Identification method for internal and external faults based on amplitude feature of backward traveling wave for HVDC transmission line

The theoretical analyses about the traveling wave transmission process for internal and external faults at HVDC transmission lines show that, in a short time, for internal faults, the backward traveling waves can be detected at both line terminals. For external faults, the backward traveling wave can be detected only at one line terminal. The backward traveling wave in the other terminal is zero in theory. Taking the calculation error and noise into account, the amplitude of the backward traveling wave is still very small. Thus, the identification method for internal and external faults for HVDC lines can be proposed by com paring the amplitude of the backward traveling waves at both ends of line. For internal faults, the ratio of the integral results is relatively small. However, for external faults, the ratio of the integral results is relatively large. Plenty of simulation results based on PSCAD/EMTDC indicate that the proposed protection method can discriminate internal faults from external faults under various fault conditions including faults with high fault resistances.