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.

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, however, 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 (Bi2Sr2Ca2 Cu 3O10-x ) and YBCO (YBa2 Cu 3O7–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, Physics Today 0031-9228 493199648 https://doi.org/10.1063/1.881492March 1996, page 48 , and Physics Today 0031-9228 584200541 https://doi.org/10.1063/1.1955478April 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 Selva-manickam, 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.”

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, Physics Today 0031-9228 5712200445 https://doi.org/10.1063/1.1878334December 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 working 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.

Flexible high-temperature superconducting wire can now be made in large reel-to-reel systems. The system shown here deposits the superconducting layer onto flexible metal substrates.

Flexible high-temperature superconducting wire can now be made in large reel-to-reel systems. The system shown here deposits the superconducting layer onto flexible metal substrates.

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Dense urban areas like New York City can replace century-old copper-based cable technology (shown here under William Street near Wall Street) with second-generation high-Tc cables that need less area and distribute more power.

Dense urban areas like New York City can replace century-old copper-based cable technology (shown here under William Street near Wall Street) with second-generation high-Tc cables that need less area and distribute more power.

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