There are three - phase symmetrical windings AX, BY and CZ in the stator core of three - phase asynchronous motor. Suppose the three-phase windings are connected into a star and connected to the three-phase power supply. Then the three-phase symmetrical current is fed into the windings and its waveform is shown in the figure below. Take the direction from the beginning to the end of the winding as the reference direction of the current. When the current is positive half cycle, its value is positive, and its practice direction is the same as the reference direction. In the negative half cycle, the value is negative, and the practice direction is opposite to the reference direction. The stator core and windings do not roll. The three phase currents in the stator windings change with time and phase, and the three phase magnetic potential adds up to a rotating magnetic field. The rotating stator magnetic field will induce a rotor magnetic field in the rotor winding and cause rotor rotation when cutting rotor guide bar. Because of the requirements of the induction field, the rotor speed is always slightly slower than the stator field speed, there is a slip, which is the name of induction asynchronous motor. If the rotor is a permanent magnet or a stable magnetic field generated by the rotor field winding, then the rotor speed synchronizes with the stator field speed, forming a synchronous motor.