ELECTRICAL LIFE THRESHOLD MODELS FOR SOLID INSULATING MATERIALS SUBJECTED TO ELECTRICAL AND MULTIPLE STRESSES - PROBABILISTIC APPROACH TO GENERALIZED LIFE MODELS

Probability distribution functions valid for solid insulating materials subjected to multiple electrical and thermal stresses, which show life lines tending towards electrical threshold, are presented in this paper. They are based on the Weibull distribution where the scale parameter is expressed by the threshold models proposed in Part 1. The probabilistic life models are checked on the basis of the results of life tests performed on different insulating materials, i.e., XLPE, composite Nomex-Mylar-Nomex, epoxy resin, polyimide. They provide the estimates of failure time percentiles at selected probabilities and stresses so that life curves at fixed failure probabilities can be drawn. These models should help in the choice of compatible thermal and electrical stresses for the design of insulation systems, apparatus and components.