Characteristics of a vacuum switching contact based on bipolar axial magnetic field

Axial magnetic field (AMF) contacts can increase the interruption capabilit y of vacuum interrupters. Depending on the design, the principles of the lo cal axial field arrangement are different. For unipolar arrangements the di rection of the axial magnetic field is the same within the whole contact ar ea. For bipolar arrangements, the polarity of the field changes once, In th is paper investigations have been carried out to characterize a bipolar AMF contact system and to test its interruption performance. The influence of the bipolar AMF on the are development and the thermal stress is described by high speed camera and contact surface pictures, In addition, three-dimen sional AMF simulations have been performed by means of a finite-element pro gram to estimate the influence of slots within the contact plates on the AM F performance. The high interruption capability of the bipolar AMF contact system has been verified in different test laboratories up to 12 kV/80 kA(R MS) (symmetrical) and 36 kV/40 kA(RMS) (including 40% DC) by three and sing le-phase tests. The investigations are completed by measuring the post-are current and the shield-potential during recovery period, both describing th e switching behavior of the contact system.