rotor time constant or magnetizing inductance identification

[abfer]

I need to find an induction motor's rotor time constant or magnetizing inductance (Lm) via inverter and while motor is at standstill. One way which i know is using bemf. But this method requires transient voltage measurement and the filter attached to the sensor doesn't allow to measure this transient and damps it. Are there any other methods to find either of them?

 

[Skogsgurra]

The rotor time constant is normally in the hundreds of milliseconds to seconds order of magnitude. I imagine that your filter has a cut off frequency well above 100 Hz, which corresponds to a 1.5 ms time constant.

So your filter will not influnce your measurement at all. Just go on measure!

Gunnar Englund

http://www.gke.org

 

[abfer]

I think you're right but the simulation that i run on simulink was problematic. May be i should try it on real hardware to decide.

 

[electricpete]

I don't understand what you are tring to measure and how you are measuring it?

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[abfer]

I'm trying to measure the voltage accross the rotor circuit. First i'm applying dc signal until it saturates then cut off the signal and measure the voltage accross the motor terminals. In this case stator circuit has no effect since it's open and behavior of the voltage is dependent on rotor circuit parameters. It decays exponentionally. We use this to find rotor time constant.

 

[electricpete]

That makes sense (as long as stator is connected wye).

Rotor current decays proportional to Lrotor/Rrotor.

Stator voltage is proportional to rate of change of rotor current. Characteristic of exp(-t*L/R) is the derivative is still proportional to exp(-t*L/R).

How this Lrotor would related to equivalent circuit parameter rotor leakage inductance L2 = X2/(2*pi*f) I'm not sure. I would think it would be a different parameter. Leakage inductance relates to flux not linked from rotor current to stator current. No stator current in this experiment so now way to tell what's linked or not.

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[abfer]

L is not leakage inductance. It's the sum of leakage and magnetizing inductance.