CHARACTERISTICS

Maximum utilization of existing transmission assets while ensuring transmission reliability makes good business sense. Especially where transmission lines are operated with open access, it is critical for operators to be able to assess and uprate existing lines at minimum cost.

Conductor performance may be affected by line sag, wind damage, corrosion, and other causes. Conductor loss rates are determined by the resistance of the transmission line conductor. As conductor line diameter is increased, resistance is lowered. Resistance, and thus losses, is also a function of the type of material of which the conductor is made. Replacing a conductor with one of a larger diameter and/or changing to a lower resistance material will reduce power loss. Segmenting shield wires eliminates losses associated with loop flow through this path. Lower loss rates result in lower generation demand and a decrease in GHG emissions.

SIZE:
Transmission line conductors range in size according to voltage, line length and power transfer requirements.

FEATURES:
Transmission conductors are fabricated from electrical grade aluminum (copper is no longer used). At higher voltages multiple bundles of conductors per electrical phase are used.

COST:
Cost is based on cost of material, installation and when replacing an existing conductor there is an added cost to strengthen support towers. Conductor costs in low labor cost markets are about 20-25% of total line costs.

CURRENT USAGE:
Upgrading of existing overhead transmission lines may be considered on shorter lines and where procurement of new right of way is difficult.

POTENTIAL USAGE:
As right of way becomes more difficult to obtain, consideration of the conductor upgrade option will increase.

ISSUES ASSOCIATED WITH IMPLEMENTING ACTION

• Replacing existing conductor lines is generally only cost-effective when a thermal capacity increase is required. Conductor losses should be considered in designing transmission lines.
• Existing transmission line pole, tower and cross arm strength may not be sufficient for a larger conductor requiring a complete rebuild of the transmission line, not just conductor replacement.
• Public misperceptions about electro-magnetic fields (EMF) increase difficulties in siting and extensive environmental permitting can be required, especially where structure rebuilding is necessary.

CLIMATE CHANGE IMPACT

EMISSION EFFECT:
    

CONDITIONS FOR EMISSIONS MITIGATION:

• The U.S.-based Commonwealth Electric Companies, participating in the U.S. DOE-sponsored Climate Challenge, estimates that upgrades to its transmission & distribution systems including voltage and equipment upgrades, conductor loss optimization and the use of loss transformer and other equipment will reduce CO₂ emissions by approximately 12,400 tons of CO₂ annually.

EMISSION ESTIMATE:
N/A

COST-EFFECTIVENESS:
N/A

SECONDARY EFFECTS:
N/A

RESOURCES

• Power Technologies, Inc. sponsors educational programs on modifying conductors when uprating transmission lines. http://www.pti-us.com
• Electric Power Research Institute Reports, EL-5478, Shield Losses in Medium-Voltage Cables, details how to design neutral conductors for maximum cost-effectiveness and includes calculations of circulating current losses and ampacities for commonly used cables.
• Electric Power Research Institute Reports, EL-6759-D, Transmission Cable Magnetic Field Research, provides magnetic field data for one cable configuration.

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