Effect of DC biasing in 3-legged 3-phase transformers taking detailed model of off-core path into account

modeling of 3-legged, 3-phase transformers under DC biasing is a challenging topic due to the need to have an adequate representation of flux paths beyond the active part including the tank. The main contribution of this paper is to present a new dual circuit model which takes the off—core flux path into consideration. An equivalent circuit is developed for this off-core path including equivalent non-linear branches for the tank elements. The adequacy of the proposed method is verified through zero sequence impedance tests at steady state. Having the new model, the behavior of a test transformer is studied under DC excitation in terms of magnetization current, reactive and active power flowing through the transformer.