Understanding the exposure of marine life to electromagnetic fields generated by subsea cables

Abstract

Electromagnetic fields (EMF) generated by wave and tidal energy subsea power cables can potentially impact marine life. The primary source of artificial EMF is subsea power cables, whose estimates of the propagating levels are typically conducted using theoretical models. However, these models must be validated with empirical data collected in situ. This study proposes a new measurement methodology that enhances the accuracy of the estimated fields in the water column. The new methodology employs two fluxgate magnetometers operating simultaneously: one stationary near the cable and the other moved around to map spatial variations. The stationary magnetometer thus serves as a reference. Changes in the magnetic field recorded by the stationary fluxgate can be attributed solely to variations in the electric current flowing through the cable. The advantage of this configuration is that it enables linear corrections of changes in the cable current during measurement. Consequently, data from the moving fluxgate can be adjusted according to the fluctuating current. This methodology will produce corrected data suitable for modelling where the current is assumed to be constant. The methodology was tested in situ on a High Voltage Alternating Current offshore wind export cable. Additionally, it was observed that there were two contributions to the observed magnetic field: the magnetic field from a balanced load that attenuates effectively with increasing distance and the magnetic field generated by an unbalanced load that decreases more slowly and, as a result, influences a larger volume.