Motor-Driven Systems Efficiency Update

Electric motors have received predominant attention from energy-efficiency standards and regulations due their vast industrial usage and well-documented design, performance, and test specifications. Major efficiency improvements have been obtained at the motor level but are reaching diminishing returns and economic limits. Recent developments focus on the larger Wriven system  connected to the motor for continued efficiency gains.
by Frank J. Bartos, PE
Interior permanent magnet (IPM) motors can push motor efficiencies above premium levels. In a cooling tower fan application, this direct-drive IPM motor (and adjustable-speed drive) eliminated a worm-gear reducer used with a two-speed induction motor to c Minimum efficiency performance standards (MEPS) have been enacted for ac induction motors in various developed countries. That motor type has drawn the main attention because of its huge installed base worldwide. Motor MEPS represent one area where the U.S. has taken global leadership with Australia, Brazil, and Canada, among others, also taking strong positions. More recently, the European Union has followed suit with mandatory MEPS. In addition, numerous countries have voluntary motor efficiency standards, some of which are making their way toward law.
In the U.S., efficiency standards for induction motors have been widened in stages. Implemented in 1997, EPAct 1992 (Energy Policy Act) applied to general-purpose motors in the 1-200 hp (0.75-150 kW) range. EPAct 2005 mandated that government motor purchases in the 1-200 hp range be at higher NEMA Premium motor efficiency levels. Energy Independence & Security Act (EISA 2007) went into effect in Dec. 2010, extending coverage to motors up to 500 hp (375 kW) rating and to motor designs/varieties previously exempted from MEPS. Motor varieties added in EISA include U-frame, NEMA Design C, close-coupled pump motors, footless motors, vertical solid shaft normal thrust motors, eight-pole (900 rpm), and polyphase motors with voltage of not more than 600 V (other than 230 or 460 V).
Full-load efficiency values for energy efficiency motors are listed in National Electrical Manufacturers Association (NEMA) Standard Publication Motors and Generators (MG 1-2011), table 12-11, and for Premium efficiency motors (random wound and form wound) in tables 12-12, 20-B (motors through 500 hp), and 20-C (medium-voltage motors), respectively.
A further initiative of the U.S. Dept. of Energy (DOE) seeks to draw smaller electric motors into the energy-efficiency picture. The so-called DOE Final Rule, Energy Conservation Program: Energy Conservation Standards for Small Electric Motors, published in March 2010 in the Federal Register (10 CFR Part 431), covers general-purpose, open drip-proof, three-phase electric motors typically below 1 hp rating, but extending up to 3 hp for some types.
Specifically, this DOE ruling applies energy conservation standards to motors through 3 hp with 2-, 4-, and 6-pole designs and frame sizes 42 through 56. Single-phase, capacitor-start motors of the same power range and pole count, as well as applicable IEC motors and corresponding frame sizes, are also included. Effective date of the ruling is March 2015.
DOE  small motors efficiency ruling has not met with enthusiasm from motor manufacturers. Objections come from various reasons, such as more diverse applications, different motor types/designs, less recognized testing methods, etc.relative to the industry  wide experience with larger induction motors (see Ref. 1, online).