2024 № 1 Електротехніка і Електромеханіка
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Документ Requirements for cables as categories of construction products and thermal resistance of power cables(Національний технічний університет "Харківський політехнічний інститут", 2024) Bezprozvannych, G. V.; Grynyshyna, M. V.; Moskvitin, Y. S.Introduction. One of the main driving factors of the demand for cable and conductor products is the modern trend of urbanization, which leads to an increase in cities with significantly increased requirements for electrical networks of transportation and distribution of electrical energy. This requires the development of appropriate infrastructure with significant demand for electricity in the commercial, industrial and residential sectors. The construction industry uses a wide range of cables with an appropriate set of electrical and mechanical properties, resistance to the influence of external climatic factors, and, first of all, must meet fire safety requirements. Increasing construction activity is stimulating the market for fire-resistant cables in the construction industry. According to the Construction Products Regulation, power, telecommunication cables, data cables, control and management, fiber optic refer to construction products in the EU member states. These cables are intended for the supply of electrical energy and communication, which are permanently installed in buildings and other engineering structures. Power, telecommunications, data and control cables are considered construction products, and are the only electrical products classified as construction. Over the next 15 years, Eastern Europe is expected to see increased growth in the construction industry, as the end of the war in Ukraine requires nearly $1 trillion in reconstruction. A strategic task in the reconstruction of the country is the use of cable and conductor products with increased operational properties, including in the construction industry. Significant efforts and investments in innovation and certification of cable and conductor products require manufacturers to create construction products of the "Power, control and communication cables" category with a high level of fire safety in accordance with the Euroclassification of cables in terms of reaction to fire depending on the level of safety. Purpose. Analysis of fire safety requirements for cables as a category of construction products and determination of thermal resistance of power cables based on experimental thermal studies of modern electrical insulating compositions. Methodology. The thermal stability of power cables with a voltage of 0,66/1 kV was determined, depending on the design, based on the conducted experimental studies of the thermal stability of electrical insulation materials, between the core filling and the polymer sheath, removed from the cable samples. On the basis of the conducted correlation analysis between thermal resistance and fire load, which are important parameters for confirming the quality and safety of the entire cable, it has been proven that the efficiency of halogen-free compositions to meet fire safety requirements increases with the increase in the cross-section and number of cores in the cable. Practical value. Determining the heat load and fire resistance of cables of various designs and areas of application based on the obtained experimental data on the heat of combustion of polymer cable materials is necessary and justified at the stage of mastering and determining the prospects for the production of cables with modern halogen-free electrical insulation compositions in accordance with fire safety requirements. References 40, figures 6.Документ Modeling and analysis of electro-thermal processes in installations for induction heat treatment of aluminum cores of power cables(Національний технічний університет "Харківський політехнічний інститут", 2024) Shcherba, A. A.; Podoltsev, O. D.; Suprunovska, N. I.; Bilianin, R. V.; Antonets, T. Yu.; Masluchenko, I. M.Introduction. The development of the electric power industry is directly related to the improvement of cable lines. Cable lines meet modern requirements for reliability, they are increasingly used. Problem. Currently, power cables with an aluminum multi-conductor core, which requires heat treatment - an annealing process at the stage of the technological manufacturing process, are widespread. This process makes it possible to desirably reduce the electrical resistance of the wire and increase its flexibility. For effective use of induction heating during annealing of an aluminum core, it is necessary to determine the optimal frequency of the power source of the inductor. Considering the long length of the inductor and the large number of its turns, the numerical calculation of the electromagnetic field, which is necessary for calculating the equivalent electrical parameters of the turns of the inductor and its efficiency, requires significant computer resources. The goal is to develop a computer model for calculating electro-thermal processes in an induction plant for heating (up to the annealing temperature) an aluminum core of a power cable moving in the magnetic field of a long multi-turn inductor, as well as obtaining frequency dependences of the equivalent R, L parameters of such an inductor and determining the optimal the value of the frequency of the power source, which corresponds to the maximum value of the electrical efficiency of the inductor. Methodology. The mathematical model was developed to analyze the coupled electromagnetic and thermal processes occurring in a core moving in a time-harmonic magnetic field of an inductor at a constant speed. The differential equations for the electromagnetic and temperature fields, taking into account the boundary conditions, represent a coupled electro-thermal problem that was solved numerically by the finite element method using the Comsol software package. For a detailed analysis of the electromagnetic processes in the inductor, an additional problem was considered at the level of the elementary cell, which includes one turn of the inductor and a fragment of the core located near this turn. Results. According to the results of the calculation of the electromagnetic field in the area of the elementary cell, the equivalent electrical parameters of one turn of the inductor and the entire multi-turn inductor were calculated depending on the frequency of the electric current. The frequency dependences of the electrical efficiency of the inductor were calculated. Originality. Taking into account the design features of the inductor (its long length and large number of turns), the method of multiscale modeling was used. Electro-thermal processes in the core were studied at the macro level, and the distribution of the electromagnetic field and electric current density in the cross-section of the massive copper turn of the inductor was calculated at the micro level – at the level of an elementary cell containing only one turn of the inductor. The frequency dependences of the equivalent R, L parameters of the inductor, taking into account the skin effect, the proximity effect, and the geometric effect, were obtained, and the quantitative influence of the electric current frequency on these effects was studied. Practical value. The dependence of the electrical efficiency of the inductor on the frequency of the power source was obtained and it was shown that for effective heating of an aluminum core with a diameter of 28 mm, the optimal value of the frequency is in the range of 1–2 kHz, and at the same time the electrical efficiency reaches values of ηind = 0.3–0.33, respectively. References 31, figures 10, table 1.