9.9.3.2.1


Alternating Current Cables


53. Data on B and E fields are available for industry standard three core AC cables from 33kV to 132kV and therefore well supported predictions can be made for these ratings. Assumptions have been provided for the higher powered and single core designs.


54.


The magnitude of EMFs that might be expected for the different AC cables under consideration for East Anglia THREE, both at the seabed immediately above the buried cable and at a distance (both horizontal and vertical) from the cable, is described in Appendix 9.2. Estimations have been based upon existing information where possible but for designs where no data exist (75kV, 220kV and 275kV) approximations have been suggested.


55.


These data show rapid attenuation of both B and iE fields with increasing distance from the cables, such that the strongest fields are limited to an area in close proximity to the seabed above where the cables are buried. The depth to which the cables are buried would affect how strong the fields at the seabed are, with shallower depths resulting in stronger fields.


9.9.3.2.2 Direct Current Cables 56.


In contrast to AC cables, the B field generated by bipole DC cables is static and thus varying iE fields would not be induced in the same way as for AC cables. However, localised static iE fields may be induced as seawater (tidal flow) or other conductors such as marine organisms pass through the HVDC cable’s B field.


57.


The magnitude of B and iE fields that might be expected from the HVDC cables under consideration for East Anglia THREE is described in Appendix 9.2. Owing to relatively few data being available for similar industry standard cables, informed predictions have been made where possible, with more general assumptions where data are lacking.


58.


These data show that both B and iE fields vary with the voltage capacity of the cable, with higher rated cables generating stronger fields. Fields attenuate rapidly with increasing distance from the cables; attenuation occurs at significantly shorter distances around bundled cables compared to those separated by 50m, owing to cancellation effects.


9.10 Existing Environment – EMF


9.10.1 Background Fields 59.


Preliminary Environmental Information May 2014


The background geomagnetic field off the coast of East Anglia is approximately 48 to 49µT.


East Anglia THREE Offshore Windfarm


Chapter 9 Underwater Noise Page 15


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