GB1579196A

GB1579196A - Forming sheathed jointed cables

Info

Publication number: GB1579196A
Application number: GB28850/77A
Authority: GB
Original assignee: Nordiske Kabel OG Traadfabriker AS
Current assignee: Nordiske Kabel OG Traadfabriker AS
Priority date: 1976-07-09
Filing date: 1977-07-08
Publication date: 1980-11-12
Also published as: DK139859C; NO139371C; SE423585B; SE7707980L; DE2731031B2; NO139371B; CH619077A5; DK310676A; FR2358039A1; DE2731031C3; DK139859B; DE2731031A1; FI772141A; FR2358039B1; FI63843B; FI63843C; NO772360L

Abstract

In this method a cable, which comprises a conductor (1), an inner semiconducting layer (3), an insulating layer (4) and an outer semiconducting layer (5), is bevelled by means of a corresponding bevelling device in such a way that a piece of the conductor (1) is exposed, in order to be welded to a second cable end treated in the same way. Furthermore, during bevelling, the insulating layer (4) is tapered, the said layer being cut off just before it tapers away to the underlying semiconducting layer (3). In this, only the cut surface of the layer (3) is exposed. Following this, an expanding device in the form of a tapering sleeve (6) is pushed between the layer (3) and the conductor (1), whereupon these two are lifted apart and the layer (3) is opened out. Remaining in this position, the intermediate space between conductor and layer (3) is filled with a semiconducting polymeric material. After that, the damaged outer layers are restored by applying the corresponding materials and the necessary after-treatment operations, such as hardening, grinding etc. This avoids cutting partially into the semiconducting layer and its after-treatment. <IMAGE>

Description

(54) FORMING SHEATHED JOINTED CABLES (71) We, AKTIESELSKABET NOR DISKE KABEL-- OG TRAADFABRIKER, a body corporate organised and existing under the laws of Denmark, of La Cours Vej 7, DK-2000 Copenhagen F, Denmark, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a method of forming a semiconductive sheath around a bared jointed region of the conductor of a cable having an inner metallic conductor and at each side of the bared region an end of a semi-conductive polymeric sheath around the conductor and a bevel-ended layer of insulating material around the sheath, and particularly to the jointing of highvoltage cables.

The invention also relates to a sheathed jointed cable produced by the method.

When joining cables the conductor is bared over a suitable length of the cable ends and is subsequently joined by soldering or welding, after which the inner semi-conductive layer, the insulation layer, and the outer semi-conduotive layer are built up, if possible, by means of materials of the same type as in the corresponding layers of the cable.

The built-up of the inner semi-conductive layer is usually performed by bevelling the insulation layer so that a length of the inner semi-conductive layer of both cable ends is bared, after which the bared parts and the conductor joint are wound with a semiconductive, possibly cross-linkable material.

Instead of a winding, moulded sleeve sections may be used.

The built-up, semi-conductive layer is then heated, for instance by being enclosed in a heatable mould so that the layer melts and is bonded to the inner semi-conductive layers of the cable ends and, if desired, is caused to cross-link.

An alternative method, described for instance in DT-AS 24 18 025, consists in winding the insulation layer around the wound, inner semi-conductive layer without effecting an intermediate heat treatment and then surrounding the joining area with a rubber pressure collar and a heat source and melting both layers together.

Both of these alternatives, however, suffer from substantial drawbacks as the bevelling of insulation and baring of the inner semiconductive layer, the thickness of which is usually less than 1 mm, required in both cases are often performed by means of cutting apparatus designed as conventional pencil sharpeners, i.e. they are provided with an angular cutting edge and adapted to be pushed over the cable end and turned thereabout. The use of such pencil sharpeners inevitably results in a helical cut wholly or partly into the semi-conductive layer which, if not treated, will result in a joint having poor properties. As it is necessary to completely bare the inner semi-conductive layer over a length of about 5-10 mm and to smooth sharp edges originating from the cutting apparatus to eliminate field intensity concentrations, the bevelling is completed by a polishing which is usually effected from the conductor end and inwards of the cable.

By this polishing semi-conductive particles are inevitably conveyed to the outermost thin part of the insulation, which results in electric field disturbances in the final joint.

The polishing itself is cumbersome and must be performed with the greatest care as there exists a considerable risk on undesired polishing into the semi-conductive layer resulting in exposure of the conductor.

In the above-mentioned alternative where the build-up, semi-conductive layer is melted and bonded to the inner semi-conductive layers of the cable ends before winding of the insulation layer, there remains partly a surface treatment of the finished layer to remove fins and surface impurities, if any, partly a polishing of edges, if any, in the area adjoining the inner semi-conductive layers of the cable ends, which again involves a risk of polishing of the inner semi-conductive layer and baring of the conductor.

The alternative on which the wound, inner semi-conductive layer is not heat-treated before application of insulation also involves a risk of field disturbances in the areas adjoining the cable since the winding must necessarily be finalized by an overlapping of the inner semi-conductive layer of the cable ends, and the edges of these overlappings may cause filed disturbances.

According ;to the present invention there is provided a method of forming a semiconductive sheath around a bared jointed region of the conductor of a cable having an inner metallic conductor and (at each side of the bared region) an end of a semiconductive polymeric sheath around the conductor and a bevel-layer of insulating material around the sheath; which comprises inserting a tool between the conductor and each sheath end thereby to flare the end outwardly; fixing the outwardly flared sheath ends in their flared position; removing the tool; and forming a semi-conductive bridging sheath about the jointed region of the conductor, to bridge the gap between the sheath ends and to fill the spaces between the conductor and the outwardly flared sheath ends by applying semi-conductive polymeric material to the conductor and heating the material thereby to bond it together to form the bridging sheath and to bond the bridging sheath to the inner surfaces of the flared sheath ends.

In the first place, this method provides a simpler bevelling without risk of conveying impurities onto the insulation and undesired baring of the conductor. The described expansion of the end portion of the bevelled area has the additional effect of giving the joint between the built-up, semiconductive layer and the inner semi-conductive layers of the cable ends a relatively large thickness so that, after cooling of the joint, both the bevelled area and the built-up, semiconductive layer can be subjected to a subsequent machining process, for instance milling or planing, to provide a smooth surface, without risk of baring the conductor and with a smooth junction to the cable insulation.

The expansion finally provides a surface character of the semiconductive layer which ensures good field distribution in the insulation, the reason being that the interfaces are formed of the original semiconductive layers of the cable, fixating in expanded position.

Following the surface treatment, the remaining layers are applied in a manner known per se, for example as described in British Patent Specification No. 1,510,842, Danish Patent Application No. 6380/73 (available to public inspection) or Danish Patent Application No. 3705/74 corresponding to (published) DT-OS No. 2,431,644.

The tool used in the method according to the invention preferably has the form of a seperable body of revolution whose diameter decreases according to a curve towards its free ends and having a through-going axial bore whose diameter is substantially equal to the conductor diameter and substantially equal to the diameter of said free ends.

The external diameter of the tool is so adapted to the internal bore that the edge is so sharp that it may be inserted without difficulties between the semiconductor layer and the conductor, however not so sharp as to damage the semiconductive layer. The external diameter may for example decrease linearly or logarithmically.

According to the present invention in another aspect there is provided a method of jointing cables each having a metallic conductor sheathed by a semiconductive layer and suurounded by a layer of insulating material about the sheath, which comprises baring an end of the metal conductor of each cable, bevelling the end of each insulation layer, jointing the metal conductors and forming a semiconductive sheath about the bared jointed region of the conductor by the method according to the invention recited above.

An embodiment of the invention will be described, by way of an example, with reference to the accompanying drawings, in which: Figure 1 illustrates a cable joint after welding of the conductor and bevelling of the insulation, Figure 2 illustrates the cable joint after expansion of the end portions of the bevelled areas by means of a tool inserted at one side, Figure 3 illustrates the cable joint after winding on the conductor joint a semiconductive tape, and Figure 4 illustrates the cable joint with the finished built-up, semiconductive layer which after heating has been bonded to the inner semi-conductive layers of the cable, after which the insulation and the semiconductive layer have been planed to the desired thickness.

The figures show a multi-wire conductor 1 and the welded conductor joint 2. Around said conductor 1 are an inner semiconductive layer 3 and the insulation 4 which, as it will appear, is bevelled so that the outside of the underlying semiconductive layer 3 is not bared. Outermost is an outer semiconductive layer 5.

Figure 2 shows a removable tool 6 inserted between the conductor 1 and the inner semiconductive layer 3 which is used to expand the end portion of each bevelled area (3a, 4a). To facilitate insertion of the tool 6 and subsequent fixation of 'the material, the end portion 3a, 4a is preferably heated to be softened after which the end portion is left to cool with the tool 6 inserted whereby the end portion is fixed in the expanded position. The opposite side shows an end portion (3b, 4b) thus expanded and fixed.

The bevelled ends and sheath ends are heated before and/or during insertion of the tool 6.

When both end portions have been fixed, the tool 6 is removed and a winding 7 of tape formed of a semiconductive polymeric material is applied to the conductor 1 as shown in Figure 3. Alternatively, one or more moulded sleeve sections can be mounted on the conductor 1.

Hereafter, the winding 7 and a length of the bevelled parts are surrounded by a heatable mould or a pressure- and heatdistributing sheathing and over said sheathing a pressure sleeve and a bent metal sheet and a heating element, analogously with the method described in British Patent Specification No. 1,510,842. This heat and pressure action causes the semi-conductive layer 7 to melt and be bonded to the inner semiconductive layers 3 of the cable. The joint is preferably cooled under continued pressure and heating means, especially if a non-crosslinkable, semi-conductive material has been used.

Depending on the care with which the winding is performed and the apparatus applied during the heating process, there may be obtained an entirely smooth surface or a surface requiring some finishing treatment.

The finishing treatment of the bevelled area and the joint is preferably performed by a machining process, especially by milling or planing. In this manner an entirely smooth surface is obtainable. Morover, said process provides the slightly conical interface 3c without sharp edges from the built-up layer 7a to ;the semi-conductive layer 3 of the cable as shown in Figure 4.

After formation of the sheath a layer of insulating material is formed therearound.

WHAT WE CLAIM IS:- 1. A method of forming a semi-conductive sheath around a bared jointed region of the conductor of a cable having an inner metallic conductor and (at each side of the bared region) an end of a semiconductive polymeric sheath around the conductor and a bevelended layer of insulating material around the sheath; which comprises inserting a tool between the conductor and each sheath end thereby to flare the sheath end outwardly; fixing the outwardly flared sheath ends in their flared position; removing the tool; and forming a semi-conductive bridging sheath about the jointed region of the conductor, to bridge the gap between the sheath ends and to fill the spaces between the conductor and the outwardly flared sheath ends by applying semi-conductive polymeric material to the conductor and heating the material thereby to bond it together to form the bridging sheath and to bond the bridging sheath to the inner surfaces of the flared sheath ends.

2. The method claimed in claim 1, in which the sheath ends do not project beyond the superjacent bevelled ends of the layer of insulating material.

3. The method claimed in claim 1 or claim 2, in which semi-conductive material is applied to the conductor in the form of a winding or one or more moulded sleeve sections.

4. The method claimed in any preceding claim, in which formation of the bridging sheath the sheath is cooled and then, if not of smooth surface, finished to provide a smooth surface.

5. The method claimed in any preceding claim, in which the cable is a cable suitable for high-voltage use.

6. The method claimed in any preceding claim, in which the outwardly flared sheath ends are fixed by heat in their flared positions before removing the tool.

7. The method claimed in claim 6, in which the bevelled ends and sheath ends are heated before and/or during insertion of the tool.

8. The method claimed in any preceding claim, in which during the heating and bonding of the semi-conductive material applied to the conductor, said material is subjected to pressure from a fluid fed under pressure to a pressure sleeve wrapped about the material, separated therefrom by a pressuredistributive heat-conductive sheathing, and surrounded by a folded metal sheeting.

9. The method claimed in any preceding claim, in which the surface of the bevelled ends of the insulation layer and the surface of the bridging semi-conductive sheath, after formation of the latter, are machined to provide a smooth surface.

10. The method claimed in claim 1, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

11. The method claimed in any of claims 1 to 9, in which the polymeric material applied to the conductor to form the bridging sheath is a cross-linkable polymeric material and is cross4inked during the heating and bonding to form the sheath.

12. A method of jointing cables each having a metallic conductor sheathed by a semiconductive layer and surrounded by a

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the end portion of each bevelled area (3a, 4a). To facilitate insertion of the tool 6 and subsequent fixation of 'the material, the end portion 3a, 4a is preferably heated to be softened after which the end portion is left to cool with the tool 6 inserted whereby the end portion is fixed in the expanded position. The opposite side shows an end portion (3b, 4b) thus expanded and fixed. The bevelled ends and sheath ends are heated before and/or during insertion of the tool 6. When both end portions have been fixed, the tool 6 is removed and a winding 7 of tape formed of a semiconductive polymeric material is applied to the conductor 1 as shown in Figure 3. Alternatively, one or more moulded sleeve sections can be mounted on the conductor 1. Hereafter, the winding 7 and a length of the bevelled parts are surrounded by a heatable mould or a pressure- and heatdistributing sheathing and over said sheathing a pressure sleeve and a bent metal sheet and a heating element, analogously with the method described in British Patent Specification No. 1,510,842. This heat and pressure action causes the semi-conductive layer 7 to melt and be bonded to the inner semiconductive layers 3 of the cable. The joint is preferably cooled under continued pressure and heating means, especially if a non-crosslinkable, semi-conductive material has been used. Depending on the care with which the winding is performed and the apparatus applied during the heating process, there may be obtained an entirely smooth surface or a surface requiring some finishing treatment. The finishing treatment of the bevelled area and the joint is preferably performed by a machining process, especially by milling or planing. In this manner an entirely smooth surface is obtainable. Morover, said process provides the slightly conical interface 3c without sharp edges from the built-up layer 7a to ;the semi-conductive layer 3 of the cable as shown in Figure 4. After formation of the sheath a layer of insulating material is formed therearound. WHAT WE CLAIM IS:-

1. A method of forming a semi-conductive sheath around a bared jointed region of the conductor of a cable having an inner metallic conductor and (at each side of the bared region) an end of a semiconductive polymeric sheath around the conductor and a bevelended layer of insulating material around the sheath; which comprises inserting a tool between the conductor and each sheath end thereby to flare the sheath end outwardly; fixing the outwardly flared sheath ends in their flared position; removing the tool; and forming a semi-conductive bridging sheath about the jointed region of the conductor, to bridge the gap between the sheath ends and to fill the spaces between the conductor and the outwardly flared sheath ends by applying semi-conductive polymeric material to the conductor and heating the material thereby to bond it together to form the bridging sheath and to bond the bridging sheath to the inner surfaces of the flared sheath ends.

layer of insulating material about the sheath, which comprises baring an end of the metal conductor of each cable, bevelling the end of each insulation layer, jointing the metal conductors and forming a semi-conductive sheath about the bared jointed region of the conductor by a method according to any of claims 1 to 11.

13. The method claimed in claim 12, in which after formation of the sheath a layer of insulating material is formed therearound.

14. A sheathed jointed cable produced by a method according to any preceding claim.