US1350925A - Insulation - Google Patents

Description

G. FACCIOLI.

INSULATION.

APPLICATION FILED MAR. 20,1917. RENEWED MAY12,I920- 1,350,925.

Patented Aug. 24, 1920.

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n: ..|H m --o i m mm m mu. m e k UNITED STATESMBATENT' OFFICE.

GIUSEPPE FACCIOLI, OF PITTSFIELD, MASSACHUSETTS, ASSIGNOR TO GENERAL ELECTRIC COMPANY. A CORPORATION OF NEW YORK.

INSULATION.

Patented Aug. 24, 1920.

Application filed March 20, 1917, Serial No. 156,220. Renewed May 12, 1920. Serial No. 380,886.

To all whom it may concern Be it known that l, GIUSEPPE FAocroLi, a citizen of the United States, residing at littsfield, in the county of Berkshire, State of Massachusetts, have invented certain new and useful Improvements in Insulations, of which the following is a specification.

My invention relates to insulators for electrical conductors or conducting bodies of both the bushing and other types; it relates particularly to insulation of the socalled bushing type, however.

It has heretofore been proposed to employ conducting material for redirecting electrostatic flIlX lines about such devices, particularly adjacent the end or ends thereof. One

Y of the objects of my invention is to improve the construction and disposition of such conducting material, to generally improve and simplify the construction of insulators, and particularly to relieve the electrostatic flux concentration, which commonly occurs beyond the ends of bushings.

My invention depends upon the fact that the insulating material" of bushings and insulators is often of a considerably greater specific inductive capacity than the surrounding medium, and my invention is applicable to such cases. Since my invention is particularly applicable to bushings in air, and in its broader aspect may be understood from a description of its application to such bushings, I shall for the most part confine the description of my invention to such embodiments for the sake of simplicity.

In carrying out myinvention, particularly as it is applied to bushings, I employ a conducting cylinder within the end (if desirable, each end) of the bushing, this cylinder being concentric with the conductor, preferably hollow, and preferably at least the end of the cylinder toward the middle of the bushing is embedded in the insulating material of the bushing. This cylinder is electrically connected to the conductor or otherwise given something like the potential of the conductor, and is arranged to receive, particularly on its edge toward the middle of the bushing, many of the electrostatic lines of force otherwise terminating on the conductor beyond the end of the bushing, both redirecting such lines and re lieving the concentration of electrostatic flux lines in the air (or other medium surrounding the bushing). /Vhile considerable concentration of the force lines may not be prevented in thus receiving these flux linesv on the cylinder, the major concentration may be made to occur within the insulating mass rather than within the air (or other surrounding medium), and hence in many cases with a reduced potential concentraillOIl (due to the difference between the specific capacities of the insulating material and the surrounding medium), and such potential concentration as occurs due to the force line concentration on the cylinder may be made subject to insulating material of a higher dielectric strength than that of the surrounding medium. The conducting cylinder is preferably made to perform its functions by locating its edgetoward the bushing center, nearer the middle of the bushing than any conducting device'exterior to the insulating material of the bushing; the degree to which it will redirect the electrostatic flux in the desired way may be varied by varying its extent into the end of the bushing, the distance of its edge from the bushing surface, and in other ways which will be understood by those skilled in this art.

Preferably the conducting cylinder is a part of a metallic cap on the end; of the bushing, the surface of the cap exposed to the surrounding medium being generally curved (to avoid sharp edges and points) to further relieve the concentration of electrostatic force lines in this medium by materially enlarging the diameter of the conductor adjacent the end of the bushing. Preferably also a ground shield is provided on the inclosing conducting member (from .which the conductor is insulated by the -outside the conductor away from the end of the bushing where they pass through the bushing surface.

In the accompanying drawing I J have mass.

illustrated, and in the following specification described in some detail, some preferred embodiments of my invention: Figure 1 is a sectional elevation of a bushing embodying my invention in its preferred form. Fig. 2 is a sectional elevation of another type of bushing embodying my invention in a somewhat modified form. Fig. 3 is a sectional elevation of an insulator embodying my invention.

The bushing of Fig. 1 comprises a mass 10 of insulating material of substantially circular cross-section. Passing through the center of the insulating mass 10 is a conductor 11; the conductor 11 may be itself the conductor carrying the current passing through the bushing, or it may be merelya metallic tube through which the power conductor is passed and to which such power conductor is usually electrically connected. The insulating mass 10 is, in the case illustrated, made up of a body of oil or other suitable insulating material of a greater specific inductive capacity than the surrounding medium, within a chamber, formed by the hollow conical porcelain member 12, the metallic or conducting member 13 and a second hollow conical porcelain member 14, the two ends of the chamber being closed by the caps 15 and 16. Any suitable material may be substituted for the porcelain in forming the conical members 12 and 14. The conical members 12 and 14 are shown rovided with corrugations or petticoats whic may be sup plied as desired or required. The whole.

structure forms a unit, and is designed to be attached to a wall, like the cover of a transformer tank, by means of the flange portion 18 of the conducting member 13. Ineffect the metallic conducting member 13 surrounds the bushing and the conductor 11 intermediate their ends and is the member ed to the conductor 11. This cap is provided with a conducting cylinder 19 projecting downward into the insulating mass of the bushing, the lower edge of the cylindrical portion 19 being embedded in the insulating The cylinder 19 or at least its lower end as shown in the drawing,-is preferably hollow so as to present a fairly narrow edge to the conductor member 13. The cylinder 19 extends farther along the conductor 11 and hence terminates nearer the conducting member 13 than any other conducting device exterior to the end of the bushing. The upper surface of the cap 15, that is the surface exposed to the air (or other surrounding medium), is generally curved as shown in the figure. Cooperating ,with the conducting cylinder 19 is a ground shield 20 attached to of the axis of the conductor 11.

from the drawing, the conducting cylinder 19 projecting into the insulating mass of the bushing so far that its edge toward the middle of the bushing is materially nearer the member 13 than any other conducting part near the same end of the bushing, receives a considerable part of the electrostatic flux which otherwise would terminate in the surrounding medium either onthe outer edge of the cap 15 or directly on the conductor 11. The concentration of the flux in the air (or other surrounding medium) has, therefore, been relieved through the flux redirection. Although the concentration of fiux has not been prevented, it now occurs within the mass of the insulating material where the concentration of potential, due primarily to the concentration of the flux is in most cases somewhat relieved by reason of the fact that the insulating material of the bushing is generally of a higher specific capacity than the surrounding medium, and such concentration of potential as occurs is subjet to insulation, presumably of a higher dielectric strength than that of the surrounding medium. As will be observed from the drawing, it is not to be expected that the conducting cylinder 19 will entirely relieve the conductor where exposed to the surrounding medium from electrostatic flux from the wall, which in the instance shown is represerrted by flange 18 for which function the bushing is provided, or from other surrounding conducting bodies of a potential different from that of the conductor. The metallic top 15 reduces such concentration in the air (surrounding medium) as may be possible in spite of the effect of the conducting cylinder 19, by materially enlarging the diameter of the conductor at the point, or points where this concentration may be expected to occur; generally enlarging the conductor adjacent the end of the bushing will be found s'uflicient. To avoid sharp points and edges on the surfaces of the cap 15, exposed to the air, this cap has been curved, as above noted particularly in planes Other conditions being equal, it is to be expected that a bushing provided with such a cap as I have illustratedand described above will stand a higher voltage difference between the conductor 11 and the conducting member 13 before breaking down or exhibiting signs of failure than a bushing without the metallic flux concentration.

In the bushing of Fig. 2 a considerable part of the concentration of stress produced at the edge of a single cylinder as illustrated in Fig. 1, is relieved by the provision of a plurality of concentric conducting cylinders 35, 36 and 37. These cylinders are of conducting material, are hollow, concentric with each other and with the conductor 40, and are carried by the bushing cap 41 which is likewise 'of conducting material. This 10 cap is somewhat differently shaped than that illustrated in the preceding figure, and comprises substantially in effect a fairly thick disk of metal with its edges gradually rounded. As before, the cyhnders 35, 36

and 37 are electrically connected to the cap 41, and the cap 41 is electrically connected to the conductor 40. The edge of the conducting cylinder 36 facing toward the middle of the bushing, is farther removed from the cap 41 (and the adjacent end of the bushing) than the corresponding edge of the adjacent exterior cylinder 35; likewise the conducting cylinder 37 extends farther into the end of the bushing than the cylinder 36. In effect, the position of these cylinder edges determines the location and curvature of the equipotential surfaces. The equipotential surfaces (at least those most nearly adjacent the cylinders) will somewhat cor- 'respond to the imaginary curved surface joining the edges of the cylinders. It is possible, therefore, as will be apparent, to redistribute the equipotential surfaces (at least those near the endof the bushing), forcing these surfaces as it were away from the end of the bushing and reforming the potential gradient along thebushing surface.

One conducting cylinder as illustrated in 40 Fig. 1 acts to relocate the equipotential surfaces as will be seen, but this result may be accomplished and equipotential surfaces bent as desired with less concentration at any one point or series of points, by employing a plurality of surfaces as shown in Fig. 2.

In Fig. 3 a type of line insulator fairly common except as it embodies my invention, is represented in vertical section. This insulator is-supported by the pin 46 (here presumed to be of metal) and carries the conductor 47. Below the conductor 47 and embedded within the material of the insulator 45, is'a conducting cylinder 48 electrically connected to the conductor 47 and substantially concentric with the axis of the pin 46 prolonged. In some cases such a construction will relieve the conductor and metallic parts of the insulator support from undue electrostatic flux concentration in the air, and hence allow the insulator to be used at higher. voltages before failure. It will of course be understood that the flux redirecting parts I have described may be employed for redirecting the flux for other specific purposes than those which alone I have, described.

While I have described the principle of my invention and the best mode I have contemplated for applying this principle, other v 'inder projecting into one end of said bushing and toward said conducting member, and concentric with, electrically connected to, and of a greater diameter than said con- 35 ductor, the edge of said cylinder facing toward said conducting :member, being nearer said conducting member than any conducting device exterior to said end of the bushing.

2. The combination with a conductor, a bushing surrounding the same, and a conducting member surrounding the bushing intermediate its ends, of means for materially reducing the number of electrostatic flux lines terminating on said conductor beyond one end of said bushing comprising a conducting cylinder projecting into one end of said bushing and toward said conducting member, and concentric with, electrically connected to, and of a greater diameter than said conductor, and terminating toward said conducting member.

3. The combination with a conductor, a bushing surrounding the same, and a conducting member surrounding the bushing intermediate its ends, of aplurality of concentric conducting cylinders within one end of said bushing, radially spaced apart, and concentric with and electrically connected to said conductor, the edge of each 0 linder facing towardsaid conducting mem er being farther removed from said end of said bushing than the corresponding edge of its adjacent exterior cylinder.

4. The combination with a conductor, a bushing surrounding the same, and a conducting member surrounding the bushing in termediate its ends, of a conducting cylinder within one end of said bushing and concentric with, electrically connected to, and of a greater diameter than said conductor, the end of said cylinder'toward said conducting member being hollow to present a fairly narrow edge thereto and being nearer said conducting member than any conduct- .ing device exterior to said end of bushing.

5. The combination with a conductor, a L

bushing surrounding the same, and a conducting member surrounding the bushing 130 intermediate its-ends, of a hollow conducting cylinder to materially reduce the number of electrostatic flux lines terminating on said conductor beyond one end of said bushing, said cylinder being concentric with, electrically connected to and of a greater diameter than said conductor and adjacent said end of said bushing, the end of said cylinder toward said conducting member being embedded in the-material of said bushmg.

6. The combination with a conductor, a bushing surrounding the same, and a conducting member surrounding the bushing intermediate its ends, of a hollow conducting cylinder to materially reduce the number of electrostatic flux lines terminating on said conductor beyond one end of said bushing, concentric with, electrically connected to and of a greater diameter than said conductor, and adjacent said end of said bushing, the end of said cylinder toward said conducting member being embedded in the material of said bushing, said conductor being provided with a conducting portion beyond said end of said bushing materially enlarging the diameter of said conductor adjacent that end of the bushing.

7. The combination with a conductor, a bushing surrounding the same, and a conducting member. surrounding the bushing intermediate its ends, of a conducting cap on one end of said bushing and electrically connected to said conductor, the surface of said cap outside said bushing being generally curved, and saidcap being provided with a cylindrical conducting portion spaced from and concentric with said conductor and extending into said bushing nearer'said conducting member than any conducting device exterior to saidend of the bushing.

8. The combination with a conductor, a bushing surrounding the same, and a conducting member surrounding the bushing intermediate its ends, of a conducting cap on one end of said bushing and electrically connected to said conductor, the surface of said cap outside said bushing being generally curved, and said cap being provided with a cylindrical portion spaced from and concentric with said conductor and extending into said bushing nearer said conducting member than any conducting device exterior to said end of said bushing, the edge of said cylindrical portion toward the conducting member being embedded in the material of the bushing.

9. The combination with a conductor, an adjacent conducting member and a mass of insulation between said conductor and conintermediate its ends, said conducting memher being provided with a ground shield, a terminal of which is embedded in said bushing, of a hollow conducting cylinder to materially redirect electrostatic flux between said conductor and said conducting member, said cylinder being concentric with, electrically connected to and of a greater diameter than said conductor, and adj acent the end of said bushing opposite said terminal of said ground shield, the end of said cylinder toward said conducting member being embedded in the material of said bushmg.

11. The combination with a conductor, a bushing surrounding the same, and a conducting member surrounding the bushing intermediate its ends and provided with a ground shield, of a conducting cylinder to cooperate with said'ground shield to materially redirect electrostatic flux between said conductor and said conducting member, said conducting cylinder being within the end of said bushing op osite said ground shield and concentric wit electrically connected to, and of a greater diameter than said conductor.

In witness whereof, I have hereunto set 'my hand this 12th day of February, 1917.

GIUSEPPE FACCIOLI.

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