Ústav elektroenergetiky

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Performance of Smart Revenue Meters Under Bidirectional Active Energy Flows in Energy Communities
(IEEE, 2024-03-28) Klusáček, Jan; Langella, Roberto; MEYER, Jan; Drápela, Jiří
Bidirectional active energy flows are expected to increase in electrical distribution systems (DSs) worldwide as a result of future incentives to exchange energy within local energy communities. Distributed generation (e.g., solar rooftop photovoltaic systems) in combination with full-cycle pulsewidth regulated loads (e.g., thermal appliances or some energy diverters), battery storage systems, or regenerative loads will result in periodic changes in the energy flow direction. If the regulation periods are close to the aggregation time window of smart revenue meters (RMs), the deviation from the correct readings of export and import registers might be significant. Subsequently, economic transactions that rely on readings from RMs, especially in community grids, might fail. The article presents an overview of the active power and energy metrics that are either already being implemented in static RMs or derived from other applications of active power measurement. A parametric analysis and an experimental case-study demonstrated quantitatively that different metrics and different influencing factors/conditions can lead to large deviations in the readings of RMs in community grids, causing significant technical and financial consequences. Finally, a new testing procedure capable of verifying the susceptibility of RMs to these quickly changing bidirectional energy flows is proposed and experimentally demonstrated with the goal of including it in future updates of the relevant standards.
Distance Learning of Fundamentals Seminars on Technical University Using Moodle Learning Platform
(Nakladatelství Gaudeamus, 2023-06-09) Koudelka, Jan
The paper presents the experience with distance teaching of fundamentals seminars on technical university. It describes the selected approach, i.e. use of Moodle learning platform for selected computational problems. Aspects to be considered for the preparation of this type of learning are described and the feasibility is discussed. Example of a selected problem is presented. Finally, the feedback from the teachers’ and students’ point of view is given.
Time-Dependent Unavailability Exploration of Interconnected Urban Power Grid and Communications Network
(MDPI, 2023-12-10) Vrtal, Matěj; Fujdiak, Radek; Benedikt, Jan; Praks, Pavel; Briš, Radim; Ptáček, Michal; Toman, Petr
This paper presents a time-dependent reliability analysis created for a critical energy infrastructure use case, which consists of interconnected urban power grid and communication network. By utilising expert knowledge from the energy and communication sectors and integrating the renewal theory of multi-component systems, a representative reliability model of this interconnected energy infrastructure, based on real network located in the Czech Republic, has been established. This model assumes reparable and non-reparable components and captures the topology of the interconnected infrastructure and reliability characteristics of both power grid and communication network. Moreover, a time-dependent reliability assessment of the interconnected system is provided. One of the significant outputs of this research is the identification of the critical components of the interconnected network and their interdependencies by the directed acyclic graph. Numerical results indicate that the original design has an unacceptable large unavailability. Thus, to improve the reliability of the interconnected system, a slightly modified design, in which only a limited number of components in the system were modified to keep the additional costs of the improved design limited is proposed. Consequently, numerical results indicate reducing the unavailability of the improved interconnected system, in comparison with the initial reliability design. The proposed unavailability exploration strategy is general and can bring a valuable reliability improvement in the power and communication sectors.
One Hundred and Fifty Years of Skin Effect
(MDPI AG, 2023-11-16) Coufal, Oldřich
In 1873, J. C. Maxwell derived relations for current density and current in a solitary long cylindrical conductor supplied with variable current. According to Maxwell, the current density in a conductor increases towards the conductor surface. This phenomenon is called the skin effect. The skin effect affects in particular the inductance of a line formed by one or several long parallel conductors. A number of papers have been published regarding the skin effect and its effect on inductance. Another phenomenon, closely related to the skin effect, is the proximity effect, which refers to the dependence of the current density in a conductor on the proximity of other conductors through which a time-variable current is flowing. Many published papers deal with the calculation of current density in two conductors, using the method for calculating current density in a solitary conductor. All the phenomena given above can be analysed and quantitatively described based on the knowledge of current density in conductors, and therefore the method for calculating current density in a group of conductors is of fundamental significance. It follows form the analysis performed that the skin effect is not a general characteristic of current density in long conductors, except for in the solitary conductor. This conclusion affects the knowledge of the phenomena associated with the skin effect.
Testing Rogowski Coils with Merging Units for Smart Grids
(MDPI, 2023-10-28) Daboul, Mayada; Orságová, Jaroslava; Jurák, Viktor; Vrtal, Matěj
As smart grids incorporate renewable energy sources and advanced power electronics, ensuring accurate measurement systems becomes paramount due to the increased complexity and potential sources of disturbances. This article focuses on the laboratory calibration of Rogowski coils (RCs) and merging units (MUs), which are fundamental for measuring, controlling, and monitoring digital power systems. A comprehensive digital calibration system is introduced, utilizing precise, commercially available components such as a fluxgate current transducer and a National Instrument. The system assesses magnitude and phase displacement errors under various operating conditions, including abnormal scenarios. Additionally, the impact of uncertainty sources on the measurement chain analysis is discussed, with test results conforming to established standards. This research contributes to enhancing the accuracy and reliability of measurement systems in the context of evolving smart grids.

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