Transformer Vector Technic

© ABB India, BMTG - 1 Apr ’02 , Author: Nag Ramesh

Electrical Installation Techniques

Medium sized Distribution Transformers

Nag Ramesh 31st December 2007

Contents

© ABB Inida, July 14-15/‘03 - 2, Author: Nag Ramesh

Sl. No.

Topic

Slide No.

1

Caution

7

2

Types of Transformers

8 - 12

3

Transformers – Standard Accessories

13 - 15

4

Transformers – Standard Accessories - Wheels

16 -17

5

Transformers – Standard Accessories - Bushings

18 - 19

6

Transformers – Standard Accessories – Arcing Horns

20

7

Transformers – Standard Accessories - Conservator

21

8

Transformers – Standard Accessories - Oil level gauge

22

9

Transformers – Standard Accessories - Silica Gel Breather

23 - 24

10

Transformers – Standard Accessories - Buchholtz Relay

25 - 26

11

Transformers – Standard Accessories - Gas drawing device

27

12

Transformers – Standard Accessories - Pressure relief valve/ Explosion vent

28 - 29

Contents

© ABB Inida, July 14-15/‘03 - 3, Author: Nag Ramesh

Sl. No.

Topic

Slide No. 30 -32

13

Transformers – Standard Accessories – Radiators, Radiators assembly and disassembly

14

Transformers – Standard Accessories - Butterfly Valve for Radiator

33

15

Transformers – Standard Accessories Oil Temperature Indicator (OTI)

34

16

Transformers – Standard Accessories Winding Temperature Indicator (WTI)

35 - 36

17

Transformers – Standard Accessories Protection Junction Box (Cable Termination Box)

37 - 38

18

Transformers – Gaskets

19

A completely assembled Transformer (typical 1600 kVA)

40 -43

20

Transportation of Transformers

44 - 45

21

Transfer of responsibility, Handling and lifting

46

22

Lifting of Transformer by Lugs and Jacks

47

39

Contents

© ABB Inida, July 14-15/‘03 - 4, Author: Nag Ramesh

Sl. No.

Topic

Slide No.

23

Lifting of Transformer by Fork Lift and transferring

48

24

Lifting of Transformer – Wire Ropes

49

25

Receiving the transformer at site

50 -51

26

Storage of Transformer prior to energizing

52 - 53

27

Indoor Installation

54 - 57

28

Outdoor Installation

58

29

Foundation Construction – rails and shims

59

30

Foundation Construction – oil pit and oil sump

60

31

Shifting to and placement on foundation

61

32

Minimizing noise emission

62

33

Oil sampling from a Transformer

63

34

Oil sampling from an oil drum or tanker

64

35

Oil sampling kit and test cup for dielectric strength

65

Contents

© ABB Inida, July 14-15/‘03 - 5, Author: Nag Ramesh

Sl. No.

Topic

Slide No.

36

Erection of Transformers transported fully assembled and filled with Oil

66

37

Erection of Transformers transported with loose parts and filled with Oil

67 - 69

38

Erection of Transformers transported with out Oil

70 -73

39

Additional Supports

74

40

Oil Filtration

75

41

Oil Filtration Machine

76

42

Oil Filtration Process

77 - 80

43

Oil Filtration Process - Oil filtration performance analysis

44

Power Circuit Connections

82 - 87

45

Pre-energisation Checks

88 - 103

46

Check-list to be filled in before energisation

47

Energisation

81

104 – 105 106 107

Contents

© ABB Inida, July 14-15/‘03 - 6, Author: Nag Ramesh

Sl. No.

Topic

Slide No.

48

Energisation – Check List

108

49

Operation – Temperature rise and loading capacity

109 - 113

50

Parallel Operation of Transformers

114 - 116

51

Load distribution between parallel running Transformers

52

Protection of Transformers

118 - 120

53

Maintenance and supervision during operation

121 - 123

54

Investigation of Transformer disturbances

124 - 128

55

Repairs and Spare Parts

56

Safety Precautions

57

Installation Record for Transformers

58

Applicable Standards

133 - 134

59

Acknowledgement and references

135 - 136

60

Disclaimer

137

61

Power and Productivity for a better world

138

117

129 130 - 131 132

Medium sized Distribution Transformers Caution 1. Installation of Transformer should be done by skilled personnel or contractors who are trained and 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 that touching the Transformer is impossible after it has been energized.

© ABB Inida, July 14-15/‘03 - 7, Author: Nag Ramesh

3. Precautions must be taken to ensure that access to the Transformer is possible only after it has been isolated from the mains (e.g., by forced interlock between the switchgear and the Transformer access doors), exceptions are customer requirements and Transformers with cable boxes for both primary and secondary and Transformers mounted on pedestals with porcelain 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.

Types of Transformers Transmission of energy is generally divided in two parts; first is transmission over long distances 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 above

Primary voltage

Up to 72,5 kV

Available fluids

Mineral oil, dimethyl silicone,

© ABB Inida, July 14-15/‘03 - 8, Author: Nag Ramesh

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 level substations (11 or 33 kV) or directly to large industrial consumers.

Types of Transformers 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.

© ABB Inida, July 14-15/‘03 - 9, Author: Nag Ramesh

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

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

Types of Transformers 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 synthetic hydrocarbons.

© ABB Inida, July 14-15/‘03 - 10, Author: Nag Ramesh

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

Types of Transformers DRY-TYPE DISTRIBUTION TRANSFORMERS Dry-type Transformers are used to minimize fire hazard and other environmental contamination on surroundings and people, like in large office buildings, hospitals, shopping centers and warehouses, sea going vessels, oil and gas production facilities 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.

© ABB Inida, July 14-15/‘03 - 11, Author: Nag Ramesh

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 cured in vacuum. The high voltage windings are typically disk winding.

Types of Transformers Resibloc® dry-type Transformers Power range

30 kVA up to 40 MVA

Primary voltage

Up to 52 kV

Climate class

C2

© ABB Inida, July 14-15/‘03 - 12, Author: Nag Ramesh

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 soaked in epoxy, cured in open atmosphere.

© ABB Inida, July 14-15/‘03 - 13, Author: Nag Ramesh

Transformers – Standard Accessories

© ABB Inida, July 14-15/‘03 - 14, Author: Nag Ramesh

Transformers – Standard Accessories

© ABB Inida, July 14-15/‘03 - 15, Author: Nag Ramesh

Transformers – Standard Accessories

Transformers – Standard Accessories Wheels They are always bi-directional, flat-type or flanged. They are usually supplied disassembled from the transformer. Their assembly can be executed lifting the transformer with a crane or with some jacks placed on special brackets in one of the three ways shown in the enc. dwg. 1. Trolley 3. Wheel 5. Pivot 7. Spacers 9. Flask

2. Flask 4. Trolley 6. Wheel 8. Fastener plaque pins with screw

© ABB Inida, July 14-15/‘03 - 16, Author: Nag Ramesh

Type 1 Medium sized Distribution Transformers: fix the flask unit (with the wheels) to the trolley by means of the two special screws in the suitable direction. Type 2 Small sized Transformers: insert the pin into the wheel and into the trolley holes in the suitable direction, together with the spacers. Fasten the pin with the help of the special plaque and screw.

Type 1

Type 2

Transformers – Standard Accessories Wheels

© ABB Inida, July 14-15/‘03 - 17, Author: Nag Ramesh

Type 3 Medium transformers: fix the flask (with the wheels) to the back flask with the four special screws in the suitable direction.

Transformers – Standard Accessories Bushings

© ABB Inida, July 14-15/‘03 - 18, Author: Nag Ramesh

1. Upper porcelain 2. Lower porcelain 3. Stem 4. Cap 5. Washer 7. Gasket 8. Gasket 9. Gasket 10. Gasket 11. Gasket 12. Washer 13. Nuts 14. C- Washer

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 Bushing replacement: Unscrew the nuts (13) without letting the stem turn (3). Remove the cap (4), the gasket (7), the porcelain (1) and the gasket (9). After replacing the damaged part reassemble the bushing operating in the opposite direction taking care not to let the stem turn (3). Breathe where necessary (Buchholz relay, bushings) loosening the nuts (13).

Transformers – Standard Accessories Bushings Bushings are usually already assembled on the transformer: in some particular cases, they are shipped separately and must be assembled upon arrival, following manufcaturer’s instruction, after removing the closing caps on the transformer and with the oil level below the transformer cover. 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 external connection, avoiding dangerous stresses. No particular maintenance is required, except the periodical cleaning (once every 6 months) of the external porcelain surface.

© ABB Inida, July 14-15/‘03 - 19, Author: Nag Ramesh

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 instruction supplied with the part. In any case, it is advisable to keep one or more spare bushing and relative gaskets as emergency spares.

Transformers – Standard Accessories Arcing Horns on Bushings They are provided on the bushings as a protection to the transformer against transient over-voltages across windings and earth due to lightning and switching surges. They are generally provided on request. The lower horn is fastened on to flange of the bushing with one of the fixing screws and the upper horn is fixed to top end nut of the bushing by means of a bracket. Adjust the gaps ‘K” and “C” as per manufacturer's recommendation.

© ABB Inida, July 14-15/‘03 - 20, Author: Nag Ramesh

System Voltage

BIL Level

Arcing Horn Distance K (mm)

kV

kV

ABB

IEC

12

75

60

85

17.5

95

70

155

24

125

100

155

36

170

140

220

Transformers – Standard Accessories Conservator

© ABB Inida, July 14-15/‘03 - 21, Author: Nag Ramesh

8

1) air inlet pipe (transformer side) 2) conservator filling plug (transformer side) 3) conservator supporting brackets 4) bracket fixing plates 5) lifting lugs 6) conservator drain plug (transformer side) 7) oil level gauge

8) pipes and fittings for connection to the transformer tank 9) pipes and fittings for connection to the tap changer 10) oil level gauge of the tap changer 11) conservator. drain plug (tap changer side) 12) conservator filling plug (tap changer side)

Transformers – Standard Accessories Oil level gauge

1 - Signalling switch 2 - Float 3 - Rod 4 - Gland

The level gauge is made up of the following components: - main body with Plexiglas graded window - float and drive - magnet with external signalling disk - minimum oil level signalling switch

© ABB Inida, July 14-15/‘03 - 22, Author: Nag Ramesh

Usually the oil level gauge is supplied already assembled on the conservator.If not, it has to be fixed to the proper stud bolts, inserting the relevant gaskets. During transformer filling utmost care has to be taken to check that the gauge index is corresponding to the oil temperature (taken by the thermometer). 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 level gauge 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, taking into consideration that the switch trips slightly in advance in respect to the minimum level signal. No particular maintenance 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.

Transformers – Standard Accessories Silica Gel Breather 1 - internal thread 2 - inox cylinder 3 - transparent hose 4 - labyrinth 5 – oil cup

Silicagel braether is a transparent tank of salts of Silica chemically pure, with Cobalt indicator. The air sucked into the transformer (due to 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 dry Purple or Pink or White = completely saturated.

© ABB Inida, July 14-15/‘03 - 23, Author: Nag Ramesh

The salts contained in the breather can be taken off and regenerated by heating them at 120-150°C until they get their original blue colour again. The upper and lower parts of the breather consist of compact casting in aluminium alloy. The transparent hose, which contains the salts, is of Plexiglas or glass (for chlorinated oil transformer) and it is protected by a stainless steel cylinder drilled in such a way as to allow the visual inspection of salts. In the lower part there is a closing system which prevents the contact between air and salts: this closing system can be mechanical or hydraulic, and allows the air passage in the two directions (inlet and outlet) only when there is a pressure difference between the inside and the outside of the transformer.

Transformers – Standard Accessories Silica Gel Breather (contd.) Silicagel breather is normally shipped disassembled to avoid alteration due to oil leakage caused by transports jolts. It must be assembled to the suitable pipes coming from the conservator 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 to the breather. Silicagel breather needs no particular maintenance, apart from periodical regeneration (or replacement) of salts, and periodical check of oil level in the cup.

© ABB Inida, July 14-15/‘03 - 24, Author: Nag Ramesh

Silicagel breather, before assembling, has to be stored in its original package. The breather should be removed during oil filtration to avoid oil getting mixed with Silica gel during oil filtartion, and the pipe from the conservator must be plugged. When 2/3rd of the Silicalgel has turned Purple, Pink or White, it has to be replaced or regenerated.

Transformers – Standard Accessories Buchholtz Relay

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 the drawing; - an internal metal frame float, mercury switches or magnetic controlled switches; a metal fan calibrated for signal at strong oil back flows (from the transformer to the conservator). Usually Buchholz relay is supplied already mounted on small & medium rating transformers and disassembled on high rating ones.

© ABB Inida, July 14-15/‘03 - 25, Author: Nag Ramesh

Eventually it must be assembled during erection as per manufacturer’s instruction, generally observing the following: 1. Before assembly, check that the Buchholz is not damaged and it is free from humidity. If not so, it has to be dried in a furnace at a temperature not higher than 70°C; 1. Terminal board 2. Breather cock 3. Mechanical test button 4. Gland 5. Drain plug 6. Inspection holes 7. Pneumatic test valves

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

Transformers – Standard Accessories

© ABB Inida, July 14-15/‘03 - 26, Author: Nag Ramesh

Buchholtz Relay 3.

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 the Buchholz 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 a continuity 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 fill the Buchholz again, and breath. In any case, both contacts have to be handled with care in order to avoid internal damages and decalibration. Such relays must be stored in their original packages during storage. However, it is advisable to keep at least one spare part complete of gaskets because model change and it is not always possible to interchange them.

Transformers – Standard Accessories Gas drawing device

The gas drawing device must be connected to the breather pipe of Buchholz relay by means of the suitable tube foreseen for this purpose, and must be fixed to proper support according to the 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 3 and 4 are closed. This way the box and the tube are filled with oil.

© ABB Inida, July 14-15/‘03 - 27, Author: Nag Ramesh

If you want to draw the eventual gas collected in the Buchholz relay, open cock 4 taking care to let cock 2 always open: thus the oil can come out from the box and the gas contained in the relay can enter the box. 1. Connection to Buchholz relay 2. cock 3. Breathing and gas drawing cock 4. Oil drawing and drain cock 5. Gas inlet valve for relays circuit test

When gas has moved into the box (check through the graduated hole) close cocks 2 and 4. To drain gas open cock 3. The gas drawing device is also equipped with a gas inlet valve for the relays circuit test. This test has to be carried out before starting the transformer up, operating the same way as stated for the Buchholz relays. Before assembling, keep the device stored in its original package.

Transformers – Standard Accessories

© ABB Inida, July 14-15/‘03 - 28, Author: Nag Ramesh

Pressure relief valve/ Explosion vent

1. Switch for opening signal 2. Breathing screw 3. Spacer 4. Gasket 5. Holes for screw stud 6. Visual Indicator for valve opening 7. Orienting cover 8. Fixing screws for the protecting cover 9. Valve body 10. Gasket seat 11. Calibrating nut

Transformers – Standard Accessories Pressure relief valve/ Explosion vent Spring 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 the transformer, as indicated in manufcaturer’s drawing. After filling the transformer with oil, trapped air must be let out by loosening the breathing screws and then tightening them back. At this point the protecting cap must be so positioned by orienting it as to direct the hot oil sprays in 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 pressure rises, and viceversa. The calibration ranges normally from about 0,2 to 0,7 atmosphere;

© ABB Inida, July 14-15/‘03 - 29, Author: Nag Ramesh

- a visual indicator for valve opening: this is a pin projecting from the central part of the protective cover when 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 the visual indicator; the contact can be normally closed or open. Signalling is continuous until the visual indiactor is put again in its normal position. Pressure relief valve/ Explosion vent has to be stored in its original packing until assembly. Before assembling, it has to be made are free from dirt and moisture. No particular maintenance is required.

Transformers – Standard Accessories Radiators

A - Lifting hook C – Gasket E - Fixing plaque for radiators G - Oil drain valve

B - Upper shut-off valve D - Upper breathing valve F - Lower shut-off valve H - Shut-off valve Lever

On distribution and small rating transformers, radiators are welded to the tank and need no particular maintenance, except for usual and periodical cleanings which are necessary in the long run. On higher rating transformers, radiators are usually of detachable type.

© ABB Inida, July 14-15/‘03 - 30, Author: Nag Ramesh

When radiators are supplied disassembled, and the storage is foreseen to be long, it is advisable to keep them stored indoor, in order to prevent deterioration of surfaces due to atmospheric condensing. The flange closing the caps must not be removed: if accidentally removed, make sure that radiators are free from humidity, rust or dirt before assembling. It is better to keep a complete set of gasket as emergency spares and to keep the closing caps of radiators and flanges for an eventual reuse.

Transformers – Standard Accessories 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;

© ABB Inida, July 14-15/‘03 - 31, Author: Nag Ramesh

d) open the upper shut-off valve (B) to permit the oil circulation. Proceeding as above, the oil level in the conservator decreases: therefore it is necessary to restore the oil level in the conservator as gradually as radiators are assembled and filled. Assemble the radiator fixing plaques by means of the proper flanges (E).

Transformers – Standard Accessories

© ABB Inida, July 14-15/‘03 - 32, Author: Nag Ramesh

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 clean receptacle;

-

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 to avoid internal dirt and moisture;

-

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

Transformers – Standard Accessories Butterfly Valve for Radiator

Opening and closing of radiators’ butterfly valves have to be performed as follows: - loosen the ring nut (2) in order to reduce the pressure on the gasket (3); - turn the lever (1) in order to open or close the valve; - tighten the ring nut (2).

© ABB Inida, July 14-15/‘03 - 33, Author: Nag Ramesh

To replace the gasket (3), remove the pin (4), remove the lever (1), unscrew and remove the ring nut (2), remove the block (5) and withdraw the gasket (3) by means of a nail. Then replace the gasket. After the replacement, fit again all parts in the reverse sequence.

Transformers – Standard Accessories Oil Temperature Indicator (OTI) 1. Bulb for temperature measurement 2. Rotating female plug 3. Capillary plated with lead and flexible pipe 4. Pipe union with spring for application of vibration damping suspension 5. Sealing threaded ring 6. Sealing box for connecting terminals 7. Pointers for fixed contacts of alarm and trip

It is generally a pneumatic tmeperature indicator and is used usually for top oil temperature measurement. It is supplied already assembled. Electrical signalling and tripping must be carried out according to the Wiring Diagram. The thermometer grounding is carried out from a suitable terminal. Dip the bulb into its pocket (thermo well filled with oil) and fit it with the rotating female plug. The trip contact pointer has to be calibrated as follows: - For OFAF: sum of the values of max. ambient temperature and max over-temperature allowed for the oil; - For OFWF: sum of the values of the cooling water temperature and max. over-temperature allowed for the oil.

© ABB Inida, July 14-15/‘03 - 34, Author: Nag Ramesh

The alarm contact pointer has to be calibrated at 5-10°C less than the trip one. Some thermometers are provided with a fourth pointer for showing the maximum temperature reached. They are usually supplied already calibrated: If not so, calibration must be carried out with its proper screw. All thermometers must be handled carefully to avoid damages of capillary. Before being assembled 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.

Transformers – Standard Accessories Winding Temperature Indicator (WTI)

© ABB Inida, July 14-15/‘03 - 35, Author: Nag Ramesh

Measurement of winding temperature is carried out in an indirect way. The windings’ hot spot is assumed to be near top of the windings where they are surrounded by top oil. Further the temperature gradient between winding hot spot and top oil is dependent on losses in the winding. Winding losses are proportaional to square of the current. Hence winding hot spot temperature can be approximated by top oil temperature + a value proportional to the temperature diffrence i.e. a value proportional to square of the current. This is realised by sensor similar to OTI inside a resistor immersed in top oil, and current from secondary of a current transformer which reflects the winding current is made to flow through the resistor. A shunt is provided across the resistor for adjusting the indicated temperature to winding temperature calculated or measured during heat run test. Hence the temperature indiactor measures the top oil temperature to which is added the temperature difference between winding and top oil. The current transformer is mounted inside the transformer tank or in the cable termination box.

Transformers – Standard Accessories Winding Temperature Indicator (WTI) 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 dispaly unit using only an OTI and winding current transformer output. Like OTI, WTI also has alarm and trip contacts. On actuation of trip contact, upstream circuit breakers must be tripped with proper wiring from WTI/ marshalling box to HT Panel. Sometimes additional contacts are provided in WTI for control of additional forced cooling equipment. Normally a WTI does not need any calibration at site. Mounting instructions are similar to that of OTI.

© ABB Inida, July 14-15/‘03 - 36, Author: Nag Ramesh

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

Transformers – Standard Accessories

© ABB Inida, July 14-15/‘03 - 37, Author: Nag Ramesh

Protection Junction Box (Cable Termination Box)

1-2-3 - Fastening methods fixing the junction box to the transformer cover 4 - Junction box 5 - Air outlet 6 - Cover 7 - Air inlet 8 - Cable Gland 9 - Cable 10 - Transformer Bushing 11 - Direct coupling to bushing 12 - Cable termination busbar 13 - Cable termination 14 - Support insulator 15 - Front Cover with manholes or flange for panel (if required) 16 - Disconnecting chamber 17 - Copper Flexibles 18 - Gland Plate

Transformers – Standard Accessories Protection Junction Box (Cable Termination Box) - Assembly

© ABB Inida, July 14-15/‘03 - 38, Author: Nag Ramesh

1. 2. 3. 4. 5. 6.

Connect the Junction box to top cover of Transformer (or its termination box already assembled on to transformer). Remember to use the gasket (although not shown in the above diagram). Connect the cable termination busbars to the bushings. Assemble the glands and the gland plate to the box. Assemble the power cables to glands. Connet cable terminals to cable termination busbars Connect the earthing of glands to junction box.

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

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 leaks can usually be stopped by tightening the bolts. When a gasket has to be detached or replaced, the sealing surfaces should be carefully cleaned and smeared with sealing varnish (oil resistant Shellac). Rubber gaskets are not to be smeared with varnish. When joining two gaskets, their ends should be bevelled and glued.

© ABB Inida, July 14-15/‘03 - 39, Author: Nag Ramesh

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 spindle gaskets. All these gaskets can be tightened and replaced from outside the tank. When tightening the gaskets utmost care must be taken to prevent breaking of bolts or gaskets. In particular stud nuts must be tightened very carefully. Cork gaskets are not re-used.

A completely assembled Transformer (typical 1600 kVA) Elevation

1. 5. 6. 7. 8. 9. 10. 15.

© ABB Inida, July 14-15/‘03 - 40, Author: Nag Ramesh

18. 20. 21. 22. 24. 25. 29. 30. 33. 34. 39.

Transformer Tank OLTC Inspection cover for OLTC connection Flat Roller (bidirectional) Base Channel Earthing Terminal Rating & Diagram Plate Conservator with lifting lugs, oil filling cap and drain plug Silica Gel Breather Pressure equaliser pipe Jacking Pad Drain cum bottom filter valve with plug Buchholtz Relay Shut-off valve OTI WTI OLTC Surge Relay Surge Relay shut-off valve Anti earth-quake clamping

A completely assembled Transformer (typical 1600 kVA) Side View

16. 17. 19.

36.

37.

© ABB Inida, July 14-15/‘03 - 41, Author: Nag Ramesh

38.

Oil level gauge Conservator compartment for OLTC Explosion vent with oil sight glass with double diaphragm Silica Gel breather for OLTC conservator compartment Bottom Oil sampling valve with plug Dial type magnetic oil level gauge

A completely assembled Transformer (typical 1600 kVA) Plan

2. 3. 4. 11. 12. 13. 14. 23. 26.

© ABB Inida, July 14-15/‘03 - 42, Author: Nag Ramesh

27. 28. 31. 32. 35. 40.

HV Cable Box with disconnecting chamber LV Busduct LV additional neutral bushing Air release plug Thermometer Pocket for Glass bulb Thermometer Radiator with air release plug, lifting lug and drain valve Radiator valve Top filter valve with plug Lifting lug for complete transformer Lifting lug for top cover and active part Marshalling Box Pocket for OTI Pocket for WTI WTI CT Neutral CT

A completely assembled Transformer (typical 1600 kVA)

© ABB Inida, July 14-15/‘03 - 43, Author: Nag Ramesh

Other Details

Transportation of Transformers Preferably all construction work should have been carried out to the Transformer bay before the Transformer reaches site to prevent it from getting dirty or damaged. The transformer is supplied filled with oil and normally all accessories fitted, except for the largest units. The radiators, condenser bushings and conservator may be dismantled during transport.

© ABB Inida, July 14-15/‘03 - 44, Author: Nag Ramesh

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 is fully immersed in oil and oil level is below the lower cover surface; however, the oil level is left sufficiently low for bushing installation.

Transportation of Transformers During transport the following should be considered: Angle of tilting exceeding 10ºmust 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 in the direction of movement; Secure against movement/ sliding by means of transport beams, wedges/ wooden blocks and fastening wire/ lashes to ensure safety during road traffic conditions;

© ABB Inida, July 14-15/‘03 - 45, Author: Nag Ramesh

Vehicle capacity/ suspension must be adequate for the transport weight of the 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 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).

© ABB Inida, July 14-15/‘03 - 46, Author: Nag Ramesh

When hydraulic jacks are used, only provided jacking points should be used, and in such a way that twisting forces on the transformer tank are avoided. Bushings, Cable Boxes or Conservators should not be used for lifting, pulling or pushing the Transformer. When lifting a transformer with cable boxes on the cover, special care must be taken.

© ABB Inida, July 14-15/‘03 - 47, Author: Nag Ramesh

Lifting of Transformer by Lugs and Jacks

© ABB Inida, July 14-15/‘03 - 48, Author: Nag Ramesh

Lifting of Transformer by Fork Lift and transferring

© ABB Inida, July 14-15/‘03 - 49, Author: Nag Ramesh

Lifting of Transformer (Wire Ropes)

Receiving the transformer at site

© ABB Inida, July 14-15/‘03 - 50, Author: Nag Ramesh

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 Transformer tank; Impact recorders indications when applicable; The receipt of the unit shall be signed for, and the result of the inspection shall be noted.

Receiving the transformer at site 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,

© ABB Inida, July 14-15/‘03 - 51, Author: Nag Ramesh

• Do not start repairs until responsibilities are clarified and actions are agreed upon by all involved parties.

Storage of Transformer prior to energizing

© ABB Inida, July 14-15/‘03 - 52, Author: Nag Ramesh

When storage of the transformer is required, the following recommendations should be noted: •

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

•

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

•

If the Transformer is not filled with oil, fix the conservator and dehydrating Breather and 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 dry air is breathed (Conservator type only). Oil samples to be analyzed regarding moisture 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 be inspected/ removed.

Storage of Transformer prior to energizing

© ABB Inida, July 14-15/‘03 - 53, Author: Nag Ramesh

When storage of the transformer is required, the following recommendations should 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: -25°C to 50oC, however for Resibloc: -60°C to 50oC. Oil filled Transformer: 5o to 50oC. Relative humidity should be less than 75%. If such a storage area is not available, then the Transformer must be kept under a sun-roof covered all around with thick plastic sheets with good ventilation.

•

Surface damage caused by transportation and installation must be repaired by touching up with 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 flange caps.

•

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 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 and inspection from all sides. Clearance between the wall and the transformer should be 0.75 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 wire mesh). 3. Height of the room is defined by the space required for bushings, cables entrance and by air flow required for cooling. Minimum vertical clearance between the top of conservator tank and ceiling shall be 0.6 m.

© ABB Inida, July 14-15/‘03 - 54, Author: Nag Ramesh

4. When required it must be possible to lift the active part of the Transformer out of the tank while in the Transformer room for inspection. Otherwise, the Transformer will have to be moved to a place with necessary clearance height for lifting the active part. 5. The Transformer room has to meet the safety regulations regarding the construction and location. Pay attention to requirements as per Indian Electricity Code regarding civil engineering of Transformer rooms, safety regulations and fire protection regulations. The door of the room must open outwards and must be built on outer wall of the building. Doors leading to other areas inside the building must be avoided. If such a door is built, it must fulfill prescribed fire resistance class.

Indoor Installation

© ABB Inida, July 14-15/‘03 - 55, Author: Nag Ramesh

6. For naturally cooled Transformer (ONAN), satisfactory ventilation must be arranged to dissipate heat losses. The principle of cooling is shown in the adjoining figure. A fresh-air channel must be built under the Transformer so that the cooling air is divided as evenly as possible between the radiators.

Indoor Installation 7. A ventilation duct or opening leading out must be built on the ceiling or upper part of the wall. The area of the duct or opening has to be at least 10% more than the area of the inlet opening. If possible, air inlet and outlet openings should be located diagonally across the room, 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 for a 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 formula given below: © ABB Inida, July 14-15/‘03 - 56, Author: Nag Ramesh

Where:

P = Total losses of the Transformer at full load; h = Effective height difference of air draught. This formula is valid for temperature difference of 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

© ABB Inida, July 14-15/‘03 - 57, Author: Nag Ramesh

If adequate natural draught is not available, then force ventilate the transformer room with exhaust fans. As a guide each kilowatt of losses requires 4 cubic meters of air circulation per minute. Fresh air intake should be 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 1. The installation site be must such that there is as little as possible direct exposure to radiation from sun. A separate sun shade roof is recommended. 2. The installation site must also not neither gather excess snow in winter and water should not drip from the roof directly onto the Transformer. 3. The Transformer location has to meet Indian electricity code requirements regarding safety and Transformer installation. 4. The Transformer must not be located near combustible material.

© ABB Inida, July 14-15/‘03 - 58, Author: Nag Ramesh

5. Clearance between protective barrier and the Transformer should be minimum 2.13 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 the protective 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 height of 600 mm above tallest part of the Transformer and extends 1 m on both sides of the Transformers, can be used as a protective wall. Protective walls also help against vandalism and noise suppression.

Foundation Construction – rails and shims 1. Transformers are usually installed on a concrete foundation equipped with horizontal mounting rails. The Transformers are delivered with rollers installed or without rollers installed. Transformers on rollers must be fastened to foundation by 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 move to the gas relay (Buchholtz relay), the Transformer has to be installed horizontally or slightly ascending towards the relay. The recommended ascent is 1-20. This can be accomplished by means of intermediate plates (shims) placed between the Transformer and foundation or between rollers and roller beams.

© ABB Inida, July 14-15/‘03 - 59, Author: Nag Ramesh

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

Foundation Construction – oil pit and oil sump 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 to damage to Transformer, is to prevent and extinguish fire and collect the oil to prevent the fire from spreading.

© ABB Inida, July 14-15/‘03 - 60, Author: Nag Ramesh

The oil pit has to extend beyond the Transformer on all sides and is generally made 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 the sump. Wire netting is suitable for this purpose. The net must be installed over the mouth of the cavity built at the bottom of the pit and which leads to the oil discharge pipe. 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. Top of the grating must be covered with 25-50 cm deep layer of flatter stones and on the surface with 35-50 cm of gravel. If the installation has several Transformers, a common oil sump for collecting oil can 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 to the oil sump. The oil pits must be periodically maintained so that they meet the requirements all the 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 1. The height of the Transformer foundation, with respect road level, depends on how the

Transformer will be transported and shifted on to its foundation. If the Transformer is transported on a carriage or by deep-load truck, it is very important that height of the foundation is same as the 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 transport path and be at the same level. 3. If the transport truck is driven close to guide rails, the Transformer can be lowered onto rails by means of cranes.

© ABB Inida, July 14-15/‘03 - 61, Author: Nag Ramesh

4. Then two jacking points which are on one of the smaller sides are lifted up simultaneously and slowly 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 all the four jacking points may be lifted simultaneously. Then all the rollers/ wheels are fixed and the Transformer is lowered not more than 50 mm on each side until the Transformer rests firmly on its wheels/ rollers. Then jacks are removed and the Transformer is drawn to its final place along 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 for moving the crane boom & hook around and above the foundation. The foundation must be provided with locations for hydraulic jacks which have to be installed according to the corresponding lifting levels of the Transformer. The foundation must be provided with hauling hooks for fixing of pulling ropes.

Minimizing noise emission Depending on the location of the Transformer room, it may be necessary to provide sound insulation, e.g. anti-vibration pads to avoid transmission of vibrations to the structure.

© ABB Inida, July 14-15/‘03 - 62, Author: Nag Ramesh

Cooling fans, reflections from walls and resonance added to the noise emitted from the Transformer may increase the noise level considerably. Therefore, it is advisable to install the Transformer as far away as possible from walls.

Oil sampling from a Transformer Accurate sampling is extremely important to ensure that the sample is representative of the oil in the Transformer.

© ABB Inida, July 14-15/‘03 - 63, Author: Nag Ramesh

Use a 300cc stainless steel oil sample bottle with plastic tubing available from a laboratory or the manufacturer. Check that sample bottle is sealed. If the seal is broken, then clean the bottle with acetone, blow it out with dry air and dry it under vacuum. To take oil sample, connect the two sections of the plastic tubing to the sample bottle through gas cock connectors. Attach one tube to the sampling valve on the Transformer. The open end of the other tube should be placed in a scarp liquid container. Open both the valves of the sample bottle. The sample bottle should be held in vertical position with connection to the Transformer sampling valve below the sampling bottle. Very carefully open the sampling valve of the Transformer and fill the sample bottle until the 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 quarts of oil have been collected in the scrap container. Close the top valve of the sample bottle, then bottom valve of the sample bottle and finally close the Transformer sampling valve and disconnect 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 for analysis. Avoid shaking and jerks to the sample bottle.

Oil sampling from an oil drum or tanker

© ABB Inida, July 14-15/‘03 - 64, Author: Nag Ramesh

The sampling bottle should have a trap at the bottom. The bottle must be rinsed with solvent thoroughly dried prior to being used. Where large number of drums are involved, samples from up to five drums are mixed and if the dielectric strength of the composite sample is 30 kV min, then oil of all the drums may be added to the Transformer. If the dielectric strength is less than 30 kV, then samples from all the drums will have to be tested. It is also necessary to check the moisture content similarly (max 50 ppm).

© ABB Inida, July 14-15/‘03 - 65, Author: Nag Ramesh

Oil sampling kit and test cup for dielectric strength

Erection of Transformers transported fully assembled and filled with Oil 1. Inspect the Transformer carefully to find possible transport damages paying special 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.

© ABB Inida, July 14-15/‘03 - 66, Author: Nag Ramesh

4. The dielectric strength of the oil will be normally given Transformer’s operation and maintenance manual. Test the dielectric strength of the oil, if less than required arrange for oil filtration. The minimum value should be 40 kV/ 2.5 mm when tested with a device as per IEC 60156.

© ABB Inida, July 14-15/‘03 - 67, Author: Nag Ramesh

Erection of Transformers transported with loose parts and filled with Oil 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 be checked 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 Transformer manufacturer. 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 by rinsing the conservator with hot and clean (vacuum treated) Transformer oil. The conservator must first be mounted on its brackets provided on the Transformer and then 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.

Erection of Transformers transported with loose parts and filled with Oil 6. During transportation, inlet and outlet of radiators (if any) are covered with solid flanges to prevent ingress of humidity and impurities into the radiators. These flanges must be removed then the radiators must be installed on the flanges provided on the Transformer tank. 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 radiators are to be removed for a longer period, e.g. for transportation, then the mounting flanges of the transformers are also blocked with solid flanges. These flanges are also to be removed after ensuring that the shut-off valves are completely closed.

© ABB Inida, July 14-15/‘03 - 68, Author: Nag Ramesh

8. After all the parts are fitted, the oil required for the radiators and oil conservator must be added 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 separate drums during filling. The lower shut-off valves must be open and upper shut-off valves must be first closed during oil filling. The air release screws on top of the radiators should also be open until the 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 to temperature that will prevail in the normal operation.

Erection of Transformers transported with loose parts and filled with Oil Then trapped air must be released after oil filling in following order: - Transformer tank cover (lid); - Bushings; - Buchholtz relay.

© ABB Inida, July 14-15/‘03 - 69, Author: Nag Ramesh

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

Erection of Transformers transported with out Oil 1. The Transformer is filled at the factory either by dry air or Nitrogen at overpressure of 50 kPA (approx 0.5 bar) or at normal pressure depending on the conditions 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 from the factory. If oil is filled after this period, the pressure must be checked continuously and dry air or Nitrogen must be added when the overpressure falls below 10 kPA (0.1 bar).

© ABB Inida, July 14-15/‘03 - 70, Author: Nag Ramesh

3. Further, humidity of insulation used inside the Transformer must be inspected before 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 a dehydrating 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.

Erection of Transformers transported with out Oil 5. Fix all the accessories in the sequence and manner indicated in the installation manual supplied along with the Transformer by the manufacturer. Precautions to be 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 of oil. The value should not be below 30 kV/ 2.5 mm. Maintaining Nitrogen pressure at 0.5 bar, force oil into the Transformer tank from bottom drain valve on the tank.

© ABB Inida, July 14-15/‘03 - 71, Author: Nag Ramesh

Then fix Radiators, Conservator and Bushings. Then fill radiators with oil as already explained and top up the conservator. Follow any recommendation or procedure given by manufacturer for oil filling. It may be necessary to filter the oil while filling using an oil filtration machine. It may also be required to fill the oil under vacuum with hot oil circulation for removal of trapped 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, consult the manufacturer. The active part may have to be dried in such cases, before oil filling.

Erection of Transformers transported with out Oil While filling oil under vacuum, bottom drain valve of the tank is connected to a vacuum machine and a vacuum of of o.5 bar (6.5 psi) is created. Then, the valve of the vacuum pump 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 is stopped 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 conservator top valve. 7. If temperature of oil in the Transformer is different from 25oC, then oil level in the conservator must 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 prevailing temperature.

© ABB Inida, July 14-15/‘03 - 72, Author: Nag Ramesh

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

Erection of Transformers transported with out Oil The volume of oil to be added or drained is calculated according to following formulae: 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) o dT is the deviation of actual oil temperature from 25 C.

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

© ABB Inida, July 14-15/‘03 - 73, Author: Nag Ramesh

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

Additional Supports It may be necessary to provide supports made out of MS angles or channels for following accessories: 1. 2. 3.

HT Cable Box; LT Cable Box; OLTC.

© ABB Inida, July 14-15/‘03 - 74, Author: Nag Ramesh

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

Oil Filtration The Transformer Oil is processed with the help of an Oil Filtration Machine on three occasions: 1. When filling oil for the first time from oil drums to prevent contaminated oil being filled into the Transformer. 2. For purifying the oil during periodic maintenance as recommended by Transformer manufacturer 3. For regeneration of oil after several years of usage.

© ABB Inida, July 14-15/‘03 - 75, Author: Nag Ramesh

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 during operation) especially light hydro-carbons; To remove acidity and restore oxidation stability; To rectify color; To remove sludge collected inside the Transformer.

© ABB Inida, July 14-15/‘03 - 76, Author: Nag Ramesh

Oil Filtration Machine

Capacity: 250 to 6000 Liter/ Hour

© ABB Inida, July 14-15/‘03 - 77, Author: Nag Ramesh

Oil Filtration Process

© ABB Inida, July 14-15/‘03 - 78, Author: Nag Ramesh

Oil Filtration Process 1.

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

2.

Once the system is filled with oil, circulate the oil for 10 minutes to eliminate air from the system, air vents provided at various points on the Transformer will have to 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 as determined by oil analysis done prior to filtration, application and manufacturer's recommendation.

4.

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

Oil Filtration Process Then the oil is pumped through a pre-filter (5 microns) and a fine filter (0.5 microns). Then it enters a vacuum chamber and passes through fiberglass coalescing elements where it is exposed to high vacuum and is degassed and dehydrated. Then it is pumped back into the Transformer. The process is repeated 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 the size of the Transformer and manufacturer's recommendation) for moisture content and dielectric strength

© ABB Inida, July 14-15/‘03 - 79, Author: Nag Ramesh

5.

Regeneration Oil is regenerated by forced percolation through columns of “adsorptive media” at around 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 degassed and 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 the Transformer.

Oil Filtration Process After several hours of regeneration, the clay beds get saturated and will have to be reactivated. It is done by circulating the hot oil between the regeneration columns and reactivation columns. After reactivation, a small quantity of (0.1% of oil processed) oil scum is collected in a holding tank which drummed for resale and 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

© ABB Inida, July 14-15/‘03 - 80, Author: Nag Ramesh

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 its aniline 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 and purification at site, the Transformer has to be in de-energized condition. When done in energized condition, Oil flow rate has to be kept low, as per manufacturer's recommendation, to prevent turbulence inside the transformer.

Oil Filtration Process - Oil filtration performance analysis Oil filtration performance analysis Test Description

Method

Unit

Initial Oil Condition

Required Results after single pass

IEC 60296

mg KOH/ g

0.25

UBy

By

UnY = Unr + UrY

23.6 Vector group Yz

5

N

U

Bb

R, r

URB = URb + UbB

R, r b y

=U

Yy

UYb

b

U

R, r

Bb

© ABB Inida, July 14-15/‘03 - 99, Author: Nag Ramesh

23.9 Vector group Dz

UYy > UYb UBb > UBy UYb = UBy

By

UyY = Uyr + UrY

B

y

>U

6

Y b R, r n y

UYy > UYb

N B

U

Bb

>U

By

UnN = Unr + UrN

Pre-energisation Checks 23. Vector group measurement 23.10 Vector group Dy

Y

U

b

R, r

Bb

© ABB Inida, July 14-15/‘03 - 100, Author: Nag Ramesh

23.12 Vector group Yz

UYy = UYb UBb < UBy UYb = UBy