In the process of fault isolation, many ultra-fast disconnectors of current-transferring HVDC circuit breaker (CT-DCB) need to be opened at the same time, which obviously reduces the operation reliability of CT-DCB and affects the fast recovery of the HVDC system. In this paper, a diode clamped multi-port HVDC circuit breaker (DM-DCB) is proposed to solve this risk. In the DM-DCB, half of conducting branches of CT-DCB is changed by diode branches and an bypass switch is added in parallel with the load commutation switch to protect the load commutation switch. Under the same dc fault clearance capacity, the investment cost of DM-DCB is comparable to the CT-DCB, and the probable investment cost increment is also few. A simulation model of a three-terminal HVDC system is built in PSCAD/ EMTDC software to verify the validity of DM-DCB. Simulation results prove the feasibility and validity and of the proposed scheme.

HVDC gird, HVDC breaker, dc fault, reliability