Characterization of Space Charge Accumulation in Polyimide at Different Temperature

Dry flat-wave reactors are important devices in high-voltage DC transmission systems, and the reliability of their insulating materials is crucial to the safe operation of the equipment. Polyimide is widely used for turn-to-turn insulation of dry type reactors due to its excellent electrical and thermal properties. However, the high temperatures of the actual operating conditions can lead to the accumulation of space charge in polyimide, which in turn leads to localized electric field distortion and insulation degradation. In this paper, the space charge distribution of polyimide specimens at different temperatures (25°C, 50°C, and 75°C) was measured and the electric field distribution inside the dielectric was calculated using a space charge test system by the pulsed electro-acoustic method (PEA)with controllable temperature. The results show that with increasing temperature, the space charge accumulation increases, the migration depth deepens, and the local electric field distortion intensifies. These findings provide a theoretical basis for optimizing the turn-to-turn insulation design of dry-type flat-wave reactors and further improving the insulating properties of polyimide films under extreme application environments.