Fast DC fault location and isolation strategy for the flexible multi-terminal DC system

Voltage source converters (VSCs) are highly vulnerable to DC fault current. Protection methods which can quickly locate and isolate DC faults are necessities in VSC-based multi-terminal DC (VSC-MTDC) systems for its safe and reliable operation. In this paper, a fast and collaborative DC fault location and isolation strategy are proposed. In this strategy, hybrid DC circuit breakers (HDCCBs) are used as the main protection device. The operation control of HDCCB is redesigned and cooperates with fault location results to achieve fast fault isolation. For the fault location method, a fast di/dt criterion is used for fault pretreatment, the transient-voltage energy difference criterion is used to make sure its selectivity. The overall protection strategy is demonstrated in a four-terminal VSC-MTDC system using PSCAD/EMTDC platform. The performances of the typical DC circuit breaker-based strategy and the proposed strategy were compared. Numerous simulation results under various conditions proved its flexibility and validity.