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Maximum TDCG

Maximum TDCG


I have a transformer with stable dissolved gasses but I was wondering..

What is the maximum acceptable value of total combustible dissolved gasses (ppm) before degassing or oil change is necessary?

I saw in IEEE Std C57.104-1991 a couple of tables where they mainly talk about gas increasing rates (ppm/day). Many articles and people told me that the rates are indeed the most important thing to monitor, but what about the absolute TDCG value?  Should the transformer be degassed when TDCG are over 4000ppm? 5000?

RE: Maximum TDCG

The interpretation of the dissolve gas analysis (DGA) is not universally uniform. There are guidelines on IEEE, EPRI, BPA, utilities, Labs and manufacturer of oil analysers.

The list of gases generated during oil degradation are: hydrogen (H2), methane (CH4), ethane (C2 H6), ethylene (C2 H4), acetylene (C2 H2), carbon monoxide (CO), and oxygen (O2).
 The enclose link may provide you with general direction for DSG concentration limits.

See table 4 on page 38.

RE: Maximum TDCG

I don't know that there is a limit on the maximum tdcg limit that would necessitate degassing as you propose.  As you know the tdcg is an indicator of what is going on in your transformer.  If the gasses are stable it is probable more an indication of what has gone on in the transformer in the past and there is likely no active problem with the transformer.  But what you should consider is what will the tdcg analysis look like when a new problem develops,  perhaps a lot of  old gases could cloud your identification and analysis of a new problem.  I guess I would look at the oil quality as more of an indication for when the oil should be processed.

RE: Maximum TDCG


This is exactly what I thought. Just wanted to confirm there was no point where the dissolved combustible gasses could become dangerous (explosion, fire, etc), even if their concentration is stable.

We did processed oil from several other transformers in the past because of their poor quality, but never had to do it only because of the gasses.

Thank you both for your answers!

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