Influence of increased gap lengths above 20 mm for rotating vacuum arcs between TMF-contacts

The development and testing of vacuum switches with long gap distances or series configurations is mostly focused on AMF-contacts. The advantages of transversal magnetic field (TMF)-contacts are currently confined to medium voltage switchgear. These contacts are inexpensive in production and show lesser contact resistance in closed position. The goal of the contact geometry is the distribution of energy over the contact surface. The derived question is whether this task can be performed at higher distance, where the magnetic field is weaker.This paper tests VIs equipped with TMF-contacts under short-circuit currents and contact gaps above 20 mm. The goal is the analysis of the TMF-effect and the derived energy distribution during the high current phase. In the experimental setup, a programmable servo drive is used to achieve gaps up to 31 mm during 50 Hz interruption at current zero. For even larger gaps, the current frequency is lower to 35 Hz to reach 47 mm at current zero.An image detection in combination with electrical data is used to investigate the high current phase under increasing gaps. Evaluating arc voltage and arc movement in form of speed and rotations, the TMF-contact is not significant affect by increasing gaps. The contact geometry could be feasible for high voltage application.