Zone partitioning protection strategy for DC systems incorporating offshore wind farm

Abstract

This study proposes a zone partitioning protection strategy for DC systems incorporating offshore wind farm. Regarding a DC system which consists of multiple local zones with radial topology, a multi-port DC hub is introduced to serve as firewall between different zones. By blocking the converter with DC fault blocking capability in the corresponding DC hub port, the fault can be prevented from spreading among zones. On the other hand, an inter-zone protection centre is designed and built in the DC hub to implement the continuous operation under the situation of any port outage. Furthermore, in every local zone, the hybrid DC circuit breaker is installed in each branch at the side near the star point in order to isolate the faulty branch quickly and selectively via installing the smoothing reactor at the other side to restrict the fault current. Especially, a zone protection centre is designed and built in the star point of each zone to implement the fault detection and fault isolation. A detailed model of the DC system with the proposed protection strategy is built under PSCAD/EMTDC™ environment. Simulation results under different operating conditions demonstrate the feasibility and validity of the proposed strategy.