Impact of Short-Circuit Impedance Model for Variable-Speed Wind Turbine Generators on Operation of Overcurrent Relays

This paper discussed different short-circuit impedance models for type 3 and type 4 wind turbine generators. IEC and IEEE-PES models are either simplified or they require additional data. The proposed model is given by a non-linear dependency of the short-circuit impedance and voltage on the medium voltage side of the unit transformer. Furthermore, the proposed model, as well as the constant impedance-based model were used for timing coordination of overcurrent relays in a radial 6-bus network. The obtained results show that the constant impedance-based model overestimates short-circuit currents. Consequently, selectivity of individual overcurrent relays might be questionable.