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The multi-terminal DC wind farm is a promising topology with a voltage source inverter (VSI) connection at the onshore grid. Voltage source converters (VSCs) are robust to AC side fault conditions, however, they are vulnerable to DC faults on the farm side of the converter. This paper analyses DC faults, their transients and resulting protection issues. All kinds of fault overcurrents are analysed in detail and these contribute to protection system design. The radial wind farm topology with star or string connection is considered. The outcomes are applicable for VSCs in both the multi-VSC DC wind farm collection grid and VSC-based high voltage direct current (HVDC) transmission systems for offshore wind farms.