Investigation into material effect on cathode spot evolution based on Molecular Dynamics Simulation

Abstract The properties of contact materials largely determine the performance of vacuum circuit breakers (VCBs). Consequently, improving material properties through modifications of conventional Cu-Cr alloys has become a central research focus, particularly in the development of VCBs for higher voltage levels. To elucidate the mechanisms underlying material effects on VCB performance, it is essential to investigate cathode spot behaviour, which fundamentally reflects the interaction between contact materials and the vacuum arc. Although numerous simulation studies have been carried out on cathode spot mechanisms, most are restricted to pure Cu contacts. In this study, molecular dynamics (MD) simulations are employed to investigate cathode spot evolution in three types of Cu-Cr contacts, categorised according to the relationship between grain size and spot size. To focus specifically on material effects, a simplified two-dimensional thermal model is adopted, and analysis is concentrated on crater profiles. The simulations reveal that Cr spots generally produce more favourable crater profiles than Cu spots. While finer Cu-Cr alloys and nanocrystalline Cu-Cr alloys typically exhibit worse erosion resistance than pure Cr contacts, they can yield improved crater profiles under certain conditions. Based on these results, guidance for material modification of Cu-Cr contacts is proposed. From the perspective of minimizing contact erosion and maintaining surface smoothness, cathode spot initiation in the Cu phase should be avoided. Moreover, nanocrystalline Cu-Cr contacts do not necessarily provide significant performance advantages. Finally, comparisons with existing experimental and simulation studies confirm the consistency and validity of the present findings.