Influence of electrode surface roughness on the impulse breakdown probabilities of SF6

Abstract

The influence of the electrode surface roughness on the impulse breakdown probabilities of pressurized SF6 was examined in a coaxial cylinder electrode geometry (cylinder diameters 70/30 mm) for both polarities at a pressure p of 6 bara. The results show that (a) for both positive and negative polarity, an increase of the maximum height of irregularities Rmax of the inner electrode leads to a reduction of the breakdown electric field E prevailing at the inner electrode; (b) for negative polarity, the 1% breakdown field on the inner electrode is lower than for positive polarity; (c) for negative polarity, the standard deviation is smaller resulting in a bigger difference between the 50% breakdown probabilities for the two voltage polarities; (d) the experimentally obtained plots of E/p versus pRmax under constant pressure (6 bara) and Rmax variable (between 10 and 50 µm) are appreciably deviating from these obtained from a one protrusion theoretical model, especially at low values of pRmax, and the E/p shows a weaker dependence on pRmax than does the theoretical model. However, plots of E/p versus pRmax obtained under variable pressure (2–6 bara) and Rmax constant (about 15 µm) are in better agreement with the theoretical model.