To address the challenges of accurately identifying faults in the T-zone of UHV three-terminal hybrid DC transmission lines and the poor resistance of protection to high fault resistance

this paper proposes a protection method based on the zero-crossing rate characteristics of line-mode current fault components. Firstly

based on the magnitude difference of the line-mode current fault components on both sides of the T-zone

a fault is discriminated as occurring either inside the T-zone or on its left/right lateral lines. Secondly

leveraging the attenuation characteristics of DC transmission line boundary elements on high-frequency transient signals

high-frequency intrinsic mode components of the line-mode current fault components are extracted using multivariate variational mode decomposition. The difference in their zero-crossing rates is then utilized to discriminate between internal and external faults. Finally

a pole selection criterion is constructed by calculating the ratio of the integrals of absolute instantaneous current variations of the positive and negative poles

thereby forming a full-line fast protection scheme for UHV three-terminal hybrid DC transmission lines based on MVMD and the zero-crossing rate characteristics of current fault components. Simulation results from a ±800 kV system model built on the PSCAD/EMTDC platform show that the proposed method can accurately identify fault zones even with transition resistances as high as 600 Ω

ensuring fast protection operation across the entire line.