CHARACTERISTICS

Increasing transmission line voltage improves the efficiency of electricity transmission over the line. Using the highest transmission voltage that is operationally and economically justified reduces line losses and increases line utilization.

Conventional line designs use porcelain or composite silicon insulators. Cable systems use oil-impregnated paper insulated cables and solid dielectric insulation. Static Var Compensation (SVC) devices are thyristor controlled devices installed at transmission line terminals, and control the flow of reactive power to maintain terminal voltage within pre-set limits; typically +/- 5% or 10% of nominal.

The increased efficiency means less electricity must be generated to provide the same level of customer service, reducing fuel consumption and greenhouse gas emissions.

SIZE:
110 kV to 765 kV alternating current transmission lines. SVC ratings in the range of hundreds of MVAr at costs in the range of $50 to $100 per kVAr of capacity rating.

FEATURES:
SVC's control terminal voltage on overhead transmission lines and cable systems.

COST:
Voltage upgrades can range from 50% of original line cost to total replacement of existing lines – costs range from $50,000 to $750,000 per km. SVC ratings (hundreds of MVAr) cost from $50-100 per kVAr of capacity rating.

CURRENT USAGE:
Conventional line designs use porcelain or composite silicon insulators. Cable systems use oil-impregnated paper insulated cables and solid dielectric insulation.

POTENTIAL USAGE:
Development of gas insulated systems with SF₆ gas and superconducting cables is underway

ISSUES ASSOCIATED WITH IMPLEMENTING ACTION

• Energy loss reductions alone do not offset the cost of additional equipment or the replacement of existing line and terminal components. Voltage upgrades are generally only cost-effective when used to increase capacity. Also, higher voltage transmission facilities have increased costs.
• Public concerns and misperceptions with electromagnetic fields (EMF) exist. Increased voltage is incorrectly associated with increased EMFs.
• Existing lines may need to be rebuilt to obtain sufficient clearance required for increased voltage. New permitting may be required for higher voltage lines.

CLIMATE CHANGE IMPACT

EMISSION EFFECT:
    

CONDITIONS FOR EMISSIONS MITIGATION:

• Increasing and stabilizing line voltage indirectly avoids emissions through increasing efficiency and reducing energy demand.

EMISSION ESTIMATE:
N/A

COST-EFFECTIVENESS:
N/A

SECONDARY EFFECTS:
N/A

RESOURCES

• Institute of Electrical and Electronics Engineers, 1993, Suggested Techniques for Voltage Stability Analysis, PES publication 93 THO 620-5
• Institute of Electrical and Electronics Engineers, 1993, System Protection for Voltage Stability, PES publication, 93 THO 596-7-PWR

CONTACTS

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

Electric Power Research Institute
Palo Alto, CA
http://www.epri.com

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