Today, Ukraine and the world face important issues related to solving the problems of the energy sector, including electricity. In networks of different voltages of power systems the level of short-circuit currents is constantly growing, while the requirements for electrical devices, live parts, power transformers and switchgear designs are becoming more stringent. There is a problem of optimal coordination in the dynamics of electrical equipment parameters and power system requirements or coordination of electrical equipment parameters with existing short-circuits current levels. The growth of short-circuit currents in electrical networks of all voltage classes makes it important to develop new effective methods and devices designed to reduce them. The article considers the issues of comparing the current of single-phase and three-phase short-circuit, average regional power system, the integrated parameters of electrical networks of such a system. Limitations of currents of single-phase short-circuits are analyzed in detail in problem nodes where autotransformers are installed. The conducted researches allowed to recommend the improved methods of calculations of electric devices and current-carrying parts on electrodynamic and thermal stability at short-circuit, including at single-phase. Recommendations for creating a mathematical model for calculating a nonlinear system in the presence of flexible conductors are given, because most of the damage (in the form of short-circuit) on high-voltage overhead power lines and switchgear is accompanied by an electric arc with parameters that change over time. In addition, significant short-circuit currents cause mechanical displacements of flexible wires in space, which leads to changes in the phase distances and inductive resistances of overhead lines of forward and reverse sequences. All these listed factors have a mutual influence during s.c. In addition, when operating electrical installations, an important factor is the switching life of switches, which affects the reliability of the installation and its technical and economic performance. The criterion for decommissioning the circuit breaker may be the residual life of the circuit breaker at the level of one tripping of the full tripping current of the circuit breaker. The analysis showed that it is necessary to take into account when calculating the short-circuit currents additional thermal action of various energy sources and the power system as a whole, synchronous generators and compensators, synchronous and asynchronous motors.
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