A novel method for measuring residual flux density of the single-phase transformer core based on phase difference

A serious inrush current may occur when a power transformer is re-energized, which will cause many adverse effects on power equipment and the power grid. The corresponding potential hazards can be reduced if the existing residual flux density (Br) can be accurately measured. Combined with the field-circuit coupling analysis method, a novel method for measuring the Br based on the phase difference between the applied AC voltage and resulting transient current is proposed in this paper. When the same AC voltage is applied to the transformer winding, the Br affects the resulting transient current. The phase difference between the applied voltage and the resulting current can be calculated by the cross-correlation technique. Based on the finite element method (FEM), the empirical formula for the quantitative measurement of Br in the transformer core is determined. Finally, an experimental study is performed on the square core of single-phase transformers. The experimental results reveal that the proposed measurement method is with high accuracy.