Table 5.16 Summary table for interconnections Interconnection design alternatives
HVAC interconnection case
HVDC interconnection case
2 x 95km
Interconnection East Anglia THREE and East Anglia ONE Number of cables 2 x 95km
Total Length (km) 190
190
5.4.11.2 Export cables: cable routes 158. East Anglia THREE offshore cable corridor would join the East Anglia ONE Offshore Cable Corridor at a location yet to be determined. The East Anglia THREE offshore export cables would then follow the East Anglia ONE offshore cable corridor and onshore cable route to the substation at Bramford. The East Anglia ONE offshore cable corridor already identified is able to sufficiently accommodate the cables for East Anglia THREE (in addition to those for East Anglia ONE).
5.4.11.3 Export and interconnection cables: pre-lay works required 159. East Anglia THREE would be connected to the National Grid Transmission System by up to four HVDC export cables. The offshore cables themselves each have a diameter of approximately 120 to 200mm and each consist of one copper or aluminium conductor with electrical insulation material, screens, communication fibre and protective armour layers. East Anglia THREE would have up to two offshore fibre optic cables.
160. In areas with large ripples and sand waves the sea bed may first require levelling (subject to detailed studies) by dredging before the cable could be laid on the sea bed.
161. Before cable-laying operations commence, it would be necessary to ensure that the offshore cable corridor is free from obstructions such as discarded trawling gear and abandoned cables identified as part of the pre-construction survey. A survey vessel would be used to clear all such identified debris, in a pre-lay grapnel run (PLGR).
162. The offshore export cable would be routed as far as possible in soft sediments to allow it to be buried into the sea bed. In the event that boulders or debris are encountered on the sea bed, they should be removed before the cable is laid. If the grapnel tool cannot remove all obstructions completely, some hydraulic removal works or ploughing may take place. No blasting is planned to take place in the offshore cable corridor to remove bedrock.
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 5 Description of the Development Page 38
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