Effect of charge accumulation on the surface discharge evolution for polyimide under high frequency sinusoidal voltage

The air-polyimide surface insulating system is regard as the weak point in high frequency power transformer, since the surface breakdown strength of the dielectric is much lower than its bulk breakdown strength. However, it still remains unclear regarding the deterioration mechanism of air-polyimide surface insulating system under high frequency sinusoidal voltage. In this paper, surface discharge evolution process and surface charge accumulation characteristic of polyimide film under high frequency voltage are studied by experiments. Firstly, in order to simulating the surface insulation defect in high frequency power transformer, a needle-rod type electrode surface insulation aging test platform was established. The evolution process of the surface discharge under the high-frequency electrical stress was discussed by analyzing the discharge parameters. Then, the surface charge distribution on polyimide film at different evolution stages of surface discharge were measured by electrostatic probe method. The spatial and temporal distributions of surface charge at different evolution stages were summarized. Finally, the study results of surface discharge evolution and surface charge distribution characteristics were comparatively analyzed to investigate the effect of surface charge on the surface discharge evolution.