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Keeping corruption out of power
Jack Raplee
05/01/2000
Mechanical Engineering-CIME
Page 35-37
Copyright (c) 2000 Bell & Howell Information and Learning Company. All rights reserved. Copyright American Society of Mechanical Engineers May 2000
Research partners look to superconductors to bring a current problem under control. By Jack Raplee, Assistant Editor
IT WOULD BE DIFFICULT to find a utility whose objective was to waste money and enemy, or to provide inefficient service that is regularly interrupted, or to render ecological harm. In fact, if there were such providers out there, they would have a simple time reaching their goals.
Providing efficient, uninterrupted, and environmentally responsible power is much more difficult. This challenge is accentuated in locations where weather and outdoor temperatures approach extremes, and where the customer base is large.
One of the hazards utilities must guard against is a fault current, a surge that can be as much as 100 times the normal current flow in power lines. If a fault current is uncontrolled, it can damage equipment, upset the system, and sometimes cause a blackout. Fault currents can have a variety of causes: Lightning, downed power lines, and unwary animals (squirrels, mice, or birds crossing lines to create shorts) are regular culprits. High air temperature during summer months also can overheat a power system and create a surge.
Research sponsored by the Department of Energy and several private-sector companies is exploring superconductors, to see if they can be developed to provide safe, efficient protection against surges on the power grid.
Superconductors have been widely viewed as an energy-saving solution in the flow of electric currents. Traditionally electricity is carried through copper or silver because these elements are the best conductors on the periodic table. Superconductors, however, can conduct current with virtually no resistance when cooled to extremely low temperatures. They carry current very efficiently in the single and double digits of the Kelvin scale. But when their temperature rises above a critical temperature, superconductors become very effective resistors.
Although superconductivity was first observed in 1911, when Dutch physicist Heike Kamerlingh Onnes found mercury to superconduct when cooled to temperatures reaching 4K (-452degF), there was no widespread use of superconductors because it was impractical to cool materials to this extreme temperature.
In 1986, Swiss researchers Alex Miiller and Georg Bednorz developed a ceramic compound that superconducted at 35K. The following year, American scientists at the University of Houston, and the University of Alabama, Huntsville, modified the Miller and Bednorz model and achieved superconductivity at 92K, reaching a temperature higher than liquid nitrogen for the first time. This opened the door to the possibility of practical high-temperature superconductivity research.
In response to these discoveries, the U.S. Department of Energy established a high-temperature superconductivity program in 1988, hoping to develop techniques for potential energy-saving applications.
Realizing that energy reliability was critical in extreme weather, and after witnessing blackouts on the West Coast in the summer and in the Northeast during the winter, the DOE selected several energy-saving projects as part of its Superconductivity Partnership Initiative. SPI is part of the department's high-temperature superconductivity program for the development of advanced power delivery technologies to increase the efficiency, reliability, and capacity of electric power systems.
One of these projects produced a large power utilitysize fault current limiter, which completed a round of testing last year at the Southern California Edison substation in Norwalk, Calif.
IN THE HOT CALIFORNIA SUN
Southern California is one of the most densely populated areas in the United States. It is also subject to some of the country's highest outdoor temperatures, weather-related anomalies (fires, floods, earthquakes, etc.), and other acts of nature not found elsewhere in the country. The efforts of Eddie Leung, former project manager for General Atomics, resulted in a team made up of Southern California Edison of Rosemead, Calif.; General Atomics of La Jolla, Calif.; Intermagnetics General Corp. of Latham, N.Y ; and Los Alamos National Laboratory.
They formed a proprietary partnership to bring advanced superconductor technology to the commercial market. The first phase-to design, build, and test a 2.4kilovolt FCL-began in May 1993, and testing at the SCE Norwalk substation was completed in August 1995. The total cost of the first phase was $4.2 million, which included $1.1 million from the DOE.
On the heels of phase one, the phase two project got under way that same summer, resulting in the much larger precommercial 15-kV FCL, which completed a round of testing last year. It is currently at Los Alamos National Laboratory for further testing, analysis, and improvements.The device contains three high-temperature superconductor coils, each measuring more than one meter in diameter and three-quarters of a meter in height. Each coil weighs over 1,500 lbs.
According to Pradeep Haldar, project manager at Intermagnetics, the three coils represent the largest hightemperature superconducting coils in the world today. Phase two is a $9.8-million, 3 1/2-year program in which the industrial partners will contribute half the funding. The DOE will fund the balance.
Each partner contributed specific technologies to the fault current limiter. Intermagnetics developed the high-temperature superconductor coils, while General Atomics spearheaded the project and functioned as the systems integrator and power electronics developer. Southern California Edison is the end-user participant, and continuing testing and modifications will be conducted at Los Alamos.
"In the first stage of testing, we were able to maintain near 100 percent utilization," explained Syed Ahmed, project manager for SCE. "Because any number of factors can cause a fault current, we were able to test the FCL under real-life situations." He added that while a current controller is always subject to high temperatures because of the amount of current in the flow, outdoor temperatures also play a role.
According to Edward Bowles, manager of power electronics systems at General Atomics, power usage in warm climates is inherently high. Air conditioners and other cooling appliances place high demands on a given utility provider in the summer months. "Our objective was to make high-temperature superconducting useful and, for the most part, this round of testing shows that we did," he explained. "It worked just as we expected, with the exception of an insulation failure that is currently being addressed at Los Alamos." Hot weather made much of the further testing at the substation impossible because, during the summer months, the substation needed to run at full capacity, and testing the FCL could limit this ability.
A GIANT SURGE PROTECTOR
The FCL's three superconductive coils each operates at 35K and carries a continuous do current of 2,000 amps and an ac pulsed current of 9,000 amps. The coils are lighter than those used in conventional power transformers because there is no iron core and superconductor coils are not subject to resistance in the way conventional coils are. The superconductor coils are cooled using refrigerators or liquid nitrogen, making them more environmentally friendly than other coils that are cooled using large amounts of naturally contaminant oils or other cooling substances. The cryogenic temperature of liquid nitrogen requires special care in handling, but the substance itself poses no long-term environmental threat.
"Because the FCL coil has no resistance, currents can be decreased gradually or quickly, depending on the nature of the fault current," explains SCE's Ahmed. The FCL is designed to reduce fault current by 50 to 80 percent as needed, and has a high-speed 3/4-cycle opening switch (12 milliseconds), so the system can shut down before a major fault becomes a problem. Because of its speed, the FCL can maintain a stable current flow in much the same way that a surge protector prevents power overloads to computers, televisions, and household appliances.
"The key function is the ability to control the current and avoid adverse effects on transformers and power lines to avoid power outages,"Ahmed continued. "We gave specifications to General Atomics and IGC, outlining the needs of a utility of our size. We hope this project is successful and will attract other power providers to this technology"
Ahmed said that cost is currently a major drawback to the use of high-temperature superconductors in utilities, but he emphasized that the cost is high because superconductivity is still experimental technology. Once the technology is proven and commercialized, he said, the cost of installing a utility-size fault current limiter will go down. In addition, according to Ahmed, once FCL technology is proven reliable, it will be an attractive option for many utilities. "Some people look at us as a technology testing ground," he added. "Utility companies want to see proven results before taking in a new technology"
According to the DOE, smaller-scale limiters have been tested for use in single facilities, but this is the first one designed to meet the needs of a full-scale utility.
GETTING THE KINKS OUT
Although an insulation failure in one of the three coils forced the tests to become single phase (like one link in a chain), each of the partners involved considers this round of tests successful. From the substation in Norwalk, the FCL was trucked to Los Alamos National Laboratory. There a site has been established to house the FCL for further testing and revision.
"Right now, we're optimizing the cryo coolers to make sure the downleads can handle high temperatures," said Dean Peterson, director of the Superconductivity Technology Center at Los Alamos. "We also plan to dismantle each cryostat and perform a detailed inspection."
From there, the unit and its individual components will undergo several tests, including trials of various technologies to improve the insulation capability of the unit.
"The primary work we will be doing here is a series of pulse tests," Peterson continued. "Because the specs call for the coils to handle pulses as high as 4,000 amps, we plan to test it at 10,000. This way there can be no question of their ability to handle the largest possible fault currents:' He said this is only one example of simulation tests the laboratory will conduct before reviewing the unit for approval by the other industrial partners.
Peterson said this round of testing should be complete by this September. At that time, Los Alamos personnel will evaluate the FCL, and the end-user utility (likely SCE) will place it in service for approximately a year for testing in real-life conditions. (The DOE is still evaluating the possibility of the team continuing to work together on the project.) Then the DOE will determine if the FCL is ready for real-time commercial use.
If all goes according to plan, this technology would be available commercially to utility providers sometime in the next two to three years.
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