This paper discusses the seven different anode discharge modes which can occur in a vacuum arc. These modes are diffuse arc (low current, with or without anode sputtering), footpoint and plume (intermediate current), plus anode spot (two types), and intense arc (high current). The plume and Type 2 anode spot modes may occur just for certain materials, since they have been seen only with CuCr electrodes. Descriptions of the various spot modes are presented, based primarily on experimental results. The effects of external magnetic fields on anode modes are briefly stated. Arc column modes are also discussed, but only as they correspond to anode modes.

Anode Modes in Vacuum Arcs: Update

The electrode surface temperatures of Cu–Cr butt electrodes exposed to vacuum arcs with sinusoidal currents of 10–20 kA and under external axial magnetic field were determined. Different experimental techniques were applied that can be distinguished by the used spectral wavelength range, their temporal, and spatial resolution. Near infrared spectroscopy was carried out by means of a fiber optic spectrometer working in the wavelength range from 900 to 1670 nm with a temporal resolution of 1–2 ms. Electrode surface temperatures after current zero were obtained from the relative shape of the spectrum using the Planck curve fitting procedure. Furthermore, electrode emissivities were derived after performing absolute calibration of the spectra. Pyrometric measurements were performed in the spectral range around 2 $\mu \text{m}$ with high temporal but without spatial resolution. 2-D distributions of the electrode temperature were obtained from high-speed video thermography using a camera with a metal interference filter at 890 nm.

Anode Surface Temperature Determination in High-Current Vacuum Arcs by Different Methods

Research on sheath expansion is critical to the understanding of the dielectric recovery process in a vacuum interrupter after interruption of vacuum arcs. In this paper, we investigated how residual plasma affects breakdown in the sheath expansion period after the current zero. To simulate sheath expansion and breakdown, we developed a fully kinetic particle-in-cell Monte Carlo collision model with one spatial dimension and three velocity dimensions. The model accounted for various collisions, including ionization, excitation, elastic collisions, charge exchange, and momentum exchange, and we added an external circuit to the model to make the calculations self-consistent. The existence of metal vapor slowed the sheath expansion in the gap and caused high electric field formation in front of the cathode surface. The initial residual plasma, which was at sufficiently low density, seemed to have a limited impact on breakdown, and the metal vapor dominated the breakdown in this case. Additionally, the breakdown probability was sensitive to the initial plasma density if the value exceeded a specific threshold, and plasma at sufficiently high density could mean that breakdown would occur more easily. We found that if the simulation does not take the residual plasma into account, it could overestimate the critical value of the metal vapor density, which is always used to describe the boundary of breakdown after interruption of vacuum arcs. We discussed the breakdown mechanism in sheath expansion, and the breakdown is determined by a combination of metal vapor, residual plasma, and the electric field in front of the cathode surface.

Fully kinetic model of breakdown during sheath expansion after interruption of vacuum arcs

/pdf/modeling-and-simulation-of-arc-and-contact-wire-molten-pool-3i2fj2mek9.pdf

Modeling and simulation of arc and contact wire molten pool behavior during pantograph lowering process

Metal vapor vacuum arcs (VAs) are widely used in various fields of industry, such as circuit breakers, ion sources, electrical thrusters, and deposition systems. VAs usually originate from metal vapors eroding from the surface of a cathode, where they burn as tiny bright points, hence their name “cathode spots” (CS). Due to their high plasma density, short life span, and micrometer scale, the in situ and non-intrusive diagnostics of CS are a challenge. Numerical simulation is one method used to study CS with the aid of high-performance computing. The well-established particle-in-cell method provides solutions for the spatial-temporal electromagnetic field and the microscopic distribution functions of plasma species in phase space from which the macroscopic parameters of the plasma can be calculated. This Perspective reviews the progress in particle modeling of VAs with an emphasis on the non-stationary and non-local physical processes that are not reproduced by fluid models. Furthermore, a personal outlook on future challenges is provided: the physical modeling of plasma–electrode interactions, the collection and evaluation of collision cross sections, the trade-off between heavy computation cost and predictive ability, and the verification and validation of the simulation code.

/pdf/particle-modeling-of-vacuum-arc-discharges-2umsg691rd.pdf

Particle modeling of vacuum arc discharges

We report our measurements of anode current density distributions for different modes in vacuum arc discharge using a split-anode and a cup-shaped axial magnetic field cathode configuration system. The modes investigated included the diffuse arc and anode spot. The anode surface was divided into four regions: one central region and three symmetrical-disposed peripheral annular-arc regions. Three different-sized central regions were selected with diameters of 12, 18, and 20 mm. The contact material was CuCr25 (25% Cr). The arc current in the tests ranged from 6 to 14 kA (rms) at 50 Hz. The opening velocities were 1.8 and 2.4 m/s, respectively. The currents of the four areas on the anode contact were measured by four Rogowski coils situated outside the vacuum chamber. The experimental results show the current density distribution in different arc modes. For the diffuse arc mode with arc currents of 6 and 8 kA (rms), the average current density in the central region at current peak ranged from 8.5 to 15.9 A/mm $^{2}$ . The anode spot current density ranged from 31.9 to 37.7 A/mm $^{2}$ , estimated from the current density in the eroded region caused by the anode spots covering the entire central region of diameters 12 and 18 mm, at currents of 12 and 14 kA, respectively, regarded as the lower limit current density of the anode spot. Moreover, the dependence of the current density distribution on opening velocity in diffuse arcs was slight. For the anode spots, the current density distribution with higher opening velocity was more concentrated.

Anode Current Density Distribution Measurements for Different Vacuum Arc Modes Subjected to Axial Magnetic Field

Anode melting and crater formation significantly affect interruption of high-current vacuum arcs. The primary objective of this paper is to theoretically investigate the mechanism of anode surface crater formation, caused by the combined effect of surface heating during the vacuum arc and pressure exerted on the molten surface by ions and electrons from the arc plasma. A model of fluid flow and heat transfer in the arc anode is developed and combined with a magnetohydrodynamics model of the vacuum arc plasma. Crater formation is observed in simulation for a peak arcing current higher than 15 kA on 40 mm diam. Cu electrodes spaced 10 mm apart. The flow of liquid metal starts after 4 or 5 ms of arcing, and the maximum velocities are 0.95 m/s and 1.39 m/s for 20 kA and 25 kA arcs, respectively. This flow redistributes thermal energy, and the maximum temperature of the anode surface does not remain in the center. Moreover, the condition for the liquid droplet formation on the anode surfaces is developed. The ...

Modelling of crater formation on anode surface by high-current vacuum arcs

The objective of this work is to reveal the effects of an axial magnetic field (AMF) on the vacuum arc characteristics between transverse magnetic field (TMF) contacts. These vacuum arc characteristics include the vacuum arcing behavior and the arc voltage waveform. In the experiments, an external AMF was applied to a pair of TMF contacts. The external AMF flux density BAMF can be adjusted from 0 to 110 mT. The arc current in the tests varied over a range from 0 to 20 kA rms at 45 Hz. The contact material was CuCr25 (25% Cr). A high-speed charge-coupled device video camera was used to record the vacuum arc evolution. The experimental results show that the application of the AMF effectively reduces the TMF arc voltage noise component and reduces the formation of liquid metal drops between the contacts. The diffuse arc duration increases linearly with increasing AMF flux density, but it also decreases linearly with increasing arc current under application of the external AMF. The results also indicate that ...

Vacuum arcing behavior between transverse magnetic field contacts subjected to variable axial magnetic field

The objective of this paper is to propose a new method to quantitatively determine the arcing rotation velocity of the constricted vacuum arc driven by a transverse magnetic field (TMF). This method is based on a split anode and TMF cathode configuration system. Experiments were set in a demountable vacuum chamber. Both electrodes have a contact diameter of 60 mm. The anode surface was divided into four regions: one central region (Area I) and three symmetrically peripheral annular regions (Area II, III and IV). The currents of the four areas on the anode contact were measured using four Rogowski coils situated outside the vacuum chamber. The observed arc modes were recorded by a high-speed CCD video camera. The rotation velocity of the constricted arc column is calculated from the arc current waveforms of the four split areas. The experimental results indicate that the maximum speed is approximately 471 m/s with the arc current of 16 kA rms. The results also reveal the corresponding anode current distribution characteristics under TMF in different arc stages during the arcing time.

Method to determine rotation velocity of constricted vacuum arcs driven by transverse magnetic field

The objective of this paper is to measure the effect of an axial magnetic field (AMF) BAMF and arc current on the anode current density in diffuse vacuum arcs. The experimental geometry included a split anode and a butt-type cathode, both with a diameter of 60 mm. The anode surface was divided into a central area and three symmetrically disposed peripheral annular areas. The central area of the split anode had a diameter of 20 mm. The contact material was CuCr25 (25% Cr). The arc current IARC ranged from 4 to 14 kA (rms) at 50 Hz. The opening velocity was 2.4 m/s. The currents of the four areas on the anode contact were measured using four Rogowski coils situated outside the vacuum chamber. An external uniform AMF BAMF ranging from 0 to 110 mT was applied during the experiment. The observed arc modes were recorded by a high-speed charge-coupled device video camera. The experimental results quantitatively reveal that the current density distribution on the anode surface in the diffuse arc mode was not unif...

Effect of an axial magnetic field and arc current on the anode current density in diffuse vacuum arcs

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