CN117099280A

CN117099280A - Power cable system having dissimilar conductor joint portion and power cable connection method having dissimilar conductor

Info

Publication number: CN117099280A
Application number: CN202180096624.6A
Authority: CN
Inventors: 金延益; 林成镇; 李齐贤; 洪性豪
Original assignee: LS Cable Ltd
Current assignee: LS Cable and Systems Ltd
Priority date: 2021-04-05
Filing date: 2021-12-09
Publication date: 2023-11-21

Abstract

The present invention relates to a power cable system having a dissimilar-conductor joint portion capable of reducing cost, weight, or volume without using an additional sleeve member or the like when connecting a power cable having a dissimilar conductor, and capable of securing sufficient bending strength or durability at the dissimilar-conductor joint portion even when pulling force and bending are simultaneously applied, and to a power cable connection method having a dissimilar-conductor.

Description

Power cable system having dissimilar conductor joint portion and power cable connection method having dissimilar conductor

Technical Field

The present invention relates to a power cable system having a dissimilar conductor joint portion and a power cable connection method having a dissimilar conductor. More specifically, the present invention relates to a power cable system having a dissimilar-conductor joint portion and a power cable connection method having a dissimilar-conductor, which can prevent damage to the joint portion and ensure durability by ensuring sufficient bending strength at the dissimilar-conductor joint portion even when pulling force and bending are simultaneously applied when connecting a power cable having a dissimilar conductor.

Background

The power cable for supplying power may be constructed to include a conductor of copper or aluminum series, an insulating layer, a semiconductive layer, an outer jacket, and the like.

The power transmission cable may be composed of a conductor and an insulator, the conductor requiring high conductivity characteristics to minimize power loss. Copper and aluminum are materials for conductors which are excellent in electrical conductivity and also ensure price competitiveness, copper is more excellent in electrical and mechanical properties in addition to density, and thus copper is mainly used for conductors for power transmission cables, and aluminum conductors are limitedly used for processing power transmission lines and the like which are important for light weight properties.

However, as the price of copper raw material increases, the price of copper is 4 to 6 times higher than that of aluminum of the same weight, and thus there is an increasing demand for applying aluminum conductors to power transmission cables. Since copper is mainly used for the existing cable conductor, the demand for direct bonding of copper conductors and aluminum conductors is expected to increase as aluminum applications expand.

As a conductor material, in the case of copper, the electrical conductivity is better than that of aluminum, but the price is high, and in the case of aluminum, the electrical conductivity is inferior to that of copper, but the price is low.

In addition, in view of flexibility and the like, a conductor of a power cable is mainly composed of a plurality of element wires, and in the case of connecting a power cable having a copper conductor and a power cable having an aluminum conductor, as in the case of connecting a power cable having a dissimilar conductor of a different material therebetween, a conductor connection by a method such as welding of a dissimilar conductor may be considered, but since the melting point of the aluminum conductor is low, there is a problem in that a gap exists between the element wires in a process of welding at a temperature between the melting point of the copper conductor and the melting point of the aluminum conductor, and an oxide film is formed along each gap in a high-temperature welding environment, and the quality of a welded portion may be degraded.

Thus, in korean patent No. 10-1128106, etc., a method of connecting conductors using a dedicated sleeve member for joining dissimilar conductors such as copper or aluminum is used. The sleeve member may be constituted by a first metal portion having an insertion port into which a first conductor constituted by copper or the like is inserted, and a second metal portion having a joint surface to which a second conductor of aluminum series is welded to Mig or Tig.

The first conductor made of copper or the like is inserted into the insertion opening on one side of the sleeve member, pressed, and the aluminum conductor is welded to the joint surface on the other side.

Such a sleeve member having a bonded metal form is costly, and requires additional extrusion and welding processes with the sleeve member as a medium, and thus there may be problems of increased cost and increased process.

In addition, in order to solve the above-described problems, korean laid-open patent No. 10-2020-0069967 describes a structure and a joining method for joining dissimilar conductors by resistance welding without using a sleeve member, but as one of performance tests of a junction box of a submarine power cable, it was confirmed that a crack is generated in a conductor joint portion of the junction box when a tensile bending test (Tensile bending Test) is performed in which a pair of dissimilar conductor submarine cables connected by the junction box are bent with a predetermined radius of curvature.

Fig. 23 is an enlarged view showing the dissimilar-conductor joint 11' after a tensile bending test is performed on a power cable having a copper conductor, a power cable having an aluminum conductor, and a power cable system including an intermediate connection structure constituting a conductor joint by the method disclosed in korean laid-open patent No. 10-2020-0069967.

In the case of omitting the sleeve member and connecting the first conductor 10A as a copper conductor and the second conductor 10B as an aluminum conductor, respectively, in the dissimilar conductor joint disclosed in korean laid-open patent No. 10-2020-0069967, although sufficient tensile strength was confirmed when only horizontal tensile force was applied, when bending and tensile force were simultaneously applied in a tensile bending test according to test standards of cable demanders, no damage such as deformation, fracture, crack or the like occurred in the first conductor and the second conductor region as each conductor region, but crack C occurred in the dissimilar conductor joint.

That is, it is understood that the crack C is generated because the bending strength at the dissimilar conductor joint portion 11' is lower than the bending strength of the first conductor as the copper conductor region and the bending strength of the second conductor as the aluminum conductor region, and the joint portion cannot secure a sufficient bending strength.

In addition, fig. 24 shows a first conductor 10A and a second conductor 10B that are broken (br) during the execution of a tensile bending test performed on a power cable including a connection conductor that uses a method for joining dissimilar conductors, that is, as described in korean laid-open patent No. 10-2020-0069969, uses an intermediate connection structure that includes a first metal portion that is composed of the same material as copper as the first conductor 10A in the dissimilar conductors and includes an insertion portion, and a second metal portion that is composed of the same material as aluminum as the second conductor 10B and includes a projection portion, and has a structure in which the projection portion of the second metal portion is inserted at the insertion portion of the first metal portion and joined by friction welding.

Also, the joint structure disclosed in korean laid-open patent No. 10-2020-0069969 was confirmed to have sufficient tensile strength only in the case of providing a horizontal tensile force, but in the case of providing both bending and tensile force, the conductor joint was broken (br) by joint rupture. The insertion portion and the protruding portion, which form the locking groove at the periphery of the conductor joint portion, are joined to be able to withstand horizontal pulling force or the like by the locking structure, but also in an environment where both bending and bending are provided, sufficient bending strength cannot be ensured.

Therefore, a method of improving the bending strength at the conductor joint portion of the intermediate connection structure constituting the power cable of the dissimilar conductor has been demanded, so that the intermediate connection structure of the power cable having the dissimilar conductor is ensured to have sufficient durability even in a severe submarine environment or the like.

Disclosure of Invention

Problems to be solved by the invention

The present invention provides a power cable system having a dissimilar-conductor joint portion and a power cable connection method having a dissimilar-conductor, which can prevent damage to the joint portion and ensure durability by ensuring sufficient bending strength at the dissimilar-conductor joint portion even when a tensile force and bending are simultaneously applied when connecting a power cable having a dissimilar-conductor.

Technical proposal for solving the problems

In order to solve the above-described problems, the present invention provides a power cable system including: a first power cable comprising a first conductor; a second power cable comprising a second conductor; and a cable connection structure connecting the first power cable and the second power cable, characterized in that the first power cable includes a first conductor composed of a plurality of element wires, the second power cable includes a second conductor composed of a plurality of element wires and having a material different from that of the first conductor, a melting point of the first conductor is higher than a melting point of the second conductor, the cable connection structure includes a dissimilar conductor joint joining the first conductor and the second conductor, the dissimilar conductor joint includes a first conductor volume rate increase region formed by performing a pre-process of the first conductor that increases a volume rate from a joint surface cs1 of the first conductor to a predetermined length, and a second conductor volume rate increase region formed by performing a post-process of the second conductor that decreases a volume rate from a joint surface cs2 of the second conductor to a predetermined length, and the dissimilar conductor joint portion includes a first conductor and a second conductor.

The first conductor may be prepared by welding a pair of first conductors, cutting the joint portion, and forming the cut surface as the joint surface cs1 of the first conductor.

Further, the first conductor is prepared so that the volume fraction of the first conductor from the joint surface cs1 of the first conductor to a predetermined length can be 98% or more.

Here, the first conductor may be made of copper or copper alloy, and the second conductor may be made of aluminum or aluminum alloy.

In this case, the second conductor may be prepared so that a melt infiltration path is formed from the joint surface cs2 of the second conductor in the longitudinal direction of the second conductor before the second conductor is joined to the first conductor.

Further, the volume fraction of the second conductor from the joint surface cs2 of the second conductor to a predetermined length can be made to be 90% or less by the pretreatment of the second conductor.

In addition, the melt penetration path may be formed by drilling a plurality of points of the junction surface cs2 of the second conductor using a drill.

Further, the melt penetration path may be formed by cutting and removing a part of a plurality of element wires constituting the second conductor from the joint surface cs2 of the second conductor with a cutting tool.

Here, the volume ratio of the volume ratio increasing region of the second conductor may be 98% or more from the junction surface cs to at least 3mm in the length direction of the second conductor.

In this case, the dissimilar conductor joint portion may be characterized by the diameter of the first conductor being smaller than the diameter of the second conductor.

Further, the dissimilar-conductor joint portion may be joined together with an O-ring whose outer peripheral surface is inclined in order to terminate a step generated by a difference in diameter of the first conductor and the second conductor with an inclined surface.

The dissimilar conductor joint portion may be formed by joining the first conductor and the second conductor by resistance welding.

Here, the first conductor or the second conductor may be a circular compressed conductor.

In this case, the first conductor or the second conductor may be a rectangular conductor.

In order to solve the above problems, the present invention provides a power cable system including: a first power cable comprising a first conductor; a second power cable comprising a second conductor; and a cable connection structure connecting the first power cable and the second power cable, wherein the first power cable includes a first conductor composed of a plurality of element wires, the second power cable includes a second conductor composed of a plurality of element wires and having a material different from that of the first conductor, a melting point of the first conductor is higher than a melting point of the second conductor, the cable connection structure includes a dissimilar conductor joint portion joining the first conductor and the second conductor, the dissimilar conductor joint portion includes a volume rate increase region of the first conductor and a volume rate increase region of the second conductor with respect to a joint surface cs, and a bending strength of the dissimilar conductor joint portion is greater than a bending strength of the second conductor.

The volume ratio of the volume ratio increasing region of the second conductor may be 98% or more from the joint surface cs to at least 3mm in the length direction of the second conductor.

Further, the first conductor may be copper or copper alloy material, and the second conductor may be aluminum or aluminum alloy material.

Here, the wire may have a dissimilar conductor joint portion, wherein the first conductor has a smaller diameter than the second conductor.

In this case, the differential conductor joint may be provided with a differential conductor joint, and the differential conductor joint may be joined together with an O-ring having an inclined outer peripheral surface so as to terminate a step generated by a difference in diameter between the first conductor and the second conductor with an inclined surface.

In addition, the volume-rate increasing region of the first conductor may be previously processed to a volume-rate increase of a predetermined length before welding the first conductor and the second conductor.

Further, the first conductor may be processed to have a volume fraction of 98% or more from the junction surface cs1 of the first conductor to a predetermined length before being joined with the second conductor.

Here, the first conductor may be processed such that the volume ratio from the joint surface cs1 of the first conductor to a predetermined length is increased to a predetermined size or more, a pair of first conductors may be joined by welding and then the joint portion may be cut, and the cut surface may be formed as the joint surface cs1 of the first conductor.

In this case, the second conductor may be processed so that the volume ratio is equal to or less than a predetermined value by forming a melt permeation path from the joint surface cs2 of the second conductor in the longitudinal direction of the second conductor before the first conductor is joined to the second conductor.

Further, the second conductor may be processed so that the volume fraction of the second conductor is 90% or less.

In order to solve the above-described problems, the present invention provides a power cable connection method for connecting a first power cable including a first conductor made of a plurality of circular element wires and a second power cable including a second conductor made of a plurality of circular element wires having a material different from that of the first conductor, the power cable connection method including: a first conductor pre-processing step of increasing a volume fraction from a joint surface cs1 of the first conductor to a predetermined length to a predetermined size or more; a second conductor pre-processing step of reducing a volume fraction from a joint surface cs2 of the second conductor to a predetermined length to a predetermined size or less; and a resistance welding step of forming a dissimilar conductor joint portion by joining the joint surface cs1 of the first conductor and the joint surface cs2 of the second conductor by resistance welding.

In addition, the resistance welding step may be performed by a method of melting the first conductor and the second conductor by passing a current through the first conductor and the second conductor and pressurizing the first conductor and the second conductor.

Further, in the resistance welding step, in a welding jig for welding the first conductor and the second conductor, an exposed length of the first conductor may be smaller than an exposed length of the second conductor.

Here, the step of pre-processing the first conductor may be performed in such a manner that a pair of first conductors are joined by welding to form a joint, the joint is cut, and the cut surface is used as the joint surface cs1 of the first conductor, so that the volume ratio from the first conductor joint surface cs1 to a predetermined length becomes 98% or more.

In this case, the step of pre-processing the second conductor may be performed in such a manner that a melt penetration path is formed from the joint surface cs2 of the second conductor to a predetermined length in the second conductor longitudinal direction before the conductor is joined to the first conductor, so that the volume ratio from the joint surface cs2 of the second conductor to the predetermined length becomes 90% or less.

In addition, the volume ratio of the volume ratio increase region of the second conductor constituting the dissimilar conductor joint portion after the resistance welding step may be 98% or more from the joint surface cs to at least 3mm in the second conductor length direction.

The welding temperature at the time of the resistance welding may be a temperature lower than the melting point of the first conductor and 5% to 15% higher than the melting point of the second conductor.

Effects of the invention

According to the power cable system having the dissimilar-conductor joint portion and the power cable connection method having the dissimilar-conductor, even when the tensile force and the bending are simultaneously applied, the volume ratio of the conductor at the dissimilar-conductor joint portion can be increased to secure a sufficient bending strength, so that the damage of the dissimilar-conductor joint portion can be prevented, the durability can be improved, and the reliability of the intermediate connection structure can be improved.

Further, according to the power cable system having the dissimilar-conductor joint portion and the power cable connection method having the dissimilar-conductor according to the present invention, the operability of the dissimilar-conductor joint can be improved by applying fusion resistance welding.

Drawings

Fig. 1 shows a state in which copper round compressed conductors as a pair of first conductors are respectively mounted to a welding jig.

Fig. 2 shows a process of joining a pair of first conductors by resistance welding.

Fig. 3 shows a process of cutting the joint along a cutting line after removing burrs from the joint of the joined first conductors.

Fig. 4 is an image showing a state where a pair of copper first conductors are bonded.

Fig. 5 shows an image of a state in which burrs are removed from the joint portion of the first conductor of fig. 4.

Fig. 6 (a) shows an image of a new joint surface of a first conductor formed by cutting a joint portion of a pair of first conductors, and fig. 6 (b) shows an original first conductor joint surface before joining a pair of first conductors by resistance welding.

Fig. 7 to 9 are conceptual views showing a process of forming a melt permeation path at the junction surface of the second conductor in the form of a circular compressed conductor or a flat angle conductor of the aluminum series of the present invention.

Fig. 10 shows a state in which a pair of copper round compressed conductors as a first conductor and aluminum round compressed conductors as a second conductor are respectively mounted to a welding jig.

Fig. 11 shows a process of joining the joint faces of the first conductor and the second conductor by resistance welding.

Fig. 12 shows a state in which burrs are removed from the joint portion of the first conductor and the second conductor joined and joining is completed.

Fig. 13 shows a perspective view of the decortication of a power cable employing the copper or aluminum series element wires of the present invention compressed into a circular conductor and XLPE insulation.

Fig. 14 shows a perspective view of the decortication of a power cable employing the copper or aluminum series of flat angle conductors and XLPE insulation of the present invention.

Fig. 15 shows a cross-sectional view of an intermediate connection structure of a power cable according to an embodiment of the present invention.

Fig. 16 shows a cross-sectional view of an intermediate connection structure of a power cable according to an embodiment of the present invention.

Fig. 17 is a perspective view showing a dissimilar conductive joint portion applicable to the intermediate connection structure of the power cable shown in fig. 16.

Fig. 18 to 20 show a conductor joining process of the dissimilar conductor joint shown in fig. 17.

Fig. 21 shows a three-point bending test as a test method capable of confirming bending strength.

Fig. 22 shows an image of a three-point bending test result of a dissimilar-conductor joint portion joined by a dissimilar-conductor joint method according to the present invention.

Fig. 23 shows an example in which cracks are generated at the joint portion of the dissimilar conductors joined by the technology related to korean laid-open patent No. 10-2020-0069967.

Fig. 24 shows an example in which cracks are generated at the joint portion of the dissimilar conductors joined by the technology related to korean laid-open patent No. 10-2020-0069969.

Detailed Description

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described herein, and may be embodied in other forms. Rather, the embodiments described herein are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. Throughout the specification, like reference numerals denote like constituent elements.

The power cable may change the suitability of the conductor according to the laying environment (land or sea floor, etc.) considering costs, etc. Even if the types of conductors constituting the power cable are different depending on the conductor characteristics of the power cable and the like required for different sections, intermediate connection can be performed.

In the case where the types of conductors of the power cables to be connected are different, a difference in the degree of oxide film may occur due to a difference in melting point or the like, and therefore it is difficult to secure the quality of the joint at the joint portion with a usual joining method.

The conductor may be a round compressed conductor formed by twisting and compressing a plurality of round wires, or a rectangular conductor formed by twisting a plurality of rectangular wire layers of a plurality of rectangular wires. First, a method of connecting a pair of conductors will be described.

In the case of forming an intermediate connection structure for connecting a first power cable and a second power cable, when a first conductor of the first power cable and a second conductor of the second power cable, which are formed of a plurality of circular or rectangular wires, are joined to each other to form a dissimilar conductor joint portion, a volume rate increase region of the first conductor and a volume rate increase region of the second conductor are formed on the dissimilar conductor joint portion with respect to a joint surface, whereby sufficient bending strength can be ensured, and the problem of damage such as deformation, breakage, and cracking of the dissimilar conductor joint portion can be solved. The following is a detailed description.

In the following description, the round compressed conductors of the plurality of round element wires are twisted and compressed as an example for the conductors of each power cable, but even in the case of a flat angle conductor constituted by flat angle element wires, the same conductor bonding method may be applied, and only the form of the conductors may be changed.

As an index for determining the hollow space inside the conductor of a predetermined volume, the conductor volume ratio means the volume occupied by the conductor except for the hollow space between the element wires with respect to the total volume (=conductor cross-sectional area×conductor length) of the conductor except for Zhou Dingyi, and as defined by the following equation 1, the larger the conductor volume ratio means the smaller the hollow space.

[ 1]

The conductor volume fraction is a concept similar to the occupation rate of the conductor section reference, but can be distinguished from the concept that it is a volume reflecting the lengthwise direction variable of the conductor.

Fig. 1 to 6 show a conceptual diagram of a process of processing a volume ratio from a joint face cs1 of a circular compressed conductor of copper material as a first conductor 10A to a conductor of a predetermined length to a predetermined size or more and an image during the processing.

In the case of resistance welding a conductor of copper (or including copper alloy) and a conductor of aluminum (or including aluminum alloy), since the melting point of the aluminum conductor is low, voids are present at the joint surface of the copper conductor and a thick oxide film is formed along each void during welding at a temperature between the melting point of the copper conductor and the melting point of the aluminum conductor, whereby the quality of the joint may be degraded.

Therefore, in the present invention, before resistance welding is performed on the copper conductor and the aluminum conductor each composed of the round compressed conductor, a process of increasing the volume ratio from the junction surface cs1 of the copper conductor having a higher melting point to the conductor having a predetermined length to a predetermined size or more can be performed.

That is, the bonding surface of the copper conductor formed of the circular compressed conductor is provided in such a manner that the void or the like is removed or minimized, so that the generation of an oxide film or the like which may occur during the welding is suppressed, and the bonding quality of the bonding portion bonded by the welding or the like can be improved.

On the other hand, the meaning that the volume ratio of the conductor is 100% can be interpreted as meaning a state in which there is no void inside the conductor.

Therefore, the processing of the volume ratio from the bonding surface cs1 of the copper conductor to the predetermined length to be greater than or equal to the predetermined size means a process of reducing the hollow space ratio of the copper conductor to be less than or equal to the predetermined size.

A process of processing the volume ratio of the conductor from the joint surface cs1 of the first conductor to the predetermined length as the copper conductor joined to the second conductor as the aluminum conductor described later to be equal to or larger than a predetermined size will be described in detail.

Fig. 1 shows a state in which copper round compressed conductors as a pair of first conductors 10A are respectively mounted to a welding jig j, fig. 2 shows a process of joining the pair of first conductors 10A by resistance welding, and fig. 3 shows a process of removing burrs from a joint portion of the joined first conductors 10A and cutting the joint portion along a cutting line.

As shown in fig. 1 to 3, a method of forming the junction surface of the first conductor 10A having a relatively high melting point to a size equal to or larger than a predetermined size by welding the junction surface cs1' of the first conductor 10A of the same material by resistance welding, removing burrs (burr) b of the junction 11' and cutting the junction 11' along the cutting line cl to form a new junction surface cs1 may be used. The welding of the joint surface cs1' of the pair of the first conductors 10A may use a fusion resistance welding method, but is not limited thereto.

Fig. 4 shows an image of a state where a pair of first conductors 10A are joined, fig. 5 shows an image of a state where burrs b are removed from the joined portion 11' of the first conductors 10A, fig. 6 (a) shows a new joined surface cs1 of the first conductors 10A formed by cutting the joined portion 11' of the pair of first conductors 10A, and fig. 6 (b) shows an original joined surface cs1' of the first conductors 10A before joining.

As shown in fig. 4 and 5, a pair of first conductors 10A are formed with burrs b and welded and recrystallized during compression by a method such as fusion resistance welding, and if recrystallized joint 11 'is cut, as shown in fig. 6 (a), new joint surface cs1, which is a cut surface of joint 11' of first conductor 10A, may be processed to a smooth metal surface where voids existing in a circular compressed conductor are hardly found, and may be processed to increase the conductor volume ratio from joint surface cs1 to a predetermined length.

That is, by the preliminary process shown in fig. 1 to 5, the first conductor shown in fig. 6 (b) in which the area ratio and the conductor volume ratio of the original joint surface cs1' are relatively low can be changed from the processed first conductor shown in fig. 6 (a) in which the area ratio and the conductor volume ratio of the predetermined length of the joint surface cs1 are very high due to the existence of a plurality of voids between the element wires 1.

As described above, a process of processing the occupation ratio of the junction surface cs1 of the first conductor 10A having a high melting point and the volume ratio up to a predetermined length out of the first conductor 10A and the second conductor 10B to be joined to a predetermined size or more may be regarded as a process of making the conductor at the junction region conductive.

In addition to the method of joining the same pair of first conductors 10A and cutting the joint 11' as shown in fig. 1 to 6, a method of recrystallizing the joint cs1' of the first conductor 10A by heating the joint cs1' of the first conductor 10A with a heating jig or the like having a higher melting point than the first conductor 10A may be adopted as the process of increasing the volume ratio of the conductor from the joint cs1 of the first conductor 10A to a predetermined length to a predetermined size or more.

In addition, the volume ratio of the conductor from the new joint surface cs1 of the first conductor 10A to the predetermined length is preferably about 98% or more higher than that of the normal circular compressed conductor.

On the other hand, in order to further increase the volume ratio of the new joint surface cs1 of the first conductor 10A formed by cutting the joint portion 11 'in fig. 3 to 6 to the conductor of the predetermined length, at least one melt permeation path may be formed in advance in at least one joint surface cs1' of the pair of first conductors 10A and the inside thereof before joining the pair of first conductors 10A shown in fig. 1 to 5 (refer to reference numeral 4 of fig. 7 to 12). As described later, the melt infiltration path functions as a volume rate increase by allowing the melt of the first conductor 10A to flow in during the joining between the pair of first conductors 10A in the second conductor 10B. For example, the melt infiltration path may be a hole formed in the joint surface cs1' of the first conductor 10A by using a drill or the like or a region where the circular element wires are cut and reduced in diameter or removed (see fig. 7 to 9).

Specifically, the holes may be formed or the lines may be formed by cutting so that the volume ratio from the joint surface cs1 'of the first conductor 10A to a predetermined length in the longitudinal direction is 90% or less, and in this case, the melt permeation paths are preferably formed so as to be dispersed in the joint surface cs1' of the first conductor 10A.

Fig. 7 to 9 are conceptual views showing a process of forming a melt permeation path at the junction surface of a second conductor in the form of a circular compressed conductor or a flat angle conductor of an aluminum series.

As described by way of background, the method disclosed in korean laid-open patent No. 10-2020-0069967 and the like has an advantage in that in the case of joining a first conductor 10A of copper series and a second conductor 10B of aluminum series, an additional sleeve member can be omitted, but a crack phenomenon of the joint can be confirmed by a tensile bending test (Tensile bending Test) or the like.

The disadvantage described above is because the bending strength at the joint region of the first conductor 10A and the second conductor 10B is insufficient in the case where the pulling force and the bending are simultaneously applied.

Herein, "flexural strength" may be defined as the maximum stress applied by a sample in a flexural test before it is damaged by deformation, fracture, crack, etc.

According to the present invention, it was confirmed that when the first conductor 10A and the second conductor 10B, which are dissimilar conductors, are joined by resistance welding or the like, the bending strength of the dissimilar conductor joint portion can be improved by penetrating the melt into the inside of the conductor to form the conductor volume rate increasing region.

That is, in the present invention, the dissimilar-conductor joint portion joining the first conductor and the second conductor is formed to include the volume-rate increasing region of the first conductor and the volume-rate increasing region of the second conductor with respect to the joint surface cs, so that the bending strength of the dissimilar-conductor joint portion can be improved.

For this reason, as described above, the first conductor having a relatively high melting point forms the volume-rate increasing region of the first conductor by the preliminary processing of increasing the volume rate of a predetermined length, and thus, when bonding with the second conductor, the bonding strength can be improved by maximizing the bonding area.

In contrast, in the case of the second conductor having a relatively low melting point, since it is mainly a molten object in performing fusion resistance welding as a joining process with the first conductor, an operation of increasing the volume rate of the conductor from the joining face to a predetermined length by the pre-processing is meaningless.

In the present invention, therefore, in order to form the volume-rate increasing region of the second conductor, a method is adopted in which the volume rate is reduced by forming a melt permeation path from the joint surface of the second conductor to a predetermined length, and then, in the resistance welding process with the first conductor, a melt formed by melting the second conductor having a relatively low melting point is flowed in through the melt permeation path, as a result of which the bending strength is increased by increasing the volume rate of the second conductor region of the joint portion in the state where welding is completed.

Specifically, fig. 7 is a conceptual diagram for explaining the concept of forming a melt permeation path in the second conductor 10B made of aluminum according to the present invention.

As shown in fig. 7 (a), the second conductor 10B may be a circular compressed conductor that compresses a plurality of circular element wires 1 into a circular shape, and even if the plurality of circular element wires are assembled and compressed, the gaps between the element wires cannot be completely removed.

As described above, even in the case where the volume ratio of the predetermined length in the direction from the joint surface of the dissimilar conductor joint portion to the second conductor 10B having a relatively low melting point is insufficient, the tensile strength against the horizontal tensile force can be ensured, but in the case where bending is applied together with the tensile force, damage problems such as deformation, breakage, or cracking may occur, and therefore, the bending strength at the conductor joint portion of the dissimilar conductor eventually forms a volume ratio increase region of the second conductor on the assumption that the volume ratio of the predetermined length in the direction from the joint surface of the dissimilar conductor joint portion to the second conductor having a relatively low melting point is proportional, and as a preparatory operation therefor, a preparatory process for reducing the volume ratio from the joint surface of the second conductor as a joint object to a predetermined length section is performed before the fusion resistance welding process of the first conductor 10A and the second conductor 10B.

That is, in the present invention, as shown in fig. 7 (B), as a preliminary process for increasing the volume ratio from the joint surface cs of the dissimilar conductor joint portion where the first conductor 10A and the second conductor 10B are joined to the predetermined length in the direction of the second conductor 10B having a low melting point, at least one melt permeation path 4 is formed in the joint surface cs2 of the second conductor 10B and the inside thereof before the joining of the second conductor 10B.

The melt infiltration path 4 shown in fig. 7 (B) may be a hole formed in the joint surface cs2 of the second conductor 10B by a drill or the like or a region where a circular element wire of a predetermined length is cut and thinned or removed, and may be formed by forming a plurality of holes or cutting a plurality of element wires so that the volume ratio of the predetermined length in the longitudinal direction from the joint surface cs2 of the second conductor 10B becomes 90% or less.

The melt permeation path 4 is preferably formed so as to be dispersed in the joint surface cs2 of the second conductor 10B, because the melt of the second conductor 10B is introduced during the joining of the first conductor 10A and the second conductor 10B to increase the volume ratio, thereby improving the bending strength.

The second conductor 10B shown in fig. 8 shows a cross section of a circular compressed conductor of a plurality of circular plain wires made of compressed aluminum, and the second conductor 10B shown in fig. 9 shows a cross section of a conductor made of a plurality of rectangular conductors made of aluminum.

The method of forming the melt permeation path 4 in the second conductor 10B shown in fig. 8 and 9 may employ a method of forming a plurality of holes of a predetermined depth using a drill, but cutting work or cutting work other than drilling may be used.

The number of holes formed by a drill and the like may be determined so that the volume fraction of the second conductor 10B to the depth of forming the melt permeation path 4 becomes 90% or less by forming the melt permeation path 4 at the joint surface cs2 of the second conductor 10B.

In order to ensure bending strength irrespective of the bending direction, the melt permeation path 4 is preferably distributed on a concentric circle with respect to the center of the conductor.

Therefore, in the case where the second conductor 10B, which is formed into the melt permeation path 4 by drilling, cutting processing, or the like as described above, is joined to the first conductor 10A, which is processed to have a volume ratio of about 98% or more from the joint surface cs1 to a conductor of a predetermined length, the aluminum melt permeates into the melt permeation path 4 during resistance welding, so that the volume ratio to the predetermined length with respect to the joint surface cs of the joint portion can be increased.

In the case where resistance welding is experimentally performed in a state where a melt permeation path is formed from the joint surface cs2 of the second conductor 10B to a predetermined length before joining the first conductor 10A and the second conductor 10B so that the volume fraction from the joint surface cs2 of the second conductor 10B to the predetermined length is reduced to 90% or less, after joining the first conductor 10A and the second conductor 10B, a second conductor volume fraction increasing region 11B of a predetermined length in the direction of the second conductor 10B with respect to the joint surface cs of the dissimilar conductor joint portion 11 may be ensured, and the conductor volume fraction of the second conductor volume fraction increasing region 11B may preferably be 98% or more. The length of the melt permeation path 4 formed on the joint surface cs2 of the second conductor 10B is preferably at least 20 millimeters (mm) or more.

Fig. 10 shows a state in which a pair of copper conductors as a first conductor 10A and aluminum conductors as a second conductor 10B are respectively mounted on a welding jig j, fig. 11 shows a process in which joint surfaces of the first conductor 10A and the second conductor 10B are joined by resistance welding, and fig. 12 shows a state in which burrs B are removed from dissimilar conductor joint portions 11 of the joined first conductor 10A and second conductor 10B and joining is completed.

As shown in fig. 10, if the joint surface cs1 of the first conductor 10A and the joint surface cs2 of the second conductor 10B are brought into contact with each other and energized in a state where each of the first conductor 10A and the second conductor 10B is mounted on the welding jig j, the second conductor is melted in the vicinity of the contact surface, and at this time, as shown in fig. 11, if both conductors are pressed in the contact direction, burrs B can be formed and dissimilar conductor joint portions 11 can be formed around the joint surface cs.

As described above, the first conductor 10A is in a state where the volume ratio of the conductor processed to a predetermined length increases, and the second conductor 10B is in a state where the melt permeation path 4 is formed so that the volume ratio from the joint surface cs2 of the second conductor 10B to a predetermined length decreases.

As a welding method for joining the first conductor 10A and the second conductor 10B shown in fig. 11, fusion resistance welding (upset butt welding) may be used. In the case of the fusion resistance welding of the present invention, the fusion resistance welding is a joining method using joule heat generated by current supply as a direct heat source for heating the joining region and melting the material, and may be constituted by a current-supplied heating process and a pressurizing process in which the conductor starts to be pressed at the time of melting the joining interface.

According to the present invention, at the time of the fusion resistance welding, the welding temperature is resistance welded at a temperature lower than the melting point of the first conductor 10A and higher than the melting point of the second conductor 10B.

Here, although the first conductor 10A needs to be hardly melted, it is important to select an appropriate welding temperature because the second conductor 10B is sufficiently melted to allow the second conductor 10B melt to easily infiltrate into the melt infiltration path 4 formed in the joint surface cs2 of the second conductor 10B.

In the case where the welding temperature is higher than the melting point of the second conductor 10B but the difference is not large, the viscosity of the melt is too large to easily flow the melt into the melt permeation path, and in the case where the welding temperature is too high than the melting point of the second conductor 10B, the melt cannot be held in the vicinity of the joint portion in the form of burrs and flows down, and may not sufficiently permeate into the melt permeation path. In this regard, the welding temperature is preferably a temperature at which resistance welding is performed 5% to 15% higher than the melting point of the second conductor 10B.

Further, as shown in fig. 10, the lengths (d 1< d 2) of the first conductor 10A and the second conductor 10B exposed in the joining direction may be different in a state of being attached to the respective welding jigs j.

When the first conductor 10A and the second conductor 10B are brought into contact with each other by the fusion resistance welding method and energized, the first conductor 10A having a high melting point is not fused, and therefore the exposed length d1 of the first conductor 10A is made short, whereas the second conductor 10B having a low melting point is fused, and therefore the exposed length d2 of the second conductor 10B is determined in consideration of the amount of fusion for sufficient bonding.

Specifically, the exposed length d2 of the second conductor 10B may be twice or more, preferably 10 times or more, the exposed length d1 of the first conductor 10A.

The second conductor 10B may be aluminum or an aluminum alloy, and the first conductor 10A having a lower melting point than the copper material is configured to have a longer length exposed from the welding jig, so that the second conductor 10B can be sufficiently melted and uniformly joined to the dissimilar conductor joint portion 11 even when welded in a circular compressed conductor state.

In addition, as shown in fig. 11, the aluminum melt m is slowly immersed in the melt infiltration path 4 of the second conductor 10B in the course of performing the melt resistance welding, and as shown in fig. 12, in a state where the melt resistance welding is completed, the inside of the melt infiltration path 4 is filled with the aluminum melt m to constitute the dissimilar conductor joint portion 11.

Here, the "dissimilar conductive joint" refers to a region where the first conductor 10A and the second conductor 10B are joined by recrystallization or the like around the joint surface cs during the joining process, and may be defined as a region indicated by a broken line including the volume-rate increasing region 11A of the first conductor 10A and the volume-rate increasing region 11B of the second conductor 10B with the joint surface cs as a reference.

Further, as shown in fig. 12, the melt permeation path 4 of the second conductor 10B may be shortened by melting of the second conductor 10B as the welding process is performed, but the length of the volume-rate increasing region 11B of the second conductor 10B constituting the dissimilar-conductor joint portion 11 may be configured to be longer than the length of the volume-rate increasing region 11A of the first conductor 10A.

The volume-rate increasing region 11A of the first conductor 10A in the dissimilar-conductor joint 11 may be a region in which the volume rate increases from the joint surface cs1, which is formed by removing the burr B of the joint 11 'and cutting the joint 11' after welding the first conductor 10A of the same material by resistance welding, to a predetermined length, as described with reference to fig. 1 to 3, and the volume-rate increasing region 11B of the second conductor 10B may be a region in which the volume rate increases by flowing the aluminum melt m from the joint surface cs2 of the second conductor 10B in the direction of the second conductor 10B during the joining with the first conductor 10A. Here, the volume-rate-increasing region 11B of the second conductor 10B is formed to increase the bending strength of the joint, and as shown in fig. 10 to 12, the volume-rate-increasing region 11B of the second conductor 10B is formed by forming the melt permeation path 4 in the second conductor 10B, but is not limited thereto.

In the volume-rate increasing region 11B of the second conductor 10B of the dissimilar-conductor joint 11, the volume rate of the second conductor 10B is also preferably increased to about 98% or more, whereby the bending strength of the dissimilar-conductor joint 11 can be increased.

That is, it can be understood that the aluminum melt m, which penetrates into the inside of the melt penetration path 4 and hardens, while performing the skeleton function of connecting the joint surface cs and the second conductor 10B, achieves an effect of increasing the conductor volume ratio of a predetermined length in the direction from the joint surface cs constituting the dissimilar conductor joint section 11 to the second conductor 10B.

When the fusion resistance welding is completed, as shown in fig. 12, the foreign-conductor joint 11 can be completed by removing the burrs b on the outer peripheral surface of the foreign-conductor joint 11 after the joining is completed. In the tensile bending test, in order to prevent damage such as cracking or breaking of the dissimilar conductor joint portion 11, the volume fraction increase region 11B of the second conductor 10B preferably has a volume fraction of 98% or more under various test conditions, and the length thereof should be at least 3 mm.

In the embodiment referring to fig. 10 to 12, when dissimilar conductors having different melting points are connected, a melt permeation path is formed only in the second conductor 10B having a lower melting point, and the conductor volume ratio of the second conductor 10B in the dissimilar conductor joint 11 is increased during the joining process, so that the bending strength of the dissimilar conductor joint 11 is made greater than that of the second conductor 10B.

However, the method of increasing the volume ratio of the conductor by forming the melt permeation path as described above can be applied not only to the second conductor having a lower melting point but also to the first conductor having a higher melting point.

That is, in fig. 3, in order to further increase the volume ratio of the joint face cs1 of the first conductor 10A formed by cutting of the joint 11' to a conductor of a predetermined length and to increase the joint strength between the first conductor 10A and the second conductor 10B at the joint face, at least one melt permeation path may be formed in advance in the joint face cs1 of the first conductor 10A and the inside thereof before joining the first conductor 10A and the second conductor 10B.

The melt permeation path may function to allow the melt of the second conductor 10B to flow in during the joining between the first conductor 10A and the second conductor 10B to further increase the volume rate of the volume rate-increasing region 11A of the first conductor 10A.

In addition, as the melt of the second conductor 10B permeates between the first conductors 10A through the melt permeation path, the bonding strength between the first conductor 10A and the second conductor 10B at the bonding surface cs increases. That is, it can be easily estimated that the aluminum melt that penetrates into the melt penetration path of the first conductor 10A and hardens can be effective in increasing the conductor volume ratio from the joint surface cs constituting the dissimilar conductor joint section 11 to a predetermined length in the direction of the first conductor 10A while performing the skeleton action of connecting the first conductor 10A and the second conductor 10B with the joint surface cs as a reference.

Referring to fig. 13, the power cable 100 is provided with a conductor 10 in a central portion. The conductor 10 functions as a path through which an electric current flows, and may be made of copper (including copper alloy) or aluminum (including aluminum alloy), for example. As shown in fig. 14, the conductor 10 may be formed of a circular compressed conductor in which a plurality of circular element wires are compressed into a circular shape for flexibility, but may be formed of a rectangular conductor as described later with reference to fig. 14.

The conductor 10 may have uneven electric field due to its uneven surface, and corona discharge may be locally generated. In addition, if a gap is generated between the surface of the conductor 10 and the insulating layer 14 described later, the insulating performance may be degraded. In order to solve the above-described problem, an inner semiconductive layer 12 composed of a semiconductive substance such as semiconductive carbon paper or the like may be provided outside the conductor 10.

The internal semiconductive layer 12 makes the electric field uniform by making the charge distribution on the conductor plane uniform, and further improves the insulation resistance of the insulating layer 14 described later. Further, the function of preventing corona discharge and ionization can be performed by preventing the formation of a space between the conductor 10 and the insulating layer 14.

An insulating layer 14 is provided on the outside of the inner semiconductive layer 12. In general, the breakdown voltage of the insulating layer 14 is high, and the insulating performance should be stable for a long period of time. In addition, it is required to have heat resistance such as heat resistance while having a small dielectric loss.

The insulating layer 14 of such a power cable is mainly made of an insulating or resin material (XLPE, etc.).

The insulating layer of the power cable shown in fig. 13 illustrates an example composed of a resin material, but an insulating layer that insulates earth may be applied.

The insulating layer 14 made of a resin material is made of a polyolefin resin such as polyethylene and polypropylene, and preferably a polyethylene resin. The polyethylene resin may be a crosslinked resin, and may be produced by silane or an organic peroxide, for example, dicumyl peroxide (DCP), or the like, as a crosslinking agent.

Further, an outer semiconductive layer 16 is provided on the outside of the insulating layer 14. The outer semiconductive layer 16 is grounded to equipotential the distribution of electric lines of force between it and the inner semiconductive layer 12, thereby improving the insulation resistance of the insulating layer 14. In addition, the outer semiconductive layer 16 may reduce electric field concentration by smoothing the surface of the insulating layer 14 in the cable, thereby preventing corona discharge.

A metal sheath 18 or the like may be provided on the outside of the outer semiconductive layer 16 depending on the type of cable. The metal sheath 18 may serve as a return path for the electrical shielding and short-circuit current, and the metal sheath 18 may be replaced by a shielding layer formed in the shape of a neutral wire.

The outer jacket 20 is provided on the outermost side of the power cable 100. The jacket 20 may be disposed at the outermost side of the cable 100 to protect the internal construction of the power cable 100. Thus, the jacket 20 may generally be constructed of PVC (Polyvinyl chloride; polyvinyl chloride) or PE (Polyethylene) or the like.

Such a power cable may be a power cable laid in the ground or within a pipeline in the ground. The power cable may be a power cable (hereinafter referred to as "submarine power cable") installed in water such as a river or ocean outside the ground or a pipeline in the ground. In the case of a submarine power cable, it may have a different structure from that of an in-ground power cable in order to accommodate a severe underwater environment and protect the cable.

Fig. 14 shows a perspective view of the decortication of a power cable employing the copper or aluminum series of flat angle conductors and XLPE insulation of the present invention. Although the structure of the in-ground power cable is substantially similar to that with reference to fig. 13, the description will be centered on the differences.

Referring to fig. 14, a power cable 100 includes a conductor 10, an inner semiconductive layer 12, an insulating layer 14, an outer semiconductive layer 16, and a cable core a that transmits power only along the conductor 10 in the length direction of the cable and prevents leakage current in the radial direction of the cable.

The conductor 10 functions as a passage through which current flows for transmitting electric power, and may be composed of a material having excellent conductivity and strength and flexibility suitable for cable manufacture and use, such as copper (including copper alloy) or aluminum (including aluminum alloy), etc., to enable minimizing electric power loss.

As shown in fig. 11, the conductor 10 may be a rectangular conductor 10 having a rectangular element wire layer 1C formed of a circular center element wire 1a and rectangular element wires 1b twisted so as to surround the circular center element wire 1a and having a circular cross section as a whole.

As another example, as shown in fig. 13, the conductor 10 may be a circular compressed conductor formed by twisting a plurality of circular element wires and compressing the twisted circular element wires into a circular shape.

The flat angle conductor 10 has a relatively high volume ratio compared to the circular compressed conductor shown in fig. 13, and has an advantage of being able to reduce the outer diameter of the cable.

An inner semiconductive layer 12 may be formed on the outside of the conductor 10, and an insulating layer 14 may be provided on the outside of the inner semiconductive layer 12. The insulating layer 14 may be made of insulating material or resin material, but the submarine power cable 100 of the present invention shown in fig. 14 is also made of XLPE material, as in the case of the in-ground power cable shown in fig. 13.

An outer semiconductive layer 16 may be provided outside the insulation layer 14, and a moisture absorbing portion 17 for preventing moisture from penetrating into the cable may be provided outside the outer semiconductive layer 16. The moisture absorbing portion 17 may be formed between the twisted wires of the conductor 10 and/or outside the conductor 10, and may be formed of a powder, tape, coating, film, or the like containing a super absorbent resin (super absorbent polymer; SAP) having a high water absorption rate and an excellent water absorption maintaining ability, and functions to prevent the penetration of moisture in the cable length direction. In addition, the moisture absorbing portion may have a semi-conductivity to prevent abrupt electric field changes.

The moisture absorbing portion 17 may be provided together with a copper wire implanting tape (not shown). The Copper wire implant tape is composed of Copper wire (Copper wire), a nonwoven fabric tape, etc., and serves to promote point contact between the outer semiconductive layer 16 and the metal sheath 18, and the moisture absorbing layer 17 is composed of a powder, tape, coating, film, etc., containing a super absorbent resin (super absorbent polymer; SAP) which absorbs moisture penetrating into the cable at a high rate and is excellent in the ability to maintain a water-absorbing state, and serves to prevent moisture penetration in the cable longitudinal direction. The copper wire implant tape and the moisture absorbing layer 17 are preferably provided with semi-conductivity to prevent abrupt electric field changes, and may be configured to include copper wires in the moisture absorbing layer 17 to enable both energization and moisture absorption.

The cable protection part B may be provided outside the cable core a configured as described above, and the submarine power cable 100 laid on the seabed may be additionally provided with the cable exterior part C. The cable protecting portion B and the cable exterior portion C protect the core portion a from various environmental factors such as moisture permeation, mechanical trauma, corrosion, etc., which may affect the power transmission performance of the cable.

The cable protection part B includes a metal sheath 18 and a polymer sheath 20, and protects the cable from fault current, external force or other external environmental factors.

The in-ground power cable shown in fig. 13 is illustrated as having a structure in which a cable sheath is provided outside a metal sheath, but it is understood that a polymer sheath 20 is provided outside a metal sheath 18 of the submarine power cable shown in fig. 14.

In particular, the metal sheath 18 constituting the submarine power cable may be formed to surround the core 10 for shielding, grounding, sealing, or the like. In particular, when the power cable 100 is laid in an environment such as the sea floor, it is possible to seal the cable core a to prevent foreign matter such as moisture from entering the cable core a, and to form a continuous outer surface having no seam by pressing metal melted outside the cable core a, thereby making it possible to provide excellent water blocking performance. In the case of the power cable 100 laid on the sea floor, lead (Lead) or aluminum is preferably used as the metal, and Lead alloy (Lead alloy) to which a metal element is added for improving mechanical properties is more preferably used. The metal sheath 18 is grounded at the end of the power cable 100, and serves as a path through which a fault current flows when a fault such as a ground fault or a short circuit occurs, thereby protecting the cable from external impact and preventing an electric field from discharging to the outside of the cable.

In addition, the metal sheath 18 may be coated with an anti-corrosion compound, such as blown asphalt, etc., on the surface to further improve the corrosion resistance, water resistance, etc., of the cable and to increase adhesion to the polymer sheath 20.

The polymer sheath 20 may be formed outside the metal sheath 18 to improve corrosion resistance and water resistance of the cable, and may perform a function of protecting the cable from mechanical injury and other external environmental factors such as heat and ultraviolet rays. The polymer jacket 20 may be formed of a resin such as polyvinyl chloride (PVC) or polyethylene, and in the case of the power cable 100 laid on the sea floor, a polyethylene resin excellent in water resistance is preferably used, and in an environment where flame retardancy is required, a polyvinyl chloride resin is preferably used.

The power cable 100 may be provided with a metal reinforcing layer 21 made of a galvanized steel tape or the like on the outer side of the polymer sheath 20, thereby preventing the expansion of the metal sheath 18 due to the expansion of the insulating oil. Further, a cushion layer (not shown) made of a semiconductive nonwoven fabric tape and cushioning external force applied to the power cable 100 may be provided on the upper and/or lower portion of the metal strong layer 21, and an outer sheath 22 made of a resin such as polyvinyl chloride or polyethylene may be provided to further improve corrosion resistance, water blocking property, etc. of the power cable 100, thereby functioning as a cable protection portion B for further protecting the cable from mechanical injury and other external environmental factors such as heat and ultraviolet rays.

In addition, since the power cable 100 laid on the sea floor is easily damaged by a damage due to an anchor of a ship or the like, and also by a bending force due to a ocean current, a wave or the like, a friction force with the sea floor, or the like, a cable exterior part C may be additionally provided outside the cable protection part B in order to prevent such a situation.

The cable jacket C may include a metallic armor layer 34 and an outer jacket 38. The metal armor layer 34 may be formed of steel, galvanized steel, copper, brass, bronze, or the like, and may be formed of at least one layer by winding a wire having a circular or flat-angled cross-sectional shape, or the like, thereby not only performing the function of enhancing the mechanical characteristics and performance of the power cable 100, but also protecting the electrical connection from external forces.

The outer coating 38 formed of polypropylene yarn or the like is formed in one or more layers on the upper and/or lower portion of the metal armor layer 34 to protect the cable, and the outer coating 38 formed on the outermost periphery may be formed of two or more materials of different colors to secure the visibility of the cable laid on the sea floor.

In the case of laying the power cable as described above, the intermediate connection may be performed at intervals of several hundred meters or several kilometers.

The intermediate connection structure shown in fig. 15 may be a factory connection structure or a flexible connection structure mainly used for a submarine power cable or the like.

That is, a method of connecting the intermediate connection of the power cables 100A and 100B to the power cable factory or the like, winding the power cable around a reel, a turntable, or the like, and carrying the power cable to the laying site to lay the power cable is applied, and thus the cost can be reduced by shortening the power cable laying time.

The conductors of the pair of power cables connected by the power cable connection structure 300 as described above may be heterogeneous conductors.

For example, the first conductor 10A of the first power cable 100A may be composed of a copper conductor, and the second conductor 10B of the second power cable 100B may be composed of an aluminum conductor.

The factory connection structure may be configured by a restoration layer that restores the internal configuration of the intermediate connection structure to be similar to the internal configuration of the two power cables, without using an external case in the form of a case.

That is, the pair of first conductors 10A and second conductors 10B may be formed into a dissimilar-conductor joint by performing fusion resistance welding in a state in which the volume ratio of the first conductors 10A is increased and the volume ratio of the second conductors 10B is decreased at the joint surface as described above, the inner semiconductive recovery layer 12 'is formed by a semiconductive tube outside the conductor joint 11, the XLPE tape or insulating paper is wound outside the inner semiconductive recovery layer 12' so as to interconnect the insulating layers of the two power cables to form the insulating recovery layer 14 'of the recovery insulating layer, and the semiconductive tube may be used outside the insulating recovery layer 14' to form the outer semiconductive recovery layer 16', as in the inner semiconductive recovery layer 12'.

The metal sheath for connecting the power cable is formed by a lead (lead) tube or the like to form a metal sheath restoration layer 18 for shielding, water blocking, or sealing, and an outer sheath restoration layer 20 'is restored outside the metal sheath restoration layer 18', and a metal strong restoration layer, an outer sheath restoration layer, and the like may be formed as necessary.

In the case of such a factory connection structure, if laid in a water environment such as the sea floor, it is continuously exposed to bending and continuously applied with tensile force under the influence of tidal current or the like, whereby it is necessary to secure sufficient bending strength of the conductor joint portion constituting the intermediate connection structure.

Therefore, as described above, the first conductor 10A made of copper of the first power cable increases the volume fraction of the predetermined length, and the second conductor 10B made of aluminum of the second power cable decreases the volume fraction from the joint surface to the predetermined length, so that the melt having a lower melting point than the first conductor 10A flows into the melt permeation path formed in the joint surface of the second conductor 10B to fill the hollow space of the second conductor during the fusion resistance welding, as a result of which the volume fraction of the second conductor 10B is increased, and the bending strength can be further improved.

The dissimilar-conductor joint shown in fig. 1 to 15 is exemplified by the case where the conductors of two power cables are dissimilar but have the same diameter. Since the diameters of the conductors are the same, the power cable provided with copper as the first conductor 10A generates less heat and has a high power supply capability, but the problem of heat generation in the submarine region is not great in the cable connecting the land region and the submarine region, and therefore, the power cable using the aluminum-series conductor is arranged in the submarine region, and the power cable using the copper-series conductor is arranged in the land region, and when the intermediate connection is performed in the boundary region, the effects of reducing the cost and improving the stability can be obtained at the same time.

However, in addition to the above-described special boundary region, it is also necessary to intermediately connect two power cables having a pair of dissimilar conductors, and in this case, it is sometimes necessary to intermediately connect power cables having different diameters of conductors and different cable diameters corresponding thereto due to a difference in power-on capability or heat generation.

Specifically, the diameters of the first conductor 10A as a copper conductor and the second conductor 10B as an aluminum conductor may be different due to the energization capability or heat generation.

The present invention can provide a dissimilar conductor joint portion that can be applied even when the diameters of the first conductor 10A and the second conductor 10B are different (different diameter and dissimilar conductor). With reference to fig. 16 and 17, a description will be given of a connection structure of different diameters and different conductors, and an intermediate connection structure of a power cable including the same.

Fig. 16 shows a cross-sectional view of an intermediate connection structure of a power cable according to an embodiment of the present invention, and fig. 17 shows a perspective view of a dissimilar conductor joint portion applicable to the intermediate connection structure of a power cable shown in fig. 16.

Referring to fig. 16, the intermediate connection structure 300 may include: a pair of first and second conductors 10A, 10B of first and second power cables 100A, 100B; an O-ring 30 simultaneously engaged with the ends of the first conductor 10A and the second conductor 10B; a corona discharge shield 320 connected to the insulating layers 14A and 14B of the first and second power cables 100A and 100B, and configured to surround the dissimilar conductive joint section; and a sleeve member 360 that surrounds the outer sides of the pair of first power cables 100A and second power cables 100B, is made of an elastic resin material that is shrinkable at normal temperature, and takes a PMJ (Pre molded Joint) form. The sleeve member 360 may have a hollow-shaped configuration.

The corona discharge shield 320 is formed extending from the insulating layer 14A of the first power cable 100A toward the insulating layer 14B of the second power cable 100B. In this case, the corona discharge shield 320 has a flat outer surface configured to surround the O-ring 30, form a continuous surface with the surfaces of the pair of insulating layers 14A, 14B opposite to both sides without steps to prevent or reduce electric field concentration, and can prevent corona discharge that may occur at the pair of first and second conductors 10A, 10B connected by the O-ring 30 and the sleeve member 360.

In an embodiment of the present invention, a pair of cables 100A, 100B having different diameters from each other are connected, and thus the corona discharge shield 320 is also constructed of a structure having different diameters on both sides, and the outside may have a structure inclined from the second power cable 100B having a relatively large diameter toward the first power cable 100A having a relatively small diameter.

The sleeve member 360 may include: a first electrode 330 disposed outside the corona discharge shield 320, and having a first end 330A made of copper material into which an end of a first power cable 100A having a relatively small diameter of a conductor is inserted, and a second end 330B made of aluminum material into which an end of a second power cable 100B having a relatively large diameter is inserted; a pair of second electrodes 340 disposed to be spaced apart from and opposite to the first electrodes 330; and a sleeve insulating layer 350 surrounding the first electrode 330, the second electrode 340, and the insulating layers 14A, 14B of the pair of the first power cable 100A and the second power cable 100B. The sleeve insulating layer 350 may be formed of EPDM (Ethylene Propylene Diene Monomer ) or liquid silicone rubber (LSR: liquid Silicon Rubber).

The first electrode 330 is made of a semiconductive material and is electrically connected to the first conductor 10A and the second conductor 10B of the power cable, and functions as a so-called high-voltage electrode (electrode). The second electrode 340 is also made of a semiconductive material and is connected to the outer semiconductive layers 16A, 16B of the power cable, functioning as a so-called shielding electrode (Deflector). Accordingly, the electric field distribution inside the intermediate junction box 300 is distributed along the first electrode 330 and the second electrode 340, and the first electrode 330 and the second electrode 340 function to uniformly spread therebetween without being locally concentrated.

At this time, the first electrode 330 may be configured such that a distance D1 from the center of the cable to the outer surface at the position of the first end 330A is the same as a distance D2 from the center of the second end 330B to the outer surface, and distances L1 and L2 from the centers of the first end 330A and the second end 330B to the inner surface are different from distances P1 and P2 from the surfaces of the insulating layers 14A and 14B of the first power cable 100A and the second power cable 100B.

The first conductor 10A and the second conductor 10B are made of different materials and diameters, and thus the distances from the cable center to the outer peripheral surfaces of the insulating layers 14A, 14B of the first power cable 100A and the second power cable 100B are different, but by making the respective distances L1, L2 from the respective centers of the first end portion 330A and the second end portion 330B to the inner surfaces different from the distances P1, P2 from the surfaces of the insulating layers 14A, 14B of the respective first power cable 100A and the second power cable 100B, the distances D1 from the cable center to the outer surfaces of the first electrode 330 at the position of the first end portion 330A and the distances D2 from the center of the second end portion 330B to the outer surfaces can be made uniform.

The intermediate connection structure 300 includes an outer case member 200 formed of a so-called "shielding case" or "metal case" surrounding the sleeve member 360. At this time, a space between the case 200 and the sleeve member 360 may be filled with a waterproof material (not shown) or the like.

Even in the case where the diameters of the conductors connected as described above or the outer diameters of the power cables are different, although there is a difference in electric field concentration in the vicinity of the conductor joint portion by applying the O-ring 30, similarly, increasing the volume ratio from the joint surface of the first conductor 10A of the copper material of the first power cable to a predetermined length and decreasing the volume ratio from the joint surface to a predetermined length of the second conductor 10B of the aluminum material of the second power cable allows the melt of the second conductor to flow into the melt penetration path formed in the joint surface of the second conductor 10B at the time of fusion resistance welding, filling the hollow space of the second conductor to increase the volume ratio of the second conductor 10B, whereby the bending strength can be improved.

Fig. 16 illustrates an example of an intermediate connection structure of a power cable having an insulating layer made of XLPE as a pair of power cables having dissimilar and dissimilar-diameter conductors, but the power cable having conductors connected by dissimilar-conductor joints according to the present invention may be a ground insulating cable.

That is, the dissimilar-conductor Joint portion and the dissimilar-conductor connection method according to the present invention with reference to fig. 1 to 16 can be applied to the connection of the same-diameter conductors and the connection of the dissimilar-diameter conductors simultaneously joined with the O-rings, and can be applied to an intermediate connection structure having a reinforcing insulating layer formed by winding insulating paper around the dissimilar-conductor Joint portion to connect with the ground insulating layers of the ground-insulated power cable in two directions, in addition to an intermediate connection structure having a corona discharge protection screen and a sleeve member installed outside the dissimilar-conductor Joint portion, according to the type of insulating layer of the power cable to be connected in the intermediate connection, and in the case of such a ground-insulated intermediate connection structure, can be applied to a flexible factory or flexible connection structure having an outer box member (rib Joint) or a manner of omitting the outer box member and restoring each cable layer outside the reinforcing insulating layer.

As described above, in order to eliminate the problem of current carrying capacity or heat generation when a power cable composed of a dissimilar conductor such as copper and aluminum is interposed, the diameters of the conductor and the cable may be configured to be different. Hereinafter, a method of connecting a pair of power cables each having a different diameter and a different conductor is described.

Hereinafter, the order of connecting the pair of first power cables 100A and second power cables 100B having different diameters of conductors to each other through the intermediate connection box 300 and the intermediate connection structure 300 will be described in detail with reference to the accompanying drawings.

Referring to fig. 17, in order to join the dissimilar conductors and the different diameters, an O-ring 30 may be provided so as to surround the dissimilar conductor joining section 11.

The O-ring 30 may be inserted into and mounted on the first conductor 10A, and the O-ring 30 may have a maximum outer diameter corresponding to the outer diameter of the second conductor 10B and a minimum outer diameter (through hole diameter) corresponding to the outer diameter of the first conductor 10A.

Therefore, in a state where the O-ring 30 is attached, if the fusion resistance welding is completed, the side surface of the maximum outer diameter portion B of the O-ring 30 may be joined to the joint surface cs2 of the second conductor 10B, and the inner peripheral surface of the through hole of the O-ring 30 may be joined to the outer peripheral surface of the first conductor 10A.

Therefore, the diameter of the through hole of the O-ring 30 is preferably set to a size corresponding to the diameter of the first conductor 10A.

With the above configuration, each joint surface of the first conductor 10A and the second conductor 10B, which are different-diameter and dissimilar conductors, can be joined, and the inner peripheral surface of the through hole of the O-ring 30 and the joint surface are joined to the outer peripheral surface of the first conductor 10A and the joint surface cs2 of the second conductor 10B, respectively, to be integrated.

The O-ring 30 may be provided to compensate for the difference in diameter of the second conductor 10B of the second power cable 100B and the first conductor 10A of the first power cable to remove the step at the dissimilar conductor joint 11. Accordingly, the cross-section of the O-ring 30 may be configured in a right triangle or a tapered configuration, respectively. The O-ring 30 may have a tapered outer peripheral surface to remove steps at the dissimilar conductor joint 11 of the first conductor 10A and the second conductor 10B, and may prevent or reduce electric field concentration at the steps or the like.

The material of the O-ring 30 may be the same as that of the first conductor 10A or the second conductor 10B, but preferably, the material of the second conductor 10B may be the same as that of the second conductor 10B having a lower melting point.

The conductor bonding process of the dissimilar conductor bonding section shown in fig. 18 to 20 is the same as the dissimilar co-radial conductor bonding process described with reference to fig. 1 to 12, except that the O-ring 30 is applied to reduce electric field concentration at the dissimilar conductor bonding section 11.

That is, even if there is a difference in the diameter of the connected conductors or the outer diameter of the power cable in terms of reducing the concentration of the electric field in the vicinity of the dissimilar-conductor joint 11 by applying the O-ring 30, similarly, as shown in fig. 1 to 6, before joining the first conductor 10A and the second conductor 10B, the volume ratio from the joint surface cs1 of the first conductor 10A of the first power cable to the predetermined length is increased, and as shown in fig. 7 to 10, the volume ratio is decreased by forming the melt permeation path from the joint surface cs2 of the second conductor 10B of the second power cable to the predetermined length, and at the time of fusion resistance welding, the melt of the second conductor having a lower melting point than the first conductor 10A is made to flow into the melt permeation path formed at the joint surface cs2 of the second conductor 10B to fill the hollow space of the second conductor, thereby increasing the volume ratio of the second conductor 10B.

Therefore, a description of the repetition of the dissimilar co-radial conductor joining process with reference to fig. 1 to 12 will be omitted.

As shown in fig. 18, when the first conductor 10A and the second conductor 10B having different diameters are mounted on the welding jigs j', j ", an O-ring 30 may be mounted on the end portion of the first conductor 10A. Accordingly, the welding jig j' shown in fig. 18 may be constituted by a structure including the receiving portion of the O-ring 30 so that the first conductor 10A to which the O-ring 30 is mounted can be mounted.

The O-ring 30 may be composed of the same aluminum series as the second conductor 10B having a low melting point, and may be joined by melting and recrystallizing together with the first conductor 10A and the second conductor 10B when energized and pressurized, as shown in fig. 19. The O-ring 30 may be made of the same copper-based metal as the first conductor 10A, but in order to improve the adhesion between the O-ring 30 and the inner peripheral surface of the through hole of the O-ring 30 and the first conductor 10A inserted into the through hole, the O-ring 30 is preferably made of a second conductor 10B having a low melting point.

The dissimilar conductor joint portion 11 of the first conductor 10A, the second conductor 10B, and the O-ring 30 joined by the above-described method can be joined in such a manner that the end portion of the first conductor 10A is inserted into the second conductor 10B as shown in fig. 20, and the outer peripheral surface of the dissimilar conductor joint portion 11 is replaced with the outer peripheral surface of the O-ring 30, whereby even with a dissimilar conductor, it is possible to configure an inclined surface instead of a step.

As described above, the outer diameter of the minimum outer diameter portion x of the outer peripheral surface of the O-ring 30 is identical to the outer diameter of the first conductor 10A, and the outer diameter of the maximum outer diameter portion y is identical to the outer diameter of the second conductor 10B, so that the step at the dissimilar conductor joint portion 11, which may be caused by the difference in diameters between the first conductor 10A and the second conductor 10B having different diameters, is formed as a gentle inclined surface, thereby having an effect of being able to alleviate the problem of electric field concentration or the like. In addition, in the same manner, during the fusion resistance welding, the aluminum melt flows into the melt infiltration path formed at the joint surface of the second conductor 10B, and the volume ratio and bending strength of the second conductor 10B can be improved.

The O-ring 30 is recrystallized during the fusion resistance welding process, surrounds the vicinity of the joint portion of the first conductor, and has a structure in which the joint surface is connected to the aluminum conductor in the melt infiltration path functioning as a skeleton inside the second conductor, whereby the tensile bending strength can be further improved.

Fig. 21 shows a three-point bending test as a test method capable of confirming bending strength. Fig. 22 shows an image of a three-point bending test result of a dissimilar-conductor joint portion joined by a dissimilar-conductor joint method according to the present invention.

The three-point bending test (3 point bending test) shown in fig. 21 is a method in which after a sample is placed on a first roller r1 and a third roller r3, a second roller r2 is positioned to be in contact with the sample, the second roller r2 is moved downward, a load is recorded at predetermined time intervals, and when the sample breaks or the load applied thereto is lowered beyond the highest point, the test is stopped, whereby the bending strength of the point pressed by the second roller r2 is tested.

For example, according to the test conditions described in the ISO 7438 metallic material bending test (Metallic materials bend test), the separation distance L of the first roller and the third roller may be 240mm, the diameter D of the second roller may be 100mm, the sample diameter D may be 48mm on average, the descent speed V of the second roller r2 may be 10mm/min, and the test conditions may be changed within an appropriate range.

Specifically, the sample shown in fig. 22 is a result of a test performed according to a three-point bending test. The sample may include a dissimilar conductive joint portion 11, a first conductor 10A as a copper conductor, and a second conductor 10B as an aluminum conductor, the first conductor 10A being subjected to a preliminary treatment for increasing the volume ratio from the joint surface to a predetermined length, the second conductor 10B being subjected to a preliminary treatment for forming a melt permeation path at the joint surface to reduce the volume ratio as shown in fig. 10, the dissimilar conductive joint portion 11 being a joint structure of the first conductor 10A and the second conductor 10B, the joint structure being a joint structure for increasing the volume ratio of the first conductor 10A and the second conductor 10B.

As a result of the three-point bending test, as shown in fig. 22, as an example of deformation pd of the second conductor 10B having a relatively low melting point, a cleavage of the element wire occurs before the first conductor 10A made of copper material and the dissimilar conductor joint portion 11 are deformed, broken, cracked, or the like. Deformation of the second conductor 10B with a load smaller than the load applied to the dissimilar-conductor joint portion 11 means that the bending strength of the dissimilar-conductor joint portion 11 is relatively higher than that of the second conductor 10B.

In general, the conductor is designed to have a sufficient bending strength under a severe environment such as a submarine environment, and the dissimilar conductor joint section 11 having a relatively higher bending strength than the second conductor 10B can be regarded as the dissimilar conductor joint section 11 ensuring a sufficient bending strength.

From this test result, it was confirmed that in the case where the first conductor 10A processed to have an increased volume fraction of the conductor from the joint surface cs1 to the predetermined length and the second conductor 10B processed to have a decreased volume fraction of the joint surface cs2 to the predetermined length and having a melting point lower than that of the first conductor 10A were joined by the fusion resistance welding method, the bending strength of the dissimilar conductor joint portion 11 was greater than that of the second conductor 10B at a temperature lower than that of the first conductor 10A and higher than that of the second conductor 10B. In addition, due to the characteristics of the material, it can be considered that the bending strength at the dissimilar conductor joint portion 11 is smaller than that of the first conductor 10A.

Therefore, in the case of connecting a power cable having a dissimilar conductor, when sufficient bending strength is ensured by forming the volume-rate increasing region 11A of the first conductor 10A and the volume-rate increasing region 11B of the second conductor 10B on the basis of the joint surface cs at the dissimilar conductor joint portion, it is possible to solve the problem of damage such as deformation, breakage, and cracking occurring at the dissimilar conductor joint portion.

In the present specification, the present invention has been described with reference to the preferred embodiments thereof, but those skilled in the art can make various modifications and alterations to the present invention without departing from the spirit and scope of the invention as described in the claims to be described below. Therefore, if the implementation of the modification basically includes the constituent elements of the scope of the claims of the present invention, it should be regarded as all falling within the technical scope of the present invention.

Claims

1. A power cable system comprising: a first power cable comprising a first conductor; a second power cable comprising a second conductor; and a cable connection structure connecting the first power cable and the second power cable, characterized in that,

the first power cable comprises a first conductor formed by a plurality of pixel wires,

The second power cable comprises a second conductor which is composed of a plurality of element wires and is made of different materials from the first conductor,

the first conductor has a melting point higher than the second conductor,

the cable connection structure includes a dissimilar conductive joint that joins the first conductor and the second conductor,

the dissimilar conductive joint includes a first conductor volume rate increase region and a second conductor volume rate increase region,

the first conductor volume fraction increasing region is formed by performing a pre-process of the first conductor that increases the volume fraction from the joint surface (cs 1) of the first conductor to a predetermined length, and the second conductor volume fraction increasing region is formed by performing a pre-process of the second conductor that decreases the volume fraction from the joint surface (cs 2) of the second conductor to a predetermined length, followed by resistance welding the first conductor and the second conductor.

2. The power cable system of claim 1, wherein the cable system comprises a plurality of conductors,

the first conductor is prepared by welding a pair of first conductors, cutting the joint portion, and forming the cut surface as a joint surface (cs 1) of the first conductors.

3. The power cable system of claim 2, wherein the cable system further comprises a plurality of conductors,

The first conductor is prepared so that the volume fraction of the first conductor from the joint surface (cs 1) of the first conductor to a predetermined length is 98% or more.

4. The power cable system of claim 1, wherein the cable system comprises a plurality of conductors,

the first conductor is made of copper or copper alloy, and the second conductor is made of aluminum or aluminum alloy.

5. The power cable system of claim 1, wherein the cable system comprises a plurality of conductors,

the preparation of the second conductor forms a melt infiltration path along the length direction of the second conductor from the joint surface (cs 2) of the second conductor before conductor joint with the first conductor.

6. The power cable system of claim 5, wherein the cable system further comprises a plurality of conductors,

the volume fraction of the second conductor from the junction surface (cs 2) of the second conductor to a predetermined length is made to be 90% or less by the pre-processing of the second conductor.

7. The power cable system of claim 5, wherein the cable system further comprises a plurality of conductors,

the melt infiltration path is formed by drilling a plurality of points of the joint surface (cs 2) of the second conductor using a drilling machine.

8. The power cable system of claim 5, wherein the cable system further comprises a plurality of conductors,

The melt infiltration path is formed by cutting and removing a portion of a plurality of element wires constituting the second conductor from a joint surface (cs 2) of the second conductor with a cutting tool.

9. The power cable system of claim 1, wherein the cable system comprises a plurality of conductors,

the volume ratio of the volume ratio increasing region of the second conductor is 98% or more from the joint surface (cs) to at least 3mm in the length direction of the second conductor.

10. The power cable system of claim 1, having dissimilar conductive joints,

the diameter of the first conductor is smaller than the diameter of the second conductor.

11. The power cable system of claim 10 having dissimilar conductive joints,

the dissimilar-conductor joint portion is joined together with an O-ring having an inclined outer peripheral surface so as to terminate a step generated by a diameter difference between the first conductor and the second conductor with an inclined surface.

12. The power cable system of claim 1, wherein the cable system comprises a plurality of conductors,

the dissimilar conductor joint section is configured by joining the first conductor and the second conductor by resistance welding.

13. The power cable system of claim 1, wherein the cable system comprises a plurality of conductors,

The first conductor or the second conductor is a circular compressed conductor.

14. The power cable system of claim 1, wherein the cable system comprises a plurality of conductors,

the first conductor or the second conductor is a rectangular conductor.

15. A power cable system comprising: a first power cable comprising a first conductor; a second power cable comprising a second conductor; and a cable connection structure connecting the first power cable and the second power cable, characterized in that,

the first conductor has a melting point higher than the second conductor,

the dissimilar conductive joint section includes a first conductor volume rate increase region and a second conductor volume rate increase region with respect to a joint surface (cs),

the dissimilar conductor joint portion has a bending strength greater than that of the second conductor.

16. The power cable system of claim 15, wherein the cable system is configured to connect to the power cable system,

17. The power cable system of claim 15, wherein the cable system is configured to connect to the power cable system,

18. The power cable system of claim 15 having dissimilar conductive joints,

19. The power cable system of claim 18, having dissimilar conductive joints,

20. The power cable system of claim 15, wherein the cable system is configured to connect to the power cable system,

21. The power cable system of claim 15, wherein the cable system is configured to connect to the power cable system,

the volume-rate-increasing region of the first conductor is pre-processed to a volume rate increase of a predetermined length prior to welding of the first conductor to the second conductor.

22. The power cable system of claim 21, wherein the cable system further comprises a plurality of conductors,

the first conductor is processed to have a volume fraction of 98% or more from the junction surface (cs 1) of the first conductor to a predetermined length before being joined to the second conductor.

23. The power cable system of claim 21, wherein the cable system further comprises a plurality of conductors,

the first conductor is processed so that the volume ratio from the joint surface (cs 1) of the first conductor to a predetermined length is increased to a predetermined size or more, a pair of first conductors are joined by welding and then the joint portion is cut, and the cut surface is formed as the joint surface (cs 1) of the first conductor.

24. The power cable system of claim 15, wherein the cable system is configured to connect to the power cable system,

the second conductor is processed so that the volume ratio is less than or equal to a predetermined value by forming a melt infiltration path from the joint surface (cs 2) of the second conductor in the longitudinal direction of the second conductor before the first conductor is joined to the second conductor.

25. The power cable system of claim 24, wherein the cable system further comprises a cable system,

is processed to make the volume ratio of the second conductor below 90%.

26. The power cable system of claim 24, wherein the cable system further comprises a cable system,

The melt infiltration path is formed by drilling a plurality of points of the junction surface (cs 2) of the second conductor using a drilling machine.

27. The power cable system of claim 24, wherein the cable system further comprises a cable system,

the melt penetration path is formed by cutting and removing a part of a plurality of element wires constituting the second conductor from a joint surface (cs 2) of the second conductor with a cutting tool.

28. The power cable system of claim 15, wherein the cable system is configured to connect to the power cable system,

the first conductor or the second conductor is a circular compressed conductor.

29. The power cable system of claim 15, wherein the cable system is configured to connect to the power cable system,

the first conductor or the second conductor is a rectangular conductor.

30. A power cable connection method of connecting a first power cable including a first conductor composed of a plurality of circular element wires and a second power cable including a second conductor composed of a plurality of circular element wires of a material different from the first conductor, comprising:

a first conductor pre-processing step of increasing the volume fraction from the joint surface (cs 1) of the first conductor to a predetermined length to a predetermined size or more;

A second conductor pre-processing step of reducing the volume fraction from the joint surface (cs 2) of the second conductor to a predetermined length below a predetermined size; and

and a resistance welding step of forming a dissimilar conductor joint portion by joining the joint surface (cs 1) of the first conductor and the joint surface (cs 2) of the second conductor by resistance welding.

31. The method of claim 30, wherein the power cable has a dissimilar conductor,

the resistance welding step is performed by melting the first conductor and the second conductor and pressurizing the first conductor and the second conductor by energizing a current to the first conductor and the second conductor.

32. The method of claim 30, wherein the power cable has a dissimilar conductor,

in the resistance welding step, in a welding jig for welding the first conductor and the second conductor, an exposed length of the first conductor is smaller than an exposed length of the second conductor.

33. The method of claim 30, wherein the step of connecting the power cable to the cable,

the step of pre-processing the first conductors is performed by a method of joining a pair of first conductors by welding to form a joint, cutting the joint and taking the cut surface as a joint surface (cs 1) of the first conductors so that a volume ratio from the joint surface (cs 1) of the first conductors to a predetermined length becomes 98% or more.

34. The method of claim 30, wherein the power cable has a dissimilar conductor,

the step of pre-processing the second conductor is performed by forming a melt penetration path from the joint surface (cs 2) of the second conductor to a predetermined length in the second conductor length direction before conductor joining with the first conductor such that the volume fraction from the joint surface (cs 2) of the second conductor to the predetermined length is 90% or less.

35. The method of claim 30, wherein the step of connecting the power cable to the cable,

the volume ratio of the volume ratio increase region of the second conductor constituting the dissimilar conductor joint section after the resistance welding step is 98% or more from the joint surface (cs) to at least 3mm in the second conductor longitudinal direction.

36. The method of claim 30, wherein the step of connecting the power cable to the cable,

the welding temperature in the resistance welding is a temperature which is lower than the melting point of the first conductor and 5% -15% higher than the melting point of the second conductor.