الفهرس 
Introductionيوجد فقط 14 صفحة متاحة للعرض العام
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المستخلص
Very Fast Front Transient Overvoltages (VFTO) in a 220 kV Wadi-
Hoff gas insulated substation has been analyzed using ATP_EMTP
package. The Gas insulated substation (GIS) components have been
represented using equivalent circuits and distributed parameter lines that
take into account the GIS high frequency response during transients.
Different switching events leading to VFTO generation are analyzed and
discussed, such as disconnector switching at the incoming and transformer
feeders and Circuit Breaker switching at the incoming and transformer
feeders, during energizing the line and transformer bay. Also, different
effective factors affecting on VFTO generation are discussed and analyzed.
Several classical and new methods used for mitigation and protection from
VFTO are also analyzed and discussed. The following main points can be
concluded from this work.
1- Due to switching operation of DS and CB in 220/66/11kV Wadi-Hoff
GIS, VFTO at transformer points reach to about 2.04 Pu and 2.83 Pu
respectively.
2- When trapped charge change from 0 to 1 pu, VFTO will be changed
from 2.04 pu to 3.09 pu respectively, i.e. Fast operating disconnector
switches which are usually used to reduce time of the breakdown cannot
eliminate the harm of the VFTO.
3- As the trapped charge on the line increases, the VFTO levels is
increased, but this increase is not proportional to the magnitude of the
trapped charge.
4-The points near switching operation have high amplitude and high
oscillation frequency of VFTO compared with the far away points.
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5- The switching type has a great effect, i.e. CB switching has a high
amplitude and high oscillation frequency of VFTO as compared with
that generated with DS switching.
6- To mitigate the generated VFTO in the 220/66/11 kV Wadi-Hoff GIS
the following methods can be used effectively, for its low cost
implementation and minimum required changes (where the GIS is
currently under operation). These methods are;
a) Using a cable terminal would result in the lowest voltage for both
source and load-side terminal components. A suitable terminal types
can be suggested for other substations using the generalized method
proposed in this research.
b) The entrance capacitance components can damp the peak magnitude
of VFTO at transformer terminals and improve the VFTO
distribution along the transformer windings. A 10nF used can reduce
the VFTO at transformer terminal from 2.04 pu to 1.01 pu. Because
of the impossibility of adding capacitance in the high voltage
systems, the suggestion is the use of the coupling capacitor voltage
transformer with capacitance (10nF) instead of the potential
transformer or using an extra surge arrester with 10nf capacitor or
using a shunt capacitor with surge arrester.
7- Before starting the design of a HV substation, if the maximum VFTO is
below the (LIWV), no measures need to be taken. Otherwise it is
necessary to design considering the VFTO level as dimensioning
criteria or to suppress the generated VFTO by damping devices. These
devices can be as follows;
a) Installing shunt resistor on disconnector can decrease VFTO peak
but has no effect on oscillation. So shunt resistor in series with capacitor or inductor is used to reduce the VFTO amplitude and
damping its oscillation frequency.
b) Ferrite rings can obviously decrease the amplitude and steepness of
VFTO.
c) R-C filter, R-C suppressor and shunt reactor can obviously decrease
the amplitude and steepness of VFTO. But they are protecting the
transformer only.