GB2091029A

GB2091029A - Electric traction cable

Info

Publication number: GB2091029A
Application number: GB8133743A
Authority: GB
Original assignee: ECA SA; SOC ECA
Current assignee: ECA SA; SOC ECA
Priority date: 1980-12-30
Filing date: 1981-11-09
Publication date: 1982-07-21
Also published as: DE3146238A1; FR2497392A1; GB2091029B; DE3146238C2; FR2497392B1

Abstract

An electric cable has at least one connecting terminal 6 adapted to transmit mechanical traction forces and comprises at least one bundle of wires 1 e.g. of steel or bronze, to provide mechanical strength and conduct electricity. The bundle is secured to the terminal, so as to transmit traction forces, by a bronze cone 12 around the inner strand 1a and conical bronze sleeves 10 with hard plastics linings 11 around the remaining strands. A bundle 3 of armouring wires is secured between sleeve 10 and plastics sleeve 9. Insulating washer 20 and metal washer 21 are provided in the terminal 6. The inner strand 1a may be replaced by an optical fibre bundle. <IMAGE>

Description

SPECIFICATION Electric traction cable The technical sector of the invention is that of electric traction cables.

It is known that cables of this type have a dual function. On the one hand, they withstand a traction force which is applied to their two ends, or when passing over pulleys or drums; on the other hand, they transmit electrical energy either for supplying power to an apparatus located at one end, or for feeding information in one or other direction. In the current state of the art, in the case of high-performance cables, each of these two functions is performed by a different type of component of the cable.

A good resistance to traction is ensured by an armoring or bundle consisting of wires (steel, bronze) or of natural fibers (hemp, manila) or synthetic fibers (glass, aramide). A good electrical conductivity is obtained with wires or braiding made of copper or aluminum. Optical fibers (glass, silica), relayed at their ends by opto-electronic couplers, are also used for transmitting information. Metal braiding furthermore screens the conductors from the stray electromagnetic fields. Other components, made of plastic, ensure the electrical insulation, the dielectric properties, the corrosion resistance and the necessary leaktightness according to the applications.

Finally, the electric traction cables are equipped at their two ends with, on the one hand, mechanical clamps ("socks", terminals) and, on the other hand, electrical connectors, optionally associated with opto-electronic couplers.

The known electric traction cables exhibit disadvantages.

During their use, electric traction cables are subjected not only to the nominal traction force but also to mechanical stresses which can be extremely severe, for example during passage over pulleys or drums, creating alternate tensions and flexions in several directions, crushing on storage drums, sudden traction, and vibrating traction or flexion.

The known electric traction cables have a very heterogeneous constitution which is generally devoid of perfect axial symmetry. Where the metal components offer precision of the order of a hundredth of a millimeter in respect of their thickness or their diameter, the dimensions of the plastic components are at best within a tenth of a millimeter. As a result, the bundles of wires or fibers operate under poor conditions and, consequently. provide poor protection for the copper or aluminum conductors. The various wires stretch, form loops and break. The broken steel wires pierce the sheaths provided for leaktightness.

Consequently, it is recognized that electric traction cables never have a high durability.

Now, it is not always possible to separate the two functions into two different cables, namely an electric cable and a traction cable. In many applications, the two cables must be very close to one another and, whether they are placed in the air or immersed, the risks of entanglement are excessive, in particular in the cases where winds or currents are involved.

Furthermore, in numerous cases, electric traction cables are used immersed, either statically or under tow, and they are thus subjected to currents. The hydrodynamic resistance, which is the main cause of the traction force in these cables, is proportional to their diameter and it is found that it is frequently too high for the known cables.

An object of the invention is to create an electric traction cable which does not exhibit the disadvantages mentioned and is distinguished by a high mechanical durability and a low hydrodynamic resistance.

The invention thus relates to an electric traction cable designed for transmitting mechanical traction forces and electric currents and comprising at least one bundle of wires (which can be twisted into strands) which imparts to the cable its mechanical resistance towards the said traction forces and is mechanically joined, at each end of the cable, to an anchoring terminal.

According to the invention, in a cable of this type, each bundle of wires providing its mechanical strength is electrically insulated, its mechanical connection has regard for its electrical insulation, and it can carry an electric current, the said bundle being electrically connected, at each end of the cable, to an electrical conductor for the input or output of the said electric current.

Thus, in a cable according to the invention, it is the same constituent elements of the cable, namely the bundles of wires (for example steel wires) contained therein, which perform the dual function of the cable, that is to say withstanding the traction force and transmitting the electric current. Special copper or aluminum conductors therefore become unnecessary for conveying the electric current which the cable has to carry. The omission of these conductors results in a cable of very high durability because of its homogeneity, very simple and compact structure and reduced cost.

The use of the cable according to the invention imposes one condition. The known electric traction cables generally comprise a large number of mutually insulated copper conductors for performing different functions, namely supplying electric power in some cases and transmitting various signals in others. With only two or not many more than two bundles of wires, it is necessary, in order to ensure these multiple functions, to use electronic sequential-logic or multiplexing equipment at the two ends of the cable. However, these techniques are now well known.

The electrical conductivity of steel, which is about ten times less than that of copper, is not a disadvantage, because the cross-section of steel in the cable is much more than ten times greater than that which copper conductors would have.

As had already been mentioned, it is important, in the electric traction cable according to the invention, for the mechanical clamps required at its ends to ensure, at the ends, the electrical separation between the various conducting bundles of the cable, which are furthermore insulated by layers of insulating material over the entire length of the cable.In the case of a cable comprising one or more bundles of which the mechanical connection is effected by wedging and self-locking of the ends of the wires or metal strands between the cone-shaped internal surface presented by the anchoring terminal and a force-fitted central conical part, the bundle or bundles should be cylindrical and arranged coaxially in the cable (an arrangement which is moreover advantageous in all cases), each bundle should be electrically insulated and the ends of its wires or stands should be inserted between a conducting part in the shape of a male cone and an insulating part in the shape of a female cone, the corresponding electrical connection conductor (which ensures the input or output of the current) being connected to the said conducting part.

In a particular embodiment, a cable according to the invention then comprises two coaxial cylindrical bundles of wires, electrically insulated from one another, each of which is mechanically and electrically connected to each end of the cable by a connecting unit comprising, from the outside to the inside, the mechanical anchoring terminal, a first insulating conical sleeve, the end of the outer bundle bared and opened out into a cone, a conducting conical sleeve, a second insulating conical sleeve, the end of the inner bundle, also bared and opened out into a cone, and a conducting cone consisting of the abovementioned conical central part, the two corresponding electrical connection conductors being connected respectively to the said conducting conical sleeve and to the said central conical part.

In a first variant of a unit for mechanical and electrical connection of the cable, self-locking conical sleeves are not used, but, at the end of each bundle of wires of the cable, a ring is crimped or welded which ensures an electrical connection between the wires of the bundle and to which the corresponding electrical connection conductor is connected, and, for the purpose of the mechanical connection of the cable, the wires, spread out and shaped into hooks, are trapped in an insulating material bonded to the anchoring terminal.

In another variant, the arrangement of the mechanical connection is different from the arrangement of the electrical connection. The ends of the wires of the cable are only connected electrically and, for the purpose of its mechanical connection, the cable is enclosed over a great length by large wires pre-shaped into a helix and fastened in the anchoring terminal by being wedged between the cone-shaped internal surface presented by the said terminal and a force-fitted central conical part.

Preferably, the conductor or conductors for electrical connection to the bundle or bundles of wires of the cable originate from an electric cable extending the electric traction cable and mechanically fixed to the anchoring terminal.

In the case where the cable has to transmit information at very high speed, for example for television pictures, conducting bundles of large diameter are not suitable. The impedance characteristic of the cable, which contains a relatively small amount of dielectric material, is low and the attenuation would be excessive. For this kind of use, the cable is advantageously completed by one or more optical fibers contained inside a sheath. The cable can then comprise, axially, an optical cable containing one or more fibers, which passes coaxially through the central conical part which may have been used, and can extend into the said electric cable, either by means of another optical cable, with the interposition of an optical coupler, or by means of electrical conductors, with the interposition of an optoelectronic coupler housed in the terminal.

The description which now follows, with reference to the single plate of drawings attached by way of a non-limiting example, will provide a clear understanding of how the present invention can be put into practice, whilst at the same time indicating a multiplicity of possible variants.

Figure 1 shows, in the cross-section, a cable according to the invention in a preferred embodiment.

Figure 2 shows, in longitudinal section, on a scale reduced by a factor of two, a mechanical terminal of this cable, also according to the invention and in a preferred embodiment.

The cable 5 shown possesses, from the center to the periphery, an inner armoring or bundle 1 consisting, for example, of 7 strands each containing 1 9 wires made of galvanized steel, stainless steel or bronze, an insulating layer 2 made of a plastic such as polyethylene, polypropylene, PVC, polyurethane, polytetrafluoroethylene or the like, an outer armoring or bundle 3 consisting, for example, of 25 strands each containing 19 wires, as above but smaller, and an insulating and protecting outer sheath 4 made of plastic, as above. In the case shown, the surface areas, in cross-section, of the two bundles are equal, so that the latter offer substantially the same mechanical resistance to traction and the same electrical conductance. The two bundles 1 and 3 are preferably assembled in helices wound in opposite directions, so that a traction force applied to the cable 5 does not result in a twisting torque ("anti-twist" cable). If the cable is to be immersed, the outer sheath 4 is preferably leaktight so as to preserve its insulating properties in this case.

If it is to be immersed in the sea, the cable 5 can be restricted to the inner bundle 1 and the insulating layer 2, the electrical return taking place via the sea water, with the aid of consumable electrodes.

On the contrary, the inner bundle 1 can be replaced at least partially by single conductors, coaxial cables, twin cables or quad cables, assembled in various ways.

A valuable arrangement consists in replacing the central strand 1 a of the inner bundle 1 by an optical cable 1 b. The latter can comprise a fiber or several optically separate fibers each forming a helix and sliding freely inside a sheath, for withstanding, without stresses, the elongations and flexions of the whole cable. A cable 5 made up in this way, with optical fibers at the center, can withstand traction forces and large mechanical stresses by being anti-twist, and can transmit electrical power and low-frequency information by means of its two bundles of strands 1 and 3, and low-frequency and high-frequency information, in both directions, by means of its axial optical fibers.

Figure 2 shows the connecting unit placed at one end of the cable 5 in order to ensure its mechanical connection and electrical connection.

The cable 5 is engaged in a terminal 6 to which it is fastened, as will be explained, in order to apply the traction force of the cable to a structure or a vehicle. An electric or opto-electric extension cable 7 emerges at the other end of the terminal 6 and makes it possible to transmit the electrical energy or the signals which are emitted or received by an apparatus supported by the structure or the vehicle.

The terminal 6, which ensures the mechanical connection of the cable 5, is fixed to the structure or the vehicle by screwing, either directly or, preferably, in an articulated manner by means of two screws bearing in pockets 8 located diametrically on the terminal, or via a universal joint.

In the example shown in Figure 2, the strands or the wires of the bundles 1 and 3, bared over a certain length, are fastened to the terminal 6 by self-locking between two cones, according to a known arrangement; however, according to a characteristic peculiar to the invention, they are not all placed in this way, by locking, at the same potential as the metal mass of the terminal 6, but, on the contrary, each bundle remains insulated.

The body of the terminal 6 constitutes a female cone into which an insulating conical sleeve 9, made of a hard plastic such as "RILSAN", technical-grade "NYLON", "HOSTAFORM", "DELRIN" or the like, is threaded. The grip of this sleeve in the cone can be improved by gluing or by indenting the surface of the cone.

The outer bundle 3 is locked between this female cone, insulated in this way, and a mixed conical sleeve 10/11. The mixed sleeve consists of a metal sleeve 10, preferably made of bronze, into which a hard plastic sleeve 11 is threaded. The grip of the plastic sleeve in the metal sleeve is ensured by the pressure used to drive it in; it is improved, if appropriate, by gluing or by indenting the internal surface of the metal sleeve 10.

The inner bundle 1 is locked between the mixed sleeve 10/11 and a metal male cone 12, preferably made of bronze. This cone can possess an axial channel to allow either an optical cable 1 b, or the central metal strand 1 a of the cable, to pass through. In the latter case, the cone 12 possesses one or two slits 1 3 for ensuring the self-locking of the central strand.

The operation for mounting a terminal 6 for mechanical connection at each end of a cable 5 preferably takes place in the following manner.

The cable is stripped over the desired lengths of its outer insulation sheath 4 and inner insulation sheath 2.

The terminal 6, equipped beforehand on the inside with the insulating sleeve 9, is threaded over the end of the cable. The whole is held vertical as indicated in Figure 2 and the terminal 6 simply rests on the outer sheath 4 of the cable.

The various strands of the outer bundle 3 are attached to an appropriate special tool so that, by applying a vertical traction force between the tool and the cable 5, each strand is subjected to the same tension. The mixed sleeve 10/11 is then threaded between the outer bundle 3 and the inner bundle 1 and, with the aid of a tube, it is driven with a mallet inside the outer bundle 3, which it presses firmly against the internal surface, forming a female cone, of the terminal 6.

Then, the male cone 12 is driven in the same manner inside the inner bundle 1, its strand being kept under tension by the special tool, the axial strand 1a or the optical cable ib being allowed to pass through.

The mechanical strength of the unit is tested by detaching the strands from the special tool and by applying the traction force directly to the mechanical terminal 6, for example by means of two screws screwed into a structure and bearing in the holes 8.

The electrical or opto-electrical connection of the electric traction cable 5 is produced in the following manner.

The various metal strands are cut flush with the terminal 6 and their ends extending beyond the various cones are covered with insulating sheaths 14, for example made of a heat-shrinkable material. The extension cable 7 can be either an existing cable comprising insulated conductors 15, insulating and protecting sheaths 1 6 and 1 8 and, if appropriate, a braid for resistance to traction 17, or a cable of the same type which is specially produced during assembly, in particular with the aid of heat-shrinkable sheaths.In the case where the electric traction cable 5 comprises a central optical cable 1 b, the latter can continue into the extension cable 7 specially designed for this purpose, as shown, or can terminate in an opto-electronic coupler, housed in the mechanical terminal 6 and connected to several electrical conductors of the extension cable 7.

An insulating washer 20 and a flanged metal washer 21 insulated on its periphery, both of which are pierced with the desired number of holes, are threaded onto the ends of the strands of the bundles 1 and 3, insulated beforehand, and of the conductors 1 5, bared beforehand at their ends.

Some of the conductors 1 5 are brazed in holes provided at the edge of the metal part 10 of the mixed sleeve, and the others in holes similarly provided in the male cone 12, so that an electrical continuity of low resistance is created on the one hand between the inner bundle 1 of the electric traction cable 5 and one or more conductors 1 5 of the extension cable 7, and on the other hand between the outer bundle 3 and one or more other conductors 1 5.

With the connections made in this way, a joint 22 is screwed into the terminal 6 in order to press the central flange of the metal washer 21 onto the male cone 12, and thus to ensure that the various cones are incapable, under the effect of shocks or vibrations, of coming apart and freeing the strands of the cable. To prevent the washer 21 from being rotated when the joint 22 is screwed in, the said washer is provided either with a central "screwdriver" pin anchored in a groove in the male cone 12, or with a lateral pin sliding in a groove provided in the axial direction in the tapping of the terminal 6.

The leaktightness between the terminal 6 and the joint 22 can be ensured by means of an O-ring 23.

If the extension cable 7 comprises a braid for resistance to traction 17, the latter can be firmly joined to the mechanical terminal 6. In a known process, the wires of the braid are pinched between, on the one hand, a ring 24 of semicircular cross-section, enclosing the inner sheath 16 of the extension, and, on the other hand, conical bearings of the joint 22 and of a pressure lining 25, the locking being effected by means of a nut 26 screwed onto the joint 22.

With the assembly of the unit for mechanical and electrical connection thus completed, an adhesive, such as Araldite, can be injected through two orifices 28 in order to form an insulating coating mass inside the terminal 6, so as to improve the mechanical strength, to ensure the leaktightness and the corrosive protection and to ensure the two screwed connections.

Araldite is a Registered Trade Mark.

At the ends of the electric traction cable 5 and of the extension cable 7, molded casings 29 made of a flexible plastic, such as polyurethane, are advantageously made, in accordance with a known process, in order to complete the leaktightness of the cables 5, 7 and of the mechanical terminal 6 and to protect the cables against the effect of excessive flexions.

Whilst at the same time preserving the new principle of the transmission of electricity by means of a metal traction bundle, the invention can be put into effect in a different manner from that which is shown in the drawing.

-The various conical sleeves and the male cone can be omitted; rings are crimped or welded to the various strands of the bundles 1 and 3 so as, on the one hand, to produce shunts between the strands of one and the same bundle, and, on the other hand, to ensure the electrical continuity with conductors 1 5. Moreover, according to a known arrangement, the wires of each strand are spread out and shaped into hooks in order to bear directly in the mass of adhesive 27. In another variant, the cable 5 is enclosed over a great length by large contiguous wires pre-shaped into a helix, which are fastened in the mechanical terminal 6 by selflocking between two cones such as 6 and 1 0.

At its other end, the extension cable 7 is provided with an electrical or opto-electronic connector, which is leaktight if appropriate, making it possible to connect the cable 5 to an apparatus, a structure or a vehicle mechanically linked to the mechanical terminal 6.

Claims

1. Electric traction cable designed for transmitting mechanical traction forces and electric currents and comprising at least one bundle of wires (which can be twisted into strands) which imparts to the cable its mechanical resistance towards the said traction forces and is mechanically joined, at each end of the cable, to an anchoring terminal, wherein each bundle of wires providing the mechanical strength of the cable is electrically insulated, has its mechanical connection regarding for its electrical insulation and can carry an electric current, the said bundle being electrically connected, at each end of the cable, to an electrical conductor for the input or output of the said electric current.

2. Cable according to Claim 1, comprising one or more bundles of which the mechanical connection is effected by wedging of the ends of the wires or metal strands between the coneshaped internal surface presented by the anchoring terminal and a force-fitted central conical part, wherein the bundle or bundles are cylindrical and arranged coaxially in the cable, each bundle is electrically insulated and the ends of its wires or strands are inserted between a conducting part in the shape of a male cone and an insulating part in the shape of a female cone, the corresponding electrical connection conductor being connected to the said conducting part.

3. Cable according to Claim 2, comprising two coaxial cylindrical bundles of wires, electrically insulated from one another, each of which is mechanically and electrically connected to each end of the cable by a connecting unit comprising, from the outside to the inside, the mechanical anchoring terminal, a first insulating conical sleeve, the end of the outer bundle bared and opened out into a cone, a conducting conical sleeve, a second insulating conical sleeve, the end of the inner bundle, also bared and opened out into a cone, and a conducting cone consisting of the abovementioned central conical part, the two corresponding electrical connection conductors being connected respectively to the said conducting conical sleeve and to the said central conical part.

4. Cable according to Claim 1 , wherein, at the end of each bundle of wires, a ring is crimped or welded which ensures an electrical connection between the wires of the bundle and to which the corresponding electrical connection conductor is connected, whilst, for the purpose of the mechanical connection of the cable, the wires, spread out and shaped into hooks, are trapped in an insulating material bonded to the anchoring terminal.

5. Cable according to Claim 1, in which the ends of its wires are only connected electrically, whilst, for the purpose of its mechanical connection, it is enclosed over a great length by large wires pre-shaped into a helix and fastened in the anchoring terminal by being wedged between the cone-shaped internal surface presented by the said terminal and a force-fitted central conical part.

6. Cable according to any one of Claims 1 to 5, in which the electrical-connection or conductors originate from an electric cable extending the electric traction cable and mechanically fixed to the anchoring terminal.

7. Cable according to Claim 6, comprising, axially, an optical transmission cable containing one or more fibres, which passes coaxially through the central conical part which may have been used, and extends into the said electric cable, either by means of another optical cable, with the interposition of an optical coupler, or by means of electrical conductors, with the interposition of an opto-electronic coupler housed in the terminal.

8. Cable substantially as hereinbefore described and shown in the accompanying drawings.