The Coefficients of Fundamental Harmonic Component Effective Values for Calculating the Magnetizing Inrush Current

This article addresses the problems of offsetting the current cutoff protection setpoints without a time delay for microprocessor protection devices to ensure their remaining silent to magnetizing current inrushes. The above-mentioned problems are associated with outdated calculation methods from the existing relay protection guidelines. To solve these problems, the dependences for calculating the coefficients of the fundamental harmonic component effective values are considered for calculating the magnetizing current inrush. By using the suggested dependences, it is possible to calculate the coefficients of the magnetizing inrush current fundamental harmonic component effective values taking into account the generalized attenuation curve, various steel grades, and various types of power transformer connection configurations. The coefficients of the magnetizing inrush current fundamental harmonic component effective values are given in the form of curves, including those reflecting the magnetizing inrush current attenuation with time. In accordance with the value of the coefficient at the moment of time, which depends on the protection response time, it is possible to calculate the magnetizing inrush current value from which it is necessary to offset the protection. By applying the described approach, it is possible to obtain the effective values of the magnetizing inrush current fundamental harmonic component for accurately calculating the response parameters of any relay protection device, regardless of the type of its hardware. To facilitate the magnetizing inrush current value calculation, an automated software for calculating the magnetizing inrush current fundamental harmonic component effective value has been developed.