Traveling wave travels between fault point and the end of line for a lot, forming natural frequencies which have mathematical relationship with fault distance. Smoothing reactor and DC filter constitute the boundary of UHVDC, making the natural frequencies more clear. Based on these, a UHVDC transmission line pilot protection method based on features of dominant components of natural frequencies is put forward. Changing ratio is used to form fault start principle; MUSIC method is used to conduct a spectral analysis of the transient current after fault, and the difference between dominant components of natural frequencies of internal fault and external fault is used to form protection principle; the dominant components extracted by formal signals and modal signals are used to form fault line principle, forming the whole protection scheme. UHVDC model is established in PSCAD/EMTDC and lots of simulations on different fault conditions are done on this model. Lots of simulations show that this method can work precisely and quickly under different fault conditions, and has good adaptability and practical values. This work is supported by National High-tech R&D Program of China (863 Program) (No. 2012AA050208).% 故障后行波在故障点与线路终端间来回反射，形成的固有频率与故障距离有明确的数学关系。特高压直流(Ultra High Voltage Direct Current, UHVDC)输电线路的边界由平波电抗器和直流滤波器构成，与交流线路相比，线路故障后形成的行波固有频率更加清晰。基于此，提出了一种利用线路两端固有频率主成分特征的特高压直流输电线路纵联保护方案。根据电流变化率构造故障启动判据；用MUSIC方法对故障后的暂态电流数据进行频谱分析，利用区内外故障时线路两端固有频率特征差异构造保护判据；利用原始行波信号和解耦后行波信号提取的固有频率主成分构造选极判据，形成完整的基于行波固有频率的特高压直流输电线路纵联保护方案。在PSCAD/EMTDC中建立特高压直流输电系统模型，并在不同故障工况下对该保护方案的适应性进行仿真。大量仿真结果表明，该保护方法在不同故障工况下均能可靠、快速动作，具有较好的适应性和实用价值。
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