Measurement and analysis of surface potential decay of polyimide films under high temperature

Accumulating of surface charge on insulation dielectrics will gradually cause electrical properties deterioration in the whole insulation system of electrical apparatus. In the field of high voltage technology in electrical engineering, polyimide (PI) occupies an utmost important position which requires insulating dielectrics to work in a steady condition under different working temperature of electrical equipment. In addition, for avoiding unexpected flashover events in high voltage apparatus it is necessary to understand the dynamic behaviors of the surface charge accumulation and decay. Thus, it is of critical importance to investigate the surface charge decay mechanism of polyimide dielectric under different temperature condition. This paper reports on the accumulating effect of surface charge on polyimide dielectric under high temperature. In order to investigate the effect of the temperature to the surface charge dissipation, the decay tendencies of the surface potential after corona discharge have been analyzed and compared under different working temperature. In the experiments, the surfaces of insulating dielectrics exposed to corona discharge system which were kept open to ambient air and high temperature whereas the opposite surfaces were in contact with a grounded copper plate and surface charge dissipation situation on the samples were measured continuously by using an electrostatic measurement system. It was found that the decay speed increased with the temperature rise. Beyond that, apparently, the elevated temperature weakened the effect of charge accumulation when we measured the surface potential of polyimide. The result shows that temperature has great influence on the performance of PI insulation material. Reducing the surface charge accumulation and speeding up the surface charge dissipation is the key to solve the problem which needs to be further researched.