East Anglia ONE
EMF Assessment 5. Predicted magnetic (B) and induced electric (iE) fields
Estimates of likely EMF emissions have been made based on review of available literature and previous work undertaken by CMACS. 4.1. Alternating current cables
4.1.1. Existing information Three-core AC cables under consideration for use for the EAONE project, including array cables and HVAC export cables, range from 33kV to 220kV. 275kV single core cables are also being contemplated (see Section 2.2) but their use will depend on cable and installation technology being developed in time for EAONE. Data are available for similar, industry standard three-core cables ranging from 33kV to 132kV, and therefore certain well supported predictions can be made, whereas more general assumptions must be made for the higher powered and single core designs.
33kV cables were installed at Kentish Flats OWF and CMACS (2004; cited in Gill et al. 2005) reported that B fields of up to 0.015 µT and iE fields of up to 2.5 µV/m would be anticipated at the seabed-seawater boundary under full power generation conditions and burial to a depth of 1m.
Engineers predicted slightly higher B fields of 0.54 µT for similar 33kV cables at Burbo OWF (SeaScape Energy 2008), also at maximum power and buried to 1m. They also estimated that the B fields would attenuate by approximately ten times to 0.05 µT over a distance of 10m through seawater (SeaScape 2008). iE fields would attenuate at a similar rate, owing to their dependence on B field magnitude.
The University of Liverpool modelled EMF generation by industry standard, 132kV cables operating at maximum load and buried to 1m, and concluded that B fields of 1.6 µT might be expected at the seabed, inducing iE fields of 91 µV/m (CMACS 2003). They suggested the magnitudes would attenuate by approximately ten times through 8m of seawater, which matches, approximately, the attenuation rate estimated for Burbo OWF 33kV cables.
These figures have been used to inform many assessments using similar designs, and generally match similar trends reported by Tricas and Gill (2011), who averaged and plotted B field generation predicted from ten, buried, subsea AC cables of varying designs against distance from the cables (Figure 4 & Table 1). Projects incorporated in calculations included Naikun Wind Energy Project, San Juan Cable Project, Nysted OWF, Kentish Flats OWF, Horns Rev 2 OWF and North Hoyle OWF, among others.
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