ABSTRACT
This chapter introduces the basic theory of short circuits as applicable to transformers. It discusses thermal capability of transformer windings under short-circuit forces. The short-circuit strength of a transformer enables it to survive through-fault currents due to external short circuits; an inadequate strength may lead to mechanical collapse of windings, deformation/damage to clamping structures. Generator transformers are generally subjected to lower short-circuit stresses than interconnecting autotransformers. A high value of the generator impedance in series with the transformer impedance reduces the fault current magnitude for faults on the high voltage side of the generator transformer. In the case of bending, the actual short-circuit stress should be less than the yield strength of the material. Short-circuit stresses decide their dimensions. The stresses in the frames are determined from the calculated values of short-circuit forces acting on them and assuming the core bolt points and locking arrangements between flitch plates and frames as support locations.
