A Coordinated Protection Scheme for DC Faults in Multi-terminal MMC-HVDC Transmission System

When a pole-to-pole dc fault occurs, it is desirable that the stations continue contributing to power transfer, rather than blocking. Thus, the current limiting module is connected in series with each arm branch to reduce the large current before the faulty lines are totally isolated by DC circuit breakers. The pole-to-pole fault requires fast identification to trigger the current limiting module. Additionally, the pole-to ground dc fault with high resistance is another concern. Based on the significant voltage drop on the boundary device of inductance caused by the current surge on the faulty pole, the voltage fault components of both positive pole and negative pole are utilized to conduct a novel protection scheme. The coordinated protection scheme for DC line faults in multi terminal MMC-HVDC transmission system is presented and simulations based on PSCAD/EMTDC software confirm its effectiveness.