基于暂态行波幅值积分的柔性直流电网纵联保护

Pilot Protection for Flexible DC Grids Based on Amplitude Integral of Transient Wavelet

对于"网孔结构"的多端直流电网,边界元件的缺失使其线路之间的电气距离大大减小,传统的边界保护可能不再适用。为此,该文首先分析故障行波在环状直流电网中的传播特性,揭示故障线路与非故障线路前、反行波幅值差异,进而利用故障发生后一段时间内,正向行波幅值积分与反向行波幅值积分的比值进行故障识别。针对双极柔直系统提出一种故障选极判据。结合突变量启动判据,形成一套不依赖边界元件及同步对时的纵联保护方案。最后,对保护判据和主要影响因素利用PSCAD/EMTDC进行仿真分析。结果表明,所提方案能够快速、可靠地识别线路区内外故障,具有较强的抗过渡电阻、抗干扰能力。

Absence of the boundary elements greatly reduces the electrical distance between the lines, which makes traditional boundary protection no longer applicable to mesh DC networks. To address the issue, this paper first analyzed the propagation characteristics of the fault traveling wave in ring DC grids, and revealed the difference between the amplitudes of forward and backward traveling waves of the faulty line and the non-faulty line. A fault-pole discrimination criterion for bipolar flexible DC networks was proposed. Combining with the superimposed energy based start-up criterion, a novel protection scheme independent of boundary components and synchronization was proposed using the ratio of forward and backward-wave amplitude integrals within a period after the fault. Finally, the protection principle and main influencing factors were simulated and analyzed via PSCAD/EMTDC. The results show that the proposed scheme can quickly and reliably identify internal and external faults, and has strong anti-fault resistance and anti-interference abilities.