High-current diffuse vacuum arcs on axial magnetic field contacts: arc visualization and contact temperature

We have investigated the behavior of drawn vacuum arcs for several designs of axial magnetic field (AMF) CuCr contacts using high-speed digital photography, arc voltage measurements and near IR photography of the contacts after current zero. As the peak current was increased, a gradual transition occurred in the arc appearance from a multiple cathode-spot arc to the high-current diffuse mode, and then to a high-current diffuse columnar mode. This is in contrast to the very homogeneous contact temperature measured immediately after interruption. The pattern of contact cooling suggests that the contact erosion is dominated by processes induced by flowing liquid metal, which redistributes the heat input from the axially concentrated arc over most of the contact surface. The two models we use to explain the arc behavior are compared to our experimental and analytical results.