ABSTRACT
Transformers must be mechanically designed to withstand the large forces that occur during fault conditions. Fault currents for the standard fault types such as single line to ground, line to line, double line to ground, and all three lines to ground must be calculated. The electromagnetic forces acting on the coils can be obtained using an analytic or finite element magnetic field calculation in conjunction with the Lorentz force law. This chapter focuses on the stresses produced by the axial forces, and considers the stresses due to the radial forces. It examines the worst-case stresses in the copper winding turns, key spacers, pressure rings, and tie plates, which are attached to the top and bottom clamps. The maximum axial compressive force is used to determine the worst-case compressive stress in the key spacers. The tie bars or tie plates are used to join the upper and lower clamping structures, which keep the coils under compression.
