The Block Island Wind Farm's unique equipment

Fri, 07/15/2016 - 11:00am

As the Block Island Wind Farm enters into its final stages of construction, some unusual equipment and materials are being utilized for the project, both by Deepwater Wind and National Grid. 

On Tuesday, June 28, National Grid spliced its sea2shore cable with a terrestrial cable connecting, for the first time, Block Island to the mainland. The cable will be activated later in the construction process.

The project involves two submarine cables: one to the Block Island Wind Farm, and the other to a parking lot located at Scarborough Beach in Narragansett. National Grid owns the 20-mile long sea2shore cable, while Deepwater Wind owns the eight-mile long export submarine cable installed from Town Beach each to the Wind Farm.

According to National Grid Engineer David Campilii, the utility’s “sea2shore cable is a 34.5 kilovolt (34,500 volts) cable with a capacity of approximately 30 megawatts. The cable is about seven inches in diameter and weighs about 46 pounds per foot.”

Campilii said that the sea2shore cable arrived aboard the BBC Ruby "as a single length of cable a little over 20-miles long. The cable weighs about 4.9 million pounds. The Deepwater Wind submarine cable is identical in construction. The 8.2 miles of Deepwater Wind’s submarine cable weighs about two million pounds.”

For installation, both the National Grid and Deepwater Wind submarine cables were coiled on the deck of the cable-laying-barge CLB Big Max. “With both cables aboard Big Max, the barge was carrying 6.9 million pounds of cable,” he said.  

The CLB Big Max, designed specifically for laying submarine cables, will drag a jet plow, a sled-looking vehicle, along the seafloor to forge a six-foot deep trench in the seabed to install the submarine cable.

As for the submarine cable manufacturer, LS Cable in South Korea designed and built the two submarine cables for the project. Campilii said the reason that National Grid selected LS Cable because “there are only a few cable manufacturers in the world who can make submarine cables of this length. These manufacturers are primarily located in Europe and Asia. National Grid developed a cable material specification, and installation specification, and evaluated a number of suppliers through our bidding process. The evaluation was based on the supplier’s ability to make and install the cable for the sea2shore project, including price, schedule, environmental record, safety record, and other factors. LS Cable had the best overall proposal for the project, and was selected on that basis.”   

The sea2shore cable was floated ashore via a specially-designed winch and a string of airbags, installed via the jet plow, and threaded through a conduit in a steel cofferdam in the surf zone at the beach. A cofferdam is a watertight enclosure, or pool-like structure, that is created by driving large, steel beams into the sand.

National Grid pulled the submarine cable through the conduit, or pipe, 10 to 15 feet under the dunes, to a manhole situated in the north parking lot. A few days later, National Grid technicians spliced the submarine cable with the terrestrial cable, linking Block Island to the mainland.

Deepwater Wind is in the process of installing the submarine cable linking the five steel foundations at the wind farm site. In August, the company will begin erecting the 270-foot tall wind turbine towers with their accompanying 246-foot long blades.

The company has engaged the services of the Atlantic Pioneer to deliver technicians to the wind farm site. The 70-foot vessel is capable of cruising at a top speed of 30 knots, can fill an Olympic size swimming pool in 10-seconds with one thrust of its two engines, and attach to one of the wind farm’s steel foundations.

Meaghan Wims, spokesperson for Deepwater Wind, informed The Times that the lift-boat vessel Fred. Olsen Windcarrier’s Brave Tern is gearing up to work on the wind farm. “The vessel completed its mobilization in Denmark, and is now en route to General Electric’s facility in St. Nazaire, France, where it will load up the wind farm’s nacelles for transport to the Block Island Wind Farm,” said Wims.

The Haliade nacelles, each of which weigh 370 tons, are the components that sit atop the wind turbines and house the generator, gearbox, drive train and brake assembly. The five six-megawatt GE Haliade wind turbines will produce 125,000-megawatt hours of electricity.

The three separate tower sections comprising the turbines weigh a total of 440 tons. Once fully installed, the wind turbine towers will stand 560-feet tall, twice the height of the Statue of Liberty.

The Wind Farm should be operational in the fourth quarter of 2016.