CA1175924A - Gas insulated electrical device with dielectric particle traps - Google Patents

Abstract

7 49,525 ABSTRACT OF THE DISCLOSURE
A gas-insulated electrical device includes a high voltage conductor disposed in a hollow grounded tank, with an insulating spacer supporting the conductor. A
dielectric element having a groove thereon is disposed on the interior surface of the tank surrounding the insulat-ing spacer.

Description

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1 49,525 GAS-INSULATED ELECTRICAL DEVICE
WITH DIELECTRIC PARTICLE TRAPS
BACKGROUND OF THE INVENTION
This invention relates generally to gas insu-lated electrical devices which have SF6 gas as the insu-lating medium, and relates particularly to gas-insulated electrical devices of a construction whereby foreign matter suspended in the grounded tank of the electrical device does not attach to the surface of the spacer sup-porting the high voltage conductor disposed therein.
Heretofore, gas-insulated electrical devices of this type have typically been of the construction shown in Figure l. As shown in Figure 1, a high voltage conductor 1 is supported in a grounded tank 2 by means of an insu-lating spacer 3, and a metal plate 4 is supported concen-trically around the high voltage conductor 1 by the insu-lating spacer 3. Provided in the metal plate 4 are slits5, and a trapping area 20 for suspended particles is formed in the space 20 between the metal plate 4 and the tank 2. The metal plate 4 is supported by the tank 2 through a support rod 6, and a compressed yas 7, typical of which is SF6 yas, is contained in the tank 2.
Generally, in gas-insulated electrical devices, there are instances where, from whatever cause, foreign matter such as particles find their way into the device, or are produced after installation. On such occasions, a lifting force acts on the foreiyn matter inside the device :.

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2 4g,525 due to the electrostatic force generated by the electric field, and ~hen this lifting force exceeds the force of gravi-ty on the-forei~n matter itself, the foreign matter lifts upwards, and attaches to the surface of the conduc--5 tor support insulating spacer, inviting a state of easy flashover along the surface, this being a major cause of a reduction in the dielectric strength of the device.
Consequently, in a prior device as shown in Figure 1, there is provided inside the gas-insulated electrical device a trapping space 20 for capturing the particles suspended within the gas-insulated electrical device. The metal plate 4, which is an intermediate electrode between the high voltage conductor 1 and the tank 2, i5 maintained at substantially the same potential as the earthed tank 2. When the foreign matter suspended within the tank 2 has once entered the spac~ 20 between the inner surface 21 of the tank 2 and the intermediate electrode metal plate ~ through the slits 5, the field in this space 20 is low so that the particles do not fly out again.
However, in this trap device there is the defect that the foreign particles are not uniformly caught in the trap space 20 between the metal plate 4 and the tank 2, but in fact there is a tendenc~ for the foreign particles to accumulate on the surface 21 of the tank 2 adjacent to the insulator of the metal plate 4, and when an unusual voltage occurs, the once trapped foreign matter once again lifts up. Also there is the defect that the aforemen-~;tioned trap device is constructed of earthed metal, so the size of the trap device itself reduces the insulating .~space, and so the diameter of the tank 2 of the gas insu-lated electrical device has to be made large.
SUMMAR OF T~E INVE;NTION
,This invention was made in order to eliminate ~he ore~oing clefects in the prior art, and provides a gas insulated electrical device w:ith a trap device which is " :
~capable of reliably capturing foreign matter. The ~as :, , , ; , .

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3 49,525 insulated electrical device is of a construction which includes a dielectric material such as polytetrafluoro-ethylene, having a groove therein, disposed on the inner peripheral surface of a grounded tank, in contact with the inner peripheral surface, which dielectric material is capable of effectively preventing the adhesion of foreign matter within the device to the surface of the insulating spacer which supports the inner-disposed high voltage conductor.

Figure 1 is a vertical sectional view of a gas insulated electrical device provided with a prior art trap device;
Figure 2 is a vertical sectional view similar to ; 15 Figure 1 showing an embodiment of a gas-insulated elec-trical device o~ this invention;
Figure 3 is a side sectional view taken along the line III-III in Figure 2;
Figure 4 is a perspective view of a dielectric material employed in the gas-insulated electrical device of this invention; and ~igures 5A to 5D are portional sectional views of dielectric materials showing examples of the cross-sectional shape of the groove portion.

Hereinbelow, this invention is explained with relation to an illustrated embodiment. In Figure 2, the high voltage conductor 1 being supported in the grounded tank 2 by means of an insulating spacer 3 is the same as ~ 30 in Figure 1, but a dielectric material 8 is disposed on a v portion of the inner peripheral surface 21 of the tank 2, and, as shown in Figure 3, the inner peripheral surace 21 of the tank 2 and the outer surface 22 of the dielectric material 8 are positioned so as to be in contact. The ; 35 dielectric material 8 h~s the shape shown in Figure 4, and `~ is provided with a groove portion 9 extending in the axial direction thereof. A trap device 23 constructed with a ..

4 49,525 . dielectric material 8 such as this, is provided so as to surround the insulating spacer 3 from both sides.
The cross-sectional form of the groove 9 in Figure 3 is shown as having a dovetail shape, but as shown in Figures 5A to 5D, the various cross-sectional shapes of grooves 9a, 9b, 9c, and 9d, may be used.
While minute foreign matter (not shown) in the . gas-insulated electrical device is floating in the gas ; space, it does not have much effect on the di.electric : 10 strength of the gas insulated electr:ical device. However, ` when the aforementioned foreign matter adheres to the .
surface of the insulating spacer 3 which supports the high ;voltage conductor l, the surface of the insulating spacer 3 is deteriorated by corona discharging, and surface ~ 15 flashovers are produced, bringing about a reduction in the .~. dielectric strength of the device.
When alternating current voltage is applied to the high voltage conductor 1 of Figures 2 to 4, the con-:. ductive foreign matter is lifted up by the electric field 20 and moves back and forth in the space 24 between the tank . 2 and the high voltage conductor 1, and begins a certain ; .amount of random movement in the axial direction.
.; However, the conductive foreign matter goes into the groove portion 9 provided in the dielectric material 8, and does not contact the insulating spacer 3.
Also, the dielectric 8 of the trap device 23 shown in the Figures is constructed of a dielectric mater-;,~
: ~ial such as polytetrafluoroethylene, and by the charged .foreign matter coming into contact with the dielectric .~30 material 8 in the groove 9, an image charge is formed in ithe dielectric material 8, and so the attraction for the charged ~oreign matter acts, and the charged orei~n ;;matter is eaught inside the groove portion 9 by this ~:at~raction, and does not fly out again.
35As he~ei.nabove, according to this lnvention a ; trap deviee is eonstructed of a dielectric material, an~
., thus without the electric field within the gas-insulated , . ...

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49,525 electrical device, and consequently the insulating charac-teristics of the electrical deivce, being upset, it is possible with a-simple construction to shut foreign matter out of the insulated spacer section, and to capture it, with the effect that it is possible to improve the relia-bility of the device.

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Claims (3)

6 49,525 I claim as my invention:

1. A gas-insulated electrical device compris-ing:
a grounded hollow tank;
a high voltage conductor disposed within said tank;
means for insulatably supporting said conductor within said tank;
an insulating gas having a high dielectric strength filling said tank;
a solid dielectric element mounted on and conforming to,a portion of the inner surface of said tank;
and a groove in the inner surface of said dielectric element generally parallel to said conductor.

2. The device according to claim 1 wherein said dielectric element is constructed in a shape so as to sur-round said support means and is disposed spaced-apart from said support means.

3. The device according to claims 1 or 2 where-in said dielectric element is of a material comprising polytetrafluoroethylene.