Generator protection from unbalanced currents

WHEN A GENERATOR is subjected to unbalanced short-circuit currents, a negative-sequence current (I2) is caused to flow in the stator windings, establishing a counter rotating flux that induces double-frequency rotor currents. The rotor currents flow in the surface parts of the rotor and cause detrimental heating. The generator is susceptible to varying degrees of damage depending on the magnitude of the negative-sequence current.