On investigation of PD aging of epoxy resin under distorted voltage

The first results of a research program carried out in Palermo University, dealing with the degradation mechanisms of epoxy resins due to partial discharges (PD) under 50 Hz distorted voltage, are presented. Accelerated life tests were performed until breakdown, measuring PD evolution with time in an electrical grade epoxy resin and making use of a standard Cigre´ II cell. The tests were performed on samples of five specimens and using an harmonic voltage superimposed to the fundamental 50 Hz component. The long term goal of the research is to scan either different effective voltage amplitudes and different frequencies and phase values of harmonics having different amplitude percentage, in the range of those usually recorded in electrical plants, e.g. up to 11th harmonic. Actually, a test session of 10 kV effective is going to be completed in terms of sinusoidal and distorted voltages. Either reduction or increase of lifetime, with respect to the sinusoidal conditions, were detected dependently on the way as the harmonic voltage is summed up in consequence of its phase angle value. In particular, significant life shortening was obtained in the cases when voltage maximum is increased. Further comments on the subject are finally presented.