0.5m, the maximum length of installed cable and the highest power rating as given in Table 11.2 and summarised below:
• •
Up to 745km of inter-array (up to 75kv of alternating current) and HVAC export cables between collector and converter stations (up to 275kv).
Up to 620km of HVDC export cables (up to 600kv).
220. HVDC export cables may be rated between 320kV and 600kV. HVDC cables currently in use are restricted to 320kV and are most likely to be used for the East Anglia THREE project. However, 500kV designs are planned for deployment in the near future and due to the rate of technological change in this field and it is thought that there is a possibility that such cables or slightly larger may be available for the East Anglia THREE project.
221. During the operational phase AC cables (inter-array and export cables) would generate an electric field (E) and a magnetic field (B). The total E field cancels itself out to a large extent and the remaining E field is shielded by the metallic sheath and the cable armour. The varying magnetic field (B), however, produces an associated induced electric field (Ei); therefore both B and Ei fields would be generated by inter- array cables during the operational phase.
222.
Information on the predicted magnetic (B) and induced electric fields (Ei) from the range of cable types proposed for the project has been summarised in Chapter 9 Underwater Noise Vibration and Electromagnetic Fields, and is described in further detail in Appendix 9.1.
223. Whilst for the purposes of impact assessment it is appropriate to adopt a worst case approach, it is of note that EN- 3 guidance (paragraphs 2.6.75 and 2.6.76) states that EMF may be mitigated by the use of armoured cable and burial to sufficient depth (greater than 1.5m) means impacts are likely to be negligible. Therefore, once installed, operational EMF impacts are unlikely to be of sufficient range or strength to create a barrier to fish movement.
224. Normandeau et al. (2011) modelled expected magnetic fields using design characteristics taken from 24 undersea cable projects. Of the 10 AC and DC cables modelled, in eight of these it was found that the intensity of the field was roughly a direct function of voltage (ranging from 33kV to 345kV) although separation between the cables and burial depth also influenced field strengths. The predicted magnetic fields were strongest directly over the cables and decreased rapidly with vertical and horizontal distance from the cables (Table 11.29). The averaged
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 11 Fish and Shellfish Page 74
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