Finite element analysis of AMF vacuum contacts

It has been known for some time that the presence of an axial magnetic field (AMF) can increase the upper limit on the interrupting ability of vacuum contacts by keeping the arc plasma in the diffuse mode. Many designs have been proposed for contact structures to induce this magnetic field, most of which involve forcing the current to travel in a coil-like pattern. Some of these structures are described and then analyzed using a three-dimensional finite element package, allowing a new understanding of how different aspects of physics may interact in these designs. Different contact structures are compared based on magnetic field strength, magnetic field distribution and current flow. The resulting eddy currents from 60 Hz excitation are considered, as these are believed to be a major factor in the generation of post-arc current