very fast transient over-voltage generated by switching operations has caused more and more attention.In this paper a 750 kV GIS system has been set up referring to the Laxiwa substation.VFTO at the transformer terminal of different switching operations have been computated.The protective effects of shunt resistor of CB or DS
MOA
R-C surge suppresser and the connections of transformer to GIS have been studied
which provides useful reference for the safe operation of GIS and transformer.