CO in Transformer Oil

[unclebob]

Hi! Just a weird one. Is it possible to have more CO than CO2 when doing an DGA on a regular transformer oil? Possible causes?

Thanks all!

 

[Sargardani]

CO is normally the key indicator of overheated cellulose where as CO2 is the secondary indicator of overheated cellulose.

Both are also secondary indicators of Arcing if the fault involves cellulose.

Sarg

 

[electricpete]

Higher ratio CO/CO2 suggests the insulation thermal breakdown is occuring at a higher temperature.

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[alehman]

Was this a single test? If so, you should consider repeating the test. Are concentration of H2, CH4, C2H6 or C2H4 elevated? These are also indicators of heating. If they are all normal, it is possible you have a bad test or oil contaminated by other sources. If arcing is present, you would expect to see elevated C2H2 as well.

See

http://www.usbr.gov/power/data/fist/fist3_31/fist3-31.pdf

 

[electricpete]

The hydrocarbon gases come from oil heating. The CO and CO2 come from insulation heating. High ratio CO/CO2 suggest the insulation heating is occuring at higher temperature of the insulation.

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[electricpete]

Here is an excerpt from IEEEC57.104 1991 page 13.... does not exactly talk about temperature so maybe I am mistaken.

"...thermal decomposition of the cellulose insulation occurs at much lower temperatures than that for decomposition of oil and at rates exponentially proportional to the temperature. Because the paper begins to degrade at normal operating temperature in the transformer, its gaseous byproducts are found at normal operating temperatures in the transformer...."

"..The ratio of CO2/CO is sometimes used as an indication of thermal decomposition of the cellulose. The ratio is normally more than seven. For the CO2/CO ratio, the respective values should exceed 5000 and 500 to improve the certainty factor i.e. the ratios are sensitive to minimum values. As the magnitude of CO increases, the ratio of CO2/CO decreases. This may indicate that an anomly is occuring within the transformer"

I'm not sure exactly what it means except perhaps they place more emphasis on CO as an indicator of actual abnormal thermal degradation whereas CO2 levels may become high without an anomaly, especially for GSU type transformers which operate almost continuously at full load. Or maybe I am misunderstanding... draw your own conclusions.

I agree resample is always helpful and also can you tell us all the results?

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