CABLE JOINTS AND TERMINATIONS

Abstract: A kit for a cable joint (52) for joining two cables (10). Each cable (10) has an outer sheath (12) and conductors (18). The kit includes conductor sleeves (28) which can be heat shrunk over ferrules (30) which join the conductors (18) together. The kit also includes a consolidation sleeve (26) which can be heat shrunk over all the conductors (18) and a cover sleeve (24) which can be heat shrunk over the consolidation sleeve (24) and which overlaps the outer sheaths (12) of the cables (10). The conductor sleeves (28), consolidation sleeve (26) and the cover sleeve (24) are all made of an elastomer which is radially expanded and heat shrinkable. A kit for a cable termination (89) is also provided. The cable termination kit includes radially expanded, heat shrinkable elastomeric elements (90) and (124).

Description: CABLE JOINTS AND TERMINATIONS FIELD OF THE INVENTION This invention relates to electrical cable joints and terminations. BACKGROUND TO THE INVENTION Heat shrinkable polyolefins (predominantly polyethylene and polyethylene copolymers) have also been available for many years. These materials find very widespread use wherever a quick and convenient method of achieving electrical and/or mechanical insulation is required. Typically an exposed electrical joint between a copper wire and terminal or connector has a short length of heat shrinkable polyolefin tubing slid over the exposed connection. Heat is then applied to the tubing to cause it to shrink radially inwardly to form a snug, electrically insulating cover over the exposed joint. Tubing of this type for low voltage applications is in very common use and is typically made of PVC. More complex shapes are also very commonly used. For example, where a multi-cored cable is to be terminated to make a connection to an electrical supply a moulded, heat shrinkable plastic boot is used. Cold shrink rubber sleeves have also been available for many years. The rubber sleeve is pre-vulcanized and is expanded radially outwardly and supported on an interlocking plastic tape spiral. When the tape is pulled from the inside of the sleeve, the sleeve collapses radially inwardly to form a snug fit over an exposed joint. The weakness of the cold shrink joining and terminating system is that the rubber compound used must be soft enough so that it can be radially expanded. Furthermore, the compressive force it exerts on the plastic spiral must not be so great as to cause premature collapse during storage. Compounding rubber to give good extensibility, low modulus and good recoverability (low permanent set) severely restricts the range of hardnesses available to the rubber compounder. Specifically, the hardness of the element is usually much lower than the adjacent cable sheath or insulation. Furthermore, the extensibihty/recoverability requirement of cold shrink elements severely restricts the freedom of the compounder to impart other desirable properties to the element. Such restrictions can result in high material costs and cold shrink systems are usually expensive. Flexible trailing cables with rubber sheaths have been joined by curing vulcanised rubber in situ around the conductors utilising a heated mould. Such joints are time consuming to make since the vulcanisation time of rubber is typically not less than forty minutes. In addition the moulds and vulcanising press used in the in situ method are expensive and require regular maintenance. SUMMARY OF THE INVENTION According to the invention a kit for a cable joint for joining two cables having outer sheaths and conductors includes at least one radially expanded, heat shrinkable, electrically insulating, elastomeric, conductor sleeve which can in use, upon the application of heat, be shrunk over an electrical joint between individual conductors. The conductor sleeve is preferably made of ethylene propylene rubber. The kit may include at least one radially expanded, heat shrinkable, elastomeric, semi-conductive sleeve which can in use, upon the application of heat, be shrunk over the conductor sleeve. The semi-conductive sleeve is preferably made of ethylene propylene rubber. The kit may include at least one radially expanded, heat shrinkable, elastomeric, oil barrier sleeve which can in use, upon the application of heat, be shrunk over the conductor sleeve. The oil barrier sleeve is preferably made of nitrile rubber. The kit may include a radially expanded, heat shrinkable, elastomeric, consolidation sleeve which can in use, upon the application of heat, be shrunk over at least two individual conductors and their conductor sleeves to consolidate the individual conductors. The consolidation sleeve is preferably made of polychloroprene rubber. The kit may include a radially expanded, heat shrinkable, elastomeric, cover sleeve which can in use, upon the application of heat, be shrunk over the cable joint to provide a cover sleeve for the joint which cover sleeve overlaps the outer sheaths of the two cables. The cover sleeve is preferably made of polychloroprene rubber. The consolidation sleeve is preferably shorter than the cover sleeve so that in use the consolidation sleeve does not overlap the outer sheaths of the two cables. According to another aspect of the invention a method of forming a joint between two cables having conductors and outer sheaths includes the steps of exposing the ends of electrical conductors within the cables, electrically joining respective electrical conductors, and shrinking radially expanded, heat shrinkable, electrically insulating, elastomeric, conductor sleeves over the joints between the respective electrical conductors by heating the conductor sleeves. The method may include the step of shrinking radially expanded, heat shrinkable, elastomeric, semi-conductive sleeves over the conductor sleeves by heating the semi-conductive sleeves. The method may include the step of shrinking radially expanded, heat shrinkable, elastomeric, oil barrier sleeves over the conductor sleeves by heating the oil barrier sleeves. The method may include the step of shrinking a radially expanded, heat shrinkable, elastomeric, consolidation sleeve over the electrical conductors by heating the consolidation sleeve. The method may include the step of shrinking a radially expanded, heat shrinkable, elastomeric, cover sleeve over the electrical conductors by heating the cover sleeve to form a cover sleeve for the joint which cover sleeve overlaps the outer sheaths of the two cables. According to another aspect of the invention a joint between two electrical cables having electrical conductors and outer sheaths includes electrically insulating, elastomeric, conductor sleeves heat shrunk over joints between the respective electrical conductors. The joint may include elastomeric semi-conductive sleeves heat shrunk over the conductor sleeves. The joint may include elastomeric, oil barrier sleeves heat shrunk over the conductor sleeves. The joint may include an elastomeric consolidation sleeve heat shrunk over the electrical conductors. The joint may include an elastomeric, cover sleeve heat shrunk over the electrical conductors to form a cover sleeve for the joint which cover sleeve overlaps the outer sheaths of the two cables. According to another aspect of the invention a kit for an electrical cable termination includes a radially expanded, heat shrinkable, elastomeric boot which can in use, upon the application of heat, be shrunk over a crutch of the electrical cable termination. The boot is preferably made of silicone rubber. The kit may include radially expanded, heat shrinkable, elastomeric, anti- tracking sleeves which can in use, upon the application of heat, be shrunk over individual conductors extending from the crutch of the termination. The anti-tracking sleeves are preferably made of silicone rubber. According to another aspect of the invention a method of forming an electrical cable termination includes the steps of forming a termination crutch with separated conductors extending therefrom, shrinking a radially expanded heat shrinkable, elastomeric boot over the crutch of the termination by heating the boot. The method may include the step of shrinking radially expanded, heat shrinkable, elastomeric, anti-tracking sleeves over the separated conductors by heating the anti-tracking sleeves. According to another aspect of the invention an electrical cable termination includes an elastomeric boot heat shrunk over a crutch of the electrical cable termination. The electrical cable termination may include elastomeric, anti-tracking sleeves heat shrunk over individual separated conductors extending from the crutch. Each anti-tracking sleeve preferably overlaps a turret of the boot. According to another aspect of the invention a kit for a cable joint or cable termination includes at least one radially expanded, heat shrinkable, elastomeric element. According to another aspect of the invention a method of forming a cable joint or a cable termination includes the step of shrinking a radially expanded, heat shrinkable elastomeric element over conductors of the cables being joined or over the conductors of the cable being terminated. According to another aspect of the invention a cable joint or cable termination includes an elastomeric element heat shrunk over the conductors of the cables being joined or over the conductors of the cable being terminated. According to another aspect of the invention a sleeve for use in a cable joint is made of ethylene propylene rubber and is radially expanded and heat shrinkable. BRIEF DESCRIPTION OF THE DRAWINGS Figures 1 to 13 illustrate the steps involved in forming a joint between two cross-linked, polyethylene, 12 kV, 3 core cables; Figures 14 to 20 illustrate the steps involved in forming a joint between two paper insulated, lead covered, 12 kV, 3 core cables; and Figures 21 to 23 illustrate the steps involved in forming a termination on a cross-linked, polyethylene, 12 kV, 3 core cable. DETAILED DESCRIPTION OF THE DRAWINGS Referring firstly to figures 1 to 13, two cross-linked, polyethylene. 12 kV, 3 core cables 10 are each prepared in known fashion as shown in figure 1 for being joined together. Each cable 10 has an outer sheath 12, armouring 14, inner bedding 16 and three copper conductors 18. The copper conductors 18 are covered with copper screening tape 20 and cross-linked, polyethylene insulation 22. Prior to joining the two cables 10 together, a polychloroprene cover sleeve 24, a polychloroprene consolidation sleeve 26 and three ethylene propylene conductor sleeves 28 are slid into position over one of the cables 10 as can be seen in figure 2. These sleeves are all elastomers and are all radially expanded and heat shrinkable. The exposed ends of the copper conductors 18 are joined together by crimping ferrules 30 over the copper conductors 18 as can be seen in figure 3. Semi-conductive tape 32 and then butyl tape 34 are wrapped over the ferrules 30 as can be seen from figures 3 and 4. The conductor sleeves 28 are then slid over the butyl tape 34 and shrunk into position by the application of heat as can be seen in figure 5. The heat is applied by a propane torch initially at the centre of each sleeve to drive air out of the sleeves 28. Care should be taken not to overheat the sleeves 28 since a temperature of about 80°C is sufficient to shrink the sleeves 28. Semi-conductive tape 36. tinned copper mesh tape 38 and black filler profiles 40 are then applied as can be seen from figures 6 to 8. The semi-conductive tape 36 may be replaced with a radially expanded, heat shrinkable, elastomeric semi-conductive sleeves 42 (figure 6) which can be heat shrunk over the conductor sleeves 28. The semi-conductive sleeves 42 would have substantially the same length and a slightly larger diameter than the conductor sleeves 28, so that they can fit over the conductor sleeves 28 in their preshrink configuration. A supporting core (not shown) is removed from the consolidation sleeve 26 which is then centralised over the joint and heat shrunk into position as shown in figure 9. A layer of sealant tape 43 is applied to either end of the cable sheath 12 as shown in figure 9. An earth braid 44 is clamped with clamps 46 to the exposed armouring as can be seen from figure 10. Galvanised steel mesh 48 and white sealant tape 50 are then applied as shown in figures 11 and 12. The cover sleeve 26 is then slid into position after removal of its supporting core (not shown), and heat shrunk into position as shown in figure 13 to complete the cable joint 52. The cover sleeve 26 may consist of two sleeves (not shown) which may be heat shrunk into position to effectively form a single cover sleeve. The sealant tape 43 forms a seal between the cable sheath 12 and the ends of the cover sleeve 26. Referring now to figures 14 to 20, two paper insulated, lead covered, 12 kV, 3 core cables 54 have their conductors joined in known fashion with ferrules 56 as can be seen from figure 14. Each cable 54 has an outer sheath 60, steel tape armouring 62, a lead sheath 64, paper belting 66 and oil barrier paper insulation 68 as can be seen from figure 16. Prior to joining the conductors, conductor sleeves 58, a consolidation sleeve 70 and two cover sleeves 72 are slid into position on the cables 54. These sleeves are all elastomers which have been radially expanded and are heat shrinkable. The conductor sleeves 58 are heat shrunk (see figures 15 and 16) into position over φe ferrules 56, after a stress relief void filler tape (not shown) has been wrapped around the ferrules 56. The joint 74 is then further prepared in known fashion by the application of mastic, a core separator, filler profiles 76, black filler tape 78, stress relief tape 80 and sealant tape 82 to form the joint 74 shown in figure 17. The inner or consolidation sleeve 70 is then slid into position as shown in figure 18 and heat slirunk into position. The ends of the consolidation sleeve 70 overlap the sealant tape 82 so that a seal is formed at the ends of the consolidation sleeve 70. The joint 74 is then prepared further in known fashion by the application of an earth braid, galvanised steel mesh and white sealant tape 84 and a red sealant tape 86. The cover sleeves 72 are then slid into position and heat shrunk in partially overlapping configuration as shown in figures 19 and 20 to complete the joint 74. The outer ends of the cover sleeves overlap the red sealant tape 86 to form a seal between the cover sleeves 72 and the outer sheath 60 of the cables 54. A typical general purpose heat shrinkable rubber formulation suitable for a conductor sleeve is as follows: The grade of elastomer, the levels of the reinforcing filler, plasticiser and curing agent all have an effect on the stiffness of the compound and its tendency to resist spontaneous recovery upon deformation. Changing the elastomer from an ethylene propylene diene monomer (EPDM) to nitrile rubber (NBR), together with other appropriate changes, would make the compound resistant to mineral oils. Blending compatible elastomers results in properties intermediate between the two. Referring now to figures 21 to 23, a cross-linked, polyethylene, 12kV, 3 core cable 88 is terminated in known fashion for a termination 89 as can been seen from figure 21. The cable 88 has an outer sheath 90, red sealant 92, a clamp 94 clamping armouring 96 in position, a filler 98, earth braids 100 held by roll springs 102, copper tape screens 104, core screens 106, cross-linked polyethylene insulation 108 and lugs 110. A radially expanded, heat shrinkable, silicone rubber boot 112 is slid over the crutch 114 of the cable 88. The boot 112 has a skirt 116 and three turrets 118. Heat is applied to the boot 112 to shrink it into position over the crutch 114. The heat is first applied to the skirt 116 in the centre of the skirt 116 and then to the turrets 118. The termination 89 is then further prepared by the application of stress relief tape and stress control sleeves 120. The stress control sleeves 120 may be in the form of radially expanded, heat shrinkable, elastomeric sleeves. Red sealant tape 122 is then wrapped around the barrels 124 of the lugs 110, and around each turret 118 of the boot 112. Radially expanded, heat shrinkable, silicone rubber, anti-tracking sleeves are then heat shrunk into position as can be seen from figure 23. The anti- tracking sleeves 124 overlap the sealant tape 122 to form seals at the ends of the anti-tracking sleeves 124. Radially expanded heat shrinkable, elastomeric rain shields 126 are heat shrunk into position over the anti -tracking sleeves 124 as can be seen from figure 23. The various components for the cable joints and the termination described above are supplied in kit form. The use of heat shrinkable, elastomeric elements such as sleeves and boots in cable joints and terminations have the following advantages over the prior art: The ability to add diluent fillers to the elements leads to lower material costs. In addition, since the elements may be produced on conventional rubber processing machinery, capital costs are also substantially lower. The inherent flexibility of rubber leads to the ability to join flexible cables. This also results in the joint being easier to manipulate. It also has the advantage that higher thicknesses of material can be used without the joint becoming too rigid. The flexibility of the elements also leads to ease of installation and handling. Since the temperature at which the elements shrink can be varied, low temperature shrinkage is achievable. If less heat needs to be applied to achieve shrinkage, there is less likelihood of damage to surrounding cable. Rubbers can be compounded to give a wider range of properties than plastics. Higher electrical resistivity, lower electrical conductivity and a broader range of dielectric constants are available in rubber compounds than in plastics. Heat shrinkable silicone joints can withstand higher temperatures and have improved track resistance. Heat shrinkable rubbers can be compounded to give hardnesses the same as the cable material or as high as heat shrinkable polyolefins. The higher hardness leads to enhanced toughness and a corresponding ruggedness of the joint. Furthermore, low cost systems can be designed if the constraints of low hardness/good recoverability are removed. The electrical properties of the elements of a high voltage electrical joint or termination vary in accordance with radial distance from the conductor. In the case of heat shrinkable polyolefins, this is achieved by either sequential application of elements with differing electrical properties or by nesting the elements one within the other. Care must be always be exercised with such systems, whether polyolefin or rubber, to ensure removal of air, especially between insulating and semi-conducting layers since the inclusion of air at this interface in high voltage cables leads to corona discharges and joint failures. Heat shrinkable rubbers may be moulded to form a composite having differing electrical properties, ensuring the elimination of air and also speeding up and simplifying the joining process. Such composites are available in cold shrink form, but at very high cost. Electrical cables are subject to varying power loads during service. Under heavy load conditions, a cable tends to heat up and expand. The cable joints and terminations are also subject to these load/temperature cycles. However, under extreme loads, in the case of heat shrinkable polyolefins, the heating and subsequent expansion of a joint is not necessarily followed by subsequent shrinkage as the cable cools. This is a result of the polyolefin being stretched at temperatures below the temperature at which it softens. After repeated cycles under extreme loads, a permanent set or stretch can be exhibited in the heat shrinkable material. This allows the joint to shrink within the outer and inner sleeves. The resultant cavities formed within the joint can lead to corona discharges and/or moisture ingress and subsequent joint failure. Since heat shrinkable rubber is inherently elastic, the expansion/contraction cycles of the joint are easily accommodated by the elasticity of the rubber and joint porosity is thus avoided. The ability to compound rubber used for heat shrink elements results in the versatility in the jointing or termination systems. It also results in the ability of the joints to meet very specific end user requirements. It will be appreciated that many modifications or improvements of the invention are possible without departing from the spirit or scope of the invention.

Claims: CLAIMS 1. A kit for a cable joint for joining two cables having outer sheaths and conductors including at least one radially expanded, heat shrinkable, electrically insulating, elastomeric, conductor sleeve which can in use, upon the application of heat, be shrunk over an electrical joint between individual conductors. 2. The kit of claim 1 wherein the conductor sleeve is made of ethylene propylene rubber. 3. The kit of claim 1 or claim 2 including at least one radially expanded, heat shrinkable, elastomeric, semi-conductive sleeve which can in use, . upon the application of heat, be shrunk over the conductor sleeve. 4. The kit of claim 3 wherein the semi-conductive sleeve is made of ethylene propylene rubber. 5. The kit of claim 1 or claim 2 including at least one radially expanded, heat shrinkable, elastomeric, oil barrier sleeve which can in use, upon the application of heat, be shrunk over the conductor sleeve. 6. The kit of claim 5 wherein the oil barrier sleeve is made of nitrile rubber. 7. The kit of any of the above claims including a radially expanded, heat shrinkable, elastomeric, consolidation sleeve which can in use, upon the application of heat, be shrunk over at least two individual conductors and their conductor sleeves to consolidate the individual conductors. 8. The kit of claim 5 wherein the consolidation sleeve is made of polychloroprene rubber . 9. The kit of any of the above claims including a radially expanded, heat shrinkable, elastomeric, cover sleeve which can in use, upon the application of heat, be shrunk over the cable joint to provide a cover sleeve for the joint which cover sleeve overlaps the outer sheaths of the two cables. 10. The kit of claim 9 wherein the cover sleeve is made of polychloroprene rubber. 11. The kit of claim 9 insofar as it is dependent on claim 7 wherein the consolidation sleeve is shorter than the cover sleeve so that in use the consolidation sleeve does not overlap the outer sheaths of the two cables. 12. A method of forming a joint between two cables having conductors and outer sheaths including the steps of exposing the ends of electrical conductors within the cables, electrically joining respective electrical conductors, and shrinking radially expanded, heat shrinkable, electrically insulating, elastomeric, conductor sleeves over the joints between the respective electrical conductors by heating the conductor sleeves. 13. The method of claim 12 including the step of shrinking radially expanded, heat shrinkable, elastomeric, semi-conductive sleeves over the conductor sleeves by heating the semi-conductive sleeves. 14. The method of claim 12 including the step of shrinking radially expanded, heat shrinkable, elastomeric, oil barrier sleeves over the conductor sleeves by heating the oil barrier sleeves. 15. The method of any of claims 12 to 14 including the step of shrinking a radially expanded, heat shrinkable, elastomeric, consolidation sleeve over the electrical conductors by heating the consolidation sleeve. 16. The method of any of claims 12 to 15 including the step of shrinking a radially expanded, heat shrinkable, elastomeric, cover sleeve over the electrical conductors by heating the cover sleeve to form a cover sleeve for the joint which cover sleeve overlaps the outer sheaths of the two cables. 17. A joint between two electrical cables having electrical conductors and outer sheaths including electrically insulating, elastomeric, conductor sleeves heat shrunk over joints between the respective electrical conductors. 18. The joint of claim 17 including elastomeric semi-conductive sleeves heat shrunk over the conductor sleeves. 19. The joint of claim 17 including elastomeric, oil barrier sleeves heat shrunk over the conductor sleeves. 20. The joint of any of claims 17 to 19 including an elastomeric consolidation sleeve heat shrunk over the electrical conductors. 21. The joint of any of claims 17 to 20 including an elastomeric, cover sleeve heat shrunk over the electrical conductors to form a cover sleeve for the joint which cover sleeve overlaps the outer sheaths of the two cables. 22. A kit for an electrical cable termination including a radially expanded, heat shrinkable, elastomeric boot which can in use, upon the application of heat, be shrunk over a crutch of the electrical cable termination. 23. The kit of claim 22 wherein the boot is made of silicone rubber. 24. A kit of claim 22 including radially expanded, heat shrinkable, elastomeric, anti-tracking sleeves which can in use, upon the application of heat, be shrunk over individual conductors extending from the crutch of the termination. 25. The kit of claim 24 wherein the anti-tracking sleeves are made of silicone rubber. 26. A method of forming an electrical cable termination including the steps of forming a termination crutch with separated conductors extending therefrom, shrinking a radially expanded heat shrinkable, elastomeric boot over the crutch of the termination by heating the boot. 27. The method of claim 26 including the step of shrinking radially expanded, heat shrinkable, elastomeric, anti-tracking sleeves over the separated conductors by heating the anti-tracking sleeves. 28. An electrical cable termination including an elastomeric boot heat shrunk over a crutch of the electrical cable termination. 29. The electrical cable termination of claim 28 including elastomeric, anti-tracking sleeves heat shrunk over individual separated conductors extending from the crutch. 30. The electrical cable termination of claim 29 wherein each anti-tracking sleeve overlaps a turret of the boot. 31. A kit for a cable joint or cable termination including at least one radially expanded, heat shrinkable, elastomeric element. 32. A method of forming a cable joint or a cable termination including the steps of shrinking a radially expanded, heat shrinkable, elastomeric element over conductors of the cables being joined or over the conductors of the cable being terminated. 33. A cable joint or cable termination including an elastomeric element heat shrunk over the conductors of the cables being joined or over the conductors of the cable being terminated. 34. A sleeve for use in a cable joint, the sleeve being made of ethylene propylene rubber and being radially expanded and heat shrinkable.

Inventors: ROPER ROBERT STEPHEN, ROPER, ROBERT, STEPHEN
Applicants: ROPER ROBERT STEPHEN, ROPER, ROBERT, STEPHEN
Application year: 2000
Main classification: H02G15
IPC codes: H02G15