On the detection and control of metallic particle contamination in compressed GIS equipment

Metallic particles drastically impair the insulation integrity of compressed gas insulated substation (GIS) equipment. Such particles present a special hazard when in close proximity of support insulators. For GIS equipment to be reliable and economic, the problem of particle contamination should be overcome. Most GIS equipment manufacturers employ a variety of techniques and devices, such as electrostatic particle traps, to control metallic particle contamination. Conductors in gas-insulated systems may be coated with a dielectric material to restore some of the dielectric strength of the compressed gas that is lost due to surface roughness and contamination with conducting particles. Free metallic particles are a major cause of partial discharge (PD) in GIS. Several methods have been used in checking for PD activity. Recent diagnostic techniques include VHF and UHF-band PD detecting systems and ultrasonic vibration detecting systems. The methods used for the detection of pre-discharge caused by contaminating particles in GIS and the means of using this detection as a diagnostic tool for particle contamination are presented.