In a conventional 3-phase induction motor, a balanced 3-phase supply is fed to the stator of the motor from the supply mains. Whereas, in an inverted or rotor fed induction motor, the rotor has 3-phase windings and being fed with the 3-phase balanced supply from the AC mains. The rotor windings of the inverted induction motor must be in star configuration.
The figure shows the block diagram of a typical inverted or rotor fed induction motor.
The stator of the inverted or rotor fed induction motor has three phase windings which are short-circuited. The rotor also has 3-phase windings which are connected in star configuration. The end of each coil terminates to the slip ring. The slip rings are mounted on the rotor shaft and the brushes ride on the slip rings. The three phase supply is fed to the motor through the slip rings.
When the rotor windings are fed from a balanced 3-phase supply, a rotating magnetic field is established in the rotor. The rotor rotates in the same direction as the rotating magnetic field of the rotor.
By the action of electromagnetic induction, the rotating magnetic field of the rotor will create an induced EMF and hence the current in the stator windings. Therefore, there is also a magnetic field due to the currents in the stator windings. These two magnetic fields try to oppose each other. Consequently, the rotor goes to be slow or to be stopped. The speed of the rotor depends upon the difference between the frequency of the stator and rotor, i.e., (fs - fr).