基于高频注入信号时空分布特性的特高压直流接地极线路保护及故障处理策略研究

The earth electrode line is an important part for HVDC transmission project. It is significant to detect and isolate the electrode line fault in time and reliably. The fault signal based protection methods are influenced by the HVDC system operation modes and may be invalid at certain operation modes. The high frequency signal injection based protection method has good adaptability and is suitable for every operation mode. However, the signal injection based protection method is affected by line parameter variation and has no perfect threshold setting principles. This subject considers the reflection and refraction of the high frequency injected signal under different operation conditions of electrode line and analyze the temporal and spatial distribution characteristics. The high frequency voltage superimposed components, the high frequency voltage standing wave ratio and impedance-frequency characteristic are studied to reflect the fault. On this basis, the new protection principles are proposed for earth electrode line to solve the problem that the traditional high frequency signal injection based protection has low reliability. Meanwhile, the arc extinguishing conditions of DC current at the fault point of electrode line are carried out. The fault isolation strategy which has minimum effect on AC system is proposed based on the control of UHVDC and the arc-extinguishing ability of the grounding breaker in converter station. This project aims to propose an effective fault identification and fault processing methods to ensure the stable and reliable operation of UHVDC system.

接地极线路是直流输电工程的重要组成部分，及时可靠地检测和隔离接地极线路故障对直流工程的安全运行具有重要作用。传统基于故障信号的保护方法受直流系统运行方式影响较大，在部分方式下将失效。现有基于高频信号注入的保护方法适应性强，对各种直流运行方式均适用，但存在保护性能受线路参数变化影响大、门槛值整定不完善等问题。本课题拟通过考察接地极线路不同工况下高频注入信号的折反射规律，研究注入信号的时空分布特性，分析高频电压突变、高频电压驻波比特征和线路阻抗-距离特性对故障的反映能力，构建接地极线路保护新原理，解决传统利用高频注入保护方法可靠性不高的问题；同时，开展接地极线路故障点直流电弧熄弧条件的研究，利用特高压直流的受控特性与换流站内接地开关的灭弧能力，提出对交流系统冲击影响最小的接地极线路故障处理策略。课题的研究旨在提出有效的接地极线路故障识别与处理方法，保障直流系统的安全可靠运行。

接地极线路是直流输电工程的重要组成部分，及时可靠地检测和隔离接地极线路故障对直流工程的安全运行具有重要作用。传统基于故障信号的保护方法受直流系统运行方式影响较大，在部分方式下将失效。现有基于高频信号注入的保护方法适应性强，对各种直流运行方式均适用，但存在保护性能受线路参数变化影响大、门槛值整定不完善等问题。本项目首次研究了不同故障情况下的接地极线路首端测量所得高频阻抗变化的规律，以此为基础完成高压直流接地极线路阻抗监视策略保护死区机理分析。同时，为解决目前基于高频电流信号注入的高压直流系统接地极线路阻抗监视策略存在拒动的问题，提出了一种改进的接地极线路保护方法，基于线路实测参数实现注入信号频率优化，以此消除保护死区。在新型保护判据方面，为解决高压直流输电系统接地极线路高阻、远端接地故障保护灵敏度低的问题，提出了基于频带电压幅值积分的接地极线路保护方法和基于测量阻抗横差的接地极线路保护方法，仿真结果表明所提方法能够有效提升接地极线路故障识别准确度，适用于不同运行方式。为实现直流输电单极故障引发接地极线路击穿故障点的快速准确定位，缩短供电恢复时间，提出一种基于换流站故障录波的接地极线路击穿点定位方法。仿真结果表明：方法的有效性和精度满足实用要求，且无需额外增加换流站软硬件配置，便于工程应用。提出了接地极线路故障隔离策略，利用直流开关的短时过流能力，减少直流闭锁概率。