إن استخدام المعدات والأجهزة الكهربائية بالمنازل والمعامل والمختبرات والمكاتب وآافة أماآن العمل التى تشع مجالات آهرومغناطيسية يؤدي الي ارتفاع درجة التلوث الكهرومغناطيسي بتلك الأماآن مما يجعل مستخدميها أآثر تعرضا لتلك المجالات وبقيم عالية ولفترات ليست بالقصيرة مما يؤثر سلبا علي صحتهم. آما أن التوصيلات الكهربائية المنفذة بطريقة غير سليمة بالمنشآت المختلفة يصاحبها أيضا زيادة في قيمة المجالات الكهرومغناطيسية المنبعثة مما يؤدي الي ارتفاع درحة التلوث الكهرومغناطيسي واتساع مناطق التلوث. ومن ناحية أخري فإن النمو المتزايد للمدن والمجتمعات أدى إلى ظهور مجتمعات جديدة والي الزحف تجاه خطوط نقل وتوزيع الطاقة الكهربائية فأصبحت المبانى التجارية والسكنية والحدائق والمنتزهات والملاعب قريبة جدا من تلك الخطوط الكهربائية التى تشع مجالات آهرومغناطيسية التي قد تترك أثرا صحيا سيئا لمتعرضيها. فى هذه الورقة يتم إلقاء الضؤ علي مشكلة التعرض للمجالات الكهرومغناطيسية بالوسط المحيط متضمنا عرض تأثير التعرض لتلك المجالات بالمناطق الملوثة آهرومغناطيسيا علي صحة الإنسان وآذلك أهم مصادر بالوسط المحيط بنا ملوثات البيئة آهرومغناطيسيا. آما يتم دراسة ومناقشة النتائج التي تم الحصول عليها بإجراء بعض القياسات لقيم المجالات المغناطيسية المنبعثة من مصادر التلوث الكهرومغناطيسي بالوسط المحيط بنا لتقنين وتحديد درجة التلوث. آما يتم مقارنة النتائج بالمناطق الملوثة آهرومغناطيسيا بالقيم المرجعية للمجال المغناطيسى المسموح بها حتى يمكن تقييمها ومعرفة ما إذا آانت قيما آمنة للإقامة والعمل الدائمين أم غير آمنة. آما يتم وضع بعض الاقتراحات والتوصيات التى تتعلق بالتصدى لهذه الظاهرة والتى تخص التلوث الكهرومغناطيسي الناتج من استخدامنا للكهرباء

The present work discusses the friction and wear of polyethylene as bearing materials scratched by steel insert in the presence of magnetic field. Tests were carried out at dry and oil lubricated surfaces. Paraffin, fenugreek, camphor, cress and Habet El-Baraka oils were used as lubricants. The friction coefficient and wear of the tested composites were nvestigated using a tribometer designed and manufactured for that purpose. It was found that, at dry sliding, friction coefficient displayed the highest values, where a value of 1.5 was approached. Application of magnetic field on the sliding surface caused significant friction decrease. As the intensity of the magnetic field increases, friction coefficient decreased. Wear of polyethylene increased with increasing applied load, and significantly increased under the application of the magnetic field. Lubricating the sliding surface by paraffin oil significantly decreased friction coefficient, while magnetic field significantly decreased friction and increased wear. Friction coefficient displayed by fenugreek oil represented relatively higher values indicating the weak lubricating properties of that oil. As the magnetic field was applied, friction coefficient decreased. Wear in the presence of magnetic field significantly decreased. Camphor oil displayed relatively lower friction and wear values than that observed for fenugreek oil. Application of magnetic field on the sliding surface caused significant friction and wear reduction. Besides, friction coefficient and wear displayed by cress oil decreased as a result of the magnetic field. Finally, Habit El-Baraka oil displayed the lowest values of friction coefficient among the tested oils. The wear resistance observed was quite good.

Grounding grid performance can be measured in terms of grounding resistance, but it is preferable to include the distribution of surface potential and, subsequently, the touch and step voltages over the area above the substation ground grid and beyond. Two methods are used in this paper to compute the grounding resistance (Rg) and the earth surface potential (ESP) due to discharging current into grounding grids. The first one is the charge (current) simulation method (CSM) and the other is the boundary element method (BEM). For BEM, commercial software TOTBEM by university of La Cournia, Spain is used for computing ESP and Rg. The owned FORTRAN code is provided to calculate the ESP and Rg. The soil is assumed to multilayer soil. The paper focuses the comparison between these two methods for calculating ESP and Rg. In case of grounding resistance, a comparison between the two methods results and IEEE Standard formula is presented.

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.)