Published efficiency of NEMA design motors
Published efficiency of NEMA design motors
(OP)
Hello,
I'm looking for a NEMA publication which states the efficiencies of each motor NEMA design type and horsepower. I have not been able to find this on the NEMA website. Can someone send me a link to such a document?
thanks,
EE
I'm looking for a NEMA publication which states the efficiencies of each motor NEMA design type and horsepower. I have not been able to find this on the NEMA website. Can someone send me a link to such a document?
thanks,
EE





RE: Published efficiency of NEMA design motors
Google NEMA Premium Efficiency.
This only applies to motors specified as "Premium Efficiency". Also note that these efficiencies are NOMINAL, not guaranteed minimums. Variations from the nominal are allowed within a specified range.
I don't believe there was a required NEMA efficiency for the old standard efficiency motors.
If you can let us know specifically what you are interested in, we can probably provide more information.
RE: Published efficiency of NEMA design motors
Thanks. I have that document. Maybe if I tell you what I'm trying to do, I will be clearer.
I will be doing an energy inventory of a power plant, and I will be looking at all of the major loads (motors of 100 Hp or more). For each of these loads, I will determine the generated mechanical Hp and then decide whether or not the motor is properly sized. If it is sized properly, then I will look at the cost benefit of changing the motor to a high efficiency motor. But I cannot establish a cost benefit unless I know the efficiency of the existing motor. Most of these motors are nema B. So, I need a NEMA document which states the efficiency of non-premium motors.
thanks
EE
RE: Published efficiency of NEMA design motors
I have some typical efficiency data for older motors somewhere. If you are interested, I can try to find it and scan it in.
RE: Published efficiency of NEMA design motors
EE
RE: Published efficiency of NEMA design motors
Table 12-10 standard
Table 12-11 energy efficient
Table 12-12 premium
Of course if your motors were purchased according to this standard,they would have the efficiency stamped on the nameplate. You might have to look at older versions of MG1 to see what it said (if anything), depending on the vintage of your motors.
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(2B)+(2B)' ?
RE: Published efficiency of NEMA design motors
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RE: Published efficiency of NEMA design motors
RE: Published efficiency of NEMA design motors
davidbeach,
There are two parts to my study. The first part is to determine if the motor is over or under sized. For that I will need to look at the estimated mechanical power and then determine the ideal motor size for that mechanical load. If the motor is grossly over sized, such as a 50 Hp pump which is throttled back to the point of running a 20 Hp load, then I can consider the efficiency loss based on a partially loaded motor compared to a fully loaded motor. A 20 Hp motor driving a 20 Hp load costs less to run than a 50 Hp motor running the same load.
The second part of the study is to look at the large motors and consider how much the efficiency comes into the overall cost. If an existing 1000 Hp fan motor is 88% efficient, and a new premium motor is 95% efficient, well that's a 7% loss. In dollars, that's over $30k/year, based on a kwh rate of 9 cents.
EE
RE: Published efficiency of NEMA design motors
Maybe. A 25 Hp motor would likely be more efficient because motors are seldom at their peak efficiency at full load.
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If we learn from our mistakes I'm getting a great education!
RE: Published efficiency of NEMA design motors
RE: Published efficiency of NEMA design motors
For new candidate replacement motors, you can get that info from the OEM. For existing motors operating at less than full load, it may be tough to reconstruct without info from OEM or other measurements.
A little bit of a sidetrack - Reliance has a widget that purports to estimate operating motor "efficiency" based only on input electrical measurements and speed measurements and some standard nameplate data. Basically it builds a model of the motor and computes the efficiency based on the model. Some people's reaction may be to dismiss such an approach out of hand because it doesn't directly measure output power. No-one will argue that inference from a model is inferior to direct measurement. However, when direct measurement is not available we sometimes use the info available to make predictions and then and try to estimate the degree of accuracy of our predictions. The last part is the tough part for this thing imo.
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RE: Published efficiency of NEMA design motors
I'm just mentioning this in passing (I suspect even if I didn't, someone else would). I realize it may be outside your scope. If you already know what I've said anywhere, I apologize in advance.
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RE: Published efficiency of NEMA design motors
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