Runming Zhang’s research while affiliated with Xi’an Jiaotong-Liverpool University and other places

Recent advancements in vacuum arc technology have heightened interest in the evolutionary behavior of cathode spots, particularly in metal deuteride cathodes, due to their critical role in influencing device performance and longevity. Extensive research has elucidated various aspects of cathode spot erosion. A novel two-dimensional (2D) axisymmetric swirl model is established to study the impact of different thermo-field emission functions and Nottingham effect on the formation and evolution of cathode spots in metal deuteride cathodes under vacuum arc conditions. Deuterium diffusion equation, Nottingham effect, and two distinct thermo-field emission functions are incorporated in this model. Current simulation results reveal that the Nottingham effect initially acts as a heating mechanism within the first 2 ns before transitioning to a cooling mechanism. Notably, the maximum temperature predicted by the comprehensive electron emission model, proposed by Jensen, consistently surpasses that of the high-intensity thermo-field emission model, developed by Hantzsche. Consideration of the Nottingham effect also reduces the potential on the cathode spot crater surface and increases the velocity of the liquid metal. Additionally, the deuterium desorption rate and total deuterium desorption are strongly temperature-dependent.

In order to further understand the formation and development process of cathode spot crater on copper-chromium (CuCr) nanocrystalline alloy electrode in vacuum arc, a new simulation method considering the distribution of different components is proposed. And a two-dimensional axisymmetric model is established to study the effects of different components on the formation and development of cathode spot crater. The differences in physical properties are considered in the model, and the interface between the Cu component and the Cr component is effectively tracked. The distribution, flow, and heat transfer of the Cu and Cr components are simulated. To directly demonstrate the advantages of the method, the simulation results are compared with those adopting the method that linearly combines the physical property parameters according to the weight percentage of components. Simulation result shows that the presence of Cr components has an important influence on the formation and development of cathode spot crater on CuCr nanocrystalline alloy electrode. The effects of different weight percentages of Cr components on the formation and development of cathode spot crater on CuCr nanocrystalline alloys are also studied. The results indicate that with the improvement of Cr component weight percentages, the temperature on the cathode spot crater is increased, and the fluidity of liquid metal is reduced during erosion. Finally, the simulation results have been compared with experimental results of other researchers.

In this paper, a three-dimensional cathode spot erosion model is proposed to study the development of cathode spot motion process on the surface of copper cathode. The formation and development process of cathode spots motion without external magnetic field is studied. In this model, energy flux density, pressure, and current value are considered as external parameters. The simulation results compared the cathode spot ablation trajectories and temperature distribution under different motion forms and motion velocities. The results indicated that during the spots expansion process, the flow of liquid metal will form a convex structure on the surface of the cathode and a hollow structure inside the cathode. Comparing different motion types, the annular motion significantly increased the roughness of the cathode surface. With the increase of the speed of spots movement, the interaction between the craters is significantly weakened, which will reduce the temperature and the roughness of the cathode surface. The simulation results are consistent with the experimental results.

A 3-D asymmetric model has been proposed to study the formation and development of copper cathode spots on different shapes of protrusions and the interaction with a nearby spot in a vacuum arc. In addition to comparing protrusions of different shapes, the effect of the distance between two spot craters is also considered. The article compared the morphology and temperature of the erosion process of the spots with spherical protrusions, two different ellipsoidal protrusions, and the case of no protrusions as a comparison. Through the simulation calculation, it is found that there will be an obvious liquid metal ridge at the intersection of the two spots no matter what kind of shapes of protrusions when the two cathode spot craters are not very close. The maximum surface temperature of the cathode always appears at the junction of the two spots. For the protrusion with a certain volume and distance, the temperature rise of the cathode is higher when its height is higher. When the shape of the protrusion remains unchanged, the closer distance between the two spots causes the temperature to rise more. The temperature rise caused by the distance factor is more obvious than the shape factor.

Vacuum arc widely appears in vacuum interrupters, ion sources, thrusters, and other related application fields. Understanding the components’ characteristics in vacuum arc is very important for the above application fields. At present, modeling and numerical simulation technology is becoming more and more important for the study of vacuum arc mechanisms. In this article, multicomponent magnetohydrodynamic (MHD) models of vacuum arc with passive and active anode modes will be reviewed, and the commercial alloy electrode materials in vacuum interrupters will be considered. The influence of the spatial magnetic field generated by commercial electrodes on the arc was studied. Furthermore, transient plasma characteristics and component evolution processes of vacuum arcs with different situations (fixed gap distance and electrode movement) in vacuum interrupters are reviewed. Vacuum arc plasma jet characteristics with a ring anode under different external magnetic fields will also be introduced, and the separation mechanisms of light and heavy ions in vacuum arcs will also be studied. Finally, the challenge of vacuum arc modeling in the future is also discussed.

Vacuum circuit breakers are widely used in medium-voltage power systems, and the post-arc breakdown is a key factor limiting performance of the vacuum circuit breakers. In this work, a 2-D particle-in-cell/Monte Carlo collisional model is developed to investigate the post-arc breakdown. The residual plasma, metal vapor, inhomogeneous temperature distribution and electron emission on the post-arc cathode surface and various collisions between charged particles, and metal vapor are taken into consideration in the model. Simulation results show that the post-arc breakdown initiates in the vicinity of the post-arc cathode center. At the moment when the post-arc breakdown occurs, a potential hump forms near the post-arc cathode center, and the plasma density increases by two orders, which are consistent with the published result obtained by 1-D hybrid simulation model. Simulation results on the effect of metal vapor density show that the post-arc breakdown occurs earlier with increasing metal vapor density, and the post-arc breakdown cannot occur when the metal vapor density is below 10 $^{\text{20}}$ m ^{\text{ - 3}} .

As one of the key components of new energy vehicles, DC contactors have received extensive attention. Based on the DC contactor arc breaking experimental platform, the DC breaking experiments in hydrogen, nitrogen, air and argon gas at different current levels are carried out respectively. The experimental results show that the arc-extinguishing performance in hydrogen is the best, and that in argon gas is the worst. It is found that the arc moves the fastest between the contacts when the hydrogen-nitrogen mixing ratio is 3:2. Breaking experiments are carried out in hydrogen and argon medium at 1-3 atmospheres. The experimental results show that although the high-pressure environment helps to shorten the arcing time, it will make the arc burning more concentrated, which is not conducive to the arc heat dissipation. Concerning the effect of magnetic field strength on the arcing characteristics of air arcs, the experimental results show that stronger the transverse magnetic field is, faster the arc moves, and smaller the arcing energy is. The influence of the reverse magnetic field on the motion of the gas arc is studied, and it is found that the arc in the nitrogen environment is more susceptible to the reverse magnetic field than in the hydrogen environment. The experimental results show that the retrograde motion of the vacuum arc cathode spots is more obvious under the condition of low current and strong transverse magnetic field.

In the field of vacuum interrupting, an important research is to improve the erosion resistance properties of contacts. In this paper, a two-dimensional axisymmetric swirl model based on basic parameters has been proposed to describe the formation and development of cathode spots of micro-scale alloy and nano-scale alloy electrode in a vacuum arc. In this model, the peak ion density of the plasma cloud, the mean charge state in near-cathode region, the electron temperature, and the near-cathode voltage drop are adopted as external parameters. Ions and electrons originating from the plasma cloud, thermo-field (T-F) emission, vaporization of metal atoms, backing ions and back-diffused electrons are all taken into consideration. The morphology and temperature of cathode spots crater and the liquid metal velocity of pure copper electrode (Cu), copper-chromium (Cu-Cr) electrode and tungsten-copper (W-Cu) electrode under the conditions of micro-scale grains and nano-scale grains are compared, respectively. Simulation results show that the cathode spot crater of the Cu-Cr electrode is smaller than that of the pure copper electrode. Moreover, it can hold more current and inhibit the formation of new cathode spots nearby. Cathode spots appearing on tungsten grains are smaller in size and have a lower probability of forming liquid metal droplets than Cu-Cr electrodes. Contacts made of nano-scale grain alloys have stronger erosion resistance properties than that of micro-scale alloy contacts and can reduce the maximum temperature of the cathode. The simulation results are in good agreement with other researchers’ results.