Alternating-current Arc Research Articles

Research on an Equivalent Heat Source Model of the AC Arc in the Short Gap of a Copper-Core Cable and a Fire Risk Assessment Method.

The magnetohydrodynamics (MHD) model of the alternating current (AC) arc is complex, so a simplified equivalent heat source (EHS) model can be used to replace the complex model in studying the AC arc's thermal characteristics and cable fire risk. A 2D axisymmetric AC arc MHD simulation model in the short gap of a copper-core cable is established in this paper. The AC arc voltage and current obtained by the model are consistent with experiments. The AC arc's heat source distribution obtained by the MHD model is fitted to obtain the heat source function Q of the AC arc. Q is divided into 16 independent segmented heat sources, and a correction matrix is constructed to optimize the segmented heat sources. A neural network and a genetic algorithm give the prediction model and the optimal correction matrix of the segmented heat source. The EHS model optimized by the optimal correction matrix can obtain a minimum temperature error of 5.8/4.4/4.2% with the MHD model in different AC arc peak currents 2/4/6 A. The probability of a cable fire is calculated by using AC arc's optimized EHS model when different numbers of AC arcs are generated randomly in AC half-waves. The EHS model can replace the complex MHD model to study the thermal characteristics of AC arcs and quickly calculate the probability of a cable fire caused by random AC arcs.

Numerical investigations of AC arcs’ thermal characteristics in the short gap of copper-cored wires

Excessive alternating current (AC) arcs generated in electric systems will accumulate heat and easily cause fire. This paper studies the thermal characteristics of different numbers of AC arc plasma generated in a short gap of copper-cored wires in the air. The number of AC arcs is controlled in the AC arc experiment and an infrared thermal imager measures the temperature change at the specified position. Based on magnetohydrodynamics (MHD), a two-dimensional axisymmetric AC arc discharge numerical simulation model is established. The volt-ampere characteristic of the AC arc is used to solve the MHD simulation model to obtain the same 'zero current' characteristics as the real AC arc in the experiment. A large amount of heat accumulates in the electrode gaps when the arc generation, and then the heat dissipates in the 'zero current' stage. The continuously generated arc makes the temperature higher. The volume of the space area with a temperature higher than 10,000 K increases with the arc current, but is unrelated to the number of arcs. The volume of the space area with a temperature higher than 524.15 K and the temperature on the electrode are both positively correlated with the number of AC arcs and arc current. The results of this study can provide a reference for the detection standard of AC arc faults and the prevention of electrical fire.

Combustion enhancement in a model scramjet by a simple pin-to-pin AC arc plasma

A simple pin-to-pin alternative-current (AC) arc plasma located upstream of the cavity was developed to achieve significant combustion enhancement in a Mach 2.52 C2H4-fueled and cavity-based model scramjet. The arc plasma-enhanced combustion process was recorded by high-speed CH⁎ chemiluminescence imaging, optical emission spectroscopy, static pressure measurements, and discharge waveform measurements. In the absence of the arc plasma, the flame heat release intensity was low, and the heat release region was located at the shear layer of the cavity; the flame stayed in a relatively weak combustion state and even appeared in a lower heat release intensity. Once the arc plasma was turned on, the static pressure of the model scramjet at the typical positions was increased by up to 9 %, and the flame area and the flame intensity were significantly enhanced. In the presence of the arc plasma, the position of the flame heat release region moved upstream and even caused the long-scale displacement for the flame with a higher heat release intensity several times. The arc plasma provided a large number of reactive species and Joule heat at the practical influence region of the arc plasma, which contributed to igniting an initial flame upstream of the cavity. The propagation and development of the continuous initial flame generated by the arc plasma can enable the flame to be more frequently transferred into the cavity-assisted jet-wake stabilized combustion mode, leading to significant combustion enhancement.

Laboratory Research on Design of Three-Phase AC Arc Plasma Pyrolysis Device for Recycling of Waste Printed Circuit Boards

Accumulation of electronic waste (e-waste) will place a heavy burden on the environment without proper treatment; however, most ingredients contained in it are useful, and it could bring great economic benefits when recycled. A three-phase alternating current (AC) arc plasma pyrolysis device was designed for resourcing treatment of waste printed circuit boards (WPCBs). This paper focuses on the analysis of plasma pyrolysis gas products, and the results showed that the plasma could operate stably, and overcame the problems of the poor continuity and low energy of single-arc discharge. Air-plasma would generate NOx contaminants, burn the organics, and oxidize the metals; therefore, air had not been selected as a working gas. Ar-plasma can break the long chains of organic macromolecules to make a combustible gas. Moreover, the strong adhesion between the metals and fiberglass boards would be destroyed, which facilitates subsequent separation. Ar/H2-plasma promoted the decrease of carbon dioxide and the increase of combustible small molecular hydrocarbons in the pyrolysis product compared with Ar-plasma, and the increase of the H2 flow rate or plasma power intensified that promotion effect. The percentage of other components, except the hydrogen of CO2, CO, CH4, C2H4, and C3H6, accounted for 55.7%, 34.2%, 5.6%, 4.5%, and 0% in Ar-plasma, and changed to 35.0%, 29.0%, 11.2%, 24.3%, and 0.5% in Ar/H2-plasma. Ar/H2-plasma could provide a highly chemically active species and break chemical bonds in organic macromolecules to produce small molecules of combustible gas. This laboratory work presents a novel three-phase AC arc plasma device and a new way for recycling WPCBs with high value.

Numerical investigation of AC electric arc plasma heat dissipation in EAF

ABSTRACT The alternating current (AC) electric arc furnace (EAF) is a crucial steelmaking facility consuming electricity to melt the recycled scrap. The arc heat dissipation impacts the scrap melting rate. The present study established a mathematical model to simulate the AC electric arc and estimate its heat dissipation under different arc operations. The study was aimed to deduce the relationship between arc operating current, arc length and the share of different arc heat dissipation mechanisms for future application in the scrap melting model. Validations of arc modelling were conducted by comparing the results against experimental data and simulations in the literature. A statistical method based on data sampling was proposed to determine the AC arc state variables to approximate the arc heat dissipation. A scrap melting experiment was designed and implemented in NLMK EAF to validate the amount of share determined in the present study for different arc heat dissipation mechanisms.

Numerical study on instantaneous heat transfer characteristics of AC arc-fault

Studying the heat transfer characteristics of alternating current (AC) arc-fault to electrodes is a key issue in electrical fires. In this paper, an instantaneous heat transfer numerical model of AC arc-fault is developed based on the magneto-hydrodynamic principle. The temperature distribution of the AC arc at the microseconds level and the influence of heat transfer on electrodes at the seconds level when the arc heats are studied. The numerical simulation of the axial temperature of the electrodes is verified by experiments, and the temperature variation in the electrodes at different currents and times is discussed. The results show that the arc temperature varies periodically similar to the current at the microseconds level but it does not go out when the current passes zero. The high-temperature region of electrodes diffuses with the increase in current or time. However, the axial temperature gradient of the electrode decreases with time and increases with current. Furthermore, the range of temperature increase in the electrode position decreases with the increase in current and time, but the electrode position near the arc has a higher initial temperature increase.

Numerical modelling for characteristics of the meso-pressure six-phase alternative current arc discharge plasma jet

In the re-entry process of hypersonic vehicle in near space,the violent interaction between the vehicle and the surrounding air will ionize the air and leaves a complex environment in the vicinity of the vehicle surface.Both the flow field and the communication between the vehicle and the controlling center on the earth are significantly affected by the generated plasma layers.This will result in serious system operation problems such as the communication blackout or radio blackout.Numerical modelling is one of the most widely used methods to investigate such complicated physical-chemical processes involving coupled magneto-hydrodynamics,heat transfer,dissociation,ionization,excitation and their reverse processes.Due to the strong collision,non-uniform and non-equilibrium characteristics of the plasma layers formed in the vicinity of the vehicle surface,a self-consistent physical-mathematical model,as well as a database for the transport properties of non-equilibrium plasmas,describing the non-equilibrium features of plasmas is one of the pre-requisites for numerical simulations.This paper focuses on the non-equilibrium plasmas produced near the bluff body surface in the re-entry process of hypersonic vehicles in near space,and a new non-equilibrium plasma model which has been developed previously by our group is employed for conducting two-dimensional (2D) simulations on the characteristics of the non-equilibrium argon plasma jets based on the multiphase gas discharge plasma experimental platform-2015(MPX-2015) established in our laboratory.The modelling is conducted under two different flow conditions, i.e.,the sub-sonic flow condition and the super-sonic flow condition.Under the sub-sonic flow condition,the 2D nonequilibrium modeling results are consistent well with the experimental measurements which validates the reliability of the non-equilibrium physical-mathematical model,as well as the developed computer codes in this study.The modeling results under the super-sonic flow conditions show that the spatial uniformity of the plasma layer surrounding the bluff body,as well as the total heat flux to the bluff body surface from plasmas,decreases significantly with the increase of the plasma jet velocity;while the local electron number density increases in the vicinity of the head of the bluff body, the thickness of the plasma layer surrounding the bluff body first decreases,and then increases.These modelling results provide a theoretical guidance for conducting experimental studies under a super-sonic flow condition on MPX-2015. In the future research,we will extend the physical-mathematical model to investigate of the transient,non-equilibrium features of the air discharge plasmas,and the complicated interactions between the plasma jet and the surrounding air, and/or the downstream bluff body under different operating conditions.Simultaneously,we will also try to develop the in-situ experimental methods to obtain the spatiotemporal distributions of the temperature,velocity and species concentrations in the plasma layer,and conduct a comparison between modelling results and measured data.

Effect of laser pulse on alternative current arc discharge during laser-arc hybrid welding of magnesium alloy

The coupling effect between a laser and arc plasma was studied in situations in which the laser acts at the positive and negative waveforms of the arc discharge during the laser-arc hybrid welding of magnesium alloy. Using the methods of direct observation, high speed imaging, and spectral analysis, the surface status of weld seams, weld penetration depths, plasma behavior, and spectral characteristics of welding plasma were investigated, respectively. Results show that, as compared with the laser pulse acting at the negative waveform of the arc plasma discharge, a better weld seam formation can be achieved when the laser pulse acts at the positive waveform of the arc discharge. At the same time, the radiation intensity of Mg atoms in the arc plasma increases significantly. However, the weld penetration depth is weaker. The findings show that when the laser pulse is acting at the negative waveform of the arc plasma discharge, the position of the arc plasma discharge on the workpiece can be restrained by the laser action point, which improves the energy density of the welding arc.

Continuous preparation of structure-controlled carbon nanoparticle via arc plasma and the reinforcement of polymeric composites

Environmental-friendly continuous process of manufacturing structure-controlled carbon black (CB) nanoparticles has been developed by the combination of advantages of alternative-current (AC) gliding arc plasma and direct-current (DC) arc discharge plasma. In this process, methane was first decomposed in the low temperature AC gliding arc plasma and then further thermally pyrolyzed in the DC arc discharge plasma area. CB was generated in the AC arc plasma area and then continued to grow or surface modified by DC arc plasma according to different arc positions, which was determined by the operating gas flow rate. The effects of AC arc and DC arc on the yield, size, morphology and structure of particles have been investigated. The connection of AC and DC plasma areas might cause totally different growth process of nanoparticles. Formation mechanism has been discussed based on series of physical characterizations to illustrate the different growth process. The essential properties of CB prepared by plasma have been compared with three kinds of CB purchased, and then all the CB nanoparticles have been blended with acrylonitrile-butadienestyrene/ethylene-propylene-diene monomer composites. Electrical conductivity and mechanical properties as well as the morphology of fracture surface of composites have been characterized. The results indicate that CB prepared from AC plasma process shows excellent mechanical reinforcement and CB from AC+DC plasma process owns outstanding electrical conductivity.

Preparation of carbon nanomaterials using two-group arc discharge plasma

Carbon nanomaterials were prepared using two-group arc discharge plasma method in this study. A combination of an alternating current (AC) arc discharge plasma and a direct current (DC) arc discharge plasma in a fluidized bed was used, in which propane was cracked into carbon blacks (CB) with controlled structure and hydrogen. The effects of parameters such as electrode type, frequency of AC arc discharge, current of DC arc discharge and gas flow ratio (propane/argon) on the synthesis and properties of CB were investigated. A systematic study of the size, morphology, microstructure and surface chemical composition of CB was conducted using various characterization techniques. By using this process, spherical and hydrophobic CB with a narrow size distribution, high degree of graphitization and large specific surface area were produced under optimal experimental conditions. Then, as-prepared CB were used to adsorb heavy-metal ions in water and to reinforce the engineering plastic. The results verified that the adsorption rate of the Cr (VI) ion was increased significantly and that the CB enhanced the electrical and mechanical properties of acrylonitrile–butadiene–styrene (ABS)/natural rubber (NR) composites.

Investigation of In‐Flight Glass Melting by Controlling the High‐Temperature Region of Multiphase AC Arc Plasma

A large volume discharge produced by a stable 12‐phase alternating current (AC) arc plasma is preferable to melt the granulated glass materials for time and energy saving. The discharge behavior and the high‐temperature region of the plasma system can be controlled by the electrode configurations. In this study, the spatial characteristics of the arc discharge were examined by image analysis with a high‐speed camera. The melting characteristics of alkali‐free glass particles were investigated by microscope and X‐ray diffractometry. This is the first time to investigate the relationship between spatial characteristics of plasma and glass particle property. Results show the arc existence area is strongly related to the electrode configuration. Distributions of in‐flight powders and the spatial characteristics of arc are important factors when using multiphase AC arc for in‐flight melting. This study provides information of efficient particle treatment according to the electrode configuration.

Investigation of Electrode Phenomena in an Innovative Thermal Plasma Process for Glass Melting

A multi-phase alternating current (AC) arc has been applied to glass melting technology. The large volume discharge produced by a stable multi-phase AC arc is preferable to melt the granulated glass materials. The discharge behavior and the high-temperature region of the plasma can be controlled by the electrode configurations. In this study, the spatial characteristics of the arc discharge were examined by image analysis of high-speed camera. Results show arc existence area is related with electrode configuration. This study provides the useful information of efficient particle treatment in the preferred electrode configuration. However, the electrode erosion is one of the most considerable issues to be solved. The combination of high-speed video camera and band-pass filters was introduced to measure the electrode temperature to investigate the erosion mechanism of the multi-phase AC arc. The dynamic behavior of the electrode vapors in the arc was investigated by using the same high-speed camera system. Results show the tungsten electrode mainly evaporates at the anodic period during AC cycle.

Implementation of an improved power supply with simple inverters for arc welding machine

Summary The paper provides a simple control, energy recovery inverter without voltage spike. The proposed inverter can be used for arc welding machines. The output of the inverter has two inductors and two switches. These components are in charge of processing positive and negative cycle of alternating current (AC) load current, respectively. They are able to keep the load current continuous to avoid generating voltage spikes during commutation period. Besides, the energy in the inductors can be stored by switches. The stored energy can provide high slope current to avoid arc extinction during commutation. Besides, the energy stored in inductors can be released to improve the conversion efficiency in the next transferring cycle. The operations and design procedures of the circuit are verified. Also, the experimental results of the proposed inverter are measured to demonstrate that the scheme is effective to drive a 100 A AC arc welding machine. Copyright © 2014 John Wiley & Sons, Ltd.

The Production of Plasma Pulses With Convoluted Arc Columns in Atmospheric Pressure Air

Experimental results for the operation of a device which generates radially propagating pulses of plasma are reported. These are produced from a convoluted arc plasma column formed using a suitably configured magnetic field (B-field). Both quasi-steady-current and alternating-current arc plasmas in atmospheric pressure air have been studied. High-speed photographic records of the convoluted plasma column during the main arcing phase are presented along with video images of propagating plasma clouds formed when the B-field and arc current collapse. Measured time variations of current and arc voltage during the main current phase are correlated with features on the photographic records. Results are presented, showing the effect of different operating conditions upon the propagation rates of the plasma pulses.

Carbon Nanostructures Produced by an AC Arc Discharge

Carbon nanostructures are under deep investigation due their peculiar properties and possible applications. In particular, development of new methods for the synthesis of these materials and their mechanism of formation represent interesting research fields. Arc discharge allows to produce different forms of carbon nanostructures. The parameters involved in the process, voltage, current density, type and pressure of the surrounding gas can be controlled especially for achieving high quantity of material with enhanced characteristics in terms of purity while the use of transition metal-graphite mixtures has been used to produce single wall structures. Moreover direct current (DC) and alternating current (AC) are suitable for producing carbon nano-materials, but different results can be obtained. In this work the effect of the power frequency in an AC arc discharge technique on the synthesis of carbon nanostructures is reported. Pure graphite electrodes have been arched in air in an homemade apparatus where the material can be collected directly on a cylindrical collector fixed near the arc. In order to avoid the formation of deposits under the arc a symmetrical configuration of the electrodes has been set. The production of carbon soot containing Single Wall Nanohorns (SWNH) and highly convoluted graphene sheets is optimized. The range of power frequencies 32-1000Hz has been investigated and the arcs have been ignited fixing the voltage at 28 V. The materials has been analyzed by field emission scanning electron microscope and high resolution transmission electron microscope. The microstructure of the material synthesized by this apparatus is affected by the power frequency, as the experimental results demonstrate. The samples produced at low frequency presented high amounts of single wall structures, SWNH-type. More compact structures, similar to large onion-like structures, have been found in samples synthesized at high frequency values.

Effect of Laser Pulse on Arc Plasma and Magnesium Target in Low-Power Laser/Arc Hybrid Welding

Low-power laser/arc hybrid welding process of magnesium alloy shows that the weld capability of tungsten-inert-gas arc is improved under the action of laser pulses. The effect of laser pulse on arc plasma is analyzed by studying the plasma spectra, plasma shapes, and arc voltage in this paper. On the one hand, laser pulse attracts arc plasma to laser keyhole and improves the stability of arc plasma; on the other hand, laser pulse expands the arc plasma and concentrates the electric conducting route of arc plasma. All these increase the output power and energy density of arc plasma, so the welding penetration is improved. In addition, laser pulses are controlled to act on the negative wave of alternating-current arc (the target metal has negative polarity) in hybrid welding process to improve the stability of arc plasma and weld penetration.

Investigation on in-flight melting behavior of granulated alkali-free glass raw material under different conditions with 12-phase AC arc

Abstract An innovative in-flight melting technology with 12-phase alternating current (AC) arc has been developed to investigate the melting behavior of granulated alkali-free glass raw material. Results show that the melted particles have spherical shape with smooth surface and compact structure. Lower vitrification and decomposition degrees of raw material as well as lower volatilization of B 2 O 3 are attributed to less heat transferred per particle under larger flow rate of carrier gas and higher feed rate. The high vitrification and decomposition degrees indicate that the new in-flight glass melting with 12-phase AC arc will be a promising technology for glass production.

A multi-phase AC arc discharge and its application in in-flight thermal treatment of raw glass powders

The in-flight melting technology with multi-phase alternating current (AC) arc was developed for the purpose of saving energy and shortening production cycle for glass industry. The 6-phase arc and 12-phase arc were used to investigate the in-flight melting behavior of soda-lime and alkali-free glass powders. Results showed that the vitrification degree of raw materials and the shrinkage of particle diameter increased with the increase of input power. The higher melting temperature and viscosity were responsible for the lower vitrification degree of alkali-free glass powders. Compared with 6-phase arc, 12-phase arc improved the vitrification degree of raw material for the longer residence time and higher plasma temperature under the same transformer current. The high vitrification degree achieved in short time indicated that the new in-flight melting technology with multi-phase ac arc would be a promising method for energy conservation in glass industry.

Analytical Description of the Process of Influx of the Sample Material into an Alternating-Current Arc Discharge Plasma

Physical and mathematical models of the influx of the sample material into an alternating-current arc discharge plasma are suggested. Analytical expressions describing changes in the rate of influx of the base metal and impurities into the discharge have been derived. Experimental results on the rates of influx of elements from metal samples of gold and silver are presented. They are in good agreement with theoretical data.

Spectrographic Analysis of Molybdenum Metal Powder

ABS>The following elements in molybdenum metal powder are determined spectrographically: aluminum, barium, calcium, chromium, copper, iron, potassium, magnesium, manganese, sodium, nickel, lead, silicon, tin, strontium, and fungsten. Samples are buffered with graphite mixtures containing the internal standard. A high-voltage alternating-current arc is used for all the elements except ihe alkalies and tungsten, for which direct current is used. The combined effect of graphite buffering and high-voltage alternating-current excitation produces as extremely refractory matrix during arcing, depressing molybdenum, and enhancing the medium volatility elements. Tungsten is enhanced by buffering wiih zinc oxide. The method is far superior io wet chemical analysis in simplicity, speed, and sensiiiviiy. It is reasonably accurate and has been applied to ihe control of molybdenum purity. (auth)