الفهرس 
LITERATURE REVIEW OF THE VERY FASTOnly 14 pages are availabe for public view
 |  | from | 288 |  |  |
| | | from | 288 | | |
Abstract
Electrical equipment and installations are exposed to stresses from
overvoltages under normal and abnormal conditions. Some of these
overvoltages may cause damage to the electrical equipment in the
substations.
gas insulated substations (GIS) disconnector switch operation
generates fast transient overvoltages in the system. Therefore, the present
investigation has been devoted to study the fast transient phenomena in
the Egyptian Electricity National Grid.
Since the disconnector has a relatively slow speed of the moving contact
the switching problems increase in direct proportion to the system
voltage, in addition to the potential stressing of the insulation relative to
the earthed housing and across the open contacts. The switching of
capacitive charging currents are of special significance under these
conditions pre-or restikings occur and cause fast transient overvoltage on
the supply and load sides.
This phenomena cannot be investigated in public supply system owing to
the inherent possibility of earth fault. Therefore an actual test object
220kV disconnector has been constructed in the Extra High Voltage
Laboratory and the tests were carried out to record the performance of
the disconncctor under different values of SF6 pressure .
Also, the disconnector has been tested in open position under steady state
conditions with the combined stresses across the isolating distance of
rated power frequency voltage at one terminal and standard lightning
impulse voltage applied to the other terminal.
Field measurements on switching capacitive currents with disconnector
in 220kV gas insulated substation were carried - out and compared with
the calculated waveforms by EMTP.
The work is described in eight chapters:
• The first chapter includes a summary of the review of overvoltage
types in high and extra high voltage networks and a brief explanation of both GIS and AlS relevant to the insulation behavior and overvoltage
stresses.
• Chapter two includes a review of the previous work in the field of
very fast front overvoltage phenomena in GIS. Most of the previous
investigations in the area of the research work did not consider the
variation of the arc behavior with the SF6 gas pressure.
• Chapter three presents the statistical analysis of GIS outages in the
Egyptian Electricity E.H.Y. Grid; also it includes a comparison between
the failure frequency values of GIS in Egypt and the values obtained
from international surveys.
• Chapter four describes the testing arrangement and instrumentation
techniques, which are used in both the High Voltage Laboratory tests and
field measurements. A detailed and special considerations of the
experiment arrangements and test procedures are also presented.
• Chapter five presents the records obtained from the experimental
results and the analysis of the overvoltages including fast transient (Y-t)
curves under different gas pressure.
• Chapter six contains the results of the actual field overvoltage
measurements 011 220k Y system and the analysis of these results.
• Chapter seven offers details of digital computation model of fast
transient overvoltages for the following cases:
I. Switching operation of 500 kY line disconnector in GIS substation.
2. Switching operation of220 kY line disconnector in GIS substation.
3. Switching operation of220 kY GIS floating B.B
4. Switching operation of220kY test object
It also includes the simulation of the arc in the disconnector during a
closing operation. Computation results of the fast transient overvoltages
are compared with field measurements and laboratory tests.
• Finally chapter eight presents the main recommendations which are
drawn through out the work and its analysis. Further some proposals for
future investigations ill this field are given.