Effect of surface deviation of solid insulation on impulsive flashover voltages under varying environmental conditions

In pulsed power engineering, the modification of dielectric surfaces is a potential method in order to increase the flashover strength of solid insulation. In this work, dielectric materials are subjected to a knurled finish, where small indentations are machined on to the surface resulting in quick consistent modification. These flashover voltages from the knurled dielectric spacers have been compared to spacers with a ‘smooth’ machined finish. The three materials which have been tested are HDPE (High Density Polyethylene), Delrin (Polyoxymethylene) and Ultem (Polyetherimide). The materials were tested under a 100/700 ns impulse voltage. Cylindrical spacers made of these materials were located in the center of a parallel-plane electrode setup in air, which provided a quasi-uniform field distribution. Breakdown tests published in this work were performed in a sealed container at air pressures of −0.5, 0 and 0.5 bar gauge, with relative humidity levels of <10% RH and >90% RH.