When an Induction motor is supplied by 3 phase AC source on the rotor side and the stator terminals are short circuited through resistances the Induction motor is called as Inverted Induction motor or rotor fed Induction motor.
This configuration is only possible for Slip ring Induction motor (SRIM) and not for Squirrel cage Induction motor (SCIM).
Step 1 :- A 3 phase AC source of frequency “f” is connected on rotor.
:-rotor produces a rotating magnetic field that rotate at Ns (rpm) w.r.t rotor.
Step 2:- Rotor magnetic fields cuts stator conductors induced e.m.f and due to short circuit produces current in stator.
Step 3:- To reduce relative speed Nrel w.r.t stator rotor rotates in opposite direction to the magnetic field
In Induction motor the rotor rotates in the same direction as the rotating magnetic field but in case Inverted Induction
the rotor rotates in the opposite direction to the magnetic field
Speed of rotor magnetic field (rmf) w.r.t rotor = Ns
Speed of rotor = Nr
Speed of rotor magnetic field w.r.t stator = (Ns-Nr) = s*Ns
Frequency induced in stator = (P∗s∗Ns)/120 = s*f
Relative Speeds Of Normal Induction Motor
Relative Velocity=Actual velocity -Velocity of Observer
Relative Speeds Of Inverted Induction Motor
In Inverted Induction motor the roles of stator and rotor are interchanged and that is why sf frequency is produced on the stator and “f” frequency on the rotor.