Non-unit Transient Protection for LCC-HVDC Transmission Lines Using Similarity of Current Derivatives and Faulty Pole Selection

Background: High-voltage direct-current (HVDC) transmission technology has been applied frequently in high-voltage power systems for long-distance and large-capability power transmission in recent years. However, there are some problems with the reliability and sensitivity of HVDC transmission-line protection, leading to protection malfunction or maloperation. Objective: For line-commutated converter-based HVDC transmission lines, a non-unit transient protection patent using a similarity of current derivatives and faulty pole selection is studied. Methods: During the fault transient period, based on the superimposed networks for different types of faults, the similarity of line current derivative (LCD) and dc filter current derivative (DFCD) and the numerical characteristics of DFCD are derived in detail. The Pearson correlation coefficient is employed to calculate the similarity between LCD and DFCD. Based on the polarity characteristics of earth-mode DC filter current, the criterion of faulty pole selection is proposed. A ±800kV UHVDC system model built in PSCAD/EMTDC is used to verify the performance of the proposed protection. Results: Simulation results show that the non-unit transient protection can correctly identify different fault types for HVDC transmission lines over 1900 km, even with 500 Ω fault resistance. Conclusion: The proposed model’s protection and high performance of fault identification prove that it is highly sensitive and reliable under different fault conditions. A non-unit transient protection using the similarity of current derivatives and faulty pole selection has been proposed in this study.