Boiling Transformer

[haisa]

We have a 30MVA, 132/33KV Transformer that was removed from service due to leakage, for about 3years and the oil was beign removed and used elsewhere. Recently, the leakages were sealed and it was filled with oil and energised without picking any load for five days. On the fifth day the primary breaker triped due to a fault on another transformer sharing the same primary breaker.
After clearing the fault the two transformers were restored, but this very transformer started making a noise as if something is boiling inside and after some time it made a big bang noise with the whole trasformer vibrating. When bleeded a white gas like steam was coming out. What could the cause.
We have no means of testing the gas, please.

 

[itsmoked]

There are so many problems with this that it's hard to start anywhere...

Was the transformer kept warm while out of service?
Any condensed water get in? Was it hermetically sealed?

How do you protect two transformers with one primary breaker?

Whatever caused the trip probably damaged this transformer. There is now some sort of insulation failure in it that is allowing current to flow. The gas can be steam or boiling oil vapor. I suspect that soon you will have fire coming out too.

You should get a transformer specialist to investigate your transformer immediately.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[alehman]

It is probably arcing internally. You should shut it down immediately and investigate.

 

[haisa]

I very much agree with you itsmoked. We have been using a filtration machine to heat the oil and the windings as well. But what is the best way of drying the insulation at site?

 

[itsmoked]

It is tooooooooooo late for it now, in my opinion, I think a winding is now damaged.

I'm more of the, "keep the moisture out in the first place", kind of guy.

The way you do that is either run heaters that keep the oil about 2 or 3C warmer than the surrounding air. This will prevent condensation.

Now I think your heating filtration machine is likely the best bet. Have you meggered the beast? Can you get the oil tested?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[haisa]

Thank you very much itsmoked, but the insulation resistance and the oil dielectric result are within acceptable limits.

 

[DanDel]

I'm assuming the transformer is shut down now. You performed a full test procedure, including oil analysis and dissolved gas analysis of the oil? And everything was acceptable?

 

[oldfieldguy]

haisa-

I concur with "itsmoked's" assessment of a damaged winding. It is quite possible that this transformer delivered sympathetic fault current when other transformer faulted, resulting in a damaged winding, quite possibly one or more shorted turns.

This sort of damage will likely not show up on an insulation resistance test nor will it affect oil dielectric strength. It will show up on excitation tests if you have equipment to perform that test.

Additionally, a TCG (Total Combustible Gas) test set will probably show combustible gases in the transformer's gas space if it is a sealed, nitrogen-padded transformer. If you don't have one of these meters, your local utility company may have one, or certainly a specialty contractor will have one.

In either case: Failed excitation test or failed TCG or dissolved gas test, your transformer is dead.

Sorry...

old field guy

 

[haisa]

Actually we cannot conduct oil analysis and dissolved gas analysis of the oil.We dont have the laboratory for such analysis.

 

[DanDel]

I would advise calling in a power equipment testing company to perform complete testing. This is the only way to determine the extent of the problem.

 

[dpc]

I agree with itsmoked and oldfieldguy - the limited testing you were able to do cannot prove the windings are sound. You need an excitation test.

It seems very probable that this transformer has a failed winding and will need major repair/rewind work done.

 

[oldfieldguy]

haisa--

The TCG test sets I referred to are relatively inexpensive. If you're responsible for critical transformers and you're far away from full service testing companies and labs, I think you ought to look into having one in your possession.

The market is constantly adding very capable and relatively inexpensive test equipment for us to use, and much of it is getting EASIER to use.



old field guy

 

[stephenw22]

You can always take an oil sample and ship it to a lab for analysis. Depending on how much you are willing to pay, you can get results very quickly.