Comparison of different methods available for evaluating remaining life of OIP insulation used in power transformers

This paper provides an analysis of various methods for estimating the remaining life of in-service power transformer. Degree of Polymerization (DP) value is perhaps the most effective parameter for determining the remaining life of an Oil-Impregnated-Paper insulation system. Due to the invasive nature of the test, DP value determination using paper samples is not practically feasible for in-situ transformers. On the other hand, commercial equipment's make it relatively easy to obtain the values of paper-moisture and tanδ. Hence, these parameters have become popular among utilities. In the present paper, paper-moisture and tanδ are used to obtain several important dielectric properties (like tensile strength, Degree of Polymerization, hotspot temperature) which are subsequently used for estimating the remaining life of several real-life power transformers. Efforts are also made to identify the method which is capable of identifying remaining life of power transformer with minimum error.