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  1. 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 thereceived great interest in the recent years. One of inner surface of the enclosure. The origin of thesethe advantages of GIS over conventional substations particles may be from the manufacturing process, fromis their compactness which makes them a favourite mechanical vibrations or from moving parts of thefor 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. GISenclosure filled with sulphur hexafluoride (SF6) gas. also suffer from certain drawbacks. One of them isThe voltage withstands capability of SF6 bus duct is outage due to conducting particles which accounts orstrongly dependent on field perturbations such as nearly 50% of GIS failures. The particles can be liftedthose caused by conductor surface imperfections by the electric field and migrate to the conductor orand by conducting particle contaminants. These insulators where they initiate breakdown at voltagesacquire charge due to the electric field intensity. significantly below the insulation characteristics. TheseNearly 50% of GIS failures are due to metallic particles move randomly in a horizontally mounted Gasconducting particles lifted by electric field and Insulated Bus duct (GIB) system due to the electricmigrate to conductor or insulator initiating field, and this movement plays a crucial role inbreakdown at voltages significantly below the determining the behaviour of GIS [2]. Under 50 Hz ACinsulation characteristics. This paper analyses the voltages, the particle motion is complex, and underelectric field intensity for different dimensional appropriate conditions, the particle may cross theconductor and enclosures at various applied gaseous gap from the low field region near the outervoltages in a three phase Gas Insulated Bus duct. enclosure to the high field region near the centralElectric field intensity decreases with increase in electrode. In order to know behaviour of particlesdiameter of enclosure. analysis of the electric field intensity was made for different dimensional conductors, enclosures at variousKeywords - Bus duct, Image charge, Field applied voltages.intensity. 2. GIB MODELLING TECHNIQUE1. INTRODUCTION The Fig.1 shows the cross sectional view of The Electric power industry worldwide has typical horizontal three phase bus duct. The enclosuresome 35 years of manufacturing and field experience is filled with SF6 gas at high pressure. A particle iswith 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 sufficientcompactness, reliable and maintenance free operations. enough to lift the particle and move it in the direction ofBasic components of GIS bay are circuit breakers, field is applied. After acquiring an appropriate chargedisconnectors, earthing switches, bus ducts, current and in the field, the particle lifts and begins to move in thevoltage transformers etc. The inner live parts of GIS are direction of field having overcome the forces due to itssupported 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 thefilled with sulphur hexafluoride (SF6) gas. It has particle charge-to-mass ratio at lifting increases withexcellent dielectric and heat transfer properties. Sulphur length.Hexafluoride (SF6) gas is the electric power industry’spreferred gas or electric insulation and especially forarc quenching current interruption equipment used intransmission and distribution of electrical energy. Theusefulness of SF6 gas is mainly due to its high dielectricstrength, good thermal stability, economically inert,non-flammable, non-corrosive and non-toxic. Eventhough SF6 exhibits very high dielectric strength, thewithstand voltage of SF6 within GIS is drastically 1756 | P a g e
  2. 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 fieldwill be subjected to a collective influence of several R1forces. These forces may be divided into electrostatic q1 R 1force (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 invertical direction, g = gravitational constant. E2 g2 E3 q2Here,(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 ) 2Electric 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) 1757 | P a g e
  3. 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 isolatedE  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  1E 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 threeV1 = Vm sint, V2 = Vm Sin (t+120º), and phase common enclosure Gas Insulated Busduct with Monte Carlo Technique”, ARPNV3 = 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 forfield intensity at different level of voltages and for different values of diameter of enclosure (D) anddifferent dimension of enclosure and conductor. The diameter of conductor (d) for Vm 300KV, 400 KV, 600distance between the conductor is taken as K=215mm. KV, 800 KV and 1000KV .Table 1 shows the variation of field intensity fordifferent values of dimeter of enclosure and diameter of Vm=300KVconductor at various values of maximum voltages and K=215mm,x=1mm K=215mm,x=1mmfixed values of x=1mm.as shown in figure 2. A h=1mm,d=100mm h=125mmconducting 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-034. CONCLUSION 500 1.65E-03 30 1.49E-03 An attempt has been made to simulate the 600 1.49E-03 40 1.66E-03electric field intensity in a 3-phase isolated GIB on bare 700 1.39E-03 50 1.82E-03electrodes system considering the effect of field due to 800 1.31E-03 60 1.98E-03image charge.. It is seen that the field intensity is a 1000 1.20E-03 70 2.13E-03function of dimensions of enclosure and conductor. The 1500 1.06E-03 80 2.29E-03electric field intensity is in linear relation with diameter 2000 9.78E-04 90 2.45E-03of conductor and it decreases with an increase in thediameter of enclosure resulting in reduction of rate ofmotion 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/mREFERENCES (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 1758 | P a g e
  4. 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.1756-17160Vm=600KVK=215mm,x=1mm K=215mm,x=1mmh=1mm,d=100mm h=125mmD(mm) E(KV/mm) d(mm) E(KV/mm)300 5.48E-03 10 2.14E-03400 3.89E-03 20 2.61E-03500 3.31E-03 30 2.98E-03600 2.98E-03 40 3.32E-03700 2.77E-03 50 3.64E-03800 2.62E-03 60 3.95E-031000 2.41E-03 70 4.26E-031500 2.12E-03 80 4.58E-032000 1.96E-03 90 4.89E-03Vm=800KVK=215mm,x=1mm K=215mm,x=1mmh=1mm,d=100mm h=125mmD(mm) E(KV/mm) d E (mm) (KV/mm)300 7.31E-03 10 2.85E-03400 5.19E-03 20 3.47E-03500 4.41E-03 30 4.43E-03600 3.98E-03 40 4.00E0-3700 3.69E-03 50 4.86E-03800 3.49E-03 60 5.27E-031000 3.21E-03 70 5.69E-031500 2.82E-03 80 6.10E-032000 2.61E-03 90 6.52E-03Vm=1000KVK=215mm,x=1mm K=215mm,x=1mmh=1mm,d=100mm h=125mmD(mm) E(KV/mm) d E(KV/mm) (m m)300 9.14E-03 10 3.57E-03400 6.59E-03 20 4.34E-03500 5.5133E-03 30 4.96E-03600 4.97E-03 40 5.53E-03700 4.62E-03 50 6.07E-03800 4.36E-03 60 6.59E-031000 4.01E-03 70 7.11E-031500 3.53E-03 80 7.63E-032000 3.26E-03 90 8.15E-03 1759 | P a g e
  5. 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) anddiameter of conductor (d) 1760 | P a g e