National Grid and Orsted have started mobilising teams that will work throughout the autumn and winter to replace segments of the transmission cables for the 30MW Block Island offshore wind farm off the US east coast.
The aim is to achieve greater burial depths beneath the ocean floor, the companies said.
The work will involve replacing approximately 520 metres of National Grid’s sea2shore submarine cable that carries electricity between Block Island and mainland Rhode Island, and approximately 945 metres of Orsted’s subsea cable that carries electricity from the wind farm to Block Island.
The original cables were installed in the spring/summer of 2016 and subsequently experienced challenges with sediment coverage over the cables, Orsted and National Grid said.
Orsted and National Grid said that they determined the best approach to maintain the required burial depths of the two transmission cables is to reinstall these limited segments with new sections adjacent to where the existing cables now sit.
Over the next few weeks, teams from both National Grid and Orsted will begin staging equipment and barges that will be used for the work.
The cable landings will be constructed using a horizontal directional drill (HDD) and a conduit will be installed for the new length of onshore cable, including a new access pit.
The drilling phase of the construction work at Town Beach is scheduled to begin this autumn, with the ocean-based cable installation scheduled to begin in early spring.
The HDD will bury the cables at a depth of between eight to 15 metres below the seafloor, as compared with the current 1.2 to 1.8 metres.
This is deep enough to withstand changing ocean floor conditions and provide a continued reliable interconnection for Block Island and the wind Ffarm for years to come, the two companies said.
The new cables will be spliced onto the existing cable that connects the Island, the wind project, and the mainland.
The existing portions of the exposed cables are scheduled to be removed at the end of construction.
Construction-related activities will be ongoing throughout the fall and winter, with an anticipated completion date before the end of May.
Block Island and Rhode Island will continue to receive electricity from the wind farm during the construction, except for a brief outage in the spring, when the new cable will be spliced with the existing cable.
During the outage, Block Island Power Company will provide the needed electrical power to the Island utilising its on-island diesel generation.
Orsted North America, Offshore head of operations Mikkel Maehlisen said: “We’re confident in the solution we’ve developed to ensure the Block Island wind farm transmission cable remains buried deeply below the ocean floor.
“We’re working closely with the town of New Shoreham to ensure that all of our work is completed in the offseason, with as little impact to Town Beach visitors and as minimal interruption to the energy supplied from the wind farm as possible.
“We are grateful to town and state leaders for their close collaboration on this important work.”