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- ItemComparative studies of low-intensity short-length arcs(Praha : Czech Technical University in Prague, Faculty of Electrical Engineering, Department of Physics, 2019) Baeva, M.; Siewert, E.; Uhrlandt, D.We present results obtained by two non-equilibrium modelling approaches and experiments on low-intensity short-length arcs in argon at atmospheric pressure. The first one considers a quasi-neutral arc column combined with boundary conditions on the electrodes based on the energy balance in the space-charge sheaths. The second approach applies a unified description over the entire gap and solves the Poisson equation for the self-consistent electric field. The experiments provide the arc voltage.
- ItemAnalysis of Arc Processes in Multi-chamber Arrester for Lightning Protection at High-voltage Overhead Power Lines(Praha : Czech Technical University in Prague, Faculty of Electrical Engineering, Department of Physics, 2017) Murashov, I.V.; Frolov, V.Y.; Uhrlandt, D.; Gortschakow, S.; Ivanov, D.V.; Sivaev, A.D.Nowadays multi-chamber arresters are widely distributed as devices of lightning protection of overhead power lines. A mathematical modelling of processes in the discharge chamber of multichamber arrester is necessary to carry out in order to improve its breaking capacity. A three-dimensional mathematical transient model of thermal, gas-dynamic and electromagnetic processes taking place in the discharge chamber of multi-chamber arrester is presented in the article. Basic assumptions, model equations, a computational domain and the boundary conditions are described. Plasma turbulence is taken into account. The results of the calculation i.e. distributions of plasma temperature and overpressure in the discharge chamber at different time points are shown. The analysis of the results was carried out. It is shown that the presence of cavities in the electrodes design promotes electric arc extinction in the discharge chamber of multi-chamber arrester.
- ItemInvestigation of an Ablation-dominated Arc in a Model Chamber by Optical Emission Spectroscopy(Praha : Czech Technical University in Prague, Faculty of Electrical Engineering, Department of Physics, 2017) Methling, R.; Khakpour, A.; Wetzeler, S.; Uhrlandt, D.A switching arc in a model chamber is investigated by means of optical emission spectroscopy. Ignition wire is applied to initiate an arc of several kiloampere between tungsten−copper electrodes. Radiation emitted by the arc plasma is absorbed by a surrounding PTFE nozzle, leading to an ablation–dominated discharge. Video spectroscopy is carried out using an imaging spectrometer combined with a high–speed video camera. Carbon ion and fluorine atom line emission from the heating channel as well as copper, oxygen and nitrogen from ignition wire and ambient air are analyzed with focus on the low–current phases at the beginning of discharge and near current zero. Additionally, electrical parameters and total pressure are recorded while the general behavior of the discharge is observed by another video camera. Considering rotational symmetry of the arc the corresponding radial emission coefficients are determined. Finally, radial temperature profiles are calculated.
- ItemInteraction of a free burning arc with regenerative protective layers(Bristol : Institute of Physics Publishing, 2014) Uhrlandt, D.; Gorchakov, S.; Brueser, V.; Franke, S.; Khakpour, A.; Lisnyak, M.; Methling, R.; Schoenemann, T.The possible use of protective layers made of ceramic powders for walls in thermal plasma applications is studied. A stable free burning arc of currents up to 5 kA between copper- tungsten electrodes is used to analyse the arc interaction with samples coated by mixtures of CaCO3, MgCO3, and Mg(OH)2 with plaster. By means of optical emission spectroscopy the maximum arc temperature and the radiation impact on the surfaces are estimated to be around 15000 K and 20 MWm-2, respectively. Thermographic measurements confirm the efficient protection of substrates by all layer materials. Layers containing CaCO3 lead to the lowest heating of ceramic samples which may be caused by a strong evaporation of the layer material.
- ItemAnalysis of erosion resistance of CuC arcing contacts manufactured by plasma spraying technology(Praha : Czech Technical University in Prague, Faculty of Electrical Engineering, Department of Physics, 2019) Derevyankin, P.; Frolov, V.; Gonzalez, D.; Gortschakow, S.; Methling, R.; Uhrlandt, D.Results of the erosion resistance study of the CuC electrodes manufactured by plasma spraying technology are presented. The diagnostics has have been performed by means of high-speed camera technique and optical emission spectroscopy which has been synchronised with electrical diagnostics. After the load material analyses, namely determination of mass loss and analysis of micro sections, have been done. It has been found that the erosion rate depends on conditions applied for the formation of coating layer, which was deposited either in air or in argon plasma. Furthermore, the erosion rate is significantly lower in the case of air plasma spraying.
- ItemSignificance of the Resonance Condition for Controlling the Seam Position in Laser-assisted TIG Welding(Amsterdam [u.a.] : Elsevier, 2016) Emde, B.; Huse, M.; Hermsdorf, J.; Kaierle, S.; Wesling, V.; Overmeyer, L.; Kozakov, R.; Uhrlandt, D.As an energy-preserving variant of laser hybrid welding, laser-assisted arc welding uses laser powers of less than 1 kW. Recent studies have shown that the electrical conductivity of a TIG welding arc changes within the arc in case of a resonant interaction between laser radiation and argon atoms. This paper presents investigations on how to control the position of the arc root on the workpiece by means of the resonant interaction. Furthermore, the influence on the welding result is demonstrated. The welding tests were carried out on a cooled copper plate and steel samples with resonant and non-resonant laser radiation. Moreover, an analysis of the weld seam is presented.
- ItemAnalysis of C2 SWAN bands in ablation-dominated arcs in CO2 atmosphere(Praha : Czech Technical University in Prague, Faculty of Electrical Engineering, Department of Physics, 2019) Methling, R.; Franke, St.; Götte, N.; Wetzeler, S.; Uhrlandt, D.A model circuit breaker in a high-pressure chamber filled with CO2 atmosphere is used to operate a wall-stabilized arc of several kilo-amperes between tungsten-copper electrodes surrounded by polytetrafluoroethylene nozzles. Optical emission spectroscopy (OES) is carried out via quartz plates inserted into the nozzles using a combination of an imaging spectrometer either with a high-speed video camera or with an ICCD camera. Depending on the nozzle geometry and the current, continuum from C2 Swan bands was detected as absorption as well as emission pattern. After current zero, optical absorption spectroscopy (OAS) using a xenon flashlamp as broadband background radiator was applied. An absorption around 493 nm was detected and attributed to CuF molecules. The study proofs the existence of C2 in the active phase and the formation of CuF near to current zero.
- ItemDetermination of Cr Density in the Active Phase of a High-current Vacuum Arcs(Praha : Czech Technical University in Prague, Faculty of Electrical Engineering, Department of Physics, 2017) Gortschakow, S.; Khakpour, A.; Popov, S.; Franke, S.; Methling, R.; Uhrlandt, D.Melting and evaporation of the anode surface strongly influence the interruption capability of vacuum circuit breakers, because they lead to injection of atomic vapour into the inter-electrode gap. Determination of the vapour density and its dynamics with respect to different anode phenomena is therefore of great importance. Results of Cr density measurements in a high-current vacuum arc by using broadband absorption spectroscopy are presented. The vapour density of atomic Cr is determined after the formation of anode spots as well as close to the current zero. Cr I resonance lines at 425.43 nm have been used for the analysis. An AC current pulse with maximum value of 7 kA and a frequency of 100 Hz is applied to a vacuum arc between two cylindrical butt electrodes made of CuCr7525 with a diameter of 10 mm. The high-current anode modes are observed by means of high-speed camera imaging. The temporal evolution of the Cr ground state density is presented and discussed.
- ItemAdvanced Nonequilibrium Modelling of DC Tungsten-Inert Gas Arcs(Praha : Czech Technical University in Prague, Faculty of Electrical Engineering, Department of Physics, 2017) Baeva, M.; Uhrlandt, D.The paper is concerned with the state-of-the-art nonequilibrium modelling of a DC tungsten-inert gas arc plasma. The advanced description involves the two-way interaction between the plasma and the electrodes. Results in atmospheric pressure argon demonstrating important features of the arc plasma are presented and discussed. First results in the presence of metal vapour released from the molten anode are presented. Outlook for further developments in nonequilibrium arc modelling are discussed.
- ItemInfluence of the arc plasma parameters on the weld pool profile in TIG welding(Bristol : Institute of Physics Publishing, 2014) Toropchin, A.; Frolov, V.; Pipa, A.V.; Kozakov, R.; Uhrlandt, D.Magneto-hydrodynamic simulations of the arc and fluid simulations of the weld pool can be beneficial in the analysis and further development of arc welding processes and welding machines. However, the appropriate coupling of arc and weld pool simulations needs further improvement. The tungsten inert gas (TIG) welding process is investigated by simulations including the weld pool. Experiments with optical diagnostics are used for the validation. A coupled computational model of the arc and the weld pool is developed using the software ANSYS CFX. The weld pool model considers the forces acting on the motion of the melt inside and on the surface of the pool, such as Marangoni, drag, electromagnetic forces and buoyancy. The experimental work includes analysis of cross-sections of the workpieces, highspeed video images and spectroscopic measurements. Experiments and calculations have been performed for various currents, distances between electrode and workpiece and nozzle diameters. The studies show the significant impact of material properties like surface tension dependence on temperature as well as of the arc structure on the weld pool behaviour and finally the weld seam depth. The experimental weld pool profiles and plasma temperatures are in good agreement with computational results.