Abstract: Based on the recorded wave data of a 220 kV line grounding fault in a power plant, the fault characteristics of equipment in each of its units are analyzed. The grounding short circuit current in the relay protection setting calculation sheet is checked by using the recorded wave data. The characteristics of fault current for each unit are calculated and analyzed. The problem is found out that the neutral point zero-sequence voltage transformation ratio of the stator grounding protection of two generators is inconsistent, and analyses are conducted on the influence of a system grounding fault on 400 V plant equipment, etc.