Study on Estimation of Lifetime of Transformer Oil in Service

Lifetime of a transformer depends on the age of its electrical components, liquid and solid insulation. So study on ageing of oil is equally important as that of the solid insulation. The oil under service is subjected to thermal and electrical stress. Presence of oxygen and moisture and contaminants act as catalyst to accelerate the ageing process. Oil is regularly monitored to assess the extent of ageing. It is also desirable to establish the remaining life of the oil at various point of time during its service period. In order to do that it is required know the rate of degradation of oil under operating conditions. It is well known that the operating conditions vary from one transformer to other and which is further infl uenced by the environmental factors. Due to these facts, the ageing of oil is considered to be a complex process. This suggests that the study to be conducted on large number of transformers in order to get a representative ageing characteristics. In the present study, a large number of oil samples drawn from power transformers of various age groups were analyzed. It is observed that deterioration of Interfacial tension and acidity is almost linear with service period and can fi nd application in assessing lifetime of the oil.