Aluminum plays a major role in the lives of the people charged with building and maintaining the country's electric grid. Besides being cost-effective, aluminum cable has the conductivity and mechanical properties needed for overhead installation.
"Aluminum conductors are the backbone of the world's overhead transmission system," said Eric Engdahl, principal engineer of transmission line asset engineering at American Electric Power Co. Inc. (AEP) in Columbus, Ohio. "Aluminum combines the strength and conductivity required for overhead lines. At AEP, aluminum is the material of choice."
In transmission applications, there is a continuing market for aluminum conductor cable as the nation builds up the electric grid. "From all indicators I see, consumption will continue at least at present levels," Engdahl said.
Aluminum cable manufacturers are sold out, suggesting a robust level of demand, one source said.
"You'll see new transmission capacity being overlaid as an addition to the existing grid," Engdahl said, looking ahead. "You will also see local additions to serve the ever-increasing needs of localities."
There also will be a great deal of refurbishing, reconfiguration and rebuilding of existing systems. "You'll see a tremendous push across the country to refurbish what is a massive infrastructure," he said. Much of this activity will involve aluminum components.
Engdahl did not provide estimates for the cost and scope of such projects, but 2005 projections for upgrading the U.S. power grid to meet projected demand—roughly 2 percent per year—by the end of this decade ranged from a low of $27 billion to as much as $100 billion, although these figures included power generation as well as transmission.
So far, power grid growth has never met projected demand, falling roughly 30 percent short on an annual basis, according to the North American Electric Reliability Council.
Upgrading an existing transmission line can cost upwards of $1 million per mile, and building a new line can cost two to three times as much for the same distance, an industry source said, although he cautioned that the large number of variables in any transmission line project makes generic cost estimates unreliable.
Mike Hervey, vice president of operations for the Long Island Power Authority (Lipa), also sees aluminum playing a major role as transmission capacity is added. "We definitely have ongoing plans for building additional overhead transmission lines," he said, adding that Lipa spends between $20 million and $40 million annually on new transmission lines, most of which will use aluminum conductors.
In addition to being less expensive than copper, aluminum also is more durable, Hervey said. Aluminum also can be a choice for underground lines, he added, in places where overhead lines are impractical or otherwise unsuitable. "In high-capacity transmission, copper is almost always outpriced by aluminum," he said. Since aluminum is close to one-third the price of copper, aluminum cable—often sold on a commodity basis—can provide substantial savings.
Consolidated Edison Inc., responsible for powering New York City, also uses aluminum conductors for overhead transmission lines, a company spokesman said. Aluminum conductors have sufficient current-carrying capacity and structural strength for long spans, he said, such as wide water crossings where towers cannot be built or other areas where rights of way cannot be secured for new towers. Aluminum is light in weight, easy to handle and companion hardware is easily available, he said. "We have not encountered any major problem with aluminum conductors for overhead transmission circuits."
Both AEP and Lipa have considered new composite core cables, saying it offers certain solutions not possible with conventional cables.
"The composite core cable has low thermal expansion properties, which mitigates line sag due to thermal expansion," Engdahl said. "The design allows you to use the conductivity of the aluminum to a greater extent."
The new cable "allows you to increase power flow in a short time and at a reasonable cost over an existing right of way" using existing towers, Engdahl said. "Such retrofitting is where I see the advantage of the composite core cable."
Hervey also sees the composite core design as a niche product because it costs three times as much as traditional steel-reinforced aluminum cable. "We have looked at the composite core material and the price differential, which puts it in the area of special uses, where span length and higher capacity are issues," he said. "For example, if you had a large water crossing where you can't build towers, it makes perfect sense to use the composite core cable."