Auxiliary Protection Scheme for Assembly Hybrid HVDC Breakers

The trending for HVDC systems is to becoming MTDC systems with variable generation. Implementing effective and viable overcurrent protection schemes represent a challenge for these systems. The rudimentary process for DC fault interruption consists of opening the ACCB, but the interruption times for this process are unacceptable. Today, there are few DCCB options with interruption times of less than 30 ms however, their studies are limited in transmission lines (or cables), nonpermanent faults and lack of selectivity. A permanent fault located at station output or bus, is not fully protected by a DCCB, since the AC system continues to feed this fault. This paper proposes a protection scheme based on a hybrid DCCB and auxiliary devices. The scheme demonstrates its ability to selectively interrupt station output and bus faults in MTDC systems with fault interruption time of 20 ms. The case studies to evaluate the performance are verified by modifying the Cigré MTDC-MMC grid implemented in PSCAD.