Evaporation erosion of the contacts is one of the fundamental failure mechanisms for relays. In this paper, the evaporation erosion characteristics are investigated for the copper contact pair breaking a resistive direct current （dc） 30 V/10 A circuit in the air. Molten pool simulation of the contacts is coupled with the gas dynamics to calculate the evaporation rate. A simplified arc model is constructed to obtain the contact voltage and current variations with time for the prediction of the current density and the heat flux distributions flowing from the arc into the contacts. The evaporation rate and mass variations with time during the breaking process are presented. Experiments are carried out to verify the simulation results.
Species composites of Ag-N2, Ag-H2 and Ag-He plasmas in the temperature range of 3,000-20,000 K and at 1 atmospheric pressure were calculated by using the minimization of Gibbs free energy. Thermodynamic properties and transport coefficients of nitrogen, hydrogen and helium plasmas mixed with a variety of silver vapor were then calculated based on the equilibrium composites and collision integral data. The calculation procedure was verified by comparing the results obtained in this paper with the published transport coefficients on the case of pure nitrogen plasma. The influences of the silver vapor concentration on composites, thermodynamic properties and transport coefficients were finally analyzed and summarized for all the three types of plasmas. Those physical properties were important for theoretical study and numerical calculation on arc plasma generated by silver-based electrodes in those gases in sealed electromagnetic relays and contacts.
在慢速分断阻性负载条件下,试验研究了Ag、Ag Ni10、Ag Sn O_212、Ag Cd O124种触头9V/10.5A和9V/19A条件下的分断金属液桥现象。得到了分断过程中金属液桥电压、电流、电阻和功率的变化规律,使用高速摄像机和显微镜拍摄分断过程,得到了金属液桥几何形貌,用激光共聚焦显微镜研究了分断后阴极和阳极的表面形貌特征。结果表明,4种触头电特征曲线具有类似的变化规律,在金属液桥分断过程中发现多次火花放电现象,4种触头金属液桥产生的材料转移都是由阳极转移到阴极。
