The flux-current characteristic of the voltage transformer plays an important role for non-linear Ferro-magnetic analysis. The disadvantage of traditional excitation curve fitting method using the model of polynomial terms lies in that the linear part fitting is not perfect, while, the non-linear part has the good fitting results, which is not accord with the PT excitation characteristic. With fitting order number increasing, insufficient samples will also lead to unfavorable fitting results. In this paper, line interpolation will be first carried out for the linear part of the measuring volt-ampere characteristics, then sample points will be increased by utilizing least squares fit, which will greatly improves the fitting precision of the linear part and the overall fitting accuracy of the non-linear part. The simulation results show that the error of the linear part does not exceed 0.3% and the error of the non-linear part drops from 2.5% to 1.5% when the linear part is given 11 order line interpolations.
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