Dynamical modeling and analysis of asymmetric unbalanced three-phase transformers

In this paper we carried out dynamical modeling studies and analyzed of the three-phase three legged transformers of the laboratory. The unbalance and hysteresis phenomenon are also treated and two models are used, namely the T- and PI-models. The PI-model as developed by De-Léon et al [14] in the EMTP simulator (Electro-Magnetic Transients Program) does not give good results. That is why we proceeded to the correction of this model by reversing the two transformers keeping the same parameters of the magnetizing branch. However, the inductance Lsh determined by a short-circuit test should be reduced to the secondary winding of the second transformer. An adequate correction of the model gave simulation results very similar to those of experimental ones. Another solution giving the same results is presented in this paper. We also addressed the unbalance of the three-phase transformer by the symmetrical components method and by the FPEM (Feature Pattern Extraction Method).