The AC electric motor is made up of a three-phase winding, which is composed of three single-phase windings spaced apart from each other by 120 °. AC motors are based on the principle of the rotating field and that to achieve this field there must be several windings, notably one per phase, around the magnetic cores in the stator that formed the pole pairs of an electromagnet.

If this winding is fed by a three-phase system, the currents I1, I2 and I3 will likewise create their own magnetic fields H1, H2 and H3. Thus, as they are proportional to the respective currents, they will also be time lagged by 120º between them and can be represented by a graph.

The resulting total field H will be equal to the graph sum of the three fields H1, H2 and H3 at that instant. We then check this graph sum for six successive instants and thus, when a three-phase winding is fed by three-phase currents, a rotating field is created, as if there were a single pair of rotating poles of constant intensity. As the rotating field rotates according to the maximum and minimum current flowing through each winding, the faster the current will alternate.