US2806897A - Corona and grading shield - Google Patents

Description

J. M. SHEADEL ET AL CORONA ANDGRADING SHIELD Sept. 17,,1957

Filed March 16, 1954 Frq. 4

E m0 V H m8 M N w J BY ALPHA D.LANTZ.

Arron/vs)! finned States Patent CORONA AND GRADING SHIELD John M. Sheadel and Alpha D. Lantz, Barberton, Ohio, assignors to The Ohio Brass Company, Mansfield, Ohio, a corporation of New Jersey Application March 16, 1954, Serial No. 416,586

14 Claims. (Cl. 174-140) Our invention relates to high voltage transmission lines and has particular reference to corona and grading shields for controlling the electrostatic field at the lower end of a string of suspension insulator units by suppressing the corona discharge, improving the voltage distribution over the insulator units and providing arc-over protection for the insulators.

One object of our invention is to provide a shield which will prevent localized overstress and breakdown or ionization of the air adjacent the suspension clamp and associated insulators which is the direct cause of radio interference and visual corona associated with transmission line insulators and hardware.

In order to efiect this control it is necessary to surround the said offending members with an appropriately shaped shield and grading means of conducting material such as steel, aluminum, etc.

Another object of our invention is to provide a corona and grading shield of such formation as to alter the electrostatic field with a redistribution of the voltage along the insulator string.

Another object of our invention is to provide a unitary control means which is preferably formed from a single elongated metallic member of proper length and crosssection, or formed from two or more units and welded together into a unitary means continuous from end to end.

Another object is to provide a control member which is uniformly distributed and located on opposite sides and ends of the suspension clamp and supported by the clamp.

Another object is to provide a corona and grading shield which can be applied to and removed from the clamp without disturbing the already installed clamp and conductor.

Another object of our invention is to provide a control which is simple and easily constructed.

Another object is to provide a device which will not only meet the above requirements but will also draw any are or flash-over away from the insulator string.

Suspension insulators and clamps may be used in con nection with transmission lines operating at 250 kv. and over and to properly shield and grade such insulators and clamps the control means must practically surround the clamp and should extend enough above and away from the clamp and its metallic support to advantageously control the electrostatic field and voltage distribution along at least the lower portion of a string of suspension insulator units and keep any flash-over arc away from the string. The control means should extend below the clamp and the transmission line conductor at the clamp.

Applicants device has been designed with the various objects hereinabove recited, and other objects and advan tages will occur based on the specification and accom- In the embodyment shown in the conductor.

Fig. 2 is an end view of Fig. 1, less the conductor, in partial section on the line 2-2 of Fig. 1.

Fig. 3 is atop view of Figs. 1 and 2.

Fig. 4 is a top view in partial section of the corona and grading shield only.

Fig. 5 is an end view of Fig. 4.

Figs. 6 and 7 are two side views respectively of means for supporting the clamp from the lower insulator unit and is provided with means to receive and support the shield.

The combined corona and grading shield S herein disclosed is shown as combined with a suspension clamp C and the lower unit U of a string of insulator units. The clamp C is suspended from the insulator unit by a link L.

The insulator shown is of the conventional ball and socket type. The clamp is also a conventional design and consists of a saddle 1, a clamping members 2 and a pair of U bolts 3 which draw the clamping member 2 into engagement with the conductor 4.

The clamp is suspended from the link L which intercouples with insulator unit U and is shown secured to the clamp by the pin 5 whereby any movement of the shield will be independent of the clamp and insulator, but its ends may be attached to means on the lugs of the clamp if desired.

The corona and grading shield S is preferably continuous from end to end and may be formed from a single member of predetermined length or from several preformed units having their ends butt welded; if of two units the joint would come at the point X in Fig. 4.

The shield is made of metal preferably aluminum or steel tubing (Fig. 4) and having an outer surface free from points or sharp edges. In describing the shield it is considered as broken up into several portions each integrally united end to end to one or two adjacent portions.

The shield has a lower portion of predetermined length 10 which is the central portion and is positioned below the clamp and crosses diagonally from side to side with its center point at the vertical center line a-a of the clamp and insulator such that an equal length projects to each side from the longitudinal vertical central plane bb.

The portions of the member projecting from the ends of the central portion 19 are bent upwardly, laterally and longitudinally thereby forming the portions 11 and 12 connected by bights 13 and 1 respectively. The portions 1%), 11 and 12 constitute an inverted yoke, being so formed as to extend longitudinally an equal distance in both directions beyond the clamp C and insulator unit U in order to assure uniform control thereof.

The portions of the member of which the shield is constituted projecting from the ends of the predetermined length of the bent-up portions 11 and 12 are bent to form the parallel portions 15 and 16 connected by the bights 17 and 18 respectively.

The portions 15 and 16 are of the same predetermined length and equally spaced laterally from the insulator unit and clamp and extend equally in both directions longitudinally beyond the insulator unit and clamp to insure proper control thereof.

The common horizontal plane 0-6 of the portions 15 and 16 is shown as substantially common with the insulator unit U and at right angles to the vertical plane bb. The portions 10 to 16 may be so formed that their plane cc will be above or below the insulator U depending upon requirements and the portions 15 and 16 spaced laterally a greater or lesser amount from the vertical longitudinal plane b-JJ, as required.

The portions of the member forming the shield S and projecting from the ends of the predetermined length of the portions 15 and 16 are bent to form the loops or return bends 19 and 20 respectively; these portions extend obliquely downward and inward in equally spaced rela- Patented Sept. 17,

3 tion to the insulator unit U and the clamp C and are so bent as to form the short longitudinally aligned reflex portions 21 and 22 respectively.

The portions 21 and 22 are shown parallel to the portions 15 and 16 and in longitudinal alignment with the central vertical plane 12-12 and which includes the vertical central axis a-a.

The portions 21 and 22 terminate on opposite sides of the link L and their ends are connected to lugs 6 thereof or to the lugs 7 of the clamp.

The ends 23 and 24 of the portions 21 and 22 which are the ends of the member of which the corona and grading shield is formed are prepared for securing the shield in position by flattening each end in a vertical plane forming top and bottom flanges 25 between which the iugs 6 fit giving the shield a more secure hold on the ugs.

I The end portions 23 and 24 and the associated lugs 6 are formed with registering openings 26 to receive the securing means 27.

The above is a description of the specific construction of the shield shown in the drawing, but it will readily and clearly be understood that the same may be altered and still be within the scope of our invention, in order to meet varying conditions. For instance, the relative diameter of the insulator unit and length of the clamp may vary from that shown, requiring a change in the length of the portions ll, 15 and 16; the spacing between the insulator unit U and the clamp may vary, thus requiring a change in the lengths of the portions 11 and 12; also any change may require a change in the return bends 19 and 20, as, for instance, if the portions 19 and 20 (Fig. coincide with the plane cc, then the portions 21 and 22 would slope downward in place of being aligned as in Figs. 1 and 4; also the spacing between the portions and 16 may be varied.

The combination of the various portions comprising the shield and their relation is such that the shield is entirely symmetrical relative to the insulator units and the clamp and of the central vertical axis aa. T-he several like portions correspond in size and shape such that there results a balanced corona and grading shield which will uniformly control the electrostatic field surrounding the insulator units and the clamp.

The shield is so constructed that it may be installed after the conductor and clamp have been installed, and may be removed Without first disturbing the conductor.

Three of the portions are uniformly positioned on each side of the central vertical plane bb and one of the three portions projects equally on each side of the plane below the clamp; this clearly distributes the seven portions 10 to 22 inclusive symmetrically with respect to the insulators, clamp and conductor respectively, a condition very necessary in effecting proper and uniform control of the electrostatic field about the lower end assembly of an insulator string in order to depress corona and give uniform distribution of voltage over the insulator units of the string.

The clamp C and link L taken separately or integrally united constitute supporting means for the conductor and for the shield.

Merely as an example, in the several views of the invention disclosed in the drawing, the various portions are in quite accurate proportion for one embodiment of the shield with respect to an assembly with a 10 inch insulator unit and a 16 inch clamp and with a spacing of about 7 inches between the plane cc and the center of the conductor 4. As a further example the shield when formed from tubing of about 1.66 inch 0. D. has been found satisfactory for a transmission line carrying 345 kv. and for higher voltages the diameter would be increased. However the data given is merely indicative of a specific arrangement and other conditions may require material changes therefrom. We do not, therefore, wish to be held to these specific dimensions as a limitation to the scope of our invention, and intend such modifications as will be apparent to those familiar with the art, and which will fall within the scope and intent of our invention.

We claim:

1. In combination, an insulator forming one of a series of connected units, a transmission line conductor clamp, metallic means for suspending the clamp from and below the insulator, and a metallic corona and grading shield member to control the electrostatic field surrounding at least the lower insulator and the clamp and spaced from the insulator, the shield comprising a plurality of portions forming a unitary member, a pair of the said portions being elongated parallel and laterally positioned on opposite sides of the insulator and paralleling the vertical plane through the insulator and the clamp, a loop portion projecting from one end of each said elongated portion and having a short reflex portion spaced from and substantially paralleling the associated elongated portion and the portion of the conductor at the clamp with the free end of each reflex portion secured to the said metallic means on opposite longitudinal sides thereof, an inverted yoke formed of two spaced side portions and a connecting portion therebetween, the said side portions of the yoke extending upwardly and outwardly and connected to the other ends of the elongated portions thereby completing the shield member, and the connecting portion of the yoke passing diagonally from side to side of and below the clamp at its longitudinal center.

2. The combination with a high voltage line conductor clamp, means associated with the clamp to connect the clamp to a unit of a string of connected insulator units and suspend the clamp below the insulator unit, the center of the insulator unit and of the clamp having a common vertical central axis and a common vertical plane including the said axis and the longitudinal axis of the clamp and conductor, a corona and grading shield formed of a plurality of metallic portions forming a continuous member between free ends of the shield, the shield being uniformly disposed relative to the insulator unit and the clamp and the vertical axis and comprising, an inverted yoke formed of three portions namely two oppositely disposed upwardly extending portions positioned on opposite sides of said vertical plane adjacent opposite ends of the clamp and a connecting portion, the said upwardly extending portions being sloped upward and outward relative to the said vertical plane, the connecting portion of the yoke being equally positioned on opposite sides of the clamp and obliquely crossing the clamp from side to side below the clamp, elongated portions extending longitudinally from the upper end of each said upright extending portion in parallel and spaced relative to each other and positioned in a common plane at right angles to the said vertical axis, the said elongated portions being longer than the said connecting portion and extending longitudinally an equal amount in each direction beyond the insulator unit, a loop extending from the ends of the elongated portions opposite the upwardly extending portions and forming return bends with a short reflex portion, the reflex portions being secured to the clamp whereby the control shield is supported in uniform spaced relation to the insulator unit and the conductor.

3. The combination set forth in claim 2 characterized by the elements forming the loop at the ends of the elongated members being positioned in planes obliquely disposed to the said vertical plane.

4. A corona and grading shield comprising, a plurality of metallic portions of substantially uniform cross-section forming a continuous member from end to end of the shield, three of the portions forming the principal control member of the shield, two of the three portions consisting of parallel elongated members positioned in a common plane and in equally spaced relation on opposite sides of a central vertical axis to the said common plane,

the third portion consisting of an elongated member positioned in a plane spaced from and parallel to the said common plane, the said third portion diagonally disposed relative to the longitudinal axis of the said two elongated portions, and portions extending between one end of each of the two elongated members and the adjacent end of the diagonally disposed third portion, short longitudinally aligned portions parallel to the axis of the said two elongated members and equally spaced therefrom, the adjacent ends of the short portions spaced apart and spaced from the said central axis and the longitudinal axis of the short portions passing through the central axis, and portions extending between the other end of each of the said two elongated portions and the outer end of the adjacent short portion, the adjacent inner free end of each short portion provided with means to receive supporting means for the shield.

5. A corona and grading shield as described in claim 4 in which the diagonally disposed third portion is shorter than the said two parallel elongated portions.

6. A corona and grading shield as described in claim 4 in which the said short portions are located in a plane positioned between the common plane of the elongated members and the planes of the third portion.

7. A grading and corona shield formed of a plurality of portions forming a single continuous member from end to end and disposed about a central vertical axis, the portions being substantially of uniform cross-section with a smooth, even exterior surface, the shield comprising an inverted yoke of three portions namely two oppositely disposed upwardly extending portions positioned on opposite sides of a central vertical plane passing through the central vertical axis, the said two portions being longitudinally and laterally spaced relative to the said axis while the connecting portion of the yoke crosses said plane at the central vertical axis, elongated portions extending from the upper end of each upright extending portion in parallel and spaced relative to each other and positioned in a common plane at right angles to said central vertical axis and parallel to the said vertical plane, a portion extending from the end of each elongated portion distant from the upper end of the said upwardly extending portions and forming a downwardly and an inwardly extending return bend with a short reflex portion spaced from the associated elongated portion, the free ends of the said short reflex portions spaced apart. and positioned in a substantially common longitudinal axis and provided with means whereby the ends may be secured to a support member whereby the shield will be supported in a uniformly distributed relation to the central vertical axis.

8. A corona and grading shield formed of a plurality of portions constituting a metallic member extending continuously from one end to the remaining end thereof, one portion being substantially straight and positioned on opposite sides of a longitudinal vertical plane through the vertical axis and the said portion extending in an oblique direction relative to the said vertical plane and passing through the said vertical axis, a pair of parallel elongated portions positioned in a common plane at right angles to the vertical axis and spaced vertically above the said one portion, and two portions each extending from one end of each elongated portion to the adjacent end of the said one portion, and an end portion of the member extending from the other end of each elongated portion and forming a reverse bend, the return portion of the bends being short and in substantial axial alignment and disposed in spaced and parallel relation to their associated elongated portion, and means at the free ends of the end portions of the member whereby the shield may be secured to a support.

9. A corona and grading shield as set forth in claim 8 in which the said one portion is shorter than the said elongated portions and is uniformly positioned relative to the elongated portions, and the said two portions are angularly disposed to each other and to the longitudinal vertical plane.

10. A corona and grading shield as set forth in claim 8 characterized by the connecting portions of the bends extending downward and inward relative to the said vertical plane whereby the said short reflex portions are positioned in said vertical plane and in a plane below the said common plane of the elongated portions.

11. A corona and grading shield according to claim 4 having in combination therewith a conductor clamp whose longitudinal vertical central plane is parallel to the axis of the said two elongated portions, the elongated portions and the said third portion are longer than the clamp, and means associated with the clamp which cooperate with the ends of the short portions to support the shield relative to the clamp.

12. A combined grading and corona shield adapted to be utilized with a conductor cable and an insulator, and a conductive suspension member supporting the cable from the insulator, comprising a continuous loop member connected at the ends thereof to the suspension member for the conductor cable and extending from each end thereof away from the suspension member in the direction of the cable, along a reverse bend back parallel to the cable and past the insulator in a plane perpendicular to the axis of the insulator, along a second reverse bend diagonally downward below the cable, and back to cross under the cable below the insulator to continue with the portion of the loop member extending from the remaining end thereof.

13. A combined grading and corona shield adapted to be utilized with a conductor cable and an insulator, and a conductive suspension member supporting the cable from the insulator, comprising a continuous loop member of metallic tubing connected at the ends thereof to the suspension member for the conductor cable and extending from each end thereof away from the suspension member in the direction of the cable and upwardly and away from the cable, along a reverse bend back parallel to and above the cable and past the insulator in a plane perpendicular to the axis of the insulator, along a second reverse bend diagonally downward below the cable, and back to cross under the cable below the insulator to continue with the portion of the loop member extending from the remaining end thereof.

14. A combined grading and corona shield adapted to be utilized with a conductor cable, a series of insulators, and conductive suspension means supporting the cable from the insulator, comprising a continuous loop conductor attached at the ends thereof to the suspension means and having two extending portions along and above the cable, one disposed on one side and the other disposed on the other side of the cable, and the two portions being disposed generally in a plane perpendicular to the axis of the insulators for distributing stresses uniformly between the insulators, and a portion connecting the said two portions and extending below and generally along the cable for preventing stress concentration at the suspension means.

References Cited in the file of this patent UNITED STATES PATENTS 2,597,590 McCoy May 20, 1952

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