Ústav výkonové elektrotechniky a elektroniky

Browse

Recent Submissions

Now showing 1 - 5 of 21
  • Thumbnail Image
    Item
    Synthesis of Ag and Cu nanoparticles by plasma discharge in inorganic salt solutions
    (De Gruyter, 2023-06-30) Horák, Jakub; Nikiforov, Anton; Krčma, František; Březina, Matěj; Kozáková, Zdenka; Dostál, Lukáš; Kalina, Michal; Kalina, Lukáš
    In recent years, nanoparticles have emerged as an important player in a broad range of applications, especially thanks to recent advances in their synthesis. The silver and copper nanoparticles are often used due to their antibacterial and fungicidal activities, and this article presents the results of the nanoparticle synthesis using electrical glow discharge generated directly in a volume of their salt solutions. Therefore, there is no influence of air (i.e. reactive nitrogen species) as it is usual in other commonly used approaches. Nanoparticles were prepared under various experimental conditions, and they were characterized by ultraviolet/visible spectrometry, dynamic light scattering, X-ray photoelectron spectroscopy, and high-resolution scanning electron microscopy. Particles were produced without any surfactant or stabilizing agent, and some of them showed higher resistance against agglomeration during their short-term (days) storage. The nanoparticle formation mechanism was confirmed by the fast camera imaging. Thus, the developed approach can be applied for simple environmentally friendly nanoparticle production for various applications.
  • Thumbnail Image
    Item
    Influence of metal vapours on radiation characteristics of air arc plasmas
    (ČVUT, 2020-11-18) Bartlová, Milada; Kloc, Petr; Aubrecht, Vladimír; Bogatyreva, Naděžda
    This paper deals with the evaluation of radiation properties of air arc plasma with various admixtures of Cu, Ag, and Fe, respectively. Under assumption of isothermal plasma cylinder, the net emission coefficients were calculated for various arc radii as a function of the plasma temperature up to 30 000 K. For plasma with prescribed temperature profile, the equation of radiation transfer was solved in the P1 approximation, and the radiation flux and its divergence were calculated.
  • Thumbnail Image
    Item
    TRIZ already 35 years in the Czech Republic
    (Elsevier B.V., 2016-02-10) Bušov, Bohuslav; Žídek, Jan; Bartlová, Milada
    In this paper the authors summarize the experience of teaching and implementation TRIZ at technical universities and findings from teaching and applications in companies in the Czech Republic and Slovakia for the last 35 years.
  • Thumbnail Image
    Item
    On the Selection of Integration Intervals for the Calculation of Mean Absorption Coefficients
    (Springer US, 2015-10-18) Kloc, Petr; Aubrecht, Vladimír; Bartlová, Milada; Coufal, Oldřich; Rümpler, Christian
    In radiation modeling of thermal plasmas non-grey models are applied where the radiative transport is described in several frequency bands (spectral intervals). Hereby mean absorption coefficients have to be calculated by a spectral integration procedure, providing a constant mean absorption coefficient for each band. Depending on the number of bands, one or more integration boundaries have to be selected in order to do the integration. In this paper we evaluate the influence of the selection of these integration boundaries on the mean absorption coefficient and the also radiation transfer by applying the mean absorption coefficients in a radiation transport model. Using a simplified two-band model we demonstrate that the selection of the integration boundary has a large impact on the total model accuracy. We show that in some cases selecting a band boundary right at the frequency where the continuum absorption shows a jump can introduce a significant error into the radiation calculation. The process of the integration interval selection thus demands a global optimization procedure to properly evaluate the boundaries of each frequency band.
  • Thumbnail Image
    Item
    Dynamic Model of Medium Voltage Vacuum Circuit Breaker and Induction Motor for Switching Transients Simulation Using Clark Transformation
    (MDPI, 2023-01-17) Pígl, Jan; Cipín, Radoslav
    A derivation of the dynamic model of a medium voltage vacuum circuit breaker and induction motor in space vectors in coordinates 0 allow us to model switching transients in various dynamic states of the motor. In the case of the Clark transformation, the corresponding numerical integration technique can be selected including variable time-step integration techniques to avoid numerical instabilities due to the stiffness of the system. Assymetrical operations such as switching cause the power system to become unbalanced and the transformed equations , , and 0 are not uncoupled. Therefore, it is necessary to derive a coupling matrix between circuit breaker voltages and currents in the coordinate system 0. The subject of our interest is switching overvoltages that arise when turning off small inductive currents by a vacuum circuit breaker. When deriving the model of a vacuum circuit breaker, all its properties encountered during this action are taken into account, i.e., current chop, virtual current chop, dielectric barrier in the circuit breaker and its recovery rate, and the ability of the vacuum circuit breaker to extinguish high frequency currents. Simulation results are compared with the measured results on a medium voltage motor as well as with the simulation results of the mathematical model of the test circuit according to IEC 62271-110 resolved using the nodal method (EMTP algorithm). Models are implemented in the MATLAB/Simulink programming environment.