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Berlin Environmental Atlas

08.05 Electromagnetic fields

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Methodology

Electric and magnetic fields are characterised by strong spatial variations and rapid fluctuations over time. Time-variation predominantly affects the magnetic field, which responds in proportion to current flow and can pass unchanged through any substance, with the exception of ferromagnetic or conducting materials. The electric field, on the other hand, is heavily distorted by buildings or vegetation, where these objects provide a shielding effect.

In procuring the displayed values, various methods were used. These partly rely on pure measurements or calculations, and partly on a combination of both.

Measurements

Measurements generally only served for categorising objects (e.g. substations, 1 kV cables etc.) and for standardising calculation data (e.g. railway traction currents), because although measurements describe a precise field condition, they only represent a very brief moment of time. When establishing information about large areas, measurements are not necessarily the best approach, in that they incur a substantial workload. Measurements are preferable in complex scenarios, which is often the case at workplaces.

Calculations

Calculation techniques (Utmischi 1976, Haubrich 1974, FGEU 1997) should not be regarded merely as a substitute for complicated measurements. They can be irreplaceable, such as in planning new installations or simulating different operating conditions.

Fields, in contrast to conventional environmental factors, can be fully described by the properties of the field source. We do not have to compensate for phenomena such as the drift of gaseous emissions due to air movements, followed by off-site inputs after precipitation.

However, this advantage only comes into play if the field can spread undisturbed. This is practically always the case for low-frequency magnetic fields, as ferromagnetic materials do not occur in the environment in sufficient quantities. Electric fields, meanwhile, are often distorted by buildings or vegetation. Nevertheless, the assumption of undisturbed field strengths generally represents the worst-case scenario.

The undisturbed field strengths along high-voltage overhead lines were calculated for the entire area under study. Measurements only served to verify the calculations. The field distribution around rail installations was determined locally and extrapolated for whole sections of track.

Calculations were carried out with the program package WinField® (FGEU 1997).

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