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

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 overcurrents may cause an unnecessary operation of an overcurrent 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.