Contact Welding Mechanism With Bounce Arc on Ag and Cu Contacts in Low-Voltage Switches

This paper describes a basic mechanism of contact welding formed by bounce arc upon contact making, based on experiments and analytical simulation of thermal conduction in the contact. We measured the weld force after every contact making in a low-voltage condition (200 V ac). The arc current was set to 60-500 A using a reactor load, the arc duration was within 0.12-2.42 ms, and the contact materials were pure silver (99.99%) and copper (99.9%). In this condition, we clarified that the weld force increases depending on arc energy supplied to the contact surface. We also measured the melted area on the contact surface and clarified the area dependence on the arc energy. Considering the tensile strength of the contact material, we found that the real welded area corresponds to about 25%-40% of the melted area. We concluded that the evaporation of contact material is a significant factor in reduction of the welded area.