Performance of particle contaminated GIS with dielectric coated electrodes

Electrical insulation performance of compressed gas insulated switchgear (GIS) and gas insulated transmission line (GITL) system is adversely affected by metallic particle contaminants. Dielectric coatings help to improve the insulation performance in several ways. For example, it is known that dielectric coated electrodes in compressed gas give 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 particle contamination, the electrostatic particle charging is impeded and hence the maximum particle excursion in a coaxial GIS/GITL is significantly reduced for a given applied AC voltage. A simple particle charging model, however, has some significant shortcomings, for example, the charge exchange mechanism between the particle and the electrodes is poorly understood and very complex to model. In this paper, the dynamics of a wire particle in a coaxial GITL system with coated electrodes under AC voltage is studied using a computational algorithm. The possibility of SF₆ gas insulation breakdown due to the presence of metallic contaminants was computed at different applied voltages and gas pressures. Results of laboratory experiments conducted at Chalmers University to verify the computational outcome are presented