To address the pronounced end-of-travel rebound and the increased potential risk of vacuum interrupter bellows damage during the ultra-fast opening process of a 12 kV dual-speed vacuum circuit breaker, a coupled circuit-electromagnetic field-mechanical dynamics model of the repulsion mechanism is established, and a multiphysics simulation model is developed in COMSOL. First, the structural composition of the repulsion mechanism and the operating principle of ultra-fast opening in the dual-speed vacuum circuit breaker are analyzed. Then, the effects of key parameters, including the outer radius and thickness of the repulsion disc as well as the coil turns, on the opening displacement and velocity characteristics are investigated. Furthermore, combined with the end-impact process, the formation mechanism of opening rebound under high-speed opening conditions is discussed, and the constraint relationship between terminal velocity and rebound displacement is analyzed from the perspective of energy conversion. Finally, the vacuum interrupter bellows are incorporated into the analysis framework to evaluate the equivalent stress distribution and potential fatigue damage risk under high opening-speed conditions. Research findings indicate that the outer diameter and thickness of the repulsion disc have a significant impact on the mechanism's acceleration capability and opening time. When considering stroke establishment time, speed response, the mass of moving parts, and the risk of end-of-stroke impact as comprehensive constraints, the repulsion disc with an outer radius of 75 mm and a thickness of 8 mm exhibits superior overall performance; variations in the number of coil turns simultaneously affect loop resistance, the current rise process, and the electromagnetic repulsive force output characteristics. Within the range of 180 to 200 turns, a good balance between opening speed and motion smoothness is achieved. Although high-speed opening helps shorten the operating time, it leads to an increase in residual kinetic energy at the end of the stroke, thereby exacerbating opening bounce and increasing local stress levels in the bellows. The research findings provide a reference for optimizing the parameters of the repulsion mechanism, suppressing opening bounce, and designing the reliability of the vacuum interrupter in 12 kV dual-speed vacuum circuit breakers.
