Magnetic fields around heavy-current-carrying multi-core cables I. Theoretical model

For understanding and evaluation of such ELF magnetic fields, current-carrying parallel-helix-filament theoretical model was proposed. Based on the model, theoretical and simplified formulas for calculating the magnetic fields were deduced. The patterns of the magnetic fields are disclosed. It is found that the magnetic field decay with the radial distance at rate greater than exponentially. On an observation path parallel to the cable axis, or on a coaxial circular path, both the magnitude and the phase angle of the magnetic field change with the observation position periodically. The magnetic fields around some cables predicted by the proposed simplified formulas were compared with the limits in some international standards. It is found that for most of the cables employed in engineering practices, in the space of 2 meters away from the cable, the magnetic fields are in compliance with the standards.