Electrical life threshold models for solid insulating materials subjected to electrical and multiple stresses. I. Investigation and comparison of life models

In the paper, life models, are collected valid for solid insulating materials subjected to electrical and multiple thermal-electrical stresses whose life lines show a tendency to reach an electrical threshold. Their fit is investigated with reference to several sets of data derived from accelerated life tests performed on different insulating materials (XLPE, composite Nomex-Mylar-Nomex, epoxy bisphenolic resin, polyimide). In particular, two phenomenological life models, characterized by four parameters and based on exponential and inverse-power relationships, are compared with three-parameter life models taken from the literature and derived considering different aging and breakdown mechanisms. Discussion of the ability of these models to provide significant parameters for insulation endurance evaluation and electrical system design closes the paper.