Investigation of impacts of different three-phase transformer connections and load models on unbalance in power systems by optimization

This paper investigates the impacts of different three-phase transformer connections and load models on unbalance in power systems. New three-phase transformer models are presented. These models are derived from a new primitive impedance matrix incorporated with positive, negative and zero sequence elements. The constant power and constant impedance load models are discussed. The three-phase models are implemented in a general-purpose optimization software package. Two power systems are used to illustrate the test results. The test results provide assistance to engineers in understanding the effect of different connections on the transformers. This paper also emphasizes that a proper load model should be used; otherwise, an incorrect solution will be obtained.