高压直流接地极线路断线故障高频阻抗特性及阻抗监视系统适应性

基于输电线路分布式参数模型，对高压直流输电系统接地极线路断线故障下高频阻抗特性进行推导和分析。研究发现，当接地极线路长度超过高频注入信号半波长时，一旦接地极线路出现双回断线故障，首端高频测量阻抗的虚部将随故障距离呈周期性变化，但变化量超过正常运行时的阻抗值；当线路长度与注入信号半波长的整数倍接近时，线路某些特定位置发生单回断线故障，测量高频阻抗与正常运行时几乎相等，阻抗监视系统存在明显死区。为了提升阻抗监视策略的可靠性，提出了一种高频注入信号频率优化选择策略，基于线路实测参数，选择注入信号频率，消除保护策略死区。根据某实际 ±800 kV/8 000 MW特高压直流系统参数，搭建PSCAD电磁暂态仿真模型，仿真算例验证了分析及结论的有效性。

High frequency impedance characteristics of HVDC grounding electrode line under breakage fault and adaptability of impedance monitoring system

Based on the distributed parameter model of transmission line, the high frequency impedance cha-racteristics of HVDC(High Voltage Direct Current) grounding electrode line under breakage fault are deduced and analyzed. When the length of grounding electrode line is longer than the half-wavelength of injected signal, for breakage faults in double transmission lines, the imaginary part of high frequency measured impedance at the head end of the grounding electrode line changes periodicity with fault position, but the variation exceeds the impedance value at normal operation. When the length of grounding electrode line is close to the integer multiple of half-wavelength of the injected signal, the measurement of high frequency impedance is almost equal to that of normal operation, breakage faults at some special position cannot be identified. To improve the reliability of impedance monitoring device, a strategy based on frequency optimization selection for high frequency injected signal is proposed. Based on the measured parameters of line, the injection signal frequency is selected to eliminate the dead band of protection strategy. Finally, an electromagnetic transient simulation model is established in PSCAD according to the parameters of an actual ± 800 kV/8 000 MW UHVDC(Ultra HVDC) system, and the validity of the analysis and conclusion is verified.