Transformers are susceptible to damage by secondary short-circuit currents having magnitudes that can be many times rated load current. The damage results from the following effects: >> The I 2 R losses in the winding conductors are increased by the square of the current. This increases the temperature rise of the windings. >> Because protective devices limit the duration of short circuits (as opposed to overloads), the temperature rise of the winding can be calculated by dividing the total energy released by the I 2 R losses by the thermal capacity of the conductor. >> The short-circuit currents exclude flux in the core and increase stray flux around the core. This stray flux induces currents in metallic parts other than the winding conductors, which can be damaged thermally. >> A short circuit applied to the secondary circuit of an auto-transformer can substantially increase the voltage across the series winding ...