Download Session 1 Topic # 3

ELECTROMAGNETISM A COMPREHENSIVE REVIEW
Dr. Ibrahim Y. Al-Hamoudi*
Vice President – Consolidated Transmission Area
Saudi Electricity Company
Kingdom of Saudi Arabia
ABSTRACT
1.0
This paper presents a comprehensive review on the
topic electromagnetism. It begins with a description
of some electric and magnetic phenomena which occur
in nature, such as lightning and the geo-magnetic field,
followed by the observable relationship between
electricity and magnetism.
Electromagnetism is the physics of the electromagnetic
field, a field which is present in all of space. It is
actually composed of of two individual but interrelated
fields, namely, the electric and magnetic fields. The
electric field is produced by stationary electric
charges, and gives rise to the electric force. It is this
force that drives the flow of electrons (and hence
current) in electrical conductors. The magnetic field is
a field produced by the motion of electric charges,
giving rise to the magnetic force one associates with
magnets. The term "electromagnetism" comes from
the fact that the electric and magnetic fields are closely
intertwined.
Under most circumstances, it is
impossible to consider the two separately.
For
instance, a changing magnetic field gives rise to an
electric field.
This is the phenomenon of
electromagnetic induction, which forms the basis for
the principle of electrical generators, induction motors,
and transformers.
A detailed description of electromagnetism, discussion
of the electromagnetic theory and the scientists
Faraday, Coulomb and Maxwell who formulated and
applied such theory is presented in the next section.
The third part describes the practical application of
electromagnetism and some of the more important
devices employing electromagnetism, such as
generators, motors and power transformers.
The last section focuses on the concerns arising from
living and/or working in or near high levels of powerfrequency electromagnetic fields (EMF). The effects
of EMF on live tissues and the potential health risks
are discussed.
This topic has been the focus of
numerous clinical and epidemiological studies
conducted by government and industry organizations
world-wide since the 1970's. Without exception, these
major studies have reported that there is no conclusive
evidence which correlates the increased risk of cancer
or other health risks with exposure to electromagnetic
fields. However, this lack of categorical evidence does
not mean that health risks do not exist, but rather
highlights the need for broader studies and further
research.
*PO Box 5190 Dammam 31422 Saudi Arabia
Saudi Electricity Company – VP-CTA
E-mail: [email protected]
1.1
Electromagnetism
Magnetism from Electricity
Magnetism is a phenomenon by which materials exert
an attractive or repulsive force on other materials. All
materials are influenced to some extent by the
presence of a magnetic field, although in most cases
the influence is too small to be detected without
special equipment. Some well known materials that
exhibit easily detectable magnetic properties are iron,
some types of steel, and the mineral ore lodestone.
Magnetic forces are generated by the movement of
electrical charge.
Thus, magnetism is present
whenever electrically charged particles are in motion.
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In 1820, the Danish scientist Hans Christian Oersted
demonstrated that magnetism was related to electricity
by bringing a wire carrying an electric current close to
a magnetic compass. This caused a deflection of the
compass needle. It is now known that whenever a
current flows, there will be an associated magnetic
field in the surrounding space, or more generally that
the movement of any charged particle will produce a
magnetic field, hence the term "Electromagnetism".
particle is moving. Thus magnetic forces cause the
charged particles to change their direction of motion.
However, they do not change the speed of the
particles. This phenomenon is used in high-energy
particle accelerators to focus beams of charged
particles, and direct them to collide with targets to
produce new particles.
Another way to understand this is that according the
basic laws of physics, if the force is perpendicular to
the motion, then no work is done. Hence magnetic
forces do no work on charged particles and cannot
increase their kinetic energy. If a charged particle
moves through a constant magnetic field, its speed
remains the same, but its direction of motion is
constantly changing. A device in which this property
is used is the mass spectrometer, which is used to
identify elements. In this device a beam of charged
particles (ions) enters a region of magnetic field, where
they experience a force and are bent in a circular path.
The amount of deflection depends on the mass (and
charge) of the particle. By measuring this amount, one
can deduce the type of element present by comparing
to the deflection of known elements.
An electromagnet is a type of magnet in which the
magnetic field is induced by a flow of electric current.
The magnetic field disappears when the current flow
stops.
The force from an electromagnetic field is a resultant
of the electric and magnetic components. The vector
relationship is shown as follows:
Current flowing through a wire produces a magnetic
field (M) around the wire. The field is oriented such
that if the right-hand thumb is pointed in the direction
of current flow, the direction of the magnetic field is
represented by the direction of the curved fingers.
The force that the electromagnetic field exerts on
electrically charged particles, is called the
electromagnetic force.
It is one of the four
fundamental forces of nature.
The other three
fundamental forces are the strong nuclear force (which
holds the atomic nuclei together), the weak nuclear
force (which causes certain forms of radioactive
decay) and the gravitational force. All other forces are
ultimately derived from these fundamental forces.
Of the four fundamental forces, electromagnetic force
is responsible for practically all the phenomena one
encounters in daily life, with the exception of gravity.
Roughly speaking, all the forces involved in
interactions between atoms can be traced to the
electromagnetic force acting on the electrically
charged protons and electrons inside the atoms. This
includes all forms of chemical phenomena, which
manifest the interactions between the orbiting
electrons of atoms of different elements.
1.2
Magnetic Force-Right Hand Rule
The strength of electric fields is measured in unit of
kV/m. The strength of magnetic fields is usually
expressed as the magnitude of the magnetic flux and is
measured in unit of Tesla (T). One Tesla is actually a
very strong magnetic field. The earth's magnetic field
is of the order of 0.0001 T.
Magnetic Forces on Moving Charges
One basic feature of magnetism is that a moving
charged particle in the vicinity of a magnetic field will
experience a force. The force on the charged particle
is always perpendicular to the direction that the
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2.0
Electromagnetic Theory:
2.2
2.1
Maxwell's Equations
Maxwell also discovered the electromagnetic nature of
light. The Maxwell's Equations suggested that
oscillating electromagnetic fields could be transmitted
by wave motion, travelling through empty space at a
speed that could be predicted from simple electrical
experiments.
On the strength of this, Maxwell
correctly hypothesized that light is in fact a form of
electromagnetic wave.
The theories of electromagnetism, sometimes known
as classical electromagnetism, were developed by
various physicists such as Ampère, Gauss, Faraday and
others during the 19th century. The British scientist,
James Clerk Maxwell, unified all the previous
developments into a single theory. He demonstrated
that the electromagnetic field obeys a set of equations.
These equations represent the most simple and concise
way to describe the fundamental relationships of
electricity and magnetism. These equations were later
named the Maxwell's equations after him.
Electromagetic Wave Theory
What is more remarkable is that Maxwell developed
his ideas in 1862, more than thirty years before Sir
Joseph John Thomson discovered the electron in 1897,
the particle that is so fundamental to our current
understanding of both electricity and magnetism.
Maxwell's equations are:
 . E = 4
xE=
-1
c
Travelling Electromagnetic Fields (waves)
x
B
t
Using the data available at the time, Maxwell obtained
a velocity of 310,740,000 m/s. Maxwell wrote:
"This velocity is so nearly that of light, that it
seems we have strong reason to conclude that
light itself (including radiant heat, and other
radiations if any) is an electromagnetic
disturbance in the form of waves propagated
through the electromagnetic field according
to electromagnetic laws".
.B=0
xB=
Where:
4J
c
+
-1
c
x
E
t
Maxwell's hypothesis was correct, though he did not
live to see its verification by Heinrich Hertz.
Maxwell's quantitative explanation of light as an
electromagnetic wave is considered one of the greatest
triumphs of 19th-century physics. Moreover, it laid
the foundation for many future developments in
physics, such as Albert Einstein’s special relativity and
its unification of electric and magnetic fields as a
single tensor quantity, and Kaluza and Klein's
unification theory of electromagnetism with gravity
and general relativity.
( .) is the Divergence operator
( x) is the Curl operator
C is the velocity of light
E is the electric field
B is the magnetic field
J is the current density vector
 is the charge density
The four Maxwell's equations express:




How electric charges produce electric fields
(Gauss's Law)
How changing magnetic fields produce
electric fields (Faraday's Law of Induction)
The
absence
of
magnetic
charges
(monopoles)
How currents produce magnetic fields
(Ampère's Law)
In 1886, Heinrich Hertz of Germany showed that an
electric current alternating back and forth in a wire (an
"antenna") is the source of some form of
electromagnetic waves (radio waves). The current also
produces a magnetic field in accordance with
Ampere's law, but that field decreases rapidly with
distance. Electric sparks also create such back-andforth waves when they jump across an air gap. An
example of this is evidenced by the crackling caused
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
by lightning on an AM radio. Hertz used such sparks
to send a radio signal across his laboratory. Later
Marconi, with more sensitive detectors, extended the
range of radio reception, and in 1903 while in North
America, he detected radio signals from as far away as
Europe.

Gradually other electromagnetic waves were
discovered. X-rays, like light, are also electromagnetic
waves but with a much shorter wavelength. Later it
was discovered that beams of electrons in a magnetic
field, inside a vacuum tube, could become unstable
and emit waves with wave-lengths longer than light.
This discovery led to the invention of the magnetron
tube which was applied as a top-secret radar device in
World War II. It was later adapted and applied in a
nowadays common kitchen appliance known as the
microwave oven.
3.0
Applications of Electromagnetism
3.1
Power Transformers
3.2
Hence, the transformer equation:
Vp
Np
=
Vs
Ns
The reverse application of the generator principle is
the electric motor. In a motor, electric energy is
converted into mechanical energy via an intermediate
magnetic field. An electric current passing through a
series of coils in the stator turns them into
electromagnets. The resultant magnetic field interacts
with the magnetic field of the rotor, causing it to
rotate. Invention of the electric motor drastically
revolutionized and improved our lives. The electric
motor is applied in almost every appliances and
equipment of our daily lives and virtually in all
industrial machines.
Where Vp is the voltage in the primary coil, Vs is the
voltage in the secondary coil, Np is the number of turns
of wire on the primary coil, and Ns is the number of
turns of wire on the secondary coil. Based on this
principle, a transformer converts power at one voltage
to a different voltage.
The difference between the power input and the power
output is called the loss. An ideal transformer would
have no loss, and would therefore be 100% efficient.
Real transformers are often more than 98% efficient;
the remaining 2% (or less) of the input energy is lost
to:


Electric Motors/Generators
In a generator, mechanical energy is converted into
electrical energy via a magnetic field. If a coil of
conducting wire is connected across a volt-meter, no
voltage will be observed. If a magnet is then quickly
inserted into the coil, a voltage is momentarily
recorded. Removing the magnet from the coil would
generate another momentary voltage, but in the
opposing direction. The phenomenon of a moving
magnet in an electric coil would produce a voltage
(and hence a current) was simultaneously discovered
in 1831 by Michael Faraday and Joseph Henry. It is
known nowadays as electromagnetic induction.
Faraday used his discovery to invent the first generator
in which the continuous rotation of a conducting
copper plate between the poles of a permanent magnet
produced a continuous current. However, it would
take a further fifty years before Faraday's discovery
was applied to the commercial generation of
electricity.
A power transformer operates on the principle that
several sets of coils ("windings") are wound on an iron
(laminated) core. Alternating current is impressed on
one set of coils which induces a magnetic field in the
core. In turn, the varying magnetic field induces a
voltage in the other set of coils.

The alternating magnetic field causes
fluctuating electromagnetic forces between
the coils of wire, the core and any nearby
metalwork,
causing
vibrations
which
consume power.
Magnetostriction, a minor effect that causes
periodic stresses (at 120 Hz), and therefore
losses due to frictional heating, in laminated
stacked cores. This is also the source of the
humming noise of an energized transformer,
3.3
Data storage
The magnetic storage of data is very important for
modern life. Magnetic tapes were originally used for
storage of analogue audio signals and are now used to
store both analogue and digital information.
Nowadays, the magnetic media is no longer limited to
tapes which have slow access times. Magnetic discs
(floppies, hard disks) offer rapid storage and access of
ever increasing amounts of information. A wide
variety of plastic cards with magnetic strips for storage
of personal information are also in common use
Induced eddy currents circulating in the core
causing resistive heating of the core
The current flowing in the windings causes
resistive heating of the conductors
Not all the magnetic fluxes produced by the
primary is intercepted by the secondary, the
remainder (stray fluxes) are absorbed by other
nearby objects and converted to heat.
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nowadays, e.g., bank
credit/debit cards, etc.
3.4
ATM
cards,
ID
cards,
develops an induced repulsive magnetic field which
permits the train to float above the track. As the threephase current generates a magnetic wave, the train is
carried forward by this magnetic wave on a repulsive
magnetic cushion. The overall result is an almost
frictionless linear motion, where very high speeds can
be achieved.
NMR Spectroscopy
In the field of chemistry, the magnetic properties of
certain atomic nuclei can be applied in Nuclear
Magnetic Resonance (NMR) Spectroscopy. This
technology was developed from the fact that some
atomic nuclei behave like little magnets. They can
align themselves either with or against the field of a
powerful magnet. NMR Spectroscopy is a valuable
tool used in determining the molecular structure of
complex compounds.
3.7
Powerful magnets are the main features of particle
accelerators, e.g., cyclotrons and synchrotrons which
are widely used by physicists in their quest to
understand more about the fundamental nature of
matter and its constituent sub-atomic particles.
Electromagnet fields accelerate charged particles to
speeds approaching that of light and the particles
collide with the heavier target particles. The short lived
particles generated by the high speed collisions give
nuclear physicists valuable information about the subatomic nature of matter.
A further development from the NMR technology is
Magnetic Resonance Imaging (MRI). MRI has rapidly
become a powerful imaging technique in the medical
world for scanning internal organs of the human body
to generate 3-dimensional images of the organs.
3.5
Nuclear Fusion
4.0
Power Frequency Electromagnetic Fields –
Health Concerns
Nuclear fusion of light elements has the potential to
generate vast amounts of clean energy at low cost and
with no radioactive byproducts. In conventional
nuclear fusion, the positively charged atomic nuclei
must be heated to very high temperatures in order to
give them enough kinetic energy to overcome the
repulsion force between their positive charges, so that
they may collide and fuse. The required temperature
(100,000,000 °C) is so high that the gaseous matter
(plasma) cannot be contained in any normal material.
This very hot plasma is contained inside the fusion
reactor in “magnetic bottles”, where the plasma is
suspended in a powerful magnetic field without
making physical contact with the reactor vessel.
3.6
motor
Particle Physics
Magnetic
levitation/
Linear
This is a topic of immense interest and covers a
tremendous amount of research, studies, publications,
etc. A detailed dissertation on this issue is beyond the
scope and limits of this paper. Nevertheless, this paper
endeavours to present an introduction and summarize
the salient points.
4.1
EMF
Potential Health Hazards Associated with
Since the 1960's, various groups have raised health
concerns for people who either work in the presence of
elevated electromagnetic fields or who live close to
sources such as high voltage power transmission lines.
There have been a large number of studies undertaken
at various industrialized countries world-wide, to
determine any adverse health correlation with
exposure.
induction
The repulsive force between like poles of magnets can
be used for linear motor and magnetic levitation,
which is applied in the next generation of train
systems. Conventional train's rolling-stock systems
are limited to about 300 km/hour by friction and track
and wheel stresses. A train floating on a magnetic
levitation field could travel at over 500 km/hour.
Conventional train motors generate circular motion to
turn wheels that push backwards against a track, which
in turn push the train forward. Linear induction motor
generates linear motion which is a much more efficient
way of moving an object along a straight line.
The potential hazards with suspected links to EMFs
are:




The magnetic levitation (MagLev) train's linear motor
basically consists of a row of separately activated
electromagnets that are energized by a three phase
current and results in north and south pole properties
sweeping like a wave down the row of electromagnets.
The part of track near to each of these electromagnets




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Cancer (childhood/adults – including
leukemia)
Cardiac Disorders
Reproductive Disorders (impotency,
infertility)
Fetal exposure during pregnancy (genetic
defects, miscarriages)
Neurodegenerative disorders (such as
Multiple-Sclerosis)
Mental Disorders (depression, suicides)
Hypersensitivity
Effects on animals and plants
These researches and studies can be categorized into
three types:
Laboratory studies, by design, can clearly show that
cause and effect are possible. However, to-date,
virtually all of the laboratory studies evidence in
animals and humans and most of the mechanistic work
done on cells and tissues fail to support a causal
relationship between exposure to ELF-EMF at
environmental levels and changes in biological
function or disease status. This lack of consistent,
positive findings in animal or mechanistic studies
weakens the belief that the association is actually due
to ELF-EMF. Nevertheless, it cannot completely
dispute some of the associations found by
epidemiological studies.
Epidemiological
Epidemiological study is the statistical study of
disease in human populations. It is useful because
it directly looks at specific groups of human
population. Its drawback is that only statistical
associations may be made, but cannot eliminate the
numerous other factors that can distort the statistical
results. Therefore, epidemiological studies cannot
conclusively prove if a particular disease is caused
by exposure to EMF or not.
Numerous internationally recognized scientific
organizations and independent regulatory advisory
groups have also conducted and reported on scientific
reviews of the available EMF research literature. The
ability of these organizations and groups to bring
together experts from a variety of disciplines to review
the full body of research on this complex issue, gives
their reports credibility and recognition.
Biological
Biological study is the laboratory study of the effect
of EMF on cells and tissues. A particular study
result may be considered proven and valid if is
reproducible (repeatable) at different laboratories.
Theoretical
Since 1977, some 32 major reviews have been carried
out. Without exception, these major reviews have
reported that the body of data, as large as it is, does not
demonstrate that exposure to power-frequency
magnetic fields causes cancer or other health risks,
although the possibility cannot be dismissed. The
weakness of the reported associations, the lack of
consistency and the severe limitations in exposure
assessment in the epidemiology studies together with
the lack of support from laboratory studies were key
considerations in the findings of the scientific reviews.
Most reviews recommend further research.
Theoretical studies concentrates on identifying
theoretically probable mechanisms (physical,
mechanical, chemical, biological, etc.) that can
demonstrate and explain how EMF interacts with
living organisms.
By the end of the 20th century, there were well over
200 published epidemiological studies in the general
scientific literature world-wide.
An early study
suggested a linkage between ELF-EMF (power
frequency electromagnetic fields) and leukemia.
Subsequent review of this study's methodology has
refuted the findings.
4.2
Epidemiological studies have serious limitations in
their ability to demonstrate a cause and effect
relationship. Because they are based on statistical
correlation from a defined population. For example,
one study suggested a weak association between a
population living close to power lines with increased
risk of cancer. However, some of the people in that
population who had indeed contracted cancer were
also exposed to other hazards such as chemicals, fumes
or radiation at work or elsewhere. Epidemiological
studies do not take this into consideration. Therefore,
no definite conclusions can be drawn.
Limits of Exposure to EMF
Since the dawn of the human race, we have been
exposed to the earth's magnetic field. In our daily
lives, we are constantly exposed to electromagnetic
fields of one form or another. The typical electrical
and magnetic field strengths present at various
situations of our daily lives are as follows:
TYPICAL ELECTRIC FIELD STRENGTHS
(Source: National Radiological Protection Board, UK)
Location
Many other epidemiological studies also points to
association of exposure to EMF with varies other types
of ailments.
However, none of them could
demonstrate positively the cause and effect. Clear
distinction must be made between Association and
Cause. Association does not mean establishing
causation.
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kV /m
Under 400 kV Power Lines
11.2
25 m from 400 kV Power Lines
1.0
Under 132 kV Power Lines
3.8
Under 11 kV Power Lines
0.2
Near domestic appliances
0.01 – 0.25
Inside typical homes
As it has not yet been categorically quantified and not
even demonstrated that exposure to EMF would be
hazardous to health, there is no firm basis on which
limits of exposure may be specified. Nevertheless,
various government and scientific bodies has made
recommendations.
The
National
Radiological
Protection Board and the National Institute of
Environmental Health Sciences – National Institutes of
Health of the UK recommend that: "People should not
be exposed to magnetic fields above 1600 μT or
electric fields above 12 kV/m."
These
recommendations are based on the fact that at those
field strengths, current densities of 10 mA/m2 can be
induce in the human neck and torso, which is
comparable to the currents produced naturally by nerve
and muscle action. Other countries have similar
recommendations of exposure made on similar basis.
0.001 – 0.01
≤ 0.001
Free outdoors
TYPICAL MAGNETIC FIELD STRENGTHS
(Source: National Radiological Protection Board, UK)
Location
µT
Under 400 kV Power Lines
40.0
25 m from 400 kV Power Lines
8.0
Under 275 kV Power Lines
22.0
25 m from 275 kV Power Lines
4.0
Under 132 kV Power Lines
11.0
25 m from 132 kV Power Lines
7.0
At substation fence
Up to 10.0
0.3 m from domestic kWH meters
0.02 – 0.05
The National Radiological Protection Board, UK also
made recommendations regarding the maximum
electric and magnetic field strengths beneath overhead
power lines, as shown in the following table. These
recommendations are adopted by the electric utilities
in the UK.
MAXIMUM EMF STRENGTHS
DIRECTLY BENEATH O/H LINES
(Source: National Radiological Protection Board, UK)
Electric
(kV /m)
Magnetic
(µT)
400 kV Power Lines
11.2
40
µT
132 kV Power Lines
3.8
11
Using vacuum cleaners/hand drills
2.0 – 20.0
11 kV Power Lines
0.2
7
Using food processors
0.6 – 10.0
5.0
Dish washers
0.6 – 3.0
Washing machines
0.15 – 3.0
Fluorescent lamps
0.5 – 2.0
Conventional ovens
0.15 – 0.5
1 m from TV/ CRT screens
0.01 – 0.15
Inside domestic homes
0.01 – 0.2
The effects of EMF on live tissues and the potential
health risks have been the focus of numerous clinical
and epidemiological studies conducted by government
and industry organizations world-wide since the
1970's. Without exception, these major studies have
reported that there is no conclusive evidence which
correlates the increased risk of cancer or other health
risks with exposure to electromagnetic fields.
However, this lack of categorical evidence does not
mean that health risks do not exist, but rather
highlights the need for broader studies and further
research.
TYPICAL MAGNETIC FIELD STRENGTHS
(Source: National Radiological Protection Board, UK)
Location
Free outdoors
Location
≤ 0.001
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Conclusion