Three-core submarine cable has been widely used in the offshore wind power transmission field, and its fault characteristics are different from single-core submarine cable. The short-circuit current mechanism in three-core submarine cable for offshore wind power transmission system under grid faults is studied in this paper. The positive, negative and zero sequence mathematical models are established under different fault states. On this basis, the reason of the fault current dc offset problem and its impact to the circuit breaker is analyzed. In addition, the main influence factors of the fault current zero-crossing time are analyzed. Finally, comparative simulation studies are conducted under different fault conditions. Simulation results show that the fault position and the duration time of different fault states have major influence to the fault current. When the time intervals between different faults are around 5ms, and the fault position is near the step-up transformer, the fault current dc offset problem will be pretty serious.

offshore wind power;three-core submarine cable;grid fault;current dc offset