Simulation study on VFTO and its supressing methods in 500 kV GIS

Based on real GIS system and ATP-EMTP software,three different methods for suppressing VFTO were simulated,which were parallel resistor in disconnecting switch,parallel capacitor before main transformer and series inductance before main transformer.As simulation revealed,installing parallel resistors in disconnecting switches had the best suppressing effect on VFTO of all the three methods by apparently reducing VFTO and its wave-edge steepness;adding parallel capacitor before main transformer was effective but not so good as installing parallel resistors;installing series inductance before main transformer can protect the main transformer,but it may break down when VFTO emerges because of the steep overvoltage on it,making it infeasible in practice.