I'm a bit confused with this question.

Given the high torque cage induction motor name plate data

and the full equivalent circuits parameters

The friction and windage loss is 0.910 kW and may be considered constant

over speed range 1500 rev/min to 1000 rev/min.

It is required to control the speed of the motor over a limited range by voltage control.

I need to determine for a motor speed of 1355 rev/min:

a) the required stator line voltage;

b) the motor efficiency at 1355 rev/min;

c) comment on the suitability of running the motor in this reduced voltage mode.

I'm finding it difficult to fined much information on this kind of question. For part 'a', isn't the stator line voltage = (√3)(Phase voltage)?

Is phase voltage = 415V

I can't see how how the motor speed relates to the voltage Can anyone show me the formulas required in this?

I also can't fined anything on determining the efficiency at a given speed.

Thanks a lot guys