Determination of the thermal aging factor for life expectancy of 550 kV transformers with a preventive test

It is feasible to survey actual performances of degradation for 550 kV transformers by a preventive test. By means of condition monitoring, it is possible to forecast the transformers' lifetime. Such data, particularly in an application where few or no failures are expected, can provide considerably more information than the failure-time data from a traditional accelerated life test. In order to develop a life model for 550 kV transformers, the effect of temperature on a thermal aging factor is taken into account since it is associated with various degradation performances of a transformer. With the aid of measurement, the thermal aging factor is analysed by the probability plot and the least-squares fitting of data so that all unknown parameters of the life model are estimated. The method will extrapolate the lifetime of large power transformers from a preventive test in practice.