Inrush, LRA and Motor Load Question

[leeave96]

With regards to an AC electric motor, if the locked rotor amps (LRA) are known, can one expect the inrush current at start-up to be higher if the motor is starting with a load present vs unloaded? How would this be same/different with a single vs 3 phase motor?

Thanks!
Bill

 

[Marke]

Hello Bill

If you are full voltage starting your motor, the start current will be independent of the load and after an initial very short inrush, will drop to the Locked Rotor Current and then dropping as the motor accelerates.
Load on the motor will affect the time to reach full speed.
The current for any given motor, full voltage started follows the speed current curve for that motor.

Best regards,

Mark Empson
L M Photonics Ltd

 

[ScottyUK]

Adding a little to Mark's post, the inrush is present as a transient condition while the magnetic fluxes in the stator settle down to steady state conditions. You would need some reasonably fast instruments to capture this. LRA will persist for as long as the rotor is locked, but as the rotor accelerates it drops way, eventually falling to running current.


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