Cable Fitting

Abstract

An inventive cable fitting (1) for high voltage cables, comprises a rigid core insulator (5) with a central duct suitable to receive a high voltage cable conductor. An elastomeric stress relief element (8) is cast around and thereby attached to a first part of the rigid core insulator (5). The stress relief element (8) comprises an insulating volume (9) made of elastomeric material, a field deflector (11) and a shield electrode (10). The stress relief element (8) is arranged so that it can receive a high voltage cable.

Claims

1. Cable fitting for high voltage cables, comprising a) a core insulator with a central duct suitable to receive a high voltage current conductor and b) a carrier tube, which is electrically conducting or semiconducting along its length and located within the central duct of the core insulator or being a part of the core insulator and c) a stress relief element being elastomeric and comprising an insulating volume made of a cast material which is elastomeric and electrically insulating, a field deflector made of elastomeric, electrically conductive or semiconductive material and a shield electrode made of elastomeric, electrically conductive or semiconductive material, d) wherein the insulating volume is cast around a first part of the core insulator thereby establishing a tight connection between the core insulator and the stress relief element.

2. Cable fitting according to claim 1, wherein the core insulator is more rigid than the insulating volume of the elastomeric stress relief element.

3. Cable fitting according to claim 1, wherein the insulating volume is made of an elastomeric polymer.

4. Cable fitting according to claim 1, wherein the core insulator comprises a rigid, polymeric material.

5. Cable fitting according to claim 1, wherein the outside of the stress relief element is at least partially covered with a semiconductive cover.

6. Cable fitting according to claim 1, wherein the core insulator is a capacitive grading body.

7. Cable fitting according to claim 1, further comprising a fixing flange acting as a barrier to the insulating volume such that the stress relief element is only on one side of the fixing flange and the core insulator extends on both sides of the fixing flange.

8. Cable fitting according to claim 1, wherein the carrier tube extends from a contact region with the shield electrode to the head armature of the cable fitting to which the carrier tube is connected in a fluid-tight way.

9. Cable fitting according to claim 1, further comprising a protection box which surrounds the stress relief element and which is connected to the fixing flange with spring elements in order to allow thermal expansion of the stress relief element in axial direction.

10. Cable fitting according to claim 1, further comprising a connector wherein the connector is placed inside the carrier tube.

11. Cable end comprising a) a high voltage cable comprising i) a cable conductor, ii) a first semiconductive layer in direct contact with the cable conductor, iii) an insulation layer made of a polymer surrounding the cable conductor and the first semiconductive layer, iv) a second semiconductive layer surrounding the insulation layer, v) protective layer surrounding the second semiconductive layer, and b) a cable fitting according to claim 1, c) wherein the second semiconductive layer and/or the cable sheath contacts the deflector and d) and wherein the cable conductor contacts, at least indirectly, the shield electrode in such a way that both are at the same electric potential.

12. Cable end according to claim 11, wherein the cable conductor is connected to the connector and wherein there is an insulator arranged between the connector and the carrier tube such that there is no direct but only an indirect electrical contact between the connector and the carrier tube and wherein there is a direct electrical contact between the connector and the fitting conductor, wherein there is a direct electrical contact between the fitting conductor and the connection bolt, wherein the connection bolt either directly contacts the carrier tube or the connection bolt directly contacts the head armature and the head armature directly contacts the carrier tube, and the carrier tube is in direct contact with the shield electrode and wherein in this way, during operation, the shield electrode is on the same potential as the cable conductor but a current flowing through the carrier tube is essentially inhibited.

13. Cable end according to claim 11, wherein the cable conductor is in direct contact with the connection bolt or the head armature and wherein the connection bolt or the head armature is in direct contact with the carrier tube, and wherein the carrier tube is in direct contact with the shield electrode.

14. Method to produce a cable fitting according to claim 1, comprising the following steps: a) Providing a core insulator with a central duct suitable to receive a high voltage current conductor and a carrier tube which is located within the central duct or which is part of the core insulator and which is semiconducting or conducting along its length, b) Providing a mandrel of cylindrical shape having over most of its length a diameter equal to the smallest inner diameter of the deflector and, c) Providing a field deflector and a shield electrode, both made of elastomeric and conductive or semiconductive material d) Providing a mould, wherein the mould has a first central opening of the size of the outer diameter of the mandrel located on an extension of the central duct when the mould is mounted to the core insulator and the mould has a second central opening on the end opposing the first central opening e) Placing the shield electrode at least partially on the carrier tube or the core insulator and thereby establishing a direct contact between the shield electrode and the carrier tube f) Arranging the mandrel with respect to the carrier tube and the core insulator in such a way that the mandrel follows the extension of the carrier tube and, g) Placing the field deflector on the mandrel at a given distance from the shield electrode h) Placing the mould around the mandrel carrying the shield electrode and the field deflector such that the mandrel closes the first central opening in the mould, i) pouring a cast material in its liquid state inside the mould and thereby covering at least the first part of the core insulator, the shield electrode and the field deflector with the cast material, j) curing the cast material such that is becomes the insulating volume k) after curing, removing the mandrel.

15. Method to produce a cable fitting according to claim 1, comprising the following steps: a) Providing a core insulator with a central duct suitable to receive a high voltage current conductor and a carrier tube which is located within the central duct or which is part of the core insulator and which is semiconducting or conducting along its length, b) Providing a field deflector and a shield electrode, both made of elastomeric and conductive or semiconductive material c) Providing a mandrel of cylindrical shape having over most of its length a diameter equal to the smallest inner diameter of the deflector and, d) Providing a first and a second mould, each having two ends and each end having a central opening, e) Placing the first mould around the core insulator such that the core insulator or the fixing flange closes one of the central openings of the mould and such that the carrier tube or the core insulator closes the other one of the central openings of the first mould, f) Pouring a cast material in its liquid state inside the first mould and thereby covering at least the first part of the core insulator with the cast material, curing the cast material such that is becomes the insulating volume and thereby forming a first part of the stress relief element g) Placing the shield electrode and the field deflector on the mandrel in a given distance from each other, h) Placing the first or the second mould around the mandrel carrying the shield electrode and the field deflector such that each of the central openings of this mould is closed by either the mandrel or the shield electrode or the field deflector, i) pouring a cast material in its liquid state inside the mould placed around the mandrel and thereby covering at least partially the shield electrode and the field deflector with the cast material, curing the cast material such that it becomes the insulating volume and thereby forming a second part of the stress relief element j) connecting the first and the second part of the stress relief element by pushing the first and the second part of the stress relief element against each other such that the shield electrode has electrical contact with the carrier tube.

16. Method of producing a cable end according to claim 11, comprising the steps of a) Providing a cable fitting according to claim 1 b) Providing an end piece of a high voltage cable, whereby the high voltage cable comprises a cable conductor, an insulation layer made of a polymer and a second semiconductive layer surrounding the insulation layer c) Exposing the second semiconductive layer over a first length, the insulation layer over a second length and the cable conductor over a third length and thereby producing a prepared end piece, d) Placing the prepared end piece in the cable fitting in such a way, that the deflector contacts the second semiconductive layer and that at least part of the shield electrode touches the insulation layer and that the cable conductor directly contacts either the connector or the head armature or the connection bolt.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0242] The drawings used to explain the embodiments show:

[0243] FIG. 1 A first embodiment of a cable fitting according to the invention.

[0244] FIG. 2 A second embodiment of a cable fitting mounted on a high voltage cable. The cable fitting comprises a connector of the click-in type. Further the carrier tube is a high voltage current conductor.

[0245] FIG. 3 A third embodiment of a cable fitting mounted on a high voltage cable. Its core insulator uses geometrical field control. The cable fitting uses a fitting conductor as high voltage current conductor and a connector of the crimped type.

[0246] FIG. 4 A fourth embodiment of a cable fitting mounted on a high voltage cable. The cable conductor is prepared in such a length that it reaches the head armature and connection bolt when the cable is inserted into the fitting. No fitting conductor or connector is needed.

[0247] FIG. 5a The first step of a first method for producing a cable fitting.

[0248] FIG. 5b A second step of a first method for producing a cable fitting.

[0249] FIG. 5c The cable fitting resulting from the production method shown in FIGS. 5a and 5b and a fitting conductor with a connector of bolted type only partially inserted in the cable fitting.

[0250] FIG. 6a The first step of a second method for producing a cable fitting.

[0251] FIG. 6b A second step of a second method for producing a cable fitting.

[0252] FIG. 6c The cable fitting resulting from the production method shown in FIGS. 6a and 6b and a fitting conductor with a connector of bolted type only partially inserted in the cable fitting.

[0253] In the figures, the same components are given the same reference symbols.

PREFERRED EMBODIMENTS

[0254] FIG. 1 shows a first embodiment of a cable fitting 1 according to the invention. The cable fitting 1 comprises a core insulator 5, a carrier tube 27, a fixing flange 3 and a stress relief element 8.

[0255] FIG. 1 shows a cross-section. The cable fitting 1 is, with the exception of the wire 21x, axially symmetric.

[0256] The core insulator 5 has the shape of a concentric cylinder with two flat ends. The volume inside the core insulator 5 is the central duct 7. The diameter of the central duct 7 equals the inner diameter of the core insulator 5. The central duct 7 has a constant diameter along the whole length of the core insulator 5. The core insulator 5 has a first part 5a and a second part 5b.

[0257] A carrier tube 27, having the shape of a concentric cylinder with constant inner and outer diameter, runs inside the central duct 7. The outer diameter of the carrier tube 27 equals the diameter of the central duct 7. The carrier tube 27 is longer than the core insulator 5 and extends out of the first end of the core insulator 5.

[0258] A shield electrode 10 has essentially the shape of a concentric cylinder with rounded edges. One of its inner diameters is slightly smaller or equal to the outer diameter of the carrier tube 27. The shield electrode 10 is made of elastomeric material. In this embodiment, there is a small distance between the first end of the core insulator 5 and the shield electrode 10. However, most part of the carrier tube 27 which extends from the first end of the core insulator 5 is covered by the shield electrode 10.

[0259] In some distance from the shield electrode 10, there is a deflector 11. The deflector 11 has roughly a shape resembling a hollow cone without a tip. The side with the large opening is oriented towards the core insulator 5. The small opening has an inner diameter equal to the smallest inner diameter of the shield electrode 10, i.e. the smallest inner diameter on the side of the shield electrode 10 which is oriented towards the deflector 11 itself.

[0260] At some point along the core insulator 5, in FIG. 1 approximately in the middle of the core insulator 5, there is a fixing flange 3. The fixing flange 3 has the shape of a round disc with a circular hole in its centre, which has at least the diameter of the core insulator.

[0261] There is an insulating volume 9. The insulating volume 9 is made of cast material and it is elastomeric. The insulating volume 9 is cast around the first part 5a of the core insulator 5, the shield electrode 10 and the deflector 11. Insulating volume 9, shield electrode 10 and deflector 11 form the stress relief element 8. In the embodiment shown in FIG. 1, the insulating volume 9 does not reach the fixing flange. In FIG. 1, there is therefore a gap between the fixing flange 3 and the stress relief element 8.

[0262] The outer shape of the insulating volume 9 is, in FIG. 1, that of a concentric cylinder which is tapered in the axial region partially in common with the deflector 11 in the direction pointing away from the fixing flange 3. In other embodiments the insulating volume 9 may retain the cylindrical shape. The inner diameter of the insulating volume 9 equals the inner diameters of the shield electrode 10 and the deflector 11. The outer diameter is, in FIG. 1, larger than the outer diameter of the core insulator 5 but smaller than the outer diameter of the fixing flange 3. The shield electrode 10 and the deflector 11 are not completely surrounded by the insulating volume: In the regions where the shield electrode 10 and the deflector 11 have their smallest inner diameter, they define the inner boundary and an electrically conducting contact can be established by touching the electrodes in these regions.

[0263] A semiconductive cover 21 covers part of the outer surface of the stress relief element 8. The distance between the shield electrode 10 and the semiconductive cover 21 is chosen such that the resulting electric field does not exceed the dielectric strength of the used insulating material for the insulating volume 9. The semiconductive cover 21 is brought at the ground potential by means of electrical contacting directly or indirectly to a grounded part. In FIG. 1, a wire 21x is shows as an example of an electrical contact for grounding the semiconductive cover 21. The wire 21x contacts the deflector and the semiconductive cover 21. In other embodiment, there could also be an electrical contact between the semiconductive cover 21 and the fixing flange 3. In the shown embodiment, the semiconductive cover 21 extends in axial direction from an axial position which is also common to the deflector to an axial position which is common to the outermost conductive foil 6a, thereby concentrating the electric field between the deflector 11, being of ground potential, and the shield electrode 10, being on the high voltage potential inside the stress relief element 8.

[0264] It is also possible that the semiconductive cover 21 covers more of the stress relief element 8 or that is covers the complete outer surface of the stress relief element 8.

[0265] The core insulator 5 shown in FIG. 1 uses capacitive grading. The core insulator 5 comprises therefore concentrically arranged conductive foils 6 embedded in a solidifying polymer material. This casted polymeric material is used to impregnate the crepe paper into which the conductive foils 6 are arranged or any other synthetic material which is used to build the capacitive grading body. The axial extent of the foils decreases with increasing radial distance. Thereby the foils define a shape of a concentric cylinder which is tapered on both ends. The polymer material adds volume to this tapered cylinder such that the overall shape of the core insulator 5 is the one of a concentric cylinder with flat ends described above. The innermost conductive foil 6b is electrically contacted to the carrier tube 27 and therefore at the same voltage potential. The electrical contact is a direct electrical contact because the carrier tube 27 and the innermost conductive foil 6b touch each other in this embodiment. In further embodiments, the contact between the carrier tube 27 and the innermost conductive foil 6b is established via a contact device like a wire or a soldered point.

[0266] The insulating volume 9 is made of an elastomeric polymer, like silicone rubber. The conductive shield electrode 10 and the deflector 11 are made of a conductive or semiconductive elastomeric material. For example, the material can be silicone rubber with mixed in carbon black particles.

[0267] The fixing flange 3 is typically made of a metal, like steel or aluminium. It is possible that there is no fixing flange 3.

[0268] In further embodiments, the inner diameter of at least a part of the shield electrode 10, the deflector 11 and the insulating volume 9 is larger than the diameter of the carrier tube 27. This allows the use of the cable fitting on cables with thicker insulation layers.

[0269] In further embodiments, it is possible that the inner diameter of at least a part of the shield electrode 10, the deflector 11 and the insulating volume 9 is smaller than the inner diameter of the carrier tube 27. This allows the use of the cable fitting on cables with thinner insulation layers.

[0270] The inner diameter of at least a part of the shield electrode 10, the deflector 11 and the insulating volume 9 is preferably chosen such that it is slightly smaller than the outer diameter of the insulation layer of the cable on which the fitting should be used.

[0271] Further, it is possible that it is the innermost conducting foil 6b of the core insulator 5 which extends into the shield electrode 10 in addition or instead of the carrier tube 27. It is also possible that the carrier tube 27 acts as innermost conducting foil 6b and that therefore the carrier tube 27 is in direct contact with insulating bulk material.

[0272] The outermost conducting foil 6a of the core insulator is, in the embodiment of FIG. 1, on ground potential and directly contacted to the fixing flange 3. In other embodiments, the outermost conductive foil 6a is indirectly contacted to the fixing flange 3. In other embodiment, the outermost conductive foil 6a is directly or indirectly connected to another part on ground potential.

[0273] FIG. 2 shows a second embodiment of a cable fitting 1 mounted on a high voltage cable 17. The cable fitting 1 comprises a connector 22a of the click-in type. Further the carrier tube 27a is a high voltage current conductor. The view is again a cross-section, as it was the case in FIG. 1.

[0274] FIG. 2 comprises all parts of FIG. 1 which the following differences:

[0275] The core insulator 5 follows the shape of the concentric foil arrangement and is tapered on both of its ends.

[0276] The fixing flange 3 comprises a connection section 3a which has the shape of a concentric cylinder with thin walls and an inner diameter which essentially equals the outer diameter of the hollow tube body 26. The connection section 3a extends, beginning at the fixing flange 3, in the direction away from stress relief element 8. The length of the connection section 3a is small compared to the length of the core insulator 5.

[0277] The outermost conductive foil 6a of the core insulator 5 does not touch the fixing flange 3 directly, but a grounding device 30 is connected to the outermost conductive foil 6a. The grounding device 30 can serve as a test tap for the cable fitting and provide the direct grounding of the outermost conductive foil 6a. This grounding device 30 can be a braid or wire which connects the outermost conductive foil 6a with the fixing flange 3 or another point, which is on ground potential during use of the cable fitting.

[0278] There is a connector 22a of the click-in type mounted inside the carrier tube 27. The connector 22a can be placed anywhere between the shield electrode 10 and the end of the carrier tube 27a within the electric field free zone. The connector 22a is rigid. The connector 22a establishes a good electrical contact and ensures the current flow from the cable conductor 18 to the carrier tube 27a with a low contact resistance. The connector 22a is shaped like a concentric cylinder which is closed on one end. Its inner surface is equipped with barbs and multiple lamellae. A cable conductor pushed into the connector 22a is fixed by the barbs and contacted by the lamellae. The connector 22a has essentially an outer diameter which equals the inner diameter of the carrier tube 27a. The connector 22a is connected to the carrier tube 27a for example by soldering such that there is a well conducting contact between the connector 22a and the carrier tube 27a. It is also possible that the connector 22a can move inside the carrier tube 27a and that the well conducting contact is established by multiple lamellae, i.e. multicontact.

[0279] In another embodiment, the connector of the click-in type 22a is an integral part of the carrier tube 27a.

[0280] The carrier tube 27a is designed in such a way that it can carry the needed cable conductor current without overheating. Overheating occurs, if the steady-state temperature at any point of the cable fitting exceeds the maximum allowed operation temperature for the surrounding materials and components. The carrier tube 27a is for example made of copper or a copper alloy or another well conducting, thermal and electrical, material. Further its diameter and wall thickness are chosen appropriately.

[0281] The stress relief element 8 comprises an insulating volume 9 which contacts the fixing flange 3.

[0282] The shield electrode 10 overlaps slightly with the first end of the core insulator 5. The shield electrode 10 covers therefore all of the carrier tube 27 which extends beyond the first part of the core insulator 5.

[0283] The whole outer surface of the stress relief element 8 is covered with a semiconductive cover 21. The semiconductive cover 21 of this embodiment contacts directly the fixing flange 3 and the second semiconductive layer 19 of the cable 17 due to the extent of the semiconductive cover 21 and the placement of the stress relief element 8. The semiconductive cover 21 is grounded via the fixing flange 3 and/or via the second semiconductive layer 19 of the cable 17.

[0284] A hollow tube body 26 in the shape of a concentric round cylinder with thin walls and an outer diameter being equal or slightly smaller than the inner diameter of the connection section 3a, is fixed to the fixing flange 3. The fixing can be done by a press fit into the connection section 3a, by an adhesive between the inner surface of the connection section 3a and the outer surface of the hollow tube body 26 or by screws or similar means. Preferably, the fixing is done in such a way, that there is a fluid tight connection between the fixing flange 3 and the hollow tube body 26. The length of the hollow tube body 26 is greater than the extent of the core insulator 5 on the same side of the fixing flange 3. The hollow tube body 26 is made of an insulating material like fibre reinforced epoxy. Sheds 24 made of silicone rubber or other insulating composite materials are arranged on the outside of the hollow tube body 26. The hollow tube body 26 and the sheds 24 form an outdoor insulator.

[0285] In another embodiment, the hollow tube body 26 and the sheds 24 are made of porcelain.

[0286] One end of the hollow tube body 26 contacts the fixing flange 3. The other end of the hollow tube body 26 contacts the head armature 28. The head armature 28 is a concentric adapter piece in the shape of a round disc made of a conducting material. In the embodiment shown in FIG. 2, it has a concentric hole in its centre which extends into a short, thin walled, concentric cylinder. The outer diameter of this cylinder equals the inner diameter of the carrier tube 27a. There is a fluid tight connection between the head armature 28 and the hollow tube body 26. Further, there is an electrical connection between the carrier tube 27a and the head armature 28.

[0287] Hollow tube body 26, head armature 28, carrier tube 27a, core insulator 5 and fixing flange 3 delimit a volume which is filled with an insulating medium 25. This insulating medium 25 can be an insulating gel, oil, air, insulating gas or a polymeric material that has a good dielectric strength, good thermal conductivity to allow heat transfer resulting from the current flow and the dielectric power losses and is compressible to allow for thermal expansion of the core insulator 5, of the hollow tube body 26 and of itself.

[0288] A protection box 12 is arranged around the stress relief element 8. It has the shape of a concentric cylinder with thin walls which is tapered at one end and comprises an outwards extending flange at the other end. The angle in which it is tapered equals the angle in which the stress relief element 8 is tapered. In an embodiment, where the stress relief element 8 is not tapered but has a flat end, the protection box 12 follows the shape of this stress relief element 8, too and ends in a flat end. The length of the protection box 12, measured on its inside, equals the length of the stress relief element 8, measured on its outside. The inner diameter of the protection box 12 is along its cylindrical part larger than the outer diameter of the stress relief element 8 to allow for expansion of the stress relief element 8. There is consequently a gap 14 between the stress relief element 8 and the protection box 12 in radial direction along the cylindrical part of the protection box 12. The protection box 12 is fixed to the fixing flange 3 by spring elements 13 which push the flange of the protection box 12 towards the fixing flange 3. The spring elements 13 can be realized by nuts and bolts and coil springs: The coil spring is compressed between the nut and the flange of the protection box 12 which is thereby pushed against the fixing flange 3 which is pushed against the head of the bolt.

[0289] In the tapered part of the stress relief element 8 there is no gap between the protection box 12 and the stress relief element 8. The protection box 12 supports in this way the weight of the stress relief element 8. The spring elements/bolts 13 allow for expansion of the stress relief element 8 in axial direction.

[0290] In the embodiment shown in FIG. 2, the protection box 12 has no electrical function but only protects the stress relief element 8 from the environment. In other embodiments, a conducting protection box 12 can establish an electrical contact between a semiconductive cover 21 and the fixing flange 3 and/or the cable sheath 20 which are both on ground potential.

[0291] FIG. 2 shows further the end of a high voltage cable 17. From the inside to the outside, the cable comprises a cable conductor 18, an insulation layer 16, a second semiconductive layer 19, a cable sheath 20 and a protective layer. At the cable end, one layer after the other is removed such that every one of these layer is the outermost layer for a certain length. At first the protective layer is removed, leaving the cable sheath 20 as outermost layer. In the embodiment shown in FIG. 2, the protective box 12 touches the cable sheath 20 in this region. Shortly behind this contact point, the cable sheath 20 is removed, leaving the second semiconductive layer 19 to be the outermost layer. The deflector 11 contacts the second semiconductive layer 19. Shortly behind this contact point, the second semiconductive layer 19 is removed, leaving the insulation layer 16 to be the outermost layer. The insulation layer 16 is the outermost layer in the region contacting the shield electrode 10 and, in the embodiment shown in FIG. 2, it even extends into the carrier tube 27a. Shortly before the connector of click-in type 22a, the insulation layer 16 stops and only the free cable conductor 18 enters the receiving section of the connector of mulitcontact type 22a and is mechanically fixed and electrically connected by its barbs and/or lamellae.

[0292] FIG. 3 shows a third embodiment of a cable fitting 1 mounted on a high voltage cable 17. It is again a cross-section which is shown. This third embodiment is very similar to the second embodiment shown in FIG. 2. In contrast to the second embodiment, the core insulator 5 of the third embodiment uses geometrical field control. Further, the cable fitting uses a fitting conductor 23 as high voltage current conductor. The connector 22b is of a crimped type.

[0293] The core insulator 5 is mainly made of an insulating material and it has the shape of a concentric cylinder with both ends being tapered. Its inner diameter equals the outer diameter of the carrier tube 27b and its outer diameter equals the diameter of the circular hole of the fixing flange 3. The core insulator 5 comprises a geometric field control guard electrode 6c which contacts the fixing flange 3. The geometric field control guard electrode 6c is at the same potential as the fixing flange 3, which is typically the ground potential.

[0294] The cable conductor 18 is connected to the connector 22b of crimped type. The connector 22b has the shape of a hollow, concentric cylinder with an inner diameter being larger than the diameter of the cable conductor 18 and an outer diameter being smaller than the inner diameter of the carrier tube 27b. The ends of this concentric cylinder are receiving sections. In other embodiments, there is a solid wall in the inside of the cylinder separating the two receiving sections from each other. The cable conductor 18 is inserted in one receiving section of the connector 22b. Afterwards the connector 22b is locally deformed in such a way that the cable conductor 18 is mechanically and electrically fixed to the connector 22b.

[0295] A fitting conductor 23 of essentially the same construction as the cable conductor 18 is placed and fixed in a similar way to the other receiving section of the connector 22b. The fitting conductor 23 is fixed to the connection bolt 29 on its other end.

[0296] There is a connector insulation 31 arranged around the connector 22b. The connector insulation 31 can be an insulating tape wound around or an insulating tube slipped on the connector of crimped type 22b after the crimping of the cable conductor 18 and the fitting conductor 23.

[0297] In this embodiment, the current is carried by the fitting conductor 23. The connector of crimped type 22b connects the cable conductor 18 and the fitting conductor 23 in a mechanical stable and well conducting way.

[0298] The semiconductive cover 21 covers only part of the stress relief element 8: It does not extent all the way to the fixing flange 3 but only up to an axial position which is common to an axial position of the geometric field control guard electrode 6c.

[0299] FIG. 4 shows a forth embodiment of a cable fitting 1 mounted on a high voltage cable 17. It is again a cross-section which is shown. The cable conductor 18 is prepared in such a length that it reaches the head armature 28 and connection bolt 29 when the cable 17 is inserted into the fitting 1. No fitting conductor 23 or connector 22 is needed.

[0300] The core insulator 5 and the carrier tube 27 of this cable fitting 1 are similar to the one shown in FIG. 1. In contrast to the embodiment shown in FIG. 1, this core insulator 5 is tapered on its first end.

[0301] In this forth embodiment, the core insulator 5 is directly surrounded by the sheds 24. The core insulator 5 and the carrier tube 27 end at the same axial position. A head armature 28 is located at this end. In contrast to the second and the third embodiment, the forth embodiment does not comprise a connector 22. However, other embodiments have all features of the fourth embodiment but comprise a connector 22 and possibly a fitting conductor 23 as shown in FIG. 2 or 3.

[0302] The fixing flange 3 comprises a connection section 3a as shown in FIGS. 2 and 3. The ways to connect the core insulator 5 are analogue to the ways to connect the hollow tube body 26 to the connection section 3a and the way the outermost conducting foil 6 of the core insulator 5 are the same as shown in FIG. 2. The fourth embodiment comprises a grounding device 30 similar to the one of FIG. 2.

[0303] The shield electrode 10 of this embodiment sits on the carrier tube 27 and partially on the core insulator 5. The innermost conductive layer of the core insulator 5 and the carrier tube 27 are both in direct contact and therefore electrically contacted with the shield electrode 10.

[0304] The insulating layer 16 of the cable 17 has an outer diameter which is about the same as the outer diameter of the carrier tube 27.

[0305] The stress relief element 8 has an outer diameter which is slightly larger than the outer diameter of the outermost conductive foil 6a but smaller than the outer diameter of the core insulator 5. Therefore, the insulating volume 9 is not in contact with the fixing flange 3 but only with the core insulator 5 in its tapered region.

[0306] There is also a protection box 12, with a shape similar to the ones shown in FIGS. 2 and 3.

[0307] In contrast to the one shown in FIG. 2, the internal length of the protection box 12 of the forth embodiment is slightly larger than the external length of the stress relief element 8. Therefore, there is a gap 14 everywhere between the protection box 12 and the stress relief element 8. As thermal expansion in axial direction is possible due to the gap 14, the spring elements can be omitted and the protection box 12 can be mounted to the fixing flange 3 in any common way, for example with an adhesive, by soldering or by screws.

[0308] In FIG. 4, the semiconductive cover 21 extends on the outside of the stress relief element 8 from the contact point with the core insulator 5 to an axial region common with the deflector 11. The arrangement is such that there is a common axial region to the outermost conductive layer 6a of the core insulator 5 and the semiconductive cover 21. The semiconductive cover 21 is grounded by a contact to the fixing flange 3, to the grounding device 30, to the deflector 11, to the second semiconductive layer 19 and/or to the cable sheath 20. This contact is not shown in FIG. 4.

[0309] Due to the fact, that the inner diameter of the carrier tube 27 is smaller than the outer diameter of the insulating layer 16 of the cable, this embodiment is particularly easy to install: The cable 17 is prepared outside of the cable fitting 1 where distances can be measured precisely. Then the cable 17 is inserted in the fitting 1. The carrier tube 27 inhibits any further forward movement of the cable 17 once it has reached its final position. Thereby, it is sufficient to know the distances between the head armature 28, the end of the carrier tube 27 and the deflector 11 as well as the minimum length of the cable conductor 18 needed to establish a connection to the connection bolt 29 to enable a precise positioning of the cable 17 inside the cable fitting 1.

[0310] FIGS. 5a and 5b illustrate a first method for producing a cable fitting 1. All parts are shown in cross-sections along the longitudinal axis.

[0311] FIG. 5a illustrates the first step of the first method for producing a cable fitting 1. A prefabricated subunit 40, a mandrel 41, a shield electrode 10, a deflector 11, a mould 42 and preferably a fitting conductor 23 equipped with a connector of the bolted type 22c are provided. The prefabricated subunit 40 comprises a core insulator 5, a fixing flange 3 and a carrier tube 27b. The core insulator 5 extends on both sides of the fixing flange 3. A candidate for becoming the first part 5a of the core insulator 5 protrudes from the prefabricated subunit 40. The mandrel 41 is a rod with a diameter equal to the smallest inner diameter of the deflector 11. The shield electrode 10 has the shape of a hollow circular cylinder with rounded edges and is made of a conducting or semiconducting elastomeric material. The deflector 11 has a shape similar to a hollow cone with a central hole of the same diameter as the inner diameter of the shield electrode 10. The inner diameter of the shield electrode 10 and of the deflector 11 is the same as the outer diameter of the mandrel 41 in this embodiment. The mould 42 has the shape of a concentric cylinder with thin walls and which is tapered on one end in this embodiment. The tapered end has a first central hole in it with a diameter which equals the outer diameter of the mandrel 41. In addition, on the mould 42 there is at least one inlet and one outlet through which a deaeration of the mould 42 can be performed and then a liquid cast material 43 can be filled into the mould 42. The first step of the method for producing a cable fitting 1, which is illustrated here, comprises the step of providing these objects.

[0312] In the next steps, illustrated in FIG. 5b, the shield electrode 10 is partially slipped over the carrier tube's 27b extension outside the first end of the core insulator 5. At the second step the mandrel 41 is partly slipped within the shield electrode 10 and the deflector 11 is slipped on the mandrel 41. At the next step the mould 42 is placed in such a way that the mandrel 41 is in the first central hole of the mould 42 where the mandrel 41 is rigidly fixed, providing a fluid and air tight sealing. The mould 42 is fixed on the flange 3 of the prefabricated subunit 40 or, in another embodiment, on the core insulator 5, such that there is a fluid and air tight sealing. Once the mould 42 is mounted, the liquid cast material 43 is poured into the mould 42 through the inlet. The air which is displaced by the liquid cast material 43 escapes through the outlet.

[0313] Another way of casting is by producing a vacuum inside the hollow volume within the mounted mould 42 and then injecting the liquid cast material 43. Depending on the type of liquid cast material 43, injection moulding under elevated temperatures and high pressure may be necessary. The mould 42 has at least two openings, one inlet and one outlet, which offer a variety of possibilities for casting the liquid cast material in many standardised and well known ways.

[0314] After curing, the mould 42 and the mandrel 41 are removed. A cable fitting 1 is the result. The cable fitting 1 comprises a stress relief element 8 with an insulating volume 9 which is cast around a first part 5a of the core insulator 5. This is shown in FIG. 5c.

[0315] A cable conductor of a suitably prepared cable can be connected to the connector of the bolted type 22c. The bolted type of connector 22c connects the conductors by bolts which are inserted perpendicular to the longitudinal axis of the conductors though holes in the sides of the connector 22c. The bolts and holes can have thread such that the bolts are screwed into the conductor 22c. Once the conductors of the cable 18 and the fitting 23 are connected to the connector 22c, the connector 22c is surrounded by a connector insulator 31. The connector insulator 31 can be a layer of insulating paint which is sprayed on the connector 22c or an insulating cover piece surrounding the connector.

[0316] An arrow in FIG. 5c indicates the direction in which the cable is pushed into the cable fitting.

[0317] FIGS. 6a and 6b illustrate a second method for producing a cable fitting 1. All parts are shown in cross-sections along the longitudinal axis.

[0318] FIG. 6a illustrates the first step of the second method for producing a cable fitting 1. It is very similar to the first method according to FIGS. 5a-c with the only difference being the presence of a first mould 42a having an end 421a which forms with a first end shape of the first part 8a, which is flat in this example, and the presence of a second mould 42b having an end 421b which forms a complementary formed second end shape of the second part 8b.

[0319] The second mould 42b has the shape of a concentric cylinder with thin walls, which is tapered on one end in this embodiment. The tapered end has a central opening with a diameter which equals the outer diameter of the mandrel 41.

[0320] The first mould 42a has the shape of a cylinder with thin walls. One of the ends of this cylinder is in this embodiment completely open while the other end forms the first end shape 421a which is a plane. This plane has a central opening with a diameter equal to the outer diameter of the carrier tube 27.

[0321] In addition, on the first and the second mould 42a, 42b, there are at least one inlet and one outlet through which a deaeration of the moulds 42a, 42b can be performed when liquid cast material 43 is filled into the moulds 42a, 42b. The first step of the method for producing a cable fitting 1, which is illustrated here, comprises the step of providing these objects.

[0322] In the next steps, illustrated in FIG. 6b, the first mould is mounted on the core insulator 5 such that the central opening in the end which forms the first end shape 421a of the first part 8a is closed by the carrier tube's 27b extension outside the first end of the core insulator 5. The other end of the first mould 42a is fixed on the flange 3 of the prefabricated subunit 40 or, in another embodiment, on the core insulator 5, such that there is a fluid and air tight sealing. Once the first mould 42a is mounted, the liquid cast material 43 is poured into the first mould 42a through the inlet. The air which is displaced by the liquid cast material 43 escapes through the outlet. After curing, the first part 8a of the stress relief element 8 with a tight connection to the core insulator 5 has formed.

[0323] At the second step the shield electrode 10 and the deflector 11 are slipped on the mandrel 41. The second mould 42b is placed in such a way that the mandrel 41 extends through both central holes of the second mould 42b, providing a fluid and air tight sealing. Once the second mould 42b is mounted, the liquid cast material 43 is poured into the second mould 42b through the inlet. The air which is displaced by the liquid cast material 43 escapes through the outlet. After curing, the second part 8b of the stress relief element 8 comprising the shield electrode and the field deflector has formed.

[0324] Another way of casting is by producing a vacuum inside the hollow volume within the mounted moulds 42a,b and then injecting the liquid cast material 43. Depending on the type of liquid cast material 43, injection moulding under elevated temperatures and high pressure may be necessary. The moulds 42a, b have at least two openings, one inlet and one outlet, which offer a variety of possibilities for casting the liquid cast material in many standardised and well known ways.

[0325] After curing, the moulds 42a,b and the mandrel 41 are removed.

[0326] The first and the second part 8a, 8b of the stress relief element 8 are then pushed together in order to produce the stress relief element 8 and the cable fitting 1 according to the invention. In the embodiment at hand, the first and the second part 8a, 8b of the stress relief element 8 are connected by the vulcanization of the cast material. In the resulting cable fitting 1, the boundary between the first and second part 8a, 8b of the stress relief element is difficult to detect and it is only for illustrative purposes marked by a dashed line in FIG. 6c.

[0327] A cable conductor of a suitably prepared cable can be connected to the connector of the bolted type 22c. The bolted type of connector 22c connects the conductors by bolts which are inserted perpendicular to the longitudinal axis of the conductors though holes in the sides of the connector 22c. The bolts and holes can have thread such that the bolts are screwed into the conductor 22c. Once the conductors of the cable 18 and the fitting 23 are connected to the connector 22c, the connector 22c is surrounded by a connector insulator 31. The connector insulator 31 can be a layer of insulating paint which is sprayed on the connector 22c or an insulating cover piece surrounding the connector.

[0328] An arrow in FIG. 6c indicates the direction in which the cable is pushed into the cable fitting.

[0329] In one embodiment, which is not shown, no connector insulator 31 is applied onto the connector 22c. In this way, the connector 22c will be in direct electrical contact with the shield electrode 10 or the carrier tube 27b once the cable is installed on the cable fitting.

[0330] In summary, it is to be noted that the different ways to design the protection box 12, the stress relief element 8, the core insulator 5, the carrier tube 27 with the ways to connect the cable conductor 18, and the left hand side of the cable fitting 1 can all be combined with each other. The “left hand side of the cable fitting 1” includes everything which is shown on the left side of the fixing flange 3 in the FIGS. 1 to 5c: The design of the left hand side of the cable fitting comprises therefore the presence or absence of the following parts and their design: the connection bolt 29, the head armature 28, the sheds 24, the hollow tube body 26, the insulating medium 35 and the grounding device 30, as well as the connection section 3a.

[0331] It is also possible to exchange the electric field controlling conductive elements: Instead of a capacitive grading field control system with conductive foils 6, a geometric field control system using a geometric field control guard electrode 6c can be used and vice versa.

[0332] The conductive foils 6 and the insulating bulk material can be replaced, completely or partially, by conductive and insulating layers. For example, conductive foils may be coated with an insulating material or a layer of insulating material can be painted with a conductive or semiconductive paint resulting in a conductive layer, before another layer of insulating material is applied on top of it.

[0333] Besides using a prefabricated subunit 40, the method to produce a cable fitting 1 can also include the steps of only providing the core insulator 5, the shield electrode 10, the deflector 11, the mandrel 41 and a suitable mould 42 and to cast the stress relief element 8 onto the first part 5a of the core insulator 5 as shown in FIG. 5b. All further parts on the left hand side of the cable fitting 1 as well as the carrier tube 27 and the fixing flange 3 can be mounted later. It is also possible that a subset of these components are mounted before the casting and the rest of it later or not at all. Further, a fitting conductor 23 and a connector 22 can be omitted.

[0334] All connector types 22 can be exchanged: Instead of a click-in type connector 22a, one can use a bolted type connector 22c or a crimping type connector 22b or any other common type of connector 22. It is possible that a connector 22 comprises two receiving sections and both are of a different type. The combination of a connector 22 and a fitting conductor 23 can be replaced by an elongated connector. A fitting conductor 23 can be replaced by a well conducting carrier tube 27 and vice versa.

[0335] The shield electrode 10 can be in direct contact with the cable conductor 18.