The term ‘electromagnetic field’ (EMF) combines two components: electric fields and magnetic fields. Electric fields are generated by voltage. They surround all electrical equipment connected to a power supply, regardless of whether it is switched on or not. Magnetic fields, on the other hand, are produced by current. They occur around electrical equipment when it is switched on and disappear when it is switched off.
Effects of power transmission
The effects of electromagnetic waves depend on their frequency and wavelength. Electricity transmission produces electric and magnetic fields at very low frequencies. Like in many other countries, the frequency of electricity transmission in Iceland is 50 Hz. In comparison, the frequency of microwaves is 1-100 GHz and that of X-radiation approximately 106 GHz. Microwaves’ high frequencies and short wavelengths cause molecular rotation, the friction from which generates heat.
Potential difference in thunderstorms
Electric and magnetic fields are part of the Earth’s environment. Electric fields are normally due to clouds being negatively charged compared with the ground. The electric potential difference between the ground and a cloud is usually so minimal that no visible effect is discernible. In thunderstorms, however, the potential difference is so great that the atmosphere does not provide sufficient insulation between the ground and the cloud, so lightning strikes. The Earth’s natural magnetic field is what makes it possible to use a compass, the Earth being approximately a magnetic ‘dipole’ with the magnetic field running from the North Pole to the South Pole.
Many studies have been undertaken to investigate whether electromagnetic fields due to power transmission are harmful to human health. The studies have yielded no clear answers, while indicating a limited link between electromagnetic fields and leukaemia in children exposed to constant electromagnetic radiation for long periods.
Rights of way
Around transmission lines are right-of-way areas, where construction is prohibited. A right-of-way area for 220 kV transmission lines generally ranges between 65 and 85m. Since the intensity of electromagnetic radiation drops very rapidly with increased distance from the source, the radiation is usually below the reference limit where the right of way ends.