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Driven Object Drive The Rotor Of Ac Motor

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#1 AB2005


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Posted 26 October 2008 - 01:05 AM

Dear Friends

I have some confusion in my mind which i want to clear before startimg a project:

A simple AC motor is connected with VFD and drives a roller, what happen with VFD if roller drives the rotor of motor at about 80% of motor's desiagned speed (if VFD is powered but in stop mode)? Can back EMF dammage the VFD?

"Don't assume any thing, always check/ask and clear yourself".

#2 marke


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Posted 27 October 2008 - 08:19 AM

Hello AB2005
Provided that the VFD is not supplying any voltage to the motor, there will be no problem.
A spinning motor will generate voltage at it's terminals provided there is some excitation to the rotor. This is caused by voltage applied to the stator. There is some residual magnetizim in the rotor which decays to a low figure after the driving voltage is supplied. The output voltage from the motor will not be high enough to cause problems to the VFD.

If you start the VFD with a spinning rotor, there can be major problems unless the VFD is able to and is set up to "catch a spinning rotor".

Best regards,

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