Cable connection structure, connected power cable, and method of producing cable connection structure

Abstract

A conductor connection part of a cable connection structure has: a central weld part; and a sleeve provided to surround an outer circumference of a region including the central weld part at a position coinciding with at least a part of the first outermost layer in a radial direction of the first conductor, wherein the sleeve has a plurality of first slit parts, penetrating in a thickness direction of the sleeve, extending from the first end toward the second end, being provided at intervals in a circumferential direction of the sleeve, and each having at least one of the plurality of first outermost wires inserted therein, and a first outermost weld part where the sleeve is welded to at least one of the plurality of first outermost wires at least inside each of the plurality of first slit parts.

Description

CABLE CONNECTION STRUCTURE, CONNECTED POWER CABLE, AND METHOD OF PRODUCING CABLE CONNECTION STRUCTURE

[0001] The present disclosure relates to a cable connection structure, a connected power cable, and a method of producing the cable connection structure.

[0002] In cable connection structures, a pair of conductors may be welded to each other in some cases (e.g., Patent Literature 1).

[0003] PTL. 1: European Patent Publication No. 3261181

[0004] According to an aspect of the present disclosure, there is provided a cable connection structure including: 　　　a first power cable having a first conductor; 　　　a second power cable having a second conductor; and 　　　a conductor connection part connecting the first conductor and the second conductor, 　　　wherein 　　　the first conductor has a first inner layer including a plurality of first inner layer wires, and a first outermost layer including a plurality of first outermost wires surrounding the first inner layer, 　　　the second conductor has a plurality of second wires, 　　　the conductor connection part has: 　　　　　　a central weld part where end parts of the plurality of first inner layer wires of the first conductor are welded to end parts of at least some of the plurality of second wires of the second conductor; and 　　　　　　a sleeve configured as a metallic cylindrical member and provided to surround an outer circumference of a region including the central weld part at a position coinciding with at least a part of the first outermost layer in a radial direction of the first conductor, 　　　　　　wherein the sleeve has 　　　　　　　　　a first end in an axial direction of the sleeve; 　　　　　　　　　a second end opposite to the first end; 　　　　　　　　　a plurality of first slit parts, penetrating in a thickness direction of the sleeve, extending from the first end toward the second end, being provided at intervals in a circumferential direction of the sleeve, and each having at least one of the plurality of first outermost wires inserted therein, and 　　　　　　　　　a first outermost weld part where the sleeve is welded to at least one of the plurality of first outermost wires at least inside each of the plurality of first slit parts.

[0005] Fig. 1 is a schematic cross-sectional view along an axial direction of a conductor, illustrating a cable connection structure according to a first embodiment of the present disclosure.Fig. 2 is a schematic side view, illustrating a conductor connection part according to the first embodiment of the present disclosure.Fig. 3 is a schematic cross-sectional view along an axial direction of a conductor, illustrating the conductor connection part according to the first embodiment of the present disclosure.Fig. 4(a) and Fig. 4(b) are cross-sectional views along the lines A-A' and B-B' in Fig. 3, respectively.Fig. 5 is a schematic perspective view illustrating a partial enlargement of the conductor connection part according to the first embodiment of the present disclosure.Fig. 6 is a partial enlargement of Fig. 2.Fig. 7 is a flow chart illustrating a method of producing the cable connection structure according to the first embodiment of the present disclosure.Fig. 8 is a schematic side view, illustrating a conductor connection part according to a modified example 1-1 of the first embodiment of the present disclosure.Fig. 9 is a partial enlargement of Fig. 8.Fig. 10 is a schematic cross-sectional view along the axial direction of the conductor, illustrating a conductor connection part according to a modified example 1-2 of the first embodiment of the present disclosure.Fig. 11 is a schematic side view, illustrating a part of a conductor connection structure according to a modified example 1-3 of the first embodiment of the present disclosure.Fig. 12 is a schematic side view, illustrating a part of a conductor connection structure according to a modified example 1-4 of the first embodiment of the present disclosure.Fig. 13 is a schematic side view, illustrating a conductor connection part according to a modified example 1-5 of the first embodiment of the present disclosure.Fig. 14 is a schematic side view, illustrating a conductor connection part according to a modified example 1-6 of the first embodiment of the present disclosure.Fig. 15 is a schematic side view of a conductor connection part according to a second embodiment of the present disclosure.Fig. 16 is a schematic cross-sectional view along the axial direction of the conductor, illustrating the conductor connection part according to the second embodiment of the present disclosure.Fig. 17 is a schematic cross-sectional view along the axial direction of the conductor, illustrating a conductor connection part according to a modified example 2-1 of the second embodiment of the present disclosure.

[0006] An object of the present disclosure is to improve mechanical performance and electrical performance of a cable connection structure.

[0007] According to the present disclosure, mechanical performance and electrical performance of the cable connection structure can be improved.

[0008] <Knowledges Obtained by the Inventors> 　　　First, the knowledges obtained by the inventors will be described.

[0009] For example, the connection structure of the power cable that is laid on the bottom of water requires a so-called factory joint (FJ) technology to connect a pair of power cables so that the cable connection structure has the same outer diameter as the outer diameter of the power cable. In the conductor connection part of such a cable connection structure, a central weld part is formed where a pair of conductors are welded.

[0010] When there is a crack or an unwelded area in the central weld part of the conductor connection part, mechanical performance of the conductor connection part may be degraded due to the tension at the time of laying the connected power cable having the cable connection structure. Additionally, when there is a crack or an unwelded area in the central weld part, resistance of the conductor connection part will be higher. For this reason, the crack or unwelded area in the central weld part may locally generate abnormal heat due to the current upon energization.

[0011] Therefore, the central weld part is required to have both mechanical performance and electrical performance. As a result, high level of technology is required to form the central weld part.

[0012] The present inventors investigated the cable connection structure mentioned above, and as a result, found that the following new problems arise.

[0013] (i) New problem regarding welding 　　　Welding of the conductor in the central weld part has been performed manually by workers. For this reason, welding has been highly dependent on the skill of the worker, the performance of the equipment, and the like. In other words, mechanical performance and electrical performance of the central connection part has been prone to variation. For this reason, it has been difficult to stably ensure mechanical performance and electrical performance with good reproducibility in the central connection part.

[0014] In particular, the tensile strength of the central weld part in which the conductor contains aluminum is lower than the tensile strength of the central weld part in which the conductor contains copper. Therefore, extremely advanced technology has been required to form the central weld part in which the conductor contains aluminum.

[0015] (ii) Novel problem regarding sleeve compression 　　　A possible cable connection structure is one in which a sleeve is placed to surround the outer circumference of a region including a central weld part that is welded up to a conductor outermost layer and the sleeve is compressed.

[0016] In the cable connection structure mentioned above, when the sleeve is compressed too strongly, cracks may occur in the central weld part. Furthermore, in this case, the end part of the sleeve bites into the wires of the conductor with which the sleeve is in contact. Therefore, mechanical performance and electrical performance of the wire may be degraded.

[0017] Furthermore, even when the sleeve is compressed in the cable connection structure mentioned above, the outer diameter of the sleeve is larger than the outer diameter of the conductor. In this case, local mechanical strain can occur in the vicinity of the end part of the sleeve when bending or twisting is applied to the cable connection structure. Thus, excessive stress is applied to the insulating layer in the cable connection structure. As a result, mechanical performance and electrical performance of the cable connection structure may be degraded. Furthermore, when voltage is applied to the power cable, the electric field stress is non-uniform in the vicinity of the end part of the sleeve that protrudes outward from the conductor of the power cable. In this respect, the electrical performance of the cable connection structure may be degraded.

[0018] (iii) New problems regarding different diameter connections 　　　In a cable connection structure connecting a first conductor and a second conductor, there is a case where the outer diameter of the second conductor is smaller than the outer diameter of the first conductor (case of different diameter connection). In the central weld part of the cable connection structure, the first conductor and the second conductor are welded such that the outer diameter of the central weld part gradually decreases from the first conductor toward the second conductor.

[0019] In the above-mentioned cable connection structure for different diameter connection, bending or twisting strain is likely to accumulate in the central weld part where the outer diameter gradually changes. As a result, mechanical performance and electrical performance of the cable connection structure may be degraded.

[0020] (Investigation by inventors) 　　　The present inventors have studied intensively, and as a result have found a configuration that solves the new problems mentioned above and improves mechanical performance and electrical performance of the cable connection structure by improving the shape and welding aspect of the sleeve.

[0021] The present disclosure is based on the above-described knowledges found by the present inventors.

[0022] <Embodiments of Disclosure> 　　　Next, embodiments of the present disclosure will be listed and described.

[0023] [1] A cable connection structure according to an aspect of the present disclosure includes: 　　　a first power cable having a first conductor; 　　　a second power cable having a second conductor; and 　　　a conductor connection part connecting the first conductor and the second conductor, 　　　wherein 　　　the first conductor has a first inner layer including a plurality of first inner layer wires, and a first outermost layer including a plurality of first outermost wires surrounding the first inner layer, 　　　the second conductor has a plurality of second wires, 　　　the conductor connection part has: 　　　　　　a central weld part where end parts of the plurality of first inner layer wires of the first conductor are welded to end parts of at least some of the plurality of second wires of the second conductor; and 　　　　　　a sleeve configured as a metallic cylindrical member and provided to surround an outer circumference of a region including the central weld part at a position coinciding with at least a part of the first outermost layer in a radial direction of the first conductor, 　　　　　　wherein the sleeve has 　　　　　　　　　a first end in an axial direction of the sleeve; 　　　　　　　　　a second end opposite to the first end; 　　　　　　　　　a plurality of first slit parts, penetrating in a thickness direction of the sleeve, extending from the first end toward the second end, being provided at intervals in a circumferential direction of the sleeve, and each having at least one of the plurality of first outermost wires inserted therein, and 　　　　　　　　　a first outermost weld part where the sleeve is welded to at least one of the plurality of first outermost wires at least inside each of the plurality of first slit parts. 　　　According to this configuration, mechanical performance and electrical performance of the cable connection structure can be improved.

[0024] [2] In the cable connection structure according to [1], 　　　the central weld part has no cracks. 　　　According to this configuration, mechanical performance and electrical performance of the central weld part can be maintained.

[0025] [3] In the cable connection structure according to [1] or [2], 　　　the first outermost weld part is uncompressed. 　　　According to this configuration, mechanical performance and electrical performance of the first outermost weld part can be maintained.

[0026] [4] In the cable connection structure according to any one of [1] to [3], 　　　the sleeve is uncompressed. 　　　According to this configuration, excessive stress can be prevented from being applied to the central weld part and each wire of the conductor.

[0027] [5] In the cable connection structure according to any one of [1] to [3], 　　　the sleeve is compressed, and 　　　a single inner layer wire among the plurality of the first inner layer wires, which is in contact with the sleeve, satisfies formula (3): 　　　0 < di0 - dimin ≦ 0.5 ・・・ (3) 　　　wherein 　　　di0 is a diameter of a part of a single first inner layer wire among the plurality of first inner layer wires, which is not in contact with the sleeve, expressed in mm, and 　　　dimin is a minimum diameter of the single first inner layer wire among the plurality of first inner layer wires, which is in contact with the sleeve, expressed in mm. 　　　According to this configuration, excessive stress can be prevented from being applied to the central weld part and each wire of the conductor.

[0028] [6] In the cable connection structure according to any one of [1] to [3], and [5], 　　　the sleeve is compressed, and 　　　the first inner layer satisfies formula (4): 　　　0 < Di0 - Dimin ≦ 1 ・・・ (4) 　　　wherein 　　　Di0 is a diameter of a circumscribed circle of the first inner layer at a position not in contact with the sleeve, expressed in mm, and 　　　Dimin is a minimum diameter of a circumscribed circle of the first inner layer at a position in contact with the sleeve, expressed in mm. 　　　According to this configuration, excessive stress can be prevented from being applied to the central weld part and each wire of the conductor.

[0029] [7] In the cable connection structure according to any one of [1] to [3], [5], and [6], 　　　the sleeve has convex parts or concave parts on its inner circumferential surface, and 　　　the sleeve is compressed so that the convex parts bite into the first inner layer or the first inner layer fits into the concave parts. 　　　According to this configuration, adhesion between the sleeve and the first conductor can be improved.

[0030] [8] In the cable connection structure according to any one of [1] to [7], 　　　an outer diameter of the sleeve is 1.1 times or less an outer diameter of the first outermost layer in a region where the sleeve is not disposed. 　　　According to this configuration, it is possible to reduce electric field stress and suppress the occurrence of mechanical strain in the vicinity of a first end and a second end of the sleeve.

[0031] [9] In the cable connection structure according to any one of [1] to [8], 　　　a single first outermost wire among the plurality of first outermost wires is inserted into and welded to one of the plurality of first slit parts. 　　　According to this configuration, a single first outermost wire can be reliably fixed to the sleeve within the first slit part of the first outermost weld part.

[0032]

[0010] In the cable connection structure according to any one of [1] to [8], 　　　two or more first outermost wires among the plurality of first outermost wires are inserted into and welded to one of the plurality of first slit parts. 　　　According to this configuration, the weld area per first slit part of the first outermost weld part can be easily increased.

[0033]

[0011] In the cable connection structure according to any one of [1] to

[0010] , 　　　each of the plurality of first slit parts satisfies formula (1): 　　　d1 - Σd2 ≧ 0.2 ・・・ (1) 　　　wherein 　　　d1 is a width of each of the plurality of first slit parts in a circumferential direction of the sleeve, expressed in mm, 　　　d2 is a diameter of one first outermost wire inserted in each of the plurality of first slit parts, expressed in mm, and 　　　Σd2 is a sum of d2. 　　　According to this configuration, the first outermost wire can be easily inserted into the first slit part, and the sleeve and the first outermost wire can be easily welded.

[0034]

[0012] In the cable connection structure according to any one of [1] to

[0011] , 　　　the sleeve has a plurality of first non-slit parts between the plurality of first slit parts, and 　　　in the first outermost weld part, each of end parts of first outermost wires other than first outermost wires inserted into the plurality of first slit parts is further welded to each of end parts of the plurality of first non-slit parts. 　　　According to this configuration, the weld area between the sleeve and the first conductor in the first outermost weld part can be further increased.

[0035]

[0013] In the cable connection structure according to

[0012] , 　　　each of the plurality of first non-slit parts has a gap between itself and each of the first outermost wires other than the first outermost wires inserted into the plurality of first slit parts, and 　　　in the gap in the first outermost weld part, each of end parts of the first outermost wires other than the first outermost wires inserted into the plurality of first slit parts is further welded to each of end parts of the plurality of first non-slit parts. 　　　According to this configuration, the first non-slit part and the first outermost wire can be easily welded.

[0036]

[0014] In the cable connection structure according to

[0012] or

[0013] , 　　　a single first outermost wire other than the first outermost wires inserted into the plurality of first slit parts is welded to one of the plurality of first non-slit parts. 　　　According to this configuration, the single first outermost wire can be reliably fixed to the first non-slit part in the first outermost weld part.

[0037]

[0015] In the cable connection structure according to

[0012] or

[0013] , 　　　two or more first outermost wires other than the first outermost wires inserted into the plurality of first slit parts are welded to one of the plurality of first non-slit parts. 　　　According to this configuration, the weld area per first non-slit part of the first outermost weld part can be easily increased.

[0038]

[0016] In the cable connection structure according to any one of

[0012] to

[0015] , 　　　each of the plurality of first non-slit parts satisfies formula (2): 　　　Σd4 - d3 ≧ 0.2 ・・・ (2) 　　　wherein 　　　d3 is a width of each of the plurality of first non-slit parts in a circumferential direction of the sleeve, expressed in mm, 　　　d4 is a diameter of one first outermost wire welded to each of the plurality of first non-slit parts, expressed in mm, and 　　　Σd4 is a sum of d4. 　　　According to this configuration, it is possible to easily obtain a width of the first slit part that allows the first outermost wire to be inserted therein.

[0039]

[0017] In the cable connection structure according to any one of [1] to

[0016] , 　　　the plurality of first outermost wires are twisted together in a spiral shape, and 　　　each of the plurality of first slit parts is provided along a twisted direction of the plurality of first outermost wires. 　　　According to this configuration, the plurality of first outermost wires can be stably engaged with the sleeve when a pulling force is applied to the first conductor in the axial direction of the first conductor.

[0040]

[0018] In the cable connection structure according to any one of [1] to

[0016] , 　　　each of the plurality of first slit parts is provided linearly in an axial direction of the sleeve. 　　　According to this configuration, the plurality of first slit parts can be easily formed in the sleeve.

[0041]

[0019] In the cable connection structure according to any one of [1] to

[0018] , 　　　the first outermost wire inserted into each of the plurality of first slit parts is arranged obliquely with respect to an extending direction of each of the plurality of first slit parts. 　　　According to this configuration, at least a part of the first outermost wire can be easily brought into abutment with an inner wall of the first slit part.

[0042]

[0020] In the cable connection structure according to any one of [1] to

[0019] , 　　　at least a part of the first outermost wire inserted into each of the plurality of first slit parts abuts against an inner wall of each of the plurality of first slit parts. 　　　According to this configuration, the first outermost wire can be stably engaged with the inner wall of the first slit part.

[0043]

[0021] In the cable connection structure according to

[0020] , 　　　an end part of the first outermost wire inserted into each of the plurality of first slit parts abuts against the inner wall of each of the plurality of first slit parts. 　　　According to this configuration, the first outermost wire can be stably engaged with the inner wall of the first slit part.

[0044]

[0022] In the cable connection structure according to

[0020] or

[0021] , 　　　a part of the first outermost wire inserted into each of the plurality of first slit parts abuts against a corner of an open end part of each of the plurality of first slit parts. 　　　According to this configuration, the first outermost wire can be stably engaged with the inner wall of the first slit part.

[0045]

[0023] In the cable connection structure according to any one of [1] to

[0018] , 　　　at least a part of the first outermost wires inserted into each of the plurality of first slit parts is not in contact with an inner wall of each of the plurality of first slit parts. 　　　According to this configuration, a welding material can be easily flowed into a gap between the first outermost wire and the inner wall of the first slit part.

[0046]

[0024] In the cable connection structure according to any one of [1] to

[0023] , 　　　among the plurality of first slit parts, at least one first slit part has a length different from those of other first slit parts. 　　　According to this configuration, a shape of the first outermost weld part can be complicated to improve the mechanical performance of the cable connection structure.

[0047]

[0025] In the cable connection structure according to

[0024] , 　　　the central weld part has a short weld part which has a weld length shorter than those of other parts in an axial direction of the first conductor, and 　　　among the plurality of first slit parts, at least one first slit part closer to the short weld part than other first slit parts has a length longer than those of the other first slit parts. 　　　According to this configuration, a part of the central weld part having low welding strength can be strengthened by the first outermost weld part.

[0048]

[0026] In the cable connection structure according to

[0024] , 　　　the plurality of first slit parts includes: 　　　　　　at least one first short slit part; 　　　　　　at least one first medium slit part which is longer than the first short slit part; and 　　　　　　at least one first long slit part which is longer than the first medium slit part. 　　　According to this configuration, the reduction in strength of the first outermost weld part at the end parts of the plurality of first slit parts due to heat history can be suppressed.

[0049]

[0027] In the cable connection structure according to any one of [1] to

[0026] , 　　　an outer diameter of the second conductor is equal to an outer diameter of the first conductor, 　　　the second conductor has a second inner layer including a plurality of second inner layer wires, and a second outermost layer including a plurality of second outermost wires, 　　　in the central weld part, end parts of the plurality of first inner layer wires of the first conductor and end parts of the plurality of second inner layer wires of the second conductor are welded, 　　　the sleeve is provided to surround an outer circumference of a region including the central weld part at a position coinciding with both at least a part of the first outermost layer in the radial direction of the first conductor and at least a part of the second outermost layer in a radial direction of the second conductor, 　　　the sleeve further has: 　　　　　　a plurality of second slit parts, penetrating in the thickness direction of the sleeve, extending from the second end toward the first end, being provided at intervals in the circumferential direction of the sleeve, and each having at least one of the plurality of second outermost wires inserted therein, and 　　　　　　a second outermost weld part where the sleeve and at least one of the plurality of second outermost wires are welded at least inside each of the plurality of second slit parts. 　　　According to this configuration, the second outermost weld part can also provide the same effect as that provided by the first outermost weld part.

[0050]

[0028] In the cable connection structure according to

[0027] , 　　　a position of at least a part of each of the plurality of first slit parts in the circumferential direction of the sleeve is equal to a position of at least a part of each of the plurality of second slit parts. 　　　According to this configuration, the first outermost weld part and the second outermost weld part can be formed in a well-balanced manner.

[0051]

[0029] In the cable connection structure according to

[0027] , 　　　a position of at least a part of each of the plurality of first slit parts in the circumferential direction of the sleeve is different from a position of at least a part of each of the plurality of second slit parts. 　　　According to this configuration, parts with low stiffness in the sleeve due to the plurality of first slit parts and the plurality of second slit parts can be dispersed.

[0052]

[0030] In the cable connection structure according to any one of [1] to

[0026] , 　　　an outer diameter of the second conductor is smaller than an outer diameter of the first conductor, and 　　　the sleeve has an outer diameter gradually decreasing from a position close to the first conductor toward the second end. 　　　According to this configuration, the cable connection structure can be stably formed at the position where the outer diameter changes from the first conductor toward the second conductor.

[0053]

[0031] In the cable connection structure according to any one of [1] to

[0030] , 　　　the first conductor and the second conductor contain aluminum or an aluminum alloy. 　　　According to this configuration, mechanical performance and electrical performance of the cable connection structure can be improved even when the conductor contains aluminum or an aluminum alloy.

[0054]

[0032] In the cable connection structure according to any one of [1] to

[0030] , 　　　the first conductor and the second conductor contain copper or a copper alloy. 　　　According to this configuration, mechanical performance and electrical performance of the cable connection structure can be improved even when the conductor contains copper or a copper alloy.

[0055]

[0033] In the cable connection structure according to any one of [1] to

[0032] , 　　　the sleeve contains aluminum, copper, or stainless steel. 　　　According to this configuration, high mechanical performance and high electrical performance of the sleeve itself can be obtained.

[0056]

[0034] A connected power cable according to another aspect of the present disclosure includes at least one cable connection structure according to any one of [1] to

[0033] . 　　　According to this configuration, mechanical performance and electrical performance of the cable connection structure can be improved.

[0057]

[0035] A method of producing a cable connection structure according to another aspect of the present disclosure is a method of producing the cable connection structure according to any one of [1] to

[0033] . 　　　According to this configuration, mechanical performance and electrical performance of the cable connection structure can be improved.Details of Embodiment of Disclosure

[0058] Next, an embodiment of the present disclosure will be described below with reference to the drawings. The present disclosure is not limited to these illustrations, but intended to be indicated by claims and encompass all the changes which fall within the meaning and scope equivalent to claims.

[0059] <First Embodiment of the Disclosure> (1) Outline of connected power cable and cable connection structure 　　　The connected power cable 10 and the cable connection structure (cable connection part) 20 according to the first embodiment of the present disclosure will be described with reference to Fig. 1. Fig. 1 illustrates a side surface of the power cable 100 which has been peeled off stepwise. The lower part of Fig. 1 is omitted.

[0060] As illustrated in Fig. 1, the connected power cable 10 of this embodiment is configured, for example, as a subaqueous cable laid on the bottom of water (bottom of the sea), and has a plurality of power cables 100 and at least one cable connection structure 20.

[0061] In the followings, an "axial direction" of the power cable 100 refers to a direction along the central axis of the power cable 100. A "radial direction" of the power cable 100 refers to a direction from the central axis toward the outer circumference of the power cable 100. A "circumferential direction" of the power cable 100 refers to a direction along an outer circumference of the power cable 100. The same terms as used above for the power cable 100 may also be used for columnar or cylindrical members such as a conductor 110, a wire 112, and a sleeve 210.

[0062] (Power cable) 　　　The power cable 100 is configured as a solid insulated cable which is a high-voltage power transmission cable.

[0063] The power cable 100 are not particularly limited. There are several types of power cables 100 that differ in structure outside the cable external semiconductive layer 140 described below. Specific examples of types of the power cable 100 include Dry Type (a type including a cable anticorrosive layer containing polyethylene on a cable metal coating layer such as lead), Semi Dry Type (a type including a cable anticorrosive layer containing polyethylene on a cable metal tape layer such as aluminum), Semi Wet Type (a type including only an anticorrosive layer containing polyethylene outside the cable external semiconductive layer), and Wet Type (a type including neither a cable metal coating layer nor a cable anticorrosive layer containing polyethylene outside the cable external semiconductive layer).

[0064] The power cable 100 as Dry Type, for example, has, from the central axis of the conductor 110 toward the outer circumference of the power cable 100, the conductor 110, the cable internal semiconductive layer, the cable insulating layer 130, the cable external semiconductive layer 140, the water absorbing layer (not shown), the cable metal coating layer 150, and the cable anticorrosive layer 160. The base resin included in the cable insulating layer 130 is, for example, polyethylene or polypropylene.

[0065] Although omitted in Fig. 1, the conductor 110 has a plurality of wire layers 114 provided by twisting together a plurality of wires 112, for example. A wire 112 may contain, for example, aluminum or an aluminum alloy. Alternatively, the wire 112 may contain, for example, copper or a copper alloy. In this embodiment, the wire 112 has a circular cross-section, for example. Hereinafter, as an example, a case where the wire 112 contains aluminum or an aluminum alloy will be described.

[0066] In each of wire layers 114 except for the center of the conductor 110, the plurality of wires 112 are arranged, for example, to cover the outer circumference of a wire layer 114 located inside of the plurality of wires 112, and are twisted in a spiral shape along the outer circumference of the wire layer 114 located inside of the plurality of wires 112.

[0067] The power cable 100 is stripped stepwise from the tip toward the opposite in the axial direction of the conductor 110. That is, the conductor 110, the cable internal semiconductive layer 120, the cable insulating layer 130, the cable external semiconductive layer 140, the cable metal coating layer 150, and the cable anticorrosive layer 160 are exposed in this order from the tip toward the opposite of the conductor 110.

[0068] As illustrated in Fig. 1, a plurality of power cables 100 are provided. Among the plurality of power cables 100, a pair of power cables 100 are butted against each other with the axes of their conductors 110 coinciding with each other. Hereinafter, a single power cable 100 of a pair of power cables 100, and a conductor 110 and a wire of the single power cable 100 may also be referred to as a "first power cable 100a," a "first conductor 110a," and a "first wire 112a," respectively. On the other hand, the other power cable 100, and a conductor 110 and a wire of the other power cable 100 may also be referred to as a "second power cable 100b," a "second conductor 110b," and a "second wire 112b," respectively.

[0069] As illustrated in Fig. 3 and Fig. 4(b) below, the first conductor 110a of the first power cable 100a has, for example, a first inner layer 114ai including a plurality of first inner layer wires 112ai, and a first outermost layer 114ao including a plurality of first outermost wires 112ao surrounding the first inner layer 114ai. The "first inner layer 114ai" is a region including a plurality of wire layers 114 from the central axis of the first conductor 110a to the inner side of the first outermost layer 114ao.

[0070] In this embodiment, the second conductor 110b of the second power cable 100b has a second inner layer 114bi and a second outermost layer 114bo, similar to the first inner layer 114ai and the first outermost layer 114ao of the first power cable 100a, respectively. That is, in this embodiment, the diameter of wires 112, the number of wires 112, the number of wire layers 114, and the outer diameter of the second conductor 110b in the second power cable 100b are equal to the diameter of wires 112, the number of wires 112, the number of wire layers 114, and the outer diameter of the first conductor 110a in the first power cable 100a. The "outer diameter of the first conductor 110a" used herein means the diameter of the circumscribed circle of the first outermost layer 114ao. The outer diameter of the second conductor 110b is defined in the same manner as the outer diameter of the first conductor 110a. The "second inner layer 114bi" is a region including a plurality of wire layers 114 from the central axis of the second conductor 110b to the inner side of the second outermost layer 114bo.

[0071] (Cable connection structure) 　　　As illustrated in Fig. 1, the cable connection structure 20 includes, for example, a first power cable 100a, a second power cable 100b, a conductor connection part 200, an internal semiconductive layer 220, an insulating layer 230, an external semiconductive layer 240, a water-absorbing tape layer 242, a metal tube (protective tube) 250, and an anticorrosive layer (connection part sheath) 260.

[0072] (Conductor connection part) 　　　At the conductor connection part 200, a first conductor 110a and a second conductor 110b of a pair of power cables 100 are connected. The conductor connection part 200 includes, for example, a central weld part 201 and a sleeve 210. Although the conductor connection part 200 includes the sleeve 210, the outer diameter of the conductor connection part 200 is approximately equal to the outer diameter of the conductor 110 of the power cable 100. The conductor connection part 200 will be described below.

[0073] (Configuration outside of conductor connection part) 　　　An internal semiconductive layer 220, an insulating layer 230, an external semiconductive layer 240, a water-absorbing tape layer 242, a metal tube 250, and an anticorrosive layer 260 are provided in this order outwardly from a region close the conductor connection part 200, to cover the outer circumference of the conductor connection part 200. They can be configured as a general configuration of a factory joint, for example, as described in Japanese Patent Laid-Open Publication No. 2023-065809. On the other hand, the metal tube 250 and the anticorrosive layer 260 do not have to be provided.

[0074] (2) Conductor connection part 　　　Next, with reference to Fig. 2 to Fig. 6, the conductor connection part 200 according to the first embodiment of the present disclosure will be described.

[0075] As illustrated in Fig. 2 to Fig. 6, the conductor connection part 200 of this embodiment includes, for example, a central weld part 201 and a sleeve 210.

[0076] In this embodiment, in the central weld part 201, for example, end parts of the plurality of first inner layer wires 112ai of the first conductor 110a and end parts of the plurality of second inner layer wires 112bi of the second conductor 110b are welded.

[0077] In this embodiment, the central weld part 201 is configured as a so-called "V-shaped joint". Specifically, the first conductor 110a and the second conductor 110b include inclined surfaces (numeral not shown) which are cut obliquely with respect to the axial direction of the first conductor 110a and the second conductor 110b, respectively. The first conductor 110a and the second conductor 110b are butted against each other so that their inclined surfaces form a V shape. In this state, the first conductor 110a and the second conductor 110b are welded to fill the V-shaped groove. The welding material for the central weld part 201 is not particularly limited. However, when the wire 112 contains aluminum or an aluminum alloy, the welding material of the central weld part 201 may be, for example, aluminum MIG A1100.

[0078] The sleeve 210 is configured, for example, as a metallic cylindrical member. The sleeve 210 contains aluminum, copper, or stainless steel. Accordingly, high mechanical performance and high electrical performance of the sleeve 210 itself can be obtained.

[0079] The sleeve 210 is provided to surround an outer circumference of a region including the central weld part 201, for example, at a position coinciding with at least a part of the first outermost layer 114ao in the radial direction of the first conductor 110a. In this embodiment, the sleeve 210 is provided to surround an outer circumference of a region including the central weld part 201, for example, at a position coinciding with both at least a part of the first outermost layer 114ao in the radial direction of the first conductor 110a and at least a part of the second outermost layer 114bo in a radial direction of the second conductor 110b. In this manner, the sleeve 210 covers the central weld part 201, thereby protecting the central weld part 201.

[0080] With the configuration of the sleeve 210 mentioned above, the outer diameter of the sleeve 210 is approximately equal to the outer diameter of the first conductor 110a, for example. Specifically, the outer diameter of the sleeve 210 is 1.1 times or less the outer diameter of the first outermost layer 114ao of the first conductor 110a in a region where the sleeve 210 is not disposed. Accordingly, it is possible to reduce electric field stress and suppress the occurrence of mechanical strain in the vicinity of a first end E1 and a second end E2 of the sleeve 210. The sleeve 210 may be shaved to have the outer diameter of sleeve 210 that falls within the above range.

[0081] On the other hand, the lower limit of the outer diameter of the sleeve 210 is not particularly limited. However, the outer diameter of the sleeve 210 may be 0.9 times or more, or 0.95 times or more the outer diameter of the first outermost layer 114ao of the first conductor 110a in a region where the sleeve 210 is not disposed.

[0082] The thickness of the sleeve 210 is, for example, approximately equal to the diameter of the first outermost wire 112ao. Specifically, the thickness of the sleeve 210 is, for example, 1.1 times or less the diameter of the first outermost wire 112ao. Accordingly, the outer diameter of the sleeve 210 can be easily made approximately equal to the outer diameter of the first conductor 110a.

[0083] On the other hand, the lower limit of the thickness of the sleeve 210 is not particularly limited. However, the thickness of the sleeve 210 may be 0.9 times or more, or 0.95 times or more the diameter of the first outermost wire 112ao.

[0084] The sleeve 210 includes, for example, a first end E1 in the axial direction of the sleeve 210, a second end E2 opposite to the first end E1, a plurality of first slit parts 211a, a plurality of first non-slit parts 212a, a first outermost weld part 214a, a plurality of second slit parts 211b, a plurality of second non-slit parts 212b, and a second outermost weld part 214b.

[0085] The plurality of first slit parts 211a penetrate the sleeve 210 in the thickness direction, for example. The plurality of first slit parts 211a extend, for example, from the first end E1 toward the second end E2. The plurality of first slit parts 211a are provided, for example, at intervals in the circumferential direction of the sleeve 210. For example, at least one of the first outermost wires 112ao is inserted into each of the plurality of first slit parts 211a.

[0086] In this embodiment, each of the plurality of first slit parts 211a is provided, for example, along a twisted direction of the plurality of first outermost wires 112ao.

[0087] In the first outermost weld part 214a, the sleeve 210 and at least one of the plurality of first outermost wires 112ao are welded at least inside each of the plurality of first slit parts 211a. That is, in the first outermost weld part 214a, the sleeve 210 and the plurality of first outermost wires 112ao are welded in a comb-tooth shape. Accordingly, the sleeve 210 and the first conductor 110a can be welded over a wide area. As a result, mechanical performance and electrical performance of the cable connection structure 20 can be improved.

[0088] The welding material of the first outermost weld part 214a is not particularly limited, but may be, for example, the same material as the welding material of the central weld part 201 or a material containing the same material as the welding material of the central weld part 201.

[0089] As illustrated in Fig. 5, the first outermost weld part 214a may be formed to cover the outer circumference of the first outermost wire 112ao inserted into each of the plurality of first slit parts 211a.

[0090] In this embodiment, the sleeve 210 is uncompressed. Accordingly, excessive stress can be prevented from being applied to the central weld part 201 and each wire 112 of the conductor 110.

[0091] In this embodiment, since excessive stress from the sleeve 210 is prevented from being applied to the central weld part 201, the central weld part 201 has no cracks. Accordingly, mechanical performance and electrical performance of the central weld part 201 can be maintained.

[0092] In this embodiment, after the sleeve 210 is placed to surround the outer circumference of a region including the central weld part 201, the first outermost weld part 214a is welded. Accordingly, the first outermost weld part 214a is naturally uncompressed. As a result, mechanical performance and electrical performance of the first outermost weld part 214a can be maintained.

[0093] As illustrated in Fig. 6, in this embodiment, each of the plurality of first slit parts 211a satisfies formula (1): 　　　d1 - Σd2 ≧ 0.2 ・・・ (1) 　　　wherein 　　　d1 is a width of each of the plurality of first slit parts 211a in a circumferential direction of the sleeve 210, expressed in mm, 　　　d2 is a diameter of one first outermost wire 112ao inserted in each of the plurality of first slit parts 211a, expressed in mm, and 　　　Σd2 is a sum of d2. 　　　When n first outermost wires 112ao are inserted into one first slit part 211a, Σd2 is nd2.

[0094] Accordingly, the first outermost wire 112ao can be easily inserted into the first slit part 211a, and the sleeve 210 and the first outermost wire 112ao can be easily welded.

[0095] In this embodiment, for example, a single first outermost wire 112ao among the plurality of first outermost wires 112ao is inserted into and welded to one of the plurality of first slit parts 211a. Accordingly, a single first outermost wire 112ao can be reliably fixed to the sleeve 210 within the first slit part 211a of the first outermost weld part 214a.

[0096] In this embodiment, since each of the plurality of first slit parts 211a is provided along the twisted direction of the plurality of first outermost wires 112ao, the first outermost weld part 214a can be formed along the twisted direction of the plurality of first outermost wires 112ao, i.e., along a direction oblique to the axial direction of the sleeve 210. Accordingly, the plurality of first outermost wires 112ao can be stably engaged with the sleeve 210 when a pulling force is applied to the first conductor 110a in the axial direction of the first conductor 110a. As a result, mechanical performance of the cable connection structure 20 can be improved.

[0097] In this embodiment, at least a part of the first outermost wires 112ao inserted into each of the plurality of first slit parts 211a may abut against the inner wall of each of the plurality of first slit parts 211a. In this respect, the first outermost wire 112ao can be stably engaged with the inner wall of the first slit part 211a when a pulling force is applied to the first conductor 110a in the axial direction of the first conductor 110a. As a result, mechanical performance of the cable connection structure 20 can be improved. Furthermore, the first outermost wire 112ao can be temporarily fixed during the outermost weld part formation step S250 by bringing at least a part of the first outermost wire 112ao into abutment with the inner wall of the first slit part 211a. Accordingly, welding operations can be easily and stably performed.

[0098] At least a part of the first outermost wire 112ao inserted into each of the plurality of first slit parts 211a may undulate with respect to the extending direction of each of the plurality of first slit parts 211a, for example.

[0099] On the other hand, in this embodiment, the first outermost wire 112ao inserted into each of the plurality of first slit parts 211a does not have to be in contact with the inner wall of each of the plurality of first slit parts 211a. Accordingly, it is possible to form a gap between the first outermost wire 112ao inserted into the first slit part 211a and the inner wall of the first slit part 211a. Formation of the gap makes it possible to easily flow a welding material into the gap between the first outermost wire 112ao and the inner wall of the first slit part 211a. As a result, the first outermost wire 112ao and the inner wall of the first slit part 211a can be easily welded.

[0100] A plurality of first non-slit parts 212a are provided between a plurality of first slit parts 211a. In the first outermost weld part 214a, for example, each of end parts of the first outermost wires 112ao other than the first outermost wires 112ao inserted into the plurality of first slit parts 211a is further welded to each of end parts of the plurality of first non-slit parts 212a. Accordingly, the weld area between the sleeve 210 and the first conductor 110a in the first outermost weld part 214a can be further increased. As a result, mechanical performance and electrical performance of the cable connection structure 20 can be improved.

[0101] In the first outermost weld part 214a, the weld region between the sleeve 210 and the first outermost wire 112ao within the first slit part 211a and the weld region between the end part of the first outermost wire 112ao and the end part of the first non-slit part 212a may be connected to each other.

[0102] In this embodiment, each of the plurality of first non-slit parts 212a has a gap (clearance, numeral not shown) in the axial direction of the first outermost wire 112ao between itself and each of the first outermost wires 112ao other than the first outermost wires 112ao inserted into the plurality of first slit parts 211a, for example. In the gap in the first outermost weld part 214a, each of end parts of the first outermost wires 112ao other than the first outermost wires 112ao inserted into the plurality of first slit parts 211a is further welded to each of end parts of the plurality of first non-slit parts 212a. Accordingly, a welding material can be easily flowed into the gap in the first outermost weld part 214a. As a result, the first non-slit part 212a and the first outermost wire 112ao can be easily welded.

[0103] The length of the gap between the first non-slit part 212a and the first outermost wire 112ao is, for example, 5 mm or more. By setting the length of the gap to 5 mm or more, the welding material can easily enter between the first non-slit part 212a and the first outermost wire 112ao. Accordingly, the first non-slit part 212a and the first outermost wire 112ao can be stably and reliably connected. The upper limit of the length of the gap is not limited, but the length of the gap may be 20 mm or less, for example.

[0104] As illustrated in Fig. 6, in this embodiment, each of the plurality of first non-slit parts 212a satisfies formula (2): 　　　Σd4 - d3 ≧ 0.2 ・・・ (2) 　　　wherein 　　　d3 is a width of each of the plurality of first non-slit parts 212a in a circumferential direction of the sleeve 210, expressed in mm, 　　　d4 is a diameter of one first outermost wire 112ao welded to each of the plurality of first non-slit parts 212a, expressed in mm, and 　　　Σd4 is a sum of d4. 　　　When n first outermost wires 112ao are welded to one first non-slit part 212a, Σd4 is nd4.

[0105] Accordingly, it is possible to easily obtain a width of the first slit part 211a that allows the first outermost wire 112ao to be inserted in the first slit part 211a.

[0106] In this embodiment, a single first outermost wire 112ao other than the first outermost wires 112ao inserted into the plurality of first slit parts 211a is welded to one of the plurality of first non-slit parts 212a. In the first outermost weld part 214a, the single first outermost wire 112ao can be reliably fixed to the first non-slit part 212a.

[0107] In this embodiment, the plurality of second slit parts 211b are provided opposite the plurality of first slit parts 211a across the center of the sleeve 210 in the axial direction.

[0108] Specifically, the plurality of second slit parts 211b penetrate the sleeve 210 in the thickness direction, for example. The plurality of second slit parts 211b extend, for example, from the second end E2 toward the first end E1. The plurality of second slit parts 211b are provided, for example, at intervals in the circumferential direction of the sleeve 210. For example, at least one of the second outermost wires 112bo is inserted into each of the second slit parts 211b.

[0109] In this embodiment, each of the plurality of second slit parts 211b is provided along a twisted direction of the plurality of second outermost wires 112bo.

[0110] In the second outermost weld part 214b, the sleeve 210 and at least one of the plurality of second outermost wires 112bo are welded at least inside each of the plurality of second slit parts 211b. The sleeve 210 and the second conductor 110b can be welded over a wide area.

[0111] A plurality of second non-slit parts 212b are provided between a plurality of second slit parts 211b. In the second outermost weld part 214b, for example, each of end parts of the second outermost wires 112bo other than the second outermost wires 112bo inserted into the plurality of second slit parts 211b is further welded to each of end parts of the plurality of second non-slit parts 212b. Accordingly, the weld area between the sleeve 210 and the second conductor 110b in the second outermost weld part 214b can be further increased.

[0112] As for other configurations, the plurality of second slit parts 211b, the plurality of second non-slit parts 212b, and the second outermost weld part 214b are configured in the same manner as the plurality of first slit parts 211a, the plurality of first non-slit parts 212a, and the first outermost weld part 214a, respectively. Accordingly, it is possible to obtain an effect similar to that obtained by the plurality of first slit parts 211a, the plurality of first non-slit parts 212a, and the first outermost weld part 214a.

[0113] In this embodiment, for example, the position of at least a part of each of the plurality of first slit parts 211a in the circumferential direction of the sleeve 210 may be the same as the position of at least a part of each of the plurality of second slit parts 211b. Accordingly, the first outermost weld part 214a and the second outermost weld part 214b can be formed in a well-balanced manner. As a result, mechanical performance of the cable connection structure 20 can be improved in a well-balanced manner.

[0114] (2) Method of producing cable connection structure (Method of producing connected power cable) 　　　Next, a method of producing a cable connection structure (method of producing connected power cable) according to this embodiment will be described with reference to Fig. 1 to Fig. 7.

[0115] As illustrated in Fig. 7, the method of producing the connected power cable 10 of this embodiment includes, for example, a preparation step S100, a conductor connection step S200, and an exterior formation step S300. Note that the step is abbreviated as "S".

[0116] (S100: Preparation step) 　　　First, a plurality of power cables 100 are prepared. Specifically, the power cable 100 is stripped stepwise from the tip toward the opposite in the axial direction of the conductor 110.

[0117] Additionally, each of other members constituting the cable connection structure 20 are prepared. A sleeve 210 on which a plurality of first slit parts 211a and a plurality of second slit parts 211b are formed in advance is prepared.

[0118] After the preparation of each member is completed, the first power cable 100a is inserted, for example, into a semiconductive tube constituting the external semiconductive layer 240, the metal tube 250, and a tube constituting the anticorrosive layer 260.

[0119] (S200: Conductor connection step) 　　　After the preparation step S100 is completed, a conductor connection step S200 is performed. The conductor connection step S200 of this embodiment includes, for example, an outermost wire stripping step S210, a sleeve insertion step S220, a central weld part formation step S230, an outermost wire cutting step S240, and an outermost weld part formation step S250.

[0120] (S210: Outermost wire stripping step) 　　　In the first conductor 110a of the first power cable 100a, the plurality of first outermost wires 112ao of the first outermost layer 114ao are stripped from the first inner layer 114ai. The tips of the plurality of first outermost wires 112ao are folded back in a direction opposite to the tip of the first inner layer 114ai. Thus, the first inner layer 114ai is exposed.

[0121] As with the first conductor 110a, the plurality of second outermost wires 112bo of the second outermost layer 114bo are stripped from the second inner layer 114bi, in the second conductor 110b of the second power cable 100b.

[0122] (S220: Sleeve insertion step) 　　　After the outermost wire stripping step S210 is completed, the first power cable 100a, for example, is inserted into the sleeve 210 of this embodiment. Next, the sleeve 210 is placed (released) in a region where the first inner layer 114ai is exposed by folding back the tips of the plurality of first outermost wires 112ao.

[0123] (S230: Central weld part formation step) 　　　When the sleeve insertion step S220 is completed, in the first conductor 110a and the second conductor 110b, inclined surfaces are formed, which are cut obliquely with respect to the axial direction of the first conductor 110a and the second conductor 110b, respectively. Then, the first conductor 110a and the second conductor 110b are butted against each other so that their inclined surfaces form a V shape. In this state, end parts of the plurality of first inner layer wires 112ai of the first conductor 110a and end parts of the plurality of second inner layer wires 112bi of the second conductor 110b are welded. Thus, a central weld part 201 configured as a so-called V-shaped joint are formed.

[0124] (S240: Outermost wire cutting step) 　　　When the central weld part formation step S230 is completed, the sleeve 210 is moved to a region including the central weld part 201 between the first conductor 110a and the second conductor 110b. Thus, the sleeve 210 is arranged to surround an outer circumference of a region including the central weld part 201 at a position coinciding with both at least a part of the first outermost layer 114ao in the radial direction of the first conductor 110a and at least a part of the second outermost layer 114bo in a radial direction of the second conductor 110b.

[0125] After the sleeve 210 is placed, a part of each of predetermined first outermost wires 112ao among the plurality of first outermost wires 112ao is cut. Thus, the length of the first outermost wire 112ao is shortened to match the length of the first slit part 211a. At least one of the plurality of first outermost wires 112ao is inserted into each of the plurality of first slit parts 211a.

[0126] A part of each of the first outermost wires 112ao other than the first outermost wires 112ao inserted into the plurality of first slit parts 211a is cut. At this time, the length of the first outermost wire 112ao is shortened to match the length of the first non-slit part 212a so that a gap is formed between each of the plurality of first non-slit parts 212a and the first outermost wire 112ao in the axial direction of the first outermost wire 112ao.

[0127] Parts of the plurality of second outermost wires 112bo are also cut to match the plurality of second slit parts 211b and the plurality of second non-slit parts 212b, similarly to the plurality of first outermost wires 112ao.

[0128] (S250: Central weld part formation step) 　　　When the outermost wire cutting step S240 is completed, as a first outermost weld part 214a, the sleeve 210 and at least one of the plurality of first outermost wires 112ao are welded at least inside each of the plurality of first slit parts 211a. Further, as the first outermost weld part 214a, each of end parts of the first outermost wires 112ao other than the first outermost wires 112ao inserted into the plurality of first slit parts 211a is further welded to each of end parts of the plurality of first non-slit parts 212a.

[0129] Similarly to the first outermost weld part 214a, the plurality of second outermost wires 112bo and the sleeve 210 are welded, in the second outermost weld part 214b.

[0130] (S300: Exterior formation step) 　　　Thereafter, an internal semiconductive layer 220, an insulating layer 230, an external semiconductive layer 240, a water-absorbing tape layer 242, a metal tube 250, and an anticorrosive layer 260 are formed in this order outwardly from a region close the conductor connection part 200, to cover the outer circumference of the conductor connection part 200. These steps can be performed, for example, as described in Japanese Patent Laid-Open Publication No. 2023-065809.

[0131] As described above, the cable connection structure 20 and the connected power cable 10 of this embodiment are produced.

[0132] (3) Summary of this embodiment 　　　According to this embodiment, one or more effects described below are achieved.

[0133] (a) The cable connection structure 20 of this embodiment is provided with not only the central weld part 201 but also the first outermost weld part 214a. In the first outermost weld part 214a, the sleeve 210 and at least one of the plurality of first outermost wires 112ao are welded at least inside each of the plurality of first slit parts 211a. Accordingly, the sleeve 210 and the first conductor 110a can be welded over a wide area.

[0134] Furthermore, at least inside each of the plurality of first slit parts 211a, the first outermost weld part 214a is formed to fill the gap between the plurality of first outermost wires 112ao by the length of the first slit part 211a. In this respect, the sleeve 210 and the first conductor 110a can be welded over a wide area.

[0135] As described above, by increasing the weld area of the first outermost weld part 214a, when a force is applied to pull the first conductor 110a in the axial direction of the first conductor 110a, the first conductor 110a can be held not only in the central weld part 201 but also in the first outermost weld part 214a. As a result, mechanical performance of the cable connection structure 20 can be improved.

[0136] In the first outermost weld part 214a, the sleeve 210 and the first outermost wire 112ao are welded to fill the first slit part 211a and a gap between the plurality of first outermost wires 112ao, so that a cross-sectional area of the first conductor 110a, including the first outermost weld part 214a orthogonal to the axial direction of the first conductor 110a, can be increased. Accordingly, the electrical resistance per unit length of the first conductor 110a including the first outermost weld part 214a can be reduced. As a result, electrical performance of the cable connection structure 20 can be improved.

[0137] (b) In this embodiment, the sleeve 210 can be uncompressed. Accordingly, excessive stress can be prevented from being applied to the central weld part 201 and each wire 112 of the conductor 110. In this respect, mechanical performance of the cable connection structure 20 can be improved.

[0138] (c) In this embodiment, the outer diameter of the sleeve 210 can be approximately equal to the outer diameter of the first conductor 110a.

[0139] The first end E1 and the second end E2 of the sleeve 210 do not protrude from the outer circumference of the first conductor 110a. This makes it possible to suppress occurrence of local mechanical strain in the vicinity of the first end E1 and the second end E2 of the sleeve 210 even when bending or twisting is applied to the cable connection structure 20. Suppressing the mechanical strain can suppress application of excessive stress to the insulating layer 230 and the like in the cable connection structure 20. As a result, degradation in mechanical performance and electrical performance of the cable connection structure 20 can be suppressed.

[0140] Furthermore, at the time of applying voltage to the power cable 100, localized non-uniformity of electric field stress can be suppressed in the vicinity of the first end E1 and the second end E2 of the sleeve 210. In this respect, degradation in the electrical performance of the cable connection structure 20 can be suppressed.

[0141] (d) In this embodiment, the second outermost weld part 214b is provided for the second conductor 110b, similar to the first outermost weld part 214a for the first conductor 110a. Accordingly, the second outermost weld part 214b can also provide the above-mentioned effect similar to that provided by the first outermost weld part 214a. As a result, mechanical performance and electrical performance of the cable connection structure 20 can be stably improved.

[0142] (4) Modified examples of first embodiment 　　　The above-mentioned embodiment can be modified where appropriate, as in the following modified examples. Hereinafter, only elements different from the above-mentioned embodiment will be described, and elements substantially the same as those described in the above-mentioned embodiment will be designated by the same reference numerals and their description will be omitted. In the second embodiment and modified examples thereof described below, the same explanation is omitted as in the modified examples of the first embodiment.

[0143] <Modified Example 1-1> 　　　As illustrated in Fig. 8 and Fig. 9, in a modified example 1-1 of the first embodiment, each of the plurality of first slit parts 211a is provided linearly in the axial direction of the sleeve 210, for example. Accordingly, the plurality of first slit parts 211a can be easily formed in the sleeve 210.

[0144] The first outermost wire 112ao inserted into each of the plurality of first slit parts 211a may be arranged obliquely with respect to the extending direction of each of the plurality of first slit parts 211a, for example. Accordingly, at least a part of the first outermost wire 112ao can be easily brought into abutment with an inner wall of the first slit part 211a.

[0145] An end part of the first outermost wire 112ao inserted into each of the plurality of first slit parts 211a may abut against the inner wall of each of the plurality of first slit parts 211a.

[0146] A part of the first outermost wire 112ao inserted into each of the plurality of first slit parts 211a may abut against a corner of an open end part of each of the plurality of first slit parts 211a. The open end part of the first slit part 211a is an end part where the first slit part 211a opens at the first end E1 of the sleeve 210.

[0147] The first outermost wire 112ao inserted into the first slit part 211a abuts against the first slit part 211a at two points mentioned above, so that the first outermost wire 112ao can be stably engaged with the inner wall of the first slit part 211a. As a result, mechanical performance of the cable connection structure 20 can be improved.

[0148] In the modified example 1-1, the extending direction of the first slit part 211a is different from the twisted direction of the first outermost wire 112ao, so that the first outermost wire 112ao can be easily brought into abutment with the first slit part 211a at the two points mentioned above.

[0149] <Modified Example 1-2> 　　　As illustrated in Fig. 10, in the modified example 1-2 of the first embodiment, a sleeve 210 has, for example, convex parts 218 on its inner circumferential surface. The convex parts 218 may be formed spirally on the inner circumferential surface of the sleeve 210. The height of the convex part 218 is, for example, more than 0 mm and 0.5 mm or less. By setting the height of the convex part 218 to 0.5 mm or less, compressive stress can be prevented from becoming excessively large.

[0150] In this modified example, the sleeve 210 is compressed (slightly compressed). Specifically, the sleeve 210 is compressed, for example, so that the convex parts 218 bite into the first inner layer 114ai of the first conductor 110a. Accordingly, adhesion (friction) between the sleeve 210 and the first conductor 110a can be improved.

[0151] As illustrated in Fig. 10, the first inner layer wire 112ai among the plurality of first inner layer wires 112ai, which is in contact with the sleeve 210, satisfies formula (3): 　　　0 < di0 - dimin ≦ 0.5 ・・・(3) 　　　wherein 　　　di0 is a diameter of a part of a single first inner layer wire 112ai among the plurality of first inner layer wires 112ai, which is not in contact with the sleeve 210, expressed in mm, and 　　　dimin is a minimum diameter of the single first inner layer wire 112ai among the plurality of first inner layer wires 112ai, which is in contact with the sleeve 210, expressed in mm.

[0152] Furthermore, the first inner layer 114ai satisfies formula (4): 　　　0 < Di0 - Dimin ≦ 1 ・・・ (4) 　　　wherein 　　　Di0 is a diameter of a circumscribed circle of the first inner layer 114ai at a position not in contact with the sleeve 210, expressed in mm, and 　　　Dimin is a minimum diameter of a circumscribed circle of the first inner layer 114ai at a position in contact with the sleeve 210, expressed in mm.

[0153] In this modified example, the second inner layer wire 112bi may satisfy formula (3) wherein the first inner layer wire 112ai is replaced with the second inner layer wire 112bi. Furthermore, the second inner layer 114bi may satisfy formula (4) wherein the first inner layer 114ai is replaced with the second inner layer 114bi.

[0154] In this modified example, as mentioned above, the sleeve 210 is slightly compressed so that the first inner layer wire 112ai satisfies formula (3) and the first inner layer 114ai satisfies formula (4). Accordingly, excessive stress can be prevented from being applied to the central weld part 201 and each wire 112 of the conductor 110. Thus, the central weld part 201 has no cracks. As a result, mechanical performance and electrical performance of the central weld part 201 can be maintained.

[0155] Furthermore, in this modified example, the first outermost weld part 214a is naturally uncompressed. Accordingly, mechanical performance and electrical performance of the first outermost weld part 214a can be maintained.

[0156] In this modified example, a sleeve slight-compression step S238 is performed between the central weld part formation step S230 and the outermost wire cutting step S240. In the sleeve slight-compression step S238, the sleeve 210 is moved to a region including the central weld part 201 between the first conductor 110a and the second conductor 110b. Next, the sleeve 210 is compressed so that the convex parts 218 bite into the first inner layer 114ai of the first conductor 110a.

[0157] The sleeve slight-compression step S238 mentioned above can temporarily fix the sleeve 210 before the outermost weld part formation step S250. Thus, the outermost wire cutting step S240 and the outermost weld part formation step S250 can be easily and stably performed.

[0158] The sleeve slight-compression step S238 mentioned above can allow the central axis of the first conductor 110a and the central axis of the sleeve 210 to coincide with each other. Accordingly, the positional accuracy of the first outermost weld part 214a can be improved.

[0159] In this modified example, the same effect can be obtained for the second conductor 110b as for the first conductor 110a.

[0160] Furthermore, in this modified example, the sleeve 210 may have concave parts on its inner circumferential surface, and the sleeve 210 may be compressed so that the first inner layer 114ai fits into the concave parts. In this case, the depth of the concave part is, for example, more than 0 mm and 0.5 mm or less. In this case, the same effect can be obtained as in the case where the above-mentioned sleeve 210 has the convex parts 218 on the inner circumferential surface.

[0161] <Modified Example 1-3> 　　　As illustrated in Fig. 11, in this modified example 1-3 of the first embodiment, as the first outermost weld part 214a, two or more first outermost wires 112ao among the plurality of first outermost wires 112ao may be inserted into and welded to one of the plurality of first slit parts 211a, for example. Accordingly, the weld area per first slit part 211a of the first outermost weld part 214a can be easily increased. Even when the diameter of the first outermost wire 112ao is small, the weld area can be easily increased.

[0162] The second outermost weld part 214b may be configured similarly to the first outermost weld part 214a of this modified example.

[0163] <Modified Example 1-4> 　　　As illustrated in Fig. 12, in the modified example 1-4 of the first embodiment, as the first outermost weld part 214a, two or more first outermost wires 112ao other than the first outermost wires 112ao inserted into the plurality of first slit parts 211a may be welded to one of the plurality of first non-slit parts 212a, for example. Accordingly, the weld area per first non-slit part 212a of the first outermost weld part 214a can be easily increased. Even when the diameter of the first outermost wire 112ao is small, the weld area can be easily increased.

[0164] The second outermost weld part 214b may be configured similarly to the first outermost weld part 214a of this modified example.

[0165] The above-mentioned modified examples 1-3 and 1-4 may be combined. Alternatively, three or more first outermost wires 112ao among the plurality of first outermost wires 112ao may be inserted into and welded to one of the plurality of first slit parts 211a. Alternatively, three or more first outermost wires 112ao other than the first outermost wires 112ao inserted into the plurality of first slit parts 211a may be welded to one of the plurality of first non-slit parts 212a. The configurations described above may be combined.

[0166] <Modified Example 1-5> 　　　As illustrated in Fig. 13, in the modified example 1-5 of the first embodiment, among the plurality of first slit parts 211a, at least one first slit part 211a may have a length different from those of other first slit parts 211a. Accordingly, the shape of the first outermost weld part 214a can be complicated. As a result, mechanical performance of the cable connection structure 20 can be improved.

[0167] Since the central weld part 201 is configured, for example, as a V-shaped joint, the central weld part 201 has a short weld part SW whose weld length in the axial direction of the first conductor 110a is shorter than those of other parts.

[0168] In this modified example, among the plurality of first slit parts 211a, at least one first slit part 211a which is closer to the short weld part SW of the central weld part 201 than other first slit parts 211a may have a length longer than those of the other first slit parts. In accordance with the shape of the V-shaped joint of the central weld part 201, the lengths of the plurality of first slit parts 211a may gradually increase from the opposite side of the short weld part SW toward the short weld part SW.

[0169] As in this modified example, the lengths of the plurality of first slit parts 211a can be adjusted in accordance with the shape of the central weld part 201. Thus, a part of the central weld part 201 having low welding strength can be strengthened by the first outermost weld part 214a.

[0170] The plurality of second slit parts 211b may be configured similarly to the plurality of first slit parts 211a of this modified example.

[0171] <Modified Example 1-6> 　　　As illustrated in Fig. 14, in the modified example 1-5 of the first embodiment, the plurality of first slit parts 211a include, for example, at least one first short slit part 211as, at least one first medium slit part 211am which is longer than the first short slit part 211as, and at least one first long slit part 211al which is longer than the first medium slit part 211am. The first short slit part 211as, the first medium slit part 211am, and the first long slit part 211al are, for example, repeatedly provided in this order in the circumferential direction of the sleeve 210.

[0172] The plurality of second slit parts 211b include, for example, at least one second short slit part 211bs, at least one second medium slit part 211bm which is longer than the second short slit part 211bs, and at least one second long slit part 211bl which is longer than the second medium slit part 211bm. The second short slit part 211bs, the second medium slit part 211bm, and the second long slit part 211bl are, for example, repeatedly provided in this order in the circumferential direction of the sleeve 210.

[0173] For example, the first short slit part 211as and the second long slit part 211bl are positioned opposite to each other across the center of the sleeve 210 in the axial direction. For example, the first medium slit part 211am and the second medium slit part 211bm are positioned opposite to each other across the center of the sleeve 210 in the axial direction. For example, the first long slit part 211al and the second short slit part 211bs are positioned opposite to each other across the center of the sleeve 210 in the axial direction.

[0174] Here, in the first outermost weld part 214a, heat history accumulates as the welding of the plurality of first slit parts 211a is repeated. In particular, when the plurality of first slit parts 211a have the same length, the strength of the first outermost weld part 214a at end parts of the plurality of first slit parts 211a decreases as the heat history accumulates at the end parts of the plurality of first slit parts 211a (the end parts of the plurality of first slit parts 211a which is close to the center of the sleeve 210 in the axial direction). Furthermore, when the plurality of first slit parts 211a have the same length, stresses for bending stresses tend to concentrate at the end parts of the plurality of first slit parts 211a.

[0175] In contrast, in this modified example, the first short slit part 211as, the first medium slit part 211am, and the first long slit part 211al are made to have different lengths, thereby dispersing the effects of heat history at the end of the plurality of first slit parts 211a. Accordingly, the reduction in strength of the first outermost weld part 214a at the end parts of the plurality of first slit parts 211a due to heat history can be suppressed. The first short slit part 211as, the first medium slit part 211am, and the first long slit part 211al are made to have different lengths, thereby suppressing the concentration of stress to bending stress at the end part of the plurality of first slit parts 211a. As a result, mechanical performance of the cable connection structure 20 can be improved.

[0176] The same effect as mentioned above can be achieved by varying the length of the second short slit part 211bs, the length of the second medium slit part 211bm, and the length of the second long slit part 211bl.

[0177] <Modified Example 1-7> 　　　In the modified example 1-7 of the first embodiment, for example, the position of at least a part of each of the plurality of first slit parts 211a in the circumferential direction of the sleeve 210 may be different from the position of at least a part of each of the plurality of second slit parts 211b. In other words, the sleeve 210 does not have to be symmetrical.

[0178] In this modified example, by actively shifting the positions of the plurality of first slit parts 211a and the plurality of second slit parts 211b, it is possible to disperse the portions of the sleeve 210 that have low rigidity due to the plurality of first slit parts 211a and the plurality of second slit parts 211b.

[0179] <Second Embodiment of Disclosure> 　　　As illustrated in Fig. 15 and Fig. 16, in the second embodiment, a cable connection structure 20 is configured by a so-called different diameter connection.

[0180] In this embodiment, an outer diameter of the second conductor 110b is, for example, smaller than an outer diameter of the first conductor 110a. The second conductor 110b has no wire layer 114 that corresponds to the first outermost layer 114ao of the first conductor 110a, for example.

[0181] In this embodiment, the sleeve 210 has, for example, an outer diameter gradually decreasing from a position close to the first conductor 110a toward the second end E2. That is, the sleeve 210 has, for example, a tapered shape and has a conical surface 217 that is inclined with respect to the axial direction of the sleeve 210.

[0182] On the other hand, the inner diameter of the sleeve 210 is uniform in the axial direction of the sleeve 210. The sleeve 210 has an inner circumferential surface that is in contact with the outer circumference of the first inner layer 114ai of the first conductor 110a and the outer circumference of the second conductor 110b.

[0183] In this embodiment, the sleeve 210 has no second slit part 211b in the vicinity of the second end E2.

[0184] (Effects of this embodiment) (a) In this embodiment, the cable connection structure 20 can be stably formed at the position where the outer diameter changes from the first conductor 110a toward the second conductor 110b.

[0185] (b) In this embodiment, the central weld part 201 between the first conductor 110a and the second conductor 110b, which differ from each other in their outer diameters, can be protected by the sleeve 210. This makes it possible to suppress the accumulation of bending or twisting strain in the central weld part 201. As a result, degradation in the mechanical performance and electrical performance of the cable connection structure can be suppressed.

[0186] (c) In this embodiment, the sleeve 210 has an outer diameter that gradually decreases from a position close to the first conductor 110a toward the second end E2, so that the outer diameter at the second end E2 of the sleeve 210 can be made approximately equal to the outer diameter of the second conductor 110b.

[0187] The second end E2 of the sleeve 210 does not excessively protrude from the outer circumference of the second conductor 110b. This makes it possible to suppress occurrence of local mechanical strain in the vicinity of the second end E2 of the sleeve 210 even when bending or twisting is applied to the cable connection structure 20. Suppressing the mechanical strain can suppress application of excessive stress to the insulating layer 230 and the like in the cable connection structure 20. As a result, degradation in mechanical performance and electrical performance of the cable connection structure 20 can be suppressed.

[0188] Furthermore, at the time of applying voltage to the power cable 100, localized non-uniformity of electric field stress can be suppressed in the vicinity of the second end E2 of the sleeve 210. In this respect, degradation in the electrical performance of the cable connection structure 20 can be suppressed.

[0189] <Modified Example 2-1> 　　　As illustrated in Fig. 17, in the modified example 2-1 of the second embodiment, the outer diameter of the second conductor 110b is smaller than the outer diameter of the second conductor 110b of the above-mentioned second embodiment, for example. The second conductor 110b has no wire layer 114 that corresponds to two wire layers 114, for example, inwardly from the outermost circumference of the first conductor 110a.

[0190] In this modified example, in the central weld part 201, the wire layers 114 of the first conductor 110a, excluding two wire layers 114 inwardly from the outermost circumference, are welded to the second conductor 110b.

[0191] In this modified example, the outer diameter of the sleeve 210 gradually decreases toward the second conductor 110b, which has two fewer wire layers 114 than the first conductor 110a.

[0192] The inner circumferential surface of the sleeve 210 has a step 219, for example, so that a region in which the outer diameter of the sleeve 210 gradually decreases has a smaller inner diameter than the inner diameters in other regions.

[0193] The inner diameter Di1 of the sleeve 210 in the region where the outer diameter of the sleeve 210 gradually decreases is, for example, 1.0 times or more and 1.1 times or less the outer diameter of the second conductor 110b.

[0194] On the other hand, the inner diameter Di2 of the sleeve 210 in a region other than the region where the outer diameter of the sleeve 210 gradually decreases is uniform in the axial direction of the sleeve 210 and is, for example, 0.7 times or more and 0.9 times or less the outer diameter of the first conductor 110a.

[0195] A wire 112 of a wire layer 114, which is the second layer from the outermost circumference of the first conductor 110a, is inserted up to the step 219 on the inner circumferential surface of the sleeve 210.

[0196] As in this modified example, the cable connection structure 20 can be adjusted arbitrarily in accordance with the outer diameter of the first conductor 110a and the outer diameter of the second conductor 110b. Accordingly, even when the outer diameter changes in various ways from the first conductor 110a toward the second conductor 110b, the cable connection structure 20 can be stably formed at the location where the outer diameter changes.

[0197] <Modified Example 2-2> 　　　In the modified example 2-2 of the second embodiment, the sleeve 210 and the second conductor 110b may be welded at the second end E2 where the outer diameter of the sleeve 210 is reduced. At the second end E2 of the sleeve 210, a portion where the sleeve 210 and the second conductor 110b are welded may be polished smooth along the conical surface 217 of the sleeve 210.

[0198] In this modified example, even when the sleeve 210 does not have the second slit part 211b and the second outermost weld part 214b, a portion can be formed in which the sleeve 210 and the second conductor 110b are welded at the second end E2 of the sleeve 210, thereby to combine the sleeve 210 and the second conductor 110b. Thus, mechanical performance and electrical performance of the cable connection structure 20 can be improved, even when the cable connection structure 20 is configured with different diameter connections.

[0199] <Other Embodiments of Disclosure> 　　　Although embodiment of the present disclosure has been specifically described, the present disclosure is not limited to the above-mentioned embodiment, and various modifications can be made without departing from the gist of the present disclosure. The "above-mentioned embodiment" used herein include the first embodiment and modified examples thereof, and the second embodiment and modified examples thereof.

[0200] The above embodiment describes the wire 112 of the conductor 110 having a circular cross-section. However, the wire 112 may have a fan-shaped cross section.

[0201] The above embodiment describes a case where the diameter of the wire 112 of the first conductor 110a and the diameter of the wire 112 of the second conductor 110b are equal, but the diameter of the wire 112 of the first conductor 110a and the diameter of the wire 112 of the second conductor 110b may be different. When at least a part of the first outermost layer 114ao of the first conductor 110a and at least a part of the second outermost layer 114bo of the second conductor 110b are coincident in the radial direction of the conductor 110, the first embodiment and its modified example can be applied. On the other hand, when the outer diameter of the second conductor 110b is smaller than that of the first conductor 110a, the second embodiment and its modified example can be applied.

[0202] The above embodiment describes a case where the wire 112 contains aluminum or an aluminum alloy and the central weld part 201 is configured as a V-shaped joint, but the present disclosure is not limited to this case. When the wire 112 contains copper or a copper alloy, for example, one wire 112 of the first conductor 110a and one wire 112 of the second conductor 110b may be welded at the central weld part 201. Alternatively, when the wire 112 contains copper or a copper alloy, for example, at the central weld part 201, the first conductor 110a and the second conductor 110b may be welded to each other in a state where the tips of each of the first conductor 110a and the second conductor 110b are machined into a conical shape. When the wire 112 contains copper or a copper alloy, the welding material of the central weld part 201 may be, for example, "phosphor bronze brazing filler".

[0203] The above embodiment describes a case where the first outermost wire 112ao is inserted in the first slit part 211a, but the present disclosure is not limited to this case. The first outermost wire 112ao and a wire 112 in at least one wire layer 114 located inside of the first outermost layer 114ao may be inserted into the first slit part 211a and welded to each other. In the first embodiment and its modified examples, the second slit part 211b may be configured similarly to the first slit part 211a.

[0204] The above embodiment describes a single cable connection structure 20 of the connected power cable 10. However, the connected power cable 10 may include a plurality of cable connection structures 20.

[0205] 10 Connected power cable 20 Cable connection structure 100 Power cable 100a First power cable 100b Second power cable 110 Conductor 110a First conductor 110b Second conductor 112 Wire 112a First wire 112ai First inner layer wire 112ao First outermost wire 112b Second wire 112bi Second inner layer wire 112bo Second outermost wire 114 Wire layer 114ai First inner layer 114ao First outermost layer 114bi Second inner layer 114bo Second outermost layer 120 Cable internal semiconductive layer 130 Cable insulating layer 140 Cable external semiconductive layer 150 Cable metal coating layer 160 Cable anticorrosive layer 200 Conductor connection part 201 Central weld part 210 Sleeve 211a First slit part 211b Second slit part 212a First non-slit part 212b Second non-slit part 214a First outermost weld part 214b Second outermost weld part 217 Conical surface 218 Convex part 219 Step 220 Internal semiconductive layer 230 Insulating layer 240 External semiconductive layer 242 Water-absorbing tape layer 250 Metal tube 260 Anticorrosive layer E1 First end E2 Second end SW Short weld part

Claims

1. A cable connection structure, comprising: 　　　a first power cable having a first conductor; 　　　a second power cable having a second conductor; and 　　　a conductor connection part connecting the first conductor and the second conductor, 　　　wherein 　　　the first conductor has a first inner layer including a plurality of first inner layer wires, and a first outermost layer including a plurality of first outermost wires surrounding the first inner layer, 　　　the second conductor has a plurality of second wires, 　　　the conductor connection part has: 　　　　　　a central weld part where end parts of the plurality of first inner layer wires of the first conductor are welded to end parts of at least some of the plurality of second wires of the second conductor; and 　　　　　　a sleeve configured as a metallic cylindrical member and provided to surround an outer circumference of a region including the central weld part at a position coinciding with at least a part of the first outermost layer in a radial direction of the first conductor, 　　　　　　wherein the sleeve has 　　　　　　　　　a first end in an axial direction of the sleeve; 　　　　　　　　　a second end opposite to the first end; 　　　　　　　　　a plurality of first slit parts, penetrating in a thickness direction of the sleeve, extending from the first end toward the second end, being provided at intervals in a circumferential direction of the sleeve, and each having at least one of the plurality of first outermost wires inserted therein, and 　　　　　　　　　a first outermost weld part where the sleeve is welded to at least one of the plurality of first outermost wires at least inside each of the plurality of first slit parts.

2. The cable connection structure according claim 1, 　　　 wherein the central weld part has no cracks.

3. The cable connection structure according to claim 1 or 2, 　　　 wherein the first outermost weld part is uncompressed.

4. The cable connection structure according to any one of claims 1 to 3, 　　　wherein the sleeve is uncompressed.

5. The cable connection structure according to any one of claims 1 to 3, 　　　 wherein the sleeve is compressed, and 　　　a single inner layer wire among the plurality of the first inner layer wires, which is in contact with the sleeve, satisfies formula (3): 0 < di0 - dimin ≦ 0.5 ・・・ (3) 　　　wherein 　　　di0 is a diameter of a part of a single first inner layer wire among the plurality of first inner layer wires, which is not in contact with the sleeve, expressed in mm, and 　　　dimin is a minimum diameter of the single first inner layer wire among the plurality of first inner layer wires, which is in contact with the sleeve, expressed in mm.

6. The cable connection structure according to any one of claims 1 to 3, and 5, 　　　wherein 　　　the sleeve is compressed, and 　　　the first inner layer satisfies formula (4): 　　　0 < Di0 - Dimin ≦ 1 ・・・ (4) 　　　wherein 　　　Di0 is a diameter of a circumscribed circle of the first inner layer at a position not in contact with the sleeve, expressed in mm, and 　　　Dimin is a minimum diameter of a circumscribed circle of the first inner layer at a position in contact with the sleeve, expressed in mm.

7. The cable connection structure according to any one of claims 1 to 3, 5, and 6, 　　　wherein the sleeve has convex parts or concave parts on its inner circumferential surface, and 　　　the sleeve is compressed so that the convex parts bite into the first inner layer or the first inner layer fits into the concave parts.

8. The cable connection structure according to any one of claims 1 to 7, 　　　wherein an outer diameter of the sleeve is 1.1 times or less an outer diameter of the first outermost layer in a region where the sleeve is not disposed.

9. The cable connection structure according to any one of claims 1 to 8, 　　　wherein a single first outermost wire among the plurality of first outermost wires is inserted into and welded to one of the plurality of first slit parts.

10. The cable connection structure according to any one of claims 1 to 8, 　　　wherein two or more first outermost wires among the plurality of first outermost wires are inserted into and welded to one of the plurality of first slit parts.

11. The cable connection structure according to any one of claims 1 to 10, 　　　wherein each of the plurality of first slit parts satisfies formula (1): 　　　d1 - Σd2 ≧ 0.2 ・・・ (1) 　　　wherein 　　　d1 is a width of each of the plurality of first slit parts in a circumferential direction of the sleeve, expressed in mm, 　　　d2 is a diameter of one first outermost wire inserted in each of the plurality of first slit parts, expressed in mm, and 　　　Σd2 is a sum of d2.

12. The cable connection structure according to any one of claims 1 to 11, 　　　wherein the sleeve has a plurality of first non-slit parts between the plurality of first slit parts, and 　　　in the first outermost weld part, each of end parts of first outermost wires other than first outermost wires inserted into the plurality of first slit parts is further welded to each of end parts of the plurality of first non-slit parts.

13. The cable connection structure according to claim 12, 　　　wherein each of the plurality of first non-slit parts has a gap between itself and each of the first outermost wires other than the first outermost wires inserted into the plurality of first slit parts, and 　　　in the gap in the first outermost weld part, each of end parts of the first outermost wires other than the first outermost wires inserted into the plurality of first slit parts is further welded to each of end parts of the plurality of first non-slit parts.

14. The cable connection structure according to claim 12 or 13, 　　　wherein a single first outermost wire other than the first outermost wires inserted into the plurality of first slit parts is welded to one of the plurality of first non-slit parts.

15. The cable connection structure according to claim 12 or 13, 　　　wherein two or more first outermost wires other than the first outermost wires inserted into the plurality of first slit parts are welded to one of the plurality of first non-slit parts.

16. The cable connection structure according to any one of claims 12 to 15, 　　　wherein each of the plurality of first non-slit parts satisfies formula (2): 　　　Σd4 - d3 ≧ 0.2 ・・・ (2) 　　　wherein 　　　d3 is a width of each of the plurality of first non-slit parts in a circumferential direction of the sleeve, expressed in mm, 　　　d4 is a diameter of one first outermost wire welded to each of the plurality of first non-slit parts, expressed in mm, and 　　　Σd4 is a sum of d4.

17. The cable connection structure according to any one of claims 1 to 16, 　　　wherein the plurality of first outermost wires are twisted together in a spiral shape, and 　　　each of the plurality of first slit parts is provided along a twisted direction of the plurality of first outermost wires.

18. The cable connection structure according to any one of claims 1 to 16, 　　　wherein each of the plurality of first slit parts is provided linearly in an axial direction of the sleeve.

19. In the cable connection structure according to any one of claims 1 to 18, 　　　wherein the first outermost wire inserted into each of the plurality of first slit parts is arranged obliquely with respect to an extending direction of each of the plurality of first slit parts.

20. The cable connection structure according to any one of claims 1 to 19, 　　　wherein at least a part of the first outermost wire inserted into each of the plurality of first slit parts abuts against an inner wall of each of the plurality of first slit parts.

21. The cable connection structure according to claim 20, 　　　wherein an end part of the first outermost wire inserted into each of the plurality of first slit parts abuts against the inner wall of each of the plurality of first slit parts.

22. The cable connection structure according to claims 20 or 21, 　　　wherein a part of the first outermost wire inserted into each of the plurality of first slit parts abuts against a corner of an open end part of each of the plurality of first slit parts.

23. The cable connection structure according to any one of claims 1 to 18, 　　　wherein at least a part of the first outermost wires inserted into each of the plurality of first slit parts is not in contact with an inner wall of each of the plurality of first slit parts.

24. The cable connection structure according to any one of claims 1 to 23, 　　　wherein among the plurality of first slit parts, at least one first slit part has a length different from those of other first slit parts.

25. The cable connection structure according to claim 24, wherein 　　　the central weld part has a short weld part which has a weld length shorter than those of other parts in an axial direction of the first conductor, and 　　　among the plurality of first slit parts, at least one first slit part closer to the short weld part than other first slit parts has a length longer than those of the other first slit parts.

26. The cable connection structure according to claim 24, 　　　wherein the plurality of first slit parts includes: 　　　　　　at least one first short slit part; 　　　　　　at least one first medium slit part which is longer than the first short slit part; and 　　　　　　at least one first long slit part which is longer than the first medium slit part.

27. The cable connection structure according to any one of claims 1 to 26, 　　　wherein an outer diameter of the second conductor is equal to an outer diameter of the first conductor, 　　　the second conductor has a second inner layer including a plurality of second inner layer wires, and a second outermost layer including a plurality of second outermost wires, 　　　in the central weld part, end parts of the plurality of first inner layer wires of the first conductor and end parts of the plurality of second inner layer wires of the second conductor are welded, 　　　the sleeve is provided to surround an outer circumference of a region including the central weld part at a position coinciding with both at least a part of the first outermost layer in the radial direction of the first conductor and at least a part of the second outermost layer in a radial direction of the second conductor, 　　　the sleeve further has: 　　　　　　a plurality of second slit parts, penetrating in the thickness direction of the sleeve, extending from the second end toward the first end, being provided at intervals in the circumferential direction of the sleeve, and each having at least one of the plurality of second outermost wires inserted therein, and 　　　　　　a second outermost weld part where the sleeve and at least one of the plurality of second outermost wires are welded at least inside each of the plurality of second slit parts.

28. The cable connection structure according to claim 27, 　　　 wherein a position of at least a part of each of the plurality of first slit parts in the circumferential direction of the sleeve is equal to a position of at least a part of each of the plurality of second slit parts.

29. The cable connection structure according to claim 27, 　　　wherein a position of at least a part of each of the plurality of first slit parts in the circumferential direction of the sleeve is different from a position of at least a part of each of the plurality of second slit parts.

30. The cable connection structure according to any one of claims 1 to 26, 　　　wherein an outer diameter of the second conductor is smaller than an outer diameter of the first conductor, and 　　　the sleeve has an outer diameter gradually decreasing from a position close to the first conductor toward the second end.

31. The cable connection structure according to any one of claims 1 to 30, 　　　wherein the first conductor and the second conductor contain aluminum or an aluminum alloy.

32. The cable connection structure according to any one of claims 1 to 30, 　　　 wherein the first conductor and the second conductor contain copper or a copper alloy.

33. The cable connection structure according to any one of claim 1 to 32, 　　　 wherein the sleeve contains aluminum, copper, or stainless steel.

34. A connected power cable, comprising at least one cable connection structure according to any one of claims 1 to 33.

35. A method of producing the cable connection structure according to any one of claims 1 to 33.

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