Low speed protection methodology for a symmetrical monopolar HVDC network

Protecting a future HVDC network from short circuit DC faults is presently expected to require extensive implementation of fast HVDC circuit breakers, allowing for rapid fault isolation. The requirement for circuit breakers may, however, be reduced or removed depending on the protection methodology, resulting in a slower post-fault recovery. The expected fault response and the subsequent network recovery is dependent on the circuit breaker, network, and converter configurations. This paper examines a low speed protection methodology for a symmetrical monopolar HVDC system, a configuration which requires pole to pole balancing following a pole to ground fault. The fault clearance and network recovery timings are therefore evaluated for both pole to pole and pole to ground faults on several case study networks.