A novel voltage projection component-based protection scheme for hybrid multi-terminal HVDC transmission lines

Abstract

Combining the technical advantages of line commutated converter (LCC) and modular multilevel converter (MMC), hybrid multi-terminal HVDC (Hybrid-MTDC) system provides larger capacity, more economical and flexible transmission mode, which has become an important development trend of dc technology in the future. However, high fault resistance, complex topology and large transmission network pose great challenges to the protection of Hybrid-MTDC transmission lines. In this paper, the variation trajectories of internal and external fault voltage vectors with fault resistance are elaborated, and a projection axis through the origin is constructed on the vertical direction of the external metallic fault voltage vector. Combining the voltage amplitude and phase characteristics, the projection component amplifies the characteristic difference between internal and external high-resistance faults. On this basis, a voltage projection component-based protection scheme for Hybrid-MTDC transmission lines is proposed, which can sensitively and reliably identify the line faults under high fault resistance. Finally, the proposed method is thoroughly validated in the PSCAD/EMTDC simulation model of Kun-Liu-Long hybrid three-terminal HVDC system, and the results demonstrate that the proposed protection scheme is practicable, highly sensitive and reliable.