A novel non-unit transient based boundary protection for HVDC transmission lines using synchrosqueezing wavelet transform

Since high voltage direct current (HVDC) transmission system takes on significant tasks in coordinating the power grids asynchronous interconnection and the comprehensive utilization of energy resources, the reliable and fast faults clearance to guarantee the safety and stability of the power system should be attached great attention. This paper, based on the analysis of the HVDC boundary characteristics, proposes a novel non-unit transient based boundary protection as the main protection for HVDC transmission lines, and uses the novel synchrosqueezing wavelet transform (SWT) for time-frequency (T-F) representation. By synchrosqueezing and reassigning the T-F spectrum of the continuous wavelet transform (CWT), SWT can obtain a high resolution T-F spectrum, which brings higher reliability to protection. Based on the transmission differences between tuning voltage and low-frequency voltage by the boundary, this paper proposes the SWT-based non-unit transient boundary protection algorithm, and the ratio of the positive and negative voltage micro-increment is used to select the faulty line. Extensive PSCAD simulations of +/- 800 kV HVDC project and some field data are used to test the proposed protection scheme. Compared with the CWT-based boundary protection, experimental results verified the proposed method could perform rapidly and reliably in various types of fault, especially can be immune to commutation failure and shows good performance for switching operation as well as fault closer to the very begging of the line, and with high selectivity and sensitivity.