Dynamic observation of dc surface charge dissipation for epoxy-resin/alumina composite

The low surface DC flashover voltage for the cone-type insulator has restrained the industrial application of high voltage apparatus especially for gas-insulated substation and gas-insulated transmission lines. However, the surface charge under DC, which produces uniform electric fields resulting in surface flashover under low direct voltage, are still not investigated clearly. In this paper, the dissipation characteristics of the surface charges are studied and the mechanism of the dissipation for surface voltage potential is discussed. The experiment sample is from a 550kV cone-type insulator of GIS with the surface shined by 220# sandpaper, and cut into the size of 140mm×40mm×4mm. 30kV was applied by a cylinder electrode for 10 minutes in atmosphere. To gain the dissipation characteristics of the surface voltage potential, several consecutive points along the insulator surface were chosen, and the voltage potential was detected continuously with an electrostatic probe after the voltage being removed. In addition, the overall surface potential was detected by sliding the probe along the surface of the insulator. The results showed that only negative voltage potential appeared along the surface when the voltage was applied. After the voltage was removed, the surface potential suffered great changes and positive charges were found “flooding” suddenly from both electrodes and moving towards the middle of the insulator surface with time. Only positive voltage potential was detected on the surface after more than 6 hours.