Source: Ali Bazzi, Department of Electrical Engineering, University of Connecticut, Storrs, CT. Transformers are stationary electric machines that step up or down AC voltage. They are typically formed of primary and secondary coils or windings, where the voltage on the primary is stepped up or down at the secondary, or the other way around. When a voltage is applied to one of the windings and current flows in that winding, flux is induced in the magnetic core, coupling both windings. With an AC current, AC flux is induced, and its rate of change induces voltage on the secondary winding (Faraday's law). Flux linkage between both windings depends on the number of turns of each winding; therefore, if the primary windings have more turns than the secondary winding, voltage will be higher on the primary than on the secondary, and vice versa. This experiment characterizes a single-phase transformer by finding its equivalent circuit parameters. Three tests are performed: open-circuit test, short-circuit test, and the DC test.