Transformer Vector Technic

8/12/2019 Transformer Vector Technic

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ABB

India,BMTG-1-

Apr02

,Author:NagRamesh

Electrical InstallationTechniques

Medium sizedDistributionTransformers

Nag Ramesh

31st December 2007


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Contents

21Transformers Standard Accessories - Conservator722Transformers Standard Accessories - Oil level gauge8

23 - 24Transformers Standard Accessories - Silica Gel Breather9

25 - 26Transformers Standard Accessories - Buchholtz Relay10

27Transformers Standard Accessories - Gas drawing device11

28 - 29Transformers Standard Accessories - Pressure relief valve/

Explosion vent

12

20Transformers Standard Accessories Arcing Horns6

18 - 19Transformers Standard Accessories - Bushings5

16 -17Transformers Standard Accessories - Wheels4

7Caution1

8 - 12Types of Transformers2

13 - 15Transformers Standard Accessories3

Slide No.TopicSl. No.


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Contents

47Lifting of Transformer by Lugs and Jacks22

40 -43A completely assembled Transformer (typical 1600 kVA)19

35 - 36Transformers Standard Accessories -

Winding Temperature Indicator (WTI)

16

30 -32Transformers Standard Accessories Radiators, Radiators

assembly and disassembly

13

46Transfer of responsibility, Handling and lifting21

44 - 45Transportation of Transformers20

39Transformers Gaskets18

37 - 38Transformers Standard Accessories -Protection Junction Box (Cable Termination Box)

17

34Transformers Standard Accessories -Oil Temperature Indicator (OTI)

15

33Transformers Standard Accessories - Butterfly Valve for Radiator14



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Contents

65Oil sampling kit and test cup for dielectric strength35

48Lifting of Transformer by Fork Lift and transferring23

49Lifting of Transformer Wire Ropes24

50 -51Receiving the transformer at site25

52 - 53Storage of Transformer prior to energizing26

54 - 57Indoor Installation27

64Oil sampling from an oil drum or tanker34

63Oil sampling from a Transformer33

62Minimizing noise emission32

61Shifting to and placement on foundation31

60Foundation Construction oil pit and oil sump30

59Foundation Construction rails and shims29

58Outdoor Installation28



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Contents

106 107Energisation47

75Oil Filtration40

66Erection of Transformers transported fully assembled and filled with

Oil

36

67 - 69Erection of Transformers transported with loose parts and filled with

Oil

37

70 -73Erection of Transformers transported with out Oil38

74Additional Supports39

104 105Check-list to be filled in before energisation46

88 - 103Pre-energisation Checks45

82 - 87Power Circuit Connections44

81Oil Filtration Process - Oil filtration performance analysis43

77 - 80Oil Filtration Process42

76Oil Filtration Machine41



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Contents

108Energisation Check List48

109 - 113Operation Temperature rise and loading capacity49

114 - 116Parallel Operation of Transformers50

117Load distribution between parallel running Transformers51

118 - 120Protection of Transformers52

121 - 123Maintenance and supervision during operation53

135 - 136Acknowledgement and references59

137Disclaimer60

138Power and Productivity for a better world61

133 - 134Applicable Standards58

132Installation Record for Transformers57

130 - 131Safety Precautions56

129Repairs and Spare Parts55

124 - 128Investigation of Transformer disturbances54



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Medium sized Distribution Transformers

Caution

1. Installation of Transformer should be done by skilled personnel or contractors who are trainedand qualified in installation of Transformer and similar electrical equipment. All on-site

regulations must be carefully observed (installation regulations for electrical systems,regulations for Transformers and environmental safety).

2. In order to eliminate danger to anyone, the Transformer must be installed in such a way thattouching the Transformer is impossible after it has been energized.

3. Precautions must be taken to ensure that access to the Transformer is possible only after ithas been isolated from the mains (e.g., by forced interlock between the switchgear and theTransformer access doors), exceptions are customer requirements and Transformers withcable boxes for both primary and secondary and Transformers mounted on pedestals withporcelain to ground clearance > 2,74 m.

4. To prevent any risk, suitable measures must be taken during erection and maintenance work to

ensure that the Transformer cannot be reconnected by any unauthorized persons.


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Types of Transformers

Transmission of energy is generally divided in two parts; first is transmission over longdistances at high voltages, which is supported by Power Transformers.

The second part is distribution of the energy from substations to the various users; this

is supported by Distribution Transformers in various hierarchies.

1. LARGE DISTRIBUTION TRANSFORMERS, LDT

Power range 5000 kVA and abovePrimary voltage Up to 72,5 kV

Available fluids Mineral oil, dimethyl silicone,

esters and synthetic hydrocarbons.

Transformers of this type are used for receiving the energy from higher voltage

levels and to transform and distribute the energy to lower voltage levelsubstations (11 or 33 kV) or directly to large industrial consumers.


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2. MEDIUM DISTRIBUTION TRANSFORMERS, MDT

Power range 315 - 5000 kVA

Primary voltage Up to 36kV

Available fluids Mineral oil, dimethyl silicone, esters and synthetic

hydrocarbons.

Transformers of this type are used to step down three phase high voltage to lowvoltage for energy distribution, mainly in metropolitan areas and for industrial

applications.

These transformers are available in three phase dry type and oil filled (hermeticallysealed or with Oil Conservator and Breather). In hermetically sealed type, flexiblecorrugated tank walls enable sufficient cooling of the transformer and compensatefor changes in the oil volume due to temperature variations during operation.


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SMALL DISTRIBUTION TRANSFORMERS, SDT

Power range Up to 315 kVA

Primary voltage Up to 36kV (generally 11 kV)

Available fluids Mineral oil, dimethyl silicone, esters and synthetichydrocarbons.

Transformers of this type are used to step down three-phase high voltage to lowvoltage for energy distribution, mainly in the countryside or low-density populatedareas.


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DRY-TYPE DISTRIBUTION TRANSFORMERS

Dry-type Transformers are used to minimize fire hazard and other environmentalcontamination on surroundings and people, like in large office buildings, hospitals,shopping centers and warehouses, sea going vessels, oil and gas productionfacilities and other sites where a fire has potential for catastrophic consequences.They are available as resin impregnated, vacuum cast resin and Resibloc versions.Resin impregnated Transformers are rarely used in distribution applications.

Vacuum cast resin dry-type Transformers

Power range 50 kVA up to 30 MVA

Primary voltage Up to 52 kV (generally 33 kV)

Climate class C2

Vacuum cast means that the high voltage windings are cast-in in epoxy and curedin vacuum. The high voltage windings are typically disk winding.


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Resiblocdry-type Transformers

Power range 30 kVA up to 40 MVA

Primary voltage Up to 52 kV

Climate class C2

Resibloc is an ABB patented process for the high voltage winding. The high

voltage winding is multi layer type with a cross wound glass fiber insulation soakedin epoxy, cured in open atmosphere.


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Transformers Standard Accessories


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WheelsThey are always bi-directional, flat-type or flanged. They are usually supplied disassembledfrom the transformer. Their assembly can be executed lifting the transformer with a crane orwith some jacks placed on special brackets in one of the three ways shown in the enc. dwg.

1. Trolley 2. Flask3. Wheel 4. Trolley5. Pivot 6. Wheel7. Spacers 8. Fastener plaque pins with screw9. Flask

Type 1 Medium sized Distribution

Transformers: fix the flask unit (withthe wheels) to the trolley by means ofthe two special screws in the suitabledirection.

Type 2 Small sized Transformers:

insert the pin into the wheel and intothe trolley holes in the suitabledirection, together with the spacers.Fasten the pin with the help of thespecial plaque and screw.

Type 1 Type 2


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Wheels

Type 3 Medium transformers: fix the flask (with the

wheels) to the back flask with the four special screwsin the suitable direction.


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Bushings The components of the bushings are:- metallic stem coupling internal and

external live parts of the transformer;

- insulating porcelain;- oil-tight gaskets;

- coupling and clamping nuts;- Arcing horns.

Instructions for Bushingreplacement:

Unscrew the nuts (13) without letting thestem turn (3). Remove the cap (4), the

gasket (7), the porcelain (1) and thegasket (9). After replacing the damaged

part reassemble the bushing operating in

the opposite direction taking care not tolet the stem turn (3). Breathe wherenecessary (Buchholz relay, bushings)loosening the nuts (13).

1. Upper porcelain2. Lower porcelain3. Stem

4. Cap5. Washer7. Gasket8. Gasket9. Gasket

10. Gasket11. Gasket

12. Washer13. Nuts

14. C- Washer


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Bushings

Bushings are usually already assembled on the transformer: in some particular cases, they areshipped separately and must be assembled upon arrival, following manufcaturers instruction,after removing the closing caps on the transformer and with the oil level below the transformercover.

Bushings must be stored in their original package, until their assembly. The porcelain part is

particularly fragile, therefore maximum care must be taken when handling or fixing the externalconnection, avoiding dangerous stresses.

No particular maintenance is required, except the periodical cleaning (once every 6 months) of

the external porcelain surface.

In case of oil leakage, check:

- the pressure on the gasket;- the porcelain conditions;

- the gaskets conditions.

When the replacement of one of the bushing components is required, follow the instructionsupplied with the part. In any case, it is advisable to keep one or more spare bushing and

relative gaskets as emergency spares.


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22014017036

15510012524

155709517.5

85607512

IECABBkVkV

Arcing HornDistance K (mm)

BILLevel

SystemVoltage

Arcing Horns on Bushings

They are provided on the bushings as a protection to thetransformer against transient over-voltages acrosswindings and earth due to lightning and switching surges.

They are generally provided on request. The lower hornis fastened on to flange of the bushing with one of the

fixing screws and the upper horn is fixed to top end nutof the bushing by means of a bracket.

Adjust the gaps K and C as per manufacturer's

recommendation.


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Conservator

1) air inlet pipe (transformer side) 8) pipes and fittings for connection to the transformer tank2) conservator filling plug (transformer side) 9) pipes and fittings for connection to the tap changer3) conservator supporting brackets 10) oil level gauge of the tap changer4) bracket fixing plates 11) conservator. drain plug (tap changer side)5) lifting lugs 12) conservator filling plug (tap changer side)6) conservator drain plug (transformer side)

7) oil level gauge

8


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Oil level gauge 1 - Signalling switch2 - Float3 - Rod4 - Gland

The switch contact is normally closed. Perform the electrical connections according to the Wiring Diagram

(being the terminal numbered on the board), or find the terminals through a simple continuity test. The levelgauge grounding is performed by a suitable little connecting terminal.

Before the transformer start-up, it is advisable to check the gauge and the switch for perfect operation, takinginto consideration that the switch trips slightly in advance in respect to the minimum level signal. No particularmaintenance is required for the level gauge. Eventual oil leakage can be eliminated by replacing the tight

gasket, after having lowered the oil level in the conservator.

The level gauge is made up of the followingcomponents:- main body with Plexiglas graded

window- float and drive- magnet with external signalling

disk- minimum oil level signalling switch

Usually the oil level gauge is suppliedalready assembled on the conservator.If not,it has to be fixed to the proper stud bolts,inserting the relevant gaskets. Duringtransformer filling utmost care has to betaken to check that the gauge index iscorresponding to the oil temperature (takenby the thermometer).


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Silica Gel Breather

1 - internal thread2 - inox cylinder3 - transparent hose

4 - labyrinth5 oil cup

Silicagel braether is a transparent tank of salts of Silica chemicallypure, with Cobalt indicator. The air sucked into the transformer (dueto thermic contractions of oil mass) passes through this.Silicagel absorbs humidity in the air signalling the reached degree of

saturation by change of colour:Orange or Blue = completely dryPurple or Pink or White = completely saturated.

The salts contained in the breather can be taken off and regeneratedby heating them at 120-150C until they get their original blue colour

again. The upper and lower parts of the breather consist of compactcasting in aluminium alloy. The transparent hose, which contains thesalts, is of Plexiglas or glass (for chlorinated oil transformer) and it isprotected by a stainless steel cylinder drilled in such a way as toallow the visual inspection of salts.

In the lower part there is a closing system which prevents the contactbetween air and salts: this closing system can be mechanical orhydraulic, and allows the air passage in the two directions (inlet and

outlet) only when there is a pressure difference between the insideand the outside of the transformer.


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Silica Gel Breather (contd.)

Silicagel breather is normally shipped disassembled to avoid alteration due to oil leakagecaused by transports jolts. It must be assembled to the suitable pipes coming from theconservator of the transformer. The oil cup must be attached to the breather after removing the

cork plug on the breather. Fill the oil cup with oil up to the mark on the cup before fitting it on tothe breather. Silicagel breather needs no particular maintenance, apart from periodical

regeneration (or replacement) of salts, and periodical check of oil level in the cup.

Silicagel breather, before assembling,

has to be stored in its original package.

The breather should be removed duringoil filtration to avoid oil getting mixedwith Silica gel during oil filtartion, andthe pipe from the conservator must be

plugged.

When 2/3rd of the Silicalgel has turned

Purple, Pink or White, it has to bereplaced or regenerated.


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Buchholtz Relay

1. Terminal board2. Breather cock3. Mechanical test button4. Gland5. Drain plug

6. Inspection holes7. Pneumatic test valves

Buchholtz relay usually has two contacts (tripping and alarm)And can operate closed - open - or one closed and one open.It Is made of:

- an external case complete with its parts as shown on thedrawing;

- an internal metal frame float, mercury switches or magnetic

controlled switches; a metal fan calibrated for signal at strongoil back flows (from the transformer to the conservator).

Usually Buchholz relay is supplied already mounted on small& medium rating transformers and disassembled on highrating ones.

Eventually it must be assembled during erection as permanufacturers instruction, generally observing the following:

1. Before assembly, check that the Buchholz is not damagedand it is free from humidity. If not so, it has to be dried in a

furnace at a temperature not higher than 70C;

2. Assemble the Buchholz and related gaskets betweenthe flanges of the pipes placed between the cover of thetransformer and the conservator; an arrow on the relayshows the direction of assembly from the transformer to

the conservator.


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Buchholtz Relay3. Connect the earth, alarm & tripp terminals: their identification is

made with the diagram on the relay.

4. Make sure that eventual shut-off valves are open; then fill theBuchholz relays with oil through the conservator.

5. Breath the Buchholz with the breather cock.

6. Test operation of Buchholz relay as follows:

6.1 Mechanical test:Remove the protective cap screwed on the button (item 3); push

the button checking the contact closing (or opening) by acontinuity test;

6.2 Pneumatic test:Blow-in air through the suitable valve (item 7) checking the closing (or opening) contact as above;Alternatively, close the shut-off valves (if there are any) at the top and at the bottom of the Buchholz:drain the relay through the drain plug checking the contact closing (or opening) as above. Then fillthe Buchholz again, and breath.

In any case, both contacts have to be handled with care in order to avoid internal damages and de-calibration. Such relays must be stored in their original packages during storage. However, it isadvisable to keep at least one spare part complete of gaskets because model change and it is notalways possible to interchange them.


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Gas drawing device

1. Connection to Buchholz relay2. cock3. Breathing and gas drawing cock4. Oil drawing and drain cock5. Gas inlet valve for relays circuit test

The gas drawing device must be connected to the breather pipeof Buchholz relay by means of the suitable tube foreseen forthis purpose, and must be fixed to proper support according tothe overall dimension drg.

After filling it with oil, breathe from the cock (item 3).During the normal working the cock (item 2) is open, while 3and 4 are closed. This way the box and the tube are filled withoil.

If you want to draw the eventual gas collected in the Buchholz

relay, open cock 4 taking care to let cock 2 always open: thusthe oil can come out from the box and the gas contained in therelay can enter the box.

When gas has moved into the box (check through thegraduated hole) close cocks 2 and 4. To drain gas open cock 3.

The gas drawing device is also equipped with a gas inlet valvefor the relays circuit test. This test has to be carried out beforestarting the transformer up, operating the same way as statedfor the Buchholz relays. Before assembling, keep the devicestored in its original package.


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Pressure relief valve/ Explosion vent 1. Switch for opening signal2. Breathing screw3. Spacer4. Gasket5. Holes for screw stud6. Visual Indicator for valve opening

7. Orienting cover8. Fixing screws for the protecting cover9. Valve body10. Gasket seat11. Calibrating nut


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Pressure relief valve/ Explosion ventSpring loaded explosion valve is usually supplied already mounted on the transformer.Its assembly must be carried out placing the valve case and its gaskets on the proper hole on thetransformer, as indicated in manufcaturers drawing.

After filling the transformer with oil, trapped air must be let out by loosening the breathing screwsand then tightening them back.

At this point the protecting cap must be so positioned by orienting it as to direct the hot oil spraysin the least dangerous direction, in case of eventual opening.

These vents are equipped with the following devices:

- a calibrating nut placed on the central stem, which blocks the springs. If the nut is screwed up the pressurerises, and viceversa. The calibration ranges normally from about 0,2 to 0,7 atmosphere;

- a visual indicator for valve opening: this is a pin projecting from the central part of the protective coverwhen the valve opens. To make it go back to its right position it is necessary to push it in side wards;

- a signalling switch: this is a quick-trip limit switch enclosed into a tight box. It operates simultaneously with thevisual indicator; the contact can be normally closed or open. Signalling is continuous until the visual indiactoris put again in its normal position. Pressure relief valve/ Explosion vent has to be stored in its original packinguntil assembly. Before assembling, it has to be made are free from dirt and moisture. No particularmaintenance is required.


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Radiators A - Lifting hook B - Upper shut-off valveC Gasket D - Upper breathing valveE - Fixing plaque for radiators F - Lower shut-off valveG - Oil drain valve H - Shut-off valve Lever

On distribution and small rating transformers, radiators are

welded to the tank and need no particular maintenance, exceptfor usual and periodical cleanings which are necessary inthe long run.

On higher rating transformers, radiators are usually ofdetachable type.

When radiators are supplied disassembled, and the storage isforeseen to be long, it is advisable to keep them stored indoor,in order to prevent deterioration of surfaces due to atmosphericcondensing.

The flange closing the caps must not be removed: ifaccidentally removed, make sure that radiators are free fromhumidity, rust or dirt before assembling.

It is better to keep a complete set of gasket as emergencyspares and to keep the closing caps of radiators and flanges foran eventual reuse.


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Radiators Assembly

- Make sure that the shut-off valve (B&F) are safely closed: remove the caps from

valves and radiators;

- Place the gasket (C) in the proper seats;

- Assemble one radiator at a time, fill it with oil, proceeding as follows:

a) open the breathing valve (D) of the upper header;

b) open the lower shut-off valve (F) making the oil flow into the radiator

very slowly, in order to avoid air bubbles;

c) when the radiator is filled with oil, close the upper breathing valve;

d) open the upper shut-off valve (B) to permit the oil circulation.

Proceeding as above, the oil level in the conservator decreases: thereforeit is necessary to restore the oil level in the conservator as gradually asradiators are assembled and filled.

Assemble the radiator fixing plaques by means of the proper flanges (E).


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Radiators disassembly

- Close both the shut-off valves (F&B);

- Open the upper breathing valve (D);

- Open the drain valve (G); empty the radiator pouring oil into a dry cleanreceptacle;

- Remove the radiator, place the closing caps on the shut-off valves (B&F)

without removing the gasket (C) from their seats;

- Place the rubber blanking caps on the radiators headers in order toavoid internal dirt and moisture;

- Close the breathing and drain valves (D&G).


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Butterfly Valve for Radiator Opening and closing of radiatorsbutterfly valves have to beperformed as follows:

- loosen the ring nut (2) in orderto reduce the pressure on the

gasket (3);

- turn the lever (1) in order toopen or close the valve;

- tighten the ring nut (2).

To replace the gasket (3), removethe pin (4), remove the lever (1),unscrew and remove the ring nut(2), remove the block (5) andwithdraw the gasket (3) by meansof a nail.

Then replace the gasket.After the replacement, fit again allparts in the reverse sequence.


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Oil Temperature Indicator (OTI)1. Bulb for temperature measurement2. Rotating female plug3. Capillary plated with lead and flexible pipe4. Pipe union with spring for application of

vibration damping suspension

5. Sealing threaded ring6. Sealing box for connecting terminals7. Pointers for fixed contacts of alarm and trip

It is generally a pneumatic tmeperature indicator and is usedusually for top oil temperature measurement. It is suppliedalready assembled. Electrical signalling and tripping must becarried out according to the Wiring Diagram. The thermometergrounding is carried out from a suitable terminal.

Dip the bulb into its pocket (thermo well filled with oil) and fit itwith the rotating female plug. The trip contact pointer has to becalibrated as follows:

- For OFAF: sum of the values of max. ambienttemperature and max over-temperature allowed forthe oil;

- For OFWF: sum of the values of the cooling watertemperature and max. over-temperature allowed for the oil.

The alarm contact pointer has to be calibrated at 5-10C lessthan the trip one. Some thermometers are provided with a fourthpointer for showing the maximum temperature reached.

They are usually supplied already calibrated: If not so, calibrationmust be carried out with its proper screw. All thermometers mustbe handled carefully to avoid damages of capillary. Before beingassembled they have to be stored in their original packing.

When a remote temperature indication is required, a pt100

sensor inserted into the thermo well is used.


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Measurement of winding temperature is carried out in anindirect way. The windings hot spot is assumed to be near topof the windings where they are surrounded by top oil. Furtherthe temperature gradient between winding hot spot and top oilis dependent on losses in the winding. Winding losses areproportaional to square of the current. Hence winding hot spottemperature can be approximated by top oil temperature + avalue proportional to the temperature diffrence i.e. a valueproportional to square of the current.

This is realised by sensor similar to OTI inside a resistorimmersed in top oil, and current from secondary of a current

transformer which reflects the winding current is made to flowthrough the resistor. A shunt is provided across the resistor for

adjusting the indicated temperature to winding temperaturecalculated or measured during heat run test. Hence thetemperature indiactor measures the top oil temperature towhich is added the temperature difference between windingand top oil. The current transformer is mounted inside thetransformer tank or in the cable termination box.


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For remote indication, a pt100 element is used instead of pneumatic instrument.

In some designs, winding top oil temperature gradient is added to top oil temperature in the dispalyunit using only an OTI and winding current transformer output. Like OTI, WTI also has alarm andtrip contacts. On actuation of trip contact, upstream circuit breakers must be tripped with properwiring from WTI/ marshalling box to HT Panel. Sometimes additional contacts are provided in WTIfor control of additional forced cooling equipment.

Normally a WTI does not need any calibration at site. Mounting instructions are similar to that of

OTI.

In case of dry type type transformers, WTI will be 3 or 6 pt100 elements or thermistors embeded inthe top of the winding and the sensors are connected to a temperature indicator-cum-scannermounted on terminal box.


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Protection Junction Box (Cable Termination Box)

1-2-3 - Fastening methods fixing the junction box to the transformer cover4 - Junction box 5 - Air outlet 6 - Cover7 - Air inlet 8 - Cable Gland 9 - Cable10 - Transformer Bushing 11 - Direct coupling to bushing12 - Cable termination busbar 13 - Cable termination14 - Support insulator 15 - Front Cover with manholes or flange for panel (if required)

16 - Disconnecting chamber 17 - Copper Flexibles18 - Gland Plate


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Protection Junction Box (Cable Termination Box) - Assembly

1. Connect the Junction box to top cover of Transformer (or its termination box already assembled on totransformer). Remember to use the gasket (although not shown in the above diagram).

2. Connect the cable termination busbars to the bushings.

3. Assemble the glands and the gland plate to the box.4. Assemble the power cables to glands.5. Connet cable terminals to cable termination busbars6. Connect the earthing of glands to junction box.

Some accessories like Surge Arrestors and Current Transformers are also mounted inside the Cable

Termination Box.


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Transformers Gaskets

Gaskets of the cover, flanges and bushings are usually made of oil-resistant,vulcanized cork-sheets or oil resistant rubber. When the gaskets are leaking, the leakscan usually be stopped by tightening the bolts. When a gasket has to be detached orreplaced, the sealing surfaces should be carefully cleaned and smeared with sealingvarnish (oil resistant Shellac).

Rubber gaskets are not to be smeared with varnish.

When joining two gaskets, their ends should be bevelled and glued.

Oil-resistant rubber rings are used as gaskets for bushing bolts, shafts and spindles.Oil-resistant and heat-resisting plastic gaskets can also be used as shaft and spindlegaskets. All these gaskets can be tightened and replaced from outside the tank. Whentightening the gaskets utmost care must be taken to prevent breaking of bolts orgaskets. In particular stud nuts must be tightened very carefully.

Cork gaskets are not re-used.

A l l bl d T f


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A completely assembled Transformer (typical 1600 kVA)1. Transformer Tank

5. OLTC6. Inspection cover for

OLTC connection7. Flat Roller (bi-

directional)8. Base Channel

9. Earthing Terminal10. Rating & Diagram Plate15. Conservator with lifting

lugs, oil filling cap anddrain plug

18. Silica Gel Breather

20. Pressure equaliser pipe21. Jacking Pad22. Drain cum bottom filter

valve with plug24. Buchholtz Relay25. Shut-off valve29. OTI30. WTI33. OLTC Surge Relay34. Surge Relay shut-off

valve39. Anti earth-quake

clamping

Elevation

A l t l bl d T f


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A completely assembled Transformer (typical 1600 kVA)

Side View 16. Oil level gauge17. Conservatorcompartmentfor OLTC

19. Explosion ventwith oil sight

glass withdoublediaphragm

36. Silica Gelbreather forOLTCconservatorcompartment

37. Bottom Oilsampling valvewith plug

38. Dial typemagnetic oil

level gauge

A l t l bl d T f


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A completely assembled Transformer (typical 1600 kVA)Plan

2. HV Cable Box withdisconnecting chamber

3. LV Busduct4. LV additional neutral

bushing11. Air release plug

12. Thermometer Pocketfor Glass bulbThermometer

13. Radiator with airrelease plug, lifting lugand drain valve

14. Radiator valve23. Top filter valve with

plug26. Lifting lug for complete

transformer27. Lifting lug for top cover

and active part

28. Marshalling Box31. Pocket for OTI32. Pocket for WTI35. WTI CT40. Neutral CT

A l t l bl d T f


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A completely assembled Transformer (typical 1600 kVA)

Other Details

Transportation of Transformers


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Preferably all construction work should have been carried out to theTransformer bay before the Transformer reaches site to prevent it fromgetting dirty or damaged.

The transformer is supplied filled with oil and normally all accessories fitted,except for the largest units. The radiators, condenser bushings andconservator may be dismantled during transport.

The Transformer may be provided with dehydrating breather or sealed if

provided with pressure relief device.

During transportation the transformer is filled with oil so that active part isfully immersed in oil and oil level is below the lower cover surface;

however, the oil level is left sufficiently low for bushing installation.



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During transport the following should be considered:

Angle of tilting exceeding 10 must be specified in the contract;

Prevention of damage to bushings, corrugated panels or radiators and

accessories;

Larger transformers should preferably be positioned with the longitudinal axis inthe direction of movement;

Secure against movement/ sliding by means of transport beams, wedges/wooden blocks and fastening wire/ lashes to ensure safety during road trafficconditions;

Vehicle capacity/ suspension must be adequate for the transport weight ofthe transformer;

Adapt vehicle speed to the road conditions;

Any impact recorders to be specified in the contract;

Any use of crates or containers.

Transfer of responsibility Handling and lifting


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Transfer of responsibility, Handling and lifting

Transfer of responsibility This depends of the agreed terms and conditions of the contract.

Handling, lifting The Transformer must be kept in normal upright position, unless otherwise indicated by the

documents.

Only approved and suitable lifting equipment should be used.

Forklift should be used only under transport pallets or transformer bottom.

Load should not be applied to corrugated fins or radiators and their supports.

While lifting the Transformer, only the fixtures provided should be used (transport eyebolts/lifting lugs, bugles, lifting/ jack pads).

When hydraulic jacks are used, only provided jacking points should be used, and in such away that twisting forces on the transformer tank are avoided.

Bushings, Cable Boxes or Conservators should not be used for lifting, pulling or pushing theTransformer.

When lifting a transformer with cable boxes on the cover, special care must be taken.

Lifting of Transformer by Lugs and Jacks


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Lifting of Transformer by Lugs and Jacks

Lifting of Transformer by Fork Lift and transferring


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Lifting of Transformer by Fork Lift and transferring

Lifting of Transformer (Wire Ropes)


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Lifting of Transformer (Wire Ropes)

Receiving the transformer at site


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1. Upon receiving the transformer at site, do the following:

- Check the way in which the transformer has been secured on the trailer,

- Check whether the delivery is complete according to order confirmation,

- Compare the packing list with the goods received:

- Check standard accessories:- Packed together with transformer;- Separately packed.

2. Inspect the following:

- The transformer nameplate;

- Liquid level, when applicable. Any leakages?;

- External damage, e.g. cracks in bushings; any damage to Radiator Fins;

- Dents or damages to Radiators;

- Colour matching of loose parts like conservator and radiator with colour of Transformertank;

- Impact recorders indications when applicable;

The receipt of the unit shall be signed for, and the result of the inspection shall be noted.



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3. Transformer shipments are normally insured.In case of damage revealed during the receiving inspection, do the following:

Make necessary arrangement to avoid further damage,

Contact the insurance company concerned and Supplier,

Make a report of the damage immediately,

Do not start repairs until responsibilities are clarified and actions are agreedupon by all involved parties.

Storage of Transformer prior to energizing


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When storage of the transformer is required, the followingrecommendations should be noted:

Store preferably in dry and clean locations, without any possibilities of mechanicaldamage and on a solid foundation.

If the transformer does not have a structural steel base, it should be placed uponsupports to allow ventilation under the bottom of the transformer base.

If the Transformer is not filled with oil, fix the conservator and dehydrating Breatherand fill it with oil up to the level corresponding to normal service temperature.

The Oil conservator and dehydrating breather must be checked to ensure that dryair is breathed (Conservator type only). Oil samples to be analyzed regardingmoisture content prior to energizing.

Humidity/ condensation in control cubicles, driving mechanism for on-load tap

changer, cable boxes and in cabinets of dry-type transformers etc. should beinspected/ removed.



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When storage of the transformer is required, the following recommendationsshould be noted:

Any drying and heating equipment of the cabinet (if any) must be connected to electric supply,to prevent the Transformer getting damp (especially in the case of dry type Transformer).

Storage temperature for dry-type transformer is in general: -25C to 50oC, however for

Resibloc: -60C to 50oC. Oil filled Transformer: 5o to 50oC. Relative humidity should be lessthan 75%. If such a storage area is not available, then the Transformer must be kept under asun-roof covered all around with thick plastic sheets with good ventilation.

Surface damage caused by transportation and installation must be repaired by touching upwith paint of original color and shade. It is better to get a small can of the paint from the

manufacturer of Transformer along with the Transformer. Prior to energizing, perform a megger test between the different windings, and from the

windings to earth. This applies to dry-type in particular.

Conservators must be stored into closed rooms without removing the gauges and the flangecaps.

Bushings must be kept in a dry indoor space, in their original packing.

Radiators can be kept outdoor, but their mounting flanges must be protected against corrosion.

Indoor Installation


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1. The Transformer room has to be dry, dust-free, suitably spacious and adequately

ventilated.

2. Floor area must be adequate so that the Transformer is accessible for cleaning andinspection from all sides. Clearance between the wall and the transformer should be0.75 m (wall on one side), 0.75 m (wall on two sides), 1.0M (wall on three sides),1.25 m (wall on four sides, for transformers installed in cell/ collapsible front wiremesh).

3. Height of the room is defined by the space required for bushings, cables entranceand by air flow required for cooling. Minimum vertical clearance between the top ofconservator tank and ceiling shall be 0.6 m.

4. When required it must be possible to lift the active part of the Transformer out of thetank while in the Transformer room for inspection. Otherwise, the Transformer willhave to be moved to a place with necessary clearance height for lifting the activepart.

5. The Transformer room has to meet the safety regulations regarding the construction

and location. Pay attention to requirements as per Indian Electricity Code regardingcivil engineering of Transformer rooms, safety regulations and fire protectionregulations. The door of the room must open outwards and must be built on outerwall of the building. Doors leading to other areas inside the building must beavoided. If such a door is built, it must fulfill prescribed fire resistance class.

Indoor Installation


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6. For naturally cooledTransformer (ONAN),satisfactory ventilationmust be arranged todissipate heat losses.

The principle of cooling isshown in the adjoiningfigure.

A fresh-air channel must

be built under theTransformer so that thecooling air is divided asevenly as possiblebetween the radiators.

Indoor Installation


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7. A ventilation duct or opening leading out must be built on the ceiling or upperpart of the wall. The area of the duct or opening has to be at least 10% morethan the area of the inlet opening.

If possible, air inlet and outlet openings should be located diagonally across theroom, however both of them should lead out of the building and not into the

building.

Give customer or civil agency the calculation of ventilation openings fora normal Transformer room when ventilation is based on natural draught. Let

them take help of a ventilation expert if required.

Unless more complete air flow planning is available (which the expert can do),the free cross section of air inlet opening can be calculated from the formulagiven below:

Where:

P = Total losses of the Transformer at full load;h = Effective height difference of air draught.

This formula is valid for temperature differenceof 150C between inlet and outlet air.

If the space available does not allow big enough cooling openings,

motorized fans will have to be used.

Indoor Installation


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If adequate natural draught is not available, then force ventilate thetransformer room with exhaust fans. As a guide each kilowatt of lossesrequires 4 cubic meters of air circulation per minute. Fresh air intake shouldbe at floor level, and a ventilation duct leading to outer air must be built on

the ceiling or upper part of the wall.

Outdoor Installation


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1. The installation site be must such that there is as little as possible directexposure to radiation from sun. A separate sun shade roof is recommended.

2. The installation site must also not neither gather excess snow in winter andwater should not drip from the roof directly onto the Transformer.

3. The Transformer location has to meet Indian electricity code requirementsregarding safety and Transformer installation.

4. The Transformer must not be located near combustible material.

5. Clearance between protective barrier and the Transformer should be minimum2.13 m.

6. Transformers must not be placed closer than 10 m from each other unless a

protective wall exists between them. Depending on the structure of theprotective wall, they can be placed as close to each other as cooling and access

conditions allow. For example, a steel concrete wall, which reaches to a heightof 600 mm above tallest part of the Transformer and extends 1 m on both sidesof the Transformers, can be used as a protective wall. Protective walls also help

against vandalism and noise suppression.

Foundation Construction rails and shims


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1. Transformers are usually installed on a concrete foundation equipped withhorizontal mounting rails. The Transformers are delivered with rollers installed orwithout rollers installed. Transformers on rollers must be fastened to foundationby wedges welded or bolted to rails or other means to prevent movement.

2. In order that gas, which may be generated in the Transformer, can freely moveto the gas relay (Buchholtz relay), the Transformer has to be installedhorizontally or slightly ascending towards the relay. The recommended ascent is1-20. This can be accomplished by means of intermediate plates (shims) placedbetween the Transformer and foundation or between rollers and roller beams.

Shims may also be used to adjust any minor height difference betweenTransformer secondary terminations and bus ducts leading from secondary toSwitchgear Panels.

Foundation Construction oil pit and oil sump


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3. An oil pit is recommended to be built under the Transformer location to prevent any

oil fire spreading to other equipment. Its purpose, in case of oil leakage due todamage to Transformer, is to prevent and extinguish fire and collect the oil toprevent the fire from spreading.

The oil pit has to extend beyond the Transformer on all sides and is generallymade of concrete. It must be big enough to contain the total oil quantity or

alternatively allow the oil to be led via a discharge pipe into a separate oil sump.

The oil pit must be so designed that the oil is extinguished when it runs into thesump. Wire netting is suitable for this purpose. The net must be installed over themouth of the cavity built at the bottom of the pit and which leads to the oil dischargepipe. Coarse gravel is also suitable for this purpose. Then the pit must be covered

with a dense steel grating at the bottom leaving 7.5-10 cm bottom clearance. Topof the grating must be covered with 25-50 cm deep layer of flatter stones and onthe surface with 35-50 cm of gravel.

If the installation has several Transformers, a common oil sump for collecting oilcan be built outside the building. The oil pits of different Transformers must not be

connected to each other, but they can be connected to a common pipe leading tothe oil sump.

The oil pits must be periodically maintained so that they meet the requirements allthe time. The stone layers, net and grating must be kept clean.

It also has to be seen that excessive amount of water is not collected in the pit.

Shifting to and placement on foundation


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1. The height of the Transformer foundation, with respect road level, depends on how theTransformer will be transported and shifted on to its foundation. If the Transformer is transportedon a carriage or by deep-load truck, it is very important that height of the foundation is same asthe loading height of the carriage or truck. Then the Transformer can be un-loaded sideways.

2. In case of a large Transformer, it is advisable for the rails of the foundation to reach the transportpath and be at the same level.

3. If the transport truck is driven close to guide rails, the Transformer can be lowered onto rails bymeans of cranes.

4. Then two jacking points which are on one of the smaller sides are lifted up simultaneously andslowly by hydraulic jacks by 50 mm max and then other two jacking points are similarly lifted.

This is repeated until the Transformer is lifted enough to fix the rollers/ wheels. Alternatively allthe four jacking points may be lifted simultaneously. Then all the rollers/ wheels are fixed andthe Transformer is lowered not more than 50 mm on each side until the Transformer rests firmlyon its wheels/ rollers. Then jacks are removed and the Transformer is drawn to its final placealong the rails.

5. If a crane is used to move the Transformer from its place of storage or unload from a truck on to

its foundation, the foundation height is not of great importance, but space must be allowed formoving the crane boom & hook around and above the foundation. The foundation must beprovided with locations for hydraulic jacks which have to be installed according to thecorresponding lifting levels of the Transformer. The foundation must be provided with haulinghooks for fixing of pulling ropes.

Minimizing noise emission


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Depending on the location of the Transformer room, it may be necessary to providesound insulation, e.g. anti-vibration pads to avoid transmission of vibrations tothe structure.

Cooling fans, reflections from walls and resonance added to the noise emitted from

the Transformer may increase the noise level considerably. Therefore, it isadvisable to install the Transformer as far away as possible from walls.

Oil sampling from a Transformer


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Accurate sampling is extremely important to ensure

that the sample is representative of the oil in theTransformer.

Use a 300cc stainless steel oil sample bottle withplastic tubing available from a laboratory or themanufacturer. Check that sample bottle is sealed. Ifthe seal is broken, then clean the bottle with acetone,

blow it out with dry air and dry it under vacuum. Totake oil sample, connect the two sections of the plastictubing to the sample bottle through gas cockconnectors. Attach one tube to the sampling valve onthe Transformer. The open end of the other tubeshould be placed in a scarp liquid container.

Open both the valves of the sample bottle. Thesample bottle should be held in vertical position withconnection to the Transformer sampling valve belowthe sampling bottle. Very carefully open the samplingvalve of the Transformer and fill the sample bottle untilthe oil overflows through the top and into the scrap

container.

Continue overflowing until no bubbles can be seen through the plastic tubing and until two quartsof oil have been collected in the scrap container. Close the top valve of the sample bottle, thenbottom valve of the sample bottle and finally close the Transformer sampling valve anddisconnect the plastic tubing. Tag the sample bottle showing the Transformer serial number,

date of sampling, location and owner of the Transformer and send the bottle to a laboratory foranalysis. Avoid shaking and jerks to the sample bottle.

Oil sampling from an oil drum or tanker


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The sampling bottle should

have a trap at the bottom.

The bottle must be rinsedwith solvent thoroughly driedprior to being used. Where

large number of drums areinvolved, samples from up tofive drums are mixed and ifthe dielectric strength of the

composite sample is 30 kVmin, then oil of all the drums

may be added to theTransformer. If the dielectricstrength is less than 30 kV,then samples from all thedrums will have to be tested.

It is also necessary to checkthe moisture contentsimilarly (max 50 ppm).

Oil sampling kit and test cup for dielectric strength


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Erection of Transformers transported fully assembled and filled with Oil


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1. Inspect the Transformer carefully to find possible transport damages payingspecial attention to possible oil leaks, surface damages and bushings.

2. Check and tighten all gaskets and carry out cleaning operations.

3. Check oil level in the oil conservator and top up with oil if necessary.

4. The dielectric strength of the oil will be normally given Transformers operationand maintenance manual. Test the dielectric strength of the oil, if less thanrequired arrange for oil filtration. The minimum value should be 40 kV/ 2.5 mmwhen tested with a device as per IEC 60156.

Erection of Transformers transported with loose parts and filled with Oil


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1. The transformer must be inspected on receipt as already mentioned.2. All parts removed for transportation must be re-fitted as per manufacturer's

manual/ instructions.

3. The condition of the oil in the Transformer and in the separate drums must bechecked and their dielectric strength tested. The minimum dielectric strength must

be 40 kV/ 2.5 mm when tested with a device conforming to IEC 60516 (IS 335).

4. Bushings must be installed as per separate instructions given by the Transformermanufacturer.

5. The conservator must preferably dried in a furnace at a temperature of 80-900C.The inside of conservator must be cleaned. The cleaning can be performed byrinsing the conservator with hot and clean (vacuum treated) Transformer oil. Theconservator must first be mounted on its brackets provided on the Transformer andthen following accessories must be assembled:

- any pipes for the tap changer oil and tap changer;- pipes to transformer flanges

- Buchholz relay,- shut off valves,- silicagel breather;- level gauges,

with manufcaturer supplied gaskets.



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6. During transportation, inlet and outlet of radiators (if any) are covered with solid flanges toprevent ingress of humidity and impurities into the radiators. These flanges must beremoved then the radiators must be installed on the flanges provided on the Transformertank.

7. For removal and installation of radiators, the fixing flanges of the Transformers are provided

with shut-off valves which ensure that the Transformer is not emptied of oil. If the radiatorsare to be removed for a longer period, e.g. for transportation, then the mounting flanges ofthe transformers are also blocked with solid flanges. These flanges are also to be removedafter ensuring that the shut-off valves are completely closed.

8. After all the parts are fitted, the oil required for the radiators and oil conservator must beadded to the Transformer. While filling the oil, ensure that clean Transformer oil is carefully

pumped into the oil conservator. If possible use a vacuum filter to process the oil in separatedrums during filling.

The lower shut-off valves must be open and upper shut-off valves must be first closed duringoil filling. The air release screws on top of the radiators should also be open untilthe radiators are filled with oil. Keep them open until oil starts oozing out of the air release

screws of the radiators. Then upper shut-off valves of the radiators must be opened.

Top-up the conservator with oil until oil level indicator rises up to the height corresponding totemperature that will prevail in the normal operation.



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Then trapped air must be released after oil filling in following order:

- Transformer tank cover (lid);- Bushings;- Buchholtz relay.

Releasing air can be carried out by using air release screws fitted at suitableplaces. For bushings which do not have air release screws, upper gaskets mustbe loosened and retightened after the air is released.

Erection of Transformers transported with out Oil


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1. The Transformer is filled at the factory either by dry air or Nitrogen atoverpressure of 50 kPA (approx 0.5 bar) or at normal pressure depending on theconditions of the journey, transport method, distance, etc.

2. For supervising the over pressure, the Transformer is provided with a manometer.

The Transformer should be filled with oil at site with in six weeks of dispatch fromthe factory. If oil is filled after this period, the pressure must be checkedcontinuously and dry air or Nitrogen must be added when the overpressure fallsbelow 10 kPA (0.1 bar).

3. Further, humidity of insulation used inside the Transformer must be inspectedbefore filling the Transformer with oil. More details on inspection of insulation,humidity and filling of the oil are given subsequent slides.

4. Transformer provided with normal-pressure dry air is generally provided with adehydrating breathers and sealed for transportation. The operating condition of

the dehydrating breather must be checked until the Transformer is filled with oil.Further details on maintaining the breather are given in subsequent slides.


5 Fix all the accessories in the sequence and manner indicated in the installation


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5. Fix all the accessories in the sequence and manner indicated in the installation

manual supplied along with the Transformer by the manufacturer. Precautions tobe taken while assembling conservator and radiators have already been explained.

6. Before filling, take samples of oil from each drum and test the dielectric strength ofoil. The value should not be below 30 kV/ 2.5 mm.

Maintaining Nitrogen pressure at 0.5 bar, force oil into the Transformer tank frombottom drain valve on the tank.

Then fix Radiators, Conservator and Bushings. Then fill radiators with oil asalready explained and top up the conservator.

Follow any recommendation or procedure given by manufacturer for oil filling. Itmay be necessary to filter the oil while filling using an oil filtration machine. It mayalso be required to fill the oil under vacuum with hot oil circulation for removal oftrapped air in the active part and moisture in the windings. In case the active part

has been exposed to outside atmosphere or in case external air ingress, consultthe manufacturer. The active part may have to be dried in such cases, before oilfilling.



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While filling oil under vacuum, bottom drain valve of the tank is connected to a vacuummachine and a vacuum of of o.5 bar (6.5 psi) is created. Then, the valve of the vacuumpump is closed and the oil is forced into the tank from bottom drain valve. Filling speed is

correct if the vacuum does not considerably decrease during filling. Oil filling isstopped when the windings and insulation parts are below the oil level. When de-aerated oil

is used, the vacuum must be maintained for several hours so that all the residual gas is

removed from the oil. Then the oil level is made up by filling the oil through the conservatortop valve.

7. If temperature of oil in the Transformer is different from 25oC, then oil level in the conservatormust be corrected to correspond to actual temperature. If the oil level indicator has

temperature scale, then oil is added or drained until the oil level is up to the prevailingtemperature.

If the oil level indicator does not have temperature scale, then the conservator is first filled up

to half the volume and then:

- if the oil temperature is higher than 25oC, oil level must be made up to above the middlelevel;

- if the oil temperature is less than 25oC, then oil must be drained from the tank below middlelevel.



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The volume of oil to be added or drained is calculated according to followingformulae:

V = 0.00088 x dT x M for mineral oil;V = 0.00104 x dT x M for silicone oil;

Where V is the volume of oil to be added or drained in liters;M is the mass of oil in the Transformer at 25oC (given on the name plate)dT is the deviation of actual oil temperature from 25

oC.

8. After filling the oil, allow the oil to settle to settle for 24-72 hours as permanufacturer's recommendation for trapped air to come out and collect at the top.

9. Release any trapped air by opening air release vents provided on the Transformer.

Additional Supports


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It may be necessary to provide supports made out of MS angles or channels forfollowing accessories:

1. HT Cable Box;2. LT Cable Box;

3. OLTC.

Refer Transformer manufacturer's manual and drawings for dimensional details.

Oil Filtration


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The Transformer Oil is processed with the help of an Oil Filtration Machine onthree occasions:

1. When filling oil for the first time from oil drums to prevent contaminated oilbeing filled into the Transformer.

2. For purifying the oil during periodic maintenance as recommended byTransformer manufacturer

3. For regeneration of oil after several years of usage.

It is done to:

Extract moisture from the oil;

Filter the particulates (solid particles and carbon residues);

Degas the oil (removal of gases generated and dissolved in the oil duringoperation) especially light hydro-carbons; To remove acidity and restore oxidation stability; To rectify color;

To remove sludge collected inside the Transformer.

Oil Filtration Machine


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Capacity: 250 to 6000 Liter/ Hour

Oil Filtration Process


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1. Connect the Oil Filtration Machine to the Transformer by hoses in a closedloop arrangement (Oil should enter the Transformer through bottom valve of thetank and go out through its top valve of the tank) and fill the entire systemincluding hoses with oil before starting the filtration process.

2. Once the system is filled with oil, circulate the oil for 10 minutes to eliminate airfrom the system, air vents provided at various points on the Transformer will haveto be slowly opened occasionally to let out the air and then closed.

3. The Filtration machine may have two modes of operation: Purification and

Regeneration. The choice of the mode depends on degree of contamination asdetermined by oil analysis done prior to filtration, application and manufacturer'srecommendation.

4. Purification:

This is limited to moisture extraction, degassing and particulate filtration. The oilenters the machine where it is first heated by a set of electric heaters to maintainthe oil temperature between 65 to 70oC.



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Then the oil is pumped through a pre-filter (5 microns) and a fine filter (0.5microns). Then it enters a vacuum chamber and passes through fiberglasscoalescing elements where it is exposed to high vacuum and is degassed anddehydrated. Then it is pumped back into the Transformer. The process isrepeated until moisture content falls below desired level and the required dielectric

strength is reached. The oil is tested at 4 to 12 hour interval (depending on thesize of the Transformer and manufacturer's recommendation) for moisture contentand dielectric strength

5. Regeneration

Oil is regenerated by forced percolation through columns of adsorptive media ataround 65oC. The adsorptive media consists of Fuller Earth (a type of clay).Regeneration removes acids, sludge, restores oxidation stability and rectifies color.After regeneration, oil is pumped through a 0.5 micron filter and then it is degassedand pumped back into the Transformer. The process of regeneration takes around

8-12 hours depending on the quality of oil being treated and the size of theTransformer.



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After several hours of regeneration, the clay beds get saturated and will have tobe reactivated. It is done by circulating the hot oil between the regenerationcolumns and reactivation columns. After reactivation, a small quantity of (0.1% ofoil processed) oil scum is collected in a holding tank which drummed for resaleand reprocessing or for disposal as hazardous waste. Clean oil trapped in the

clay is recovered. Reactivation takes around 16 hours and upon its completion,oil regeneration can be resumed.

6. De-sludging

Transformer may have to be de-sludged after several years of operation. The

process is similar to regeneration except that oil temperature will be above itsaniline point of about 75oC in order to dissolve the sludge inside the Transformer.It is done with freshly regenerated oil.

Oil purification, regeneration and de-sludging can be done with the Transformer in

either de-energized or energized condition. However for first filling of oil andpurification at site, the Transformer has to be in de-energized condition. When donein energized condition, Oil flow rate has to be kept low, as per manufacturer'srecommendation, to prevent turbulence inside the transformer.

Oil Filtration Process - Oil filtration performance analysis


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Oil filtration performance analysis

RestoredDepleted---IEC 61125

164 Hours

Oxidation Stability

0.018% v/ vGCGas content

>35


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1. All electrical connections to the Transformer must be made by using appropriate

terminals. Refer outline (general assembly) drawing given by the manufacturer.

2. Cables and busbars must be of sufficient cross section in accordance with loadcurrent.

3. Sharp bends in high voltage connections must be avoided.

4. Connections must be made with out causing mechanical tension or torque onthe connection terminals. All cables must be brought into termination box throughcable glands or must be secured appropriately.

5. For connections above 1000 A, flexible links must be used between busbars andthe Transformer terminals to compensate for thermal expansion of busbars.

Power Circuit Connections

6. Following minimum clearances in air for phase-to-phase and phase-to earth


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g p p p

parts must be maintained. This also applicable for distances between cables andwindings.

32525017012595756040Lightning Impulse withstandvoltage (kV)

6304502802101701109060Minimum Clearance acc. ToIEC 60076-3 phase-to-phase orphase-to-earth (mm)

72.552362417.5127.23.6System Voltage (kV)

As most sites in India are lightning prone, it is advisable to consider above values.

7. Bolted connections must be protected against corrosion by applying petroleum jellyon exposed metal surfaces and between joints.


8. Spring washers must be used to compensate for thermal expansions and for plastic


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deformations and maintain the necessary contact pressure.

1. Bushing terminal2. Al. Busbar or cable lug3. Pressure Washer (SFS 3738)

4. Conical Spring Washer (SF 3737)5. Galvanized bolt and Nut

Tightening should be stopped when the conicalWasher just becomes flat.

Bolted Copper connections are made in the sameway as Al joints. It is not however necessary touse pressure Washers. In Sulphurousatmospheres, the joint surfaces must be protectedby Petroleum Jelly. All joints must be tight andsecure. Torque Wrenches must be used fortightening. Aux. circuits of the Transformer and

Tap changer must be connected as per wiringdiagrams. All current transformers must beconnected to measuring or instrumentationcircuits. Secondary terminals of any CT not usedmust be shorted or earthed.

120190M16

5075M12

3044M10

1522M86 9M6

Tightening Torque (Nm)Bolt Size Cl. 8.8


9. Earthing connections


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The earthing terminals of the Transformer must be connected to protective earthing system.

The earthing terminals are usually provided diagonally on the base beams. Cross section ofearthing conductors/ connections must be according to regulations and conditions at site.

10. Cable/ Busbar terminations

Cable terminations must be selected according to cables used and as per cable

manufacturers recommendation. Normally indoor terminations are used insideenclosures. Cables must be fixed by clamps welded on to the enclosure or by glandson removable gland plates. With single core cables, it is better to use stainless steel gland

plates to avoid gland plate heating. In case of busduct connection, flexible connectors arerecommended.



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10. Cable/ Busbar terminations (continued)

High voltage connection is normally performed by copper cables and copper cable lugs. Insome cases heat shrinkable connectors or elbow connectors are used.

For aluminium-copper joints the copper is coated with tin, or bi-metal sheets (one side of

copper and the other of aluminium) can be used between the joint.

The aluminium surface must be larger than the copper surface. Aluminium parts shall alwaysbe placed above copper parts so that water cannot drain from the copper parts onto thealuminium (corrosion).

It must be remembered that good contact between joined aluminium surfaces can be achievedonly if non-conducting oxide film is removed with a wire brush, file or similar immediately before

joining, and renewed oxidation is prevented by applying a thin protective film of grease (neutralVaseline).

Jointing compound, which prevents the access of air and humidity into joints, must be used in

the joint. The zinc crystals of the compound break down the layer of oxide on the aluminium.


11. Neutral Link


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Neutral link must be provided at a convenient location between Transformer

Neutral terminal and Earth. If it is mounted on a wall, it must be at height of 1.8 to2.6 m. Cables used for neutral earthing should be taken only through PVC pipes.

12. Tap Changer

Tap changer to be tried in all the positions for free operations and ensure equalresistances between 3 phases in all taps of tap changer.

Pre-energisation Checks

The following checks have to the performed after erection and before


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start-up.

1. Deaeration of HV and LV bushing

Remove the eventual air within the HV and LV bushing as indicated in manufacturers

instructions.

2. Deaeration of radiators

Open the upper breathing plug of radiators and remove the eventual air within.

3. Deaeration of Buchholz relay

Open the lower drain plug of Buchholz relay for remove the eventual air within.

4. Check nameplate data against data sheets

Check whether details given on name plate are same as those in technical submittalapproved by customer and our specification.


5. Check mechanical damage and paint


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Repair either of painted parts, or of parts damaged during the transport or during the placingof the transformer on its site.

For repairing damage paint consider the following cases:

A. Scratches in the paint, of limited depth, the metal is still covered with a

coat of paint, even of just some mm:

Use a clean cloth imbued with non-oil solvents (for example thinner used for vinyl paints)to clean accurately the area, then proceed with the repairing of paint, with brush or roller

respect to the range of damage paint.

B. Deep cuts, up to the metal, with rust where the paint has been taken away:

Using abrasive paper, remove the paint from the area till the metal is white and

completely devoid of rust. Clean with a cloth imbued with non-oily solvents. Apply thepaint cycle suitable for such transformer, following strictly the suggestions provided forthis type of transformer


5. Check mechanical damage and paint (contd.)


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C. Rusted metal-plates, devoid of paint;

If possible, sand blast till the metal becomes white, or alternatively take off the rust witha metal brush; then rub down the border and, if necessary, retouch the brushed area.

Apply the painting cycle scheduled for the transformer, following the suggestionsindicated.

D. Paint swellings, with disjunction of the paint from metal.

With a metal spatula lift and take away the paint as far as possible, insisting on

the borders, and then carry out the workings indicated in the previous point.

Before the application, check whether the the paint to be used for the retouches is of

the same type as the paint applied originally by the Transformer manufacturer. It isbetter to get a can of the original paint from the Transformer manufcaturer.

The above described suggestions are valid for all the metallic parts of the transformers.

As far as radiators are concerned, in case C or D check either the possibility of restoringthe paint or of replacing them. Do not use stucco to level the surface.


6. Check oil leakage.


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7. Check nuts and bolts tightness with torque wrench as per values givenearlier, setting the torque on the wrench in the middle of the range given.

8. Check alarm-trip contacts of Buchholz relay

Check the alarm-tip contacts release:

a) acting on the test buttons;b) lowering the relay oil level.

9. Check trip contact of pressure relief deviceCheck the contact trip release by acting manually on microswicht pin.


10. Check contact calibration of thermometer


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11. Check alarm contact of oil level indicator

Check the alarm contact release through shunting the contact terminals.

12. Check all valves

Verify correct state of valve.

13. Check oil level

Verify the oil level of conservator and add or drain oil if necessary.

Oil temperature indicator: take out the bulb of the temperature indicator, dip it in hot water

and check the alarm contact release and insert the bulb back into the thermpmeter pocket onthe tank and fill the pocket with oil.

135C105CWinding temperature indicator setting

105C90COil thermometer setting, when combined with a

winding temperature indicator

100C85COil thermometer setting

TripAlarmRecommended settings for ONAN transformers Temperature settingsfor dry-typetransformers shouldbe according to therelevant temperatureclass of insulation.


14. Check silicagel breather

V if th l f lt f ili i d h h th if i d Ch k il l l


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Verify the colour of salts of silicium and change or re-charge them if required. Check oil level

in the liquid seal of the breather and make it up if necessary up to the mark.

15. Earthing correct

Check that all metallic parts are correctly grounded.

16. Auxiliary circuits & Terminal blocks

Check whether auxiliary circuits are wired up as per schematic diagram and whether wires

coming to terminal blocks are properlu fixed and are in correct position. If not correct them

after discussing with the manufacturer.

17. Check auxiliary (marshalling box) wiring

Verify that the connections are in according of the schematic diagram.

18. Check installation of emergency push button switch near the Transformer or on thedoor of its enclosure and wiring to upstream breaker trip circuit in HT Panel.

19. Instruments correctly installed

Verify that the instruments are in according of the overall dimensions (GA) drawing.


20 Insulation resistance (M Ohm)


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20. Insulation resistance (M Ohm)Resistance of Insulation between:

- HV Terminals and LV Terminals+Tank/

Earth;

- LV+HV Terminals and Tank/ Earth;- HV and LV Terminals;- Tank and Earth before making earth

connections, in some special cases.

Test results should conform to Test

Certificates/ reports submitted bymanufacturer.

2500 V22 to 33 kV

1000 VUp to 11 kV

Voltage of MeggerVoltage of HV Wdg.


20. Insulation Resistance (Contd.)


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The insulation resistance must be several thousand Mega-Ohm. However the value widelydepends on measuring time and the temperature of the Transformer. Convert the measured

values by multiplying with the conversion factors given in the following table:

44.70751.9830

31.75701.4025

22.40651.020

15.85600.7515

11.20550.510

7.85500.365

5.60450.250

3.95400.18-5

2.8350.13-10Correction FactorT (Ambient) oCCorrection FactorT (Ambient) oC

Two readings must be taken one at 15 s and another at 60 s. Minimum value of 60 s reading must be1000 Mega-Ohm. Further, difference between the readings taken at 15 s and 60 s is used to determinedryness of the Transformer. R60/ R15 is normally between 1.2 3.0 in a dried Transformer. Value lessthan 1.2 indicates that the Transformer has moisture.


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23. Vector group measurement


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This test is important especially when two or more transformers are to be operated in parallel.

It is always better to carry out this test at the same time as voltage ratio measurement andverify that the actual vector group corresponds to that indiacted on the rating plate.

1. Discommect any and all neutral earthing (both primary an seconday side)2. Connect R phase terminal of primary to R phase terminal of secondary3. Apply 3ph, 415 V, 50 Hz supply to HT side (which is usually primary).

Measure various voltages given below and verify that measured values conform to realtionsindiacted for concerned vector group.

23.1 Vector group Dd0

23.2 Vector group Yy0

R, r

Y

B

y

b

UYy

< UYb

UBb < UBy

URY

= URy + UyYR, r

Y

B

y

b

UYy

< UYb

UBb < UBy

URN

+ URn

= UnN

N

n


23. Vector group measurement


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23.3 Vector group Dz0

23.4 Vector group Dy5

UYy

< UYb

UBb

< UBy

URB

= URb

+ UbB

R, r

Y

B

Transformer Vector Technic

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