As air conditioners hum at full capacity during the summer heat, Tennessee Tech University researchers are watching high-voltage power lines that heat up, stretch and sag during the power demand.

Power line sag caused two major U.S. blackouts in 1996 and 2003, and researchers at our Center for Energy Systems Research have collaborated with TVA and Oak Ridge National Laboratory to measure power line sag with global positioning system technology.

	At the National Transmission Technology Research Center at Oak Ridge National Lab, assembly of the “power donuts” used to transmit to a GPS system is completed. Participating are TTU R&D engineer Robert Craven, ORNL’s Dr. John Stovall, TTU student Craig Schuff, and ECE professor Satish Mahajan.

“When an excess of current is passed through a section of power line, it thermally expands and can sag even 16 feet or more,” says Sastry Munukutla, director of our Center for Energy Systems Research (formerly the Center for Electric Power). “Overloaded lines may break or collide with other objects, causing power interruption.

“Since power lines typically have unobstructed views of global positioning satellites, the technology provides a means of direct measurement of sag,” Munukutla says.

Referred to as “power donuts,” the devices placed on the power lines to transmit information to a GPS resemble tubular, sliver wheels with spokes. Satish Mahajan, professor of Electrical and Computer Engineering directing the university’s portion of the project, says his team’s goal is to measure sag within one inch.

“It’s a big deal to replace high-voltage lines that have been in operation for 30 to 40 years; it’s expensive,” says Mahajan. “We are testing to be able to push more power through the existing lines, even overloading some components in the line by 400 percent in the lab, to monitor what the lines are truly capable of handling.

“We want to find out how much overload the lines can stand and for how long,” he explains.

David Till, TVA’s transmission planning department manager, says having this information can greatly increase the efficiency of power providers, who can pass the savings on to customers.

“This is a tremendously practical research and development project,” says Till. “If we overload a line and it causes immediate problems, it costs the consumer a lot of money.

“If we have information that allows us to know that the line can stand an overload for a certain period of time — like 30 minutes to an hour — we can anticipate the consequences and operate more efficiently so that unexpected costs don’t occur.”

After receiving a $1 million grant from the Department of Energy last year, TTU has led the effort to solve issues related to high-voltage transmission. HV lines crisscross the country to transport electrical power relatively long distances from generators at power plants to substations and ultimately consumers.

TTU is working in two other areas related to HV transmission beyond the GPS measurement. The Center established a $200,000 current transformer lab and is conducting thermal modeling of current transformers using computational fluid dynamic techniques.

“We want to complement our excellent work in the lab by following through with modeling techniques,” says Munukutla. “We also are investigating reactive power compensation.”

In its 21-year history, the Center has worked with 22 major utility companies in the United States, India, New Zealand, and China.