Contact Resistance and Arc Erosion of W/Ag and WC/Ag

A multitude of tungsten/silver (W/Ag) and tungsten carbide/silver (WC/Ag) contact materials of different compositions, origins, manufacturing methods, and contact sizes are investigated over a wide current range I = 60-1800 A. Resistance is measured after each switching-off operation and evaluated statistically. The results are a strong dependence of contact resistance on switching current and contact size, with high values caused by semiconducting layers at low arc currents and low metallic values at high currents. Investigations of the contact surfaces after switching help to explain this phenomenon. The resistance decrease nearly coincides with a considerable increase in erosion. While at low currents there is no significant difference in the erosion rates between W/Ag and WC/Ag, the latter tends to have lower rates at high currents.