Substations are buildings where the voltage is changed from extra high voltage to high voltage or medium voltage to low voltage by transformers. Converter stations are used to convert alternating current to direct current and vice versa (Converter station). Substations and converter stations are surrounded by metal fences which restrict the access to trained personal only for maintenance purposes. In publicly accessible areas the magnetic fields are below the public exposure limits.
Substation in Meerbusch-Osterath/Germany
photo: Tetris L, license: CC BY-SA 3.0, via Wikimedia Commons
Typical measurement values are available in the database of exposure sources.