Cathode-constriction and column-constriction in high current vacuum arcs subjected to an axial magnetic field

Abstract

The influence of the applied axial magnetic field on the current density distribution in the arc column and electrodes is intensively studied. However, the previous results only provide a qualitative explanation, which cannot quantitatively explain a recent experimental data on anode current density. The objective of this paper is to quantitatively determine the current constriction subjected to an axial magnetic field in high-current vacuum arcs according to the recent experimental data. A magnetohydrodynamic model is adopted to describe the high current vacuum arcs. The vacuum arc is in a diffuse arc mode with an arc current ranged from 6 kA rms to 14 kA rms and an axial magnetic field ranged from 20 mT to 110 mT. By a comparison of the recent experimental work of current density distribution on the anode, the modelling results show that there are two types of current constriction. On one hand, the current on the cathode shows a constriction, and this constriction is termed as the cathodeconstriction. On the other hand, the current constricts in the arc column region, and this constriction is termed as the column-constriction. The cathode boundary is of vital importance in a quantitative model. An improved cathode constriction boundary is proposed. Under the improved boundary, the simulation results are in good agreement with the recent experimental data on the anode current density distribution. It is demonstrated that the current density distribution at the anode is sensitive to that at the cathode, so that measurements of the anode current density can be used, in combination with the vacuum arc model, to infer the cathode current density distribution.

Anode Input Heat Flux Density in High-Current Vacuum Arcs as Anode Spot Formation

“…The validity of the present model has been checked by the comparison of the anode current density [32]. For a wide range of arc current and AMF strength, the calculated anode current density is with great agreement with the experimental results.…”

“…Generally, the uniform cathode boundary condition is used in the vacuum arc model. However, the previous work shows that the uniform cathode distribution is not suitable for the high-current vacuum arcs [32]. Therefore, the current constriction is considered in the present study.…”

“…where J c is the cathode current density distribution, and r is the radius from the cathode center. The validation of this cathode boundary is discussed in [32] by the comparison of current density between the simulation results and the experimental results over a wide range of arc current and AMF strength. The results showed that with the uniform cathode boundary condition, the calculated current density at the anode center area is about 60% of the measured results.…”

“…In this work, a numerical method is used to obtain the heat flux density. At present, the numerical model has been developed as an effective way to get further insight of vacuum arc, especially in obtaining the plasma parameters [27], [28], [29], [30], [31], [32], [33], [34], [35], [36], [37]. In this study, a two-temperature magnetohydrodynamic (MHD) model is used to calculate the critical heat flux density as anode spot formation.…”

Numerical investigation on the influence of circuit breaker structure parameters on vacuum arc behaviors

“…An external magnetic field exerts a considerable influence on vacuum circuit breakers (VCBs). Many researchers studied the vacuum arc under the influence of magnetic fields [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. An external transverse magnetic field (ETMF) may weaken the interruption capacity of VCBs.…”