US2790842A - Insulator for high voltage cable terminator or bushing - Google Patents

Description

April 30, 1957 J. H. NICHOLAS,

INSULATOR FOR HIGH VOLTAGE CABLE TERMINATORv OR BUSHING Filed Oct. 3, 1955 IOO 27 3774 |0| F I G. 2

FIG.

' INVENTOR. JAMES H. NICHOLAS BY f United States Patent a INSULATOR FOR HIGH VOLTAGE CABLE TERMINATUR 0R BUSHNG James H. Nicholas, Chicago, Ill., assigner to G & W

Electric Specialty Company, Chicago, lit., a corporation of Illinois Application October 3, 1955, Serial No. 533,173

4 Claims. (Cl. 174-20) This invention relates to stop joints for interconnecting an insulating-iluid-lled high voltage cable with a terminator, switch, transformer or the like.

ln high voltage cable joints, it is often desirable to utilize a porcelain insulator as part of the joint insulation. In such case, a metal connector usually extends through the insulator.

The radial wall thickness of the porcelain insulator is determined by the operating voltage involved. At very high voltages the thickness requirements of the insulator make it desirable to fabricate the insulator in sections, one telescoping within the other. Where the composite insulator is utilized in a stop joint, the problem of providing a reliable long lasting, fluid-tight joint between the separate parts of the insulator arises as does the additional problem of preventing voltage breakdown in the gaps or spaces between the parts thereof.

This invention relates to a stop joint including a composite insulator which is constructed and arranged to provide an effective and long lasting fluid-tight joint between the insulator parts and also to prevent voltage breakdown in the spaces between the parts of the insulator.

It is a still further object of the invention to provide a stop joint as above described wherein the fluid tightness etween the parts of the composite insulator are maintained by a gasketing means compressed between a shoulder on one of the parts of the insulator and another part thereof. It is a still further object of this invention to provide means for maintaining said gasketing means under compression through the use of a nut threaded around the connector which passes through the insulator.

lt is a still further object of this invention to provide a stop joint as above described wherein the insulator, the connector and the cable end are suitably wrapped with insulation taping and are shielded and confined within a fluid-tight casing.

These and other objects, advantages and features of the invention will become apparent upon making reference to the specification to follow, taken in conjunction with the drawings showing an exemplary embodiment of the invention.

In the drawings:

Fig. l is a longitudinal section through a stop joint constructed in accordance with the invention;

lFig. 2 is a fragmentary enlarged sectional view through a part of the stop joint of Fig. l; and

Fig. 3 is an enlarged fragmentary View of still another portion of 4the stop joint of Fig. l.

Reference should now be made to the drawings where like reference characters indicate like parts throughout.

The stop joint structure of the invention illustrated in the drawings is generally indicated by the reference numeral 1, and it electrically and mechanically interconnects a gas or oil-filled cable 2 and a terminator or pothead insulator structure 4. The stop joint of the invention, however, is useful in other high voltage connections, as between a cable and transformer, switch, and the like. The terminator structure has an oil filled com- Patented Apr. 3o, 1957 fice 2 partment 5 and the stop joint isolates the fluid therein from the insulating fluid in the cable 2.

In preparing the cable 2 for jointing, the outer sheathing 8 and the shielding braid 9 of the cable 2 are removed from the cable end exposing the machine-applied insulation 1l of the cable, as is the usual practice in forming high voltage cable joints. The bared end of the cable conductor 14 is connected with a metal connector ferrule l5 having a semi-cylindrical portion i6 which interfits with a like semi-cylindrical portion 17 of a connector rod 20. The connector rod 2t) extends axially through an oversized axial through-bore 21 formed in the innermost of a pair of telescoping porcelain insulator parts 23 and 24.

The inner insulator part 24 has a tapered bottom end 25 and a reduced cylindrical upper portion 26 which telescopes within the somewhat larger cylindrical bore 27 of the outer insulator part 23. At the junction between the cylindrical upper portion 26 and the tapered lower end 25 of the inner insulator part is formed an annular shoulder 31. Resting on the shoulder 31 is a gasket assembly 29 comprising an annular ring 28 having grooves in the opposite axial faces thereof which grooves receive, respectively, resilient ring gaskets 32 and 34. The bottom of the outer insulator part bears against the top of the gasket assembly to compress the gaskets against the shoulder 31 of the inner insulator part 24.

Proceeding upward from the bottom of the outer insulator part 23, the outer surface thereof is tapered to form a continuation of the tapered end 25 of the other insulator part Z4 and this tapered portion merges with a cylindrical neck portion 37. At the top of the neck portion, the outer surface of the insulator part suddenly increases in diameter at an axially facing annular shoulder 39 to provide a narrow collar or flanged portion 4t). Above the ilanged portion 46 is a reduced cylindrical portion 4l which terminates in an annular recess '42 within the insulator part. rlhe recess is formed by a downwardly inclined annular skirt 43. A conductive glaze is applied around the outer insulator part from the extremities of the annular recess 42 thereof down to a point a small distance below the insulator neck portion 37. The insulator part above the skirt has a number of peripheral insulating skirts 44, and this portion of the insulator generally tapers to a cylindrical neck 44 at the top of the insulator part.

T he connector rod 20 together with the inner and outer insulator parts form an integral fluid-tight assembly. To this end, the connector rod 20 is provided with a metal cap i6 which fits over a reduced neck at the upper end of the inner insulator part. The cap compresses a basket 47 against the upper part thereof to provide a fluid-tight seal between the connector rod and the inner insulator part.- The compression of the gasket 47 is maintained by securing the connector rod to the inner insulator part under tension by a cementitious bond Si). The cementitious bond 50 extends between a knurled portion 51 spaced from the upper end of the inner insulator part and the defining walls of the bore 21 thereof. The cementitious bond includes a coating of a resilient compressible material, such as Glyptol, applied to the knurling 5l, and a relatively rigid adhesive material, such as poreclain or lumnite cement which fills the rest of the space between the connector knurling and the inner insulator part. The cement bond is, of course, applied while the connector rod is held under tension with the connector cap 46 bearing against the gasket 47 to place it under sufficient compression that a seal will be maintained under the limits of expected relative thermal expansion and contraction of the connector rod and inner insulator part.

To prevent insulation breakdown in the region between :Moussa the connector rod and the inner insulator part, the delining walls of the bore 21 are initially coated with a conductive glaze 57 which maintains the walls ol this bore at the same potential as the connector rod 20.

Below the knurling 51, the space between the connector rod and inner insulator part is packed with lead wool 59 down to the bottom of the inner insulator part.

The gap between the ferrule and the bottom end of the connector rod is filled with lead wool packing 553. Also, lead foil is applied to the sharp corners bete' the bottom of the inner' insulator part 24 and the t ing portion of the connector rod 20, and at 61 between the ferrule 15 and the cable conductor 14, to form tapered fairings at these locations to insure a gradually sloping contour along the conducting surfaces of the stop ,it t.

The outer insulator part 23 is held securely arf i i Y reduced upper portion 26 of the inner insulator part by an assembly of a metal cap 60 fitting over the cylindrical upper neck 44 of the outer insulator part and a nut G2 threaded around the connector rod 20 and bearing downward upon the top of the cap 60. A cushioning ring 63 is interposed between the cap 60 and the top of the porcelain insulator part 23 to prevent damage to the latter by the pressure of the cap thereagainst. Also, a lock washer 64 ,is interposed between the nut 62 and the top of the cap 60 to eliminate play between the nut 62 and the connector threading.

It should be appreciated that threading of the nut 62 upon the connector rod draws the inner insulator part 2.4 connected thereto upward while pushing the outer insulator part downward to thereby compress the gasket rings 32 and 34 between the bottom of the outer insulator part and the shoulder 31 of the inner insulator part.

The cap 60 is provided with holes 66 permitting passage of the `insulating fluid, usually oil, from inside the terminator insulator 6 into the space between the inner and outer insulator parts to prevent insulation breakdown therein.

The insulator bushing assembly just described is mounted within an opening 68 formed in a grounded mounting plate 70. The outer insulator part 2.3 below the anged portion thereof is sized to fit through the opening 68.

To insure grounding of the glazing around the outer surface of the outer insulator part 23, lead wool 73 is packed in the space between the insulator neck 37 and the mounting plate. A uid-tight seal is provided between the insulator bushing and the defining walls of the hole 68 by a gasket 72 located within a groove formed in the upper surface of the mounting plate 7i! and compressed between the shoulder 39 of thc outer insulator part and the bottom of the aforementioned groove. Compression is maintained by a stainless steel ring 74 cemented to the neck 37 of the outer insulator part immediately below the mounting plate while the outer insulator part is held against the gasket 72.

Due to the fact that it is often necessary to grind llat the shoulder 39 on the outer insulator part after the outer surface thereof is glazed, removal of the glazing at the shoulder 39 during the grinding operation requires the provision ol' some means to insure the grounding of the glazing 45 above the shoulder 39. This means preferably includes a conductive wire 75 wound about the glazing :aurount'ling the langed portion 40 of the outer insult r part. The wire 75 is connected to the mounting plat.: t) by s lug 77 threading thereinto.

The terminator' insulator 6 surrounds the upper portion of the composite insulatorbushing assembly and is so cured to the mounting plate 70 by means including a metal collar 79 cemented to the bottom of the tern .f l tor insulator 6, threaded studs 80 which are anch red to the mounting plate 70 and extend upward through he :s in the collar 79, and nuts 82 threaded around the top ot the mounting plate studs 80.

After the insulator bushing assembly has been secured to the mounting plate 7l), hand wrapped insulation 85 is applied around the cable covering insulation from a point immediately above the shielding braid 9 thereof, and around the ferrule 15, the projecting bottom end of the connector rod 20, the tapered bottom portion 25 of the inner insulator part, and. the tapered bottom portion ot the outer insulator part up to a point immediately below the bottom of the stainless steel ring 74. The tapfig is prefer' bly an oil-packed crepe paper material. The contour of the taping is generally conical and, proceeding upward from the end of the cable shielding braid 9, initially tapers outward a small amount reaching a cylindrical contour at 37 around the tapered portion of the covering insulation and the bottom portion of the ferrule 15. Then the taping gradually flares outward to follow the general contour of the bottom end 25 of the inner insulator part 24 which the latter portion surrounds. At approximately the junction between the inner and outer insulator parts, the taper orn the taping reverses and merges with the tapered bottom end 36 of the outer insulator part 23.

Metal tinsel braid is then applied over the wrapped insulation 85 along its entire length. The bottom end of the tinsel braiding overlaps the grounded shielding braid 9 of the cable 2 and at the other end overlaps the glazing 45 of the outer insulator bushing to ground the latter.

The stop joint between the cable 2 and the bottom of the mounting plate 70 is surrounded by a casing assembly 92. The casing assembly comprises a bottom cylindrical casing part 93 and an upper cylindrical casing part 94. The bottom casing part 93 has an inturned bottom end 96 which is sealed around the cable sheathing 8 in any suitable manner. The upper end of the sleeve part 93 is slightly enlarged at 98 and the enlarged upper end thereof receives the bottom of the upper casing part 94. The two casing parts 93 and 94 are secured together by a wiped solder joint 99.

Secured to the upper end of the upper casing part 94 is a mounting flange 100 which is sealed to the bottom of the mounting plate 70 by a gasket 101 maintained under compression by screws 102 passing through the mounting llange and threading into the mounting plate 70.

It should be understood that numerous modifications may be made of the preferred embodiment of the invention above described without deviating from the broader aspects of the invention.

I claim:

1. A high voltage cable joint interconnecting an insulatingluid-containing high voltage cable with an insulating-liuidlled high voltage apparatus, comprising an insulator formed of at least two separate insulator parts, one telescoped within the other, a connector extending through the inner of said insulator parts, a shoulder formed on one of said insulator parts, gasket means compressed between said shoulder and the other insulator part and providing a fluid-tight seal extending completely around the innermost of said insulator parts, the space between said insulator parts on one side of said gasket means communicating with the insulating uid of one of said apparatus and cable and the other side of said gasket means communicating with the insulating fluid of the other of same, means xedly securing said connector to the shouldered one of said insulator parts, means carried by said connector bearing against the other insulator part to force the same toward said shoulder to compress said gasket means, and means forming a uidtight seal between said connector and the innermost of said insulator parts.

2. A ihigh voltage cable joint comprising an insulator formed of at least two separate insulator parts, one telescoped within the other7 a connector extending through the inner of said insulator parts, a shoulder formed on one of said insulator' parts, gasket means compressed between said shoulder and the other insulator part and providing a fluid-tight seal extending completely around the innermost of said insulator parts, means tixedly securing said connector to the shouldered one of said insulator parts, means carried by said connector bearing against the other insulator part to force the same toward said shoulder to compress said gasket means, and means forming `a fluid-tight seal between said connector and the innermost of said insulator parts.

3. A high voltage cable joint comprising an insulator formed of at least two separate insulator parts, one telescoped within the other, a connector extending through the inner of said insulator parts, a shoulder' formed on the innermost of said insulator parts, gasketing means compressed between said shoulder and the outer insulator part to provide a fluid-tight seal extending completely around the innermost of said insulator parts, means xedly securing said connector to the inner of said in sulator parts, and means carried by said connector bear ing against the outer insulator part to force the same toward said shoulder, and means forming a huid-tight seal between said connector tand the inner insulator parts.

4. A high voltage cable joint comprising an insulator assembly formed of at least two separate insulator parts, one part having a reduced end portion telescoping within the other part and also having a portion located outside of said other part which portion tapers from the end of said other part to a minimum thickness at the end of said one part, gasket means compressed between said parts to provide a fluid-tight seal therebetween, a connector extending through said one insulator part, a cap xedly secured to said connector, gasket means held under compression between said cap and an end of said one insulator part to provide a fluid-tight seal between the connector and the latter insulator part, said latter gasket means being held under compression by a cementitious bond between the connector and said one insulator part which bond holds the connector under tension7 and a nut threaded about saird connector and forcing said .other insulator part toward said one insulator part to compress said former gasket means therebetween.

Engster May 7, 1935 Brandt May 17, 1938

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