Hi all,

I am interseted in being able to generate (calculate) speed torque curves for motors. I work in a motor repair shop, and would have the ability to perform electrical tests and visual observations as necessary to help achieve decent results. I am curious how it is done, and if I can perform this type of service in my environment.

Thanks, sean

Your best bet is the IEEE 112 standard. The measurement of the speed-torque is described there in great detail. The speed-torque curve is based on the measurement of the elements of the equivalent diagram. However the measurements are not easy to do. First of all you need a 3-phase variable voltage source with sufficient current capacity (It must be a sine wave source, such as the induction regulator. The variable speed drive is not good). Performing a no load test is a must. It is also necessary to measure the impedances at the nameplate currents, in order to account for the saturation effects. Anything less will introduce unacceptable errors.
Even more difficult is measuring the rotor resistance and reactance. Since the frequency in the rotor changes from line frequency to a virtual zero, you have to measure the resistance and reactance at several frequencies lower than the line frequency. You have to get to sufficiently low frequencies to be able to extrapolate the curves all the way to zero frequency. The resistance of the rotor easily triples as the frequency is increased. On the other hand the reactance drops in a similar manner. All measurements involve measuring currents, voltages and watts.
I would say that what you learn performing the test is priceless.
jank