Short-circuit stress calculation in oval windings

In this paper an analytical approach for calculation of mechanical strength of oval windings in distribution transformers is presented. The calculation is given for radial forces resulting from interaction of the axial component of leakage flux density and the current in the windings. The analysis is focused on the inner foil winding subjected to radial forces acting inwards where winding could fail either by collapsing or by bending between the supports. The most common failure mode is free buckling where foil conductors (usually outer half of low voltage winding) bulge outwards as well as inwards usually at one specific point along the circumference.