Three phase models of specially connected transformers

To reduce the system imbalance, various types of specially-connected transformers have been adopted in Taiwan and abroad. Because three-phase transformer models are necessary for three-phase load flow simulation, specially-connected transformers which have been adopted so far are selected to derive three-phase models in this paper. These transformers include the single-phase connection, the V-V connection, the Wye-Delta connection, the Scott connection, the Le Blanc connection, and the Modified-Woodbridge connection. The three-phase models with the specially-connected transformers offered in this paper distinctly represent the HSR feeding system by means of the physical three-phase circuit and the symmetrical-component equivalent circuit. The three-phase model could be joined to the three-phase load flow program to exactly analyze the system imbalance in the future. The symmetrical-component equivalent circuit may also be used to derive the approximate unbalance-estimating formula.