Avoiding Spiraling Effects on Helical Windings with Appropriate Dynamic Axial Short-Circuit-Force Calculation and Evaluation Methods

It is crucial for the operational safety of electrical grids that the windings of power transformers can withstand all external short-circuit events. Although very established methods for evaluating withstand-strength of disk windings are available today, there are mainly uncertain calculations and evaluation methods for evaluating the withstand strength of layer- and helical windings against spiraling effects. In this failure scenario, the tangential forces acting at the top and bottom open winding turns exceed the counteracting frictional clamping and radial support forces, leading to tangential movements of winding end turns and vertical winding lead exits.