Silver tungsten carbide contacts fork circuit breaker applications

Silver tungsten carbide (AgWC) contacts are often applied to circuit breaker applications due to their good arcing erosion properties. The low material loss is beneficial for repeatable high interruption capacity. This paper characterizes the influences of contact material microstructure and sintering agents on the switching properties of AgWC40 material. A detailed description of the microstructure by quantitative metallurgy methods is a key aspect of this work. Furthermore, the influence of contact material microstructure and composition on the sintering shrinkage are evaluated. Model switches are applied to study the switching performance of AgWC40 materials under defined and reproducible boundary conditions. Performance parameters studied are dynamic sticking tendency at make, arcing erosion and contact resistance after break operation. Cross sections after switching are used as basis for interpretation of achieved test results. The studies show that effects of sintering agents dominate the resulting contact resistance after arcing, while no differences in erosion can be observed at chosen overload conditions. In addition dynamic sticking tendency could be reduced by finer microstructure and reduced amounts of sintering agents.