A systematic study of arc faulting between two cables in aeronautic conditions is performed and a power balance of the arc is realized. Electrical characteristics and radiative heat flux are recorded. The effect of the current mode (AC/DC), cable material and pressure is highlighted with the assessment of the power balance, which includes the mean power of the arc, power transferred to the cables that can cause melting and vaporization, and the power lost by radiation, conduction and convection in the arc column. The evaporated mass of the cables can be estimated in this way. Optical emission spectroscopy measurements of the induced plasma are performed rendering the overall temperature of the arc using a Boltzmann plot method. The overall temperature is higher for copper-contaminated plasma than for aluminium-contaminated plasma. Despite the erratic behaviour of the plasma, the trend shows that the DC as well as the use of lighter aluminium-based cables lead to higher power.

This tutorial is intended to provide a basic overview of non-equilibrium phenomena for thermal plasmas. Thermal plasmas (TPs) mainly issued from electrical discharges are often assumed to be in ≪ equilibrium ≫ as opposed to ≪ non-equilibrium plasmas ≫ where non-equilibrium phenomena are more pronounced. As a first approximation it can be shown that TPs are close to a local thermodynamic equilibrium (LTE) which is often taken as their reference state. However, in many situations, deviations from LTE can clearly exist. The main goal of this brief tutorial is to explain to interested scientists the main phenomena, mechanisms and characteristics associated to TPs or quasi-TPs. Then we introduce the different laws of the thermodynamic equilibrium applied to these plasmas and show that not all of them are valid in TPs, which lead us to define the LTE. However, even if the transport phenomena are non-equilibrium mechanisms, we show with illustrations that they are studied and estimated within the framework of the LTE. The next sections focus on phenomena named ‘departures from equilibrium’ for thermal plasmas. For convenience and educational reasons, we split them into the departures from the chemical and the thermal equilibria respectively. In each case we present and clearly define the mechanisms that promote equilibrium and those that tend to create departures. We present not only experimental setups that highlight these deviations but also the basis for the mathematical models that allow them to be simulated, before concluding the tutorial with the outlooks and challenges currently under research.

The calculation of net emission coefficient NEC is done for mixtures He–Ar/N2–[C100−x−y−z,Bz,Nix/Cox,Yy] used in the synthesis of single-wall carbon nanotubes SWNTs by arc discharge technique, at pressure of 60 kPa and at temperature interval going from 1 kK to 30 kK. These mixtures contain helium–argon as a gaseous atmosphere, nitrogen–boron as a doping atoms and a carbon anode filled with yttrium–nickel/cobalt as catalysis. Different proportions of metallic catalysts are considered going from 0.01 atomic% (at%) to 5 at%. Whereas for doping atoms the concentration amounts are much higher and do not exceed 8 at% for boron and 50% for nitrogen. The results of NECs are obtained by summing over all wavelengths, the contributions of atomic and molecular continuum, results of free–free and free–bound transitions, and line and molecular bands emissions corresponding to bound–bound transitions. Doppler broadening, resonance, van der Waals, electron and ion Stark broadening are taken into account for the calculation of the lines widths. As Stark broadening is the most important broadening mechanism at intermediate and high temperature, an empirical correction factors determined for some resonance lines, are added to the semi-empirical Stark formulas for a best reproducing of the experimental Stark widths. The comparisons of the NECs of the pure plasmas of argon, helium, nitrogen and carbon to those given in literature present an acceptable agreement. For the studied mixtures containing He–Ar/N2–[C100−x−y−z,zBz, Nix/Cox,Yy], the obtained results show that the addition of boron or the nitrogen induces a few little changes in the NEC, in contrary to the metal catalysts where we noted a considerable increase in the plasma emission especially at low temperatures. The effect of the addition of yttrium in carbon anode even in a small amount (<0.1 at%) affects strongly the NEC compared to that of cobalt or nickel which have given similar results.

This paper is focused on the state-of-the-art and challenges concerning the thermophysical properties of thermal plasmas used in numerical modelling devoted to high voltage circuit breakers. For Local Thermodynamic Equilibrium (LTE) and Non-Local Thermodynamic (NLTE) and/or Chemical Equilibrium (NLCE) plasmas, the methods used to calculate the composition, thermodynamic, transport and radiative properties are presented. A review of these last data is proposed and some comparisons are given for illustrations.

This work is devoted to the study and comparison of theories to calculate densities of chemical species in a SF6 plasma in thermal non equilibrium conditions. The limits of the 2T law of mass action are shown. Then, the reaction rates are studied for several types of processes and they are implemented in a chemical kinetic model to acess the composition of the plasma. Finally, a comparison with the densities obtained with the law of mass action is performed and the results are discussed.

The Divergence of Radiative Flux (DRF) is the term present in the energy balance of the plasma that describes the radiative behavior of the arc. This property is obtained by the resolution of the Radiative Transfer Equation (RTE). Because of its complexity, many approximate methods are developed to reduce the computational time. This paper will describe the approximate methods already used in numerical simulation: Net Emission Coefficient (NEC) and Mean Absorption Coefficient (MAC). This last property requires having a good definition of spectral ranges and mean functions to have a physical representation of radiative losses. In this paper, the spectral ranges will be defined from the continuum of the absorption coefficient and Planck Modified Mean Function (PMMF) will be used to calculate MACs. This mean function requires a good definition of the characteristic absorption length R. In this paper, we will develop an optimization methodology that allows finding the best R in order to have an accurate DRF using MACs. To quantify the accuracy of these approximate methods, a 1D resolution of RTE will be performed in the case of Air plasma at P=1bar in Local Thermodynamic Equilibrium (LTE). The exact DRF solution will be considered as a reference when compared with the DRF of approximate methods.

This paper introduces a method allowing a fast determination of space- and time-resolved plasma temperature and iron concentration in MAG arcs during the high-current phase. This method consists of measuring the plasma spectral radiation of a 82%Ar-18%CO2 plasma with iron vapours using a high-speed camera filtered by narrow band filters in the spectral intervals of 570-590 nm and 606-627 nm respectively; calculating theoretically the dependence of the absolute emissivity epsilon(570-590 nm) and relative emissivity epsilon(570-590 nm)/epsilon(607-627 nm) versus the plasma temperature and the iron concentration, and comparing the two results in order to deduce the plasma temperature (T) and iron concentration (Y-Fe) fields of the experimental measurements. The evolution of their profile in time and space are coupled to arc recorded images. This method has also been validated for three layers of plasma at the positions of 0.5 mm, 1.5 mm and 2.5 mm above the workpiece by using a high-resolution spectrometer and adopting other existing diagnostics such as Stark broadening. The plasma temperature and iron concentration show good agreement throughout the different methods, which demonstrates the effectiveness of this new method.

The study of gas-metal arc welding (GMAW) often relies on the hypothesis of local thermodynamical equilibrium (LTE). Few works are dedicated to its validation and none is focused on the case of pulsed metal active gas welding. This paper presents the result of a spectroscopic diagnostic performed on a pulsed welding arc with 82% Ar-18% CO2 shielding gas. High-speed imaging and electrical data recording are also performed. The excitation temperature is obtained with the Boltzmann plot method, while iron and argon line Stark broadening measurement is used to obtain the electron temperature and density. The iron mole fraction in the plasma is calculated by solving the conservation equations. Partial LTE hypothesis validity across the arc is discussed considering the agreement between the two temperatures, electron density and iron content. The results show supporting evidence for the main part of the plasma, along radial and axial directions. This can be associated with high iron vapour concentration, close to 100% near the consumable anode tip. Discrepancies occur only at the fringe of the arc, where the two temperatures differ by more than 2000 K. The temperature drop close to the arc axis observable for the upper part is weaker when compared with an inert gas welding operation.

Stark broadening of isolated lines plays a crucial role in the calculation of radiative transfer of thermal plasmas. The most popular methods used are: the simple formula based on the semi-empirical method developed by Griem; the more elaborated method of Dimitijevic and Konjevic and the well-known Lindholm formula. Their accuracy are investigated through comparisons of obtained Stark widths with previous experimental and theoretical results for HeI, ArI, ArII, ArIII, FeI and Fell lines at different temperatures and electron number density values. An improvement of the calculated Stark results is proposed and discussed by adding an empirical correction factor to the proposed formulas. All the calculated factors are supplied in tables in order to use them in the calculation of radiative properties of thermal plasmas. The influence of the Stark models and of the empirical correction factors in the calculation of the net emission coefficient (NEC) of line are analyzed and discussed for pure helium, argon and iron plasmas, in a temperature range from 0.3 kK to 30 kK, and the atmospheric pressure. The obtained results show that the effect of the empirical correction factor does not exceed 31% but the choice of the proposed Stark broadenings models can induce huge variations in line radiation.

Arc tracking tests have been carried out between two voluntarily damaged aeronautic cables. Copper or aluminum conductors have been exposed to short circuits under alternating current. Various data have been recorded (arc voltage and current, radiated power and ablated mass), enabling to determine a power balance, in which every contribution is estimated. The total power is mainly transferred to the cables (between 50 and 65%, depending on the current and the cable type), and causes the melting and partial vaporization of the metallic core and insulating material, or is conducted or radiated. The other part is deposited into the arc column, being either radiated, convected or conducted.

The paper gives an overview on the basics of CFD arc simulation tools with respect to the simulation of the fluid mechanical processes in the interrupter unit of SF6 high-voltage circuit-breakers at no-load and short-circuit switching-off processes. On the example of SF6 self-blast circuit-breakers the complete process from the analysis of the switching-off process to the creation of a modular simulation model consisting of several sub models is illustrated. Details to the modelling in the particular sub modules and to the implementation are given. The capability of a CFD arc simulation tool based on the program package ANSYS/FLUENT is demonstrated on the basis of selected simulation results. Furthermore case examples for the application of the presented CFD arc simulation tool in the development process of high-voltage circuit-breakers are given.

In this paper, we present the mean absorption coefficients (MACs) calculated for plasma mixtures of argon-helium-nitrogen-carbon-nickel-cobalt at 60 kPa and in a temperature range from 1 kK to 20 kK. These coefficients have been computed under the assumption of a local thermodynamic equilibrium (LTE), isothermal plasma, including atomic and molecular continuum, molecular bands and lines radiation splitted into nine spectral intervals. The results show that the continuum absorption coefficients strongly depend on photodissociation and photoionization processes of the molecular species N-2, CN and C-2, with a significant effect on photodetachment processes of C- in a frequency interval lower than 1 x 10(15) Hz and for low temperature (<6 kK). While at high temperature, the main contribution in continuum absorption coefficient comes from radiative recombination processes except in the infrared region (<0.5 x 10(15) Hz) where the inverse bremsstrahlung represents the most important component in continuum processes for all temperature values. On the other hand, the calculation of MAC shows that the role of molecular continuum, molecular bands and line absorption of the neutral catalysis species Ni/Co are only important in a small range of temperature and in a few spectral bands located in visible and infrared regions, while at high temperature and in UV and visible regions, the foremost contributions to MAC come from atomic continuum and line absorption.

The complex technique of plasma property studies is suggested. As the first step the radial profiles of temperature and electron density in plasma of free burning electric arc discharge in air between Cu-C composite and brass electrodes, as well as copper electrodes in air flow, were measured by optical emission spectroscopy techniques. As the next step the radial profiles of electric conductivity of plasma mixture were calculated by solution of energy balance equation. The electron density is obtained from electric conductivity by calculation in assumption of local thermodynamical equilibrium in plasma.

This work presents the radiative properties of argon-helium-nitrogen-carbon-nickel-cobalt thermal plasmas by the computation of net emission coefficients (NECs) under the assumption of a local thermodynamic equilibrium and at temperature range 1000-20 000 K. These mixtures were often used in the study of carbon nanotubes (CNTs) synthesis with arc plasma which becomes one of the most useful techniques in terms of flexibility of carbon nanostructures produced with fewer defects. The values of NEC allow estimation of total radiation losses in plasmas, by taking into account the emission radiation resulting from the atomic continuum, the molecular continuum, the atomic lines and some molecular bands. Free-free transitions (Bremsstrahlung) and free-bound (electron-ion recombination), have been considered for the calculation of atomic continuum. For bound-bound transitions, natural, resonance, Van der Waals, Stark and Doppler effects have been taken into account in the calculation of the lines broadenings while the self-absorption of the resonance lines has been treated using their escape factors. Molecular continuum has been only considered for N-2, C-2 and CN molecules whereas we have only taken into account diatomic systems N-2, N-2(+), CN and C-2 for the emission of the molecular bands. The results obtained show that even for low concentrations of Ni and Co in the plasma, the NECs are modified and considerably increase only at a low temperature (T < 8000 K) and the major contribution in the total radiation arises from the lines emission. However, the effect of the thickness of the plasma on plasma radiation has been analysed based on the self absorption phenomenon of resonance lines.

This paper deals with investigations of air plasma with admixing of copper and carbon. Model plasma source unit with real breaking arc was used for the simulation of real discharges, which can be occurred during sliding of Cu-C composite electrodes on copper wire at electromotive vehicles. The complex technique of plasma property studies is developed. From one hand, the radial profiles of temperature and electron density in plasma of electric arc discharge in air between Cu-C composite and copper electrodes in air flow were measured by optical spectroscopy techniques. From another hand, the radial profiles of electric conductivity of plasma mixture were calculated by solution of energy balance equation. It was assumed that the thermal conductivity of air plasma is not depending on copper or carbon vapor admixtures. The electron density is obtained from electric conductivity profiles by calculation in assumption of local thermodynamic equilibrium in plasma. Computed in such way radial profiles of electron density in plasma of electric arc discharge in air between copper electrodes were compared with experimentally measured profiles. It is concluded that developed techniques of plasma diagnostics can be reasonably used in investigations of thermal plasma with copper and carbon vapors.

This article is devoted to the calculation of the net emission coefficient (NEC) of Ar–Al, Ar–Fe and Ar–Cu mixtures at atmospheric pressure for arc welding processes. The results are given in data tables for temperatures between 3 kK and 30 kK, for five plasma thicknesses (0, 0.5, 1, 2, 5 mm) and ten concentrations of metallic vapours (pure gas, 0.01%, 0.1%, 1%, 5%, 10%, 25%, 50%, 75% and pure metal vapours in mass proportions). The results are in good agreement with most of the works published on the subject for such mixtures. They highlight the influence of three parameters on the radiation of the plasma: the NEC is directly related to temperature and inversely related to plasma radius and is highly sensitive to the presence of metal vapours. Finally, numerical data are supplied in tables in order to develop accurate computational modelling of welding arc and to estimate both qualitatively and quantitatively the influence of each metallic vapour on the size and on the shape of the weld pool.

This paper characterizes an electric arc discharge in CO2 (3.5A) comparing two types of results: registered experimental spectra and simulated emission spectra. The plasma’s temperatures and the plasma’s compositions were carried out by optical emission spectroscopy. Theoretical investigations were realized to simulate the corresponding emission spectrum in order to validate the experimental techniques or the LTE assumption.

A gaseous plasma in a non-local thermodynamic equilibrium (NLTE) can be characterized by the thermal disequilibrium Te ≠ Tex ≠ Tvib ≠ Trot ≠ Th, where Te and Th are respectively the translational temperatures respectively for the free electrons and heavy species, and Tex, Tvib, Trot are the internal temperatures respectively associated with the electronic, vibrational and rotational excited states of the species in the plasma. The accurate knowledge of these temperatures is crucial if one wants to determine for example the composition of a NLTE plasma or, more generally, its physical properties like thermal conductivity or heat capacity. To the best of our knowledge, even if one gets the assumptions Te≈Tex and Trot≈Th, no theory allows nowadays to evaluate Tvib which should be considered like a third free parameter of the current NLTE plasma models and which is fixed usually at Th or Te2, 3.

Spectroscopy investigations of plasma of free burning electric arc discharge as well as discharge in air flow of 6.45 slpm at currents 3.5, 30, 50 and 100 A were carried out. Plasma state deviation from thermodynamic equilibrium was found at arc current 100 A. Two-temperatures model was used to estimate plasma composition at arc current 100 A.

The aim of this paper is to present an accurate evaluation of the phenomena appearing for high pressure air plasmas supposed to be in local thermodynamic equilibrium (LTE). In the past, we already calculated the net emission coefficient for air mixtures at atmospheric pressure and for temperatures up to 30kK (molecular contribution being restricted to 10kK). Unfortunately, the existence of high pressures does not allow us to use this database due to the non-ideality of the plasma (Viriel and Debye corrections, energy cut-off ... ), and due to the significant shifts of molecular reactions towards upper temperatures. Consequently, this paper proposes an improvement of our previous works with a consideration of high pressure corrections in the composition algorithm in order to take into account the pressure effects, and with a new calculation of all the contributions of the plasma radiation (atomic lines and continuum, molecular continuum, and molecular bands) using an updated database. A particular attention is paid to calculate the contribution of all the major molecular band systems to the radiation: O-2 (Schumann-Runge), N-2 (VUV, 1st and 2nd positive), NO (IR, beta, gamma, delta, epsilon) and N-2(+) (1st negative and Meinel). The discrete atomic lines and molecular bands radiation including the overlapping are calculated by a line-by-line method up to 30kK and 100 bar. This updated database is validated in the case of optically thin plasmas and pressure of 1bar by the comparison of our integrated emission strength with the published results. Finally, this work shows the necessity to extend the molecular radiation database up to 15kK at high pressure (bands and continuum) since their corresponding contributions could not be neglected at high temperature.