Development of a transformer magnetizing circuit model for inrush current and residual flux calculations

For accurate simulations of transformer inrush currents, modeling of magnetizing circuits which represent iron-core characteristics is important. Existing magnetizing circuit models are classified into the two categories: behavior-based modes and physics-based models. The parameter determination process of the behavior models is relatively simple, but these models cannot properly reproduce residual fluxes which has a significant influence on the magnitudes of inrush currents. On the other hand, the physics-based models are able to reproduce residual fluxes, but their parameter determination process is complicated. Considering the above, this paper proposes a behavior-based magnetizing circuit model which is capable of reproducing residual fluxes. The proposed model consists only of standard circuit elements, and its parameters are determined in a simple way using the information of name plate, test report and current-flux curve. In this paper, inrush currents of two transformers with Y-Δ and Δ-Δ connections have been calculated using the proposed magnetizing circuit model, and good agreement is found with laboratory test results. © 2014 The Institute of Electrical Engineers of Japan.