Integrated Scheme of Protection and Fault Localization for All-DC Collection Network in Offshore Wind Farm

With the development of offshore wind power towards the deep and distant sea, the DC collection and DC transmission (all-DC) wind farm demonstrates distinct advantages, including the absence of the Ferranti effect and elimination of multi-level voltage conversion requirements. For the protection of the all-DC collection network in offshore wind farms, this paper first analyzes the zero-mode current relationship at line outlets of the collection network and wind turbine outlets during single-pole-to-ground (SPG) faults. Analysis reveals that (1) zero-mode current polarities are opposite between fault and non-fault lines, and (2) zero-mode current polarities are opposite between the upstream and downstream of the fault point. Based on these characteristics, a polarity comparison-based protection and fault localization scheme is proposed. The method implements waveform peak–valley detection through mathematical morphology algorithms, with detection results quantified by similarity algorithms to achieve fault section localization. An all-DC offshore wind farm simulation is built in PSCAD/EMTDC. A variety of simulations under different operating conditions are delivered, demonstrating the validity and effectiveness of the proposed protection and fault localization scheme. The method accurately distinguishes the SPG fault on lines and buses while remaining unaffected by fault resistance.