Transformer Trip - Oil and/or Electrical?

[SSEENE]

Hello,
Wanted to touch base with others in regards to their company philosophy when it comes to activities to complete after a transformer has tripped offline in a substation. Particularly, transformer testing oil/electrical.
It is our company philosophy that once a transformer has tripped, an oil sample is usually drawn within a few hours of the trip occurring, and analyzed. Based off the gassing from the sample determines whether we put the transformer back into service or need to do further investigating (electrical testing of the transformer). Electrical would consist of SFRA/winding resistance/excitation/overall insulation/etc. The full suite.
Question for discussion:
1) Does your company perform only oil sampling before re-energizing?
2) Does your company perform only electrical testing before re-energizing?
3) Does your company perform both oil sampling and electrical testing before re-energizing?

Thoughts/comments are appreciated!

 

[beyond86]

3. Yes, after each trip of transformers we perform tests of oil and gas from Buchholz relay before energizing. If a transformer trips from main protections, it's necessary to perform electrical tests. Also, we analyze records from relays and look at the level of currents that go through a transformer.

 

[bacon4life]

3)Usually both kinds of tests.

I am not sure if SFRA is a routine test.

If there is an obvious protection maloperation, the transformer might be put back in service without additional testing. Often a review of the relay event reports can very quickly confirm no internal fault occurred. If relay miscoordination is suspected but not provable, there can be some flexibility as to which tests are performed.

 

[SSEENE]

Very nice thank you both for the information

 

[low1]

Oil samples are standard for us, but electrical testing is only done if the transformer has been subjected to a through-fault, or if recordings from the TFR lead us to believe testing is warranted. Following a through-fault, we do ratio, winding resistance and capacitance bridge.

Edit: Saying that, ours are generator step-up transformers, and "transformer tripping" is almost always the result of a protection operation on different equipment.

 

[stevenal]

Low1,
Every feeder fault is a through fault. Care to modify that statement?

 

[low1]

Sure. We have protection schemes that will trip off the GSU that don't have anything to do with electrical quantities on the bus. So more often than not, we will have transformer trips that have nothing to do with electrical faults whatsoever.

 

[Palletjack]

1) No.
We oil test yearly and XF test every five years. From that we can see trends.

Going to depend on what or why it tripped.
51 trips? Look for what caused it, clear it up and turn it back on.

In 35 years we had only one 87 trip.
Believe me, there was no need to oil test or electrical test.