Influence of anisotropic contact materials on the vacuum arc’s chopping behavior

Low current vacuum arcs have the natural tendency to interrupt currents before the natural current zero of a system, which is known as current chopping. This paper presents results of investigations comparing the chopping current performance of isotropic and anisotropic WCCu contacts for two compositions (WCCu 60 wt.% and WCCu 79 wt.%). The goal is to show the influence of the contact microstructure, and the role of the associated increase in the electrical and thermal conductivities of the anisotropic material on the chopping current. The results indicate an improved median chopping current value for the anisotropic compositions compared to the isotropic ones. It is lower of about 1A for WCCu 60 wt.% (5.1A vs 6.0 A), while is it is only slightly lower for WCCu 79 wt.% (9.0 A vs 9.4 A). The SEM investigations of the top surface structure do not show significant changes after a few arcing operations at 75A peak current between the two types of microstructures. It is assumed that the current flow localized below the contact surface is affected by the microstructure in a way that favors local heating at the last cathode spots and help to sustain the arc stability.