Transformer Oil Degradation

check this please

Transformer Oil Degradation

There are several reasons that you could have the dissolved gas levels increase & decrease over multiple samples. The usual cause of variation that goes up and down (if the tranformer is a sealed tank or conservator type) is that you are taking the oil sample while the transformer is at different oil temperatures each time. The solubility of gases in oil varies with temperature, and if you don't record the oil temp when you take the sample, the laboratory cannot compensate the DGA values for the temp variation.

Another possibility, if the transformer is free-breathing, is that it is generating methane and ethane, but the gases are coming out of solution and venting off to the atmosphere. Common cause of methane is general overheating of the transformer, and is usually accompanied by some increase in carbon monoxide as the paper insulation is oxidized. Ethane is usually caused by somewhat higher, more localized heating such as from a hot internal connection or because of corona / discharge within the tank. However, discharge also usually also causes an increase in hydrogen.

If the levels of methane and ethane are not higher than alarm limits, then just watch them over time. If they are steadily increasing, then eventually you will need to do an internal inspection to see if the source of the heating can be determined and corrected. If it is overheating due to load, then your solution is to reduce the load or cool the transformer better (add fans).

Thanks PeterT. You've explained alot. Our DGA reported that we may have overheating causing our problems. It was reported to us that general overheating would have produced temperatures between 150 and 300 degrees celsius but our maximum winding and oil temp have only reached 84 and 69 degrees celsius respectively. I will be noting from now on the winding and oil temps when we take samples. Also I wondering as we are a peaking plant and not a base load plant, would you expect differering results due to our cyclic operation?

Again thanks for your help.

Are the transformers yours or the utility? Are you seeing acetylene as well in the DGA. You don't say the levels as others have mentioned. Are you working with a transformer repair / inspection company at present and what are they saying.