US3141061A - High voltage cable terminal - Google Patents

Description

y 14, 1964 E. w. BIANCO ETAL HIGH VOLTAGE CABLE TERMINAL Filed March 25, 1959 "kc '(llllld UVVE/VTORS ERNEST W B/A/VCO LeROY H. FRANKLIN PATENT AGENT United States Patent 3,141,061 HIGH VQLTAGE CABLE TERMINAL Ernest W. Bianco, Mountain View, and Le Roy H. Frankhn, Los Altos, Califi, assignors to Components for lie search, Inc., Palo Alto, Calif., a corporation of California Filed Mar. 25, 1959, Ser. No. 801,891 1 Claim. (Cl. 174-75) The present invention relates generally to terminals for high voltage coaxial cables, and more particularly, to improvements in high voltage cable terminals over those disclosed in the patent applications of LeRoy H. Franklin, Ser. No. 672,048, filed July 15, 1957, now Patent No. 3,018,313, and Ser. No. 681,238, filed August 30, 1957, now abandoned.

It is a general object of the present invention to provide a prefabricated high voltage cable terminal which is easy to install and provides for the ready connection thereto or disconnection therefrom of the coaxial cable.

More specifically, it is a feature of the invention to provide a high voltage cable terminal which can be mounted in an oil bath or in air and is effectively sealed so that neither air nor water can enter its interior wherefore unequal electrical stress distribution within the terminal is effectively precluded.

It is a further feature to provide for the easy connection of the coaxial cable to the terminal without the attendant creation of any high electrical stress points wherefore arcing or other breakdown is precluded.

Additionally, it is a feature to provide a spring-type socket for reception of the central conductor of the coaxial cable to form an effective electrical connection, which, however, requires no soldering or other ancillary connection procedures.

Similarly, it is a feature of the invention to provide a readily-formed yet secure clamp-type joint to the external conductor of the cable, wherefore, again, no soldering or other similar operation is required during the installation.

These as well as other objects and features of the invention will become more apparent from a perusal of the following description of the accompanying drawing wherein:

FIG. 1 is a side elevational view of a high voltage cable terminal constructed in accordance with the present invention with the high voltage cable attached thereto and with the terminal mounted on the wall of an oil tank within which the insulator portion of the terminal is disposed,

FIG. 2 is a central, longitudinal sectional view on a slightly enlarged scale of the structure shown in FIG. 1, and

FIG. 3 is a central, longitudinal sectional view similar to FIG. 2 of a modified high voltage cable terminal embodying features of the present invention.

With initial reference to FIGS. 1 and 2 of the drawing, the first embodiment of the invention constitutes a high voltage cable terminal capable of operation at 125 kilovolts or higher. Generally, the terminal includes a first conductor adapted for connection to the outer conductor or sheath 12 of the cable 14 and a second conductor 16 arranged for connection to the central conductor 18 of the coaxial cable. The two conductors 1t) and 16 are supported at opposite ends of a generally tubular insulator 20 of cast epoxy, polyester or other suitable casting resin, the length of such insulator being determined by the applied voltages and also by the environment within which the terminal is mounted. For example, for operation at 125 kilovolts, the tubular insulator 20 need be only approximately 12 inches or less in length if the terminal is mounted in an oil bath, while it must be almost twice this length to preclude voltage breakdown if mounted directly in air.

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In order to provide for mounting the terminal in an oil bath, a radial flange portion 22 of the first conductor 10 extends outwardly beyond the periphery of the tubular insulator 2d and is provided with a series of holes through which bolts 24. may be passed to attach the entire terminal to the wall 26 of the oil tank, which normally serves as a ground connection. The insulating oil (not shown) thus surrounds substantially the entire insulator 2t) and the second conductor 16, and is precluded from leaking between the flange 22 and the tank wall 2% by a suitable neoprene O-ring or gasket 23 mounted in sealing relationship therebetween.

With more specific reference to FIG. 2, the main body portion of the first conductor 113 includes a central hub portion 311 from which the described radial flange 22 projects outwardly. The tubular insulator it) is cast in position against one face of the first conductor 10 so that the hollow interior of the tubular insulator 2t and the hollow interior of the hub are in alignment to accommodate therewithin the interior portion of the cable 14 including the central conductor 18 and the annular insulator 32 that separates such central conductor from the outer conductor or sheath 12 of the cable. Preferably, the face of the flange 22 against which the insulator 2t) is cast is provided with annular projecting portions indicated at 22a Wherefore the insulator is in engagement with both radially and axially extending metal surfaces which provide for secure connection between the insulator 20 and the first conductor ill. From one extremity of the hub portion 30 of the first conductor 10, a stress cone 34 projects in an outwardly flaring path, such stress cone being embedded within the insulator 2% during the casting process in a known fashion constituting no part of the present invention. It should be observed, however, that the smooth inner surface of the stress cone 34 forms a continuous extension of the smooth inner surface of the hub 30, wherefore no points or projections producing electrical stress concentrations exist.

In accordance with one aspect of the present invention, a conductive clamp 40 is provided for initial connection to the outer conductor 12 of the coaxial cable 14 and this clamp in turn is connected both physically and electrically to the hub portion MD of the first conductor 10. The clamp 40 includes a first clamping member 42 in the form of a metal tube which is adapted to encompass the outer conductor 12 of the coaxial cable 14 and is tapered outwardly at one end, as indicated at 42a. The other clamping member 44 is also a metal tube but of slightly smaller inner diameter so as to encompass the annular insulator 32 of the coaxial cable 14 and has an exterior tapered surface 44a which substantially matches the taper of the first clamping member 42 wherefore the outer conductor or sheath 12 of the cable 14 can be disposed be tween such two tapering surfaces 42a and 44a and, when the clamping members 12, 44 are moved toward one another, will be clamped therebetween to establish secure physical and electrical contact. In order to provide such clamping motion, small screws as project from the second clamping member 44 into threaded bores in the first clamping member 42 so that upon turning of such screws, the clamping members will be moved axially toward or away from one another. As a consequence, no torque is applied to the outer conductor or sheath 12 of the cable when the clamp 41) is applied Wherefore no severance or fraying of the cable sheath will occur. A small gasket 48, preferably triangular in cross-section, is disposed between the cable sheath 12. and the annular insulator 32 thereof adjacent the end of the second clamping member 44 so that when the described clamping motion takes place, such gasket will be compressed to establish a seal between the clamp 40 and the cable insulator 32. Preferably, such gasket 48 is formed of elec- :1 all) trically conductive material so that no electrical discontinuity occurs between the end of the clamping member 44 and the cable sheath l2 and thus no electrical stress discontinuities are experienced at the juncture. t will also be observed that the first clamping member 32 ex tends a considerable distance along the cable sheath l2 beyond the clamping position wherefore support for the cable 14 and the maintenance of even stress distribution is maintained. The extremity of the clamping member 42 is tapered outwardly as indicated at 42b wherefore any bending of the cable 14 can be accommodated without pressure against a sharp metallic edge.

The assembled clamp 40 is secured to the hub portion 30 of the first conductor 10 by a series of bolts 50 which project through openings in annular flanges formed on both of the clamping members 42, 4 and enter respective threaded bores in the hub portion. When so secured, the interior tubular surface of the second clamping member 44- is brought into registering engagement with the end of the tubular interior of the hub portion 36, wherefore, again, no electrical stress discontinuity is experienced. An annular recess a is provided in the hub portion 30 to contain a neoprene O-ring 52 which serves to form a radial seal between the hub portion 3% and the clamp structure secured thereto. Through the combined use of this O-ring and the previously described gasket 48, the cable 14 assembled within the terminal is effectively sealed against entry of air into the spaces between the exterior of the cable and the interior of the terminal structure and furthermore the insulating oil or grease, normally inserted into such annular spaces, cannot have egress therefrom. Such oil can be supplied from a suitable reservoir of known design (not shown).

The second conductor 16 at the remote end of the annular insulator includes a body member 60, generally in the form of a hollow, oblate spheroid with openings at its respective poles. One opening accommodates an inserted cable 14 while the other receives a threaded stud 62 that is sealingly brazed into such opening and enables connection of an exterior conductor 64 to its projecting threaded portion by application of a conventional Washer and nut 66. The interior end of the stud is provided with a circumferentially-spaced series of leaf springs which, together, form a spring-type socket 68 within which the central conductor 18 of the cable 14 can be received to establish physical and electrical connection without necessity for soldering or other operations.

In order to secure the body member 6% firmly to the end of the annular insulator 20, a small annular projection a is provided thereon to be encompassed by the cast material wherefore, as in the case of the first conductor Ill, the cast material engages both radially and axially extending surfaces to assure the desired rigidity. When secured as described, the interior of the oblate spheroid body member 665 is sealed to the insulator 2t and entirely encloses the end of the hollow terminal structure Wherefore the oil in the surrounding bath cannot enter the interior of the terminal.

Since the interior of the terminal is thus sealed against entry of the surrounding oil, and the first conductor I0 is also sealed to the wall 2 6 of the tank within which the oil is contained, if the described clamp 4a is disconnected from the hub portion 36 of the first conductor 10, the entire cable Ila: with the clamp 4% attached thereto can be withdrawn from the terminal structure without the disconnection of any other elements or emptying of the oil from the tank. T0 reinsert the cable lid, it is merely necessary to replenish the supply of insulating oil or grease Within the interior of the terminal and shove the cable telescopically into the terminal and tighten the bolts 50 between the clamp 4th and the hub portion 30 of the first conductor 10 to reestablish the assembled unit, as shown in FIGS. 1 and 2.

In the initial installation, it is, of course, necessary to secure the flange 22 of the first conductor It) in sealing engagement with the wall 26 of the oil tank, make the described connection of the second conductor 16 to the exterior conductor 64 and thereafter fill the tank with oil whereupon the terminal is immediately ready for reception of a cable 14. The cable 14 is prepared by cutting back the outer conductor or sheath 12 to a predetermined distance from the cable end and thereafter cutting back the annular insulator 32 a small distance from the end of the central conductor 18, as illustrated in FIG. 2. The two clamping members 4-2, 44 are then brought into clamped engagement with the outer conductor 12 in the manner illustrated which both establishes electrical connection and places the gasket 48 in sealing relationship with the clamp 40 and the annular insulator 32 of the cable 14. There after, a supply of insulating oil or grease is inserted into the hollow interior of the terminal and the entire cable structure is telescopically shoved into the terminal to automatically establish connection between the central cable conductor 18 and the spring socket 68 of the second terminal conductor 16 and thereafter, the bolts Sll are applied to secure the clamp ill to the hubportion 30 of the first terminal conductor Ill whereupon operation can immediately be commenced. Thus, it will be apparent that both installation of the terminal and connection or disconnection of a cable 14 are readily achieved even by unskilled electricians.

With reference now to FIG. 3, there is shown a somewhat simplified embodiment of the invention which is preferably applicable in instances where lower voltages are being handled. In this embodiment, the first conductor 70 takes the form of a tubular member which is exteriorly threaded at one end and is curved outwardly and thence rearwardly at its remote end so as to form an integral stress cone 72. Such stress cone 72 is partially embedded in the tubular insulator 74 which is of generally the same configuration as in the first embodiment of the invention. The stress cone 72 and the surrounding portion of the insulator 74 are machined to provide a flat surface so that they can be brought into engagement with the wall 76 of the tank or other mounting element and a nut 78 is turned on the threaded tubular portion of the first conductor 79 to engage the remote face of the wall to secure the entire terminal in position thereon and establish electrical connection between such first conductor and this wall or other conductive mounting member. An O-ring fill is disposed between the wall '76 and the stress cone 72 to provide a conventional seal.

The interior of the first conductor 70 closely encompasses the annular insulator 32' of the cable 14' and a modified clamp structure 82. is arranged at the remote end of the first conductor 79 to establish electrical connection between the outer conductor 12' of the cable and such first conductor. Immediately adjacent the end of the first conductor '79 an O-ring 84- or gasket of triangular crosssection, as in the first embodiment of the invention, is positioned and a metallic packing gland S6 is urged thereagainst, such packing gland having a triangular face so as to urge the O-ring 84 both against the end of the first conductor 70 and an inserted cable 14' so as to establish an effective seal. This packing gland 86 also constitutes a clamping member arranged to engage one surface of the outer conductor or sheath 12' of the cable, the other surface of such outer conductor being engaged by the interior end of a packing nut 88 which serves both to establish clamping engagement with the outer sheath of the cable and to urge the described O-ring 84 into sealing engagement with the first conductor 70 and the inserted cable 14-. The packing nut 88 is adapted to be turned on the threads of the first conductor 70 so as to establish both physical contact therewith and establish electrical connection between the first conductor 79 and the outer conductor 12' of the cable 14'.

The second conductor 90 is generally similar to that of the first embodiment of the invention, being cast integrally with the annular insulator 74 and having a projecting stud 92 enabling connection to an exterior conductor 64. In the hollow interior of the second conductor 90, a springtype socket 94 is formed to receive and establish electrical connection with the inner conductor 18" of the coaxial cable 14'.

The installation of this terminal is generally similar to that of the first embodiment so that it need not be repeated in detail, it being only necessary to mention that the first conductor 70 is secured to the wall 76 by the mounting nut 78 rather than a series of peripheral bolts. Insertion of the cable 14' is also generally similar, the cable being initialy cut back a predetermined distance in accordance with the overall dimensions of the terminal. Preferably, a supply of insulating grease (not shown) is provided in the interior of the terminal and when the cable 14' is shoved therein, the voids between the cable and the surrounding terminal are completely filled with such grease so as to preclude any air or other material being left therein. After the cable has been shoved into the terminal so that its central conductor 18 is received within the springtype socket 94 of the second conductor 90 of the terminal, the packing nut 88 is turned on the exterior threads of the tubular first conductor 70 to press the O-ring 84 into sealing engagement with the central annular insulating portion 32 of the cable and to clamp the outer conductor or sheath 12' of the cable between such packing nut and the metal packing gland 86.

Various alterations and/ or modifications can obviously be made in the described structures Without departing from the spirit of the invention, wherefore those described structures are to be considered as purely exemplary and not in a limiting sense. The actual scope of the invention is to be indicated by reference to the appended claim.

What is claimed is:

In a high voltage coaxial cable terminal having conductors for respective connection to the inner and outer conductor of the coaxial cable, an arrangement for connecting the outer conductor of the cable to one terminal conductor which comprises a first conductive tubular member arranged to encompass the outer cable conductor and tapered outwardly at one end, a second conductive tubular member having a tapered portion arranged for insertion between the outer cable conductor and the cable insulator therewithin, means for moving said tubular members toward one another to clamp the outer cable conductor be tween the tapered portions thereof, independent means for removably connecting said tubular clamping members to one conductor of the terminal, and an electrically-conductive resilient gasket arranged adjacent the tapered end of said second tubular member so as to form a seal between said tubular member and the cable insulator therewithin and with its interior surface substantially in concentric alignment therewith.

References Cited in the file of this patent UNITED STATES PATENTS 2,273,538 Rogers Feb. 17, 1942 2,397,735 Grieb Apr. 2, 1946 2,673,233 Salisbury Mar. 23, 1954 2,785,384 Wickesser Mar. 12, 1957 2,858,358 Hawke Oct. 28, 1958 FOREIGN PATENTS 1,180,413 France Dec. 29, 1958 460,156 Great Britain Jan. 22, 1937

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