الفهرس 
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Abstract
Gas Insulated Substations (GIS) are increasingly used in electric power
systems. GIS has several advantages over the conventional substations.
Some blackout accidents were recorded due to GIS problems. Switching
operations in GIS cause very fast transient overvoltage (VFTO). These
transients are associated with very short rise times in the nanoseconds
range, and are normally followed by oscillations having the frequency
spectrum well above several MHz. These transients have traveling wave
behavior and travel to external systems through discontinuities and
interface such as enclosures, bushings, cable joints etc.
With the development of EHV and UHV GIS, depending on the GIS
configuration, the amplitude of the electric and magnetic fields could be of
the order of a few tens of kilovolts per meter and a few hundreds of amps
per meter (Tesla), respectively. The resulted VFTO is a real problem in
protection circuits and control circuits and may cause faults in cables,
transformers and secondary circuits, which result in malfunctioning of the
primary equipment. VFTO could cause larger damage in GIS than
expected.
To improve the GIS safety and reliability, computation, characteristics
and hazards of VFTO in GIS should be analyzed.
In this thesis the VFTO inside Wadi-Hoff GIS are computed and
analyzed at different sensitive points. The different factors affect the values
of VFTO. Different mitigating methods are used and compared. The
Electro-Magnetic Transients Program EMTP-ATP is used through the
simulation studies. Many events of switching operations were performed
and discussed. The best operating constraints and remarks are introduced
to prevent blackout.