Machine Design

Energy efficiency standards could spell an end to some induction motor types

Today, the electric motors that are of most concern with regard to energy effciency are those of one horsepower and larger. But that situation will soon change as efficiency regulations phase in for what are classified as small electric motors.

To get ready for those new regulations, the National Electrical Manufacturers Association (NEMA) recently published a white paper — NEMA MGW 1-2013 — clarifying some of the ideas contained in the Dept. of Energy's Small Electric Motor Standards Final Rule and Technical Support Document of March 9, 2010.

The NEMA document covers issues pertaining to the rulemaking for Energy Conservation Standards for Small Electric Motors.

A perusal of the NEMA document shows that capacitor-start and capacitor-run fractional horsepower motors will be affected by the new standards which in general,  will become effective on March 9, 2015. But some kinds of  small electric motors will need to be certified for efficiency levels by an independent third-party testing lab. For those, the effective date is March 9, 2017.

The motors affected by this regulation are defined as NEMA general purpose ac single-speed induction motors, built in a two-digit frame number series. Additionally, the DOE has opened a new round of rulemaking directed at small electric motors.

Under DOE rules, the new efficiency standards will apply only to capacitor-start motors, including CSIR [capacitor-start induction-run] and CSCR [capacitor-start capacitor-run], because only these types can meet the torque requirements for NEMA general-purpose motors. But the standards will apply to both single-phase and three-phase CSIR and CSCR motors. 

NEMA points out there is still some ambiguity in the DOE standards documents, however.  DOE observed that there were polyphase and single-phase CSIR and CSCR motors in two-digit frame sizes with power ratings above one horsepower for two-poles, above 3/4 horsepower for four-poles, and above half horsepower for six poles which some manufacturers identified as “general purpose” motors. In the NEMA electric motor standard called MG 1, such power ratings are associated with medium motors built in NEMA T-frame sizes. Consequently, there are no performance standards defined in MG1 for motors of such power ratings in two-digit frame sizes. DOE hasn't addressed how to determine which of these motors are covered by efficiency standards when there are no performance standards in MG1 for them.

DOE decided that because some manufacturers identify motors with higher horsepower ratings as “general purpose” it was logical to consider them small electric motors. So DOE established efficiency standards for small electric motors in two-digit frame sizes rated up to three horsepower.

NEMA says that implementing this new regulation will require many changes for both motor manufacturers and their customers. Motor manufacturers may have to modify their mechanical, cooling/ventilation, and/or electrical designs. Typically, more efficient motors use more copper and steel, and motors can grow longer to accommodate the extra windings. NEMA says the DOE did not consider customer installation costs when determining the economic feasibility of this regulation.

However, DOE did point out that setting the efficiency standards for CSIR motors to the same level as CSCR motors may effectively make CSIR  motors impractical to manufacture. So many users of CSIR small electric motors will need to prepare to switch to using CSCR electric motors, NEMA says.

There are also two new ongoing DOE rulemakings that will also have a great impact on motor manufacturer’s certification and compliance procedures. The Small and Electric Motor Test Procedure and Alternative Efficiency Determination Method (AEDM) rules for testing motors do not provide clarification on certification registration and labeling requirements, NEMA says. They also do not require the use of a formal accreditation program for small electric motor efficiency test facilities. At the present time DOE does not require a manufacturer to submit any statement of certification as to compliance with the small motor efficiency standards. Also, at the present time DOE does not require that small electric motors be marked in any way to identify compliance. 

NEMA also says there are concerns that the value of the average full-load efficiency of a basic motor model determined by testing could vary widely without a minimum technical and quality requirement for the motor test facility. Variation in test results between various test facilities could make enforcement of the standards probelmatic. All of these issues contribute to an increasingly difficult situation for enforcement of the efficiency standards in the marketplace, says NEMA. NEMA also says it will continue to engage the DOE on these issues with the goal of further leveling the global playing field for testing and certification of motors for use in the United States.

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