Robustness Evaluation of Fast Breaker Failure Backup Protection in Bipolar HVDC Grids

To ensure a reliable fault clearing, a backup protection scheme is required for selective HVDC grid protection. One way to achieve this is to use both voltage and current measurements to distinguish uncleared faults from cleared ones during the fault clearing process of the primary protection. This paper studies the applicability of such a backup protection algorithm in meshed bipolar HVDC grids and evaluates the robustness of the algorithm against system operating conditions and breaker opening delays. The influence of different operating conditions on the fault waveforms is analysed using a three-terminal bipolar test system. The robustness of the fast breaker failure backup protection algorithm is evaluated via simulation studies on the bipolar test system in PSCAD. The simulation results show that the fast breaker failure backup protection algorithm can distinguish between uncleared and cleared faults with sufficient margin for all considered operating conditions.