A measurement on contact resistance and surface profile of arcing Ag contacts

The arc duration, the contact resistance, and the electrode surface profile were measured at every operation in order to observe the detailed relationship between them. The amount of loss or gain of an electrode was also calculated from the change of the electrode surface profile. In the case where the arc duration was short and ended within the metallic phase, the contact resistance was stable and low, and the surface profile was smooth. When the arc became of long duration and transformed into the gaseous phase, the contact resistance increased and grooves and ridges were observed on the electrode surface after the first long arc. The change was reversible, but it took several consecutive operations to recover low resistance and smooth surface.