ISSN: International Journal of Advanced Research in Computer Engineering & Technology Volume 1, Issue 3, May2012

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1 ISSN: International Journal of Avance esearch in Computer Engineering & Technology Volume, Issue 3, May Moeling an Simulation of Trajectories of a Wire Like Particle in a Three Phase Common Enclosure Gas Insulate Busuct (GIB) with an Without Image Charges M.Siva Sathyanarayana, J.Amarnath G.Pulla ey Engg College Kurnool, Anhra Praesh, Inia Jawaharlal Nehru Technological University, Hyeraba, Anhra Praesh, Inia Sathya_varma@eiffmail.com Abstract In recent years, SF6 gas insulate switchgear (GIS) has become more wiesprea in electrical power substations an GIS rate from 66 to kv are working successfully. The GIS is use in close vessels, isolate from the atmosphere. This gives it intrinsically high insulation reliability because there is no contact with irt or contaminates. To assure even better reliability, measures must be taken against metallic particle contamination. Some of these in use inclue changes in the manufacturing environment, moification of the structures, careful cleaning of the GIS both uring an after assembling, etc. Even at most measures are taken to eliminate particle contamination effect metallic particle contamination in a compresse Gas Insulate Busuct (GIB) system Is inevitable an may substantially lower the corona onset an breakown voltages of the system. The ranom movement of metallic particles in a GIB system plays a crucial role in etermining the insulation performance of the system. In this stuy a statistical approach has been use to evaluate the probability of SF6 insulation breakown ue to the presence of contaminating metallic particles. Uner 5-Hz AC voltage, the particle motion is complex, an uner appropriate conitions, the particle may cross the gaseous gap from the low-fiel region near the outer enclosure to the high-fiel region near the central conuctor. For the commonly encountere size of metallic particles in practical Gas Insulate systems, such a crossing of the gaseous gap takes several cycles of the 5-Hz voltage. In orer to etermine the particle trajectories in a three-phase common enclosure GIB) an outer enclosure of iameter 5 mm an inner conuctors of iameters 64 mm space equilaterally are consiere. Wire like particles of aluminum an copper has been consiere to be present on enclosure surface of a three-phase bus uct. A metho base on particle movement is propose to etermine the particle trajectory in GIS or GIB for a three phase common enclosure while the image charge effects of the conuctors are consiere. The motion of the wire particle was simulate using the charge acquire by the particles, the macroscopic fiel at the particle site, the rag coefficient, eynol s number an coefficient of restitution. The computation of particle movement has been carrie out on bare electroe system for ifferent voltages. The results have been presente an analyze. l ights eserve IJACET 33

2 ISSN: International Journal of Avance esearch in Computer Engineering & Technology Volume, Issue 3, May crossing voltage, at a given pressure. As the particle I. INTODUCTION It is well known that metallic particle contamination in a compresse Gas Insulate Busuct (GIB) system may lower the corona onset an breakown voltage of the system consierably Metallic particles move ranomly in a horizontally mounte GIB system ue to the electric fiel, an this movement plays a crucial role in etermining the insulation behavior of GITL systems. Uner 5 Hz ac voltage the particle motion is complex since the riving force acting on the particle perioically changes its irection an is not constant. After the particle is raius increases, the rag forces increase, thus raising the voltage necessary for the crossing. On the other han, as the net charge on the particle increases with the raius, the electrostatic riving force also increases, thus reucing the voltage necessary for the crossing. It is known that wire particles, uner a 5 Hz AC fiel, may remain in the mi-gap region in a GIB system for several cycles. They may be charge by one electroe at the maximum voltage uring one half-cycle, an return to the electroe at the peak voltage of opposite polarity, thus causing micro ischarges. elevate against gravity, the characteristic particle motion is epenent on the applie voltage level an particle parameters, i.e., shape, size an material. For the commonly encountere size of metallic particles in practical GIB systems, such a crossing of the gaseous gap takes several cycles of the 5 Hz voltage. The movement of spherical an wire particles has been investigate by the authors using a computational algorithm taking into account the effect of rag force on the particle motion in several horizontally mounte coaxial electroe systems. Uner an applie 5 Hz AC voltage a metallic particle's ability to cross the inter-electroe gap may be characterize by the minimum peak AC voltage necessary for the crossing. An iealize wire particle is shown in Fig.. The shape an physical imensions of a particle affect the minimum Fig. Basic wire like particle This presentation is focuse on the motion of elongate particles, since these particles are consiere the ones most frequently foun in GIS []. The aim of the work has been to learn more about the motion an thereby to suggest improvements to the moels that traitionally have been use. With a goo moel, a more accurate calculation of the motion of a particle an, in turn, a better estimation about its severity in a system can be mae. l ights eserve IJACET 34

3 ISSN: International Journal of Avance esearch in Computer Engineering & Technology Volume, Issue 3, May A metallic particle is lifte from a resting position on a groune electroe an kept in motion by the electrostatic force, which basically equals the prouct of the surrouning electric fiel an the charge carrie by the particle. The voltage require to lift the particle is often well below the operating voltage level of the system. Once the particle lifts from the surface, it moves in the irection of the electric fiel. Unless the applie fiel changes its irection or magnitue, the particle hits the inner electroe of the system, where it gets a new net charge. The magnitue of the net charge epens, besies the imension of the particle, on the value of the surrouning fiel at the time of impact with the electroe []. For an ac fiel, one may expect the motion of a particle to be ranom-like, since the charge on the particle interacts with the Experimental stuies have shown that the probability of breakown for elongate particles is highest when the particle is locate close to (< mm) but not in contact with the inner electroe [5]. The voltage breakown uring such an event is assume to start when a small ischarge first briges the istance from the inner electroe to the particle, which brings the particle to the same potential as the inner electroe. A ischarge then briges the rest of the gap since the particle, at that position, acts as a protrusion on the inner electroe, pointing towars groun. Discharges from the sharp ens of a particle, often referre to as in-flight corona, can also occur if conitions for corona inception are fulfille [6-8]. In this case, the particle can moify its carrie charge between impacts with the electroes. continuously changing electric fiel. so, since the charge on it epens on when it hits the electroes, the charge varies after each consecutive impact. However, by statistical analysis of the time between impacts of the particle with the enclosure, one can fin that the motion of the particle is, in fact, influence by the power frequency [3,4]. For an applie ac fiel, the maximum height that the II. MODELING TECHNIQUE II. Without Image Charges Fig shows a typical horizontal three phase busuct comprising of inner conuctors space equilaterally in a metal enclosure. The enclosure is fille with SF6 gas at a high pressure (.3 Mpa). particle can elevate from the electroe is limite compare with a c fiel. If the applie voltage is sufficient, several voltage cycles might be necessary for the particle to be able to cross the gap. l ights eserve IJACET 35

4 ISSN: International Journal of Avance esearch in Computer Engineering & Technology Volume, Issue 3, May - y(t) ππr (6μ6 (y).656(μμ ly (t).5 g ) The above equation is a secon orer non-linear equation which is solve using anga Kutta 4 th orer metho is aopte. II. With Image Charges Figure. Schematic Diagram of a Three Phase Common Enclosure GIB Typical horizontal three-phase bus uct shown in Figure 3 has been consiere for the analysis. A particle is assume to be at rest on the enclosure inner surface, just beneath the bus bar until a voltage sufficient enough to lift the particle an move it in the irection of the fiel is applie. After acquiring an appropriate charge in the fiel, the particle lifts an begins to move in the irection as Fig 3. Horizontal Three Phase Bus Duct escribe earlier. During the return flight, a new Unerstaning the ynamics of a metallic particle in a coaxial electroe system is of vital importance for etermining the effect of metallic contamination in a Gas Insulate System. If the motion pattern of a metallic particle is known, the probability of particle crossing a coaxial gap an causing a flashover can be estimate. The lift-off fiel for a particle on the surface of an electroe can be estimate by solving the motion equation. π l E(t ) my(t) l ln r charge on the particle is assigne base on the instantaneous electric fiel. The electric fiel intensity from the surface of the enclosure, ue to three conuctors at a given point acts simultaneously. The resultant electric fiel intensity at a poiny p at the inner surface of the outer enclosure is 3 Cosθo E Sint KV/m.5- x 3 x 48.64x.5- x Cosθ Sinωin- mg l ights eserve IJACET 36

5 ISSN: International Journal of Avance esearch in Computer Engineering & Technology Volume, Issue 3, May parameters e.g. the macroscopic fiel at the surface of the particle, its weight, eynol s number, coefficient of restitution on its impact to both enclosures an viscosity of the gas. During return flight, a new charge on the particle is assigne base on the instantaneous electric fiel. Total electrical fiel intensity at the point P is E E E E3 Figure 4. Three Phase Common Enclosure Bus Duct with Image Charges Cos Cos Cos Cos V V V 3 h x h x h h h ln ln ln r r r A conucting particle in motion in an external electric fiel will be subjecte to a collective influence of several forces. The forces may be ivie into Electrostatic force (FE), Gravitational force (mg) an Drag force (F). Figure 4 shows a horizontal three phase bus uct comprising of inner conuctors space equilaterally in a metal enclosure with images. The enclosure is fille with SF6 gas at a high pressure (.3MPa). A particle is assume to be at rest at the enclosure surface, just beneath the bus bar, until a voltage sufficient enough to lift the particle an move in the fiel is applie. After acquiring an appropriate charge in the fiel, the particle lifts an begins to move in the irection of fiel having overcome the forces ue to its own Cosθ Cosγ V (V V ) ln(h/r) h x h x 3 V/mm Where V, V, V3 are the three phase voltages given by V VmSint V VmSin( t ) V3 VmSin( t 4) E ln(h/r) V m Sinωi h x h x Cosθ Cosγ (V m Sin( ωi ) V m Sin( ωi 4)) weight an rag. The simulation consiers several l ights eserve IJACET 37

6 ISSN: International Journal of Avance esearch in Computer Engineering & Technology Volume, Issue 3, May The motion equation is III. SIMULATION ESULTS AND ANALYSIS Where Where m y t F e F mg F = Drag force mg = Force ue to gravitation. F e = Electrostatic force = q E E is the Electrostatic fiel intensity in three phase GIS taking the image charge effect of the conuctor into consieration q is the charge of the particle. πε l E t Vsinωs my t l r ln r ytln r r i.5 mg y tπr6μμ y.656 μρ g ly t Table I gives the values of maximum raial movement of a aluminum an copper type of wire like particle of length 4mm with variable raius.mm,.mm an.3mm when applie with three ifferent voltages 4KV, 45KV an 5KV when charges are not taken into consieration an Table II gives the values of maximum raial movement of a aluminum an copper type of wire like particle of length 4mm with variable raius.mm,.mm an.3mm when applie with three ifferent voltages 4KV, 45KV an 5KV when charges are taken into consieration. The corresponing particle movement for aluminum type of particle is presente in Fig 5 for.mm raius of the particle an applie voltage of 4KV when image charges are not taken into consieration an Fig 7 presents the particle movement when image charges are taken into consieration. From the results it can be my y t πε l Et V 43. l ln r 5 x 5 x tπr 6μμ y.656 μρ g ly t Cosγ Cosθ.5 Sinωi mg observe that when image charges are not taken into consieration the electric fiel at the location of the particle is less hence the particle attains less maximum raial movement but when the image charges are taken into consieration the fiel stress The above equation is a secon orer non-linear equation which is solve using anga Kutta 4th at the particle increases an the maximum raial movement of the particle will be more. orer metho is aopte. l ights eserve IJACET 38

7 Movement(mm) Movement (mm) ISSN: International Journal of Avance esearch in Computer Engineering & Technology Volume, Issue 3, May Voltage (KV) Type Maximum aial Movement in mm for l=4mm r=.mm r=.mm r=.3mm Table I. aial Movement of a Wire like particle with fixe length of l=4mm an variable raius of.mm,.mm an.3mm without image charges Fig 5 Particle Movement in a 3-phase 5/64 GIB without images for 4KV/AL/4mm/.mm raius. Voltage (KV) Type Time(Sec) Maximum aial Movement in mm for l=4mm r=.mm r=.mm r=.3mm Table II. aial Movement of a Wire like particle with fixe length of l=4mm an variable raius of.mm,.mm an.3mm Time(Sec) Fig 6 Particle Movement in a 3-phase 5/64 GIB with images for 4KV/AL/4mm/.mm raius. IV. CONCLUSIONS An uncharge metallic particle resting on bare electroe in a Gas Insulate System will graually acquire charge ue to the application of electric fiel aroun it. The charge accumulate is a function of Electric fiel, shape, size an orientation of the particle. When electrostatic force excees the gravitational an rag forces the particle lifts from its position. A further increase in the applie voltage makes the particle move into the inter electroe gap in the irection of applie fiel. This increases the probability of a flashover. The motion pattern of ifferent metallic particles uner ifferent AC voltages been investigate in a three phase common enclosure for a pressure of 3 bar. The macroscopic electric fiel at the surface of the enclosure for the 3-phase system is calculate in Cartesian coorinates. The electric fiel has been use to etermine the charge as well as the force on the particle. The raial movement is calculate using l ights eserve IJACET 39

8 ISSN: International Journal of Avance esearch in Computer Engineering & Technology Volume, Issue 3, May the stanar equation of motion. It can be note that aluminum particles are more influence by the voltage than copper particles ue to their lighter mass. This results in the aluminum particle acquiring greater charge-to-mass ratio. The present work eals the movement of a wire like particle without an with the Image Charge Effect in a Three 7) M. Wohlmuth, Measurement an Calculation of Lift-off Fiels an Charges for Free Moving Particles, Int. Conf. on GD, Swansea, pp. 44, 99. 8) H.D. Schlemper, K. Feser, Estimation of Mass an Length of Moving Particles in GIS by Combine Acoustical an Electrical PD Detection, Conference on Electrical Insulation an Dielectric Phenomena (CEIDP), San Francisco, CA, USA, October 996. Phase GIS is taken into consieration. V. EFEENCES ) CIGE Working Group 5.3, Effects of Particles on GIS Insulation an the Evaluation of elevant Diagnostic Tools, CIGE 994 Session, August 8-September 3, 994. ) N-J. Ftlici, Forces et charges e petits objets en contact avec une tlectroe affectke un champ Clectrique, evue GCnCrale e L tlectricitt, pp. 45-6, Octobre ) A.H. Cookson,.E. Wotton, Movement of Filamentary Conucting Particles Uner AC Voltages in High Pressure Gases, International Symposium Hochspannungstechnik Zurich, ) M.E. Holmberg, M.L-A. Sjoberg, A.E. Vlasths, Ientification of Metallic Particles in GIS by Statistical Analysis of Acoustical Measurements an Computer Simulations, 9th International Symposium on High Voltage Engineering, Graz, Austria, August ) Westinghouse esearch an Development Center, Investigation of High Voltage Particle-Initiate Breakown in Gas Insulate Systems, EPFU Project 7835 eport, Pittsburgh, Pennsylvania, March ) F.A.M. izk, C. Masetti,.E Comsa, Particle-Initiate Breakown in SF6 Insulate Systems uner High Direct Voltage, IEEE Transactions on Power Apparatus an Systems, Vol. PAS-98, No. 3, May/June 979. l ights eserve IJACET 3