With the ever-increasing integration of wind power into the distribution network (DN) in the form of distributed generations (DGs), the optimal application environment for the conventional three-stage overcurrent protection no longer exists. Meanwhile, a majority of advanced protection schemes cannot be implemented due to the lack of voltage information and weak communication conditions in DN. As the most typical wind-based DG used in the DN, the doubly fed induction generator (DFIG)-based DG is focused in this paper. First, the frequency and amplitude characteristics of the fault current supplied by a DFIG-based DG are studied. Then, the amplitude differential protection (ADP) scheme is described using the weak-infeed characteristics of the DFIG-based DG. Furthermore, the frequency spectrum index, which is constructed based on the different frequency characteristics of DFIG-based DGs from synchronous generators, is introduced as a regulator factor to further improve the sensitivity of the ADP. Since only the current amplitude information is needed and the strict synchronization of the sampling data at the two ends of the line is not required, the proposed scheme is easy to implement under the limited hardware conditions in present DN. The simulation results show that the proposed scheme has a high sensitivity to the internal faults and has absolute selectivity for external faults, especially under the existing DG permeability rules. INDEX TERMS Distribution network (DN), distributed generations (DGs), doubly fed induction generator (DFIG), amplitude differential protection (ADP), weak-infeed characteristics, frequency spectrum index.

With high sensitivity and strong tolerance capability for the fault resistance, the fault component-based directional relay (FCBDR) has drawn considerable attention from industry and academia. However, the best application environment for FCBDR no longer exists when considering the large-scale connection of the doubly fed induction generator (DFIG)-based wind farms. Through a detailed analysis of the superimposed impedance of DFIG, this paper reveals that the performances of FCBDRs may be shown negatively impacted by the fault behaviors of DFIG when the crowbar protection inputs. In addition, this paper proposes a mitigation countermeasure to deal with those issues. The proposed countermeasure takes advantage of the different superimposed impedance features of DFIG compared with that of the synchronous generator (SG) to enhance the adaptability of the conventional FCBDRs. Extensive simulation results show that the proposed countermeasure can differentiate the fault direction clearly under different fault conditions.

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