利用峰值频率的高压直流输电线路纵联保护方案

A Pilot Protection Scheme for HVDC Transmission Lines Based on Specific-Frequency

根据高压直流输电线路两端直流滤波器和换流器的阻抗频率特性,提出一种基于直流滤波器峰值频率的纵联保护方案。峰值频率下,直流滤波器近似为开路,换流器直流等值阻抗近似表现为感性元件。以此为基础,对直流输电线路进行区内外故障分析发现,区内故障时,整流侧、逆变侧峰值频点阻抗阻抗角均为-90°;区外故障时,故障侧峰值频点阻抗阻抗角为90°,对侧峰值频点阻抗阻抗角仍为-90°。根据此特征构造出区内外故障识别判据。针对利用单端故障信号选极可靠性差的弱点,进一步提出了含权重系数的双端选极判据。仿真结果表明,该方案原理简单、方法可靠、抗过渡电阻能力强且不受分布电容电流的影响。

By virtue of the impedance frequency characteristic of the converter and the DC-side filter, a pilot protection scheme based on the specific-frequencies of the DC-side filter was proposed. At the specific-frequencies, the equivalent impedance of DC-side filter is very large and the DC side equivalent impedance of converter behaves like an inductor. On this condition, the fault characteristic was analyzed. During internal faults, the specific-frequency impedance angle at both terminals is equal to -90°; during external faults, the specific-frequency impedance angle at faulty terminal is 90° and the one at the other terminal is -90°. According to those properties, the fault identification criterion can be constructed. Since the using of single-terminal signal makes poor reliability of faculty pole identification, a novel faulty pole identification criterion based on double-terminal signal was introduced. Comprehensive simulation experiments have shown that the proposed method is simple and of high reliability. Besides, it is not affected by the fault resistance and the distributed caoacitive current of transmission line.