Research of VFTO in 110kV minimized GIS

110kV minimized gas insulated substation (GIS) has been widely used in China, due to its great electrical properties. The closing or opening operation of disconnector switches (DS) and circuit breaker (CB), and single-phase ground fault are all probable to cause the very fast transient overvoltage (VFTO), which is a threat to the power system. Compared to the structure of higher voltage GIS, three-phase electrical equipment in 110kV minimized GIS is placed in the same box. So we must establish the three-phase model of GIS and then calculate its VFTO. This paper referred to 110 kV minimized GIS power system. Using the Electro-magnetic Transient Program (EMTP), numerical simulation and analysis of VFTO in different DS, CB operation modes and single-phase grounding fault were carried out. And the data of VETO under different operation modes, including the frequency, amplitude, steepness and waveform were obtained. Then it calculated and analyzed the influence on VFTO of length of branch bus and transformer entrance capacitance, in order to provide reference basis to the structure design of GIS and analysis of VFTO.