A Method for Estimating the Current-flux Curve of a Single-phase Transformer for Electromagnetic Transient Simulations of Inrush Currents

Abstract

When a transformer is energized, inrush currents whose magnitudes may reach tens of its nominal current occur. Since the inrush currents lead to a voltage drop, this may cause stops and malfunctions of electrical appliances. In addition, the over-currents may cause an unnecessary operation of an over-current relay and affect the power quality of the distribution system. Currently, distribution system operators use current-versus-time curves of transformer inrush currents for the studies of such phenomena. However, the studies based on the current-versus-time curve give approximate results, and studies based on the current-versus-flux curve is required so as to obtain accurate results. Considering this point, this report proposes a method to convert a given current-versus-time curve to a current-versus-flux one for the case of single-phase transformers. Using the current-versus-flux curve obtained, detailed simulations can be performed using an electromagnetic transient analysis program such as XTAP. In this report, the proposed method is validated by experimental results using a single-phase transformer.