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Dissolved gas analysis question

Dissolved gas analysis question

Dissolved gas analysis question

(OP)
Hello,
In reviewing some DGA reports, I find that the transformer is likely to be having "partial discharge".  I have the definition of partial discharge from IEEE C57.104, but I don't really understand what this means.  Can someone please explain what this means, and what can be done to mitigate it.

thanks
EE

RE: Dissolved gas analysis question

In reviewing some DGA reports, I find that the transformer is likely to be having "partial discharge".  I have the definition of partial discharge from IEEE C57.104, but I don't really understand what this means.  Can someone please explain what this means, and what can be done to mitigate it.


In areas where the local electric stress exceeds the local dielectric withstand, there can be localized breakdown.    We use the word "local" or "partial" to distinguish from complete breakdown (which would be a fault).

Depending on the equipment, small amounts of partial discharge is sometimes expected/normal.  Overhead insulators frequently have corona noise which is similar to partial discharge.  I have 30 13.2kv motors monitored by Iris pd equipment, and all have detectable partial discharge occurring every time we monitor them (normal).  

Motor insulation systems include air (outside of conductors, and possibly as voids in the insulation).  That is quite a bit different than transformers where everything is surrounded by oil, and insulation is impregnated by oil.  I tend to think any partial discharge inside the tank is not normal (although I haven't used any technologies for detecting pd in transformers).

If you have symptoms of partial discharge in oil, there are a number of things to check.  A few of them include oil dielectric strength and moisture, since these are obvious possible causes of abnormal partial discharge.
 

=====================================
(2B)+(2B)'  ?

RE: Dissolved gas analysis question

One more extremely random thought to toss out - hydrogen can be created by reaction of oil with galvanized sampling fittings.

=====================================
(2B)+(2B)'  ?

RE: Dissolved gas analysis question

(OP)
Thank you for your reply.  I asked the plant about sampling, and I did mentioned the problem in using galvanized fittings.  I don't think that's the problem.  We have very high H2, high CO, and high CO2.  And the transformer was degassed about a year ago.  H2 has gone from 40ppm to 360ppm in 8 months.

RE: Dissolved gas analysis question

Doble has some new tools for online analysis of  partial discharge.  http://www.doble.com/files.php?file=5_TransformerGuard_Brochure.pdf

During factory acceptance testing of transformers we require partial discharge measurements done during the induced voltage test.  It wasn't quite clear to me though how much of the measured PD activity was inside the transformer and how much was the the bushing to air interface.

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