Comparison of Vacuum Arc Behaviors Between Axial-Magnetic-Field Contacts

We compared vacuum arc behaviors of three slottype axial-magnetic-field (AMF) contacts at two fixed contact gaps using high-speed digital photography and arc-voltage measurements. Solid angle is subtended by anode at the center of cathode or the ratio of the anode diameter to the gap length $(D/g)$ . With coupled influence of the AMF, we observed that with the $D/g$ ratio 48 mm/14 mm, the arc kept in low current modes until higher current compared with the $D/g$ ratio 48 mm/8 mm case. With the $D/g$ ratio 58 mm/14 mm, the arc-mode transitions with the increase of current were similar as the $D/g$ ratio 58 mm/8 mm case. However, with the $D/g$ ratio 66 mm/14 mm, the arc became high current modes at lower current compared with the $D/g$ ratio 66 mm/8 mm case. Correspondingly, with the $D/g$ ratio 48 mm/14 mm, arc voltages at current peaks were close to the $D/g$ ratio 48 mm/8 mm case, whereas arc voltages at current peaks with the $D/g$ ratio 58 mm/14 mm were close to that of the 58 mm/8 mm case. However, with a contact diameter of 66 mm, the arc voltages with the $D/g$ ratio 66 mm/14 mm were higher than the 66 mm/8 mm case. The arcs with the $D/g$ ratio 66 mm/8 mm were more diffuse than the 48 mm/8 mm case. Moreover, the arcs with the $D/g$ ratio 66 mm/14 mm were also more diffuse than the 48 mm/14 mm case when the current peak was 17.8 kA and above. The relationship between interrupting capacity of vacuum interrupters with the slot-type AMF contacts could be expressed as $I = k \times (D/g) + b$, where $k$ and $b$ are constants.