Make-and-Break Erosion of Ag/MeO Contact Materials

摘要

Make-only erosion, break-only erosion and the combined make-and-break erosion of contacts made from powderrnmetallurgically produced Ag/CdO and three differently produced Ag/SnO_2 materials were investigated employing both arncommercial contactor and a model switch. The test conditions were chosen according to IEC H947-4 AC3 duty, yieldingrnmake and break arc energies of the same order of magnitude.rnThe model switch simulates both make and break operations with the same parameter values occurring in modernrncontactors but in a much better reproducible way and with the opportunity to vary the single parameter values in order torngain information about its influence on the erosion behavior.rnMake-only erosion tests demonstrated that Ag/SnO_2 materials suffered either three times higher or about 50% lowerrnerosion losses than Ag/CdO depending on the manufacturing process and/or the additives of the materials. Therefore thernstructure of the materials rather than the kind of the main metal oxide component (CdO or SnO_2) is decisive.rnThe combined make-and-break tests yielded significantly lower erosion rates than make-only tests. This unexpected resultrnwas reproducible for all contact materials investigated, although the arc energy per operation was more than doubled duernto the additional break operation.rnInspection of the micro-structure of the stressed contacts suggested that this reduction of the erosion rates is due to thernmotion of the break arc and its effect on the eroded surfaces.