الصفحات

Alexandria Engineeing Libraries

بحث هذه المدونة الإلكترونية

شرح طريقة تحميل الامتحانات من المدونة

الأحد، 23 مارس، 2014

Scattering of Electromagnetic Waves from Corner Reflectors with Different Dimensions

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.

ليست هناك تعليقات:

إرسال تعليق