CONCORD — Development of underground power transmission lines has been growing for three decades, but it is usually more expensive than high-power transmission lines, a legislative study committee was told Thursday.

Roger Rosenqvist, of the international cable manufacturing company ABB, whose North American headquarters are in North Carolina, told the 361 Commission that the proven technology does exist and is preferred through National Park lands and areas with sensitive aesthetics.

But its economic feasibility is largely dependent on the geography.

Blasting ledge to bury lines is far more expensive than laying cable under a few feet of sand, he said.

The commission is studying the feasibility of developing a state-owned underground power corridor, as an alternative to future development of high-voltage transmission lines and as an income source.

Rosenqvist, who is vice president of business development for grid systems in ABB's Power Systems Division in North America, was invited to come to the commission to help it understand the technology of underground cables.

Rosenqvist outlined projects from Sweden to Australia to Connecticut that have been successful both underwater and underground.

“People don't like to see transmission line towers,” he said.

Polymer insulated cable systems for transmission began to be developed in the 1970s first with 145 kilovolt lines. By the 1980s, it was a proven technology and today there are a number of projects in the United States, including 24 miles between Middletown and Norwalk Conn., developed in a densely populated area by Northeast Utilities, which cost $1.2 billion.

In 2008 the 345 kilovolt line was completed, making it the longest underground cable in the U.S. at the time.

It has been used in the New York City area, between New Haven, Conn. and Long Island and in the San Francisco area, mostly underwater.

Alternating current is used to transmit short distances while DC is better for long distance, Rosenqvist explained.

Another benefit when compared to above-ground transmission is there are no problems with weather.

“There is enormous interest in the industry for this technology,” he stressed, in large part due to aesthetic concerns.

One example is Australia's Murray Link HVDC cable project, 112 miles long, built in a recreational area in 2002.

The Mid-Atlantic Power Pathway Project was considered in Maryland's Chesapeake Bay but was shelved due to a downturn in the economy.

But when compared to above-ground transmission, it would have been slightly less expensive than buying a new right of way, Rosenqvist said.

The Champlain Hudson Power Express is a proposed 330-mile project underwater and underground from Quebec to New York City. The plan will use a large barge to lay cable but it would not be suitable for New England-size rivers, Rosenqvist said.

The 361 Commission is looking at existing rights of way for development of underground cable. The Department of Transportation has suggested it look primarily at state-owned rather than leased rights of way, including highway medians and breakdown lanes and rail corridors.

Maine has designated the median of Interstate 95 for such an underground corridor and already has a potential customer, the Northeast Energy Link (NEL), which would run 220 miles of underground cable carrying renewable power to the New England grid.

The project has been compared to the Northern Pass, a proposed, $1.2 billion, 180-mile hydro power line from Canada to Deerfield, but it differs in that developers here want to use high-power transmission lines, varying in size from 80 to 135 feet high.

Opponents claim the towers would destroy scenery and property values.

Northeast Utilities, which is proposing the project with Hydro-Quebec, argues that the cost of burying the cable is prohibitive and could do more environmental damage. It wants to “improve” 140 miles of existing right of way from Groveton to Deerfield, which is owned by its subsidiary, Public Service Company of New Hampshire, as well as 40 miles of right of way.

For proprietary reasons, Rosenqvist declined to say whether his company is involved in developing cable for the NEL project. But the company has built a $100 million factory just outside of Charlotte, N.C. that will start manufacturing the cable at the end of this year.

If the topography requires laying the line above ground, the cable can be in a protected box.

There is no average cost per mile of buried cable compared to above-ground lines, Rosenqvist said, because the cost varies so greatly.

“In a farm field it's very close,” he said. “But over a mountain ... (it's) much more expensive. ... If you decide to go underground, you look for a route that makes sense.”

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Paula Tracy may be reached at ptracy@unionleader.com.