Behavior of initial columnar arc in vacuum interrupters with axial magnetic field contacts

To improve current interruption capability of vacuum interrupters with axial magnetic field (AMF) contacts, it is necessary to make an initial columnar arc diffused on a larger area of the contacts as rapidly as possible after the opening of the contacts, and also to suppress local temperature rise at the arc initiation points on the contacts. We observed behavior of the initial columnar arc between AMF contacts set in a vacuum chamber using a high-speed video camera, and experimentally investigated the relation between the arc initiation point and the behavior of the initial columnar arc, employing various contacts with different contact separation points. We also found that the direction of motion of the initial columnar arc and its velocity were dependent on the arc initiation point on the contacts. It was shown that the motion of the initial columnar arc was dominated by the Lorentz force due to the arc current and the radial magnetic field (RMF) parallel to the contact surface.