Study on Electromagnetic-Mechanical Coupling Effect of Transformer Winding under Short Circuit

Windings' electromagnetic(EM) forces are traditionally calculated based on the current density as well as coils' static position. However, coils' position can change significantly during the external short circuits and consequently changes EM forces. To further investigate the coupling effect between EM forces and coils' dynamic position, this paper firstly proposes a model to calculate EM forces based on the image method and the influence of coils' position on EM forces is discussed. Then, EM forces were taken into the numeric solution of windings' displacement and EM forces where the EM forces are recalculated according to the current density and dynamic windings' axial displacement in each time step. Finally, the above methodology is deployed to investigate the windings' dynamic forces and displacement of an SZ-50000/110kV transformer during short circuit. The results show that the radial component of EM forces is barely influenced by the coil displacement, but the maximum axial EM forces and displacement are higher than the results without coupling. When the natural frequency of winding is close to the excitation frequency, the axial forces increase. The proposed model can be used in analyzing windings' dynamic responses during external short circuits.