US2155846A - Insulator - Google Patents

Description

W. A. SMITH April 25, 1939.

'INSULATOR Filed Jan. 27, 1938 2 Sheets-Sheet l W. A. SMITH April 25, 1939.

INSULATOR Filed Jan. 2'7, 1938 2 Sheets-Sheet 2 FIG.7

Inventor Patented Apr. 25, 1939 UNITED STATES INSULATOR William A. Smith, Akron Ohio, assignor to The Ohio Brass Company, Mansfield, Ohio, a corporation of New Jersey Application January 27, 193a,v Serial No. 187,190

5 Claims.

This invention relates to electrical insulators, particularly of the bushing type, and has for one of its objects a more advantageous distribution of the insulating material.

A further object of the invention is to provide an insulator of relatively thin plates or sheets arranged face to face and of such form and size that they may be made of porcelain or other ceramic material.

A further object of the invention is to provide a bushing insulator having an insulating baille formed of thin concentric rings of ceramic material of a size and proportions that can be practically manufactured, the rings being disposed so as to give a maximum amount of insulation.

A further object is to provide a better voltage gradient in the dielectric material between the electrodes of a bushing insulator and to apportion the voltage stress among the various insulating media more nearly in proportion to the ability oi. the various media to withstand such stress.

A further object is to prevent overstress of the insulating medium next adjacent the internal conductor.

A further object is to allocate a greater portion of the electrostatic stress at the outer zones of the bushing and to provide improved means in these zones for withstanding this stress with out increasing the total diameter of the bushing.

A further object of the invention is to provide a bushing insulator which shall be of improved construction and operation.

Other objects and advantages will appear from the following description.

This application is a continuation in part of application Serial No. 59,710 filed January 18, 1936.

The invention is exemplified by the combination and arrangement of parts shown in the accompanying drawings and described in the following specification, and it is .more particularly pointed out in the appended claims.

In the drawings: v

Fig. 1 is an elevation of a bushing insulator with parts in section showing one embodiment of the present invention.

Fig. 2 is a fragmentary section of a portion of the bushing insulator shown in Fig. 1 but on a larger scale.

Fig. 3 is a fragmentary elevation of the abutting ends of a pair of tube sections of one of the bailies shown in Figs. 1 and 2.

Mg. 4 is a view similar to Fig. 1 showing a Iorm of the invention.

of the dielectric.

Fig. 5 is a fragmentary section of a portion of the insulator shown in Fig. 4 but on a larger.- scale.

Fig. 6 is a top plan view of one of the units forming the bame inFigs. 4 and 5.

Fig. 7 is an elevation partly in sectic unit shown in Fig. 6.

Fig. 8 is a fragmentary section showing a modified form of baflle.

Fig. 9 is a detail of one of the spacers in Fig. 8.

Fig. 10 is a half plan view of the central spacer shown in Fig. 8.

Fig. 11 is a view similar to Fig; 8 showing a diflerent form of central spacer.

Figs. 12 and 13 are edge and front elevations respectively of the center spacer shown in Fig. 11.

Fig. 14 is a fragmentary section showing another modification of the invention.

Fig. 15 is a view similar to Fig. 14 showing another modification.

In bushings for insulating a conductor which passes through an opening in a grounded mem her, there is normally a high voltage stress in the medium directly adjacent the conductor, due to the restricted path for the lines of force'in this area. Since the surface extent of the zones surrounding the conductor vary in proportion totheir distances from the axis of the bushing, it is apparent that the stress per unit area at any point outside the conductor, will be inversely proportional to the distance of that point from the axis of the conductor. provided other tics tors are equal. Another factor, however, that has an important bearing on the stress in an zone is the specific inductive capacity (SIC) e! the dielectric at that point. The stress for a given thickness of dielectric subject to a given voltage will be inversely proportional to the 810 Where porcelain insulation is used, it is not practical, under the present state of the art, to make the porcelain fit directly against the surface of the conductor so that heretofore in porcelain bushings there has gen: erally been a thin zone of some other dielectric! between the innermost porcelain barns and the inner conductor. If this zone is filled with oil which has a lower SIC than porcelain, there is danger that the zone will be overstressed. To overcome this danger; the present invention contemplates coating the inner surface of the inririnost porcelain baille with a conductor such as metal which may be applied by any one of several different methods now well known in the art. One method of coating the porcelain is disclosed in Austin Patent No. 1,536,749 dated May 5 noithe 5, 1925. Another suitable method is disclosed in Higgins Patent No. 2,119,989 dated June 7, 1938. There are also several other well known methods of metallizing the surface of porcelain that may be used and that will readily suggest themselves to those skilled in the art. This metallized surface is electrically bonded to the conductor, this shunting the thin oil zone next the conductor, and thus avoiding overstress in this zone. This will bring the conductor potential to the metal coating on the inner surface of the innermost baifle. will, however, be less than it would have been in the oil zone, both because of the increased area due to the greater diameter and also due to the higher SIC of the porcelain. Furthermore, the porcelain has a higher puncture resistance than oil. This greatly reduces the danger of breakdown at the inner zone, but of course, reduces the total insulation between the conductor and the bushing flange due to the elimination of the insulation of the oil zone. In order to compensate for the elimination of this inner insulation zone and to further improve the insulation of the bushing, advantage is taken of the well known fact that for a given thickness, greater dielectric strength is provided if the insulation is arranged in thin plates than if the same space is occupied by a solid block.

In the manufacture of high potential insulators, it is generally recognized that the most desirable insulating material at present known is porcelain, but heretofore it has been rather difficult to manufacture porcelain pieces of thin section and of a size and shape adapted for arrangement face to face in a bushing insulator. Long concentric tubes having thin walls would provide a desirable form of insulation, but at present it is not practical to manufacture long porcelain tubes with very thin walls, due to the difficulty in maintaining the shape of these tubes during drying and firing. This difficulty is overcome in the present invention, as shown in Fig. 1, by arranging thin walled porcelain tubular members, of a length that can be practically manufactured, in such a way as to secure practically the effect of long thin concentric tubes.

In Fig. 1 the numeral l0 designates the outer cone and Ii the outer dome of a conventional form of bushing insulator having a central conductor I2 surrounded by an inner porcelain baffle or tube I 3. The walls of the baffle l3 are thick enough to permit the manufacture of a tube of sufiicient length to extend substantially the full length of the bushing. To prevent overstress of the oil in the space between the conductor I0 and the tube l3 the inner surface of the tube is coated with a thin film i3 of copper or other conducting material and this coating is bonded to the conductor as indicated at l3". The bushing is supported on a flange M which supports a porcelain keg l5 provided on its outer surface with a metal coating terminating at its top and bottom with flux control members l6 as shown in the drawings. This form of fiux screen is more fully shown and described in Patent No. 1,972,590 granted September 4, 1934 to Ralph Higgins and assigned to The Ohio Brass Company, Mansfield, Ohio. The parts of the bushing are held together by proper terminal members and a spring I! oooperating with the terminal members and the central conductor [2. A supporting ring i8 is secured by cement [9 to the lower end of the inner tube l3 and provides a shoulder or shelf at the bottom of the space between the tube i3 and The stress in this baffle the keg l5. This space is occupied by an in sulating bafile, formed by a plurality of thin walled hollow cylinders, the cylinders, each comprising a plurality of tubular units or shells 20, arranged in registration end to end and separated by spacers 2|. The metal coating l3 will, of course, have the potential of the conductor l2 so that the space between the inner surface of the tube l3 and the metal coating on the outer surface of the keg l5 will have to withstand the total voltage impressed on the bushing conductor. Since this space is limited, and all the more so because of the shunting of the oil zone immediately surrounding the conductor :2, the special insulator construction provided by the unit 20 is employed in order to secure the greatest pos sible insulating strength in the space available. The arrangement is shown better in Figs. 2 and 3.

The units 20 will be made short enough so that they can be conveniently manufactured with walls of the desired thickness. A practical length, for instance, for most bushing insulators requiring a baille of this kind, will be 12 inches, with a wall thickness of inch. The spacers 2| may be of any suitable insulating material, such as fiber, rubber or phenolic condensation product. As shown, the spacers 2| are U-shaped and have their legs alternately reversed so that when several of the units are placed together, adjacent concentric cylinders will have their walls spaced apart and the registering units will be held in alignment by the engagement of the overlapping units with the legs of the U-shaped spacers. It will also be apparent that the spacers provide for free circulation of oil between the adjacent cylinders.

The joints of the several cylinders are staggered relative to one another, as shown in Figs. 1 and 2; the arrangement being such that the leakage or oil puncture resistance of the staggered path along the oil zones and through the joints from one side of the baffle wall to the other is substantially equal to or a little greater than the puncture resistance of the composite baffle wall. It is desirable, of course, that each joint shall be overlapped by more than a single thickness of insulation as otherwise the puncture strength of the baffle would be but little if any greater than that of a single layer of the dielectric. In order that each joint may be lapped by as many layers of dielectric as possible, the ends of adjacent concentric layers are offset by an amount equal only to a small fraction of its total length so that each layer overlaps several joints.

It will be noted that each of the joints between adjacent ends of baffle units are overlapped by N-l thicknesses of cylinder walls, where N is the total number of baffle clyinders; and the puncture resistance of N1 cylinder walls should therefore be approximately equal to or slightly less than the leakage or oil puncture resistance of the circuitous path from any point on one side of the composite baflle wall to the opposite side. This leakage path, as will be seen from the drawings, will extend through the joints in the concentric walls in succession and along the intervening oil zones from each joint to the joint in the next cylinder. The resistance to puncture of the composite bafile will be slightly less than it would be if the baffle were made of a plurality of continuous tubes of the same thickness as the tubular units but it will be very much greater than would be provided by full length tubes occupying the same space and of a thickness that is practical to nmmmeture or by" a; single tube occupying the space filled by thecomposlt'e'balile. It'is'thought that this'increase' in dielectric strength is probably dire to" the better voltage-gradient provided by the laminated dielectric strucmre.

Suitablespacing means 22 is provided at the base of the same to permit free access of oil'- to the various spaces between the concentric cylinders. Of course, the oil may circulate from one or these spaces to the other at" the various joints between theuni't's and may also-"pass freely in a rel-near direction in thespaces between the con-- centric cylinders.

In the form of the invention shown in Fig. 4, v

the space between theinner tube I3 and keg i5 is occupied by nested conical units or shells 23 which are so proportioned that the overlapping Wall's eithe shells at any point provide a punctare resistance substantially equal to or a little less than the leakage or oil puncture resistance about the ends of the shells. at that point. The conical shape of the baille units in this form of the invention facilitates the manufacture of the units, due to the fact that the taper permits ready formation by plunging and provides easy clearance for withdrawing the plunging tools and removing the formed pieces. The shape also adds stiffness to the formed pieces and permits advantageous nesting during curing and firing.

Various means may be employed for properly spacing the units of the baffle. As shown in Fig. 4,, a support 24 may be cemented to the lower end of the tube I 3 for supporting the lowermost unit. The edges of the units may be perforated, as shown clearly'in Figs. '6 and 7, and suitable cords may be laced through the perfora tiorrs and. about the edges of the units to bear against adjacent units and provide the desired spacing. Shoulders 28 are preferably provided on the innersurfaces of the units nearthei'r upper for resting on the tops of the nested units to provide suitable supports for the units upon one another and to provide vertical spacing.

Another form of spacer is shown in Figs. 8 and 10 which consists of a dielectric washer 21 having slots 28 separating the co-planar portions of the washer, the washer having an upstanding rim 29 which joins the sections of the washer separated by the slots 23. The washer sections are notched at to provide clearance at their inner edges for vertical circulation of oil. The rim 29 is provided with slots 34 staggered relative to the slots 28. It will be seen that these washers will space the conical members 23 vertically relative to one another and radially relative to the inner conductor l2 and provide for free circulation of oil. In this instance the inner tube I3 is omitted. The outer edges of the units 23 may be spaced from each other by a tapered ring 30 which fits about the outer surface of one conical member just below the lower edge of the next adjacent conical member. The ring 30 is provided with tongues 3i which extend upwardly a sufllcient distance to engage the lower surface of the next adjacent conical member and thus space the members apart; the space between the tongues providing for circulation of oil between the overlapping walls of the conical units.

In order to prevent overstress in the oil zone adjacent the conductor where the inner porcelain tube is omitted, and also to shield the joints at the ends of the dielectric members from overstress, flux control pockets 36 are formed in the upper portions of the members 23 adjacent the conductor l2 and these pockets are lined with metallic coatings which are electrically connected to the conductor l1 by bonds. These bonds may be in the form of spring contact members inserted in the pockets in position to bear on the conductor when the members 23' are slid into place. The pockets 36 preferably extend entirely around the inner surfaces of the members 23. It will be apparentthat electrostatic lines of force from the inner conductor will emanate from the metallic lining of the pockets 36 and pass directly into the porcelain rather than into the oil, thus reducing the liability of corona streamers and discharge across the oil zone around the conductor and through the spaces between the insulator elements 23.

In the form of the invention shown in Figs. 11, 12 and 13, the arrangement is similar to that shown in Figs. 8 and 9 except that the washer Z! is replaced by spaced strips 32 of insulating material having their ends 3-3 bent outwardly and extending between the bearing shoulders of adjacent dielectric members.

As shown in Fig. 14 the tube l3 may be metal lized on both its inner and outer surfaces, the metal coatings terminating a suflicient distance from the ends of the tube to prevent arcing over the ends of the tube. With this arrangement the baiiles 23 may be provided with flux control pockets 36 like those in Fig. 8, the inner conductor coatings of the pockets being electrically con nected to the outer conducting coating of the tube [3 by the spring jumpers 31.

In the modification shown in Fig. 15 porcelain rings 33 are distrflmted longitudinally of the conductor i2 and are spaced from one another and from theconductor by spacers 39 that may be circumferentiaily spaced from one another to permit circulation of oil. The rings 38'are tapered toward their edges to reduce the length of the oil path between adjacent edges. A second set of rings 40 alternate with the rings 38 and have their inner faces shaped to conform to the outer faces of the rings 38. Each ring 38 carries a rib 4| which is supported on the upper edge of the next lower ring 40 and in turn supports the lower edge of the next higher ring 40. Spacers 42 and 43 may be interposed between the ribs 4| and the adjacent rings 40. Each ring 40' carries a downwardly extending flange or petticoat 44, preferably of sufficient length that each joint between adjacent rings is overlapped by a plurality of thicknesses of porcelain having a puncture resistance approximately equal to or a little less than the oil puncture or leakage resistance from one side of the baille to the other through that joint.

I claim:

1. The combination with a conductor of an electrode surrounding said conductor and spaced therefrom, a dielectric bushing surrounding said conductor between said conductor and said electrode, said bushing comprising a plurality of nested conical shells having transverse joints between adjacent portions thereof, and having relatively thin walls overlapping said joints, the walls of some of said shells each overlapping a plurality of longitudinally spaced joints and each joint being overlapped by a plurality of said walls to provide puncture resistance opposite each joint equal to the puncture resistance of a plurality of shell walls but at most no greater 2. An insulator comprising a plurality of nested conical dielectric members, the wall of each member consisting of a single layer only of dielectric material the smaller end of each of said members being overlapped by a plurality of walls of like, cooperating members, the wall of each member overlapping a portion of the wall oi each of a plurality of like members nested therewith, the combined puncture resistance of said overlapping walls at any point being at most no greater than the resistance of the leakage path from the interior to the exterior of said insulator about the edges of said walls at the same point.

3. An insulating bafile for bushing insulators comprising a plurality of porcelain shells having openings therethrough, the walls of which shells are too thin to permit practical manufacture of a porcelain shell member of the full length of the baffle, the wall of each shell consisting of a single layer only, the shells being distributed longitudinally of a common axis and having registering portions forming joints, each joint being overlapped by a plurality of shell walls, the Walls of adjacent shells being spaced apart and the Walls of some of said shells, each overlapping a plurality of longitudinally spaced joints to provide a puncture resistance at the overlapped joint which is at least twice .as great as the puncture resistance of a Single shell wall but at most no greater than the resistance of the leakage path along the surfaces of the shells and through said joint from one surface to the other of the baiile, the space between said shells at said joints and between said shell walls being filled with dielectric material.

4. Electrical apparatus comprising a supporting ring, a conductor passing through said ring, a dielectric housing supported by said ring and surrounding said conductor and providing a container for insulating liquid about said conductor and a tubular baflle disposed within said container and surrounding said conductor, said baflle being formed of a plurality of porcelain shells, said shells being nested together with their walls overlapping, the walls of some of said shells each overlapping a plurality of longitudinally spaced joints between adjacent shells in said baffle and of sufiicient longitudinal extent to provide a plurality of layers of dielectric material registering with each joint between adjacent shells, said overlapping layers being spaced apart, the spaces between said layer being open at their ends to permit circulation of insulating liquid through said spaces in the direction of the axis of said tubular baflle.

5. Electrical apparatus comprising a supporting ring, a conductor passing through said ring, a dielectric housing supported by said ring and surrounding said conductor and providing a container for insulating liquid about said conductor, and supplemental insulating means arranged for controlling the voltage gradient between said conductor and ring, said supplemental means comprising a tubular bafile disposed within said container and surrounding said conductor, said baflle being formed of a plurality of conical porcelain shells, the wall of each shell consisting of a single layer only, said shells being nested together with their walls overlapping and of sumcient longitudinal extent to provide a plurality of layers of dielectric material registering with each joint between adjacent shells, each shell wall having a projection on its inner side adjacent the smaller end of the shell and forming a shoulder for engaging the end of the inner shell nested therewith, and a plurality of circumferentially separated spacers between each shoulder and the end of the shell next adjacent thereto to space said shell walls apart and provide for circulation of insulating liquid through the space between said shell walls and the joints between adjacent shells.

WILLIAM A. SMITH.

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