Stainless steel screen and non-insulating jacket arrangement for power cables

Abstract

A cable including a conductor. An insulation system surrounds the conductor. A metallic screen surrounds the insulation system. A jacket surrounds the insulation system. The metallic screen is constructed of stainless steel.

Claims

1. A cable comprising: a conductor; an insulation system directly surrounding the conductor, wherein the insulation system is a three part insulation system that includes a semi-conductive polymer layer surrounded by an insulative polymer layer surrounded by a semi-conductive polymer layer; a metallic screen directly surrounding, and in contact with, the insulation system; and a conductive jacket surrounding the metallic screen, wherein said metallic screen is constructed of non-corrugated stainless steel, and wherein said conductive jacket includes sufficient carbon black density added to control sheath voltage by reducing the accumulation of induced sheath voltage, but simultaneously does not include sufficient carbon black density that would allow accumulation of circulating currents.

2. The cable as claimed in claim 1, wherein the metallic screen is bonded to either one of an outside surface of the insulation system or an inside surface of said jacket.

3. The cable as claimed in claim 1, wherein said metallic screen is less than 0.5 mm thick.

4. A cable comprising: a conductor; an insulation system directly surrounding the conductor, wherein the insulation system is a three part insulation system that includes a semi-conductive polymer layer surrounded by an insulative polymer layer surrounded by a semi-conductive polymer layer; a stainless steel non-corrugated metallic screen directly surrounding, and in contact with, the insulation system; and a conductive jacket surrounding the metallic screen, wherein said jacket includes conductive particles, and wherein said conductive jacket includes sufficient carbon black density added to control sheath voltage by reducing the accumulation of induced sheath voltage, but simultaneously does not include sufficient carbon black density that would allow accumulation of circulating currents.

5. The cable as claimed in claim 4, wherein the metallic screen is bonded to either one of an outside surface of the insulation system or an inside surface of said jacket.

6. The cable as claimed in claim 4, wherein said metallic screen is less than 0.5 mm thick.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention can be best understood through the following description and accompanying drawings, wherein:

(2) FIG. 1 is a prior art underground electric cable according to the prior art;

(3) FIG. 2 is an underground electric cable according to one embodiment;

(4) FIG. 3 is a multi-phase underground electric cable according to the embodiment of FIG. 2;

(5) FIG. 4 is an underground electric cable according to one embodiment; and

(6) FIG. 5 is a multi-phase underground electric cable according to the embodiment of FIG. 4.

DETAILED DESCRIPTION

(7) In one embodiment of the present arrangement as shown in FIG. 1, an underground electric cable 10 has a primary conductor 12 surrounded by a three part insulation system of a semiconductor layer 14, an insulator layer 16 and a semiconductor layer 18. This three part insulation system 14/16/18 is covered by a metallic screen 20 and cable 10 is finally surrounded by a jacket 22.

(8) Unlike the prior art, metallic screen 20 is a preferably (<0.5 mm) laminate of stainless steel, preferably without corrugation, firmly bonded to either an outside surface of cable core (semiconductor layer 18) or to an inside surface of cable jacket 22. The low conductivity of stainless steel laminate screen 20 reduces the losses from circulating current and eddy currents in the metallic sheath of the individual cable cores owing to its lower conductivity relative to prior art screens. The preferably non-corrugated application of the laminate screen 20 allows for a reduction of the odiameter of cable 10. The firm bonding of screen/laminate 20 to either jacket 22 or semiconductor layer 18 allows for improved bending tolerances for cable 10 and likewise prevents wrinkling of screen 20 as the bonded elements will move together and not move (abrasion) relative to one another.

(9) In an alternative embodiment, shown in FIG. 3, a three phase cable 100 is shown. Cable 100 has three cores each having conductors 102, semiconductor layers 104, insulation 106, and semiconductor layer 108. As with cable 10, in cable 100, each of the cores has a metallic screen 110 and jacket 112. The metallic screen 110 is a preferably (<0.5 mm) laminate of stainless steel preferably without corrugation, firmly bonded to either the outside of semiconductor layer 108 or to the inside of cable jacket 112. Outside of the cores, the three phases are surrounded by a steel pipe 114 with a polymer coating 116.

(10) FIG. 4 shows another embodiment of the present arrangement for a cable 200 with a non-insulating outer jacket 222. This arrangement can be used in conjunction with prior art structures (having copper/aluminum sheaths) as well as with cable design implementing the stainless steel screen 20/110 described above.

(11) In FIG. 4, an underground electric cable 200 has a primary conductor 212 surrounded by a three part insulation system of a semiconductor layer 214, an insulator layer 216 and a semiconductor layer 218. This three part insulation system 214/216/218 is covered by a metallic screen 220, with all of the components of cable 200 being surrounded by a jacket 222.

(12) Unlike the prior art jackets, jacket 222 is preferably made from Poly Ethylene, Poly Amide, Poly Esther with included conductive charge carrying particles (Carbon Black). Jacket 222 may be extruded onto and firmly bonded to metallic screen 218 (lead, copper laminate, aluminum laminate or steel laminate). The amount of conductivity (i.e. carbon black density) added to non-insulating jacket 222 is sufficient to control sheath voltage by reducing the accumulation of induced sheath voltage, but simultaneously not conductive enough to allow for its own significant circulating currents.

(13) In an alternative embodiment, shown in FIG. 5, a three phase cable 300 is shown. Cable 300 has three cores each having conductors 302, semiconductor layers 304, insulation 306, and semiconductor layer 308. As with cable 200, each of the cores of cable 300 has a metallic screen 310 and jacket 312. The metallic screen 310 is a preferably (<0.5 mm) laminate of stainless steel preferably without corrugation, firmly bonded to either the outer surface of semiconductor layer 308 or to the inner surface of cable jacket 312. Metallic screen 310 could otherwise be a copper or aluminum screen (prior art), but ideally is made of stainless steel. The jackets 312 are made from Poly Ethylene, Poly Amide, Poly Esther) with included conductive charge caring particles (Carbon Black) are applied by extrusion onto and is firmly bonded to the metallic screen 310, with an amount of conductivity sufficient to reduce the accumulation of induced sheath voltage, but simultaneously not conductive enough to allow for its own significant circulating currents. Outside of the cores, the three phases are surrounded by a steel pipe 314 with a polymer coating 316.

(14) While only certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes or equivalents will now occur to those skilled in the art. It is therefore, to be understood that this application is intended to cover all such modifications and changes that fall within the true spirit of the invention.