The Block Island Wind cable project involved installing a 22-mile transmission cable from Rhode Island to Block Island, a 6-mile export cable from Block Island to the offshore wind towers, and four inter-array cables between the five turbines. The power cables were buried 6 feet using a jet plow in up to 130 feet of water. All cable installation was performed successfully off of a dynamically positioned cable lay barge capable of precise auto-pilot navigation along the lay route. Read More
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 5 offshore wind turbines, four 3,200 linear foot array cables between turbines, and the 6-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. To accomplish this project 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’ x 72’ x 16’ 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 6 feet along the cable lay routes.
A video of our project can be found at https://www.youtube.com/watch?v=tgVn748oZO0
The Deepwater Wind Farm is the first offshore wind project constructed in North
America. It consists of five wind turbines which are located approximately 6 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 5 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 were scheduled to go into commercial service December of 2016
The wind farm is located approximately 20 miles from the mainland. Our first obstacle was to construct a USCG approved installation barge. It took a year of planning and 4 months to construct the installation barge for this project. Work began in a shipyard in Florida and was completed onsite in Rhode Island. We purchased and installed 6-500 HP Thrustmaster units and an integrated Kongsberg Navigation system for the vessel’s Dynamic Positioning. This was the first barge of this type to be approved by the USCG under their new regulations that took effect January 1, 2016.
The cable installation faced daily obstacles. During our installation we simultaneously laid and buried the cable with sub-meter accuracy along the entire 28 mile cable route. Our crews faced weather, currents, and water depths of 130 feet. Our crews also had to navigate in close proximity and between the 5 – wind turbines without damaging those structures.
Along the route from shore to Block Island we had to locate and cross an existing Fiber Optic cable. We successfully crossed the Fiber Optic cable without incident.
All cable was installed without incident.
Working on the water is always dangerous. Working offshore on a dynamically positioned barge laying power cable adds an element of danger. Our core personnel are highly trained marine professionals. Each year these field people are trained in safety, first aid, and HAZWOPER. They are also trained to operate specific pieces of equipment.
To operate the Dynamic Positioning system (DP) we retained the services of a DP Master Operator, a DP Mate, and a DP Engineer. These people were trained and certified to operate and maintain the DP system throughout the project.
Part of this project required ascending onto the 5 wind turbine structures, which stood 100 ft above the water surface. Our personnel had to complete a 3 day PST training seminar to be allowed to climb onto the structures.
Fueling is always a risk, especially when working on the water. There is always the risk of spilling large quantities of fuel, and the constant risk of explosions and fire. To mitigate that risk we used 3-5,000 gallon double walled fuel tanks, which were built in an ISO container. These tanks can be transported at full capacity, and are designed for the marine environment.
The Kongsberg Survey system was integrated with the Dynamic Positioning system. The Kongsberg system was a doubly redundant system that controlled the position and movement of our installation barge at all times (24/7). The system was programmed with the installation routes and was capable of following the pre-planned routes within a meter of tolerance. The system corrected for wind, waves, current, external loads, and the cable jet sled.
Our cable installation sled was towed behind our installation barge. To monitor what was happening at the sled we installed several electrical components. These included heave, pitch, and roll monitors. An integrated DGPS system. Blue View sonar. Video cameras. Gyro Compass. Blade embedment sensors. Tensionometers. All this information was relayed into our control tower and was monitored and recorded at all times during the installation. This data reduced and often eliminated the need for divers tending the sled during burial.
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