الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 115 |  |  |
| | | from | 115 | | |
Abstract
Lightning strokes represent a considerable cause of short
interruptions in overhead transmission line networks. The over voltages
caused by lightning can’t be avoided but their influence can be limited by
appropriate overvoltage protection. Lightning strikes mostly the top of a
transmission tower (shield-wire) rather than the transmission line phaseconductor.
This causes voltage to develop across line insulators. If the
induced voltage across string insulators equals or exceeds the critical
flashover voltage (CFO), back flashover will occur .
This thesis concentrates on back flashover studies as they are
important to evaluation of lightning performance. This study is focused
on modeling the Egyptian high-dam 500kV single circuit tower with two
overhead ground wires, Egyptian 220kV line with a double circuit tower
with one overhead ground wire, a common 220-66kV line found in Sinai
area with double circuit 220kV line and double 66kV line on the same
tower with one overhead ground wire, and ±400kV HVDC bipolar
overhead transmission tower with one ground wire. The models were
developed by using ATP-EMTP software package. The voltages across
string insulators resulted from hitting a lightning stroke the shielding wire
are measured and compared with CFO. The effect of different factors
such as the lightning current, lightning wave front, wave tail and tower
footing resistance on the voltage induced on the string insulators and the
back flashover voltage are presented and discussed .