MODIFICATION IN THE MICROSTRUCTURE OF MATERIALS WITH AIR-BREAK SWITCHING AT HIGH CURRENTS

Under the effect of an electrical arc, the surface layer of contact materials undergoes extreme thermal constraints which modify its microstructure. Since electrical performance depends, to a great measure, on the surface structure of the material, it is essential to understand the mechanism by which these rearrangements take place. Sections and surfaces of disrupted areas were examined by a scanning electron microscope. AgZnO, AgC, AgNi, AgSnO2, and AgCdO were tested for high current separation (2000 A) on a testing apparatus which simulated the operation of a low voltage circuit breaker. This paper deals predominantly with AgZnO. With respect to this material, we were able to ascertain that the structures after a single separation at 2000 A or after life tests AC4-type electrical are similar and can be reproduced by simulating the thermal effect of an arc on the superficial layer by a LASER fusion or by melting in a furnace. The results obtained in these tests allowed us to explain the structural modifications by correlating them to composition, granulometry, and the physical and chemical properties of the material, and thus gain a better understanding the electrical properties of AgZnO.