Residual Flux Measurement of the Single-Phase Transformer Based on Transient Current Method

When the no-load transformer is connected to the power grid, an inrush current may be resulted as the existed residual flux in the transformer core. To suppress this inrush current, the detail information of the residual flux needs to be known. In this paper, a transient current method for obtaining the residual flux density in the single-phase transformer is proposed. Firstly, two DC voltages with opposite polarities are sequentially applied in the measuring winding, and then two corresponding transient response currents can be detected. Based on above information, an empirical equation in regarding of the residual flux density and the transient current difference will be obtained. To make sure the initial residual flux density does not change greatly, the magnitude of the DC voltage has been determined as well. Finally, the proposed method is verified by the experiment results.