Life testing of solid insulating materials

1) The lifetimes of sets of identical samples of solid insulation, aged by electric stress, can be successfully modelled by the Weibull distribution provided the lifetimes are measured from a common time origin. The history of the samples, the cumulative exposure of each sample and the way the exposure was accumulated have no effect on the applicability of the Weibull distribution. 2) The first conclusion has been supported by accelerated ageing experiments on polyethylene and by service life data for transformers. 3) This result can be very useful in predicting the future performance of the electrical insulation in electric power systems because the history of transformers, cables etc. may vary widely and may be unknown.