Creating stability in a world of unstable electricity distribution
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Voltage instability
Argonne's researchers are also taking another approach to understanding grid behavior by combining the laboratory's historical data with recent advances in nonlinear dynamics techniques. This approach incorporates substantially greater amounts of Argonne data with a much longer-range focus than the TELOS research.
 VULNERABLE – The nation's transmission lines that bring electricity to homes and businesses are vulnerable to damage. |
Nonlinear dynamics, also known as chaotic dynamics, is a mathematical approach to understanding the behavior of systems that do not respond proportionately to outside influences. These systems are complex, but not random. Many such systems can be found in nature as well as in engineering usage. Chaotic dynamics is often described as the "butterfly effect" – from the early chaos researcher Edward Lorenz's talk: "Predictability: Does the Flap of a Butterfly's Wings in Brazil Set off a Tornado in Texas?"
The nation's electric power grid is a dynamic system with complex connections and time-dependent behavior. For these systems, seemingly small influences can have immense future consequences. In retrospect, such small events – equivalent to flapping butterfly wings – are precursors, or warnings, of grave potential consequences – analogous to Lorenz's tornadoes. Scientists want to determine what these precursors are and then monitor and detect them as a way to pre-empt and prevent larger problems.
Argonne's researchers are just getting started. By treating the laboratory's 1999 electrical consumption data as a record of the behavior of a nonlinear dynamical system, they found that the dynamic systems analysis yielded a single, composite performance measure that appears to effectively describe the Argonne power grid in its normal, stable mode of operation. This parameter is derived from and related to a number of factors that govern and reflect the behavior of the Argonne grid.
"Many conditions go into this complex system," explained scientist Shiu-Wing Tam, "but we know that as long as this particular output from the nonlinear dynamics analysis remains at the critical value, it serves as an indicator that the laboratory's power system remains normal. When the system drifts from this state, it suggests an upcoming problem. But what type of problem and when it may surface cannot be predicted as yet.
"It helps to think of Argonne's electric grid as a human system," Tam said. "When the grid remains at this critical value, it is comparable to a "normal" pulse or blood pressure in the human body. Many complex systems in the human body interact in similar harmony to provide such stable indications of the body's state of health."
When an individual is rushed to the emergency room with chest pains, doctors monitor the patient's vital signs in an attempt to identify aberrant physical systems that could be causing the problem. Once specified, the health problem can usually be diagnosed, treated and, hopefully, repaired.
Butterfly search Now that researchers have a measure of the stable state of the laboratory's power system, they propose to search back through many years of Argonne data to find serious incidents. But just as a doctor would not rely on one – albeit valuable – health factor such as blood pressure to specify one's health state, Argonne researchers want to identify additional performance measures using nonlinear dynamics to increase their understanding of the labora-tory's electric grid system.
This data could one day be used by grid operators to quickly detect incipient changes in the grid's state. Then they will seek the "butterfly" – the small influence that led to the much larger consequence.
"Medical researchers are doing the same thing with heart attack victims," Tam said. "They review patient histories in an effort to determine what early indications might have predicted the heart attack."
The search for electrical incidents will involve detailed analyses of years of data and a lot of computing power and time, but Tam believes that identifying the nature and importance of small precursor incidents can make it possible to maintain the power grid in a stable state. In operational practice, the grid would be monitored for precursors of abnormal behavior. When one of these is observed, grid controllers would use a predetermined control strategy to restore the grid to its normal state. These remedial actions could be facilitated by using hardware of the kind described below.
In addition to the mathematical approaches described above, Argonne researchers are developing new mechanical devices to protect the electric power grid.
New current control device
The laboratory's engineers have designed electrical and mechanical devices to control large power line current surges caused by electrical faults or short circuits. A familiar example of such controlling devices is found in almost every home - circuit breakers. An excessive current surge causes circuit breakers to open. The flow of electricity is shut off, protecting the building's wiring system and electrical appliances.
For high, abnormal fluctuations, fault current limiters instantly intervene and limit power to an acceptable level, such that no valuable transmission equipment will be damaged. Researchers in Europe and Japan are developing fault current limiters, but none are on the market yet.
Argonne's designers took advantage of the natural properties of high-temperature superconductors in developing an advanced fault current limiter. Power overloads normally result in the generation of strong magnetic fields. Since high-temperature superconductors stop working in these strong fields, a transmission and distribution system that incorporates such superconducting components at critical junctions will automatically limit the current flow.
Argonne has combined this fault current limiter concept with a current controller that behaves very much like a large-scale circuit breaker to regulate normal, relatively small, fluctuations of current in electrical transmission lines. The laboratory's researchers believe that this combination of technologies can improve the flexibility and reliability of transmission and distribution systems, protect and extend equipment life, avoid costly upgrades and maximize the effectiveness of power transmission systems.
For more information, please contact Catherine Foster (630/252-5580 or media@anl.gov) at Argonne.
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