Public power supply and traction power network

Public electricity supply networks

Electrified railway line

In many places, the public power supply at low-voltage grid level is provided by means of underground cables. Overhead power lines are mainly used for the national distribution and transmission of electricity over long distances. The main frequency is 50 hertz. Low-frequency magnetic fields occur in the vicinity of the lines; in the case of overhead power lines electric fields are also produced. Houses, elevations on the ground or vegetation may result in distortions of the electric field below overhead power lines.

In addition to lines, substations and transformer stations are further components of public electricity supply networks.

Traction power network

Diurnal variation of the magnetic flux density (at 16.7 hertz) for an individual who lived immediately next to a traction power system and also worked there (from 7.30 to 10 a.m.)

Railway overhead lines and the electrical traction power network supplying the overhead lines are operated at a frequency of 16.7 hertz. Railway overhead lines are strung above the tracks as contact wires; traction power network lines are generally constructed as overhead power lines.

Local rail traffic

In contrast to mainline railways, trams and underground trains as well as the Berlin S-Bahn (rapid transit railway in Berlin) are supplied with direct current generated in rectifier stations from the public alternating current grid. The overhead contact wires of trams and the power rails of underground railways produce static electric and magnetic fields.

Exposure from electric and magnetic fields

Both with overhead power lines as well as underground cables, the field strengths drop off rapidly with increasing distance. Electric fields occur only in the case of overhead power lines. In this context, it is interesting that construction materials used for the walls of a house can shield its interior against up to about 90 per cent of the external electric field acting on the house, whereas shielding buildings against external magnetic fields is not possible without great effort.