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

Axial magnetic field (AMT) 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 section, both principles are discussed. This is followed by three-dimensional field simulations performed by means of a finite-element-analysis 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 a constant contact gap. Furthermore, the influence of motion during the contact opening on the previously-mentioned parameters is investigated. An important parameter during the design phase of AMT 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. Finally, it is reported about the short-circuit performance of both contact systems. Contact plates after high-current interruption are presented revealing the arcing behavior during the high-current phase.