Insulation properties of SF6/N2 gas mixtures under high pressure and low ratio

SF6/N2 mixture has been used in gas insulation transmission lines (GIL) for years in order to reduce the use of SF6 gas in electrical industry. Considering the insulation performance and environmental effect, the SF6/N2 mixture in practical use of GIL is advised to ensure SF6 content as low as possible, which can reduce the use of SF6 to the most. However, the applicable lowest content of SF6 in the mixture still remains unknown. In order to investigate the optimization of SF6/N2 mixture as an alternative choice to SF6, this paper reports the insulation properties of the mixture with SF6 content from 10% to 40% and the pressure of 0.4MPa to 0.7MPa under 50Hz power frequency voltage, which can reach equal insulation performance to SF6 at 0.4MPa∼0.5MPa. The rod-plate and ball-plate electrode models are adopted in the voltage breakdown experiment, the sensitivity to uneven electrical field is obtained through the experimental results. The experimental results indicate that, in the absolute pressure range of 0.4MPa to 0.7MPa, the breakdown voltage of SF6/N2 increases linearly with gas pressure and presents a power function with SF6 content, the power index decreasing as filling pressure becomes higher. The filling pressure should increase 1.4∼1.8 times to reach similar insulation performance with SF6, and different content of SF6 is discussed.