Analysis on the Influence of the Switching Speed of Disconnector on Very Fast Transient Overvoltage

During the switching of the disconnectors in gas insulated switchgear(GIS),repeated strikes of the contact gap will lead to very fast transient overvoltage(VFTO) with high amplitude and steepness.Severe VFTO may damage transformers and other equipment.One of the important influential factors on VFTO is the switching speed of the disconnector,and there are still different opinions on this factor.In this paper the whole repeated strike process associated with the switching operation of the disconnector was simulated and analyzed.The polarity effect and the probability characteristics of breakdown voltage and residual voltage were analyzed.The impacts of the switching speed of the disconnector on VFTO were analyzed with the statistical method.Comparisons were made between simulation and measured results.The simulation result shows that within certain range of speed,disconnectors with low speed generate lower residual voltage after opening,and lower VFTO during opening and closing processes.