|
Summary:
"Transformer Efficiency Standards Are on the Way" With
trilingual summary
Transformers in electrical power
systems are the most efficient electromagnetic devices known.
Nevertheless, transformer losses are important because these units
are so widely used. Of all electrical energy generated in the United
States, for example, whereas only two-thirds is supplied to motors,
100 percent flows through one or more transformers.
The same U. S. law (the Energy Policy
Act of 1992, or EPACT) now regulating standard a-c motor efficiency
also provides for imposition of efficiency requirements for
distribution transformers. That process is now nearing completion
following eight years of intensive study by the U. S. Department of
Energy (DoE), its associated National Laboratories, the National
Electrical Manufacturers Association, transformer manufacturers,
consultants, and the public.
The DoE first needed to define
"distribution transformers," which are now considered to be either
liquid-filled or dry-type, rated 10 to 2500 kVA, with primary
voltage of 34.5 kV or below, and secondary voltage 600 volts or
below. Special types (such as welding, grounding, or isolation
transformers) are excluded.
However, within that definition, the
DoE recognized 13 variations or "engineering design lines" based on
characteristics such as BIL (Basic Insulation Impulse Level). In its
July 2004 proposed rule for establishing transformer efficiency
standards, the DoE published five possible values for representative
ratings in each of the design lines. Final values were to be derived
following public comment on those proposals.
A second July 2004 announcement
proposed procedures for testing transformer efficiency, based on
NEMA Standard TP 2 plus several existing ANSI/IEEE C57 documents.
Included were statistical sampling and evaluation methods for
demonstrating product compliance with efficiency standards and the
terms of EPACT.
Throughout, the process has resembled
that leading to the EPACT motor efficiency requirements. Although
transformer losses and test methods are less complex than for
motors, measurement precision must be greater because transformer
efficiency is inherently so high. Also, transformer life span often
greatly exceeds motor life, complicating the economics of energy
losses and unit replacement.
From "Transformer
Efficiency Standards Are on the Way" ...by
Richard L. Nailen, EA Engineering Editor - published in
Electrical Apparatus
May 2005
Visit our online
webstore to
order a
copy. © 2005
Barks Publications, Inc. All Rights Reserved.
|
