Space charge accumulation characteristics in multilayered polyimide films under DC high stress

Space charge distributions in multilayered polyimide films under dc high stress was measured using pulsed electro acoustic (PEA) method. Judging from our previous research works, the space charge accumulated in a single layer polyimide film under dc high electric field is closely related to electrical breakdown. However, there is almost no example to investigate the space charge accumulation characteristics in the multilayered polyimide films. Since the multi-layered films are usually used for a printed circuit board of electronic devices or a cover layer of motor windings, it is necessary to investigate the space charge accumulation properties in the multi-layered films to improve the insulating system for them. In this paper, we measured the space charge behavior in multilayered polyimide films using the PEA method under dc high electric field at 80°C. Furthermore, we measured the conductivity in the multilayered polyimide films to analyze the space charge degradation process. From the space charge distribution measurements, we found that the insulation performances of the multilayered samples are better than that of the single layer sample. From the conductivity measurements, we found that the conductivity increased after the voltage application which generated the space charge accumulation.