Dissolved gas analysis of alternative fluids for power transformers

In order to detect incipient faults in mineral oil-filled transformers, dissolved gas analysis (DGA) is used. Meanwhile, there are alternative fluids that can be used such as ester-based transformer fluids that demand more precise dissolved gas measurements and modified or new ration criteria to allow fault detection and diagnosis. In order to find out the effects of alternative fluids on DGA, thermal tests of oil and oil/paper mixes have been conducted. In the case of the inclusion of paper, it caused an increase in the concentration of carbon monoxide and dioxide for a certain temperature, which indicate cellulose degradation in both mineral esters and oil. Meanwhile, in all samples, acetylene was found in both samples. It should be noted that acetylene is one of the main gases produced during low energy arc discharge faults. In addition, hydrogen, as being a key indicator for low-energy discharges, were found in all oils. Nevertheless, mineral oil had the highest generation rate while Midel had the lowest. Such results were then taken as inputs into DGA diagnosis based on the various standards used for the testing. Results show that for faults that involved overheating of oil, the key gas is ethylene while the dominant gas was hydrogen in all tests. The test confirms that carbon monoxide and dioxide are the key indicators of cellulose degradation in both ester and mineral oil.