Analyzing short circuit forces in transformer with single layer helical LV winding using FEM

The low voltage winding in a distribution transformer is generally helical type. As the helical winding winds up relative to the high voltage winding, the electromagnetic forces along the circumference would change due to inherent asymmetry. During short circuit condition these forces are of very large magnitude. In this paper the short circuit forces in the single layer helical winding are computed using Finite Element Method (FEM) with an objective of finding the nature of axial forces and identifying regions where maximum stresses occur. The calculations are carried out for a 3 legged 630kVA, 11000/433V transformer. Asymmetry due to tapping is also considered separately.