Power transformers work by transferring energy between circuits via a shared magnetic core. Alternating current in the primary winding creates alternating flux in the core. This flux links secondary windings and induces voltages according to the turns ratio. Because magnetic coupling rather than direct electrical connection carries energy, transformers provide isolation and can step voltage up or down while conserving power minus losses. Carefully designed cores, windings, insulation and cooling systems let them achieve high efficiency and reliable operation at high voltages and large power levels.