By Dr. Venkat Selvamanickam, IGC-SuperPower
On a site in Schenectady, NY, IGC-Superpower, a wholly owned subsidiary of Intermagnetics General Corporation, is currently building pilot-scale second-generation high-temperature superconducting (HTS) technology.
Until now, the promise of high-temperature superconductors has not found practical application, for both cost and performance reasons. First-generation, silver-based HTS materials are inherently costly. Moreover, their performance advantage over conventional copper and aluminum wires has not been large enough to stimulate widespread interest.
High-purity silver accounts for about two-thirds of the materials composition of first-generation BSCCO-based superconductors, making them too expensive for practical use. In addition, they are fabricated using a labor-intensive batch process, in which the superconducting material is packed into silver tubing, heat-treated and then drawn and rolled in several stages to form HTS tapes. This process also potentially impacts product quality in two ways: in materials consistency and in the opportunity for operator error.
A sample of a 2nd generation coated conductor, which is flexible enough to wind. Click here to enlarge image
Second-generation HTS technology, however, is made from less-costly materials using a continuous, highly automated process. These attributes represent major steps toward achieving a cost-benefit ratio favorable enough to make HTS technology commercially viable.
Second-generation HTS technology uses inexpensive nickel or stainless steel alloys. Less than 5 percent of the material’s composition is silver, which is used only as a protective coating. Using an automated, continuous thin-film deposition process similar to those found in the semiconductor industry, multiple layers of thin films-buffers, the HTS layer itself, and a silver overlayer-are deposited on a flexible metal substrate. This is done in reel-to-reel mode, similar to the way aluminum foil or adhesive tapes are produced.
The process facilitates intermediate quality-control (QC) steps, also performed in reel-to-reel mode, to track and eliminate defects that may arise in any processing step. These QC steps include monitoring the substrate’s surface quality with laser-based roughness monitoring equipment, and monitoring the crystalline quality of the buffer layers with X-ray-based texture measurements.
Operator handling of the materials is minimal.
Second-generation HTS technology also offers better performance. It offers higher currents, at higher temperatures, and in background magnetic fields. By the end of 2002, IGC-SuperPower intends to achieve rated performance of 100 amp-meter in greater than one-meter tape lengths, and by the end of 2003 to achieve rated performance of 1000 amp-meter in greater than 10-meter lengths.
Also, since second-generation HTS tapes will operate at higher temperatures, they will require less cooling than existing HTS technology.
The bane of high-temperature super-conductors has been their brittleness. Second-generation HTS technology is flexible enough to be wound into coils and on formers. It will enable products like:
- Transformers that are efficient, compact, lightweight and can operate indefinitely at twice their rating with no impact on reliability. Because they contain no hazardous or flammable materials, they can be used in dense urban areas and on the upper floors of buildings.
- Fault current controllers, which increase the grid’s flexibility and improve safety, reliability and power quality. They limit damaging high-current fault transients (like lightning strikes) without shutting down sensitive electronic equipment, and allow substation capacity upgrades with no need to replace existing switchgear.
- Underground distribution cables that carry three to five times more power than conventional cables. They need no cooling oil, allow longer pull lengths because they are lighter, and will enable capacity increases with no need to dig up the streets.
IGC-SuperPower recently reached a key milestone by achieving continuous production of meter-long second-generation HTS tapes. This demonstration of continuous production is a critical stepping-stone toward achieving ever longer lengths of HTS tapes and, ultimately, routine volume production of the material in kilometer lengths.
In 2001, IGC-SuperPower was granted an exclusive license for second-generation HTS process technology from the DOE’s Los Alamos National Laboratory, and has developed additional technology exclusively with Los Alamos and Argonne National Laboratories during the past year. Los Alamos and Argonne are assisting in scaling up their process to commercial lengths. IGC-SuperPower also has extensive intellectual property via patents and a fundamental composition-of-matter license from Lucent Technologies.
Real world demonstration project
IGC-SuperPower is leading a $20 million project to install an underground HTS distribution cable to power portions of Albany, NY. A 400-meter-long section of HTS cable will be installed in Niagara Mohawk Power Corporation’s power grid, the first HTS cable to be installed between two substations.
A glimpse into the pilot-scale coated conductor processing facility at IGC-SuperPower. Click here to enlarge image
The New York State Energy Research and Development Authority (NYSERDA) is contributing $6 million for the project, expected to be completed in three to four years.
While first-generation HTS technology will be used, the project will include a laboratory-scale test of a cable section made from second-generation HTS, in line with IGC-SuperPower’s goal of developing a commercial-level manufacturing process.
The success of such efforts will have a far-reaching impact on the electric power industry and its customers.
Selvamanickam, program manager, materials for IGC-SuperPower, can be reached at vselva @igc.com. He directs the effort to commercialize the production of long lengths of HTS coated conductor that are partially supported by contracts from the DOE, Air Force, and NYSERDA.