Phase variable transformer models for unbalanced distribution system power flow

Three-phase transformer modeling for unbalanced distribution power flow has not been successful in phase variables. A satisfactory solution to this problem has been developed earlier, using a hybrid of phase and sequence variables. These models are not suitable for power flow methods which can provide sensitivities for optimization. This paper presents new pie models for various transformer winding connections, which overcomes this limitation. Results of sample systems have been obtained to demonstrate the potential of the proposed method.