直流偏磁影响下继电保护的误拒动机理分析及对策研究

偏磁电流经变压器中性点入侵电力系统后，线路CT将发生一定程度的饱和，影响二次系统的测量、控制等环节，严重时甚至会诱发系统继电保护的误拒动，对电力系统的安全稳定运行造成严重威胁。为此，提出了一种基于相空间轨迹识别的继电保护改进方案。首先，分析直流偏磁对保护用CT的不利影响。在此基础上，以线路保护与变压器保护为例，揭示直流偏磁影响下继电保护的失效机理。进一步地，利用相空间轨迹不受时域饱和影响的特点，提出了一种基于相空间轨迹识别的继电保护改进方案，使得所提方案能有效应对CT饱和导致的保护失效难题。最后，以典型保护失效场景为例，对比传统方法与所提改进方案的保护动作情况，验证了所提方案的有效性及优越性。

Analysis and countermeasures of relay protection false rejection mechanism under the influence of DC bias

Once DC with high amplitude penetrates the power system through the neutral point of the transformer, line CT will saturate to some extent. This saturation will affect the measurement and control of the secondary system. When the DC bias is very serious, it will even induce an incorrect relay protection of the system. This poses a serious threat to the safe and stable operation of the power system. Therefore, an improved scheme of relay protection based on phase space trajectory identification is proposed. First, the adverse effect of DC bias on protective CT is analyzed. Then, taking line protection and transformer protection as examples, the failure mechanism of relay protection under the influence of DC bias is revealed. An improved relay protection scheme based on phase space trajectory identification is proposed, one which can effectively deal with the protection failure problem caused by CT saturation, based on the characteristic that the phase space trajectory is not affected by time-domain saturation. Finally, taking a typical protection failure scenario as an example, the effectiveness and superiority of the proposed scheme are verified by comparing the protection actions of the traditional method and the proposed scheme. This work is supported by the General Program of National Natural Science Foundation of China (No. 51877088).