US 3715532 A
An encapsulated high voltage-switching installation, the cylindrical conductor of which serves to carry a high voltage and is surrounded by a grounded cylindrical sheath filled with an insulating gas. The conductor is concentrically attached within the sheath by means of insulating supports. According to important aspects of this invention at least one trumpet-shaped foil possessing a rotationally symmetrical construction and widening in the axial direction of the conductor is arranged between the conductor and the sheath, this trumpet-shaped foil being formed of an insulating material.
Description (OCR text may contain errors)
Morva  ENCAPSULATED HIGH VOLTAGE- SWITCHING INSTALLATION FOREIGN PATENTS OR APPLICATIONS 239,349 12/1960 Australia ..l74/73 R  Inventor: Tibor Morva, Oberentfelden, Swit- 242,226 7/1963 Austria t ..l74/73 Zefland 910,437 5/1954 Gennany ....174/73 879,712 10/1961 Great Britain ..174/28  Assignee: Sprecher & Schuh AG, Aarau, Switzerland Primary Examiner-Robert K. Schaefer Assistant Examiner-William J. Smith  Flled: 1971 Att0rneyEric H. Waters et a1.  Appl. No.2 210,366
 ABSTRACT  Foreign Application Priority Data An encapsulated high voltage-switching installation, the cylindrical conductor of which serves to carry a April 19, 1971 Switzerland ..5629/7l high voltage and is urrounded by a grounded cylindrical sheath filled with an insulating gas. The conductor  US. Cl. ..174/28, 174/73 R is concentrically attached within the sheath by means  Int. Cl. ..H0lb 9/04 of insulating supports. According to important aspects 58 Field of Search ..174/l6 B, 28,73 R, 73 so; of this invention at least one p pe foil P 2 4 sessing a rotationally symmetrical construction and widening in the axial direction of the conductor is ar-  References Cited ranged between the conductor and the sheath, this 7 trumpet-shaped foil being formed of an insulating UNITED STATES PATENTS material.
3,446,741 5/1969, Hervig et a1 ..-......174/73 R X 4 Claims, 2 Drawing Figures PATENTED FEB 6 I973 SHEET 10F 2 Fig. 1
ENCAPSULATED HIGH VOLTAGE-SWITCHING INSTALLATION BACKGROUND OF THE INVENTION The present invention relates to a new and improved encapsulated high voltage-switching installation, the cylindrical conductor of which serving to carry a voltage is surrounded by a grounded cylindrical sheath filled with an insulating gas and concentrically secured therein by insulating supports.
Disc-shaped insulating supports consisting of a casting resin are known in the art for encapsulated high voltage-switching installations, these disc-shaped insulation supports being arranged between the conductor and the sheath. The electrical field strength or intensity is not constant between two concentrically arranged cylindrical electrodes and as is known extends in radial direction in accordance with a function containing a logarithmic component. However, the electrical field strength is practically constant at the surface of the known disc-shaped insulation supports, because the electrical field is controlled by the thickness of the discshaped insulation supports, this thickness increasing in the direction of the conductor.
A drawback of these disc-shaped insulation supports resides in the fact that they are extremely sensitive to soiling or contamination. In particular, metallic particles present at the switching installation owing to wear of the contact locations or which emanate from assembly operations and which deposit themselves upon the surface of the insulation supports bring about a localized increase in the field strength or intensity and lead to surface discharges and to flashover or arcing.
Trumpet-shaped insulation supports are also known in the art for the purpose of supporting the inner conductor in concentric cylindrical coaxial transmission lines. The voltage distribution is uniform at the surface of a very thin trumpet-shaped insulating layer suitably arranged between two concentric cylindrical electrodes and hence there is also present a constant electrical field strength. However, the heretofore known trumpet-shaped insulation supports possess a relatively large wall thickness owing to mechanical strength considerations. Due to interruption or breaking of the lines of theelectrical field at the'insulation walls there appears an irregular electrical load at the surface of the known trumpet-shaped thick-wall insulation supports.
These insulation supports are also markedly sensitive to contamination.
' SUMMARY'OF THE INVENTION Hence, from what has been discussed above it will be recognized that a real need still exits in the art for an encapsulated high voltage-switching insulation of the character described which is not associated with the aforementioned drawbacks and limitations of the prior art constructions. Thus, a primary object of the present invention is to provide an encapsulated high voltageswitching installation which is not associated with these drawbacks and limitations and which effectively and reliably fulfills the existing need in the art.
Another and more specific object of the present invention is to provide a novel construction ofencapsulated high voltage-switching installation wherein the sensitivity of the insulation supports against contamination or soiling is reducedand therefore the operational reliability increased.
Now, in order to implement these and still further objects of the invention, which will become more readily apparent as the description proceeds, the encapsulated high voltage-switching installation of the present invention contemplates providing at least one rotationally symmetrical trumpet-shaped foil or sheet formed of insulating material between the conductor and the sheath and which trumpet-shaped foil enlarges or widens in the axial direction of the conductor.
A particularly advantageous modification of the invention resides in the features that through appropriate curvature of the surface of the foil for the same electrical potential differences determined from the field pattern between the conductor and the sheath there are chosen the same creepage path lengths.
Owing to the inventive construction and arrangement contamination or soiling of the insulation supports is prevented in that the contaminant particles only can deposit upon the surface of the foil where there prevails a considerably smaller electrical field intensity that at the surface of the installation supports. The foil is chosen to be so thin that as a practical matter it does not influence the course of the lines of the electrical field.
BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood and objects other than those set forth above, will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein:
FIG. 1 is a fragmentary longitudinal sectional view of an encapsulated gas insulated conductor secure within a grounded sheath by means of disc-shaped insulation supports; and
FIG. 2 is a fragmentary longitudinal sectional view of a modified form of encapsulated gas insulated conductor secured within a grounded sheath by means of discshaped insulation supports. 7
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Describing now the drawings, the cylindrical conductor l depicted in FIG. 1 is intended to carry a voltage. This cylindrical conductor 1 is surrounded by a cylindrical sheath 2 formed of an aluminum tube and which is at ground potential. A disc-shaped insulation support 3 is clamped between both flanges 4 of the sheath 2 and carries an inner electrode 5 electrically coupled with the conductor 1.
The disc-shaped insulation support member 3 consists of a suitable casting resin extended by a filler and enlarges in the direction of the conductor 1, as shown. Since the dielectric constant of the filled extendedcasting resin is four to five times greater than that of the insulating gas which is located between the conductor 1 and the sheath 2 it is possible to obtain a practically uniform voltage distributionover the surface of the insulation support or support member 3. The capacitance of the insulation support member 3 present in the radial direction along each unit length increases somewhat towards the inside in order to obtain the desired uniform voltage distribution.
Now to both sides of the insulation support member 3 there are mounted the trumpet-shaped foils or sheets 6 formed of an insulating material and constructed so as to be rotationally symmetrical. These trumpetshaped foils 6 widen in the axial direction of the conductor 1, as shown. The foils 6 are clamped at the outside i.e., at their largest opening 6a between the flanges 4 and the insulating support 3 and at the inside i.e., at the smaller opening 6b such foils 6 are attached to the conductor 1 by means of a tape 7 or equivalent structure. Each foil 6 is formed ofa suitable plastic material, such as for instance polyethylene, polypropylene, TEFLON, polymonochlorotrifluoroethylene, fluorinated ethylene-propylene, polyvinylchloride, polyvinalfluoride, polyester or a high-molecular cellulose derivative such as cellulose acetate. The thickness of the foil amounts to less than 1 millimeter for a 200 kV switching installation.
in FIG. 2 there is illustrated a modified embodiment of encapsulated high voltage-switching installation wherein generally the same reference characters have been employed for the same components. It should be understood that this embodiment resorts to the use of a modified insulation support 8. Here the disc-shaped insulation support member 8 is provided with the tubular-shaped extensions 9 which directly surround the conductor 1. The inner surface of the insulation support 8 equipped with the extensions 9 and facing the conductor 1 is metallized and electrically conductively connected with the conductor 1. The extensions 9 serve for supporting the region of smaller openings 6b of the foils 6. Here also the foils 6 are clamped at the outside regions i.e., at the region possessing the largest opening 6a between the flanges 4 and the insulation support 8, as shown, and bear against the disc-shaped portions 8a of the insulating member 8. The foils 6 can be adhesively bonded at their contact surfaces with the extensions 9 and with the insulation support 8. Thus While there is shown and described present preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims. AC- CORDINGLY,
What is claimed is:
1. An encapsulated high voltage-switching installation comprising a cylindrical conductor intended to carry a high voltage, a grounded cylindrical sheath filled with an insulating gas surrounding said conductor, insulating support means for concentrically connecting said conductor with said sheath, and at least one rotationally symmetrical substantially trumpetshaped foil formed of insulating material arranged between said conductor and said sheath, said trumpetshaped foil widening in the axial direction of the conductor.
2. An encapsulated high voltage-switching installation as defined in claim 1, wherein the same creepage path lengths are selected by appropriate curvature of the surface of said foil for the same electrical potential differentials determined from the field pattern between the conductor and the sheath.
An encapsulated high voltage-switching installa tion as defined in claim 2, wherein said insulating support means comprises a disc-shaped insulation support member, and wherein said trumpet-shaped foil at the end thereof having the largest opening bears against said insulation support member.
4. An encapsulated high voltage-switching installation as defined in claim 2, wherein said insulating support means comprises a substantially disc-shaped insulation support member having disc-shaped portions and substantially tubular-shaped extensions which directly surround said conductor, and wherein said trumpetshaped foil has its end possessing the largest opening bearing against said disc-shaped portions of said insulation support member and having its smaller opening bearing against said tubular-shaped extensions of said insulation support means which directly surround said conductor.