US2925459A - Branch joint for electric cables - Google Patents

Description

Feb. 16, 1960 P. G. PRIAROGGIA BRANCH JOINT FOR ELECTRIC CABLES v Filed Aug. 30, 1955 wQwe" mw mm United States Patent O BRANCH JOINT FOR ELECTRIC CABLES Paolo Gazzana Priaroggia, Milan, Italy, assigner to Pirelli Societa per Azioni, Milan, Italy Application August 30, 1955, Serial No. 531,506 Claims priority, application Italy September 14, 1954 6 Claims. (Cl. 174-73) This application is a continuation in part of my copending application Serial No. 424,729 filed April 21, 1954.

The present invention relates to the improvements in the construction of joints for high voltage electric cables and is particularly, although not exclusively, applicable to branch-type joints wherein three or more conductors are electrically joined.

It is one of the objects of the present invention to provide a connector for the conductors of high voltage cables for effecting a branch-type connection, which con-A nector is so insulated as to eliminate the diflicultiesl heretofore encountered in applying hand made taping insulation to branch joint connections, particularly at the crotch of the connection. y j

lt is another object of the present invention to overcorne the taping diiiiculties heretofore encountered. This is accomplished by covering the connector, which may be of any standard shape, with a suicient thickness of insulating plastic material which may be cast or molded around the connector, using an insulation having the typical property of perfectly adhering to the connector surface, thereby eliminating any space that might otherwise result between the connector and the solid insulating mass, since such space would be subjected to electrical stress that is responsible for rapid deterioration of the insulation. The plastic insulating material must have a very high dielectric strength and very low dielectric losses.

It is a still furthery object of this invention to provide an improved single or multi-branch joint for high voltage electric cables of all types, wherein there is provided a metal connector joining the bared ends of the cable conductors, which connector is embedded in a special solid dielectric of similar shaped made of one or more synthetic resins, preferably of the ethoxyline type, in case loaded and suitably hardened, so that the connector and the dielectric are in contact with one another at their interfaces, and firmly bonded together by exceptionallyihigh adhesion forces. The synthetic resins which are suitable for the purposes of the present invention are preferably those derived from the ethylene oxides or its homologues, case loaded with inorganic excipients (as, for instance,v quartz, coalin, etc.), to which are to be added the proper hardening agents, namely those known as ethoxyline, epoxyde, epichlorydrin and epoxy resins, as well as the products known under the trade name of Araldite or Araldit, both as casting and bonding resins. Resins of the above-mentioned type show a very low casting shrinkage, of the order of .1% to 2% by volume. and a very high adherence strength with very low dielectric losses.

The attainment of the above and further objectsA of the present invention will be apparent from the following specication taken in conjunction with the accompanying drawing forming a part thereof.

The single ligure of drawing is a cross. sectional View of a T-shaped branch connecting joint connecting three high voltage cables.

Reference may now be had more particularly to the drawing. A T-shaped branch-type joint which is built up in accordance with the present invention joins three single core, high voltage electric cables I, II and III. At l there is indicated a T-shaped metallic connector embedded in a solid special dielectric 3 which is also T-shaped and which is tapered at each of its three ends. The dielectric 3 is a monolithic structure. Said monolithic structure may be made both by casting and molding or may be built up at the site, but preferably it is prefabricated as an assembly with the connector 1.

The dielectric 3 is a synthetic resin. The synthetic resins which mainly serve this purpose are preferably those derived from ethylene oxide or its homologues, in case loaded with inorganic excipients (as, for instance, quartz, caolin, etc.), to which the proper hardening agents are to be added, namely those known as ethoxyline, epoxy, epichlorydrin and epoxyde resins. These resins, suitable for dielectric 3, are marketed under tradenames as follows: Araldit, or Araldite, produced by Ciba, Inc., of New York; Epen or Epikote produced by Shell Chemical Corp., of New York; Devrani produced by DeVoe & Reynolds Co., luc., of Louisville; C-8, produced by Bakelite Co. of New York. The resins here used for dielectric 3, it is apparent, may be any of the insulating resins described in my pending application above referred to.

TheA ends ofthe three branches of the connector 1, covered by the insulation 3 as above set forth, may be connected to the respective current carrying conductors of the cables I, Il and Ill and suitably joined thereto. A compression jointing is preferred and for this purpose a hydraulic press may be employed for pressing the metal strands constituting the respective cable. conductors into the respective sockets 1a at the ends of the connector 1. In lieu of a press tit, the cable conductors may be soldered in the respective sockets 1a. When the mechanical and electrical connections have been made between the stranded ends of the cable conductors and the respective sockets of the connector 1, the insulation 2 is applied as by manually Winding sealing tape in place, as is known in the art. Thereafter, metallic screens 4 are formed by winding metallic tape, generally of copper, around the insulation 2 and joining said screens to the grounded sleeve or screen surrounding the corresponding cable.

The surfaces 5 of the connector insulation 3 are rendered electrically conductive previous to the assembly ofthe connector with the cable, or it may be done during or after such assembly. The surfaces 5 are rendered electrically conductive in any way known in the art, as, for instance, by spraying conductive material thereon, such as copper or tin, or by graphitization, or by coating with varnish having a conductive material such as, for instance, carbon black, incorporated therein, or in any other desired manner. rlhe surfaces 5 could be termed by applying to the insulation 3, at those places, a layer of the same insulation as the insulation 3 but having a conductive material (such as, for instance, carbon black) incorporated therein as set forth in my co-pending cation Serial No. 424,729, or the surfaces 5 could be formed by applying to the insulation 3 a metallic screen of a corresponding shape which either may perfectly adhere to the dielectric being bonded with the synthetic resins of the Araldite bonding type, or may even be separated from the dielectric by means of an interposed layer of insulating oil or compressed gas.

The entire cable joint as above set forth is enclosed Within ametallic box or casing formed by three similar Patented Feb. 16, 1960V sleeves 6 one end of each of which is tapered to be slidable onto the cable sheath and the opposite ends of which are shaped to intert to form a T-shaped joint. .These intertted ends of the three sleeves arejoined by soldering or the like to form a hermetic s'eal, and the opposite endV in each case is joined by a wiped'solder joint with the cable sheath, as is known in the art.

'Ihe dielectric 3 has a very high dielectric strength, a very high tensile strength, and adheres to the connector 1 with high adhesive force (of the value of 100 to 300 kg./sq. cm.). The physical characteristics of that dielectric are set forth in my pending application Serial No. 424,729 to which reference may be had.

In compliance with therequirements of the patent statutes I have herein shown and described a preferred embodiment of the present invention. It is, however, to be understood that this is merely one example of the application of the principles of the present invention which may be carried out in different ways within the purview of the principles hereinabove set forth and the following claims.

What is considered new and desired to be secured by Letters Patent is:

1. A branch joint for at least three converging high tension electric cables each having surrounding grounded means, a surrounding conductive casing into which the conductors extend and from which they are insulated,

. which casing is adapted to be grounded, a metallic con- Vnector within the casing and connecting the cable con- Vrluctors converging in the joint, which connector includes branches for the converging cable conductors, the connector including its branches comprising Va oneV piece structure which is embedded'in a monolithic mass comprising a solid dielectric of the same shape, made of synthetic epoxy resin, and is bonded-to it by high adhesion forces at the entire facing surfaces between them thus eliminating any empty space between the connector and the solid insulating mass which could be subjected to electric stresses, and a conducting shield surrounding the dielectric mass and located within the casing and electrically connected to but spaced from the casing, and means electrically connecting said conducting shield and casing with the aforesaid surrounding grounding means.

2. A branch joint for at least three high tension electric cables each having aY conducting surrounding sheath, a one piece metallic connector having parts for receiving at least three cable conductors, said parts converging in Y the joint, which connector is embedded in a one piece solid dielectric of the same shape, made of synthetic resins based on ethylene oxide, and is bonded to it by high adhesion forces at the entire facing surfaces between them thus eliminating any empty space between the connector rand the solid insulating mass which could be subjected to electric stresses, and a conductive shield covering the outer surface of the solid dielectric at the juncture of the converging parts thereof, said shield being an integral part of and bonded to the dielectric, and means electrically connecting said conductive shield with said sheath.

3. A high voltage cable joint for the conductors of cable cores that are surrounded by grounded means comprising a grounded conductive casing into which a cable conductor extends, said cable conductor having covering insulation which tapers to a minimum thickness adjacent to the conductor end, a connector and insulator assembly in said casing, the latter assembly being a monolithic body comprising cable conductor receiving Y connector means within a one piece solid mass of dielectric material intimately united with and surrounding the connector means and tapering to a minimum thickness toward one end thereof that is adjacent to the cable conductor receiving end of thev connector, wrapped insulation "extending between the Vtap-eed end of said delctricmass and the tapered 'insulation at the cable end, a rst conductive shield bonded to and covering and in intimate contact with the entire outer part of the dielectric at the portions thereof of maximum thickness, and a second conductive shield covering the wrapped insulation and in intimate contact therewith over substantially the entire outer part thereof and connected with said iirst conductive shield and with the casing.

4. A branch type joining connector for a high tension electric cable, said connector comprising a one piece metallic body having at least three terminal branches converging toward a common point, a one piece solid dielectric in which said connector is embedded with the ends thereof exposed each for lreceiving a cable conductor, said dielectric being molded around the connector and intimately bonded therewith by high adhesion forces and being of maximum thickness in the region surrounding the point of convergence of the branches and tapering to a minimum thickness surrounding the cable con- Vductor receiving ends of the branches, said tapering por- Vductors of at least three converging high tension electric cables, characterised in that there is provided a one piece metallic connector for the corresponding conductors of the cables, said connector having converging branches one for each of the cable conductorsv being joined, said connectorl being embedded in a monolithic mass of solid Vdielectric of the same number of branches and in thetsame angular relationship as are the branches of the connector, the dielectric being bonded to the connector'by high adhesion forecs at the entire facing surfaces between them thus eliminating all empty spaces between the connector and the dielectric which could be subjected to electrical stresses, there being an electrical conductive layer bonded to covering the surface of the dielectric between the intersection of the respective branches of the dielectric and constituting an intimate part of the connector, a conductive casing surrounding and spaced from the connector, and means electrically connecting the conductive layer with said casing, each of said branches of the connector extending at least to the end of the surrounding branch of the monolithic mass dielectric.

6. Means for joining the corresponding conductors of at least three converging high tension electric cables each including a surroundingv grounded sheath, said means comprising a one piecemetallic connector for the corresponding conductors of the cables, said connector having 'converging branches one for eachof the cable conductors Veach branch being of a frusto conical shape of a minimum diameter at the end of the surrounded branch and of progressively increasing diameter in the direction of convergence of the branches, there being an electrical conductive layer covering the surface'of the dielectricrbetween the intersections of the respective branches'of the dielectric and bonded thereto, each of said branches of the connector extending at least to the end of the surrounding branch of the monolithic mass dielectric, wrapped insulation covering the tapered ends'of the respective branches of the dielectric, and conductive shields surrounding and @intimate contact with the entire outer surfaces of the wrapped insulation of the respective branches and extending up to and electrically connected with the rst mentioned conductive layer.

References Cited in the le of this patent Phillips July 21, 1942 5 UNITED STATES PATENTS Halperin et al. Oct. 2, 1934 Lee July 20, 1937 Miller et al Oct. 14, 1941 lo 6 2,459,004 Rogol Jan. 11, 1949 2,785,319 Simpson et al. Mar. 12, 1957 FOREIGN PATENTS 408,033 Great Britain Apr. 5, 1934 OTHER REFERENCES Article I, Ethoxylines, Preiswerk and Charlton, published in Modern Plastics, November 1950 (pages 85-88 relied on.)

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