Ústav elektroenergetiky

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Multi-objective optimization of smart grid operations via preventive maintenance scheduling using time-dependent unavailability
(Elsevier, 2025-08-15) Krpelík, Daniel; Vrtal, Matěj; Briš, Radim; Praks, Pavel; Fujdiak, Radek; Toman, Petr
This paper presents a method for multi-criteria optimization of system operations using transient operation models. Real systems often combine long-living components with rapid repairs, creating challenges for numerical integration due to fine discretization requirements. These challenges significantly increase the computational cost when evaluating renewal processes with recurrent terms of quadratic complexity in mission time. To address this, we derive new mathematical formulas for evaluating unavailability and operational costs of components under periodic, age-based preventive restoration. The key innovation is a decomposition of the renewal equation: repair-related terms are approximated analytically, eliminating the need for fine discretization throughout the process. A special formula is introduced for components with uniformly distributed repair times and mean time to repair much shorter than mean time to failure, applicable to many real-world systems. The accuracy of the proposed approach is validated against Monte Carlo simulations, showing significant reduction in computational effort. This efficiency enables repeated evaluations in optimization tasks, demonstrated on a real-world case involving interconnected energy and communication infrastructure in the Czech Republic. A multi-objective NSGA-II algorithm is employed to optimize the preventive replacement policy, minimizing both system maintenance cost and expected downtime. We also explore systems with components of non-zero initial age. Results show that relying solely on asymptotic approximations may lead to suboptimal strategies, potentially worsening performance. However, allowing preventive renewal of selected components at time zero enables identification of superior solutions.
Transient and steady currents in a parallel RL circuit
(Elsevier, 2025-01-21) Coufal, Oldřich
Part of electrical engineering is circuit theory, which includes methods for calculating steady and transient currents in a parallel RL circuit. Power systems are typically inductive and can be modelled with RL circuits. The proposed methods can be used in the calculation of short-circuit currents and in the calculation of current density in solid conductors that form transmission lines. An RL circuit is formed by real voltage sources, inductors and resistors. The inductance and resistance of the circuit elements do not depend on time. The ideal voltage source, which is part of the real source, has voltage depending on time. Currents in a parallel RL circuit are solutions to ordinary differential and algebraic equations, which are mathematical expressions of Kirchhoff's laws. The original contribution of this paper is the derivation of equations for the calculation of currents in a circuit for all possible combinations of circuit elements. The importance of the initial conditions of currents whose first derivative occurs in the equations is emphasized. An original definition of steady current and transient current is proposed. The theory is supplemented with solutions of illustrative examples.
14N break-up emission with 59Co, 93Nb, and 197Au targets at an incident energy of 250 MeV
(SPRINGER, 2024-05-23) Bhuptani, C.; Patel, Dipika; Ojha, V.K.; Mukherjee, Surjit
The emission of alpha particles has been analyzed using a N-14 projectile beam on Co-59, Nb-93, and Au-197 targets at an incident energy of 250 MeV, in the angular range from 8 degrees to 40 degrees. The estimated alpha particles from the break-up channel and the pre-equilibrium mode were compared with the experimentally measured inclusive double differential cross sections at various angles at 250 MeV beam energy. The present results indicate that at such a high incident energy, a significant contribution to the alpha-particle emission comes from direct reactions, which are dominant at forward angles. At larger emission angles, non-equilibrium and evaporation processes increase and compete with direct reactions.
Determination of Photoneutron Production from Different Targets Irradiated by Electron Beam
(National Academy of Sciences of Armenia, 2024-11-28) Melyan, Elmira; Katovský, Karel; Mukherjee, Surjit
In the present work, a study has been conducted to estimate the production of photoneutrons from different targets irradiated by a 70 MeV electron beam. The linear electron accelerator at the Yerevan Physics Institute in Armenia was used for the purpose. The reaction rates were determined through detailed off-line analysis of experimental data and subsequently compared to theoretical predictions by using the MCNP (Monte Carlo N-Particle Transport) and Cascade Exciton Physics Model (CEM03.03) codes.
Smart Grids Transmission Network Testbed: Design, Deployment, and Beyond
(IEEE, 2024-12-13) Blažek, Petr; Bohačík, Antonín; Fujdiak, Radek; Jurák, Viktor; Ptáček, Michal
Our test environment incorporates a unique blend of physical, emulated, and virtualized components, spanning from electrical substations to SCADA systems, thereby offering a versatile platform for testing against cyber threats, facilitating educational programs, and supporting advanced traffic simulation. Motivated by the increasing digitalization of energy networks and the growing risks associated with cybersecurity and crisis management, this work responds to geopolitical situations and a series of attacks on electricity infrastructure, such as in Ukraine between 2015 and 2024. For instance, in 2015 and 2021, major cyberattacks caused power outages in Ukraine and the USA, emphasizing the urgent requirement for robust testing platforms. Key findings from our deployment highlight the testbed’s effectiveness in identifying vulnerabilities, enhancing cybersecurity measures, and providing valuable hands-on learning experiences. The integration of such diverse components not only exemplifies a significant step forward in testbed design but also showcases its potential in fostering innovation and security in the power sector. Through detailed comparisons with existing testbeds, we underscore our testbed’s distinct features and its contribution to bridging the gap in current methodologies, setting a new benchmark for future developments in smart grid testing and education.

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