In a Gas insulated substations, the operation of disconnector switches and circuit breakers can cause Very Fast Transient Over voltages (VFTOs), which will bring an instantaneous change in voltage with a very short rise time and it is normally followed by oscillation having high frequencies. For designing the insulation level of a substation, it is essential to know the maximum value of VFTO. Fast operating disconnector switches are usually used to reduce time of the breakdown; however, it cannot eliminate fully the effect of the VFTO. This Book results the most accurate results of Very Fast Transient over Voltages of 132 KV transformer caused by the switching operation. A 132KV transformer is designed using EMTP-RV simulin, the VFTOs generated by the switching operations have been analyzed and are presented. The VFTOs generated due to Disconnector switching operation can cause insulation failure at very high voltage levels. The reasons of these problems are travelling waves which is generated during switching operations in a gas-insulated substation (GIS). Calculation of Very Fast Transient Overvoltage has been carried out using EMTP-RV for various switching.