Improved Blocking Scheme for CPL Current Protection in Wind Farms Using the Amplitude Ratio and Phase Difference.

Large-scale wind generators connected to a power system turn the collector system into a multi-power wind farm network. With increasing fault current supplied by wind generators, the collector power line (CPL) current protection may lose selectivity. Directional elements are widely used to block the CPL current protection. However, wind generators are different from synchronous generators. The reliability and adaptability of traditional directional elements used in wind farms have not been well researched. For this reason, the fault current characteristics of doubly fed induction generators (DFIGs) are first analyzed in different low voltage ride-through (LVRT) strategies. It is concluded that the traditional directional elements may be insufficiently sensitive or malfunctioning to block the CPL current protection in wind farms. Hence, constructing the amplitude ratio and phase difference-based directional blocking scheme is proposed in view of the DFIG weak-feed. The proposed scheme, based on the system side and CPL current, is easy to implement and suitable for the application. Finally, the simulation of a DFIG-based wind farm system with the four CPLs is carried out with MATLAB/Simulink. The simulation results show good preference, strong adaptability, and high reliability for the proposed method, and the validity is demonstrated.