With aluminum, it's all about give and take.
Aluminum production consumes a great deal of electricity, but
the material itself gives back as a major component of power
The metal has been the material of choice for
electrical transmission applications for more than 100 years
for investor-owned utilities, rural electric authorities and
electrical cooperatives, said Ian Hewett, president of the
Alcan Cable unit of Alcan Inc., Montreal.
Aluminum cable accounts for the vast majority
of the 212,000 miles of existing transmission lines that exceed
230 kilovolts in North America, Hewett said.
"The key advantages of aluminum are its light
weight, high strength and reliable performance over many
diverse operating environments around the world," Hewett said.
"Aluminum cables are the most economical solution for
transporting power over long distances compared to copper or
other conductive materials."
He pointed to the price and performance
advantage of aluminum cable for transmission applications
compared to other materials. "It takes 2 pounds of copper to
equal 1 pound of aluminum for the same current-carrying
capacity, and the tension to support copper is much greater
than aluminum. The higher material cost of copper and the
increased tension requires more steel in the towers and more
concrete in the foundations." And at less than half the price
of copper cable, aluminum cable offers substantial cost savings
when used in long-distance electrical transmission, Hewett
said, although he could not provide actual cost comparisons.
(From a pure metal standpoint, copper is nearly three times
more expensive than aluminum $3.30 per pound for copper vs.
$1.15 for aluminum based on recent London Metal Exchange
three-month settlement prices.)
The market for aluminum transmission cable
will grow as the country expands power transmission
capabilities. The Edison Electrical Institute said member
companies plan to increase transmission investment by nearly 60
percent to $31.5 billion between 2006 and 2009 vs. 2002 to
2005. The institute's figure represents the total spending
forecast for transmission projects, including towers,
engineering, construction and more. No dollar figure for the
cable or aluminum components was available.
Despite the fact that aluminum cable has been
in service for more than a century, Alcan continues to develop
new products, Hewett said. "We have introduced our HiTemp line
of ACSS (aluminum conductor, steel support) conductors that can
be operated up to 250 degrees Celsius with low sag. This gives
customers a cost-effective option to relieve line sections that
are overloaded or would be in emergency circumstances."
Another new product making its way into the
market is the ACCC (aluminum conductor, composite core)
transmission cable from Composite Technology Corp., Irvine,
Calif. In place of the steel core used in traditional cable,
Composite Technology's new cable uses a carbon-fiber core for
added strength and functionality.
Although the cable, introduced in 2003 on a
demonstration basis, is three times more expensive than ACSR
(aluminum cable, steel reinforced) products, it offers specific
advantages, according to Benton Wilcoxon, the company's chief
executive officer. The composite core of the new cable is less
than one-quarter the weight of existing steel cores but is
twice as strong, and it utilizes trapezoidal-shaped bands of
aluminum for conductors vs. the round strands found in
conventional cable products, which allows a greater amount of
aluminum to be used.
"For any given diameter, we can put in more
aluminum conductor material, resulting in greater conductivity
with the same size cable," Wilcoxon said. The resulting
combination of the composite core and the shaped conductor is a
cable that can not only carry more voltage, but can run cooler
at similar loads. This minimizes thermal expansion and "line
sag," which was at the root of the 2003 blackout that swept
across much of the northeast United States and parts of
The new ACCC cable suffers less "line loss"
than ACSR cable, Wilcoxon said. With lower line loss, ACCC
cable can deliver as much power as ACSR cable with lower
generator loads. The new cable, according to Wilcoxon, can
allow power providers to dial down generators in proportion to
the lower line loss by as much as 10 percent.
The market seems to have taken notice of
Composite Technology's product. Wilcoxon expects 2007 cable
sales of around $30 million, 10 times the $3-million level seen
in 2005. The bulk of the company's sales are in China, which is
rapidly building grid capacity as it undergoes its own
Composite Technology's cable is manufactured
under contract by traditional aluminum wire companies,
including the Quebec facility of General Cable Corp., Belgium's
Lamifil NV and Midal Cables Ltd. of Bahrain. Composite
Technology makes the core from aircraft-grade composite, and
then the various contractors wind the specially shaped aluminum
conductor around it.
Any bare overhead transmission line (as they
are known) needs a grounding wire, and supplying this falls
into the purview of Conex Cable LLC, DeKalb, Ill. "You need
something to protect transmission cables from lightning
strikes," said Jerry Bliss, Conex's sales and marketing
consultant. About 90 percent of overhead bare transmission
cables use ground wires, with aluminum cables serving in this
role as well as in the actual transmission of electricity, he
Superior corrosion resistance, especially in
marine or coastal applications, and greater conductivity makes
aluminum cable ideal for serving as ground wires, Bliss said.
The size or ratio of ground wire to transmission cable is a
function of the voltage being carried on the line, he
With power transmission lines carrying
ever-higher loads, ground wires have grown in importance. As
the level of power being transmitted grows, aluminum's superior
electrical properties in this application will become more
important, Bliss said.