Anodic Arc Research Articles

Advanced temporal analysis of anode activity during mode transitions in high current vacuum arcs

Abstract Anode activity in high current vacuum arcs leads to the formation of various high current modes and transitions between them. Intense material evaporation during the anode spot mode and formation of a neutral vapour cloud during the anode plume mode modify the arc plasma properties and, hence, can have a crucial impact in applications, like e.g. reduction of interruption performance of switching devices. The influence of anode mode appearance on arc plasma parameters and on anode surface temperature was studied in detail by a novel optical diagnostic technique—intensified video optical emission spectroscopy. Employing advanced diagnostic methods, the ground state density, excitation temperature and pressure profiles close to the anode surface have been determined. For the anode plume mode, higher copper vapour pressure was found in the plume shell compared to its core. The copper ion density distribution shows a maximum outside of the plume shell. Consequently, a higher electrical conductivity in the surrounding area of the plume might be expected, i.e. the arc current flows around the plume rather than through it. Analysis of the temporal evolution of electrical and optical signals reveals that voltage jumps and drops during the mode transitions are accompanied by noticeable changes in the anode surface temperature. Thus, the formation of the anode plume leads to temperature lowering while the transition to the anode spot mode is accompanied by a temperature increase. In general, a clear correlation between electrode surface temperature and arc voltage in the case of constricted anode attachment is found. The results of this study give new insights into anode plume properties and consequences of anode mode transitions. Reversible mode transitions and correlations between arc voltage and anode surface temperature, as well as changes in the current path during anode plume mode, have to be considered as factors for optimization of electrode design and choice of materials for switching applications.

Numerical simulation of CuCr alloys vacuum arc under conditions of arc contraction, deflection, and anode vapor

In practical arc ignition processes of high-current vacuum arcs, despite the calibration effect of the axial magnetic field, the strong magnetic constriction force still causes the arc to contract. Additionally, during the actual electrode opening process, due to the random nature of the arcing position, the center of the arc column is often not located at the center of the electrode. At this point, the behavior of the vacuum arc can be understood as an asymmetric three-dimensional (3D) process under the influence of the spatial magnetic field, affecting the generation of anode vapor and the characteristics of arc species. Therefore, it is useful to conduct simulation studies on multi-species vacuum arc behavior considering arc contraction and arc deflection. In this paper, the spatial magnetic field distribution under different electrode effective areas and different arc center deflection distances have been simulated, and the influence of actual magnetic field-induced by arc contraction and deflection on 3D spatial distribution characteristics of arc plasma has been studied based on a 3D multi-species (CuCr alloys) vacuum arc model with anode vapor. The simulation results show that with the contraction of the arc column, the area occupied by neutral atomic vapor decreases correspondingly, but the ionization and recombination process between the arc column regions becomes more intense. The axial current density and electron temperature distribution around the neutral atomic vapor area become more non-uniform. When the arc column deviates from electrode center, the neutral atomic vapor area shows an asymmetrical distribution on both sides of the arc column center axis, and the axial current density and electron temperature gather and enhance in the opposite direction of the arc deflection, thereby significantly affecting the distribution of arc species.

Effect of contact materials on the transient characteristics of vacuum arc plasma and anode erosion

In this study, the mechanisms of the anode phenomena and anode erosion with various contact materials were investigated. Arc parameters were calculated, and the anode temperature was predicted with a transient self-consistent model. The simulation results predicted a constricted arc column and obvious anode phenomena in Cu–Cr alloy contacts than in W–Cu alloy contacts. This observation could be the reason for the concentrated anode erosion in Cu–Cr alloys. For the contacts made by pure tungsten (W) and W–Cu alloy, the anode temperature increased rapidly because of the low specific heat of W. However, the maximum energy flux from the arc column to the anode surface was lower than in other cases. The simulation results were compared with experimental results.

Arc root dynamics in the context of lightning strikes to aircraft

During lightning strikes to aircraft, there is a displacement of the impacted area on the aircraft’s surface and the dynamic of the arc root is a key to understanding and predicting the damage produced on the aircraft skin. This work aims at studying experimentally this dynamic with a new method of producing sweeping arcs based on a stationary arc and an electromagnetic launcher propelling aeronautical test samples. The experiments are also achieved with a wind tunnel that blows the arc on the test sample for comparison. After a description of the previous experiments of arc root displacement and a distinction between the cathodic and anodic emission processes, this paper characterizes the arc root physical properties with direct visualization through high-speed cameras and electric measurements for different initial conditions. The results are separated by the arc root polarity and discussed to give an insight into the influence of the experimental conditions on the interaction between the electric arc root and the test sample during swept-stroke. It is shown that for a cathodic arc root, the nature of the displacement—continuous or jumping—highly depends on the current level and the speed of the relative motion between the electric arc and the test sample. For an anodic arc roots, the variations of these parameters provoke jumping modes of displacement with different characteristics.

Diamond-like films of tetrahedral amorphous carbon deposited by anodic arc evaporation of graphite

A physical vapor deposition process using anodic arc evaporation in combination with a hollow cathode arc discharge was applied to the evaporation of graphite for deposition of hydrogen-free carbon layers. The diamond-like carbon (DLC) films deposited on 100Cr6 steel substrates were investigated by nanoindentation, Raman spectrometry, FE-SEM, AFM and spectroscopic ellipsometry. The relationships between the process parameters and the coating properties are discussed. Coatings deposited without bias voltage at substrate temperatures <200 °C are very hard (61–75 GPa) with also very high Young's modulus (588–685 GPa). The evaluation of the Raman spectra indicated a high proportion of tetrahedral sp3 bonds in the range of 70–88 %. Obviously, the vapor particle energies are high enough to achieve such high hardness values even without application of a bias voltage. The coatings proved to be completely droplet-free and have a very low surface roughness as confirmed by FE-SEM and AFM. The deposition rates in the range of 4–18 nm/s are exceptionally high for such tetrahedral amorphous carbon (ta-C) coatings, which is a good prerequisite for industrial applications. The ta-C layers with very high hardness and smooth surface are well suited as wear resistant layers.

Influence of Electrode Surface Evolution on the Properties of High-current Vacuum Arcs in Switching Applications

Properties of high-current vacuum arcs in dependence on electrode surface status have been studied. The AC current pulses with 16kA (rms) at 50Hz have been applied to spiral contact system made of conventional CuCr material. Each contact pair was loaded with 20 shots. Arc diagnostics comprises arc current and voltage measurements as well as various optical diagnostics. Two high-speed cameras were used for analysis of arc dynamics. Near infrared radiation spectroscopy was applied for determination of the anode surface temperature after the arc extinguishing. The results show clear changes in arc dynamics and anode surface temperature with progressing surface ageing.

Experimental study and characteristic analysis of vacuum arc between cup-type axial magnetic contacts under different diameter-to-gap ratios

Since vacuum circuit breakers gradually advanced to higher voltage levels, axial magnetic field (AMF) contacts have drawn a great deal of attention due to their excellent breaking ability. The cup-type AMF contact is a common kind of AMF contact, which has much potential in contact design and application of high voltage grade systems due to the advantages of strong structural strength, uniform magnetic field distribution, lower resistance, etc. This study analyzes the arcing characteristics of a cup-type AMF contact with a large slotted rotation angle at various diameter-to-gap ratios (DGRs). The arcing process is divided into five stages as follows: initial diffusion, contracting, fully constricted, re-diffusion, and extinguished. Arc self-rotation and anode separation phenomena in the re-diffusion stage appear when the DGR is 58/24. The reasons for these occurrences were discussed and explained with regard to the magnetic field vector's spatial distribution. The duration of each stage and the current threshold of a fully constricted arc will both differ with the change of the DGR. The structural parameters of the fully constricted arc were computed through the method of imaging the luminous intensity distribution after the arc was fully constricted. The source of the change in the arc voltage can be seen in the variation of arc structural parameters, which also reflect anode activity intensity to a certain extent. The transient magnetic field simulation method was used to explain why the arc under the same instantaneous current shows variable morphology at the extinguished stage and contracting stage in one arcing process. The research results presented in the article can be used as a reference for developing high-voltage cup-type AMF contacts.

Modeling and Comparative Analysis of Atmospheric Pressure Anodic Carbon Arc Discharge in Argon and Helium-Producing Carbon Nanostructures.

In this work, within the framework of a unified model for the discharge gap and electrodes, a comparative numerical analysis was carried out on the effect of evaporation of graphite anode material on the characteristics of the arc discharge in helium and argon. The effect of changing the plasma-forming ion, in which the ion of evaporated atomic carbon becomes the dominant ion, is demonstrated. For an arc discharge in helium, this effect is accompanied by a jump-like change in the dependence of the current density on voltage (CVC), and smoothly for a discharge in argon. With regard to the dynamics of the ignition of an arc discharge, it is shown that during the transition from glow discharge to arc in helium, the discharge parameters are also accompanied by an abrupt change, while in argon, this transition is smooth. This is due to the fact that the ionization potentials, as well as the ionization cross sections, differ significantly for helium and carbon, and are close in value for helium and argon. For various points on the CVC, the density distributions of the charged and neutral particles of an inert gas and evaporated gases are presented.

Study of the electric arc dynamics in a cascaded-anode plasma torch

In plasma spraying process, the plasma jet stability depends on the electric arc movement inside the plasma torch. For conventional plasma torches with rod cathode and a large anodic surface, arc roots are free to move along the anode wall, leading to high plasma jet fluctuations. To overcome these instabilities, cascaded-anode plasma torches have been developed, reducing considerably the electric arc movement and thus the plasma jet fluctuations. Unfortunately, a small number of studies reports on the behaviour of theses torches including the arc instabilities and on electrode erosion process as well. In this work, several diagnostics have been set up to further understand the cascaded-anode plasma torch behaviour under different sets of operating conditions. Influence of plasma forming gas composition on the electric arc dynamic has been studied through anodic imaging. The issue of the intense plasma radiation masking is discussed since the light emitted by the arc column interferes with anodic arc roots observations. Multiple constricted arc roots have been observed and a preferential site for anodic arc root has been identified for all experimental conditions. The addition of a secondary plasma forming gas promotes a higher number of reattachments. The influence of the electric arc movement on plasma jet stability is also studied by following the plasma jet brightness fluctuations. The low voltage fluctuation frequency is also observed on brightness spectra, which means that these fluctuations could have an impact on in-flight particle treatment.

Research on the Energy Characteristics of a Transferred Arc Plasma-Chemical Reactor for Waste Treatment

This study has been performed to reveal the main characteristics of operating a direct current (DC) plasma-chemical reactor (PChR) designed for hazardous waste treatment. The PChR employs thermal plasma as the operating environment. The investigations presented in this paper were conducted to study the electrical and energy characteristics of the plasma torch and plasma-chemical reactor during the destruction of inorganic waste. The PChR is equipped with a plasma torch with a nominal capacity of 50 kW and a free-burning arc. The zone of heat release from the atmospheric pressure DC arc cathode and arc anode (melted waste) spot is combined with the area of chemical reactions. The plasma torch (PT) parameters vary in the range of arc current I = 120–180 A, arc voltage U = 250–280 V, arc length x = 0–100 mm, and gas flow rate G = 1–3 g/s at atmospheric pressure, using air as the plasma-forming gas. The experimental results confirmed that plasma technology has several advantages over conventional incineration, including higher temperatures, heat source independence from the waste being processed or additional fuel, and a shorter exposure time in the high-temperature area. It was determined that the arc current increases with increasing arc length. With increasing arc length, the initial part begins to operate in a turbulent regime. This study determines the dependence on the heat flux transferred by electrons to the anode on the arc current. The convective heat flux density distribution over the anode heating spot was measured and discussed.

(Invited) Advances in Synthesis of Nanomaterials By Atmospheric Arc Discharge with Pulsed Power

Plasmas are common tools used for synthesis and modification of nanoparticles. All techniques aim at providing high quality, nanostructured materials with well-defined crystalline state and functional properties. The most consolidated cold plasma nanosynthesis methods are pulsed-DC physical/chemical vapour deposition (PVD/CVD), high power impulse magnetron sputtering (HiPIMS), and pulsed cathodic arc. However, atmospheric arc discharge processes excel in production of stand-alone nanomaterials thanks to their high throughput and excellent quality and wide variety of obtained materials. Carbon nanostructures, like graphene and carbon nanotubes, core-shell nanoparticles, and transition metal dichalcogenide monolayers constitute some remarkable examples. Pulsed atmospheric arc nanosynthesis shows unique capabilities due to its flexibility and wide range of plasma parameters achievable by adjusting repetition frequency, pulse length, and peak values of pulse waveform. Here, we review the highlights of pulsed arc discharges applied on synthesis of low-dimensional materials, and the main contributions of this technique and other concurrent plasma methods are compared. The advantages of operating atmospheric pressure arc discharges in pulsed mode have enabled addressing instability issues via a more efficient arc control. Such milestones are discussed according to the intended research goal or application, namely: high-temperature tailoring of material nanostructure, control of deposition with a spatial resolution, nanosynthesis using liquids in plasma, and enhanced stabilization and power management of anodic arcs.

Numerical investigation on transient arc characteristics and anode surface temperature considering the electrode movement

This work investigates the transient anode temperature and plasma parameters considering the electrode movement and the arc expansion. A transient self-consistent model is established using the dynamic mesh approach. Two cases with different maximum arc currents, representing various anode activity, have been studied. The simulations predict significant changes in spatial distribution of species densities, electron temperature and anode surface temperature in case with the anode spot formation. Furthermore, the influence of opening velocity on the plasma parameters has been studied numerically. The model was validated by comparison with experimental data for anode surface temperature as well as spectrally filtered arc images. Results of this comparison are presented and discussed.

Experimental study on the effect of argon shielding gas on the suppression of nitrogen arc anode ablation

The high heat flux density of the DC arc often leads to severe anode ablation, which is a key factor limiting the wider use of the DC plasma torches. In this study, a series of comparative experimental studies are conducted with the goal of suppressing nitrogen arc anode ablation by combining argon shielding flow and anode structure. It is found that for the planar electrode structure, the use of argon shielding gas can alleviate the ablation of the anode by nitrogen arc to some extent. If a boron nitride channel is installed on the anode surface to constrain the argon shielding flow, the electrode ablation can be significantly reduced. The experimental results show that there is no significant ablation on the anode surface after 1 h of operation of the nitrogen arc device with an arc current of 100 A. Further analysis reveals that, on the one hand, argon shielding gas can extend the range of motion of the nitrogen arc root along the anode surface and increase the speed of arc root motion, which has the effect of expanding the time-averaged arc anode attachment area. On the other hand, argon shielding gas can also increase the size of the nitrogen arc root and decrease the temperature of the arc root. The use of constraining channels can effectively control the range of motion of the arc root along the anode surface and strengthen the influence of argon shielding gas. The combination of these effects can substantially suppress the anode ablation of the DC arc device.

Numerical Simulation of the Effect of Annular Boss Structure on DC Arc Anode Attachment

Numerical Simulation of the Effect of Annular Boss Structure on DC Arc Anode Attachment

Dynamic characteristics of multi-arc thermal plasma in four types of electrode configurations

The enhanced volume of thermal plasma is produced by a multi-arc thermal plasma generator with three pairs of discharge electrodes driven by three directed current power suppliers. Combined with a high-speed camera and an oscilloscope, which acquire optical and electric signals synchronously, the dynamic behavior of different kinds of multi-arc discharge adjusted by the electrode arrangement is investigated. Also, the spatial distributions and instability of the arc discharge are analyzed in four electrode configurations using the gray value statistical method. It is found that the cathodic arcs mainly show a contracting state, while the anodic arcs have a trend of transition from shrinkage to a diffusion-like state with the increase of the discharge current. As a result of the adjustment of the electrode configuration, a high temperature region formed in the center of the discharge region in configurations of adjacent electrodes with opposite flow distribution and opposite electrodes with swirl flow distribution due to severe fluctuation of arcs. The discharge voltage rises with increased discharge current in this novel multi-arc plasma generator. It is also found that anode ablation mainly occurs on the conical surface at the copper electrode tip, while cathode erosion mainly occurs on the surface of the inserted tungsten and the nearby copper.

Two-dimensional self-consistent numerical simulation of the whole discharge region in an atmospheric argon arc

A 2D self-consistent numerical model of the whole argon-arc discharge region that includes electrodes is developed in this work to facilitate analysis of the physical processes occurring in atmospheric arc plasma. The 2D arc column model contains the ionization and thermal non-equilibrium, which is coupled with a 1D electrode sheath model. The influence of plasma-species diffusion near the electrode region is investigated based on Maxwell–Stefan equations and the generalized Ohm’s law. The numerical results of argon free-burning arcs at atmospheric pressure are then investigated. The simulation shows that the plasma is obviously in the state of thermal and ionization equilibrium in the arc core region, while it deviates from thermal and ionization equilibrium in the arc fringe region. The actual electron density decreases rapidly in the near-anode and near-cathode regions due to non-equilibrium ionization, resulting in a large electron number gradient in these regions. The results indicate that electron diffusion has an important role in the near-cathode and near-anode regions. When the anode arc root gradually contracts, it is easy to obtain a positive voltage drop of the anode sheath (I = 50 A), while it remains difficult to acquire a positive anode sheath voltage drop (I = 150 A). The current–voltage characteristics predicted by our model are found to be identical to the experimental values.

Investigation on the arc root characteristics of vacuum arc between the iron-core cup-shaped transverse magnetic field contacts

The severity of the contact surface ablation determines the breaking capacity of the vacuum circuit breaker, and the interaction between the arc root and the electrode is the main cause of the contact surface ablation. The characteristics of the arc root determine the magnitude of the electromagnetic force received by the arc during the movement stage as well as the shape and speed of the arc movement. It will eventually affect the temperature of the contact surface and the ablation situation. This paper studied the arc root characteristics of high-current constricted vacuum arcs between the iron-core cup-shaped transverse magnetic field contacts and put forward the idea of using the ratio of cathode and anode arc root areas to quantitatively analyze the concentration of vacuum arc. The research on the arc root characteristics of the vacuum arc can help to improve the arc characteristics and arcing mechanism, and the proposition of the ratio can provide a new method for the study of constricted arc. This can provide a basis for improving the arc extinction performance of the switch, reducing the ablation of the contact material, and improving the contact life.

Determination of positive anode sheath in anodic carbon arc for synthesis of nanomaterials

In the atmospheric pressure anodic carbon arc, ablation of the anode serves as a feedstock of carbon for production of nanomaterials. It is known that the ablation of the graphite anode in this arc can have two distinctive modes with low and high ablation rates. The transition between these modes is governed by the power deposition at the arc attachment to the anode and depends on the gap between the anode and the cathode electrodes. Probe measurements combined with optical emission spectroscopy are used to analyze the voltage drop between the arc electrodes. These measurements corroborated previous predictions of a positive anode sheath (i.e. electron attracting sheath) in this arc, which appears in both low and high ablation modes. However, the positive anode sheath was determined to be ∼3–8 V, significantly larger than ∼0.5 V predicted by previous models. Thus, there are apparently other physical mechanisms not considered by these models that force the anode sheath to be electron attracting in both ablation regimes. Another key result is a relatively low electron temperature (∼0.6 eV) obtained from OES using a collisional radiative model. This result partially explains a higher arc voltage (∼20 V) required to sustain the arc current of 50–70 A than predicted by existing simulations of this discharge.

Carbon arc for nanoparticle production: Ablation rate calculation. Comparison to experiments

A graphite anode ablates in an arc system producing nanoparticles. Experiments show that the ablation rate increases sharply when the current density at the anode exceeds some critical value, which separates the low ablation and high ablation modes. According to the existing hypotheses, the high ablation mode takes place when the anode voltage drop, which is negative in the low ablation mode, turns positive. Based on the work of Nemchinsky [J. Appl. Phys. 130, 103304 (2021)], where the anode voltage drop was evaluated, in this paper, the thermal regime of the anode is considered. It is shown that the main heating mechanism is electron condensation on the anode. The main cooling mechanism is radiation in the low ablation mode and cooling by sublimation in the high ablation mode. In the last case, the energy necessary to compensate for the strong cooling effect of sublimation is delivered by electrons accelerated at the positive anode drop inside the anode sheath. The proposed model allows one to find the ablation rate for a wide range of arc currents and anode diameters. Comparison to the available experimental data shows reasonable agreement. Based on analysis of the experiments and calculations, it was hypothesized that the ablation rate is not sensitive to the presence of a catalyst.

Arc dynamics in a vortex-stabilized non-transferred plasma torch with a tangential gas feed

The mode of anode arc attachments in a thermal plasma torch, such as constricted arc, multi-arc or diffused arc attachment, has operational as well as economic consequences on the use of plasma torches in industrial applications. The mode of arc attachment is strongly dependent on the gas flow dynamics, gas vortex formation and wall energy exchange. To gain more insight into arc attachment behaviour, this article presents a transient flow plasma model implemented using OpenFOAM computational fluid dynamics code to study the effect of gas swirl and arc rotation on modes of arc attachments. A tangentially fed plasma gas creates a gas swirl that helps to induce the arc rotation. The investigations were carried out at arc currents between 200–450 A and input gas flow rates in the range of 5–20 slpm. High gas swirl and low arc currents are found to favour constricted attachment on the anode surface. The local gas vortex driven by the plasma swirl creates hot spots inside the torch that dictate the arc attachment. The transition of arc attachment from the diffuse to constricted mode was simulated by imposing a step-change in the gas flow which shows the evolution of different arc attachment behaviour. During the transition from constricted to diffused attachment, the arc tends to undergo a transitionary multi-attachment mode at specific selected current and flow parameters.