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.