【摘要】 柔性直流输电系统的快速故障发展给直流保护的研究带来了巨大的挑战，严苛的速动性要求不得不使保护的研究聚焦在故障暂态量上．在高压大容量输电系统中，为更贴合实际工程，线路的频变特性以及行波传输过程是不容忽略的，因此文中以此展开了故障分析．针对单端量保护在耐过渡电阻能力上的不足，文中对保护区内外故障发生时的测量点电压频率特征进行了分析，以过渡电阻为变量观察不同故障情况下的频率比值差异变化趋势，并利用S变换设计了一种基于电压频率成分比值差异的保护方案；其次，根据噪声在S变换下的频谱特点，给出了噪声识别判据；最后，在PSCAD/EMTDC仿真平台上搭建了四端柔性直流输电系统模型对所提方法进行了验证．结果表明，区内外故障下的电压频率成分比值存在明显差异，所提保护方案可以准确识别线路不同位置的短路故障，并可判断故障极．与基于电压变化量和高频段能量的保护方法相比，文中方法具备更高的耐过渡电阻能力．即便是远距离高阻故障，保护方法也具备明显的区分度，可见，所提方法可以更好地适用于大容量远距离输电系统．同时，在不同信噪比的噪声环境下，保护方法仍旧可以准确识别出噪声以及故障．保护方法可以在2 ms内完成故障识别，满足柔直系统的速动性要求，可作为系统运行的主保护．更多还原

【Abstract】 The rapid failure development of flexible DC transmission systems has introduced significant challenges to the research of DC protections,and the strict requirements of quick motion must enable the research of protections to focus on the fault transient quantity. To optimally fit the actual project,the frequency-dependent characteristics of the line and the traveling wave transmission process cannot be ignored in the high-voltage large-capacity transmission system. Thus,we perform a fault analysis in this study. Aiming at the insufficiency of the single-ended protection in withstanding transition resistance,this paper analyzes the voltage and frequency characteristics of the measurement point when faults occur inside and outside the protected area and uses the transition resistance as a variable to observe the changing trend of the frequency ratio difference under different fault conditions. A protection scheme,based on the difference in the ratios of the voltage-frequency components inside and outside the protection zone,is designed by using the S-transform. Next,the noise identification criterion is provided according to the frequency spectrum characteristics of noise under the S-transform;Finally,a four-terminal flexible DC transmission system model is built on the PSCAD/EMTDC simulation platform to verify the proposed method. The results show obvious differences in the ratios of voltage-frequency components under faults inside and outside the zone. The proposed protection scheme can accurately identify short-circuit faults at different positions of the line and judge the fault pole. Compared with the protection method based on voltage variation and high-frequency energy,the method in this paper demonstrates a higher resistance to transition resistance. The protection method displays obvious discrimination even in the case of long-distance high-resistance faults. Thus,it can perform better in large-capacity long-distance power transmission systems. Concurrently,in the noise environment with different signal-to-noise ratios,the protection method can still accurately identify noise removal and faults. The protection method can complete the fault identification within 2 ms and meet the quick-action requirements of the flexible straight system. Thus,it can be used as the main protection of the system operation.更多还原