Electromagnetic fields are everywhere in today’s society. In addition to transmission lines, they are produced by underground cables, transformers and electrical centres, electrical grids in buildings, home appliances, the electric motors and related power supply systems in trains, security gates at shops, computers, radio stations, mobile phones and base stations, and industrial equipment. The Earth’s own magnetic field, lightning and the sun also produce electromagnetic fields.
Electric and magnetic fields created by transmission lines occur only in the immediate vicinity of the lines themselves.
The magnetic field of a transmission line is proportional to the current flowing along the lines, which is largest in lines with a voltage of 400 kilovolts. However, the action level of 200 μT set for public exposure to magnetic fields is not exceeded even directly underneath the lines, where the magnetic field, even at its strongest, is only about 20 μT. At a distance of 50–70 meters from the central line of a 400 kV transmission line and 25–40 meters from the central line of a 110 kV transmission line, the magnetic field is only about half a percent of the action level set for the public.
The strength of an electric field depends on the voltage in the transmission line. For example, the strength of an electric field under a 400 kilovolt transmission line is a maximum of 10 KV/m and 2–3 kV/m under a 110 kilovolt line. The electric field decreases rapidly when a person moves farther away from the transmission line. Vegetation and buildings also effectively reduce the electric field.
The new act does not apply to the limit values for electric fields of transmission lines, because the Electrical Safety Act and its provisions set requirements for transmission lines that restrict the strength of electric fields under conductors to a safe level.
The limit values for electromagnetic fields were confirmed in the Ministry of Social Affairs and Health decree that took effect in December. The supervising body is the Radiation and Nuclear Safety Authority (STUK).
- Further information: Fingrid – Land use and environment