Modeling induction machines and core-form transformers in unbalanced distribution circuits

Three phase power distribution systems often experience voltage imbalance due to unbalanced loading of the system. The unbalanced load flow is increasingly being used in all aspects of distribution system analysis. Many three phase devices, particularly induction motors and transformers, behave differently when connected to an unbalanced supply. Advanced models can be necessary to properly account for these differences. This paper proposes models for induction motors and core-form transformers suitable for load flow simulation. The models are based on symmetrical component theory. The induction motor models involve an additional iteration loop, and are validated against EMTP time domain simulations. Case studies are presented that show the impact of using these models in unbalanced distribution system conditions.