US 3296366 A
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Jan. 3, 1967 R. J. BRONIKOWSKI 3,296,366
OUTDOOR HIGH TENSION INSULATOR HAVING LONG CREEPAGE PATH Filed Dec. 25, 1965 F/G 2A E76 25 w F/G. 2c
' m/viuroe RA YMOA/D u. emu/nous United States Patent C "ice 3,296,366 OUTDOOR HIGH TENSION INSULATOR HAVING LONG CREEPAGE PATH Raymond J. Bronikowski, South Milwaukee, Wis., assignor to McGraw-Edison Company, Milwaukee, Wis., a corporation of Delaware Filed Dec. 23, 1965. Ser. No. 515,916 3 Claims. (Cl. 174-209) This invention relates to outdoor high tension insulators for electrical apparatus used on high voltage distribution and transmission systems.
High tension insulators are conventionally constructed of porcelain and are designed to withstand predetermined magnitude of power frequency and impulse voltage. When subjected to excessive voltage, the insulator should fiashover, not puncture, and without the formation of a conducting surface path on the insulator. The requirement must be met against any form of lightning voltage wave, surge frequency, or climatic condition.
For service in contaminatingatmospheres, it is necessary to provide an over-surface path on the insulator of a length several times the withstand distance in air. This is frequently accomplished by increasing the diameter of the petticoats on the insulator. If a flashover should occur in service, the resultant power are may chip off several pettic-oats and scorch the insulator surface. Further, porcelain members are not light in weight; are diflicult to fabricate to close tolerances; and upon high impact are apt to fracture into many small flying pieces. High tension insulators of organic resin material for use indoors or within enclosures are known, but they are of such construction that it is diflicult to obtain sufficient length of creepage path for a given air strike distance, and the possibility of voids occurring during the molding of the resin material introduces the danger of failure of the insulators by puncture under high voltage stress. In outdoor installations where dust, contaminants or rain may accumulate, random surface discharges or arcing, known as over-surface scintillation, are promoted and form carbonaceous deposits in the insulation which ultimately yield low resistance paths, or tracks, that destroy the utility of the insulator. Further, differential weather effects on the exposed and protected portions of the same resin insulator may unbalance the surface gradient under moist and contaminated conditions, and the resultant unbalanced voltage distribution may cause flashover of the insulator below normal withstand levels.
It is an object of the invention to provide an improved insulator having an exceptionally long creepage path per unit volume. It is a further object to provide an improved insulator having high resistance to arc tracking and surface creepage and which may be constructed of a material having relatively low puncture strength without danger of fiashover of the insulator. It is a further object of the invention to provide such an improved insulator which is capable of absorbing high impact forces, such as recoil forces generated upon operation of an expulsion fuse, without rupture and without transmitting the force to the mounting.
These and other objects and advantages of the invention will be more readily apparent from the following detailed description when considered in conjunction with the accompanying drawing wherein:
FIG. 1 is an elevation view of an open type fuse cutout embodying the invention, the fuseholder being shown in dotted lines;
FIGS. 2A-2D are views taken on lines 2-2 of FIG. 1 through alternative embodiments of the invention; and
FIG. 3 is an elevation view of a post type insulator in accordance with the invention.
3,2963% Patented Jan. 3, 1967 Referring to FIG. 1 of the drawing, a fuse cutout of the open type comprises an elongated insulator 10 in accordance with the invention secured between its ends to mounting bracket 11 and at its upper and lower ends to an upper terminal assembly 14 and a lower fuseholder supporting means 15 respectively. A fuseholder 16 shown in dotted lines is pivotally mounted at its lower end on fuseholder supporting means 15 and is normally latched at its upper end to upper terminal assembly 14. Upper terminal assembly 14 may include an upper terminal portion 17 of a backing member 18 supporting resilient conductive members 19 which carry upper contact members 20 normally bearing against the laterally extending arm 22 of an upper contact 23 atfixed to the upper end of fuseholder 16. Fuseholder 16 comprises an expulsion fuse tube surrounding a rupturable fuse link 24 and closed at its upper end by a metallic cap 25 which is electrically connected tothe upper end of fuse link 24 and to the upper contact 23. A rotatably mounted latch member 26 normally engages laterally extending arm 22 on upper contact 23, and a pull ring and latch release member 27 pivotally mounted on a pin 28 is adapted when operated by a hookstick to impart an upward force on latch 26, thereby releasing laterally extending arm 22 and permitting fuseholder 16 to pivot clockwise to open position about trunni-ons 28 engaged within C-shaped bearing portions 29 of the fuseholder supporting means 15. A protector hood 30, which may be of fiber glass reinforced resin, may be afiixed to backing member 18 by suitable fastening means. The lower end of fuse link 24 may be affixed by means of a thumb screw 33 to a hinge contact member 34 which is pivotally connected by a pin 35 to a metallic collar member 36 secured to the lower end of the fuse tube.
The components of the fuse cutout do not constitute part of the invention and are described only by way of example and may be similar to the elements of the fuse cutout disclosed in US. Patent 3,002,070to Raymond J. Bronikowski et al. which has the same assignee as the subject invention.
Insulator 10 comprises an elongated member in the configuration of a helix having a plurality of convolutions which advance parallel to the axis of the helix so that each convolution is spaced from both adjacent convolutions in a direction parallel to said axis. The word helix is used in the detailed description and in the appended claims to connote a curve formed on any cylinder, not necessarily a right circular cylinder, by a straight line in a plane that is wrapped around the cylinder and is intended to cover such configuration as spindle-shape, conical volute shape, and double volute shape, i.e., a hyperboloid which is more familiar as the shape of a chair spring. Insulator 10 may be of an organic resin insulating material such as epoxy resin or polyester resin reinforced with a suitable filler such as glass fiber to increase mechanical strength. Insulator 10 may be of any desired cross section such as circular, cruciform, halfmoon, Y-shape or U-shape as illustrated in FIGS. 2A 2D, and certain of the indented cross sections, such as a Y-shape cross section, form a path for rain or water to flow readily and rapidly off the insulator without leaving an accumulation of dirt or other foreign matter in its wake and providing uniform voltage grading under conditions of rainfall. Suitable materials such as hydrated alumina for preventing formation of carbonaceous deposits due to creepage may be interspersed in the resin material or coated on the surface of the insulator 10. In certain embodiments the insulat r 10 is of a material having a high resistance to are tracking and surface creepage such as acetyl resin with a suitable filler such as filament wound glass fiber to increase mechanical strength.
The upper end of insulator may be disposed generally parallel to the axis of the helix and formed into a loop 40 which receives a bolt 41 for clamping backing member 18 to the insulator 10, similarly the lower end of insulator 10 may be generally parallel to the axis of the helix and for-med into a loop 43 which receives a bolt 44 for clamping insulator 10 to the cross-piece of a U-shaped lower support member 46 which is integral with the C-shaped bearings 29 of the fuseholder supporting means 15. Mounting bracket 11 may comprise an elongated metallic member bent back upon itself in surrounding relation to a convolution of insulator 10 between the insulator ends and clamped against insulator 10.
The convolutions of helical insulator 10 are spaced in a direction parallel to the axis of the helix and do not touch, thereby providing an extremely long helical creepage path along all the convolutions of insulator 10 in comparison to conventional insulators wherein the creepage path is approximately in an axial direction. Further, it will be apparent that the length of the helical creepage path may readily be changed by varying the helix angle. Puncture of the insulating material of insulator 10 is eliminated because the portions of convenhaving a relatively high modulus of elasticity in shear, for
example, nylon or polyacrylic resin, in order to minimize deflection.
In an alternative embodiment, the insulator 10 is of double torsion spring configuration wherein the convolutions above and below the mounting bracket 11 are oppositely wound, for example, the convolutions above bracket 11 may be wound clockwise and those below bracket 11 wound counterclockwise. This construction compensates for any shrinkage of the organic resin material which might be caused by further curing of the resin due to outdoor exposure since the deflection of the upper and lower ends of the insulator will be in opposite directions and thus prevent misalignment of the upper and lower contact assemblies.
FIG. 3 illustrates a post type conductor support in-.
sulator 50 embodying the invention and supported on the cross arm 51 of a power pole. Insulator 50 is helical in configuration and of spindle shape and comprises a plurality of convolutions which advance parallel to the axis of the helix and do not touch. The convolution 53 at the lower end of helical insulator 50 may be in a plane perpendicular to the axis of the helix and embraces a thread-shaped portion 54 of a lower support member 55 resting on cross arm 51. The head of a bolt 56 may be secured by suitable means such as cement 57 within an aperture 58 in the bottom surface of lower support member 55, and bolt 56 may extend through crossarm 51 and be secured thereto by a nut 59. The convolution 60 at the upper end of insulator 50 may also be in a plane perpendicular to the axis of the helix, and convolution 60 may embrace the thread-shaped portion 61 of an upper support member 63 of suitable insulating material and having a diametrically extending groove 64 therein for receiving a power line conductor 65. Conductor 65 may be secured to upper support member 63 by a thin wire 66 wrapped around power line conductor 65 and the circumferential flange on upper support member 63.
While only a few embodiments of the invention have been illustrated and described, many modifications and variations thereof will be readily apparent to those skilled in the art, and consequently it is intended in the appended claims to cover all such modifications and variations which are within the true spirit and intent of the invention.
1. An electrical insulator having an exceptionally long vcreepage path per unit volume and being capable of absorbing mechanical forces comprising an elongated member of insulating material in the configuration of a helix having a plurality of convolutions which advance parallel to the axis of the helix and each of which is spaced from adjacent convolutions in a direction parallel to said axis, said material having a high modulus of elasticity in shear, said elongated member having at least one upwardly facing groove formed therein and extending along the length thereof.
2. An electrical insulator in accordance with claim 1 wherein one portion of said convolutions advance in one direction and the remainder thereof advance in an opposite direction.
3. An electrical insulator in accordance with claim 2 wherein at least the surface of said insulator is covered with a material having high resistance to are tracking and surface crcepage.
References Cited by the Examiner UNITED STATES PATENTS 345,767 7/1886 Buckley 267--1 1,247,500 11/1917 Bulmer 267-1 2,852,092 9/1958 Fruth et al.
FOREIGN PATENTS 1,085,331 7/1954 France.
915,052 1/ 1963 Great Britain.
LARAMIE E. ASKIN, Primary Examiner.
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