Material transfer characteristic of silver contacts under resistive DC load conditions

Arc discharge between electrodes of electromechanical relays and mechanical switches often causes contact surface damage through material transfer and arc erosion. Especially, material transfer sometimes occurs even with a very small load current such as DC50 to 100 mA, which is quite a bit smaller than the minimum arc current value of each contact material. In this paper, material transfer characteristic of silver contacts installed in telecommunication relays were studied with a scanning laser microscope under various resistive load conditions. The relation between electrical load conditions (load current and power supply voltage) and contact surface configuration caused by material transfer (craters and pips) was studied. It is confirmed that material transfer occurs by anode arcs even with the load condition of DC10 V-50 mA, which might be considered too light to have an arc discharge. The tested samples can be categorized into two groups; material transfer phase and arc erosion phase. Transition from transfer phase to erosion phase is believed to occur and is related to the contact activation process. The results also indicate that load current has an influence on the material transfer phenomena and power supply voltage is related to the arc erosion phenomena.