Insulation properties and degradation mechanism of insulating spacers in gas insulated switchgear (GIS) for repeated/long voltage application

Gas insulated switchgear (GIS) has been increasingly being used in recent years and high reliability and rational insulation design are required. This research provided V-N characteristics (the dielectric breakdown voltage versus number of repetitions characteristics) regarding the internal insulation and creeping insulation of the epoxy spacer, which are the main insulation elements of GIS, in order to help set LIWV (lightning impulse withstand voltage) and SIWV (switching impulse withstand voltage). The insulation strength decreased the most when the lighting impulse voltage was applied to internal insulation of the spacer, however, taking the absolute values into consideration, it turned out that the impact of frequent surges is slight. In the experiment in which alternating current voltage is applied for a long period of time, it was found that there is no decline in the insulation properties even after the voltage is applied for the equivalent of 30 years when the electric field intensity is 12 kVrms/mm or less although the combination with the multiple lightning impulse application may bring about damages to the spacer insulation. The degradation mechanism caused by generation of micro-pits was also understood through simultaneous microscopic observation of the surface and of the interface between the electrode and epoxy