A Pilot Protection Principle Based on the Structure Similarity of Transient Energy Waveform for Hybrid HVDC System

To improve the ability of rapid fault clearing of hybrid multi-terminal High-voltage direct current transmission (HVDC) lines and ensure the safe operation of electric power transmission, a principle of hybrid HVDC system pilot protection based on the structure similarity for the of transient energy waveform is proposed. In this paper, the fault additional network diagrams of the S-domain under different fault conditions are analyzed, and it is found that there are differences in the transient power of the protection measurement points at both ends of the line during internal or external faults. On this basis, the time-domain transient power obtained by time-domain voltage and current convolution is used to characterize the S-domain power characteristics. Integrate the transient power in the time domain and obtain the transient energy waveform through a sliding window. Structural similarity is used to compare the similarity of transient energy waveforms at both ends of the transmission line, to identify internal and external faults and select fault poles. Simulation verification based on PSCAD/EMTDC shows that the proposed protection principle can reliably identify the fault area and fault pole in the case of 300 Ω fault resistance and 30dB noise interference. It is highly resistant to fault resistance and noise interference. Besides, it is not affected by transient processes and can achieve protection quickly.