Analysis of the occurrence of magnetic flux surges and magnetizing current when the transformer is turned on at idle

Abstract

This article discusses the transients that occur in power transformers when they are turned on at idle. The main negative consequences arising from magnetizing current surges and their impact on the quality of electrical equipment, in particular, false alarms of relay protection devices and deformation of transformer structural elements by electrodynamic forces, are given. The mathematical derivation of physical quantities determining the process of occurrence of magnetic flux and magnetizing current surges is presented on the example of switching on a power single-phase transformer in idle mode. As a result of mathematical analysis, the main factors affecting the flow of the transient process when the power transformer is switched on in idle mode were identified. A mathematical expression was obtained that allows determining the phase of the mains voltage for a favorable moment of switching on a single-phase transformer, depending on the magnitude of the residual magnetic flux in the steel core of the transformer. Based on the analysis of transients that occur when transformers are switched on at idle, methods or algorithms for switching on power transformers can be developed that allow for a smooth start of the transformer and avoid or minimize negative consequences.