Analysis and reduction of magnetizing inrush current for switch-on unloaded transformer

Abstract

Transformer magnetizing inrush current can lead false-actions of differential protection and, reduce transformer lifetime, and send higher harmonics to power grid. The paper deals with the harmful problem of magnetizing inrush current for switch-on unloaded transformer. We derive the mathematical model of magnetizing inrush current. Based the analysis of relation among magnetizing inrush current, residual magnetism, switch angle, magnetizing impedance, the current interrupting angle and its magnitude, we presents the approach of reduction the magnetizing inrush current. By properly control the voltage initial angle for switch-on break, the primary winding current go into steady without transition. Simulation results indicate the validity and feasibility of the proposed algorithm. It is necessary to popularize the proposed approach in switch-on unload transformer.