and disengages itself through hook.

The roller lever losing the hold of the tripping trigger is freed, and the roller that had been caught by the tripping

latch becomes free. The operating lever is rotated by the force of the tripping spring.

TRIP FREE: When a trip signal is give to the breaker on the way of closing. It trips immediately after the closing has

been completed. This is known as TRIP FREE operation.

GAS CHARACTERISTICS: To work as a insulating & arc quenching medium SF6 should have some specificcharacteristics about gas pressure depending on temperature.

CONTROL SYSTEM: To control circuit breaker there is a control system having 4 steps.1. The circuit breaker is open.

2. The closing spring is discharged.

3. Auxiliary power is not applied.

4. The gas pressure is zero.

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ANTIPUMPING : The ANTIPUMPINGfeature is provided to assure that only one closing operation will resultwhen the closing control device is initiated and continuously energized. This feature is provided with both electrical

controls and mechanical controls.

RATINNG OF THE SF6 CIRCUIT BREAKER

TYPE 30-SSGP-25A.

STD IEC-56.

RATED VOLTAGE 36KV.

RATED NORMAL CURRENT 1250A.

RATED SHORT CIRCUIT BREAKING CURRENT 25KA.

RATED LIGHTNING IMPULSE WITHSTAND

VOLTAGE

170KV.

RATED GAS PRESSURE 5Kg/cm2.

RATED CIRCUIT VOLTAGE (CLOSING) 220V DC.

RATED CIRCUIT VOLTAGE (TRIPPING) 220V DC.

MOTOR VOLTAGE 230V AC.

RATED FREQUENCY 50Hz.

RATED MAKING CURRENT 63 KA.

RATED SHORT TIME CURRENT 25KA FOR SECONDS

GAS WEIGHT 205Kg.

TOTAL WEIGHT 750Kg.

RATED OPENING TIME 100ms

LIGHTNING ARRESTOR:These are used for the protection of substation equipments including the power transformer. They are capable of

discharging lightning & switching surges & temporary power frequency overvoltages. It should be capable of

withstanding continuous overvoltages. They are normally mounted on the secondary side of the transformer. The several

types of arrestor are Rod Gap, Explosion type, Valve type or Tynite type. In TITAGARH substation gapless arrestors areused. Typical specification is:

To Indian Standard : 3070.

Model No. : 2AB 120SM.

Voltage : 30KV.

ISOLATOR:The isolator operates under no-load condition& has no specified making or breaking capacity. It is not even used

for breaking load current. They are used in addition to circuit breakers & are provided on each side of every circuit

breaker to provide isolation & enable maintenance. Automatic switching of isolators is preferred. Three pole isolators are

generally used in substations.

The poles are identical & consist of 2 or 3 insulator posts connected in a fabricated support. The conducting parts

are supported on insulator rod fixed & moving contacts. For all three-pole isolators there is a common pneumaticmechanism. The operating mechanism is manual plus either electrical motor mechanism or it is pneumatic. There are

generally three types of isolators according to construction- vertical break type, horizontal break type & vertical

photograph type (used for >400 KV).

SPECIFICATION OF ISOLATORS AT TITAGARH SUBSTATIONRATED VOLTAGE : 33 KV.

IMPULSE WITHSTAND VOLTAGE : 170 KV.

RATED CURRENT : 1250 A.

RATED SHORT TIME CURRENT FOR 3 SEC : 27 A.

TYPES OF RELAYS IN A SUBSTATION:1. Solenoid type.

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2.

Attached Armature Type.

3. Electrodynamics Type.

4. Moving Coil Type.

5. Induction Type.

6. Directional or Reverse Current Type.

7. Under Voltage, Under Current & Under Power Type.

8. Direction or Reverse Power Type.9. Thermal Relay.

10. Differential Relay.

11. Distance Relay.

CONTROL PANEL:This is the main operating unit of the whole substation. All equipments such as switchboard, carrier control

equipments, batteries, battery charger etc are housed in the control room. There are different sections in charge of

different devices having many panels for each. The major sections are:

132KV SECTION:There are several panel boards for transformers, incoming feeders & the bus coupler. The transformer has panels

provisioned for metering (ammeter for each phase, MVA meter & TOD meter), control (main bus isolator, transfer bus

isolator) & protection relays. The protection relays include:DIFFERENT PROTECTION RELAYS PRESENT IN CONTROL PANEL

RELAY ALARM TRIP

1. OVER CURRENT

2. EARTH FAULT

3. RESTRICTED EARTH FAULT IN

OVER CURRENT

4. BUCHOLZ

5. DIFFERENTIAL

6. a) TEMPARATURE OIL

b) WINDING

7. PRESSURE RELEASE VALVE

(P.R.V)

8. MAGNETIC OIL BREAK (M.O.B)

9. OVER FLUX RELAY

10. UNDER FREQUENCY RELAY

11. DISTANCE RELAY

12. AUXILIARY RELAY

The Bus Coupler panel has provision for metering (ammeter, KV meter), control (isolator bus section) &protection (zone time relay, distance relay). The feeder panel has definite time relays, instantaneous over current relay,

Earthfault relay & tripping or auxiliary relay.

33KV SECTION:The section has 12 panels for 12 outgoing feeders & one for maintenance bay. Each has provisions for ammeter,

MVA meter & Overcurrent, Earthfault, DC supply failure relay etc.

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AUXILIARY POWER:This is divided in two parts, the auxiliary AC power that comes from auxiliary Ac transformer & Auxiliary DC

power that comes from the Battery room. The panels in this section are Ac panel, DC panel & Battery charger.

D.C. SYSTEM:Although the substation carries AC power, the protecting devices are used in DC & so a Dc battery system is

essential. The battery room consists of 110 cells each of 2.2V. These are used to control the relay & alarm panel

operation. A system of regular charging is used to maintain the power.

METERING:Electrical energy meter is very important of each EHV substation. TITAGARH substation has got energy

metering equipments against the following feeders:

1. WBSEB-CESC interconnection (132 KV).

2. WBSEB-Eastern Railway (25KV).

For Traction power TOD meter(Time of Delay meter) is used having appropriate capacity.

POWER LINE CARRIER COMMUNICATION (PLCC):PLCC is used to communicate from one substation to another. The communication is of high frequency & low

amplitude & passes through existing circuit for power transfer. The equipments are:

COUPLING CAPACITOR:It blocks the low frequency signal & acts as a high pass filter. The protecting devices connected with coupling

capacitor are Earthing Isolator, Drainage coil, Lightning arrestor etc. WAVE TRAP:

It is basically an inductor connected with R & Y phases of the incoming feeders, which blocks the high frequency

signal.

VERY HIGH FREQUENCY SET:It is Transreceiver. It remains in receiving mode. But when a signal is to be transmitted it is switch to transmitting

mode. It is run by 12V DC source.

CARRIER SET:It helps to send signal from mother substation to other places. For its operation 18V DC is needed.

FOUR WIRE GROUP SELECTOR:After some processing it sends the signal to its destination through carrier.

PRIVATE AUTOFORMAT EXCHANGE (PAX):It denotes whether the signal is internal or external and accordingly it selects the signals path ofprogress. EPAX

(Electronic PAX) does the job of both FGS & PAX.

PLCC is used to maintain communication between load dispatch unit & the substation. Sometimes point-to-point

communication is also employed.

Remarks:By this vocational training we are very much benefited. Not only the theoretical conception is cleared but also the

practical considerations to make power system economical, cleared. As power sector is a public organization therefore the

revenue collection procedure, perfect metering, & repairing jobs are also noticeable subject. Also in real life how can a

control room attendant manage the problems is a remarkable thing.

Most important thing is all of the personals in TITAGARH help us to understand every single thing and we are

glade to get your proximity.Also to H.R.D. DEPARTMENT, thanking you for arranging vocational training for us.

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Documents

Distribution Substation