Investigation on Effects of Low-Content W Additives on Post-Arc Process of Cr-Based Contact in Vacuum Circuit Breakers: MD Simulation

Low-content W addition in conventional Cu-Cr contacts for vacuum circuit breakers has the potential to enhance breakdown strength and hardness. However, high W content in contacts can induce interruption failure in the post-arc period due to strong thermal electron emissions from the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{W}$</tex> surface, raising the question of whether the low-content <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$W$</tex> addition might also lead to arc reignition. To investigate the influence of the low-content <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{W}$</tex> addition on the post-arc recovery of vacuum gap, this work combined MD simulation and theoretical calculation methods to examine the arcing and postarc behaviours on localised Cr phases with W additions. The thermal electron emission was calculated by analysing the evolution of surface temperature and the structural change of the substrate during the arcing and post-arc stages. Simulation results indicated that low concentrations of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$W$</tex> in small particle form do not adversely affect post-arc recovery, suggesting that small addition of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$W$</tex> into <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$C u-C r$</tex> contact materials could potentially improve vacuum circuit breaker performance without the risk of thermal emission-induced failure. This work offers insights into the contact material design for vacuum circuit breakers, with the aim to balance the mechanical and electrical properties by controlling the form and concentration of W, ultimately optimising the post-arc recovery characteristics of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{Cu}-\text{Cr}-\mathrm{W}$</tex> contacts