Diver-less export cable repair

Paul Boughton

Pharos Offshore Group has completed cable repair and burial for the London Array Offshore Wind Farm on a section of damaged subsea export cable.

Pharos delivered a work package with the rapid mobilisation of engineering, fabrication and operational teams to locate, recover, re-lay and re-bury the power cable off the Kent coast. The 800mm HVDC export cable has a 218mm diameter and weighs over 50kg/m in water and 86 kg/m in air.
Pharos CEO Phil Walker says: “With the use of a DP-2 vessel we were able to reroute the cable away from the original route to an area within the planned cable corridors.”
Walker continued: “To our knowledge, this is the first diver-less operation to de-bury, retrieve and repair a cable of this size and weight.”

Tools for properly handling the large stiff cable did not exist in the market and standard grapnel operations were not possible due to nearby cable routes.

The Pharos team developed multiple operational plans that not only met the client’s tight schedule but allowed for the infield flexibility to deal with as found conditions.

In addition to the complexities of cable retrieval, the Pharos team also converted a conventional telecoms cable ship to accommodate the loading, storage, lay, splicing and safe handling of the product. Pharos has a strong track record of utilising commercially available off-the-shelf (COTS) technology from other markets to meet client requirements.

The equipment and procedures developed for this repair will work for other repair situations; especially those where increasingly congested cable corridors preclude anchoring and grapnel runs and/or are beyond diver limits.
London Array Limited is a consortium comprising of Dong Energy, E.ON, and Masdar who are combining their experience and expertise to develop and build the world’s largest offshore wind farm in the outer Thames Estuary between the Kent and Essex coasts.

Phase one of London Array involves installing 175 turbines, 2 offshore substations, 4 undersea export cables with a total length of around 220km and over 200km of inter-array cables to connect the turbines to each other and to the offshore substations.

The export cables connect to the National Grid at a new onshore substation located at Cleve Hill, near Graveney on the North Kent coast. Once completed, London Array’s 175 turbines will generate enough electricity for over 470,000 UK homes.
For more information, www.pharosoffshoregroup.com