High-speed protection method for DC transmission lines using fault current initial traveling wave

Voltage source converter-based high voltage DC transmission raises high demand for high-speed operation of relay. The derivative-based traveling wave protection method exposes the problem of low-sensitivity when high-impedance faults occur. In this paper, the influence factors of the fault initial traveling wave are analysed and the analytic expressions of the fault initial traveling wave are derived. In the expression, the physical meaning of the exponent coefficients is the distortion degree of the fault initial traveling wave, which is related to the location of the fault. The exponent coefficients will not be influenced by the fault impedance. According to the formation of the expression, a basic fitting function is selected to extract fault location information from the zero-mode fault current initial traveling wave by Levenberg-Marquart fitting method. Then a high-speed protection scheme is proposed using the obtained fitting coefficients. The simulation results show that the fitting coefficients b can directly correspond to the fault location, the proposed method can reliably and fast identify faults and has high sensitivity when high-impedance faults occur.