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 Summary: "
No Standards Yet for "Small Motor" Efficiency" With
trilingual summary
In both Europe
and North America, full-load efficiencies of general-purpose
three-phase induction motors rated from one to 500 hp (depending
upon speed) are governed by industry standards, governmental
regulations, or both. Smaller motors, however, are exempt. In the
United States, the Energy Policy Act empowers the federal government
to impose performance and test requirements on "small" motors if
potential energy savings from higher efficiency appear significant.
That has not happened.
That's because most small motors are either special purpose designs
with performance requirements more important than higher efficiency,
or are single-phase motors. Although some of the same design changes
that raise polyphase motor efficiency (such as higher copper
content) will do likewise for single-phase machines, the effects
(and the testing needed to verify them) can differ among the
numerous types of single-phase designs.
Also, many such motors, like those in household appliances, operate
only a few hours annually. Energy savings do not justify the
investment in higher efficiency.
In the United States, the only single-phase motor test guide is IEEE
114, most recently re-published in 2001. That document supports an
efficiency evaluation that is not equivalent to that in IEEE 112 for
polyphase motor testing. A Canadian standard (CSA C747) has been
published for small motors, both single-phase and polyphase.
However, differences of opinion exist in North America as to the
degree of efficiency measurement precision it provides.
When efficiency is measured as the ratio of directly measured input
and output powers, tolerances in those two measurements can produce
large variation in the result. Defining efficiency as the ratio of
measured output to the sum of output plus segregated losses tends to
be significantly more accurate for larger motors. For either method,
setting standard limits requires verifying the test facility's
capability of producing consistent, precise results.
More important: the viewpoint of the National Electrical
Manufacturers Association in the United States continues to be that
the population of motors below one horsepower is too varied, too
special in application, and too limited in operating hours to
justify development of either design changes or new test procedures
aimed at higher, more precisely verifiable efficiency.
From
"No Standards Yet for 'Small Motor' Efficiency" ...by
Richard L. Nailen, EA Engineering Editor -
published in Electrical Apparatus September 2004
© 2004
Barks Publications, Inc. All Rights Reserved.
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