Gas insulated substations (GIS) have received great interest in the recent years. One of the advantages of GIS over conventional substations is their compactness which makes them a favourite for service in urban residential areas. These consists conductors supported on insulator inside on enclosure filled with sulphur hexafluoride (SF6) gas. The voltage withstands capability of SF6 bus duct is strongly dependent on field perturbations such as those caused by conductor surface imperfections and by conducting particle contaminants. These acquire charge due to the electric field intensity. Nearly 50 % of GIS failures are due to metallic conducting particles lifted by electric field and migrate to conductor or insulator initiating breakdown at voltages significantly below the insulation characteristics. This paper analyses the electric field intensity for different dimensional conductor and enclosures at various applied voltages in a three phase Gas Insulated Bus duct. Electric field intensity decreases with increase in diameter of enclosure

D. Subbarayudu

J. Amarnath

CiteSeerX

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 
1756 | P a g e  
Analysis of Electric Field Intensity in Gas Insulated Busduct 
 
Nagbhushan
1, J. Amarnath
2, D. Subbarayudu
3 
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 
received  great  interest  in  the  recent  years.  One  of 
the advantages of GIS over conventional substations 
is their compactness which makes them a favourite 
for service in urban residential areas. These consists 
conductors  supported  on  insulator  inside  on 
enclosure filled with sulphur hexafluoride (SF6) gas.  
The voltage withstands capability of SF6 bus duct is 
strongly  dependent  on  field  perturbations  such  as 
those  caused  by  conductor  surface  imperfections 
and  by  conducting  particle  contaminants.    These 
acquire  charge  due  to  the  electric  field  intensity. 
Nearly  50%  of  GIS  failures  are  due  to  metallic 
conducting  particles  lifted  by  electric  field  and 
migrate  to  conductor  or  insulator  initiating 
breakdown  at  voltages  significantly  below  the 
insulation characteristics.  This paper analyses the 
electric  field  intensity  for  different  dimensional 
conductor  and  enclosures  at  various  applied 
voltages  in  a  three  phase  Gas  Insulated  Bus  duct.  
Electric  field  intensity  decreases  with  increase  in 
diameter of enclosure. 
 
Keywords  -    Bus  duct,  Image  charge,  Field 
intensity. 
 
1. INTRODUCTION 
The  Electric  power  industry  worldwide  has 
some 35  years of manufacturing and field experience 
with Gas Insulated Substations (GIS). The advantages 
of  GIS  over  conventional  substations  are  their 
compactness, reliable and maintenance free operations. 
Basic  components  of  GIS  bay  are  circuit  breakers, 
disconnectors, earthing switches, bus ducts, current and 
voltage transformers etc. The inner live parts of GIS are 
supported by insulators called spacers, which are made 
up  of  alumina  filled  epoxy  material  [1].  The  GIS 
enclosure  forms  an  electrically  integrated,  ground 
enclosure  for  the  entire  substation.  The  enclosure  is 
filled  with  sulphur  hexafluoride  (SF6)  gas.  It  has 
excellent dielectric and heat transfer properties. Sulphur 
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  
 
reduced due to the presence of metallic particles on the 
inner  surface  of  the  enclosure.    The  origin  of  these 
particles may be from the manufacturing process, from 
mechanical  vibrations  or  from  moving  parts  of  the 
system like breakers or disconnectors etc.  Aluminium, 
copper and silver are the types of metal particles. GIS 
also  suffer  from  certain  drawbacks.    One  of  them  is 
outage due to conducting particles which accounts or 
nearly 50% of GIS failures.  The particles can be lifted 
by  the  electric  field  and  migrate  to  the  conductor  or 
insulators  where  they  initiate  breakdown  at  voltages 
significantly below the insulation characteristics.  These 
particles move randomly in a horizontally mounted Gas 
Insulated  Bus  duct  (GIB)  system  due  to  the  electric 
field,  and  this  movement  plays  a  crucial  role  in 
determining the behaviour of GIS [2].  Under 50 Hz AC 
voltages,  the  particle  motion  is  complex,  and  under 
appropriate  conditions,  the  particle  may  cross  the 
gaseous gap from the low field region near the outer 
enclosure  to  the  high  field  region  near  the  central 
electrode.    In  order  to  know  behaviour  of  particles 
analysis  of  the  electric  field  intensity  was  made  for 
different dimensional conductors, enclosures at various 
applied voltages. 
 
2. GIB MODELLING TECHNIQUE 
The  Fig.1  shows  the  cross  sectional  view  of 
typical horizontal three phase bus duct.  The enclosure 
is filled with SF6 gas at high pressure.  A particle is 
assumed to  be  at rest  on  the  enclosure inner  surface, 
just  beneath  the  bus  bar  until  a  voltage  sufficient 
enough to lift the particle and move it in the direction of 
field is applied.  After acquiring an appropriate charge 
in the field, the particle lifts and begins to move in the 
direction of field having overcome the forces due to its 
own weight and drag due to the viscosity of the gas [3]. 
The particle motion largely depends on applied voltage. 
Under AC voltages, for a wire particle of given radius, 
the  activity  increases  with  particle  length  since  the 
particle  charge-to-mass  ratio  at  lifting  increases  with 
length. 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 
1757 | P a g e  
 
Fig.1 Three Phase Bus Duct 
  A conducting particle motion is an electric field 
will  be  subjected  to  a  collective  influence  of  several 
forces.  These forces may be divided into electrostatic 
force (Fe), gravitational force (mg) and drag force (Fd).  
 
The motion equation is given by  
d e F mg F
dt
y d
m   
2
2
                                    (1)
 
Where m = mass of particle, y = displacement in 
vertical direction, g = gravitational constant. 
 
Here, 
(i)  ) ( . . t E q K Fe 
   
 
                                                     (2) 
K  = Correction factor <1, and charge  q is, 
l
r
l
t E l
q
 






2
ln
) ( 0
2
0 
                                             (3)
 
) ( 0 t E  is ambient electric field at t=t0 
 
Electric field
 


 




i
m
R
R
t y R
t V
t E
0
0 ln ) (
sin
) (

             (4)
 
 
Where  0 R  are  Enclosure  radices  and  i R is 
conductor radius.  y(t) = position of particle which is 
vertical distance from the surface of enclosure towards 
inner electrode. 
g l r mg  
2                (5) 
where, 
8 10 68 . 1
  x  for Cu. 
 
(iii)  d F = Drag force=  
5 . 0 ] . . [ 6560 . 2 ) ( 6 [ . . y l y K r y g d             
                                                                              (6) 
 
           Where  y   is velocity,  is viscosity, r is particle 
radius.  g is gas density, l is length of particle,  d K ( y  ) 
is drag coefficient.  
2.1 Electric  Field  Intensity  in  3-phase  GIB  (including 
image  
      charges):  
 
Fig.2  shows  t hree  phase  GIB  with  image  charge 
conductors. 
A
B C
F E
R
R
R
R
k
h
P
E E
E E
D
D
1 50
q
g
g1
q
d
1
1
2
2
1
0
2 2
2
3
2
3
 
Fig.2 Three phase GIB with image charge conductors 
 
Let  the  particle  moves  to  a  distance  x  from  the  inner 
surface of the enclosure at point P, then from Fig. 2.  
 
From triangle PAB 
) 150 cos( . ) ( 2 ) (
0 2 2 2
1 K x h K x h R     
 
         (7) 
The  electric  field  intensities  for  different 
conductors  A,  B,  C  taking  i nto  account  their  image 
charge effect, are E1, E2 and E3 respectively [4,5].  
 






 

 



 
r
h
x h x h
V
E
2
ln 2
1 1
1
1
 V/mm                  (8) 
                                                                                                  














r
h
R
Cos
R
V
E
2
ln 2
cos
2
2
1
2
2
2
g q
 V/mm and         (9) 
 
 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 
1758 | P a g e  














r
h
R
Cos
R
V
E
2
ln 2
cos
2
2
1
2
3
3
g q
 
V/mm.          (10) 
 
The total electric field intensity E at point P is  
 
3 2 1 E E E E                                                        (11) 
 





  


 


  














 3 2
2
2
1
2
1
cos cos 1 1
2
ln 2
1
V V
R R x h x h
V
r
h
E
g q
    (12)                                                       
volts per mm, where, 
1 V = Vmsint,  2 V =VmSin (t+120º), and  
  3 V = Vmsin (t+240º). 
 
3. RESULTS AND DISCUSSION. 
Simulation  has  been  carried  out  for  electric 
field  intensity  at  different  level  of  voltages  and  for 
different dimension of enclosure and conductor.  The 
distance between the conductor is taken as K=215mm. 
Table  1  shows    the  variation  of  field  intensity  for 
different values of dimeter of enclosure and diameter of 
conductor  at various values of maximum voltages and 
fixed  values  of    x=1mm.as  shown  in  figure  2.  A 
conducting particle moving in an external electric field 
will  be  subjected  to  a  collective  influence  of 
electrostatic force, Gravitational force and Drag force 
 
4. CONCLUSION 
An  attempt  has  been  made  to  simulate  the 
electric field intensity in a 3-phase isolated GIB on bare 
electrodes system considering the effect of field due to 
image  charge..  It  is  seen  that  the  field  intensity  is  a 
function of dimensions of enclosure and conductor. The 
electric field intensity is in linear relation with diameter 
of conductor and it decreases with an increase in the 
diameter of enclosure resulting in reduction of rate of 
motion of particle.   
 
 
 
REFERENCES 
[1]  M.  Ramya  Priya,  G.V.  Nageshkumar,  J. 
Amarnath,  R.  Prabhadevi,  “Effect  of  various 
design parameters of Gas Insulated Busduct in 
the performance of Gas Insulated Substations”, 
International  Conference  on  Control, 
Automation,  Communication  and  Energy 
Conservation, 4
th-6
th June 2009. 
[2]  G.V. Nageshkumar, J. Amarnath, B.P. Singh, 
K.D.  Srivastava,  “Electric  Field  Effect  on 
metallic  particle  contamination  in  a  common 
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 
excitations  on  the  performance  of  Gas 
Insulated  Substations  with  metallic  particle 
contamination”  World  Journal  of  Modelling 
and Simulation, Vol.4 (2008), No.4, pp. 305-
311 
[4]  K.B.  Madhusahu,  J.  Amarnath, 
K.S.Lingamurthy,  B.P.Singh,  “Simulation  of 
Particle Movement in a single phase isolated 
Gas  Insulated  Busduct  with  image  charge 
effect”,  2008  International  Conference  on 
High  Voltage  Engineering  and  Applications, 
Chongquing, China, November 9-13, 2008. 
[5]  M.  Venugopala  Rao,  J.  Amarnath,  S. 
Kamakshaiah, “Particle Trajectories in a three 
phase  common  enclosure  Gas  Insulated 
Busduct with Monte Carlo Technique”, ARPN 
Journal of Engineering and Applied Sciences, 
Vol.3, No.6, December 2008. 
 
Table  1  shows,  the  variation  of  Field  intensity  for 
different  values  of  diameter  of  enclosure  (D)  and 
diameter of conductor (d) for Vm 300KV, 400 KV, 600 
KV, 800 KV and 1000KV . 
 
 
 
 
 
 
 
Vm=300KV 
K=215mm,x=1mm 
h=1mm,d=100mm 
K=215mm,x=1mm 
h=125mm 
D 
(mm) 
E(KV/mm
) 
d 
(mm) 
E(KV/mm) 
300  2.74E-03  10  1.07E-03 
400  1.95E-03  20  1.30E-03 
500  1.65E-03  30  1.49E-03 
600  1.49E-03  40  1.66E-03 
700  1.39E-03  50  1.82E-03 
800  1.31E-03  60  1.98E-03 
1000  1.20E-03  70  2.13E-03 
1500  1.06E-03  80  2.29E-03 
2000  9.78E-04  90  2.45E-03 
Vm=400KV 
K=215mm,x=1mm 
h=1mm,d=100mm 
K=215mm,x=1mm 
h=125mm 
D 
(mm) 
E(KV/mm)  d 
(mm) 
E(KV/m
m) 
300  3.66E-03  10  1.43E-03 
400  2.60E-03  20  1.99E-03 
500  2.21E-03  30  1.99E-03 
600  1.99E-03  40  2.21E-03 
700  1.85E-03  50  2.43E-03 
800  1.75E-03  60  2.64E-03 
1000  1.75E-03  70  2.84E-03 
1500  1.41E-03  80  3.05E-03 
2000  1.41E-03  90  3.26E-03 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 
1759 | P a g e  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Vm=600KV 
K=215mm,x=1mm 
h=1mm,d=100mm 
K=215mm,x=1mm 
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 
h=1mm,d=100mm 
K=215mm,x=1mm 
h=125mm 
D(mm)  E(KV/mm)  d 
(mm) 
E 
(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 
h=1mm,d=100mm 
K=215mm,x=1mm 
h=125mm 
D(mm)  E(KV/mm)  d 
(m
m) 
E(KV/mm) 
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 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 
1760 | P a g e  
 
 
                                                                                                                                     
 
 
 
 
 
 
 
 
 
(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) 

Analysis of Electric Field Intensity in Gas Insulated Busduct

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Analysis of Electric Field Intensity in Gas Insulated Busduct

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