Numerical study on temperature rise and mechanical properties of winding in oil-immersed transformer

In the present paper, the electromagnetic-fluid-thermal-mechanical stress coupling process in an oil-immersed transformer is numerical studied with finite element method. The relationship between electromagnetic force and flux leakage, interaction of losses, temperature and oil flow, and the influence of electromagnetic force and temperature rise on mechanical characteristics of coil are carefully analyzed. Firstly, the leakage flux is mainly generated at the ends of coil and core corner end. The electromagnetic force of B-Phase low voltage coil is the highest due to the leakage flux superimposition caused by A-Phase and C-Phase coils and higher current on B-Phase low voltage coil itself. Secondly, the interaction between losses, temperature and oil flow is remarkable. Compared with the results as heat source is constant, the loss density of high and low voltage coil increased by 18.18% and 14.87%, respectively, and the hot spot temperature increased by 7.06 K. Finally, it is revealed that the coil deformation is mainly caused by thermal load, and little affected by electromagnetic force. The frequency of stress is twice as high as that of energized current. The stress at both ends of the coil is the highest and it would lead to fatigue failures.