Based on the analysis of a typical stator ground fault and its recording data

the protection action is proved to be correct. From the data it can be found that when the fault locates far from the start point

the earth impedance decreases quickly during arc-burning and the zero sequence voltage increases rapidly at the same time

and the relays switch off the fault in time. This paper analyzes and compares the principles of stator ground fault protection with voltage injection and the 90% ground fault protection with zero sequence voltage. The concept of measuring ground fault relay is proposed to improve the sensitivity

speediness and reliability of protection. In addition

the health of the stator can be evaluated.