ABSTRACT
Transformers must be 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 force applied to the tie bars during a fault is produced by the coils. Although the forces applied to the coils are proportional to the current squared, because of the coil's internal structure, the force transmitted to the tie bars may be modified. During a short circuit, the leads or busbars are subjected to an increased force due to the higher fault current they carry together with its interaction with the higher leakage flux from the main windings and from nearby leads. Because controlled short circuit tests are rarely performed on large transformers to validate a transformer's mechanical design, there are few empirical studies that directly test the theoretical calculations.
