Centrum výzkumu a využití obnovitelných zdrojů energie

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    Evaluation of different solutions of faulted phase earthing technique for an earth fault current limitation
    (IET, 2017-06-12) Topolánek, David; Toman, Petr; Ptáček, Michal; Dvořák, Jaromír
    The study is focused on evaluation of different types of prototypes of automatics for additional faulted phase earthing (FPE), which are used for earth fault (EF) current reduction in resonant earthed distribution network. Three prototypes of these automatics have been installed in Czech distribution network, the first one utilises direct connection of faulty phase–to-earthing system of supply substation, the second one utilises connection through resistor and the last one through reactor. The contribution is mainly focused on detail analysis of operational differences of these types of FPE systems based on case study of compensated distribution network. The main aim is to specify and describe benefits and disadvantages of individual FPE applications. The results could be used for evaluation of best solution of FPE application which could be chosen for an EF current reduction in compensated distribution network.
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    The Influence of Solvents and Salts on the Properties of High-Voltage Cathode Materials
    (ESG, 2015-07-24) Kazda, Tomáš; Vondrák, Jiří; Sedlaříková, Marie; Gómez-Romero, Pedro; Musil, Michal; Čudek, Pavel; Straková Fedorková, Andrea; Kašpárek, Vít
    Lithium - ion batteries play an increasingly important role in the battery industry and they have become the dominant source of energy in the recent years, especially for portable electronic devices due to their high gravimetric energy density. This article examines the influence of mixtures of solvents with different combinations of lithium salts on the stability of two types of high-voltage cathode materials: LiNi0.5Mn1.5O4 and LiCr0.1Ni0.4Mn1.5O4 produced by a solid phase reaction. These materials were combined with several different electrolytes, cycled at various loads and higher temperature. Various combinations of solvents ethylene carbonate (EC), dimethyl carbonate (DMC) and Tetrahydrothiophene 1.1-dioxide (Sulfolane) were used for these measurements. Salts LiPF6 , LiNO3 and LiTFSI were used. The influence of solvents and salts on the properties of high-voltage cathode materials was tested by cycling at different current loads and by cycling at high temperature. It was found out, by LSV analysis, that the addition of Sulfolane increases the stability of electrolyte. The addition of chromium to the cathode material LiNi0.5Mn1.5O4 causes increasing of capacity and stability at high temperature. The combination of the cathode material LiCr0.1Ni0.4Mn1.5O4 with the electrolyte 1.5 M LiPF6 EC:DMC:Sulfolane 1:2:1 w/w/w leads to increased stability in comparison with other electrolytes.
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    Effect of Compression on Negative Lead-Acid Battery Electrodes Doped with Glass Fibres
    (ESG, 2015-11-04) Bača, Petr; Křivík, Petr; Zimáková, Jana; Fryda, Daniel
    Lead-acid battery with negative electrodes doped with microscopic glass fibres are comparable with those doped with carbon or titanium dioxide during accelerated PSoC cycling and reach a long cycle life. The performance of these electrodes can be even elevated by applying moderate compression of 4 N.cm-2.
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    Spatio-temporal description of the cavitating flow behavior around NACA 2412 hydrofoil
    (IOP Publishing, 2015-12-06) Rudolf, Pavel; Štefan, David; Sedlář, Milan; Kozák, Jiří; Habán, Vladimír; Huzlík, Rostislav
    Spatio-temporal description of the cavitating flow around hydrofoil with 8 degrees incidence using proper orthogonal decomposition (POD) is presented. POD is a suitable tool, which provides information not only about the flow dynamics, but also about relevance of different flow structures. POD also enables to track energy transport within the domain and energy transfer among the eigenmodes of the flow field. Analysis documents change of the flow structure for decreasing cavitation number, which can be most likely attributed to sheet/cloud cavitation transition.
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    Effect of Heat Treatment on the Corrosion and Mechanical Properties of Electrolytical Composite Ni-B Coatings
    (ESG, 2014-08-01) Oriňáková, Renáta; Oriňák, Andrej; Kupková, Miriam; Sabalová, Mária; Straková Fedorková, Andrea; Kabátová, Margita; Kaľavský, František; Sedlaříková, Marie
    Electrodeposition of composite coatings with nickel matrix and boron micro-particles was investigated. Nickel - boron layers were deposited potentiodynamically at 12.5 mV/s on cylindrical samples prepared from iron powder in a stirred heterogeneous system formed by a Watts type nickel plating bath and dispersed boron micro-particles. The effect of boron powder amount in plating bath and heat treatment on the corrosion resistance and hardness of the composite Ni-B coatings was evaluated. Corrosion properties of coated cylindrical iron samples were investigated in 1 mol dm-3 NaCl solution using potentiodynamic polarization method. The structure of coating layers was established using scanning electron microscopy (SEM) and light optical microscopy (LOM). The content of incorporated boron particles increased with the boron amount in plating bath. Homogeneous distribution of boron particles in deposited coating layer was observed for both as-deposited samples and samples heat treated at 400 °C. Boron particles were not observed on the surface of the deposits heated at higher temperatures. Generally, addition of boron micro-particles to the nickel matrix as well as the heat treatment deteriorated the corrosion resistance of iron samples coated with composite Ni-B films. The dependence of the corrosion properties of composite layers on boron particle loading was not proved. The decrease of microhardness on the surface but increase of microhardness on the cross- section of composite Ni-B coating layer due to the heat treatment was observed.