Non-intrusive measurement of GIS barrier surface charging

Recently obtained results from both on-site measurement and laboratory investigations have conclusively shown that surface charging of insulators in an ac gas insulated substation (GIS) can lead to flashovers. Although it has been recognised that prevention of charge accumulation on insulators is crucial for dc GIS design, many normal operations in an ac GIS result in sections being isolated with standing trapped charges on the busbars. Under such situations, an ac GIS sustains dc stresses just like a dc GIS. This means that insulators in an ac GIS can also suffer from electric charging and the associated problems. This paper offers an outline and some preliminary results of diagnostic techniques based upon detecting electric field flux emanating from unshielded barrier rims