This paper introduces the stator ground fault protection trip caused by a typical ground fault in the voltage transformer circuit，resulting in secondary voltage fluctuation of the units in the same power plant.By analyzing the data of fault recorder and inspecting the secondary loops of the voltage transformer，the cause of protection trip is found out，which is proofed by PSCAD simulation，and the effective measures are presented as well.In addition，the problems of current grounding strategy for secondary circuit of voltage transformer are also discussed.