CHARACTERISTICS

Losses in distribution feeder conductors are the result of current flow through electrical resistance of the conductors. The resistance a conductor offers to the flow of electricity is inversely proportional to its cross-sectional area – i.e., the larger the diameter of the conductor, the less resistance the current will encounter.

Resistance is also a function of the type of material of which the conductor is made. Thus, by replacing a conductor with one of a larger diameter or changing to a material that offers less resistance, power loss can be reduced when the same current is flowing through the conductor. Lower resistance losses will reduce generation and decrease GHG.

Distribution feeder losses can be minimized by upgrading existing feeders with larger-size conductors, reconnection of customers, and sectionalizing feeders with switching. On single phase systems there is also a need to balance loading among the three phases. Segmenting shield wires can also eliminate losses associated with loop flows through this path.

SIZE:
Conductors are aluminum and range in size from 35-240 sq.mm., and operating voltages range from 2,400 Volts to 69 kV.

FEATURES:
Distribution feeders can be overhead or underground. Overhead distribution uses aluminum conductors; cables use either copper or aluminum.

COST:
Costs to upgrade vary according to size of conductor, type of feeder (overhead or underground) and length. Feeder construction costs can vary from $15,000-50,000 per km.

CURRENT USAGE:
Feeder loss reduction is a regular part of distribution system operation and maintenance.

POTENTIAL USAGE:
With distribution automation, demand-side management, and time-of-use pricing there will be more sophisticated methods by which feeder resistance losses can be controlled.

ISSUES ASSOCIATED WITH IMPLEMENTING ACTION

• Requires accurate load information and estimates of type and number of consumer connected. Installation of demand metering on primary distribution feeders is a necessary data source.
• A modular standard approach to feeder design is essential – this necessitates use of computer software to optimize feeder sectionalizing
• Reconductoring existing lines is generally only cost-effective when a thermal capacity increase is needed, but existing load flow models or regional models for economic evaluation of conductor losses can be developed.
• Pole, tower, and cross arm strength are a concern for existing lines. Most distribution facilities are built and designed to the size of the conductor on the line. A larger conductor adds greater windage, weight, and ice loading levels which may exceed the design capability of the tower equipment. Therefore, in many cases, increasing the line capacity requires a complete rebuild of the line, not just reconductoring.
• Environmental permitting can be extensive, especially where structure rebuilding is necessary. Environmental regulations are often unclear for this type of project. Lengthy permitting processes and costly conditions in permits may preclude consideration of or implementing a reconductoring project. Examine ways to clarify and simplify environmental permitting, taking into account the advantages of using an existing transmission corridor and the fact that line losses would be reduced.

CLIMATE CHANGE IMPACT

EMISSION EFFECT:
    

CONDITIONS FOR EMISSIONS MITIGATION:

• Avoids the emission of greenhouse gases indirectly by reducing generation demand.

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

COST-EFFECTIVENESS:
Total losses of 9% are attributable to transmission and distribution from the point of generation to the point of use. From 2-3% of the total can be assigned to losses in feeder conductors and transformers.

SECONDARY EFFECTS:
Varies according to the generation fuel mix.

RESOURCES

• Institute of Electrical and Electronics Engineers, 1992, Tutorial Course: Distribution Planning, PES publication 92 EHO 361-6-PWR.
• Institute of Electrical and Electronics Engineers Computer Application, 1995, Distribution Engineering Tool Features a Flexible Framework, Power Magazine, (July), pp.21-24.

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
Electrical Engineer
International Programs Division
Arlington, VA
Tel: (703) 907-5669
Fax: (703) 907-5532
jim.willis@nreca.org
http://www.nreca.org

Virginia Polytechnic Institute and State University
Prof. Robert Broadwater
The Bradley Department of Electrical Engineering
Blacksburg, VA
Fax: (703) 231-3362
http://www.vt.edu