Contact Erosion: Testing Machine and Switching Devices

Silver and silver-cadmium oxide contact materials were tested on accelerated testing equipment with current only at break or at make; the bounce characteristics were kept constant during each experiment. At each operation arcing energy (at bounce or during opening) was recorded so that correlations between average arcing energy and wear could be made. Bounce at make was shown to be a critical parameter for the erosion of contact materials; for a given energy the wear rate can be ten or more times higher at make than at break. These wear rates were compared to the ones obtained with switching devices on an AC3 circuit. This was done by analyzing bounce characteristics and arcing energy at make and at break under the test current on each of the three poles of the switching devices during the test. The correlation between the erosion on the testing machine and on the contactors themselves was quite satisfactory when erosion was related to arcing energy. Further, the large spread generally observed on contactor life tests was shown to be of electrical and mechanical origin, and the contact materials were rarely involved if they had been properly manufactured.