Evaluation of the Effect of Induction Motors on Short-Circuit Current in Electrical Installations with a Rated Voltage above 1 kV

Abstract

The growth of 6(10) kV electrical networks in large cities generates the need to improve the method of calculating short-circuit (SC) currents to ensure sufficient sensitivity of the main and backup protections of cable lines, which take power supply from the generator switchgears of thermal power plants (TPP GS), which often have a galvanic link between their auxiliaries and local load. The effect an induction motor (IM) has on the SC current in electrical installations for a rated voltage above 1 kV is studied. To analyze the effect an IM has on the SC current, a computational mathematical model was developed in the MathCad software package, and variant calculations were carried out. The electrical equipment parameters and standard electric circuits of TPP GS that are applied in Russia were used as input data. It is shown that the SC current decreases depending on the IM capacity and the electrical distance of the SC from the SC current level relative to the calculations carried out without taking the IM into account. The criteria under which an IM leads to a decrease in the SC current are determined. Practical recommendations for reducing the IM influence on the SC current to ensure the necessary relay protection sensitivity are proposed.