Study of Non-Unit Transient-Based Protection for HVDC Transmission Lines

It is difficult for existing HVDC line protections to distinguish internal fault from external fault rapidly and accurately, and the protective setting work encounters problems and difficulties. As a result, these protections have a low correct action rate. According to the feature of HVDC transmission system, this paper studies the characteristics of the natural boundary composed of the smoothing reactor and the DC filters. It is proved that this boundary has obvious differences in attenuation characteristics of different frequency components of fault transient signals. Consequently, a non-unit transient-based protection (NUTBP) is proposed. Wavelet multi-resolution signal decomposition technique is used to analyze the transient current caused by the faults. Extensive simulation results indicate that non-unit transient protection can clear all faults on the whole line quickly and credibly.