The effect of electrode roughness on the behaviour of a SF6gaseous gap is studied analytically in this paper by introducing anelongated protrusion in the form of a fixed small conducting needle onan ideally smooth electrode surface. This effect is discussed byapplying the streamer theory of breakdown. The breakdown characteristicsfor elongated protrusions on the coaxial electrode system under appliedhigh voltage DC are presented. In calculating the breakdown voltage theeffect of the space charge fields of the positive ions and the electronsare taken into account. The effect of needle radius and length on theelectron avalanche size is also studied. Results are obtained forcompressed SF6 for a wide range of geometrical parameters and gaspressures
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