In gas insulated substations (GIS), very fast transient over voltages (VFTO) are generated due to disconnector switching operations, disconnector switches (DS) are primarily used to isolate the operating sectioning of HV insulation from each other as safety measure, vary fast transient over voltage(VFTO) at an insulating flange are generated due to propagation of VFTOs on the conductor of a gas bus in GIS. Generation of VFTOs cases sparkovers across the insulating flange of high pressure oil filled cable/GIS interface. The ionized path formed by spark over creates low impedance path for power frequency fault current due to disconnector switching, resulting in flange damaged with serious consequences. This paper deals the generation of VFTOs across the insulating flange and suppressions of VFTOs with shunting bars, capacitors across the flange for the providing potential have been analyzed and reported in MATLAB 7.0.