Partial discharge test for oil cooled transformers 2

[power2020]

Anyone pl. discuss :Is it possible to carry Partial Discharge test for oil cooled transformers (400kV/16,5kV)? And also pl. inform if any standard available for the above test for oil cooled transformer.
Thanks a lot.

 

[Zogzog]

Yes, IEEE 400

 

[power2020]

IEEE 400:Guide for Field Testing and Evaluation of the Insulation of Shielded Power Cable Systems. Is it contain the details of PD measurement for oil cooled transformers?

 

[Skogsgurra]

I am not so sure that you actually can get PD in an oil insulated transformer. Never seen any testing for that. Maybe in very high voltage transformers?

Gunnar Englund

http://www.gke.org

 

[power2020]

I agree with Mr. skogsgurra. But what is the reason for not getting PD in oil insulated transformer? pl. discuss.
Thanks..

 

[Skogsgurra]

I never thought about that. But my intuitive feeling is that you need a ionized gas to get partial discharge (Glow Discharge) and oil usually penetrates windings and surrounds insulators so well that there shouldn't be any gas pockets left - like you can have in voids in dry resin insulation systems.

Gunnar Englund

http://www.gke.org

 

[unclebob]

Lots of documents here:

http://www.eatonelectrical.com/NASA...CHHomeSearchResults&keyword=partial discharge

Sorry for the short link...

 

[edison123]

unclebob,

The list of papers is as short as the link

A star for you.


* If money can buy happiness, who is selling it ? *

 

[electricpete]

In dissolved gas analysis, H2 is a "key gas" for partial discharge, isn't it?

A wise transformer guy once told me to check for high water if you see the partial discharge pattern. It can turn normally satisfactory clearances into unsatisfactory clearances which allow partial discharge.

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[randyman]

Try IEEE C57.113 - Guide for PD Measurement in Liquid Filled Transformers & Shunt Reactors. And as a reference you can look at C15.13.5 (Trial guide for ITs 115kV and above) which has some PD info in it as well. There is an old IEEE std 454 which is withdrawn, but you can still get copy thru IEEE. It was an original guide to PD testing.

 

[randyman]

I realized a typo in last post, that should be C57.13.5 (not C15.13.5) OOOOpppppsss

 

[CarlPugh]

Have made many partial discharge tests of oil cooled and dry type transformers to 60 kV RMS. (test equipment limitation)
When testing dry type transformers, the partial discharge start voltage is very repeatable.
When testing oil cooled transformers, if the test voltage is held for any length of time (partial discharge for seconds or less) the corona start voltage decreases drastically. What happens is the partial discharge breaks the oil (but not the solid insulation) into a gas and the gas breaks down at a much lower voltage than the oil. The partial discharge start voltage increases to it's original value if the transformer is not energized for some time. The time required for the transformer to return to it's original partial discharge start voltage depends on how long it takes for the gas to disolve into the oil, which depends on the insulation scheme. This time can be minutes or days.

An interesting question is, if you have a cast type transformer with an inclosed gas pocket, will the partial discharge increase the gas pressure, so that the longer there is partial discharge, the higher the partial discharge start voltage?
(I don't know the answer)