The influence of various compounds on the ECT of insulating oil was investigated. The accelerated aging tests and the room-temperature addition tests were conducted with alkyl benzene with the addition of various compounds that are regard as being contained in mineral insulating oil in the brand-new condition or aged condition.
Remarkable increases of the ECT were not detected in the accelerated aging test of alkyl benzene. Remarkable increases of the ECT were also not detected in the room-temperature
addition test of alkylbenzene with various organic acid compounds that are produced by aging deterioration of hydrocarbon compounds. The deterioration of hydrocarbon compounds alone has only a small influence on increasing the ECT. On the other hand, the ECT changed in various tests of alkyl benzene with sulfur or nitrogen compounds that are regard as bei