Improved Application of Wavelet Transform in Protection of Multi-terminal HVDC Transmission Systems

Wavelet transform (WT) has proven to be a capable tool for protection purposes in high voltage direct current (HVDC) transmission lines due its desirable speed and accuracy. However, the process of waveform sampling can negatively affect the performance of WT and jeopardize the integrity of the WT-based protection principles in discrimination between internal and external faults. This paper investigates this phenomenon and proposes a method to mitigate that by analyzing the characteristics of fault-generated voltage travelling wave and modifying the sampled waveform. Analytical calculations and simulation studies are employed to fully investigate this matter. While analytical calculation establishes the basis to demonstrate and investigate this phenomenon, simulation study provides a more natural way of evaluating the detrimental impact of this phenomenon under real-time fault events. The proposed waveform modification method is implemented in a multi- terminal MMC-HVDC system to investigate its reliability and robustness. The simulation study exhibits improved performance for WT-based protection principles.