白鹤滩-江苏特高压混合直流输电线路行波保护适应性分析

为探究现有直流输电线路行波保护对白鹤滩-江苏特高压混合直流输电系统(简称：白江混合系统)的适应性，根据白江混合系统直流线路故障附加网络推导直流线路区内外故障时线路两端故障行波的边界传播特性。分析发现，直流线路正向区外故障后边界传播特性与传统直流系统存在差异。进一步分析行波保护判据的变化情况，表明行波保护判据主要受整流侧反射系数和逆变侧折射系数的影响。将白江混合系统与传统直流输电系统进行对比，发现当直流输电线路正向区外发生短路故障后，白江混合系统电压变化量、电压变化率、极波变化量和极波变化率比传统直流系统变化更大，导致行波保护误动风险增大。最后，基于PSCAD搭建白江混合系统仿真模型，仿真结果验证了理论分析的正确性。

Adaptability analysis of traveling wave protection for the Baihetan-Jiangsu serial hybrid LCC-MMC UHVDC transmission line

To explore the adaptability of existing traveling wave protection for the DC line to Baihetan-Jiangsu serial hybrid ultra-high voltage direct current (UHVDC) transmission system (Bai-Jiang hybrid system for short), this paper deduces the boundary propagation characteristics of the fault traveling wave at both ends of the DC line during faults inside and outside the DC line zone based on the fault additional network of the Bai-Jiang hybrid system. The analysis finds that the boundary propagation characteristics of the forward zone of the DC line faults differ from those of the conventional line commutated converter (LCC) HVDC system. The changes for the traveling wave protection criterion are analyzed, and this analysis shows that the traveling wave protection criterion is mainly affected by the reflection coefficient on the rectifier side and the refraction coefficient on the inverter side. Comparing the Bai-Jiang hybrid system with a conventional LCC-HVDC system, it is found that when a short-circuit fault occurs outside the forward zone of the DC line, the voltage change amount and change rate, the polar wave change amount and change rate of the Bai-Jiang hybrid system change more than those of the conventional LCC-HVDC system. That leads to an increased risk of false operation of the traveling wave protection. Finally, a simulation model of the Bai-Jiang hybrid system is built based on PSCAD, and the results verify the correctness of the theoretical analysis. This work is supported by the National Natural Science Foundation of China (No. 51977183).