Evaluation of Contact Surface Damages with an Optical Cross-Section Method

Contact surfaces of mechanical relays and switches are often damaged by arc discharges and/or mechanical wear during switching operations. Conventionally, erosion and transfer characteristics of various contact materials under different load conditions have been mainly studied based on observation and evaluation of contact surfaces after switching operation tests. A further detailed study will become possible if we can observe and numerically evaluate a changing process of surface damages (especially, growth of a crater and/or a pip) on contact surfaces during switching operations. For that purpose, a numerical evaluation system of contact surface damages by way of an optical cross-section method is being constructed. In this paper, Ag contacts were operated to break a DC inductive 14V-2A load current for 50,000 operations, and the contact surface profile (a crater growth process) was numerically evaluated with this system at every 2,000 operations during the switching operations. From the results, certain changes in the cathode surface during the switching operations were able to be observed.