Role of magnetic materials in power frequency shielding: numerical analysis and experiments

Shielding of magnetic fields at power frequencies has been investigated by computation and experiment. Different types of low-cost soft magnetic lamin ations (low-carbon steel, nonoriented Fe-Si, grain-oriented Fe-Si) and diff erent shield geometries (plane, U-shaped and box-like) have been considered . The shielding factors of model screens have been measured, together with the magnetic flux density in the sheets employed, under field levels typica l of industrial environment (similar to 100 muT). Computations have been ca rried out by means of a hybrid finite-element/boundary element model, which result in good agreement with measurements. It is shown that grain-oriente d laminations provide the highest shielding factor, which is reinforced in the plane shield configuration by the addition of an aluminium plate. It is predicted that the screening performance of the U-shaped and box-like shie lds can be appreciably impaired by the presence of air gaps at the corner j oints.