On the management of metallic particle contamination in gas insulated switchgear

Electrical insulation performance of compressed gas insulated switchgear (GIS) is adversely affected by metallic particle contaminants with a loss of up to 90% of the gas dielectric strength. Such particles play a crucial role in determining the system insulation integrity. Coating of the inside surface of GIS enclosures with a dielectric material such as epoxy resin can alleviate the adverse effect of contaminating metallic particles on the insulation, as the coated electrodes in compressed gas result in a somewhat higher breakdown voltage. Such coatings have the effect of "smoothing" the surface and reducing the pre-breakdown current in the gas gap. Also, in the presence of metallic particles, the electrostatic particle charging is impeded; hence, the maximum particle excursion in a coaxial GIS is significantly reduced for a given applied AC voltage. In this paper, the effect of the dielectric coatings is analyzed with a theoretical model which is confirmed in the high-voltage experiments. The results show the effectiveness of dielectric coating in mitigating the contamination due to the particles. The influence of other factors such as gas pressure and particle size are also discussed.