Burying electrical transmission lines not so simple

Last modified: 5/19/2014 12:20:19 AM
Arielle Wolfe brought her 6-year-old daughter, Hazel, to a New Hampshire Senate hearing in March to talk about power lines. Overhead electric transmission lines could scar New Hampshire’s landscape, the Derry resident said during public testimony on a bill that would have made putting the lines underground the state’s preference.

“It’s pretty simple,” Wolfe said. “Bury the lines, you can still get the power through the state.”

But it may not be so straightforward. The senate engaged in a lengthy debate on the burial bill last week – considering its effect on jobs, property values, future projects and costs, among other things – before ultimately voting to table the bill on a 16-8 vote.

Industry experts say it is technologically possible to run transmission lines underground; buried projects already exist around the world. But like overhead lines, underground lines have their own set of pros and cons that can be unique to each project. The biggest factor for all underground projects, they said, is the cost.

“The question is, is Bill Gates paying . . . because we can go underground no problem,” said George Gross, an electrical and computer engineering professor at the University of Illinois.

The concept of burying electrical lines in New Hampshire arose largely in response to the $1.4 billion Northern Pass project. It proposes to run 187 miles of electric transmission lines through the state – from Pittsburg to Deerfield – to bring 1,200 megawatts of Canadian hydropower to the region.

The project has agreed to bury 8 miles of line in the northern section of the route at an additional cost of $100 million. Northern Pass estimates the company would spend on average $3 million per mile on overhead and $15-20 million per mile of underground cable, spokeswoman Lauren Collins said.

Opponents of the proposal have said further burial will protect the state’s landscape and tourism industry from unsightly transmission towers.

Currently, the world’s longest underground project is a roughly 112-mile transmission line buried in Australia – 75-miles shorter than a completely buried Northern Pass. It’s more practical to run high-voltage direct current transmission lines along long distances, in part because they have fewer losses.

For those cables, no technical limitation exists on how far they can extend underground, but the cost can vary greatly depending on the terrain, said ABB Vice President of Business Development Roger Rosenqvist, in an email. ABB manufactures underground cable that has a capcity ratings up to about 1,000 megawatts.

For burial, several methods of trenching exist – from directly burying the line to encapsulating it underground in piping. The high-voltage cables – usually about 6 inches in diameter – need to be buried at least 3½ to 4 feet below the ground, Rosenqvist said.

Up above, workers keep a several-foot-wide right of way cleared of vegetation, trees and other external forces that can damage the buried line. “You don’t want roots and things impacting it,” said Kevin Jones, deputy director of the Institute for Energy and the Environment at Vermont Law School.

A major benefit of buried lines is that underground, they are largely protected from lightning strikes, falling tree branches, heavy ice storms and other forces that can take out overhead power lines, said Andrew Phillips of the Electric Power Research Institute. But if something does go wrong and there’s an outage, a buried line is less accessible and could take weeks to repair.

“You’re more likely to have things go wrong in an overhead line . . . but (it’s) much faster to restore,” Phillips said.

The digging process also could churn up new environmental issues, something Sen. Jim Rausch, a Derry Republican, brought up last week during debate on the burial bill.

“You can cut trees anywhere, can clear the land; when you are digging it opens up a whole other can of worms,” he said.

New Hampshire isn’t the only state grappling with sending lines underground.

In Vermont and New York, one company is pushing ahead with two separate plans to bring Canadian-generated power to the Northeast through completely buried transmission lines.

The $2.2 billion Champlain Hudson Power Express would carry 1,000 megawatts of power from Canada to New York City through 333 miles of cables buried both underwater and underground, said Transmission Developers Inc. CEO Donald Jessome.

About 60 percent of the project’s transmission line will be submarine, passing under Lake Champlain and parts of the Hudson River. The biggest advantage of going underwater is the lower price tag – it’s about 60 percent of the cost of burying under the land portions, Jessome said.

The underwater cable is more expensive, but it comes in longer reels – roughly 25 miles long, he said. Fitted on a boat, workers can bury long stretches of the submarine cable without any splicing.

Currently, the longest high-voltage submarine cable link runs roughly 360 miles under the North Sea, connecting Norway and the Netherlands, Rosenqvist said. In the U.S., submarine cables connect New Jersey, New York and Connecticut.

For a 1,000-megawatt underground project on land, a large flatbed truck could carry a reel of cable that is only about 2,000 to 2,500 feet long, Rosenqvist said. It means more splicing along the cable and vaults at each of those splice points, where any problems typically arise, Phillips said.

Jessome said it’s roughly $3.5 million for each marine mile versus $5 million per upland mile.

“Because of the shorter length of cable and the actual construction . . . it is just more labor intensive,” he said.

Jessome expects to get the final permits for the Champlain Hudson Power Express project this fall and, after 3½ years of construction, have the project up and running by late 2018. That all hinges on the funding; the company is in negotiations with multiple parties who would pay to use the line, Jessome said.

More recently, his company launched a similar $1.2 billion project: New England Clean Power Link. That would be a completely buried 150-mile transmission line running from Canada, under Lake Champlain and then underground for the final 50 miles to Ludlow, Vt.

The most important part of considering these projects is balance, he said.

“Can the market afford to bury transmission line? If it can, is that the most effective way?” he said. “If overhead is acceptable to the community, you should do it because it makes smart economic sense.”



(Allie Morris can be reached at 369-3307 or at amorris@cmonitor.com.)




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