交直耦合深化后换流站差动类保护误动共性问题分析及新原理研究

In recent years, several cases of mal-operation of differential protection of converter transformer, bridge differential protection of converter are reported. These affairs indicate that the electromagnetic transient phenomena relevant to the main equipment protection within the converter substation are becoming increasingly complex, which affects not only a certain specific device, but multiple devices and even the entire converter substation, leading to new problem of reliability decreasing of multiple types of differential protection within converter substations. The above-mentioned problems will possibly become more serious in the circumstance of Ultra-high Voltage(UHV) AC-DC deeply coupling of future power grid. Therefore, on the basis of studying the existing complex electromagnetic scenarios and potential mal-operation scenarios of differential-type protections due to the trends of AC-DC deeply coupling, the CT models adaptive to multiple complex electromagnetic scenarios are discussed. Furthermore, comprehensive transfer characteristics of inrush/loop current, long-duration high magnitude DC bias, multiple continuous commutation failure and CT special saturation law are studied as well. Then, the mechanism of abnormal operation of the main equipment protection such as bridge differential protection, common differential protection and zero sequence differential protection, and future potential mal-operation due to the external environments becoming more complex can be revealed. By means of advanced signal processing techniques like Hausdorff image discrimination algorithm, novel principles and schemes of differential-type main equipment protections of converter substation will be developed and the closed-loop simulation test based on RTDS will be conducted. The achievement of the project will enrich the research of the main equipment protection of UHV converter station, which has an important theoretical significance and broad application prospect.

近年来多例换流站主设备差动类保护误动事件表明，换流站内与主设备保护相关的电磁暂态现象日趋复杂，其影响涉及全站多个设备乃至整个系统，站内多种差动类保护面临动作可靠性降低的新问题，在未来特高压交直流耦合深化后还可能进一步加剧。为此，本项目在研究换流站主设备固有复杂电磁场景和交直流深度耦合趋势带来的换流站差动类保护误动潜在场景的基础上，结合适应多种复杂电磁场景的TA传变模型优选，对复杂涌流/环流传递作用、大时间尺度高直流偏磁、多重连续换相失败及TA传递异变规律开展透彻研究，揭示当前换流站桥差、大差和零差保护各种不明原因误动及未来因外部环境进一步复杂化而承受潜在误动风险的机理，借助包括Hausdorff图形识别算法在内的先进信号处理技术，提出换流站主设备差动类保护新原理与新方案，进行PSCAD仿真和RTDS闭环测试验证。项目成果将充实换流站主设备差动类保护研究体系，具有重要理论意义和广阔应用前景。

本项目针对换流站主设备差动类保护在复杂电磁环境及特殊运行工况下存在的缺陷及隐患，对换流变差动保护、零差保护和换流器桥差保护在各类场景下误动的机理及对策开展了研究。分析特高压一组换流变空投时对称性涌流的产生机理和变化特点，揭示其引起换流变大差保护二次谐波制动判据失去闭锁能力的原因，提出基于Hausdorff距离算法的换流变大差保护新判据；研究指出换流变外部故障切除后恢复性涌流使得换流变铁芯饱和产生的单向偏置电流，会在零差保护用TA的铁芯中积累偏磁分量，导致TA测量电流失真，造成零差保护判据误动，提出基于Hausdorff图形识别算法的零差保护策略；分析换流变中性线上TA在长时间单极-大地运行伴随交流系统高阻故障工况下饱和机理，揭示换流变零差保护误动原因，根据区内、外故障时保护两侧零序电流极性差异，提出基于S变换相位差的换流变零差保护闭锁新判据；针对桥差保护误动案例，分析揭示励磁涌流和恢复性涌流在星角换流变三角侧环内合成较大零序环流，与剩磁共同作用引起绕组TA饱和，其传变误差使得星角换流变保护用电流与星星换流变保护用电流之间出现虚假差流，导致桥差保护误动，提出基于互近似熵算法的桥差保护闭锁方案；研究指出在故障恢复期间，换相失败对恢复性涌流具有助增作用，导致差动保护在较轻微区内故障时存在延时动作风险，提出基于离散Fréchet距离的保护判据；研究指出连续换相失败时直流接地极入地电流经地网耦合后入侵附近换流变中性线的电流，使得换流变中性线TA传变特性劣化，导致换流变零差保护误动，提出基于谐波制动原理的解决方案。利用精确特高压直流工程仿真模型，对所提保护新判据和方案进行验证，并基于动模试验进一步验证判据和方案的适用性。本项目研究内容来源于工程实际中的事故案例，提出差动类保护解决方案以及相应的理论、算法和关键技术，具有很强的理论性，并有望解决国家重大需求当中面临的实际问题，对未来特高压直流工程大规模建设提供了更加坚实的技术保障。