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 cutter consists of a rotating wheel disc and is fitted with a number of replaceable rock cutting teeth. Progress is slow (100m/hr to 500m/hr) using these vehicles and, in extreme cases, progress of only tens of metres can be made in a full day of trenching operations. It is often the case that the vehicle has to be recovered for the cutting teeth to be replaced as they abrade quickly in the rock material thus losing their effectiveness in cutting mode. Owing to the very aggressive nature of the cutting tool, the cable is carefully guided through the tracked cable burial vehicle through an enclosed cable pathway over the top of the rock wheel cutter before being guided to the base of the cut trench. Diver intervention is usually required in any cable loading and unloading process. Figure 3.18 shows a shallow water tracked cable burial machine which is fitted with a rock wheel cutter, but has the flexibility to interchange to a mechanical chain excavator if required. Figure 3.18: Shallow Water Tracked Cable Burial Machine Fitted with a Rock Wheel Cutter (Photo courtesy of The Engineering Business Ltd) Mechanical chain excavators Mechanical chain excavators are typically used in circumstances where the seabed material is beyond the capability of a jetting system or where deeper burial is required. Mechanical chain excavators typically operate in the 2.5m to 3.0m trench depth range as opposed to the 1.0m to 1.5m depth range that 48
Cable types and installation techniques the mechanical rock wheel cutters operate in. The mechanical chain excavator tool usually consists of a number of cutting teeth similar to those used on the mechanical rock wheel cutter and a further number of mechanical scoops which are used to transport the cut material away from the trench. As with the mechanical wheel cutter, all the teeth on the mechanical chain excavator are replaceable and interchangeable depending on the seabed conditions. An auger is sometimes in place at the upper level of the mechanical chain excavator. The auger helps to move away the cut trench material and prevent it falling back into the trench or from clogging the cutting chain. The augers are usually short, and only move the cut seabed material approximately 500mm away from each side of the trench. Again, because of the very aggressive nature of the cutting tool, the cable will be guided in an enclosed pathway around the top of the cutting tool to safeguard against any potential damage before it is placed into the base of the cut trench. Therefore, as for the wheel cutter, cable loading and unloading is a diver assisted operation. Simultaneous lay and burial vehicles In 2003, a new type of tracked cable burial vehicle was introduced to the offshore wind farm cable market, with the capability to lay and bury cables simultaneously. Manufactured by SMD Hydrodivision Ltd, the LBT1 was supplied to Marine Projects International Ltd and was first used on the North Hoyle Offshore Wind Farm for the burial of the inter-turbine array cables. Figure 3.19 below shows the LBT1 being deployed over the side of the host vessel with a full reel of cable to install a section of cable between two of the North Hoyle offshore turbine generators. The LBT1 was fitted with both a forward chain excavator system for working with hard soils and a jetting tool mounted to the rear of the vehicle for the burial of the subsea cable. 49
Page 1: REVIEW OF CABLING TECHNIQUES AND EN
Page 4 and 5: Review of Cabling Techniques and En
Page 9 and 10: Abbreviations AIS Automatic Identif
Page 11: TTS Temporary Threshold Shift TWA T
Page 20 and 21: 3 Cable types and 18 installation t
Page 82 and 83: 4 Physical change 4.1 Introduction
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Review of Cabling Techniques and En
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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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