Life prediction of XLPE subjected to distorted voltages in presence of bush-like electrical treeing

This work is aimed at investigating the effect of voltage harmonics on electrical treeing inside cross linked polyethylene (XLPE). The study focus on the partial discharge (PD) activity associated to electrical treeing, which changes with the harmonic content of the supplied voltage. Different frequency components have been superimposed to a sinusoidal basic waveform and have been applied to suitable specimens. The same RMS voltage amplitude was set for all the considered waveforms. The inception and the growth of electrical treeing were monitored during short term aging tests; the breakdown of the specimens was selected as the endpoint criterion. Two parameters indicating the electrical stress intensity were considered in order to define life predictive models. PD measurements demonstrated to be a sensitive tool for the evaluation of the different stress due to harmonics.