Reducing VFD Power output without reducing speed?
Reducing VFD Power output without reducing speed?
(OP)
Hi,
My client wants to run a 500HP Pump with a 1000HP motor run on a VFD. Is it possible for the VFD to reduce the power output of the motor without reducing the motor speed?
I think if we end up reducing the motor speed, we will compromise pumping capacity as well.
Let me know what your thoughts are.
Thanks,
My client wants to run a 500HP Pump with a 1000HP motor run on a VFD. Is it possible for the VFD to reduce the power output of the motor without reducing the motor speed?
I think if we end up reducing the motor speed, we will compromise pumping capacity as well.
Let me know what your thoughts are.
Thanks,





RE: Reducing VFD Power output without reducing speed?
If the pump requires 1000HP to pump what needs to be pumped at the rate and/or pressure it needs to be pumped at, then the pump will pump roughly 1/2 of that if you only give it 500HP woth of power. Why would he think otherwise?
However, if the pump only REQUIRES 500HP to pump what needs to be pumped at the rate and/or pressure it needs to be pumped at, then having the VFD will in effect make the 1000HP motor into a 500HP motor, albeit at a reduced speed, because that is part and parcel to what a VFD does.
So without someone doing an in depth study of what is truly NEEDED from the pump system, there is no viable answer to the question yet.
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RE: Reducing VFD Power output without reducing speed?
Bill
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"Why not the best?"
Jimmy Carter
RE: Reducing VFD Power output without reducing speed?
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If we learn from our mistakes I'm getting a great education!
RE: Reducing VFD Power output without reducing speed?
So here is what a VFD really does for you. If the load only requires half of the mechanical power that the motor is capable of, the motor itself will only draw enough electrical power to do that job, plus any losses in the system, with or without the VFD. But if you have a 1000HP motor driving a 500HP pump requirement, you undoubtedly have some method of reducing output of the system. If that output reduction is restriction, there is energy loss in that process. Using a VFD to instead reduce the flow by reducing speed, you get the same results with much fewer losses. Plus you reduce the losses inside of the motor as well, because a portion of the motor losses are in the magnetics which is associated with the voltage. With a VFD, voltage ton the motor gets reduced to be only what it needs to be for the speed required. There are new types of losses introduced by having the VFD, but contrary to the belief of some, they are much less than what having the VFD reduces, so there is going to be a net increase in system efficiency. That is where they pay for themselves.
"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies
RE: Reducing VFD Power output without reducing speed?
Google search as a start, if you are interested:
http
Regards,
Lyle
RE: Reducing VFD Power output without reducing speed?
RE: Reducing VFD Power output without reducing speed?
In conclusion, I don't need a VFD, There is no problem with running a 500HP pump with a 1000HP motor other than some efficiency losses, and a VFD will not help the perceived problem anyway.
RE: Reducing VFD Power output without reducing speed?
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Reducing VFD Power output without reducing speed?
RE: Reducing VFD Power output without reducing speed?
RE: Reducing VFD Power output without reducing speed?
RE: Reducing VFD Power output without reducing speed?
Neil
RE: Reducing VFD Power output without reducing speed?
The other common misconception is that a VFD will always save energy on pumps and fans irrespective of the operating speed.
Logic suggests that oversized motors waste energy, so install a VFD to save energy.
Logic is wrong.
Mark Empson
Advanced Motor Control Ltd