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For distance protection, the measurement accuracy at the boundary of protective zone is the most important issue to distinguish internal faults from external faults correctly. Since the line parameters depend strongly on the frequencies, in order to obtain high accuracy, it should be considered during initial fault transients generally associated with plentiful harmonics. In this paper, a distance protection method considering a frequency-dependent parameters is introduced into HVDC transmission lines. According to transmission-line equations, the frequency-dependent parameter model is separated into two parts: 1) distributed parameter model and 2) a compensation matrix related to frequency-dependent parameters, and the latter is approximated in the time domain with finite impulse response filters. So the voltage and current at the setting point are calculated accurately using local sampling data, and the fault distance is obtained by solving differential equations. The proposed algorithm is able to enhance the calculation accuracy of fault distance greatly at the remote-end faults. Furthermore, it is performed in the time domain and, thus, a short data window is sufficient for it to achieve satisfactory accuracy. Simulation results show that this method is valid and is capable of detecting the faults occurring on the protected line quickly and accurately.Index Terms-Distance protection, frequency-dependent parameters, finite impulse response (FIR) filter, HVDC transmission lines.

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