Posted on Monday, April 12th, 2010 at 11:00 am in Writing
Nantucket Island, Mass. – Once a booming whaling port, this island off Cape Cod is now a hot vacation spot with a growing year-round residential community. In fact, the island’s population grew 58 percent from 1990 to 2000 (Source: U.S. Census). With this growth came the realization that the existing 35 megawatt electric transmission cable serving the island from Harwich, Mass., would soon reach its capacity.
“The growth on the island was beyond forecasts,” said Dave Fredericks, vice president, Electric Operations, Nantucket. “In an effort to preserve the reliability of service to Nantucket, it was determined that a second submarine cable would be required. For this second cable, an effort was made to create a distinct route, so we opted to feed the cable from Hyannis instead of Harwich.”
These decisions, however, would require a lengthy approval process from 2004-2005, which was preceded by routing studies and regulatory agency meetings beginning in 2001. Many federal, state and local officials needed to review the plans before the second cable could be installed from Hyannis to Nantucket.
Licensing and Permitting
“It took 18 months to secure all of the licensing and permitting required, as well as public input,” said Joe Carey, principal engineer and project manager. “Through it all, though, we received almost unanimous community and regulatory approval.”
During the permitting process, Technical Advisory Groups (TAGs) were convened in Barnstable, where the substation would be constructed, and Nantucket. The TAGs were comprised of local officials, members of civic organizations and the National Grid project team. TAG meetings were held to share information and provide input that helped determine the final land routes of the cable.
“A great benefit of the TAGs was that we were able to make sure that local officials understood the project and its benefits to Nantucket residents,” commented Carey. “The process really helped build support for the project.”
In total, 28 local permits, licenses and approvals were required before construction on the cable project could begin in January 2005.
Land Construction
To begin, the project required construction of a new substation on mainland Massachusetts as well as more than 5.5 miles of underground manhole and duct systems to connect the submarine cable to the new Merchants Way Substation in Hyannis and the existing Candle Street substation at Brant Point on Nantucket.
“However, in an effort to work with the TAGs and continue positive community relations, we agreed to a moratorium on construction in public rights of way on Nantucket and Hyannis from May to September,” said Carey. “The shortened time frame created challenges, but we were confident that we could still plan to install the submarine cable and have it in service by the end of 2005.”
Then the region experienced one of the snowiest winters on record in early 2005 – more than 100 inches of snow fell, nearly four times the normal amount.
“But, even with the weather delays and the aggressive construction schedule, we were able to achieve our goals prior to the May moratorium,” said Carey.
Once land construction was complete, the task of installing the submarine cable was next.
The Submarine Cable
“The design and benefits of the second submarine cable are very similar to the first undersea cable that serves Nantucket,” said Fredericks. “However, a distinct route and connection to the transmission grid were necessary for optimum reliability.”
To install the cable, a satellite-guided ship tows a device called a hydroplow, which liquefies the ocean floor with water jets spurting up to 400 gallons a minute through a hollow plow blade. The cable spools off the ship, down through the hollow blade of the jet plow and is laid in the trench 8 feet below the seabed. The sands and sediments then naturally settle back into the trench to cover the cable.
The installation team expected that the submarine cable would arrive in September 2005 from the manufacturer located in Naples, Italy. However, delays prevented delivery of the cable until early December. Still, with installation scheduled to begin on December 18 the project team believed the cable could be in service before the end of the year.
By December 26, 10 of the 27 miles of cable were installed. That night, however, a storm passed through the area, snapping the anchor line on the ship and damaging the cable.
“Given the damage, we decided to continue the cable installation by redeploying to the Hyannis side and work towards the damaged section,” said Carey.
Fixing the damaged section required a repair barge, as well as dive vessels to complete underwater repairs and the coordination of many National Grid departments involved in the whole project.
“We wanted to continue the cable installation while waiting on the repair barge to arrive,” explained Carey. “Once on scene, we would splice the damaged area to connect the two sides. However, this increased our original 20-day installation plan to 120 days.”
Construction Complete
Despite weather delays, aggressive construction schedules and a challenging cable installation, the second undersea transmission cable to Nantucket went into service on April 18, 2006.
“There is no doubt that this project ran into difficulties,” said Fredericks. “Not only were our contingency plans successful in mitigating various challenges, but the dedication of our people and contractors is what saw this project to the finish. The completed project is a tribute to all who have been involved for the last five years.”
SIDE BARS x 2
Project Details
Nantucket Demand
Nantucket saw a peak demand of 36 megawatts over the summer of 2005. Over the last 18 years, the island’s customer base has doubled to 14,000 with homes using more electricity to run air conditioning and other electronics.
PHOTO CAPTION
With help from a satellite-aided positioning system, the ship can stay within 40 inches of the mapped-out route from Nantucket to Hyannis, Mass.