Switching performance of AgW-Ag(Sn,In)O and AgW-AgSnO2 contact pairs

Experiments were conducted to determine the switching performance of Ag-W contacts when operated in combination with Ag-(Sn,In)O and Ag-SnO₂ materials. Contact pairs for each combination were evaluated in an experimental actuator at a current of 150 A. The Ag-W contact was always the moving contact. The experimental procedure consisted of the following steps: (1) the new contacts were closed, a steady current of 150 A was passed, and the voltage drop (V_c) across the contacts and the temperature rise ( T_r) of the back of the fixed contact were measured; and (2) the contacts then switched a 150-A, 600-V (rms) circuit for 2000 operations. After this, step (1) was repeated. Both the Ag-W vs. Ag-(Sn,In)O and the Ag-W vs. Ag-SnO₂ contact pairs gave low values of V_c when new, a characteristics of good Ag-to-Ag contact. After 2000 operations the V_c values for both contact combinations were very high and variable. Metallurgical examination of the contacts showed arc-resistant, oxide surfaces containing complex oxides of Ag, Sn, and In alloys as well as complex tungstates formed from combinations of Ag, Sn, and In