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Summary:
"Verifying"
Motor Efficiency: No Easy Task" With
trilingual summary
By
Richard L. Nailen, EA Engineering Editor
Most standard general purpose three-phase
induction motors sold in the United States (regardless of where
they're manufactured) must now exhibit full-load efficiencies as
tabulated in the Energy Policy Act (EPACT) of 1992. Defined as
"nominal," such an efficiency represents an average for a
large number of motors of identical design.
The same efficiencies are required by standards
of the National Electrical Manufacturers Association (NEMA), and are
to be marked on the motor nameplate. For each individual motor, the
NEMA standards also tabulate a required "minimum"
efficiency, representing a motor loss 20% greater than that
associated with the nominal efficiency.
A user concerned about the efficiency of a single
motor must understand that because the nominal efficiency is an
average value, it cannot be verified by testing any single unit. The
U. S. Department of Energy (DOE) has therefore established an
efficiency enforcement procedure. If a user has reason to believe
(usually from a laboratory test) that a motor does not meet the law's
requirement, a complaint to the DOE initiates a sampling process
imposed upon the manufacturer. Several motors are tested and the
results analyzed according to a complex statistical procedure; a
decision is then made as to whether or not the product complies with
the law.
Some agencies have evaluated motor performance by
a test program classifying motor designs into three categories. A
fully acceptable "green" group exhibits nominal
afficiencies meeting both NEMA and EPACT levels, and minimum
efficiencies within the NEMA requirement. An unacceptable
"red" group fails both of those criteria. In between, a
"yellow" group meets the NEMA minimum efficiency, but
testing indicates that an average (nominal) efficiency may be too
low. Only the DOE sampling procedure can evaluate performance in that
category.
In any event, the only useful tests are those
performed under laboratory conditions in facilities certified by the
Department of Energy. Field tests cannot be expected to match those
conditions.
Copyright 2003, Barks Publications, Inc., Chicago.
Reproduction by any means prohibited.
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