Interdependence of thermal and electrical stresses on initiating degradation of transformer insulation performances

Decisive purpose of transformer oil is to provide effective insulation and cooling to ensure satisfactory performance of the transformer. In practical operation, the transformer experience several stress evolving conditions due to combined thermal and electrical stresses. Both thermal and electrical stresses lead to degradation of oil performance interms of poor dielectric strength and ineffective cooling action. In this proposed work, the intention is to analyze the variation of conduction current through oil and the rate at which the oil absorbs the heat injection. From the measurement of conduction current after thermal stress, it is evident that the oil degradation is appreciable as the current variation is associated with intense discharges. The measurement of temperature rise in oil, after subjecting it to electrical stress conditions, clearly shows that there is an appreciable reduction in the cooling property of oil. Therefore, the influence of thermal and electrical stress diminishes the transformer oil from serving its two folded purpose.