East Anglia ONE
EMF Assessment
Owing to the dependence of iE field magnitude upon B field magnitude, iE fields will attenuate with both horizontal and vertical distance from the cable conductor.
3.1. Cable deployment
In some instances, the deployment methodology (alignment arrangement, rather than installation technique) chosen for different cable types may affect EMF generation magnitude.
3.1.1. Alternating current cabling
B fields (and therefore iE fields) generated by AC designs vary with cable design. Three-core cables or three single-core cables arranged in trefoil (a similar, triangular arrangement) reduce B field generation in contrast with individual single-core cables laid separately. B and iE fields generated by the latter increase with increasing separation distance (to a certain point).
3.1.2. Direct current cabling
Assuming balanced loads, owing to the fact that effectively identical B fields are generated by each cable core, the opposite alignment of these cores in bipole DC systems results in significant cancellation effects on resultant fields should the cables be bundled in close proximity to each other. The further the cables are laid apart, the more they will behave as single cables, for which reduction through cancellation would be observed. The two cable cores will also act increasingly as single cables the more unbalanced the loads carried in each become (should, for example, some current flow through to the ground following damage to one or other of the cables).
3.2. Cable burial
Surface-laying of cables is planned to be avoided as far as possible. Instead, it is proposed that cables be buried between 0.5 and 5.0m within the substratum via ploughing, trenching/cutting or jetting (burial targets to be confirmed later). If the cable cannot be buried, such as at crossings with existing cables or pipelines, or over ground that cannot realistically be penetrated to sufficient depth, the cable will be surface laid, but protected as far as possible by rock dumping, concrete mattresses or frond mattresses.
Gill et al 2005 suggest that B field propagation will not be diminished through the sediment any more than through water (in the absence of magnetic rocks; see Section 4.4). However, burial may confer benefit in reducing the maximum magnitude of EMF at the sediment-seawater interface, as the further away from the seawater the cable lies, the more the field strengths will have attenuated. Therefore, from a marine biological perspective and taking a precautionary view, the deeper cables can be buried, the better, since many fauna will be prevented from approaching the strongest EMF (except burrowing infauna) but this may not result in ecologically significant reductions.
J3184 EAONE v2 6
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