Design pasrameters effect on the particle movement in a three phase common enclosure Gas Insulated Busduct.
Rao, M. Venu Gopala ; Amarnath, J. ; Kamakshaiah, S. 等
Introduction
Sulphur hexafluoride is the electric power industry's
preferred gas for electrical insulation and, especially, for arc
quenching current interruption equipment used in the transmission and
distribution of electrical energy. Compressed Gas Insulated Substations
(GIS) and Transmission Lines (CGIT) consist basically of a conductor
supported on insulator inside an enclosure, which is filled with
[SF.sub.6] gas.
The presence of contamination can therefore be a problem with
gas-insulated substations operating at high fields [1-4]. If the effects
of these particles could be eliminated, then this would improve the
reliability of compressed gas insulated substation. It would also offer
the possibility of operating at higher fields to affect a potential
reduction in the GIS size with subsequent savings in the cost of
manufacture and installation. In this work the particles are assumed to
be wire like in nature has been presented on a three phase common
enclosure GIB with various conductor diameters have been considered for
analysis. The results have been presented and analyzed.
Modeling Technique of GIB
Figure.1 shows a typical horizontal three phase bus duct comprising
of inner conductors spaced equilaterally in a metal enclosure. The
enclosure is filled with [SF.sub.6] gas at a high pressure (0.3 MPa). A
particle is assumed to be rest on the enclosure inner surface, just
beneath the bus bar until a voltage sufficient enough to lift the
particle and move it in the direction of the field is applied. After
acquiring an appropriate charge in the field, the particle lifts and
begins to move in the direction. During the return flight, a new charge
on the particle is assigned based on the instantaneous electric field
[5,6].
[FIGURE 1 OMITTED]
The Figure 2 shows cross sectional view of a typical horizontal
three phase busduct. The enclosure filled with SF6 gas at high pressure.
A particle is assumed to be rest on the enclosure surface, just beneath
the busbar 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 forces due to its own weight and drag due to
the viscosity of the gas.
[FIGURE 2 OMITTED]
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 both enclosures and
viscosity of the gas. During return flight, a new charge on the particle
is assigned based on the instantaneous electric field.
[FIGURE 3 OMITTED]
The figure.3 shows the schematic diagram of three phase common
enclosure GIB on which the electric field applied on three conductors
simultaneously. The resultant electric field applied on a particular
point 'P' at a distance 'x' millimeters from the
enclosure surface.
Expression for electric field
The position of the three phase conductors and outer enclosure is
shown in Figure 3. 1, 2 and 3 are 3-phase HV Conductors. From the figure
the distance between the conductors are measured. The electric field
intensity from the surface of the enclosure, due to three conductors at
a given point acts simultaneously. Let the particle move to a distance
'x' from the inner surface of the enclosure at the point
'p'. For a balanced system each phase is displaced by
120[degrees].
Three phase voltages are defined as
[V.sub.1] = [V.sub.max] Sin[omega]t
[V.sub.2] = [V.sub.max] Sin ([omega]t + 120[degrees])
[V.sub.3] = [V.sub.max] Sin ([omega]t - 120[degrees]) (1)
From the graph, the variables in the general formula are:
[R.sub.1] = Distance between the conductor 1 and particle
[theta]2 = Angle between the vertical axis and R1
x = Position of the particle within the enclosure
[V.sub.m] = 200 Kv/ph [V.sub.rms] = 245 Kv (line to line)
h = Distance between the centre of the conductor and the enclosure
r = Radius of the conductor
From the Figure 3.
From [[DELTA].sup.1e] 123
[R.sub.1.sup.2] = [(h-x).sup.2] + [k.sup.2] -2(h-x)K Cos
150[degrees]
h = 125 mm
k = 215 mm
Let x = 10 mm (2)
By substituting all the distances from the graph, and calculating
field we obtain,
[R.sub.1.sup.2] = [(125-x).sup.2] + [215.sup.2] + [square root of
(3(h-x)K)] = 319.8 mm (3)
The resultant electric field intensity at a point 'P' at
the inner surface of the outer Enclosure is given by [6]
E = 48.64 x [10.sup.3] [(1/0.125 - x) + (Cos[theta]2/R1)] Sin [??]
KV/m (4)
and the motion equation is given by
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (5)
Equation 5 is a non-linear second order differential equation. The
above equation is solved using Runge-Kutta 4th order method.
The simulation results have been presented and analyzed in this
paper using all the forces acting on the particle as shown in the motion
equation.
Results and Discussions
The model of 3-phase common enclosure GIB has been formulated in
this work. Using this model the results have been presented and
analyzed. Table1 shows the peak particle movement of 300KV, 400KV,
450KV, 500KV, 600KV and 700KV system voltages respectively. Aluminium,
Copper and Silver Particles of 10mm length and 0.1mm radius have been
considered for simulation. The simulation is carried out for movement of
metallic particle in a 3-phase Bus duct with reduced conductor diameter
with a view to obtain optimum size of conductor for reliable operation.
The work is carried out by reduced the original diameter of the
conductor from 64mm to 54mm in steps of 5mm. It is required to be done
because competitive prices of several manufactures of GIS and cost of
gas are increasing. The results will have a bearing on the extent of
reduction of inner diameter of the HV conductor and the overall volume.
This will provide information on the extent of particle movement for the
same condition of the gas and particle geometry.
Figure. 4 to Figure. 6 show the movement pattern for Aluminum
particle with an applied voltage of 300KV with an inner conductor
diameter of 64mm, 59mm and 54mm respectively. From these figures it is
observed that particle movement is reduced when the diameter of the
inner conductor is reduced. It is also observed that from the figure 7
to Figure 9 show that the movement pattern for Copper particle with an
applied voltage of 400KV and an inner conductor diameters of 64mm, 59mm
and 54mm respectively. From this movement pattern it is understood that
the movement is reduced when inner conductor diameter is reduced.
Similarly from Figure 10 to Figure 12 show the movement pattern for
Silver particle with an applied voltage of 500KV with an inner conductor
diameter of 64mm, 59mm and 54mm respectively. In this case also is
observed that when the inner diameter of the conductor is decreased, the
movement also reduced. This is also shown in Table 1 by peak movement of
the particle.
[FIGURE 4 OMITTED]
[FIGURE 5 OMITTED]
[FIGURE 6 OMITTED]
[FIGURE 7 OMITTED]
[FIGURE 8 OMITTED]
[FIGURE 9 OMITTED]
[FIGURE 10 OMITTED]
[FIGURE 11 OMITTED]
[FIGURE 12 OMITTED]
Conclusions
Three phase common enclosure GIB model has been presented in this
paper. The particle is initially resting on an enclosure surface is
considered for this study. These particles move randomly in a
horizontally mounted GIB system due to the electric field, and this
movement plays a crucial role in determining the insulation behavior of
Gas Insulated sub stations. Under 50-Hz AC voltage, the particle motion
is complex, and under appropriate conditions, the particle may cross the
gaseous gap from the low-field region near the outer enclosure to the
high-field region near the central conductor. For the commonly
encountered size of metallic particles in practical Gas Insulated
systems, such a crossing of the gaseous gap takes several cycles of the
50-Hz voltage. In order to determine the particle trajectories in a
three-phase common enclosure Gas Insulated Bus duct (GIB) an outer
enclosure of diameter 500 mm and inner conductors of diameters 64 mm
spaced equilaterally are considered. Wire like particles of aluminum,
copper as well as silver of a fixed geometry has been considered to be
present on enclosure surface of a three-phase bus duct. Simulation is
carried out for movement of metallic particles in a three-phase bus duct
with reduced phase conductor diameter with a view to obtain optimum size
of conductor for reliable operation. The work is carried out by reducing
the original diameter of the conductor from 64mm to 54mm in steps of 5
mm. It is required to be done because competitive prices of several
manufactures of GIS and cost of gas are increasing. The results will
have a bearing on the extent of reduction of inner diameter of the HV
electrode and the overall volume. This will provide information on the
extent of particle movement for the same condition of the gas and
particle geometry. At each reduced diameter the electric field on moving
particle is calculated at each instant and radial movement is computed.
The results show that the maximum flight of the particle is decreased as
the phase conductor diameter is decreased as the net electric field of
the bus duct conductor is decreased. Finally it is concluded that the
diameter of the inner conductor is reduced, the particle movement also
reduced and the cost of GIS is also reduced due to reduced volume of
gas.
Acknowledgment
The authors are thankful to the management of QIS College of
Engineering and Technologly, Ongole and JNT University, Hyderabad, for
providing facilities and to publish this work.
References
[1] L. G. Christophorou, J. K. Olthoff, R. J. Van Brunt,
"[SF.sub.6] and the Electric Power Industry", IEEE Electrical
Insulation Magazine, DEIS, 1997, pp. 20-24.
[2] K.S. Prakash, K.D. Srivastava, M.M. Morcos, "Movement of
Particles in Compressed [SF.sub.6] GIS with Dielectric Coated
Enclosure", IEEE Trans. DEI, Vol. 4 pp. 344-347, 1997, No. 600.
[3] Anis H.and Srivastava K.D.," Breakdown characteristic of
dielectric coated electrodes in SF6 gas with particle
contamination,", sixth Intl symposium on HVE, New Orleans, LA,USA,
Paper No.32-06.
[4] N.J.Felici; "Forces et charges de petits objects en
contact avec une electrode affectee d'un champ electrique";
Revue generale de I' electricite, pp. 1145-1160, October 1966.
[5] J.Amarnath et.al., "Particle Trajectory in a common
enclosure Three phase [SF.sub.6] Bus dect", 12th International
Symposium on High Voltage Engineering, 20-24 August 2001, IISc
Bangalore, India.
[6] G.V. Nagesh Kumar, J. Amarnath, B.P. Singh, K.D. Srivatsava
"Electric Field Effect on Metallic Particle Contamination in a
Common Enclosure Gas Indulated Bus duct", IEEE transactions on
Dielectrices and Electrical Insulation, April 2007, pp. 334-340.
M. Venu Gopala Rao (1), J. Amarnath (2) and S. Kamakshaiah (3)
(1) QIS College of Engg. and Technology, Ongole, A.P, India
mvgrao_qis@yahoo.com
(2) J.N.T.University, Kukatpally, Hyderabad, A.P, India
amarnathjinka@yahoo.com
(3) CVR College of Engineering, Hyderabad, A.P, India
Table 1: Variation of movement of Aluminum, Copper and Silver
particles in a 3-phse GIB with various conductor diameters
Voltage (kV) Type Max. Movement (mm.)
64mm 59mm 54mm
300 Al 34.54588 33.56296 33.1185
Cu 6.959618 6.699295 6.587003
Ag N.M N.M N.M
400 Al 64.04347 63.09916 62.15208
Cu 17.68512 15.07431 14.93333
Ag 12.58007 12.3704 13.79715
450 Al 81.84347 81.00259 80.9588
Cu 26.63495 26.27919 24.48422
Ag 20.79749 20.27831 20.00559
500 Al 100.0761 99.1379 98.69654
Cu 28.68069 28.894 28.79075
Ag 25.39804 24.57452 23.06332
600 Al 140.4114 139.721 139.7768
Cu 45.5663 44.63778 44.20574
Ag 39.88366 37.22695 37.28612
700 Al 325.6726 324.9431 324.882
Cu 65.16706 64.73998 64.30928
Ag 54.26916 53.83524 53.39804
