Effect of charge injection on DC surface flashover performance of polyimide

Polymers such as polyimide (PI) are easy to initiate surface flashover phenomenon in space environment. The surface flashover phenomenon in an extremely low DC electric field of PI material is a key factor restricting the spacecraft power system insulation strength, which is also a bottleneck problem for developing the spacecraft with high voltage and high power. In order to reveal the charge injection effect on surface flashover performance, the PI/ZnO composite sample was prepared by blending physical-chemical method and the DC surface flashover testing system was established. The charge injection was obtained by pulsed electro-acoustic (PEA) method. Experimental result showed that the DC surface flashover voltage of PI/ZnO nano-composite is enhanced and the flashover voltage of PI/ZnO micro-composite is reduced compared to that of pure PI. The results show that the space charge accumulation in the bulk of nano-composite is suppressed. The experiments results can be explained as that the PI/ZnO nano-composite material has an excellent space charge suppression characteristic which owned less positive space charge packet near the cathode compared to the pure PI material, causing the reduction of the local electrical field at the cathode triple junction (CTJ). In addition, electrons and positive ions due to impurities ionization are limited in the interface regions as a result of low carriers mobility and kinetic energy. Thus the surface flashover voltage of nano-composite is promoted. The PI/ZnO micro-composite has a definite space charge suppression characteristic, whereas has macroscopic defect for introducing larger particles of ZnO inorganic additives. This will promote the distortion of the electric field near the particles and further reduce the flashover voltage.