NZ200757A

NZ200757A - Cable joint insulation:rollable elastic sleeves

Info

Publication number: NZ200757A
Application number: NZ200757A
Authority: NZ
Inventors: C D Hillyard
Original assignee: Pirelli General Plc
Priority date: 1981-06-03
Filing date: 1982-05-26
Publication date: 1985-04-30
Also published as: GB2099638B; DE3220067A1; ES8309035A1; BE893402A; ES514024A0; IT8221584A0; FR2507403A1; GB2099638A; AU8384582A; SE8203396L; IT1153522B; BR8203197A

Description

4 2007 57 NEW ZEALAND PATENTS ACT, 1953 ^ 6 may 1982 No.: Date: COMPLETE SPECIFICATION IMPROVEMENTS RELATING TO JOINTING AND/OR TERMINATING ELECTRIC CABLES ty We, PIRELLI GENERAL PUBLIC LIMITED COMPANY, a British Company of Thavies Inn House, 3-4 Holborn Circus, London EClN 2QA, England hereby declare the invention for which K/ we pray that a patent may be granted to JV^/us, and the method by which it is to be performed, to be particularly described in and by the following statement:- (followed by la) - 1Q-.

— Improvomontc rolating to jointjjig.— and/or terminating olootrio cables-— This invention concerns improvements in jointing and/or terminating of electric cables and particularly, though not exclusively, is concerned with the jointing and/or terminating of elastomeric cables wherein the 5 conductor insulation comprises an elastomeric material which is commonly extrudfed directly onto the conductor core in manufacture, of the cable and one or more screening and/or other layers are commonly provided overlying the elastomer.

As is well knownj jointing and/or terminating of such elastomeric cables requires removal of some of the cable layers oyer a length of the cable, thfe length of these layers removed being dependent upon the method of jointing and/or terminating employed. Removal of the 15 screening layer or layers gives rise to electrical stresses at the cut end, and the jointing and/or terminating methods employed must take account of these and must incorporate measures to reduce the stresses to acceptable levels. Early jointing and/or terminating 20 procedures required the building up of the cable profile at the joint or terminal location by lapping with tapes and the incorporation of electrically conductive windings of wire or metal foil or tape which were coupled to the cut-back cable screen. Subsequent y, developments employed pre-moulded stress cones formed of epoxy resin material for building up the joint or termination profile, and even more recent developments specifically intended for use in jointing and/or 5 terminating elastomeric cables have provided preformed components of elastomeric material intended to be interference fitted to the cable, such components incorporating semiconductive layers to be made electrically continuous with the cable screen for stress relief 10 purposes.

Preformed components of elastomeric material intended simply to be slipped onto the cut-back cable end at a joint or termination location are described for . example in British Patent Specifications 1 031 9^2, 15' 1 113 841 and i 124 912 of Elastic Stop Nut Corporation of America;. 1 ,0k2 590, 1 142 050 and 1 196 989 of N.V. Nederlandsche Kabelfabrieken; 1 277 217 of Sumitomo Electric Industries Ltd.; and 1 339 502 and 1 348 048 of Amerace Esna Corporation. A disadvantage Of such 20 components is that, to accommodate the many different cable sizes which are available, a large range of component sizes must be provided. Disadvantages arise also in accommodating variations in cable size resulting from manufacturing tolerances^ Another fairly recent proposal has been to use heat-shrink sleeves for cable jointing and terminating as described for example in British Patent Specification No. 1 475 .292 (Raychem Corporation) and in British Patent Specification No. 1 526 397 (Raychem Limited). Proposals 30 have been made to effect stress control in the use of heat shrinkable sleeves by incorporating materials into the heat shrink polymer such as to provide advantageous electrical properties. While the use of heat shrinkable sleeves has proven generally satisfactory, difficulties 35 can arise on account of operator error resulting in there 200757 being voids left in the joint or termination.

Another disadvantage which has manifested itself in the formation of joints, particularly multicore joints, by use of preformed and heat shrinkable components is that, by virtue of the necessity to be able to pass a number of tubular components along the cable to be brought back subsequently to the joint location as the joint is assembled, a greater length of the outer cable layers has to be cut back than is desirable and the joint tends to occupy a longer length of cable than is strictly necessary or desirable.

The present invention resides in a method of jointing or terminating an electric cable, which method includes applying one or more insulating layers over the cable' joint or cable end, each layer consisting of a preformed tubular sleeve of elastic insulating material, and in which method the or each said insulating layer is applied by passing the respective sleeve along the cable, the sleeve at this time being ifi a condition wherein it is rolled up upon itself from one or both of its ends, and then unrolling the sleeve into position over the cable joint or cable end.

The invention, together with features and advantages thereof, will best be understood from consideration of the following description in conjunction with the accompanying drawings wherein Figure 1 shows an exemplary cable joint constructed in accordance, with the present invention; Figure 2 shows a tubular sleeve of elas 2®Q7t - k - material rolled upon itself from each end towards the middle and supported upon a disposable carrier; and Figure 3 illustrates the way in which sleeves provided as in Figure 2 but only single rolled from 5 one end may be utilised in the construction of a cable joint as shown in Figure 1.

Referring first to Figure 1, there is shown therein a joint between two elastomer insulated cables each comprising a central conductor 1, elastomeric in-10 sulating material 2, a semi-conducting elastomeric material or varnished tape screen 6," and a wound metal tape screen k. Other parts of the cable, not shown in the figure, might as is well known comprise a PVC or tape bedding layer overlying the screen k and providing 15 a bedding for armouring wires, and a PVC outer sheath. The cable may be single or multicore. As shown in the figure, the conductor ends of the two cables are secured, for example by crimping, in a metal ferrule 5> the insulation 2 having been cut back to bare the conductor 20 ends. Similarly, the screens 6 and k have been cut back to a predetermined extent and a semi-conducting varnish screen 3 applied for stress relief purposes at the termination of screen 6.

As shown, a stress relief tube 7 is applied to 25 each cable end, the tube 7 comprising for example an elastomeric material loaded with Silicon Carbide for example providing a non-linear electrical resistance characteristic. Semi-conductive material 8, in the form of a lapping of a self bonding plastics tape for 30 example or an appropriate mastic compound, is provided around the ferrule 5 and in the spaces between the ends of the ferrule 5 and the cut-back insulation 2 of each cable. Then, as shown, two electrically insulating layers 9 and 10 are provided each comprising an 35 elastic tube, of rubber for example, and im ? o 7 - .5 - finally a semi-conducting layer 11 comprising a tube of elastic material loaded with carbon for example is provided on the outside of the joint. The tube 11 could be incorporated into the insulating layer 10 as an integral 5 layer thereof, and more or less than the two insulating layers 9 and 10 could be provided.

Figure 2 shows an elastic material sleeve 20 rolled upon itself from each end and .supported upon a disposable carrier 21 provided with weakened portions 10 22 around a central line so as to enable the carrier readily to be broken into two halves which can be extracted and cut off of the cable. The sleeve 20, having been appropriately positioned relative to its desired final position in the finished joint and the 15 carrier 21 having been removed, can be unrolled into place. As will be appreciated, rather than being rolled, the sleeve 20 could be concertina folded on the carrier 21 or layered back and forwards upon itself. The carrier 21, as shown, is of greater diameter at each 20 end than at its middle which serves not only to assist in retaining the sleeve 20 against its elastic tendency to unroll, but also facilitates threading of the carrier over the cable. The rolling up of the sheath 20 onto the carrier 21 can be effected at the factory or at the 25 jointing site.

Figure 3 illustrates an intermediate stage in the formation of the joint of Figure 1. The figure shows the two insulation layers 9 and 10 being unrolled along the joint from left to right, each layer comprising 30 a single rolled-up tube as opposed to the double rolled-up configuration of Figure 2. It is only necessary to thread the rolled up layers onto the cable ends in appropriate sequence, and the joint can be completed simply by unrolling the tubes over the top of one another. 35 By virtue of the use of elastic tubular sleeves 2007 ' in the joint construction, variations in joint geometry can readily be accommodated and fewer components are required to be stocked to enable a range of cable sizes to be jointed. The method of 5 the invention does not require the excessive cutting back of cable screening layers etc. •which is the hallmark of other jointing techniques, and enables short neat joints to be produced with minimal risk of defects through operator error. No heating is required to 10 perfect the joint which avoids the risk of overheating with resulting damage to cable integrity.

Whilst the invention is most advantageous in the jointing of cables where overlong joints are a problem with the conventional jointing methods, the 15 invention is also applicable to cable termination.

The invention is of course not limited to use with elastomeric cables, but can be used for jointing and/or terminating paper insulated cables and various other cable constructions, and for the making 20 of transition joints between dissimilar cable types.

Claims

200757 .what vvve claim

1. A method of jointing or terminating an electric cable, which method includes applying one or more insulating layers over the cable joint or cable end, each layer consisting of a preformed tubular sleeve of elastic insulating material, and in which method the or each said insulating layer is applied by passing the respective sleeve along the cable, the sleeve at this time being in a condition wherein it is rolled up upon itself from one or both of its ends, and then unrolling the sleeve into position over the cable joint or cable end.

2. A method as claimed in claim 1, wherein the or each preformed tubular sleeve is supported upon a tubular carrier in its rolled up condition, the said carrier enabling the sleeve to be passed along the cable by threading of the cable through the carrier.

3. A method as claimed in claim 1 or 2, wherein the said sleeve or sleeves comprise substances such as to provide desired characteristics of electrical resistance, electrical conductivity or anti-tracking.

4. A method as claimed in any one of the preceding claims, wherein two or more said layers are applied super-posed one on top of another.

5. A method as claimed in any one of the preceding claims for jointing electric cables having elastomeric insulation, wherein the elastomeric insulation of the cables to be jointed is cut back to expose respective conductor end portions to be crimped or otherwise connected together, repective pre- JAM 333 -7- __ 200757 formed tubular insulation sleeves in rolled up condition as aforesaid are fitted to one another or both of the cable ends to be jointed, the conductor end portions are then crimped or otherwise connected together, and the preformed sleeves are then unrolled so as to constitute a stress relief tube applied to each cable end, at least one electrically insulating layer extending throughout the cable joint over the stress relief tubes and over the connected conductor end portions, and at least a semiconducting layer overlying the said one or more insulating layers.

6. A method as claimed in claim 1 and substantially as herein described with reference to the accompanying drawings.

7. An electric cable joint or termination fabricated by a method as claimed in any of the preceding claims. t •

8. A method of jointing or terminating an electric cable substantially as herein described with reference to the accompanying drawings. f

9. An electric cable joint or termination substantially as herein described with reference to the accompanying drawings. DATED THIS !l^ DAY OF3S*->o^^, 19*TSS a. j. park & son o- PER ^ AGENTS FOR THE APPLICANTS