US1730250A - Insulator - Google Patents

Description

Oct. 1, 1929.

WITNESSES:

H. B. SMlTH INSULATOR Filed April 1, 1922 2 Sheets-Sheer. 1

INVENTOR ATTORN EY H. B. SMITH Oct. 1, 1929.

INSULAT OR Filed April 1, 1922 2 Sheets-Sheet I N VENTO R flora/a 5. 6m /f/1.

WITNESSES:

Patented Oct. 1, 1929 u'urrso srarssearsar ounce HAROLD B, SMITH, OF WORGESTEE, MASSACHUSETTS, ASSIGNOR TO WESTINGHGUSE ELECTRIC &;M'ANUFATURING COMPANY, A. GORPGRA'IIUN 0F FENN'SYLVA'NIA INSULATOE Application-filed April 1,

My invention relates to insulators and particularly to insulators for supporting highvoltage lines or conductors.

One object of my invention is to provide a suspension insulating structure of rela tively small dimensions and of light Weight that shall'be capable of withstanding very high voltages.

Another object of my invention is to provide a high-voltage insulator that shall so distribute and direct dielectric stresses as to reduce the likelihood of impingement of the stresses upon the insulating parts of the structure. 7

AJIOtlIGI object of my invention is to pro-- vide a high-potential insulator that shall so distribute the electric flux as to render the potential gradient substantially uniform and of desirable minimum values at all points along the insulating member.

Another object of my invention is to so adjust the dielectric field of a high-potential insulator that it may be caused to nearly con form to certain easily-constructed commer cial structures, to thereby combine the advantages oi. field-conforming structure and of a field-distributing structure with those of a structure of simple commercial manufacture Anot ier object of my invention is to provide a high-voltage insulator that shall be protected from detrimental Weather conditions,- that shall have a higher ratio of Wet to dry arc-over voltage than heretofore obtained and that shall have a Wet arc-over voltage comparable to its dry arc-oven Another object of my invention is to proviole l'iigh-voltage insulator in which the dielectric field shall be so distributed to prevent the maximum potential gradient occurring along the insulating member and. along the surface of which member corona ancl arcing shall not occur Another object of my invention is to so distribute the electrostatic iielcl of a high potential insulator that both the Wet and the dry arc-over voltages, and particularly the Wet arc-over voltage, shall materially increased over values heretofore obtained in a given spacing between conductors, at the ends of the insulator, and that shall more nearly 1922: Serial Not 548,818.

approach the theoretical maximum value for a given. distance in air,

A further object of my invention is to provide a high-voltage insulator that shall be simple and durable in construction, economical to manufacture and effective in its operationr.

It is Well known to those skilled in the art of high-potential. transmission and insulation that as commercial voltages are increased beyond those considered as limits in the past, the problem of providing safe commercial structures to support and insulate conductors carrying such voltages becomes increasingly difficult. In fact the problem has been so cliflicult and its solution. so vital to economical and eiiioient distribution of electrical energy as to malre it at present, one of the most important features; if not themost important feature, of engineering resear '1 in the electrical field,

The history of insulators since the advent of corona-forming commercia v l ages, has involve-cl diner-cut theories an production of various structures embo ring principles conforming to such theories. One of the more important of such principles being that of leak ge-current distribution Duringa considerable period of production of commercial insulators, dielectric streu terials and creepage surface or leakage-cur- "ibution were considered the main which ellective service de= pencle I Insulators constructed in accordance with the above-mentioned principles operated satisfactorily tor the insul tio'i of ages which within the range 0 F commercial gene 7 *ing apparatus the advent oi 'th of ma- U well-known principle teaches that aninsulator conforming closely, in the contour of its Surface, to the lines of the electrostatic field has substantially the same dielectric strength, along its surface, as the air in which it is disposed. However, by reason'of weather .and other conditions it was necessary, espeportion to the voltages of the transmission lines on which they might have served and they are relatively expensive or tend to cause expense by reason of the larger towers required for their use.

The distribution of dielectric stresses, as exemplified by the laterally extending distributors at the terminals of insulators, now

proposed, is a notable improvement over the rings and horns because the latter do not distribute, but rather concentrate and direct, the electrostatic field. Although the rings and horns control, to a certain extent, the general location of the are, they do so at the expense of concentration of the electrostatic field, causing a break-downmuch below the theoretical strength of air in a uniform electrostatic field. Of course, the various developments here mentioned have their distinctive individual uses in which they are of great value, and any apparent disadvantages herein mentioned are only to be construed relatively to the aim of my invention which is the'provision of a simple and eiiective commercial insulator for withstanding voltages which have not heretofore been extensively employed. While these principles and combinations. are of especial value and importance-for the higher voltages not heretofore employed, they are also of importance in many applications at voltages not now un common. I

Summarized, insulators have been constructed with a view to dielectric strength, leakage-current distribution, field direction, electrostatic field distribution and other features, but, to the best of my knowledge, none of them have incorporated and combined the features which render the insulator of my invention an exceptionally economical, compact and ehective device for service with voltages of extremely high values.

My invention was primarily conceived by a consideration of the fact that a long straight narrow rod, bar or tube of insula- .tion provides voltage protection, in a uniform parallel electrostatic field, substantially in proportion toits length and from a study of the possibilities of utilizing such a bar, rod or tube in commercial practice. Such bars, although used, have not proved especially' useful because, under conditions to which they have been subjected, and in the manner they have been applied, even with prohibitive lengths, corona, deterioration and losses occur.

As'mentioned above, while varlous lnsulator structures for'directing and distributing I an electrostatic field have been suggested, one of the principal considerations appears to have been the preventing-0t concentrated stresses in the insulating material, to thus protect it against puncture. This was done at the expense of a concentrated flux, and therefore of a high-potential gradient, along the insulating surface. I

In developing my'invention, I concieved the idea that, if the excessive electrostatic stresses could be kept away from the insulatinginember entirely, under wet and dry normal and arc-over conditions, not only would puncturing be prevented but also breakage, losses, charring and other deterioration from corona and fiashover would be prevented. This is accomplished in such manner as to more nearly approach the maximum theoretical dielectric strength of air along the path in which the arc will ultimately occur and is attained in a combination structure which, to the best of my knowledge, has not heretofore been attempted.

In practicing my invention, 1 provide an elongated insulating supporting structure and terminal members that are designed to not only very widely distribute electrostatic fluxbut also to keep the denser portion of its electrostatic field away from the insulating parts. This is accomplished by providing oppositely facing conducting terminal members having portions of substantially torus shape in which the radii of the torus portions are such as to prevent the likelihood of corona tormation at voltages for which the insulator is designed. The construction provides oppositely facing electrostaticstress-distribut ing and directing members that extend or recede away from each other along the axis of the insulator and are shaped, at substantially all points on the surfaces thereof, to lie in curves of relatively great radii. Thus, an electrostatic field is provided which is not only dist 'ibuted over maximum area but is so directed or shaped as to provide a hollow electrostatic field or zone of reduced stress along, and in the immediate vicinity of, the bar or insulating supporting member. it also provides the strongest portion of its electrostatic field along a path by which it is desirable for an arc to form in case of break down. Such held of reduced stress extends for a relatively large distance away from the insulating supporting member to preclude the concentration of the flux field in the vicinity of the supporting member, and, consequently, the possibility of a discharge between the closest longitudinally spaced points of the terminals along the length of, or adjacent, the supporting member.

' Figure 1 of the accompanying vdrawings is a side view, partially in elevation and partially in section, of a suspension insulator embodying my invention, and Y I Fig. 2 is a similar view, of a modified form of my invention, taken at right angles to the insulator, shown in Fig. 1.

As shown in Fin. 1 m invention com- )rises in eneral an elon ated central su porting member 1, terminal members 2 and 3 and upper and lower electrostatioflux distributing members 4 and 5, respectively.

The central supporting member, preferably of relatively small diameter, may be a rod or tube of wood, molded fibre or any other suitable insulating material having ends of substantially frusto-conical shape or otherwise suitably formed for the reception of metal members 6 that may be securely attached thereto, as by swaging. T he bottom member 6 may be provided with a screwthreaded stud 7, integrally or otherwise attached thereto and projecting (Jo-axially from the end thereof.

The upper electrostatic stress-distributingand-directing member 4, preferably of inverted bowl-shape and relatively deep and of large radius at its edge 8, may be provided with a receding portion 9, of inverted cupshape, having a central recess 10 to receive the upper member 6. The member 6 may be secured in position'in the recess 10, by a body of cement 11, similarly to a usual cap-and-pin insulator, or be otherwise attached to the member 4. The terminal member 2 may be constructed similarly to the cap of a cap-andpin insul tor and similarly cemented in position over the portion 9 of the member 4.

The lower electrostatic stressdistributingand-directing member 5 is formed as an annulus having toroidal surfaces 12 of relative- 1y great radius and a central'opening 13 of larger diameter than the supporting member 1, by reasonof which it may be positioned in spaced concentric relation around the latter. A bracket 14, having a collar portion 15 secured to the lower member 6 and tubular or rounded arms 16 of relatively great diamctcr, secured to the under surfaces of the member 5, and receding from the upper slrcss-distributing member 4, is provided to hold the member 5 in position. This construction permits rain or small solids to freely pass through the opening 13.

A conductor 17, which the insulator is adapted to support, may be covered by a sheath or jacket 18 of relatively great length and diameter to prevent the concentration of electrostatic stresses on the conductor adjacent to the insulator and be secured to the latter by any suitable means, such as a twopart clamp 19, the upper portion 20 of which is secured to the stud 7 of the lower member 6 and the lower portion 21 of which is secured to the portion 20 by screws 22.

The members 4 and 5 may be constructed outer surface portions 23 of metal. This construction may be obtained in any suitable manner, as by coating with metal paint, by metallic glazing, by electrolytic deposition or by other means.

[it no position, within wide limits in the electrostatic field between the ends of the insulator, are there any sharp edges, corners or points. The members 4 and 5, being rounded and of relatively great radii, both laterally and longitudinally the member 5 recedes gradually from the member 4 at both its inner and outer lateral sides, and'the member 4 recedes from the member 5 to a gradually curved portion 24 adjacent to the member 1. Thus, the opposing curved surfaces of the members 4 and 5 recede from each other inwardly toward the member 1 from the lines of shortest distance between them at such rate as to provide a hollow electrostatic field, as indicated by the dotted lines at the left half ofFig. 1. In other words, an electrostatic field is provided that is spread or distributed laterally over a rela tively great area but is also rendered weakest at its central portion through which the supporting member 1 extends; In addition to bein weakened adjacent to the member 1, the e er'trostatic field, at this central zone, is directed to lie almost parallel to the longitudinal sides thereof. The member 1 could, of course, be shaped to conform exactly to the adjacent lines of the electrostatic field but such construction would be no material addition to the art in connection with this invention, since the field-conforming principlev has been previously suggested. F urthermore, and as hereinbcfore stated, it is one of my aims to substantially incorporate, so far as desirable. the electrostatic field-com forming principle in an economical commercial structure. by so weakening the electrostatic field at its central portion, and along the insulating surfaces, where it has usually, heretofore, been very strong, if not the strongest, that the slight departure from conformation be- This has been accomplished tween the insulator and the field is a negligible factor because the stresses are so widely distributed and are weaker adjacent to the insulating member than elsewhere.

The proportions between the members 1 and 4 are such that. the member 1 will not ordinarily be subjected to rain above a certain position, such as substantially the position 25 thereon, which position, as indicated by a broken line 26, is ordinarily not as distant from the nearest point on the member 4 as the latter is from the member 5, as indicated by a broken. line 27. The field within the line 27 extends between the members 4 and 5, substantially as indicated in Fig. 1, in which the lines of force are of greatest density along the line 27 and gradually become less dense and of less curvature toward the central axis of the insulator until, theoretically, a single straight line of force lies coincident with the axis of the member 1 throughout. its length. Outwardly, beyond the line 27, the field bows convexly and becomes less dense in proportion to its distance therefrom.

An insulator, constructed substantially as shown in Fig. 1, with the distance 27 eighteen inches and the other parts in proportion, has a dry flash-over of 375,000 volts and, with the distance 27 nine inches, a dry flash-over of 242,000 volts. These are remarkable performances in comparison with former insulators of the same size, weight and cost of construction.

In operation, an are forming substantially along the line 27 has absolutely no tendency to engage the surface of the supporting member 1 and cannot be caused to do so under the most violent lateral Wind pressure. When subjected to such wind pressure, the arc is blown around the member 1 in a circle and then extinguished while still extending betweenthe outer portions of the 1netal-sur faced members 4 and 5.

In the modification of my invention shown in Fig. 2, in which similar parts are designated by similar reference numerals, the construction is substantially the same as above described. The supporting member 1 is similar to an ordinary wood strain-insulator enclosed in a tube 28 of weather protecting material, such as porcelain or glass, and the members 4 and 5 are formed of sheet metal.

The combination of definitely directing and widely distributing the electrostatic field, together with the extent to which the flow-line principle isutilized, as herein set forth, is a distinct departure from attempts heretofore made. Arcing horns and rings, while they direct, do not prevent concentration of the stresses along'the insulating members and the field between them is usually in a highly stressed condition. Also, stress-distributing shields, as heretofore employed, have been used principally to prevent con influence tending to definitely direct the fiashover arc.

\Vith an insulator constructed in accordance with my invention, the electrostatic field is not only very widely distributed over a relatively great area and the maximum dielectric strength of air in a uniform field thereby approximated to nearly conform to a commercial form of insulator structure but is also so positively and definitely directed as to prevent damage to the insulating parts.

Nhile I have shown and described particular forms of my invention, changes may be made therein without departing from the spirit and scope thereof, as set forth in the appended claims.

I claim as my invention:

1. An insulator comprising an elongated central supporting insulating member, a hood of inverted substantially bowl shape thereon and having rounded edges, said hood being electrically conducting on its under surface and on said edges, and a conducting annulus of smaller diameter than the hood disposed longitudinally opposite said hood in spaced relation around the supporting member and having a widely laterally-rounded outer perimeter, both members co-operating to spread the flux between them over large areas and to prevent concentration.

2. An insulator comprising an elongated cylindrical supporting insulating member of relatively small diameter, a terminal member of relatively deep and wide substantially bowl shape secured in position adjacent to one end thereof, said terminal member having rounded outer edges ofrelat-ively great radius and conducting surfaces on said edges and on its inner surface, and a conducting ring of less diameter than the member of bowl shape disposed in concentric relation with respect to the axis of the supporting member in spaced relation thereto and having a rounded perimeter of relatively great radius facing the open end of the bowl.

3. An insulator comprising an elongated supporting insulating member of relatively small diameter, a terminal neniber of relatively deep and wide substantially bowl shape secured in position adjacent to one end thereof, said terminal member having rounded outer edges of relatively great radius and conducting surfaces on said edges and on its inner surface, a conducting ring of less diameter than the member of bowl shape disposed in concentric relation with respect to the axis of the supporting member in spaced relation thereto and having a rounded perimeter of relatively great radius facing the open end of the bowl, and means on the side of the ring farthest removed from the bowl for supporting the ring.

4. An insulator comprising an elongated insulating member, an upper terminal member havin a conducting substantially toroidal surface of relatively great area surrounding the insulating member in widely radially-spaced relation thereto at a position downwardly removed from the upper end thereof, said surface merging at its inner edge into a conducting surface of relatively deep inverted substantially bowl shape, and

I a lower terminal member having a conducting substantially toroidal surface of relativelyv great area surrounding the insulating member in radially-spaced relation thereto, the space surrounding the insulating member between the latter and the lower toroidal surface, and for a relatively great distance below the latter surface, being open to prevent interference with the electrostatic field as directed by said surface with respect to the upper terminal member.

5. A high-voltage insulator comprising a supporting rod of insulating material, a conducting toroid surrounding the lower end of the rod and spaced therefrom laterally and longitudinally but electrically connected to the end thereof to serve as a flux-directing member and to permit accumulated moisture to pass freely down the rod, and an upper fluxdirecting and spreading element associated with the upper end of the rod for divertin the electrostatic flux outwardly from the rod to preclude the rod and/or the moisture from effecting the normal flux distribution.

6. A high-voltage insulator comprisin an elongated insulating member and terminal members therefor having substantially toroidal conducting surfaces of relatively great area disposed aboutthe insulating member in laterally spaced relation thereto to widely distribute the electrostatic flux over said surfaces and to prevent the concentration of the electrostatic field at the ends of the insulating member and to direct the electrostatic field to conform to a uniform substantiall cylindrical zone having a weakened longitudinal central portion through which the insulating member extends, the spaces surrounding the'insulator, and for relatively great distances beyond the toroidal surfaces away from each other, ing open to revent interference with the electrostatic eld as directed by said surfaces with respect to each other. 7

In testimony whereof, I have hereunto subscribed my name this twenty-fourth day of March, 1922.

HAROLD B; SMITH.

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