Research on multi-physical field coupling modeling and multi-condition dynamic load capacity evaluation of oil-immersed transformers

To address the issues of low coupling accuracy and poor adaptability to time-varying boundaries in traditional transformer thermal analysis, an electric-magnetic-flow-thermal multi-field coupling simulation model was constructed for the S11-M-630/10 oil-immersed transformer. This model covers electromagnetic fields, eddy current losses, oil-solid heat conduction, and natural convection characteristics. The discrete-velocity lattice Boltzmann method (DDF-LBM) based on dual distribution functions was introduced to achieve efficient decoupling and solution of the non-steady thermal flow field. Combined with nonlinear temperature-dependent material properties and typical daily cycle boundary conditions, the dynamic evolution mechanism of the hotspot temperature rise of the winding was systematically characterized. The model was verified by measured temperature rise data, with an error control within 4.1%. It has good engineering adaptability. On this basis, hotspot response simulations under different load rates, operating times, and seasonal temperature fields were carried out. The results show that there is a significant synergistic amplification effect between load rate and ambient temperature on the hotspot temperature rise. Especially in the summer high-temperature and heavy-load conditions, the hotspot temperature can exceed 116 °C, and the local winding temperature gradient reaches 8.4 °C. The insulation life shows an exponential decay trend. The research results provide theoretical basis and technical support for the thermal management optimization and operational safety of oil-immersed transformers in the context of high penetration of new energy.