Damage be divided into two: one is a good set of stator shielding, and the occurrence of stator windings, the breakdown phase, the coil turn-to-turnshortcircuit, overload caused by burnt windings.
Based on the analysis of AC impedance and two poles voltage test data, the reason of turn - to - turnshortcircuit fault caused by having copper dregs in generator rotor winding was found.