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ERECTION TESTING AND COMMISSIONING OF

TRANSFORMER AT SITE

Arrival of Transformer at site:

Things to be checked during the inspection of transformer:

1. Any find of Physical damages to the body of the transformer which could have incurred duringthe transportation.

2. Positive nitrogen/oxygen gas pressure indication in the transformer tank. If the pressure is zerothen gas had to be refilled into the tank from the gas cylinders being sent with the transformer

to avoid any kind of moisture entering the tank.

3. Material identification has to be completed before commencing the erection work, all thematerials has to available in-hand.

Erection of Transformer at site:

The following works has be carried out during the erection of transformers at site:

1. Transformer Rails: Rails are being provided for the transportation and movement oftransformer. The rails are to be installed at the site as per the drawing. Leveling and anchoring

of the rail plates have to be carried out properly in order to give a fine foundation for the

transformer.

2. Civil front has to be cleared before shifting of the transformer to site.3. While shifting the transformer from store to site, proper care has to be taken care against any

accident. Handling of transformer has to done seriously.

4. Once the transformer is received at site and placed at its position, other parts to be assembledhave to be shifted to start the assembly of transformer.

5. The major items along with the transformer are: Transformer Bushings Cable Box Marshalling Box Breather Line Bus Ducts for Star-Delta connections Oil Filtration Unit

6. The Bus Duct line has to available for the final positioning and alignment of the Transformer.7. The assembly of the transformer parts has to be carried out as per the specific drawings.8. Care has to be taken care while making the joints. Gaskets of specific sizes are supplied for each

joint, proper tightening of bolts has to be done to avoid any oil leakages.

9. During the installation of transformer bushing, the gas provided in the cylinders has to bereleased in the transformer tank so avoid any moisture entering the tank.

10.Once the bushing is complete and top pipelines are installed, the cylinder valve is closed.

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11.After that, vacuuming of the transformer tank is started and all the gases inside are sucked. thevacuum pressure has to be developed as per the site altitude. For Chutak -540kgm^2

12.The specified vacuum has to achieve and hold for 3 hours, Any kind of leakages has to beattended to hold the negative pressure.

13.Meanwhile, the oil filtration and degassing has to be carried out with the oil pumping unit forminimum 18 hours and the specific BDV(Break Down Voltage)of the oil has to be achieved

before it is filled in the transformer tank.

14.Once the oil is filled in the tank, the oil filtration has to be carried out once again for 8 hours andthe oil should hold the specified BDV.\

15.Once the cable box is installed, the termination of XLPE cable has to be done.16.Vacuuming of the cable box has to be done before oil filling. The BDV test of cable box oil should

also be carried out and filtration/circulation has to be done until the required BDV is obtained.

17. Installation of bushing, cable box, neural grounding etc has to be carried out only under thesupervision of an experienced person.

Tests to be conducted at site

1. IR Testa. For 66/11 KV Power Transformer, 5000 V megger is to be needed.b. Power Transformer neutral Earthing is to be disconnected.c. Line terminal of the megger is to be connected to one of the HV Bushings of Power transformer

and Earth terminal of megger is to be connected to Power Transformer Body Earth Point.

IR Values are to be read on the megger by meggering the Power transformer

i. The above Value is to be noted as HV to Body.ii. Then IR Value between LV terminal and body of Power transformer is to be measured & noted.iii. IR Values between HV & LV terminals are to be measured & noted.iv. The temperature of transformer oil at which the IR Values are measured is also to be noted.v. Particulars of megger are also to be noted.

The maximum value shall be 60M at 600C temperature for transformer which are in service.

For new transformer the value obtained shall be tallied with manufactures test results.

2. D.C. Resistance or Winding ResistanceThe Resistance of HV winding LV winding between their terminals are to be measured with precision

milli ohm meter/ micro ohm meter. The values shall be compared with original test results.

3. Turns Ratio TestWith turns Ratio meter, turns Ratio between HV & LV windings at various taps to be measured &

recorded.

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At normal tap for 33/11 KV Delta/Star transformer the turns turns ratio is 5.196. At other taps values will

be as per the percentage raise or lower at the respective tap positions.

4. Voltage Ratio TestWhen Turns Ratio meter is not available, Voltage Ratio Test is done at Various tap position by applying

3 phase LT(415V) supply on 33 KV side of Power transformer.

At Various taps applied voltage and Resultant voltages LV side between various

Phases and phases& neutral measured with precision voltmeter & noted.

5. Short Circuit TestThe four terminals on LV side of Power transformer are shorted with 50 sq. mm. copper cable. Three

phase LT supply is applied on HV side of power transformer at normal tap and currents measured in all

the phases on HV side and phases & neutral on LV side values noted.

The Resultant HV & LV currents are as follows:-

HV side current LT Voltage applied on 33 KV side of PTR X Rated HV current in all Phases = 33000 X

Impedance Volts / 100 of PTR

LV side phase LT Voltage applied on 33 KV side of PTR X Rated LV current

Current in all phases = 33000 X Impedance Volts / 100 of PTR

LV side neutral current shall be zero or less than 1.0 amp.

6. Magnetic Balance Test415V, Two phase supply is to be applied to any two phases terminals on HV side of Power transformer

and voltages in other two phase combination are to be measured.

Sum of the Resultant two values shall be equal to the voltage applied.

RY YB BR Result

a. V (415 V) V1 V2 V= V1+ V2b. V1 V (415 V) V2 V= V1+ V2c. V1 V2 V (415 V)

7. Vector Group Test

Connect HV side R Phase terminal to LV side R Phase terminal of Power transformer. Apply 3Phase 415

V supply to HV side of Power transformer.

Measure Voltage between various terminals as follows.

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R r

n y

B Y

Voltages between Rn ; Yn ; RY VRY = V RN + VYN

Voitages between Yb ; Yy ; VYb = VYy

Voltages between Bb ; By ; VY b > VBb

8. BDV Test of OilOil samples from top oil & bottom oil of Power transformer main tank as well as OLTC tank are to be

collected and tested. The Test is conducted across mushroom spheres dipped in the test sample with a

gap of 2.5 mm between them.

The test is conducted as per IEC 156-1995 standard. Six test tests are conducted wherein High Voltage is

applied across the mushroom spheres and the breakdown voltages are measured in each case. In theend the average of the six tests is taken as the final result.

9. Magnetization CurrentThree phases LT Voltage of 415 V is applied on HV side of Power transformer and currents are to be

measured with milli-ammeter.

The value shall be = (1-2 percent of rated full load current/rated HV) * Voltage Applied