taking into account the definition of pull-up torque:
Pull-up Torque: The Pull-up Torque is the minimum torque developed by the electrical motor when it runs from zero to full-load speed (before it reaches the break-down torque point)
When the motor starts and begins to accelerate the torque in general decrease until it reach a low point at a certain speed - the pull-up torque - before the torque increases until it reach the highest torque at a higher speed - the break-down torque - point.
The pull-up torque may be critical for applications that needs power to go through some temporary barriers achieving the working conditions.
I can't find anywhere in this text( and in other articles on the subject) WHY the torque lowers a bit(inflexion point) and then it raises again. What is the mechanical explanation for this?
Answer
This is what Allen Bradley say about pull-up torque: -
Please click on picture to help but in words, the specific sentence is: -
Pull-up Torque is caused by harmonics that result from the stator windings being concentrated in slots. If the windings are uniformly distributed around the stator periphery, Pull-up Torque is greatly reduced. Some motor design curves show no actual Pull-up Torque and follow the dashed line between points A and C.
Info taken from this document entitled
Drive Fundamentals, Drive/Motor Basics, Revision 1.0
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