Power lines

High-voltage power lines cause low frequency electric and magnetic fields around them. Exposure is concentrated close to the lines. Thus, only a very small percentage of the Finnish population is exposed to fields generated by power lines.

In main power grid  there are three main types of high-voltage power lines. Large 400 and 220 kilovolts power lines, suspended high above, and the most important 110 kilovolt power lines, are the basis of Finland’s main power grid. Other 110 kilovolt power lines make up the so-called regional network. Smaller, 20 kilovolt, medium voltage power lines are used in a distribution network. Electric fields can be significant when it comes to exposure directly below 400 kilovolt power lines and can even exceed exposure limits for the general public. This, however,  does not restrict occasional visits to these locations for activities such as picking berries or farming and forestry work. The electric field generated by other types of power lines do not cause significant exposure.

Magnetic fields caused by power lines are only found in the direct vicinity of the lines themselves. The magnetic fields are proportionate to the current flowing through the power lines, which is at its highest in the 400 kV main power grid. Exposure limits to the general public are not exceeded even directly beneath the power lines, where, at its strongest, the field is one-fourth of the limit values. When 60-70 metres away from 400 kilovolt power lines, and 20-40 metres away from 110 kilovolt power lines, the exposure is less than one-hundredth of the 100 µT limit value for the general public. Beneath 20 kilovolt power lines, exposure is always less than one-hundredth of the limit value.

Underground cables, used in densely populated urban areas, do not generate electric fields outside the cable. Magnetic fields, however, do extend a few metres from cables at ground level.

Only people living in the direct vicinity of power lines are exposed to magnetic fields caused by the lines. In the picture above one can see the strongest magnetic fields found in the direct vicinity of 400 kilovolt power lines. When over 65 metres away from the line, the exposure is less than 1 µT.

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