Review of statistical testing of solid insulating materials

Different statistical methods used for the determination of the insulation characteristics of solid insulating materials are reviewed. Experimental results reported in the literature indicate that the breakdown probability of the test voltages is a function of the test method, of their parameters, and of the nature of the breakdown probability function. The application of statistical methods to establish the insulation strength and lifetime is described. Techniques for determining withstand voltages of electrical insulation and for determining the low probability of breakdown of solid insulation from critical flashover data are discussed. The application of the Weibull distribution for the description of breakdown data is examined. It is noted that great care must be used in interpreting statistical test results, due to the flexibility of low-breakdown-probability test methods. Example test results are presented for three groups of epoxy specimens