Comparative Study of Calculation Methods for Short-Circuit Currents in Low-Voltage Networks with Asynchronous Motors

Abstract

The most dangerous emergency short-time operation mode of electrical installations of auxiliary system of thermal power plants with asynchronous motors is the short circuit mode. One of the reasons for the specific and timely failure of protective devices, when a short circuit occurs in the auxiliary systems of power plants and substations, which did not determine the expression in the current method, is considered in the national standard GOST 28249-93 "Method for calculating short-circuit currents". According to the existing GOST 28249-93 methodology, asynchronous motors should be considered only at the initial stage of short-circuit, when they switch to generator mode and increase the short-circuit current. One of these assumptions is to take into account the effect of asynchronous motors on the short-circuit current if the rated asynchronous motors current exceeds 1.0 % of the initial value of the periodic component of the short-circuit current in auxiliary systems of power plants and substations with low-voltage asynchronous motors. The purpose of the research in this paper is improved methodology for accounting for the effect of asynchronous motors on short-circuit current in the current GOST 28249-93 methodology and comparison of this calculation with the international standard IEC 60909 and in the ETAP (Electrical Transient Analyzer Program) software package in order to assess their qualities in terms of capability in solving problems, differences in the results, and errors allowed in the calculations of short-circuit current, scope and convenience in applying. Research methods are considered by creation of a special calculation and mathematical model based on the national standard GOST 28249-93, international standard IEC 60909 and in the ETAP software package on the example of the current VIII-section system of CHPP-1 in Dushanbe, Republic of Tajikistan with the 9th asynchronous motors.