The role of electron pin-holes in surface flashover

It has long been recognised that the prebreakdown currents observed with vacuum-insulated HV gaps stems from a highly localised process in which the surface potential barrier of the metallic electrode is electronically "perforated" to form an electron pin-hole. Subsequently, it was established that such pin-holes are associated with the presence of micron-sized particulate structures on an electrode surface. More recently, studies of the prebreakdown-to-breakdown transition of vacuum gaps that are bridged by ceramic insulating structures have indicated that the a similar localised electron injection process occurs at the cathode triple junction, and is responsible for triggering the optical and electrical signatures of this type of insulating regime