中文摘要：

在线路边界频率特性的分析基础上，深入地分析了区内外故障时的特征差异：就某一类故障而言，区外故障时反行波中（阻塞频带内的）高频分量与（1～10kHz内的）低频分量的比值显著小于区内故障时的比值。据此提出利用反行波构造新型的单端暂态量保护原理，即反行波法边界元件，并形成基于小波变换的实用算法。大量ATP仿真表明，该边界元件的算法可行，动作超高速，且性能优于利用电流波的单端暂态量保护方案。文中还指出：对于实际的输电系统，现有的单端暂态量保护方案都难以保护线路全长，因此该方法可以作为全线速动保护的一种超高速保护元件。

英文摘要：

On the basis of the characteristics of line boundary, this paper analyzes the different features of internal and external faults. The difference is that the ratio of high frequency to low frequency components in case of one external fault is less than that in case of the same internal fault, in which high frequency is in the band of line trap and low frequency is within 1-10kHz. Based on the different features, the paper presents a new non-unit transient-based protection unit using backward traveling-wave, called boundary unit （BU）. The practical BU algorithm is designed using wavelet transform. A number of ATP simulation tests show that the new algorithm is feasible, and ultra-high-speed, and that the BU performance is superior to that of the former non-unit transient-based protection using current traveling-wave. The paper also indicates that the non-unit transient based protection is difficult to reliably protect the whole line, therefore the non-unit transient based protection may be used as an ultra-high-speed unit of the whole-line protection.