Transformer preservation
Transformer preservation
(OP)
Hi..
we have a generator transformer 350MVA which not be used for a 3 years. The last Furan analysis carried out found out the DP value is around 350. The transformer winding is still under oil without keep nitrogen. The OLTC diverter switch were removed before and only covered by blanketing plate. I assume the transformer were exposed with the moisture. We have a problem and plan to use back this transformer. Is this possible to use bak this transformer, What test to be carried out in order to make good the transformer?






RE: Transformer preservation
After above, keep the trnasformer with conservator and silicagel breather.Maintain the breather regularly.Run the oil pumps once a month.
RE: Transformer preservation
RE: Transformer preservation
RE: Transformer preservation
RE: Transformer preservation
RE: Transformer preservation
finally fill up the oil under vacuum then Power factor test of insulating could be performed.
RE: Transformer preservation
1)Moisture of 8.9 ppm at what oil temperature? That is important.Taht value at 70 C temperature is good,but if it is at 5C, wetness is to be suspected.
2) Dont rely on PI for oil filled transformers.Probably winding tan delta in oil filled condition will give some indication.
3) Yes voltage shall not be applied under partial vacuum as it may cause insulation breakdown between winding parts.Taking IR during vacuum not necessary.
RE: Transformer preservation
Thanks for your answer. Just have a question, is necessary to carry out vacuuming until get below 3 torr & start counting for 36 hrs period. is there any calculation for a period of vacuum?
let say this is old transformer & not all gasket was replaced. What is the best vacuum value to apply?
RE: Transformer preservation
Once you have done the cold trap, perform the dew point test. If that comes out acceptable, then I see no reason you couldn't refill the transformer, circulate with hot oil for one complete pass and energize it.
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If it is broken, fix it. If it isn't broken, I'll soon fix that.
RE: Transformer preservation
RE: Transformer preservation
I'd recommend you contact either and have a measurement made.
RE: Transformer preservation
As I mentioned earlier first find out the extent of wetness by simple moisture in oil measurement and find out the % moisture saturation.Based on that, decide the type of dry out and time for heating,vacuum,HOC etc.
It is true that you may run in to problem to get proper vacuum.Apply slight over pressure over conservator oil level,say 3 psi.Look for oil leaks and stop by tightening or mark up for gasket change.
Drain oil and start vacuum.Achieve the possible vacuum level ( A pump of more than 250 m3/hour will be required).Stop the pump.After one hour take the pressure reading inside the tank.Measure again after 30 minutes. The pressure rise be P mbar.Then leak rate is P/1800 X oil Volume in litres.This value,leak rate in mbarlitres/sec shall be less than 20.
RE: Transformer preservation