DC protection of a muti-terminal HVDC network featuring offshore wind farms

A protection scheme for DC faults has been designed for a multi-terminal HVDC network used to transfer energy from three large offshore wind farms to shore. The system uses open access models created in the EU-funded BEST-PATHS project, including a manufacturer-supplied wind farm model. Tripping conditions for the DC circuit breakers are found through simulation, along with current limiting inductor sizes, based on the use of a hybrid circuit breaker. Simulations of faults in the HVDC network show the ability of the protection scheme to isolate the fault, and the converter stations and wind turbines are able to ride-through the fault without tripping based on the 5ms switching time of the circuit breakers Longer switching times will cause significant rises in the offshore grid frequency, which could cause the turbines to trip.