Feb 27, 2009 - Kate Rowland - energycentral.com
Transmission wires have always been
the transportation workhorses of the electric grid.
Directing electrical current from generation to
substation, these aging electricity highways have
traditionally lacked intelligence.
But faced with the daunting task of
increasing power delivery across the grid in a reliable
and secure fashion -- not one wrought with congestion
and inefficiency -- today's transmission wire manufacturers
are looking at new solutions to transmission issues.
A smart grid solution that focuses
only on information and communications infrastructure
and smart metering activities, said Jack McCall,
director of transmission and distribution systems
for American Superconductor Corporation, is "looking
only at the brain, and not at the brawn."
The brawn, in this case, is the superhighway
of wires that transport the electricity. With this
in mind, the U.S. Department began shoring up the
maturing brain of the modern grid ideal with some
super-powered brawn. With substantial federal investment
in play, it has partnered with industry to introduce
new technology into the power delivery infrastructure
by sponsoring projects showcasing the use of high-temperature
superconducting cables in modernizing electricity
transmission and distribution systems.
One of these, by the superconducting
association and the Long Island Power Authority
(LIPA), is a 2,000-foot-long, 138-kilovolt high-temperature
superconducting cable system capable of transmitting
574 megawatts. The world's first transmission voltage
superconductor cable in operation, the LIPA project
was energized last April. The Energy Department
funded $27.5 million of the $58.5 million total
The hair-thin wires produced are able
to conduct 150 times the electricity of similar-sized
copper wires. This power-density advantage means
transmission-voltage high-temp superconducting cables
can use far less wire to conduct up to five times
more power -- in a smaller right of way -- than
traditional copper-based cables.
The second-generation high-temp "wire
is the underlying smart material," McCall said.
A perfect conductor, the wire is able to instantly
switch to resistive mode when encountering a surge
in current, automatically and instantly suppressing
Another project currently under way
using such cables is being partially funded by the
U.S. Department of Homeland Security Science and
Technology Directorate. The $39-million project
will be operated by Consolidated Edison Company
of New York. Homeland Security is providing up to
$25 million for the project.
This "will enable us to parallel the
substations, improve reliability and resiliency,
and connect much more substantial power in the urban
grid," McCall said. This will better enable the
large-scale introduction of plug-in hybrid vehicles
without severely straining the downtown grid as
commuters drive in to work in the morning and plug
in their cars.
The second-generation high-temp superconducting
cable also provides the ability to bring electricity
into urban areas from more remote generation. The
wire is easy to site in a limited right-of-way because
it has no electrical or magnetic fields associated
with it, and it can also conduct electricity with
virtually no electrical losses.
But superconducting alternating current
(AC) transmission solutions are also getting some
assistance from the direct current (DC) quarter.
ABB's high-voltage direct current cable, developed
in the 1990s, is gaining some major ground in projects
both in the United States and around the world.
With overhead, underground and submarine applications,
it is being used both in environmentally sensitive
areas and in applications where the generated electricity
has to travel exceptionally long distances.
One example, the Cross Sound Cable,
is the high voltage direct current underwater cable
link between Connecticut and Long Island, N.Y. Running
for nearly 25 miles underwater, this line is buried
under the seabed, with a converter station at New
Haven, Conn., and Shoreham on Long Island. The roughly150
kilovolt line has a power rating of 330 megawatts,
and was commissioned in 2002.
"One of the biggest advantages of
direct current in general is that it is controllable,
it's dispatchable," said Mike Bahrman, products
marketing manager for ABB. "You can control the
voltage." He also noted that DC, unlike AC, does
not draw capacitive current, which becomes a limiting
factor as distance increases. "This becomes significant
over 25 to 30 miles."
Of course, the marriage of superconducting
cable and high-voltage direct current cable might
be the perfect combination of capabilities and economics.
It's something the Electric Power Research Institute
is exploring in its current Superconductivity Program,
looking at superconducting DC cable for long transmission.
The research into all types of grid
advancement is well-underway. Ultimately, a more
intelligent utility will benefit all of society
by making energy production more efficient and more