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    Analysis of Dense-Mesh Distribution Network Operation Using Long-Term Monitoring Data
    (MDPI, 2019-11-14) Ptáček, Michal; Vyčítal, Václav; Toman, Petr; Vaculík, Jan
    The technical and economic aspects and the possibility of the mesh network topology offering many radial configurations lead to the fact that large municipal networks are generally under radial operation. However, it is very important to analyze the operation and control of the mesh networks, especially in terms of their safety and durability and in the frame of the smart grid concept, respectively. The article deals with the analysis of the operation of the dense-mesh municipal distribution network of E.ON Distribuce a.s. based on the long-term data from power quality monitors. It also shows a brief view of the current lack of data usability from monitors installed in distribution networks in the context of smart grid.
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    Techno-economic comparison of various renewable energy sources for hybrid system implementation
    (International Society for Science and Engineering, o. s., 2021-08-17) Černý, Tomáš; Ptáček, Michal
    The current trends in electro-energetics indicate, that due to depletion of fossil fuels and the need of CO2 emission reduction, there is and will be a substantial development in the fields of renewable energy sources, decentralization and accumulation of electricity using battery energy storage systems in the near future. Along with the increasing power demand and penetration of renewables into electric grids, there is a need for energy mix expansion. Hybrid renewable energy sources (HRES) combine several renewables and energy storage into one system and can be used for micro-grid implementation for off-grid application or on-grid. The article is focused mostly on off-grid systems and provides an information about current state of renewable energy sources applications in HRES with techno-economic evaluation of net present cost and levelized cost of energy.
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    Evaluation of Harmonics Impact on Digital Relays
    (MDPI, 2018-04-11) Wannous, Kinan Hasan Wafaa; Toman, Petr
    This paper presents the concept of the impact of harmonic distortion on a digital protection relay. The aim is to verify and determine the reasons of a mal-trip or failure to trip the protection relays; the suggested solution of the harmonic distortion is explained by a mathematical model in the Matlab Simulink programming environment. The digital relays have been tested under harmonic distortions in order to verify the function of the relays algorithm under abnormal conditions. The comparison between the protection relay algorithm under abnormal conditions and a mathematical model in the Matlab Simulink programming environment based on injected harmonics of high values is provided. The test is separated into different levels; the first level is based on the harmonic effect of an individual harmonic and mixed harmonics. The test includes the effect of the harmonics in the location of the fault point into distance protection zones. This paper is a new proposal in the signal processing of power quality disturbances using Matlab Simulink and the power quality impact on the measurements of the power system quantities; the test simulates the function of protection in power systems in terms of calculating the current and voltage values of short circuits and their faults. The paper includes several tests: frequency variations and decomposition of voltage waveforms with Fourier transforms (model) and commercial relay, the effect of the power factor on the location of fault points, the relation between the tripping time and the total harmonic distortion (THD) levels in a commercial relay, and a comparison of the THD capture between the commercial relay and the model.
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    Current density in a group of long parallel conductors
    (IOP Publishing, 2019-09-11) Coufal, Oldřich
    An original method is proposed for the calculation of current density in a finite number of long parallel solid conductors of arbitrary cross section. Some pairs of the conductors under examination can be connected to a voltage source; they are active. The other conductors are passive. The currents, voltages and magnetic fields are assumed to be quasi-stationary and the displacement current is neglected. The permeability of the conductor material is constant and equals the vacuum permeability. No method has so far been published that would allow an exact calculation of current density in all the cases that satisfy the above assumptions. The application of the method is demonstrated by solving an example with two active conductors, one of which is of circular and the other of rectangular cross section, while a third passive conductor is of rectangular cross section.
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    Measurements of 181Ta(n,2n)180Ta reaction cross-section at the neutron energy of 14.78 MeV
    (Council of Scientific & Industrial Research - National Institute of Science Communication and Information Resources, 2020-04-30) Soni, B.; Parashari, S.; Mukherjee, S.; Makwana, R.; Mehta, M.; Chauhan, Rakesh; Suryanarayana, S.V.; Pasha, I.; Danu, L.S.; Naik, H.; Nayak, B.K.; Varmuža, Jan; Katovský, Karel
    The cross-section of the 181Ta(n,2n)180Ta reaction has been measured with respect to the 197Au(n,2n)196Au monitor reaction at the incident neutron energy of 14.78± 0.20 MeV, using neutron activation analysis and off-line -ray spectrometric technique. The present measurement has been done at the energy where discrepant measured results are available in the EXFOR data library. The result has been compared with evaluated data libraries JEFF-3.3 and ENDF/B-VII.1. The present result has also been supported by theoretical predictions of nuclear model code TALYS1.8 and TALYS-1.9. The uncertainty and the correlations among the measured cross-section has been studied using co-variance analysis.