The Impact of the Transfer Voltage with Grounding Faults on Generator Grounding Relays

When the grounded system for high voltage system get out of order,zero sequence voltage of fault is transferred to the generator by the coupling capacitance of step-up transformer,then virtual grounding of generator stator is existing.This paper calculate the grounding zero sequence voltage of high voltage single phase and two phases used for 2×300MW power plant,calculate the transition voltage to generator by approximate equivalent circuit,and check setting value of grounding protection.Finally,propose the scheme to avoid the misoperation of grounding protection caused by transfer voltage.