Electrical Engineering Arts

  Lightning Arrester surges in Power system cause damage to main station equipment and overhead lines, so they must be protected from the risk of lightning strikes. Apart from lightning, some switching operations and faults may also generate overvoltages that can be potentially hazardous to the insulation of the substation equipment and insulation of the lines, These devices have many names as surge suppressors, surge diverters, and lightning arresters . These devices are placed parallel to the device to be protected, The purpose of lightning arresters is to provide a path over which the surge can pass to the ground. When a lightning impulse or switching surge reaches the arrester terminals, it causes a spark which jumps across the air gaps, passes through the non-linear resistive element, Sic, which allows a low resistance for the high voltage surge, but presents a high resistance under the rated voltage of the lines. In other words, the lightning arrester leads off only the surge

  OVERHEAD TRANSMISSION LINES (OHTL) GROUNDING   In general, a protection system must be provided for the transmission towers, as well as a safe environment for the personnel working on these towers. A grounding wire is used above the tower. And it has several names earth wire, shield wire, skywire, static wire. Its type can be steel or OPGW wire. Lightning Protection An important use of earth wire on transmission lines is lightning protection. It is a grounded wire or more placed above phase conductors for the purpose of intercepting direct strokes in order to protect the phase conductors from the direct strokes. to take these direct lightning strokes and shield the conductors. The lightning current is expected to follow a path along the shield wire, down the tower, and through the tower footing resistance to the ground. So Tower footing impedances should be obtained as low as is economically justified. (OPGW) Ground Wire OPGW ground wire is a dual functioning cable a

 

  Thermal Characteristic of Cables Maximum  C urrent Capacity There are many reasons that prevent the cables from running when the cable is overheated, including the expansion, which may result in bubbles and ionization. Also, the expansion in the oil may lead to the explosion of the jacket and the oil may lose its viscosity and leak from the higher levels, and thermal instability may occur as a result of the rapid increase in the loss in The insulator with temperature and the latter phenomenon is not likely to occur in the cable (up to 33 KV), but it occurs in the higher voltage cables. To prevent harmful effects, the maximum temperature of the conductor must be set at 65 ° C in the cables dipped with viscous oils.  Thermal Resistance Its unit is thermal ohm, which is the thermal resistance that requires a temperature difference equal to one degree Celsius to produce an heat flow of one watt (i.e. 1 joule per second). الخواص الحرارية للكابلات                                    Therma

  Transposition tower In electrical power transmission, a transposition tower is a transmission tower that changes the relative physical positions of the conductors of a transmission line in a Polyphase system. A transposition tower allows these sections to be connected together, while maintaining adequate clearance for the conductors. To maintain balanced conditions of reactance and capacitance on the three phases of a transmission line, at least one transposition barrel should be placed between major terminals. However, it has been determined that for less than 161 km (100 mi) between terminals, the unbalance is not sufficient to affect the operation of the transmission line or the protective relays.        وهي مصممه بترتيب خاص يسمح بتبادل مواقع الموصلات الطورية على الابراج تعود الحاجة إلى تبديل مواقع الموصلات إلى أن قيمه كل من محاثه وسعه الخط الطورية غير متساوية على الأطوار الثلاثة نظرا لعدم التماثل الهندسي بين مواقع تلك الموصلات   على الحامل، الأمر الذي يؤدى إلى عدم تماثل

 

 

  Thermal Power Stations Work theory: Heat water and turn it into steam, which is directed to the turbine blades, and it turns and the generator rotates with it, producing an electric current. Features 1. The largest capacity (the largest unit is 627 MW) 2. The life span is greater 3. It increases the stability of the network 4. Efficiency 35% - 42% 5. Operating cost is normal Defects 1- The construction cost is high 2- The equipment takes a lot of space 3- They are only built near the water source 4- The length of time to access the network (it takes from 5 to 7 hours) The idea of working thermal power station

 Electric power plants   The theory of electric power generation It is known in the science of electricity and mechanics that there are three elements, these elements are the field, motion and current. In order to generate electricity, we must provide the field and movement, and according to the type of movement, the type of generation. From the previous figure, it is shown that the generator shaft must be rotated until the magnetic field of the coil is cut and the electric current is created, and the generator shaft is connected to the turbine shaft, if the turbine shaft must be rotated by any means of rotation, according to the type of rotation process called the type of the generator station.                                          fig. 1  The idea of an electricity generator Types of generating stations  Thermal Power Stations Hydraulic Power stations         Gas Turbine & Combined          Diesel Power Stations Nuclear Power Stations Renewable Power stations Wind Po