Tackling infinity

[Smart $]

If we try to find out the run up time of, say, an induction motor, we would find that it takes an infinite time to change from its dynamic state to stable state. So we take time to reach some intermediate stage, say 99.5% of its full load speed as the time for the motor to have attained the stable state. Any thoughts on this? Thanks.

I don't work with motor calculations anywhere near the depth where this would matter.... but the way I see it, an induction motor in a real life application will encounter variances in operating parameters, such as opening an exterior door in relation to an exhaust fan motor, or a pump motor on a system with fluid viscosity changing from operating processes.

Given the preceding, I'm inclined to agree with Curious Nerd...

Once you get close enough to be inside the range of the normal speed changes it no longer matters.

So IMO you would base it on the LRV parameters, and that is subject to change per application.

 

[Haji]

Thanks all for your replies.

Theoretically, the motor never reaches steady speed for a constant load but comes very close to steady speed within a finite time.

It does not happen that the motor takes an infinitely long or even long time to attain almost steady speed; otherwise the motor O/L would operate to trip the motor.

Therein lies our mastery over infinity: by choosing suitable parameters for the motor, we are able to make the motor come very close to steady speed within a finite time.

How are we doing that?