Movement pattern of metallic particle in a single phase uncoated gas insulated bus duct with image charge effect.

Sahu, K.B. Madhu ; Amarnath, J. ; Murthy, K.S. Linga 等

Introduction

The development and design improvement of GIS and Gas Insulated Transmission Line (GITL) equipment has progressed rapidly worldwide during the last few years because of the excellent insularion properties of Sulphur hexafluoride gas.

A study of CIGRE group suggests that 20% of failure in GIS is due to the existence of various metallic contaminations in the form of loose particles. These particles may exist on the surface of support insulator, enclosure or high voltage conductor. Under the influence of high voltage, they can acquire sufficient charge and randomly move in the gap due to the variable electric field. Several authors have reported the movement of particles with reference to a few parameters.

In a horizontal coaxial system with particles resting on the inside surface of the enclosure, the motion of such particles is random in nature. The randomness dependent on the coefficient of restitution and angle of incidence when approaching the conductor. The presence of contamination can therefore be a problem with gas insulated substations operating at high fields. If the effects of these particles could be eliminated, then this would improve the reliability of compressed gas insulated substations.

When a conducting particle is freely located on an electrode, it acquires a charge Q which depends on the local electric field E, the shape, orientation, and size of the particle. When the force QE on the particle exceeds the gravitational force, the particle is elevated. Once the particle is lifted, the attracting force on the particle due to the image charge decrease, so that the resultant upward force increases and the particle moves more quickly [3].

Theoretically calculated results show that without considering the image charge effect, the electric field for rms voltage of 100 KV (Line to Line) is 314 KV/mm. While considering the image charge effect the electric field for the same rms voltage 100KV is 628 KV/mm. So there will be a 100 % increase in electric field. Charge Q, acquired by the particle is increased due to the increase in the electric field E. As a result, the movement of the metallic particle in GIB increases.

The work presented in this paper analyses the movement of metallic particle inside a single phase GIB (gas insulated busduct). The simulation considers the particle movement in single-phase GIB with image charge effect. It is observed that the movement of particles for a given voltage level is higher while considering image charge effect.

Formulation for the Motion of a Particle In GIB

Case (i): Without Image Charge effect

A typical horizontal single-phase bus duct shown in Figure 1 has been considered for the analysis of without Image charge effect on the particle.

[FIGURE 1 OMITTED]

While arriving at a mathematical method of the movement of particles inside a busduct, various properties of gas particle as well as electrical properties of the system has been taken into account. Understanding the dynamics of a metallic particle in a coaxial electrode system is of vital importance for determining the effect of metallic contamination in a gas insulated substations (GIS). The dynamic equation comprises the gravitational force on the particle, charge acquired by the particle, field intensity at the particle location, drag force, gas pressure, restitution co-efficient and the Reynold's number.

A particle is assumed to be at rest at the enclosure surface, it exchanges charge with the enclosure under the effect of electric field present there. If the electrostatic force on the particle over comes the gravitational and frictional force on it, the particle lift-off from the rest position .During return flight, a new charge on the particle is assigned based on the instantaneous electric field .

The equation of motion for a particle can be expressed as [4].

M [D.sup.2]/[dt.sup.2] = [F.sub.e] - mg - [F.sub.d] (1)

Where

m = mass of the particle.

y = displacement in vertical direction

g = gravitational constant

[F.sub.e] = electrostatic force

[F.sub.d] = drag force

The direction of drag force is always opposed to the direction of motion. The expression for drag force is given as

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.] (2)

Where

[??] y is the velocity of the particle

[mu] is the viscosity of the fluid

r is the particle radius

[[rho].sub.g] is the gas density

l is the particle length

The Electrostatic force is given as

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.] (3)

The above forces are substituted in equation (1) and it becomes

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.] (4)

The above equation (4) is a second order non-linear differential equation for motion of a metallic particle. To solve the motion equation Runge-Kutta 4th order method is adopted.

Case (ii): With Image Charge effect

[FIGURE 2 OMITTED]

Figure 2. Shows a horizontal single phase bus duct has been considered for the analysis of image charge effect. In figure 2. 'A' represents the conductor and A1 be the image of the conductor A and 'a' denotes the particle which is assigned to be at rest in the enclosure surface, just beneath the conductor A, until a voltage sufficient enough to lift the particle and move in the 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 force due to its own weight and 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. The method of field calculations for image charge effect is given below.

General expression for electric field

Let the particle move to a distance 'x' form the inner surface of the enclosure at the point 'a' in figure 2. From the figure 2, the variables in the general formula are:

x = position of the particle in the enclosure.

h = Distance between centre of the conductor and enclosure.

r = Radius of the conductor.

General expression for electric field intensity due to conductor A includes the image charge effect is given as:

[MATHEMATICAL EXPRESSION NOT RPRODUCIBLE IN ASCII.] (A1)

By substituting the values of h, r & Vm in the equation (A1) becomes

[MATHEMATICAL EXPRESSION NOT RPRODUCIBLE IN ASCII.] (A2)

Where E is the resultant electric field.

The motion equation is given by

[MATHEMATICAL EXPRESSION NOT RPRODUCIBLE IN ASCII.] (A3)

The charge acquired by the particle and the lift off field is given as

[MATHEMATICAL EXPRESSION NOT RPRODUCIBLE IN ASCII.] (A4)

[MATHEMATICAL EXPRESSION NOT RPRODUCIBLE IN ASCII.] (A5)

Simulation of Particle Motion

The study of the motion of moving metallic particles in GIS requires a good knowledge of the charge of the particle. Several authors have suggested solutions for the motion of a wire like metallic particle in an isolated particle busduct system. Computer simulation of the motion of metallic wire particles were carried out on single-phase GIB of 55mm diameter of inner conductor and 152 mm diameter of the outer enclosure with 75kv and above voltages applied to inner conductor .Aluminum, copper and silver wire like particles were considered to be present on enclosure surface.

Results and Discussions

Table 1 shows the radial movement of the particle in a 1- phase isolated Gas Insulated Bus duct of Aluminum and Copper particles by considering with and without Image charge effect on the particles are shown in Figure 3 to Figure 10 for applied voltages of 100KV and 200KV respectively. The particle is taken as 10mm in length with 0.25 radius. Initially the particle is supposed to be resting at the bottom of the enclosure and positioned vertically.

It is observed in the Figure 3 and Figure 4, that the maximum movement of the Aluminum particle is greater when considering Image charge effect on the particle than without Image charge effect at a given voltage of 100KV. The simulated results of maximum movement of particles are shown in Table 1.

The movement of copper particle is also given in Table 1. It has been observed that the maximum movement of Copper particle is far less than the Aluminum particle even of same size and applied voltage. This is due to the higher density of Copper particle. It is also noticed that as the voltage increases, the maximum movement of Aluminum and Copper particles increases significantly.

Figure 5 and Figure 6 show that the maximum movement of the Copper particle is greater in case of considering Image charge effect than without Image charge effect on the particle at a given voltage of 100KV.

The movement of Aluminum and Copper particles by considering with and without Image charge effect on the particle for the voltage of 200KV is shown in Figures 7 to 10. It has been observed that the vertical movement of the particle increases when the particle is influenced by Image charge effect.

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

[FIGURE 6 OMITTED]

[FIGURE 7 OMITTED]

[FIGURE 8 OMITTED]

[FIGURE 9 OMITTED]

[FIGURE 10 OMITTED]

Conclusion

The movement patterns of Aluminium and Copper metallic particles under different voltage conditions with and without Image charge effect on the particle have been observed for a single phase isolated conductor GIS on bare electrode system. A model has been formulated to simulate the movement of wire particle in single-phase isolated Gas Insulated Busduct. The results obtained are presented and analyzed. By considering Image charge effect on the particle there is a significant increase in movement of the metallic particle. All the above investigations are carried out at voltages of 100KV and 200KV under power frequency.

Acknowledgement

The authors are thankful to the management of Aditya Institute of Technology and Management, Tekkali, Srikakulam (Dist), JNT University, Hyderabad, Andhra University, Vishakapatnam for providing facilities to publish this work.

Refrences

[1] K.S. Prakash, K.D. Srivastava and M.M. Morcos "Movement of Particles in Compressed [SF.sub.6] GIS with Dielectric Coated Enclosure", IEEE Transactions on Dielectrics and Electrical Insulation, Vol.4 No.3, pp.344-347, June 1997.

[2] K.D. Srivastava and R.G. Van Heeswi jk "Dielectric coatings Effect of break down and particle movement in GITL systems", IEEE transactions on Power Apparatus and Systems, vol. PAS- 104, No.1, pp. 22-31, January 1985.

[3] J.R. Laghari and A.H. Qureshi "A Review of Particle Contaminated Gas Breakdown" IEEE Transactions on Electrical Insulation, Vol. EI-16 No.5, pp. 388-398, October 1981.

[4] H. Anis and K.D. Srivastava "Free conducting particles in compressed gas insulation", IEEE Tranctions on electrical insulation, Vol. EI-16, pp.327-338, August 1995.

[5] H. Anis and K.D. Srivastava, "Breakdown Characteristics of Dielectric Coated Electrodes in Sulphur Hexafluoride Gas with particle contamination", sixth Intern. Sympos high Voltage engineering, paper No.32.06, New Orleans, LA, USA. 1989.

[6] M.M. Morcos, S. Zhang, K.D. Srivastava, and S.M. Gubanski, "Dynamics of Metallic particle contamination in GIS with dielectric coating electrodes", IEEE Trans. Power Delivery Vol.15, pp. 455-460, 2000.

[7] J. Amarnath, B.P. Singh, C. Radhakrishna and S. Kamakshiah, "Determination of Particle trajectory in a Gas Insulated Busduct predicted by Monte-Carlo technique", IEEE Conf. Electr. Insul. Dielectr. Phenomena (CEIDP), Texas, Austin, USA, 1991 Vol.1, pp. 399-402, 1991.

[8] J. Amaranath, S. Kamakshiah and K.D. Srivastava "Influence of Power Frequency and Switching Impulse Voltage on particle Movement in Gas-predicted by Monte-Carlo Technique", IEEE, Intern. High Voltage Workshop, California,USA,2001.

[9] G.V. Nagesh Kumar, J. Amaranath, B.P. Singh and 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, pp.334- 340, April 2007.

K.B. Madhusahu received the B.E. Degree in Electrical Engineering from College of Engineering, Gandhi Institute of Technology & Management, Visakhapatnam, India in 1985, and the M.E Degree in power Systems from College of Engineering, Andhra University, and Visakhapatnam in 1988. He is pursuing his Ph.D from Jawaharlal Nehru Technological University, Hyderabad. He is also working as professor in the Department of Electrical & Electronics Engineering, A.I.T.A.M, Tekkali, Srikakulam Dt. Andhra Pradesh. His research interests include gas insulated substations, high voltage engineering and power systems. He has published research papers in national and international conferences.

J. Amarnath obtained the B.E. degree in electrical engineering from Osmania University, Hyderabad, A.P. India. in 1982 and the M.E. degree In power systems from Andhra University, Visakhapatnam in 1984. He worked in Tata Electric Company, Bombay during 1985-1986. In 1987 he was a Lecturer in Andhra University for a period of 2 years and then he joined Nagarjuna University for a period of 4 years as Lecturer. In 1992 he joined JNTU College of Engineering, Kukatpally, Hyderabad. Presently he is professor in the department of Electrical Engineering, JNTU, Hyderabad, A.P., He presented more than 60 research papers in national and international conferences. His research interests includes high voltage engineering, gas insulated substations, industrial drives, power electronics, power systems, microprocessors and microcontroller applications to power systems and industrial drives.

K.S. Linga Murthy received his B.E. degree in Electrical Engineering from College of Engineering, Andhra University, Visakhapatnam, India in 1972. He continued his studies to obtain Master degree in power systems from the same Institute in 1975. Ph.D degree from Indian Institute of Technology, Delhi, in 1987. He worked as a Scientific Assistant for a period of 3 Years up to 1979 at NSTL, R & D organization, Ministry of Defence, Government of India, Visakhapatnam. Since 1979 he has been in the faculty of Electrical Engineering, A.U. College of Engineering, Andhra Univesity, Visakhapatnam. Presently he is Professor of Electrical Engineering, Department of Electrical Engineering, A.U. Colege of Engineering Andhra Univesity, Visakhapatnam, A.P. He obtained his Ph.D degree from Indian Institute of Technology, New Delhi, in 1987. He presented / published about 30 Technical Papers in various National / International conferences / Journals. His research interests includes Power system operation and control, P.S. Analysis & optimization in Power Systems Engineering.

B.P. Singh obtained the M. Tech degree from IISc Banglore, the Ph.D. Degree from Liverpool University, U.K. presently he is working as General Manager, BHEL Corporate (RandD), Hyderabad. He presented More than 90 research papers in national and international journals and Conferences.

K.B. Madhu Sahu

Aditya Institute of Technology and Management

Tekkali--532201, Andhra Pradesh, India.

J. Amarnath

Jawaharlal Nehru Technological University

Hyderabad--500085, Andhra Pradesh, India.

K. S. Linga Murthy

College of Engineering, Andhra University,

Vishakapatnam--530003, Andhra Pradesh, India.

B. P. Singh

H. V.Department, B. H. E. L. Corporate (R and D)

Vikas Nagar, Hyderabad, Andhra Pradesh, India

Table 1: Radial movement of Aluminum and copper
particles with and without image charge effect.

                   Max. Radial     Max. Radial
                  movement (mm)   movement (mm)
                 (Without Image    (With Image
Voltage   Type   charge effect)   charge effect)

100KV      Al        24.24            52.33
           Cu         5.05            20.13
200KV      Al        61.14              NA
           Cu        17.8             44.83