June 2010 Electrical Apparatus

June 2010 Electrical Apparatus

This is a summary of the Electrical Apparatus June2010 featured technical article,  by Richard L. Nailen, P.E.    

Have guidelines for small motor efficiency finally arrived? The U.S. Department of Energy did publish its Final Rule giving efficiency limits that must be met by “small” general-purpose electric motors, starting in 2015.

Why did getting to this point take so long? The market was far larger. Many motors (particularly single-phase) are fitted into equipment such that dimensional changes are restricted. The years of advance design effort and testing that motor manufacturers had gone through in advance of EPACT passage had not been undertaken for small motors. And the issue of “general purpose” vs. “definite purpose” and “special purpose” had to be dealt with .

For the original EPACT products, the DOE considered seven issues in arriving at the Final Rule: 1. Economic impact on motor manufacturers.2. Lifetime reduction in operating costs.3. Total project energy savings.4. Lessening of equipment utility or performance.5. Impact of any decrease in competition.6. National need for energy conservation.7. Other factors the secretary “considers relevant.”

Numbers of “small motors” cited in the DOE and other documents have varied widely, and however efficiency may be measured, defining it has been one of the DOE’s major concerns. The possible loss reduction measures cited in DOE documents contain a few surprises. They include longer stacks, larger rotor bars and end rings, a cast copper squirrel cage, a decreased air gap, “better bearings and lubricant,” and a “more efficient cooling system.” “Better lamination material” and “Less rotor skew” were other suggestions. One surprise is the die-cast copper rotor. A second surprise is the air gap decrease. Finally, changes in ball bearings cannot offer efficiency improvement except by the omission of any rubbing seals that may be present.

The Department of Energy can’t be accused of not doing its homework. Its documentation for this Rule consists of more than 1,300 pages, and much work was also done by NEMA and others. But the task has proven to be far more complex than the setting of appropriate standards for larger polyphase motors, and no, we’re not quite there yet.

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