Take three sinusoidal voltages of the same amplitude and frequency and dephase them by 120 degrees to create a balanced three-phase system. Such systems, easily generated by an alternator, distribute power in such a way that there is little loss along power lines.

Three phase systems, used all over the world, have other advantages. Running these dephased currents through coils geometrically shifted 120 degrees from each other creates a magnetic field. Remarkably, this magnetic field is "rotating". Thus a rotating magnetic field can be created from a fixed armature winding.

This opens the door to "electric" rotating machines.

Click on the "vector addition" button to see the superposition of the three individual magnetic field vectors.