Non-unit Boundary Protection using Synchro-squeezing Wavelet for HVDC lines

DC filter and the smoothing reactors, installed at both ends of the HVDC transmission line, constitute the "inherent boundary", which results in different frequency attenuation characteristics of the fault signals. Based on the amplitude difference of the transient tuned voltage between the internal and external faults of the line, and using the Synchrosqueezing Wavelet Transform to extract the voltage component, this paper proposed a non-unit transient-based boundary protection scheme. Meanwhile, The criterion of starting element and fault pole recognition element are also constructed. Extensive PSCAD/EMTDC simulation test in actual HVDC system show that the proposed algorithm can accurately and quickly distinguish the internal and external faults, and has a certain ability to resist the transition resistance.