IOWA STATE (US)—Engineers have designed a new type of transmission pole that is hinged, making it easier to install and repair. It also resists the kind of cascading failures that can lead to widespread power outages.
Current metal poles are built to take whatever weather comes at them, so they’re big and round and sturdy—as much as 12 feet in diameter and 100 feet high. But transmission poles can still fail under the stress of extreme ice and wind. They’re also vulnerable to an infrastructure attack. And when one of them falls, others are pulled down until heavy dead-end structures stop the cascading collapse.
“There are long stretches of these transmission lines across the countryside,” says Jon “Matt” Rouse, an Iowa State University assistant professor of civil, construction, and environmental engineering. “If you take down one of the poles, you take 10 miles of poles out with it. It’s very important to protect these structures.”
Rouse has worked with Casey Faber, a graduate student in civil engineering, to develop the new hinged design. They say the key was to take a new approach to structural design.
“We’re designing a structure based primarily on its deformation ability rather than its strength,” Rouse says.
The result is a nominally rectangular pole with a built-in hinge near the base. There are metal plates on either side of the hinge that act as replaceable structural fuses—they stretch and buckle when the pole sustains an extreme load, allowing it to deflect while shielding the rest of the pole from damage.
There are also tendon cables running up and down the inside of the pole that resist stretching and work to keep the pole upright. And so when there’s a failure, the fuses bend, the hinge pivots, the interior cables tighten and nearby poles are allowed to pick up some of the load.
“If a structure can deform sufficiently, it can allow the rest of the system to use reserve strength from other structures,” Rouse says. “It allows the next pole down the line to share the load of ice, wind, a broken line or an attack, rather than forcing one pole to withstand the load on its own.”
Rouse and Faber have used support from Iowa State’s Electric Power Research Center to successfully test a prototype pole and are working to secure a patent. They also say the utility and power structure industries have expressed interest in their technology.
The time is right for better power structures, Rouse says. “The country is in the midst of a major shift toward wind power,” he adds. “We’ll be building a lot of transmission lines over the next 20 years. We really need to address these reliability and security issues.”
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