High-current Arc Research Articles

Characterization of high-current pulsed arcs ranging from 100–250 kA peak

In this paper, we present the laboratory study on three experimental setups that produce a free arc channel subjected to the transient phase of a lightning current waveform. This work extends the high-current pulsed arc characterization performed in previous studies for peak levels up to 100 kA. Eleven high-current waveforms with peak value ranging from 100–250 kA with different growth rates and action integrals are studied, allowing the comparison of different test benches. These waveforms correspond to standard lightning ones used in aircraft certification processes. Hydrodynamic properties such as arc channel evolution and shock-wave propagation are determined by high-speed video imaging and the background-oriented Schlieren method. The arc diameter reaches around 90 mm at 50 μs for a current of 250 kA peak. Space- and time-resolved measurements of temperature, electron density and pressure are assessed by optical emission spectroscopy associated with the radiative transfer equation. It is solved across the arc column and takes into account the assumption of non-optically thin plasma at local thermodynamic equilibrium. For a 250 kA waveform, temperatures up to 43 000 K are found, with pressures in the order of 50 bar. The influence of current waveform parameters on the arc properties are analyzed and discussed.

Gas Metal Arc Root Welding of Pearlitic Rails Using Magnetic Arc Deflection

Magnetic arc deflection was applied to improve gas metal arc root welds on R260 pearlitic rail steel foot samples. During laboratory welding trials parameter optimization was carried out which comprised the welding current, voltage and speed, layer sequence, filler wire diameter, and the external magnetic field. Results were evaluated by visual inspection, and the lateral and diagonal penetration in cross-sections, as well as the microstructure and the hardness in the HAZ. Additionally, the influence of the external magnetic field on the process was studied using a high-speed camera. Overall best results were finally obtained in high welding current spray arc mode (380-400A) with the 1,6mm solid wire and at high welding speed (65cm/min) and two pass per layer sequence, in combination with maximum 30mT magnetic flux density and increased welding voltage (30-31V) for longer arc. A continuously well-formed root with sufficient lateral penetration was achieved and a smooth transition from base metal to weld metal at the lower edges could be achieved. Inside base metal HAZ the microstructure was fully pearlitic and no soft zone occurred. Furthermore, the size of the HAZ was in comparison to aluminothermic weld reduced by more than 75% in comparison to an AT rail weld.

Синтез квазикристаллических порошков и покрытий методом вакуумного плазменно-дугового испарения

Quasicrystalline coatings of the Al-Cu-Fe system were obtained by sputtering the cathode using a pulsed high-current low-pressure arc discharge followed by deposition on a hot (600 ° C) and cooled substrate (25 ° C). The surface morphology, chemical and phase composition of evaporation products in the form of powder and the resulting coatings were studied. Powders and coatings were also annealed and the phase composition variation was studied. It was found that during the evaporation process a significant change in the chemical composition occurs in the form of loss of Al from the surface of the particles and the coating, which leads to a decrease in the content of the ψ phase. However, subsequent annealing and sputtering on a hot substrate lead to an increase in the ψ phase, as well as the density and hardness of the coatings.

A “Resonance” Method to Decrease Electrode Erosion in Magnetically Rotated Arcs

In many industrial applications of high-current arcs with tubular or ring electrodes, the arc electrode attachments are forced to rotate in order to reduce electrode erosion. A method intended to further reduce electrode erosion is suggested. This goal is achieved by forcing the attachment to drift in the axial direction. The axial arc motion results from the Lorentz force experienced by a radial arc under the influence of an azimuthal magnetic field. This magnetic field could be created by a cable located outside the electrode. It is shown that if the current in the outside cable oscillates with a frequency close to the frequency of the arc rotation, it leads to a continuous arc axial drift. The effect has a resonance characteristic: even a low ac current in the cable causes the arc drift. As a result of the combination of fast arc rotation with a relatively slow axial drift (reversed from time to time), the arc attachment moves within a band of a controllable width. The spread of the electrode heat load over a wider electrode area reduces electrode erosion. Sources of the azimuthal magnetic field other than a cable are suggested.

The effect and dynamic behavior of particles in high-current vacuum arc interruptions

Microparticles produced by high current vacuum arcs significantly reduce the insulation performance of vacuum interrupters. The objective of this paper is to observe the generation and dynamics of microparticles during the arcing and post-arcing period, and to further reveal the possible effects of particles during interruption of a high current vacuum arc. A plasma diagnosis system based on a laser-shadow technique was used to measure the particles in a demountable vacuum chamber. The results show that contact materials affect particle generation patterns. For a CuCr contact with a higher proportion of chromium, the formation of a melting pool is much more difficult and the flow of liquid metal on the surface can be suppressed, which also impedes the formation of particles. Moreover, reignition after arc extinction was found to be triggered by some incandescent particles. These hot particles have two effects on breakdown events during the post-arcing phase: they trigger a micro-discharge between a particle and the electrode, and new weak points are left on the surface that enhance the local field. More crucially, the lifetime of spontaneous particles spans up to hundreds of milliseconds after current zero, which indicates that long-delayed breakdown is correlated with the existence of particles. In addition, some particles could remain suspended near the electrode or oscillate between the contacts. The dynamic behavior of these particles can significantly lower the breakdown threshold and increase the possibility of breakdown.

Experimental study on the jet characteristics of a steam plasma torch

Thermal steam plasma jet is promising for applications in environmental industries due to its distinctive characteristics of high enthalpy and high chemical reactivity. However, the performance of the steam plasma torch for its generation is limited by the problems of the large arc voltage fluctuation and serious erosion of the electrodes. In this study, a gas-stabilized steam plasma torch which can operate continuously and stably was designed. Experiments were conducted to reveal the effect of the different working parameters, including the anode diameter, the cooling water temperature, the arc current and the steam flow rate, on its Volt–Ampere characteristics, arc voltage fluctuation, thermal efficiency, jet characteristics and electrodes erosion. Results showed that the use of hot water to cool the electrodes can effectively prevent the condensation of steam on the inner wall of the electrodes, thus significantly reducing the arc voltage fluctuations and electrodes erosion. This is crucial for increasing the working life of the electrodes and ensuring long-term stability of the steam plasma torch. In addition, suitable anode diameter can greatly reduce the arc voltage fluctuation of the steam plasma torch and effectively improve the stability of the steam plasma jet. Furthermore, high arc current can effectively reduce the fluctuations of the arc voltage and increase the length and the volume of the steam plasma jet. Finally, using steam as the plasma forming gas can achieve higher thermal efficiency compared to air. An ideal thermal efficiency can be achieved by properly reducing the arc current and increasing the steam flow rate.

Modeling of interaction between arc and macroparticle in vacuum trigatron

This work investigates the interaction between high current vacuum arc (HCVA) and the macroparticle (MP) generated from the cathode spots in the small-size vacuum trigatron. Magnetohydrodynamic (MHD) model is used to describe the arc column. MPs are added into the MHD model, which are described by discrete phase model. The control equations of MPs include charging equation, motion equation, and heat transfer equation, in which the evaporation of MPs is also considered. Based on the above model, the effects of the diameter and initial velocity of MPs on the characteristics of them are studied. Simulation results show that MPs leave the interelectrode gap with a deflection angle larger than the initial angle under the influence of plasma. The motion of MPs is similar to that of projectiles. MPs with smaller diameter or slower velocity are influenced by the arc plasma more significantly. MPs can act as a source of the plasma, but these influences are not obvious in HCVA. What may be more harmful to the trigatron is the charging process of MPs during post-arc process.

Static stall alleviation using a rail plasma actuator

An experimental study was conducted to investigate the ability of a rail plasma actuator (RailPAc) to alleviate static stall on an airfoil. The RailPAc device consists of parallel rails flush mounted on the upper surface of a VR-12 airfoil, with a high-current (∼1.3 kA) arc bridging the gap between the rails. A Lorentz force (∼0.3 N lasting ∼1 ms) generated on the arc propels it along the airfoil chord and transfers momentum to the surrounding flow. Experiments were conducted in a low speed wind tunnel at two different Reynolds numbers ( and ) and various static angles of attack (up to ∼30°). Particle image velocimetry (PIV) was used to measure the flow over the passive and actuated airfoil, while the airfoil lift was measured using a force balance. The experiments showed that the RailPAc promotes flow reattachment and can suppress static stall over a wide range of angles of attack. Operation of a single RailPAc resulted in ∼40 improvement in post-stall lift and ∼4° increase in stall angle compared to a passive airfoil with an unpowered RailPAc. The results provide insight into the actuation mechanism and demonstrate, for the first time, the ability of the RailPAc to alleviate static stall on an airfoil.

Fast and Cost-Effective Synthesis of High-Quality Graphene on Copper Foils Using High-Current Arc Evaporation.

In this paper, we present an innovative and ultra-fast process for the deposition of high-quality graphene on different metal foils and thin metal films. The graphene layer can be homogeneously deposited in only 30 s process time. Due to the weak adhesion to the substrate material, the monolayer graphene is easy to transfer using the established processes. For the production, we use magnetic filtered high-current arc evaporation (Φ-HCA) with a solid, graphitic carbon source. This ultra-fast growth process can pave the way towards a cost-effective graphene synthesis for the mass production e.g., in a roll-to-roll process, avoiding time consuming established processes.

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

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 kArms to 14 kArms 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 cathode-constriction. 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.

The development of shock wave overpressure driven by channel expansion of high current impulse discharge arc

During the formation of a high current impulse discharge arc, objects near the discharge arc will be strongly impacted. In this paper, a high power, high current gas switch is used as the site of the impulse discharge arc. The explosion wave theory and the arc channel energy balance equation are introduced to analyze the development of the shock wave overpressure driven by the high current impulse discharge arc, and the demarcation point of the arc channel is given, from which the energy of the arc channel is no longer converted into shock waves. Through the analysis and calculation, it is found that the magnitude of the shock wave overpressure caused by impulse discharge arc expansion is closely related to the arc current rising rate. The arc shock wave overpressure will undergo a slow decay process and then decay rapidly. The study of this paper will perform the function of deepening the understanding of the physical nature of the impulse arc discharge, which can be used to explain the damage effect of the high current impulse discharge arc.

Influence of Ion Nitriding Regimes on Diffusion Processes in Titanium Alloy Ti-6Al-4V

The paper reports on the results of two-stage-experiments of low-temperature ion nitriding of the Ti-6Al-4V titanium alloy in a non-self-sustained high-current arc discharge and in a glow discharge under various conditions. The diffusion of nitrogen into the interior of the material was determined by the thickness of the layer being modified. It was established that the depth of the nitrided layer greatly depends on temperature, composition of the working medium, as well as on process duration. When treated in non-self-sustained high-current arc discharge, the depth of the nitrided layer increases from 4 to 17 μm, and in the glowing discharge the depth increases from 9 to 13 μm. The nitriding temperature affects the sign and magnitude of the residual stresses.

Increase in the Acceleration Efficiency of Solids in a Hybrid Coaxial Magnetoplasma Accelerator

It is shown that in a hybrid coaxial magnetoplasma accelerator with a channel length of 350 mm and a diameter of 23 mm, the acceleration velocity and the energy conversion efficiency increase as the length of the plasma structure formation channel filled with a gas-generating material decreases from 17 to 9 mm. It is found that it is reasonable to use paraffin as the gas-generating material as it has a less significant deionizing effect on the high-current arc discharge and hence causes a less significant decrease in the discharge current intensity and an increase in conductive and inductive electrodynamic forces.

Multiply charged metal ions in high current pulsed vacuum arcs

We show that vacuum arc plasma discharges with a current of several kiloamperes and duration of a few microseconds can generate multiply charged metal ions with charge states greater than 10+. The physical mechanism behind this is discussed, suggesting an optimum arc current for higher charge states depending on the pulse duration and cathode material. Measurements of ion mass-to-charge ratio and images taken with nanosecond resolution suggest that, higher charge state ions are produced at characteristic distances of ∼10 mm from the cathode as the arc current peaks, and the process responsible for their generation is additional ionization as the discharge is pinched by its self-magnetic field. The maximum and mean ion charge states reveal a considerable increase for the all cathode materials studied: magnesium, aluminum, zirconium, tin, tantalum, gold, lead, and bismuth. For bismuth ions, the maximum charge state reaches a record-breaking value of 17+ and the mean of the charge state distribution is 12.6+. The results obtained are of interest for vacuum arc discharge physics and for ion beam technologies.

Generation of High Charge State Metal Ions in an Arc Plasma

Generation of high charge state metal ions in arc plasma is investigated and methods of elevation of the average ion charge state are analyzed. To realize multiple ionization of the arc plasma, a strong magnetic field in the arc cathode area, an ark current spike, an injection of a high-current electron beam or a high-power microwave radiation flow into the plasma, and a creation of a short high-current arc are realized. For each method, the main features are considered and the maximum ion charge states are determined.

The Studies of a Vacuum Gap Breakdown after High-Current Arc Interruption with Increasing the Voltage

Vacuum-gap breakdown has been studied after high-current arc interruption with a subsequent increase in the transient recovery voltage across a gap. The effects of factors, such as the rate of the rise in the transient voltage, the potential of the shield that surrounds a discharge gap, and the arc burning time, have been determined. It has been revealed that opening the contacts earlier leads to the formation of an anode spot, which is the source of electrode material vapors into the discharge gap after current zero moment. Under the conditions of increasing voltage, this fact results in the breakdown. Too late opening leads to the breakdown of a short gap due to the high electric fields.

Characterization of molten pool behavior and humping formation tendency in high-speed gas tungsten arc welding

The humping defect which easily forms in high-current and high-speed gas tungsten arc welding (GTAW) severely deteriorates the homogeneity of weld properties. However, the complicated and multi-coupled transport phenomena in molten pool make the quantitative characterization of humping formation tendency difficult. In this paper, dimensionless groups containing characteristic heat and fluid-flow variables of molten pool are determined based on Buckingham π-theorem. These groups with clear physical implication correspond to important and peculiar molten pool behaviors during humping formation, and they can be combined to evaluate humping formation tendency. Scaling analysis is then employed to study the molten pool behaviors in high-speed GTAW, in which the analytical equations between characteristic molten pool variables and process variables are formulated. The scaling laws are well verified and calibrated by numerical data from a numerical heat transfer and fluid flow model. The dimensionless groups and scaling equations show an explicit relation between process variables and humping formation tendency. The proposed methodology has low computational intensity, and can be easily applied to give a quantitative description of humping formation tendency at different welding parameters and to predict humping formation.

An optimal method for the computation of the parameter Rs of the net emission coefficient approximation approach for determining the electrical and thermal characteristics of plasma arcs

Large-scale industrial plasma torches and processes use primarily high-current electric arcs. Therefore, their basic design must inevitably account for radiative transfer which becomes the prevailing heat loss mechanism at high currents. This heavily increases the complexity of the governing equations. Many approximate approaches have been proposed. The present work relies on the method of approximate average net emission coefficient (NEC) using the isothermal sphere approximation with a radius Rs to solve semi-analytically the Ellenbaas–Heller equation and compares it with exact calculations obtained using an iterative method. To our knowledge no study has provided yet a method to determine the most accurate value of Rs. In this paper, we present an optimal method for determining the best value of Rs that leads to the best agreement between the approximate and the exact methods. As a result, the complete electric characteristic has been obtained for hydrogen at 1 bar in a detailed case study.

Investigating Characteristics of N2, CO2 and CF3I in Contrast to High Current Arcs in Circuit Breakers to Choose a Suitable Substitute for SF6

Investigating Characteristics of N2, CO2 and CF3I in Contrast to High Current Arcs in Circuit Breakers to Choose a Suitable Substitute for SF6

Influence of Axial Magnetic Field on Cathode Plasma Jets in High-Current Vaccum Arc

The cathode plasma jets in vacuum arc and the effect of magnetic field on them have been studied for several years and these studies are helpful to understand the arc characteristics and improve the controlling effect of magnetic field on arc plasma. In this paper, the experiments of the cup-shaped axial magnetic field (AMF) contacts were conducted in which a Helmholtz coil was introduced to generate different external imposed AMFs. It was found that the appearance of arc plasma was changed by variation of the external imposed AMF. If the composite AMF in arc column increased gradually, the obvious individual cathode plasma jets were detected, the arc constriction decreased, and the arc stability increased. Meanwhile, the inclination of cathode plasma jets was observed and the inclination direction was found to be consistent with the magnetic field vector direction which is closely related to the composite AMF. By variation of the external imposed AMF and its direction, the inclination direction of cathode plasma jets also changed. The criterion to detect obvious cathode jets in arc column is obtained that at the contact peripheral where R> 80.5% R0 (R0 is the contact radius), the AMF strength is no less than 4.5 mT/kA. It was also found that if the composite AMF in interelectrode gap points to different directions at a certain moment, it may lead to the transfer of arc column from the center to the edge of the interelectrode region and the arc instability until when the composite AMF in the interelectrode gap points to the same direction. It can be concluded that the appearance of individual cathode plasma jets can be manipulated by the variation of AMF, which is helpful to study the interaction between arc plasma and electrodes, especially the anode, and improve the interruption performance at higher current.