A protection scheme for hybrid multi-terminal HVDC networks utilizing a time-domain transient voltage based on fault-blocking converters

Abstract Combining the advantages of the line commutated converter (LCC) and modular multilevel converter (MMC), hybrid multi-terminal HVDC (Hybrid-MTDC) systems have become the most competitive candidate for future power transmission systems. However, for conditions of high fault resistance (HFR), large transmission networks and lacks of boundary components between adjacent lines, economic and practical traveling-wave (TW) protection is an immediate challenge for Hybrid-MTDC networks. In this paper, the fault-generated TW characteristics of Hybrid-MTDC networks are elaborated, and a time-domain transient voltage with different sampling periods is constructed to adapt to the attenuation of HFRs and the band-stop characteristic of T areas. Utilizing the ratio of the transient voltage indexes and based on a fault-blocking converter (FBC), the coordination of relays can be designed to realize internal fault detection and faulty line location for Hybrid-MTDC networks. Furthermore, a comprehensive FBC-based protection scheme for Hybrid-MTDC networks is proposed. Finally, the proposed protection scheme is validated based on the Wudongde project using PSCAD/EMTDC. The protection results show the high sensitivity and reliability of the proposed protection scheme.