特高压直流系统接地极线路阻抗监视系统适应性研究

Adaptability Analysis of Fault Supervision System for Long Electrode Line of UHVDC

利用输电线路分布参数模型,对特高压直流输电系统接地极线路的高频阻抗特性进行分析,推导出不同故障情况下接地极线路首端高频测量阻抗表达式。研究发现,金属性接地故障时,若接地极线路长度超过注入信号波长的 1/2,测量阻抗的虚部随故障距离呈周期性变化;当接地极线路长度接近注入信号半波长的整数倍时,接地极线路某些特殊位置发生单回金属性故障后,高频测量阻抗与正常运行时几乎相等,接地极线路阻抗监视系统存在死区。为提高阻抗监视系统可靠性,提出一种注入信号频率选择策略。该策略基于线路实测参数,通过对注入信号频率的优化,消除监视系统死区。根据某实际±800kV 特高压直流输电系统参数,利用PSCAD/EMTDC 搭建仿真模型,对接地极线路不同故障进行仿真研究,仿真结果证明了该文分析及结论的有效性。

Based on the distributed parameter model, high frequency fault impedance characteristic of long grounding electrode line of ultra high voltage direct current (UHVDC) is researched. The expression of high frequency fault impedance is deduced in different fault types. For metallic faults, imaginary part of measured impedance changes periodicity with fault position when the length of grounding electrode line is longer than the half wavelength of injected signal. Especially when the length of grounding electrode line is integer multiple of half wavelength of injected signal, metallic faults at some special position cannot be identified. To improve the reliability of impedance monitoring device, a strategy based on frequency selection of injected signal is proposed. According to the measured parameter, make the wavelength of injected signal have a great difference with length of grounding electrode line. The reliability of the research is demonstrated by PSCAD.