Dielectric strengths of CO₂ and N₂ containing SF₆ under alternating voltage in non uniform field

At present work AC breakdown strengths of N₂, CO₂, SF₆ and the mixtures of SF₆+N₂ and SF₆+CO₂ containing 20, 10, 1% of SF₆ in non uniform field were experimentally studied. The rod-plane of 5, 15 and 25 mm gap spacing was used as an electrode system. The relative gas pressure was varied within the range of 100-500 kPa. The experimental results have shown that addition of SF₆ to CO₂ and N₂ can significantly increase the AC breakdown voltage with respect to CO₂ and N₂. Especially within the pressure range of 150-300 kPa, the breakdown voltages of some of the SF₆+CO₂ mixtures are higher than that of pure SF₆. For example, the breakdown voltages of 20, 10% SF₆ mixtures for 25 mm gap spacing are about 2.4 and 2.8 times those of CO₂ and N₂ respectively at a pressure of 200 kPa. In the case at 25 mm gap spacing, mixtures with 1% of SF₆ content have breakdown levels same as the corresponding values in pure CO₂ and N₂ gas pressure in excess of 400 kPa and 350 kPa respectively.