Question on induction motor

[yzou_ua]

The IM I have is a "wound rotor IM", whose rotor terminals are accessible (just like 3 stator terminals, so I have 6 terminals)...
Suppose I use another motor to drive this wound rotor IM rotating and meantime feed three ROTOR terminals by 3ph sinusoidal voltages(synchronous w. rotor position), and leave the three STATOR terminals OPEN. Then, what the ph-ph stator voltage would be? Anything there? I know they won't be synchronous w. rotor voltage, but are they gonna be 3ph sinusoidal as well??

 

[emontllo]

If you compensate the mechanical rotation with a reverse rotating magnetic field the magnetic field will be almost constant. Supposing of course an ideal winding and a perfect compensation of the rotation.
In this case the magnetic field variation (dB/dt) would be zero from the point of view of the stator; therefore, the induced electric voltage should be zero. Of course, the voltage will not be exactly zero in the real application.

 

[yzou_ua]

constant magnetic field?? Then the rotor speed is reducing as well??

If you compensate the mechanical rotation with a reverse rotating magnetic field the magnetic field will be almost constant. Supposing of course an ideal winding and a perfect compensation of the rotation.
In this case the magnetic field variation (dB/dt) would be zero from the point of view of the stator; therefore, the induced electric voltage should be zero. Of course, the voltage will not be exactly zero in the real application.

 

[emontllo]

I mean, it will be constant from the point of view of the stator. This will happen if you rotate the magnetic field (applying a sinusoidal voltage at a frequency = motor speed * nº of motor poles) in the oposite direction of the rotation. (Always in a ideal model) the net magnetic field vector will be fixed in direction and magnitude.

If you apply this sinewave in the same direction, the frequency of the sinusoidal voltage at the output of the stator will be 2 x input frequency...

 

[FvM]

In a short, the output frequency will be either the sum or difference of electrical rotation frequency and applied signal frequency.

 

[yzou_ua]

Thank you, FvM and emontllo ! I think I got it...

In a short, the output frequency will be either the sum or difference of electrical rotation frequency and applied signal frequency.