This work deals with investigations of model plasma source realised as electric arc discharge in gas atmosphere between Cu-Cr composite electrodes. Radial distributions of temperature and electron density in arc plasma column were studied by optical emission spectroscopy. The content of electrode metals' vapours in discharge was calculated on the base of experimentally obtained plasma parameters as initial data. So, in this way the erosion properties of such composition can be determined

Bartlova, M.

Boretskij, V.

Fesenko, S.

Ivanisik, A.

Khomenko, O.

Kleshych, M.

Murmantsev, A.

Tolochyn, A.

Veklich, A.

English

This work deals with investigations of model plasma source realised as electric arc discharge in gas atmosphere between Cu-Cr composite electrodes. Radial distributions of temperature and electron density in arc plasma column were studied by optical emission spectroscopy. The content of electrode metals\u27 vapours in discharge was calculated on the base of experimentally obtained plasma parameters as initial data. So, in this way the erosion properties of such composition can be determined

CTU Open Journal Systems (Czech Technical University, Prague / České vysoké učení technické v Praze)

doi:10.14311/ppt.2019.1.27Plasma Physics and Technology 6(1):27–30, 2019 © Department of Physics, FEE CTU in Prague, 2019THERMAL PLASMA OF ELECTRIC ARC DISCHARGE BETWEEN Cu–CrCOMPOSITE ELECTRODESA. Veklicha,∗, V. Boretskija, M. Kleshycha, S. Fesenkoa,A. Murmantseva, A. Ivanisika, O. Khomenkob, O. Tolochynb,M. Bartlovaca Taras Shevchenko National University of Kyiv, 64/13, Volodymyrska str., Kyiv, Ukraineb Frantsevich Institute for Problems of Materials Science NAS of Ukraine, 3, Krzhizhanivsky str., Kyiv, Ukrainec Brno University of Technology, Czech Republic, bartlova@feec.vutbr.cz∗ an.n.veklich@gmail.comAbstract. This work deals with investigations of model plasma source realised as electric arc dischargein gas atmosphere between Cu–Cr composite electrodes. Radial distributions of temperature andelectron density in arc plasma column were studied by optical emission spectroscopy. The content ofelectrode metals’ vapours in discharge was calculated on the base of experimentally obtained plasmaparameters as initial data. So, in this way the erosion properties of such composition can be determined.Keywords: optical emission spectroscopy, plasma of arc discharge, erosion of surface electrode,composite materials, electrical contact.1. IntroductionComposite materials on copper base with additionof refractory metals, particularly chromium, haveadvanced applications in electric power industry.Namely, such composition are mostly used as con-tact material in vacuum arc-quenching chambers ofhigh and middle loads systems [1, 2]. The erosionproperties of abovementioned material play key role,which determined the efficiency of circuits’ commuta-tion performance.It is well-known that heterogeneous compound mate-rials of two or more components with different meltingand boiling points, such as Cu–Cr, are mostly man-ufactured by sintering and/or infiltration techniques.The compositions between 75/25% and 50/50% byweight of Cu–Cr contact material has proved opti-mum behavior in many respects for circuit-breakers[1–3]. Namely, high breaking capacity, gettering ef-fect, smooth surface after arcing with subsequent highelectrical strength, moderate chopping current of suchcomposition are just those properties which are re-quired in this kind apparats [1].There are some investigations of plasma producedby high current vacuum arcs between Cu–Cr contactsin literature. Namely, in paper [3] was shown, thatmicroparticles can be produced during interruption ofa high current vacuum arc between such contacts. It isthe reason, which causes the reduce of the insulationperformance of vacuum interrupters. The authorsconcluded, that the contact material has a great effecton the particle generation patterns. It was found thatit is much more difficult to form a melting pool ona Cu–Cr contact surface with a higher proportion ofchromium. The refractory material can suppress theflow of metal liquid and, consequently, fewer particlescan be produced from it.In paper [4] the spatially resolved optical emissionspectroscopy was used to study plasma parameters ofhigh-current vacuum arcs between Cu–Cr contacts. Itwas found that the plasma layer in front of the anodeis not in local thermal equilibrium (LTE). The two-temperature plasma model is suggested by authors touse in study of such non-equilibrium plasma areas.The aim of this paper is investigation of plasmaparameters of model source realised as electric arc dis-charge in air atmosphere between Cu–Cr compositeelectrodes. In assumptions of LTE the optical emis-sion spectroscopy techniques are developed to studythe content of electrode metals’ vapours in discharge,which can be calculated on the base of experimentallyobtained plasma parameters as initial data.The results of calculation of metal component con-centration in arc discharge plasma can be used andapplied to development and optimization of novelcomposite materials.2. Experimental setup2.1. Measurements of temperatureThe arc was ignited between the end surfaces ofvertically-oriented non-cooled copper-chromium elec-trodes. Electrodes were produced by powder metal-lurgy in the form of a rectangular parallelepiped witha cross section 3.5× 3.5mm. The Cu–Cr compositewas formed at a temperature of 750◦C in a volumeratio of 65% Cr and 35% Cu. Discharge gap was of8 mm and arc current 3.5A.Radial profiles of emission intensities in the aver-age cross section of the free burning in air electricarc plasma were investigated. Technique of one-passtomographic recording of the spatial distribution of27A. Veklich, V. Boretskij, M. Kleshych et al. Plasma Physics and Technologyspectral line intensities was used [5]. MonochromatorMDR-12 with 3000-pixels CCD linear image sensorSony ILX526A (B/W) accomplished fast scanning ofspatial distribution of radial intensity. Due to theinstability of the discharge, statistical averaging of therecorded spatial distributions of the radiation charac-teristics was carried out.Because side-on (lateral) observation of plasma ob-ject was realized in proposed experimental setup, itis necessary to use Abel inversion [6] for obtaining oflocal values of intensity.The radial distributions of plasma temperature weredetermined in the middle section of discharge gap. Thetechniques of Boltzmann plot in the assumption oflocal thermodynamic equilibrium (LTE) were used.In this study spectral lines Cu I 510.5 nm, 515.3 nm,521.8 nm, 570 nm, 578.2 nm, 793.3 nm, 809.3 nm andCr I 435.1 nm, 458 nm, 464.6 nm, 487 nm, 532.8 nm,540.9 nm were used.It must be noted, that in our previous investigation[7] of electric arc discharge between Cu–Cr electrodeswith addition of 1% of W the realisation of LTE inplasma column was found at the same arc current. Itis a reason of the application of such model in theframe of this study.2.2. Electron density measurementsThe electron density was obtained from electric con-ductivity, which can be calculated by solution of en-ergy balance equation (Elenbaas-Heller) in assumptionof LTE in plasma. Preliminary, the measurement ofelectric field has been carried out in positive plasmacolumn of arc discharge. So, radial distribution of elec-trical conductivity can be calculated in the followingmanner:σ(r) = − 1rE2[ddr(rλ(T )dTdr)]. (1)It must be noted, that radiation loss term wasneglected in Eq.1 according to results of work [8].The author found, that the arc radiation losses areinsignificant for current up to 30A.It must be noted as well, that according to results,obtained in [9], the metal vapour does not noticeablychange the thermal conductivity of air as plasma-forming gas in the investigated temperature range.Naturally, we took into account the temperature de-pendency of air thermal conductivity.At the next step of investigation the radial profiles ofelectron density in arc discharge were obtained fromcalculated profiles of electrical conductivity. Sincethe mobility of electron is much higher than the ionmobility, the ion current in plasma can be neglected.Then plasma electrical conductivity can be writtenas:σ(r) = eNe(r)µe(r), (2)where e is the elementary electrical charge, Ne(r) -electron density distribution, µe - electron mobility.Thus, electron densities can be obtained from Eq.1-2. Peculiarities of performed calculation of electrondensity in plasma and the cross sections determinationare discussed in detail in papers [10, 11].2.3. Calculation of plasma compositionThe calculation of the component composition of theplasma in the air atmosphere with the impurities ofcopper and chromium vapours is performed on thebase of the preliminary determined radial distributionsof the temperature T (r) and the electron densityNe(r)(Fig.1). In addition, the radial profiles of two spec-tral lines intensities of different elements were used.Namely, copper and chromium atoms spectral linesintensities were measured to obtain the necessary incalculation the ratio of these element concentrations.Figure 1. Radial distributions of plasma temperatureand electron density of arc discharge between compositeCu–Cr electrodes at current 3.5A.To calculate the component composition on thebase of the aforementioned parameters, the followingset of equations is solved:1. four Saha equations for atoms of copper,chromium, nitrogen and oxygen:Si(T,Ne) =NeN+iNi, i→ Cu, Cr, N, O; (3)2. two equations for dissociation of nitrogen andoxygen molecules:D(T ) = N2iNi2, i→ N, O; (4)3. electroneutrality equation:Ne =∑N+i , i→ Cu, Cr, N, O; (5)4. perfect gas equation:B(T ) = Ne +NO2 +NN2 +∑Ni +∑N+ii→ Cu, Cr, N, O;(6)28vol. 6 no. 1/2019 Thermal plasma of electric arc discharge5. the ratio between the number of nitrogen andoxygen particles in the air:(NN + 2NN2 +NN+) == 3.72(NO + 2NO2 +NO+).(7)To solve this set of equations, it was necessary to de-fine additionally the radial profile of the ratio betweenthe concentrations of different metals atoms NCu andNCr. With this aim, the intensities of spectral linesCu I 515.3 nm and Cr I 540.9 nm in the plasma radia-tion were experimentally measured in the assumptionof Boltzmann population distribution of copper andchromium atom levels (see Fig.2).3. Results and DiscussionsCalculated plasma composition in assumption of LTEwas used to obtain the radial profiles of copper XCuand chromium XCr vapour contents in mid-section ofarc discharge channel. These contents are defined asfollows:XCu,% = (NCu +NCu+) · 100/∑jNj , (8)XCr,% = (NCr +NCr+) · 100/∑jNj . (9)The total concentration of particles in plasma∑j Nj without electron density is used in Eq.8-9.In Fig.3 the radial distributions of copper andchromium vapours contents in plasma of electric arcdischarge in air between composite Cu–Cr electrodesat current 3.5A are shown. It must be noted, that inspite the fact, that chromium in the electrode mate-rial plays role as refractory component, the contentof both metals in plasma is comparable. Moreover,it must be stressed, that electrical conductivity inplasma of arc discharge channel was provided justmainly by thermal ionization of chromium component(see Fig.4). This phenomenon can be explained due tothe relatively low ionization energy of chromium atom(6.76 eV) in comparison with copper atom (7.74 eV).The qualitatively and quantitatively behavior ofmetal vapours contents in mid-section of arc dischargechannel does not reflect in fact the real distribution ofmetal concentration near electrodes working surface.Nevertheless, the suggested in this study techniquescan be used as indirect way with aim of study ofcomposition material erosion properties.To clarify the role of air atmosphere in such ero-sion behavior of both metal component in electrodecomposition it seems reasonable to carry out similarstudy of plasma parameters of arc discharge in argonflow at the next stage of investigation.Figure 2. The ratio of the radiation intensity of thespectral lines Cu I 515.3 nm and Cr I 540.9 nm ().The ratio of concentrations of copper and chromiumatoms (4).Figure 3. The radial distributions of copper andchromium vapours contents in plasma of electric arcdischarge between composite Cu–Cr electrodes at cur-rent 3.5A.Figure 4. The radial distributions of Cu,Cr atomsand Cu+, Cr+ ions concentrations.29A. Veklich, V. Boretskij, M. Kleshych et al. Plasma Physics and Technology4. ConclusionsPlasma parameters of electric arc discharge in air at-mosphere between Cu–Cr composite electrodes wereinvestigated. In assumptions of LTE the optical emis-sion spectroscopy techniques are developed to studyerosion properties of such composite materials.It was found, that in spite of the fact, that chromiumin the electrode material plays role as refractory com-ponent, the content of both metals in plasma is com-parable. The electrical conductivity in plasma of arcdischarge channel was provided just mainly by thermalionization of chromium component. This phenomenoncan be explained due to the relatively low ionizationenergy of chromium atom in comparison with copperatom.AcknowledgementsThis work was supported by joined project in the frameof research and technology collaboration between Ukraineand Czech Republic No.7AMB197UA.References[1] P. G. Slade. Electrical contacts, principles andapplications. CRC Press, 2014.[2] A. Papillon, J. Missiaen, J. Chaix, S. Roure, andH. Schellekens. Sintering mechanisms of Cu-Cr metalliccomposites. Int. Journal of Refractory Metals and HardMaterials, 65:9–13, 2016.doi:10.1016/j.ijrmhm.2016.11.010.[3] Z. Wang, W. Yan, Y. Jiang, Y. Li, J. Liu, W. Wang,Y. Geng, J. Wang, Z. Liu, and L. Sun. The effect anddynamic behavior of particles in high-current vacuumarc interruptions. Journal of Physics D: Applied Physics,52(7):1–20, 2018. doi:10.1088/1361-6463/aaf557.[4] R. Methling, S. Gorchakov, M. Lisnyak, S. Franke,A. Khakpour, S. Popov, A. Batrakov, D. Uhrlandt, andK. Weltmann. Spectroscopic investigation of a Cu-Crvacuum arc. IEEE Transactions on plasma science,43(8):2303–2309, 2015.doi:10.1109/TPS.2015.2443856.[5] R. Semenyshyn, A. Veklich, I. Babich, andV. Boretskij. Spectroscopy peculiarities of thermalplasma of electric arc discharge between electrodes withZn admixtures. Advances in Space Research,54:1235–1241, 2014. doi:10.1016/j.asr.2013.11.042.[6] K. Bockasten. Transformation of observed radiancesinto radial distribution of the emission of a plasma.Journ. of Opt. Soc. of Am, 9:943–947, 1961.doi:10.1364/JOSA.51.000943.[7] A. Veklich, A. Lebid, and T. Tmenova. Spectroscopicdata of W I, Mo I and Cr I spectral lines: selection andanalysis. J. Astrophys. Astr., 36(4):589–604, 2015.doi:10.1007/s12036-015-9342-0.[8] J. J. Lowke. Simple theory of free-burning arcs. J.Phys. D: Appl. Phys., 12:1873–1886, 1979.doi:10.1088/0022-3727/12/11/016.[9] V. Boretskij, Y. Cressault, P. Teulet, and V. A.Plasma of electric arc discharge incarbon dioxide withcopper vapours. XIX th Symposium on Physics ofSwitching Arc (FSO 2011), Brno, Czech Republic, pages121–124, 5-9 September 2011.[10] A. Veklich, S. Fesenko, V. Boretskij, Y. Cressault,A. Gleizes, P. Teulet, Y. Bondarenko, and L. Kryachko.Thermal plasma of electric arc discharge in air betweencomposite Cu-C electrodes. Problems of atomic scienceand technology. Series: Plasma Physics, 6:226–229, 2014.[11] A. Murmantsev, A. Veklich, V. Boretskij, S. Fesenko,and M. Kleshych. Thermal plasma of electric arcdischarge between evaporated electrodes. PlasmaPhysics and Technologies, 5(2):87, 2018.30

Thermal Plasma of Electric Arc Discharge Between Cu-Cr Composite Electrodes

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Thermal Plasma of Electric Arc Discharge Between Cu-Cr Composite Electrodes

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