July 28, 1999 ROLLA, Mo. -- The current heat wave throughout the continental United States is straining the nation's aging power system, says Dr. Mariesa Crow, an associate professor of electrical and computer engineering at the University of Missouri-Rolla.
"The more uncomfortable it becomes with all the heat and humidity, the more people run their air conditioners," says Crow, an associate professor in UMR's Power Engineering program. "The more the air conditioners run, the more strain is put on our power transmission system."
With temperatures in the 90s throughout much of the nation for the past several days, "it's gotten to the point where air conditioners are running all of the time," says Crow, who conducts research to model and predict the behavior of large and complex power systems. Through funding from the National Science Foundation, Crow is looking into the causes of "voltage collapse" -- a sudden drop in power with little or no warning.
The problem many utility companies are currently facing is not due to a lack of power to run those air-conditioning units, but problems with the distribution of power, Crow says.
"The problem we have is trying to ship power from one place to another over long distances," she says. Because most major power plants are located in remote areas away from large cities, electricity must travel over miles of transmission lines that also are subject to stress during the hot summer.
As the metal transmission lines heat up -- a result not only of the rising temperatures, but also of the electrical power they are carrying -- they expand and sag. For safety reasons, transmission lines can sag only so far. A breezy day can carry away some of the heat and reduce expansion and sagging, Crow says. "But now that it's hot and still, this is one of the worst conditions for transmission lines that we have," she says.
Adding to the transmission problems is the fact that much of the U.S. power infrastructure was built in the years immediately following World War II. The nation's economic growth since then has simply "outstripped the growth of the power system," Crow says.
Yet another problem has to do with the buying and selling of power. In the summer, utility companies in the United States often purchase surplus power from Canada. When the heat wave expands into Canada, however, Canadian companies cut off that supply, Crow says.
Utility companies are trying to alleviate some of the stresses on the power transmission system by building smaller "peak units" nearer to population centers to generate power during these critical times. "That brings the power closer to the people who use it," Crow says, but it costs more to produce electricity with these natural gas- or oil-fired units than with the main power plants.
Another alternative in cities involves planned "rotating blackouts" -- shutting down power in certain sections of a city to relieve some of the stress of demand. "Rather than having the whole system come crashing down around you, only a part of the system is down at one time, and that alleviates some of the stress on the system as a whole," Crow says.
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