Arc Velocity Research Articles

Repetition frequency of a DC gliding arc discharge in plasma-assisted fuel-rich combustion

Plasma-assisted combustion is a growing field of applied physics. In this study, a DC gliding arc plasma reactor used as part of a swirler stabilized burner was characterized to evaluate the discharge repetition frequency as a function of process parameters. The discharge was generated in fuel-rich premixed mixtures of air and natural gas. The repetition frequency was determined by applying a fast Fourier transform to the voltage waveforms. The results show that the mean voltage and mean current of the gliding arc remain almost constant as a function of the total gas flow rate. The increase in fuel concentration promotes a drop in the breakdown voltage, which leads to a rise in the discharge repetition frequency. However, for a fixed natural gas flow rate, the repetition frequency grows with the increased total mass flow rate due to a higher arc velocity.

Coupled gas flow-plasma model for a gliding arc: investigations of the back-breakdown phenomenon and its effect on the gliding arc characteristics

We present a 3D and 2D Cartesian quasi-neutral plasma model for a low current argon gliding arc discharge, including strong interactions between the gas flow and arc plasma column. The 3D model is applied only for a short time of 0.2 ms due to its huge computational cost. It mainly serves to verify the reliability of the 2D model. As the results in 2D compare well with those in 3D, they can be used for a better understanding of the gliding arc basic characteristics. More specifically, we investigate the back-breakdown phenomenon induced by an artificially controlled plasma channel, and we discuss its effect on the gliding arc characteristics. The back-breakdown phenomenon, or backward-jump motion of the arc, as observed in the experiments, results in a drop of the gas temperature, as well as in a delay of the arc velocity with respect to the gas flow velocity, allowing more gas to pass through the arc, and thus increasing the efficiency of the gliding arc for gas treatment applications.

Modeling Arc in Transverse Magnetic Field by Using Minimum Principle

A method to calculate the properties of a high-current arc exposed to a transverse magnetic field is proposed. Using only the arc current and the magnetic field, the method predicts the arc size, electric field, temperature, and velocity of the arc. Comparison is presented for the calculated arc velocity V as a function of the magnetic field B with the available experimental data. The computed velocity of a 100-A arc at one atmosphere showed that: 1) the functional dependence of $V(B) \sim B^{\mathrm {0.63}}$ is close to that experimentally observed and 2) the difference between the computed velocity and the experimental one does not exceed the factor of 2 in a wide diapason of magnetic fields. The prediction of the velocity of an arc at superhigh pressure (100 atm) is made.

Diagnostic of Neutralization Current for Arcs on Satellite Solar Panel Coupons

Risk of arcing in space plasma environment on satellite solar panel has always been an issue of major concern in the aerospace community. The outcome of round robin tests performed in various laboratories has resulted in finalization of the guidelines for the ground test of satellite solar panel coupons (SSPCs). This is documented as ISO-11221 standards. Authenticity of arc plasma flashover (FO) parameters are still under debate. Some experimental findings that support the perimeter theory of arc FO on geostationary (GEO) satellites are discussed in this paper. It has been observed that characteristics of an the arc are dependent on its location on the solar coupon, bias charge (charge due to bias voltage and external capacitance), and the total charge dissipated during the arc discharge. It is also observed that the duration between the two consecutive arcs is directly proportional to the dissipated charge or energy of the latter arc. A combined dielectric consisting of solar cell, adhesive, Kapton, and Carbon Fiber Reinforced Polymer sheet holds charge during irradiation by the electron gun. This resembles surface FO capacitance. Arc energy is governed by the combined effects of a surface flashover capacitor (C-sf) and an external capacitor. It is observed that if intermittent arc duration is sufficiently longer than the gradual accumulation of charge on the SSPC, body may lead to a major arc. This would increase the probability of secondary arcs when the sustained arc environment is experienced by the satellite. To understand primary arcs on dielectrics, an artificial triple junction is prepared and exposed under adverse GEO-like space conditions. Various signatures identified from the arc current and arc neutralization current waveforms specify the behavior of these arcs at different locations on the coupon surface. In this paper, current waveforms of arcs captured on different types of solar panel coupons and their significance are studied. Information about arc energy, arc velocity, and neutralization velocity are extracted from the measured waveforms.

Dynamic modeling of AC multiple ARCS of EHV post station insulators covered with ice

The present contribution proposes a multi-arc dynamic model to predict the parameters of AC flashover propagating over EHV ice-cover insulators. The model considers the arc as time-dependent impedance consisting of a resistance in series with an inductance. The residual ice layer is specified in terms of an equivalent resistance, where the equivalent surface conductivity is calculated by taking into account the water film flowing over the glass surface. The temporary arc length developing over an ice-covered insulator is calculated through the arc velocity, determined using high-speed image recording techniques. The principal characteristics of flashover, including minimum flashover voltage, leakage current and arc velocity are investigated through the proposed multi-arc dynamic model. The proposed models were successfully validated in the laboratory using station post insulators - typically used in Hydro-Quebec 735 kV substations - under AC voltage based on the standard method presented in IEEE Std 1783. Good agreement was also observed between the flashover voltage calculated from the proposed multi-arc model and those obtained experimentally on ice-covered EHV insulators. The proposed model is helpful for properly designing and selecting the EHV insulators used in cold climate conditions.

Heat transfer to a cathode of a rotating arc

In gas heaters and other plasma devices that use tubular electrodes, the arc is rotated in order to spread the heat load to the electrodes and to reduce their erosion. A method to calculate spatiotemporal temperature development along the surface of these electrodes is suggested. The important feature of the method is that it takes into account the heat prehistory of the electrode: the temperature field created by the previous arc rotations. The result of these calculations shows that the average temperature created by these previous rotations could be very high. In the considered cases, it reaches almost 30% of the peak temperature (the Peclet number Pe = 25) and 50% of the peak temperature at the high arc velocity of rotation (Pe = 250). In particular, the method allows one to predict the number of rotations necessary to reach the steady-state heat transfer. These results clearly demonstrate that calculations that do not take into account the heat transfer history are not capable of providing correct results.

Low Computational-complexity Model of EAF Arc-heat Distribution

The paper presents a computational model and the corresponding algorithm for estimating the arc energy distribution to conductive, convective and radiative heat transfer in an electric arc furnace (EAF). The proposed algorithm uses channel arc model (CAM) in order to compute the distribution of the arc energy through empirical equations (to approximate arc radius), ideal gas law (to approximate arc density) and results of magneto-hydro-dynamic (MHD) models (to approximate arc pressure, temperature and velocity). Results obtained using the proposed algorithm are comparable with other similar studies; however, in contrast to other arc-energy distribution models, this model requires only two input variables (arc length and arc current) in order to calculate the energy distribution. Furthermore, simple algebraic equations used in the algorithm ensure minimal computational load and consequently lead to short calculation times which are approximately one hundred thousand (100 000) times smaller than solving the MHD model equations, making the algorithm suitable for real-time applications, such as smart monitoring and model-based control. The algorithm has been validated by two different approaches. First, the simulation results have been compared to a study dealing with arc-heat distribution in plasma arc furnace; and second, the proposed arc module has been integrated into the frame of a comprehensive EAF model in order to estimate the EAF temperature levels and compare them with operational EAF measurements. Both validations show high levels of similarity with the comparing data.

Mechanisms and processes of arc propagation over an ice-covered surface

The general objective of this paper is to investigate the physical mechanisms and processes involved in the propagation of arc over the surface of ice. In the present research work, high-speed imaging and optical emission spectroscopy techniques were synchronized with the electrical measurements to study the various parameters of arc on an ice surface, i.e. channel radius, propagation velocities, arc column temperature and electron density. These results, together with observation of the propagation patterns and arc foot geometries, calculation of arc energy and the examination of the state of thermal equilibrium provide background information for understanding the ice-covered insulator flashover phenomenon. Arc root structure, current profile, propagation pattern and velocity were investigated under different type of applied voltage and different polarities. Water film conductivity and thickness, relative air humidity and the direction of arc propagation were also analyzed as influencing parameters of arc propagation. The effects of different possible mechanisms, e.g. collision and thermal ionization, buoyancy force and electrostatic force, on different stages of arc propagation has been discussed.

Modeling of Cold Metal Transfer Spot Welding of AA6061-T6 Aluminum Alloy and Galvanized Mild Steel

In this article, a three-dimensional (3D) transient unified model is developed to simulate the transport phenomena during the cold metal transfer (CMT) spot welding process of 1 mm thick aluminum AA6061-T6 and 1 mm thick galvanized mild steel (i.e., AISI 1009). The events of the CMT process are simulated, including arc generation and evolution; up-and-down movement of electrode, droplet formation and dipping into the weld pool; weld pool dynamics; zinc evaporation, and zinc vapor diffusion in the arc. The effects of the gap between the two workpieces and effects of zinc vapor evaporated from the steel surface on CMT process are studied. The results show that the arc temperature, velocity, and pressure keep changing during the CMT process, which is related to the variations of welding current, arc length, and zinc evaporation. It is found that the zinc evaporation leads to the extremely high arc pressure and the upward flow of zinc vapor near the steel surface, which would induce the arc instability and provide the drag force for the droplet impingement. The presence of the gap between the two workpieces can improve the expansion of the arc plasma, resulting in the smaller arc pressure and the more intensive upward flow of zinc vapor from the steel surface. The phenomena observed in the experiment are in agreement with the modeling results.

Synthesis of aluminium nanoparticles by arc evaporation of an aluminium cathode surface

Aluminium nanoparticles (Al Nps) are synthesized using arc discharge method by applying direct current between aluminium electrodes in liquid environment without any use of vacuum equipment, heat exchangers, high temperatures furnaces and inert gases. After synthesis of Al Nps, in situ coating process on the nanoparticles was performed immediately. The effects of media on the yield and morphology of aluminium nanoparticles were investigated. Analysis result of the samples indicated that particle size was less than 30 nm, when 120 A/cm2 arc current was used. In addition, coating agent can affect arc velocity, arc stability, morphology and composition of the nanoparticles. Resultant nanoparticles were identified using X-ray powder diffraction (XRD), also their surface morphology was studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and finally the accuracy of coating was assessed with infrared (IR) spectroscopy.

Spectroscopic Study and Motion Analysis of Arc Spot Initiated on Nanostructured Tungsten

Arcing on the nanostructured tungsten surface has been examined recently because it gives rise to the erosion of materials and impurity transport toward the core plasma in a nuclear fusion reactor. Arcing was initiated on a helium-exposed tungsten surface, on which nanostructured tungsten was formed, by irradiation with ruby laser pulses of 0.08 MJ·m-2. The motion of an arc spot was observed with a fast-framing camera. The magnetic field strength and arc current dependences of velocity were discussed on the basis of experimental observation. Arc trails were observed using a digital fine scope to determine the relationship between the grouping width of an arc trail and arc velocity; the changes in grouping width and condition of the specimen surface are discussed. Spectroscopic measurements were performed to determine the electron temperature by the Boltzmann plot method.

Arc Movement of Intermediate-Frequency Vacuum Arc on TMF Contacts

This paper describes the arc behavior in the transverse-magnetic-field (TMF) contacts at intermediate frequency (400-800 Hz). With high-speed photography, three different arc modes were identified: expansion arc column, moving arc, and diffuse arc. In the expansion arc column mode, the arc column is immobile and the diameter of the arc column increases with the current. During this stage, the bright anode spots appear with high amplitude noise of arc voltage at high current. The expansion arc column mode plays an important role in the anode erosion. In the moving arc column mode, the average velocities were observed about 10-100 m/s, and the arc velocity increases with the increased frequency at the same current. The arc voltage expressed by arc current and frequency was obtained in this paper. The cross-section area of the arc column decreases with the increased frequency at the same current. The current density increases with the increased frequency at the certain current. Consequently, it is deduced that the arc velocity increases with the increased frequency at the same current. The mean power input concentrates in a smaller area at a higher frequency. It may be one of the reasons why the anode local melted.

Effect of different electrode tip angles with tilted torch in stationary gas tungsten arc welding: A 3D simulation

In this study, the effect of different tip angles (30°, 60°, 90° and 120°) on the arc and weld pool behavior is analyzed in 2 mm and 5 mm arc lengths with tilted (70°) torch. Arc temperature, velocity, current density, heat flux and gas shear are investigated in the arc region and pool convection and puddle shapes are studied in the weld pool region. The arc temperature at the tungsten electrode is found the maximum with sharp tip and decreases as the tip angle increases. The arc temperature on the anode (workpiece) surface becomes concentrated with increase in tip angle. The arc velocity and gas shear stress are observed large with sharp tip and decreasing as the tip angle increases. Current density on the anode surface does not change with tip angle and observed almost the same in all the tip angles in both 2 mm and 5 mm arc lengths. Heat flux due to conduction and convection is observed more sensitive to the tip angle and decreases as the tip angle increases. The electromagnetic force is slightly observed increasing and the buoyancy force is observed slightly decreasing with increase in tip angle. Analyzing each driving force in the weld pool individually shows that the gas drag and Marangoni forces are much stronger than the electromagnetic and buoyancy forces. The weld pool shape is observed wide and shallow in sharp and narrow and deep in large tip angle. Increasing the arc length does not change the weld pool width; however, the weld pool depth significantly changes with arc length and is observed deep in short arc length. The arc properties and weld pool shapes are observed wide ahead of the electrode tip in the weld direction due to 70° torch angle. Good agreement is observed between the numerical and experimental weld pool shapes.

Crustal structure across the Costa Rican Volcanic Arc

AbstractIsland arcs are proposed to be essential building blocks for the crustal growth of continents; however, island arcs and continents are fundamentally different in bulk composition: mafic and felsic, respectively. The substrate upon which arcs are built (oceanic crust versus large igneous province) may have a strong influence on crustal genesis. We present results from an across‐arc wide‐angle seismic survey of the Costa Rican volcanic front which test the hypothesis that juvenile continental crust is actively forming at this location. Travel‐time tomography constrains velocities in the upper arc to a depth of ~15 km where average velocities are <6.5 km/s. The upper 5 km of crust is constrained by velocities between 4.0 and 5.5 km/s, which likely represent sediments, volcaniclastics, flows, and small intrusions. Between 5 and 15 km depth, velocities increase slowly from 5.5 to 6.5 km/s. Crustal thickness and lower crustal velocities are roughly constrained by reflections from an inferred crust‐mantle transition zone. Crustal thickness beneath the volcanic front in Costa Rica is ~40 km with best‐fit average lower‐crustal velocities between 6.8 and 7.1 km/s. Overall, velocities across the arc in central Costa Rica are at the high‐velocity extreme of bulk continental crust velocities and are lower than modern island arc velocities, suggesting that continental compositions are created at this location. These data suggest that preexisting thick crust of the Caribbean Large Igneous Province has a measurable effect on bulk composition. This thickened arc crust may be a density filter for mafic material and thereby support differentiation toward continental compositions.

The Dynamic Volt-Ampere Characteristics of a Vacuum Arc at Intermediate-Frequency Under a Transverse Magnetic Field

In this study, the changes of a vacuum arc's appearance were observed and the volt-ampere characteristics of the vacuum arc at intermediate frequency were analyzed under a transverse magnetic field (TMF). The TMF and phase shift time were calculated by using the TMF contact model and the large phase shift of the magnetic field at a higher frequency was conductive to the dispersion process of residual plasma. The arc velocity was higher at 800 Hz than at 400 Hz. It can be inferred that TMF will encourage arc movement at 800 Hz. Moreover, the arc movement has an impact on the arc voltage. Because of the increasing length of the arc column with a high arc velocity, the elongated arc causes the arc voltage to increase. Specifically, the volt-ampere characteristics of the vacuum arc are divided into three stages in this paper. The higher the frequency, the greater the initial rate of rise in the arc voltage and the larger the area surrounded by arc volt-ampere characteristics. The correlations between the arc voltage and the amplitude and frequency of the current are also presented.

Theoretical and Experimental Analysis of Breech Fed and 40-Distributed Energy Stage Plasma Arc Railguns

The design and experimental results of a 40-stage distributed energy store (DES) plasma arc railgun are presented. The railgun drives a free running hypervelocity plasma arc, one that is not pushing a payload, to velocities in excess of 10 km/s. These high velocities are of interest as they are required to successfully launch payloads into low earth orbit (LEO). The ability to launch payloads into LEO using a hypervelocity electromagnetic launcher has many financial benefits over the more conventional chemical combustion launchers. In collaboration with an Air Force Office of Scientific Research funded Multidisciplinary University Research Initiative project, the Center for Pulsed Power and Power Electronics at Texas Tech University in Lubbock, Texas has been responsible for developing and investigating a functional scale model of a multistage DES railgun to determine its effectiveness to suppress restrike phenomenon and increase plasma armature railgun performance. The distributed energy scheme is theorized to suppress restrike arc formation because the back emf voltage is localized to active stage regions where high gas density and low temperature inhibits breakdown. B-dot sensors positioned along the length of the launcher provide data to measure the plasma arc velocity and detect restrike, arc splitting, or additional secondary arc formation phenomena.

Calculation of the Arc Velocity Along the Polluted Surface of Short Glass Plates Considering the Air Effect

To investigate the microphysics mechanism and the factors that influence arc development along a polluted surface, the arc was considered as a plasma fluid. Based on the image method and the collision ionization theory, the electric field of the arc needed to maintain movement with different degrees of pollution was calculated. According to the force of the charged particle in an arc plasma stressed under an electric field, a calculation model of arc velocity, which is dependent on the electric field of the arc head that incorporated the effects of airflow around the electrode and air resistance is presented. An experiment was carried out to measure the arc velocity, which was then compared with the calculated value. The results of the experiment indicated that the lighter the pollution is, the larger the electric field of the arc head and arc velocity is; when the pollution is heavy, the effect of thermal buoyancy that hinders arc movement increases, which greatly reduces the arc velocity.

Contribution for Iron Vapor and Radiation Distribution Affected by Current Frequency of Pulsed Arc

Pulsed GTA welding has been used for improvement of stability, weld speed, and heat input control. However, the temperature and radiation power of the pulsed arc have not been elucidated. Furthermore, arc contamination by metal vapor changes the arc characteristics, e.g. by increasing radiation power. In this case, the metal vapor in pulsed GTA welding changes the distribution of temperature and radiation power as a function of time. This paper presents the relation between metal vapor and radiation power at different pulse frequencies. We calculate the Fe vapor distribution of the pulsed current. Results show that the Fe vapor is transported at fast arc velocity during the peak current period. During the base current period, the Fe vapor concentration is low and distribution is diffuse. The transition of Fe vapor distribution does not follow the pulsed current; the radiation power density distribution differs for high frequencies and low frequencies. In addition, the Fe vapor and radiation distribution are affected by the pulsed arc current frequency.

Arcing Behavior on Different TMF Contacts at High-Current Interrupting Operations

Vacuum circuit breakers are widely used in the medium-voltage area. The majority of the installed vacuum tubes are equipped with electrodes using the transverse-magnetic-field design forcing the electric arc on a circular motion to avoid severe local overheating. A vacuum test switch was used to investigate the arc movement behavior between spiral- and cup-shaped electrodes at high-current interrupting operations. The switch was equipped with viewing ports allowing an observation from two rectangular views. Mounted sample contacts were made of CuCr 75/25 in different diameters. A digital 8-bit high-speed camera was used to record the arcing process with frame rates of 33 000 frames per second. Behavior patterns were investigated and compared with the arc voltage and the instantaneous current. Parameters such as the arc velocity and the current density on the contacts could be determined by means of the recordings. A static simulation model delivered Lorentz forces for a comparison between both designs. The experiments were conducted with short circuit currents from 20 to 60 kA (root mean square) with a frequency of 50 Hz.

Study of a High-Power Rotary Arc Gap Switch

Switch is one of the key issues in the pulsed power generation and applications. The closing switch is an essential part in capacitor-based energy-storage systems, and the spark-gap switches are a popular choice. These switches have very limited lifetime due to electrode erosion resulting from localized arc heating in high current. To extend the switch lifetime by minimizing electrode erosion, rotary arc gap (RAG) switches are proposed in previous literatures. The rotation of the arc can be achieved by providing magnetic field from external or self-induced by arc current. This paper investigates a RAG switch working in open air. It has a coaxial cylindrical structure. The arc is driven by an axial magnetic field which is generated by the coils that are placed both at the top and bottom of the switch. The coils are connected with an inner electrode. The switch can operate in a wide voltage range of 0.5-24 kV, and its specifications of current and coulomb per shot can reach 320 kA and about 730 C, respectively. The results of high-current experiments show that the electrode erosion is slight. Rotating arc velocity is measured by B-dot probes. The relationship between arc velocity and the current and magnetic flux density is obtained from the experimental data. The switch voltage drop is also measured in these experiments.