Fast breaker failure backup protection for HVDC grids

• Algorithms for breaker failure detection in HVDC grids are proposed.
• One algorithm is developed to detect local breaker failure.
• One algorithm is developed to detect remote breaker failure.
• The algorithms detect breaker failure a few milliseconds after fault inception.
• Due to the high operation speed, short-circuit ratings for equipment can be reduced.

High voltage direct current (HVDC) grid protection must clear dc faults within a time-frame of milliseconds to avoid damages to power electronic components due to fast rising dc fault currents. If the breaker associated with the primary protection fails, backup must be provided to clear the faults which would otherwise persist. Backup relaying algorithms originally developed for ac systems delay the detection of primary protection failure until the expected primary fault clearance instant. Application of similar algorithms to HVDC grids results in a long fault clearing time, which requires converters and breakers to withstand unrealistically large currents. To reduce the fault clearing time, this paper proposes two fast backup relaying algorithms which detect local and remote breaker failure before the expected primary fault clearance instant. The proposed algorithms use thresholds on the voltage and current measurements to detect breaker failure. They are evaluated using a four-terminal HVDC grid test system implemented in PSCAD. The study results show that the proposed algorithms can reliably detect breaker failure within few milliseconds after fault inception. Furthermore, the algorithms provide faster backup protection compared to methods based on ac backup protection philosophy. The resulting decreased fault clearance time reduces the maximum dc fault current and consequently, leads to lower required ratings for HVDC grid equipment.