Depending on what motor you are looking at, effeciencies can vary from as low as 10-15% for a shaded pole motor to as high as 90-95% for some DC motors and brushless DC's.
Induction motor efficiency could varies mainly with the motor HP rating and less degree with the type of manufacturing technology that had been used historically
Roughly the efficiency could be suggested in average as follow:
Per Jbartos suggestion, the average efficient for induction motors presented in the previous thread are supported by the enclosed references:
a- Paul M. Anderson, “ ANALYSIS OF FAULTED POWER SYSTEMS” .IEEE Power Engineering Series, Table 6.3
b- R. Doughty, R. Puckett and D. Brethauer “The Impact of Efficiency on the Economics of New Motor Purchase, Motor Repair and Motor Replacement”, IEEE Transactions on Industry Applications, Vol. 30, No 6, Nov/Dec 1994. (Fig 7.: Energy efficient electric motors systems, Three phase four pole –1955-1993).
The values of reference "a" are in agreement with the values of reference "b" for standard motor manufactured after 1993.
The enclosed values have been reasonably comparable with recent motor data used in power plant and industrial applications. However, any recent or accurate references are welcome.
Suggestion: Without much effort, one can open Baldor Electric Motor catalog, e.g. 501 dated December 19, 1994, page 80 where for example 3HP, 1425 RPM, Cat. No. M3211T-50 has listed efficiency 84% at full load. Page 72 lists three phase 575V motor, 3HP, 1760 RPM, Cat. No. EM3211T-5 with the full-load efficiency of 89.5%. These are just samples for comparisons with the first row stating: HP < 5 ~ % Efficiency 75-80
I see that above posting data on the lower side.
Other motor manufacturer catalogs could be cited.
c)IEEE: Std 841-2001for severe duty motors. (Hard copy)
References:
1- Induction Motor Efficiency Standards-J. Douglas, Univ of Washington
2- Motor efficiency - Oak Ridge National Lab ORNL-TM-13237
3- Energy Efficient Electric Motor - BPA DOE/GO 10096-290
