effects of EMF on sensitive species from cable infrastructure during operation are likely to be not significant. The mitigation described (Paragraph 2.6.76) includes the use of armoured cables and cable burial to a sufficient depth, both of which are proposed for East Anglia THREE project.
9.9.2 Data sources 48. A research and literature review was undertaken by CMACS, see Appendix 9.2.
9.9.3 Impact Assessment Methodology
9.9.3.1 Introduction to Electromagnetic Fields 49.
Submarine power cables of the types that would be used in the proposed East Anglia THREE project are widely employed for offshore power transmission. The transportation of electricity within cables results in the generation of electric (E) and magnetic (B) fields. The design of the cables, including lead sheathing and armoured cores, prevents the propagation of the E fields beyond the cable. However, these materials are permeable to B fields that therefore emanate into the surrounding environment. The magnitude of the B field produced is directly dependent on the amount of current flow through the cable. The B field attenuates with both horizontal and vertical distance from the cable conductor.
50.
Three core AC cables transmit three current flows that fluctuate between positive and negative polarity. Because of the alternating current, the B fields produced are not static but fluctuate in time according to the frequency of the AC. The fluctuating B fields induce another E field, the induced E field (iE), in the surrounding medium. This iE field has been the focus of much industry research, specifically its potential effects on elasmobranchs (CMACS 2003; Gill et al. 2009).
51.
In contrast, the B field generated by bipole DC cables is static and thus varying iE fields are not induced in the same way as for AC cables. Review of the literature reveals a large number and wide variety of organisms that are sensitive to EMFs. The main concerns relating to B field emanation are potential impairment of navigation and physiological effects. The main concerns relating to iE field emanation are potential repulsion, confusion with bioelectric fields and physiological effects.
52. Whilst there is good understanding of the physical processes that result in EMFs, research into electromagnetically sensitive species and their interactions with anthropogenic EMF has been largely inconclusive. The assessment of potential impacts has therefore been carried out using the best information available.
9.9.3.2 Predicted Fields from the Cables Proposed for the East Anglia THREE project
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 9 Underwater Noise Page 14
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31