33 kV yard

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33 kV yard

Components of the 33kV yard

1. Generator Transformer(GT)2. Unit Auxiliary Transformer(UAT)3. Station Transformer(ST)4. Potential Transformer5. Lightening Arrestor(LA)6. Isolator7. Current Transformer8.

Circuit Breaker9. Capacitor Bank

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Generator Transformer (GT)

The generator transformer is the first essential component for energy transmission,

allowing energy supplied by the generator to be transferred to the network at the

required voltage.

This is a type of Power Transformer where the LV winding is connected to the

generator through the bus duct and HV winding to the transmission system.

Generator Transformer is designed to withstand over voltage caused by sudden

load throws off from the generator. It is built as a single or three phase unit and

located in power stations.

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BHARAT HEAVY ELECTRICALS LIMITED

FOR 85/59.5/42.5 MVA, 10.5/33.5 KV, 3 phase, 50 Hz

OFAF/ONAF/ONAN cooled power transformer

2 x 67.5 MW

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TECHNICAL DATASHEET

Item Unit Particulars

Name of Manufacturer BHEL Jhansi

Reference Standards IS 2026

Service OutdoorInstallation Outdoor

Rated No Load Voltage

HV Winding KV 33.5

LV Winding KV 10.5

Type of Cooling

(ONAN/ONAF/OFAF/OFWF)

OFAF/ONAF/ONAN

Rated Power under site conditions corresponding

to various methods of cooling.

ONAN MVA 42.5

ONAF MVA 59.5

OFAF MVA 85.0

No. of Phases 3

Rated Frequency Hz 50

Winding Connections

HV windings Star

LV windings delta

VectorGroup Reference Ynd11

Type of Tap Changer

On Load / off circuit Off circuit

On HV/MV/LV winding ON HV for HV

variation

Total range of tapping +/- % +/-5%

Size of tapping step % 2.5% step

Impulse voltage withstand level

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HV winding KVp 170

LV winding KVp 75

Power frequency withstand voltage for one minute

HV winding KV(rms) 70

LV winding KV(rms) 28

No Load Losses at rated frequency

90% rated voltage KW 28.71 23.92


110% rated voltage(58 KW approx.)

KW 40.71 37.00

Load losses at normal ratio rated current and 75deg.C

KW 281.96 276.93

Tolerance on losses +a) No Load Lossesb) Load Lossesc) Total Losses

% Nil on Guaranteedlosses

Guaranteed Max. Temp. Rise of

Oil by thermometer Deg.C 50

Winding by resistance fora) ONANb) ONAFc) OFAF

Deg.C 55

5555

Efficiency at 75 deg.C and unity power factor for

100% full load % 99.63 99.64

75%full load % 99.70 99.71

50%full load % 99.75 99.77

Voltage Regulation at Full Load at 75 deg.C

Unity power factor % 1.21 1.23

0.8 power factor (lagging) % 8.79 8.90

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Terminals of Tertiary winding brought out tobushing

Yes/No NA

Type of magnetic circuit Core/Shell Core

Type of core joints Mitred

Type of Windings

H.V. Helical

L.V. Helical

Type of insulation

H.V. winding Kraft + Press Board

L.V. winding + Transformer Oil

Core to adjacent windings Press Board + OilBetween Windings Press Board + Tr. Oil

Bushings

HV Bushings

Rated Voltage KV 36

Rated Current A 2000

1.2/50/ U/S impulse withstand1 minute power frequency

KVp(rms)

170

LV Bushings

Rated Voltage KV 24


1.2/50/ S impulse withstand

1 minute power frequency

Maximum Flux Density

At Rated Voltage Wb/mxm 1.58

At 110% rated voltage Wb/mxm 1.74

Maximum current density

H.V. A/cmxcm 350 to 400

L.V. A/cmxcm 350 to 400

Magnetizing current at rated voltage and 0.17 0.21

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Unit Auxiliary Transformers (UAT)

The Unit Auxiliary Transformer is the Power Transformer that provides power tothe auxiliary equipment of a power generating station during its normal operation.

This transformer is connected directly to the generator out-put by a tap-off of the

isolated phase bus duct and thus becomes cheapest source of power to the

generating station.

It is generally a three-winding transformer i.e. one primary and two separate

secondary windings. Primary winding of UAT is equal to the main generator

voltage rating. The secondary windings can have same or different voltages i.e.

generally 11KV and or 6.9KV as per plant layout.

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FOR 9 MVA , 10.5/6.8 KV , 3 phase, 50 Hz

ONAN cooled power transformer

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TECHNICAL DATASHEET

Item Unit Particulars

Name of Manufacturer BHEL Jhansi

Reference Standards IS 2026

Service OutdoorInstallation Outdoor

Type of Transformer

Three/two windings/auto Two winding

No. of Transformers 2


HV Winding KV 10.5

LV Winding KV 6.8

Type of Cooling(ONAN/ONAF/OFAF/OFWF)

ONAN

Rated Power under site conditions correspondingto various methods of cooling.

ONAN MVA 9.0

ONAF MVA -

OFAF MVA -

No. of Phases 3


Winding Connections

HV windings Delta

LV windings Star

VectorGroup Reference Dyn1

Type of Tap Changer

On Load / off circuit Off circuit

On HV/MV/LV winding ON HV for HVvariation

Total range of tapping +/- % +/-5%


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HV winding KVp 75

LV winding KVp 60

Power frequency withstand voltage for one minuteHV winding KV(rms) 28






KW 09.77 10.46

Load losses at normal ratio rated current and 75

deg.C

KW 38.88 42.8

Tolerance on losses +

d) No Load Lossese) Load Losses

) Total Losses




Winding by resistance for

d) ONANe) ONAFf) OFAF

Deg.C

55-

-


100% full load % 99.49 99.44

75%full load % 99.57 99.53

50%full load % 99.63 99.60


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Terminals of Tertiary winding brought out to

bushing

Yes/No NA



Type of Windings

H.V. Disc

L.V. Helical

Type of insulation

H.V. winding Kraft Parer + PressBoard

L.V. winding + Transformer OilCore to adjacent windings Press Board + Tr. Oil

Between Windings Press Board + Tr. Oil

Bushings

HV Bushings

Rated Voltage KV 17.5



KVpKV(rms)

9545

LV Bushings

Rated Voltage KV 7




KVp

KV(rms)

60

20







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Magnetizing current at rated voltage and

frequency (% of full load current )

0.3 0.41

(less than 1%)

Cooling Fans NA

d)

Typee) Quantityf) Rating

--

-

Cooling Oil Pump NA

d) Type No. -e) Quantity No. -

f) Rating KW -

Approximate Weight ofCore & Winding Kg 14000

Tank Fittings & Coolers Kg 8630

Oil Kg 5470

Total Weight without oil Kg 22630

Untanking Weight Kg 14000

List of test which may be carried out at extra costquoted elsewhere 1) Impulse test2)Temperature rise

test3)Acoustic noise level

4)3rd

harmoniccontent in no load

current

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Station Transformer (ST)

Station transformer forms one of the essential components of the power station. It

is used for provides power to some of the equipments of the power plant in normal

functioning mode. Unlike UAT, it draws power form the grid.

ST forms important part when station is not operational. In that case, all power

supplied to the equipments of station by ST.

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FOR 15/10.5 MVA, 32/7 KV, 3 phase, 50 Hz

ONAF/ONAN cooled power transformer

With on load tap changer

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TECHNICAL DATASHEET

S.No. Item Unit Particulars

01 Name of Manufacturer BHEL Jhansi

02 Reference Standards IS 2026

03 Service Outdoor04 Installation Outdoor


HV Winding KV 32

MV Winding KV 7

LV Winding KV 7

Type of Cooling

(ONAN/ONAF/OFAF/OFWF)

ONAF/ONAN

Rated Power under site conditions correspondingto various methods of cooling.

ONAN MVA 10.5

ONAF MVA 15.0

OFAF MVA -

No. of Phases 3


Winding Connections

HV windings Star

MV windings Star

LV windings Delta closed with only

one terminal broughtoutside

VectorGroup Reference YYnod11

Type of Tap Changer

On Load / off circuit On load

On HV/MV/LV winding ON HV for HV

variation

Total range of tapping +/- % +/-10.0

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HV winding KVp 170

MV winding KVp 60LV winding KVp 60

Power frequency withstand voltage for one minute

HV winding KV(rms) 70

MV winding KV(rms) 20






KW 12.57 13.83

Load losses at normal ratio rated current and 75deg.C

KW 70.82 76.00

Tolerance on losses +

g) No Load Lossesh) Load Lossesi) Total Losses




Winding by resistance forg) ONANh) ONAFi) OFAF

Deg.C55

55-


100% full load % 99.46 99.41

75%full load % 99.56 99.52

50%full load % 99.63 99.60

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Terminals of Tertiary winding brought out to

bushing

Yes/No Only one terminal

brought out



Type of Windings

H.V. Disc

M.V. Helical

L.V. Spiral

Type of insulation

H.V. winding Kraft + Press Board

M.V. winding + Transformer Oil

L.V. winding Press Board + Oil

Core to adjacent windings SRBP cylinder + Tr.

Oil

Between Windings Press Board + Tr. Oil

Bushings

HV Bushings

Rated Voltage KV 36

Rated Current A 630


KVpKV(rms)

170840

MV Bushings

Rated Voltage KV 7

Rated Current A 20001.2/50/ S impulse withstand1 minute power frequency

KVpKV(rms)

6020

LV Bushings

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Rated Voltage KV 17.5




KVp

KV(rms)

95

45







M.V. A/cmxcm 350 to 400

Magnetizing current at rated voltage andfrequency (% of full load current )

0.35 0.42(less than 1%)

Cooling Fans

g) Typeh) Quantityi) Rating

Outdoor

6 (4 running & 2stand by)

0.085 KW

Cooling Oil Pump

g) Type No. -h) Quantity No. -

i) Rating KW -

Approximate Weight of

Core & Winding Kg 20000

Tank Fittings & Coolers Kg 12720

Oil Kg 8280

Total Weight without oil Kg 32720

Untanking Weight Kg 20000

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DESCRIPTIONOF

TRANFORMER(GT,UAT,ST)

General

The transformer is oil immersed with a rating of 9 MVA under ONAN conditions respectively.

The transformer is provided with tank mounted radiators and associated control equipment. It is

also equipped with off circuit load tap switch on HV winding.

Transformer

Core

The magnetic circuit is a three limbed core type construction, each limb being mitered with top

and bottom yokes. The laminations are made of high grade non-ageing cold rolled grain oriented

silicon alloy steel. The insulation of lamination is of carlite coating.

The yokes bolts, End frame, clamp plates and core are insulated from each other to withstand a

test pressure of 2 KV rms 50 Hz for one minute.

Windings

The windings are arranged in concentric formation with LV winding next to the core, then HVand HV tapping winding.

Conservator

As the temperature of the transformer oil increases or decreases there is a corresponding rise and

fall in the oil volume. To account for this an expansion vessel (conservator) is connected to the

transformer tank. It has the capacity between the maximum and the minimum oil level equal to

7.5% of the total oil in the transformer (tank + cooling system)

The conservator is filled to level appropriate to the filling temperature and in the remaining

portion is Air Cell which I connected to atmosphere through a breather. If the volume of the oil

in the transformer increases the conservator breathes out air and if the volume of oil in the

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PressureReliefValve

In the case of severe fault in the transformer, the internal pressure may build up to a very high

level, which may result in an explosion of the tank. To avoid such a contingency a pressure relief

valve is fitted at the transformer top cover. It is a spring loaded and has contacts for tripping the

transformer.

Oil Transformer Indicator

Oil Transformer Indicator is a distance thermometer operating on the principle of liquid

expansion (mercury in steel capillary). It provides a local indication of the top oil temperature at

the Marshalling kiosk. The bulb is enclosed in a pocket and the pocket is fixed on the

transformer at the hot test oil region. The pocket has to be filled with the transformer oil. The oil

temperature indicator is provided with a maximum pointer and two mercury switches; one for

alarm and other for trip.

Switches are suitable for 250 volt AC or DC. The mercury switches are adjustable to make

contact between 50deg.C and 120deg.C.

The temperature for alarm and trip contact setting shall be as under:

i) Alarm = 85 deg.Cii) Trip = 90 deg.C(At an ambient temperature of 45 deg.C)

Winding TemperatureIndicator

This indicator operating on the principle of liquid expansion provides local indication at the

marshalling box of hot spot temperature of winding. The winding hot spot to top oil temperature

differential is simulated by means o heater coil fitted around the operating below. A current

proportional to the load current is fed to the heater coil from a current transformer, fitted on the

2U phase of LV winding.

The bulb of the WTI fitted at the top cover senses top oil temperature. Thus winding temperatureindicators temperature reading are proportional to load current plus top oil temperature.

The indicator is fitted with maximum pointer and four mercury switches. One is used for alarm

and 2nd

is used for trip and other two switches are as spare. All the switches are adjustable on

their individual scales over the entire working range of the instrument and are suitable for 250

volts AC or DC.

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The temperature for the alarm and the trip contact setting shall be as followed:

i) Alarm = 90 deg.Cii)

Trip = 100 deg.C(Ambient temperature considered for the above settings 45 deg.C)

Earthing Arrangement

i) Core to end frame earthingii)

Tank to Tank cover earthing

iii) Earthing of the Tank

Marshalling Kiosk

The M.Kiosk is a weather proof steel housing which is suitable for ground mounting. The kiosk

is provided with a metal clad heater along with thermostat switch for the prevention of

condensation.

Gas and OilRelay

(Buchholz Relay)

A protective device on transformers

Company: ATVUS

It keeps round the clock vigilance on transformers and indicates the faults with help of two

floats, upper and lower

i) Giving alarm signal for minorii) Isolating the transformer from the main supply in the event of heavy faults inside the

transformer or fail of level below the mounting height of the relay.

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It is connected in the pipe connection between the transformer and the expansion vessel so that

normally it is usually connected to an external alarm circuit.

Dehydrating

Breather

A dehydrating breather is used to dry the air that enters a transformer as the volume of the

transformer oil decreases because of a fall in the temperature.

Air entering the breather is first drawn through an oil seal and passes upwards through the silica

gel crystals to the connecting pipe at the top. During the upward passage of air, any moisture

present is absorbed by the dry silica gel.

The oil seal ensures that the gel absorbs moisture only when the transformer is breathing.

MaintenanceInspect the breather every 3 months more frequently if found by experience to be necessary.

When the crystal is first installed, the crystals have a blue tint, and after a period of operation the

colour of the tinted crystals gradually changes to pink; this is the indication that the silica gel is

becoming saturated and losing its absorbent properties. When there is preponderance of pink

crystals the gel should be changed or reactivated.

Silica gel may be reactivated by heating in a shallow pan at a temperature of 150deg.C to

200deg.C for two or three hours when the crystals should have regained their original blue tint.

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Voltage Transformer

Voltage transformers (VT) or potential transformers (PT) are another type of instrumenttransformer, used for metering and protection in high-voltage circuits.

They are designed to present negligible load to the supply being measured and to have a precise

voltage ratio to accurately step down high voltages so that metering and protective relay

equipment can be operated at a lower potential.

Typically the secondary of a voltage transformer is rated for 69 V or 120 V at rated primary

voltage, to match the input ratings of protective relays.

Specification oftransformer

1. Standards IS 3156

2. High system voltage K.V. 36

3. Frequency Hz 50

4. Oil Ltrs/kg 16

5. Insulation level KV

KVp

70 170

6. RVF/times Sec 1.2/1.57. Total weight Kg 90

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Lightening Arrester (LA)

A lightning arrester is a device used on electrical power systems to protect the insulation on thesystem from the damaging effect of lightning. Metal oxide varistors (MOVs) have been used for

power system protection since the mid 1970s. The typical lightning arrester also known as surge

arrester has a high voltage terminal and a ground terminal. When a lightning surge or switching

surge travels down the power system to the arrester, the current from the surge is diverted around

the protected insulation in most cases to earth.

Specification ofLightening Arrestors

Zinc Oxide Lightening Arrestor

1. Rating KV 30

2. Frequency Hz 50

3. C.O.V KV 25

4. P.R. Class A,40KV

5. N.DC KA 106. Model MWL

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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.

SF6 circuit breaker is used in the station. In this type of breaker the arc in chamber is

extinguished by sulfur hexafluoride gas.

(All above Circuit breaker are medium-voltage circuit breakers rated between 1 and 72 kV.

These are also operated by current sensing protective relays operated through currenttransformers)

Circuit Breakers may be connected into the circuit by bolted connections to bus bars or wires,

especially in outdoor switchyards.

Specification ofCircuit Breaker

y Type: Gas Circuit Breaker,SF61. Type 70-SFM-32 A

2. Rated Lightening Impulse withstand voltage KVp 350

3. Rated short circuit breaking current KA 31.5

4. Rated operated pressure Kg/cmxcm.g 15 (at 20 deg.C)

5. First pole to clear factor 1.5

6. Rated duration of short circuit current Sec 3

7. Gas Weight Kg 6

8. Rated voltage KV 72.5

9. Frequency Hz 50

10. Rated normal current A 2000

11. Rated closing voltage V(DC) 220

12. Rated opening voltage V(DC) 220

13. Total weight of the gas Kg 1650

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Current Transformer

A curren

t transf

ormer (CT) is used for measurement of electric currents.

Use:

y When current in a circuit is too high to directly apply to measuring instruments, a currenttransformer produces a reduced current accurately proportional to the current in the

circuit, which can be conveniently connected to measuring and recording instruments.

y It also isolates the measuring instruments from what may be very high voltage in themonitored circuit.

Safety precautions

Care must be taken that the secondary of a current transformer is not disconnected from its load

while current is flowing in the primary, as the transformer secondary will attempt to continuedriving current across the effectively infinite impedance. This will produce a high voltage across

the open secondary (into the range of several kilovolts in some cases), which may cause arcing.The high voltage produced will compromise operator and equipment safety and permanently

affect the accuracy of the transformer.

Specification ofTransformer

1. Standard IS 2705

2. Insulation Level K.V. K.V.p 75/170

3. S.T. Current K.A./sec 31.5/3

4. Frequency Hz 50

5. Rated primary current A 2000

6. System voltage KV 33

7. Electrical specification number 6306162

8. Serial number 2216368

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Aluminum Conductor SteelReinforced(or

ACSR)

Aluminum Conductor Steel Reinforced (or ACSR) cable is a specific type of high-capacity,

high-strength stranded cable typically used in overhead power lines. The outer strands arealuminum, chosen for its excellent conductivity, low weight and low cost. The center strand is of

steel for the strength required to support the weight without stretching the aluminum due to itsductility. This gives the cable an overall high tensile strength.

ACSR cables are available in several specific sizes, with multiple center steel wires andcorrespondingly larger quantities of aluminum conductors. For example, an ACSR cable with 72

aluminum conductors that requires a core of 7 steel conductors will be called 72/7 ACSR

cable.

[1]

The higher resistance of the steel core is of no consequence to the transmission of electricity

since it is located far below the skin depth where essentially no AC current flows.

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Capacitor Bank

A capacitor bank is a grouping of several identical capacitors interconnected in parallel or in

series with one another. These groups of capacitors are typically used to correct or counteract

undesirable characteristics, such as power factor lag or phase shifts inherent in alternating current

(AC) electrical power supplies. Capacitor banks may also be used in direct current (DC) power

supplies to increase stored energy and improve the ripple current capacity of the power supply.

The use of a capacitor bank in the power supply system effectively cancels out or counteracts

these phase shift issues, making the power supply far more efficient and cost effective. The

installation of a capacitor bank is also one of the cheapest methods of correcting power lag

problems and maintaining a power factor capacitor bank is simple and cost effective. One thingthat should always be kept in mind when working with any capacitor or capacitor bank is the fact

that the stored energy, if incorrectly discharged, can cause serious burns or electric shocks. The

incorrect handling or disposal of capacitors may also lead to explosions, so care should always

be exercised when dealing with capacitors of any sort.

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33 kV yard