Review of Cabling Techniques and Environmental Effects Applicable

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Review of Cabling Techniques and Environmental Effects Applicable to the Offshore Wind Farm Industry – Technical Report Table 3.15: Guidance on the performance of burial devices (with burial device options) in various seabed sediments Cable Burial Devices Burial Device Options Sediment Type 72 Sands Silts Gravel Weak Clays Stiff Clays Cable Burial Ploughs Conventional narrow share cable ploughs Tracked Cable Burial Devices Free Swimming ROVs with Cable Burial Capability Rock Advanced cable ploughs Modular cable ploughs Rock ripping ploughs Vibrating share ploughs Jetting systems ? Rock wheel cutters P P P Chain excavators P P Dredging systems ? ? Jetting systems ? Dredging systems ? ? Burial Sleds Jetting systems ? KEY = Should be capable of burial. Rock wheel cutters P P P Chain excavators P P Dredging systems ? ? ? = Performance will be related to the type of sediment and the power delivery to the burial device. P = Performance possible in the sediment type but not an ideal application. = Unlikely to be capable of burial. Cable burial for offshore wind farms is usually undertaken using a barge which is specifically mobilised with cable handling and burial equipment. The same barge will also be equipped with a number of heavy duty tow winches which are capable of deploying a six or eight point anchor system to provide stability during cable burial operations. An anchor handling vessel is independently used to lift and place anchors in order to allow the cable installation barge to appropriately reposition itself as the burial works progress. In circumstances where the cable installation barge is the host vessel for cable burial operation using a towed subsea plough, the anchors are deployed in such a
Cable types and installation techniques manner which allows the barge to tow the plough whilst hauling on the deployed anchor array until such time as the slack is taken up on the anchor wires and the anchors have to be repositioned. The frequency of change of anchor positions will be dependent on a number of factors such as water depth, predicted tow forces and the size of barge etc. However, as a typical guide on a number of wind farm projects undertaken to date, a burial length of between 100m and 200m has typically been achieved on a single set of anchor deployments before the anchors have to be repositioned. The deployment of anchors must be carefully monitored and controlled whilst in the vicinity of other cable or pipeline systems as would typically occur at a pipeline or cable crossing location to avoid any potential damage to such existing infrastructure. 3.9.2 CABLE CORRIDORS FOR EXPORT CABLES It is standard practice for the export cables from an offshore wind farm to be consented to be installed within a cable corridor. The cable corridor may typically be 500m to 600m wide of the centreline of the planned cable route and provides the wind farm developer and cable installation contractor a degree of flexibility to cope with the following: ● ● ● Avoidance of any localised obstructions such as wrecks etc. which do not appear on Admiralty Charts but are discovered in later surveys specific to the project; Localised areas of difficult ground conditions where burial may prove difficult. For example small rock outcrops, boulder formations or glacial till outcrops; and Routing of cables within the corridor limits to follow the troughs of sandwaves in areas where mobile seabeds are known to exist. 3.9.3 CABLE INSTALLATION ON OFFSHORE WIND FARMS TO DATE This section of the report contains cable installation information for offshore wind farms which have been installed to date. It should be noted that only limited information was available for a number of sites listed in Table 3.16. Supplementary information has been obtained from additional news items and data published on websites and with reference to articles which have appeared in the technical press. Therefore, the assembled data is a collection of market information from a wide variety of sources. 73
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REVIEW OF CABLING TECHNIQUES AND EN
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Review of Cabling Techniques and En
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Abbreviations AIS Automatic Identif
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TTS Temporary Threshold Shift TWA T
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3 Cable types and 18 installation t
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6 Good practice measures This secti
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7 Gaps in understanding Research fo
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References Introduction Sinden, G.
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Appendix A: Standards and codes of
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Printed in UK on recycled paper. De
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