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Berlin Environmental Atlas

08.05 Electromagnetic fields

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Map 08.05.6: Influence of trees on the spread of electric fields beneath overhead lines (50 Hz)

Houses, trees or hedges noticeably distort the electric field. The example of 3 trees of 5 m height beneath an overhead 220 kV line is shown here. The field strength between the trees' branches is higher than on the opposite, undistorted side (left). However, field strength directly beneath the trees is lower, as the electric field is deflected by the tree canopy. Without the trees, a completely symmetric field strength pattern would prevail (the field could be perfectly mirrored on an axis vertically traversing the centre of the pylon).

The reduction of electric field strength in the immediate vicinity of a tree is around 85 % beneath a 380 kV line, and 5 m further on it is still about 50 % (IZE 1994).

Map 08.05.7: Magnetic flux density at a substation (50 Hz)

At the time of measurement at 1 m above ground, this station was operating at about 50 % of its nominal capacity (630 kVA).

No field strengths are marked for the interior of the station as this normally inaccessible area could not be entered for measurement. In the vicinity of the station there are two local peaks in magnetic flux density: the bottom right-hand corner, where the transformer and low-voltage distribution are located, and by the upper wall, where we find the high-voltage switchgear. At 9 different substations the magnetic flux densities measured for these peaks ranged from 0.85 to 3.54 µT. As the distance from the wall increased, flux density fell rapidly and at 1.75 m only measured 0.3 µT.

Depending on design, higher field strengths may occur at substations. This is always the case when parts of the electric installation, especially the low-voltage distribution, are fitted directly to an outer wall. Situations where the image quality of visual data displays may be disturbed by low-frequency magnetic fields in the immediate vicinity of the building (approx. 1-2 m) only occur when the station is integrated into a building ("fitted stations").

Map 08.05.8: Magnetic flux density by the Railroad Track (16 2/3 Hz) at Savignyplatz

Shown here is the oscillating magnetic field at 16 2/3 Hz in the vicinity of the railway section near Savignyplatz station which is generated by the railroad overhead traction supply and the tracks. This field is not constant, only occuring when trains are passing between Zoologischer Garten and Savignyplatz. Two heights were chosen for calculation. 1 m above ground is relevant for people on the pavements and streets or in the shops at Savignyplatz, while 1 m above the station platform at Savignyplatz applies to passengers and rail personnel.

At a traction current of 226 A, the maximum railroad induced field strengths calculated for people waiting on the platform at the S-Bahn station Savignyplatz is 4.8 µT or 0.4 kV/m (16 2/3 Hz).

The average magnetic flux densities are at least one magnitude lower. By the viaduct, at 1 m above ground level, the maximum flux density is 2 µT (16 2/3 Hz).

The peak values caused at rail installations by railroad trains are relatively high compared to those of 50 Hz power supply. However, they are only of short duration - and the limit values for 16 2/3 Hz fields are higher (10 kV/m and 300 µT). Station platforms are not designed for people to remain for long periods, and usually their "dwell-time" is brief. The 26th BImSchV does not, therefore, apply. Rail-based transport systems are also not covered by the 26th BImSchV, as these vehicles are not fixed installations.

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