A new protection scheme for transmission line of three-terminal hybrid HVDC system

Abstract Since the line-commutated converter-voltage source converter (LCC-VSC) hybrid technology combines the advantages of line-commutated converter-based high voltage direct current (LCC-HVDC) and voltage source converter-based high voltage direct current (VSC-HVDC), it has a very good prospect for engineering applications. But, the LCC-VSC HVDC system has characteristics such as LCC converter and VSC converter control strategies, fault response, and uneven boundary elements, which makes it difficult to directly apply the existing protection schemes. To solve the above problems, this paper proposes a single-ended protection scheme based on wave impedance. First, the amplitude-frequency characteristics of the wave impedance of the LCC-VSC three-terminal hybrid DC transmission line are analyzed. Subsequently, a protection scheme is proposed to identify internal faults and external faults by combining the wave impedance amplitude criterion with the current starting criterion. Finally, the model of the LCC-VSC three-terminal transmission system is used for simulation. The simulation results show that the proposed protection scheme has a strong anti-fault capability (800 Ω) and noise interference (20 dB).