Hybrid travelling wave/distance protection for HVDC transmission lines based on phase angles of characteristic harmonic impedances

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.