Induction Motor Rotor Speed: Beyond Synchronous Speed

[boonsiang]

What will happen if the rotor speed becomes larger than the synchronous speed for induction motor?

 

[Averagesupernova]

Instead of the motor being an inductive load it will become a capacitive load.

 

[Antiphon]

The sneaking suspicion is that it will become negative capacitive.

In order to make the shaft spin faster would not energy need to be delivered into the shaft instead of extracted from it?

 

[Averagesupernova]

The sneaking suspicion is that it will become negative capacitive.

In order to make the shaft spin faster would not energy need to be delivered into the shaft instead of extracted from it?

Yes energy will need to be delivered to the shaft. And the motor will resist this torque. It will expend energy to do this and will look like a capacitive load.

 

[Antiphon]

The motor with a light mechanical load looks slightly inductive. Positive power enters the motor and leaves through the shaft minus some small losses.

If the shaft is forced to rotate faster than the line, it's reasonable that it would look capacitive. If however power is being delivered to the shaft and subsequently delivered to the generator, then the capacitance would appear to be negative. No?