A Single-Pole Grounding Fault Line Selection Method for Full DC Offshore Wind Farm Based on Zero-Mode Information Extraction

With the development of offshore wind power towards deep and distant seas, all DC wind farm technology solutions can not only avoid the issues of cable capacity rise and reactive power, but also eliminate the need for grid-following control and multiple voltage transformations, which have been widely adopted. However, as a current cutting-edge hot topic, there are many technical gaps in the relay protection of all DC offshore wind farms. For a fully DC offshore wind farm, the fault characteristics of a single-pole grounding fault in the collection line were first analyzed by fault current circuit of single-pole fault. The study found that the zero-mode current at the outlet of the collection line is a decaying sine signal, and the zero-mode current of the faulty line is greater than that of the healthy line. Based on this, a fault line selection method based on zero-mode information extraction is proposed. In this method, the bus zero-mode voltage is used as the starting threshold, and then the fault line is selected by comparing the zero-mode current amplitude of each line outlet. A full DC offshore wind farm model was built on the PSCAD/EMTDC platform to verify the effectiveness of the proposed fault line selection method.