Make-and-break erosion of Ag/MeO contact materials

Make-only erosion, break-only erosion and the combined make-and-break erosion of contacts made from powder metallurgically produced Ag/CdO and three differently produced Ag/SnO/sub 2/ materials were investigated employing both a commercial contactor and a model switch. The test conditions were chosen according to IEC H947-4 AC3 duty, yielding make and break arc energies of the same order of magnitude. The model switch simulates both make and break operations with the same parameter values occurring in modern contactors but in a much better reproducible way and with the opportunity to vary the single parameter values in order to gain information about its influence on the erosion behavior. Make-only erosion tests demonstrated that Ag/SnO/sub 2/ materials suffered either three times higher or about 50% lower erosion losses than Ag/CdO depending on the manufacturing process and/or the additives of the materials. Therefore the structure of the materials rather than the kind of the main metal oxide component (CdO or SnO/sub 2/) is decisive. The combined make-and-break tests yielded significantly lower erosion rates than make-only tests. This unexpected result was reproducible for all contact materials investigated, although the are energy per operation was more than doubled due to the additional break operation. Inspection of the micro-structure of the stressed contacts suggested that this reduction of the erosion rates is due to the motion of the break arc and its effect on the eroded surfaces.