October 2008 Electrical Apparatus

October 2008 Electrical Apparatus

This is a summary of the Electrical Apparatus October 2008 featured technical article,  by Richard L. Nailen, P.E.    

Transformers are the most efficient components of any a-c electrical system. Yet almost all electrical energy generated in the U.S. passes through one or more distribution transformers. Because they’re on-line continuously, their losses are collectively important.

Hence, Section 124 of the 1992 Energy Policy Act called for the Department of Energy (DoE) to develop minimum efficiency standards for such transformers. Low-voltage dry-type units were covered by DoE rules in 2005. A Final Rule in October 2007 has added minimum efficiencies for higher voltage and liquid-filled transformers rated 10 to 833 kVA (single-phase) and 15 to 2500 kVA (three-phase), either made in the U.S. or imported, beginning Jan. 1, 2010. Test procedures to verify compliance with the standards had already been established in 2006.

In arriving at standard efficiencies, the DoE considered various effects of enhanced performance on both manufacturers and users. They included:

1. Material costs; factory capacity; availability of improved lamination steel.

2. Life span, including influence of lower operating temperature.

3. Cost of energy and the effect of transformer loading.

4. Detriment to users of larger unit size and greater weight resulting from higher efficiency design.

5. Maintaining competition–the ability of all manufacturers to produce and test the more efficient product.

6. Importance of energy conservation to reducing greenhouse gas emissions and the need for more generating capacity; increased system reliability.

7. Other factors, such as the influence of voltage rating.

The lengthy DoE study began with six “trial standard levels” based on different design approaches, each resulting in different evaluations of those basic concerns.

In the process, the DoE consulted with numerous manufacturers, users, and industry groups. As with the establishment of motor efficiency standards, some special products were exempted from the Final Rule. For example, mining transformers are used in confined spaces and liable to be moved frequently. Size and weight increases were considered undue burdens on the industry. Autotransformers, rectifier transformers, and “sealed” units were also exempted.

As with motors, the DoE also exempted “rebuilt and refurbished products.” Published requirements apply only to “newly manufactured transformers” that have not yet been sold to a user.

To order a back issue with the full article, “U.S. finalizes distribution transformer efficiency standards,” call 312-321-9440 or visit our online webstore.

Share Button