Induction motor At constant RMS current and different frequencies.

[James20]

What will happen with Power and Torque if I supply simple induction motor with constant RMS current at different frequencies.

Let's consider "Ideal" Motor. No or very low losses (Eddy current, friction , stray , hysteresis and so on).

Let's say range 50Hz to 500Hz , interval 10Hz.

Power at constant RMS AC Sinewave current ranging 50Hz ... 500 Hz
Increasing, Stays the same, Decreasing

Torque at constant RMS AC Sinewave current ranging 50Hz ... 500Hz.
Increasing, Stays the same, Decreasing

Thank you.

 

[crutschow]

For an ideal motor:
The torque is determined by the load.
So, since motor speed is proportional to frequency, for a constant torque load, the power output and the power (current) input to the motor will also increase.

 

[rjenkinsgb]

AC Induction motors are usually rated for maximum load with a certain "slip"; eg. A common 50 Hz speed is 1440 RPM. That's 4% slip. (4% less than synchronous speed).

Assuming you keep the load adjusted to maintain 4% slip over the speed range, I'd expect the torque to initially increase as the frequency increases then drop off as eddy current and inductive losses reduce efficiency.

(Mechanically, any large motor is likely to disintegrate before 10x rated speed! They do have some safety margin, but nowhere near that, more like 1.5x to 2x speed at most).

 

[James20]

Also The rms of supply current is kept constant at 50...500Hz frequencies.

 

[crutschow]

Also The rms of supply current is kept constant at 50...500Hz frequencies.

Do you mean the voltage is kept constant?

 

[ChrisP58]

Generally, the supply voltage is constant and the load draws whatever current it needs to do the work at hand.

You can supply a constant current, but then the supply voltage must vary to match the required power.

Generally, constant current supplies are really voltage supplies whose output voltage is varied to keep the current constant.