Protection and post-fault recovery of large HVDC networks using partitioning and fast acting DC breakers at strategic locations

DC fault protection arrangements for a large multi-terminal HVDC network are proposed where fast-acting DC circuit breakers are only used at strategic locations with the large DC network to be operated interconnected but partitioned into islanded DC zones in case of any DC fault events in one of the DC zones. Each DC network zone can be protected using low cost, slow protection devices such as AC circuit breakers coordinated with DC switches or slow mechanical type DC circuit breakers. This ensures the maximum ‘loss-of-infeed’ for any AC networks connected to the large HVDC system is kept within acceptable limits with reduced investment in protection cost as expensive fast acting DC circuit breakers are kept to a minimum. A post-fault recovery method of the faulty section is proposed including the reconnection with the healthy part of the network to ensure reliable and smooth restoration of the large multi-terminal HVDC network. A detailed pre-fault and post-fault power flow analysis is also conducted in a multi-terminal DC network with DC voltage droop control. The proposed protection arrangements and post-fault recovery method are validated by simulation of a two-zone, six-terminal DC network with respective radial and meshed configurations.