JPH0241843B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a metal wire shield for a power cable having a predetermined number of inter-twisted cable cores, and in particular the metal wire shield is arranged in the interior thereof. The shield is made from a prefabricated thin strip of conductive rubber or plastic material that wraps around the parallel metal wires, and the shield encloses a predetermined number of intertwisted core wires together, thereby The wire relates to a metal wire shield running parallel to the insulated cable core.

[Prior Art] The metal wire shield of a power cable has the role of guiding the current flowing through the insulation layer of the cable core wire, and also prevents the ground fault current from occurring in the event of an operational failure such as dielectric breakdown of the cable insulation layer. It serves as a conductor for Such shields usually consist of a plurality of metal wires or ribbons along the surface of the cable, but can also be integral metal tubes, such as lead.

For example, a metal wire shield made of copper wire,
From the main conductor or phase conductor of the cable, usually
It has a much smaller conducting area. There are standards that specify that the conductors of the shield must have a certain density or maximum average path around the cable. The number of wires in the shield is thereby minimized and the diameter of the wires is relatively small, typically around 1 mm.

A problem with small diameter shielded wires is that due to their low stiffness and high friction against the surroundings, they are easily deformed when the cable is wound onto or from a drum. Stresses are often greater during bending tests, which must be carried out in accordance with the requirements specified in the standard, in which the cable is bent in the outward direction of its diameter. In such cases, the wire shall not be cut or otherwise seriously damaged. Making the substructure as uniform as possible and making the pitch of the normally helically wound shield wire sufficiently small is usually sufficient to meet the specified requirements. The uniformity of a cable body consisting of, for example, three cable conductors can be improved by the aid of a filling shape between the conductors or by the aid of a band around the three conductors. However, these methods require extra material. Similarly, even if the pitch is narrowed,
More metal is required because of the standard requirements prescribed for the conductivity of the shield to be met.

Also known from British Patent No. 644753 is a flexible power cable of electrically conductive rubber composite, the shield comprising several cables arranged parallel to the longitudinal axis of the power conductor. Contains metal wire.
The shield is preformed as a plurality of ribbons that contact the power conductors. One or more ribbons surround the plurality of power conductors individually or collectively.

[Problems to be Solved by the Invention] One object of the present invention is to provide a metal wire shield that reduces the risk of breakage and maintains good bending properties of the cable. Another purpose is to provide a metal wire shield that is protected from corrosion. A third object is to provide a metal wire shield that simplifies the manufacture of shielded power cables.

Means for Solving the Problems The metal wire shield of the present invention consists of a plurality of prefabricated ribbons of flakes equal to the number of core wires, each of these ribbons attached to the outer surface of its corresponding strand. engaging and extending parallel to the centerline of its corresponding conductor.

[Example] The perspective view of a power cable with three core wires is
As shown in the figure, each core comprises a conductor 1, for example of copper or aluminum, on which is extruded a semiconducting layer 2 of, for example, conductive plastic. An insulating layer 3 is extruded onto said layer 2, and furthermore a second semiconducting layer 4, for example of conductive plastic, is extruded onto said insulating layer 3. The cross-section of each conductor is sector-shaped, and the arrangement between the three conductors is such that their cylindrical backs face outward, creating a substantially circular cross-section of the assembled conductors. It is beginning to form a shape.

Around the assembled twisted core wires is a metal wire shield according to a first embodiment of the invention. The shielding is constituted by a separate shielding ribbon 8 for each conductor, ie in this case three shielding ribbons 8. These shielding ribbons 8 are prefabricated and contain a predetermined number of metal wires 7 arranged in parallel and are coated within ribbons of electrically conductive corrosion-protective material, such as electrically conductive rubber or plastic material. embedded in. The shield ribbon 8 is arranged on the back side (outside) of each core wire and extends along each twisted core wire. To the shield wire 7,
In order to give a well-defined position and to ensure that the shield wire retains its position during movement and bending of the cable, the shield wire 7 is preferably covered with conductive rubber or a material that is electrically conductive and protects the wire from corrosion. Embedded within a shielding ribbon 8 of plastic material. The thickness of this layer exceeds the thickness of the wire by several tens of millimeters. When three conductors are housed together in a cable, three shielding ribbons 8 are placed on the back of each conductor, and after the cable is thus constructed, the band 9 is wound, and then the first
As shown in the figure, a jacket 6 made of, for example, plastic is provided on the cable body.

FIG. 2 shows an embodiment of a cable with a core of circular cross section, for small cable dimensions. The core wire shown in FIG.
It is constructed similarly to the core shown in the figure, ie a conductor 1 is surrounded in sequence by a semiconducting layer 2, an insulating layer 3 and a second semiconducting layer 4. In order to obtain a cable of circular cross section with the conductors shown in FIG. 2, the intermediate spaces between the conductors must be filled. This can be achieved, for example, by using a shielding ribbon 8 of the type shown in FIG. 2 and thickening it outwardly along its edges in the manner shown in FIG. The shielding ribbon 8 shown in FIG. 2 also includes a predetermined number of shielding wires 7, which are pre-embedded, for example, in a layer of conductive plastic or rubber material.

For example, as shown in Figure 1, when bending a cable with several core wires arranged in a twisted arrangement, the core wires slide relative to each other, so that the bending causes the center of the wires to align with the outer surface (outward curve) of the cable. This results in a deficiency in the length of the line, which is compensated by a corresponding excess in the inner surface (inward curve). This condition is utilized in the metal wire shield according to the present invention, and since the shield ribbon of the metal wire shield extends along each associated twisted core wire, even if the cable is bent, there will be no tensile force or Not subject to compressive force.

[Effects of the Invention] In the metal wire shield of the present invention, each ribbon engages with the outer surface of the corresponding core wire and extends parallel to the center line of the corresponding core wire, so that the power cable does not bend. The risk of breakage is reduced, as it is not subjected to tensile or compressive forces.

[Brief explanation of drawings]

FIG. 1 shows a first example of a metal wire shield according to the present invention.
FIG. 2 is a perspective view of a power cable according to an embodiment, and FIG. 2 is a cross-sectional view of a power cable according to a second embodiment of the metal wire shield according to the present invention. In the figure, 1... core wire, 2... semiconductive layer,
3... Insulating layer, 4... Semiconductive layer, 6... Jacket, 7... Metal wire, 8... Ribbon, 9... Band.

Claims (1)

[Scope of Claims] 1. A metal wire shield for a power cable having a predetermined number of twisted core wires 1, wherein the shield has a conductive wire that fills around a plurality of parallel metal wires 7 arranged inside the shield. made of prefabricated flakes of rubber or plastic material, said shield encircles said predetermined number of intertwisted core wires 1 together, so that said metal wires of said shield are connected to an insulated cable core. In parallel to the wire, said metal wire shield consists of a plurality of prefabricated ribbons 8 equal to the number of said core wires, each of these ribbons 8 extending outside of its corresponding strand 1. A metal wire shield for a power cable, characterized in that it engages the sides and extends parallel to the center line of its corresponding conductor 1. 2. The metal wire shield for power cables according to claim 1, wherein both side edges of each of the ribbons manufactured in advance are thickened.