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- 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.
- 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.
- ItemModelling and experimental investigations of DC electric arcs in argon and carbon dioxide(Praha : Czech Technical University in Prague, Faculty of Electrical Engineering, Department of Physics, 2019) Mohsni, C.; Baeva, M.; Franke, S.; Gortschakow, S.; Gonzalez, D.; Araoud, Z.; Charrada, K.In this work an arc model is employed along with electric and spectroscopic measurements to study DC electric arcs in Ar and CO2. The model is aimed at describing the arc and the electrodes. Simulation and experimental results are shown for currents between 150 A and 210 A.
- 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.
- Item3D analysis of low-voltage gas-filled DC switch using simplified arc model(Praha : Czech Technical University in Prague, Faculty of Electrical Engineering, Department of Physics, 2019) Gortschakow, S.; Gonzalez, D.; Yu, S.; Werner, F.Electro-magnetic simulations have been used for the visualization of distribution of Lorentz force acting on a DC switching arc in low-voltage contactor. A simplified plasma model (black-box model) was applied for the description of arc conductivity. Arc geometry was gained from the high-speed camera images. Influence of arc position, arc current and of external magnetic field has been studied. Results have been compared with optical observations of the arc dynamics.
- 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.
- 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.
- 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.
- ItemOn the interaction of a microwave excited oxygen plasma with a jet of precursor material for deposition applications(Praha : Czech Technical University in Prague, Faculty of Electrical Engineering, Department of Physics, 2019) Methling, R.; Hempel, F.; Baeva, M.; Trautvetter, T.; Baierl, H.; Foest, R.A plasma source based on a microwave discharge at atmospheric pressure is used to produce an oxygen plasma torch. A liquid precursor material is evaporated and injected into the torch through a nozzle, causing oxidization and deposition of silica at a nearby quartz substrate. The temperature generated inside the plasma source and in the plume, in the region of treatment, and at the substrate surface are key parameters, which are needed for process description and optimization of plasma-chemical reactions. Optical emission spectroscopy and thermography were applied to observe and characterize the jet behavior and composition. The experimental results are compared with self-consistent modeling.