Patent Description:
High voltage direct current (HVDC) cables, such as HVDC mass impregnated cables (HVDC-MI cables) are known and often used for long distance electrical transmission.

The conductor inside the cable is often made of copper or aluminium having a circular cross-section centre wire surrounded by concentric layers of stranded, keystone-shaped wires, resulting in a very compact conductor with a smooth surface. The keystone-shaped strands/wires are wound in a spiral, with the layers being wound in alternating directions. The first layer is e.g. wound in a clockwise spiral, the next layer is wound in a counter clockwise spiral and so on. The configuration of a central wire surrounded by such stranded wires provides the cable with improved flexibility.

The conductor of for example a HVDC cable can be surrounded by a plurality of insulating/protective layers. The insulation system usually consists of lapped paper tapes impregnated with a high viscosity compound (hence the term "mass impregnated"). A moisture-proof barrier, a lead alloy sheath, is usually applied above the insulation system. For mechanical and corrosion protection, a polyethylene sheath may be applied. Further, for mechanical strength, transversal reinforcement and steel wire armoring may be applied. To achieve a torsion-balanced design, two layers of armor wires applied in opposite directions are often used, and the armor is corrosion protected by a protective layer. A specific example is a bitumen compound and two layers of polypropylene yarn.

HVDC cables are often used to traverse extremely long distances, for example <NUM>. However, the cables are not able to be manufactured and/or transported in one continuous length, therefore the cables must be joined together at a transition joint/joint section.

Several conductor joints are known in the art for connecting the conductors of two high-voltage direct current (HVDC) cables.

<CIT>) discloses a method for joining the interfacing ends of two cables having a plurality of conductor strands. The method involves i) providing each of the cable ends with an enlarged terminal portion/enlarging member/metal inner sleeve of a greater diameter than the cable adjacent the end, ii) inserting the ends into a connecting tube/sleeve having an outer layer of explosive charge, and iii) detonating the explosive layer so as to compress the connecting tube/sleeve around the conductor strands. The terminal portions abut each other within the connecting tube to provide a joint after denotation.

The enlarging member/metal inner sleeve is provided longitudinally within the cable through the terminal portion to effect the enlargement to splay the outer strands of the cable. The resulting increased terminal extremity diameter of the cable relative to the cable adjacent the terminal portions results in the cable having a lager diameter than the rest of the conductor inside the sleeve of the connector/connecting tube. Thus, the conductors are so anchored within the sleeve/connecting tube that it cannot disadvantageously slip or be displaced. However, this known method provides a cable joint having areas of larger diameter than the remaining cable thereby providing a cable joint having an impaired bending property which is not capable to withstand the same tensile forces as the cables themselves without the joint.

<CIT>) discloses a method for connecting two cable ends by arranging the cable ends in an abutting or overlapping alignment inside a metal conductor sleeve followed by compressing the sleeve onto the cables by circumferential compression. The cable ends are thereby spliced together with little or no elongation of the cables. The sleeve has a regular smooth barrel shape avoiding corners and sharp edges and may have a roughened inner surface for better gripping the cable ends during compression. The resulting splice has a larger cross-sectional diameter than the conductor's cross-sectional diameter.

A compression connector for electric cable conductors is disclosed in <CIT>. Further conductor joints are disclosed in <CIT> and <CIT>.

It is thus an object of the present invention to provide a conductor joint that does not reduce the bending properties of the cables/conductors to be connected.

It is a further object of the invention to provide a conductor joint that can withstand the same tensile forces as the cables/conductors to be connected.

It is a further object of the invention to provide a conductor joint having similar or same cross-sectional diameter as the cross-sectional diameter of the two conductors to be connected.

It is a further object of the invention to provide a conductor joint having a short longitudinal length.

It is a further object of the invention to provide a method for installing a conductor in a time efficient and simple manner.

The invention provides a conductor joint for connecting conductors of two HVDC cables, for example HVDC-MI cables as disclosed in <CIT>.

The joint comprises two separate parts; an open-ended outer tubular sleeve and an elongated core element arranged within a sleeve opening, which together join the conductor ends of the two HVDC cables under circular hydraulic pressure. The conductors of the HVDC cables to be joined comprise a circular center wire surrounded by concentric layers of stranded wires, wherein the wires may be keystone-shaped.

Before joining the two HVDC cable conductors, any protective layers and insulating layers are removed from the end portion/terminal portion of each cable, thereby exposing the conductors.

More specifically the invention concerns a conductor joint for connecting a conductor end of a first cable with a conductor end of a second cable. The conductor joint comprises a tubular longitudinal sleeve of a sleeve length Ls having a sleeve opening at each longitudinal end and an elongated element arranged within the sleeve openings, preferably concentrically within the sleeve.

That the joint comprises a combination of a sleeve and an elongated element therein forms a double acting conductor joint which is configured such that, during connection of the conductor ends, compression of the sleeve causes the layers of stranded wires to be squeezed between the outer sleeve and the inner elongated element. Thus, when the external compression is performed directly on the sleeve by for example a hydraulic press, an internal compression of the joint is performed indirectly by the elongated element.

The resulting joint will have the same, or almost the same, outer diameter as the conductors of the first and second cable. Hence the sleeve, the elongated element and the layers of stranded wires are lengthened in the longitudinal direction during compression.

The inner diameter of the sleeve has a size and shape that allows insertion of the conductor ends of the first and second cable.

Further, the sleeve may have an inner surface shaped as two tubular stairs mirrored around a radial cross-sectional area at a longitudinal center of the sleeve.

The elongated element comprises a core rod having a core rod length Lr and a terminal rod wall at each longitudinal end and is preferably arranged longitudinally centered within the sleeve.

The conductor of both the first and the second cable that is to be interconnected may comprise a circular center wire surrounded by a plurality of concentrically layers of stranded wires. With such an arrangement the center wire would be the innermost wire of the conductor.

In an embodiment, the lower and higher step-surfaces of the inner surface of the sleeve form a step-shaped inner surface of the sleeve. After compression, the inner longitudinal step-shaped surface of the sleeve, the longitudinal outer surface of the layers of stranded wires and the outer longitudinal surface of the elongated element is altered into a wave-shape/S-form or partial wave-shape/S-form in the longitudinal direction, thereby forming a locked configuration/locking mechanism/ward between the layers of stranded wires of the conductor ends of the first and second cables and the conductor joint.

The compressed joint has a high mechanical and tensile strength, a strength that preferably corresponds to the mechanical tensile strength of the conductors of the cables. Further, the joint has a bending diameter that corresponds to the bending diameter of the conductor of the cables.

Before connecting the conductor ends of the first and second cable, a longitudinal portion of the circular center wire is removed from the conductor ends, thereby creating a recess surrounded by the layers of stranded wires. During insertion of the conductor ends into the sleeve, the core rod is inserted into the recess of each conductor end.

In a preferred embodiment the core rod comprises a core rod length Lr that is longer than the sleeve length Ls such that the core rod extends outside the sleeves inner surface during connection. As a result, the circular center wire of the conductors is not inserted inside the sleeve and therefore not radially compressed by the outer sleeve during compression. The resulting joint comprises an improved mechanical strength and tensile force.

The outer surface of the sleeve may have an inclination angle at each end towards the central longitudinal axis. The inclination angle may be from <NUM> to <NUM>° relative to the central longitudinal axis, more preferably from <NUM> to <NUM>°, e.g. <NUM>°.

This particular configuration is preferred when the conductor to be connected comprise more than two layers of stranded wires.

In one embodiment where the sleeve comprises a step wall arranged at a lower step surface end, distal to the nearest sleeve opening, each stair may further comprise an intermediate step surface and an intermediate step wall arranged between the step wall and the higher step surface.

Depending on the number of outer layers of stranded wires on the conductors to be connected, more steps can be arranged inside the inner sleeve and/or on the elongated element.

To make a joint that has the same tensile strength and bending diameter as the conductors to be connected the sleeve length Ls should be the same or longer than the diameter of at least one of the conductors of the cables to be connected. For example, the sleeve length may be at least <NUM> % longer than the diameter of one of the conductor ends to be connected, preferably at least <NUM>% longer, for example <NUM>% longer. Further, it is preferred that the sleeve is not longer than <NUM>% of the diameter of the conductor.

The core rod length Lr may be at least <NUM>% longer than the sleeve length Ls to ensure that the circular center wires of the conductors are not inserted inside the sleeve.

The core rod length may for example be <NUM>% longer than the sleeve length Ls. However, the core rod length Lr is preferably not more than <NUM>% longer than the sleeve length Ls.

The radial distance/thickness of the core wall may be equal or near equal to a radial distance/thickness of a layer of a stranded wire arranged immediately adjacent to a center wire of the conductor ends to be connected.

As already mentioned, a longitudinal portion of the circular center wire of the conductor ends of the first and second cable is removed creating a recess surrounded by the layers of stranded wires before inserting the conductor ends into the sleeve. During insertion of the conductor ends into the sleeve, the core rod is inserted into the recess of each cable end, thus the diameter of the core rod should be smaller or correspond to the diameter the recess/diameter of the circular center wire of the conductors to be connected.

Further, to provide a stronger locking mechanism within the joint after compression, a longitudinal length of the terminal rod wall at at least one longitudinal end may have a larger diameter than the remaining longitudinal length of the core rod, thereby creating a step. The diameter of the terminal rod wall is smaller or equal to the diameter of the recess. Such step may at contribute to a stronger locking mechanism of the joint.

In a preferred embodiment the dimeter of the terminal rod wall is less than <NUM>% larger than the dimeter of the remaining part of the core rod, preferably less than <NUM>% larger, for example <NUM>% larger.

The lengths of each step surface along a longitudinal axis of the sleeve may be equal or near equal for each stair.

After compression it is important that the joint has good conductive properties, preferably the same conducting properties as the conductors to be connected. To ensure that the conductive properties are not reduced when compared to the conducting properties of the conductors to be connected, the contacting surface between the radially adjoining surfaces inside the sleeve should have a high degree of friction/abutting surfaces. The radial distance of each step wall of the sleeve may thus equal or near equal to the corresponding radial thickness of a layer of a stranded wire. The radial direction is in this context facing perpendicular to the longitudinal axis of the sleeve. Further, the step surface of each step surface of each stair may have a length along the longitudinal axis of the sleeve which is at least twice the radial thickness/height/distance of the step wall. Further, more than <NUM>% of the outer surface of the elongated element may be threaded and/or more than <NUM>% of the inner surface of the sleeve is threaded for achieving a high degree of friction between the radially adjoining surfaces.

The crossing/corner between a step surface and a step wall can be curved having corners being rounded by an arc of a circle, and wherein the radius of the circle is in the range from <NUM> to <NUM>, preferably between <NUM> and <NUM>, more preferably between <NUM> and <NUM>, for example <NUM>.

The present invention further discloses a method for connecting the conductor end of the first cable with the conductor end of the second cable using a conductor joint.

The conductor ends of the first and second cable comprise.

The conductor joint comprises any one of the above-mentioned embodiments which include.

Before inserting the conductor ends of the first and second cable into the sleeve the conductor ends can be prepared using for example a milling tool, drill and/or any other kind of equipment such that a longitudinal part of the center wire is removed creating a recess surrounded by the innermost layer of stranded wires.

Further, if the sleeve is step-shaped, the layers of stranded wires may be prepared into stepped layers so that they may abut or be arranged adjacent to another layer of stranded wires or abut or be arranged adjacent to a corresponding step wall of the sleeve.

During insertion of the cable ends into the sleeve, the core rod of the elongated element is inserted into the recess of the conductor ends of the first and second cable such that the terminal rod wall abuts or is adjacent the terminal wall of the circular center wire.

In the embodiment where the elongated element comprises the core tube arranged around the core rod, the conductor ends can be further prepared for the innermost layer of stranded wires to abut or be adjacent to the core wall.

Further, the terminal wall of a third layer of stranded wires of the conductor end of the first cable may abut or be adjacent to a terminal wall of a third layer of stranded wires of the conductor end of the second cable.

Step iii) may further involve circularly compressing the sleeve until the diameter of a jointed section is the same or similar to the diameter of the conductor ends of the first and second cable.

The first and second cable may have the same configuration and dimensions.

Both the circular center wire and the stranded wires of the conductor can be made of a metal, such as copper or aluminum. The conductor joint parts are preferably made of the same metal as the conducting wires of the cable. The conductors of the two HVDC cables to be connected are preferably having the same or close to the same cross-sectional diameter.

Within the context of the application, the term "conductor" refers to the center wire and the total number stranded wires surrounding the center wire.

The term "conductor end" refers to an end-section of the conductors of the cables which is inserted into the sleeve of the conductor joint before compression, wherein any outer insulating layers and/or protective layers have been removed.

The term "stranded wires" refer to the relative thinner (compared to the central wire) wires wrapped about the central wire. In one embodiment the stranded wires have a key-shaped cross-section.

The term "keystone-shaped" means that the cross-section of each wire/strand has a key shaped form which can be of any form which allows each strand to lock itself to the adjacent strand such that a tight configuration between the strands is achieved. Such key-shaped strands and HVDC cables comprising such key-shaped strands are known in the art.

The term "radial" may not only refer to a direction perpendicular to the axial longitudinal direction but may also refer to a direction having an inclined angle and/or wherein the radial component is more than <NUM>% if not stated otherwise.

The term "wall" refers to a radial wall which can have different radial shapes such as straight, curved or arrow-shaped and is merely used to describe the terminal ends where the components abut or are arranged adjacent to each other before compression. Thus, the term should not be interpreted as a limiting feature. Further, the step wall does not have to be straight but may be uneven having recesses and/or being bulky.

The term "circular hydraulic pressure" refers to a hydraulic press exerting circular pressure onto the sleeve by a circular shaped die, thereby forming a circular shaped conductor joint causing some elongation of the conductor joint and conductors of the first and second cable during compression.

In the following description, numerous specific details are introduced to provide a thorough understanding of embodiments of the claimed joint and method. One skilled in the relevant art, however, will recognize that these embodiments can be practiced without one or more of the specific details.

In the drawings, like reference numerals have been used to indicate like parts, elements or features unless otherwise explicitly stated or implicitly understood from the context.

The invention will now be described with reference to a specific example of joining the conductors ends of two HVDC-MI cables. It should be understood however that the invention is suitable for joining other types for conductors as long as the conductor is of the type having a circular center wire surrounded by stranded wires.

<FIG> shows a first and second HVDC-MI cable <NUM>, <NUM>' known from prior art. Each cable <NUM>, <NUM>' comprises a conductor <NUM>, <NUM>' having a circular central wire <NUM>, <NUM>' surrounded by layers <NUM>, <NUM>' of stranded wires <NUM>, <NUM>' providing flexibility of the cables <NUM>, <NUM>'. Surrounding the conductor <NUM>, <NUM>' are a plurality of insulating and/or protective layers. Immediately adjacent conductor <NUM>, <NUM>' is an insulation layer <NUM>, <NUM>' which can be a mass-impregnated paper insulation known in the art, comprising a plurality of wrapped layers of oil-impregnated paper. Outside the insulation layer <NUM>, <NUM>' is a water tight lead barrier/layer <NUM>, <NUM>'. About the lead layer <NUM>, <NUM>' is arranged a polyethylene layer <NUM>, <NUM>'. A strengthening layer <NUM>, <NUM>' of galvanized steel is arranged about the polyethylene layer <NUM>, <NUM>'. An armor layer <NUM>, <NUM>' comprising galvanized steel bands protects the cable from abrasion and other forces. Finally, the cables <NUM>, <NUM>' comprise an outer protective layer <NUM>, <NUM>' bitumen / polypropylene yarn.

As shown in <FIG>, the central wire <NUM>, <NUM>' is a round/circular wire, and the stranded wires <NUM>, <NUM>' are keystone-shaped to be tightly packed about the central wire <NUM>, <NUM>'. In the examples used herein the first and second cable <NUM>, <NUM>' have five layers 26a-e, 26a'-e' of stranded wires <NUM>, <NUM>'. The stranded wires <NUM>, <NUM>' are wrapped in a spiral about the central wire <NUM>, <NUM>', with alternating layers being wrapped in alternating directions as shown in <FIG>. Each layer 26a-e, 26a'-e' of stranded wires <NUM>, <NUM>' has a terminal wall 27a-e, 27a'-e'. Further, the circular center wire <NUM>, <NUM>' has a terminal wall <NUM>, <NUM>'.

<FIG> shows an open view the tubular longitudinal sleeve <NUM> of the conductor joint showing a part of the inner and outer surface <NUM>, <NUM> of the sleeve <NUM>. The inner surface <NUM> of the sleeve <NUM> is shaped as two tubular stairs, referred to as a first and a second tubular stair <NUM>, <NUM>', which are mirrored around the radial cross-sectional area Y at the longitudinal center of the sleeve <NUM>. The longitudinal center of the sleeve being arranged where the X-axes and Y-axes in <FIG> meet.

The inner diameter of the sleeve <NUM> is decreasing towards the longitudinal center of the sleeve <NUM>, being at the largest at the sleeve openings <NUM>, <NUM>'. Each tubular stair <NUM>, <NUM>' has a lower step surface 2a, 2a' arranged nearest the corresponding sleeve opening <NUM>, <NUM>'. As shown, the lower step surface 2a of the first stair <NUM> is arranged nearest sleeve opening <NUM>, and the lower step surface 2a' of the second stair <NUM>' is arranged nearest sleeve opening <NUM>'. Further, each stair <NUM>, <NUM>' has a higher step surface 2c, 2c' and an intermediate step surface 2b, 2b'. The higher step surface 2c of the first stair <NUM> is flush with higher step surface 2c' of the second stair <NUM>'. The intermediate step surface 2b of the first stair <NUM> is arranged between the lower step surface 2a and the higher step surface 2c, while the intermediate step surface 2b' of the second stair is arranged between the lower step surface 2a' and the higher step surface 2c'.

In the first stair <NUM>, arranged between the lower step surface 2a and the intermediate step surface 2b, is a first step wall 3a oriented parallel to the radial cross-sectional direction/radial axis Y of the sleeve <NUM>.

Further, the crossing/corner between the lower step surface 2a and the first step wall 3a is curved and the crossing/corner between the first step wall 3a and the intermediate step surface 2b is curved.

Between the intermediate step surface 2b and the higher step surface 2c, is arranged a second step wall 3b oriented parallel to the radial cross-sectional direction of the sleeve <NUM>.

The crossing/corner between the intermediate step surface 2b and the second step wall 3b is curved and the crossing/corner between the second step wall 3b and the higher step surface 2c is curved.

It is also shown that the step surfaces 2a, 2b, 2c have equal longitudinal lengths arranged parallel to the longitudinal axis X of the sleeve.

Also, the first and second step wall 3a, 3b have the same radial distance/thickness.

Since the first and second stair <NUM>, <NUM>' are mirrored, it is implicit that the second stair <NUM>' has the same, but mirrored configuration and will not be described in further detail.

The outer surface <NUM> of the sleeve is shown in <FIG> and is substantially tubular. The outer surface <NUM> of the sleeve <NUM> is parallel to the longitudinal axis X of the sleeve <NUM> and is having an inclination angle at each end towards the central longitudinal axis X of the sleeve. The shown inclination angle is <NUM>°. Further, about <NUM>% of the outer surface <NUM> of the sleeve <NUM> is shown being parallel with the longitudinal axis X of the sleeve <NUM>.

<FIG> illustrate the elongated element <NUM> of the conductor joint having a core tube <NUM> arranged around the core rod <NUM>. The core tube <NUM> and the core rod <NUM> are concentric and the core tube <NUM> is longitudinally centered to the core rod <NUM>.

A first and second core wall <NUM>, <NUM>' is arranged at each longitudinal end of the core tube <NUM> between the core rod <NUM> and the core tube <NUM>. Each core wall <NUM>, <NUM>' is oriented parallel to the radial cross-section direction of the elongated element <NUM>.

The core walls <NUM>, <NUM>' create a step from the outer surface of the core rod <NUM> to the outer surface of the core tube <NUM>.

The crossing/corner between the outer surface of the core rod <NUM> and the first and/or second core wall <NUM>, <NUM>' is curved and the crossing/corner between the outer surface of the core tube <NUM> and the first and/or second core wall <NUM>, <NUM>' is curved.

Further the illustration of the elongated element shows that the outer surface of the core rod <NUM> and core tube <NUM> are threaded.

It is also shown that the core element <NUM> has a first terminal wall <NUM> the one longitudinal end, and a second terminal wall <NUM>' at the other terminal end.

In <FIG> the terminal walls <NUM>, <NUM>' have an arrow shape and a longitudinal part having a larger diameter than the remaining longitudinal length of the core rod <NUM> creating a step near the longitudinal ends of the core rod <NUM>.

In <FIG> a longitudinal length of the terminal walls <NUM>, <NUM>' also have a larger diameter than the remaining longitudinal length of the core rod <NUM> thereby creating a step near the longitudinal ends of the core rod <NUM>. Such step may contribute to a stronger locking mechanism of the joint. Further, the terminal walls <NUM>, <NUM>' are radially oriented.

<FIG> shows a cross sectional view along A-A in <FIG> which illustrate that the diameter of the core tube <NUM> is greater than the diameter of the core rod <NUM>.

<FIG> shows the connection between the conductor joint and the conductor ends of the first and second cable after inserting the conductor ends into the sleeve <NUM>.

The inner surface of the sleeve <NUM> of the conductor joint has the same configuration as shown in <FIG> and the elongated element <NUM> has the same configuration as shown in <FIG>.

The first cable comprises the circular center wire <NUM> being the innermost wire of the cable. The center wire <NUM> has a terminal wall <NUM> which is shown to have a corresponding shape to the arrow-shaped first terminal wall <NUM> of the core rod <NUM> of the elongated element <NUM> and the radial face of the terminal wall <NUM> of the center wire <NUM> is abutting the radial phase of the first terminal wall <NUM> of the core rod <NUM>.

A first layer 26a of stranded wires of the first cable is immediately surrounding the circular center wire <NUM>. The first layer 26a of stranded wires is therefore the innermost layer of stranded wires. The first layer 26a of stranded wires has a terminal wall 27a which abuts the first core wall <NUM> of the elongated element <NUM>.

The second cable comprises the circular center wire <NUM>' being the innermost wire of the second cable. The center wire <NUM>' has a terminal wall <NUM>' which is shown to have a corresponding shape to the arrow-shaped second terminal wall <NUM>' of the core rod <NUM> of the elongated element <NUM> and the radial face of the terminal wall <NUM>' of the center wire <NUM>' is abutting the radial phase of the second terminal wall <NUM>' of the core rod <NUM>.

A first layer 26a' of stranded wires of the second cable is immediately surrounding the circular center wire <NUM>'. The first layer 26a' of stranded wires is therefore the innermost layer of stranded wires. The first layer 26a' of stranded wires has a terminal wall 27a' which abuts the second core wall <NUM>' of the elongated element <NUM>.

A second layer 26b of stranded wires of the first cable is immediately surrounding the first layer 26a of stranded wires, and a second layer 26b' of stranded wires of the second cable is immediately surrounding the first layer 26a' of stranded wires. The second layer 26b has a terminal wall 27b which abuts a terminal wall 27b' of the second layer 26b' of stranded wires of the second cable.

A third layer 26c of stranded wires of the first cable is immediately surrounding the second layer 26b of stranded wires, and a third layer 26c' of stranded wires of the second cable is immediately surrounding the second layer 26b' of stranded wires. The third layer 26c has a terminal wall 27c which abuts a terminal wall 27c' of the third layer 26c' of stranded wires of the second cable.

A fourth layer 26d of stranded wires of the first cable is immediately surrounding the third layer 26c of stranded wires. The fourth layer 26d is further having a terminal wall 27d abutting the second step wall 3b of first stair of the sleeve <NUM>.

A fourth layer 26d' of stranded wires of the second cable is immediately surrounding the third layer 26c' of stranded wires. The fourth layer 26d' is further having a terminal wall 27d' abutting the second step wall 3b' of second stair of the sleeve <NUM>.

A fifth layer 26e of stranded wires of the first cable is immediately surrounding the fourth layer 26d of stranded wires. The fifth layer 26e, which is the outermost layer of stranded wires of the first cable, is further having a terminal wall 27e abutting the first step wall 3a of the first stair of the sleeve <NUM>.

A fifth layer 26e' of stranded wires of the second cable is immediately surrounding the fourth layer 26d' of stranded wires. The fifth layer 26e', which is the outermost layer of stranded wires of the second cable, is further having a terminal wall 27e' abutting the first step wall 3a' of the second stair of the sleeve <NUM>.

<FIG> show the connection between the conductor joint and the conductor ends of the first and second cable shown in <FIG> before and after compressing the conductor joint respectively. The rectangular box B in <FIG> is shown in <FIG> and the connection between the conductor joint and the conductor ends of the first and second cable is therefore having the same configuration as shown in <FIG>.

The compression of the sleeve <NUM> causes the layers of stranded wires to be squeezed between the outer sleeve <NUM> and the inner elongated element <NUM>. This external compression is performed directly on the sleeve by for example a hydraulic press of <NUM> tons (<NUM><NUM>) or more. An internal compression of the joint is performed indirectly by the elongated element.

The resulting joint shown in <FIG> same outer diameter as the conductors of the first and second cable. The elongated element <NUM> and the layers of stranded wires 26a-e, 26a'-e' have been lengthened in the longitudinal direction during compression.

After compression, as shown in <FIG>, the inner longitudinal step-shaped surface of the sleeve <NUM>, the longitudinal outer surface of the layers 26a-e, 26a'-e' of stranded wires and the outer longitudinal surface of the elongated element <NUM> is altered into a wave-shape/S-form in the longitudinal direction and a locked configuration/locking mechanism/ward between the layers 26a-e, 26a'-e' of stranded wires of the conductor ends of the first and second cables and the conductor joint is formed.

As can be seen from <FIG> air pockets <NUM> are formed between the terminal wall of the second layer 26b of stranded wires of the first cable which before compression was abutting the terminal wall of the second layer 26b' of stranded wires of the second cable. Air pockets are also formed between the terminal wall of third layer 26c of stranded wires of the first cable which before compression was abutting the terminal wall of the third layer 26c' of stranded wires of the second cable. Thus, the electric current passing through the conductor joint after connection is also moved in an alternating direction having a wave-shape/S-form in the longitudinal direction thereby avoiding being terminated by the air pockets <NUM>. A threaded outer surface of the elongated element and a threaded inner surface of the sleeve is therefore advantageous for achieving a high degree of friction between the radially adjoining surfaces allowing the electric current to pass therethrough.

This example relates to the connection of the conductor ends of two HVDC cables comprising conductors having a center wire and five layers of stranded wires as shown in <FIG>. The conductors of the two cables have an outer diameter of <NUM> and has a bending diameter of <NUM>.

The largest outer diameter of the sleeve is <NUM> the longitudinal length of the sleeve, sleeve length, Ls is <NUM>. The inclination angle at each longitudinal end towards the central longitudinal axis X of the outer surface of the sleeve is <NUM>°.

The inner diameter of the sleeve at each longitudinal end is about <NUM>. The inner diameter at the radial cross section of the sleeve at the lower step of the sleeve is also about <NUM>. The inner diameter at the radial cross section of the sleeve at the intermediate step is about <NUM>, while the inner diameter at the radial cross section of the sleeve at the higher step is about <NUM>. The longitudinal length of each step surface is about <NUM>.

The elongated element has a core rod length Lr of <NUM>, wherein the arrow shaped terminal wall at each longitudinal end of the elongated element has a longitudinal length of <NUM>. The tube length Lt is <NUM>. The length of the core rod at the terminal rod wall having a larger diameter than the remaining longitudinal length of the core rod is <NUM> and is having a diameter of <NUM>, while the remaining part of the core rod has a diameter of <NUM>. The diameter of the core tube is <NUM>.

In the preceding description, various aspects of the conductor joint according to the invention have been described with reference to the illustrative embodiment. For purposes of explanation, specific numbers, systems and configurations were set forth in order to provide a thorough understanding of the joint and its workings. However, this description is not intended to be construed in a limiting sense. Various modifications and variations of the illustrative embodiment, as well as other embodiments of the conductor joint, which are apparent to persons skilled in the art to which the disclosed subject matter pertains, are deemed to lie within the scope of the present invention.

Claim 1:
Assembly comprising a first cable, a second cable, and a conductor joint connecting a conductor end (<NUM>) of the first cable (<NUM>) with a conductor end (<NUM>') of the second cable (<NUM>'), wherein the conductor joint comprises
- a tubular longitudinal sleeve (<NUM>) of a sleeve length Ls having a sleeve opening (<NUM>, <NUM>') at each longitudinal end with an inner diameter allowing insertion of the conductor ends (<NUM>, <NUM>') to be connected, and
- an elongated element (<NUM>) arranged within the sleeve openings (<NUM>, <NUM>'), wherein the elongated element (<NUM>) comprises a core rod (<NUM>) having a core rod length Lr and a terminal rod wall (<NUM>, <NUM>') at each longitudinal end, wherein the elongated element (<NUM>) further comprises
• a core tube (<NUM>) concentrically arranged around the core rod (<NUM>) having a core tube length Lt shorter than the core rod length Lr and wherein the diameter of the core tube (<NUM>) is larger than the diameter of the core rod (<NUM>), and
• a core wall (<NUM>, <NUM>') arranged between the core rod (<NUM>) and the core tube (<NUM>) oriented along a radial orientation of the elongated element (<NUM>)
characterized in that the conductor ends of the first and second cable comprise
- a circular center wire (<NUM>, <NUM>') comprising a terminal wall (<NUM>, <NUM>'),
- a plurality of concentrical layers (26a-26e, 26a'-26e') of stranded wires (<NUM>, <NUM>') surrounding the circular center wire (<NUM>,<NUM>') wherein each layer (26a-e, 26a'-26e') of stranded wires (<NUM>,<NUM>') comprises a terminal wall (27a-e, 27a'-27e'),
such that a recess is created by a removal of a longitudinal portion of the circular center wire (<NUM>,<NUM>') from the conductor ends and by the surrounding layers of stranded wires (<NUM>,<NUM>'), such that each longitudinal end of the core rod (<NUM>) is inserted into said recess.