Converter Control Impacts on Efficacy of Protection Relays in HVDC-Connected Offshore Wind Farms

The high-voltage dc (HVDC)-connected offshore wind farms (OWF) is a power electronic converter dominated power system, where conventional protections, including overcurrent protection, distance protection, and differential protection, may not operable effectively. To reveal the impact of converter control on the efficacy of conventional protection relays, this paper first investigates the highly controlled fault current characteristics of HVDC system and OWF. Then, the basic operation principles of conventional protection relays are presented to elaborate their responses to the fault currents of HVDC system and of OWF, based on which, scenarios that lead to the malfunction of protection relays are identified. Finally, the theoretical analysis is verified by electromagnetic transient (EMT) simulations.