Discussion of space-charge life model features in dc and ac electrical aging of polymeric materials

In this paper, the features of a thermodynamic life model for polymeric insulation, based on the effect of space-charge trapped within the dielectric, are investigated by comparing the application of the model to dc and ac life data obtained from accelerated tests. The changes of parameter values when the model is used to fit both dc and ac life data are pointed out and indications derived from the corresponding variations in activation enthalpy and entropy of the degradation process. This leads to a deeper understanding of the alteration of the aging mechanisms from dc to ac regime and suggests ways to achieve the formulation of a proper model valid for life under ac electrical stress.