Review of Cabling Techniques and Environmental Effects Applicable

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3 Cable types and 18 installation techniques 3.1 Introduction This section of the report lists all of the cable types which are anticipated to be used in the near future for offshore wind farm development work and sets the background to the methodologies which have been developed in other industries for the safe installation and protection of subsea cables. It then outlines the various cable protection methods, including all of the various cable burial methodologies together with details of alternative external cable protection systems. This includes details of the cable protection methods which are most applicable and relevant for the offshore wind farm industry. Information on burial assessment survey techniques which are commonly used as a pre-survey activity before the main cable installation is included. Finally, this section reviews how legislation on decommissioning of the installed cable systems could also give rise to procedures which could have an impact on the environment. 3.2 Cable Types 3.2.1 GENERAL This section of the report contains details of offshore subsea cables which would typically be used for offshore wind farms. It also contains details of the cables which are commonly used in the subsea telecommunications and power cable industries. The design and construction of a particular subsea cable will be directly governed by the functionality of the cable and any requirement to protect the cable from any potential hostile seabed intervention. Figure 3.1 illustrates a typical range and size of cables which can be used for a variety of different applications. Some of the cables included in this figure are not all subsea cables. 3.3 Offshore Wind Farm Cables 3.3.1 GENERAL The design of subsea cable systems for offshore wind farms will be influenced by a number of factors. Some of the factors are generic, while others are projectspecific:
● ● ● ● Cable types and installation techniques Connection voltage – Offshore wind farm projects need to be connected to regional distribution networks, rather than to the national transmission system. In England and Wales, these distribution networks currently include 132kV and 33kV systems. Some of the early Round 1 offshore wind farm projects have made connections at 33kV while several others have connections at 132kV. It is probable that all Round 2 sites will secure connections at 132kV. Cable design – Three-core subsea cables using solid insulation (ERP or XLPE) are typically used for operation at voltages up to 132kV. Higher voltage cables that use oil as an insulating medium are not deemed to be environmentally acceptable owing to the potential risks associated with oil leakage in the near shore environment. The cables are typically designed to give a power transmission capacity of up to 40MW for a single 33kV cable and 160MW for a single 132kV cable. Turbine size – Offshore wind farm developers are continually looking to the turbine manufacturers to develop larger and more energy efficient turbines. The early UK Round 1 developments such as North Hoyle, used 2.5MW wind turbine generators (WTGs). Current offshore wind farm developments are planning to use 3.0MW and 3.6MW machines and plans for a 5.0MW machine are already well advanced. Distance from shore – The use of a single 132kV cable to shore provides a cost-effective alternative to the use of three or four 33kV cables. The installed cost (per kilometre) of a single 132kV cable is considerably lower than the installed cost of three 33kV cables, but this solution requires an offshore substation in order to step up to 132kV from the wind farm collection voltage (usually 33kV). Some of the current projects under consideration have more than one 132kV export cable to link the offshore wind farm to shore. 19
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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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