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Hazards from Extra High Voltage Lines
Raghu N
Research Scholar, Electrical and Electronics Engineering Department,
School of Engineering and Technology, Jain University, Kanakapura, Bengaluru-562112.
E-mail: raghu1987n@gmail.com
Dr. Krishnamurthy N
Professor, Electrical and Electronics Engineering Department,
School of Engineering and Technology, Jain University, Kanakapura, Bengaluru-562112.
E-mail: krishnamurthy.access@gmail.com
Nagendra K
Research Scholar, Electrical and Electronics Engineering Department,
School of Engineering and Technology, Jain University, Kanakapura, Bengaluru-562112.
E-mail: kbnagendra@gmail.com
Trupti V N
Research Scholar, Electrical and Electronics Engineering Department,
School of Engineering and Technology, Jain University, Kanakapura, Bengaluru-562112.
E-mail: trupti.vrn@gmail.com
ABSTRACT
Almost in every part of India, a sprawling network of Extra-High-Voltage (EHV), High
Voltage (HV) lines have sprung up associated with wide spread of distribution lines. These lines
produce EMF and there are areas where EMF so generated is of high intensity as to cause great
concern about the health of humans and live stock. This work deals with the measurement of
Electro Magnetic Field (EMF) radiation levels by using NFA1000 TM device so as to locate the
areas where levels of Electro Magnetic Field (EMF) have exceeded tolerable limits. Such
surveys are essential to take steps to alleviate the short term and long term suffering of people
who are exposed to Electro Magnetic Field (EMF) in such areas and also arrive at levels which
have to be recommended as limiting values.
NOMENCLATURE
VHF Very High Frequency
VLF Very Low Frequency
HV High Voltage
EHV Extra High Voltage
EMF Electro Magnetic Field
EHF Extremely High Frequency
ELF Extremely Low Frequency
HFVT High Frequency Voltage Transients
T Tesla
Hz Hertz
mG milligauss
Kv/m kilovolts per meter
A Ampere
kW kilowatt
Hz Hertz
1.0 INTRODUCTION
Electricity is very useful, convenient from of energy which is used throughout the world.
It is clean, easy to switch on and off at our convenience and can be made to perform a variety of
jobs of our needs and it can be made available all the time and even at remote places. In the
beginning of electrical age there were a few generating stations and a few transmission times
feeding power to cities and these lines were run along areas uninhabited or sparsely habitated
and also the HV lines were terminated outside the cities. With more and more developments, the
voltage levels of transmission lines have elevated, due to pressure on land people have started
living close to transmission lines and substations. Thus they are exposed to EMF due to the
power lines and substations and that too at higher levels of exposure. The figure 1 shows the
electrical power flow.
Figure 1 Generation and Transmission of Electric Power
Since the beginning of electrical age through the numerous advantages of using electrical
energy became more and more apparent, at the same time the possible dangers associated with
electricity was also realized. It was the electric shock that people may be subjected to when they
come into contact with a live wire was paramount in the minds of authorities and general public.
Precautions and adequate safety measures have been taken to prevent people from getting
electric shock as long as they follow simple procedures in use of electricity. Failing to follow
rules of use of electricity either by ignorance or by over confidence leads to electric shock. Also
there have been cases where fire hazard has taken place in buildings, factories and even at homes
due to electric short circuit. This is again due to improper wiring, using substandard materials,
overloading the system etc... Which may lead to short circuit. Loose connections can lead to
localized sparks and if flammable materials are in the vicinity of such sparks, fire can take place.
Though the hazard from electric shock was much recognized and precautionary and safety
measures were followed, what were not realized are the hazards due to electric and magnetic
fields associated with the use of electricity [11]. As prosperity of people has increased, they are
using more and more equipments rum by electricity at homes, offices and factories. In the
beginning electricity was used at homes to light a few lamps that too for a few hours during
night. Then a typical home may be drawing a current of 1A or less. Nowadays, homes have
connected load of 5kW and above and draw currents of 15A and above such currents flowing
inside the homes create magnetic fields of levels 10 to 20 times what it was during a few decades
ago. The case of offices and commercial places, malls are no different. Heavy currents are
involved consequently elevated levels of magnetic fields are encountered. Though these facts are
brought to notice of authorities they have not changed the allowable limits of electric and
magnetic fields at low frequencies (i.e.. 50Hz and harmonics).
ICNIRP (International committee for Non-ionizing Radiation Protection) has given a
guide line of field’s exposure at 50 Hz to be limited to 1000 mg. this was recommended to avoid
any possibility of electric shock to people exposed to EMF fields. This is still followed in India
in-spite of overwhelming evidence of hazards of exposure to men and animals at much lower
levels for longer duration. So there is an urgent need to make authorities and general public
aware of the hazards of electric and magnetic fields at low frequencies so that reasonable levels
based on the latest research studies is stipulated. This chapter deals with the nature of electric
and magnetic fields, how they affect human health, and the levels of this fields limited by
advanced countries.
To give an idea of electric and magnetic fields prevailing in our country, results of a
survey conducted in and around Bangalore are included. According to ICNIRP there is no place
on earth which is free from electric and magnetic fields. According to RCEP (Royal commission
for environmental pollution) setting environmental threshold for safe electric and magnetic fields
is very difficult. The really safe level of exposure to 50 Hz fields is zero. An after deliberating on
the aspects cited above, levels for electric and magnetic fields, which are practical and
reasonably safe as recommended by various researchers is included.
1.1 Nature of Electric and Magnetic fields
Whenever the voltage is applied to the conductor an electric field is produced around it.
The conductor voltage affects the area surrounding the conductor as shown in figure 1.1. The
strength of an electric field depends on two specifications — Applied voltage on the conductor
and the distance from the conductor. The magnitude of an electric field is measured in kilo volts
per metre.
Figure 1.1 Electric and Magnetic Field flow in nature
1.1.1 Electric fields: whenever a source of electric voltage is there, then an electric field is
associated with it all round. The intensity of the field is proportional to the voltage level and
decreases according to inverse square law as we move away from the source.
Any electrical wire that is charged will produce an electric field. This field exists even when
there is no current flowing, as long as the wire is held at a higher potential with respect to
ground. The strength of electric field is measured as volts per meter (V/m) or in kilovolts per
meter (kV/m). Electric fields are weakened by objects like trees, buildings and vehicles. Burying
power lines can eliminate human exposure to electric field from this source.
1.1.2 Magnetic fields: magnetic fields result from the motion of the electric charge or current,
such as when there is current flowing through a power line or when an appliance is plugged in
and turned on. Appliances plugged in but not turned on do not produce magnetic fields. magnetic
fields lines run in circles around the conductor (i.e.. produces magnetic induction on objects and
induced currents inside human and animal bodies causing possible health effects and a multitude
of interference problems) the higher the current, the greater the strength of the magnetic field.
Magnetic fields are typically measured in Tesla (T) or more commonly, in gauss (G) and
milligaus (mg). One Tesla equals 10,000 gauss and one gauss equals 1000 milligaus.
1.1.3 Electromagnetic field: The strength of an Electro Magnetic Field (EMF) decreases
significantly with increasing distance from the source. Electric field part of an EMF can easily be
shielded. As the strength of an electric field is proportional to the voltage, the field under a HV
transmission line is greater than under a distribution line. Magnetic field strength, by contrast, is
proportional to current in the lines, so that a low voltage distribution line with a high current load
may produce a magnetic field that is as high as those produced by some high voltage
transmission lines.
Electric field under a high voltage line is constant as the voltage in the line does not
change but the magnetic field keeps on changing depending on the load current being carried by
the line. In fact, electric distribution systems account for a far higher proportion of the
population’s exposure to magnetic fields than the larger and more visible high voltage
transmission lines.
Magnetic field part of the EMF can penetrate stone, steel and human flesh. In fact, when
it comes to magnetic fields, human flesh and bones has the same penetrability as air. Both fields
are invisible and perfectly silent: people who live in an area with electric power, some level of
artificial EMF is surrounding them. The magnetic field strength produced from a transmission
line is proportional to load current, phase to phase spacing and the inverse square of the distance
from the line. Many studies have been made to study the effect of different parameters on the
produced magnetic field such as the distance from the line, the conductor height, line shielding,
and the transmission line configuration and compaction. Extremely high voltages in EHV lines
cause electrostatic effects where as short circuit currents and line loading currents are responsible
for electromagnetic effects. The effect of these electrostatic fields is seen prominent with living
beings like humans, plants, animals along with vehicles, fences and buried pipes under and close
to the lines.
1.2 Line configuration and compaction
Line compaction means bringing the conductors close together keeping the minimum (safe)
phase to phase spacing constant. Keeping all the parameters the same and vary only the phase –
to-phase spacing. The magnetic field is proportional to the dimensions of the phase-to-phase
spacing. Some studies have shown that increasing the distance between phases by increasing the
height of the central phase conductor above the level of the other phase conductors leads to
reduction of the peak value of the magnetic field. Reducing the phase-to-phase distance leads to
the decrease of the magnetic field. This reduction between phases is limited by the electrical
insulation level between phases.
For single circuit lines, compaction causes a great reduction to the maximum magnetic field
values. This reduction of magnitude field allows for lower conductor heights above the ground.
This leads to transmit the same power on shorter towers thus a reduction in the cost is achieved.
For double circuit lines, some studies showed that the use of optimum phase arrangement causes
a drastic reduction to the maximum magnetic field values.
A detailed study and research is needed to establish the convincing evidence that exposure to
extremely low frequency (50Hz) EMF emanated by HV lines is associated with detrimental
health problems. In Indian cities there has not been a growth of power lines and distribution
lines, many times there has been not in an orderly way. So there is necessity to study the EMF
field in cities and locate high risk areas.
Where further epidemiological studies may be undertaken to find the occurrences of field related
health problems. In this direction a survey was made by electrical engineering department of Jain
University and the highlights of which is included as a case study of a typical Indian city.
2. PRESENT SCENARIO
People living near HV power lines are subjected to electric and magnetic fields. Electric
field produced directly related to the voltage level of the power line and to the distance of the
people living close to it [14]. Magnetic field is related to the amount of current passing in the
line. Though magnetic fields are employed in magnetic therapy they are of low intensity but
when high intensity levels are present they can cause severe health problems [12].
Figure 2 Extra-High-Voltage Transmission lines for different voltage level
In greater Bangalore EHV lines of 132 kV, 220 kV and 400 kV are running and
residential areas have come up in the vicinity of these lines and surprisingly more such areas are
coming up and getting closer to the lines and ROW. Figure 2 shows extra high voltage
transmission lines for different voltage levels. As a first observation areas where buildings have
come up under EHV lines and ROW are considered for measurements. IE rules, 1956, Rule
77(4) stipulates the minimum permissible ground clearance as follows. But one can see, though
the lines are drawn to maintain the above clearances in Table 1, structures have come up close to
EHV lines, the effective clearances have shrunk to a great extent causing serious concern [19].
Areas are found in bangalore to have housed buildings near or under HV lines. Such areas are
high risk locations and so measurements have been made in such areas. Effects of EMF fields on
human beings, live stock and plants over short term and long term effects.
TABLE 1 : Ground clearance with voltage level
Sl. No.
Voltage level
Ground clearance (m)
1.
≤ 33 kV
5.20
2.
66 kV
5.49
3.
132 kV
6.10
4.
220 kV
7.01
5.
400 kV
8.84
3.0 MEASUREMENTS OF EMF FIELD IN AND AROUND BANGALORE
The electricity is mainly generated at the remote locations of a country. The generated
power is to be transmitted from remote location to the residential areas [1]. Therefore the
generated power is transmitted through over head lines with support of the transmission towers.
Since the first large scale generation of power and supply to general public by Edison in 1882,
we have come a long way in achieving great progress in generation and utilization of electric
power which has enormously increased the quality of human life and greatly responsible for
industrial and commercial growth. This great beneficial progress is associated with some
problems which have to be urgently addressed.
Figure 3.1 Overhead transmission line in a residential building.
For efficient transmission of power it has to be transmitted at high and EHV lines which
produce EMF which is inheritable. Since last few decades, this was not considered as a problem
as the HV lines were running through forest and agricultural land which were not habitated by
people. But due to increase of population people have started living close to HV lines which is a
matter of concern [2, 3] for example as shown in figure 3.1 and 3.2. There is no awareness
among people about the ill effects of continuous exposure to EMF and many authorities also
need to be appraised. In such a situation it is essential to take proper survey of the existing areas
near HV lines in and around cities like Bangalore to locate areas which are exposed to dangerous
levels of EMF [4, 5]. Also the paper enlists the health hazards due to exposure to EMF fields as
published in various research publications and WHO.
A series of concentrated effort is required from academicians and medical fraternity to
appraise the general public and authorities to create due awareness about the above pressing
problem. The measurement made in this investigation and presented along with the related health
risk is one such attempt in the above campaign [7, 17]. It may be realized that a lot of efforts by
various agencies took several decades before the injurious health effect of smoking could be
universally accepted and remedial measures being taken. Such efforts are needed to save people
from injurious effects of exposure to dangerous levels of EMF by taking suitable remedial
measures.
Figure 3.2 Electric field and magnetic field intensity measured surrounding the transmission line.
3.1 Methodology
This procedure is used to receive the signals from power lines to measure the levels of
electric field (V/m) and magnetic fields (T) are shown in figure 3.1.1. The available radio
frequency (RF) signals from 50 Hz to more than 2 kHz in free space were collected and recorded
in the NFA1000 TM device as shown in Fig 3.1.1. The radiation level present in the radio
frequency signals is loaded to the NFA1000 TM device which is analyzed by using NFA software.
The survey covered around the transmission lines which are spread over in various parts of
Bangalore. The survey was conducted thrice and the best readings were plotted using the
software.
Figure 3.1.1 Measurement of radiation level
3.2 EMF fields measurements
In figure 3.2.1, shows the magnetic field intensity level of 220 kV line. The average magnetic
field level is observed was 213.67 nT (2.136 mG) and the variation of the level in and around the
line is plotted and in figure 3.2.2 shows the electric field intensity. Similarly the survey under
and around 66 kV line conducted and the result 0.36 mG magnetic field are shown in figure
3.2.3. In figure 3.2.4 shows the magnetic field intensity level of 132kV line and electric field
intensity are shown in figure 3.2.5.
Figure 3.2.1 Magnetic field measured under the 220 kV line.
RF Signals
High
Low
Display of radiation level on device in terms of Electric field
(V/m) and Magnetic fields (T)
NFA 1000
device
Figure 3.2.2 Electric field intensity measured under the 220 kV line.
Figure 3.2.3 Magnetic field intensity measured under the 66 kV line.
Figure 3.2.4 Magnetic field measured under the 132 kV line.
Figure 3.2.5 Electric field intensity measured under the 132 kV line.
3.3 Tolerable limits of EMF levels
In India its is stipulated that electric field intensity should not exceed 4.16 kV/m and
magnetic intensity should not exceed 100 µT (1000 mG) in public areas. These levels are
according to international commission on non – ionizing radiation protection (ICNIRP). These
limits seem to be stipulated from the point of levels which may cause mild shocks [16, 17]. But
the levels which may affect short term and long term health problems are much lower. In
advanced countries the level EMF fields particularly magnetic field is contemplated to be fixed
below 2 mG near residential areas, schools and hospitals.
4.0 HEALTH HAZARDS ON HUMAN BEINGS
The human body is composed of biological materials like blood, brain, lungs, muscle,
skin etc. the permeability of human body is equal to permeability of air but within a human body
different electromagnetic values at a certain frequency for different materials exists. The human
body contains free electric charges (largely in ion-rich fluids such as blood and lymph), that
move in response to force exerted by changes on and currents flowing in nearby power lines. The
processes that produce these body currents are called electric and magnetic induction.
In electric induction, charges on a power line attract or repel free charges within the
body, since body fluids are good conductors of electricity, charges in the body move to its
surface under the influence of this electric force. For example, a positively charged overhead
transmission line induces negative charges to flow to the surfaces on the upper port of the body.
Since the charge on power lines alternates from positive to negative many times each second, the
charges induced on the body surface alternate also. Thus power-frequency electric fields induce
currents in the body (eddy current) as well as charges on its surface.
The magnitude of surface charge and internal body currents that are induced by any gives
source of power-frequency fields depends on many factors. These include magnitude of the
charges and current in the source, the distance of the body from the source, the presence of other
objects that might shield or concentrate the field and body posture, shape and orientation.
Where a person who is shielded from ground by some insulating material comes in close
proximity to an over head transmission line, an electrostatic field is set in the body of human
being, having a resistance of about 2000 ohms. When the same person touches a grounded
object, it will discharge through his body causing a large amount of current to flow through the
body. Discharge currents from 50-60Hz electromagnetic fields are weaker than natural currents
in the body, such as those from electrical activity of the brain & the heart [9, 10]. For human
beings the limit for undisturbed field is 15kV/m, to experience possible shock. Where designing
a transmission lines this limit is not crossed, as long as a person takes care to keep minimum
clearance from transmission lines [4, 5]. According to research and publications put out by the
World Health Organization (WHO), EMF such as those from power lines can cause the
following health problems.
4.1 Short term Health problems
1. Head ache
2. Fatigue
3. Anxiety
4. Insomnia
5. Prickling and /or burning skin
6. Rashes
7. Muscle pain
4.2 Long term Health problems
(1) Risk of damaging DNA: Our body acts like an energy wave broadcaster and receiver,
incorporating and responding to EMFs. In fact, scientific research has demonstrated that every
cell in your body may have its own EMF, helping to regulate important functions and keep you
healthy. Strong artificial EMFs like those from power lines can scramble and interfere with your
body’s natural EMF, harming everything from your sleep cycles and stress levels to your
immune response and DNA.
(2) Risk of Cancer: after hundreds of internationals studies, the evidence linking EMFs to
cancers and other health problems is loud and clear. High voltage power lines are most
dangerous culprits and other sources in the grid like transformers & substations are equally
effective though to a lesser extent and even EMFs generated inside homes cannot be ignored [6].
(3) Risk of Neurodegenerative diseases: “Several studies have identified occupational
exposure to low frequency EMF as a potential risk factor for neurodegenerative disease”
(According to Epidemiology, 2003 Jul: 14(4): 413-9).
(4) Risk of miscarriage : there is |strong evidence that parental maximum magnetic field
exposure above a certain level (possibly around 16mG) may be associated with miscarriage risk
(As per epidemiology, 2002 jan,13(1)9-20).
(5) Child leukemia: It is observed all over the world that childhood leukemia has
significantly increased from 1940 onwards when electricity supply increased to residents in cities
and extended to rural area. The exposure of young children to power frequency EMF in schools,
near transmission lines and at home to levels as low as 0.2mG can also lead to leukemia.
Children in the age group 2 to 4 years are found to be vulnerable to this occurrence. Measured
values of magnetic fields at home, at schools and near transmission lines show to be of the order
of 1mG which is rather high for children to grow up [3].
For children the skull bones are not yet fully developed in the sense they are tender and
magnetic field penetration will be higher [7]. The production of melatonin, a protective hormone
is less and as their immune system is low. Thus they are more vulnerable. Statistically it has been
overwhelmingly noticed both in Europe and America that childhood leukemia has been on the
increase since the last war and it is attributed to exposure to EMF fields. Use of electric blanket
by children has resulted in an increase number of cases of leukemia. Researchers in England
have reported that children living within 650 feet of power lines had a 70% greater risk for
leukemia than children living 2000 feet or more away (British medical journal June 2005).
4.3 EMF effects on Maintenance works
For providing continuous and uninterrupted supply of electric power to consumers,
maintenance operations of power lines are after performed with systems energized or live as
shown in figure 4.3. Thus the maintenance staff and others involved in electrical supply industry
are exposed to magnetic fields of 0.2mG and above for long durations. Among such people it
was noticed that suicide rate among them was 23% higher than normal population and it
increased to 70% and above among those exposed to 1.1mG & above this shows that level of no
effect is very close to zero 50 Hz magnetic field exposure [15].
Figure 4.3 Maintenance and Operations of over head transmission lines
4.4 Step potential and touch potential
Transmission lines when subjected to faults or over voltages, insulators flash over and
heavy current flows through the transmitting towers to ground. Under such cases, if a person
touches a tower the potential between the points of touch to ground may be high and give a
shock to the person who has touched as shown in figure 4.5.
Likewise when heavy current is passing from the towers to the ground there will be an
electric field around the foot of the tower so if a person approaches a tower a voltage appears
between his two feet called step potential which can give him a shock. If the touch potential or
step potential is higher than 30v, the person experiences a shock. If cattle approaches a tower it is
subjected to a greater value of step potential as the distance between front & hind legs in cattle
are longer.
Figure 4.5 Representation of step and touch potentials
4.5 Effect on pacemakers
Under some circumstances voltages and currents from power lines, distribution lines and
electrical devices can interfere with operation of some implanted cardiac pace makers as shown
in figure 4.5. However no case where a HV line has harmed a pace maker patient has been
reported [8, 9]. Still a person with a pacemaker in an electrical environment and the pacemaker
begins to produce a regularly paced pulse that is not related to a normal heart beat, the person
should leave the environment and consult a physician.
Figure 4.5 Maximum effect of EHV line on mono-polar cardiac pacemaker
implant.
4.6 EMF effects on Animals
Many researchers have studied the effect of electrostatic field on animals. In order to do
so they kept the cages of animals under high electrostatic field of about 30 kV/m (an order of
extremely high field that may be experienced under power lines). The results of these
experiments are shocking as animals which acquired charge during the above exposure, when
they tried to drink water a spark started jumping from their nose to grounded water and hens who
had acquired charge were unable to pick up grain because of the chattering of their beaks which
also affected their growth[10].
4.7 EMF Effects on plant life
Most of the areas under HV power lines are agricultural and forest land. The voltage level
of high power transmission lines are 400kv, 230kV, 110kV, 66kV etc. The electromagnetic field
from such high voltage power lines affects the growth of plants [2]. From various studies
conducted on growth of plants under such HV lines showed that growth characteristics like shoot
length, root length, leaf area, and leaf fresh weight, specific leaf weight, shoot/root ratio, total
biomass content and total water content of the four crop plants were reduced significantly
compared to control plants as shown in figure 4.7. Similar trend were observed in the
biochemical characteristics like chlorophyll.
Reduced growth and physiological parameter was primarily due to the effect of reduced cell
division and cell enlargement. Further the growth was started which may be due to poor action of
hormones responsible for cell division and cell enlargement [18]. It is concluded that the reduced
growth parameters shown in the crop plants would indicate that the EMF has exerted a stress on
the plants and this EMF stress affects the production leading to economic loss, so further
research activities are needed to safe guard plants from EMF stress.
Figure 4.7 Effect of EHV line on growth of trees
4.8 Living and working safely around HV power lines
i) Use of ROW: Right of way which is a narrow strip of land below transmission lines is
not a public property, it is acquired by power companies through easements from land owners so
trespassing, collecting vegetation, cutting any plant by general public amounts to stealing and
can be prosecuted. It is the job of engineers and educated people to make people around aware of
the status of ROW.
ii) General precautions: Avoid bringing yourself or any object you are holding too close to
an overhead power line. As a general precaution when under a HV line never put you or any
object higher than 14ft from the ground. Vehicles and large equipment should not extend more
than 14ft in height such as harvesting machines, cranes etc.
iii) Nuisance shocks: which are experienced by touching metal objects even away from HV
lines. Such objects include vehicles, fences, metal buildings or roofs and irrigation systems.
iv) Irrigation systems: While moving irrigation pipes under or near power lines, keep the
equipment in a horizontal position to keep it away from overhead lines electricity can conduct
through water so never allow irrigation system to spray a continuous stream directed towards the
power line or tower.
Underground pipes, telephone cables and electrical cables should not be installed closer
than 50ft to a HV tower as in figure 4.8. The grounding system of the tower is not visible and run
up to 300ft along the ROW, so these systems have to be located before installing any
underground utilities.
Fences are discouraged from locating in ROW as they can cause a potential safety hazard and an
access problem. If electric fences were to be installed it can be done after consulting with the HV
line authorities.
(v) Buildings located off ROW may collect an induced voltage. This voltage is often drained
through the building plumbing, electrical service, metal sheeting or metal frame. If the voltage
does not drain through the systems described, then it can result in a situation of nuisance shock.
Large electrical supply companies recommend grounding metallic components on buildings near
a power line when
Within the building is written 100ft of the outside wire
The building has more than 2000 square feet of metal surface and is within 100 to 150ft
of the outside wire
The building is used to store flammable materials and is within 250ft of the outside wire.
Figure 4.8 Safety zone for living beings
5.0 HIGH FREQUENCY VOLTAGE TRANSIENTS
These refer to harmonics and transients in the lower radio frequency spectrum, in the
KHz range (approximately 1 to 100 KHz). Deviations from 50/60Hz sine wave are generally in
the tower radio frequency spectrum and better described as radiofrequency transients or high
frequency voltage transients (HFVT). HFVT can be produced in the power system due to
lighting strokes, switching events and short circuits. Harmonics can also be introduced to the
power system by electronic items that draw non-sinusoidal current from the power supply [17].
Such equipments can include computers, fax machines, dimmer switches and house hold
appliances with electronic controls. HFVT can interact with electrical equipments and can
damage them. Also long term exposure to EMF fields produced by HFVT can be harmful to
human beings [16].
For electric fields in 3 kHz 100 kHz range unintentional stimulation of excitable tissues
can occur when electric or magnetic fields are strong enough. There have been a limited number
of studies published on health effects associated with HFVT. A review published in 2010 cited
various methodological problems in the design of the studies and has recommended more in
depth studies to be made before causal link between HFVT exposure and adverse health effects
can be found. Electric and magnetic fields generated by HFVT on main circuits can be measured
using standard radiofrequency and low frequency EMF measurement equipment.
5.1 Radio frequency interference from HV lines
HV lines are associated with corona and other effects which generate radiofrequency
EMF. This can be observed when your car approaches a HV line the radio in the car develops
disturbance. This radiofrequency waves generated near HV lines have adverse effect on
communication system and their effect on human health has not been studied in detail though
evidences point out that these are potential sources of health hazard.
5.2 Electricity problems under Distribution lines
Distribution lines are spread out and run in densely populated areas as they have to reach
every customer. Though the voltage levels are less (220V to 11000V) they have been a cause for
a number of accidents. Also as the currents in these lines are large, magnetic field produced can
have adverse effect on human beings if they fail to follow the safe clearance distances as
recommended. The clearance between a building and a medium voltage line is 2m horizontally
and 3m vertically and these clearances must take into account the lines swinging in the wind and
line sag. A medium-voltage line must never run above a permanent building, even with a 3m
clearance.
5.3 EMF hazards in the vicinity of a substation
Substations receive power from generating stations through HV transmission lines, step
down the voltage from 220kV the voltage from 220kV to about 11kV and supplies to the
distribution system at this reduced voltage. These were located at outside the cities and
surrounded by uninhabited area. Due to pressure on land and expansion of cities, nowadays
residential areas are located quite close to substations. People residing in these areas are
subjected to EMF fields generated at the terminals of the equipments in the substation. In HV
lines, the lines which are subject to High voltage area at a safe height but the line when
terminated at the equipments in substation, it is towered to the tip of the equipments. Thus the
EMF field is quite close to the ground. So save distance should be measured in building
residential houses close to substations.
5.4 Tolerable levels of EMF fields and methods to mitigate the hazards
For genotoxic substances RCEP (Royal commission on Environmental protection 1998)
states that it is not possible to demonstrate that there are a threshold dose. This is also clearly true
for electromagnetic fields and radiation. So the safe level of exposure to 50/60 Hz fields is zero.
This is impossible, because in that case we have to dismantle entire electric system throughout
the world. So we have to identity intensity levels of fields and mark them as worst, bad,
tolerable, good and excellent. This has to take into account whether the people exposed are
children, old people and also how long they are exposed. For example the fields at home, in
schools, hospitals vulnerable sections are exposed for long periods. Here the levels should be
excellent.
School and home environments should be assessed and where possible 90% of room
space at head height, especially at the head position when sleeping or in school should be less
than 0.2mG. Fields produced by the substation and power lines should not exceed this limit in
residential, school or working environment
If the above limits cannot be maintained it is common practice to set an achievable
management guideline that will produce a significant reduction in health effects. In India, there
are no stipulated levels which should not be exceeded. In such a situation the guidelines
recommended by international commission on Non-Ionizing Radiation Protection (ICNIRP) is to
be followed. The reference levels according to ICNIRP are 5kV/m for electric fields and for
magnetic fields 100µT (1000mG). This is very much high particularly regarding magnetic fields.
Modern researches suggest a threshold level of 1mG for magnetic fields and lower levels of 0.2
to 0.5mG at sensitive place like schools & hospitals etc. There is an urgent need to educate the
general public and make them aware of the hazards from higher field levels of EMF. Also many
precautions to be taken as follows to be made known
1. Observe clearances an stipulated from HV lines and distribution lines
2. Do not construct any building or structure under distribution lines
3. Residential houses should not be built close to substations
4. Inside residences the magnetic fields can be got measured and limit the equipments to be
used at a time so that tolerable limits of magnetic fields are maintained.
5. Where children sleep, electric appliance switched on at the head level to be avoided also
near the head & behind the wall at head level no appliance switched on to be used.
6. Children should not be allowed to use electric blanket
In areas where electromagnetic fields are noted to be high due to power lines there are
several methods as follows to reduce the field. Electric field can be reduced by shielding the wire
but it is more complex to reduce the magnetic field. Regarding line shielding for magnetic field
mitigation, there are two basic methods.
Passive magnetic field mitigation uses rigid magnetic shielding with ferromagnetic and
highly conductive materials and the use of such passive shield wires installed near transmission
lines that generate opposing cancelation fields from electromagnetic induction
Active magnetic field mitigation uses electronic feed back to sense a varying 50Hz
magnetic field, then generates a proportionally opposing cancellation field within a defined area
(room or building) surrounded by cancellation coils. Ideally, when two opposing 180 degrees out
of phase magnetic fields of equal magnitude intersect, the resultant magnetic field is completely
cancelled. This technology has been demonstrated to be practical but not applied very much.
5.5 Mitigation of electric and magnetic fields
Where the lines cannot be shifted or residential buildings have come up near the lines and
the areas have become high risk areas there are certain steps to mitigate the risks by reducing the
levels of the field. For electric field it is easy by providing a conducting shield around the
conductor. For magnetic field there are several methods though complex and expensive. Passive
Magnetic field mitigation includes rigid magnetic shielding with ferromagnetic and highly
conductive materials. Active magnetic field mitigation uses electronic feed back to sense 50 Hz
magnetic field then generates proportionally apposing (null), cancellation field within a defined
area (building). Line configuration and compaction can be adopted where the distance between
the phases is reduced (Keeping the minimum safe spacing).
6. CONCLUSION
The survey conducted in and around metropolitan city shows there are some high risk
areas. For example in figure 3.23 area shows the maximum level of magnetic field, which is for
lower than stipulated but higher than what the researchers are advocating. There is over
whelming evidence as per researchers that there is health risk at EMF filed levels as low as 2 to 5
mG. But the WHO feels that there is no conclusive and convincing to link EMF related diseases
to low levels of radiation so there is a pressing need to conduct large scale survey of residential
areas in large cities, locate high risk areas and take health (Particularly mental health) check up
to gather more and more evidence to link up EMF field levels and health hazards in a convincing
way.
In this direction the survey has been done in metropolitan city and some of the high risk areas
are indentified for further work and follow up studies by health organizations / authorities.
Where the risk areas exist and shifting of lines is difficult, mitigation efforts to be taken as
suggested. These will cause health hazards even at low intensity, when living beings are
exposed for longer duration, especially children and old people. Hence it is concluded that to
avoid high density radiations area from living beings.
FUTURE WORK
There are many transmission lines in and around Bangalore which is likely to cause greater
concern for the area in the vicinity where people are habituated such studies need to be done,
also with the co-operation of a hospital a survey of the people living in the risky area can be
conducted along with radiation measurement for a better study of the hazard involved. This may
help in arriving at a realistic safe level of magnetic fields that is tolerable as the maximum level
stipulated in India is 100 µT seems to be very high and a detailed studies are required to arrive at
a lower limit which is tolerable.
ACKNOWLEDGEMENT
This work is carried out with the help of group of students and Staff members in the department
of Electrical and Electronics Engineering, School of Engineering & Technology, Jain University.
The authors would like to thank all the faculty members, students and Prof. Suresh D, HOD,
Department of Electrical & Electronics Engineering and Management of Jain University for their
continuous support.
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