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.
Influence of AC interruption points on AC arc erosion of silver based contact materials
This paper presents experimental results obtained from a study into the reduction of contact erosion on break, using controlled AC point interruption principles. Five thousand break tests are carried out for a utilisation category of AC-1, at a current of 6 A rms, a gap-length of 2 mm on AgCdO (90%, 10%), AgCu3 (97%,3%) and Ag (fine, 99.9%) contacts, each with a diameter of 5 mm. The results show that by interrupting the circuit at selected points on the AC waveform, the rate of erosion varies significantly for different contact materials and the fine silver in general loses material. The minimum mass change for AgCdO is at interruption point /spl alpha/=135/spl deg/ and for AgCu3 surprisingly is at /spl alpha/=45/spl deg/. In the random break operation both AgCdO and fine Ag lose materials from both electrodes, but AgCu has an equal amount of material transfer. The paper also discusses the practical benefits of a controlled interruption technique within three-phase switching devices by incorporating a logic sequencer.
Erosion Characteristics of Silver-Based Contact Materials In a DC Contactor
Electrical life tests in a dc contactor are performed under DC4 and DC5 conditions. Results from our observations and erosion measurements are compared for different silver-based contact materials. For the device used a relation can be established between the arc energy and material loss and transfer. The erosion mechanism during the make operation determines the overall arc erosion to a larger than expected extent. Silver nickel 90/10 stands out as the contact material with the lowest erosion rate under both conditions.