Winding Arrangement Effects on Electromagnetic Forces and Short-Circuit Reactance Calculation in Power Transformers via Numerical and Analytical Methods

Calculation of radial and axial forces and leakage reactance of transformer coils is performed in many papers using different analytical and numerical methods. But most of the analytical methods are extended only for transformers with uniform equal-height windings and then are not very accurate for transformer with no uniform winding arrangement. In this paper, some simple techniques for calculating leakage reactance and forces acting on the transformer coils are presented. This study is accomplished by using 2-1) planar models utilizing the finite element and Roth methods. Just by modeling the transformer and using FEM, the magnetic vector potential is calculated over each node of model and then using several post-processing procedures, the transformer leakage reactance is calculated. Also, this reactance is obtained by analytical method (Roth method) and then results are verified by experiments. The short circuit current and hence the radial and axial forces on the transformer coils during short circuit condition are calculated. Considering some especial cases, the impact of the windings arrangement on the axial force is analyzed and net axial force acting against the yoke are calculated