الفهرس 
Introduction and aim of the workOnly 14 pages are availabe for public view
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Abstract
ABSTRACT The study of the transient overvoltages in the distribution system especially for both medium and high voltage is very important , because such transient overvoltages may cause serious problems for both distribution system and consumer’s equipment’s. Therefore, such a study is necessary for reliable design and economic operation. Power systems are usually subjected to many forms of transient overvoltages due to sudden changes in the steady state value of voltages or currents. Such changes may be caused due to external aspects such as lightning or due to internal operation such as switching. These disturbances cause transient overvoltage surges with different wave shapes and duration, which can be classified into three groups, such as transient, steady state or resonance overvoltages. These overvoltage surges are characterized with very high rate of rise and high amplitude so these overvoltages have bad effects on the distribution system. This search presents a new picture to avoid switching transient overvoltages in the 11 kV of Mansoura Electrical Distribution Network (MEDN). The calculations of transient overvoltages phenomena in distribution systems are complicated. This is because the power system itself consists of components whose characteristics vary widely. Overhead lines and cables have parameters which are distributed in nature in contrast to those of generators, transformers, and loads which may be considered as lumped. These calculations cannot be achieved by hand calculation as the complexity of such calculation increases rapidly with an increase in network size. The use of analogue or digital computers is therefore nearly always essential. Because of the complexity of the system, the special simulation program (PSCAD/EMTDC) has been used for carrying out the calculations in the time domain as well as in frequency domain. Thereby, a preliminary scanning study about the possible overvoltages is undertaken to localize the points exposed to overvoltages higher than permissible limits. Two methods have been suggested for suppressing the overvoltages in this system. The results obtained can be very helpful for future development of this or any other distribution network.