Low-frequency Magnetic Shielding against Unbalanced Currents

Magnetic shielding is an effective means to reduce low-frequency magnetic fields emitted from power cables and busbars. However, shielding against unbalanced currents has not been addressed well. This paper introduces equivalent magnetic dipoles for discussing magnetic shielding under a monopole current source. It is found that shielding is achieved by the cancellation of magnetic fields from both equivalent dipoles and the source monopole. However, the performance is not satisfactory because of a fast decaying rate of distance in the equivalent dipoles. To improve shielding performance under an unbalanced current source, it is recommended using either highly-permeable plates or multiple highly-conductive and electrically-connected plates.