Why large alternator is grounded with large resistance?

Large capacity of alternators are typically provided with resistance grounding. High value of resistor is connected to the neural path to the ground. If the generator is delta connected, then it is grounded with the help of zig-zag transformer or (Delta-Star) transformer such that a high resistor is connected between the neutral point and the ground.

Resistance grounding is provided so as to limit the short circuit current flowing during earth fault to stator winding in order to provide protection against mechanical stresses and melting of winding during Line to Ground short circuit. In large generators fault current is limited as low as 10 to 15 amperes during short circuit.