Zongqian Shi

Numerical simulation of vacuum arc under different axial magnetic fields

Based on the improved two-dimensional axisymmetric magnetohydrodynamic model, the vacuum arc characteristics under different distributed axial magnetic fields (AMFs) were analysed in this paper. First, a uniform cathode spot distribution was assumed, and the influences of the azimuthal self-magnetic field and different radially distributed AMFs on the vacuum arc characteristics were analysed. Then, in order to simulate the real situation, according to the experimental results of other researchers, a non-uniform distribution of cathode spots was considered in the simulation. The simulation results showed that the effect of the current density of the cathode side on the vacuum arc characteristics (such as distribution of axial current density at the anode side and heat flux density to the anode) was significant.

Modelling and simulation of anode activity in high-current vacuum arc

Anode activity is critical for the success or failure of vacuum interrupters when the arc current attains a certain limiting value. Anode vapour from anode activity will influence high-current vacuum arc (HCVA) characteristics, and further influence interrupting successfully or not. In order to investigate the interaction between the arc column and anode vapour, a transient two-dimensional anode activity (subjected to HCVA column) model is established in this paper. Based on this model, the anode thermal process under ideal heat flux density and heat flux density from the arc column are simulated, respectively. The simulation results show that for sinusoid current, anode surface temperature first increases rapidly, then decreases slowly. With the increase in the heat flux density to the anode, the anode surface temperature will increase. The maximal value of the anode surface temperature appears near 7 ms (50 Hz current waveform), which is also in agreement with other simulation results. Anode evaporation cools the anode surface, which leads to a more uniform anode surface temperature at the contact centre than that near the contact edge. When the anode is melted, the radial distribution of the anode surface temperature appears as an inflection point. The simulation results are also compared with the experimental results and the results of other researchers. Reasonable agreement is observed. According to the anode activity model, the anode boundary condition of the HCVA model with anode vapour can be defined.

Vacuum arc under axial magnetic fields: experimental and simulation research

Axial magnetic field (AMF) technology is a most important control method of vacuum arc, particularly for high-current vacuum arcs in vacuum interrupters. In this paper, a review of the state of current research on vacuum arcs under AMF is presented. The major aspects of vacuum arc in an AMF such as arc voltage, the motion of cathode spots, and anode activities are discussed, and the most recent progress both of experimental and simulation research is presented.

Experimental Investigation of Anode Activities in High-Current Vacuum Arcs

It is well known that the melting of electrodes (mainly anode melting) in vacuum arc can increase the metal vapor density around current zero and even lead to interruption failure. In order to clarify the anode activities and their influence on arc appearance and interruption capacity, series experiments of cup-shaped axial magnetic field copper electrodes were conducted. Obvious anode melting was detected; the liquid copper flowed on the contact plate of anode and formed a clockwise swirl flow. The appearance of anode melting is likely to correlate to the transition of arc mode from high-current diffuse mode to high-current diffuse column mode. The melting of anode was severer than cathode and was influenced by the distribution of cathode spots. Various kinds of copper particles at macroscopic level can be seen in arc column. Even at the interruption limit, the majority of melted copper of anode sputtered out of gap in form of liquid droplets or was pressed into the cup of anode, the copper vapor evaporated into arc column only accounted for a few portion and no obvious anode jets was found due to large plasma pressure in arc column.

Axial magnetic field contacts with nonuniform distributed axial magnetic fields

It is well known that axial magnetic fields (AMFs) can keep vacuum arc in diffuse mode at high current. According to our recent research and other published papers, it has been found that vacuum arc can be maintained in high-current diffuse mode at much higher current if nonuniform AMF is applied, that the axial magnetic field is higher at contact periphery than at center. The influence of spatial distribution of AMF on vacuum arc is mainly studied in this paper. Furthermore, two types of AMF contacts with new structures to generate nonuniform AMF are presented.

High-current vacuum arc under axial magnetic field: Numerical simulation and comparisons with experiments

Based on a magnetohydrodynamic model, a numerical simulation of high-current vacuum arc (HCVA) is carried out. In this model, the kinetic energy terms and ion viscosity terms in energy conservation equations are considered. Compared with the supersonic constricted vacuum arc, the ion flow in HCVA is in the subsonic status. Therefore, boundary conditions of cathode and anode sides have to be adjusted for HCVA. According to the simulation results of HCVA, we can find that the maximal plasma pressure appears near the cathode side. The characteristics of HCVA are significantly different from those of supersonic vacuum arc. Then, we make the comparisons between simulation results and experimental results (such as electron number density, electron temperature, ion temperature, high speed charge-coupled device photographs, and so on). The simulation results are in agreement with the experimental results. In addition, we also analyze the influence of different arc models on the distribution of current density in the anode side.

Modeling and simulation of anode melting pool flow under the action of high-current vacuum arc

In this paper, a transient magnetohydrodynamic (MHD) model of an anode melting pool (AMP) flow (AMPF) is established. Mass equation, momentum equations along axial, radial and azimuthal directions, energy equation, and current continuity equations are considered in the model. In the momentum equations, the influence of electromagnetic force, viscosity force and Marangoni force (anode surface shear stress) are included. Joule heating is also included in the energy equations. According to the MHD model of AMPF, the influence of different heat flux densities to melting pool flow velocities (including azimuthal, radial, and axial velocity), anode temperature, fraction of liquid, melting depth, melting radius, and anode vapor flux will be analyzed. In the AMP, the azimuthal velocity is dominant, whose value approximately approaches velocity magnitude, the radial velocity is much smaller than azimuthal velocity, and the axial velocity is the smallest one compared with radial and azimuthal velocity. According to...

Three-dimensional model and simulation of vacuum arcs under axial magnetic fields

In this paper, a three-dimensional (3d) magneto-hydro-dynamic (MHD) model of axial magnetic field vacuum arcs (AMFVAs) is established. Based on this model, AMFVAs are simulated and analyzed. Three-dimensional spatial distributions of many important plasma parameters and electric characteristics in AMFVAs can be obtained, such as ion number density, ion temperature, electron temperature, plasma pressure, current densities along different directions (x, y, and z), ion velocities along different directions, electric fields strength along different directions, and so on. Simulation results show that there exist significant spiral-shaped rotational phenomena in the AMFVAs, this kind of rotational phenomenon also can be verified by the many related experiments (AMFVAs photographs, especially for stronger AMF strength). For current simulation results of AMFVAs, the maximal rotational velocity at anode side is about 1100 m/s. Radial electric field is increased from arc center to arc edge; axial electric field is ...

Numerical simulation of high-current vacuum arc characteristics under combined action of axial magnetic field and external magnetic field from bus bar

In this paper, the two-dimensional high-current vacuum arc (HCVA) model under the combined action of axial magnetic field (AMF) and external magnetic field from bus bar (EMFBB) is established. Based on this model, the influence of AMF and EMFBB on HCVA characteristics can be simulated and analyzed. Simulation results show that the HCVA column will be deflected by the Lorentz force generated by EMFBB and higher arc current. Moreover, the deflection level will be increased with the increase in external EMFBB strength. For HCVA, due to the smaller axial velocity near cathode side, the deflection of plasma parameters (such as ion number density, ion temperature, electron temperature, plasma pressure, and so on) near cathode side is more significant than that near anode side. The current deflection near cathode side toward direction of Lorentz force is more significant than that near anode side.

Experimental investigation of vacuum arcs in nonuniform axial magnetic fields

Experiments were conducted in a detachable vacuum chamber with conventional cup-shaped axial magnetic field (AMF) electrodes and three types of AMF electrodes with different nonuniform AMFs. The radial distributions of the AMF were varied by introducing ferromagnetic material into the cup-shaped AMF electrodes. The vacuum arc column and the distribution of cathode spots were photographed with a high-speed charge coupled device (CCD) camera. Experimental results indicate that a nonuniform AMF with higher axial magnetic flux density at the contact periphery than that at the center (saddle-shaped AMF) can resist arc constriction and increase the cathode and anode utilization ratios more effectively than the ordinary bell-shaped AMF profile.