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Vfd Behavior


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#1 onyxgaze

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Posted 02 October 2010 - 12:45 PM

I have a vertical schumacher type desolventiser which has a shaft with wiper arms affixed to move solid biomass from chamber to chamber.

The motor driving this shaft is drawing near abouts full load amps.

If i use a VFD and reduce the speed, will the current drawn by motor reduce?

I was told the intertial load of the shaft would reduce with reduced speed and this will reduce the load on the motor thus reducing current.

For such an equipment would a constant torque (vector control) vfd or a v/f (scalar) control VFD be suitable?

Thanks in advance.


#2 jOmega

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Posted 04 October 2010 - 02:36 PM

QUOTE (onyxgaze @ Oct 2 2010, 06:45 AM) <{POST_SNAPBACK}>
I have a vertical schumacher type desolventiser which has a shaft with wiper arms affixed to move solid biomass from chamber to chamber.

The motor driving this shaft is drawing near abouts full load amps.

If i use a VFD and reduce the speed, will the current drawn by motor reduce?

I was told the intertial load of the shaft would reduce with reduced speed and this will reduce the load on the motor thus reducing current.

For such an equipment would a constant torque (vector control) vfd or a v/f (scalar) control VFD be suitable?

Thanks in advance.



With the limited information provided, the answer would be ... either.

Unless the inertial load is in a state of continual acceleration, the inertial load would drop off once stead state speed is attained. At that point, the load should be friction and windage and fixed losses; which you have not identified for consideration.

You have not said anything about the importance of speed regulation, both dynamic and static; are either a consideration?

Nor have you related anything about the constancy of the load over time, particularly once the wiper is up to speed; does the load remain constant ? or is it subject to changes for whatever reason? etc.

By definition, a Constant Torque drive is one that it capable of supporting motor rated torque over a specified operating range. For example, a 4:1 turndown of a 1500 rpm motor rated for constant torque means that from 375 to 1500 rpm, the VFD will support the motors ability to produce up-to-and-including rated torque output continuously.

Not being intimately familiar with your particular application, but based upon the knowledge of scraper type applications, I would offer that the steady state load would be primarily made up of friction losses. I would also expect that the friction losses remain relatively constant at any speed; the exception being that speed and friction have a viscous impact that would factor into the load profile; and/oró if at slower speed, the bio-mass packs up on/against/under the wiper, resulting in an increase in friction loading.

Kind regards,




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