Abstract: The fault location methods of UHVDC transmission lines can be divided into traveling-wave-based algorithm, fault-analysis-based algorithm and natural-frequency-based algorithm according to the principle. The traveling-wave-based algorithm is not reliable due to its wave head identification problem, and the choice of wave speed also affects the accuracy of fault location; The fault location accuracy of the fault-analysis-based algorithm is not high because of model accuracy; The natural-frequency-based algorithm has dead zone when the fault occurs at the end of the line. This paper presents a novel fault location algorithm, when the DC line fault occurs, the first backward-wave has not been reflected, and it is not affected by the frequency variation of the reflection coefficient, the backward-wave head is easy to identify, so the backward-wave is used for fault location in this paper. The identification of wave head uses the à trous algorithm with excellent singularity detection capability. In the case of inconsistent wave speeds caused by the use of different types of conductors on the DC line, the calculation is performed with different wave speeds to improve the range accuracy further. Compared with the existing fault location algorithm, the reliability of the wave head identification of this algorithm is improved, and since the variation of the wave speed is taken into consideration, the ranging accuracy is improved further when different types of wires are used in the DC line.

Key words: UHVDC, transmission line, backward wave, à trous algorithm, two-terminal fault location