Coconut oil as transformer liquid insulation - Ageing and simulated thermal and electrical faults

This paper presents performance comparison of coconut oil as an alternative liquid insulation for transformer mineral oil during ageing and under simulated electrical and thermal fault conditions. In the ageing study, 6 wet coconut oil, 6 wet and 6 dry transformer oil samples were aged (each half as sealed and unsealed with inclusions of Cu, Al, Fe and Zn metal substances) inside an oven at 120°C. Six sample sets were taken out at three different ageing intervals i.e. 2, 5 and 7 weeks and were tested by visual inspection (color), chemical tests (interfacial tension, acidity, DGA) and electrical tests (breakdown voltage, FDS). In the electrical fault study, 2 coconut oil and 2 transformer oil samples were exposed to corona for four hours and for 20 electrical breakdowns with a point-plane gap of 15mm. In the thermal fault study, 2 coconut oil and 2 transformer oil samples were aged at 160°C for 12 hours and at 200°C for 1 hour. The DGA and FDS measurements were taken on the aged samples. FDS Results were analyzed by using Davidson-Cole Model. It was found that the coconut oil samples gave comparable results with those for transformer oil.