GIS barrier modelling and the effects of surface charge

Gas insulated substations (GIS) use pressurised SF₆ as the primary insulating medium, with the electrical conductor being held concentrically within bus-ducts by support barriers. These barriers are usually conical in shape, although disk and post are occasionally used, and are normally manufactured from a cast epoxy resin. Conical barriers have the advantage of a long creepage path while introducing little distortion to the electrical field distribution under AC conditions. Under DC conditions conical barriers do not perform as well. The presence of charge on the surface of GIS barriers has been shown to reduce the DC flashover voltage of the barrier. This paper discusses how the field distribution is altered under such conditions