Int J Performability Eng ›› 2022, Vol. 18 ›› Issue (2): 79-91.

Coupled Field Magnetostatic Analysis for Free Buckling in Double Layer Helical Winding of a Distribution Transformer

Vibhuti Rehaliaa,*, Deepika Bhallab, and Genius Waliaa

1. aGuru Kashi University, Talwandi Sabo, Punjab, 151302, India;
bIK Gujral Punjab University, Kapurthala, Punjab,155603, India
• Contact: * E-mail address: vibhu18rehalia@gmail.com

Abstract: Hoop stresses are produced due to the electromagnetic forces in the winding. Free buckling of winding turns can lead to failure of the transformer. Design issues are a major reason for the catastrophic failure of 11kV/433kV distribution transformers. In a distribution transformer (DT), the LV winding is generally of helical type and is asymmetrical. Asymmetry in the transformer design causes change in the direction and magnitude of the forces. In this work, a comprehensive analysis of the short-circuit forces has been done for a DT with a double-layer helical winding with all three of the limbs modelled and phases energized. The forces are computed using magnetostatic analysis of a 315kVA DT. The transformer has been modelled in 3D CAD software and forces are computed using 3D finite element method (FEM) and the results obtained are compared to that obtained from first principals. The windings are assessed for the presence of hoop stresses in its turns, and along with it the safety factor is computed for free-bucking using von-Mises equivalent. The intent is to find the weak section of the double layer helical winding from short circuit forces a transformer is designed to withstand. Such simulations of energy conversion create a robust and sustainable design, which can prevent catastrophic failure and reduce the environmental impact due to major repairs or replacement of equipment.