The transverse magnetic field (TMF) contacts make the vacuum arcs deviate from the axisymmetric structure, so complete spatiotemporal evolution information of the plasma cannot be obtained by adopting one- or two-dimensional (2D) diagnostic methods. To address the issues, computer tomography was introduced in this paper. First, a multi-angle diagnostic imaging system based on split fiber bundles was proposed, which used a high-speed camera to simultaneously acquire eight angles of the arc image over time. In addition, a tomography algorithm called the maximum likelihood expectation maximum with Split Bregman denoising was proposed to reconstruct the dynamic spatiotemporal characteristics of the arc under complex conditions. Then, the three-dimensional (3D) distribution of Cu i and Cr i particles inside the contact gap was obtained by adopting optical filters. The 3D distribution of the vacuum arc had shown an obvious asymmetrical pattern under the TMF contacts, and there was a ring-like aggregation zone inside the arc, which can cause severe ablation on the anode contacts. According to the reconstructed 3D distribution of Cu i and Cr i, it is found that the metal vapor was mainly concentrated near the electrode surface and showed a clear distribution of non-uniform aggregates, while the concentration of particles in the gap was low. Moreover, on the cathode surface, the cathode spots moved in the form of groups driven by the TMF, while the anode surface was ablated by the electric arc, and the metal vapor existed in the form of bands.
In this paper, the interaction between the vacuum arc plasma jet and the hot metallic particle near current zero was investigated by numerical simulation. A vacuum arc plasma jet model was developed using the hybrid simulation method, in which electrons were considered as a massless fluid, while heavy particles such as atoms and ions were modeled as particles. In this model, the effect of the evaporation of metal atoms from the metallic particle was considered. Additionally, the Monte Carlo collision method was used to model inelastic collisions between electrons and heavy particles. The simulation results demonstrate that the metallic particle blocks the plasma jet, causing an asymmetric and nonuniform distribution in the plasma jet. Furthermore, some of the evaporated atoms from the hot metallic particle are converted into Cu1+ ions by ionization collisions with electrons. The drift velocity of Cu1+ ions coming from the ionization of metal vapor is much lower than that of highly energetic ions emitted from the cathode spot, making it difficult for them to be completely dissipated as soon as possible during the extinguishing phase. Moreover, the presence of a hot metallic particle causes an increase in the density of plasma in its surroundings, which increases the probability of arc reignition in the post-arc phase.
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