Suppression Strategy of the Inrush Current in the Transformer Phase Selection Closing Considering the Residual Flux

The inrush current of the transformer may cause serious safety problems, and the traditional phase selection closing suppression strategy still has room for improvement. In this paper, an inrush current suppression strategy for transformer phase selection closing considering the residual flux is proposed. Firstly, the theory of the inrush current suppression for phase selection closing considering the residual flux is analyzed. Secondly, a transient model of the transformer breaking considering the distributed capacitance is established. Finally, a residual flux estimation method considering the transient voltage is proposed, and the ideal closing time considering residual flux is calculated for phase selection and closing. Using a nuclear power plant auxiliary transformer as a prototype, the simulation platform is constructed. The random closing strategy, the voltage peak closing strategy, and the closing strategy considering residual flux is analyzed. The result shows that the proposed phase selection closing strategy can completely suppress the inrush current under ideal conditions, and the estimation error of residual flux considering transient voltage is reduced by 90% compared to the conventional voltage integration method on average.