US1822485A - Insulator - Google Patents

Description

K. A. HAWLEY Sept. 8, 1931- INSULATOR Filed July 192 2 Sheets-Sheet l Sept. 8, 1931. K. A. HAWLEY 1,822,485

INSULATOR Filed July 15 1 2 2 Sheets-Sheet 2 Patented Sept. '8, 1931 UNITED STATES PATENT @FFWE KENT A. HAWLEY, OF VICTOR, NEW YORK, AESIGINQB T LOCKE INSULATQB GOBPOBA- T1011", 0]? BALTIMORE, MARYLAND, A UQRPORATIGN 631 "EAEKLAND INSULATGR Application filed July 15, 1924. Serial Mo. 726,158.

to insulators of the type embodying a member of insulating electric material connected to a metalhc part through the intervention of a resilient medium. At the present time the connecting medium generally employed is Portland cement. j The primary object of the invention is to afliord simple, practical and eflicient means for effecting the orderly distribution and control of the internal mechanical forces to which insulators of the character indicated are su jected.

The dielectric material most commonly used in insulators is porcelain which, as is well known, is capable of sustaining very heavy compressive loads but is of comparatively low strength when acted on by shearing stresses or when subjected to tension. These characteristics of porcelain have rendered it apparent that. the mechanical forces applied to this dielectric material in an insulator should, so far as possible, be compressive, andthat shearing and tensile forces 5 should be avoided or maintained within safe ,low limits. If porcelain or other dielectric material having similar strength characteristics is subjected to a compressive force applied to a small area, the elasticity of the maso terial permits a compression of the area subjected to the force, thus causing shearing forces to be developed between such area and the surrounding portions of the porcelain body, and thereby frequently resulting in the failure of the insulator by shearing rather than by direct compression. Not only has it been realized that concentrated loads applied to the dielectric material often produce the effect described but it is also appreciated that such loads are a cause of incipient cracks in the dielectric material leading to electrical b1 cal; down of the insulator. Attempts have heretofore been made to apply the mechanical forces to the porcelain or dielectric body of an insulator so as to load the dielectric material in a manner avoiding excessive concentrations of force thereon, thus producing an insulator of high mechanical strength. These attempts have in general sought to distribute the load to the insulating member and to relieve the latter of undue stress in any particular 'part either by radially slitting or otherwise forming the metallic bolt or cap of an insulator so that such metallic part would be capable of yielding, stretching or flexing, or by providing upon the metal members associated with the insulating member, or upon the insulating member itself, resilient or relatively flexible projections embedded in the cement interposed between and emto ployed to connect the metal parts of the insulator with the insulating member of porcelain or other dielectric material. These projections, which at one end are integrally attached or rigidly anchored to the insulator 05 part by which they are carried, act after the fashion of flexible or. resilient cantilevers which deflect under stress and thus, by their yielding, efiect a reduction in the stress which otherwise might have a higher degree 7 of concentration at a given'point. Where the resilient projections have been in the form of flexible flanges it has been proposed to control their relative flexibility either by varying their angularity or their thickness so as to modify stifiness and effect a corresponding distribution or" the load to the member of dielectric material, and it has also been proposed to efiect such distribution by varying the spacing between the projections. Means of this character not only have the disadvantage of increasing the cost of insulators but it is obvious that the control of the mechanical stresses in the insulator can thereby be obtained only in a general way and with considerable uncertainty, because the forces transmitted from the projections to the porcelain or dielectric member of the insulator are aiiected and subject to modifiiii it ot the cemen cation in being transmitted through the intervening cement.

By my invention the desired distribution of forces upon. the dielectric body is accomplished by proportionally varying the thicle ness of the elastic cement interposed between said dielectric body and the metallic members associated therewith and by forming the surfaces of the metallic members which bear upon the cement so as to result in the desired distribution of force to the latter. It will be perceived that by suiting the thickness of cement to the form of the metallic surface bearing thereon the stresses comniiunicatecl to the porcelain body member may be controlled with substantial deliniteness and certainty Before proceeding with a description of the particular applicationsol the invei lion illustrated in th drawings, the general characteristics thereof will be explained inoroicr that he production of modified forms in sulators involving such other distributions stresses as may be desired to suit special conditions can be readily effected. The load delivered to the cement at point depends upon the ability of the cement to receive i that is to say it is de ident upon the ri in other Words is vcrsely proportioi'ial to the amount merit yields. As the abilit oi 's proportional its thickness, Y

is theref inversely prcpo the cez'n e "iovei'nen's of the l i perc a the t the metallic member occurs in the direction of its axis, Which is the direction of application of the external load. This movement produces a compression of the cement in a direction normal to the Working surface of the angularly disposed face, the amount of said compression being equal to the amount of said movement multiplied by the sine of the angle subtended between the axis of the metallic part and the bearing surface of the angular face at the point in question. Since, as has been pointed out, the load which the cement is capable of receiving and transmitting to the porcelain inversely proportional to the thickness of the cement, it will be appreciated that the value of this load or stress mat he caused to vary in proportion to variations in the ratio defined by the compression the cement divided by its thickness; and as the extent of compre -"siani oil the cement for an axial movement the metallic part oi: the insulator corresponding) o the aj iplication. thereto oi'f a ven '4 to tcrce varies with the sine of the ang the Working face of the metallic as L l t r l lo percei l. vetl that the load o porcelain (liif'ying either (ll 'erent points V saic. part, lL .vi

transmitted by l c may be varied as tie the thickness of the While maintaining of the Working; bearing against annular l n taming o by vowing the -ces while mam the cement,

Forms With the axis of t ungulari t5 1 A 1 v y or the laces the equality of these ratios results in equal loadings of the cement, since the modulus of elasticity of the cement and the extent of axial movement of the metal member of the insulator under the application of a given external load are constant factors. On the other hand, if itis,desired to impress different loadings on the porcelain at different points, as at times may be advantageous, such result may be effected by causing the said ratios at the respective points to bear the relations it'is desired that the stresses on the porcelain shall have to each other.

In the foregoing formula no factor is introduced allowing for the elasticity of the insulating and metallic members, which are relatively inelastic as-compared with the cementing material interposed between them. If, however, it is desired in any special case to carry the accuracy of the distribution of load on the insulating member to a point of refinement where the elasticity of the insulating and metallic members cannot be regarded as negligible, then a corresponding modifying factor may be introduced into the formula.

In the drawings illustrating embodiments of the invention in preferred forms of insulators,'

Figure 1 is a view partly in elevation and partly in section of an insulator of the suspension type in which the mechanical stresses imparted to the porcelain are distributed with portion of one of the metallic eye bolts of the substantial uniformity.

Figure 2 is a View partly in elevation and partly in section of a slightly different form of suspension insulator in which the loading of the porcelain or dielectric body is substantially uniform.

Figure 3 is an enlarged detail view of a insulators illustrated in Figs. 1 and 2.

Figure 4 is a view', partly in elevation and partly in verticalsection, of a strain insulator esp'eciall suitable for connection to guy wires for ra io towers or for use under similar conditions where the voltage is high, the amperage low, atid the mechanical stresses are great. t

Figure 5 is a diagrammatic view of an insulator unit suitable for the insulation of radio towers.

The insulator illustrated in Fig. 1 is of the suspension type involving a metal cap 1, a dielectric body member 2 anda metallic eye bolt 3. The insulating body member 2 is commonly formed of porcelain and the metal members 1 and 3 are connected thereto thrbugh the intervention of Portland cement or other elastic cementing material interposed between the said metal members and the dielectric-body member 2, as indicated at 4 and 5. To enable the bodies of cen'ient 4 and 5 to be firmly bonded to the porcelain insulating body member 2, the inner and outer faces of the latter may advantageously be sanded, as at 6 and 7; and to provide an elastic joint or cushioning means to compensate for temperature changes the upper outer portion of the body member 2 and the upper end of the eye bolt 3 may be advantageously coated, as at 8 and 9, respectively, with cut sarco.

The metallic cap 1 and the bolt 3 are each provided with working faces for transmitting force to the cement which are inclined to the axis of the insulator, each of said metal parts preferably having a plurality of the working faces arranged in the form of steps. The working faces 10 of the cap 1 are annular and formed on the interior of the cap, while the working faces 11 of the eye bolt 3 are, of course, on the exterior of the latter near the upper end thereof. To facilitate slippage of the bearing faces 10 of the cap with respect to the cement 4 with which said faces cooperate, it is preferred to coat the stepped working faces of the metal cap with sarco or other material suitable for the purpose, as indicated at 12. For a similar reason it is preferred" to coat the stepped working faces 11 of the eye bolt 3 with a sarco dip, as indicated at 13. As will be appreciated, the load which an insulator is required to support when in service causes a movement of the bolt along its axis and a movement of the cap 1 along its axis, these movements of the metal parts being due to the stretching and yielding of the insulatorelements under the imposed load and inducing corresponding slight movements of the cap 1 and bolt 3 with respect to the adjacent bodies of cement and porcelain body member 2.

The working faces 10 and 11 of the cap 1 and bolt 3, respectively, are convexly'curved, the curvature of the said surfaces being such that the distance to the adjacent surface of between the axial line of the metal member.

and the surface of its Workingface at the point in question. This most advantageous character of the curved working faces or bearing surfaces of the metal cap and bolt will be readily understood from a consideration of Fig. 3., which is a diagrammatic view illustrative of one of the bolt members. In this diagram the line 111-00 indicates the center line of thebolt; the line 22 is tangent to the upper curved working face 11 at the point f; and the line yg which extends at right angles to the tangent zz therefore is normal to the direction of curvature of the step 11 at the point The angle at subtended between the lines mean and z-2 will vary, it will be noted, as the point f shifts along the curved working face 11 of the bolt, becoming greater as the point upon the curved surf are approaches the next lower stepand growing less as it approaches the upper end of the bolt. The sine of the angle thereforewill correspondingly vary and the distance to the adjacent face of the porcelain body member 2 should therefore be increased or diminished as the case may be to vary the thickness of cement corresponding substantially thereto. In the case of the metal cap 1 the angle on subtended between its axis and the line which is tangent to a curved bearing face at any given point is preferably less than the corresponding angle or of the working face 11 of the eye bolt 3 opposed thereto. This results in enabling the working faces of the cap 1 to deliver inwardly directed radial pressure to the porcelain body member 2 in excess of the radial outward pressure communicated to the porcelain member from the bolt 3, thus ensuring that the porcelain shall be in compression instead of being subjected to tension forces, which latter condition would result if the outwardly directed pressure induced by the bolt exceeded the inwardly directed pressure from the cap and thus applied to the porcelain member 2 a bursting force lending to increase its diameter. a

It has already been pointed out that the weights or loads which insulators are required to sustain in service. cause an elongation of the metal cap 1 in the direction of its axis and also produce a corresponding movement.

of the bolt 3 with respect to-its axis. lVhere the portion of the ap 1 on which the working faces 10 are formed is of a thickness such that the stretching or yielding of the cap is substantially equal for corresponding units of length, the movement of the uppermost Working face 10 in the direction of length of the axis of the cap will, it will be appreciated, be greater than the movement of the lower inclined faces 10, the extent of movement progressively decreasing and that of the lowermost face 10 being least. The load supported by the insulator similarly induces movements of varying amount of the working faces 11 of the bolt3 in the direction of length of the axis of the latter, but in this case the lowermost working face 11 of the bolt moves to the greatest extent. As compared with the movement of the working faces of the cap, the movement of the working faces of the bolt is usually less in amount because of the far greater ability of the bolt to resist stretching. \Vhcn, as in some instances is advantageous. it is desired to eliminate or compensate for such variations in the loading of the porcelain body member 2 as may bedncluced by unequal movements of the inclined working faces 10 and 11 of the cap 1 and suspension bolt 3, respectively. this may be accomplished by varying the thickness of the cement between the porcelain and the respective metal parts in corrcs iondcnce to the differences in movement of the inclined working faces of the cap and bolt, the cement being thicker opposite the working faces having the greater movement. As shown by the upwardly diverging dot and dash lines 14 and 14, the thickness of the body of cement 4 between the working faces of the cap 1 and the adjacent surface of the porcelain body member 2 illustrated in Fig. 1 is gradually increased upwardly for this purpose, While, as indicated by the dot and dash lines 15 and 15 the thickness of the body of cement 5 between the working faces of the bolt 3 and the adjacent surface of the dielectric member 2 is increased downwardly.

A somewhat different form of suspension insulator involving the same principles of construction is illustrated in Fig. 2, such insulator being intended for use where lighter loads are required to be sustained. In this insulator the metallic cap 17 is provided with only two curved inclined working faces 18, and the curved working faces 19 of the suspension-bolt 20 are fewer than those with which the suspension bolt 3 is provided. The metallic members of the insulator are con nected to the porcelain body member 21 thereof through the intervention of interposed bodies of Portland or other resilient cement. The insulator shown in Fig. 2 preferably is otherwise similar to the construction heretofore described, and accordingly corresponding reference numerals have been applied thereto to indicate the similar features of construction.

Fig. +1 shows an application of my invention' to a compression type of insulator in' tended to operate under-very heavy mechanical loads. This insulator comprises a pair of metallic housings which are rigidly connected by means of bolts 23. For the purpose of forming a moisture excluding joint a lead filling may be interposed between the housing members as indicated at 24. Encircled by the enveloping frames or housings 22 are oppositely disposed insulating members 25 of porcelainor other suitable dielectric material. each of the said insulating members being provided with an inclined shoulder or working face 26 hearing against a body of insulating cement 27 interposed between the insulating member 25 and the metallic housing 22. The inner surface of each of the porcelain members 25 is also formed with an inclined working face 28 which is preferably parallel to the corresponding outer face 26. Between this inner face and a metallic nut 29 upon the end of one of the metal eye bolts 30 forming a part of the insulator unit is an interposed body of resilient cement 31. The slope of the POIiI'dICIlll surface of the nut 29 preferably corresponds to that of the bearing faces 26 and 28 of the insulating member 25. To hold the internal parts in proper relation during erectingand shipping, a porcelain spacer block 32 may be employed, springs in Fig. 4 illustrates an application of the in- 33 being interposed between the block and the respective nuts 29.

' The particular design of lnsulator shown vention wherein the stresses imparted to the porcelain insulating bodies are not umformly distributed but are varied for the purpose of producing a somewhat gradual transmission of the stress from the area subjeeted to maximum pressure to the portion 7 of the porcelain which is unstressed. To effeet this purpose the bodies of cement 27 and 31 are gradually increasedfin thickness at their ends as indicated at 34. These thickened portions of the cement may be conveniently provided for by forming correspon'ding grooves in the housing members 22 and nuts 29, said grooves, asshown, preferably being lipped to prevent the cement fromspalling at the ends. Since, as has already been pointed out, the load delivered to the cement at any point depends upon the ability of thecement to receive it, and as this ability depends upon the thickness of the cement which determines the extent to which it may yield, it will be perceived'that by thicken-- .ing the cement bodies at the points 34 the stresses imparted to the porcelain insulating members 25 at these points are enabled to be gradually reduced as desired. The bodies of cement 27 and 31- are preferably made comparatively thick so that irregularities of the metal housings 22' and porcelain body members 25 cannot cause concentration of excessive loads on the porcelain.

The insulator unit for radio towers illustrated'in Fig. 5 diagrammatically discloses an elementary design for delivering compression load from one metal part to another through a porcelain body which is separated from said metal parts by intervening layers j able foundation.

of resilient cement, the thickness of the cement being varied to distribute the load to the porcelain as desired. In the construction here shown two metal members 35 are disposed on opposite sides of a plate-like porcelain body 36 and between the latter and the meansfor controlling the stresses induced in the dielectric member of an insulator by the load the insulator is required to sustain,

' and that a uniform distribution of stresses or a non-uniform distribution thereof of a 'tained.

I claim 1. An insulator comprising a dielectric member, a load receiving member in spaced relation to said dielectric member, and a body of material interposed between said members and serving to transmit stress from one to the other, the said load receiving member having a working surfaee'whose distance from said dielectric member at axgiven point as measured in a direction normal to said working surface is approximately proportional to the sine of the angle subtended between the axis of said load receiving member and the direction of said working surface at said point. r

2. An insulator comprising a dielectric member, a load receiving member in spaced relation to said dielectric member, and a body of cementitious material interposed between said members and serving to transmit stress from one to the other, said load receiving member having a plurality of working surfaces disposed in stepped relation and adaptand the thickness of said material at corresponding points varying respectively with the sine of said subtended angles.

- 3. An insulator comprising a dielectric member, a load receiving bolt in spaced relation to said dielectric member, and a body of cementitious material interposed between said bolt and said dielectric member and serving to transmit stress from one to the other. said boltbeing provided with a plurality of working surfaces for imparting compressive force to said I material, and. each of said working surfaces being convexly curved and spherical throughout the area thereof by which compressive force is communicated to said material.

4. An insulator comprising a dielectric member, a load receiving bolt in spaced relation to said dielectric member, a body of cementitious material interposed between said bolt and said dielectric member and serving to transmit stress to said dielectric memher, a load receiving cap encircling said dielectric member in spaced relation thereto, and a body of cementitious material interposed between said cap and said dielectric member and serving to transmit compressive stress to the latterysaid, bolt and said cap each being provided with a plurality of inclined working surfaces for imparting compressive force to the said material adjacent thereto, the inclination of said working surfaces of the cap with respect to its axis being less than the inclination of said working surfaces of said bolt with respect to its axis,-

whereby tensional forces tending to be induced in said dielectric member by the outward radial thrust of said bolt are overcome.

5. In an insulator, a dielectric member having a cavity therein, a load receiving bolt located Within said cavity, a mass of material embedding said bolt, the bolt having a plurality of steps'each of spherical formation throughout its major portion and connected with the next adjacent step by a frustoconical portion.

In testimony whereof I afiix my signature.

KENT A. HAWLEY.

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