Analysis of the fuse melting mechanism of potential transformer on the busbar of 35 kV distribution system

10–35 kV distribution networks typically operate with non-effectively grounded neutral systems. Frequent fuse failures on the high-voltage side of bus potential transformers (PTs) significantly compromise the operational reliability and stability of these networks. However, existing research into the underlying failure mechanisms remains limited. To identify the root causes of such failures, this study analyzes an actual fault case from a 35 kV substation. Initially, the system configuration, operational modes, and fault characteristics are evaluated. Subsequently, a 35 kV system simulation model is developed using PSCAD/EMTDC, and its fidelity is validated by benchmarking simulation results against field measurements from a real single-phase-to-ground fault. Furthermore, the fuse rupture mechanism is investigated by simulating ferromagnetic resonance, low-frequency nonlinear oscillations, PT excitation characteristics, and switching operations. The results demonstrate that the proposed model accurately captures the system’s transient electrical characteristics and fault dynamics. Specifically, the analysis reveals that overcurrent induced by ferromagnetic resonance, current increments resulting from abnormal PT excitation, and transient overcurrents generated during switching operations are the primary factors contributing to fuse failures.