Reversible Wideband Hybrid Model of Two-winding Transformer Including the Core Nonlinearity and EMTP Implementation

Accurate high-frequency modeling of transformers is crucial for the analysis and simulations of the fast electromagnetic transients of power systems and smart grids. However, most high-frequency models do not include the effects of core nonlinearity and may lead to inaccurate results. This article proposes an improved wideband model considering core nonlinearity for single-phase two-winding transformers and its implementation in the Electromagnetic Transients Program (EMTP). The hybrid model is developed by merging the wideband admittance module and the duality-derived π module using filters with compensation. The duality-derived π module is developed from the direct application of the principle of duality. The wideband admittance module is developed based on discrete state equations using the technology of the modified vector fitting method. All parameters of the hybrid model are easy to be obtained because they are determined using terminal tests instead of the detail information of the transformer. Simulations and experiments, including inrush current, lightning excitation, and ferroresonance tests, show that the proposed hybrid model can accurately simulate both the low- and high-frequency transients of a single-phase two-winding transformer with a maximum difference of 5%.