Effect of electrode shape on particle-initiated breakdown in SF/sub 6/ gas under DC voltage

Three methods are presented for improving the particle-initiated breakdown voltage of a spacer in sulfur hexafluoride (SF/sub 6/) gas: the metal insert, recessed electrode, and shield ring methods. To find the basic method for improving the withstand voltage of the spacer, electrode shapes are changed and electric field calculations on these shapes are performed by using a cylindrical spacer. The distribution of charge accumulation on its surface was observed using the dust figure technique. The effect of electrode shape on the flashover voltage when a metallic particle is located on the spacer in SF/sub 6/ gas under DC voltage was investigated. Experimental investigations show that the change of electrode shape leads to improvement of breakdown voltages by 30.9% in the metal insert method, 33.8% in the recessed electrode method, but very little in shield ring method.>