Transient Characteristics Under Ground and Short-Circuit Faults in a ${\pm \text{500}\,\text{kV}}$ MMC-Based HVDC System With Hybrid DC Circuit Breakers

The development of voltage-source-converter (VSC)-based high-voltage direct current (HVDC) systems has increased significantly. However, the implementation of VSC-HVDC systems is limited for lacking fast, low-loss, and reliable circuit breakers. Hybrid dc circuit breakers (DCCBs) may help to improve this situation. In this paper, an efficient modular multilevel converter (MMC) HVDC system model based on the Zhangbei- Beijing ±500 kV bipolar MMC-HVDC transmission (overhead line) project is first established. Then, the system transient characteristics are investigated involving permanent line-to-ground faults (LGFs), permanent short-circuit faults (SCFs), temporary LGFs, and temporary SCFs with either ac circuit breakers (ACCBs) or DCCBs in service. Finally, the performances, including the fault clearance and recovery, comparison of DCCBs with two different breaking methods, and comparison of ACCBs and DCCBs, in the MMC-HVDC system are presented. This paper provides a deep understanding of LGF and SCF in the MMC-HVDC systems, operation of DCCB, and comparison of faults clearance and recovery under these faults conditions using ACCB and DCCB, respectively. Results also benefit the application of the DCCB and the operation strategies in high-voltage and high-power MMC-HVDC systems with overhead lines.