Evolution of microscopic contact surface condition in VCB during closing operations after inrush current erosion

Vacuum circuit breakers (VCBs) show significant prestrike gap dispersion under high-frequency inrush current, largely influenced by microscopic contact surface condition. However, existing studies offer only basic measurements, lacking quantitative analysis of surface evolution during closing. This paper uses a DC dynamic gap measurement method to evaluate the evolution of microscopic contact surface condition in vacuum interrupters (VIs) following inrush current erosion. Through this approach, the quantitative relationship governing contact surface evolution and prestrike gap dispersion is established. The surface condition is characterized by the field enhancement factor β, and a clear correlation between β and the prestrike gap is identified. Results demonstrate that the combined effects of mechanical contact collisions and thermal influence from field emission current contribute significantly to the observed prestrike gap dispersion.