US3325584A - High voltage insulator filled with semiconductive foam containing gas under superatmospheric pressure - Google Patents

Description

June 13, 1967 K. H. HERZIG 3,325,584

HIGH TAG NSULATOR FILLED WITH SEMICONDUCTIVE FOAM C AIN AS UNDER SUPERATMOSPHERTC PRESSURE Original Filed May 12, 1965 3 Sheets-Sheet I H. HERZIG 3,325,584

LLED w TH SEMICONDUCTIVE FOAM SUPERATMOSPHERIC PRESSURE S Sheets-Sheet 2 K. TOR Fl UNDER June 13, 1967 HIGH VOLTAGE INSULA CONTAINING GAS Original Filed May 12, 1965 5 Z 2 x. /M W 3,325,584 FOAM SEMICONDUCTIVE PHERIC PRES K. H. HERZIG OR FILLED WITH NDER SUFERATMOS June 13, 1967 ets- Sheet a A 5 ir: {it

United States Patent 3,325,584 HIGH VOLTAGE INSULATOR FHLLED WITH SEMICONDUCTHVE FOAM CONTAINING GAS UNDER SUlERATMOSPI-IERIC PRES- SURE Karl Heinz Herzig, Viernlieim, Hesse, Germany, assignor to Brown, Boveri & Cie Alktiengesellschaft, Mannheim- Kafertal, Germany, a corporation of Germany Continuation of application Ser. No. 455,261, May 12, 1965. This application Oct. 21, 1966, Ser. No. 588,625 (Ilaims priority, application Germany, May 14, 1964, B 76,760 18 Claims. (Cl. 1174-30) This application is a continuation of my prior copending application Ser. No. 455,261, filed May 12, 1965, and now abandoned.

My invention relates to high voltage insulators and more particularly to compound insulators which are made up of composite portions or layers.

High voltage insulators for use in the open air to suspend, brace or support voltage-carrying conductor lines or bus bars, generally consist of massive procelain members. Such massive construction is necessary to withstand external mechanical loads in tension or compression and in bending. Suspension-type cap or pin insulators and massive elongated rod or post insulators for suspending conductor lines from overhead line poles and cross-arms, are known.

The pin insulators, which can be provided with insulating bodies made of porcelain or glass, have an advantage over the post insulators in that the mechanical integrity of the pin insulators is maintained for the most part when mechanical damage is done to the insulating body, because due to the disposition of the pin extending into the cap thereof, the insulating body lying therebetween acts as a type of wedge even in broken condition. Nevertheless, pin insulators have the disadvantage that their insulating body becomes loaded electrically to the breakdown or discharge point and also does break down occasionally so that constant inspection and supervision of the conductor line is necessary.

Insulators with massive porcelain members of bodies, such as post-type or strain insulators for example, are not subject to danger of electrical breakdown because the arcing path thereof through the air is substantially the same as the path through the solid insulating. material which, of course, has different and higher electrical stress properties than air.

There is, however, a disadvantage to such insulating members in that they deteriorate due to external mechanical action and consequently conductor lines secured thereto can loosen and drop. In addition thereto, the mechanical strength of a post-type insulator loaded in tension is determined and limited by the tensile strength of its procelain element or member.

In order to obtain insulators having-better mechanical properties which will ensure against dislodging and drop ping of the conductor lines, several compound insulators have been proposed which are provided with a core of insulating material of high mechanical strength, for example of fiber-reinforced synthetic rods. Tests of such compound insulators have, nevertheless, not led to the desired results because trouble-free production thereof is prevented by the different thermal expansion or contraction of the porcelain and the plastic or synthetic core. Moreover, the space between fiber strand and porcelain body is not capable of being filled with cement devoid of shrink holes so that during use, undesired glow dischargestake place in the hollow spaces of the shrink holes.

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High voltage compound insulators are also known that are made up of an insulating member of arbitrary outer shape provided with a bore and having an inner suspension element which is a fiber strand, for example of synthetic material reinforced with glass fibers. For such a compound insulator it has already been suggested to fill the intermediate space between the insulating member and the suspension element located within its bore with a foamed synthetic material which serves as an elastic cushion for absorbing the forces arising due to heat stresses. This synthetic foam material must have such small hollow spaces as to avoid the formation of glow discharges therein for the particular working voltage. For this purpose, a foam material is selected from which nitrogen is freed during the foaming operation and the foamed material, after the foaming operation is ended, is subjected to an inner superpressure. In actual practice it has, however, been found that it is diflicult to produce a foam material with such small hollow spaces. The statistical distribution of the hollow spaces in the foam material is such that even for a large percentage of very small hollow spaces there is always present a specific number of hollow spaces with larger diameter.

It is accordingly an object of my invention to provide high voltage insulators of improved construction which avoid the disadvantages of the aforementioned insulators of known construction.

With this and other objects in view, and in accordance with various features of my invention, I provide an insulator comprising an insulated body of suitable outer shape formed with a bore, in which a fiber strand, for example of synthetic material reinforced with glass fibers, is located as a component of the suspension element. A hollow space or interspace between the suspension component and the outer insulating body is filled with a synthetic foam material consisting, for example, of the polymer resins polystyrol, polyethylene, and the like, which is formed with small closed cells after foaming. The resistance against arcing provided by such synthetic foam is considerably greater because of the small dimensions of the foam material cells than the resistance to arcing of a corresponding distance through air so that inner breakdown or arcing of the aforementioned insulating body is no longer probable. Because nitrogen is freed moreover during foaming of the synthetic material located in the interior of the insulator and the foaming proper can take place in a nitrogen atmosphere, the resistance to breakdown of the synthetic foam is thereby able to be further increased. If the insulating body is sealed tightly on all sides before or during the foaming operation, a pressure increase then takes place in the insulating body due to the foaming action or after the foaming action, which can be used for further increasing the resistance to breadown and which simultaneously provides the synthetic foam with the characteristics of an expansion cushion or padding for equalizing thermal and tensile expansions of the suspension element or of the outer insulating body.

In order to limit to a specific value the superpressure or excess pressure arising in the hollow space located in the insulating body during the foaming operation, in accordance with a feature of my invention, a tubular opening is provided in one of the two cover plates located at the end faces of the insulator, which is tightly sealed after the termination of the foaming operation by soldering, compression or by any other suitable method. If the foaming operation is to be performed in a nitrogen atmosphere or in an atmosphere of an electronegative gas, it is necessary to rinse the hollow space of the insulating body with the desired gas after installing the suspension element and after applying the cover plates. To this end, the aforementioned tubular opening is formed advantageously in both cover plates.

The pressure increase in the interior of the insulating body can also be effected, in accordance with another feature of my invention, subsequent to the foaming action, by feeding a gas of higher pressure slowly through one of the tubular openings so that it can diffuse slowly into the cells of the foam material. After the desired superpressure is achieved, the tubular openings provided in the cover plates are tightly sealed in the aforementioned manner.

In accordance with yet another feature of the invention, the suspension element or securing armature ex tending into the bore of the insulating member is made of metal which is electrically conductive and is surrounded with insulating material free of hollow spaces. In order also to control the mechanical force relationships in the insulator, a foam material is located between the insulating member and the suspension element or elements located in the bore thereof. By surrounding the voltage carrying metallic armature with insulating material free of hollow spaces, the field strength at the surface of the insulating member thus constructed is reduced so greatly, however, that an arc glow in the synthetic foam material at operating voltage can no longer take place. In order to additionally protect against the disadvantageous glowing of the synthetic foam material, the foam material is made semiconductive by additives mixed with the raw materials necessary for producing the foam. Materials that are suitable for this purpose are graphite, very fine-grain silicon carbide, such as known by the trademark name Carborundum, or similar material. The semiconductive synthetic foam material effects, for example for a unit insulator, a slight current flow between the voltage carrying and the grounded electrodes and thereby provides for an equalization or balancing of the entire electrical field. In this manner, local field strength peaks and therewith the glowing within the hollow spaces of the foam synthetic material for the operating voltage and over-voltages acting upon the respective insulating members, are prevented or avoided. For specific lower voltage loads, it is possible to do away entirely with the cladding or coating of the voltage carrying metal portions with insulating material free of hollow spaces. The semiconductive synthetic foam material is then brought directly in contact with the metal components. For specific higher voltage loads an overloading of the insulating layer free of hollow spaces and the layer of foam material, especially when these are not conductive, is prevented by providing a metallic electrode located along the length of the portion of the metal armature extending into the insulating member on the inner surface of the insulating member or in the direct vicinity thereof. This electrode can for example consist of a coating of conductive silver or of a deposited layer of copper. In order to achieve additional security against the disadvantageous glowing, in accordance with a further feature of my invention, the surfaces located in the bore of the insulating member are advantageously also provided with a semiconductor layerfor the purpose of effecting a uniform voltage distribution; that is, both the upper surface of the suspension rod of synthetic material reinforced with glass fibers as Well as the inner surface of the insulating member are coated with a thin layer of semiconductor material which, before the foaming operation, is just liquid and later dried or hardened by heating. Semiconductive lacquer admixed with graphite or Carborundum is employed for this purpose. The semiconductor layers and, if necessary, the semiconductive foam are electrically connected trouble-free with the voltage carrying and grounded metal portions of the insulator in order to achieve definite voltage relationships. For smaller specific voltage loads, if the surrounding walls are semiconductive, it is unnecessary to make the foam semiconductive.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims.

While the invention has been illustrated and described as high voltage insulator, it is not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing in any way from the spirit of the present invention. Such adaptations should and are intended to be comprehended within the meaning and range of equivalents of the claims herein.

The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

FIGS. 1 to 4 are longitudinal sectional views of one end portion of different embodiments of a high voltage insulator constructed in accordance with my invention;

FIG. 5 is an axial view of a modified form of the cylindrical r-od.

Referring now to the drawings and first particularly to FIG. 1, there is shown an end portion of an insulator having a supporting or suspension component formed of a chain-link or elongated ring 1 for example of synthetic material reinforced with glass fibers. Polyester or epoxy resins are suitable for this purpose. Transmission of force takes place through cable thimbles or eyes 2 which are provided with a bore 3 for receiving suitable connecting elements (not shown). A hollow insulating member 4 which is provided with insulating petticoats 5 of conventional dimensions and spacings one from the other serves as the outer insulation. This insulating member 4 can be made either of porcelain or glass or of molded resin resistant to ambient air. In the interior of the insulating member 4 the suspension element .1, 2 is centrally located and is maintained in this position by tightly sealing cover plates 6 located at the ends of the insulating member 4. The cover plates 6 are tightly secured to both the insulating member 4 and the eye member 2 for example by cementing, soldering or welding, or any other suitable manner. The cover plates 6 are suitably provided with expansion grooves '6' whereby thermal expansions, arising due to the different thermal coefficients of expansion of the materials used as well as from expansions caused by electrical loading of the suspension element 1, 2, can be absorbed. The hollow space in the interior of the insulator, defined by the insulating member 4, carrying element 1, 2 and cover plates 6, is filled with insulating synthetic foam material 7 formed with closed cells in the interior hollow spaces of which nitrogen or an electronegative gas is stored at a superpressure with respect to ambient atmosphere for example.

An insulator is shown in FIG. 2 which is similar to the embodiment shown in FIG. 1 except that the carrying or suspension element thereof includes a tube 11 of synthetic material reinforced with glass fibers. Force transfer in the embodiment of FIG. 2 takes place by means of a forked or shackle-type pin 12 which is cemented at its lower end 13 into the tube 11 by means of a molded resin 14. A metal sleeve 15 is slid on the outer side of the tube 11 at the location of the cemented section so as to take up transverse forces and is glued or press-fitted thereto. To prevent interior arcing or breakdowns, the tube 11 is filled with solid synthetic material or foamed synthetic material 16.

The unitary carrying or suspension element 11, 12, 13, 14, 15 is in turn inserted into the interior of the insulating member 17. The hollow space located between the insulating member 17, the carrying element 11-15 and the cover plate 18 is also filled with a foamed synthetic material 19 corresponding to the material 7 of the compound insulator embodiment of FIG. 1. The assembly of the pin 12 is similar for the opposite end of the insulator that is not shown in the figure.

Another embodiment constructed in accordance with my invention is shown in FIG. 3 wherein the carrying or suspension element is formed of a cylindrical rod 22 consisting of synthetic material reinforced with glass fibers and provided at both ends with compression clamps 21 (only one end shown in FIG. 3). The compression clamps 21, which are formed at the ends thereof with bores 23 for receiving suitable connecting members (not shown), are press-fitted in a known manner onto the rod 22 of synthetic material. For increasing the clamping action of the compression clamps 21, the cylindrical rod 22, as shown in FIG. 5, can be split at both ends by driving plates or cross-shaped wedges into the same so that conical thicknened ends are formed which are then pressed into the correspondingly formed clamping portions 21' of the compression clamps 21. It is thereby possible to shorten the length of the clamping portions 21, of the clampingmember, if necessary. Instead of pressing the clamps onto the rod 22 of synthetic material, the rod 22 can also be glued to the clamps or be molded thereto with a suitable molding resin or a similar moldable material.

-As in the case of the embodiments of FIGS. 1 and 2, in the embodiment of FIG. 3, the hollow space of the insulating member 24, which is sealed tightly at both ends by cover plates 25, receives the carrying or suspension element 21, 22. The remaining hollow space between the carrying element 21, 22 and insulating member 24 is filled with synthetic material foam 26 as in the case of the embodiments of FIGS. 1 and 2.

In order that there be good adhesion between the synthetic material foam and the surfaces of the adjacent structural elements, that is the inner surfaces of the insulating member 4, 17, 24, as the case may be, and the outer surfaces of the carrier element 1, 2; 11-15; 21, 22, respectively, during thermal expansions or mechanical loadings, these surfaces can be covered with an adhesive before the synthetic material is foamed in the hollow space between the respective cover plates, carrying elements and insulating member. This measure or step is particularly advisable when the synthetic material foam is not subjected to a super-pressure with respect to the ambient atmosphere.

In the embodiment of FIG. 4, the carrying or suspension component 31 of the insulator is formed of a cylindrical rod consisting of synthetic material reinforced with glass fibers. This rod is secured at both ends thereof in clamps 32 (only one shown) which can be made for example of pressed metal components, such as steel, copper or aluminum. The outer insulation is provided by the hollow insulating member 33 which is formed with insulating petticoats 34 of conventional dimensions and spacings therebetween. This insulating member 33, as for the corresponding embodiments of FIGS. 1-3, can be made of porcelain or glass or of a molded resin which is resistant to ambient air. The carrying component 31 is located in the bore of the insulating member 33 which is tightly sealed at its ends by the cover plates 35. The cover plates 35 may consist of metal and are soldered or welded to the suspension eyes of the clamps 32, it being noted that components 32 and 35 are shown only at one end of the insulator, and are glued or cemented to the insulating member 33. The hollow space between the carrying component 31 and the insulating member 33 is filled with synthetic foam material 39 formed with the smallest possible closed hollow spaces.

To reduce the electrical field strength in the synthetic foam material adjacent the current conducting metallic components of the suspension element 31, 32, the clamps 32 are surrounded with a body 36 of insulating material free of any interior hollow spaces which can consist of insulating material wound thereon or of molded resin. The molded resin can if desired also be\provided with insulating fillers. For voltage equalization or compensation in the interior of the insulating member, especially in the vicinity of the voltage or current conducting and grounded metal components, a synthetic foam material 39 is employed for filling the hollow space between the insulating member and the suspension structural components 31, 32 of the insulator, and semiconductor ma terials are added to the synthetic foam material 39. In order to form a semiconductive foam material, graphite or Carborundum, for example, are added to the materials employed for making the foam, and in such quantity as is necessary for achieving a specific resistance to arcing or breakdown of the insulator in the order of magnitude of 10 to 10 ohms. To prevent an electrical overload of the insulating member 36 that is free of hollow spaces, on the metal armatures 32 and the adjacent layer of synthetic foam material, especially when these are formed of nonconducting material, a conductive electrode 37 is provided along the inner wall of the insulating member 33 extending up to the inner end of the metal armature 32 and is electrically connected, as is the foam, with the metal armature 32. For further voltage adjustment or equalization, the inner wall-of the insulating member 33 and the surface of the cylindrical rod 31 of glass fiber-reinforced synthetic material are coated with a semiconductive layer 38. Such a layer 38 can consist of thermosetting or thermoplastic synthetic gum-lac or resins to which graphite or Carborundum has been added. The semiconductor layers 38 are also electrically connected with the metal armatures 32, the layer located on the inner surface of the insulating member 33, for example, being connected with the armatures 32 by means of bridge members 40 of semiconductor material.

I claim:

1. High voltage compound insulator comprising a hollow tubular insulating member externally formed with a plurality of axially aligned petticoats, a suspension element extending axially into the interior of said hollow insulating member in spaced relation to the tubular wall thereof, and synthetic foam material located in the space between said suspension element and the wall of said insulating member, said foam material being filled with gas at greater than ambient pressure and containing dispersed particles of material rendering said foam material semiconductive.

2. Insulator according to claim 1, wherein said insulating member consists of a material selected from the group consisting of porcelain, glass and molded resin.

3. Insulator according to claim 1, wherein said synthetic foam material consists of a foamable polymerized resin formed, after foaming, with a multitude of small closed cells.

4. Compound insulator according to claim 1, wherein said insulating member has a tubular wall, and including a cover plate at each end of said tubular wall sealingly closing the hollow interior thereof.

5. Compound insulator according to claim 4, wherein at least one of said cover plates is formed with an opening, and including means tightly sealing said opening.

6. Compound insulator according to claim 4, wherein said cover plates are formed with expansion grooves.

7. Compound insulator according to claim 1, wherein said suspension element comprises an elongated ring of synthetic material reinforced with glass fibers and an eye member secured to each end of said elongated ring.

8. High voltage compound insulator comprising a hollow tubular insulating member externally formed with a plurality of axially aligned petticoats, a suspension element extending axially into the interior of said hollow insulating member in spaced relation to the tubular wall thereof, and synthetic foam material located in the space be tween said suspension element and the wall of said in sulating member, said suspension element comprising a tube consisting of synthetic material reinforced with glass fibers, a pair of eye members each having an end portion extending into one of the ends of said tube, respectively, and cemented thereto, and a metal sleeve coaxially mounted on the exterior of said tube and tightly secured thereto at the location of the cemented end portion of said eye members respectively.

9. Compound insulator according to claim 1, wherein said suspension element comprises a cylindrical rod consisting of synthetic material reinforced with glass fibers, and a compression clamp press-fitted on each end of said rod. 7

10. Compound insulator according to claim 9, wherein me ends of said cylindrical rod are formed with a cleft respectively in which a wedging member is received whereby said respective ends are enlarged.

11. Compound insulator according to claim 1, including an adhesive layer located respectively between said insulating member and said foam material and between said suspension element and said foam material for securing said foam material to said insulating member and said suspension element.

12. Compound insulator according to claim 1, wherein said suspension element comprises an intermediate member consisting of insulating material capable of absorbing applied mechanical forces and end members of metallic material secured to the ends respectively of said intermediate member,

13. Compound insulator according to claim 12, wherein graphite is dispersed in said synthetic foam material for rendering the same semiconductive.

14. Compound insulator according to claim 12, including a layer of solid synthetic material devoid of cells surrounding said metallic end members of said suspension element, said synthetic foam material being located in the space between said suspension element and layer of solid synthetic material on the one hand and the wall of said insulating member on the other hand.

15. Compound insulator according to claim 12, wherein a semiconductor layer is located respectively on the inner surface of said insulating member and the outer surface of said intermediate member.

16. Compound insulator according to claim 15, wherein said semiconductor coatings are electrically connected with said metallic end members respectively.

17. Compound insulator according to claim 12, wherein only a portion of the metallic end members of said suspension element extends into the interior of said hollow insulating member, and an electrode is located adjacent the inner surface of said insulating member and extends into the hollow interior thereof from each end thereof coextensively with said portion of said metallic end members respectively, said electrode being electrically connected with the respective metallic end member.

18. Compound insulator according to claim 17, where in said electrode is formed of a metal selected from the group consisting of copper and silver deposited on the inner surface of said hollow insulating member.

- References Cited UNITED STATES PATENTS 6/ 1963 Great Britain.

OTHER REFERENCES German application No. 1,063,668, Zenger, publishe Aug. 20, 1959.

LARAMIE E. ASKIN, Primary Examiner.

Claims (1)

1. HIGH VOLTAGE COMPOUND INSULATOR COMPRISING A HOLLOW TUBULAR INSULATING MEMBER EXTERNALLY FORMED WITH A PLURALITY OF AXIALLY ALIGNED PETTICOATS, A SUSPENSION ELEMENT EXTENDING AXIALLY INTO THE INTERIOR OF SAID HOLLOW INSULATING MEMBER IN SPACED RELATION TO THE TUBULAR WALL THEREOF, AND SYNTHETIC FOAM MATERIAL LOCATED IN THE SPACE BETWEEN SAID SUSPENSION ELEMENT AND THE WALL OF SAID INSULATING MEMBER, SAID FOAM MATERIAL BEING FILLED WITH GAS AT GREATER THAN AMBIENT PRESSURE AND CONTAINING DISPERSED PARTICLES OF MATERIAL RENDERING SAID FOAM MATERIAL SEMICONDUCTIVE.

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