Creepage discharge propagation in air and SF6 gas influenced by surface charge on solid dielectrics

Influence of surface charging on creepage discharge propagation in air and [SF sub. 6] gas was investigated. We have employed a surface charging system using corona discharges, which permitted the deposition of surface charge on solid dielectrics with a given density distribution. By applying a lightning impulse across the charged surface of polyester film, we measured the discharge extension length as a function of surface potential generated by the surface charge. It was found that the impulse creepage discharges along the charged surface under a potential of 2 to 3 kV, extended a distance which was maximum 6x longer than the case of the uncharged surface both in air and S[F.sub.6] gas. Experimental results were also discussed from the viewpoint of the specific capacitance, permitting their application to actual HV apparatus such as GIS.