Somewhere under Albany, New York, 350 meters of chilled
high-temperature superconducting cable is delivering electricity at three to five times the
capacity of copper.
Downstate, below the bustling
streets of New York City, Consolidated Edison is making room to install space-saving HTS technology
with security features in one of the world's largest systems of underground electric cables, some
34 000 kilometers of them below Manhattan alone.
East of the city, a 600-meter
span of 138-kV HTS cable prepares to power part of Long Island in the first high-Tc
live grid demonstration conducted at transmission voltages.
"High-temperature superconductivity
is a revolutionary and cross-cutting technology that can transform our nation's electricity
infrastructure," says Deborah Haught, superconductivity program manager for the US Department
of Energy. In 2007 DOE pledged more than $51 million for two to five years of grid demonstrations
through additional superconducting power equipment (SPE) projects that involve partnerships
among the utility industry, wire and cable manufacturers, and US national laboratories.
Commercial challenges
When Georg Bednorz and Alex Müller
at IBM's Zürich Research Laboratory in Switzerland announced superconductivity at 35 K,
scientists and nonscientists alike projected a future of levitating trains, lighter power equipment,
and cheaper electricity. The excitement spiked in 1986 when Paul Chu at the University of Houston
and others discovered novel cuprate-perovskite materials that exhibited no resistance or heat
loss under current flow at temperatures above 77 K, the boiling point of nitrogen. Flexible superconducting
wires were hailed as the building blocks for the "superconductivity revolution," according to
a 1987 Time magazine cover story. HTS technology was all but assured greater commercial
success than its helium-thirsty, niobium-based low-Tc counterparts that
thrive in medical magnetic resonance imaging systems and particle accelerators.
For the next several years,
how-ever, HTS commercialization remained crouched in the starting blocks. Most applications
awaited the development of an affordable, reliable, flexible wire, and only two of the cuprates
had emerged as candidates—BSCCO (Bi2Sr2Ca2Cu3O10-x)
and YBCO (YBa2Cu3O7–x). Both are brittle
ceramics characterized by suppressed current densities due to misoriented grain boundaries
and magnetic flux creep, but BSCCO received the initial nod from manufacturers because the metal
oxide precursor could be packed into a sheath of silver and mechanically and thermally deformed
into flexible filaments. The process, known as the powder-in-tube method, partially aligned
the grain boundaries in BSCCO and mitigated the problem of intergranular current flow. BSCCO wire
is now made in kilometer lengths with critical current densities on the order of 104 A/cm2.
Those first-generation (1G) wires have since been exploited for many bulk applications around
the world (see the articles on power applications of HTS in PHYSICS TODAY, March 1996, page 48, and
April 2005, page 41).
The Long Island Power Authority
is close to energizing its HTS demonstration transmission cable, which is made of 1G BSCCO wire
from American Superconductor Corp (AMSC) in Westborough, Massachusetts. LIPA has plans to retain
an HTS cable permanently if the demonstrations are successful, says Tom Welsh with KeySpan Corp,
a company that provides R&D support to LIPA. Another major 1G cable demonstration using AMSC-manufactured
BSCCO wire is currently in operation at an American Electric Power substation in Columbus, Ohio.
The 13.2-kV cable rated at 3000 amperes was assembled by Ultera—a joint venture of Georgia-based
Southwire Co and NKT Cables Group of Denmark.
However, both AMSC and
its major US competitor, SuperPower Inc, in Schenectady, NY, have abandoned BSCCO due to long-awaited
manufacturing success in depositing nearly single-crystal layers of YBCO onto nickel-alloy flexible tapes. "The first-generation
wires were somewhat of a stopgap because they contain a high amount of silver, which presents a barrier
to reducing the cost," said Patrick Duggan, a project manager with Con Edison. YBCO exhibits critical
current densities on the order of 106 A/cm2 and also outperforms BSCCO
at elevated temperatures in high magnetic fields.
Second-generation (2G)
wires, also called coated conductors, are now being manufactured primarily by two processes:
ion beam assisted deposition and rolling assisted biaxially textured substrates. IBAD and RABiTS
were advanced in the mid-1990s by Los Alamos and Oak Ridge national laboratories, respectively.
IBAD relies on texturing the buffer layers between the YBCO and the metal substrate, while RABiTS
textures the metal substrate and then grows the superconducting layer epitaxially onto the biaxially
aligned template. "A key advantage of our technique [IBAD] that we have been able to exploit is deposition
of the YBCO layer at very high rates over large areas," says Venkat Selvamanickam, vice president
and chief technology officer at SuperPower, which obtained an exclusive license to IBAD from LANL.
Both 2G processes feature
the inclusion of nanoparticles that strongly enhance the critical current density by effectively
pinning magnetic flux. The potential for further wire optimization through the two processes
has prompted both AMSC and SuperPower to focus exclusively on 2G wire production. "It's an exciting
time for this field because in the last 12 months, it's become quite clear that these processes really
do work on the production scale," says David Larbalestier, a researcher at Florida State University's
applied superconductivity center.
In October 2007, National
Grid USA, Albany's electric provider, began cooldown to 77 K of what is expected to be the world's
first in-grid demonstration of 2G HTS cable. Since 2006 the company has demonstrated problem-free
operation of a 1G BSCCO wire manufactured by SuperPower and assembled into cable by Sumitomo Electric
Industries Ltd of Japan. The cable was installed in two segments—320 meters joined to 30
meters. National Grid is scheduled to re-energize the system after exchanging the 30-meter segment
for a 2G cable.
"LIPA will almost certainly replace
the BSCCO cable with 2G cable," says Welsh, adding that 2G cable should be installed in late 2009.
Other utilities are adopting
more of a wait-and-see approach. "This technology seems promising and nearer than what people
expect, but at this point we are closely following the progress," said Shih-Min Hsu, a planner with
Southern Co, a utility based in Atlanta, Georgia, serving the southeastern US.
Hsu and others believe
that HTS cables are best suited for dense, urban areas. Says Welsh, "It's going to be a niche market
where you need more power transmitted than you have the room for . . . or if you're forced
to go underground."
The US Department of Homeland
Security sees security benefits to HTS technology and is supplying up to $25 million of the $39 million
price tag for AMSC to deploy HTS technology in lower Manhattan. Code-named Project Hydra, the system
will permit Con Edison to add more connections between substations while simultaneously protecting
the higher-capacity system from fault currents—power surges that could damage costly
breakers and other grid equipment. Above a critical current, 2G HTS wire transitions from being
highly conductive to being resistive. That enables the wire to suppress power surges.
The technology in Project
Hydra will feature Secure Super Grids, an AMSC cable system that inherently limits fault currents.
"We are developing an inherent fault-current-limiting cable for demonstration later in 2008.
With this success, we will then make the full-length cable, using several hundred meters of wire,
for installation in New York City's [electrical] grid by 2010," says Alex Malozemoff, chief technical
officer at AMSC. AMSC and other companies also are developing standalone fault-current limiters
using 2G wire.
The Electric Power Research
Institute in conjunction with Con Edison "expects to set up a forum to engage other utilities on
Project Hydra so that lessons learned would be immediately passed on," says EPRI technical manager
Steven Eckroad. "Any success from an HTS cable demonstration will promote the paradigm shift that
the utilities need."
Smart grid
Deregulation has left utility companies
undermotivated to make risky, large-scale upgrades, says Phillip Schewe, a science writer at
the American Institute of Physics and author of The Grid (Joseph Henry Press, 2007), a popular
book on the electrical infrastructure. But after the unprecedented blackout of 2003, Congress
mandated several efforts to modernize the grid, including the formation, through EPRI, of a grid-improvement
task force that highlighted the need for an additional $8 billion to $10 billion above the current
annual $18 billion to $20 billion investment in the grid (see PHYSICS TODAY, December 2004, page 45).
Massoud Amin, an electrical
engineer at the University of Minnesota and developer of the "self-healing grid" model, lists
HTS cables as a critical enabling technology for a smarter, modernized grid. Smart, self-healing
grids are highly networked and rapidly communicate failures to minimize their impact. HTS fault-current
limiters provide the failure mitigation that smart grids would need. "New technologies for the
grid will require sustained funding and commitment to R&D," Amin says. He adds that while investments
in a smarter grid are not cheap, the estimated $80 billion per year cost of electrical failure makes
it worthwhile. AMSC and SuperPower both expect volume production to lower the cost of HTS wires,
but more research needs to be done on lowering the cost of the entire HTS cable system, says Eckroad.
Not all wire manufacturers
are completely abandoning BSCCO technology. Sumitomo, which makes both HTS wires and cables,
continues to advance the performance of its BSCCO wire, which is made by a high-pressure modification
of the powder-in-tube method. Randy Shaw, a manager at Sumitomo, says that the company has a coated-
conductor development program and purposefully does not use "2G" to refer to its wire design. Shaw
also confirmed that the world's first commercial sale of HTS cable—a contract signed in
2004 with the Korea Electric Power Research Institute to construct a 100-meter, 22.9-kV distribution
cable—will use Sumitomo's BSCCO wire. "For applications that require high field, 2G is
better," says David Lindsay of Southwire, "but BSCCO is a very good product that meets all the technical
requirements for cabling, and it's still the cheaper option." He also said that there is "no economic
or technical justification" to retrofit the Columbus demonstration with 2G cable.
Takashi Saitoh, a manager
at Fujikura Ltd in Japan and member of the International Superconductivity Technology Center
also in Japan, says that although there are no current plans to insert HTS devices into the Japanese
power grid, ISTEC and several wire companies are continuing the development of 2G HTS wires with
support from Japan's Ministry of International Trade and Industry. The Dutch utility NUON is work-ing
with NKT Cables to develop a 6-kilometer-long HTS transmission cable—10 times the length
of the LIPA cable—to service Amsterdam, said Heinz-Werner Neumüller of Siemens and
chairman of the Consortium of European Companies Determined to Use Superconductivity (Conectus).
According to Lindsay, funding details or even the choice of wire for the Amsterdam project has not
been finalized.
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