Proposal of a space-charge life model for electrical polymeric insulation aged under ac voltage

A new life model, able to predict the time-to-failure of polymeric insulation subjected to ac voltage and temperature, is developed on the basis of the effect of space-charges trapped within the dielectric. The model is derived from the dc one, recently proposed by the authors. The extension to ac relies on a fatigue mechanism. The variations of parameter values when the model is applied to both dc and ac life data obtained on the same material provide indications about the changes in the degradation mechanisms on passing from dc to ac electrical aging. The proposed ac space-charge model is applied to the results of accelerated life tests performed on Polypropylene films at room temperature and different values of supply frequency, from 60 Hz to 30 kHz, showing a very good agreement with the experimental data.