An important aspect during planning and operation of transformer stations and other electrical operating rooms and plants in compliance with §1 26 BImSchV (air pollution control legislation) is the protection of the public against electromagnetic fields.

26th Federal Air Pollution Control Ordinance (version from 16.12.1996)

Technical frequencies normally encountered in the supply and distribution of energy (see Appendix 1) are assigned to low frequency plants in accordance with §3.

In order to ensure protection against harmful effects on the environment, low frequency plants should be installed and operated so that:

  • within their range of influence in buildings and on property
  • which is not only intended for the temporary presence of people,
  • limit values are not exceeded at maximum plant operating loads (transformer measurement; Delta T) and
  • where other low frequency plant is taken into consideration.

According to Appendix 1 of the 26th BImSchV, the following limit values apply

Low frequency plants  
Frequency (f) in Hertz (Hz)Effective value of electrical field strength and magnetic flow density

Electric field strength in
kilovolt per metre (kV/m)
Magnetic flow density in microtesla (µT)
50 Hz fields5100
162/3 Hz fields10300

§4 stipulates requirements governing supply: »For supply purposes, maximum effective values of electrical field strengths and magnetic flow densities in these buildings or on these sites should comply with $3 in the case of the installation or important modifications to low frequency plants near living accommodation, hospitals, schools, kindergartens, playgrounds or similar facilities.«

Immission locations. A differentiation is made between significant and insignificant in this context. Locations classified as insignificant are those which serve the temporary presence of persons, although the duration of presence is decisive here. In contrast to this, persons are regularly present for several hours in significant immission locations in compliance with the correct use of such locations.

Where a significant immission location of this nature exists within a radius of one metre around a substation (measured from the outer wall), distances for measurements to determine the strength of the field must be adhered to.

The limit values should be determined in these cases at specified distances from the wall (varies from federal state to federal state in Germany). In certain buildings (residential accommodation, schools, kindergartens or similar) or accessible higher surfaces with a height < 1.3 m, field strengths should be determined directly on the walls or directly on the floor.

According to § 5 of the 26th BImSchV, the following applies for the determining of field strengths and flow density values:
»Where applicable, measurement and calculation procedures from the norm draft VDE 0848 Part 1 (May 1995) should be employed. Measurements should be realised in the influenced location with the respectively strongest exposure, this being a location where not only the temporary presence of people is to be expected.«

§7 stipulates a formal obligation to report findings in these cases to the authorities and the relevant time-limits and deadlines pertaining to said.

Offences relating to reporting in compliance with §7 are  described in §9. Responsibility  for adherence to the 26th BImSchV lies with the operator.