Observation of space charge distribution in thin insulating films using improved PEA system

Space charge accumulation behavior under DC stress in a thin polyimide film which is including filler added layers to improve its resistance against a corona discharge was investigated using an improved pulsed electro acoustic (PEA) measurement system. PD (partial discharge) in motors is one of significant problem to be resolved for improvement of its efficiency and operating life, and some newly developed insulating materials, which have a corona discharge resistance, are supposed to be used. However, the basic electrical performance of them as insulating materials under high electric stresses have not been confirmed yet. Especially, the space charge accumulation characteristics, which is said one of important factor governing the PD characteristics, have not been clear yet. Therefore, we tried to investigate the characteristics in one of the newly developed materials. The material is commercially available and it is made by giving the surface layers including inorganic fillers. However, since only a thin (25 μm-thick) film of the material is provided by the manufacturing company, we needed to have an improved PEA measurement system with high positional resolution because the ordinary PEA system had the resolution of more than 3 μm. We measure the space charge distribution in the material under dc high stress using the improved PEA measurement system with the positional resolution of less than 5 μm. We found that the charge accumulation characteristics are completely different from those observed in a film without the filler.