采用余弦相似度的混合三端直流输电线路保护原

To improve the protection reliability, selectivity, rapidness and sensitivity of the hybrid three-terminal DC transmission line, this paper proposes a line protection principle based on the cosine similarity algorithm according to the voltage and current fault characteristics of the transmission line. The principle uses the transient current components of three terminals in T-area to form the fault area selection criterion to realize fault area identification. Then data normalization is performed on the single-end current-voltage fault component of the fault line, and the difference in cosine similarity between the two is used to identify internal or external fault and fault pole. A hybrid three-terminal HVDC transmission line model is established in PSCAD/EMTDC, and the proposed protection principle is simulated and verified in MATLAB. The simulation results show that the proposed protection principle can identify faults within 3 ms under different fault conditions, with high reliability and good rapidity; it can withstand 500 Ω transition resistance, with strong resistance to transition resistance; it can still identify faults under 20 dB noise, with strong resistance to noise interference.