Can anyone tell me how to find the optimal operating speed of a 3-phase motor. That is, the speed at which the most input power goes into shaft power, and the least is wasted in heat/other losses. Any references to good online sources would be helpful.

Thanks

 

Hi,

Not a specified answer to your question but losses in motor are not determined only by speed.

Regards,
[email protected]

 

Responding to Qball's query:

For an induction (asynchronous) motor the maximum efficiency occurs when load losses equal no-load losses.

The above is based on the standard motor model, from which output torque, hence output power, and efficiency, vs speed can be calculated. Differentiation of the efficiency curve with respect to speed will yield the speed at which maximum efficiency occurs. Alternatively, a "Circle-Diagram" can be constructed using the calculated stator and rotor parameters! Typically, either method will yield a max efficiency between 75 and 90 % of rated load. Please note, however, that the model or circle-diagram approach is sensitive to the accuracy with which the parameters are determined, while the method of equating no-load to load losses will introduce smaller errors!

One of the best references on efficiency determination can be found in NEMA Standard MG-1 covering Motors and Generators. Test methods and parameter determination are contained therein.

Regards,
Phil Corso, PE Boca Raton, FL
[[email protected]] ([email protected]) {[email protected]}

 

As long as I understand:

First of all, What is driven by the motor? Because usually you should not look not for motor but what is moved by the motor, and this is going to have a rendiment curve.

If you are desingning an installation you would like to obtain the maximun monetary economy, this is to be done by running the motor at its maximun speed, because it will give Power=Torque*angular_speed. The motor has a nominal torque should not be increased.

If you are connecting the motor directly to the mains, the maximun rendiment is going to be in a 1 pair of poles motor, because the wirings are simpler and the magnetic field created inside is better.

Best Regards,
Forgoselo

 

http://www.mech.uwa.edu.au site:a quite good explanation about 3-phase motors and performance/speed calculations.