Arc behaviour in axial magnetic field vacuum interrupters equipped with an external coil

The simplicity of vacuum interrupters equipped with an external magnetic field coil makes them a privileged object of study. Commercial application has however been hindered by the ohmic losses in the coil. The latest developments allow a reduction of these losses. Their reduction also leads to a much lower applied axial magnetic field, close to the so called "minimum required axial magnetic field" strongly affecting both current distribution and contact erosion. A model is presented which allows estimation of current distribution, contact temperature and contact erosion. The model results are presented and compared with experimental results.