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Anonymous Poster #1

VVVF Drive- Multi Motor Application

08/06/2013 1:26 AM

If a single VVVF Drive is used to operate two or more sq cage induction motors in parallel (e.g. for EOT crane LT drives), will dynamic braking (with a brake chopper & resistance) be effective to stop both the motors simultaneously ? Is there any special protection needed for such an application ?
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PWSlack
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#1

Re: VVVF Drive- Multi motor application

08/06/2013 3:02 AM

Presumably this scheme has been discussed and approved by both the crane's original supplier and the facility's insurance company?

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Tornado
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#2

Re: VVVF Drive- Multi motor application

08/06/2013 4:09 AM

No; yes; separate drives.

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JRaef
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#3
In reply to #2

Re: VVVF Drive- Multi motor application

08/07/2013 12:10 PM

What he said.

If you do not have separate drives, how do you compensate for wheel slippage or rail buildup anyway? I never recommend a single VFD on an EOT crane long enough to need two drive motors. That's a bad design at the outset.

But braking makes it even worse. Dynamic Braking uses kinetic energy off of the load as braking energy via regeneration through the motors. Each motor will have a different amount of load on it, and therefor differing amounts of kinetic energy to try to share, it will never be even. Therefore one motor will always bear the brunt of the braking while the other goes along for the ride.

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