Along 240 Miles of Power Lines, Preparing Every Tower for Winter’s Wrath
Eric DeChent, an inspector for Con Edison, scaled a tower in Verplanck, N.Y., to check for structural problems.
With the leaves turning and the temperatures dropping, homeowners are chopping wood, storing lawn furniture and weatherizing windows.
Mr. DeChent and Doug Wassil, driving, can inspect about 30 towers a day.
Doug Wassil and Eric DeChent have a different winter checklist: Help inspect the 1,600 towers that support high-voltage electrical lines in New York City, Westchester County and points farther north. On a recent morning, the two men, who work in Con Edison’s transmission line maintenance department, used binoculars, hoists and voltage meters to ensure that the towers’ concrete bases, steel beams, ceramic insulators and other hardware will be able to withstand the high winds, freezing cold and heavy snow that winter brings.
“Basically, we want to batten down the hatches,” said their boss, George Czerniewski, standing below a tower not far from the Indian Point nuclear power plant.
The stability of Con Edison’s towers, some nearly 500 feet tall, is critical to the health of the state’s electrical grid, which carries much of the power New York City needs from upstate. If one of the lines carrying up to 500,000 volts of electricity were downed by a falling tree, high winds or ice, parts of the city and its suburbs could go dark.
That is why each of the towers along the 240 miles of Con Edison-owned pathways that stretch from Dutchess County to the Bronx-Yonkers border is inspected twice a year, or more if maintenance is required. Every month, inspectors in helicopters fly over the towers and the hundreds of miles of cables between them.
Winter weather, though, brings additional risks and can make it more difficult for workers to get to the towers, some of which can be reached only by all-terrain vehicle.
“The worst for us is when ice builds up and wind pushes the cables and puts stress on the towers, which can break an arm,” said Mr. Wassil, 53, who has worked on transmission lines since 1983 and was finishing the fall patrol with Mr. DeChent late last month.
Like Con Ed’s half-dozen other inspection teams, the two men inspect about 30 towers a day. First, they use binoculars to survey the joints of the steel towers and the health of the equipment at the top. The ceramic, circular insulators, for instance, can be damaged by lightning — or by frustrated hunters, who have been known to shoot at them when deer are scarce.
They search the base of the tower for cracks and graffiti, a telltale sign of potential damage elsewhere. Sometimes, intruders dump washing machines, cars and barrels of toxic chemicals around the towers. Thieves try to remove grounding wires in hopes of selling the copper in them.
Nests are another potential hazard. Hawks, vultures and raptors carry food to their perches that can end up damaging equipment. Red-tailed hawks and turkey vultures can also short-circuit feeders when they leap off cables and discharge streams of excrement that, at up to 12 feet long, can simultaneously touch a live wire and a grounded structure. Nests without eggs in them are removed.
Then there are the trees — hundreds of thousands of them. Con Edison uses light detection and ranging technology, or Lidar, to keep track of every tree, cable, tower and other structure on its property. To create a map accurate to within two feet, helicopters equipped with devices that shoot 50,000 laser pulses a second survey the pathways. The heights of the objects below are determined by how fast the laser beams bounce back.
Con Edison paid a contractor about $500,000 in 2005 to create a map and a parallel database. On a spreadsheet of one stretch between Buchanan and the Hudson River, Mr. Czerniewski could see each tower, the sag of the cables and their horizontal and vertical clearance from trees nearby. He could also see the distance of the cables between towers.
The database helps Con Edison prioritize its three-year tree-trimming cycle. On his spreadsheet, Mr. Czerniewski could see that trees that were less than 10 feet from a cable were colored red and had to be trimmed first. Those that were 10 to 20 feet from a cable were marked yellow, while those more than 20 feet from a cable were green and considered out of harm’s way.
Con Edison also uses the database to determine whether residents living along its rights of way can plant trees abutting the property, and to decide whether trucks would have enough room to pass under transmission lines.
On a computer at Con Edison’s headquarters near Union Square in Manhattan, each tree along one stretch looked like a lollipop: Circles had been drawn around the trunks indicating how far they could fall in every direction. Some trees had circles that crossed over the circles around other trees and transmission lines, suggesting potential problems.
Orville O. Cocking, an engineer in the utility’s substation and transmissions group, can also analyze the impact of extreme temperatures, high winds and ice to determine whether cables and other equipment need to be replaced.
“You can play a lot of what-if games,” Mr. Cocking said. “This lets us know whether we can add extra weight to the towers.”
With winter approaching, though, Con Edison is intent on clearing trees in danger of falling into towers or transmission lines. Along a 9.5-mile corridor between Buchanan and Millwood, a team of contractors was busy removing oaks, birches and other trees to create a quarter-mile clearing. In one clearing, a feller buncher — a kind of bulldozer with a giant claw in front — grabbed the trunk of a black locust.
In one motion, the machine ripped the tree out of the ground. Shrubs and small trees nearby were left intact because they do not grow fast enough or high enough to pose a danger, according to Mike Amato, a field operations planner who oversees the tree-trimming and removal program.
“Lidar kind of sets a benchmark and puts into perspective whether your eye is right, whether the tree might hit the line,” he said.
http://www.nytimes.com/2008/11/10/nyregion/10tree.html?_r=1&ref=nyregion
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