A Simple Method to Derive Correlation Curves for Insulation Diagnosis

In insulation diagnosis it is essential to know the correlation between some nondestructive measurements and the residual breakdown voltage. All the nondestructive measurements should be translated to the assumed residual breakdown voltages with the aid of correlation curves. This paper discusses a simple method to derive the correlation curves. Model coils of epoxy-mica splittings insulation were subjected to voltage-endurance tests. Nondestructive tests were also conducted at alloted intervals during the voltage application. The change of the residual breakdown voltage with time was assumed on the basis of certain calculations. The measured nondestructive values were related to the assumed residual breakdown voltages at each time of measurement, and the correlation curves were drawn. In our previous paper [l], the correlation curves were derived from nondestructive and destructive test data of a number of aged coils. In our new method, we made use of only a few coils and were able to derive the same correlation curves.