In the vacuum DC circuit breaker based on the artificial current zero, the change of arc luminosity delays the change of current value significantly in the fast current-zero stage. This phenomenon has impacts on the breaking capacity of the DC vacuum circuit breaker. Therefore, it is necessary to study the dynamic characteristics of the arc plasma under the above condition. In this work, a 3D transient magneto-hydro-dynamic model based on the commercial cup-type axial magnetic field (AMF) contact is established to study this phenomenon. The simulation results show that the fast current-zero stage is too short for the plasma to diffuse. The changes of the physical characteristics of the arc plasma lag the change of current value. Moreover, the magnetic field hysteresis caused by the eddy current on the electrode occurs in this stage, resulting in a continuous stronger AMF. It makes the distributions of the plasma uniform, while the diffusion of the arc plasma reduced at low currents, which is detrimental to the post-arc dielectric recovery stage. In addition, in the fast current-zero stage, the AMF near the contact slot is smaller than in other areas. This indicates that the slotting is effective in suppressing eddy currents and avoiding the negative effect of excessive AMF on plasma diffusion at this stage. The simulation results are consistent with the experimental results.

This paper aims to investigate the anode modes of vacuum arc at different opening speeds, especially at a high opening speed that exceeds 3 m/s. The butt contacts made of CuCr30 and CuCr50 with a diameter of 15 mm are used. Experiments are conducted at the current of 3.3, 4.4, 5.5, and 6.3 kA with a frequency of 50 Hz. An electromagnetic repulsion actuator provides the average opening speed from 1.7 to 3 m/s. The experimental results show that the number of droplets splashing into electrodes increases as the arc current increases, while a higher opening speed decreases the droplets. A higher opening speed will reduce the transferred charge before the anode spot type 2, and a higher Cr content increases the transferred charge before the anode spot type 2. Increasing opening speed will decrease the starting time of anode spot type 2, but it increases the gap distance when anode spot type 2 appears. Meanwhile, the increase in Cr content delays the formation of anode spot type 2.

In this study, to investigate vacuum arc characteristics under different diameter-to-gap distance ratios ( D/ g), experiments are conducted on axial magnetic field (AMF) contacts with varying D/ g. The peak current value ranges from 15 to 35 kA. The experimental results show that the ability of AMF contacts to control the arc decreases with D/ g. Furthermore, the 2/3 coil contact can control the arc under long gap distances, whereas the cup-shaped contact cannot effectively control the arc under long gap distances. The arc energy and noisy period duration decrease with increasing D/ g. The arc voltage of the 2/3 coil contact at the peak moment is always the lowest compared to the cup-shaped contact and the 1/2 coil contact, and the arc voltage of the 2/3 coil contact at the peak moment has an approximate power function relation with D/ g. The simulation results show that the AMF distribution changes from saddle shape to bell shape with decreasing D/ g. The 2/3 coil contact is more suitable for high-voltage vacuum interrupters (VIs), while the cup-shaped contact is more suitable for medium-voltage VIs.