New principle of busbar protection based on a fundamental frequency polarity comparison

To overcome the contradiction between speed and reliability in existing busbar protection schemes, a new busbar protection algorithm based on a polarity comparison of fundamental frequency currents is proposed. The algorithm extracts the fundamental frequency components of the fault reference current and the virtual current through a wavelet transform. The angle between the two currents is used to characterize the polarity relationship. The polarities of the virtual current and the reference current are the same when an internal fault occurs, and the angle will be small. The polarities of the two currents are opposite for an external fault, in which case the angle is larger. By analysing the variation characteristics of the angle between faults inside and outside busbar, a protection criterion is established, and the fault area is determined. In simulation results based on PSCAD/EMTDC, the algorithm can quickly and reliably identify the faults inside and outside the busbar area, and its performance is not affected by the initial fault angle, fault resistance, fault type or capacitor voltage transformer (CVT) transmission characteristics.

为解决现有母线保护方案中速度与可靠性难以兼顾的矛盾，本文提出一种基于基频电流极性比较的新型母线保护算法。该算法通过小波变换提取故障参考电流与虚拟电流的基频分量，以两路电流间的相位角表征二者的极性关系。当母线内部发生故障时，虚拟电流与参考电流极性一致，此时相位角较小；而外部故障时两路电流极性相反，相位角则较大。通过分析母线内外故障下相位角的变化特性，构建保护判据并确定故障区域。基于PSCAD/EMTDC的仿真结果表明，该算法可快速且可靠地识别母线区域内外故障，其性能不受故障初始角、故障过渡电阻、故障类型以及电容式电压互感器（Capacitor Voltage Transformer, CVT）传输特性的影响。