The Problem of Coordination of Levels of Short-Circuit Currents in Power Systems

Abstract

The problem of coordination of short-circuit (fault) currents is considered. Data on the dynamics of variation of the levels of single-phase and three-phase short-circuit currents (their highest values) in networks rated for different voltage are presented for a long-term period. The main factors (integral parameters of the networks) affecting the values of short-circuit currents are listed. Statistics of variation of rated parameters of electrical equipment in past years and in the recent period is presented and predictions for the future are made. Basic methods and means for limiting short-circuit currents are discussed. A method of automatic and stationary network separation and a method of circuit design are described in detail. The efficiencies of different methods are compared. The effect of integral parameters of the network on the maximum level of short-circuit currents is shown. The aspects of the switching life of breakers and of allowance for probabilistic characteristics of faults and for the risk factor of decision-making are considered. It is shown that coordination of the levels of short-circuit currents is a possible means for raising the reliability of power installations and systems.Keywords: short-circuit current, coordination of levels of short-circuit currents, level of short-circuit current, limitation of short-circuit currents, parameters of electrical equipment, structure and parameters of power systems, influencing factors, standardization of parameters of electrical equipment, methods and means for limiting short-circuit currents.Statement of the problem. In different-voltage networks of power systems the level of short-circuit (fault) currents increases continuously to this or that degree. The requirements on electrical equipment, conductors, line (auto)transformers, and design of switchgears become more and more rigid. The problem of optimum agreement between the dynamics of the parameters of electrical equipment and the requirements of power systems or of coordination of the parameters of electrical equipment with the existing or expected levels of short-circuit (SC) currents becomes urgent [1].The problem is comparatively new; it appeared in the 1960 -1970s due to the rapid development of the power industry manifested by growth in the unit power of generating units, power plants, substations, and power systems rated for medium, high, extrahigh, and ultrahigh voltages. The problem should be solved by a system approach with allowance for the dynamics of variation of SC currents and parameters of electrical equipment, results of new developments in electrical power engineering, and requirements on the reliability and efficiency of operation of power systems. This is part of the more general problem of designing the structure, parameters, and operating conditions of power systems and their components, which is solved in all stages of power system control from prediction and planning to design and operation. The problem is quite complex and requires consideration of interrelated aspects. ...

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