Investigations Into the Stray Gassing of Oils in the Fault Diagnosis of Transformers

In this paper, we present an analysis of the gases generated by mineral oil and cellulose transformer insulation, at temperatures lower than those expected to be caused by an actual thermal fault. Gassing at relatively low temperatures, 100°C to 200°C, often presents a problem to the asset manager since it can be difficult to distinguish this event from that caused by an actual fault. Previous stray gassing tests were only performed for 164 h, at two temperatures, and two oxygen contents. We tested a mineral oil under 20 different conditions of oxygen and water content, for up to nearly 100 days. We found that at low-temperature levels and that by using high oxygen levels, the generation of ethylene can be more significant when compared to the other hydrocarbon gases than first thought.