利用故障电流首行波拟合的柔性直流输电线路单端行波保护原理

The derivative-based traveling wave protection method has the problem of operation failure when high-impedance faults occur. In this paper, the characteristics of the fault initial traveling wave in DC transmission lines were analyzed first, and the expressions of the fault initial traveling waves at the protection installation site when internal and external faults occur were derived respectively. Then the physical meaning of each part of the fault initial traveling wave expression was analyzed, and the exponential coefficients reflecting the fault location not affected by the fault impedance were extracted by the fitting method. On this basis, the principle of non-unit traveling wave protection for VSC-HVDC transmission line using fault current initial traveling wave fitting was proposed. The simulation results show that the obtained exponential coefficient can effectively reflect the location of fault. The proposed protection method can complete fault identification within 1ms, even with high fault impedance. Furthermore, the influence of the sampling frequency and noise on the protection method was analyzed and verified. The results show that the proposed protection method has high robustness to the change of sampling frequency and the influence of noise.