The increasing electrification of society in recent years has put the spotlight on possible health risks caused by electromagnetic fields. The phenomenon is defined as ‘electromagnetic litter’ and is mentioned in the context of man-made electric, magnetic and electromagnetic fields. These are different from the magnetic fields that occur naturally in nature. Magnetic litter is given more attention in some countries, such as Switzerland, where a special ordinance (ORNI) is designed to protect people from harmful non-ionizing radiation.
In electrical installations such as transformers and substations, low-frequency magnetic fields are present. Measures that need to be implemented to avoid or reduce magnetic fields depend on the type of installation. In installations of this type, magnetic fields can be eliminated by means of magnetic or superconducting iron wall cladding. Even a mixture of these two, in the appropriate thickness, can effectively create the desired shielding. This is a method that is usually expensive to implement. Another method, which focuses on the source of the problem, is to redesign the transformer and its supply.
GBE manufactures both oil and cast resin insulated transformers with a created magnetic field in the immediate vicinity of the transformer of as little as 1µT (microtesla). This low level is achieved by creating a shield around the active parts of the transformer. In oil-insulated transformers, the shield is placed inside the tank, while for dry-type models it is mounted in a special enclosure. The shield consists of flanges made of magnetic material that control the magnetic fields. In addition, the bushings on the secondary side of the transformer are customized. The higher the amperage, the more important these adaptations are. For oil-insulated transformers, the secondary-side bushings are divided by means of crossed sockets to create vector compensation of the magnetic fields generated and allow reduction of the magnetic fields.
For cast resin insulated transformers, in addition to the above, a rail connection is added on the secondary side and on the enclosure furthest from the location that needs to be protected. These measures together offer major advantages over more costly solutions that are not necessarily as effective.