Research on Transformer Inrush Current Suppression and Optimal Closing Angle Considering Switching Resistance and Residual Flux

Inrush currents are a common issue in transformer operations, particularly when initial residual flux is present. These currents can lead to mechanical stresses, heating, and increased energy losses, especially during transformer energization. To mitigate these effects, optimizing phase-closing strategies is crucial for both single-phase and multi-phase transformer systems. This paper investigates the inrush current characteristics of single-phase, YY, and YD transformers, taking into account both residual flux and closing resistance, and proposes different phase-closing strategies for each transformer type. Additionally, the inrush current behavior of single-phase transformers is analyzed using theoretical models and simulation verification. The study shows that the proposed strategies effectively mitigate inrush currents in both single-phase and three-phase transformers, providing insights into the design of phase-closing strategies for reducing inrush currents in converter stations.