Title : Scattering
of Electromagnetic Waves from Corner Reflectors
with Different Dimensions
Author
: Ehab Mohamed Ali Mohamed
Collection : M.Sc. Electric Power
Abstract:
This
thesis investigates the interference between electromagnetic field produced by
high voltage power lines and both of living organisms and metallic objects
underneath the transmission lines. The metallic objects such as metallic
pipelines buried in the same corridor with high voltage power lines, ships at
rivers crossing and vessels passing under or near to power lines. This
interference caused by The electric and magnetic fields produced by a
transmission line which caused induced voltage and currents in both of living
organisms and metallic objects underneath the transmission lines. The strength
of this induced current depends on the electromagnetic field strength, the size
and shape of the object and the object to ground resistance. The magnetic field
produced by a power line is calculated as the vectorial sum of the magnetic
fields produced by each conductor current separately. A method to derive the
analytical formula of the magnetic field vector produced by any power line is
developed in this thesis. The specific formulas for the magnetic field produced
by any single circuit line in flat, vertical, or delta arrangement, as well as
for hexagonal lines considered as double circuit lines in low reactance phase
arrangements, are given. The derived formulas are valid at any point with
practical importance, close to or far from the power lines. The close proximity
of power lines and buried metallic pipelines has become more and more frequent.
Therefore, there has been and still is a growing concern about possible hazards
resulting from the influence of power lines on metallic pipelines. Underground
pipelines that run parallel to or in close proximity to power lines are subjected
to induced voltages caused by the time-varying magnetic fields produced by the
power line currents. The induced electro- motive force causes current
circulation in the pipeline and voltages between the pipeline and surrounding
earth which caused risk of electric shock to working personnel making contact
with the pipeline, risk of damage to the pipeline coating and to the metal,
risks of damage to the flange used to insulate different sections of pipeline,
risks of damage to the equipment connected to the pipeline and threat to
integrity of the pipeline. This induced voltage results from three types of
coupling which namely: Capacitive Coupling, Inductive Coupling and Conductive
Coupling. Under fault conditions, the voltage on influenced pipelines can reach
a magnitude between several hundred volts and a few kilovolts. In normal
operation, influences are normally much lower, but nevertheless they can make
problems. Since the capacitive effect is negligible for the buried pipelines
then only the inductive couplings are considered in this thesis. It is common
that electromagnetic fields produced by transmission lines causes dangerous
effects on living organisms. If the human bodies are projected to high levels
of magnetic fields the main effect of interferences is the production of
electric currents within the body. Electric and magnetic fields differ, in
their effects, when they pass across the body of living organisms at low
frequencies. An electric field directed on an unshielded person discharges to
ground while the magnetic field permeates the body inducing a magnetic flux
that generates secondary electric fields inside the body and then induce
currents density that causes a change in protein, DNA syntheses, enzyme
activity, heart dysfunction and possible nervous effects.
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