CHARACTERISTICS

Transformers are used to step-up the generator voltage for transmission and to step-down the transmission voltage to intermediate levels for distribution and customer use. Commonly used transformers are oil-filled, pole-mounted types for overhead distribution; and oil-filled, pad-mounted models for underground feeds. Dry-type transformers, used for smaller, special applications, are typically located inside buildings away from harsh environments. Current standard practice is to design large power transformers based on economic considerations, rather than on maximum operating efficiency. Transformers consume power even when loads are switched off or disconnected, and every time a transformer is energized, an electrical loss in the transformer known as "core loss" occurs.

Recent technological advances have succeeded in reducing core losses, thereby improving efficiency. Increasing transformer efficiency requires less electricity generation to provide the same level of customer service; this will reduce fuel consumption and GHG emissions. Also, because of the large number of transformers installed throughout the world, even small improvements in transformer performance can add up to a significant reduction in greenhouse gas emissions.

Transformer failure may be catastrophic and cause power interruptions; other transformer problems are more subtle and may result in energy waste that goes unchecked for years. Current research is seeking ways to further reduce core losses as well as decreasing winding loss.

SIZE:
Transmission grid power transformer: 110 kV to 765 kV, 200 MVA to 1,500 MVA Distribution transformer: 37.5 kVA, 120 to 600 V.

FEATURES:
Transmission power substation transformers; pad or pole mounted distribution transformers. Many transformers operate at more than 98% efficiency, but even losses of 2% of total electricity generation translates into billions of kilowatt hours of wasted electricity each year.

COST:
Transformers are evaluated in terms of total ownership cost, equal to net selling price plus discounted value of future load and no-load losses. Transmission power substation: ~$4,145/MVA plus $4,100-6,000/kW for load loss Distribution transformer: ~$750/kVA plus $3,000-6,000/kW for load loss.

CURRENT USAGE:
Conventional steel core transformers are commercially available. In newer transformers, PCB-containing oils are not used in cooling systems, which increases their attractiveness.

POTENTIAL USAGE:
Low temperature and high temperature superconducting transformers are under development. Amorphous core transformers offer potential loss reduction benefits.

ISSUES ASSOCIATED WITH IMPLEMENTING ACTION

• Increased capital cost of high efficiency transformers may not be offset by direct cost- savings from reduced generation demand.
• Replacement of older transformers requires treatment and disposal of PCB containing oils.
• Transformers consume power even when loads are switched off or disconnected. Disconnecting the primary side of transformers to save transformer standby losses is safe provided that critical equipment such as clocks, fire alarms, and heating control circuits are not affected.
• For three-phase transformers, ensure that each phase balances in voltage with others to within the minimum transformer step. If this fails to yield equal tap settings, redistribution of loads is necessary.

CLIMATE CHANGE IMPACT

EMISSION EFFECT:
    

CONDITIONS FOR EMISSIONS MITIGATION:

• If demand shifts as a result of improved efficiency, total emissions may not be reduced.

EMISSION ESTIMATE:
Produces no direct emissions. Avoids the emissions associated with a 0.25% reduction in total transmission losses (usually 5% to 6%).

COST-EFFECTIVENESS:
N/A

SECONDARY EFFECTS:
N/A

RESOURCES

• Dirks, J., et al. September, 1993. High-Temperature Superconducting Transformer Performance, Cost, and Market Evaluation, Battelle Pacific Northwest Laboratory, PNL-7318.
• Fink, D., and H. Beaty, 1993, Standard Handbook for Electrical Engineers, 13th Edition, McGraw-Hill.
• Oak Ridge National Laboratory, The Feasibility of Replacing or Upgrading Utility Distribution Transformers During Routine Maintenance, Oct 1972.
• The U.S. EPA's Energy Star Transformer Program has information about manufacturers of distribution transformers that have committed to produce and market efficient transformers. http://www.epa.gov/appdstar/transform/

CONTACTS

ABB Power T&D
Henry Chao
Raleigh, NC
Tel: (919) 856-2394
http://www.abb.se/pow/home.htm

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

U.S. Environmental Protection Agency
EnergyStar Transformer Program
Alison ten Cate
Tel: (202) 544-9023
Fax: (202) 565-2079
tencate.alison@epamail.epa.gov
http://www.epa.gov