The Short-Circuit Radial Response Of Core-Form Transformer Coils

The straps near the high-low space of a heavily-loaded core-form transformer can be deformed plastically during a short circuit. The radial deformation increases the mechanical stress on the strap insulation, enlarges the high-low space, and increases the transformer impedance. A computer program that calculates the radial deflections and hoop loads of a disk-type core-form coil during short circuits is described; it includes models of the applied electromagnetic load distribution, the elastic-plastic characteristics of the strap material, and the nonlinear stiffness of the strap insulation. The program was verified with a pneumatic test rig which is described. The effects of strap material, coil tightness, and interface stiffness on the radial response and stresses of a disk coil during a short circuit were studied with the program; some typical results are given.