Partial discharge tests using CIGRE method II

In this paper, the results of an experimental project on insulating materia l aging, performed in both Denmark and Italy, are reported. This study was concerned with partial discharge (PD) behavior at temperatures between 30 a nd 80 degrees C using CIGRE method II. The material tested was a commercial polymethylmethacrylate (PMMA) which was chosen not for its good dielectric properties but rather because much of its discharge resistance data at amb ient temperature is already well documented. A description is given of the theoretical and experimental methodology followed in this work. Mixed Weibu ll analysis techniques in terms of the PD amplitude and phase distribution characteristics were employed to distinguish the presence of different agin g mechanisms. Such a difference was observed at 30 and at 80 degrees C. At 30 degrees C the analysis inferred a single discharge aging process acting until breakdown, while at 80 degrees C the results suggested the predominan ce of a single the PD aging mechanism for the first half of the insulation life time; however, for the remainder of the insulation life time, an addit ional degradation mechanism was evinced.