A study of charge accumulation and spacer flashover in compressed gas insulation

Compressed gas insulated substation (GIS) and transmission line (GITL) equipment have been developed rapidly throughout the world during the past decades. Compactness is the main advantage of GIS and GITL over conventional air-insulated substations and transmission lines. Sulphur hexafiuoride (SFQ) is used as an insulation gas in GIS and GITL because of its excellent insulating properties. Supporting spacers are identified as the most likely places for flashover to occur and they often determine the overall strength of a system. For energized system, surface charges have been observed on spacer surfaces and are considered to play an important role for anomalous flashover of a GIS or GITL system. The purpose of this research is to study the mechanisms and factors governing the magnitude and distribution of surface charges and their influence on flashover voltage. In this investigation, experiments to study surface charge accumulation under different experimental conditions have been conducted, with a rod-spacer-plane electrode system. The parameters varied are applied voltage levels, insulating gases, gas pressures, spacer materials, rod electrode diameters, and the duration of applied voltages. Experiments with impulse voltage pre-charging were also conducted. It was found that the mechanisms of surface charging are corona, gas conduction, and photoionization. Surface charge magnitude and distribution

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