A Concept of Multi-Circuit HVDC Transmission System for Selective Fault Clearing without DC Circuit Breakers

This paper proposes a multi-circuit high voltage dc (HVDC) transmission system for realizing fault-tolerant HVDC grid without dc circuit breakers. The proposed system consists of multiple dc lines connected in parallel by fault-blocking diodes. When a fault occurs in one of the dc lines, the system clears the faulted dc line using an ac circuit breaker and the diode. Thus, the proposed system realizes the selective fault clearing without dc circuit breakers, whereas the existing HVDC grids usually require dc circuit breakers. In addition, the power plants connected to the faulted line can immediately restart their operation by changing their connection to the other non-faulted dc line. Therefore, all the power plants in the proposed system can continue their operation under a single dc fault, which corresponds to the N-1 criteria of the existing ac grid. Simulation results verify that all the power plants in the proposed system can continue or restart their operation after a fault in the dc line.