US3051770A

US3051770A - Normal joint for high tension cables and process of making the same

Info

Publication number: US3051770A
Application number: US51712A
Authority: US
Inventors: Palmieri Nicola
Original assignee: Pirelli SpA
Current assignee: Pirelli and C SpA
Priority date: 1959-08-26
Filing date: 1960-08-24
Publication date: 1962-08-28
Anticipated expiration: 1979-08-28

Description

Aug. 28, 1962 N. PALMIERI NORMAL JOINT FOR HIGH TENSION CABLES AND PROCESS OF MAKING THE SAME Filed Aug. 24, 1960 IIIIIIII NICOLA FALMI nl United This invention relates to normal or straight-through joints on high tension cables insulated with impregnated paper. i

When the conductors of high tension electric cables, of the type with which the present invention is concerned, have been jointed by soldering or by a compression clamp, and the insulation has been suitably stepped on the two cable lengths being jointed, the insulation is generally rebuilt by using tapes of dielectric material or tubes of impregnated paper, or combinations of the two. This operation is delicate and requires a considerable time during which the cable ends are exposed to atmospheric conditions, which is generally undesirable.

The diameter of insulation rebuilt at the jointing zone is generally greater than the diameter of the original cable insulation and an appropriate conical or bell shaped tapering is provided at the two ends of the joint for the purpose of giving `a proper bearing to the electric screening wound around them. In this way the electric field in the cable insulation of the jointing zone which is rather intense is gradually reduced to an allowable value. The tapered ends of the insulating sleeve are generally obtained by suitable disposition of tapes, or are manually shaped as by cutting the paper tubes at the desired places. The joint so built up is then screened by a conductive paper and with a tape of metallic-fabric, or by winding a wire in close turns on the bell shaped surfaces and a metal tape on the cylindrical portion.

It is one of the objects of the present invention to provide a normal joint for high tension cables which joint is such that it maybe made and installed by non-skilled workmen, and, at the same time, allows an appreciable saving in assembly time.

In accordance with the principles of the present invention, there is provided a prefabricated sleeve having an imbedded screening electrode, the sleeve being used in lieu of the paper tubes or tapes of insulating material, thus eliminating the stepping of the insulation. The sleeve is preferably made of suitable insulation, for instance, ethoxylinic resin or any of the other insulating materials set forth in Italian Patent 516,653 and the corresponding pending United States patent application Serial No. 424,729 owned by the assignee of this application, to which reference may be had.

I t is a further object of the present invention to provide a connector for high tension cables wherein the jointing clamp or connecting member that provides the electrically conductive path between the cable conductors is completely screened by a conductive electrode that is separate from and embedded within a solid dielectric mass, preferably constituted of a casting of synthetic resins of the ethoxylinic type, sometimes loaded with inorganic excipients (such as, for instance, powdered quartz or kaolin) and suitably added with hardening agents, such as, for instance, the resins known on the market under the trade name Araldit The attainment of the above and further objects of the present invention will be apparent from the following specification taken in conjunction with the following drawing forming a part thereof.

In the drawing:

FIG. l is a transverse sectional view of a three-phase line consisting of a trefoil of single core cables placed within a single pipe, and to which the present invention is applicable.

FIG. 2 is a diagrammatic longitudinal view in partial section of a portion of a cable joint embodying the present invention and connecting cable cores in a system such afs shown in FIG. l;

FIG. 3 is an enlarged diagrammatic view of a part of FIG. l with some of the cross sectioning omitted to facilitate illustrating the shapes of the equipotential surfaces in the joint; and

FIG. 4 is a longitudinal view, in partial section, corresponding to FIG. 2, of a cable joint embodying the present invention as applied to lead sheathed cables.

In the accompanying drawing like reference numerals designate like parts throughout.

FIG. l shows a cross section through a three-phase pipe cable system consisting of three identical single core cables A-A-A devoid of metal sheathing and having an insulation of impregnated paper to be more fully described in the description of FIGS. 2 and 3, screened with overlapped copper tapes. The three cables are drawn in a steel pipe B which is then filled with nitrogen or oil under pressure, for instance, a pressure of fifteen atmospheres. The presence of the uid under pressure improves the service of the joint to be hereinafter described. Consecutive lengths of the cable cores of the same phase are joined by a joint such as illustrated in FIG. 2. Each cable includes a stranded wire conductor `2. Each conductor 2| has a wrapping of cable insul lation 5, and a screen 7 formed of metallic and semiconductive tapes. rIlhe cable 1, here shown, is one of the three identical single core cables each devoid of metal sheath which extend lengthwise in a steel pipe B.

The joint of FIG. 2 between two identical cables 1--1' of FIG. 1 is a normal joint or straight-throug joint. The only function of such a joint is that of joining two lengths of cable pertaining to the same section of a line.

A cylindrical metal ferrule 10 serves to connect the cable conductors 2 both mechanically and electrically.

The ferrule 10 is surrounded by a sleeve 12 in which is embedded a generally cylindrical electrode 13.

lThe sleeve 12 is a monolithic dielectric casting of ethoxylinic resins, preferably of the type set forth in Italian Patent 516,653 and Italian Patent 536,349 which is a iifth addition to Italian Patent 516,653, and the conductive material of the electrode 13 may also be that set forth lin said `Italian patents, reference being made to those patents for a further description the same as though that description were incorporated herein. A corresponding reference is made to United States patent applications 424,729 and 589,458, that correspond, respectively, to the above Italian patents and are assigned to the assignee of this application. The synthetic resins of the epoxy type have exceptionally high adherence to the metal surfaces embedded therein so that there is a complete absence of empty spaces or voids in the casting. The dielectric is of a low thermal co-etiicient of linear expansion approximating that of the embedded electrode 1-3, and has high dielectric properties, all as set forth in the Italian patents above referred to. The electrode 13 extends to the inner surface of a centrally located longitudinally extending bore 15 in the dielectric sleeve 12 where it -makes mechanical and electrical contact with the ferrule .'10 to maintain the potential of the electrode 13 the same as the potential of the cable conductors 2. Part of the material of the dielectric 12 extends into and covers the inner surface of the screening electrode 13 as indicated at 14.

`In order to build up the joint in accordance with the present invention the following steps are taken. The screen 7 is removed from each length of cable being jointed to the point 1S, the cable insulation 5 being thus exposed. The insulation 5 is then removed from a surfficient length of the end of the cable conductor as required by the ferrule for the establishment of good rnechanical and electrical connections. This length as shown, is half of the length of the ferrule. After the ferrule is applied, the sleeve 1 2 (previously slid over the end of one cable before jointing the conductors) is moved into place, which brings the metallic electrode 13 embedded therein into electrical contact with the ferrule 10.

Y Thereafter, two bell shaped lmasses of insulation 19-19 are formed with a tape of insulating material, for instance, impregnated crepe insulating paper tapes, starting yfrom the points of the cables where the metallic andV semiconductive tapes of the screen 7 had been interrupted. These masses extend up to the sleeve 12. Then the whole joint is screened with a tight wrapping of tape of conductive (carbon) paper 20 and a tape of metallic fabric or any other cond-uctive or semiconductive screening material 21 that extends from the screen 7 on the cable l to the screen 7 on the cable 1 and closely overlies the sleeve 12 and the insulation 19. The space between the tape 2i) and the insulation 19, and the corresponding space between 20 and 21, are there merely to facilitate illustration.

In the joint those spaces do not exist. The screening material 21 over the insulation 19 constitutes a stress control cone supported by that insulation. The screening material 21 may consist of close turns of wire over the bell shaped surfaces connected to a wound metal strip on the cylindrical portion of the dielectric sleeve 12, and electrically connecting the screens 77 of the connected cables 1 1.

The bore is of a size only large enough to permit sliding over the thin screen 7, so that it makes a close sliding t over the cable insulation 5 that extends thereinto. The cable insulating fluid fills the small interspace 17 `between the cable and the inner surface of the sleeve 12.

FIGURE 3 shows the equipotential surfaces 22 caused by the electrode 13 embedded in the prefabricated sleeve 12, successive -surfaces 22 representing voltage increments of 10% of the cable conductor voltage.

The electrode 13 within the sleeve 12 has the following functions:

(a) To screen electrically the ferrule 10 and its ysurface irregularities;

(b) To modify the electric 4field in the joint zone in order to space the equipotential surfaces 22, thereby reducing the electric stresses in the zone corresponding to the inter-space between the sleeve 12 and the cable insulation 5.

Among the advantages of the joint of the present invention are:

(a) The use of a prefabricated piece (the sleeve 12) which can be factory tested Ibefore assembly;

(b) Simple assembly of the joint, which does not require the employment of highly skilled workmen;

(c) Reduction in time required to make the joint, with a consequent technical and economical advantage since the cable ends remain exposed to the atmospheric agents for only a short time;

(d) Elimination of the conventional stepping operations usually required to be carried out on the insulation of the two cable ends being jointed;

(e) Manual operation in the making of the joint lim- -ited only to the application of small amount of insulating tapes (for instance, crepe paper) for bell shaping the two ends at 19--19 of the joint insulation.

lFIG. 4 shows the principles of the present invention as applied lto a joint between two single conductor oil filled metal sheathed cables 31--31. Each cable of FIG. 4 is an oil-filled cable the stranded cable conductor 2 of which is hollow, being formed of `strands of Wire surrounding an open helix 3 and forming an axial channel or duct 4 for passage of insulating oil lengthwise of the cable, and each of the cables 31-31 differs further from the corresponding cables of FIG. 2 in that each is provided with a lead sheat-h 32 instead of the screen 7. The joint between the cable cores is enclosed by an outer rigid metallic casing 33 which is of a conventional construction and is solder-sealed to the sheaths in a conventional manner as by wiped joints 34--34 Outlets, closed by plugs 36-36, serve for evacuating the air from the joint after the joint has been completed, and for filling the joint with oil.

In compliance with the requirements of the patent statutes I have herein shown and described a preferred embodiment of the invention. It is, however, to be understood that the invention is not limited to the precise construction herein shown, the same being merely illus- -trative of the principles of the invention.

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

l. A joint for high tension cable cores each having a conductor surrounded by solid insulation which is in turn surrounded by conductive screening, a ferrule connecting the cable conductors, a prefabricated sleeve of synthetic resin having `an embedded screening electrode, said sleeve and electrode surrounding said ferrule with the sleeve closely surrounding that part of the cable core insulation near the end of the conductor and adjacent to the ferrule, said sleeve being of an inner diameter greater than the outer diameter of the cable insulation only by an amount required for sliding of the sleeve over the cable insulation, the end of `the insulation of the cable adjacent to the ferrule being at right angles yto the longitudinal axis of the sleeve, the cable core screening terminating short of the sleeve by an amount exceeding the thickness of the sleeve, bell shaped insulation around the cable and varying `from a minimum diameter where the cable screening ends to a maximum diameter surrounding a part of the sleeve, and conductive screening means surrounding the bell shaped insulation and the sleeve and electrically connected to the cable core screening.

2. A pipe system housing cables joined by joints as set forth in claim l and means for maintaining the pipe system under uid pressure of the order of many times the atmospheric pressure.

3. A pipe system housing cables joined by joints as set forth in claim l and means for maintaining the pipe system under gas pressure of the order of many times the atmospheric pressure.

4. A pipe system housing cables joined by joints as set forth in claim l and means for maintaining the pipe system under oil pressure of the order of many times the atmospheric pressure.

5. A joint such as is dened in claim l wherein each of the cable conductors is hollow to constitute a duct for insulating fluid and the ferrule is hollow to allow the flow of fluid between the ducts Of the connected conductors.

6. A joint such as is defined in claim l wherein each of the cable conductors is a solid stranded conductor.

7. A pipe system such as defined in claim 6 wherein there are at least three side by side cables in the same pipe of the system.

8. A process for forming a normal joint between high tension electric cables wherein each includes a conductor surrounded by solid cable insulation which is in turn surrounded -by a conductive screen, which process comprises providing a prefabricated sleeve of synthetic resin embedding a screening electrode and which slee-ve has an inner diameter that exceeds the outer diameter of the cable insulation only by an amount required for sliding of the sleeve over the cable insulation, providing a connecting ferrule, removing the cable screen from the end of each cable for a length substantially greater than half the length of the sleeve, removing the cable insulation from the end of each cable conductor for a length of the order of half of the ferrule length and terminating the end of the insulation remaining on the cable at substantially right ang-les to the longitudinal axis of the projecting cable conductor, sliding the sleeve over the end of one of the cables, joining the bared cable conductors through `the ferrule, sliding the sleeve to a position centered around the ferrule and at the same time establishing elec-trical connections between the ferrule and the embedded screening elec-trode, then forming separate bell shaped masses on each side of the sleeve by winding tape insulating material around the cable insulation starting from the place where the cable conducting screen ends and continuing in increasing thickness to the sleeve Where said material is built up to the periphery of the sleeve, then winding a conductive screen over said bell shaped masses and said sleeve and connecting said last screen with the cable screen.

9. A joint maintaining electric conductivity and a uid flow path between conductors of two high voltage cables of the type wherein the conductors are formed with longitudinal `duct means for carrying an insulating iluid and are surrounded by solid cable insulation that is permeated by the iluid that ows through the duct means and which solid cable insulation is in turn surrounded by shielding means, said joint including a precast sleeve of dielectric material into the opposite ends of which the ends of the cable conductors and the ends of the solid insu-lation thereon extend, a conductive member connecting the ends of the conductors and maintaining the continuity of the longitudinal duct means of the connected conductors, the inner diameter of said sleeve being greater than the outer diameter of the cable insulation only by an amount required for sliding of the sleeve over the cable insulation, the end orf the insulation of t-he cable adjacent to the conductive member being at right angles to the longitudinal axis of the sleeve and said sleeve making a close iit around the solid cable insulation extending thereinto, a screening electrode embedded in the dielectric and surrounding the connecting member and the adjacent ends of the cable insulation of the two connected cable conductors, said dielectric sleeve extending axially a greater length than said electrode and surrounding a greater length of cable insulation of both cables than is surrounded by the electrode, means connecting the electrode to the cable conductors, bell shaped insulation on each side of the dielectric sleeve, each bell shaped insulation extending from the cable insulation shielding means to the adjacent end of the dielectric sleeve.

10. A structure as defined in claim 9 wherein the cable shielding means comprises an enclosing fluid tight metal sheath and wherein there is provided a joint enclosing casing joining and sealed to the metal sheaths of the connected cables and there is a lling of insulating fluid in said casing under pressure above atmospheric pressure.

11. A joint maintaining electric conductivity between conductors of two high voltage cables surrounded by solid cable insulation which is in turn surrounded by shielding means, said joint including a precast sleeve of dielectric material into the opposite ends of which the ends of the cable conductors and the ends of the solid insulation thereon extend, a conductive member connecting the ends of the conductors, the inner diameter of said sleeve being greater than the outer diameter of the cable insulation only by an amount required for sliding of the sleeve over the cable insulation, the end of the insulation of the cable adjacent to the conductive member being at right angles to the longitudinal axis of the sleeve and said sleeve making a close t around ,the solid cable insulation extending thereinto, a screening electrode embedded in the dielectric and surrounding the connecting member and the adjacent ends of the cable insulation of the two connected cable conductors and separated radially lfrom the surrounded cable insulation by some of said dielectric, said dielectric sleeve extending axially a lgreater length than said electrode and surrounding a greater length of cable insulation of both cab-les than is surrounded by the electrode, means connecting the electrode to the cable conductors, bell-shaped insulation on each side of the dielectric sleeve, each bellshaped insulation extending from the cable insulation shielding means to the adjacent end of the dielectric sleeve, and conductive screen-ing means surrounding the bell-shaped insulation and the sleeve and electrically connected to the cable screening.

l2. A joint maintaining electric conductivity and a uid ilow path between conductors of tiwo high voltage cables of the type wherein the conductors are formed with longitudinal duct means for carrying an insulating iluid and are surrounded by solid cable insulation that is permeated by the fluid that flows through the duct means and which solid cable insulation is in turn surrounded by shielding means, said joint including a precast sleeve of dielectric material into the opposite ends of which the ends of the cable conductors and the ends of the solid insulation thereon extend, a conductive member connecting the ends of the conductors and maintaining the continuity of the longitudinal duct means of the connected conductors, the inner diameter of said sleeve being greater than the outer diameter of the cable insulation only .by an amount required for sliding of the sleeve over the cable insulation, the end of the insulation of the cable adjacent to the conductive member being at right angles to the longitudinal axis of Ithe sleeve and said sleeve making a close iit around the solid cable insulation extending thereinto, a screening electrode embedded in the dielectric and surrounding the connecting member and the adjacent ends of the cable insulation of the two connected cable conductors and separated radially from the lsurrounded cable insulation by some of said dielectric, said dielectric sleeve extending axially a greater length than said electrode and surrounding a greater length of cable insulation of both cables than is surrounded by the electrode, means connecting the electrode to the cable conductors, stress cones on each side of the dielectric sleeve, each stress cone extending from the cable insulation shielding means to the adjacent end of the dielectric sleeve.

References Cited in the le of this patent UNITED STATES PATENTS 1,834,864 Phillips Dec. 1, 1931 2,288,373 Smith i June 30, 1942 2,386,185 Beaver 1 Oct. 9, 1945 2,967,899 Priaroggia Jan. 10, 1961

Claims

1. A JOINT FOR HIGH TENSION CABLE CORES EACH HAVING A CONDUCTOR SURROUNDED BY SOLID INSULATION WHICH IS IN TURN SUUROUNDED BY CONDUCTIVE SCREENING, A FERRULE CONNECTING THE CABLE CONDUCTORS, A PREFABRICATED SLEEVE OF SYNTHETIC RESIN HAVING AN EMBEDDED SCREENING ELECTRODE, SAID SLEEVE AND ELECTRODE SURROUNDED SAID FERRULE WITH THE SLEEVE CLOSELY SURROUNDING THAT PART OF THE CABLE CORE INSULATION NEAR THE END OF THE CONDUCTOR AND ADJACENT TO THE FERRULE, SAID SLEEVE BEING OF AN INNER DIAMETER GREATEAR THAN THE OUTER DIAMETER OF THE CABLE INSULATION ONLY BY AN AMOUNT REQUIRED FOR SLIDING OF THE SLEEVE OVER THE CABLE INSULATION, THE END OF THE INSULATION OF THE CABLE ADJACENT TO THE FERRULE BEING AT RIGHT ANGLES TOT HE LONGITUDINAL AXIS OF THE SLEEVE, THE CABLE CORE SCREENING TERMINATING SHORT OF THE SLEEVE BY AN AMOUNT EXCEEDING THE THICKNESS OF THE SLEEVE, BELL SHAPED INSALTION AROUND THE CABLE AND VARYING FROM A MINIMUM DIAMETER WHERE THE CABLE SCREENING ENDS TO A MAXIMUM DIAMETER SURROUNDING A PARAT OF THE SLEEVE, AND CONDUCTIVE SCREENING MEANS SURROUNDING THE BELL SHAPED INSULATION AND THE SLEEVE AND ELECTRICALLY CONNECTED TO THE CABLE CORE SCREENING.