الفهرس 
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Abstract
ABSTRACT
The underground cables play vital role in the transmission and distribution of
the electrical energy over wide range of voltages especially inside towns. It
replaced the overhead transmission lines (O.H.T.L) all over the electrical
networks due to their operational advantages. On the other hand, the
underground cables have some disadvantages compared to O.H.T.L for
example, the fault repairing process is hard and time-consuming process.
Also, the fault location process requires special instruments and high
qualified teamwork. To overcome some of underground cable disadvantages
this study intended to:
Firstly: A practical study is conducted to analyze the different types of
underground cable faults and their causes, in addition to a practical
statistical study is performed on an actual underground cable
network to show the rate of occurrence of each fault over the
previous twelve years.
Secondly: Analyzing the statistical study results and correlating it to the actual
cable faults analysis. from this analysis, it is noticed that the partial
discharge activities inside the cable itself or inside one of its
accessories (junction or termination) are the main cause of the
underground cable faults. Also this help us in determining the best
techniques to be followed during the underground cables
manufacturing, constructing, operating and finally repairing, so as
to minimize the fault rate in the future.
Thirdly: A medium voltage cable having an air cavity is simulated using
COMSOL program to study the effect of changing the cavity
IV
configuration, size and position on the partial discharge activities
inside the cable. So, precautions can be taken during the cable
manufacturing and installing to avoid the partial discharge activities
during the cable operation. The simulation results showed that the
cavity configuration, size and position have a great effect on the
partial discharge activities inside the cable, which is matched with
practical measurements by others.
Fourthly: The techniques and practices of underground cable fault location are
discussed, in addition to applying these techniques on two practical
case studies to evaluate their efficiency. The deep understand of the
fault nature helps in selecting the suitable technique. The study
showed that these fault location techniques achieved accurate and
fast fault location especially when the suitable technique is correctly
selected.
It is noteworthy that the COMSOL program is a powerful tool in the
underground cable simulation, providing multiple possibilities for studying
the different factors effecting on the cable operation and design. Especially
these factors which occur fortuitously such as voids and impurities formation
inside the cable insulation or inside glass and porcelain insulators, the
creation of these defects artificially for practical study is nearly impossible.
Also, the COMSOL program provide an accurate and clear measurement for
the different parameters such as electric field strength and electric potential
at any point inside the insulation, with charts for the electric field and
electric potential distribution all over the simulated cable layers, which is
difficult to achieve practically.