Insulation performance of 10% SF6/90% N2 mixture

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 breakdown behavior in the presence of defects (roughness, particles). In this paper, experimental data for breakdown of 10% SF₆/90% N ₂ mixture and pure SF₆ in the presence of oblong particles are presented and interpreted in the frame of discharge mechanisms in electronegative gases. To estimate the effect of roughness, streamer inception calculations for single protrusions are given for both gases. For oblong particle contamination the 10% SF₆ /90% N₂ mixture is found to reach about 65% of the insulation capability of pure SF₆ as is the case for defect-free electrodes. For typical roughness of 50 μm at pressures above 3 bar, the performance of 10% SF₆/90% N₂ mixture is about 90% of pure SF₆