Effects of Irradiation on Surface and Space Charge Behavior of Polyimide Film for Superconducting Magnet Insulation

摘要

Polyimide film is widely used as the insulation material in high-temperature superconducting devices considering its excellent insulation performance at low temperature. Irradiation will cause changes in the molecular chain structure of the material and affect charge behaviors. While operating, the accumulation of charges can accelerate partial discharge and insulation aging. In this paper, different doses of high-energy electron beam irradiation were applied to polyimide films. Charge and discharge behaviors were investigated at room temperature and in liquid nitrogen. Experimental results show that the trap density of the specimen increases with the increase of irradiation dose and the irradiation mainly causes the increase of deep trap density. Higher density of traps results in more serious charge accumulation and lower partial discharge inception voltage, which is mainly caused by electric field distortion and difference in permittivity of the solid and liquid.