Creating stability in a world of unstable electricity distribution

The U.S. power grid resembles the Interstate Highway System criss-crossing the country, and like the interstate system, the power grid has experienced some notorious traffic jams. Based on 1950s technology, the grid is composed of three main geographic sections – one in Texas and two others split roughly along the Continental Divide.

2003 BLACKOUT – A satellite image of the northeastern United States taken at 9 p.m. EDT August 13, 2003 – the evening befoe the blackout. Images courtesy of the National Oceanic and Atmospheric Administration and the Defense Meteorological Satellite Program.

The original power grid

The grid was originally laid out to enable a utility to deliver power to local residential, commercial and industrial costumers. Deregulation has encouraged utilities and other generators to produce more electricity and to transfer it outside their local service area to meet electricity demand elsewhere. Researchers at the Electric Power Research Institute (EPRI) suggest that deregulation is stressing the national transmission system by causing it to operate beyond its design. This possibility is described in the foreword to the Nov. 20, 2003 white paper: "Factors Related to the Sources of Outages on August 14, 2003."

Growing power demand

EPRI analysts also assert that power demand is outgrowing supply. Between 1988 and 1998, demand grew 30 percent, but according to the white paper, only enough new transmission capacity was added to handle about half that amount. A recent North American Electric Reliability Council assessment predicted that electricity demand would grow 20 percent from 2002-2011, but only 3.5 percent new transmission capacity is planned. This imbalance will further stress an already overtaxed electricity supply.

"Argonne's local-area grid is ideal for testing software," Liu explained. "We are one of ComEd's 40 largest customers." More than 4,000 people work at Argonne's one-square-mile Illinois site, and in addition to maintaining office buildings and laboratories, Argonne operates three energy-intensive, national user facilities that operate around the clock.

TELOS tells a lot

Argonne's researchers have been training and testing an intelligent software program that is designed to monitor and control the laboratory's local electrical grid. Similar software may one day be able to detect and correct problems much faster than a human, and on a much larger scale than that of the laboratory system.

POWER GRID – The electric power grid crosses the entire United States.

To accomplish this, Argonne engineers are using software created by the laboratory's research partners at Purdue University. The software is called Transmission Entities with Learning-Capabilities and On-Line Self-Healing (TELOS). Telos is also the Greek word for "purpose."

One of the most unique features of this software is that it was designed to have learning capability. Purdue originally developed the software to be "trainable" using relatively advanced programming techniques called "neural network" and "fuzzy logic." Compared to the "Boolean logic" that governs traditional software, these learning methods more closely resemble the way a human brain works. Neural network software is trained with information and rules about data relationships, much like humans are taught, and eventually the software becomes capable of making decisions.

The TELOS code is written in the Java language and is modular, so that key components can be modified or replaced without affecting other parts of the software. It has been "taught" to understand the sequence in which various electric loads can be "shed" and the best methods to bring new power generating units into service.

TELOS was adapted and set up to accommodate the Argonne local-area grid, which comprises two 138kV lines, eight transformers and a substation – enough equipment and capacity to power a small city. Argonne's researchers trained TELOS with a year's worth of data, including the laboratory's hourly electrical consumption, temperature and humidity information.

Using this historical data, the software "learned" to correlate the historical patterns of electricity consumption with temperature and humidity and, on that basis, to make intelligent forecasts of future energy loads. TELOS was then run for varying time periods – ranging from a few hours to slightly over three months – of Argonne electricity use and weather data to test how accurately it could predict the laboratory's power demand 30 minutes into the future. It proved to be accurate within 3 percent.

"We were surprised," Liu said. "It was encouraging that TELOS was so accurate with no fine-tuning."

The next step is to test TELOS in real time online when Argonne's supervisory power control and data acquisition system is installed to manage the laboratory's power systems. Researchers also want to test TELOS on larger parts of the grid and to study the dynamic behavior of local-area grid interactions.

The nation's electricity grid is so complex that it makes sense to have intelligent computers operating it to make the split-second decisions needed, Liu explained. "We would like to have a self-healing grid one day."

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.

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?"

VULNERABLE – The nation's transmission lines that bring electricity to homes and businesses are vulnerable to damage.

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.