The DC inclined-plane tracking and erosion test and the role of inorganic fillers in silicone rubber for DC insulation

The first polymer insulator for AC transmission lines was developed in the late 1950s. This insulator consisted of a flexibilized epoxy resin weathershed cast onto a fiberglass rod, and field trials on a 138-kV line took place in 1959. Insulators failed almost immediately on energization due to severe tracking and erosion of the bisphenol-A epoxy material, which was later, through inclined-plane tests, shown to be inherently unsuitable for use in outdoor insulation [1]. This article describes a study of the DC dry-band arcing mechanism as a foundation for the development of a standard DC inclined-plane test and its employment in the evaluation of silicone-rubber housing composites for outdoor DC insulation.