Movement of Metallic Particle in Coated and Uncoated SF6/N2 Gas Mixture GIB

Metallic particle contaminations impair the insulation integrity of gas insulated equipment. The contaminants can be produced by an abrasion between components during assembly or operations. These particles can either be free to move in the GIS bus or they may stick either to an energized electrode or to an insulator surface. In case a metallic particle crosses the gap and comes into contact with the inner electrode or if a metallic particle adheres to the inner conductor, the particle will act as a protrusion on the surface of the electrode. Consequently, voltage required for breakdown of the GIS may be significantly decreased. Diluted SF6/N2 mixtures could be a substitute to pure SF6 as insulation medium for high voltage gas insulated systems. They promise to have a lower environmental impact than a system insulated with pure SF6 for the same rating. The main issue concerning the practical use of such mixtures is their behavior in the presence of particle contamination. In this paper, particle movement is determined in both coated and uncoated gas insulated bus-duct (GIB) with Sulphur Hexafluoride (SF6) and Nitrogen (N2) gas mixtures as insulating medium on application of 175 kV switching impulse voltage. In the gas mixture, conducting particle material considered for this study is Copper and Aluminum.