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Abstract

This paper focuses on rotor protection for wound-rotor asynchronous generators, often referred to as doubly fed induction generators. This paper introduces and explains a new kind of differential protection element that balances ampere-turns between the stator winding and the rotating rotor winding. Because the differential element monitors ampere-turns, it is capable of detecting both turn and phase faults in both of the windings. The presented differential element uses only currents and requires neither the stator and rotor voltages nor an encoder for the rotor position. The differential element is instantaneous and can operate on the order of one to two power cycles.