Single-end traveling wave protection method in flexible DC transmission line based on dominant frequency attenuation characteristics

•The initial traveling wave is analyzed considering the frequency attenuation law and discrepancy between internal and external faults.•Based on the frequency domain expressions of the initial traveling wave, the ITWDF is constructed, enhancing the high-frequency components in energy calculation reasonably.•The expressions of the ITWDF show that the ITWDF decreases as the fault distance increases, and there is a notable difference in ITWDF between internal and external faults.•The method is immune to the fault impedance, and the expressions of the ITWDF provides a theoretical basis for protection threshold setting as well.