Effects of surface “micro-holes” on the flashover properties of a disk-type ceramic-vacuum insulator

A surface treatment method is proposed which creates surface “micro-holes” to improve the flashover properties of large disk-type alumina ceramic-vacuum insulators operating under high pulsed voltages. This method eliminates residual surface flashover traces and recovers the insulation strength. A structure optimized ceramic vacuum insulator was treated with this method and tested using a high-voltage pulse modulator (600 kV, 100 ns). Experimental results show that this treatment can improve the insulation reliability greatly. Scanning electron microscope (SEM) and laser scanning confocal microscope (LSCM) were applied to investigate the influence of surface micro-hole on flashover properties. It was found that the width (W) and depth (D) of micro-holes greatly influenced flashover properties. A D/W ratio was introduced to explain the mechanism of this improvement. The surface micro-holes had the greatest beneficial effect on insulation strength when the ratio was between 1.2 and 2.0. A mechanism explaining the effect of surface “micro-hole” on the flashover properties was proposed. Simulation results of VSim-PIC code corroborate our observations and explanation.