The arcing-contact erosion behavior of a DC air circuit breaker’s contacts is the key determinant of its electrical lifetime and interruption reliability. In an air environment

oxygen participates directly in the dynamic depletion and transformation of the contact material via high-temperature oxidation reactions

thereby altering both erosion morphology and droplet splashing characteristics

and ultimately affecting service life and arc interruption performance. To elucidate the complex mechanisms by which ambient oxygen influences contact erosion

a two-dimensional

transient contact erosion model is developed in this paper. Unlike conventional approaches that consider only heat and mass transfer and fluid flow within the arc erosion region

oxidation-kinetics equation is adopted to describe the mass flux into the molten pool driven by high-temperature oxidation. The surface oxygen concentration is treated as a temperature-dependent variable and is introduced into the expression for the surface-tension coefficient. An improved level-set method tracks the free surface evolution while accounting for mass transfer due to both oxidation and evaporation. The model also couples the effects of surface tension

recoil pressure

Marangoni convection

and shear stress on the evolving erosion morphology. By using this model

the influences of different arc energies in air on the contact erosion profiles and on the droplet splashing ejection angle

size distribution and velocity are investigated. The results indicate that

at arc energies below the contact’s melting threshold

a “flat-top” oxide cap forms on the surface

with oxide growth rate increasing with temperature until reaching a saturation threshold. When arc energy exceeds the melting point

changes in surface-tension coefficient induced by oxygen exert a greater effect on erosion morphology than the additional mass influx from oxidation. Under these conditions

droplets splashing become smaller in size and angle but higher in velocity. However

as arc energy continues to rise

the oxidation-induced mass gain diminishes and the surface-tension coefficient further decreases; consequently

recoil pressure and gravitational forces dominate over the surface tension in shaping the erosion morphology.