柔性直流输电线路自整定保护原理研究

Protection performance is the key to the flexible DC power grid. However, the primary protections of flexible DC transmission lines need setting with the help of simulation, and problems of setting will affect the protection performance. The key to avoiding the setting problem is to reveal an electrical quantity relationship that only occurs in internal faults, and to construct new self-setting protection principles based on this. However, the primary protections of flexible DC transmission lines are expected to be fast, and the electrical quantities of DC fault have no fixed dominant frequency component. The primary protections need not only to use very short instantaneous values to complete fault identification, but also to withstand various transient disturbances. How to achieve self-setting protection is a big challenge. Based on the correlation characteristics between the travelling wavefront and memory voltage, this project proposes a non-unit self-setting protection, which can withstand high fault resistance. This project also establishes a model of the spatiotemporal relationship between two-terminal electrical quantities of flexible DC transmission lines, and proposes a reliable unit self-setting protection based on dynamic state estimation, which can deal with parameter errors and measurement abnormalities. This research is expected to contribute to the protection performance of the flexible DC grid.

继电保护性能提升是柔性直流电网安全运行的关键，但目前柔性直流输电线路主保护依赖于仿真整定，潜在的定值问题影响保护性能。解决定值问题的关键在于揭示出区内故障特有的电气量关系，以此构造自整定保护新原理。然而，柔性直流电网对保护速动性要求严苛，直流故障时没有固定主频分量，主保护需利用极短瞬时值判别故障，还要耐受各种暂态干扰，如何实现自整定保护是一大挑战。本项目深度挖掘首行波与记忆电压的波形相关特性，利用单端量揭示出柔性直流线路区内故障特有的电气量关系，实现不依赖于仿真整定的单端量保护，并可应对高阻故障。本项目还对柔性直流线路双端电气量时空关系建立模型，利用动态状态估计充分挖掘量测冗余优势，实现高可靠的模型校验保护，不依赖于仿真整定，并可应对参数误差和测量异常。本研究有望丰富柔性直流线路现有保护体系，对保护性能提升做出贡献。

在新能源并网、海岛输电、异步联网等多个场景，柔性直流以其控制灵活、便于组网、无换相失败等优势成为国内外争相研究的新一代输电技术。但柔性直流的关键问题在于如何应对直流故障，继电保护是其安全运行的关键。但目前柔性直流输电线路主保护的定值计算严重依赖于仿真，成为威胁柔性直流系统安全运行的隐患。本项目旨在提出无须整定计算的保护新原理，解决上述定值隐患。.提出了基于首行波相关性的柔性直流线路单端量自整定保护，利用行波波形随传输路径衰变的单调特性，引入了区内、外记忆行波电压的概念，通过比较故障行波与记忆行波电压的相似性实现区内、外故障的判别。所提单端量保护，无需定值整定计算，可1.1ms内动作，且在原理上不受过渡电阻影响，仿真结果显示可耐受500Ω过渡电阻。.提出了基于模型校验的柔性直流线路双端量自整定保护，通过校核所建模型与实际线路是否匹配，实现区内、外故障判别。基于线路两端电气量关系进行模型搭建，考虑了柔性直流线路分布特性和频变特性，利用动态状态估计法对所建立模型进行状态估计，根据状态估计残差的大小使用卡方分布进行模型校核，实现自整定保护。所提双端量保护具有天然的选择性，对于200km内的线路，可在3ms内完成故障判别，可以耐受300Ω过渡电阻以及30dB噪声和雷击干扰。.本项目针对现有柔性直流线路保护性能依赖于仿真整定的问题，通过揭示区内故障特有电气量关系，提出了单端量和双端量自整定保护原理，消除了柔性直流线路保护的定值隐患，并提升了保护性能，丰富了现有柔性直流保护体系，拓展了柔性直流继电保护理论，保障柔性直流系统安全运行水平，具有良好的应用前景。