A probabilistic life model for insulating materials showing electrical thresholds

A probabilistic life model for insulating materials showing lifelines for combined thermal-electrical stresses which tend towards electrical thresholds is proposed. The model is obtained by starting from the two-parameter Weibull distribution of times to failure, and explaining scale and shape parameters so that time-to-failure percentiles agree with life curves showing an upward curvature and a tendency to infinite life. The parameters of the probabilistic life model are explained as a function of stresses, thus providing a complete characterization of the combined-stress endurance and, hence, estimation of electrical threshold at each selected temperature, including service stresses. The validity of the model is verified by means of experimental results from a test cycle carried out on XLPE (cross-linked polyethylene)-insulated cable models