DC surface flashover characteristics of polyimide under low temperature and low pressure

The insulation system of superconducting power equipment often works under cryogenic vacuum environment. However, due to special cases such as material gas releasing and helium leakage, local low pressure environment is prone to be formed and this will lead to damage the insulation system so as to influence the normal operation of power equipment. Polyimide (PI) has been widely used as insulation material in various superconducting power equipments for its excellent dielectric performance and mechanical properties. In this paper, by using the home-made test system which is developed for testing cryogenic electrical characteristics of dielectrics, a series of tests for studying polyimide films´ DC surface flashover characteristics have been done at temperature range from 78 K to 300 K under low pressure environment. The test results show that the surface flashover times under low pressure environment have little influence on the DC surface flashover strength of polyimide films. In the pressure range of 10 to 2000 Pa, the flashover strength decreases with the pressure increasing, but the decrement becomes slow gradually. However, the flashover strength increases to a certain extent in the range of 2000 to 3000 Pa.