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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.
- 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.
- 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.
- ItemOptical diagnostics of streamers: From laboratory micro-scale to upper-atmospheric large-scale discharges(Bristol : Institute of Physics Publishing, 2014) Simek, M.; Hoder, T.; Prukner, V.; Ambrico, P.F.Optical emission produced by streamers is determined by spatial distribution of electronically excited atomic and diatomic species within the streamer head and streamer channel. Peculiarities of emission and LIF diagnostics dedicated to investigating the basic structure of streamers with high spatio-temporal resolution are discussed. Possible strategies based on the 2D projections of cylindrically symmetric streamers to determine radial distributions of excited species within the streamer channel are illustrated for streamers produced in volume or on the dielectric surface at atmospheric and low pressures.
- 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.
- ItemGas-discharge plasma-assisted functionalization of titanium implant surfaces(Baech : Trans Tech Publications Ltd., 2010) Schröder, Karsten; Finke, Birgit; Polak, Martin; Lüthen, Frank; Nebe, Barbara; Rychly, Joachim; Bader, Rainer; Lukowski, Gerold; Walschus, Uwe; Schlosser, Michael; Ohl, Andreas; Weltmann, Klaus DieterA crucial factor for in-growth of metallic implants in the bone stock is the rapid cellular acceptance whilst prevention of bacterial adhesion on the surface. Such contradictorily adhesion events could be triggered by surface properties. There already exists fundamental knowledge about the influence of physicochemical surface properties like roughness, titanium dioxide modifications, cleanness, and (mainly ceramic) coatings on cell and microbial behavior in vitro and in vivo. The titanium surface can be equipped with antimicrobial properties by plasma-based copper implantation, which allows the release and generation of small concentrations of copper ions during contact with water-based biological liquids. Additionally, the titanium surface was equipped with amino groups by the deposition of an ultrathin plasma polymer. This coating on the one hand does not significantly reduce the generation of copper ions, and on the other hand improves the adhesion and spreading of osteoblast cells. The process development was accompanied by physicochemical surface analyses like XPS, FTIR, contact angle, SEM, and AFM. Very thin modified layers were created, which are resistant to hydrolysis and delamination. These titanium surface functionalizations were found to have either an antimicrobial activity or cell-adhesive properties. Intramuscular implantation of titanium samples coated with the cell-adhesive plasma polymer in rats revealed a reduced inflammation reaction compared to uncoated titanium. © (2010) Trans Tech Publications.
- ItemSearching for order in atmospheric pressure plasma jets(Bristol : IOP Publ., 2017-11-10) Schäfer, Jan; Sigeneger, Florian; Å perka, JirÌŒÃ; Rodenburg, Cornelia; Foest, RüdigerThe self-organized discharge behaviour occurring in a non-thermal radio-frequency plasma jet in rare gases at atmospheric pressure was investigated. The frequency of the azimuthal rotation of filaments in the active plasma volume and their inclination were measured along with the gas temperature under varying discharge conditions. The gas flow and heating were described theoretically by a three-dimensional hydrodynamic model. The rotation frequencies obtained by both methods qualitatively agree. The results demonstrate that the plasma filaments forming an inclination angle α with the axial gas velocity uz are forced to a transversal movement with the velocity uφ=tan(α)*uz, which is oriented in the inclination direction. Variations of ${u}_{\phi }$ in the model reveal that the observed dynamics minimizes the energy loss due to convective heat transfer by the gas flow. The control of the self-organization regime motivates the application of the plasma jet for precise and reproducible material processing.