A study on flashover characteristics of supporting insulators in SF6 under lightning impulse

In recent years, SF₆ gas insulated switchgear (GIS) is increasingly widely used among the power system of China and the flashover characteristics on GIS insulator have attracted widely attention of many researchers. According to the previous research, it´s found that surface conditions of the insulators have a great impact on flashover voltage. In this paper, the influence of the surface roughness of the insulator on its flashover characteristics in SF₆ had been studied. A 1000kV standard lightning impulse (SLI) generator was constructed to study the influence of surface roughness of insulators on flashover voltage under SLI. 72.5kV supporting insulators with different roughness were obtained by polishing the surface with different mesh numbers of abrasive paper. A laser scanning confocal microscope (LSCM) was used to observe the roughness of the insulator. The results showed that the flashover voltage of insulator increases within the SF₆ pressure ranges from 0.1MPa to 0.4MPa under SLI and decreases with the increasing surface roughness. This phenomenon was analyzed in consideration of the surface area and adsorption. It´s also found that the roughness has a bigger impact on the flashover voltage under the negative SLI. The flashover voltage of rough insulator under negative SLI is higher than that under positive SLI, which is different from the flashover characteristics of the new smooth insulator.