This document analyzes the electric field intensity in a three-phase gas insulated bus duct. It finds that the electric field intensity decreases with increasing diameter of the enclosure and is affected by the dimensions of the conductors. A model is presented to simulate the electric field intensity considering effects such as image charges. Simulation results show that the field intensity is directly proportional to the diameter of the conductor and inversely proportional to the diameter of the enclosure. The field intensity values are reported for different enclosure diameters, conductor diameters, and applied voltages.

1. Nagbhushan, J. Amarnath, D. Subbarayudu / International Journal of Engineering Research
and Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 2, Issue 5, September- October 2012, pp.1756-17160
Analysis of Electric Field Intensity in Gas Insulated Busduct
Nagbhushan1, J. Amarnath2, D. Subbarayudu3
1Asst. Prof., PDA College of Engg, Gulbarga. Karnataka India.
2 Professor, Electrical Engg. Department,Jawaharlal Nehru Technological University, A.P. India.
3 Professor,Srinivasa College of Engineering and Technology, Kurnool, A..P. India.
ABSTRACT
Gas insulated substations (GIS) have reduced due to the presence of metallic particles on the
received great interest in the recent years. One of inner surface of the enclosure. The origin of these
the advantages of GIS over conventional substations particles may be from the manufacturing process, from
is their compactness which makes them a favourite mechanical vibrations or from moving parts of the
for service in urban residential areas. These consists system like breakers or disconnectors etc. Aluminium,
conductors supported on insulator inside on copper and silver are the types of metal particles. GIS
enclosure filled with sulphur hexafluoride (SF6) gas. also suffer from certain drawbacks. One of them is
The voltage withstands capability of SF6 bus duct is outage due to conducting particles which accounts or
strongly dependent on field perturbations such as nearly 50% of GIS failures. The particles can be lifted
those caused by conductor surface imperfections by the electric field and migrate to the conductor or
and by conducting particle contaminants. These insulators where they initiate breakdown at voltages
acquire charge due to the electric field intensity. significantly below the insulation characteristics. These
Nearly 50% of GIS failures are due to metallic particles move randomly in a horizontally mounted Gas
conducting particles lifted by electric field and Insulated Bus duct (GIB) system due to the electric
migrate to conductor or insulator initiating field, and this movement plays a crucial role in
breakdown at voltages significantly below the determining the behaviour of GIS [2]. Under 50 Hz AC
insulation characteristics. This paper analyses the voltages, the particle motion is complex, and under
electric field intensity for different dimensional appropriate conditions, the particle may cross the
conductor and enclosures at various applied gaseous gap from the low field region near the outer
voltages in a three phase Gas Insulated Bus duct. enclosure to the high field region near the central
Electric field intensity decreases with increase in electrode. In order to know behaviour of particles
diameter of enclosure. analysis of the electric field intensity was made for
different dimensional conductors, enclosures at various
Keywords - Bus duct, Image charge, Field applied voltages.
intensity.
2. GIB MODELLING TECHNIQUE
1. INTRODUCTION The Fig.1 shows the cross sectional view of
The Electric power industry worldwide has typical horizontal three phase bus duct. The enclosure
some 35 years of manufacturing and field experience is filled with SF6 gas at high pressure. A particle is
with Gas Insulated Substations (GIS). The advantages assumed to be at rest on the enclosure inner surface,
of GIS over conventional substations are their just beneath the bus bar until a voltage sufficient
compactness, reliable and maintenance free operations. enough to lift the particle and move it in the direction of
Basic components of GIS bay are circuit breakers, field is applied. After acquiring an appropriate charge
disconnectors, earthing switches, bus ducts, current and in the field, the particle lifts and begins to move in the
voltage transformers etc. The inner live parts of GIS are direction of field having overcome the forces due to its
supported by insulators called spacers, which are made own weight and drag due to the viscosity of the gas [3].
up of alumina filled epoxy material [1]. The GIS The particle motion largely depends on applied voltage.
enclosure forms an electrically integrated, ground Under AC voltages, for a wire particle of given radius,
enclosure for the entire substation. The enclosure is the activity increases with particle length since the
filled with sulphur hexafluoride (SF6) gas. It has particle charge-to-mass ratio at lifting increases with
excellent dielectric and heat transfer properties. Sulphur length.
Hexafluoride (SF6) gas is the electric power industry’s
preferred gas or electric insulation and especially for
arc quenching current interruption equipment used in
transmission and distribution of electrical energy. The
usefulness of SF6 gas is mainly due to its high dielectric
strength, good thermal stability, economically inert,
non-flammable, non-corrosive and non-toxic. Even
though SF6 exhibits very high dielectric strength, the
withstand voltage of SF6 within GIS is drastically
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2. Nagbhushan, J. Amarnath, D. Subbarayudu / International Journal of Engineering Research and
Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 2, Issue 5, September- October 2012, pp.1756-17160
Where y is velocity,  is viscosity, r is particle

radius. g is gas density, l is length of particle, K d ( y )

is drag coefficient.
2.1 Electric Field Intensity in 3-phase GIB (including
image
charges):
Fig.2 shows three phase GIB with image charge
conductors.
D
C B g1
F E
Fig.1 Three Phase Bus Duct k
A conducting particle motion is an electric field
will be subjected to a collective influence of several
R1
forces. These forces may be divided into electrostatic q1 R
1
force (Fe), gravitational force (mg) and drag force (Fd). R2
R2 A
The motion equation is given by 0
150
d2y
m 2  Fe  mg  Fd h
dt (1) P
Where m = mass of particle, y = displacement in
vertical direction, g = gravitational constant. E2 g2 E3
q2
Here,
(i) Fe  K .q.E (t )
E2 E3
(2)
D
K = Correction factor <1, and charge q is,
d
 0 l 2 E (t 0 )
q Fig.2 Three phase GIB with image charge conductors
 2l 
ln    l
 r  (3) Let the particle moves to a distance x from the inner
surface of the enclosure at point P, then from Fig. 2.
E (t 0 ) is ambient electric field at t=t0
From triangle PAB
Vm sin t R1  (h  x) 2  K 2  2(h  x) K . cos(150 0 )
2
Electric field E (t )  (7)
R  The electric field intensities for different
R0  y (t ) ln  0 
R  conductors A, B, C taking into account their image
 i (4) charge effect, are E1, E2 and E3 respectively [4,5].
Where R 0 are Enclosure radices and R i is  1 1 
V1  
h  x h  x  V/mm
 (8)
conductor radius. y(t) = position of particle which is E1 
 2h 
vertical distance from the surface of enclosure towards 2 ln  
inner electrode.  r 
mg  r 2 lg (5)
 c osq 2 Cosg 2 
where,   1.68 x10 for Cu.
8 V2   
E2   R1 R2  V/mm and (9)
 2h 
2 ln  
(iii) Fd = Drag force=  r 
y. .r[6K d ( y)  2.6560[ g .l. y]0.5
  
(6)
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3. Nagbhushan, J. Amarnath, D. Subbarayudu / International Journal of Engineering Research and
Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 2, Issue 5, September- October 2012, pp.1756-17160
 c osq 2 Cosg 2  excitations on the performance of Gas
V3    Insulated Substations with metallic particle
 R1 R2  V/mm. (10)
E3  contamination” World Journal of Modelling
 2h 
2 ln   and Simulation, Vol.4 (2008), No.4, pp. 305-
 r  311
[4] K.B. Madhusahu, J. Amarnath,
The total electric field intensity E at point P is K.S.Lingamurthy, B.P.Singh, “Simulation of
Particle Movement in a single phase isolated
E  E1  E 2  E3 (11) Gas Insulated Busduct with image charge
(12) effect”, 2008 International Conference on
  1 1   cosq 2 cosg 2   High Voltage Engineering and Applications,
V2  V3 
1
E V1    
 2h    h  x h  x   R1
 R2    Chongquing, China, November 9-13, 2008.
2 ln  
 r  [5] M. Venugopala Rao, J. Amarnath, S.
volts per mm, where, Kamakshaiah, “Particle Trajectories in a three
V1 = Vm sint, V2 = Vm Sin (t+120º), and phase common enclosure Gas Insulated
Busduct with Monte Carlo Technique”, ARPN
V3 = Vm sin (t+240º). Journal of Engineering and Applied Sciences,
Vol.3, No.6, December 2008.
3. RESULTS AND DISCUSSION.
Simulation has been carried out for electric Table 1 shows, the variation of Field intensity for
field intensity at different level of voltages and for different values of diameter of enclosure (D) and
different dimension of enclosure and conductor. The diameter of conductor (d) for Vm 300KV, 400 KV, 600
distance between the conductor is taken as K=215mm. KV, 800 KV and 1000KV .
Table 1 shows the variation of field intensity for
different values of dimeter of enclosure and diameter of Vm=300KV
conductor at various values of maximum voltages and K=215mm,x=1mm K=215mm,x=1mm
fixed values of x=1mm.as shown in figure 2. A h=1mm,d=100mm h=125mm
conducting particle moving in an external electric field D E(KV/mm d E(KV/mm)
will be subjected to a collective influence of (mm) ) (mm)
electrostatic force, Gravitational force and Drag force 300 2.74E-03 10 1.07E-03
400 1.95E-03 20 1.30E-03
4. CONCLUSION 500 1.65E-03 30 1.49E-03
An attempt has been made to simulate the 600 1.49E-03 40 1.66E-03
electric field intensity in a 3-phase isolated GIB on bare 700 1.39E-03 50 1.82E-03
electrodes system considering the effect of field due to 800 1.31E-03 60 1.98E-03
image charge.. It is seen that the field intensity is a
1000 1.20E-03 70 2.13E-03
function of dimensions of enclosure and conductor. The
1500 1.06E-03 80 2.29E-03
electric field intensity is in linear relation with diameter
2000 9.78E-04 90 2.45E-03
of conductor and it decreases with an increase in the
diameter of enclosure resulting in reduction of rate of
motion of particle. Vm=400KV
K=215mm,x=1mm K=215mm,x=1mm
h=1mm,d=100mm h=125mm
D E(KV/mm) d E(KV/m
REFERENCES (mm) (mm) m)
[1] M. Ramya Priya, G.V. Nageshkumar, J. 300 3.66E-03 10 1.43E-03
Amarnath, R. Prabhadevi, “Effect of various 400 2.60E-03 20 1.99E-03
design parameters of Gas Insulated Busduct in 500 2.21E-03 30 1.99E-03
the performance of Gas Insulated Substations”, 600 1.99E-03 40 2.21E-03
International Conference on Control, 700 1.85E-03 50 2.43E-03
Automation, Communication and Energy 800 1.75E-03 60 2.64E-03
Conservation, 4th-6th June 2009.
1000 1.75E-03 70 2.84E-03
[2] G.V. Nageshkumar, J. Amarnath, B.P. Singh,
1500 1.41E-03 80 3.05E-03
K.D. Srivastava, “Electric Field Effect on
metallic particle contamination in a common 2000 1.41E-03 90 3.26E-03
enclosure Gas Insulated Busduct”, IEEE
Transactions on dielectrics and Electrical
insulation, Vol. 14, No.2, April 2007.
[3] M. Venugopal Rao, G.V. Nageshkumar, J.
Amarnath, S. Kamakshaiah, “Effect of various
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4. Nagbhushan, J. Amarnath, D. Subbarayudu / International Journal of Engineering Research and
Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 2, Issue 5, September- October 2012, pp.1756-17160
Vm=600KV
K=215mm,x=1mm K=215mm,x=1mm
h=1mm,d=100mm h=125mm
D(mm) E(KV/mm) d(mm) E(KV/mm)
300 5.48E-03 10 2.14E-03
400 3.89E-03 20 2.61E-03
500 3.31E-03 30 2.98E-03
600 2.98E-03 40 3.32E-03
700 2.77E-03 50 3.64E-03
800 2.62E-03 60 3.95E-03
1000 2.41E-03 70 4.26E-03
1500 2.12E-03 80 4.58E-03
2000 1.96E-03 90 4.89E-03
Vm=800KV
K=215mm,x=1mm K=215mm,x=1mm
h=1mm,d=100mm h=125mm
D(mm) E(KV/mm) d E
(mm) (KV/mm)
300 7.31E-03 10 2.85E-03
400 5.19E-03 20 3.47E-03
500 4.41E-03 30 4.43E-03
600 3.98E-03 40 4.00E0-3
700 3.69E-03 50 4.86E-03
800 3.49E-03 60 5.27E-03
1000 3.21E-03 70 5.69E-03
1500 2.82E-03 80 6.10E-03
2000 2.61E-03 90 6.52E-03
Vm=1000KV
K=215mm,x=1mm K=215mm,x=1mm
h=1mm,d=100mm h=125mm
D(mm) E(KV/mm) d E(KV/mm)
(m
m)
300 9.14E-03 10 3.57E-03
400 6.59E-03 20 4.34E-03
500 5.5133E-03 30 4.96E-03
600 4.97E-03 40 5.53E-03
700 4.62E-03 50 6.07E-03
800 4.36E-03 60 6.59E-03
1000 4.01E-03 70 7.11E-03
1500 3.53E-03 80 7.63E-03
2000 3.26E-03 90 8.15E-03
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5. Nagbhushan, J. Amarnath, D. Subbarayudu / International Journal of Engineering Research
and Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 2, Issue 5, September- October 2012, pp.1756-17160
(a) (b)
(d) (c)
(f) (e)
(h) (g)
Fig 3. (a) to (h) Shows, the variation of Field intensity for different values of diameter of enclosure (D) and
diameter of conductor (d)
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