This paper presents a hybrid travelling wave/distance protection for HVDC transmission lines by constantly monitoring the phase angles of characteristic harmonic impedances, measured from one head of the line. Waveform analysis, using the fast Fourier transform, reveals that the behaviour of the phase angles of characteristic harmonic impedances is periodic, and based on their results, the transmission line can be divided into distinctive segments for distinguishing internal and external faults. According to these results, majority of the line length can be protected in the event of internal faults, solely by monitoring the phase angles of the input impedances of characteristic harmonics. However, there are some sections of the line (fail-to-trip regions) where the results of the phase angles of the characteristic harmonic impedances under internal faults are very similar to those under the external faults. Therefore, if an internal fault occurs in one of these regions, the proposed protection method will fail to operate. To reliably overcome this problem, wavelet analysis is adopted, which can safely detect the internal faults inside the fail-to-trip regions. It will be shown that the proposed method established based on these principles is fast and reliable, and has excellent performance in identification of the remote-end fault conditions. The validity of the proposed method is evaluated using the Hydro-Quebec HVDC benchmark model, simulated in MATLAB/SIMULINK software environment.

本文通过不断监测特征谐波阻抗的相角（从线路的一端开始测量），提出了一种用于HVDC输电线路的混合行波/距离保护。使用快速傅里叶变换进行的波形分析表明，特征谐波阻抗的相角行为是周期性的，并且根据其结果，可以将传输线划分为不同的段，以区分内部和外部故障。根据这些结果，仅在监视特性谐波的输入阻抗的相位角的情况下，就可以在发生内部故障时保护大部分线路长度。然而，在线路的某些部分（故障跳闸区域），内部故障下特征谐波阻抗的相角结果与外部故障下非常相似。因此，如果在这些区域之一中发生内部故障，则所提出的保护方法将无法运行。为了可靠地克服这个问题，采用了小波分析，可以安全地检测故障跳闸区域内部的内部故障。结果表明，基于这些原理建立的方法是快速，可靠的，并且在识别远端故障条件方面具有优异的性能。该方法的有效性使用在MATLAB / SIMULINK软件环境中模拟的Hydro-Quebec HVDC基准模型进行了评估。