Frequency Response Analysis (FRA)

[unclebob]

Does anybody here uses this when testing transformers?
I have read alot on this subject and found it very interesting. I included a document for those of you who are curious...

Any comments are welcome.

 

[ScottyUK]

We started using it a few years ago to provide a 'fingerprint' of our GSU and unit auxiliary transformers. The test was developed by CEGB in the UK in the 1970's as a non-intrusive means of assessing transformer winding movement. I think one of the CEGB engineering team was recruited by Doble UK a few years ago, if he is still there.

The primary reason for us using the test is to detect winding movement following a fault: we had a major transformer fault here in 2001 and didn't have the FRA 'fingerprint' available so we ended up doing a time-consuming detailed internal inspection and an extensive set of tests to convince ourselves that no significant winding movement had taken place and that the transformer was fit for service. The cost of the FRA test would have been saved many times over if we had access to the FRA signature pre-fault. We carried out an FRA test after the transformer was made ready for service so that information is available should we need it again.

I think one of the key things to do is perform the FRA test at initial commissioning, then use that response as a comparision for tests performed over the life of the transformer. I don't see it as a routine test, but a useful tool if the transformer is subjected to a heavy through fault which could cause winding movement.


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If we learn from our mistakes I'm getting a great education!

 

[22574]

Hi Unclebob,

We are using sfra for testing transformer, specially after a fault.

I attached sfra traces from 3 identical 1-phase transformers
that I tested. This is very interesting because the instrument reveals that one of the 3 transformer got problem after a fault..

 

[payalelectrical]

SFRA - sweep frequency response analysis test is done,
1) during manufacturing and FAT to confirm the integretiy of the winding after High Voltage Test.
2)Further this sweep waveform obtained forms the basis for conditional monitoring of transformers.
as in these waveform there are different frquency bands for different faults any major deviation from the FAT waveform indicates a fault in the corresponding region.
Very useful diagnostic test.