Flashover of smooth and knurled dielectric surfaces in dry air

In pulsed power engineering, solid spacers are used to insulate high voltage parts from extraneous metal parts, providing electrical insulation as well as mechanical support. The breakdown/flashover voltage, at which a discharge process initiates across the solid/air interface, is important in the design process, as it informs designers of specific threshold ‘failure’ voltages of the insulation system. In this paper, a method to potentially increase the failure voltage, tested under multiple environmental conditions, without increasing the length of the solid spacer, was investigated. Three dielectric materials: HDPE (high-density polyethylene), Ultem (polyetherimide) and Delrin (polyoxymethylene), were tested under a 100/700 ns impulse voltage. Cylindrical spacers made of these materials were located in the centre of a plane-parallel electrode arrangement in air, which provided a quasi-uniform electric field distribution. Breakdown tests were performed in a sealed container at air pressures of -0.5, 0 and 0.5 bar gauge, with a relative humidity (RH) level o