Surface Flashover Characteristics of Modified Polyimide Under DC Voltage in Vacuum

Direct current(DC) surface flashover characteristics of modification technology on polyimide(PI) in vacuum are investigated accompanied with the theoretical analysis.Two kinds of semi-conductive powders(nano scale and micro scale) are chosen as the modifier of raw PI,and the experiments for DC surface flashover characteristics of PI material in vacuum(10-3 Pa) are carried out.Meanwhile,the surface flashover mechanism under DC voltage in high vacuum is analyzed following the test results of secondary electron emission(SEE) coefficient and the observed surfaces state of flashover experimented samples by scanning electron microscopy(SEM).The experimental results show(1) In vacuum,DC surface flashover voltage of nano modified PI which used nonlinear conductivity filler is higher than pure PI,while that of micro modified PI is lower than pure PI;(2) The surface SEE coefficient of nano modified is reduced and the roughness of surface is increased;(3) Gas overflow phenomenon appears in the moment of prebreakdown.In combination with the results of SEM and physical analysis,it is considered that the nano modified composite sample has a lower electron-stimulated desorption coefficient,thus leading to gas desorption,is the key factor affecting DC surface flashover voltage in vacuum.