study of dynamics of contamination in single phase …

STUDY OF DYNAMICS OFMETALLIC PARTICLE

CONTAMINATION IN SINGLEPHASE GIB/GITL WITH VARIOUSINSULATING GAS MIXTURES

G.Angit Kumar1, S.S.Tulasi Ram2,1Dr.B.V.Raju Institute of Technology,Narsapur, Medak, Telangana, India.

2G. Narayanamma Institute of Technology & Science,Hyderabad, Telangana, India.

[email protected],[email protected]

July 18, 2018

Abstract

The design stress of sulphur hexafluoride Gas InsulatedSwitchgear (GIS) systems are limited by the harmful ef-fects resulting from the almost inevitable Presence of par-tical contamination in GIS equipment. Mixing SF6 withother gas is a possible way of improving GIS performanceunder particle contamination condition. This paper studiesthe breakdown of SF6-gas mixture (SF6-Air, SF6-N2 andSF6-C02) in the presence of contaminating particles underapplied AC voltage with different particle dimensions. Thebehaviour of these gas mixtures in the presence of parti-cle contamination at various proportions is studied and themovement of the particle contaminants inside a single phaseGas Insulated Busduct for various power frequency voltages

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International Journal of Pure and Applied MathematicsVolume 120 No. 6 2018, 7997-8010ISSN: 1314-3395 (on-line version)url: http://www.acadpubl.eu/hub/Special Issue http://www.acadpubl.eu/hub/

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like 121KV and 145KV is determined. The conducting par-ticles assumed here is wire like aluminium and copper par-ticles having 8mm length and 0.2 mm radius present on thesurface of the enclosure of the GIB. Different dimensions aretaken for the busduct based on the voltages applied. Theelectric field is calculated at various gas proportions usinganalytical method and movement patterns of the particle istraced out. . The movement of the particle with respect totime is plotted under different gas mixtures. with differentfractional concentration of SF6 in mixture are carried out.From this study it is concluded that some SF6-gas mixturescan be alternative insulating medium to that of pure SF6.

1 INTRODUCTION

Pure SF6 gas is being used as an insulating medium in gas insulatedequipment due to its excellent properties of dielectric strength, heattransfer properties and arc quenching capability. It is notable thatSF6 is a green-house gas with a high dangerous global worming po-tential (GWP) of 23900.The application of other gases with lowerGWP is to be investigated. Three of such gases that might be ofinterest to replace SF6 in further applications are carbon-dioxide(CO2), dry air and nitrogen (N2).SF6 is expensive when comparedwith other gaseous dielectrics which are commonly used.SF6 is veryconscious to local field enrichment which are imminent in engineer-ing applications due to the defects on electrode surface, sharp edgesproduced by assembly deception, and existence of free conductingparticles.In any case, there are some genuine worries about its fu-ture work from the ecological perspective. SF6 has been groupedat the Kyoto meeting on environmental change among the ozoneharming substances.Also; its emanation in the air ought to be di-minished. For this reason one searches seriously for the conceivablenaturally well-disposed substitutes .Under ordinary conditions, i.e.with no supply connected from outside, practically there no freeelectrons to convey a charge in gas. Just within the sight of a freeelectron, which is expected to deliver a torrential slide, the break-down can succeed. Contingent upon the quantity of free electronsin the gas, after certain field quality is achieved the sudden differ-ence in electric conductivity takes place. This intense difference in

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dielectric properties comes about in quick drop of the connectedvoltage, which is called an electric breakdown in a gas.When N2blends with a little bit of SF6 the dielectric quality of N2 can bealtogether expanded. SF6-N2 is presumably the best gas blend tobe utilized as a part of GIS and GIC, it can likewise be utilized asa part of GIT to enhance the impulse breakdown characteristics.In the last case SF6-CO2 may have a few favourable circumstancesover SF6-N2 in light of the fact that gas/film Insulation and non-uniform field issues are experienced. Despite the fact that a fewmakers determine that SF6 fixation in their C-GIS isn’t under 0.95, it is in reality better to utilize the Dry Air mixture blend withsF6 fixation being around 0.8[1-7].

2 MODELING TECHNIQUE

The conventional single phase gas insulated busduct is shown infigure (1). For simulating the particle trajectory in GIB/GITL us-ing computer programs, it has been assumed that particle is restingon inner surface of outer enclosure and initial velocity of particle iszero. Various forces experienced by a moving conducting particleunder external electrical field are 1. Electrostatic force (Fe) 2.Grav-itational force (Fg) 3.Drag force (Fd) and 4.Forces formed due tospace charges near the particle and finally force due to coronalwindage effect. The forces are neglected in this simulation work.

Figure 1: Typical 1-Φ Gas Insulated Busduct (GIB)

The influences of gas pressure and gas properties are also takeninto consideration. The movement of the metallic particle can beestimated by

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(1)

Where ’m’ is mass of the particle and ’y’ is radial movement ofthe particle towards the conductor .Electrostatic Force:

The electrostatic force experienced by wire like aluminium orcopper metallic particle resting on inner surface of outer enclosureis given by

(2)

Where K is correction factor ,ε0 is permittivity of free vacuum,l is length of the particle, E (to) is Electric Field Intensity at timeto and r is radius of the particle.The correction factor depends onlength-to-radius ratio of particle.Gravitational Force:

The gravitational force acting on metallic particle can be esti-mated by using equation (3).

mg = πr2lρg (3)

Wherer is the radius of the particlel is the length of the particleg is the acceleration due to gravityρ is the density of the particle.

Drag force:The drag force plays important role in particle movement at

higher gas pressures and at higher velocities of the particle in GIB/GITL.The drag force acts in opposite direction to particle movement andcauses the loss of energy due to shockwaves and skin friction ofmetallic particle. In compressed Gas Insulated Systems energy dis-sipation due to shock waves for metallic particles more and forgreater length to radius ratio particles skin friction energy loss ismore.

The total drag force is given as [6]

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(4)

Wherey is velocity of the particle,µ is viscosity of the gas,Kd(y) is drag force coefficient andρg is gas density .The equation (1) is a second order differential equation and

can be solved by Runge-Kutta 4th order method to obtain radialmovement ’y’ with respect to time.

After few approximations in kinetic theory of dissemination,Wilke have built up the articulation for ascertaining the viscosityof gases. This viscosity of gas mixture based on the significant eval-uation of inter molecular forces and the use of collision integrals,which repeat the trial information for non-polar gases with highaccuracy for n number of gases is given in equation (5).This vis-cosity equation is independent of the diffusivity and density of thegas content. In this work we considered binary gas mixtures for thecomputer simulation. The viscosity of n number of gases can beestimated by using this equation[9].

(5)

Where,xi and xj are proportions of two individual gases,µi and µj are individual gas viscosities andMi and Mj are molecular weights of two individual gasses.

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3 RESULTS AND DISCUSSIONS

The simulation study has been carried out on the movement ofAl/Cu metallic particles in a single phase GIB with two differentpower frequency voltages 121kV and 145kV. The enclosure dimen-sions are 165mm/51mm.The inner radius of the enclosure is 165mmand outer radius of the conductor is 51mm. The gas mixture pres-sure is considered as 0.5MPa at restitution coefficient 0.9.Threedifferent SF6 gas mixtures are considered for this simulation study.The length and radius of the wire like particle are 8mm and 0.2mmrespectively. The radial movement of the particle towards the liveconductor is estimated by solving the above equation. Tables IIIshows the maximum radial movements of the copper metallic par-ticle contaminants at 121kV and 145kV respectively for variousproportions of the gas mixtures of SF6 +CO2, SF6 +N2andSF6 +Air.Similarly Tables III IV shows the maximum radial movementsof the aluminium particle contaminants for the same voltages andgas mixtures. In each case the percentage of other gas mixedwith the SF6 gas is varied from 0 to 100. The radial movementof the metallic particle is estimated for each proportion of gases

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in each gas mixture is estimated.to find the best gas mixture weshould consider less radial movement of the particle at the sametime percentage of SF6 must be low. The 10% SF6 and 90% othergases like (N2,CO2,Air) in any gas mixture can be recommended asthe insulation medium for the reliable operation of GIB/GITL.Themovement of the particle is traced with the variation of the othergases(N2,CO2,Air) for all gas mixtures and voltages at each pro-portion of the gases.

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4 CONCLUSIONS

A model has been formulated to simulate the movement of wirelike particle in a single phase GIB/GITL in the presence of SF6gas mixed with N2, CO2 and Dry Air gases. The results have beenpresented and analyzed in this paper. Distance travelled in theradial direction towards the live conductor is found to be reducedwhen small amounts of other gases are mixed with SF6 which inturn reduces the greenhouse effect of SF6 gas. The movement ofaluminium particle is more compared with copper particle due toits light weight. The movement of the particle is increased as thevoltage is increased. The Movement of the particle for SF6+Air ismore compared with SF6+CO2, SF6+N2 gas mixtures.

5 ACKNOWLEDGMENT

The authors are thankful to managements of B.V.Raju Instituteof Technology, Narsapur and G. Narayanamma Institute of Tech-nology Science, Hyderabad for providing facilities to publish thiswork.

References

[1] Y. Qiu and Y. P. Feng, Investigation of SF6-N2, SF6-CO2and SF6-Air as Substitutes for SF6 Insulation, ConferenceRecord of the 1996 IEEE International Symposium on Elec-trical Insulation,pp-766-768,June 1996.

[2] Sayed A. Ward, Assessment of Optimum SF6-Air, SF6-N2, SF6-C02 According to Particle Contamination Sensi-tivity, Conference on Electrical Insulation and DielectricPhenomena,pp.415-418,1999.

[3] Denis Denissov and et al, Dielectric Strength of Different Gasesin GIS, Proceedings of the XIVth International Symposium onHigh Voltage Engineering, pp. 1-5,August 2005.

[4] Masayuki Hikita, Shinya Ohtsuka, Nobuhiro Yokoyama, Ef-fect of Electrode Surface Roughness and Dielectric Coating on

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Breakdown Characteristics of High Pressure CO2 and N2 in aQuasi-Uniform Electric Field IEEE Transactions on Dielectricsand Electrical Insulation Vol. 15, No. 1, pp. 243-250, February2008.

[5] S. Meijer, J.J. Smit andA. Girodet,Comparison of the Break-down Strength of N2, CO2 and SF6 using the Extended Up-and-Down Method IEEE, pp.653-656, 2006.

[6] J.Amarnath, B.P.Singh, C. Radhakrishna and S. Kamak-shaiah,Determination of Metallic particle trajectory in aGas insulated Busduct predicted by Monte-Carlo tech-nique,CEIDP,October 17-21,1999, Texas, Austin, USA.

[7] S. Ohtsuka and et al, PD time sequential and light emissionproperties as pre-breakdown phenomena of SF6/N2/CO2, gasmixture, Conference on Electrical Insulation and DielectricPhenomena, pp 801-804,2002.

[8] N.J. Felici, Forces et charges de petits objects en contact avecune electrode affectee dun champ electrique, Reveue generalede I electricite, October 1966, pp.1145-1160.

[9] C.R. Wilke, Viscosity Equation for gas mixtures,Jour.Chem.Phys., vol.18, 1950, pp.517-519.

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study of dynamics of contamination in single phase …

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