Partial discharge patterns and degradation diagnosis in polyethylene and polyimide

The temporal change of partial discharge (PD) pattern (φ-q-n pattern) was measured up to breakdown for both polyimide (PI) and low-density polyethylene (PE) films with CIGRE Method-II electrode system by using a prototype computer-aided PD measurement and expert system. As a result, the amount of adsorbed water, the humidity and the gas constituent in the gap proved to heavily affect the temporal change of PD patterns. It was suggested that these results were interpreted in terms of the electron attachment-detachment process of both oxygen and moisture, which led to an increase of the discharge time lag. The frequency acceleration by a factor of 3 proved that the temporal change of PD patterns was invariable under certain conditions