Marco Gaxiola via EV wrote:
I have a question: Is that possible to have an AC induction motor to work apparently normal but, after a moderate use, get the rotor coils very hot? Not the stator neither the controller, just the rotor.
Yes. The rotor is in effect the secondary of a transformer. This secondary is *shorted*, which leads to the high current, and heating. But the current produces a magnetic field. The stator coils create a rotating magnetic field that drags the rotor field along with it to make the motor work.
The rotor windings are usually low resistance, to minimize losses and heating. However, it is pretty common to wind (cast) the rotor windings in aluminum, which has higher resistance and more heat. High rotor resistance also makes the motor easier to start, so it's sometimes done deliberately.
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