INSIDE THE PROJECT
The Block Island Wind cable project involved two owners: Deepwater Wind and National Grid. Deepwater Wind owns and was responsible for installing the five offshore wind turbines, four 3,200 linear foot array cables between turbines and the six-mile export cable to Block Island. National Grid owns and installed the 22-mile transmission cable between Block Island and Narragansett, Rhode Island. LS Cable was contracted to supply and install all of the 35 kV power cables for the project. LS contracted with Kokosing Industrial Durocher Marine Division to install and bury all cables.
The Durocher Marine installation team designed and constructed a self-propelled, USCG approved, Dynamic Positioned Barge (DP-2) to safely and precisely lay and bury the subsea cable installations. The system utilized six 500 HP thrusters for propulsion that were mounted on a 260-foot by 72-foot by 16-foot ABS barge. Mobilization of the cable lay vessel began in January of 2016 in Florida and was completed in April in Rhode Island. The total 28 miles of cables weighed 3,400 metric tons and were coiled in a holding tank built on the deck of the lay vessel. The installations began in May with the export cable and ended in July of 2016 with the installation of the array cables. The subsea cables were all installed successfully and buried to six feet along the cable lay routes.
WHY IT MATTERS
The Deepwater Wind Farm is the first offshore wind project constructed in North America. It consists of five wind turbines which are located approximately six miles off the East coast of Block Island, Rhode Island and approximately 20 miles from mainland Rhode Island. The combined electric power output from the five wind turbines is 30 MWs which will service 17,000 homes. Prior to the installation of the National Grid transmission line to Block Island and the Deepwater Wind farm, the island relied entirely on diesel generators for electricity. The wind farm will be able to produce electricity for the island at a lower cost and environmental impact than the existing diesel powered infrastructure. The five wind turbines went into commercial service in December 2016.
Inside the Project
Sumitomo Electric subcontracted the subaqueous installation of the three 240kV transmission and fiber optic cables between the Potrero and Embarcadero Substations in downtown San Francisco. Prior to our arrival the owner installed three HDPE conduits at each substation. The conduits extend out from the harbor into 35 feet – 85 feet of water and were 1,000 feet and 1200 feet long. Ships from Japan delivered the three cables in individual tubs to the Port in San Francisco. Each tub weighed approximately 320 tons. After mobilizing our lay barge a single tub was set onto our 1,000-ton portable turntable. The lay barge moved into position and pulled the first power and fiber cable to the Potrero substation via the conduits. After the cable was secure the lay barge simultaneously laid and buried the 5-13/16-inch power cable and fiber optic cable with our water jet plow. Each lay route was a distance of 12,700 feet to the second conduit. At the second conduit the lay barge stopped, floated 2,100 feet of cable in a tidal zone, and winched the cables up the conduit to the Embarcadero Substation. The process was repeated two more times.
Why it matters
Downtown San Francisco is a very busy and highly developed area. The owner investigated three options for the 240kV installation. Two of the options were through the city streets of San Francisco. Each of these routes crossed the I-280 corridor and other sensitive areas. These options were not economically viable. Moving the lay route out into the bay circumvented most of the logistical problems associated with navigating this construction through the city.
For a deeper look into the project, read the latest story in Transmission and Distribution World.
About the Project
McLean’s Mountain Wind Farm is located on Manitoulin Island, Ontario Canada. The wind farm is rated to produce 60MW of electricity from 103 turbines. Getting power to the Provincial Grid required crossing the 2,000 ft Little Current Channel between Manitoulin and Goat Islands with 3 – 115kV submarine power cables and grounds. Both the northern and southern shorelines required extensive shoreline excavation to guarantee adequate trench depth for the cables. The north shore also required 860 ft of duct bank cut into rock. At each end of the project the submarine cables were terminated at junction boxes. The cables were laid individually. Upon completion of laying the cables a stone sub-base, cable separators, and articulated concrete mats were added to protect the cables.
Why it matters
This is the first project Durocher Marine has completed in Canadian Waters. The Coasting Trade Act in Canada required all floating equipment to be constructed in Canada. We worked with a local marine contractor for the marine support. Several of our managers were allowed onsite with work permits. In 2009 the Ontario legislature introduced the…