特高压直流输电系统接地极引线阻抗监视策略

摘要

为提升特高压直流输电系统接地极引线的故障识别性能，提出一种新的接地极引线阻抗监视策略。对输电线路的全频带阻抗—距离特性进行了理论分析，以此为基础提出了基于高频信号注入的接地极引线阻抗监视策略，并给出了注入信号频率选择原则及故障告警判据。研究表明：若接地极引线长度超过注入信号的1/2波长，金属性接地故障时，阻抗监视装置测量阻抗的虚部随故障距离呈周期性变化，加大了判据整定的难度。因此注入信号频率的选择应保证金属性故障时，线路阻抗随故障距离的增加而单调变化，同时最大的故障阻抗模值应小于线路正常运行时的阻抗，且留有一定裕度。PSCAD仿真验证了该策略的有效性。%A novel impedance monitoring scheme is proposed in this paper in order to detect faults occurring in the ground electrode lines of ultra high voltage DC(UHVDC)transmission systems reliably and rapidly. Firstly,the theoretical analysis of the full-band impedance vs. distance characteristic of the ground electrode line is carried out. Because a high frequency signal injection-based method is used in the proposed scheme,the principle of determining the frequency of the injection signal is discussed and the criterion of fault alarm are given. The study shows that the imaginary part of the measured impedance has a periodic variation with the distance of the bolted fault when the length of the ground electrode line is larger than half the injection signal ’s wave length,which increases the difficulty of setting the criterion. Therefore the selected frequency of the injected signal should ensure that in case of a bolted fault the line impedance changes monotonically with the fault distance,and the modulus value of the maximum fault impedance should be less than that of a normal operation case with a certain margin. Some PSCAD based simulations are performed to verify the proposed scheme. The results show that the faults occur in the ground electrode line can be detected rapidly and reliably,and the proposed scheme has good practice perspective.