East Anglia ONE 4.2. Direct current cables
4.2.1. Existing information DC cables under consideration for use for the EAONE project, specifically bipole HVDC export cables, range from 320kV to 600kV designs, with current loads of 1407A and 1667A respectively, although it is most likely that 320kV will be utilised (see Section 2.2). Owing to relatively little data being available for similar, industry standard cables, informed predictions are made where possible, with more general assumptions made where data are lacking.
Poleo et al (2001) calculated a B field of 5500µT at the surface of a 1600A HVDC cable, attenuating to 50 µT at a distance of 10m. Modelling of EMF for Docking Shoal & Race Bank OWF export cabling, which consists of an HVDCLight 150kV design, predicted a B field of 1369µT at the seabed assuming 0.5m burial, reduced to 37µT assuming 1m burial (CMACS 2008). B fields were also predicted to attenuate almost completely at a distance of 10m from the cable.
Modelling undertaken by Swedpower for the BritNed Inteconnector HVDC cable, rated at 450kV with a maximum load of 1320A, predicted the following B and iE fields for different deployment methods and distances from the cables assuming 1m burial (Table 3; Voet 2005). Note that iE fields were assumed to be caused by tidal flow through the B field, and an estimated 0.85m/s tidal flow rate was used in calculations.
Table 3. Magnetic and electric fields generated by BritNed Interconnector assuming 1m burial (adapted from Voet 2005)
Cable deployment B field (µT) 1m from cable 5m from cable Bundled (0.2m) 72 2.2 61 iE field (µV/m) 1m from cable 5m from cable 1.9 2m separation 310 21 260 18
Another project CMACS has recently worked on1 predicted EMF generated for similar 500kV HVDC cables (assuming no burial) with slightly higher maximum current loads than BritNed. B fields were estimated at approximately 5000 µT at the cable surface, with attenuation to approximately 800 µT at 0.5m distance (horizontal or vertical) and approximately 80 µT at 5m for cable separation of 50m. Attenuation for bundled cables was more rapid to approximately 250 µT at 0.5m distance and approximately 2 µT at 5m. iE fields at the cable surface were predicted to be approximately 6500 µV/m, with attenuation to approximately 1000 µV/m at 0.5m and approximately 100 µV/m by 5m for a cable separation distance of 50m. Again, attenuation for closely bundled cables was more rapid to approximately 500 µV/m at
1 Unpublished as yet, and therefore project details unavailable at time of writing J3184 EAONE v2 11
EMF Assessment
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