Overcurrent protection scheme for collector lines in wind farm based on fault component current correlation analysis and multi-agent system

Collector line relay failures of large-scale grid-connected wind farms have not received much attention so far. In this study, the adaptability of conventional overcurrent setting method is analysed when used in doubly fed induction generator-based wind farms, revealing the coordination difficulties between collector line relay and fuse protection of wind turbine (WT) branch as well as the potential maloperation causes of backup overcurrent relays (BOCRs). Then, a novel three-stage setting method of overcurrent relays is proposed. In view of time-bound instantaneous overcurrent relays, a time delay setting approach is put forward considering the time-current characteristic of fuses. Based on the multi-agent system, which is both flexible and effective, comprehensive criteria containing fault component current correlation analysis and differential current criterion are applied to BOCRs. The proposed scheme is validated by the simulation of 46-WT wind farm on DIgSILENT/Powerfactory platform. Simulation results show that the relay is able to trip within 0.32 s and the BOCRs perform well when confronting single fault or even multiple faults.