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Total drive efficiency

Total drive efficiency

Total drive efficiency

(OP)
I am trying to estimate and compare the total efficiency of various blower systems.  One style is driven by a standard induction motor (2-pole or 4-pole) with a constant torque VFD.  Power range: 50 to 400 HP and speed range 3:1 typical.  The other style is high speed turbo with permanent magnet, same power rating; speed range 2:1 (speeds are typically in the 20,000 ...40,000 range).  Can anyone guide me as to where I could find some information on this subject?

RE: Total drive efficiency

I'm not too clear what you are trying to compare. It would appear you have two different technologies for two different applications. I'm not sure a direct comparison is going to make too much sense.
We operate IM and PM for the same applications and can see that the overall efficieny of PM is better, but the applications and speed ranges etc are the same.
High speed applications are very different to low speed applications in many ways and it would, I think, be a case of apples and oranges.
 

RE: Total drive efficiency

(OP)
Ozmosis,  thank you for your clarifying question.  It would take long to provide all the details, so to simplify, let us imagine that we need to drive the same equipment that has a constant torque characteristic.  In one case, we use an intermediate gear box that has a 100% efficiency to increase the speed from 3550 RPM (60 Hz output of IM) to 30,000 RPM and in the other case, we have a direct driven machine with 30,000 RPM output of the PM motor.  In both cases, we vary the speed in a 3:1 ratio.
I looked at "Electric Motor Efficiency under Variable Frequencies and Loads" by Charles M. Burt; Xianshu Piao; Franklin Gaudi; Bryan Busch; and N. F. N. Taufik for IM but I have not been able to find a lot of material on PM systems.  I am also wondering about the effects of working with high frequencies with respect to distances, cables, heat generation, etc...
 

RE: Total drive efficiency

If you have a gear box with 100% efficiency, I think your problems are all solved.  

Additional losses due to higher frequencies in the cabling are negligible compared with other losses.  If you take into account the VFD efficiency and motor efficieny on the VFD, you have anything worth considering covered.  

As for the 30,000 rpm motor, I have no idea.  

"Theory is when you know all and nothing works. Practice is when all works and nobody knows why. In this case we have put together theory and practice: nothing works... and nobody knows why! (Albert Einstein)

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