An electrical device consisting of  two or more coupled windings, with or without a magnetic core, for introducing mutual coupling between electric circuits. Transformers can be used to control voltage and phase shift (active power flow).<br /></p><p>A power transformer may be composed of separate transformer tanks that need not be identical.<br /></p><p>A power transformer can be modelled with or without tanks and is intended for use in both balanced and unbalanced representations.   A power transformer typically has two terminals, but may have one (grounding), three or more  terminals.<br /></p>