التعليم الإلكتروني هو أحد الوسائل التعليمية التي يمكن استخدامها لإتاحة التعليم والتدريب والتعليم المستمر للدارسين والمهتمين بمجال معين خاصة من هم خارج دور العلم دون التقيد بالمكان والزمان. والجدير بالذكر أن عصرنا هذا عاصر ويعاصر تقدما كبيرا ومتناميا في الأجهزة والمعدات التقنية وفي تكنولوجيا الاتصالات والمعلومات وعلي قمة ذلك شبكة الإنترنت. ولقد اتجهت المؤسسات التعليمية ـ مثلها مثل باقي المؤسسات ـ إلي استثمار هذا التقدم واستخدامه كوسيلة تعليمية سواء داخل حجرة الدراسة أو خارجها والسعي إلي اعتماد التعليم الالكتروني كتعليم متكامل علاوة علي السعي في استخدامه في التدريب والتعليم المستمر. تهدف هذه الورقة إلى إلقاء الضوء على التعليم الإلكتروني عامة ، ومدي استخدامه في التعليم الهندسي والتدريب والتعليم المستمرحيث تستعرض مقدمة عن التعليم الالكتروني , ما هو, ما أنواعه, ما هي متطلباته وتقنياته, ما هي أهمية ومعوقات استخدامه، وكيف يمكن توظيفه في التعليم الهندسي.

The primary concern with any source of electricity is the fact that electromagnetic fields are naturallyemitted as a consequence of the transmission, distribution and use of electricity. While the electric fields are relatively easy to block, the magnetic fields are difficult to block and can cause some problems including human biological effect. Since electromagnetic field is present wherever electricity is used, there is a level of EMF in any building due to multiple sources of electromagnetic fields. These sources include the structure's electrical distribution systems, lights, transformers, electric fans, copiers, underground wires, ground-mounted transformers, common sources within the home and work places etc. Also the nearby high voltage power lines are considered one of the EMF sources. This makes the ambient level of indoor electromagnetic pollution exceeds the tolerable limits. To reduce indoor electromagnetic pollution, different electromagnetic fields mitigation methods could be used. Different mitigation methods are summarized in this paper. The cancellation method by using the correct indoor electrical wiring is discussed in this paper. The using of metal tubes as wall conduits for wires is considered, in this paper, a way of electromagnetic fields mitigation. The effect of material shielding on the indoor electromagnetic pollution is discussed also in this paper.

NULLn this paper, the electrical parameters of the duct electrostatic precipitators with bundle wires, as discharge electrodes, are calculated and reported. Variation of mobility for both ions and particles in the space surrounding the energized subwires is taken into consideration. The method used is based on numerically solving the main set of equations, defining the ionized field surrounding the subwires of the bundle wire‐duct electrostatic precipitators (BWDEP) with the presence of dust particles. This method predicts the electrical performance in the BWDEP irrespective of the number of subwires per bundle. The corona onset voltage around the periphery of each subwire of the bundled discharge electrodes of the duct electrostatic precipitators is determined. It changes from point to point at the subwire surface. The effects of different numbers of subwires per bundled electrode, as well as the subwires arrangement, on the electrical performance of the BWDEP are also reported and discussed in this paper. The present findings are correlated to the physics of the electrical corona discharge.

Early locating and identifying basic weak-points (sharp-edge corona, polluted-insulator "baby arcs" and loose contact arcing) in electrical power systems significantly decrease the imminent failure, outage time and supply interruption. We previously introduced a method for detecting the basic weakpoints based on sound/waveform patterns and frequency analysis of their ultrasonic emissions. However, nonstationary patterns of the basic weak-points’ emitted signals and background noise frequently led to confusing discrimination. Therefore, this paper develops an effective pattern recognition scheme, employing wavelet feature extraction and Artificial Neural Network (ANN) classification, to identify the basic weak-points and two weakpoint combinations (polluted insulator stressed by a transmission line with a sharp-edge and multiple sharp-edges on the same line), based on their modulated ultrasonic emissions. Extensive testing proved that the proposed scheme achieved average recognition rate of 98% when tested using weak-points underneath 33-kV and 132-kV transmission lines with 2-second detected signals. Moreover, increasing the acquisition time (>30 seconds) and classifying the weakpoints based on majority voting over the ANN’s responses of multiple (15) consecutive sections, consistently led to 100% successful recognition of the considered weak-points.

Early locating and identifying basic weak-points (sharp-edge corona, polluted-insulator "baby arcs" and loose contact arcing) in electrical power systems significantly decrease the imminent failure, outage time and supply interruption. We previously introduced a method for detecting the basic weakpoints based on sound/waveform patterns and frequency analysis of their ultrasonic emissions. However, nonstationary patterns of the basic weak-points’ emitted signals and background noise frequently led to confusing discrimination. Therefore, this paper develops an effective pattern recognition scheme, employing wavelet feature extraction and Artificial Neural Network (ANN) classification, to identify the basic weak-points and two weakpoint combinations (polluted insulator stressed by a transmission line with a sharp-edge and multiple sharp-edges on the same line), based on their modulated ultrasonic emissions. Extensive testing proved that the proposed scheme achieved average recognition rate of 98% when tested using weak-points underneath 33-kV and 132-kV transmission lines with 2-second detected signals. Moreover, increasing the acquisition time (>30 seconds) and classifying the weakpoints based on majority voting over the ANN’s responses of multiple (15) consecutive sections, consistently led to 100% successful recognition of the considered weak-points.

NULLOn the basis of the experimental analysis presented, the following conclusions may be drawn about the effect of wind on positive corona on thin wires: 1. As the applied voltage is increased, the following modes of corona are noticed on thin wires; a) burst pulses b) glow c) sparkover. 2. For thin wires, there is a critical voltage (transition voltage) at which a dc component with high frequency ripples has been observed. 3. The transition voltage confirms the inception of glow. Such a glow was termed previously “ultracorona”. 4. The transition voltage depends not only on the wire radius but also on gap spacing. 5. For thin wires, wind decreases the transition voltage. 6. The average repetition rate of the ac component increases with the applied voltage and decreases with wind. 7. The profile of the current distribution at the ground plane changes its shape with wind. Its peak increases in value and shifts in position downstream with wind. The wind effect on current distribution profiles increases as the applied voltage decreases

The author describes a simple mathematical model to calculate the saturated corona profiles (field intensity, current density and then charge density) over the ground surface and underneath HVDC monopolar lines. The relations between these saturated values and the length of the field lines are given. The results are compared with the experimental ones. (7 refs.)

A numerical method for calculating the ion- and particle-charge density, the electric field intensity, and, consequently, the ion- and particle-current density in a wire-duct electrostatic precipitator is reported. This method is based on numerically solving the main set of equations defining the ionized field. These include Poisson's equation, the current density equation, and the current continuity equation. The space-charge-free field is calculated using the charge simulation technique. The distribution of the electrical conditions is determined as a function of the applied voltage. Both cement and steel particles are considered. This method is checked against published calculations. Findings are correlated to the physics of corona discharge.

NULLIn this paper, a simple and fast method for estimating the saturated profiles of the field intensity, ions and particles charge density, ions and particles current density, relative precipitated dust and the overall precipitation efficiency of the wire-duct electrostatic precipitators is reported. Both ions and particles in space surrounding the energized wires are taken into consideration. This method is based on simple expression which define the ionized field in the interelectrode spacing surrounding the HV wires of the wire-duct electrostatic precipitator in presence of dust particles and under saturated conditions. The precipitation efficiency of the electrostatic precipitators under saturated conditions is also estimated for cement industry. The effect of some parameters on the precipitation efficiency is also reported. The precipitation efficiency of the wire-duct electrostatic precipitator as influenced by both the applied voltage and the gas flow speed is discussed in this paper. The present findings are correlated to the physics of electrical corona discharge.

NULL