Influence of switching properties of the disconnector on very fast transient overvoltage

During switching operations of disconnectors in gas insulated switchgear (GIS), very fast transient overvoltage (VFTO) is generated due to multiple strikes across the switching contact. Switching properties, such as switching speed and trapped charge, have some impacts on VFTO behavior. In this paper, the VFTO caused by switching operations of a disconnector in a 252kV GIS was measured and analyzed with different switching speed. A position sensitive detector was employed for measuring the gap length simultaneously so as to get the variation of breakdown voltage with the gap length. Experimental results show that the highest VFTO magnitude was generated when the closing speed was 0.7m/s. Results also indicate the polarity effect of the breakdown voltage and the effect of the trapped charge. A simulation method for the VFTO associated with the whole switching operation of was proposed, in which these switching properties were taken into consideration.