CHARACTERISTICS

Transformers are the devices that change the voltage of an AC electric circuit. They are most commonly used to reduce the voltage from the distribution level of 4-69 kV to the level required by the customer. However, whenever the transformer is energized, regardless of load, an electrical loss known as "core loss" occurs. Of the 9% total losses attributable to transmission and distribution from the point of generation to the point of use, 2-3% of the total can be assigned to losses in feeder conductors and transformers.

There are significant numbers of distribution transformers in the electricity supply system. The minimization of core and winding losses through the use of more efficient transformers reduces generation demand and the emission of greenhouse gases.

Significant advances have been made in reducing core losses, through improved manufacturing and treatment of steel cores, and through the development of amorphous metals (including steel). Decrease in winding loss, which is a function of the transformer load, is also possible.

SIZE:
5 kVA to 500 kVA single phase distribution transformers and 15 kVA to 1,500 kVA three phase distribution transformers.

FEATURES:
Most commonly used is the oil-filled transformer, transformers are installed on poles, in surface level distribution centers and in underground vaults. Design lifetime is 20-30 years.

COST:
Distribution transformer costs vary from $10-25 per kVA. Maximum efficiency designs may not be the most economic, since increasing the efficiency usually results in an increase in capital cost of the transformer.

CURRENT USAGE:
Conventional transformer designs are based on steel core oil filled transformers.

POTENTIAL USAGE:
Development of amorphous core distribution transformers offers the prospect for reduced excitation losses.

ISSUES ASSOCIATED WITH IMPLEMENTING ACTION

• The high cost of new transformer equipment may not be offset by the reductions in energy loss.
• There is only one supplier of amorphous core material (in the U.S.).

CLIMATE CHANGE IMPACT

EMISSION EFFECT:
    

CONDITIONS FOR EMISSIONS MITIGATION:

• Produces no carbon emissions directly, but more efficient operation will reduce demand for electricity.

EMISSION ESTIMATE:
Varies according to the fuel mix used to generate electricity.

COST-EFFECTIVENESS:
Depends on the size of transformer. The most efficient size may not be the most cost-effective size.

SECONDARY EFFECTS:
Varies according to the generation fuel mix.

RESOURCES

• The Electric Power Research Institute (EPRI) has sponsored a study as part of which Minnesota Power has installed 25 amorphous core distribution transformers. Another EPRI collaborative research project with Potomac Electric Power Company to demonstrated a cooling design for forced-oil/air-cooled transformers with advanced winding technology involved installation of a low loss transformer at a distribution substation in 1994.
• Approximately 55% of the distribution transformers purchased by the New England Electric System in 1993 were of the amorphous core design.
• The U.S. Environmental Protection Agency sponsors an Energy Star Transformer Program, whose participating utilities agree to purchase qualifying transformers and to institute early replacement where economically warranted. http://www.epa.gov/appdstar/transform/utility.html

CONTACTS

Harza Engineering
Peter Donalek
Electric Power Systems Department
Chicago, IL
Tel: (312) 831-3170
Fax: (312) 831-3999
pdonalek@harza.com
http://www.harza.com

National Rural Electric Cooperative Association (NRECA)
James Willis
International Programs Division
Arlington, VA
Tel: (703) 907-5669
Fax: (703) 907-5532
jim.willis@nreca.org
http://www.nreca.org

U.S. Environmental Protection Agency
Energy Star Transformer Program
Washington, DC
http://www.epa.gov/energystar/