Residual Flux Measurement of Single-phase Transformers based on Equivalent Resistance

Due to the presence of transformer residual flux, the magnetic flux of the core rapidly reaches saturation, thus causing an inrush current when the no-load transformer is directly connected to the grid, which affects the safe operation of the grid. Therefore, it is necessary to study the residual flux in the core to reduce the inrush current. However, the residual flux estimation has a large error. In this paper, a method is proposed to measure the residual flux of the transformer core by solving equivalent resistance and determining the direction of residual flux by the difference between the forward and reverse transient currents. In addition, the relationship between residual flux and equivalent resistance is established, and the empirical formula is obtained for calculating the residual flux. To evaluate the effectiveness of the proposed method, the residual flux of the square core is measured on the constructed experimental platform. Compared with the experimental results, the relative error of the residual flux of the core calculated by the proposed method is within 6%, which has higher accuracy and provides a reference for residual flux estimation.