Fault Analysis and Protection of a Series-DC Collection and Transmission System

Series-dc collection and transmission is suggested to be competitive for remote offshore wind farms. However, severe overcurrent, overvoltage, and other impacts that arise from faults cause challenges on system protection, which have not been fully studied yet. In this paper, simplified equivalent circuits are developed for fault analysis, based on which analytical models for fault transients are derived. The expressions can be used for stress estimation, as well as provide insight in understanding the mechanism of fault propagation. A cost-effective protection scheme characterized by a breakerless design is proposed. Parameter selection for stress mitigation is also discussed. Simulation results verify that the proposed fault protection and stress mitigation design is effective for such a series-dc system.