Abnormal dga

[setiawanmarten]

Dear all,
I have this problem with my dga result on tranformer 6545 kva 11 kv to 254 v , co 390, co2 3663, ch4 482, c2h2 0, c2h4 560, c2h6 224, h2 2361 , tdcg 4031, according to duval said thermal fault over 700 deg c..what should i do with this transformer?

 

[ScottyUK]

Some hot faults on the core can sit innocuously for years without any detriment, others go terminally bad pretty quickly. A trend over a period of time is much more useful than a snapshot when trying to analyse DGA results. The values are fairly high, but how fast are they increasing?


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

 

[DanDel]

Outside of a possible thermal fault, with hydrogen that high, you probably have a partial discharge issue also.

 

[setiawanmarten]

Scotty, we already done a few times dga and the increase was 32 ppm per day

 

[setiawanmarten]

DanDel, how to confirm the partial discharge in the winding? If the winding have partial discharge is that mean we have to rewind the transformer?

 

[prc]

If CO is not increasing, you can take it as the heating zone is away from insulating paper.Since there is no acetylene,there is no arcing inside. Most probably it will be a loose connection -at bushing ends or leads - rather than PD.

 

[setiawanmarten]

Prc, the co actualy went up from 280 ppm to 390 ppm in ten days, but still near standar 350 for CO

 

[setiawanmarten]

Just doing TTR and the result was 52.672 ; 46.891 ; 50.217 is this confirm that the problem is in the connection?

 

[DTR2011]

Are the ttr results a-b-c phase? If so, results should be the same (+/-o.5%)

 

[Zogzog]

Those TTR readings look suspect.

As far as PD detection, this link explains it.

http://www.nooutageelectricaltesting.com/transformer-testing.html

 

[7anoter4]

Since I was always only a designer-machines, transformers, cables and Power Stations-my opinion is only from the "books".
And ,of course, I am not an optimist.
As methane, ethane, ethylene and hydrogen are very high values [even for age of 10 years old transformer] that could indicate partial discharge or even arcing.
The TTR deviations are also very high [21%] that could be short-circuit on all three phases-mainly on R.
This phenomenon could happen if -short-circuiting the protection-the transformer was energized a few times on short-circuited cable or equipment.
The oil should be purged and a close examination of the windings could be required.

 

[setiawanmarten]

Smallgreek, yes it phase r s t , zog zog thank you, 7anoter 4 is it not possible the problem in the tap changer connection or lead ?

 

[setiawanmarten]

And is it possible to have a short circuit in winding without c2h2 present in the dga result?

 

[electricpete]

yes, I think you can have turn to turn fault without c2h2 present. It can proceed for example by through-fault or mechanical / thermal etc factors that cause insulation to degrade and allow contact. Results in high circulating current in the shorted turn, but does not require arcing (C2H2).

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(2B)+(2B)' ?

 

[prc]

Please check the winding resistance phase by phase at all taps.It will reveal presence of any shorted part of winding.Shorting can happen due to some defect in tap changer.Ratio values are abnormal.

 

[setiawanmarten]

Winding resistance can be done but only for primer because the secunder the resistance was so low that the winding resistance could not be measured....by the way this is a rectifier transformer