平波电抗器、直流滤波器、PLC滤波器构成特高压直流输电线路现实边界。分析特高压直流输电线路以及边界的频率特性，研究特高压直流输电线路以及边界对故障暂态电压信号高频量的衰减作用，得到当故障发生点与保护安装点的距离大于1 ln G ( jω)α−时，线路对频率为2πω高频量的衰减作用将大于边界的衰减作用的结论。证明特高压直流输电系统整流侧和逆变侧关于直流输电线路中点对称，提出利用保护元件区分对侧区内外故障的特高压直流输电线路双端电压暂态保护原理和动作判据，该原理能实现特高压直流输电线路全线保护。建立云广特高压直流输电系统实际参数仿真模型，对所提出的特高压直流输电线路双端电压暂态保护原理进行仿真验证。%The smoothing reactor, DC filter and PLC filter form the physical boundary of UHVDC transmission line. The frequency characteristics of UHVDC transmission line and line boundary are analyzed, the attenuation of high frequency fault transient signal caused by UHVDC transmission line boundary and transmission line is studied, and it is concluded that when the distance between the fault position and protector is longer than 1 ln G( jω)α−, the attenuation of transmission line affecting 2πωhigh frequency signal will be greater than that of the boundary. It proves that UHVDC rectifier side and inverter side are symmetrical regarding mid-point of DC transmission line. A double-ended transient based voltage protection principle and operation criterion for UHVDC transmission line which uses protector to distinguish the opposite internal and external fault is proposed. The theory can protect the whole transmission line without direction element. The actual parameter simulation model for Yun-Guang UHVDC transmission system is built up to simulate the double-ended transient based voltage protection method.
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