Three-phase transformer representation using FEMM, and a methodology for air gap calculation

This work deals with the representation of three-phase and three-limb transformers in two dimensions using FEMM (finite element methods on magnetics). The transformer magnetization curve is obtained using the magnetization characteristic for the silicon steel used when assembling the transformer core, associated to the air gaps inherent to the assembling process. A method for the calculation of the air gaps reluctance is presented and it is based on the transformer magnetic circuit and on the maximum value in each winding for the magnetization current waveform, such current is obtained through the no-load test. The magnetic flux distribution in the values and the effects of inherent air gaps in the magnetization current is analyzed. Through the use of post-processing procedures, the transformer leakage reactance is calculated and compared with values obtained through the experimental method. Therefore, one of the objectives, is to explain a method to insert some of the transformer assembling imperfections in the computer model.