Analysis of the residual flux influence on inrush current and electromagnetic force in large power transformer

The power transformer is the major electrical equipment in the power system and should be able to resist the damage that caused by the abnormal conditions, like the influence of the inrush current and the electromagnetic force. However, the residual flux, which is the most common influence factor of the inrush, can result in large current magnitude. This paper is to analyse inrush current and the electromagnetic force that as the result of inrush current for the impact of the safe operation of the large power transformer. The research of the inrush current under various factors has practical significance. In order to study the electromechanical forces influenced by the residual flux, the inrush current was analysed by Jiles-Atherton (J-A) hysteresis model. During transient switching process, electromechanical forces under the different residual fluxes were calculated, using the finite-element method coupled to the external circuit. The studies presented in this paper would be used in the design of the power transformer and power network protection.