Abstract: The configuration and working principle of stator grounding protection of a 650 MW steam turbine unit is described, and setting calculations are made on the grounding resistance of neutral point grounding transformer, current transformer at the secondary side of grounding transformer, injection-type and dual frequencytype stator grounding protections, and the on-site commissioning methods of protection are summarized. The commissioning results show the accuracy of the setting values and the reliability of protection device actions,which offers reference for the setting calculation of the same type of protection and selection of generator-related equipment.