US3707595A

US3707595A - Shielded cable

Info

Publication number: US3707595A
Application number: US145356A
Authority: US
Inventors: Walter J Plate
Original assignee: Anaconda Wire and Cable Co
Current assignee: ANACONDA ACQUISITION Co; Ericsson Inc
Priority date: 1971-05-20
Filing date: 1971-05-20
Publication date: 1972-12-26
Anticipated expiration: 1989-12-26

Abstract

In an electric power cable a neutral conductor comprising a plurality of separated wires is applied helically over an electrically conducting cable jacket in which longitudinal wires are embedded. The longitudinal wires serve to distribute any heavy fault currents among all the overlaid helical wires.

Description

United States Patent I 1131 3,707,595

21 7 Appl. No.: 145,356 a [56] References Cited Plate v 2 v 1 1 Dec. 26, 1972 54] SHIELDED CABLE 2 3,355,544 11 1967 Costley et al. ..174 106 R 7 3,351,706 11/1967 Gnerre etal .,..174 105R I 'J' 2,446,387 8/1948 Peterson ..174/105 sc [73] Assignee: Anaconda Wire and Cable Company 1,956,639 5/1934 Dana et'al ..174/106 30 2,337,556 12 1943 HOSkiilg 174/106 sc Flledl M 20, 1971 v H 2,140,270 12/1938 Potter... ..174/115 x Primary Examiner-Hemard A. Gilheany 52 -U.s.c1. 174/11s, 174/105'sc, 174/120 sc Gnmley [51] Int 01b 9/02 An0rney-Victor F. Volk g5C8] Field of Search ..174/102 R, 102 SC,-' 105 R, 105 ABSTRACT 106 106 1 51 R SC in an electric power cable a neutral conductor comf prising a plurality of separated wires is applied helically over an electrically conducting cable jacket in which longitudinal wires are embedded. The longitu- UNITED' STATES PATENTS dinal wires serve to distribute any heavy fault currents 3,474,189 10/1969 Plate et al ..174/115' among all the overlaid helical wires. 2,258,687 10/1941 Peterson v ...174/l l5 1 3,571,613 3/1971 Plate et a1 ..1'74/115 8 Claims, 2 Drawing Figures 8 PQLYMERIC SHEATH .IZINSULATION use-semcomoubnwe JACKET PATENTED nu: 26 I972 Fig,

POLYMERIC SHEATH SEMICONDUCTING N w T A L U S W Q INVENTOR.

W. J. PLATE y Ma-Mf y 1 SHIELDED CABLE BACKGROUND OF THE INVENTION In modern electrical distribution systems it is important that the shielding on primary distribution cables be capable of carrying all the current that is generated during fault conditions. The shielding system must keep within the temperature rating of the cable and, to ascurrent requirements, and there are cases where the I shield must be equivalent to a No. 2 AWG (American Wire Gage) copper conductor. It is known-to form a neutral conductor or shield by winding a plurality of wires in parallel over a cable jacket. A typical example of a helical shield equivalent to a No. 2 AWG copper wire would be 26 No. 16 AWG parallel helical wires. A serious defect in such known shields results from the likelihood that the fault current will be distributed among only a few of the helical wires with a resulting burn-off and relaying malfunction. It has been sug gested to wrap a copper tape over the wires to connect them to each other. This expedient would, however,.be expensive in itself and the fragility of the tape might necessitate the additional expense of a protective sheath over the shielding. It has also been suggested to apply half the shield wires with a left-hand lay and half with a right-hand lay, so that all the wires are interconnected, electrically. With this construction, however, the outer wires slip on the inner helix and do not retain their even separation. They may even bunch up and increase the cable diameter so that an assembly requires more than its alloted share of conduit space.

SUMMARY 1 have invented an electric power cable comprising a power-current carrying conductor, a layer of electrical insulation surrounding the conductor, a semiconducting polymeric jacket surrounding the insulation, a first plurality of circumferentially spaced, longitudinal wires embedded in the jacket, preferably with their outside surfaces tangent to the outer circumference of the jacket, and a second, greater plurality of wires wound helically directly over the jacket. The helical wires are separated from each other but the longitudinal wires interconnect them during a fault. The embedded wires may advantageously be undulatory as disclosed in U.S. Pat. No. 3,474,189 and/or the cable may have longitudinal bosses as disclosed in U.S. Pat. No. 3,571,613.

BRIEF DESCRIPTION OF THE APPENDED DRAWING FIG. l shows a pictorial view of a cable of my invenducting polymeric strand shielding, not separately shown. The conductor 11 is surrounded by a layer 12 of insulation such as polyethylene, ethylene-propylene copolymer, or other dielectric extrudable material of which a number of suitable compositions are known. In intimate contact with the layer 12, I have extruded a jacket 13 of semiconducting polymeric material such as, but not limited to the material disclosed in U.S. Pat. Nos. 3,474,189 and 3,571,613. Six drain wires 14 are embedded in the jacket 13 with their outer surfaces tangent to the surface of the jacket layer. The drain wires 14 are not helically wrapped around the cable, but extend longitudinally in parallel lines that are equally spaced around the cable circumference. The number of the drain wires 14 will depend on the cable diameter, a larger number of wires being used for the larger cables. I prefer, however, that there should be no fewer than three nor more than 12 embedded longitudinal drain wires to obtain the maximum advantage from the present invention. Around the jacket 13 I have helically wound 18 shield wires 16. These are evenly spaced and separated from each other by gaps 17, with the result that the wires 16 have a very long lay. A long lay is an advantage in helical shield wires because of the lower current path and consequently reduced resistance. The entire cable 10 is covered with an extruded polyethylene sheath 18 but this sheath will generally not be required where copper is used for the wires 16. Other materials, such, for two examples, polyvinyl chloride and neoprene are suitable for the sheath 18. FIG. 2 shows a section of a cable similar to that of FIG. 1 except that, instead of the smooth jacket 13 l have extruded a bossed jacket 19 with six radial bosses 21, containing the drain wires 14.

A detailed construction of an underground urban distribution (URD) cable made to my invention is described in the example.

EXAMPLE conductor: mcm 61/wire aluminum, compacted strand shield: extruded semiconducting polymer insulation: cross-linked polyethylene, 0.175 inch wall, diameter 1.46 inch jacket: semiconducting chlorinated polyethylene 0.100 inch wall, diameter 1.67 inch drain wires: 6 No. 15 AWG solid bare soft copper, corrugated, embedded in jacket neutral conductor shield wires: 18 No. 16 AWG solid bare copper separator over shield: polyester tape sheath: high-molecular-weight polyethylene 0.080 inch wall diameter 1.95 inch I have invented a new and useful electric cable of which the foregoing description has been exemplary rather than definitive and for which I desire an award of Letters Patentas defined in the appended claims.

I claim:

1. An electric power cable comprising:

A. a power-current carrying metallic conductor;

B. a layer of electrical insulation surrounding said conductor;

C. a semiconducting polymeric said insulation;

D. a first plurality of circumferentially spaced, longitudinal wires embedded in said jacket; and

E. a second plurality, exceeding said first plurality, of

wires wound helically directly over said jacket,

jacket surrounding 3 4 said helically wound wires being separated from 5. The cable of claim 2 wherein the outside surfaces each Other said longitudinal i es ele rically nv of said longitudinal wires are substantially tangent to terconnecting said helically wound wires during th t r cir umference of said jacket. u 6. The cable of claim 1 comprising an overall 2. The cable of claim I wherein said embedded wires 5 are undulatory.

3; The cable of claim 1 comprising longitudinal bosses in said jacket. Y

4. The cable of claim 1 wherein the outside surfaces of said longitudinal wires are substantially tangent to the outer circumference of said jacket.

polymeric sheath.

7. The cable of claim 2 comprising an overall polymeric sheath.

8. The cable 'of claim 3 comprising an overall polymeric sheath.

3,707,595 December 26, 1972 Patent .No. Dated Walter J. Plate Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 2, line 64 after "spaced" and before the comma insert from each other line 67 before "second" insert 1 neutral conductor comprising a Signed and sealed this 29th day of May 1973.

(SEAL) Attest! EDWARD M.FLETCHER,JR. ROBERT GOTT SCHALK Attesting Officer Commissioner of Patents FORM PO-1 050 (10-69) USCOMM-DC 6O376-P69 u.s. GOVERNMENT rnnmua OFFICE Isis mass-3:4.

CERTIFICATE OF CORRECTION 3 ,707 ,595 December 26, 1972 Patent No. Dated Walter J. Plate Inventor(s) It is certified that error appears in the ab0veidentified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 64 after "spaced" and before the comma insert es from each other line 67 before "second" insert 1 neutral conductor comprising a Signed and sealed this 29th day of May 1973.

(SEAL) Attest! EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM pomso ($69) uscoMM-oc 6037G-P69 .5. GOVERNMENT PRINTING OFFICE 2 l 0365'33.

Claims

2. The cable of claim 1 wherein said embedded wires are undulatory.
3. The cable of claim 1 comprising longitudinal bosses in said jacket.
4. The cable of claim 1 wherein the outside surfaces of said longitudinal wires are substantially tangent to the outer circumference of said jacket.
5. The cable of claim 2 wherein the outside surfaces of said longitudinal wires are substantially tangent to the outer circumference of said jacket.
6. The cable of claIm 1 comprising an overall polymeric sheath.
7. The cable of claim 2 comprising an overall polymeric sheath.
8. The cable of claim 3 comprising an overall polymeric sheath.