Experimental study on relationship between performance of surface flashover voltage and surface charging in a cylindrical insulating system

In a vacuum interrupter (VI), surface discharges are one of the obstacles for improving its higher voltage performance. To achieve higher voltages, it is important to improve the insulation performance of the vacuum interrupter VI, which is the part that interrupts the circuit. Since there is a close relationship between surface flashover and surface charges on the insulator in vacuum, it is necessary to understand the charging characteristics. The purpose of this study was to investigate how the surface charging due to AC voltage application causes the degradation of surface flashover performance, using a model sample of an actual vacuum circuit breaker. The model sample used in this study is a cylindrical insulator with a field relaxation shield ring inside to mitigate the electric field at the cathode triple junction. After applying an AC voltage of $45 {\mathrm {kV}}_{p}$ for 1 minute to the model sample, it was confirmed that occurrence rate of surface discharge rose in the high voltage test of lighting impulse voltage application. The same AC voltage was then applied for measurement of surface charging distribution on the insulator. The measurement of the charge distribution at this time showed that positive charge was formed near the tip of the shield ring on the applied side, demonstrating that the positive charge formed on the surface of the vacuum-side insulator is the cause of the dielectric strength degradation of surface flashover voltage.