199 lines
11 KiB
Plaintext
199 lines
11 KiB
Plaintext
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(word processor parameters LM=8, RM=75, TM=2, BM=2)
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Taken from KeelyNet BBS (214) 324-3501
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Sponsored by Vangard Sciences
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PO BOX 1031
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Mesquite, TX 75150
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There are ABSOLUTELY NO RESTRICTIONS
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on duplicating, publishing or distributing the
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files on KeelyNet except where noted!
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October 30, 1993
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POWERING.ASC
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Citation-> Popular Science, Jan 1989 v234 n1 p66(3)
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COPYRIGHT Times Mirror Magazines Inc. 1989
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RINGS OF POWER
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There's been a nuclear attack. An incoming warhead has just struck
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a key U.S. defense site and knocked out the region's power grid,
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leaving the country's ground-based missile-defense system without
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power. In the meantime, the United States has less than 10 seconds
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to fire laser weapons at the next round of incoming missiles. Where
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will the power come from? An emergency electrical generator takes
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15 minutes to spin up, and power is required instantly. The
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solution: tap into giant energy-storage rings that can deliver an
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awesome 1,000 megawatts to the lasers within 30 milliseconds.
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These storage rings do not exist yet, but the Strategic Defense
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Initiative Organization (SDIO) plans to build a football-field sized
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prototype by the end of 1994.
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The heart of the undergound ring, called a superconducting magnetic
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energy-storage (SMES) ring, is a superconducting coil cooled by
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liquid helium to temperatures nearing absolute zero. AT those
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temperatures the coil will have no electrical resistance, and the
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current can be stored almost indefinitely.
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Energy storage rings could also serve an important role for
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utilities. By storing excess power generated during off-peak hours
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and releasing it into the grid during peak hours, the ring could
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increase utility efficiency.
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Experts believe that a SMES unit could be built almost anywhere, and
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because it would have no moving parts, it would be easy to maintain.
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And if efforts succeed in developng high-temperature superconductors
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[July '87, April '88], refrigeration costs will drop substantially,
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making a SMES system more practical in smaller sizes.
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"I've been trying for eighteen years to get funding to build a SMES
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for a large utility," says Roger Boom, director of the University of
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Wisconsin's Applied Superconducting Center in Madison. A portly man
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with glasses and a fringe of gray-white hair, he was not dissuaded
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when the funds did not materialize. But then came SDIO with new
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reasons for investing in the technology.
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"We need a system that will provide about one gigawatt of power
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Page 1
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available immediately when the battle starts," explains Capt. Paul
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Filios, technical adviser to the Defense Nuclear Agency (DNA), the
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agency overseeing the SMES project for SDIO. "We can't get that
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kind of power straight from the power grid. For one, the grid might
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not be there after an attack. And secondly, we need the energy
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equivalent of what a nuclear power plant produces in a fraction of a
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second." The actual figures are classified, but a free-electron
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laser weapon [Dec. 87] would require at least 1,000 megawatts of
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electricity in 3/100 of a second.
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The heart of a SMES is the current-carrying conductor that is coiled
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around the ring 550 times. The number of coiled conductors varies
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from one to four, depending on the design. Each conductor is
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composed of tens of thousands of 27-millimeter-wide filaments made
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from superconducting niobium-titanium alloy and embedded in copper.
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In Boom's design, these filaments are embedded in unalloyed,
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extremely pure aluminum, a soft material about the consistency of
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toothpaste that is an extremely good conductor. If the
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superconductor warms up slightly and becomes resistant, the high-
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purity aluminum will carry the current.
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Keeping it cool
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Another conductor concept being developed by Bechtel National in San
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Francisco uses a ropelike cable of superconducting strands contained
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in a stainless-steel tube. The voids in the tube are filled with
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liquid helium to keep the conductor at 1.8 degrees Kelvin (minus 456
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degrees F).
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To ward off warm-up in Boom's design, the coil will be surrounded by
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a vacuum vessel that acts like a giant thermos bottle with
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superfluid liquid helium inside. Moving outward from the thermos,
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several heat shields are cooled to temperatures progressively higher
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than 1.8 degrees K and further protect the coil.
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In November 1987 SDIO (through DNA) awarded two $15-million
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contracts to develop plans for a test SMES unit. One contract went
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to Ebasco Services in New York and the other to Bechtel. One
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company will be chosen in the spring of 1990 to build the device. It
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will have a 300-foot diameter and be capable of storing about 20
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megawatt-hours of electricity--enough to power 1,000 100-watt light
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bulbs for 200 hours. The model must operate in two modes: fast
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discharge for the ground-based laser (400 to 1,000 megawatts for 100
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seconds), and slow discharge for utility applications (10 to 25
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megawatts for two hours).
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The design must also solve less obvious problems. When the SMES is
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first cooled down to super-low operating temperatures, the entire
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ring, including the coil and aluminum support structure, will shrink
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several feet and tend to move inward toward the ring's center. But
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if the ring needs maintenance, the liquid helium will be drained out
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and the ring will warm up, causing it to expand. To accomodate
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strain on the coil, the ring must have some radial leeway.
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One idea championed by Boom's group is to have two conductors and an
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aluminum support structure between them ripple radially around the
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ring (see drawing). "The nodes of the ripple will be fastened
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through struts to the rock wall," says Boom. "When the coil cools
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down, those nodes stay fixed while the radius between the ripples
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contracts."
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Page 2
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Terry Walsh, Bechtel's project manager, finds fault with this
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rippled support design. "As the coil cools down it's going to be
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pulling against the point where it's restrained," he says. Walsh is
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concerned that these high-stress points will cause strain on the
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conductor as well as dangerous hot spots from friction. He says
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that Bechtel is studying an alternative approach in which a
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telescoping support structure absorbs coil shrinkage and expansion.
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Ring sharing
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The benefits associated with SMES are wide ranging. "With SMES, the
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utility can operate all plants continuously at one hundred percent
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efficiency," says Boom. And in the event of a generator failure,
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"the power control equipment can prevent a blackout by switching the
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unit from charging to discharging in thirty milliseconds," he adds.
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Boom also says that SMES could make it simpler for utilities to buy
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power from intermittent alternate energy sources, such as
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cogenerators and wind and solar power plants.
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Where would a SMES site be located? "It depends on what the
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facility is going to be used for," says Filios. Although a laser
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weapon probably would not be located right next to an electric
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utility, it would be more economical if the two shared a SMES. The
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reason: A SMES is only economical if it's used continuously.
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Otherwise, the savings from generating efficiency are lost to the
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costs of refrigerating the coil. a large 5,000-megawatt-hour
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facility would require a 1-1/2-mile-diameter exclusion zone, so
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populated areas are out. This is because as the superconductor
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cools down it generates strong magnetic forces. The aluminum ring
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must also be buried in a bedrock trench to counterract these forces.
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Although the free-spending military has firm plans for SMES, the
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trick in persuading a frugal utility to build is to reduce operating
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costs. One way of achieving this is with the new generation of
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high-temperature ceramic superconductors. "Without refrigerating
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cost constraints, smaller SMES units could be economical," says
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Boom. So far the current-carrying capacity of these warmer
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superconductors is not high enough to be useful in a SMES facility.
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But the pace of developments in the field lends credence to their
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possible use in the future.
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Boom is optimistic that economical SMES rings could have even more
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exotic applications: storing energy for space platforms or powering
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rail guns or tanks.
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(Refer to 4THSTATE on MHD power generation systems on KeelyNet)
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--------------------------------------------------------------------
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If you have comments or other information relating to such topics
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as this paper covers, please upload to KeelyNet or send to the
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Vangard Sciences address as listed on the first page.
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Thank you for your consideration, interest and support.
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Jerry W. Decker.........Ron Barker...........Chuck Henderson
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Vangard Sciences/KeelyNet
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