Vacuum interrupters with axial magnetic field contacts based on bipolar and quadrupolar design

Axial magnetic field (AMF) contacts are applied within vacuum interrupters especially for high short-circuit currents. In this paper, two AMF contact designs based on a bipolar and a quadrupolar magnetic field arrangement and their characteristics are presented. In the first part, both principles are discussed. This is followed by three-dimensional field simulations performed by means of a finite-element-program. The magnitude of the axial magnetic flux density, the phase shift between current and magnetic flux density, and the residual AMF after current zero are investigated during arcing with constant contact gap. Additionally, the influence of motion during contact opening on the a.m. parameters is investigated. An important parameter during the design phase of AMF electrodes is the electromagnetic attractive force which is provided by the AMF contacts during current flow. This force can reduce the required contact force provided by the drive of the vacuum circuit breaker.