DC fault protection of multi-terminal HVDC systems using DC network partition and DC circuit breakers

This paper concentrates on using fast acting DC Circuit Breakers (DCCBs) at strategic locations to allow the entire Multi-terminal HVDC (MTDC) system to be operated interconnected but partitioned into islanded DC network zones following faults. This configuration uses least number of DCCBs in order to minimise the capital cost and power loss while retaining the benefit of system interconnection. The proposed concept has greater flexibility during normal operating condition and reduces the need for pre-fault partitioning of the system. During a DC fault, the DCCBs at the strategic cable connections that link the different DC network partitions are opened such that the faulty DC section is quickly isolated from the remaining of the MTDC system. Thus, the healthy DC network zone can recover and power transmission can be restored quickly. The faulty DC section can be protected using slow AC circuit breakers. MATLAB/SIMULINK simulations are presented to demonstrate satisfactory system behaviour during DC faults.