This paper presents the results of an experimental study of a solid-state heat engine based on a Ni-Ti shape-memory alloy, designed to utilise low-grade thermal energy and generate mechanical and electrical energy. An experimental prototype of an electromechanical system with an impeller and a system of SMA springs, operating in a cyclic heating and cooling mode, was investigated. Experimental studies were carried out to determine the dependence of the reactive force, rotational speed, torque and mechanical power of the system on the temperature of the heat transfer fluid. A pronounced non-linear nature of the mechanical energy generation processes has been established, associated with the thermomechanical kinetics of phase transitions in the SMA material. The existence of a threshold activation regime for the system has been demonstrated; upon reaching this regime, a sharp increase in the rotational speed, torque and mechanical power of the system is observed. Experimental validation of the previously developed dynamic thermomechanical model of the SMA heat engine has been carried out. A comparison of the results of numerical modelling and experimental data for the temperature dependencies of torque, rotational speed and mechanical power confirmed good agreement between the experimental and calculated characteristics, both in terms of the nature of the non-linear dependencies and the magnitude of the values obtained. It has been demonstrated that the dynamic ODE (Ordinary Differential Equation) model adequately describes the processes of heat transfer, phase kinetics and the generation of mechanical power in an SMA heat engine. Based on the research carried out, the potential for using solid-state SMA heat engines in systems for the utilisation of low-grade heat, autonomous electricity generation and distributed energy systems has been established. References 7, Figures 7.
The structure of the system for synchronizing the operation of generators and synchronous detectors of quasi-sinusoidal signals in precision meters of electrical impedance parameters is considered. Factors limiting the range of operating frequencies are determined. Mathematical expressions are given for determining errors due to the influence of higher harmonics of signals, as well as the maximum frequency of signals. Ways of increasing the speed of the system are proposed. A comparative analysis of options regarding measurement accuracy and frequency range is carried out. A method for determining the clock generator frequency depending on the required values of the device's operating frequencies is presented. The obtained mathematical expressions can be used to determine the parameters of the system blocks for different implementation options. References 5, Figure 1.
This paper addresses the current challenges associated with the recovery and development of Ukraine's electric power sector in the context of its integration into the European energy area and the ongoing digital transformation of the sector. The study identifies the key systemic challenges affecting the operation and transformation of the Integrated Power System (IPS) of Ukraine, resulting from damage to energy infrastructure caused by military actions, the increasing penetration of renewable energy sources (RES), the need to enhance the resilience of electricity supply, and the deployment of advanced digital control technologies. Strategic principles for scientific support of the recovery of Ukraine's electric power sector are presented, and the key research objectives aimed at developing a technologically advanced, adaptive, and economically efficient power system are defined. The paper substantiates the key scientific and technological priorities for the development of Ukraine's electric power sector, focusing on enhancing the resilience, flexibility, and controllability of the IPS of Ukraine. These priorities encompass scientific and technological support for infrastructure modernization, the development of local energy systems, electricity market mechanisms, and digital control technologies. It is concluded that the integrated application of scientific research, innovative technologies, and strategic planning constitutes a prerequisite for strengthening national energy security, enhancing the resilience of the electric power system, and promoting its further integration into the European energy area. References 33.
The active integration of distributed energy sources into the electrical grids of industrial enterprises reduces the load on the power system, increases the reliability of electricity supply to consumers, and improves the transmission and distribution of electricity between them. At the same time, however, the random nature of renewable energy generation and the large number of semiconductor elements in the grids result in low-quality electricity and, accordingly, electromagnetic incompatibility between consumers and with the general grid. This paper proposes a methodology for synthesizing an energy-efficient electrical grid for an industrial enterprise with distributed energy sources based on the interconnection of separate DC and AC microgrids and their subsequent structural and parametric optimization. This approach allows avoiding the main negative factors that arise and increasingly accumulate in traditional electrical grids. Using the example of an industrial enterprise, the structural and parametric optimization of the electrical grid of one of its workshops is considered. This allows you to form its configuration with the minimum length of cable lines and determine the best places to connect converters that connect the specified AC and DC grids. The calculation of daily active energy losses confirmed the effectiveness of the proposed methodology for forming an innovative electrical grid for an industrial enterprise. Thus, active energy losses in the internal workshop grid decreased almost three times compared to the traditional approach to forming the grid and amounted to only 2.58% of daily consumption. The proposed approach is particularly relevant for the design of electrical grids for industrial enterprises with a significant number of consumers that allow for deviations in power quality indicators, DC power consumers, and power converters. References 16, figures 7, tables 3.
A methodology for complex calculation of the electromagnetic and temperature fields using finite-element method under the steady-state and transient conditions of electric motors is presented. The problems for industrial consumers that arise under conditions of slow acceleration when the starting of the power asynchronous and synchronous motors con-nected to the loads with high inertia are considered. The numerical modeling of the asynchronous initiation was carried out for various parameters (time, starting voltage and current) of unsteady condition. The results of theoretical studies regarding the distribution of heat generation in rotor elements in long and short-term operating modes of the motors with slip are presented. The patterns of physical heat transfer processes in a solid rotor when powering a non-salient-pole motor by the sources of different voltages are analyzed. The magnitude of inaccuracies at determining the maxi-mum calculated temperature of the surface elements of the rotor and data on the full-scale test program at the installa-tion site of temperature sensors when starting a power motor, due to the specifics of conducting experimental studies on its rotating part, have been determined. It has been shown that the difference between the maximum heating at certain time moments of the regime can reach a double value. It has been established that the thermal processes in a solid rotor limit the load of a non-salient pole motor in asynchronous modes. References 9, figures 9.
