Research on HVDC Transmission Protection Based on DC Line Boundary Elements

In this study, the smoothing reactor and DC filter of a DC transmission line are found to significantly attenuate the high-frequency components of the transient signal through simulation and analysis of internal and external faults of high-voltage direct current (HVDC) transmission lines. Consequently, the time-domain waveforms of the voltage fault component at the measurement end of transmission lines differ significantly among different fault types. When an external fault occurs, the high frequency component is low and the waveform is smooth, while when an internal fault occurs, the high frequency component is high and the waveform is steep. A multifractal spectrum is calculated based on the curvature characteristic value K<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</inf> of the multifractal spectrum that measures the irregularity of the voltage fault time-domain waveform. If the external fault occurs, Kmax is greater than 10, and if the internal fault occurs, Kmax is less than 10. Simulation tests with PSCAD demonstrate that this criterion is highly reliable, does not depend on fault location, and is resistant to transition resistance.