Fault Analysis and Traveling-Wave-Based Protection Scheme for Double-Circuit LCC-HVDC Transmission Lines With Shared Towers

Double-circuit transmission lines, with bipolar transmission lines of two different line-commutated-converter-based high-voltage direct-current (HVDC) systems constructed on the same towers, are a new technology emerging in China to increase the power transmission capacity. Double-circuit HVDC transmission lines sharing the same towers will lead to an electromagnetic coupling effect between the two circuits. According to the geometry configuration of same-tower double-circuit transmission lines in HVDC transmission projects, double-circuit transmission lines are unbalanced without transposition. Therefore, the coupling effects on the healthy circuit cannot be completely eliminated. These coupling components will affect the sensitivity of conventional traveling-wave-based protection criteria. This work first develops a fault analysis for double-circuit HVDC transmission lines with various internal fault conditions, and then, the linear combinations of four independent modal components based only on each single circuit are obtained and investigated. Finally, an integrated traveling-wave-based protection scheme for double-circuit HVDC transmission lines is presented. Numerous simulation results verify that the proposed protection scheme can operate correctly in double-circuit HVDC transmission lines even for a fault with high resistance up to the maximum of 300 Ω.