Meet The Cable That Made Burying 52 Miles of Northern Pass Possible

Sep 3, 2015

Wednesday night marked the first in a series of open houses during which Eversource is presenting its latest proposal for a power line that will connect the massive hydro-electric dams of Quebec all the way down to the town of Deerfield, New Hampshire.

This was the public’s first opportunity to ask questions about the project since Eversource announced a new route, which included 52 more miles of buried line. Eversource hasn’t yet finalized its cost estimate, but in what seemed to be a remarkable feat, they say they expect the new burial not to substantially increase the cost of the project.

How is that possible?

“We had to change the cable technology,” explained Eversource New Hampshire’s President Bill Quinlan, “To pursue that amount of underground construction reliably and cost effectively, we had to change from our previous preferred cable to technology to what’s referred to as DC Light technology.”

Lightening up

Previously, Northern Pass was going to be using something called "mass impregnated cable," which has been around since the 1950's and is the workhorse of long-line high voltage cable. The original design would have used four such cables as well as two “metallic returns.”

By switching to a cable called "cross linked polyethylene" or XLP, the company will only be running two cables. The technology is called "light” because it allows the project to shrink from six cables to two.

But in order to shed those four cables, Eversource had to downsize the project from 1,200 to 1,000 megawatts, because that’s the maximum load the XLP cables can handle.

“So the amount of clean energy that’s going to be delivered to New England and to New Hampshire is going to be reduced by 200 megawatts,” said Quinlan on Wednesday night stressing that point, “so that’s a big deal.”

But shedding the cables saves the project money on a number of fronts, especially when it comes to buried lines.

“You don’t need as much width or depth,” says Nathan Scott, an engineer with Burns and McDonnell which helped design the project. He says not only are there fewer cables to run, but the cables themselves are less expensive.  “Basically all the things that are coming into play for the 1,000 megawatts make it cheaper.”

Eversource took the money that it saved by switching to HVDC Light, and plowed it into burying the line through the White Mountain National Forest.

Critics See an Opening

While this might be the first time you’ve heard of HVDC Light, critics of the project have been pushing Eversource to adopt the technology for years, arguing it would allow them to bury the entire line.

“The current proposal is good in that it adopts this new cable technology,” says Jack Savage, spokesman for the Society for the Protection of New Hampshire Forests, one of Northern Pass’ most resolute opponents, “but it’s disappointing in that it doesn’t take full advantage of it, and is only burying a third of a 190-mile line.”

Both the Forest Society and the Appalachian Mountain Club maintain that by going to HVDC Light Eversource could bury the entire line and still have a project that would work financially. A report from the federal Department of Energy last month found that a fully buried line would cost roughly twice as much as a completely overhead line.

Eversource’s Quinlan says to bury more of the line would make for an un-economic project. He told the crowd at the Concord open house that building this line overhead costs $3 million dollars a mile, while underground costs between $8 and $13 million.

“You know, this is a project that someone has to pay for,” he explains. “We think we’ve struck the right balance.”

Proposal Sways Some

And while the most resolute opponents remain unappeased, many politicians are waiting to see how the changes are received by the public at-large.

The rhetoric from some – including Governor Maggie Hassan – has softened substantially. In a recent press call from a meeting between the New England Governors and Canadian Premiers, she said she was “very, very encouraged” by Eversource’s most recent proposal.

“The concerns about the above-ground lines are still a concern for me, but they have decided to bury through the most beautiful areas of the state,” says Linda Kenison a member of the state House of Representatives from Concord. She says the prospect of this much low-carbon energy is what's swaying her.

“I see this as an opportunity for clean, reliable, renewable power without burning fossil fuels. So that’s kind of leaning me toward the project. I’m not 100 percent, but I’m leaning,” she explains.

How many former skeptics are swayed by this change in technology and the burial it allows will become clear as Eversource’s open houses continue.