Insulator Assembly Having Load Distribution Support

Abstract

A ceramic insulator assembly includes a plurality of parallel vertical insulators arranged with equal spacings about the circumference of a circle. Vertical loading forces are applied to the insulators by way of an adapter plate separated from a top plate on the insulators by a load distribution ring. The ring is aligned with the axes of the insulators, so that bending forces are not transferred to the insulators. A plurality of vertical tiers of insulators separated by divider plates may be provided. One end of each insulator may be mounted in a molded joint to insure substantially equal load distribution.

Description

This invention relates to insulator assemblies and is more particularly directed to the provision of means for distributing loads to insulator assemblies of the type including a plurality of vertical ceramic insulators.

In the past a number of ceramic insulator assemblies have been provided which include one or more tiers of insulators. For various structural and thermal reasons, stress concentrations occurred in such insulator assemblies so that, under conditions of high loading, the assemblies failed due to cracking of the ceramic insulators.

In order to overcome these problems, parallel oil filled ceramic tubes have been provided, mounted between steel plates. While this modification is successful for moderately high loads, it has been found that the arrangement is also subject to failure under high loading conditions.

Briefly stated, in accordance with the invention, a ceramic insulator assembly is provided that can withstand high loading forces without failure. The assembly is comprised of one or more tiers of parallel ceramic insulators positioned to be equally spaced about the circumference of a circle, i.e. to be uniformly distributed about the circle. When more than one tier is provided, the axes of corresponding insulators in the tiers are aligned, and the tiers are separated by divider plates.

A mounting plate is mounted to the tops of the insulators of the uppermost tiers, and a load distribution ring is mounted on top of the top mounting plate. The ring is aligned with the axes of the insulators, i.e., the center lines of the insulators extend through the load distribution ring between the inner and outer diameters thereof. An adapter plate is mounted on top of the distribution ring. The ring has a width, i.e. the dimensions between its inner and outer diameters, whereby bending due to loading of the assembly is taken up by the adapter plate, and is not transferred to the top mounting plate and hence the ceramic insulators.

In order to insure substantially equal distribution of vertical loads between the ceramic insulators, a molded joint, for example of an epoxy, is provided at one end of each insulator.

With the above described arrangement it has been found that high loading forces may be applied to the insulator assembly without danger of failure of the assembly by cracking of the ceramic insulators due to stress concentration effects.

In order that the invention will be more clearly understood, it will now be described in greater detail with reference to the accompanying drawing, wherein:

FIG. 1 is a side view of a multi-tier insulator in accordance with the invention;

FIG. 2 is an enlarged, partially cut-away, top view of the insulator assembly of FIG. 1;

FIG. 3 is a further enlarged, partially cross-sectional view of a portion of the insulator assembly of FIG. 2 taken along the lines 3--3; and

FIG. 4 is a partially cross-sectional view of a portion of the arrangement of FIG. 3 and illustrates the effect of loading forces on the insulator assembly.

Referring now to the drawings, FIG. 1 is a side view of an insulator assembly in accordance with the invention. The assembly is comprised of one or more tiers of parallel, vertically extending, preferably cylindrical ceramic insulators 10, two such tiers being illustrated in the arrangement of FIG. 1. It is to be understood, of course, that a greater or lesser number of tiers may be provided. The ends of each insulator are provided with mounting flanges 11 according to conventional practice. The insulators 10 are equally spaced about the circumference of a circle, as is apparent in FIG. 2, and as shown in FIG. 1 the axes of corresponding insulators in the tiers are aligned.

When two or more tiers of insulators are provided, they are separated by a center plate 12. The bottoms of the insulators of the lowermost tier are mounted on a base plate 13, and a top plate 14 is mounted on the tops of the insulators of the uppermost tier. The insulator flanges 11 are affixed to the respective plates 12, 13 and 14 by conventional means, such as bolts (not shown). The base plate 13 may be conventionally mounted on a spacer plate 15.

An adapter plate 20 aligned with the insulator assembly is spaced from the top of the top plate 14 by a load distribution ring 21. The load distribution ring 21, as is apparent in FIGS. 2 and 3, is aligned with the axes of the ceramic insulators, i.e., the axes of the ceramic insulators intersect the ring 21 between its inner and outer diameters. FIG. 1 illustrates the application of a vertical load to the insulator assembly by the arrow P directed downwardly onto the adapter plate 20.

The plates 12, 13 and 14 are preferably circular, as illustrated in FIG. 2. These plates may, if desired, be annular, with the chain line 22 illustrating their inner edges, since the effective region of these plates from the standpoint of loading is annular.

While the insulators 10 shown in the drawing are depicted with smooth external surfaces, it will be understood, of course, that these insulators may be provided with annular ridges according to the conventional practice. Further, as illustrated in FIG. 1, the diameters of the ceramic insulators are greater at their ends than at their middle portions. While this feature is not essential, it is desirable since the highest bending stresses on the assembly occur at the ends, not at the axial centers of the insulators.

In order to increase the ability of the assembly to carry shear loads, the lengths of the ceramic insulators 10 are reduced, and a plurality of tiers of such insulators are provided as illustrated in FIG. 1, thereby distributing the bending in the ceramic insulators from shear loads evenly to each end of each ceramic insulator. The divider plate or plates 12 in a multi-tier arrangement have equal flexibility with respect to the top and base plates 14 and 13 respectively. In this arrangement the column length of the insulators is thus effectively shortened and shortens the effect of construction eccentricity.

The load distribution ring 21 is provided in order that all bending from the vertical load P within the circle of the ceramic insulators is taken in the adapter plate 20, and is thereby not transferred unevenly to the ceramic insulators. For this purpose, it is preferred that the width (i.e. the dimension between the inner and outer diameters) of the ring 21 be as small as possible. The minimum width is limited, according to conventional design practice, by the compressive strength of the material of the ring and the material in the top plate 14 and the adapter plate 20. The ring is aligned with the axes of the ceramic insulators, so that approximately equal areas of the tops of the ceramic insulators appear on the inside and outside of the ring 21, as is apparent in FIG. 2.

The effect of the ring 21 in the assembly is illustrated in exagerated form in the partially cross-sectional view of FIG. 4. In this illustration, the vertical force P on the adapter plate 20 is shown as being of sufficient magnitude to effect bending of the adapter plate 20. This bending has effectively shifted the point of loading between the adapter plate and the ring 21 inwardly, but the shift of the loading force is limited by the width of the ring 21. As a consequence, the forces acting on the ceramic insulator 10 by way of the top plate 14 and distribution ring 21 are maintained within tolerable limits with respect to the axes of the ceramic insulators, and substantially none of the bending force acting on the plate 20 is transferred to the ceramic insulator 10. As pointed out above, the illustration of FIG. 4 is exaggerated, and in actual design of the insulator assembly it is preferred that the elements of the assembly be designed so that the load center acting on the distribution ring shifts no more than 1/8th of the ring width for the worst case of load distribution.

It will be understood, of course, that suitable means, such as bolts, may be provided for maintaining the alignment of the adapter plate 20 on the structure, although this feature does not form a part of the invention per se.

In order to enable the distribution of vertical force to within 10% between the ceramic insulators of each tier, a molded joint 25 (see FIG. 3) is provided at each insulator. The molded joints are provided at only one end of each insulator. The joint material must have high compressive strength, and as high as possible a modulus of elasticity, and it must also have low creep characteristics. Epoxy resin materials have been found to be suitable for this purpose. The maximum thickness of the joint 25 is ascertained by adding together all of the construction tolerances in the fabrication of the insulators and insuring that the total vertical deflection of the molded joint is less than 10 percent of the total vertical deflection of the ceramic insulator under maximum load. The molded joint is employed so that all of the insulators acting in parallel, start their load cycles simultaneously upon the application of load to the assembly, whereby no stress concentrations are created.

In an actual embodiment of the invention, ceramic insulators were employed having lengths of 46.25 inches, with root diameters at their centers of 8 inches, and root diameters at 9 inches from their ends of 8.5 inches. The insulators were of normall station post design. The heights of the flanges were 4.125 inches. The top plate 14, divider plate 12 and base plate 13 were 5 inches thick and had diameters of 55.25 inches. The effective inner edge 22 of these plates had a diameter of 19 inches. The diameter of the assembly between axes of opposite insulators was 37.2 inches. The load distributing ring 21 had an inner diameter of 35.7 inches, and outer diameter of 38.7 inches, and a thickness of 0.25 inches. The adapter ring had a thickness of 12 inches. The molded joints 25 were of an epoxy material, and had maximum thicknesses of about 0.016 inches.

In an illustration of the design of the molded joints, assume that the total vertical deflection of an insulator assembly having two ceramic insulators, under a loading of 1,631 kips, is approximately 0.235 inches, that the effective diameter of the molded joint is 12.5 inches at the bolt circle and that the ceramic insulators and top and bottom plates of a single tier unit have tolerances of plus or minus 0.002 inches. In this case, the total possible mismatch in the assembly could be 8 .times. 2 .times. 0.002 = 0.032 inches. If an epoxy joint of 0.032 inches thickness is employed, then the total deflection of the epoxy joint under the above loading is:

.DELTA. = PL/AE = 0.0008 inches

where P is the applied load, L is the thickness of the moldable joint, A is the area of the joint, and E is the modulus of elasticity, in this case being equal to 520,000.

The total deflection of the epoxy under the above load was thus less than 1 percent of the total vertical deflection.

While the invention has been disclosed and described with reference to a single embodiment, it will be obvious that many variations and modifications may be made therein without departing from the invention, and it is therefore intended in the following claims to cover each such variation and modification as falls within the true spirit and scope of the invention.

Claims

What is claimed is:

1. An insulator assembly comprising a plurality of parallel cylindrical insulators equally spaced about the circumference of a circle, mounting plate means mounted on one end of said insulators, an adapter plate means aligned with said mounting plate means for receiving a loading force, and a load distribution ring between said mounting plate and said adapter plate for transmitting said loading force to said insulators, said ring being aligned with the axes of said insulators, said ring having a width dimension between its inner and outer diameters that is less than the diameters of said insulators at said one end thereof whereby bending due to said loading force is not transferred to said insulators.

2. An insulator assembly comprising a plurality of parallel vertical elongated ceramic insulators equally spaced about the circumference of a circle, a top plate means on the upper ends of said insulators, an adapter plate overlying said top plate means, and a load distribution ring between said adapter plate and said top plate and aligned with the axes of said insulators, said ring having a width dimension between the inner and outer diameters thereof that is less than the diameters of the upper ends of said insulators whereby bending forces due to vertical loads applied to said adapter plate means are not transferred to said insulators.

3. The insulator assembly of claim 2 further comprising a molded mounting joint on one end of each of said insulators whereby said vertical loads are substantially equally distributed between said insulators.

4. The insulator assembly of claim 3 wherein said molded joints are of an epoxy material.

5. The insulator assembly of claim 3 wherein said molded joints are at only one end of each of said insulators.

6. The insulator assembly of claim 3 wherein said molded joints comprise a layer of a molded material of a thickness whereby vertical deformation of said layer is less than 10% of the vertical deformation of the corresponding insulator under maximum load.

7. The insulator assembly of claim 2 wherein the diameters of said insulators are greater at the axial ends thereof than at their axial centers.

8. An insulator assembly comprising a plurality of aligned tiers of parallel vertical cylindrical insulators equally spaced about the circumference of a circle with the axes of the insulators in separate tiers being aligned, divider plate means separating said tiers, a top plate mounted on the upper ends of the uppermost tier of insulators, an adapter plate above said top plate, and a load distribution ring between said adapter plate and said top plate and aligned with the axes of said insulators for transferring vertical loads on said adapter plate to said tiers of insulators, said ring having a width dimension between its inner and outer diameters that is less than the diameters of the upper ends of said insulators whereby bending due to said vertical load is not transferred from said adapter plate to said top plate.

9. The insulator assembly of claim 8 wherein only one end of each of said insulators has a molded joint for assuring substantially equal loading of said insulators.

10. The insulator assembly of claim 9 wherein said molded joints are of an epoxy material.

11. The insulator assembly of claim 8 further comprising a base plate mounted on the bottoms of the insulators of the lowermost tier of insulators, said top plate, divider plate means and base plate having substantially equal flexibility.