The electric machines can start operating from the instant in which the electric current is capable of producing a magnetic field, which when it varies in relation to a conductor, causes an electric current. Two magnets are constituted, one being in the stator and the other in the rotor, in which its interaction generates the movement of the motor. In the three-phase motor, the distribution of the coils of the three phases in the stator, degressed by 120 degrees, ends up making the sum of the magnetic fields generated by each of them is a uniform and rotating field. https://www.mrosupply.com/electrical/transformers/2835710_c1f1c0les_hps/ This field capable of circulating in the magnetic stator and rotor cores causes a current flow in the rotor bars.
In this way, the rotational current produces a magnetic field that must oppose the movement that caused it, in relation to the opposite poles of the stator. In this way, the stator field has the possibility of pushing the rotor at the exact moment of rotation, however, always with a considerably higher speed, thus causing the rotor to slip in relation to the rotating field. When a load is inserted into the motor shaft, the rotor slows down, increasing sliding.