Substantiation of the choice of the replacement scheme of line for mathematical modeling of 20 kV power supplies.
Authors:   State Institution of Higher Education «Donetsk National Technical University», S. SKRYPNYK 
Published: September 2021

In the current global economic crisis and acute shortage of energy resources, increasing importance is attached to energy saving measures, economical and careful consumption of raw materials, materials, electricity and heat, environmental safety of industrial production. During the reconstruction of existing power supply systems of industrial enterprises, modern progressive solutions should be considered and implemented, morally and physically obsolete electrical equipment should be replaced, namely the introduction of new electrical equipment for transition from 6/10 kV to 20 kV in Ukrainian power systems. It is also necessary to pay attention to the improvement of power supply circuits and distribution networks, the implementation of complex automation of complex technological processes, rational compensation of reactive power at all levels of power supply systems. In the power system, the main transport link is the power line. Power lines (transmission lines) are long conductors suspended at a safe distance from the ground overhead lines (overhead lines) or cable lines (overhead lines) in which conductors are insulated from each other and from the environment and protected by insulation and armor electricity. Power lines are the most massive elements of the power supply system, they connect the individual nodes of its circuit. Longitudinal and transverse parameters are distinguished in alternative schemes. The load current flows through the longitudinal parameters, voltage is applied to the transverse ones. The replacement circuit of the electrical network consists of replacement circuits of the following elements: power lines, transformers, reactors, capacitors, loads, power sources. Calculating the steady-state modes of power systems, the substitution schemes of the elements are given in a single-line design, because the parameters of all phases are symmetrical. In local and local electrical networks with a relatively short length and low rated voltage, the conduction currents are small compared to load currents. Therefore, in typical electrical calculations of these networks, the capacitive conductivity of the lines is not taken into account. However, for these networks, the accounting of capacitive conductivities is necessary when considering some modes, the existence of which in itself is due only to the presence of capacitive conductivities. For example, the mode of single-phase ground fault in a network with isolated or compensated neutral or analysis of the modes of operation of neutrals of electrical networks of different voltage classes cannot be performed without taking into account the capacitive conductivity of these networks. When switching the power system of Ukraine to the nominal voltage of 20 kV, it should be taken into account that the transmission line will be replaced in the sections of both the overhead power line and cable power line, namely 35, 10, 6 kV. The replacement scheme must describe all the characteristics and properties of the elements of cable and overhead lines in accordance with real conditions. Thus, it is not expedient to use simplified substitution circuits that neglect energy parameters and properties of conductors to study the parameters of transmission lines. The use of a complete "P" -shaped scheme for the analysis of the parameters of transmission lines and transmission lines for a voltage of 20 kV is the basis of mathematical modeling of the transmission system in the distribution networks of our country.