Barks Publications, Inc.

Magazines and Books for Business and Industry

Transformer Efficiency Standards Are on the Way"

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.

Industry news...

 
Copyright © 2010 Barks Publications, Inc.
400 N. Michigan Avenue, Suite 900
Chicago, IL  60611
312-321-9440 tel  ...call for our email addresses...  fax 312-321-1288