Journal of Informatics and Computer Engineering (JICE)
Vol. 2(4), Jul. 2016, pp. 150-156
Investigation of Very Fast Transient over Voltages in
Gas Insulated Substations
S. Rahmani, A. A. Razi-Kazemi, IEEE member
K. N. Toosi University of Technology, Tehran, Iran
Rahmani.Soleyman@ee.kntu.ac.ir, razi.kazemi@kntu.ac.ir
of the disconnector switch or breaker is overreached by the
given over-voltage, pre-strike between the contacts occurs.
This is a common event in GIS, which generates VFTO. It
could enter the substation and may propagate inside the
substation layout. The level and shape of VFTO depends on
the GIS infrastructure. Consequently, the analysis of switching
transients and VFTOs in GIS is desperately important.
Abstract—Gas Insulated Substations (GISs) have found a
broad range of applications in power system over the last three
decades because of their high reliability, easy maintenance, small
ground space requirements, etc. Although GIS have been
involved in power systems since long time ago, some of the
problems are of more attention. These problems include
generation and propagation of very fast transient over-voltages
(VFTO) during switching of circuit breakers or disconnector
switches or earth faults. The generated VFTO causes stress in the
air-insulated switchgear and secondary equipment. This paper
presents a modeling guideline for VFTO in GIS. The origin of
VFTO, its propagation and impacts on GIS have been discussed
in this paper. Estimation of VFTO has been carried out using
EMTP-RV for various switching conditions. The variations in
VFTO peak along the GIS bus nodes regarding the different
magnitudes of trapped charges have been studied. The results
indicate a distinct pattern of variation of VFTO peak along the
nodes of the GIS bus in the case of DS operation as compared to
that of CB operation. Moreover, the increase of trapped charge
on the line increases VFTO levels. Finally, the beneficiary of
several methods has been discussed to reduce VFTO amplitudes
such as damping resistor, Ferrite rings and Nanocristalline rings.
Keywords—EMTP; Very Fast Transient Overvoltage (VFTO);
Gas Insulated Substation (GIS); Damping Resistor; Ferrite Rings;
Nanocristalline Rings; Trapped Charge
According to IEC 60071-4, VFTO is characterized by rise
time of 3 to 100 ns with oscillations at frequencies 0.3 MHz to
100MHz [9-14], [17]. Surge arresters cannot control these
VFTOs due to their extreme rise time. However, the ZnO
surge arrester may effectively limit the amplitude of VFTOs
but cannot suppress the wave steepness due to its great rate of
rise [17]. The magnitude of VFTO could reach 1.5pu to 2.0pu
of the line-to-neutral voltage crest, or even 2.5pu in the worst
case. These values are commonly below BIL of the
components used in GIS. BIL is the basic impulse level which
is the peak value of standard lightning impulse withstands
voltage of system. The ratio of the BIL to the system voltage
is lower in higher voltages; accordingly the VFT in GIS is of
greater anxiety in high voltages [18]. Even though the
magnitudes of VFTO are lower than BIL of the system, they
cause reduction in the life of insulation in the system such as
transformers due to their frequent occurrences [4]. Besides the
over-voltages caused by VFT, the stress due to high
frequencies may be critical for internal components like
spacers.
I. INTRODUCTION
Power system consists of various components such as
power stations, substations, transmission lines and various
loads, etc. With increase of demand of energy, more
substations are needed to be installed It is estimated that GIS
require approximately 10% of the area required for
conventional substations because of the dielectric strength of
SF6 in GIS which is about 3 times more than air. The
application of GIS has been increasingly requested by utilities
due to its numerous excellences, such as large miniaturizing
effects and good environmental adaptability [15], [16]. In spite
of all specific advantages, the GIS system suffers with some of
the issues such as very fast transient over-voltages (VFTO).
These transients are engendered within a GIS as the result of
switching operation (opening or closing) of a disconnector
switch [2], operation of circuit breaker, closing of grounding
switch, or the occurrence of the fault. The contacts of a
disconnector switch move slowly during opening and closing
operations. While the dielectric strength between the contacts
This paper covers the estimation of VFTO at various
locations in GIS for different switching operations.
Furthermore, disconnector switching operations in comparison
with the breaker switching is investigated. To estimate the
VFTO magnitudes, the influence of trapped charge on the HV
bus have to be taken into consideration. Therefore the
variations of VFTO peak with different magnitudes of trapped
charges have been studied. In addition, the impacts of several
methods of suppressing such as damping resistor, ferrite Rings
and Nanocrystalline ring on amplitude of VFTOs have been
discussed.
II. ORIGIN OF VFTO IN GIS
VFTOs are generated in a GIS during disconnector or
breaker switching operations, or by line-to-ground faults. In
the switching operation in GIS, when the switch closes, the
150
Article History:
JICE DOI: 649123/220127, Received Date: 23 Mar. 2016,
Accepted Date: 15 Jun. 2016, Available Online: 15 Jul. 2016
S. Rahmani et al. / Vol. 2(4), Jul. 2016, pp. 150-156
JICE DOI: 649123/220127
maintenance, when closing or opening disconnector switch or
breaker in one phase, other phases cannot sense the transient
wave. Thus, the three phases can be put into a single bus bar
or separate bus bars.
distance between two contacts reduces and the electric field
between them will rise until sparking occurs. The first
reignition of arc occurs when the voltage across contacts
overreach the breakdown voltage of the gas insulation. The
first strike occurs inescapably at the crest of the power
frequency voltage, due to the slow operating speed.
Thereafter, current flow through the spark and charge the
capacitive load to the source voltage and the potential
difference across the contacts falls and the spark will
eventually quench. When switch closes, the highest amplitude
of voltage oscillation happens at the first arc reignition:
U1 =
2
3
Vn
Modeling of GIS is accomplished by utilizing electrical
equivalent circuits put together by lumped elements and
delineated by surge impedances and travelling times. The
quality of simulation depends upon surge impedance and
travelling times, and also on quality of the model of each
separate GIS component.
The typical length of a GIS bus is much smaller than a
conventional substation and since the VFTO is like a
travelling wave of particular velocity with reflections and
refractions, the bus bar can be represented by a constant
parameter line with velocity v and surge impedance Z [7]. The
inductance and capacitance of a co-axial single phase in GIS
bus is given by:
(1)
Where U1 is the voltage amplitude at the first arc
reignition; Vn is rated voltage of the power system [8].
When switch opens, the behavior is a complete reversal of
the closing operation. In this case, the highest amplitude of
voltage oscillation appears at the last arc reignition:
U2 =
2
3
Vn (1 + exp(−
1
)
2τf
L=
(2)
Where U2 is the voltage amplitude at the last arc
reignition and f is frequency of the power source and τ is the
leakage time constant of the electric charge in bus, which is
determined by the bus capacitor and leakage resistance [8].
C=
The rise time of the over-voltage resulting from strike
depends on the field strength of the gap and is thus a function
of the field utilization factor, h, the insulation medium given
by the breakdown field strength (E/P)0 and the gas pressure p.
The rise time can be obtained by:
t r = 13.3
kt
E
( ) 0 ph
p
Z=
(4)
2π ∈
b
ln( )
a
(5)
L
C
(6)
Finally, the surge impedance is given by:
b
Z = 60 ln( )
a
(3)
(7)
Where, ‘a’ is the diameter of the HV bus and ‘b’ is the
inner diameter of the enclosure and C is capacitance, L in
inductance. According to IEC 62271-4 velocity is 0.95 of
speed of light diameter of the enclosure.
The Toepler spark constant is kT=50kV/ns cm. Rise time
can be estimated in rage of nanoseconds due to the high field
of strength of the SF6 of (E/P)0=860kV/cm and the GIS gas
pressure of up to 0.5 MPa [1], [8].
The spark is modeled as an exponentially decaying
resistance (R0e-(t/T)) in series with small resistance (r=0.5Ω) to
take care of the residual spark resistance [7]. This is
implemented using the time varying resistance in EMTP-RV.
The time varying resistance is given by this equation:
III. MODELING OF GIS COMPONENTS FOR VFTO STUDY
In spite of all furtherance in electrical measurement
techniques and equipment, quantifying the VFTO at such high
frequencies (a few MHz) is still challenging. The best way to
measure the quantity of the VFTO is to investigate switching
operation in GIS; however it can cause irreparable financial
damages to the system. Thus, actual measurement in the GIS
during operation is not feasible. Consequently, modeling
techniques and appropriate assumptions can provide
reasonable accurate predictions of the VFTO magnitudes and
frequencies and their rate of rise [5], [19-24].
R(t)=R0e-(t/T)+r
(8)
R0 is taken 106 M Ω and T is 1ns. The above equation
gives a resistance whose value varies from very high value (M
Ω) to low value of 0.5 Ω within 30 ns [7].
The electrical equivalent circuits for different GIS components
are tabulated in Table I [29].
Since VFTO contains substantially high frequency
components ranging from hundreds of kHz to tens of MHz,
most of the components have their capacitances dominating
the other parameters [25]. Owing to VFTO’s short time
151
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µ
b
ln( )
2π
a
S. Rahmani et al. / Vol. 2(4), Jul. 2016, pp. 150-156
TABLE I.
JICE DOI: 649123/220127
ELECTRICAL EQUIVALENT CIRCUITS FOR GIS COMPONENTS
FOR REPRESENTATION OF VFT
IV. SIMULATIONS AND DISCUSSIONS
The approach is applied to a 400-kV GIS as shown in Fig.
1 which is a single-line diagram of a GIS. The mentioned GIS
contain four lines. Two generators are placed in LINE 3 and 4.
The incoming line of the GIS is comprised of an overhead line
of 5-km length, an XLPE cable of 8-km length, PT, CT,
lightning arrester (LA), earth switch (ES), disconnector switch
(DS), circuit breaker (CB), etc. The XLPE cable and
transformers locations are assumed as source side and as load
side, respectively.
Models
Components
Equivalent circuits
Notes
Spacer
C=15 pF
Open End
C=15 pF
Power
Trans
C=1.4 nF
Z=12.1 Ohm
L=20.9 mH
C=0.75 nF
Bushing
C=150 pF
ES
C=45 pF
LA
C=200 pF
SA
C=50 pF
CT
C=50 pF
Z=70 Ohm
XLPE
Cable
Z=30 Ohm
V=150 m/µs
In the closed position:
Estimation of VFTO is carried out using EMTP-RV for
various switching conditions. The variation in VFTO peak
along the GIS bus nodes for disconnector and circuit breaker
switching operations is investigated; in the first condition,
CB3 operate and in the next condition, DS4 operate when CB3
is kept open, respectively (See Fig. 1).
In the closed position:
C=30 pF
Z=70 Ohm
DS
In the open position:
In the closed position:
In the open position:
C=50 pF
Fig. 1. Single-line diagram of a Gas Insulated Substation [31].
In the closed position:
C=30 pF
Z=46 Ohm
The Scenarios in simulations are as follows:
1) CB3 operates( CB3 is closing after 0.4µs) in 400kV GIS
2) DS4 operates when CB3 is open in 400 kV GIS
CB
In the open position:
In the open position:
C=50 pF
Spark
R=R0 e-t/Ƽ+r
r=0.5 Ohm
R0=106 Ohm
T=1 ns
Cross
Junction
C=25 pF
Z=35 Ohm
L=450 mH
PT
C=100 pF
The VFTO waveforms for the disconnector and circuit
breaker switching conditions in LL1, LL2, LL3, LL4 and LL5
are shown in Figs. 2 and 3. The nearest node to the switching
point in the case of disconnector switch operation is node LL4
and in the case of circuit breaker operation the closest node to
the switching point is LL2.
It has been observed that the VFTO waveform has steeper
front and correspondingly, higher frequencies as compared to
other farther observation points in the GIS. As it is displayed
in Fig. 2, node LL2 has higher frequency as compare to the
other nodes. Likewise in Fig. 3, node LL4 has the same
specialty.
In the case of circuit breaker operation, VFTO peak is
found to be highest in node LL1 (at the end of the line). Its
152
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S. Rahmani et al. / Vol. 2(4), Jul. 2016, pp. 150-156
JICE DOI: 649123/220127
value is 1.83pu just as it is shown in Fig. 4-a. According to
Fig.4-b in the case of disconnector switch operation, VFTO
peak in found to be highest in node LL4; near to the switching
point. The value of VFTO peak magnitude in this node is
1.16p.u.
It is investigated that the VFTO peak magnitudes are
higher close to the switching point when disconnector switch
operates, where as in the case of circuit breaker operation,
VFTO peak magnitudes are higher at the end of the GIS and
near the junction of GIS and overhead line. In addition, with
comparison between VFTO levels of circuit breaker operation
Fig. 5. Comparison of Variation of VFTO levels for DS operation and CB
operation
and disconnector switch operation, it is detected that a higher
VFTO magnitudes occur in the case of circuit breaker
switching operation. Correspondingly, in Fig. 5, it can be
observed that a distinct signature pattern of the VFTO peak
magnitude variation for disconnector switching operation as
opposed to the circuit breaker switching operation is occurred.
Fig. 2. Analysis of VFTO waveform for switching condition 1 in LINE1
B. Influence of Trapped Charge on GIS
The trapped charge remaining on load side of the
disconnector must be taken into consideration, for the
estimation of the VFTO stress. The trapped charge left on a
floating section of switchgear depends on the disconnector
switch construction [2]. In the case of high speed
disconnectors, the maximum trapped charge could be as high
as 1.0pu or even 1.2pu in the worst case [26], [27].
The variation of the VFTO magnitudes for 0.3p.u, 1p.u and
1.2p.u of trapped charge is investigated in order to understand
the exact influence of the trapped charge on the VFTO levels
in GIS. The conditions considered are:
1) DS4 operates when CB3 is open with 0.3 pu trapped charge
2) DS4 operates when CB3 is open with 1 pu trapped charge
3) DS4 operates when CB3 is open with 1.2 pu trapped charge
Fig. 3. Analysis of VFTO waveform for switching condition 2 in LINE1
Fig. 4. VFTO waveform for switching a) condition 1 at node LL1
Fig. 6. Variation of VFTO levels for DS4 operation when CB3 is open with
0.3 p.u.,1 p.u. and 1.2 p.u. Trapped Charge
b) condition 2 at node LL4
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JICE DOI: 649123/220127
The very high intensity of the magnetic field around the
conductor causes the ferrite material to go to a completely
saturation in this high magnetic field. The aftereffect of this
saturation is damping effect reduction. It is possible to
increase the magnetic field strength by layering of ferrite
rings, but this can cause reduction in effective permeability.
Therefore, the damping effectiveness of the whole ring
arrangement decreases. Consequently, the damping effect of
ferrite rings inside the GIS for HV applications is limited
which is a malfunction of ferrite rings. Equivalent ferrite ring
model is shown in Fig. 8. The value of R is 100Ω and L is
2mH.
It is concluded that when the trapped charge on the line
increases, there is an increase in the VFTO peak magnitudes.
But this increase is not proportional to the increase in the
trapped charge magnitudes. As well the effect of trapped
charge on VFTO peak magnitudes is higher in the line where
the switching is done and specifically, at the nodes in the line
where the switching operation is done (LL4 is the nearest node
to the switching point). The variation of VFTO peak
magnitudes for different trapped charges is demonstrated in
Fig. 6.
C. Suppression Methods
Different methods are available to suppress the VFTO
magnitudes. Mitigation VFTO by integration of a damping
resistor and either by using Ferrite rings which are arranged
around the inner conductor of the GIS are well proven
technology [2], [28]. Third method of damping is by using
Nanocrystalline rings which is a new method for mitigation of
VFTO magnitudes.
The effect of the Ferrite Rings on VFTO waveform when
DS4 operate and CB3 is kept open in 230kV GIS at Node LL3
is shown in Fig. 10-c and the value of VFTO peak in this case
is 1.04p.u. It is observed that the VFTO peak decreases more
in compare to when damping resistor used in order to mitigate
the VFTO magnitude.
In these cases, it is assumed that the substation is a 230kV
GIS which is considered to estimate and compare suppression
methods. Single-line diagram of GIS is demonstrated in Fig. 1.
VFTO waveform when DS4 operated and CB3 is kept open in
GIS without any mitigation methods at node LL3 is shown in
Fig. 10-a whereas the VFTO peak in this condition is 1.232pu.
Fig. 8. Equivalent Ferrite Ring model
3) DS4 operates when CB3 is open with Nanocristalline
Rings in a 230 kV GIS
Accomplished investigations are as follows:
1) DS4 operates when CB3 is open with Damping Resistor
in a 230 kV GIS
According to the maximum calculated VFTO and the
necessitate mitigation effect; the resistance of the damping
resistor could be delineated. By increasing the resistance,
VFTO magnitude can mitigate, but the dimension of the
disconnector increases. Besides the energy absorption and the
branching behavior must be taken into consideration. A
flashover across the resistor may lead to a VFTO with
comparatively higher amplitude as compared to a DS without
such a damping resistor. Therefore it is required to overcome
the drawback of such cumbersome designs by using other
internal damping measures. Fig.7 displays the equivalent
circuit for damping resistor for simulation which its value
based on previous research is 100Ω [29].
Like the ferrite rings, these rings are arranged around the
inner conductor of the GIS. Experiments were accomplished
by ABB Switzerland with different ring types, different sizes
and different numbers of rings [30].
Fig.13 displays the equivalent Nanocrystalline rings model
for simulation where the values of R, L and C have been
selected in order to make better suppression results. Therefore,
the value of R is 150Ω and L is 0.002mH and C is 1pF
[29],[30].
The effect of the Nanocristalline rings on VFTO waveform
when DS4 operate and CB3 is kept open in 230kV GIS at
Node LL3 is shown in Fig. 10-d and the value of VFTO in this
case is 1.022pu. It is observed that the VFTO peak decreases
more in compare to when damping resistor or ferrite rings
used in order to mitigate the VFTO magnitude.
The effect of using damping resistor on the VFTO
waveform when DS4 operate and CB3 is kept open in 230kV
GIS at Node LL3 is demonstrated in Fig. 10-b. It is observed
that by using Damping Resistor, VFTO peak decreases to
1.065p.u. Furthermore, fewer level of VFTO magnitude is
obtained by using damping resistor.
Fig. 9. Equivalent Nanocristalline Ring model
The comparison of different suppression methods and the
VFTO magnitude in pu is given in Table.II.
It has been observed in Fig. 10-a that VFTO peak
magnitude is 1.232p.u when DS4 operate and CB3 is kept
open in 230kV GIS. Afterwards, the damping resistor of 100Ω
is included in the switching operation of the disconnector and
Fig. 7. Equivalent Damping resistor model
2) DS4 operates when CB3 is open with Ferrite Rings in a
230 kV GIS
154
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S. Rahmani et al. / Vol. 2(4), Jul. 2016, pp. 150-156
JICE DOI: 649123/220127
Fig. 10. VFTO waveform when DS4 operate and CB3 is kept open in 230kV
GIS at Node LL3. a)without any suppression methods b) with Damping
Resistor c) with Ferrite Rings d) LL3 with Nanocristalline Rings
it has been observed in Fig. 10-b that VFTO levels reduced to
1.065p.u. In addition lesser values of oscillation frequency
occurred in the case of using damping resistor. Another
method of suppressing VFTO’s have been carried out by
modeling the ferrite rings and it has been obtained that the
steepness and maximum peak values are reduced to
considerable amount of 1.04p.u and very less values of
oscillation frequency demonstrated in Fig. 10-c. It was
correspondingly pointed that
because of the saturation of Ferrite material, damping effect of
ferrite rings inside the GIS for HV applications is limited. A
new method has been described by using Nanocrystalline
materials. It has been concluded that the third method had the
best suppression effect. Fig. 10-d shows the effect of using
Nanocrystalline rings.
The comparison of Variation of VFTO levels with
different suppression methods is shown in Fig. 11.
Fig. 11. Comparison of Variation of VFTO levels with different suppression
methods
TABLE II.
COMRAISON OF DIFFERENT SUPPRESSION METHODS
Conditions
VFTO (p.u.)
Without Suppression method
1.232
With Damping resistor
1.065
With Ferrite Rings
1.04
With Nanocristalline Rings
1.022
V. CONCLUSION
This paper investigated a general model for assessment of
VFTO in GIS using EMTP-RV. It was observed that VFTO
waveforms have steeper front and higher frequencies near the
switching points. And there is a little trace of VFTO in farther
points and other lines. In the case of circuit breaker operation,
the VFTO peak is higher at the end of the line (near the
junction of GIS with the overhead line) where the switching
occurred. Where as in the case of disconnector switch
operation VFTO peak is higher near the switching point and it
decreases along the line where the switching has been done.
Correspondingly, higher VFTO magnitudes occur in the case
of circuit breaker operation as compared to disconnector
switch operation. Besides, it has been observed that in
comparison between the case of circuit breaker operation and
disconnector switch operation, a distinct pattern of variation of
VFTO peak along the nodes occur. The increase in the trapped
charge on load side of the disconnector, causes augmentation
155
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S. Rahmani et al. / Vol. 2(4), Jul. 2016, pp. 150-156
JICE DOI: 649123/220127
[12] D.A. Woodford, L.M. Wedepohl, “Impact of Circuit Breaker re-Strike
on Transmission Line Energization Transients”, IPST ’97, Seattle, pp.
250-253, June 22-26, 1997
[13] A. Ametani, T. Goto, S. Yoshizaki, H. Omura, H. Motoyama,
“Switching Surge Characteristics in GIS”,Universities Power
engineering Confrence,2006.UPEC’06.Proceedings of the 41st
International, vol.3, pp. 941-945, Sept. 2006.
[14] A. Ametani, K. Ohtsuki, N. Nagaoka, “Switching Surge Characteristics
in GIS in Particular Reference to Low-Voltage Control Circuits”, UPEC
2004,Bristol, UK,Sept.,2004.
[15] J. Martinez - Power Engineering Society Summer Meeting, “Statistics
Assesment of Very Fast Transient Overvoltages in Gas Insulated
Substations”, IEEE, vol.2,pp.882-883,2000
[16] V. V. Kumar, J. M. Thomas, M. S. Naidu, M. S. Naido, “VFTO
Computation in 420 kV GIS”, High Voltage Engineering, Eleventh
International Symposoum on (Conf. publ.no.467), vol.1,pp.319322,1999.
[17] Q. Li, M. Wu, “Simulation Method for the Application of Ferromagnetic
Materials in Suppressing High-Frequency transient whithin GIS”, IEEE
Transaction on Power Delivery,vol.22,no.3.July 2007
[18] J. A. Martinez, P. Chowdhuri, R. Irvani, A. Keri, D. Povh,“ Modeling
Guidelines for Very Fast Transient in GIS” Report prepared by the very
fast transient task force of the IEEE Working Group on Modeling and
Analysis of System Transients
[19] U. Riechert, “Very Fast Transient Overvoltages during switching of
Bus-Charging Currents by 1100 kV Disconnectors”, GIGRE 2010
A3_107-2010
[20] S. Yanabu, H. Murase, H. Aoyagi, “ Estimation of Fast Transient
Overvoltages in Gas Insulated Substation”, IEEE Trans. Power
Delivery, vol.5, no.4, Nov 1990
[21] S. Matsumura, T. Nitta, “ Surge Propagation in Gas Insulated
Substation”, IEEE Trans. Power Apparayus and Systems, PAS-100,
no.6 June 1981
[22] S. A. Boggs,”The Modelling of Statistical Operating Parameters and
Computation of Operation-Induced Surge Waveforms for GIS
Disconnectors”, Cigre.1984, Paper 13-15
[23] J. F. Lima Filho, “Tucurui’s 500 kV SF6 Gas-Insulated Substation Fast
Transients-Analysis,Modeling and Field
Test Comparisons”,
International Confrence on Power System Transients,2001
[24] P. Rohrbach, M. Lacorte, J. C. Mendes, “550 kV GIS VFT Simulations
as a Support for Transformer Design”, International Conference on
Power System Transient, 2001
[25] M. M. Rao, H. S. Jain, S. Rengarajan, V. V. Kumar “Estimation and
Measurement of Very Fast Transient Overvoltages(VFTO) in Gas
Insulated Substation(GIS)”,M.Sc.(Engg.) thesis, Indian Institute of
Science,Bangalore,1999.
[26] IEEE Fast Front Transient Working Group , “Modeling Guideling for
Fast Transients”, IEEE Trans on power Delivery, Vol 11, No 1, January
1996,p 493-506
[27] IEEE Fast Front Transient Working Group , “Modeling Guidleing for
Very Fast Front Transient in GIS”
[28] J. V. G. R. Rao, J. Amarnath, S. Kamakshaiah, “Simulation and
measurement of very fast transient over voltages in a 245kv GIS and
research on suppressing method using ferrite rings” ARPN Journal of
Engineering and Applied Sciences, vol. 5, no. 5, pp.88-95, May 2010.
[29] P. R. Reddy, J. Amarnath. “Nanocrystalline To Suppress VFTO And
VFTC For 245Kv Gas Insulated Substation”. International Journal of
Computer Applications 70.13 (2013): 1-6. Web
[30] S. Burow, U. Riechert, W. Köhler, S. Tenbohlen. (2013). “New
mitigation methods for transient overvoltages in gas insulated
substations”
[31] J. V. G. rama Rao , J. Amarnath , S. Kamakshiah 'Time-Frequency Of
Very Fast Transient Over Voltages For Effective of control Circuits in a
245kV
Gas
Insulated
Substation.
2010
IEEE
in the VFTO magnitudes, but this increment is not
proportional to the trapped charge increase. The results show
that the VFTO levels are reduced with all methods. Hardness
with the damping resistor is its heat losses during the
operation and maintenance issues. Better suppression results
acquired by using ferrite rings and furthermore this method
overwhelmed the disadvantages of damping resistor.
However, the malfunction of the ferrite rings is saturation
difficulties. The ferrite rings are easily got into saturation
under operating conditions. It was pointed that, by layering of
ferrite rings increasing the magnetic field strength is
applicable. But on the other hand layering of rings with a
material of lower permeability also reduces the effective
permeability. Therefore, the damping efficiency of the whole
ring arrangement reduces. Consequently, the damping effect
of ferrite rings inside the GIS for HV applications is limited.
Further investigations have been made to suppress the VFTO
in GIS using Nanocrystalline material which is proved that can
provide better solution. The per unit data of VFTO without
mitigation techniques and with different types of mitigation
techniques are tabulated in Table. II.
REFERENCES
[1]
Gigre Working Group33/13-09, “Very Fast Transient Phenomena
Associated with Gas Insulated Substations”, GIGRE paper no.3313,1988
[2] S. A. Boggs, F. Y. Chu, N. Fujimoto, “Disconnect Switch Induced
Transient and Trapped charge in Gas Insulated Substations” IEEE
Trans. on Power Apparatus and System, vol 101, no. 6, pp. 3593-3602,
Octobr 1982
[3] S. Carsimamovic, Z. Bajramovic, M. Ljevak, M. Veledar “Very Fast
Electromagnetic Transient in Air Insulated Substations and Gas
Insulated Substations due to a Disconnector switching”, International
Symposium on electromagnetic. EMC 2005, vol. 2, pp.382-387, 8-12
[4] S. Fujita, N. Hosokawa, Y. Shibyiya, “Experimental Investigation of
High Frenquency Voltage Oscillation in Transformer Winding”, IEEE
Transaction on Power Delivery ,vol. 13, no 4, Octobr 1998, pages 12011207
[5] Z. Haznadar, S. Carsimamovic, R. Mahmutcahajic, “More Accurate
Modeling of Gas Insulated Sucstation Components in Digitall
Simulation of Very Fast Electromagnetic Transient”, IEEE Trans. on
power Delivery, vol. 7, no. 1, pp. 434-441, Jan.,1992
[6] EPRI, Electromagnetic Transient Program(EMTP) Workbook 2, EPRI
Final Report, EL-4651, vol. 2, June. 1986
[7] V. V. Kumar, J.M. Thomas, M. S. Maidu, “Influence of Switching
Condoitions on the VFTO Magnitudes in GIS”, IEEE Trans. on Power
Delivery, vol. 16, no. 4, pp. 539-544, Oct. 2001
[8] L Tiechen, Z Bo, “Calculation of Very Fast Transient Overvoltages in
GIS”, 2005 IEEE/PES Transmission and Distribution Confrence &
Exhibition: Asia and Pacific Dalian, China, pp. 1-5, 2005.
[9] X. Dong, S. Rosado, Y. Liu, N. C. Wang, E. L. Line, T. Y. Guo, “Study
of Abnormal Electrical Phenomena Effects on GSU Transformers”,
IEEE Trans. on Power Delivery, vol.18, no.3, pp 835-842
[10] IEEE WOrking Group 15.08.09,Tutorial on Modeling and Analysis of
System Transient using Digital Programs, IEEE PES Special
Publication, 1998
[11] D.A. Woodford, L.M. Wedepohl, “Transmission Line Energization with
Breaker Pre-Strike”. 1997 Confrence on Communications,Power
andComputing WESCANEX’97 Proceedings, pp. 105-108, May 2223,1997.
156
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