Insulation testing for 150 kV to 10.5 kV Transformer

[wisband]

Hi...I have some problem with my Power Transformer...I have 3 phase power transformer with rating as below :
3 Phase, 50 Hz
YNyn0d
ONAF (Oil Natural Air Forced)
HV & LV winding = 54 MVA
HV Winding 150kV with Neutral is Solidly grounded
LV Winding 10.5kV with Neutral is NGR grounded

This is the problem:
After the transformer is energized (Closing Circuit Breaker) about 3 hours the protection of the transformer was worked. The protection is 87 H/T (phase differensial relay)so make the Circuit Breaker opened. we found the surge arrester at HV side on phase V was burned and the leakage current counter is 5600 times. So we decide to replace the surge arrester. But before we do that we need to check the Insulation of the transformer on HV and LV side.
Please tell me how to do that...should I remove the Neutral and Ground connection before I check the insulation (meggering)?as we know that the Neutral side on HV and LV is grounded.
and How many Voltage that I can use? 1000 VDC or 5000 VDC or higher?

or

When I meggering on HV side, Should LV side to be Grounded and vice versa?

Thank you very much for your attention and I look forward for your answer...




Sincerelly

 

[ausphil]

Firstly, you need to get someone in who does this for a living, not learning what to do on this forum. HV testing is dangerous, and not for a novice.

Secondly, an IR test won't tell you the condition of the insulation of your transformer. It's usually a good indication as to whether you will risk putting your very costly test equipment onto it.

My suggestion is to a get a testing company in to do the tests, and also take an oil sample, which should give you some extra information.

Also, the issue with the surge arrestor, is there a leakage current monitor on it, which measures current, or is it a strike counter? These are 2 quite different things.

ausphil

 

[wisband]

there is no leakage monitor but only the counter