Extended corona stabilisation in SF6/Freon mixtures

Some results are reported of static and impulse corona onset and breakdown voltage measurements in 10 mm point-plane gap in SF 6 mixture containing 0.5% and 1% by volume of Freon 113. It is found that the corona inception voltage in the mixture is higher than for pure SF 6 over the pressure range investigated (up to 4 bar) and that the corona stabilisation peak is greatly extended. Measurements of the minimum impulse breakdown voltage have shown that the improved stabilisation is associated with an increase in the leader propagation voltage in such mixtures. The results are of significance in connection with particle-triggered breakdown in commercial compressed-gas-insulated cables and sub-station equipment.