Transformers work by receiving alternating current (AC) power at one voltage and delivering it at another voltage, allowing for more efficient long-distance power transmission. They operate using electromagnetic induction: a varying magnetic field induced in one coil by a current in another coil causes a voltage to be induced in the second coil. Transformers are made up of coils wrapped around a ferromagnetic core, allowing the magnetic field to be effectively coupled between the primary and secondary coils. This induces an alternating current in the secondary coil that is proportional to the number of turns in each coil, allowing the output voltage to be stepped up or down. Three-phase transformers use three single-phase transformer cores arranged in a special configuration to provide three-phase power.