US1350936A - Insulator - Google Patents

Description

F. W. PEEK, JR.

INSULATOR.

urucmon FILED 1104.2,1919.

Patented Aug. 24, 1920.

I E .1 1 if 1 I.

.5 15: a ii Inventor: Frank W -Peek,Jr7, by WQ His Tlttorfig.

UNITED STATES FRANK W. PEEK,'J'B., OF PITTSFIELD, MASSACHUSETTS,

PATENT OFFICE ASSIGNOR TO GENERAL INSULATOB.

Continuation of application Serial No. 154,934, filed March 15, 1917.

Specification of Letters Patent.

Patented Aug. 24:, 1920 This application filed January 2,

1919. Serial No. 269,198.

To all whom it may concern:

Be it known that I, FRANK W. PEEK, J r., a citizen of the United States, residing at Pittsfield, in the county'of Berkshire, State of Massachusetts, have invented certainnew and useful Improvements in Insulators, of which the following is a specification.

My invention relates to electrical insulators, and particularly to insulators of the bushing type for high voltage conductors passing through walls, as through covers for tanks for high voltage transformers, oil switches, lightning arresters, etc; and has for its general object the provision of an improved and simplified construction for such insulators which is durable, readily manufactured and in which the materials employed are more effectively utilized than was heretofore known; my present application being a continuation of my former application, Serial No. 154,934, filed March 15, 1917.

Conductors passing through walls are commonly insulated from these walls by means of masses of insulating materials of greater dielectric strength and higher specific inductive capacity than the surround ing medium, and my invention is applicable to such cases. For the sake of simplicity I shall hereinafter generally regard the surrounding medium as the air of the atmosphere. One of the difficulties encountered heretofore has been due to the concentration of the electrostatic flux on the conductor beyond the end or ends of the insulating mass. Another difficulty has resulted from the uneven distribution of the stress along the surface of the insulating massdue to the cutting in certain regions of the surface of the insulating mass by locally concentrated and improperly directed electrostatic fiux. These difliculties have resulted in reduced arc-over voltage for the insulator because the gradient along the surface, and consequently the arc-over voltage, depends upon the flux density and the angle at which the electrostatic flux cuts the surface. If the path on the surface is weaker than the path through the adjacent air or gas, the flux direction should be such that the tangential and perpendicular components of the gradient are in the same proportion as the respective dielectric strengths of these two paths.

By my invention the electrostatic flux is to be controlled and redirected, particularly toward the end or ends of the insulating mass, preferably reducing the concentration of flux on the conductor in the air, and preferably in such a way that the surfaces of the insulating material, although the insulating mass be of simple shapes, such as cylinders, cones, etc., are cut by a very small number of electrostatic flux lines substantially evenly distributed and at a direction to the surface which gives the maximum arc-over voltage for the solid insulating material employed. Of course, I contemplate that petticoats may be applied to the surfaces of the insulating masses; since by simple shape I mean to refer to the general outlines of the insulat ing mass and it is the general outlines that are to be cut by the small number of flux lines.

To accomplish the object of my invention I employ conducting material for redirecting the electrostatic flux lines, particularly adjacent the end or ends of the insulating mass. This conducting material materially enlarges the effective diameter of the conductor adjacent the end of the insulating mass. This flux controlling conducting material has at least one portion embedded within the mass of insulating material and is so located as to attract to it a considerable part of all the electrostatic flux lines otherwise terminating in the air on the conductor beyond the end of the insulating mass. Preferably such embedded conducting material, at some distance from the end of the insulating mass, presents a fairly narrow edge to the flux emanating from the wall surrounding the conductor and may comprise a disk substantially perpendicular to the conductor axis. While this embedded conducting portion does not necessarily reduce the value of the greatest flux concentration at the surface of the conductor (it may even increase it), this concentration takes place within the mass of the insulation where the potential gradient resulting from this concentration is acting on insulation of materially greater dielectric strength than that of the atmosphere, whilethe potential gradient in the air is reduced. s a consequence, where a wholly embedded portion of conducting material is employed, it is preferably supplemented by a second conducting portion exposed to the atmosphere beyond the end of the insulating material. This second conducting portion in effect enlarges the surface. of the conductor in the atmosphere and presents a generally curved surface to the electrostatic flux lines terminating in the a1r beyond the insulating mass. By this second portion of conducting material the concentration of the electrostaticv flux lines on the conductor in the atmosphere is further controlled and reduced. It is possible, therefore, by employing either the first of these means alone or by both of these means to; gether, to reduce the length of the insulating mass without correspondingly reducing the potential difference between the conductor and surrounding wall which the insulation will withstand.

As before indicated, the conducting portions adjacent the end of the insulating mass preferably so redirect the electrostatic flux that, although the insulating mass be of some simple shape in general outline, as a cylinder, cone, etc., its surface will be cut uniformly by the electrostatic flux and in a direction to produce maximum arcover voltage for the structure. The spacing between these conducting portions and the wall through which the conductor passes, and the effective diameters of these conducting portions, are among the important factors determining in considerable measure the extent of the redirection of the electrostatic flux lines throughout their complete path between the wall and the end of the insulation. In practice it is preferable to have these flux redirecting conducting portions ofthe conductor assisted by a ground shield on the wall in securing the desired disposition of the electrostatic flux lines along. the insulator surface.

For a more complete understanding of the nature and objects of my invention reference should be had to the following detailed description taken in connection with the accompanying drawing, in which:

Figure 1 is a section of a simple oil or compound filled bushing embodying a preferred form of my invention, while Fig. 2 is an elevation partly in section of an embodiment of my invention in a bushing of the condenser 13 pe.

The bushing of Fig. 1 comprises upper and lower hollow cylinders 8 and 9 of any suitable insulating material, for example, porcelain. One end of each of these cylinders is closed, the open ends of the cylinders being carried by the metallic member 10 which may represent a wall (for example the top of a tank for electrical apparatus, like a transformer tank), or the metallic member which is often provided as a mechanical part of a bushing and by means of which the bushing is attached to the wall from which it is to insulate a conductor. For the sake of simplicity and clearness, this member 10 hereinafter in this description may be considered to be, or to be attached to, the cover of a transformer tank partially filled with oil. The conductor 12 passes through a circular opening 11 in the metallic member 10 substantially concentric with the axis of the cylinders Sand 9. The metallic member 10 is provided with an annular ground shield 13, in this case projecting at both sides of the member 10, and is further provided with the usual metallic sleeve 14 projecting downward into the tankand below the surface 15 of the oil therein. The insulating cylinder 8 engages directly the upper plane surface of the metallic member 10; the cooperating cylinder 9 engages the lower end of the projecting sleeve 14.

cylinders 8 and 9 is filled withia suitable insulating compound, solid or liquid, as for example, oil. The conductor 12 may be either the conductor which itself carries the current to and from one of the terminals of the transformer within the tank, or it may be merely a tube into which the power conductor is inserted, in which latter case it is generally electrically connected to the power conductor.

My invention is embodied only in the upper portion of this bushing of Fig. 1. Adjacent the upper end of the conductor 12 and within the insulating mass of thebushing is provided a horizontal fairly thin metallic disk 17 electrically connected to the conductor l2, and beyond the end of the cylinder 8 is provided a conducting sphere 19 also electrically connected to the conductor 12. These parts 17 and 19 (in the case illustrated with the cooperation of the ground shield 13) redirect a part of all the electrostatic lines of force between the conductor 12 and the member 10. The dotted lines 25 and 26, respectively within and without this bush ing, indicate a portion of the electrostatic lines of force or electrostatic, flux between the wall and conductor which I desire to redirect, and indicate in a general way the direction of these electrostatic lines of force which I desire to secure in the complete form of my invention. lit will be observed that these lines of force have been redirected and disposed by reason of the extended surface of the metallic disk 17 and sphere 19 over which the charge is distributed quite difierently from what might be expected were this conducting material omitted.

What I have illustrated and described so far is one form of a general scheme for re directing a considerable part of the electrostatic flux between the conductor 13 and the member 10; but in the ultimate form of my invention 1 contemplate redirecting this flux throughout the whole of its course, including both adjacent the member 10 (particularly The inclosed chamber formed by the member 10 and the insulating with the aid of the ground shield 13) and adjacent the upper end of the insulating mass (particularl by employing the parts 17 and 19). In ordinary practice, however, I contemplate redirecting this flux adjacent the upper end of the insulating mass without paying much consideration to the disposition of this flux on .the member 10, either with or without the aid of the ground shield 13.

Now considering first only the redistribution of the flux adjacent the endof the bushing; the desired redistribution of the flux adjacent the end of the bushing is se cured by abruptly and materially the conductor 12 within and adjacent the end of the solid insulating mass and especially by enhancing the effect of this enlargement by terminating the enlarging portion or member in a more or less thin edge well below the end of the bushing and embedding it within the mass thereof. The disk 17 is illustrative. This disk may or may not be an integral part of the rod 12,

although it is of substantially the potential v of the rod 12 which result is secured by electrically connecting the disk to the rod 12.

This member 17, by reason of its shape and location, shields a portion of the conductor 12 above the insulating mass, or takes to itself a considerable part of the electrostatic flux otherwise terminating on the conductor in the air and transfers to a great extent the flux concentration from the air and the con ductor 12 to the insulating mass and the edge of the disk. Since this disk, and particularly its edge where the stress is most concentrated, is embedded in the insulating material of the bushing, the potential differences along the electrostatic lines of force which have been redirected are acting across insulating material of a higher dielectric strength than the air. Other things being equal therefore, a greater voltage difference between the conductor 12 and the metallic member 10 may be sustained without failure for the same length of the member 8 than Were the member 17 omitted.

The embedded disk 17 may be and preferably is aided in reducing the concentration of stress in the air adjacent the end of the insulating mass by an enlargement of the conductor beyond the end of the insulating mass, as by the metallic sphere19. In general the location and concentration of the electrostatic lines 25 and 26 may be varied in any one of a number of ways by either varying the diameter of the disk 17, the thickness and curvature of its edge, the size of the sphere 19, or the relative spacings between these parts and the member 10. I contemplate moreover that even considerable modifications of these parts may be made to secure desirable flux relations; for example, it will be apparent from a considenlargi g before the air was displaced.

eration of the matter that the parts 17 and 19 may be united otherwise than by the conductor 12 as shown, as for instance by another conductor connected between them without changing materially the flux relation indicated in the drawing;

Now considering the effect of placing dielectric material other than air about any conductor, such dielectric material generally has a greater permittivity or specific inductive capacity than air, and as a consequence more electrostatic lines of force are drawn down into the space occupied by such material than were ori inally there 'Fhis increased number of lines as a rule will cross the surface separating the material of high specific inductive capacity from air generally, in such wise that there are regions of local concentration of electrostatic lines. on the surface so traversed; this surface on the two sides of which the specific inductive capacity is different being a surface "of discontinuity in a dielectric medium. Since these regions of local concentration are attended with increased electrostatic stresses and consequent tendency to break down, it is desirable therefore, to redirect the lines in these regions to avoid any such local concentration over the insulating surface.

In the practical working out of this redirecting of the electrostatic lines of force according to my invention, the proportions before mentioned of disk 17 and sphere 19 would be chosen so that very few lines emerge from the insulating surface of member 8; thereby avoiding the liability ofconcentration.

Considering now the effect on the cooperating ground shield 13: this ground shield acts as an extension of the member 10 in an axial direction so that by reason of the charge distributed over it, a number of electrostatic lines of force terminate upon it and are thus drawn within the space inclosed by the insulating member 8, which lines would otherwise have terminated on the member 10 exteriorly of this insulating member. As a consequence the regions of greatest electrostatic stress, which obtain near the ends of the electrostatic lines terminating on ground shield 13 as evidenced by the crowding of equipotential surfaces adjacent this ground shield (which surfaces have not been drawn in the interests of clearness) now occur in a dielectric medium other than air, such as oil, which has been selected to have than air.

The mass of insulating material, surrounding the conductor going to make up the assembled bushing, will sustain safely higher potential gradients than the air surrounding the whole. Conseguently in the practice of my invention contemplate greater dielectric strength forming and locating the conducting members. such as disk 17 and sphere 19 with respect to the dielectric media, so as to proportion the gradients interiorly and exteriorly of the member 8 to the respective di electric strengths in such manner that arcover through the air will take place at a somewhat lower voltage than the puncture voltage of the mass of insulation.

l urthermore, since it is known that the dielectric strength of the air along the surface of the member 8 is not the same as, but is as a rule less than, the dielectric strength of the air not in contact with such surface but otherwise adj acent'the member 8, I contemplate such use of the flux controlling members as will redirect the electrostatic flux emerging from the surface of member 8 in a manner that will compensate for this difference in dielectric strengths. Obviously then the most advantageous direction to impart to the flux is such that its stress component along the surface of the member 8 is numerically in substantially the same proportion tothe stress component extending out from the surface of member 8 as the respective dielectric strengths of the air; since the electrostatic flux about a conductor of the type shown at 12 must necessarily have components of stress along the surface of the member 8.

In Fig. 2 I have illustrated my invention in its complete form embodied in a bushing of the so-called condenser type. In addition to the parts described with reference to the bushing of Fig. 1, (and which bear similar reference characters in this figure) the bushing is provided with metallic cylinders 30 carried by insulating cylinders 31, the metallic cylinders being so proportioned and arranged as to constitute the whole a bushing of the condenser type. Each metallic cylinder 30 terminates in a metallic ring 32 which in effect enlarges the surface of the edge of the metallic cylinder, and hence reduces the concentration of electrostatic flux at the edge. Condenser type bushings are well known and the details of the construction of the bushing illustrated need be no further described.

While I have here shown two embodiments of my invention which are, at present, the best means known to me for carrying the same into effect, I would have it understood that this is merely illustrative and that I do not mean to be limited thereby to the precise details here disclosed since obvious alterations thereof will occur to those skilled in this art, nor in the choice of recognized equivalents except as defined in my claims hereunto annexed.

What I claim as new and desire to secure by Letters Patent of the United States, is: l. The combination with conducting members at materially different potentials,

.tration in said flux over said surfaces of discontinuity.

2. The combination with a conductor partially exposed to a gaseous dielectric medium, of a conducting structure surrounding said conductor at a materially different potential, a mass of insulating material intervening between said conductor and structure whose exterior contour is of substantially simple shape, and an electrostatic flux controlling means in conducting relation with said conductor; said means being proportioned and located interiorly oi: said mass adjacent the entrance of said conductor into the mass ata point which proportions the potential gradients due to the electrostatic flux tangentially and exteriorly perpendicular to the surface of said mass in substantially the same ratio as the respectlV8 dielectric strengths in order that the arc-over voltage in said medium may approach the maximum for the structure.

3. The combination with a conductor partially exposed to a gaseous dielectric medium, of a conducting structure surrounding said conductor at a materially different potential, a mass of intervening insulating material whose exterior contour is of substantially simple shape, and an electrostatic flux controlling means conductively related to said conductor; said means being proportioned and situated in said mass to redirect the electrostatic flux so that the gradient along the surface of the mass exposed to said medium is numerically in substantially the same proportion to the gradient in said medium not in contact with but adjacent to the surface of the mass as their respective dielectric strengths.

4:. The combination with a conductor, an adjacent member of a different potential, and a mass of insulating material extending between said conductor and said member, of means for altering the concentration of electrostatic stress at the end of the insulating mass remote from said member comprising conducting material electrically connected to said conductor and abruptly and materially enlarging the effective diameter of the conductor within said insulating mass at a point some distance from said end thereof which gives substantially the maximum arc-over voltage for the structure.

5. The combination with a conductor, a metallic member of a different potential surrounding the same intermediate its ends, and a mass of insulating material surrounding said conductor from said metallic mem- 4 ber to a point on said conductor remote from said metallic member, of means for reducing the concentration of electrostatic stress at the end of said insulating mass remotefrom said metallic member comprising a disk of conducting material located within said insulating mass adjacent said end thereof at a point giving substantially maximum arc-over voltage for the structure said disk being connected to and surrounding said conductor in a plane substantially perpendicular to its axis.

6. The combination with a conductor, a metallic member of a different potential surrounding the same intermediate its ends, and a mass of insulating material surrounding said conductor from said metallic member to a point on said conductor remote from said metallic member, of means for reducing the concentration of electrostatic stress at the end of said insulating mass remote from said metallic member comprising conducting material electrically connected to said conductor and presenting to the electrostatic flux from said metallic member a relatively thin edge surrounding said conductor and embedded in said insulating mass at some distance from said end thereof, and also comprising conducting material enlarging the diameter of the conductor beyond said end of said insulating mass and presenting a generally curved surface to the electrostatic flux from said metallic member.

7. The combination with a conductor, a metallic member of a different potential surrounding the same intermediate its ends, and a mass of insulating material surrounding said conductor from said metallic member to a point on said conductor remote from said metallic member, of means for reducing the concentration of electrostatic stress at the end of said insulating mass remote from said metallic member comprising conducting material beyond said end of the insulating mass and a conducting disk, said conducting material being electrically connected to said conductor and beyond said end of said insulating mass remote from said metallic member surrounding said conductor and having its surfaces receiving electrostatic flux from said metallic member generally curved, said disk being located within said insulating mass adjacent said end thereof and connected to and surrounding said conductor in a plane substantially perpendicular to the conductor axis.

8. The combination with a conductor, a metallic member of a different potential surrounding the same between its. ends,'and a mass of insulating material surrounding said conductor from said metallic member to a point on said conductor remote from said metallic member, of means for reducing the concentration of electrostatic stress at the end of said insulating mass remote from said metallic member comprising two portions of conducting material surrounding and electr cally connected to said conductor adjacent said end of the insulating mass, one embedded and terminating within the insulatlng mass materially nearer said metallic member than the other, said other being exposed to the medium surrounding said insulating mass.

9. The combination with a conductor, a metallic member of a different potential surrounding the same intermediate its ends, and a mass of insulating material surrounding said conductor from said metallic member to a point on said conductor remote from said metallic member, of means for reducing the concentration of electrostatic stress at the end of said insulating mass remote from said metallic member comprising conducting material embedded in said insulating mass, electrically connected to said conductor and materially and abruptly enlarging the effective diameter of the conductor within said end of said insulating mass, and at some distance from said end thereof, and also comprising conducting material enlarging the diameter of the conductor beyond said end of the insulating mass and presenting a generally curved surface to electrostatic flux from said metallic member.

10. The combination with a conductor, a metallic member of a different potential surrounding the same intermediate its ends, and a mass of insulating material surrounding said conductor from said metallic member to a point on said conductor remote from said metallic member, of conducting material electrically connected to said conductor materially and abruptly enlarging the diameter of said conductor adjacent said point thereon and at the face of said conducting material toward said metallic member, said conducting material so directing electrostatic flux from said metallic member that a relatively small amount of said flux passes through the surface of said insulating mass.

11. The combination with a conductor, a metallic member of a different potential provided with a ground shield surrounding said conductor intermediate its ends, and a mass of insulating material surrounding said conductor from said metallic member to a point on said conductor remote from and at the same side of said metallic member as said ground shield, of conducting material electrically connected to said conductor and materially enlarging the diameter of said conductor adjacent said point, said conducting material being disposed for redirecting the electrostatic flux about said metallic member in such wise that regions of local concentration in said flux are avoided at any point over the surface of the insulating mass where the flux passes into air.

12. The combination with a conductor, of a metallic member of a different potential surrounding the same intermediate its ends, and a mass of insulating material surrounding said conductor from said metallic member to a point on said conductor remote from said metallic member, of conducting material electrically connected to said conductor, materially and abruptly enlarging the diameter of said conductor adjacent said point thereon and terminating toward said metallic member and within said mass of insulating material, said conducting material being disposed for redirecting the electrostatic flux about said metallic member in such Wise that regions of-local concentration in said flux are avoided at any point over the surface ,of the insulating mass where the flux passes into air.

13. The combination with a conductor, a metallic member of a different potential provided with a ground shield surrounding said conductor intermediate its ends, and a mass of insulating material surrounding said conductor from said metallic member to a point on said conductor remote from and at the same side of the metallic member as said ground shield, of conducting material electrically connected to said conductor and materially and abruptly enlarging the diameter of said conductor adjacent said point thereon and at the face of said conducting material toward said metallic member and other conducting material electrically connected to said conductor outside said mass of insulating material, said conducting material being disposed for redirecting the electrostatic flux about said metallic member in such wise that regions of local concentration in said flux are avoided at any point over the surface of the insulating mass where the flux passes into air.

14. The combination with a conductor, a metallic member of a different potential provided with a ground shield surrounding said conductor intermediate its ends and a mass of insulating material surrounding said conductor from said metallic member to a point on said conductor remote from and at the same side of said metallic memher as said ground shield, of conducting ma- V terial electrically connected to said conductor materially and abruptly enlarging the diameter of said conductor adjacent said point thereon and at the face of said conducting material toward said metallic memher and terminating within said insulating mass, and other conducting material electrically connected to said conductor outside said insulating massand beyond said point on said conductor, said conducting material so directing electrostatic flux from said metallic member that a relatively small amount of said flux passes through the surface of said insulating mass.

15. In a device of the class described, the combination with conducting members adapted to be subjected to materially different electrical potentials, and an intervening mass of dielectric material whose dielectrio strength is greater than air arranged to insulate adjacent portions of said conducting members, of conducting means electrically connected to one of said conducting members; said means being provided with an electrostatic flux controlling edge in said mass adjacent an exterior surface thereof, disposed and arranged to secure substantially uniform distribution of the flux traversing said surface.

16. In a bushing device, the combination with a conductor and a surrounding member adapted to be subjected to materially diflerent electrical potentials, an insulating structure interposed between said conductor and member having a terminus on said conductor remote from said member and adapted to insulate adjacent portions of said conductor and member from each other, of conducting means electrically connected to said conductor adjacent the terminus of said insulating structure and provided with an electrostatic flux controlling edge within said insulating structure adjacent a surface thereof, said means being proportioned and arranged in said structure to secure substantially uniform distribution of the flux traversing the insulating surface.

In witness whereof, I have hereunto set my hand this 28th day of Dec., 1918.

FRANK w. PEEK, JR.

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