The paper deals with the issue of grounding and protection of constellations of large generators. The occurrences of earth faults in the stator winding of the generator and in its constellation were considered. The criterion for choosing a resistor for grounding the generator star is presented, and the so-called 100% ground fault protection of the generator stator. The basic task of the protection in question is to act in the event of an earth fault in the constellation of the generator and in its immediate vicinity. The mentioned problem of grounding and protection of the constellation is presented on the example of the generator motor with nominal voltage of 15.75 kV and nominal power of 155 MVA in RHE Velebit.