Induction motor fed from rotor.

[ajith.mk91]

What will happen if an induction motor is fed from rotor side. I mean if i supply say 50HZ frequency supply to rotor through slip rings and have my stator windings connected to variable resistances will the rotor start to rotate and if it does in which direction?

 

[Bob S]

The beauty of a normal induction motor is that the rotor is unpowered, and slip rings are not required. These are usually the components, besides bearings, that wear out first. The other important feature is that they are quasi-synchronous.

If the rotor is now powered, slip rings will be required. If you have a 3-phase armature with windings and with 3 slip rings, the rotor will turn in whichever direction the effective magnetic field in the stator is quasi-stationary. Do not forget to use a squirrel cage in the stator, as well as use thin laminated steel in the magnetic circuit. Another problem here is that now the I²R coil losses are now in the armature, not the stator, and the armature is harder to cool.

I have seen small unibearing induction motors (I think maybe shaded pole) where the wound stator is inside a hollow rotor (with squirrel cage). The unibearing (probably sleeve) and output shaft are only at one end.