Some aspects of magnetic shielding of a transformer substation using alternative shielding techniques

Power frequency magnetic field shielding is used for protection of sensitive electronic devices and data storage media and for prevention of interference in video display unit operation. The interest in magnetic field shielding is growing due to increasing concern of possible health effects on persons exposed to power frequency magnetic field. In the surrounding of substations, magnetic fields of power frequency can arise with flux densities in the range between 1 /spl mu/T and 10 /spl mu/T. These fields are mainly produced by busbars, cables and transformers. A primary source of the magnetic field in the substation is generally the cable section from the transformer secondary terminal. Eddy currents and magnetisation induced in metal enclosures, special shields and other conductive and ferromagnetic structures are secondary sources. When the rearrangement of substation equipment is not possible, magnetic field shielding around the sources can be implemented to reduce power frequency magnetic fields in the vicinity of a substation. It is common to associate ferromagnetic materials with magnetic field shielding. Various types of steel have frequently been used for shielding. However, conductive materials with no ferromagnetic properties, such as aluminium and copper, can also perform well as magnetic field shielding materials.