Natural frequency-based protection scheme for voltage source converter-based high-voltage direct current transmission lines

On the basis of the relation among natural frequency of travelling wave, fault distance and reflect coefficient at the terminal of transmission line, a novel transmission line protection scheme is proposed in this study. The multiple signal classification method is employed to extract the dominant natural frequency through the spectrum analysis of fault travelling wave. Performance of the proposed transmission line protection algorithm is studied through detailed simulations carried out using the electromagnetic transient simulation software PSCAD/EMTDC. The method proposed in this study does not need identifying the surge arrival time. Therefore it is more robust compared with the traditional travelling-wave-based protection scheme. The effect of fault resistance on the proposed protection scheme is also discussed in this study. The simulation results have shown the proposed method is valid and can distinguish internal faults from external faults correctly.