A sensitive single-end DC line fault detection method for MMC-HVDC grids using reactor voltage ratio.

• The reactor line-mode transient voltage fault component in dc grid is analyzed. • The mathematical morphology-based method to select the partition time for two parts is proposed. • The protection scheme using the ratio of the two-part voltage integral is proposed. • The high sensitivity to high impedance faults is validated in a four-terminal meshed DC grid. The fast, sensitive, and reliable primary protection method can ensure the continuous and reliable operation of the modular multilevel converter (MMC)–based HVDC grid during dc faults. This paper proposes a fault detection method based on the ratio of voltage integrals to improve the single-end method sensitivity to high-resistance faults. First, the reactor line-mode transient voltage caused by the initial traveling wave (TW) is analyzed in the fault component network. The exponential term of the voltage is independent of the fault resistance and can be reflected by the proposed voltage integral ratio. Next, the influence of subsequent TWs on the integral is analyzed. The partition time, selected by the mathematical morphology, is proposed to divide the voltage sampling data into two parts. Finally, the criterion using the ratio of the two-part voltage integral is proposed to detect internal faults. The ± 500 kV bipolar MMC-HVDC grid built on PSCAD/EMTDC validates that the proposed method can fast identify internal faults, and the protected zone covers the whole line length. Smulation cases analyze the influence of the reactor and sampling frequencies on the proposed method. Moreover, the method is sensitive to high-resistance faults and can work under white noise and different wiring modes. [ABSTRACT FROM AUTHOR]