Analysis of transient enclosure voltages in gis (emtp simulation studies)

IJRET: International Journal of Research in Engineering and Technology ISSN: 2319-1163
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Volume: 02 Issue: 02 | Feb-2013, Available @ http://www.ijret.org 120
ANALYSIS OF TRANSIENT ENCLOSURE VOLTAGES IN GIS (EMTP
SIMULATION STUDIES)
Kriti Chandrakar1
, R.S. Gorayan2
1
M.Tech Student, 2
Professor, Electrical Department, IIT BHU (Varanasi), Uttar Pradesh, India,
kriti.chandrakar@gmail.com, rsgorayan.eee@itbhu.ac.in
Abstract
Transient Enclosure voltage is special case of very fast transient overvoltages which occurs due to disconnect switch operation or
earth ground. Transient Enclosure Voltage appears on external of earthed enclosure of Gas Insulated Systems. Despite of proper
grounding, this phenomenon indicates presence of high potentials on Gas Insulted System enclosures so the grounding system
impedance is thoroughly examined and designed. In this study EMTP Software is used for analysis. Simulation was done by varying
the different parameters. Variations of waveforms of the Transient Enclosure Voltage with various parameters have been studied.
Index Terms: Transient Enclosure Voltage (TEV), Gas Insulated System (GIS), Very Fast Transient Overvoltages
(VFTO) Transient Ground Potential Rise (TGPR), Disconnector Switch
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1. INTRODUCTION
Gas Insulated Substations (GIS) have found a broad range of
applications in power systems over the last three decades
because of their high reliability, easy maintenance, less ground
space requirements etc. Although GIS have been in operation
for several years, some of the problems are of more attention.
These problems include generation of Very Fast Transient
Overvoltages (VFTO) during switching operations or by earth
faults.
During switching operations or earth faults in a GIS, very fast
transients occur and stress the equipment, adjacent equipment,
air insulated switchgear (AIS) and secondary equipment. The
VFTO’s at their origin in a GIS are characterized by a steep
front having 4-7 nanoseconds rise time followed by a mono-
frequent oscillation of some MHz [1].
Transient Enclosure Voltage (TEV), also known as Transient
Ground Potential Rise (TGPR) is special case of VFTO. This
phenomenon refer to short rise time, short duration high
voltage transients which appears on external of earthed
enclosure of the GIS through the coupling of initial transients
to the enclosure at enclosure discontinuities[2]. Disconnect
switch operations or breakdown during acceptance testing of
GIS are causes of TEV. Observation of sparking between
grounded enclosures and support structures, failures of
protective devices, inadvertent operation of relays etc. are
common manifestations of TEV. Despite of proper grounding,
this phenomenon indicates presence of high potentials on GIS
enclosures, which raises the issue of equipment protection
migration of these transients to adjacent equipment and of
shock hazard. Shocks ranging from a tingling sensation to that
good belt have been reported [3].
2. SIMULATION MODEL
Transient Enclosure Overvoltages in GIS due to Disconnect
Switch operation was studied for circuit shown in Fig.-1. In
this case an unloaded 66-meter long section of GIS is
disconnected from an overhead line having surge impedance
of 320Ω of length 10 Km. The GIS bushing is represented by
a capacitance of C = 500pF. The surge impedance of GIS
cable is 75Ω. A voltage source of 450 kV
[Vs=Vmcos(ωt+ф)]was connected to overhead line [4].
Fig -1: Circuit used to calculated TEV waveforms
Disconnect switch operation causes presence of high
potentials on GIS enclosures. Due to this flashover the
potential of the enclosure rises from zero (ground potential) to
a very large value for a short duration which is known as TEV,
even though the enclosure is properly grounded using ground
wire and grids. The grounding system impedance should the

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thoroughly examined and designed. As seen from Fig-2 the
total ground impedance is the sum of impedance of grounding
strip and grounding grid.
Fig -2: GIS circuit with Grounding System.
2.1 Grounding Grid Resistance Calculation
The resistance of grounding grid having overall area A is
divided into N number of meshes each having same subarea
A and side’s l buried in homogeneous soil having
resistivity ρ as shown in Fig.3 is given by formula:[5]
Fig -3: Grounding Grid
2.2 Grounding Strip Resistance Calculation
The resistance of a rectangular grounding strip made of copper
having length of l meters, width of w meters and thickness of t
meters is given by the formula:
2.3 Grounding Strip Inductance
The inductance of a rectangular grounding strip with sides of
B and C centi-meters is given by the formula:[6]
3. EFFECTS OF GROUNDING PARAMETERS ON
TEV
3.1 By varying the soil resistivity (ρ)
ρ=50 ohm-meter
Fig -4: TEV Waveform with ρ =50 ohm-meter
ρ=100 ohm-meter
Fig -5: TEV Waveform with ρ=100 ohm-meter

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Table -1: Effects on TEV by varying soil resistivity.
From above waveforms and table it is observe that the peak
value of TEV is minimum for soil resistivity ρ=200 ohm-
meter.
3.2 By varying the depth of grid (h)
h = 0.5meter
Fig -6: TEV Waveform with h=0.5meter
h = 1 meter
Fig -7: TEV Waveform with h=1meter
Table -2: Effects on TEV by varying depth of grid.
value of TEV is minimum for grid depth d=0.5 meter.
3.3 By varying number of meshes (N)
N = 1
Fig -8: TEV Waveform with N=1.
N = 9
Fig -9: TEV Waveform with N=9.
Soil
Resistivity
(ohm-meter)
Grid Resistance
(ohms)
Peak Value of
TEV(kV)
50 7.88264 495.840
75 11.8239 494.328
100 15.7653 490.930
150 23.6479 486.135
200 31.5305 481.432
Depth of Grid
(h) (meter)
Grid Resistance
(ohms)
Peak Value of
TEV (kV)
0.5 11.123 493.799
1 7.8826 495.840
1.5 4.64225 509.299
2 1.40186 502.928

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Table -3: Effects on TEV by varying number of meshes.
value of TEV is minimum for single mesh grid i.e. N=1.
3.4 By varying conductor diameter (d)
d = 0.01 meter
Fig -10: TEV Waveform with d=0.01meter
d = 0.03 meter
Fig -11: TEV Waveform with d=0.03meter
Table -4: Effects on TEV by varying conductor diameter
value of TEV is minimum for conductor diameter
d=0.01meter.
3.5 By varying overall area of the grid (A)
A = 5meters x 5meters
Fig -12: TEV Waveform with A = 5meters x 5meters
A = 7meters x 7meters
Number of
Meshes (N)
Grid Resistance
(ohms)
Peak Value of
TEV(kV)
1 7.88264 495.840
4 4.7291 508.708
9 3.7964 498.395
16 3.3664 498.668
25 3.1243 504.721
Conductor Diameter
(d) (meter)
Grid Resistance
(ohm)
Peak Value Of
TEV (kV)
0.01 7.88264 495.840
0.02 7.0264 501.102
0.03 6.5256 504.265
0.04 6.1702 496.897
0.05 5.8946 498.460
0.06 5.6694 499.878
0.07 5.4789 501.087
0.08 5.3140 502.142
0.09 5.1685 503.078
0.10 5.038 503.923

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Fig -13: TEV Waveform with A = 7meters x 7meters
Table -5: Effects on TEV by varying overall area of grid
value of TEV is minimum for grid area A=5meters x 5meters.
3.6 By varying length of grounding strip (l)
l = 1 meter
Fig -14: TEV Waveform with l=1meter.
l = 2 meters
Fig -15: TEV Waveform with l=2meters.
Table -6: Effects on TEV by varying length of grounding rod
value of TEV is minimum for Grounding Rod Length l=1
meter.
CONCLUSIONS
EMTP simulation was carried out for GIS model. The various
parameters used in calculating the resistance of grounding
grid, resistance and inductance of grounding strip were varied
and Transient Enclosure Voltage waveforms generated were
studied for different cases. It has observed that:
1. As the soil resistivity increases the peak value of
TEV decreases and TEV is minimum for soil
resistivity ρ=200 ohm-meter.
2. As the depth of grid increases the peak value of TEV
increases and TEV is minimum for depth of grid h=
0.5 meter.
3. As the conductor diameter increases the peak value
of TEV firstly increases then decreases and then
again increases, and TEV is minimum for conductor
diameter d= 0.01 meter.
4. As the number of meshes of the grid increases the
peak value of TEV increases and TEV is minimum
for number of meshes N=1.
5. As the overall area of the grid increases the peak
value of TEV increases and TEV is minimum for
overall grid area A=5meters x 5meters.
Groundin
g Rod
Length
(l)
(meter)
Grounding
Rod
Resistance
(µΩ)
Grounding
Rod
Inductance
(µH)
Peak Value
of TEV
(kV)
1 0.688 0.7764 495.840
1.5 1.032 1.2862 500.511
2 1.376 1.6300 500.733
2.5 1.720 2.3992 502.289
3 2.064 2.6883 502.515
Overall Area Of Grid
(A) (square-meters)
Grid Resistance
(ohm
Peak Value Of
TEV (kV)
5x5 7.8826 495.840
7x7 7.3196 499.280
10x10 6.1655 496.900
15x15 4.8680 508.444

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6. As the length of grounding strip increases the peak
value of TEV decreases and TEV is minimum for
length l=1meter.
ACKNOWLEDGEMENTS
We would like to thank Prof. S. P. Singh, Head, Department
of Electrical Engineering, Indian Institute of Technology
(Banaras Hindu University), Varanasi for providing effective
management, necessary facilities and valuable suggestions for
success of this work.
REFERENCES:
[1].J. Meppelink, K. Diederich, K. Feser (SM), W. Pfaff,
“Very Fast Transients in GIS” IEEE Transactions on Power
Delivery, Vol. 4, No. 1, January 1989. PP125-131.
[2].Working Group 33/13-09(1988), 'Very Fast Transient
Phenomenon Associated with Gas Insulated Substations',
CIGRE
[3].N. Fujimoto, E.P. Dick, S.A. Boggs and G.L. Ford,
"Transient ground potential rise in gas-insulated substations -
Experimental studies", IEEE Trans. On Power Apparatus and
Systems, vol. 101, no. 6, pp.3603-3609, October 1982.
[4].Boggs SA., Chu F.Y. and Pujimotor N. (1982),
'Disconnect Switch Induced Transients and Trapped Charge in
GIS', EEE Trans. PAS, Vol. PAS-101, No. 10, PP3593-3601.
[5]. Y.L. Chow, M.M.A. Salama, “A Simplified Method for
Calculating the Substation Grounding Grid Resistance”, IEEE
Transactions on Power Delivery, Vol. 9, No. 2,pp736-742,
April 1994.
[6]. “Inductance Calculations” Working formula and Tables,
FREDERICK W. GROVER, 26TH Edition.
BIOGRAPHIES:
Obtained the Under Graduate degree
from Government Engineering College
Raipur, C.G. Presently doing Post
Graduation form Indian Institute of
Technology, BHU, Varanasi
Obtained the Under Graduate and
Masters degree from University
College of Engg. Burla, Sambalpur
University, Odissa, and Ph.D. from
Institute of Technology, BHU,
Varanasi. Presently, working as
Professor in IIT (BHU) Varanasi.

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Analysis of transient enclosure voltages in gis (emtp simulation studies)