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Non-Ionizing Radiation at Extremely Low Frequencies (ELF) of the Electric Grid

 

Electromagnetic radiation from electric grids surrounds us in every aspect of modern life – in the city and in the country, at home and in the street, at work and at leisure.  It is therefore important to be better acquainted with its sources, its range of frequencies, the possible health effects resulting from exposure to it, and the guidelines drawn up by international organizations to reduce exposure.

Electric currents are the source of electromagnetic radiation.  Currents, such as those carried by electric cables, produce electric and magnetic fields, the extent of which depends on the strengths of the currents produced and their direction.  Even in the open air electric currents that produce strong fields are sometimes produced spontaneously, for example, lightning. 

 

Frequencies defined as ELF

Radiation from the electric grid is within the extremely low frequency (ELF) range.  According to the International Telecommunications Union (ITU) the range of ELF on the electromagnetic spectrum is between slightly above zero Hz and up to 300 Hz. The ELF range includes four bands: the first is in the 0.03-0.3 Hz range (very close to zero Hz) while the fourth and last band includes the range of frequencies from 30-300 Hz (wavelengths of 1-10 Km, respectively) as illustrated in the ITU's Table of Frequencies – Table 2 –(pdf document available for downloading). This definition of ELF was adopted by the Occupational Safety and Health Administration – OSHA – the safety and hygiene administration of the USA Department of Labor.

 

Range of radiation frequencies from the electric grid

Public interest in ELF generally focuses on the higher range included in the fourth band of frequencies, since this is the range of radiation from electric and magnetic fields produced by the electric grids. These grids usually operate in the 50Hz or 60 Hz frequencies.

 

The electric grid supplies electric energy to consumers by means of alternating currents (AC) at 50-60 Hz, and these produce radiation around them in the form of electric and magnetic fields.  These alternating currents are generally produced by generators, as in power stations.

 

When investigating electromagnetic radiation at extremely low frequencies (ELF) such as produced the power grid, it is mainly the physical properties of the electric and magnetic fields that are studied, while the characteristics of the radiation wave are less studied.  This is because the wavelengths at the frequency of the power grid are enormous: at a grid frequency of 50 Hz the wavelength is 6,000 Km, and at a grid frequency of 60 Hz the wavelength is 5,000 km.

 

 

 

High voltage power lines

High voltage power lines 

 

 

 

 

 

The term radiation at electric grid frequencies refers mainly to the physical properties of the electric and magnetic fields of the electric currents of the grid, such as intensity of fields and phases of voltage and current.

 

An electric field is measured in units of volts/meter (V/m); a magnetic field is measured in units of amps/meter (A/m) or in milligauss (mG) units, or Tesla (T).

 

 

 

Radiation at 50Hz or 60 Hz from the power grid

It is almost impossible to describe the infinite variety of uses of electricity that we, the consumers, obtain from the power grid.  Today we can no longer imagine life without the aid of electric energy.  The production of electricity and its utilization began at the end of the 19th century, from 1882.  At first, production and supply were through direct current (DC) – leading to energy loss and consequently to restricted usage possibilities and supply ranges, and required the deployment of closely-packed generators to provide electricity in small grids.  The invention of multiphase alternating current by Nicola Tesla in 1888 caused a world-wide change, enabling the supply of electricity over long distances with minimal energy loss, and in fact, the 'electrification' of the whole world with uniform standards, in effect to this day.

 

 

The consumption of electric energy is a function of the work done by a single electrical appliance during its operation, and it is measured in units of watts-hour or kilowatts-hour (kW h)

 

 

 

In general, sources of electric radiation are divided into three major groups:

 

Generation

Electricity is generated mainly at large power stations, as follows:  electro-mechanical power stations produce electricity from petrol, gas or coal, by converting thermal energy (heat) into electrical energy through power turbines.  Generation of electricity takes place mainly at these power stations.  Hydro-electric power stations convert hydro-gravitational energy to electricity (they convert energy from flowing water to electrical energy). Nuclear power stations convert nuclear energy from atomic reactors into electrical energy.

 

Additional sources of energy for the generation of electricity include windmills, solar energy and chemical energy – these sources are limited in the context of global production.  Electricity may be generated on a smaller scale by small generators, as required, e.g. in far-off or remote settlements, or in short-term backup systems in the case of problems in the central power supply (as for hospitals, large factories, etc.)

 

         
Power station for producing electricityPower station for producing electricity  

Electricity-producing sub-station

Electricity-producing sub-station

 

 

Dynamo in an electrical generator

Dynamo in an electrical generator

 

Distribution

The electricity generated at central power stations is carried by main high voltage power lines (400 kV) to switching and distribution stations, from which it is distributed by intermediate voltage power lines (161kV) lines to intermediate transformer stations (where high voltage is converted to lower voltage).  The electricity is then carried to local community or street level distribution lines. Local transformers convert the high voltage electricity (e.g. 22 kV and 33 kV) to the lower voltage electricity of the local grid (e.g. 110 V or 220 V), at frequencies of 60 Hz or 50 Hz, according to the local grid of the country.

 

         

Complex array of electric wires in a city

Complex array of electric wires in a city

 

Central control room for distribution of electricity

Central control room for distribution of electricity

 

Automated household electric switchboard

Automated household electric switchboard

 

Utilization

The variety of uses of electricity is enormous, and may be divided into the following main areas: industrial, commercial, business and household uses.

 

         

Electricity used in the vehicle industry

Electricity used in the vehicle industry

 

 

 

Electricity used in the textile    industry

Electricity used in the textile industry

 

Household electrical appliances

Household electrical appliances

 

Use in Transport

 

         

Electrified public trams in Vienna

Electrified public trams in Vienna

 

 

Rapid electric train

Rapid electric train

 

 

Dynamo component in a generator

Dynamo component in a generator

 

 

References

  • International Commission on Non-Ionizing Radiation Protection (ICNIRP) Guidelines for limiting exposure to time‐varying electric, magnetic and electromagnetic fields (1Hz 100kHz). Health Physics. 2010; 99:818‐836.
  • International Commission on Non-Ionizing Radiation Protection (ICNIRP)  Guidelines on limits of exposure to static magnetic fields.  Health Physics. 2009; 96:504‐514.
  • International Commission on Non-Ionizing Radiation Protection (ICNIRP)  Guidelines for limiting exposure to time‐varying electric, magnetic and electromagnetic fields (Up To 300 GHz). Health Physics. 1998; 74:494‐522.
  • United States. Bureau of Naval Personnel. Basic Electricity (Dover Books on Electrical Engineering). 2nd edition, 1970. Dover Publications. 
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