/images/TDUpdate2.gif/images/southwire_100x70.jpgUnderground High Voltage Cuts Runway Extension Costs - 2003UndergroundHiVoltageCutsRunwayExtCostsSept2003.htmWhen a northern Georgia county wanted to extend the runway of the county airport, there was a problem. An overhead 115kV transmission line ran across the path of the proposed extension.
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Underground High Voltage Cuts Runway Extension Costs - 2003

An underground short-cut reduced the cost of re-routing high-voltage transmission lines.

When a northern Georgia county wanted to extend the runway of the county airport, there was a problem. An overhead 115kV transmission line ran across the path of the proposed extension. The cost-effective answer was an underground high-voltage system buried under 55 feet of fill. The turnkey solution came from Southwire’s Forte Power Systems division.

"The county needed to extend the runway to handle corporate jets," says Lewis Waters, Forte high-voltage construction manager. "The question was how to move the existing 150kV line for the lowest cost. The answer was to bury it."

The installation was complicated by hilly north Georgia topography. The runway extension spans a valley that required fills up to 110 feet deep. There was also a schedule issue. The power line solution had to be in place before the excavation and filling started.

Underground versus overhead was a cost decision

The utility looked at the possibility of simply extending the overhead line past the end of the new runway to clear the flight path of aircraft. As an alternative, an installation buried under the runway took about one-forth the distance. "The arithmetic was clear," Waters says. "It was cheaper to go underground. The reduced distance more than made up for the cost differential of a buried installation. They came to Forte’s high voltage group for the work."

Redundant circuits support a key customer

"We provided a complete turn key project," Waters says. "We designed the system, supervised construction of the duct bank, provided the cable and terminations, and managed the installation. The utility made the connections to the grid. The construction phase took about six months, and they powered-up the circuits at the beginning of 2003, right on schedule."

The design called for two redundant, three-phase 115kV circuits in an unbroken 900-foot run. "The redundant circuits power a major food processing plant in the area," Waters explains. "The plant is a key utility customer, and they simply cannot afford a power loss."

Southwire conductors carry the load

The 1,000kcmil, XLPE-insulated conductors are about 3 1/2 inches in diameter. They were produced in Southwire's Heflin, Alabama plant. "It's the only facility in North America making extruded-dielectric high-voltage cables up to 230kV," Waters says.

The six conductors run through conduits encased in a concrete duct bank. "The subsequent filling operation put 55 feet of dirt on top of the duct bank," Waters remarks. "We had to accommodate that pressure in the duct bank with reinforced concrete."

Waters concludes, "The Forte team met the challenges of design, schedule, and implementation. And the customer got a cost-effective, hassle-free high-voltage solution."