International Journal of Electronic and Electrical Engineering. ISSN 0974-2174 Volume 3, Number 1 (2010), pp. 23--32 © International Research Publication House http://www.irphouse.com

Axial and Radial Movement of Metallic Particles in Common Enclosure Three Phase Gas Insulated

Busduct

L. Raja Sekhar Goud1, D. Subbarayudu1 and J. Amarnath2

1E.E.E. Department, G. Pulla Reddy Engineering College, Andhra Pradesh, India. 2E.E.E. Department, J.N.T.U., Hyderabad, Andhra Pradesh, India.

E-mail: lrs_76@yahoo.com

Abstract

Gas Insulated substation (GIS) is now well established. In field installation, it has been observed that metallic particle contaminations often present in GIS and such contamination adversely affect the insulation integrity. A method based on particle motion is proposed to determine the particle trajectory in a three phase Gas Insulated Substation (GIS) or Gas Insulated Busduct (GIB). In order to determine the movement of particle in a GIB, an outer enclosure of diameter 500mm and inner conductor of diameter 64mm spaced equilaterally was considered. Aluminum and Copper wires of 0.1mm / 10mm were considered to be present on enclosure surface. The motion of the wire (particle) was simulated using the charge acquired by the particle, the macroscopic field at the particle site, the drag coefficient of restitution, Reynold’s number and coefficient of restitution. The distance traveled by the particle, calculated using Cartesian coordinates, for given sets of parameters is presented in this paper. In order to determine the random behavior of moving particles, the calculation of movement in axial and radial directions was done at every time stem using rectangle random numbers. Typical results for aluminum and copper wire are also described in this paper. Index Terms: Particle movement, axial and radial movement, Monte-Carlo.

Introduction The superior dielectric properties of Sulphur hexafluoride (SF6) have long been recognized for various high voltage applications. Compressed SF6 gas has been used as in insulating medium as well as arc quenching medium in electrical apparatus over

24 L. Raja Sekhar Goud et al

a wide range of voltages. Due to the reliability of equipment, three-phase common enclosure type Gas Insulated Busduct (GIB) or Gas Insulated Substations (GIS) can be used for all services up to 500KV rating. This reduces space requirement, provides additional advantages of low maintenance and helps in cost saving. Conducting contamination could however, serious reduce the dielectric strength of Gas Insulated System. Metallic particles in GIB / GIS have their origin mainly from the manufacturing process or they may originate from mechanical vibrations during shipment and service or thermal contraction or expansion at joints. Metallic particles can be either free to move in annular gap or they may be stuck either to the bus-bar or to an Insulator surface (spacer, busing etc.). If metallic particle will crosses the gap and comes in to contact with act as protrusion on the surface of the electrode. This may lead to reduction in breakdown strength of the gap. This present paper deals with the computer simulation of particle movement in three phase common enclosure movement in three phase common enclosure GIB. The specific work reported deals with the charge acquired by the particle due to macroscopic field at the tip of the particle, the force exerted by the field on the particle, the drag due to viscosity of the gas and random behavior during the movement. Wire like particles of aluminum as well as copper of a fixed geometry in a three-phase busduct has been compared with the particle movement in a single-phase busduct. The movement pattern for three-phase busduct has been also obtained for higher voltages. Modeling Technique Fig. 1 shows a typical horizontal three phase busduct comprising of inner conductors spaced equilaterally in a metal enclosure. The enclosure is filled with SF6 gas at high pressure. A particle is assumed to be at rest at the enclosure surface, just beneath the bus-bar A, until a voltage sufficient enough to lift the particle and move in the field, the particle lift and begins to move in the direction of field, the particle lifts and begins to move in the direction of field having overcome the forces due to its own weight and air drag. The simulation considers several parameters e.g. the macroscopic field at the surface of the particle, its weight, Reynold’s number, coefficient of restitution on its impact to enclosure and viscosity of the gas. During return flight, a new charge on the particle is assigned based on the instantaneous electric field.

Figure 1 : A typical three phase common enclosure GIB A, B, C are the conductors

Axial and Radial Movement of Metallic Particles 25

Theoretical Study The primary goal of the simulations was to create an appropriate mathematical model of the particle motion in a three phase common enclosure GIS, which will enable further simulations of the motion of particle with arbitrary shapes. Several authors [1]-[10] have suggested solutions for the motion of a sphere or a wire like metallic particle in an isolated bus duct system. The theory of the particle charge and the electrostatic force on the particle is discussed in [1]-[6]. The motion equation is given by

de FmgFdt

ydm −−=

2

2 (1)

Where, y is the direction of motion and Fd is drag force. The direction of the drag force is always opposed to the direction of motion. For laminar flow the drag force component around the hemispherical ends of the particle is due to shock and skin friction. Very limited publication is available [7] for the movement for the movement of particle in three-phase bus duct, however of equation of motion is considered to be same as that an isolated phase bus duct. Simulation of Electrical Field in Tree phase busduct The charge acquired by a vertical wire particle in contact with a bare enclosure can be expressed as given by [1]. The electrical field in a three phase common enclosure GIB electrode system at the position of the particle can be written as:

)()()()( 321 tEtEtEtE ++= (2)

Where E(t) is the resultant field in vertical wire direction due to three conductors on the surface of the particle at the enclosure. )( and )( ),( 321 tEtEtE are the

components of the electrical filed in vertical direction. The gravitational force and drag forces are considered as described by several authors. Simulation results and Discussion Computer simulation of the motion of metallic wire particles were particles were carried motion out on GIB of 64mm inner diameter for each phase and 500mm outer diameter with 300KV applied to inner conductors with appropriate phase difference. A conducting particle motion, in an external electrical field will be subjected to a collective influence of several forces. The forces may be divided into [6]-[10] Electrical force (Fc), Gravitational force (mg) and Drag force (Fd). Software was developed in C language considering the above equations and was used for all simulation studies.

26 L. Raja Sekhar Goud et al

Table 1: Variation of Axial and Radial movement of Aluminum, Copper and Silver particles in Three phase uncoated GIB with application of Power Frequency. Simulation Time: 1.5 sec, l = 10 mm r = 0.1 mm Busduct Dimensions: Outer Diameter = 500mm Conductor Dia.: 64 mm

Voltage (kV) Type Max. Radial Movement (mm )

Monte-Carlo ( 1 deg ) Axial ( mm ) Radial (mm)

300 Al Cu Ag

34.54588 6.959618

N.M

535.6143 115.6291

N.M

34.54588 6.959618

N.M 400 Al

Cu Ag

64.04347 17.68512 12.58007

615.4692 311.0555 261.7634

64.04347 17.68512 12.58007

450 Al Cu Ag

81.84347 26.63495 20.79749

626.9215 511.002 325.1107

81.84347 26.63495 20.79749

500 Al Cu Ag

100.0761 28.68069 25.39804

784.7797 488.657 406.2771

100.0761 28.68069 25.39804

600 Al Cu Ag

140.4114 45.5663 39.88366

2319.624 691.7146 641.2872

140.4114 45.5663 39.88366

700 Al Cu Ag

325.6726 65.16706 54.26916

4440.911 856.8138 751.4486

325.6726 65.16706 54.26916

Table1 shows the movement of aluminum, copper and silver particles for voltages from 300 KV at 700 KV. It is noticed that even for a voltage of 300 KV the Ag particle could not leave the surface. This is expected due to lower field experienced in the three phase common enclosure GIB and heavier mass of silver. Graphical representation of radial movement in relation to time is given in Fig. 2 to Fig 13. The simulations have also been carried out for an applied voltage of 400 KV with inner and outer diameters of the same dimensions. Based on above calculation the maximum movement of aluminum particle is found to be 64.04mm and the same figure for copper is17.68mm respectively. Movement for copper particle is shown in Fig. 3.

Axial and Radial Movement of Metallic Particles 27

Fig 2 : Particle Movement in a 3-phase 500/ 64 GIB for 300KV / AL / 10mm / 0.1 mm radius

Fig 3 : Particle Movement in a 3-phase 500 / 64 GIB for 500KV / AL / 10mm / 0.1 mm radius

Fig 4 : Particle Movement in a 3-phase 500 / 64 GIB for 300KV /CU 10mm / 0.1 mm radius

28 L. Raja Sekhar Goud et al

Fig. 5 : Particle Movement in a 3-phase 500 / 64 GIB for 500KV/CU / 10mm / 0.1 mm radius

Fig 6 : Particle Movement in a 3-phase 500 / 64 GIB for 400KV / AG / 10mm / 0.1 mm radius

Fig 7 : Particle Movement in a 3-phase 500 / 64 GIB for 500KV / AG / 10mm / 0.1 mm radius

Axial and Radial Movement of Metallic Particles 29

Fig 8 : Axial and Radial Movement in a 3-phase 500/64 GIB for 300kV/AL/10mm/0.1 mm radius

Fig 9 : Axial and Radial Movement in a 3-phase 500 / 64 GIB for 500kV / AL/ 10mm / 0.1 mm radius

Fig 10 : Axial and Radial Movement in a 3-phase 500 / 64 GIB for 300kV / CU/ 10mm / 0.1 mm radius

30 L. Raja Sekhar Goud et al

Fig 11 : Axial and Radial Movement in a 3-phase 500 / 64 GIB for 500kV / CU/ 10mm / 0.1 mm radius

Fig 12 : Axial and Radial Movement in a 3-phase 500 / 64 GIB for 400kV / AG/ 10mm / 0.1 mm radius

Fig 13 : Axial and Radial Movement in a 3-phase 500 / 64 GIB for 500kV / AG/ 10mm / 0.1 mm radius

Axial and Radial Movement of Metallic Particles 31

The axial and radial movement of aluminum, copper and silver particles is calculated using Monte-Carlo technique for voltages from 300 kV to 700kV with a solid angle of 1o. It is significant to note that for all the cases considered , there is no change in maximum radial movement , even when Monte-Carlo Method is applied .A relatively high value of axial movement is achieved with the higher random angles .The axial movement of copper particle is lower than aluminum as expected. Conclusions A model has been formulated to simulate the movement of particle in three phase common enclosure Gas Insulated Busduct (GIB).The electric field at the particle position is calculated by considering three-phase voltage in rigorous equation. The radial movement obtained in a three phase common enclosure was found to be lower than the single phase isolated conductor gas insulated system. Monte-Carlo simulation is adopted to determine the axial as well as radial movement of particle in the busduct. Distance traveled in the radial direction is found to be same with or without Monte-Carlo simulation. Acknowledgements The authors are thankful to management G. Pulla Reddy Engineering College, Kurnool, AP for grant of providing facilities to do this work. References

[1] H.Anis and K.D.Srivastava; "Movement of charge conducting particles under Impulse Voltages in Compressed Gases"; IEEE Int.Conf.on industrial Applications, 1980.

[2] J.Amarnath, B.P.Singh, S.Kamakshaiah, C.Radhakrishna and K.Raghunath, “Monte-Carlo Simulation of Particle movement in a coated gas insulated Substation for power frequency and switching transients": International High Voltage Workshop (IEEE) during April 10-12, 2000, California, USA.

[3] J.Amarnath, B.P.Singh, S.Kamakshaiah, C.Radhakrishna and K.Raghunath, “movement of metallic particles in gas insulated substations under the influence of various types of voltages": National Power System Conference (NPSC-2000) IISc, Bangalore 20th -21st Dec., 2000.

[4] M.M.Morcos, K.D.Srivastava and H.Anis, “Dynamics of Metallic Contaminants in Compressed Gas Insulated Power Apparatus”, Fourth Int. Symposium on High Voltage Engineering: Athens, 1983.

[5] H.Anis and K.D.Srivastava, “Dielectric coated electrodes in Sulphur Hexafluoride Gas with Particle Contamination”, Sixth International Symposium on High Voltage Engineering, No.32.06, New Orleans, LA, USA, 1989.

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[6] Schlemper, H.D, Feser, K, “Estimation of mass and length of moving particles in GIS by combined acoustic and electrical PD detection", 1996 conf. on Electrical Insulation and Dielectric Phenomena (CEIDP), pp.90-94.

[7] H.Anis and K.D.Srivastava, “Free Conducting particles in Compressed Gas Insulation” IEEE Trans on Electrical Insulation, Vol EI-16, PP.327-338, August, 1981.

[8] H.Parekh, K.D.Srivastava and R.G.Van Heeswijk; "Lifting Field of Free Conducting Particles in Compressed SF6 with Dielectric Coated Electrodes”, IEEE Trans. on Power Apparatus and Systems, Vol. PAS-98, No.3, May / June1979.

[9] L.RajasekharGoud, J.Amarnath and D.Subbarayudu.,“simulation of particle Motion in a Gas insulated Bus duct”, Published in Engineering Today monthly Journal, Chennai (India) in October 2006 Pages21-22

[10] L.Rajasekhargoud, J.Amarnath, D.Subbarauyudu, M.Sivasathyanarana and T.Brahmananda Reddy., “Motion of particles in common enclosure three phase Gas insulated Bus duct” - PCEA-IFTOMM International conference(PICA2006) on “Recent trends in Automation & its adaptation to industries” at NAGPUR during July 11-14-2006.PP120