To know the operation of an asynchronous motor, we must see that it is realized from the moment the windings located in the stator cavities are subjected to an alternating current, generating a magnetic field in the stator, and consequently, in the rotor, guaranteeing the an induced electromotive force due to the variable magnetic flux that will cross the rotor.
A f.e.m. induced is responsible for giving rise to a current induced in the rotor, which tends to oppose the cause that gave rise to it, and can thereby create a rotating movement in the rotor. As it is possible to examine, the principle of operation of the induction motor is based essentially on two important laws of electromagnetism, the Law of Lenz and the Law of Faraday.
According to the scientist Faraday whenever the surface embraced by a circuit has a variation of flow, an induced electromotive force will be generated in this circuit. If the circuit is closed, it will be driven by an induced current. Already Lenz asserted that the direction of the induced current is such that this by its magnetic actions always tends to oppose the cause that gave rise to it.