Thread: VFD question
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Old January 12th, 2021, 02:41 PM   #5
jraef
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Join Date: May 2006
Location: Northern California
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If you apply 400V to a motor connected for 660V, the motor will develop only 58% of its running torque, and more importantly, only 33% of its PEAK torque capability. Peak torque (Break Down Torque) is what the motor uses to accelerate or re-accelerate after a step-change in load. So what usually happens is that either the motor fails to accelerate in the first place and stalls, or if it does manage to accelerate because the load is very very light, it stalls whenever there is a change in the load.

It CAN however work OK if the load is roughly 1/3 to 1/2 of what the motor is capable of. Why you would have a motor that is 2X to 3X the size it needs to be is another issue though. I have run into this when someone has a motor that was designed for a different task and is being repurposed. It may be far larger than necessary but is already owned as opposed to buying a new correctly sized motor.
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