Electrode surface roughness initiated breakdown in compressed SF6 gas

The effect of electrode roughness on the behaviour of a SF6 gaseous gap is studied analytically in this paper by introducing an elongated protrusion in the form of a fixed small conducting needle on an ideally smooth electrode surface. This effect is discussed by applying the streamer theory of breakdown. The breakdown characteristics for elongated protrusions on the coaxial electrode system under applied high voltage DC are presented. In calculating the breakdown voltage the effect of the space charge fields of the positive ions and the electrons are taken into account. The effect of needle radius and length on the electron avalanche size is also studied. Results are obtained for compressed SF6 for a wide range of geometrical parameters and gas pressures