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الثلاثاء، 5 أغسطس، 2014

Application of Reclosers on Medium Voltage Transmission Line Networks With a Case Study

Author        : Mohamed Abou El-Atty El-Ghannam
Degree        : M.Eng. Electric Communication
Title: Application of Reclosers on Medium Voltage Transmission Line Networks With a Case Study

Abstract
Nowadays Medium voltage networks have acquired great importance according to huge increase in loads and small amount of spinning reserve. Medium voltage networks can be connected in two forms, underground cables or over head transmission line. Overhead lines are far cheaper than underground cables for long distances, mainly due to the fact that air is used as the insulation medium between phase conductors, and that no excavation work is required. The support masts of overhead lines are quite a significant portion of the costs; that is the reason why aluminum lines are often used instead of copper, as aluminum lines weigh less than copper, and are less expensive. However, copper has a higher current conducting capacity than aluminum per square mm, so once again the most economical line design will depend on many factors.
Overhead lines are by nature prone to lightning strikes, causing a temporary surge on the line, usually causing flashover between phases or phase to ground. The line insulators are normally designed to relay the surge to ground, causing the least disruption and/or damage. This is of short duration, and as soon as it is cleared, normal operation may be resumed. This is why sophisticated auto-reclosers are employed on an increasing number of overhead lines.
Mainly power faults in overhead transmission line systems happen in great number more than underground cables, most of these faults are temporary faults. Temporary faults would continue for variable time ranging from few seconds to few minutes. Any power interrupt may cause great losses in money and long time fault; we may lose time and money for location of fault although there are no faults. This report handles a case study of medium voltage line suffers from great number of faults. Performance of this line will be studied before and after installation of recloser.

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