Transformer

Please follow the following

1) The test and commissioning procedures set out by the transformer manufacturer (including reviewing the tests they should have already done at the factory when they made it).

2) The test, commissioning and operation procedures set out in the sub station manuals (and associated documentation)

3) All relevant and applicable local electrical and safety standards (which vary from country to country)

It doesn't sound like you know what your doing (unless this is a homework question). Please leave this sort of testing to qualified professionals to minimise the risk of injury or death.

Yes you are right. There are several test to be conducted by the manufacturer before dispatching the transformer. Test reports run in to several pages.

Meggar transfomer for good insulation.Do a breakdown voltage test for oil provided the oil has good properties.

For 250kVA, I would suggest the following pre-commissioning tests only:

i) IR Value (HV to Earth, LV to Earth & HV to LV) (Use a 5 kV Insulation Tester for 11kV Side & a 1 kV Insulation Tester for the 433V side)

ii) OIL BDV (Must be more than 35kV)

In India, there are guide lines given by IS standards - Tests to be carried out on site prior to charging of the transformer, irrespective of the tests carried out on shop floor by manufacturer, some of these are....

1. Transformer Oil test - BDV test - > 60 KV

- Moisture content test < 30 %

- Specific resistivity test > 50000 Meg Ohms for new oil

2. Transformer Vector Group & Magnetic Balance Test

3. Transformer Ratio Test

4. Megger Test

5. Polarization Index of Transformer Insulation should be >2

Since, you have mentioned the Unitised Sub Station, Other tests for other HT equipments should also be carried out, as specified for those equipments.

Specially,

Over All Megger Test of the INstallation

Over All Earth test of the System

Physical clearances maintained - Interlocks of Door & Switch position etc...

Please don't misquote. Can you tell me which IS talks about the list of pre-commissioning tests to be done on power transformers?

do u have a USS with OIL ? ?

where are you located?