Thermography of Transformers

[zaza123]

Is Thermography of Transformers a Standard practice in the Preventive Maintenance of Transformers.
IT is good to do thermography but in any standard for transformer PM is it mentioned to do thermography.

 

[ScottyUK]

I am aware of a few plants who have thermographic windows on the IPB cubicles on the LV bushings of their generator transformers, but I would not say it is a standard practice in the UK.

It has been interesting to observe transformer radiator banks and the temperature differential among banks and from top to bottom of a bank.



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

 

[rbulsara]

If you know it is good to do, why not do it?

Rafiq Bulsara

http://www.srengineersct.com

 

[oldfieldguy]

Yes, it is good to do thermography. Easy picks in the scan are sharp temperature gradients on the case, oil flows through radiators, and terminations and hot spots on bushings. You can scan these on just about any transformer.

old field guy

 

[zaza123]

The thing is the Maintenance grioup is asking us reliability to make it as s standard practice & we are saying it is not normal practice & not a part of PM activities.
But yes they can surely say that it is part of Condition Monitoring of Transformers

 

[zaza123]

Is there in Any IEC standard for the condition Monitoring of ransformers, thermography is mentioned & what is the frequency for the Transformers i.e 3 yrs or 5yrs .

 

[rbulsara]

Your maintenance group is right.

Rafiq Bulsara

http://www.srengineersct.com

 

[prc]

I have not seen any IEC standards on the subject.There are two IEEE stds on condition monitoring/diagnostic testing of transformers.
1)C62-1995 Diagnostic Field Testing of transformers

2)C57.140-2006 Evaluation and recondition of transformers.
Eventhough these standards cover thermography, they are not covering the periodicity of this test.Most critical area for thermography in large transformers is the terminal connections of bushings to outside.For large critical units I would recommend once a year this test.

 

[rcw retired EE]

Problems we found on our transformers via thermography:

Loose connection on CT lead in control box.
Broken valve indicator on radiator. Valve was closed = radiator off line.
Overloaded bushing CT. Metering had been added above the rated burden.
Contaminated bushing with leakage current.

It didn't take but a few minutes more in the annual plant thermography survey to look at these transformers. There was not a special trip to a transfomer site just to do thermography.

 

[zaza123]

When the Transformer is in charged condition , does the areas which are closed by metal enclosure like On load Tap changer, HT & LT terminations etc can be covered in Thermography. From my experinece in LT swicthgear we were doing the Thermography by opening the Switchgear Cubible.
I think opeing cover for live parts of Transformer is not recommended.
Does any body know good lietrature on Transformer Thermography.

Thanks in advance,

 

[ScottyUK]

You can install thermographic windows in locations like air-spaced cable box covers and IPB covers. I wouldn't remove covers to do a direct inspection, it's not worth the risk. No real way of using thermography with an OLTC but there are other methods such as acoustic signature analysis.


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

 

[electricpete]

Actually LTC contact problems can show on the exterior. It will typically show as gradient top of LTC compartment hotter than bottom as well as LTC tank hotter than main tank. We have seen it. We had the benefit of two identical units with identical loading to compare.

Another common thing you may see is hot spots under the isophase bus on the tank wall and aorund the GSU low-side bushings enclosures due to circulating currents. Those are probably chronic condition without easy fix - require careful evaluation.

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[Krustabas]

Transformer (busbar, voltage and current transformer, circuit breaker etc.) thermography is regularly used in Latvia. We have our local standard for it.