A number of accidents of stator earth protection action due to inter-turn short circuit fault of voltage transformer's primary winding at generator terminal have happened in recent years

increasing the workload of troubleshooting. The formulas for phase voltages and line voltages relative to ground are deduced during inter-turn fault of voltage transformer's primary winding. The corresponding conclusions are obtained that

during the fault

the phase next to that of the zero-sequence voltage of the stator rising and being highest(relative to normal time)to the ground is the fault phase

and that the line voltage is constant. The correctness of theoretical analysis is verified by field recorded data. This paper also puts forward the thought of using the criteria for resistance of stator ground fault protection with injection voltage to distinguish between inter-turn short circuit fault of voltage transformer's primary winding and stator ground fault

providing a reference for rapid trouble shooting.