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Switching operations in a gas insulated substations generate Very Fast Transient Overvoltages (VFTO) which are dangerous for the transformer and the system insulation because of their short rise time. Under special circumstances, the terminal overvoltages can arise close to the transformer BIL. The suppression of VFTO is very important in GIS systems. Different techniques are applied to 245 kV GIS Model. The simulation used ATP-EMTP package program to evaluate the VFTO at the sensitive points in GIS. The different results are compared to determine the effective mitigation method. The results show that the wave steepness and the amplitudes of VFTO can be reduced to about 1 pu with less oscillation frequency.