Erosion and resistance characteristics of AgW and AgC contacts

The effect of arc current, silver content, and density on contact erosion and contact resistance under break operation was measured for three types of AgW circuit breaking contacts in air. The arc current ranged from 2 kA_p to 22 kA_p and the percentage of silver in each of the contact materials was 40, 45, and 49% wt. Contact density and erosion measurements showed the closer the contact density was to 100% theoretical density the lower the erosion rate. Erosion rate results showed a gradual increase in the erosion rate over the 5-16 kA _p current ranges. The increase in erosion rate corresponded to an increase in contact resistance in all three materials. Above this range, the resistance dropped bark down near its original level as current density increased and the erosion rate leveled off. A relationship was established, through measurements of are diameter and surface composition, between arc current density and contact erosion/resistance