US3843830A

US3843830A - Electric cable with corrugated sheath and semi-conductive protective layer between the sheath and the core

Info

Publication number: US3843830A
Application number: US00403962A
Authority: US
Inventors: P Priaroggia; G Maschio
Original assignee: Pirelli SpA
Current assignee: Pirelli and C SpA
Priority date: 1972-11-13
Filing date: 1973-10-05
Publication date: 1974-10-22
Anticipated expiration: 1991-10-22
Also published as: SE382519B; BR7308838D0; JPS589521B2; GB1395519A; IE38504B1; CA994442A; IE38504L; ZA738653B; JPS49124584A; IT1044874B; AU6241973A; AR196699A1

Abstract

An electric cable having one or more insulated cores with an external semi-conductive screen surrounded by a corrugated metal sheath and having a tube of soft, semi-conductive material intermediate the core and the sheath with the corrugations of the sheath embedded therein to both prevent slippage of the core with respect to the sheath and conductively interconnect the sheath and the screen. The tube may be a wound tape of semi-conductive crepe paper or such a tape surrounded by glass cloth having intercalated metal wires.

Description

United States Patent 91 Priaroggia et al.

[451 Oct. 22, 1974 1 ELECTRIC CABLE WITH CORRUGATED SIIEATII AND SEMI-CONDUCTIVE PROTECTIVE LAYER BETWEEN THE SI-IEATII AND THE CORE [75] Inventors: Paulo Gazzana Priaroggia, Milan;

Gabriele Maschio, Monza, both of Italy [73] Assignee: Industrie Pirelli Societa Per Azioni,

Milan, Italy [22] Filed: Oct. 5, 1973 21 Appl. No.: 403,962

[30] Foreign Application Priority Data Nov. 13, 1972 Italy 31581/72 [52] US. Cl. 174/102 D, 174/102 SC, 174/120 SC [5 l] Int. Cl. I-IOlb 7/20 [58] Field of Search 174/102 D, 102 R, 102 SC,

174/105 SC, 120 SC, 121 SC, 25 R [56] References Cited UNITED STATES PATENTS 3,719,769 3/1973 Miyauchi et al. 174/105 SC 3,766,309 10/1973 Calzolari 1. 174/102 D 3,773,965 11/1973 Reynolds 174/25 G Primary Examiner-A. J. Grimley Attorney, Agent, or FirmBro0ks, Haidt & Haffner [57] ABSTRACT 6 Claims, 2 Drawing Figures l SCREENS C/ (45 F re g z CORRUGATED 2 a 17 l is 111% 1 The present invention relates to improvements in electric cables provided with a metal sheath, in particular, a corrugated aluminum sheath, and of the type described in co-pending application Ser. No. 162,199, filed July 13, 1971, and entitled ELECTRIC CABLE WITH CORRUGATED METALLIC SHEATH, now U.S. Pat. No. 3,766,309. The invention is applicable to high voltage power cables and especially to Millikentype cables.

Said U.S. Pat. No. 3,766,309 describes an electric cable comprising a core, i.e., a conductor surrounded throughout its length by at least one layer of insulating material, which is surrounded by a corrugated metal sheath. A soft tubular covering, generally of the order of about one or more millimeters in radial dimension, covers said core, the corrugations of the sheath, at least for a part of their depth, penetrating into said soft tubular covering in order to provide a co-penetration of the latter and the sheath. A preferred embodiment of the invention illustrated in said patent is an electric cable comprising a core contained in a corrugated metal sheath, in which said soft tubular covering for the core is made of crepe paper.

In an electric cable of the above-described type, the possible slippage of the core with respect to the sheath, when the cable is installed in vertical direction, is substantially prevented. Moreover, the soft tubular covering, in particular when it is made of crepe paper, has provided, in practice, very suitable for the dissipation of heat in the case of power cables subjected to thermal cycles, thereby avoiding undesired over-heating of the dielectric.

However, in certain high voltage cables provided with a corrugated sheath, for example, the cables known to those skilled in the art as Milliken-type cables, due to the lack of an electrical contact between the outermost screen of the core and the corrugated sheath, capacitive currents may occur which, flowing in the screen, could give rise to considerable power losses and to a subsequent over-heating of a magnitude which cannot be balanced by the soft tubular covering. Also, abnormal voltages may be produced between the screen and the metal sheath, which could be the cause of a breakdown discharge.

The principal object of the invention of the present application is to provide an electric cable having a corrugated metal sheath which is improved with respect to the electric cable described in said patent, the improvement being also applicable to high voltage power cables, in particular, to Milliken-type cables, and the improvement substantially eliminating the hereinforementioned disadvantages.

More precisely, the object of the present invention is an improved electric cable comprising a core contained in a corrugated metal sheath, and of the type disclosed in said application, in which a soft tubular covering surrounds said core, the corrugations of the sheath, at least for a part of their depth, penetrating in said soft tubular covering so as to provide a co-penetration between the latter and the sheath, said cable being characterized in that said soft tubular covering is constituted by a material having a high electric conductivity with respect to a dielectric material.

In the preferred embodiment of the invention, the electric cable, said soft tubular covering, made of a material having a high electric conductivity, is constituted by a winding of tapes of semi-conductive crepe paperfl-w- In another embodiment of the invention, said soft tuv bular covering, made of a material having a high electric conductivity, is constituted by an internal winding of tapes of semi-conductive crepe paper and by an external winding of a cloth of glass fibers containing intercalated metal wires.

The objects and advantages of the invention will be apparent to those skilled in the art from the following description of the presently preferred embodiments thereof, which description should be considered in conjunction with the accompanying drawing in which:

FIG. 1 represents, in longitudinal section, a single core, power cable having a core surrounded by a corrugated metal sheath and having an intermediate layer of semi-conductive crepe paper; and

FIG. 2 represents, in longitudinal section, a Millikentype cable, provided with a corrugated aluminum sheath and a composite intermediate layer of semiconductive crepe paper and a cloth of glass fibers containing intercalated metal wires.

The cable represented in longitudinal section in FIG. 1 is a single core cable and comprises a core 10 and a corrugated sheath 1]. Although the sheath 11 illustrated in FIG. 1 has helical corrugations, the corrugations could be annular. The core 10 comprises a stranded conductor 12, on which is wound a first, or internal, semi-conductive screen 13 surrounded by a dielectric layer 14, which, in turn, is surrounded by a second, or external, semi-conductive screen 15. The core 10 is electrically complete, that is, except for the need to protect it from physical damage with a sheath 1 l, the core 10 may be used for carrying current between separated points.

The core 10 is protected from damage by the sheath 11, both during the application of the sheath 11 and during subsequent use and is prevented from slipping with respect to the sheath 1 1 by a soft tubular covering or layer 16, made of a material having a high electric conductivity as compared to ordinary insulation, e.g., it has a resistivity, MD, of from 30 to 5,000 ohm cm. and a bulk resistivity of from 3,000 to 500,000 ohm cm. In the embodiment illustrated, the covering 16 is constituted by a helical winding of tapes of semiconductive crepe paper thereby forming a tube of solid, self-sustaining and resilient material between the sheath 1] and the core 10. As described in said patent, the material of the covering 16 is different from the material of the layer 14 and is softer than the latter so as to permit deformation of the sheath 11 without substantial deformation of the layer 14. The covering 16 frictionally engages the external screen 15 and the sheath 11, at least partially filling the corrugations of the sheath 11, and thereby prevents significant relative movement between the sheath 1 l and the core 10 when the cable is suspended by the sheath 11. The shear strength of the covering 16 is such that it can prevent such relative movement without shearing of the covering 16 or the material thereof. The normal exterior size of the covering 16 in the absence of deformation thereof is greater than the minimum diameter of the corrugations of the sheath 11.

The inner surface 16 of the soft, tubular, conductive covering 16 is in contact with the external semiconductive screen 15, and the outer surface 18 of said covering 16 is in contact with the internal surface of the corrugated sheath 11, at least along a helical surface in the form of a generally cylindrical helix of circular section,

coincident with the inner, smallest diameter face 19 of the corrugations. The contact between the soft, tubular, conductive covering 16 and the sheath l1, besides ensuring the hereinbefore described advantages of transmitting to the core the anchoring forces applied to the sheath 1 1 and of permitting a very good dissipation of heat so that, at an equal rated current, it is possible to have cables of reduced section, namely,

\ lighter than those previously used, provides a conductive electrical interconnection between the external, semi-conductive screen and the sheath l1, preventing the existence of capacitive currents and consequently, the risk of undue over-heating and breakdown discharges.

The cable illustrated in FIG. 2 is of the type known to those skilled in the art as a MIlliken-type cable. In said cable, the core 20 is surrounded by a corrugated metal sheath 21 having annular corrugations, but the corrugations could be helical as illustrated in FIG. 1.

The conductor of the core 20 comprises three conductive strands 22 in the form of sectors which are helically would together about the longitudinal axis aa of the cable and defining a generally cylindrical passageway 23 which constitutes the duct for the supply of the cable impregnating fluid which may, for example, be sulfur hexa-fluoride, nitrogen, a mixture of sulfur hexafluoride and nitrogen, fluid oil, etc.

About the helically wound strands 22, there is a winding of a metal tape 24, which maintains the sectors 22 in their cylindrical helix configuration, so that the cross-section of the conductor of the core 20 is kept as nearly circular as possible. On the metal tape 24, there is a first, intemal, semi-conductive screen 25 surrounded by a dielectric layer 26 which, in turn, is surrounded by a second, external, semi-conductive screen 27. The latter is protected by a soft, conductive, tubular covering 28 similar to, and for the same purposes as, the covering 16. v

In the embodiment shown in FIG. 2, the soft, tubular covering 28 comprises an internal winding 29 of semiconductive crepe paper and an external winding 30 of a known type of cloth made of glass fibers and containing intercalated metal wires, namely, good electrically conductive elements which, extending from one part of the cloth to the other, can conductively interconnect What is claimed is:

1. An electric cable comprising at least one core including a conductor surrounded throughout substantially its length by at least one layer of insulating material and an external screening layer of at least semiconductive material surrounding said insulating layer,

a corrugated metal sheath surrounding said core and a tube comprising solid, at leat semi-conductive material intermediate said core and said sheath and in frictional engagement and electrical contact with said screening layer and said sheath and at least partially filling the two contiguous layers between which the cloth of glass fibers containing intercalated metal wires is interposed. In the embodiment shown, a conductive connection is established between the internal winding 29 of semiconductive crepe paper of the soft, tubular covering 28 and the corrugated sheath 21.

The cloth of glass fibers 30 containing intercalated metal wires has also the advantages of acting as a thermal and mechanical protector of the core 20 in the excorrugations of said sheath to prevent slipping of said core with respect to said sheath and to conductively interconnect said screening layer and said sheath, said tube beings self-sustaining, resilient and softer than the material of said core to permit defomiation of said tube by the corrugations of said sheath without substantial deformation of said core and said tube having a shear strength sufficient to prevent said slippage without shearing when said cable is suspended by said sheath.

2. An electric cable comprising at least one core including a conductor surrounded throughout its length by at least one layer of insulating material and an external screening layer of at least semi-conductive material surrounding said insulating layer, a corrugated metal sheath surrounding said core, and a tube of solid, at least semi-conductive, material intermediate said core and said sheath with the corrugations of said sheath embedded in said tube for preventing slipping of said core and said sheath relative to each other in a direction extending longitudinally of said cable when said cable is suspended by said sheath and for conductively interconnecting said screening layer and said sheath, said tube comprising at least one tape made of an insulating material different from that of said insulating layer, deformable by the corrugations of said sheath and having a normal exterior size in the absence of deformation thereof by said corrugations which is greater than the minimum diameter of said corrugations so that portions of said tube at least partially fill said corrugations and said tube encircling said core and having at least a portion of its interior in frictional engagement with the exterior of said core thereby to provide a tube of solid material between said core and said sheath in frictional engagement with both said sheath and said core which substantially prevents significant relative movement between said core and said sheath longitudinal of said cable when said cable is suspended by said sheath, said material of said tape being softer than the material of said core so as to permit deformation and compression of said tube by said corrugations of said sheath without substantial deformation of said core and said material of said tape also being self-sustaining and resilient and having a shear strength sufficient to prevent said relative movement without shearing thereof.

3. An electric cable comprising at least one core including a conductor surrounded throughout substantially its length by at least one layer of insulating material and an external screening layer of at least semiconductive material surrounding said insulating layer, a corrugated metal sheath surrounding said core and a tube of semi-conductive tape of crepe paper wound around said screening layer and intermediate said core and said sheath and in frictional engagement and electrical contact with said screening layer and said sheath and at least partially filling the corrugations of said sheath to prevent slipping of said core with respect to said sheath and to conductively interconnect said screening layer and said sheath, said tube being selfsustaining, resilient and softer than the material of said core to permit deformation of said tube by the corrugations of said sheath without substantial deformation of said core and said tube having a shear strength sufficient to prevent said slippage without shearing when said cable is suspended by said sheath 4. An electric cable comprising at least one core including a conductor surrounded throughout substantially its length by at least one layer of insulating material and an external screening layer of at least semiconductive material surrounding said insulating layer, a corrugated metal sheath surrounding said core and a tube of semi-conductive tape of crepe paper wound around said screening layer and a further winding of glass fiber cloth containing intercalated metal wires wound around said tape and intermediate said core and said sheath and in frictional engagement and electrical contact with said screening layer and said sheath and at least partially filling the corrugations of said sheath to prevent slipping of said core with respect to said sheath and to conductively interconnect said screening layer and said sheath, said tube being self-sustaining, resilient and softer than the material of said core to permit deformation of said tube by the corrugations of said sheath without substantial deformation of said core and said tube having a shear strength sufficient to prevent said slippage without shearing when said cable is suspended by said sheath.

5. An electric cable comprising at least one core including a conductor surrounded throughout its length by at least one layer of insulating material and an external screening layer of at least semi-conductive material surrounding said insulating layer, a corrugated metal sheath surrounding said core, and a tube of solid, at least semi-conductive, material intermediate said core and said sheath with the corrugations of said sheath embedded in said tube for preventing slipping of said core and sid said tube for preventing slipping of said core and said sheath relative to each other in a direction extending longitudinally of said cable when said cable is suspended by said sheath and for conductively interconnecting said screening layer and said sheath, said tube comprising at least one tape made of an insulating material different from that of said insulating layer and being made of semi-conductive crepe paper and said tube being deformable by the corrugations of said sheath and having a normal exterior size in the absence of deformation thereof by said corrugations which is greater than the minimum diameter of said corrugations so that portions of said tube at least partially fill said corrugations and said tube encircling said core and having at least a portion of its interior in frictional engagement with the exterior of said core thereby to provide a tube of solid material between said core and said sheath in frictional engagement with both said sheath and said core which substantially prevents significant relative movement between said core and said sheath longitudinally of said cable when said cable is suspended by said sheath, said material of said tape being softer than the material of said core so as to permit deformation and compression of said tube by said corrugations of said sheath without substantial deformation of said core and said material of said tape also being self-sustaining and resilient and having a shear strength sufficient to prevent said relative movement without shearing thereof.

6. An electric cable as set forth in claim 5, wherein said tube comprises a winding of glass fiber cloth containing intercalated metal wires would around said tape.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECHQN Patent No. 3 843 830 Dated October 22 1974 Inventor) PAOLO GAZZANA PRIAROGGIA and GABRIELE MASCHIO It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 4 (claim 1) line 25 "beings" should read -being I Col. 6 (claim 5) line 9 is a combination of lines 8 and 10 and should be deleted Signed and sealed this 1st day of July 1975.

(SEAL) Attest:

C. MARSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officer and Trademarks UNITED STATES PATENT OFFICE 3 CERTIFICATE OF CORRECTION Patent No. 3,843,830 'Dated October 22, 1974 Inventor s PAOLO GAZZANA PRIAROGGIA and GABRIELE MASCHIO It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 4 (claim l) line 25 "beings" should read -b eing- Col. 6 (claim 5) line 9 is a combination of lines 8 and 10 and should be deleted.

Signed and sealed this 1st day of July 1975.

(SEAL) Attest:

C. I-IARSHALL DANN RUTH C. MASON Commissioner of Patents Arresting Officer and Trademarks

Claims

1. An electric cable comprising at least one core including a conductor surrounded throughout substantially its length by at least One layer of insulating material and an external screening layer of at least semi-conductive material surrounding said insulating layer, a corrugated metal sheath surrounding said core and a tube comprising solid, at leat semi-conductive material intermediate said core and said sheath and in frictional engagement and electrical contact with said screening layer and said sheath and at least partially filling the corrugations of said sheath to prevent slipping of said core with respect to said sheath and to conductively interconnect said screening layer and said sheath, said tube beings self-sustaining, resilient and softer than the material of said core to permit deformation of said tube by the corrugations of said sheath without substantial deformation of said core and said tube having a shear strength sufficient to prevent said slippage without shearing when said cable is suspended by said sheath.

3. An electric cable comprising at least one core including a conductor surrounded throughout substantially its length by at least one layer of insulating material and an external screening layer of at least semi-conductive material surrounding said insulating layer, a corrugated metal sheath surrounding said core and a tube of semi-conductive tape of crepe paper wound around said screening layer and intermediate said core and said sheath and in frictional engagement and electrical contact with said screening layer and said sheath and at least partially filling the corrugations of said sheath to prevent slipping of said core with respect to said sheath and to conductively interconnect said screening layer and said sheath, said tube being self-sustaining, resilient and softer than the material of said core to permit deformation of said tube by the corrugations of said sheath without substantial deformation of said core and said tube having a shear strength sufficient to prevent said slippage without shearing when said cable is suspended by said sheath

4. An electric cable comprising at least one core including a conductor surrounded throughout substantially its length by at least one layer of insulating material and an external screening layer of at least semi-conductive material surrounding said insulating layer, a corrugated metal sheath surrounding said core and a tube of semi-conductive tape of crepe paper wound around said screening layer and a further winding of glass fiber cloth containing intercalated metal wires wound around said tape and intermediate said core and said sheath and in frictional engagement and electrical contact with said screening layer and said sheath and at least partially filling the corrugations of said sheath to prevent slipping of said core with respect to said sheath and to conductively interconnect said screening layer and said sheath, said tube being self-sustaining, resilient and softer than the material of said core to permit deformation of said tube by the corrugations of said sheath without substantial deformation of said core and said tube having a shear strength sufficient to prevent said slippage without shearing when said cable is suspended by said sheath.