Air Arc Research Articles

Numerical thermofluid simulation of high current air arcs at fault point contaminated with metal vapor from evaporation of metal electrode in open air

AbstractA numerical simulation was conducted to simulate behavior of an arc discharge in open air contaminated with metallic vapor for kA‐class high current. This simulation is concerned with a fundamental study on an arc discharge in a high‐energy arcing fault (HEAF), which can be found occasionally in electric equipment inside nuclear power plants. To understand phenomena in HEAF, it is useful to study air arc behavior at high fault currents, considering metallic vapor contamination from the metallic electrodes because the fault arcs often form in air between metallic parts in electric equipment. In this model, metal electrode evaporation and metal vapor contamination of the arcs were taken into account. Using this model, the temperature, pressure rise, and heat flux in arc plasmas established between Fe electrodes were calculated for ac currents of 3, 5, and 7 kApeak in open air. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

An improved method for fast evaluating arc quenching performance of a gas based on 1D arc decaying model

The evaluation of an arc quenching medium in circuit breakers usually requires the experimental investigation or the 2D or 3D magnetohydrodynamics simulation of switching arcs, which are expensive and time-consuming. In this work, a fast method is proposed for evaluating the arc quenching performance of gases. In this method, the arc decaying process is divided into three stages based on the results of 1D arc decaying modeling, including the thermal recovery stage, the predielectric recovery stage, and the postdielectric recovery stage. Compared to the previous method, the present method is improved mainly in the three aspects: the thermal recovery stage is featured by the average radial temperature instead of the axial temperature; the criterion of dividing the dielectric recovery stage into the pre- and postdielectric recovery stages is validated by the average electron number density instead of choosing arbitrarily; and the postdielectric recovery stage is characterized by the critical electric field strength Ecr instead of the reduced critical electric field strength (E/N)cr. The case study of SF6, CO2, CF4, and air arcs indicates that the present method yields the same descending order of the thermal recovery rate and the predielectric recovery rate for the four gases as the previous method. Moreover, the present method can avoid negative postdielectric recovery rates, which means that it is more reasonable than the previous method.

Two-dimensional temperature distribution of air arc commutating to arc runner

Molded case circuit breakers (MCCBs) are used to provide overcurrent and short-circuit protection for low-voltage devices with rated currents of several hundreds of amperes. In MCCBs, some arc discharges have been observed to remain on the contacts and hardly move to the arc runners. Information about the temperature distribution over an air arc plasma is indispensable in investigating and clarifying such arc-commutation phenomena. We propose a new optical system that enables dynamic measurement of the two-dimensional temperature distribution over air arc via the two-line radiance ratio method. The system consists of a four hold-lens array, a high-speed video camera, and interference filters whose wavelengths correspond to the emission spectra of air arcs with metallic vapor. The dynamics of the air arcs in a mock MCCB was measured with this system. The anode root commutates to the runner, where its ambient temperature exceeds threshold Tth, by contrast, there was no clear threshold temperature for cathode-root commutation. The Tth was 8000 K and 6000–7000 K for Cu runners and Fe runners, respectively. Light emitting spheres, which were presumably molten droplets, were emitted from the anode root and often triggered the commutation of the cathode root.

Direct Treatment of Liquids Using Low-Current Arc in Ambient Air for Biomedical Applications

In this work, we developed a portable device with low production and operation costs for generating an ambient air low-current arc (AALCA) that is transferred to the surface of a treated liquid. It was possible to generate a stable discharge, irrespective of the conductivity of the treated liquid, as a sequence of corona, repeating spark, and low-current arc discharges. The estimated concentration of reactive oxygen and nitrogen species (RONS) in plasma-treated water (PTW) produced using AALCA treatment was two orders of magnitude higher than that of PTW produced using conventional He nonequilibrium atmospheric pressure plasma jets or dielectric barrier discharges. The strong bactericidal effect of the treatment using AALCA and the water treated using AALCA was confirmed by survival tests of Escherichia coli. Further, the possibility of treating a continuous flow of liquid using AALCA was demonstrated.

Interruption of Low-Voltage DC Arc in Air Under Axial Magnetic Field

This paper represents the findings from our research in which a series of experiments were conducted on dc current interruption in air in axial magnetic field provided from rare earth magnets mounted in the test electrodes. The experimental range was as follows: arc voltage 80–100 V, arc length 5–10 mm, arc current 80–800 A, and applied field 35–2400 G. The free-burning arc diameter was measured in these experiments from high-speed photographs. It was found that a strong magnetic field can improve the interruption capacity of air-arc significantly. In the experiments, the successful switching time of both 220 and 330 A free-burning air-arc in 2.4 kG was less than half of the successful switching time of corresponding free-burning arcs in air. For higher current arcs, the outcome was more encouraging. An 800 A free-burning arc sustained for about 48 ms, whereas a 315 G field interrupted it within 8 ms. The information found on arc-root diameter and current density of 80–800 A free-burning arcs in air has filled a gap of data found in the literature. This information, in turn, will help to improve the theories available on free-burning arcs.

Temperature and pressure profiles of an ablation-controlled arc plasma in air

Experimental measurements of the spatial distribution of temperature and composition of ablation-controlled arc plasmas are a key to validate the predictions of metal evaporation and polymer ablation models. Thus, high-speed photography and space-resolved spectroscopic measurements have been performed to characterize a stable air arc plasma jet controlled by ablation of a polymer nozzle made of Polyoxymethylene copolymer (POM-C) or polyamide (PA6). The spectroscopic analysis is performed along a plane perpendicular to the arc jet axis for a current of 1.8 kA, corresponding to an estimated current density of ~65 A mm−2. Temperature and partial pressure profiles of the plasma for copper, hydrogen and carbon in the gas mixture are estimated as an inverse optimization problem by using measured side-on radiance spectra and radiative transfer spectral simulations. It is shown that the generated ablation-controlled arc has a complicated, non-uniform gas composition. Thus, the generated arc jet has a thin metallic core with a lower almost constant hydrogen pressure, surrounded by a thicker hydrogen and carbon mantle at partial pressures slightly lower than atmospheric pressure. The separation of hydrogen and carbon in the core is a consequence of demixing of the polymer vapour in the plasma. It is found that the overall shape of the temperature and pressure profiles obtained for the arc plasmas with the POM-C and PA6 nozzles are similar although differ in peak values and width.

Study on voltage characteristics of short air arc with high current density arc root

In this paper, the voltage characteristics of short air arc with high average current density arc root were studied at atmospheric pressure. Cu-W electrodes with diameter of 5-14mm and gap length of 0.2-3 mm were used in the experimental study. The experimental current varies from 1,000A to 16,600 A. The average current density of the arc roots in the experiment was up to 245 A/mm2. In the scope of this study, the arc voltage is a function of the average current density of arc root when the electrode gap length is fixed. For same average current density of arc root, the arc voltage is approximately the same even if the experimental currents are different. And the arc voltage increases with the increment of the average current density of arc root. Theoretical analysis and experimental results show that the electrode fall voltage almost doesn’t change with the average current density of arc root. However the arc column voltage increases with the increment of the average current density of arc root.

Thrust generation of the cathodic arc in ambient air

Thrust and current-voltage characteristics of pulsed cathodic arcs operating in vacuum and ambient air are presented and analyzed. In near vacuum conditions the thrust is proportional to the pulse duration, whereas in atmospheric pressure air the thrust reaches a maximum at a pulse duration of ∼5 s and then decreases for longer durations. A thrust model is developed based on contributions from two sources: fast ions and local pressure gradient. According to the model, for a sufficiently short pulse, the arc generates a positive local overpressure that produces additional thrust. Good agreement is obtained between the model and measurements. These results suggest that an optimal arc pulse duration exists for effective momentum transfer to the background gas.

Numerical simulation of air arc impinging to chamber shell with multi-physical coupling method of fluid-thermal-structure

The air arc impinging to chamber shell during interruption current process were studied by experiments and numerical simulation. Firstly, strain characteristics of chamber shell were measured by the strain gauge, and the strain changing with times were lagging behind the pressure in arc chamber. Experiment strain results 0.0035 and 0.0025 were slightly smaller than the calculation results 0.0055 and 0.0035. Furthermore, the thermal field mathematics model of chamber shell was proposed, and it was found that there was a large temperature gradient in the thickness of the chamber shell. Lastly, stresses-strains of three kinds of coupling methods, which were the fluid-structure coupling, the thermal-structure coupling and the fluid-thermal-structure coupling were compared. It was confirmed that the mechanical stress was concentrated in the middle of the side wall, while the maximum thermal stress was distributed on the vent area. Total stress and total strain were not equal to the algebraic sum of mechanical field and thermal field. The effect of different fixed supports on the thermal field was greater than the effect on the fluid field, and outer side wall fixed support had minimal displacement.

Characteristics of Impulse Arc Discharge in the Circuit of a Powerful Capacitive Energy Storage Device

Within the framework of the engineering approach and channel model of the electric arc, a new variant, impulse air arc discharge between metal (graphite) electrodes of an air double-electrode system (DES), which is part of the heavy-current discharge circuit of a powerful high-voltage capacitive energy storage (CES), was investigated. The amplitude–time parameters (ATPs) formed by the storage device of the current aperiodic pulse in the plasma channel of the air arc discharge corresponded to the slow current C-component of the artificial lighting intended for testing the elements of aircraft for the electrothermal lighting resistance. With respect to the rated ATP of the discharge current, the calculated ratios were obtained, in the plasma channel of the pulse electrical arc in an air DES, for determination of such main characteristics as the equivalent resistance, the released thermal energy, the maximum intensity of the longitudinal electric field, the linear power of thermal losses, the channel current density and the maximum electronic temperature. Distinctive features and general properties of pulse arc discharge in the air DES as compared with heavy-current pulse spark-discharge in similar DES were revealed. The offered ratios allow specifying the energy balance in the CE discharge circuit. The results of the approximate calculations proved the efficiency of the calculated ratios.

Time dependent 2-dimensional model of an alternating current arc

Two computed models of an ac arc are considered in the paper. The burning of the arc in air is simulated between two electrodes, one of which is blown with gas. The simulation is performed using COMSOL Multiphysics software product. An incompressible flow is considered with default settings, when the density is constant and temperature-independent and the density is temperature-dependent. An analysis of the distribution of velocities, temperature on the axis, and the voltage drop across the arc is made.

Copper electrode erosion in rotating arcs at atmospheric pressure

Copper cathode erosion of rotating arc in air at atmospheric pressure has an unusual feature: it is much higher than that of stationary arc at the same pressure. It falls with the rotation frequency up to some specific frequency and then rises almost by the order of magnitude at higher frequencies. The hypothesis to explain that erosion rate behavior is suggested.

Numerical Study of Influence of Frequency and Eddy Currents on Arc Motion in Low-Voltage Circuit Breaker

The air circuit breaker used for permanent magnet wind power generation systems should switch OFF the short-circuit current of variable frequencies. This paper focuses on the influence of frequency on the behavior of air arc. A 3-D magnetohydrodynamic (MHD) model of air arc plasma was developed to investigate the arc motion process at variable frequencies. In this model, the eddy currents in the whole calculation domains including the electrodes, the splitter plate, and the arc column were considered, and the magnetic vector potential approach was adopted to calculate the electromagnetic field produced by the current loop. A thin layer of elements with a nonlinear voltage–current density characteristic surrounding the splitter plate was employed to represent the formation of new arc roots and electrodes voltage drop. Based on this model, the evolutions of arc voltage, temperature, normalized time, and current density were obtained and compared among variable frequencies. The simulation results reveal that the normalized time, the eddy current density peak in splitter plate, and the arc voltage peak increase at a higher frequency.

Parameter estimation of extended free-burning electric arc within 1 kA

A long electric arc, as a common phenomenon in the power system, not only damages the electrical equipment but also threatens the safety of the system. In this work, a series of tests on a long electric arc in free air have been conducted. The arc voltage and current data were obtained, and the arc trajectories were captured using a high speed camera. The arc images were digitally processed by means of edge detection, and the length is formulated and achieved. Based on the experimental data, the characteristics of the long arc are discussed. It shows that the arc voltage waveform is close to the square wave with high-frequency components, whereas the current is almost sinusoidal. As the arc length elongates, the arc voltage and the resistance increase sharply. The arc takes a spiral shape with the effect of magnetic forces. The arc length will shorten briefly with the occurrence of the short-circuit phenomenon. Based on the classical Mayr model, the parameters of the long electric arc, including voltage gradient and time constant, with different lengths and current amplitudes are estimated using the linear least-square method. To reduce the computational error, segmentation interpolation is also employed. The results show that the voltage gradient of the long arc is mainly determined by the current amplitude but almost independent of the arc length. However, the time constant is jointly governed by these two variables. The voltage gradient of the arc with the current amplitude at 200–800 A is in the range of 3.9 V/cm–20 V/cm, and the voltage gradient decreases with the increase in current.

Thermal re-ignition processes of switching arcs with various gas-blast using voltage application highly controlled by powersemiconductors

This paper focuses on a fundamental experimental approach to thermal arc re-ignition processes in a variety of gas flows in a nozzle. Using power semiconductor switches in the experimental system, the arc current and the voltage applied to the arc were controlled with precise timing. With this system, residual arcs were created in decaying phase under free recovery conditions; arc re-ignition was then intentionally instigated by application of artificial voltage—i.e. quasi-transient recovery voltage—to study the arc behaviour in both decaying and re-ignition phases. In this study, SF6, CO2, N2, O2, air and Ar arcs were intentionally re-ignited by quasi-TRV application at 20 μs delay time from initiation of free recovery condition. Through these experiments, the electron density at the nozzle throat was measured using a laser Thomson scattering method together with high speed video camera observation during the re-ignition process. Temporal variations in the electron density from the arc decaying to re-ignition phases were successfully obtained for each gas-blast arc at the nozzle throat. In addition, initial dielectric recovery properties of SF6, CO2, air and Ar arcs were measured under the same conditions. These data will be useful in the fundamental elucidation of thermal arc re-ignition processes.

Influence of Magnetic Measurement Modeling on the Solution of Magnetostatic Inverse Problems Applied to Current Distribution Reconstruction in Switching Air Arcs

This paper presents a systematic analysis of the influence of magnetic measurement modeling on the regularized solution of magnetostatic inverse problems. The focus is on the application of the inverse problem technique to current distribution reconstruction of arc plasmas inside low-voltage switching devices. The inverse problems modeled with both the ideal sensor assumption and non-ideal sensor modeling are studied, considering the geometry and active area of sensors. The Tikhonov regularization is adopted to address the ill posedness of the inverse problem. Sensor arrays with random variations in sensor directions and positions are compared with arrays using perfectly aligned setup. The numerical results reveal that for mono-axial planar sensor arrays the ideal sensor assumption could be used to simplify the modeling process with serious environmental noises. Better reconstruction can be obtained using the non-ideal sensor model when the sensor variations are large.

Study of Impact Process of Air Arc on the Chamber Shell Based on the Interaction of Fluid–Structure Method

Based on the commercial ANSYS workbench simulation software, the fluid–structure interaction method is used to calculate the air arc pressure distribution in arc chamber, and its impact effect on the shell during interrupting the high current is simulated and analyzed. The stress and deformation distributions of the arc chamber shell with different materials and thicknesses are obtained. It is confirmed that the maximum stress of the shell with 6-mm thickness decreases by ~25% compared with that of 3-mm thickness shell, and the maximum deformation decreases by ~20%. Four models for thickening different local regions are proposed to optimize the shell structure based on the above analysis, including thickened middle regions of the wall inside/outside and corresponding edge regions of the wall. The simulations results indicate that the structure of the arc chamber shell could be optimized very well to achieve the most uniform stress/deformation distribution using the model with thickening the middle region of the outside wall.

Air arc erosion behavior of CuZr/Zn2SnO4 electrical contact materials

Cu-based composites are considered as one of the high performance and cost-effective materials to replace the noble metal-based electrical contact materials used in low-voltage electrical apparatus. However, the oxidation resistance of Cu-based electrical contact materials at high temperatures is still the major challenge that limits their applications. In this study, CuZr/Zn2SnO4 composites were prepared through powder metallurgy method. The air arc erosion resistance of the composites under AC 380 V and 20 A was evaluated through the mass loss and the electrical contact resistance after experienced over 10,000 arc discharge cycles. The microstructure evolution, which reflected the deterioration process of the composites, was demonstrated through SEM analysis. The results indicated that the oxidation of Zr occurred along with the oxidation of Cu at high temperature, which considerably consumed the oxygen and thus significantly enhanced the oxidation resistance of Cu-based composites. In addition, TEM result showed a smooth and clear interface between Cu and Zn2SnO4 phases, suggesting that the addition of Zn2SnO4 phases was beneficial to enhance the durability of the composite. This work will not only merit the design and development of Cu-based electrical contact materials but also expand the applications of Cu-based composites in the air at high temperature.

Influence of arc current and pressure on non-chemical equilibrium air arc behavior

The influence of arc current and pressure on the non-chemical equilibrium (non-CE) air arc behavior of a nozzle structure was investigated based on the self-consistent non-chemical equilibrium model. The arc behavior during both the arc burning and arc decay phases were discussed at different currents and different pressures. We also devised the concept of a non-equilibrium parameter for a better understanding of non-CE effects. During the arc burning phase, the increasing current leads to a decrease of the non-equilibrium parameter of the particles in the arc core, while the increasing pressure leads to an increase of the non-equilibrium parameter of the particles in the arc core. During the arc decay phase, the non-CE effect will decrease by increasing the arc burning current and the nozzle pressure. Three factors together—convection, diffusion and chemical reactions—influence non-CE behavior.

Visualization and mechanisms of splashing erosion of electrodes in a DC air arc

The splashing erosion of electrodes in a DC atmospheric-pressure air arc has been investigated by visualization of the electrode surface and the sputtered droplets, and tracking of the droplet trajectories, using image processing techniques. A particle tracking velocimetry algorithm has been introduced to measure the sputtering velocity distribution. Erosion of both tungsten–copper and tungsten–ceria electrodes is studied; in both cases electrode erosion is found to be dominated by droplet splashing rather than metal evaporation. Erosion is directly influenced by both melting and the formation of plasma jets, and can be reduced by the tuning of the plasma jet and electrode material. The results provide an understanding of the mechanisms that lead to the long lifetime of tungsten–copper electrodes, and may provide a path for the design of the electrode system subjected to electric arc to minimize erosion.