Life models for insulating materials and systems with electrical life lines tending to threshold

Electrical life models for insulating materials and systems, subjected to electrical and multiple thermal-electrical stresses, are presented. The models, based on both exponential and inverse-power relationships, describe life lines which show upward curvature and then tendency toward threshold. Fitting of experimental results is verified by resorting to data collected for several insulating materials, subjected to accelerated life tests at different temperatures, as well as insulation systems, such as capacitors and cables. A procedure is presented to achieve generalized probability distributions which allow, on the basis of the chosen life model, failure-time percentiles to be estimated. Life models are generalized in the temperature domain by expressing the dependence of their parameters on the thermal stress