Cold But Super
By using superconductors -- wires cooled to extremely low temperatures -- SuperPower creates electric power devices that promise huge energy savings and improvements in electrical transmission networks
By Tom Gibson
After exiting I-890 in Schenectady, New York, I drive through working class neighborhoods on my way to visit SuperPower. Then, just past a church and convent, the plant comes into sight. The small company operates in a building dating back to 1875, originally built as a knitting mill but refurbished to give it a modern corporate appearance.
Even with the facelift, though, these are not the trappings you'd expect for SuperPower, a company engaged in the cutting-edge science of superconductivity. A bevy of technical people there undertake the daunting challenge of developing superconductors, materials that have no resistance to the flow of electricity when cooled to a very low temperature. SuperPower builds electric power components such as underground transmission cables, transformers, motors, generators, and fault current limiters incorporating superconductors. Why? Superconductors act as perfect conductors of electricity because they dissipate no energy by resistive heating; therefore, they hold tremendous promise for saving energy and improving the performance of these devices and, in turn, our nation's electrical grid.
Superconductivity ranks as one of the last frontiers of scientific discovery, as we have not reached its limits, and scientists haven't fully explained the theories behind it. Although it seems high-tech, superconductivity was actually first observed in 1911 when a researcher cooled mercury to the boiling point of helium, four degrees Kelvin (-452F, -269C). (You remember from high school science class that Kelvin represents a temperature scale with zero meaning absolute zero and equating to -456F).
The first major commercial application of superconductivity came with magnetic resonance imaging (MRI), commonly used today for clinical diagnosis. With this, a strong superconductor-driven magnetic field permeates the body, and hydrogen atoms in water and fat molecules accept energy from the magnetic field. They release this at a frequency detected and displayed graphically by a computer, generating an image of the injured area.
Meanwhile, two researchers at the IBM Research Laboratory in Switzerland opened the possibility of applying the technology to electric power devices in 1986 when they discovered ceramic-based high-temperature superconductors (HTS). Superconductors come in two flavors, low-temperature (LTS) and high-temperature, denoting the level to which a material must be cooled to become superconducting. In this game, "high-temperature" is relative, of course. LTS requires liquid helium for cooling, while HTS can get by with liquid nitrogen, which has a boiling point of a balmy 77K (-379F). This has great significance because nitrogen is cheaper than helium and requires less than a tenth the energy to cool it to its boiling point.
SuperPower traces its origins to Intermagnetics General Corporation (IGC), a manufacturer of superconducting products started in 1971 as a spinoff from General Electric. IGC makes magnets for MRI machines, which use LTS, and in 1988, the company formed a group to develop applications for HTS. In 2000, SuperPower became a separate company with the mission of commercializing electric power devices incorporating HTS technology. Some 20 people from IGC formed the company, and today, SuperPower numbers 56 people, 80 percent of them technical, including Ph.D.s and mechanical, electrical, and chemical engineers -- President Phil Pelligrino is a electrical engineer.
Chuck Weber, project manager, describes SuperPower's mission from an engineer's point of view: "It's very exciting. I get to work on something that very few people in the world are doing, basically in my back yard. I never would've dreamed it was possible to do something to help change the way this country and the world delivers power, more efficiently and environmentally-friendly. I hope to see that come to pass in my lifetime." Weber hails from the area and has a B.S. in mechanical engineering from Union College in Schenectady and an MBA from Rensselaer Polytechnic Institute in nearby Troy, New York.
Reducing Transmission Losses
Drew Hazelton, principal engineer, says it goes even further. "The other main advantage with the HTS cables is the power density. With the same cross-sectional area, you can carry three to five times the amount of power. So in an urban area like New York City, you can pull out your old copper cable, put in HTS cable in the same ducts, and put three to five times the power through that." Hazelton also comes from the area and has a B.S. in materials engineering from RPI and an M.S. in mechanical engineering from Union College.
The challenge lies in producing the necessary lengths of cable and cooling them with cryogenics. As Weber tells it, "In this industry, we're bringing together cryogenic engineering expertise along with electrical utility environments. Putting those together is an extremely challenging task. There are very few people in the world that have experience with trying to do something at high voltage at those temperatures."
At the start, a first generation of superconductors (1G HTS) evolved using bismuth-based materials, and these demonstrated a variety of HTS power devices. Unfortunately, their high silver content and labor-intensive manufacturing process make 1G HTS too expensive for commercial applications.
Enter a second-generation conductor (2G HTS), which uses a new material consisting of yttrium, barium, and copper oxide (YBCO). This yields more than 10 times greater current density than 1G HTS, and because it uses nickel instead of silver, it cuts the production cost up to 80 percent. SuperPower has signed an agreement with Los Alamos National Laboratories to transfer technology for producing second-generation superconductors.
Their brittleness makes ceramic materials nearly impossible to form into conventional round wire, so they take a flat shape. While manufacturing 1G HTS wire involved a slow batch process, 2G HTS superconductors are produced in a continuous process using inexpensive metal alloy tape as a base substrate. Noel Rutter, thin film process engineer, reveals, "That's one of the major challenges, getting a ceramic material onto a flexible tape. The answer is to make it thin enough." Weber adds, "If you can imagine a semiconductor deposition process and now trying to do that on a moving tape for kilometers. You're making a very thin and long wafer."
The tape has five layers, the middle one being the ceramic layer, a tenth as thick as a human hair. Resulting 2G HTS tape measures 100 microns thick and typically a centimeter wide, with the process depositing a buffer, superconductor, and protective layers. SuperPower has multiple pieces of equipment for this, so they can run production on one line and conduct research on another.
Ready for Manufacture
Stepping into the manufacturing area for a tour, we first come to an aluminum ion deposition machine, the first in a line of machines for making tape. Wound on reels, tape feeds through the machines, with most processes done in a vacuum. Ken Lenseth, engineering project manager , joins us. With a B.S. in electrical engineering and a specialty in microelectronics from Rochester Institute of Technology, he came to SuperPower with expertise from the semiconductor industry.
Next we come to a machine for applying the YBCO ceramic conductor layer to the tape. Lenseth and Rutter throw around a big acronym, MOCVD, and tell me it stands for "metal organic chemical vapor deposition" system. Lenseth states, "That's the most important step." In applying the layers, they pump fluid through what he calls "a shower head," actually a nozzle.
Back in a conference room, I peruse a diagram of a superconductor cable with Weber. Many strands of tape form a helix around a copper core known as a former, which looks like a copper cable. Besides providing mechanical strength, the former protects the superconductor when a fault current occurs.
Weber then proceeds to give me a lesson in how cryogenics integrates with the cables. "All three electrical phases are contained in one pipe, and down that pipe, you flow liquid nitrogen, and it's pumped just like any other fluid. The trick is to keep the nitrogen at the proper temperature throughout the cable. Nitrogen is benign to the environment, but it does have some engineering headaches you have to overcome." If so-called warm spots occur, the nitrogen will go into the gaseous phase and expand very rapidly, as it has a gas-to-liquid volume ratio of 700 to one at room temperature, so tremendous pressure can build up inside the pipe. As the ultimate justification of superconductors, however, Weber adds that the energy required for cooling HTS cables is far less than the energy saved by having zero resistance in them.
The three wire assemblies fit within a cryostat, actually two coaxial corrugated stainless steel pipes with a vacuum space between them. The liquid nitrogen floods the space within the inner pipe and reaches the superconducting cable. "If you get a tremendous amount of current flowing through the center, you can create heat and vaporize that nitrogen. So you have to design for those kinds of upsets in the system," Weber explains. "Basically, you've got a 400-degree temperature differential across the space. Maintaining a good vacuum between the two pipes is the key." Standard electrical insulation covers the outside of the pipe assembly.
Sumitomo Electric Industries, one of Superpower's partners in the industry, has just developed a joint to splice sections of cable, enabling long lengths. Informal studies say you can pump liquid nitrogen about one kilometer to cool cable. For longer lengths, you place cryocooling units at required increments along the cable.
New Project on the Horizon
You can feel the excitement building for the Albany Cable Project at SuperPower as they enter the final months of installing equipment. They expect to have it complete and the cable energized by early this summer. Weber relates, "It's very exciting because you see all the hardware being installed." He acknowledges the risk that it won't work as they envision when they flip the switch, and it will become what he dubs "a four-year learning experience." This epitomizes working in the fledgling superconductor business. "You can have tremendous highs and lows. Hopefully, the highs are more frequent than the lows."
With all the potential superconductivity offers in transmission cables, its greatest impact may come with electric motors and generators. Initial applications will be in large AC induction motors over 1000 horsepower, typically used for continuous-duty pump and fan drives found in utilities and industries. They will eventually see use in motors as small as 300 HP. Motors consume roughly 64 percent of electrical energy generated in the U.S., and units greater than 1000 HP account for half of that.
HTS motors will be much more efficient than conventional types, saving significant energy. For example, a 5000-HP, 1800-rpm motor made with HTS would have an efficiency of 98.6 percent compared with 96.8 percent for a conventional type. That may not seem like much, but it reduces losses by as much as 50 percent. And HTS motors will be half as large as conventional ones.
In the construction of a motor or generator, the superconducting tape is woven into the windings of the rotor and stator. Liquid nitrogen is brought into the rotor through the center of the shaft to cool the windings there, using a rotating coupling. Somewhat complex, yes, but the cost of cryogenics pales in comparison to the cost of windings in large motors.
Transformers comprise another opportunity for superconductors. These convert voltage from generation level to transmission level, reducing the amount of energy lost in the transmission of power over long distances. HTS transformers operate at greater efficiency and don't require cooling oil like conventional types, eliminating the possibility of oil fires and environmental hazards. About a third the size of conventional transformers, they can be sited safely in urban areas or inside buildings.
One product SuperPower would make themselves completely is a fault current limiter. In today's high-voltage transmission network, the introduction of new generating facilities and network upgrades can result in fault-current overages on existing protective equipment. Installed in substations, SuperPower's HTS Matrix Fault Current Limiter reduces the fault current to a lower, safer level, so existing circuit breakers can still protect the electrical grid.
So where do superconducting devices stand on their way to commercialization? Weber reports, "Even at this early stage, there are a few niche applications where it would make sense for a utility to consider an HTS cable. As energy prices rise, that becomes more and more in our favor. The same for copper prices rising. We're coming down, while everything else is going up. Wherever that crossover occurs, whoever gets that right makes a lot of money." Weber realizes it will require a long-term selling job on the utility industry. "It's a very slow changing industry. Utilities aren't used to dealing with cryogenics. It's a big step for them to adopt this new technology."
But SuperPower is slowly making strides with superconductors, conquering one of the final frontiers of science in the process. Tremendous energy savings, an improved electrical grid, and a reduced occurrence of blackouts will result from their efforts. And who knows, someday they'll probably occupy a much bigger building than a former knitting mill next to a convent.
For more information on SuperPower, visit www.igc-superpower.com