This paper analyzes the power supply system of suspended monorail transit and emphasizes the necessity of DC system ground fault protection to ensure equipment and personnel safety under various operating conditions. While conventional voltagebased ground fault protection devices can provide basic protection functions, they lack selective tripping capability and may expand the fault area. Based on Kirchhoff's current law, this paper proposes an innovative sectional currentbased ground fault protection scheme. Through the implementation of inverse timecurrent characteristics and differential current components, the scheme achieves accurate and rapid fault section identification, enabling priority tripping of corresponding sections to isolate faults, thus significantly improving system selectivity. Through analysis of protection objectives, coverage, types, and operation time limits of both 64D protection and frame current protection, the study concludes that these two protection methods are complementary and can operate simultaneously. Field applications demonstrate that all protection functions perform sensitively and reliably. By calculating key parameters for 64D protection, this paper proposes protection schemes and system setting values for practical engineering applications, optimizing protection system selectivity, effectively reducing fault ranges, and ensuring operational safety.

suspended monorail  /  DC system  /  grounding leakage protection  /  64D protection