A New Method of Coordinating ZCBs and Fuses for a Reliable Short-Circuit Protection in DC Power Networks

With the increasing installations of solar energy, electric vehicles, and other dc-nature power devices in modern power systems, the short-circuit protection of high-power dc circuits is critical in HVDC transmission and MVDC distribution networks. As a promising protective device, Z-source Circuit Breaker (ZCB) has some unique good features over other approaches. But, under the circumstance of slow-developing faults, the ZCB might be “blind” and fails to protect circuits. In this paper, a new method of coordinating ZCB and fuse is developed to specify the fuse properly to compensate ZCB’s functionality and thus introduce a complete “thermal-magnetic” function of a hybrid ZCB-fuse circuit breaker. By analyzing the current-limiting features of ZCB and fuse and their interactions, two constraints are identified for the proposed coordination method and two relevant thresholds of melting energy in fuse are formulated. A five-step coordination method is developed and verified by simulation tests with various fault current levels and fault changing time. It is proven that, by following the proposed coordination method, the fuse coordinates well to the ZCB as backup protection under the designated peak tolerable fault current. This research work helps to increase the reliability of short-circuit protection with ZCBs in modern dc power systems.