Power Consumption on VFDs
Power Consumption on VFDs
(OP)
For calculating the power consumption on VFD motors, is this formula valid for use?
HPnew = HPrated [(RPMnew]^3 / (RPMold^3) ]
Since change in motor speed is proportional to motor HP then this may be applicable to get the approximate HP consumption. Does the Load factor be considered?
HPnew = HPrated [(RPMnew]^3 / (RPMold^3) ]
Since change in motor speed is proportional to motor HP then this may be applicable to get the approximate HP consumption. Does the Load factor be considered?
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RE: Power Consumption on VFDs
RE: Power Consumption on VFDs
I remember that HP as a function of torque and speed is:
HP = (Torque x Speed)/ 5252
Therefore, for decreasing speed at the same torque requirement, the actual torque increases. Is this applicable to VFD drives?
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RE: Power Consumption on VFDs
As you correctly state the HP formula, HP is a function of RPM and Torque. For, say, a constant torque load, the HP would rise lineary with RPM.
RE: Power Consumption on VFDs
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RE: Power Consumption on VFDs
Usually with VFDs one talks of constant torque loads (such as positive displacement pumps, conveyors, etc.) where the torque requirements are constant and when the speed is varied the horsepower varies linearly as sreid states. Then there are the variable torque loads as stated again by sreid (usually centifugal pumps and fans) which vary with the square of the speed (because the pressure output of the centrifugal device varies with the square of the speed).
RE: Power Consumption on VFDs
RE: Power Consumption on VFDs
When a center driven winder is taking material from a process at constant tension and constant speed, the center speed of the empty spool is high and the torque is low. As the spool fills up, the center speed is reduced to keep the surface speed constant. The spool torque is material tension times the radius of the spool at the surface of the material.
Machine tools are often operated at a constant rate of material removal. A large diameter cutting head or piece on a lathe is operated at a slow speed and a small diameter cut is taken at a high speed. The force at the cutting edge is the same, so the torque is low for small diameter, high speed cuts and high for large diameter low speed cuts.
RE: Power Consumption on VFDs
GO PLACIDLY, AMIDST THE NOISE AND HASTE-Desiderata
RE: Power Consumption on VFDs
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RE: Power Consumption on VFDs
The affinity laws definitely do NOT apply to constant torque applications. As sreid said previously the horsepower is proportional to speed in constant torque applications. I recently advised someone to replace an eddy current drive (remember those!) that was used in a constant torque application since at half speed it was wasting half the energy (the eddy current coupling was cooled with chilled water). Eddy current drives were really only useful prior to VFDs and only good on variable torque applications.
RE: Power Consumption on VFDs
GO PLACIDLY, AMIDST THE NOISE AND HASTE-Desiderata
RE: Power Consumption on VFDs
HPnew = HPrated [(RPMnew]^3 / (RPMold^3) ]
GO PLACIDLY, AMIDST THE NOISE AND HASTE-Desiderata
RE: Power Consumption on VFDs
RE: Power Consumption on VFDs
GO PLACIDLY, AMIDST THE NOISE AND HASTE-Desiderata