Effect of polymeric gassing walls during arcing on AgW/AgC contact resistance

Contact resistance was measured after arcing for AgW moving against a AgC stationary contact pair in an arc chamber. The resistance, measured at five different current levels over the range of 2 kA/sub p/ to 22 kA/sub p/, was obtained using two different arc chamber wall materials, ceramic and polyester, to measure the effects of gas evolution on contact resistance from circuit breaker walls. When compared to results using ceramic walls, polyester walls did not show any statistical difference in contact resistance. However, increased chamber pressure, resulting from ablation of the polyester walls, was measured. SEM photographs and EDS surface mapping measurements showed the change in resistance, for both wall materials, was due to a depletion of silver from the contact surface at mid-range arcing currents and redeposition of silver at higher arcing currents. Discussions include the effect of arc temperature on contact resistance and the various gases, generated by the ablation of the polymer walls, on resistance and arc chamber pressure.