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 3.16: Cable Installation Experience and Feedback on Recently Installed Offshore Wind Farms Wind Farm Cable Route Soil Conditions Burial Depth and Method Arklow Bank Export Cables Superficial sediments overlying harder sediments which are believed to possibly be glacial till. Nysted (Denmark) 74 Export Cables and Inter-Array Cables Horns Rev Inter-Array Cables It is believed there are a variety of seabed conditions across the site. A subsea cable plough was used to bury the export cables. A variety of installation techniques were employed. Jetting was used in areas of looser substrates which included sands, silts and clays with shear stress less than 75kPa. Pre-trenching and backfilling was used to cut through areas of harder substrate with back-hoe excavators working from a shallow water jack-up barge. Feedback Information (where available) It is understood that surveys undertaken post installation indicated localised exposures of cables. This was possibly caused by scouring of the superficial sediments adjacent to the bank. It is also understood that the export cable suffered a fault resulting from an anchor contact with a repair being completed within one week. Further cable protection methods are under consideration. It is understood that the cable installation and burial were successfully completed. However, the burial operations took a considerable period of time owing to poor weather. The offshore spread does not appear to be particularly weather resistant potentially which explains the apparently protracted operations. - - It is understood that the installation contractor encountered difficulties whilst installing and burying the inter-array cables. It is thought that the wave climate proved problematic during the installation operations and it is believed that divers were subsequently employed to bury the cables which were left exposed, particularly close to the offshore structures.
Wind Farm Cable Route Soil Conditions Burial Depth and Method North Hoyle Export Cables Close to the wind farm there were stiff clays associated with glacial till. However, the vast majority of the route consisted of sands and gravels. Inter-Array Cables The array on the east side of the wind farm had stiff clays associated with glacial till. The remainder of the site consisted of sands and gravels. A Sea Stallion subsea cable plough with a 2m burial depth capability was employed to achieve a target burial depth of 1.5m. The LBT1 trencher was used which simultaneously laid and buried the interarray sections of cable to a target burial depth of 1m. Cable types and installation techniques Feedback Information (where available) The installation work proceeded well without any problems. One of cables was installed from the shore to the wind farm and the other cable installed from the wind farm to the shore. Both cables crossed the BHP owned pipeline to the Hamilton offshore facility. Concrete mattresses were used to separate and protect the cables at the crossing and diver intervention was required to bury the sections of cable from the edge of the mattresses to the termination points of ploughing operations. The LBT1 is equipped with a forward mechanical cutting tool which sits in front of the main jetting unit for cable burial. It achieved good burial across the majority of the site apart from when working in the stiff clays on the eastern array where burial was only possible in the softer sediments. The LBT1 also has to overrun the cable line to allow the final cable end to be pulled in the J-tube. This typically leaves a 50m section of cable unburied close to the second WTG structure. Diver techniques were used to bury these sections of cable and this resulted in the burial works being carried over into a second season following the main installation of the offshore wind farm. 75
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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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Page 82 and 83: 4 Physical change 4.1 Introduction
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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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