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- ItemResilience Analysis of Extensive Meshed Distribution Network to Supply Feeder Outages(2025-10-08) Krčál, Vít; Koudelka, Jan; Vrtal, Matěj; Topolánek, David; Toman, PetrResilience assessment is also relevant for highly reliable power systems, such as meshed networks. The paper deals with resilience of an urban densemeshed low voltage network to supply feeder outages and subsequent cascading failures. Presented resilience analysis evaluates the amount of preserved load during multiple feeder outages. The simulations account for a timespan of 1 year of network operation with regard to load variations. Based on disturbances simulation results, the weakest elements of the network are identified. To increase resilience, corrective measures are proposed and incorporated into the simulations. Resilience improvements of applied measures are evaluated and discussed.
- ItemStabilita elektrizační soustavy(Vysoké učení technické v Brně, Fakulta elektrotechniky a komunikačních technologií, 2021-02-26) Máslo, KarelPublikace se zaměřuje na stabilitu elektrizační soustavy a její dílčí problémy – úhlovou, frekvenční a napěťovou stabilitu. Tato témata jsou popsána teoreticky i pomocí příkladů pro program MODES.
- ItemEvaluation of Filtered Spark Gap on the Lightning Protection of Distribution Transformers: Experimental and Simulation Study(MDPI, 2020-07-24) Pourakbari Kasmaei, Mahdi; Mahmood, Farhan; Krbal, Michal; Pelikán, Luděk; Orságová, Jaroslava; Toman, Petr; Lehtonen, MattiProtection of transformers, as one of the most expensive equipment in the power system, against lightning overvoltage impulses is a vital task. This paper, for the first time so far, investigates the effects of a filtered spark gap on the protection level of transformers against lightning overvoltage impulses. The filter is an inductor that is placed in series with the transformer and before the spark gap aiming to reduce the voltage at the connection point of the spark gap, and hence, enhancing the protection level of the transformer under lightning overvoltages. The experimental laboratory tests are accomplished on a 400 kVA, 22/0.4 kV, Delta-Star (Delta-Y) connection type transformer under 110 kV, and 125 kV overvoltage impulses, whereas the size of the spark gap is set to 80 mm and two inductors of 35 mu Hand 119 mu Hare considered. In order to perform a more in-depth analysis, a model that works reasonably close to the empirical case is developed in the EMTP-RV software. An optimization algorithm is used to determine the sensitive parameters of the double-exponential function, which is used to reproduce the applied laboratory lightning impulse voltages in the EMTP-RV environment. Moreover, the transformer is modeled according to the Cigre Guidelines (Working Group 02 of Study Committee 33). The behavior of the spark gap is simulated as close as the practical situation using the disruptive effect method. The preciseness of the simulated filtered spark gap model is verified by comparing the results of the simulated model in the EMTP-RV with the results of experimental tests. After verifying the model, different sizes of inductors are studied in the EMTP-RV environment to investigate whether larger or smaller inductors provide better protection for the transformer under lightning conditions. A comparison is performed among the conventional spark gap, surge arrester, and the filtered spark gap to provide a better analysis of the potential of the proposed device. The results indicate that proper sizing of the inductor, within an effective range, slightly enhances the protection level of the transformer.
- ItemInvestigation of critical heat flux on abraded inconel 625 tube(Czech Technical University in Prague, 2020-12-01) Suk, Ladislav; Števanka, Kamil; Petrosyan, Taron; Vlček, DanielAim of this work was to study flow boiling in an annular channel at low pressure and lowflow on a tube with modified surface roughness. The tube with the outer diameter of 9.14 mm and theheated length of 380 mm was made of Inconel 625 and was manually modified using 150 grit sandpaper.The tube was placed in a glass tube with an inner diameter of 14.8 mm. Outlet pressure was set to 120,200 and 300 kPa with varying mass flow from 400 to 600 kg/(m2·s). A high speed camera was used torecord several experiments to fully understand ongoing phenomena. Surface roughness was analysedusing a confocal laser microscope and the effects of different mass flux and pressure on the CHF valuewere observed. Above all, the optimization of the flow parameters was done from the collected dataand from the observed behaviour of the experimental loop
- ItemAnalysis of fast neutron transport in chloride salts using Monte Carlo method(Czech Technical University in Prague, 2020-12-01) Šťastný, Ondřej; Katovský, Karel; Král, Dušan; Krása, Antonín; Kurwitz, Cable; Števanka, KamilThe aim of this paper is to present results of fast neutron behavior analysis within the chloride salts environment using simulations based on Monte Carlo method (MCNP 6.2). Three non-fueled salts (NaCl, KCl, MgCl2) and two salts containing fissile material (UCl3, ThCl4) were studied. Results of this theoretical study will be used for design of an experimental assembly, which will serve to achieve goals of the international research project ADAR (Accelerator Driven Advanced Reactor). One of the project objectives is to investigate chloride salts as potential coolant and a dissolved fuel carrier of advanced nuclear reactor cooled by molten salts and driven by an accelerator.