East Anglia ONE 6.2.3. Mammals and chelonians
A recent demonstration of electroreception of AC fields in a dolphin (Czech-Damal et al 2011) suggests the widely held belief that cetaceans are not sensitive to E fields may be incorrect. However, the authors state that the system appears to be far less sensitive than those used by elasmobranchs (a 460µV/m threshold of sensitivity was established, approximately three orders of magnitude lower than elasmobranchs). In addition to their predominantly pelagic life histories, cetaceans are therefore expected to be unaffected by E fields induced by EAONE cables. Chelonians are also expected to be unaffected, both due to no evidence of electrical sensitivity and their pelagic life histories.
6.3. Sea electrodes
Should sea electrodes be utilised during cable maintenance, once magnitude and propagation distances of EMF, and duration of use are determined, possible factors such as avoidance of strong fields at the anode, involuntary attraction to the cathode (galvanotaxis), in addition to the production of toxic substances such as chlorine and halogenated compounds at the anode via electrolysis should be investigated.
8. Cumulative considerations
It is important to consider possible cumulative EMF effects of different cables, both within the EAONE Project, and with pre-existing operational cables at the site.
The worst-case scenario when considering the number of EAONE cables is Option 2 (see Section 2.1) with 550km of array cabling, 13 HVAC cables measuring 10km each, and 4 HVDC cables measuring 100km each. There is potential for additive or subtractive (cancelling) effects upon EMF, depending upon distance between cables and direction of alignment. B and iE fields predicted for array cabling (three-core 33kV to 75kV AC) are relatively weak, and therefore any potential additive effects are likely to be negligible. The higher rated cables most likely to be utilised for HVAC export cabling (three-core 132kV or 220kV) are expected to generate moderately stronger EMF, but any potential additive effects are only likely to extend a few to 10 meters from overlapping EMF zones, therefore deploying such cables 50m apart (as planned) should prevent such effects. Overlapping EMF zones are likely to be larger when considering single-core 275kV cabling, especially if deployed separately rather than in a trefoil, but such technology is unlikely to be utilised. HVDC cabling EMF may generate reasonably strong EMF in close proximity of cables, especially if considering separated deployment, with potential additive effects extending to tens of meters. Bundling of cables would markedly reduce overlapping EMF zones to just a few meters at most, and deploying sets of bundled cables 50m apart should prevent such effects.
The export HVDC cable corridor passes across two operational sub-sea cables either side of the halfway mark between the proposed EAONE site and the landfall north of Felixstowe. According to engineers, HVDC cables crossing HVAC cables are required to do so perpendicularly to prevent induced currents (iE field) resulting in thermal hotspots and de-rating of the cable. The EAONE export cable corridor is
J3184 EAONE v2 33
EMF Assessment
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