Magnetic field shielding concepts for power transmission lines

High current carrying cables used in power transmission lines create strong magnetic fields in their vicinity. For ac lines at 50-60 Hz, the magnetic field is quasi-static and hence uncoupled from the electric field. Shielding of such low frequency magnetic fields is a challenge. In this paper, finite element modeling is used to study the effect of various shield geometries and shield materials around a current carrying wire. Two-dimensional analysis is sufficient for this problem because the cables are very long compared to the wire diameters. Shielding effectiveness, defined as the difference in the magnetic field intensity with and without the shield, is presented. It is concluded that a partial shield is the optimal design for shielding the region below the cable. To achieve this, the shield gap must be oriented above the high current wire.