Fast mechanical switches (FMSs) are critical components of DC circuit breakers (DCCBs)

which require the switch action time to break to a sufficient distance within 3 ms in the DC line breaking scenario

while ensuring a long service life. The breaking mechanism significantly affects the current interruption capability of DCCBs. The operation of the repulsion mechanism

along with the morphology of the arc and its transformation within the interrupter chamber

collectively influence the breaking performance of the FMSs. This paper presents a comprehensive analysis of the FMSs

which serves as the pivotal component of controlled resonance combination circuit breakers (CRCBs). This study establishes a multi physics coupling simulation analysis method based on the equivalent circuit of repulsion mechanism discharge

combined with electromagnetic and solid mechanics fields. By constructing a full cycle magnetohydrodynamic particle arc (MHP) model and using a combined simulation of Finite Element joint model (FEJM)

the evolution law of arc characteristics during the superimposed current interruption process was systematically explored. The focus was on analysing the physical process of the zero zone of the superimposed arc

the multi physics field coupling relationship of the arc

and the interaction mechanism with external characteristic parameters. Further combining with optimisation design methods

the effectiveness of the model was verified through experiments

FEJM provides comprehensive technical support for effectively reflecting the stress issues of core components during the breaking process of FMS and can provide accurate theoretical references for the optimisation design of mechanical motion components in FMS. It also accurately represents the arc extinguishing process during the breaking of FMS and provides a convenient method for the selection and design of circuit parameters for the entire circuit breaker.