US2128817A - Flux distributing insulator - Google Patents

Description

Aug. 30,938. K A HAWLEY 2,128,817

FLUX DI STRIBUTING INSULATOR Filed March 5, 1933 2 Sheets-Sheet l iada Patented Aug. 30, 1938 UNITED STATES PAIENT OFFICE" FLUX DISTRIBUTING msom'roa Application March 3, 1933, Serial No. 659,576

3 Claims. (Cl. 173-318) The invention relates to insulators, particularly, but not necessarily, those intended and adapted for use in connection with high frequencycurrents, for instance in association withthe supporting legs of radio towers whether they be of the self-supporting or guyedtype.

It is known that for some time it has been.

proposed to make use of all-porcelain insulators for example for use in connection with disconnecting switches, bus bars and other equipment at sub-stations. By an all-porcelain insulator is meant one which is provided simply at its ends with metallic fittings for mounting purposes, such fittings being of a type totally dissimilar to metallic pins or posts entering the insulator. In otherwords insulators of this variety were constructed on the theory that the absenceof metallic parts within the interior would increase the insulating value. However, it has been found in actual practice that insulators of this variety possess marked objections or drawbackswhen considered from the electrical viewpoint. When efforts have been made to use insulators of this general type in connection with even normal frequency currents and particularly with high frequency currents, for instance those at radio frequencies, there is a concentration of the flux density at the high potential end and likewise excessive leakage to earth. This condition causes not only a loss of power but results in very objectionable heating effects within the porcelain. Briefly, insulators of the elongated hollow type provided simply at their ends with exteriorly locatedmetallic fittings are not satisfactory on account of the low efiiciency.

To explain what is meant by a-concentration of the flux density, it might be well to consider some of the theoretical aspects of the situation especially as in some respects some of the conditions discovered are largely a new development. To those skilled in the art there is no difiiculty in picturing what occurs where a current of electricity actually flows, for such current will follow almost exactly thesame laws that a flowing stream of water would follow, assuming that the water is not travelling at a very great speed.

It is known that if there are two paths by which electrical current can flow from oneplace to another, it will flow by both paths, the current dividing indirectly accordingto the respective resistances of the two paths. age along the way to create the flow will be in proportion to the resistance to flow-along the way, inch .by inch. This is of course an elementary proposition. When it comes to consid- The division of voltering insulators, there is of course no actual current flow, as such, from one terminal to the other though the voltage applied does endeavor to cause current to flow. This, electrically considered, is divided along the way in accordance with certain rules. Considering current flow it is relatively easy to visualize the idea that a certain current starting at one point will flow directly to the opposite point along certain channels or flow lines, and that currents starting 10 from two points 'side by side will not cross their paths but will flow side by side in separate channels. Mathematically these flow lines Where actual moving electricity is involvedare the same as the electro-static stress lines which determine the travel of the stress or electrical pressure from a live terminal to the other terminal. It is consequently merely necessary to visualize a condition corresponding to that which is physically discernible as described above. It is therefore proper toconsider porcelain of an insulator and the surrounding air not as insulators but as con- I ductors. It is known that air has seven times the resistance to the flow of electro-static flux that the porcelain has. In other words, where there are two electrical terminals with air and porcelain between them, roughly considered the air takes seven times the electrical pressure that the porcelain takes. Consequently, where there is a column of air and a column of porcelain side 30 by side with a flux in each, there will be seven times the amount of flux in the porcelain as there is in the air. This conception is a material aid in picturing the field about insulators-and the changing of the relative positions of the air and porcelain about the parts of the insulators where the air 'is over-stressed by the electrical pressure, resulting in the formation of corona which causes heating as well as lowered arc-over value.

Considering. an elementary porcelain post such as a tube or rod set on end with the ends capped and the upper end electrically alive and the lower end grounded, it is known that from the upper end the flux flow will pass in all directions. A 45 very, considerable amount of the flux will pass directly throughthe porcelain to the earth but some of it will pass outward from the live cap in all directions to the earth, even upwards through infinite distances. Now, that portion of the flux which starts downward through the porcelain toward the earth will find part way .down that the surrounding air is not filled electrically, and consequently this electrical fiuxwill wander away from the porcelain with the result that the flux density in the porcelainat the lower or grounded end of the insulator is less than above. Consequently, the electrical pressure per inch of length is not as great at the lower end as at the upper end. The air in the immediate vicinity of the porcelain naturally assumes the same rate of voltage drop as exists within the porcelain. There has therefore been pictured a condition under which the space between the live cap or terminal and the earth is not being used in the most efficient way as the space at the upper end will naturally break down appreciably before the space near the lower end has approached the critical point.

Considering now not an elementary cylindrical bolster as an insulator but in contradistinction thereto taking one shaped like the frustum of a cone such as is used for instance for the insulation of the legs of radio towers, the same electrical disadvantages are present. In many instances it has been proposed to use radio towers themselves as antennae for radio broadcasting and under such circumstances the tower itself must of course be well insulated from the ground. For mechanical reasons conical insulators used in such a connection are logically placed with their large ends down and with their upper or smaller ends supporting the tower. From an electrical viewpoint this is absolutely incorrect but it is manifestly not feasible to mount the insulators in the reverse relation which would insure proper electrical performance. Assuming that the truncated cone insulator is placer: in its normal position with its large end grounded and its smaller end electrically live I have found that the d stribution of flux density is incorrect and causes objectionable heating in the porcelain. From a series of tests and also from computation I have found that by increasing the bulk or thickness of the dielectric material at the small or live end the flux density may be properly controlled or distributed or the insulator graded within itself so as to overcome the heating effects and likewise to eliminate danger of corona which occurs as the result of overstressing a part of the field. The last mentioned characteristic is of great importance as the formation of corona is a serious disturbing feature in radio reception as well as objectionable on account of heating and the lowering of arc-over values.

It is with the above facts and discussion in view that I have devised the present invention which has for its general or primary object the provision of an insulator, particularly but not necessarily of porcelain, in which the flux density will be controlled and distributed.

An important object of the invention is to provide an insulator in which the thickness at the live end is the maximum and .decreasing to a minimum at or near or at least toward the grounded end, or in which the thickness is greatest at the stressed end or ends and decreases toward the unstressed end or intermediate portion.

Another object is to provide an. insulator preferably of the truncated cone type in which the added thickness for eifecting flux density control may be brought about in any one of numerous ways for instance by thickening the material of the insulator wall or placing within the interior auxiliary or adjunctive means more or less in the nature of bushings of appropriate shape and dimensions which will bring about the same highly desirable result.

Still another object of the invention is to provide an insulator which need not be used in association with radio towers or in connection with high frequencies but which may be used in stacks or superposed series for the support of bus bars, switches and other equipment at power stations where the frequencies are normal, the principle of grading or flux density control being the same in any instance An additional object is to provide an insulator having the above pointed out electrical characteristics and which will at the same time be simple and inexpensive to make and therefore practical from a commercial viewpoint in addition to being unusually strong, mechanically, and a general improvement in the art.

To the attainment of the foregoing and other objects and advantages, the invention preferably consists in the details of construction and the arrangement and combination or" parts to be hereinafter more fully described and claimed, and illustrated in the accompanying drawings in which;

Figure 1 is a preliminary diagrammatic view showing the flux lines in and about a simple cylindrical type insulator,

Figure 2 is a diagrammatic view showing the flux lines in and about an inverted conical insulator,

Figure 3 is a vertical sectional view through one half of a cone type insulator constructed in accordance with my invention,

Figure 4 is a similar view showing a modification,

Figure 5 is a similar view of yet another variation,

igure 6 is a half sectional View through an insulator of the post type having internally located adjunctive flux density distribution means,

Figure '7 is a similar view through thesarne type of insulator but disclosing an additional m0dification,

Figure 8 is a vertical sectional view showing half of a stack oi insulators constructed along the lines disclosed in Figures 6 and 7,

Figure 9 is a longitudinal section showing the invention embodied in a tubular type of insulator,

Figure 10 is a similar modification.

Rereiring more particularly to the drawings and especially Figure 1, it will be noted that I have pictured the electrostatic field in and about the insulator l0 which is represented as of the plain cylindrical type equipped at its top with a cap H which is electrically live. It is assumed that the lower end is grounded. From the upper end the flux flow will pass in all directions as indicated by the radiating lines. A very considerable amount will pass directly through the porcelain to the earth as indicated by the lines 52. Moreover some of this flow will pass outward from the cap H in all directions not only to the earth but even upward through infinite distances. The flux which starts downward through the porcelain toward the earth will find, part way down, that the outside or surrounding air is not filled electrically and as a consequence this electrical flux will wander away from the porcelain or other dielectric material as indicated by the lines l3. The result of this is that the flux density in the porcelain at the lower end is not as great as above and the electrical pressure per inch of length is not as great at the lower end as at the upper end. The air in the immediate vicinity of the porcelain naturally assumes the same rate of voltage drop as exists within the porcelain. The

View showing another space between the cap and the earth is consequently not being used in the most efficient way as the spaceat the upper end will naturally break down appreciably before the space near the lower end has approached the critical point.

Referring to Figure 2 it will be abserved that I have diagrammed an insulator I4 which embodies the principle of my invention in that the capped upper end i5 which is electrically live is of greater thickness than the lower end which is grounded.

' In this way it is possible to carry the greater -as it is obviously impossible to fire porcelain of excessive differences in thickness at diiierent points in the length owing to the setting up of extraordinary strains in the material during the firing process, which strains will cause distortion and probable eventual fracture or at least other defects which are present even though latent.

A practical embodiment, within reasonable limits, -of .the basic idea disclosed in Figure 2 is shown in Figure 3 wherein there is represented an insulator 16 of truncated cone shaped equipped at its lower or grounded end with a metallic ring or base I? cemented or otherwise secured in place as at I8, and provided at its upper or live end with a metal cap I9. It will be observed that the dielectric materiaLpreferably porcelain, is of much greater thickness at the upper end 20 than at any other point in the length of the insulator. The insulator body is hollow or formed with a cavity 2| the wall of which is tapered inwardly and upwardly at a greaterinclinationor pitch than the exteriorsuriace. By virtue of this formation it is clear that the maximum-bulk or thickness of material is at the upper end of the insulator, notwithstanding the fact that the upper end is oi the smallest diameter, that the walls taper gradually in thickness toward the bottom. In accordance with the previously given discussion this provides for an even flux distribution so that the upper end will be easily capable of carryiiig the burden imposed upon it without bein overstressed w i Owing to manufacturing diflicultiescinvolved in making an insulator having portions of, greatly varying thickness,I may prefer to resort to theexpedient disclosed in Figure 4 wherein I have illustrated a truncated .cone shaped insulator 22 equipped at its lower end.with a metallic ring' 23 and at its upper or liye-end with a cap 24.

The insulator is hollow or formed with a cavity 25. In this instance the requisite added thickness of material at the upper end is-shown as obtained by the use of a shell 26 which fits telescopically within the cavity 25 and which maybe'secured inplace by any suitable or preferred means, such for instance as by bituminous material or other non-conducting adhesive 265 While the thickness of the insulator body 22 is uniform throughout, the thickness of the shell 26 varies from its closed upper end to its open lower end,. thereby bringing about, from, the electrical viewpoint,the same conditions which exist in theone-piece type shown in Figure 3.

The shell 26 need not be of porcelain even if insulator 21 equipped with the ring or base 28 and cap 29 is partly filled with some appropriate insulating compound 30 which is plunged or otherwise treated so as to have the maximum thickness at the upper end and the minimum at 5 the lower end. This likewise brings about the same effect as the one-piece construction shown in Figure '3.

Figures 6 and 7 are capable of being construed to refer to insulators of the same general type as above described or to those of that variety adapted to be used either singly or in superposed series or in stacks for the support of station equipment. This may be considered as a development or enlargement of the basic idea. Re-

' ferring to Figure 6 in detail the insulator is disclosed as comprising a body 3| having a baseor ring 32 and a cap 33 and within which is located a series of nested shells 34 which may be secured in place and to each other in any desired manner. These shells are represented as having their walls of uniform thickness except at their lower edges where they are tapered off as indicated at 35 so as to vary the thickness of the insulator wall as a whole throughout the major portion of its length, the maximum thickness being at the upper or live end and the minimum being toward the lower or grounded end.

The structure in Figure '7 distinguishes from that in Figure 6 in'the single respect that the inner .shells 36 may be more accurately described as bushings in that the upper ends thereof are open instead of closed as in Figure 6. These nested bushingsv are represented as of uniform thickness except for their beveled or tapered lower ends 31. These bushings may be secured'to each other and within the outer insulator body 30' by any appropriate means or method. In this form as in Figure 6 the maximum thickness o1 there is no limitation as tothe exact use. Re-

ferring to this figure in detail it will be-observed that I have shown a plurality of "units 41, 42 h and 43 each formed as a porcelain body or shell I 44 equipped at its topand bottom with metallic fittings 45 and 46, the fittin s 46 at the bottom of each unit being customarily bolted to" the fittings 45 at the topof the units next below. In

embodying the principle of the invention in such a stack,.in which the top is naturally the line' end, I increase the thickness ofthe stressed top 50 unit 4| by securing within the'body thereof a bushing 41 of dielectric material, preferably but I not necessarily porcelain, thisbushing extendv ing the full length or height of the unit. Then, within the intermediate unit 42, there is provided a sirnilar bushing 48 which, however, willprob- 1 ably terminate short of the bottom, the lower end of this bushing being tapered off, beveled or otherwise reduced in thickness as shown at 49. I It is the assumptionthat the increased thickness 16 in the intermediate unit afiorded by the bushing 48 will relive it of any overstressing and will act to effect grading or flux density control.

However, as the maximum stress exists in the uppermost unit 4|, I take care of this by pro- 7 portion of the intermediate unit, while less than the thickness at the top of the uppermost unit, is nevertheless materially greater than that of the lowermost unit. I have found that by carrying out this scheme as indicated a very effective grading and flux density control may be had so that the objectionable stressing and corona formation will be entirely avoided and the are-over value increased, thus rendering the assembly eminently suitable, regardless of the frequencies handled.

For antenna insulation and for other more or less similar purposes, use may be made of elongated tubular insulators provided at their ends with metal fittings, one of which is of course at the live end and the other at the grounded one. As another variation of the fundamental idea involved, I contemplate constructing insulators of this type in such manner as to control the flux density properly. To accomplish this I may resort to the simple expedient disclosed in Figure 9 wherein I provide a dielectric bushing 52 within the live end portion of the tubular insulator 53 having terminal fittings 54 and 55. The bushing 52 need extend only part way of the length of the insulator and it is preferably tapered off as shown at 56 toward the intermediate portion. The added thickness afforded by the bushing 52 will take care of the flux density and provide grading. In the use of insulators of this type for the purpose mentioned it frequently occurs that there is also a flux concentration at the grounded end though of less magnitude than at the live end. In view of this condition I may, if found desirable provide a tapered bushing 51' within the grounded end. The extent of the bushings 52 and 51 compared with the length of the tube 53 is dependent upon various conditions or circumstances but the point is that the cross section of the porcelain or dielectric material should be proportioned as closely as possible to the total amount of fiux within it. In other words the thickness at any given point is dependent upon the flux density and may be varied to meet conditions which may be found existent.

In the various figures above discussed it will be noted that the increase in the thickness of the dielectric material has been brought about by the use of interiorly located auxiliary means such as the bushings. However, there is no particular limitation as to the location inasmuch as it is easily conceivable that I may resort to the expedient disclosed in Figure 10 wherein I provide a sleeve 58 telescoped exteriorly upon and appropriately secured to the live end of an elongated tubular insulator 59. In other words in accordance with my conception it makes no difference whether the increase in thickness be brought about by increasing the material of the insulator itself during manufacture thereof or whether the increase be brought about by the use of interior bushings or external sleeves, the effect being the same in any case. There is however, a point of possible advantage in the use of external sleeves, namely an increase in the area or radiating surface which would tend to effect dissipation of any heat as well as reducing concentration of stress.

In all of the various forms disclosed it is clear that the same underlying principle is involved, namely the employment or provision of the maximum thickness of material at the electrically stressed'end or ends of the insulator with a progressive decrease toward the grounded end, or the intermediate and unstressed portion, as the case may be. As mentioned in the forepart of this specification this causes a more nearly uniform flux density distribution and enables the upper or live end of the insulator to carry its electrical load without being overstressed and consequently without danger of corona which results from breaking down of the electro-static field in and about the insulator.

While I have shown and described various alternative forms it should be understood that the right is reserved to make any changes in the construction, arrangement, mode of manufacture and the like provided such constitute no de- .parture from the spirit of the invention or the scope of the claims hereunto appended.

Having thus described the invention, I claim: 1. A high tension insulator comprising a dielectric body having a live end and a grounded end each equipped with a metallic fitting, said body being hollow, and a dielectric shell located within the hollow body and having portions of its wall of varying thickness and cooperating with the walls of the dielectric body for providing the maximum dielectric thickness of material at the live end of the insulator, the thickness gradually decreasing toward the grounded end.

2. A high tension insulator comprising dielectric body having a live end and a grounded end each equipped with a metallic fitting, the body havinga cavity therein, and a series of nested shell members secured in telescoped relation within the cavity, said shell members having their walls tapered in thickness toward the grounded end of the insulator whereby the maximum thickness of dielectric material will be at the live end of the insulator.

3. A high tension insulator comprising a dielectric body equipped at its ends with metallic fittings and having one end of greater diameter than the other, said body having a cavity therein, and a dielectric member of hollow con-- ical shape with its wall tapered in thickness secured within said cavity in contacting relation to the wall thereof with its thinnest wall portion disposed adjacent the larger diameter portion of the body and with its thickest portion adjacent the smaller diameter portion of the body, the combined thickness of the walls of the body and the dielectric member at the smaller diameter portion of the former exceeding the combined thickness of the walls of the body and the dielectric member at the larger diameter portion of the former KENT A. HAWLEY.

CERTIFICATE OF CORRECTiON. Patent Non 2,128,817. 7 August 50, 1958.,

KENT A. Emma.

It is hereby certified that error appears in theprinted. specification;

of the above numbered patent requiring correction as follows: Page 5, second column, line 59, for the word "line" read live; and 1ine72, for "releive" read relieve; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 11th day of October, A. D. 1958'.

Henry Van Arsdale (Seal) Acting Commissioner of Patents.

- CERTIFICATE OF CORRECTION.

Patent No. 2,128,817. August 0, 19 8.

KENT A; HAWLEY.

It is hereby certified that error appearsv in the printed specification;

of the above numbered patent requiring correction as follows: Page 3, second column, line 59, for the word "line" read live; ar d 1ii1e72, for re1eive" read relieve; and that the said. Letters Patent should be read with this correction therein that'the same In ay conform to therecord of the case in the Patent Office.

. Signed and sealed'this 11th day oi October, A. D, 1958.

Henry Jan Arsdale I (Seal) I Acting Commissioner of Patents.

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