Method for Estimating the Thermal Life Expectancy of Distribution Transformers

The thermal life expectancy of a transformer insulating system can be estimated by analyzing the load cycle supplied by the transformer. By using the thermal and electric characteristics of the transformer, winding hot-spot temperature can be determined throughout the loading cycle and translated into aging data by means of aging curves applicable to the given insulation system. Application of this method of analysis to typical residential load cycles shows that significant thermal aging is confined to a relatively small portion of the annual load cycle and that load factor as well as peak load is important in determining life expectancy.