locked rotor current > FLA? 1

[mcteach]

Is locked rotor current always, and I do mean always greater than full load current. I know shaded pole motors LRA is close to FLA,
is their LRA always greater than their FLA? Is there ever a motor or condition where FLA could be greater than LRA?

 

[jraef]

Don't see how that could be. FLA = Full Load Amps, so how could locking the rotor not result in the motor being at LEAST fully loaded? The definition of "Load" would need to be something not related to shaft power, and why would one have a motor if that's the case?

So curious minds what to know why you are asking this question? Have you observed something along these lines?


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[mcteach]

I have not observed something else, I want to be sure the term always would apply to what I am trying to write. I want to avoid a blanket statement if there are any exceptions. Thank you for your reply.

 

[waross]

The terms "Locked Rotor Current" and "Full Load Amps" and particularly "Locked Rotor Current" are mostly used in connection with squirrel cage induction motors and synchronous motors.
In the case of torque motors locked rotor amps and FLA are often equal.
A wound rotor motor may be configured as a torque motor with lots of rotor resistance. In this case, the locked rotor amps may be less than rated full load amps. Of course the motor will not produce full load power with that much rotor resistance.
Actually, without supplementary cooling, the locked rotor amps will be a lot less than rated full load amps.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[stevenal]

So with the locked rotor providing no power to the mechanical load, you are a long way away from the full load condition.

 

[catserveng]

Wasn't this discussed some years back,

http://www.eng-tips.com/viewthread.cfm?qid=134051

When that discussion came up I also found this in regards to motors I have found helpful over the years,

http://literature.rockwellautomation.com/idc/groups/literature/documents/at/ic-at001_-en-p.pdf

MikeL.

 

[TugboatEng]

FLA or full load amps is the current the motor operates at when operating at its nameplate power rating. SEA or safe full amps is the highest current the motor can operate at continuously. It's the FLA multiplied by the service factor. Typically 1.15-1.25 times the FLA. LRA is the maximum current the motor can possibly dra. It's typically 4-6x FLA and calculated by measuring the resistance of the windings and voltage applied. It's the inrush current during a direct on line motor start.