The effect of various silver tin oxide materials on contact performance under motor load (a.c.)
The new contact material AgSnO/sub 2/ which is replacing AgCdO in many applications, requires the addition of additives to improve electrical contact performance. These additives such as copper oxide (Cu/sub 2/O) and bismuth oxide (Bi/sub 2/O/sub 3/), can significantly affect contact performance. An investigation was undertaken to compare the changes in contact performance between silver cadmium oxide (internally oxidized) and three silver tin oxide based materials containing (1) no additive, (2) copper additive and (3) bismuth plus copper additives. Performance changes and physical characteristics of each material such as formability (tensile properties), contact resistance and contact material erosion (arc erosion) were evaluated. The silver tin oxide based materials containing copper additive exhibited significantly higher resistance to arc erosion than silver cadmium oxide based material and other silver tin oxide materials evaluated. The resistance to welding and changes in electrical resistance were dependent on the chemistry of each material. The results suggested that the chemistry of the material was the chief reason silver tin oxide based material with copper additive performed better than silver cadmium oxide based material under identical motor load.
Mechanical properties and heading characteristics of some Ag/CdO and Ag/SnO/sub 2/ compositions
The tensile properties and cold heading response of two Ag/CdO and three Ag/SnO/sub 2/ electrical contact alloys have been determined and compared. Tensile data and data from a simple compression test could not be used to predict headability. The Ag/SnO/sub 2/ compositions were found to be significantly less headable than the Ag/CdO compositions.
A new doped silver tin oxide with improved electrical behaviour
Several grades of silver 10-wt.% tin oxide with tellurium oxide additions have been prepared by a powder metallurgy process involving powder mixing, compression, sintering, and second compression to maximum density. The contact parts have been submitted to different electrical tests. After 20000 openings of a 100-A circuit, the erosion loss of 1% tellurium oxide doped silver tin oxide is 13.2 mg compared with 50 mg for internally oxidized silver cadmium oxide. Another test with AC 3 conditions at 100 A of current at opening and 600 A at closing shows that 1% to 1.5% tellurium oxide doped silver/tin oxide has a low temperature rise and very low welding forces compared with nondoped silver tin oxide. 2.0 and 3.0% tellurium oxide shows the same behavior in a 1050-A making current test. The erosion rate is not increased with tellurium oxide additions. The low welding forces result in an improved making capacity in contactor applications.<<ETX>>