Low Frequency Range

Low-frequency Electric and Magnetic Fields

Electromagnetic radiation is a combination of electric and magnetic fields (electromagnetic fields) generated by charges and electric currents. At low frequencies, and especially at power grid frequencies, both fields (electric and magnetic) behave more independently, and are treated separately.

The electric field depends on the size of the voltage. It is smaller in the vicinity of low-voltage lines (domestic) and home electrical appliances, and larger in the vicinity of high and upper voltage lines.

The magnetic field depends on the size of the current. It is larger in places where large currents – such as power panels and main power lines – are running and in the vicinity of electrical appliances that are larger "consumers" of electricity. The magnetic field is also larger as the number of current-carrying loops of wire increases, so there are high magnetic fields near appliances with electric motors and transformers, such as hair dryers, electric shavers, space heaters, fans and more. 

• Low Frequency Range and Electromagnetic Field Frequencies from the Electric Grid, Electrical Infrastructure in Buildings, and Electrical and Electronic Devices
• Electric Grid: Structure and Exposures
• • Recommendations for Reduction of Exposure from the Electric Grid
• Electrical Infrastructure in Buildings: Structure and Exposures
  
  • Recommendations for Reducing Exposure from the Electrical Infrastructure in Buildings
• Exposures from Electrical and Electronic Devices
  • Recommendations for Reducing Exposure to Magnetic Field from Electrical and Electronic Devices
• Uses

Low Frequency Range and Electromagnetic Field Frequencies from the Electric Grid, Electrical Infrastructure in Buildings, and Electrical and Electronic Devices

• Electric and magnetic fields from electric grids, electrical infrastructure in buildings and electrical and electronic devices belong to the electromagnetic radiation spectrum within the low frequency range up to 300 Hz.
• In various publications on radiation and field hazards, and in past references by entities such as the WHO, the term ELF (Extremely Low Frequency) referred to the frequency range of 0-300 Hz, including the fields at the frequency of electric grids. Nowadays, the ELF range is defined by the ITU as the frequency range between 3 and 30 Hz only, and therefore its use is less common in terms of exposure risks at the frequency of electric grids.
• The electric grid fields are generated by the production, transmission and distribution network of the electric grid and electrical infrastructure in buildings (which will be addressed separately). In addition, fields are generated by electrical appliances connected to network and operating at the network voltage.
• Electric grid provides alternative current (AC), that is, electricity that is not supplied as a direct voltage (constant, like battery), but changes its rotation direction 50 times per second (in Israel) or 60 times per second (for example, in the USA). Therefore, the electric and magnetic fields generated near electric grids and electrical devices, and to which one can be exposed, are alternating fields at a frequency of 50 (or 60) Hz. The wavelength of those frequencies is enormous — 6,000 kilometers for a frequency of 50 Hz, therefore those frequencies are not acceptable to refer to exposure to radiation but to exposure to the components of the electric and magnetic fields, separately.

The main human exposures are to the components of low voltage electric grids (230 volts in Israel), to electrical infrastructure in buildings and to electrical and electronic devices operating at that voltage. For various physical reasons, it is customary to relate primarily to the health risk resulting from the magnetic field component of those exposures, which is more significant, especially for low voltage power.   

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Electric Grid: Structure and Exposures

The term "electric grid" refers mainly to infrastructures that are the responsibility of the Israel Electric Corporation (IEC), which is responsible for generation, transmission, and distribution of electricity. The IEC's infrastructure starts at the electricity generation plants and ends at the end of the electricity supply process, in the electric meter of the consumers (homes, workplaces, factories, etc.). Electrical infrastructure of consumers, apart from electric meter, is not the responsibility of the Israel Electric Corporation but rather the responsibility of the consumers (electric panels, power lines in the walls, outlets, etc.). 

Electric grid is based on a number of principles:

• Supplying Alternative Current (AC) - voltage and current that change their direction (in Israel, at a frequency of 50 Hz). This way of electricity supply is more efficient than direct current (DC) supply, since it enables the supply of long distance electricity with a relative small loss of energy. At the end of the 19th century, the "war of currents" took place between the developers of the two methods of electricity supply, and the supply by AC method became the accepted method worldwide because of its advantages.
  ​The health and safety disadvantages of the method are:
  • The ability to cause nerve stimulation and neuromuscular stimulation, up to ventricular fibrillation and death due to electrocution. It should be noted that this stimulation is also possible with exposure to high-intensity magnetic fields at the frequency of electric grids, even without direct contact with electrical conductors.
  • Magnetic fields at the frequency of electric grids are able to penetrate the human body exposed to them and induce voltages and electric currents (usually low levels) — a phenomenon that is not significant for direct current electricity in common exposures.
• Generation of electricity at very high voltage (hundreds of thousands of volts), its transmission and reduction to a lower voltage in several stages, at any stage of the distribution of electricity, until it turns into low voltage (hundreds of volts) for consumption by consumers.  This method is intended to supply electricity more efficiently and to overcome the phenomenon of reducing ("falling") the voltage along long power lines.  The health and safety disadvantages of the system are the risk of electric shock from high voltage lines, exposure to high electric fields in the vicinity of high voltage lines, the creation of ozone and additional gases due to the electrical penetration of the air, and the possibility of obtaining explosion and combustion in certain situations.
• Generation and transmission of electricity in several phases (usually three). This allows for the creation of several circuits of electricity, as well as three-phase power supply to "power consumers" (e.g. air conditioners, large motors, and industrial machines) operating in this manner.

The main components of electric grid are generation, transmission network, switching stations and substations, and distribution networks:

Generation 

• Electricity generation is usually performed by a device called a generator that turns the mechanical energy of rotation into electrical energy. In order to move the generator and generate electricity, large quantity of mechanical energy is required, which is produced by a number of technologies (as detailed below), in many cases using a turbine that converts a fluid or gas flow to a rotary motion necessary for the generator rotation. The generation of electricity by solar or chemical energy is performed by other methods.
• Electricity generation is mainly done at large power plants, in various technologies and from various sources of energy, as follows: electromechanical power stations that produce electrical energy from oil, gas or coal, and convert thermal energy (heat) into electrical energy while using turbines of various types. Electricity generation in Israel is mostly performed at those power plants; hydroelectric power stations that convert hydro-gravity energy into electricity (power plants that convert energy from waterfalls into electrical energy); nuclear power plants that convert nuclear energy from nuclear furnaces into electricity.
• Other sources of energy for generating electricity are wind plants, solar power stations and chemical energy plants, which are more limited in global output. Electricity is produced on a smaller scale even by small generators, as needed, e.g. in remote communities, as well as in short-term backup systems in cases of electrical failures (such as in hospitals and large plants).

Power plant for electricity generation		Dynamo component of the electric generator

Distribution Network

• A network designed to transmit electricity produced at long-distance power stations using the high voltage power transmission lines — high voltage lines and upper voltage lines.
• Those lines are spread throughout the country, and can be identified by larger power poles.
• In Israel, in high voltage lines, there is a voltage of 400 kV (400 thousand volts), and in the upper voltage lines, there is a voltage of 161 kV.

Switching stations and substations – Their function is to reduce the voltage received from the transmission network to a lower voltage (upper voltage or high voltage) for further distribution. Those are large stations located in separate areas, within designated structures, or open and fenced.

Distribution networks — the role of these networks is to transfer the electricity from substations to consumers, at the level of the locality and the street.

The distribution networks include:

• Distribution lines — high voltage lines and low voltage lines, overhead (above ground and on utility poles) or underground (power cables placed underground). The voltage of high voltage lines in Israel is 12.6, 22 and 33 kV, while the voltage of low voltage lines is 400 volts (230 volts per phase). It should be noted that in smaller localities, there is less or no high voltage lines, and the low voltage lines are those that usually feed the consumers directly, after distribution and through connection devices.
• Transformation stations and transformers — the function of transformation stations and transformers is to reduce (decrease) the voltage from high voltage to low voltage. Transformation stations exist as separate structures (pavilions) that are in close proximity to or within neighborhoods and can be identified by signage and warning signs, and sometimes in close proximity to or as part of buildings. Transformers — the components that reduce the voltage — are used as part of transformation stations and are sometimes located on utility poles. Other names for the transformation stations are ITS (Internal Transformation Station), and STS (Small Transformation Station).
• Switching stations — used for switching, monitoring and sharing high voltage, usually for high voltage consumers. Exist as separate structures and in proximity to or as part of buildings.
• Distribution cabinets and neighborhood cabinets — facilities used to distribute low voltage to consumers, including installations located in "fillers" stationed in the street, or in proximity to clusters of houses or buildings.
• Housing connection facilities — The final part of any distribution network, including the electricity meters, protection fuses and more. They are located adjacent to the houses (such as in "fillers"), belong to the Electric Corporation, and are under its responsibility.

At the end of the distribution process, consumers usually receive electricity as low voltage electricity (230 volts per phase) — the residential electricity voltage we know.

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Recommendations for Reduction of Exposure from the Electric Grid

The major exposures from the electric grid occur in proximity to the network's components. The magnetic field decreases very sharply as distance increases (on many occasions, according to squared distance or so), so significant exposure will occur only in proximity to the network components.

• The exposures in proximity of production facilities, large switching stations and substations are mainly applied to the population working at them as occupational exposures.
• In proximity to the transmission networks and distribution networks, the population living near power lines, transformation stations, transformers and more may be exposed.
• The degree of exposure to a magnetic field from voltage lines depends on the intensity of the current flowing through them. In high voltage lines serving a large number of consumers, flowing current is higher than the one at the distribution end of voltage lines serving few consumers.
• In Israel, the recommendations for maximum exposure to radiation from electric installations are detailed in the article "Policy in Israel"; the joint recommendation of the Ministry of Environmental Protection and the Ministry of Health is daily average of 4 milligauss, at the "busiest" day (continuous and prolonged exposure). For this purpose, separation distances from the various infrastructures were determined and published by the Ministry of Environmental Protection, as detailed in the following sections:
• On the Ministry of Environmental Protection website, separation distances between different power lines and buildings can be checked (in Hebrew). Separation distances for distribution transformers are also published. The following are the basic separation distances between electrical facilities and a building line (the values in brackets are for designers of sensitive land uses to reduce the exposure in areas intended for prolonged stays):
  • Low voltage line — 2 meters from the nearest phase conductor (3 meters)
  • High voltage line (12.6, 22, and 33 kV) — 3 meters from the nearest phase conductor (5 meters)
  • Upper voltage line (161 kV) — 20 m from the line axis (30 m)
  • Super-high voltage line (400 kV) — 35 m from the line axis (50 m)
  • Distribution transformers — 3 meters from each part of the transformer and outgoing cables (5 meters)
• The Ministry of Environmental Protection supervises electrical installations and provides them with permits according to types of facilities (in Hebrew). Those permits detail the means required to reduce exposure levels to magnetic fields, including the required separation distances between each installation and populated buildings, the manner in which the facility is installed, and more. The following are some examples of separation distances required for various installations:
  • Low voltage underground distribution cables — 0.5 meters (and a minimum depth of 0.6 meters)
  • High voltage underground distribution cables — 3 meters (and a minimum depth of 0.7 meters)
  • Non-isolated high voltage network — 6 meters (from the nearest wire), a minimum height of 5 meters from the ground
  • Distribution cabinets and neighborhood cabinets — 1 meter
  • Transformation and switching stations of various types — 3-6 meters, depending on the type of installation
  • Transformers on pillars — 5 meters for one transformer and 6 meters for two transformers

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