Electromagnetic field
When it comes to power lines or electrical devices, electromagnetic radiation and its potential risks are often a topic of discussion. Strictly speaking, this radiation consists of electric and magnetic fields. Exposure limits are in place to protect us from adverse health impacts. Switzerland’s limits are among the strictest in the world.
Electric and magnetic fields
Electric and magnetic fields are produced wherever electricity is generated, transported and used. As soon as a device is connected to a power socket, in your home for instance, it carries voltage. This creates an electric field, even if the device remains switched off and no current flows. Once the device is switched on and current is flowing, a magnetic field is created in addition to the electric field. The strength of the magnetic field is measured in microteslas (μT).
Static fields and alternating fields
Direct current, which is used in conventional electronic consumer goods such as computers, mobile phones or cameras, creates static electric and magnetic fields. These have a constant field strength.
However, in the case of alternating current, which comes out of the power sockets in every household, the voltage and current intensity change in a regular rhythm, the frequency. The electricity grid has a frequency of 50 Hz.
The intensity of a magnetic field is dependent on the current intensity and not on the voltage. The lower the current intensity on a line, the lower the magnetic field around the line. As a rule, the capacity of extra-high-voltage lines is not fully utilised, as the transmission grid is operated in such a way that in the event of a line failure, the current can flow via other lines.
The intensity of electric and magnetic fields decrease with distance. The greater the distance to the conductor or cable, the lower the electric and magnetic fields. In the case of cables in households, the fields are almost insignificant just a few decimetres away. In the case of extra-high-voltage lines working at fully capacity, this distance is around one hundred metres.
Limits – Switzerland has one of the strictest guidelines in the world
The exposure limit for a magnetic field of 100 microteslas protects against all scientifically known adverse health effects. It applies everywhere that people may be present. In addition, the Swiss Environmental Protection Act demands that the population also be protected from health risks that are not yet proven, but conceivable. The legal installation limit of 1 microtesla is used for this purpose. This limit applies wherever people spend longer periods of time, for example in bedrooms or living rooms, schools or on playgrounds. This is one of the strictest limits in Europe. Both limits apply to the maximum utilisation of a line.
| Electric field | Magnetic field | |
|---|---|---|
| Formation | As soon as a device is connected to a power socket, even if it is not switched on. | As soon as current flows. |
| Intensity determined by: | Voltage (Volt) | The amount of current flowing (Ampere) |
| Intensity measured in: | Kilovolt per metre (kV/m) | Microtesla (µT) |
| Limits (CH) | 5 kV/m | 100 µT (exposure limit) 1 µT (installation limit) |
Effects on health
The brain controls the body via electric signals, which should not be disturbed. Electric fields are largely prevented from entering the body by clothes and the skin. Magnetic fields produced by alternating current whenever current is transmitted, on the other hand, easily penetrate house walls and the body. If sufficiently strong, they can influence the biological signals. The limits are therefore set so that health risks are ruled out. The effects of weak, long-term exposure (alternating fields with field strengths below the installation limit of 1 microtesla) have still not been scientifically proven.
Magnetic fields exist around overhead lines and underground cabling
The magnetic field is much stronger right above underground cabling than it is below an overhead line. On the ground, where people normally are, the magnetic field for overhead lines is a few microtesla while it can reach up to 100 microtesla for underground cabling.
Spatial expansion of the magnetic field
Sources: The following content is reproduced with the kind permission of the Swiss Research Foundation for Electricity and Mobile Communication at the ETH Zurich. www.emf.ethz.ch
Measurements and calculations
Cooperation with research
Swissgrid has entered into a partnership with the Swiss Research Foundation for Electricity and Mobile Communication (FSM), a non-profit research foundation at the ETH Zurich. The FSM promotes research on technological, biological, health-related and social issues in the context of electromagnetic fields of radio and electricity technologies. The foundation also provides consulting for the authorities, companies and organisations, hosts conferences and imparts expert knowledge to the general public.
Noise
Unfavourable weather conditions in particular, such as rain, hoar frost or wet snow, can cause local electrical discharge in power lines. In electrical engineering, this process is known as corona discharge. The phenomenon can produce noises described as crackling or humming.
In Switzerland we have an emissions limit of 55 decibels in residential areas (45 decibels at night), which must be adhered to by law. The noise pollution from a busy street is over 80 decibels. Where necessary, Swissgrid employs all technical means to limit the corona effect. Corona noises are not present in underground lines.
The following video shows the sound intensity of high voltage power lines compared to more common ambient noise.
Environment
Environmental impact assessment
As part of the approval process (UVP), the environmental impact assessment examines whether a project complies with the legal regulations for environmental protection. The environmental impact assessment report (UVB) is the basis for the examination. As the client, Swissgrid is responsible for the preparation and submittal of the UVB documents. However, an independent, professionally qualified office is normally commissioned to prepare the UVB. Various issues are dealt with in the report, including noise, non-ionising radiation, water, soil, contamination, forest, biotope and vegetation, fauna and habitat, landscape and visual character, cultural monuments and archaeological sites.
Environmental supervision
Environmental supervision (UBB) looks after and monitors environmental concerns during construction and supports the client in the legally compliant and environmentally compatible execution of the construction project. In the process, it ensures compliance with environmental laws, regulations, guidelines, instructions and requirements of the planning approval decision. They advise and support the participants, observe and evaluate environmental problems on the construction site and ensure legally compliant execution of the project.
Enquiries on lines
Do you have questions on an extra-high-voltage line near you? Are you planning to erect a building or temporary infrastructure (e.g. livestock fence or biotope) near a line? Our experts would be pleased to answer your questions.