A Novel Traveling Wave Protection Method for DC Transmission Lines Using Current Fitting

Hybrid AC/DC transmission grids require high-speed operation and high reliability for relay protection. Traditional derivative-based traveling wave protection methods have exposed the problems of low sensitivity and low reliability. In this paper, the fault traveling wave is analyzed considering the attenuation, distortion, and boundary effect of the DC transmission line as well as three converter types. The expressions of the fault initial traveling wave are derived and the conclusions show that 1) the expressions of the fault initial traveling wave at the end of the transmission line have the formation of a(1 - exp(-bt)); 2) the index of the exponential function in the fault initial traveling wave expression is related to the fault location, and is not affected by the fault impedance and line attenuation. Then a Levenberg-Marquart fitting method is proposed to fit the measured zero-mode fault current initial traveling wave and extract the index coefficients. Finally, a novel traveling wave protection method for DC transmission lines is proposed using the obtained index coefficients. The simulation results show that 1) the proposed protection method can complete fault identification within 1 ms, even with high fault impedance; 2) the proposed protection method has high robustness to the influence of the noise.