Models of grounded mid-tap open-wye and open-delta connected transformers for rigorous analysis of a distribution system

The paper presents detailed mathematical models of grounded mid-tap open-wye and open-delta connected transformers for rigorous analysis of a distribution system. The transformers are accurately modelled in phase coordinates, The proposed transformer models consider the copper and core losses, winding connections, the phase angular displacement between primary and secondary windings, and off-nominal tapping. Open-wye and open-delta connections with mid-tap grounded on the secondary side of the transformer banks are quite often used to supply the single-phase lighting load and three-phase power load simultaneously. The detailed models of these transformers are indispensable for analysis of the inherent imbalance of a distribution system