Study on the Influence of Disconnector Characteristics on Very Fast Transient Overvoltages in 1100-kV Gas-Insulated Switchgear

The very fast transient overvoltage (VFTO) generated during switching of the disconnector (DS) in gas-insulated switchgear (GIS) may threaten the insulation of electrical equipment. DS characteristics are important influence factors for VFTO. To study the influence of DS characteristics on VFTO in GIS, an experimental study was conducted in two established full-scale 1100-kV GIS test circuits. More than 1800 tests of switching of DS in test circuits were carried out. In one circuit, the effect of operating speed on VFTO amplitude and trapped charge voltage were studied by changing the operating speed of DS. The results show that the amplitude of the trapped charge voltage and VFTO decreases with a decrease of operating speed. Operating speed was proposed to be 0.5 m/s ~ 0.8 m/s to suppress VFTO. In the other circuit, VFTO characteristics were studied by tests under two connection ways of DS. One is that the moving contact is connected with the ac power source, and the other is that the fixed contact is connected with the ac power source. The results show that the connection way will affect the breakdown characteristics of the DS, and then affect the polarity of trapped charge voltage. However, the connection way has little influence on the amplitude of VFTO. The achieved results provide a reference for the design and optimization of DS in GIS.