Three-Phase Fault Direction Identification for Distribution Systems With DFIG-Based Wind DG

Distributed generation (DG) integration necessitates upgrading some distribution system overcurrent relays to directional ones to offer selective protection. The directional feature is conventionally achieved by phase angle comparison between phasors of the fault current and a polarizing quantity, normally a voltage signal. Doubly fed induction generator (DFIG)-based wind turbines constitute an appreciable portion of today´s DG power. This paper unveils that conventional directional elements malfunction during three-phase short-circuits when a distribution system incorporates DFIG-based wind DG. The maloperation is due to the exclusive fault behavior of DFIGs, which affects the existing relaying practices. The paper also proposes a fault current classification technique that replaces the conventional directional element during problematic conditions and provides accurate fault direction quickly based on waveshape properties of the current. An extensive performance evaluation using PSCAD/EMTDC simulation of the IEEE 34 bus system corroborates the effectiveness of the proposed method. Results are exceptionally encouraging in the case of resistive crowbar circuits for DFIGs, which is the typical scenario in practice.