SF6 breakdown in GIS

SF₆ gas breakdown and spacer surface flashover volt-time characteristic curves were established for a GIS of D/d=55/25 (15 mm gap) and D/d=45/25 (10 mm gap) for 1.2/50, 0.5/50, 0.2/50 and osc/50 (1.64 MHz) μs impulse and disconnector induced VFT voltages. VFT volt-time curves established using actual breakdown voltages against actual time to breakdown were found to give a better representation of the dielectric performance, and thus are recommended for future applications. Highly inhomogeneous field geometries, such as particle contaminated gaps, caused downward turning of the v-t curves during VFT breakdowns at short times to breakdown