Determination of Magnetization Characteristics of a Three-Phase Transformer Using Inrush Current Waveform

Transformer magnetization characteristics can change from their original conditions with the aging of the transformer, and hence, the actual characteristics may deviate from the manufacturers' data. This paper presents a method to derive the magnetization characteristics of a three-phase transformer, in the form of flux-current curve by analyzing the transformer inrush current and voltage waveforms. The method presented allows the derivation of magnetic characteristics without interrupting the transformer operation for a long period and avoids any complex procedures. The program is designed and validated for a star-star type transformer. The three-phase transformer was modeled mathematically, and the resulting system of equations was observed to be a set of second order, non-linear ordinary differential equations. A MATLAB Simulink transformer model was used to obtain the inrush current waveforms, since solving the system of equations was found to be a tedious task and the results from the Simulink model could be validated using a practical transformer. A MATLAB program was developed based on the mathematical model of the three phase transformer to derive magnetization characteristics of the transformer by analyzing the inrush current waveform. Magnetization characteristics derived from the developed MATLAB program were found to be in accordance with the input magnetization characteristics used to generate the inrush current waveform. Analysis of the results show that the program is more than 98% accurate.