Adaptive reclosing strategy for the mechanical DC circuit breaker in VSC-HVDC grid

Abstract The overhead line has wide application prospect in the future VSC HVDC grid. However, compared with the dc cable, the fault probability (especially the nonpermanent fault), is much higher on the overhead line. To enhance the system power supply reliability, effective reclosing strategy must be configured for the DCCBs. The existing automatic reclosing strategy recloses the DCCB directly, resulting in serious secondary overcurrent damage to the dc grid under permanent fault. In a 500 kV dc grid, this secondary overcurrent is up to about 10kA. Therefore in this paper, the mechanical DCCB residual voltage characteristics under permanent and nonpermanent faults are analyzed. According to the obtained characteristic, the adaptive reclosing strategy is proposed for the mechanical DCCB in VSC HVDC grid. The theoretical analysis indicates that, the proposed reclosing strategy can not only reliably identify the fault property, but also limit the secondary overcurrent under permanent fault. This means the requirement on the consecutive interruption capability of DCCB is reduced significantly. Finally, simulation cases based on the PSCAD/EMTDC are carried out to verify the correctness of the theoretical analysis, as well as the feasibility and superiority of the proposed reclosing strategy.