US2892014A - Electric insulator - Google Patents

Description

June 23, 1959 c. D. EICHELBERGER 2,892,014

' ELECTRIC INSULATOR Filed Sept. 14, 1956 Inventor:

Charles D. Eichelberger,

torneg.

United States Patent ELECTRIC INSULATOR Charles D. Eichelberger, Ridley Park, Pa., assignor to General Electric Company, a corporation of New York Application September 14, 1956, Serial No. 609,924

8 Claims. (Cl. 174-212) of insulator which heretofore has typically been constructed as a porcelain cylinder with axially spaced circular ribs formed in its periphery. Such porcelain insulators, commonly used for supporting switches, fuses, buses and the like, are quite expensive due to the necessarilyinvolved nature of their fabrication process and also due to the difliculties involved in adapting the porcelain insulator for subsequent mounting upon adjacent structures. As for the fabrication process, it has been necessary to rely upon a turning or spinning procedure to form the circular ribs and also to rely upon a glazing procedure in order to render the exterior of the insulator non-porous and of the desired dielectric strength. As for adapting the insulator for subsequent mounting, it has been necessary to rely upon deeply-imbedded metallic end-fixtures cemented or otherwise bonded in place within the porcelain body of the insulator. The bond between the end fixtures and the porcelain body has been a potential source of mechanical failure and has required a number of involved time-consuming steps for its formation. Moreover, because of the deeply imbedded nature of the endfixtures, the electric field surrounding the insulator has been so distorted as to require longer creepage paths along the exterior surface of the insulator than would otherwise be required.

Accordingly, one of the objects of my invention is to provide a high mechanical strength insulator which readily lends itself to a simple and inexpensive method of fabrication.

Another object is to provide an inexpensive molded or cast insulator which has insulating properties and mechanical-strength properties at least equal to a typical porcelain insulator unit with corresponding overall physical dimensions.

Another object is to provide an insulator which can be easily and inexpensively mounted upon adjacent structure without the need for deeply-imbedded end-fixtures.

Still another object is to construct the insulator with integrally-formed end flanges which are of such a nature as to be highly resistant to damage from localized stresses which might be produced by cantilever loadings.

In carrying out my invention in one form, I provide an electric insulator which comprises an axially-extending body portion formed of molded insulating material. Integral with the body portion and projecting radially therefrom at opposite ends thereof, a pair of end-flanges is provided. At least one of the flanges contains axiallyextending apertures for receiving fastening devices which serve to secure electrical apparatus to the axially-outer surface of the flange. The other flange is adapted to be clamped to a suitable base with its axially-outer surface abutting the base. This other flange'has a polygonal 2,892,014 Patented June 23, 1959 periphery providing rectilinear surfaces located to form virtual pivots about which all of the major cantilever forces applied to the insulator act. As a result of this latter feature, those stresses which are produced by cantilever forces are distributed over a relatively extensive region of the insulator rather than being concentrated at a particular point.

For a better understanding of my invention, reference may be had to the following specification taken inconnection with the accompanying drawings, wherein:

Fig. l is a perspective view, partly in section, showing an electric insulator constructed in accordance with one form of my invention.

Fig. 2 is an elevational view, partly in section, showing the insulator of Fig. 1 used for supporting an electric bus.

Fig. 3 is a plan view of the arrangement shown in Fig. 2 with a portion broken away for clarity.

Fig. 4 is a plan view illustrating another manner in which the insulator of Fig. 1 can be used for supporting a bus.

Fig. 5 is an elevational view showing the insulator of Fig. 1 used as one of the supports for an electric switch.

Fig. 6 is a plan view of the switch shown in Fig. 5.

Referring now to Fig. 1, I have shown therein an insulator 10 which is formed of a molded, or cast, insulating material of high mechanical-strength, such as, for example, a polyester resin reinforced with glass fiber. The insulator 10 comprises an axially-extending body portion 12 and a pair of end- flanges 14 and 16 formed integrally with the body portion and extending radially therefrom at its opposite axial ends. The body portion 12 is provided with a plurality of radially projecting webs 18 each of which extends axially between the end flanges 14, 16 and is formed integrally with the flanges. In the disclosed embodiment, four of these webs 18 are angularly spaced-apart by equal amounts about the periphery of the body portion 12.

Between each adjacent pair of webs 18, there is provided in the upper end-flange 14 an axially-extending aperture 20 and in the lower end-flange 16 a similar aperture 22. Each of these apertures 20 and 22 receives an internally-threaded insert 24 which has a shoulder 25 at its axially-inner end. Each of these inserts 24 is preferably press-fitted into its aperture 20 or 22 from the space between the two flanges 14 and 16. The shoulder 25 abutting against the inner surface of the flange anchors the insert against further axial movement. As shown in Fig. 2, axially-extending knurls formed about the outer periphery of each insert 24 prevent the inserts from rotating relative to the insulator. This locking action is aided by the fact that the apertures 20 and 22 are of such a size that when the inserts 24 are pressed into position, the knurls on the inserts firmly imbed themselves into the surrounding insulator material. The knurls, being imbedded directly in the insulator material, preclude rotation of the inserts without the need for cement or other bonding agents. Other non-circular peripheral shapes can, of course, be used in a similar manner to preclude rotation of the inserts.

As will be apparent from Fig. 2, these inserts 24 are adapted to receive suitable fastening devices such as bolts 23 which have external threads adapted to mesh with the internal threads of the inserts. By tightening the bolts 28, it is possible to clamp any suitable form of structure against the axially-outer surface of either flange 14 or 16.

Referring to Fig. 2, I have shown an electric bus 30 supported on the insulator 10 by means of a pair of spaced-apart L-shaped brackets 32 which are clamped to the outer surface of the upper flange 14 by the bolts 28. The bus is shown clamped between the brackets by a suitable bolt 33. The lower flange 16 of the insulator is clamped against a base 34 by means of bolts 28 extending into the lower inserts 24 through suitable apertures provided in the base. The bus 30 is normally at a relatively high potential with respect to the base 34, and the insulator serves to electrically isolate these two parts.

Since the bus 30 is at a high potential with respect to the base, it will be apparent that those inserts 24 located at one end of the insulator 10 will be at a high potential with respect to those inserts 24 located at the opposite end of the insulator 10. In order to provide between these groups of inserts a creepage distance which is at least equal to that provided by a conventional porcelain insulator unit having corresponding overall dimensions, I provide intermediate the flanges 14 and 16 a circular barrier 36 which extends generally parallel to the endflanges. For this same purpose, I further provide each of the Webs 18 with a plurality of ribs 37 extending radially with respect to the body portion 12.

It should be apparent that the integrally-formed flanges 14 and 16 provide a very convenient means for enabling the insulator 10 to be secured to adjacent structure. With these flanges present, it is no longer necessary to rely upon the type of end-fixture which has a plug or the like extending deeply into the body portion of the insulator and bonded thereto, as, for example, in the usual porcelain insulator unit. The presence of these flanges, together with the hollowed-out region of the insulator located behind each flange, allows the use of a simple, firmly-anchored insert for receiving the fastening devices 28. Because I am able to press the shouldered inserts 24 into position from this space behind the flange, it is unnecessary to cement or otherwise bond the inserts in place. Essentially all of the clamping forces are transmitted to the flange through this direct abutment between the shoulders 25 and the flange.

It should also be apparent that the webs 18 greatly increase the rigidity and strength of both the body portion 12 and the flanges 14 and 16 and yet do not interfere with the interior space which is allowed to provide for pressing the inserts 24 into their respective apertures.

It will be observed that in the illustrated insulator each of the end- flanges 14 and 16 has been formed with a periphery which defines at its axially-outer edge a polygon having rectilinear sides. This polygonal shape and its particular disposition relative to the direction in which cantilever forces are likely to be applied to the insulator enable me to provide an insulator which is highly resistant to damage from cantilever loadings. This may be understood by considering the effect which a cantilever force applied to the upper end of the insulator would have on the lower end-flange 16. For example, assume that in Figs. 2 and 3 the bus 30 is subjected to magnetic forces acting in a horizontal direction normal to the longitudinal axis of the bus, as is indicated by the arrow F. These forces would tend to pivot the entire insulator 10 about its edge 40 resting upon the base 34. This tends to con centrate considerable localized stresses in the region of edge 40. In the disclosed insulator, however, the edge 40 extends along one entire side of the polygonal periphery, and as a result, the forces at the edge 40 are distributed over this entire side of the polygon. On the other hand, if the end-flange 16 had a circular periphery or if the edge 40 were located at a corner of the flange, contact between the edge 40 and the base 34 would tend to occur only at a single point rather than along an extended line. This point contact would result in highly concentrated stresses being produced at the edge 40, and such stresses would tend to fracture or otherwise damage the flange 16.

In accordance with the present invention, I preclude the above-described point contact, first, by predetermining the directions, or lines of action, along which the major components of cantilever force are likely to act and, then, by locating the rectilinear sides of the polygon in planes perpendicular to these directions or lines of action. With regard to this first factor, I have found that when the disclosed insulator is used as a support for most conventional forms of electric apparatus, cantilever loads, for the most part, will be applied in a direction either perpendicular to or parallel to one or more of a plurality of reference lines which can be drawn between the center lines of the inserts 24. For example, referring to the arrangements of Figs. 2 and 3, it is common to have at least one other bus (not shown) extending parallel to the bus 30, and the magnetic fields between these two buses will react in a well-known manner to produce forces acting either in the direction of the arrow F or directly opposite thereto. In either case, the major component of the cantilever force will be acting in a direction perpendicular to a reference line A-A connecting the center-lines of two of the inserts 24. As another example, reference may be had to Fig. 4, which shows the bus 30 supported on the insulator 10 by two L-shaped brackets 32a secured to the flange 14 by means of bolts 28 located in diametrically-opposed inserts. The magnetic forces F act in the same direction relative to the bus as in Fig. 3, and, accordingly, they will act in a direction perpendicular to a reference line B-B connecting the center lines of two of the inserts 24.

As still another example, reference may be had to the switch of Figs. 5 and 6, where a blade 50 is pivoted on the insulator 10 for swinging movement into and out of engagement with a stationary contact 52 mounted on an identical insulator 10a. The pivot structure for the blade comprises a U-shaped bracket 53 having its base clamped to flange 14 of insulator 10 by means of bolts 28 located in diametrically-opposed inserts. The blade 50 is mounted on this U-shaped bracket by laterally-projecting pivot pins 54 carried by the upstanding arms of the bracket. The cantilever forces produced at the pivot by the blade 50 being driven into engagement with the stationary contact 52 will act along the longitudinal axis of the blade. As can be seen from Fig. 6, this line of action would be perpendicular to a line CC connecting the center lines of a pair of inserts 24. Thus, in all of the above typical examples, the major component of cantilever force acts in a direction perpendicular to a reference line connecting the center lines of two or more of the inserts 24.

The fact that the major component of cantilever force usually acts in a direction either perpendicular to or parallel to a line connecting the center lines of two or more of the inserts is taken advantage of in my insulator by disposing the straight line sides of the polygonal flange in a particular predetermined manner relative to the inserts (or their respective apertures). More particularly, the polygon defined at the axially outer, or bottom, edge of flange 16 is so disposed that a pair of its straight line sides extends perpendicular to and another pair of its straight line sides extends parallel to each reference line which can be drawn between the center lines of any two of the inserts. Thus, irrespective of the particular combination of inserts 24 which is used for mounting the usual electric apparatus on the insulator, the major components of cantilever force will act in a direction or line of action perpendicular to a plane containing a straight line side of the polygon. This enables the straight line side, in bearing against the base 34, to distribute the cantilever-produced stresses over its entire length, as previously-described, and insures against point contact which could result in the previously-described highly concentrated stresses.

It should be apparent that the above-described insulator 10 readily lends itself to an inexpensive manufacturing process inasmuch as it can be molded, or cast, in a simple mold split along a plane which contains the longitudinal center line of the insulator. The apertures 20 are preferably formed after the molding process by a drilling operation. Thereafter, the inserts 24 are pressed into the apertures from the space behind the flanges, as previously-described.

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects and I, therefore, intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electric insulator comprising an axially-extending body portion formed of insulating material, a pair of flanges formed of insulating material integral with said body portion and extending generally radially therefrom at opposite ends thereof, at least one of said flanges containing at least four axially-extended apertures which are adapted to receive fastening devices for mounting electrical apparatus on the axially-outer surface of said one flange, the other of said flanges having a periphery of a generally polygonal shape defining at its axially-outer edge a polygon having its major sides extending in essentially straight line paths; there being for each particular reference plane that contains a pair of aperture center lines, at least one major side of said polygon extending in a straight line path substantially parallel to the reference plane under consideration.

2. An electric insulator comprising an axially-extending body portion formed of insulating material, a pair of flanges of insulating material integral with said body portion and extending generally radially therefrom at opposite ends thereof, at least one of said flanges containing at least four axially-extending apertures which are adapted to receive fastening devices for mounting electrical apparatus on the axially outer surface of said one flange, the other of said flanges having a periphery of a generally polygonal shape defining at its axially-outer edge a polygon having at least eight sides, a pair of said sides being perpendicular to and a pair of sides being parallel to each reference line connecting the centerlines of any two of said apertures.

3. In combination, an electric insulator comprising an axially-extending body portion formed of insulating material, a pair of flanges of insulating material integral with said body portion and extending generally radially therefrom at opposite ends thereof, at least one of said flanges containing at least four axially extending apertures which are adapted to receive fastening devices for mounting electrical apparatus on the axially outer surface of said one flange, electric apparatus disposed adjacent said axially outer surface, fastening devices extending into at least some of said apertures and securing said apparatus to said one flange, said apparatus being of such a nature that normal operation thereof loads said insulator in cantilever, the other of said flanges having a periphery of a generally polygonal shape defining at its axially outer edge a polygon having at least eight sides, there being for each of the reference lines that interconnects the center lines of two of said apertures a pair of said sides extending substantially parallel to the particular reference line under consideration and a pair of said sides extending perpendicular to the particular reference line under consideration, the major components of canti' lever force being applied to said insulator along lines parallel to at least one of said reference lines,

4. In combination, an electric insulator comprising an axially extending body portion formed of insulating material, a pair of flanges of insulating material integral with said body portion and extending generally radially therefrom at opposite ends thereof, at least one of said flanges containing a plurality of axially extending apertures, electric apparatus disposed adjacent the axially outer surface of said one flange, fastening devices extending into said apertures and securing said apparatus to said one flange, said apparatus being of such a character that normal operation thereof loads said insulator in cantilever, the other of said flanges having a periphery defining at its axially outer edge a polygon having a pair of sides perpendicular to and a pair of sides parallel to each reference line which can be drawn between the center lines of those apertures containing fastening devices, the major components of cantilever force produced by normal operation of said apparatus being applied to said insulator along lines perpendicular to planes containing the sides of said polygon, a base, and means for clamping the axially outer surface of said other flange against said base.

5. In combination, an electric insulator comprising an axially extending body portion formed of insulating material, a pair of flanges of insulating material integral with said body portion and extending generally radially therefrom at opposite ends thereof, at least one of said flanges containing a plurality of axially extending apertures, electric apparatus disposed adjacent the axially outer surface of said one flange, fastening devices extending into said apertures and securing said apparatus to said one flange, said apparatus being of such a character that normal operation thereof loads said insulator in cantilever, a base, means for clamping the axially outer surface of the other of said flanges against said base, the major components of cantilever forces produced by normal operation of said apparatus being applied to said insulator along predetermined lines of action, said other flange having a periphery defining at its axially outer edge a polygon having a pair of its sides disposed in planes perpendicular to each line of action along which a major component of cantilever force is applied to said insulator.

6. In combination, an electric insulator comprising an axially extending body portion formed of a moldable insulating material, a pair of flanges integral with said body portion and extending generally radially therefrom at opposite ends thereof, at least one of said flanges containing a plurality of axially extending apertures, electric apparatus disposed adjacent the axially outer surface of said one flange, fastening devices extending into said apertures and securing said apparatus to said one flange, said apparatus being of such a character that normal operation thereof loads said insulator in cantilever, a base, means for clamping the axially outer surface of the other of said flanges against said base, said other flange having a polygonal periphery providing rectilinear surfaces located to form virtual pivots about which all of the major cantilever forces applied to said insulator act.

7. In combination, an electric insulator comprising an axially extending body portion formed of insulating material, a pair of flanges of insulating material integral with said body portion and extending generally radially therefrom at opposite ends thereof, electric apparatus disposed adjacent the axially outer surface of one of said flanges, a plurality of spaced-apart axially-extending fastening devices extending into said one flange and securing said apparatus to said one flange, said apparatus being of such a character that normal operation thereof loads said insulator in cantilever, the other of said flanges having a periphery defining at its axially outer edge a polygon having a pair of sides perpendicular to and a pair of sides parallel to each reference line which can be drawn between the center lines of said fastening devices, the major components of cantilever forces produced by normal operation of said apparatus being applied to said insulator along lines perpendicular to planes containing the sides of said polygon, a base, and means for clamping the axially outer surface of said other flange against said base.

8. An electric insulator comprising an axially-extending body portion formed of insulating material, a pair of flanges formed of insulating material integral with said body portion and extending generally radially therefrom at opposite ends thereof, at least one of said flanges containing a plurality of axially-extending apertures, a pluapertures thereby to provide space for pressing said inserts into position Within said apertures.

References Cited in the file of this patent FOREIGN PATENTS Great Britain Oct. 6, 1904 France Apr. 10, 1923 Switzerland May 1, 1944 Germany June 1, 1953

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