Improved Reliability Through Advanced Short-Circuit Force Analysis in Transformer Windings: 3D magnetic field boundary conditions and dynamic effects

Traditionally, electromagnetic force (EM) analysis relies on analytic or numerical calculations, for example 2D Finite Element (FE) simulations, which can be refined using advanced 3D FE simulations and laboratory testing. These simulations consider factors like boundary conditions and winding misalignment, improving accuracy in force and stress calculations.

This paper analyses how different boundary conditions affect axial forces and stresses in transformers, utilizing 3D and 2D FE simulations to assess helical winding pitch and core saturation influence. It demonstrates the significance of pitch effects on force calculations and suggests incorporating it into simplified 2D approaches by applying an equivalent axial displacement of the LV winding.

Advanced 2D simulations including saturable core with side limb and “fictive tank delta winding”, reveals how ampere-turn (AT) imbalance due to core saturation and inrush current, during SC test, increases axial compression forces on the energized winding. At the same time axial compression forces on the shorted winding are reduced.

Additionally, SC currents and forces are dynamic, with windings responding like mechanical springs. A static-only approach to calculate the axial forces in the windings neglects the dynamic behaviour. Dynamic amplification factors (DAF) should be used to adjust static force calculations to account for dynamic effects when a more in-depth analysis is unnecessary or considered impractical.