Silber-Tungsten (Ag/W)

Silver-Tungsten Carbide Graphite-materials (Ag/WC;Ag/WC/C)

Copper–tungsten (CUWODUR) materials with typically 50-85 wt% tungsten are produced by the infiltration process with the tungsten particle size selected according to the end application. To increase the wettability of the tungsten skeleton by copper a small amount of nickel < 1 wt% is added to the starting powder mix. W/Cu materials exhibit a very high arc erosion resistance. Compared to silver–tungsten materials they are however less suitable to carry permanent current. With a solid tungsten skeleton as it is the case for W/C infiltrated materials with 70-85 wt% tungsten the lower melting component copper melts and vaporizes in the intense electrical arc. At the boiling point of copper (2567°C) the still solid tungsten is efficiently “cooled” and remains pretty much unchanged. During very high thermal stress on the W/Cu contacts, for example during short circuit currents > 40 kA the tungsten skeleton requires special high mechanical strength. For such applications a high temperature sintering of tungsten from selected particle size powder is applied before the usual infiltration with copper (example: CUWODUR H).

For high voltage load switches the most advantageous contact system consists of a contact tulip and a contact rod. Both contact assemblies are made usually from the mechanically strong and high conductive CuCrZr material and W/Cu as the arcing tips. The thermally and mechanically highly stressed attachment between the two components is often achieved by utilizing electron beam welding or capacitor discharge percussion welding. Other attachment methods include brazing and cast-on of copper followed by cold forming steps to increase hardness and strength.

The main application areas for CUWODUR materials are as arcing contacts in load and high power switching in medium and high voltage switchgear as well as electrodes for spark gaps and over voltage arresters.