Fault Analysis and Traveling Wave Protection Based on Phase Characteristics for Hybrid Multiterminal HVDC Systems

Abstract

By fully combining the advantages of line commutated converter (LCC) high-voltage direct current (HVDC) and modular multilevel converter (MMC)-HVDC systems, hybrid multiterminal HVDC (hybrid-MTDC) transmission technology has become a new technical means to overcome the shortcomings of conventional two-terminal HVDC systems. However, the conditions of high fault resistances and more sophisticated network topologies have brought considerable challenges to the existing traveling wave (TW) protection principles. In this article, a parallel hybrid-MTDC system is taken as the research object, and its mathematical analysis model is established. Based on the mathematical model, the TW characteristics that the phase of the high-frequency voltage TW during the occurrence of an internal and external fault approaches approximately 90° and 0°, respectively, are clarified. Therefore, considering the influences of reflection and refraction of TWs and line propagation, the phase-characteristics-based criterion is constructed. Using the proposed criterion, a protection scheme for hybrid-MTDC systems is proposed, which realizes the identification of line faults with high fault resistance. The proposed method is verified in detail with the electromagnetic transient simulation model using PSCAD/EMTDC, and the test results show that the proposed protection scheme is feasible and has high sensitivity, reliability, and adaptability to different operation modes.