阅读说明：本技术 一种三芯500kV交联聚乙烯绝缘光纤复合海底电缆 (Three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable ) 是由 陈果 苏欢欢 杨黎明 蔡剑 伏文如 呼文博 郝银 邓华丽 花炜 于 2021-08-27 设计创作，主要内容包括：本申请提供一种三芯500kV交联聚乙烯绝缘光纤复合海底电缆。本申请提供的三芯500kV交联聚乙烯绝缘光纤复合海底电缆包括缆芯、保护单元、填充单元和光纤单元,缆芯为三个,三个缆芯均位于保护单元内,且三个缆芯在保护单元的周向上均匀间隔分布,以在各所述缆芯之间以及保护单元与缆芯之间形成用于容纳填充单元和光纤单元的间隙；第一填充单元的内部具有供光纤单元嵌设的安装空间,安装空间的轴向与海底电缆的轴向一致,且安装空间的横截面形状为圆形。本申请的三芯500kV交联聚乙烯绝缘光纤复合海底电缆的制造成本小,且光纤单元不易受损。(The application provides a three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable. The three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable comprises three cable cores, a protection unit, a filling unit and optical fiber units, wherein the three cable cores are all positioned in the protection unit and are uniformly distributed at intervals in the circumferential direction of the protection unit so as to form gaps for accommodating the filling unit and the optical fiber units among the cable cores and among the protection unit and the cable cores; the first filling unit is internally provided with an installation space for embedding the optical fiber unit, the axial direction of the installation space is consistent with the axial direction of the submarine cable, and the cross section of the installation space is circular. The three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable is low in manufacturing cost, and an optical fiber unit is not easy to damage.)

1. A three-core 500kV cross-linked polyethylene insulated optical fiber composite submarine cable is characterized by comprising three cable cores, a protection unit, a filling unit and optical fiber units, wherein the three cable cores are all positioned in the protection unit and are uniformly distributed at intervals in the circumferential direction of the protection unit so as to form gaps for accommodating the filling unit and the optical fiber units among the cable cores and between the protection unit and the cable cores;

the gaps comprise first gaps, and the first gaps are formed between two adjacent cable cores and the protection units;

the filling units comprise first filling units, the first filling units and the optical fiber units are located in the first gaps, the first filling units are provided with two side surfaces which are respectively abutted with two adjacent cable cores, and the shape of each side surface is matched with that of the outer peripheral surface of each cable core; the first filling unit has an outer peripheral surface abutting against the inner wall of the protection unit;

the first filling unit is internally provided with an installation space for embedding the optical fiber unit, the axial direction of the installation space is consistent with the axial direction of the submarine cable, and the cross section of the installation space is circular;

the protection unit comprises an armor layer, the armor layer comprises an inner steel wire armor layer and an outer steel wire armor layer which are sequentially distributed from inside to outside along the radial direction of the submarine cable, the strength of the inner steel wire armor layer is greater than that of the outer steel wire armor layer, and the diameter of steel wires in the inner steel wire armor layer is smaller than that of steel wires in the outer steel wire armor layer.

2. The three-core 500kV crosslinked polyethylene-insulated optical fiber composite submarine cable according to claim 1, wherein the first filling unit comprises a first filling part and a second filling part distributed along the circumferential direction of the protection unit, and a first surrounding part is provided on the side of the first filling part facing the second filling part;

and one side of the second filling part facing the first filling part is provided with a second surrounding part, the second surrounding part is opposite to the first surrounding part, and the second surrounding part and the first surrounding part enclose the installation space.

3. The three-core 500kV crosslinked polyethylene-insulated optical fiber composite submarine cable according to claim 2, wherein the side of the first filling part facing the second filling part is further provided with at least two first protrusions, which are located on both sides of the first surrounding part in the radial direction of the submarine cable, the first protrusions protruding toward the second filling part;

at least two second protruding parts are further arranged on one side, facing the first filling part, of the second filling part, are located on two sides of the second surrounding part in the radial direction of the submarine cable, and protrude towards the first filling part;

at least two second convex parts are engaged with at least two first convex parts to lock the first filling part and the second filling part.

4. The three-core 500kV crosslinked polyethylene-insulated optical fiber composite submarine cable according to claim 3, wherein the first filling part has a first end portion facing the core in the radial direction of the submarine cable, and the second filling part has a second end portion facing the core in the radial direction of the submarine cable, and the first end portion is integrally connected to the second end portion, so that the first filling part and the second filling part constitute the first filling unit.

5. The three-core 500kV crosslinked polyethylene-insulated optical fiber composite submarine cable according to any one of claims 1 to 4, wherein the diameter of the installation space is 5 to 10mm larger than the diameter of the optical fiber unit.

6. The three-core 500kV crosslinked polyethylene-insulated optical fiber composite submarine cable according to any one of claims 1 to 4, wherein the number of said optical fiber units is one to three.

7. The three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable according to claim 6, wherein the number of the first filling units and the number of the optical fiber units are three, the first filling units are arranged in one-to-one correspondence with the first gaps, and the optical fiber units are arranged in one-to-one correspondence with the first filling units.

8. The three-core 500kV crosslinked polyethylene-insulated optical fiber composite submarine cable according to any one of claims 1 to 4, wherein said gap further comprises a second gap, and three of said cable cores collectively form said second gap;

the filling unit further comprises a second filling unit, and the second filling unit is located in the second gap.

9. The three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable according to any one of claims 1 to 4, wherein the strength of the inner steel wire armor layer is greater than or equal to 1970MPa, and the strength of the outer steel wire armor layer is greater than or equal to 345 MPa.

10. The three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable according to any one of claims 1 to 4, wherein the steel wires in the inner and outer steel wire armoring layers are round or flat steel wires.

11. The three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable according to claim 8, wherein the first filling unit and the second filling unit are both extruded parts formed by continuous extrusion processing of thermoplastic materials.

12. The three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable according to claim 11, wherein the first and second filling units are both hollow structures; or, the first filling unit is of a solid structure, and the second filling unit is of a hollow structure.

13. The three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable according to claim 12, wherein the second filling unit is provided with a first cavity, and the first cavity is coaxial with the submarine cable.

14. The three-core 500kV crosslinked polyethylene insulated fiber composite submarine cable according to claim 13, wherein the second filler unit is a cylindrical body and the first cavity is a cylindrical cavity.

15. The three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable according to claim 13 or 14, wherein the first and second filling units are both hollow structures;

a plurality of second cavities are formed in the first filling unit and are distributed along the circumferential direction of the submarine cable.

16. The three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable according to claim 15, wherein the openings of the second cavities are all the same shape, and the first cavity and the second cavity are all sealed cavities for filling with seawater.

17. The three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable according to any one of claims 1 to 4, wherein the cable core comprises a water-blocking conductor and a water-blocking binding tape coated outside the water-blocking conductor;

the water-blocking conductor is a compact or split type annealed copper conductor, and the surface of the annealed copper conductor is the exposed surface of the non-plated metal layer; the water-blocking conductor comprises a semi-conductive water-blocking tape formed by longitudinal wrapping and water-blocking yarns wound on the outer side of the semi-conductive water-blocking tape, and the semi-conductive water-blocking tape and the water-blocking yarns cover a stranded gap of the water-blocking conductor;

the water-blocking binding belt is formed by wrapping a water-blocking tape.

18. The three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable according to claim 17, wherein the cable core further comprises a conductor shielding layer, a crosslinked polyethylene insulating layer, an insulating shielding layer, a water blocking tape, a metal sheath and a split-phase sheath layer which are sequentially coated outside the water blocking binding tape;

the conductor shielding layer, the crosslinked polyethylene insulating layer and the insulating shielding layer are extrusion pieces formed in a simultaneous extrusion mode.

19. The three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable according to claim 18, wherein the conductor shield is a wrapping layer formed by extrusion molding of a semiconductive shield material.

20. The three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable according to claim 18, wherein the crosslinked polyethylene insulating layer is a wrapping layer uniformly extruded on the conductor shield layer with a crosslinked polyethylene material.

21. The three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable according to claim 18, wherein the insulation shielding layer is a wrapping layer wrapped on the crosslinked polyethylene insulation layer by a semiconductive shielding material.

22. The three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable according to claim 18, wherein the water-blocking tape is wrapped on the insulating shielding layer by gap lapping of a double-sided semi-conductive water-blocking tape material.

23. The three-core 500kV crosslinked polyethylene-insulated optical fiber composite submarine power according to claim 22Cable, characterized in that the volume resistivity of the water-blocking tape is less than 1 x 10³Ω·cm。

24. The three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable according to claim 18, wherein the metal sheath is a continuous sealing structure and is wrapped on the water-blocking tape by extrusion with an alloy to serve as a radial water-proof layer; wherein the alloy is lead alloy or copper alloy.

25. The three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable according to claim 18, wherein the split-phase sheath layer is made of semi-conductive polyethylene or insulating polyethylene thermoplastic sheath material and is extruded on the metal sheath to serve as a radial waterproof layer and/or a radial protective layer.

26. The three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable according to any one of claims 1 to 4, wherein the protection unit further comprises an inner liner layer and an outer coating layer, the inner liner layer and the outer coating layer are respectively located on two sides of the armor layer in the radial direction of the submarine cable, and the cable core, the filling unit and the optical fiber unit are all located in a space surrounded by the inner liner layer.

27. The three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable according to claim 26, wherein the inner liner is formed by wrapping a polypropylene fiber rope with an outer diameter of 2-4 mm.

28. The three-core 500kV crosslinked polyethylene insulated fiber composite submarine cable according to claim 27, wherein the outer layer is wrapped with a bituminous coating and polypropylene fiber ropes on the outer steel wire armor layer.

Technical Field

The application relates to the technical field of submarine cables, in particular to a three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable.

Background

Submarine cables are wires wrapped with insulating materials and laid under the sea floor and river water for telecommunication transmission. The submarine cables are divided into two types, namely submarine communication cables and submarine power cables, the submarine communication cables are mainly used for communication services, and the submarine power cables are mainly used for transmitting high-power electric energy underwater.

The bearing voltage of the current high-voltage submarine cable is generally 220kV, the cable generally comprises a cable core, an optical fiber unit and a protection unit, the cable core is of a single-core structure, the protection unit is coated outside the cable core, the optical fiber unit is positioned between the protection unit and the cable core or the optical fiber unit is arranged in the protection unit, the protection unit comprises an armor layer, and the armor layer is formed by twisting steel wires with the same strength.

Therefore, the submarine cable has high manufacturing cost, the optical fiber units are easily damaged, and the tensile and compressive properties of the submarine cable are poor.

Disclosure of Invention

The application provides a compound submarine cable of three-core 500kV crosslinked polyethylene insulation optical fiber, and low in manufacturing cost can protect the optical fiber unit, and submarine cable's tensile and compressive property is stronger.

The application provides a three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable which comprises three cable cores, protection units, filling units and optical fiber units, wherein the three cable cores are all positioned in the protection units and are uniformly distributed at intervals in the circumferential direction of the protection units so as to form gaps for accommodating the filling units and the optical fiber units among the cable cores and among the protection units and the cable cores; the gaps comprise first gaps, and first gaps are formed between two adjacent cable cores and the protection units; the filling unit comprises a first filling unit, the first filling unit and the optical fiber unit are both positioned in the first gap, the first filling unit is provided with two side surfaces which are respectively abutted with two adjacent cable cores, and the shape of each side surface is matched with the shape of the outer peripheral surface of each cable core; the first filling unit has an outer peripheral surface abutting against the inner wall of the protection unit; the first filling unit is internally provided with an installation space for embedding the optical fiber unit, the axial direction of the installation space is consistent with the axial direction of the submarine cable, and the cross section of the installation space is circular; the protection unit includes the armor, and the armor includes radially from inside to outside inner steel wire armor and the outer steel wire armor that distributes in proper order along submarine cable, and the intensity of inner steel wire armor is greater than the intensity of outer steel wire armor, and the steel wire diameter in the inner steel wire armor is less than the steel wire diameter in the outer steel wire armor.

The three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable comprises three cable cores, a protection unit, a filling unit and optical fiber units, wherein the three cable cores are all positioned in the protection unit and are uniformly distributed at intervals in the circumferential direction of the protection unit so as to form gaps for accommodating the filling unit and the optical fiber units among the cable cores and among the protection unit and the cable cores; the gaps comprise first gaps, and first gaps are formed between two adjacent cable cores and the protection units; the filling unit comprises a first filling unit, the first filling unit and the optical fiber unit are both positioned in the first gap, the first filling unit is provided with two side surfaces which are respectively abutted with two adjacent cable cores, and the shape of each side surface is matched with the shape of the outer peripheral surface of each cable core; the first filling unit has an outer peripheral surface abutting against the inner wall of the protection unit; the first filling unit is internally provided with an installation space for embedding the optical fiber unit, the axial direction of the installation space is consistent with the axial direction of the submarine cable, and the cross section of the installation space is circular; the protection unit includes the armor, and the armor includes radially from inside to outside inner steel wire armor and the outer steel wire armor that distributes in proper order along submarine cable, and the intensity of inner steel wire armor is greater than the intensity of outer steel wire armor, and the steel wire diameter in the inner steel wire armor is less than the steel wire diameter in the outer steel wire armor. The three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable provided by the application has the advantages that the manufacturing cost is low, the optical fiber unit is not easy to damage, and the tensile property and the compressive property of the submarine cable are strong.

The construction of the present application and other objects and advantages thereof will be more apparent from the following description of the preferred embodiments taken in conjunction with the accompanying drawings.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present application, and for those skilled in the art, other drawings can be obtained according to these drawings without inventive exercise.

Fig. 1 is a schematic structural diagram of a three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable provided in an embodiment of the present application;

FIG. 2 is a schematic structural diagram of a cable core in a three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable according to an embodiment of the present application;

fig. 3a is a diagram of the occupied routing width of a single-core submarine cable in the prior art;

fig. 3b is a routing width diagram occupied by a three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable according to the embodiment of the present application;

fig. 4 is a schematic diagram illustrating a positional relationship between a first filling unit and an optical fiber unit in a three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable according to an embodiment of the present application;

FIG. 5 is a schematic structural diagram of an optical fiber unit in a three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable according to an embodiment of the present application;

FIG. 6a is a state diagram of a steel wire armor in an armor layer of a three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable according to an embodiment of the present application;

fig. 6b is an expanded view of steel wires in an armor layer in a three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable according to an embodiment of the present application;

fig. 7 is a stress-strain curve diagram of an armor layer in a three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable provided by an embodiment of the present application.

Description of reference numerals:

10-three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable; 1-a cable core; 11-a water-blocking conductor; 12-water blocking binding tapes; 13-a conductor shield layer; 14-crosslinked polyethylene insulation layer; 15-insulating shielding layer; 16-a water blocking tape; 17-a metal sleeve; 18-phase separation sheath layer; 2-a protection unit; 21-an inner liner layer; 22-an armor layer; 221-inner steel wire armor layer; 222-outer steel wire armor layer; 23-outer tegument layer; 3-a filler unit; 31-a first filling unit; 311-side face; 312 — a second cavity; 313-an installation space; 314-first filling part; 3141-a first end; 315-second filling part; 3151-a second end; 316-first surround; 317-a second surrounding part; 318-a first projection; 319-second projection; 32-a second filling unit; 321-a first cavity; 4-an optical fiber unit; 41-an optical fiber; 42-a metal layer; 43-a protective layer; 5-clearance; 51-a second gap; 52-first gap; 20-single core submarine cable.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some embodiments of the present application, but not all embodiments.

All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application. The embodiments described below and the features of the embodiments can be combined with each other without conflict.

In the description of the present application, it is to be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," "circumferential," and the like are used in the orientations and positional relationships indicated in the drawings for convenience in describing the present application and for simplicity in description, and are not intended to indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and are therefore not to be considered limiting of the present application.

In this application, unless expressly stated or limited otherwise, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can include, for example, fixed connections, removable connections, or integral parts; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meaning of the above terms in the present application can be understood by those of ordinary skill in the art as appropriate.

It should be noted that, in the description of the present application, the terms "first" and "second" are used merely for convenience in describing different components, and are not to be construed as indicating or implying a sequential relationship, relative importance, or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature.

The ultrahigh-voltage submarine cable generally refers to a submarine cable with a bearing voltage of 500kV, and therefore needs to be laid in three phases, most of the existing submarine cables are high-voltage submarine cables with a bearing voltage of 220kV, most of the existing high-voltage submarine cables comprise cable cores, optical fiber units and protection units, the cable cores are of single-core structures, the protection units are covered outside the cable cores, the optical fiber units are located between the protection units and the cable cores or the optical fiber units are arranged in the protection units, however, the single-core submarine cables are laid in three phases in a busy water channel and occupy a large number of submarine routes with wide widths, and the single-core submarine cables need to be laid for three times, so that the construction cost is; moreover, when the optical fiber unit is positioned between the protection unit and the cable core, the raw material cost of the submarine cable is increased; when the optical fiber unit is arranged in the protection unit, the risk of damage to the optical fiber unit is increased; the protection unit includes the armor, and the armor adopts the steel wire transposition of same intensity to form for the tensile and the compressive property of submarine cable are relatively poor.

Therefore, the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable provided by the application has the advantages that the number of cable cores is changed from one to three, so that the transmission capacity of a submarine cable is increased, and a routing loop is reduced; in addition, in the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable provided by the application, the optical fiber unit is positioned in a gap formed by two adjacent cable cores, and the optical fiber unit is embedded in the first filling unit, so that the manufacturing cost of the submarine cable can be reduced, the optical fiber unit can be prevented from being damaged, and the optical fiber unit can be protected to a certain extent; in addition, armor in this application includes inlayer steel wire armor and outer steel wire armor, and the intensity of inlayer steel wire armor is greater than the intensity of outer steel wire armor, and the steel wire diameter in the inlayer steel wire armor is less than the steel wire diameter in the outer steel wire armor, consequently for the submarine cable's that this application provided tensile and compressive property are stronger.

The present application is described in detail below with reference to the attached drawings and the detailed description.

Fig. 1 is a schematic structural diagram of a three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable provided in the embodiment of the present application. Fig. 2 is a schematic structural diagram of a cable core in a three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable provided in the embodiment of the present application.

The embodiment provides a three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable 10, which comprises three cable cores 1, three protection units 2, a filling unit 3 and an optical fiber unit 4, wherein the three cable cores 1 are all positioned in the protection units 2, and the three cable cores 1 are uniformly distributed at intervals in the circumferential direction of the protection units 2, so that gaps 5 for accommodating the filling unit 3 and the optical fiber unit 4 are formed among the cable cores 1 and among the protection units 2 and the cable cores 1; the cable core 1 comprises a water-blocking conductor 11 and a water-blocking binding tape 12 coated outside the water-blocking conductor 11; in the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable 10 provided in this embodiment, by providing three cable cores 1, the occupied width of the submarine route is reduced, and in addition, the optical fiber unit 4 in this embodiment is disposed in the gap 5, compared with a layer structure in which a single optical fiber unit 4 is disposed, the manufacturing cost of the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable 10 in this embodiment is smaller; compared with the submarine cable structure in which the optical fiber unit 4 is arranged in the protection unit 2, the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable 10 of the embodiment can protect the optical fiber unit 4, and avoids damage to the optical fiber unit 4 due to overlarge stress.

It should be noted that the water-blocking conductor 11 is an annealed copper conductor that is tightly pressed into a round shape or a split type metal-free layer, the water-blocking conductor 11 includes a semi-conductive water-blocking tape that is longitudinally wrapped and water-blocking yarns that are wound outside the semi-conductive water-blocking tape, and the semi-conductive water-blocking tape and the water-blocking yarns cover a twisted gap of the water-blocking conductor 11; the water-blocking binding belt 12 is formed by wrapping a water-blocking tape with high water-blocking performance and high strength.

Further, the concrete method for designing the structure of the water-blocking conductor 11 is as follows, the direct current resistance RB (Ω/km) of the water-blocking conductor 11 is determined according to the product standard requirements, the coefficients K1, K2, K3 are introduced, and the volume resistivity ρ 20 (Ω · mm/m) of the material is selected²）。

Firstly, the section of the water blocking conductor 11 is calculated, and the calculation of the section of the water blocking conductor 11 is based on the following formula:

（1）

（2）

in the above formulas (1) and (2), K1 is the diameter of the monofilament, the type of metal and the lead-in coefficient of whether tin plating is performed or not; k2 is the introduction coefficient of the monofilament diameter and the twisting mode; k3 is the introduction coefficient of whether the insulated wire core is cabled or not; AJZ denotes the cross-sectional area after compaction; RB is the direct current resistance at 20 ℃; ρ 20 is the volume resistivity of the material.

Then, the contour diameter of the water blocking conductor 11 is calculated, specifically, the contour diameter D is calculated by taking the filling factor η according to the production requirement.

（3）

（4）

In the above formulas (3) and (4), D is the profile diameter of the water-blocking conductor 11; AJZ denotes the cross-sectional area after compaction; η is the fill factor.

Finally, the diameter of the single wire is calculated according to the following formula:

（5）

in the above formula (5), d is the monofilament outer diameter; AJZ denotes the cross-sectional area after compaction; μ is the coefficient of compression elongation; n number of stranding machine disks.

And the standard cross-sectional area is 2500mm²Taking the water-blocking conductor 11 as an example, determining the direct-current resistance RB of the conductor to be 0.0072 omega/km according to design requirements; the cross-sectional area AJZ of the compacted product is determined to be 2515mm²(ii) a Determining the filling coefficient eta to be 0.87; determining the compression elongation coefficient mu to be 1.1; according to the above formula(1) To (5), it can be calculated that when the number of stranding discs n =127, the single wire outer diameter d =5.27 mm; when the number of the stranding machine disks n =169, the outer diameter d =4.57mm of the single wire and the stranding cross section area is 5000mm²(ii) a Therefore, the 169 disc stranding machine is 15% smaller than the 127 disc stranding machine in single wire diameter before stranding, so that the production problem of large-diameter single wires can be solved.

To further illustrate that the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable 10 provided by the embodiment of the present application occupies fewer routes, the route occupied by the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable 10 provided by the embodiment of the present application is compared with the route occupied by the existing single-core extra-high voltage submarine cable.

Fig. 3a is a diagram of the occupied routing width of a single-core submarine cable in the prior art. Fig. 3b is a routing width diagram occupied by the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable according to the embodiment of the present application.

As can be seen from fig. 3a and 3b, the existing single-core submarine cable 20 needs to be laid three times to satisfy high-voltage operation, and therefore, the occupied route is 4L; the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable 10 provided in the embodiment of the present application includes three cable cores 1, and therefore only one cable core needs to be laid, and therefore, the occupied route is 2L, which indicates that the occupied route width of the existing core submarine cable 20 is 2 times of the occupied route width of the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable 10 provided in the embodiment, and therefore, the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable 10 provided in the embodiment saves resources.

As shown in fig. 2, in this embodiment, the cable core 1 further includes a conductor shielding layer 13, a crosslinked polyethylene insulating layer 14, an insulating shielding layer 15, a water blocking tape 16, a metal sheath 17 and a phase-separated sheath layer 18 which are sequentially coated outside the water blocking binding tape 12.

The conductor shield layer 13, the crosslinked polyethylene insulation layer 14 and the insulation shield layer 15 are molded by simultaneous extrusion, which can reduce the manufacturing process of the three-core 500kV crosslinked polyethylene insulation optical fiber composite submarine cable 10 of the present embodiment; wherein, the conductor shielding layer 13 is formed by extruding and coating ultra-smooth semi-conductive shielding material; the crosslinked polyethylene insulating layer 14 is uniformly extruded on the conductor shielding layer 13 by adopting an ultra-clean crosslinked polyethylene material; the insulation shielding layer 15 is directly extruded on the crosslinked polyethylene insulation layer 14 by adopting a super-smooth semi-conductive shielding material.

Further, when the crosslinked polyethylene insulating layer 14 is designed, the thickness of the crosslinked polyethylene insulating layer 14 is designed according to power frequency voltage and lightning impulse test data of a small sample manufactured by using specific production process parameters of the insulating material, and the thickness of the crosslinked polyethylene insulating layer 14 is designed according to actual test parameters.

Firstly, testing the breakdown field intensity of the insulating material by adopting a step-by-step boosting power frequency voltage breakdown mode, and setting the initial voltage to be 3.5U₀Each stage is 2U₀The test voltage is increased until breakdown occurs, the breakdown voltage is recorded, and the test duration of each level of voltage is 10 min.

In a specific experimental process, three model cable samples are adopted, table 1 is a power frequency breakdown electric field strength meter of an insulating layer core in the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable according to the embodiment, and the three model cable samples are named as 1#, 2# and 3# respectively in the following.

Table 1 power frequency breakdown electric field strength meter for core of insulation layer in three-core 500kV crosslinked polyethylene insulation optical fiber composite submarine cable according to this embodiment

Model cable sample	Maximum breakdown field strength kV/mm	Average breakdown field strength kV/mm
			1#	73.0	55.6
2#	78.7	60.0
			3#	78.7	60.0

As can be seen from the observation of Table 1, the power frequency average breakdown field strength of the model cable sample is greater than 55kV/mm, and the maximum breakdown field strength is greater than 73kV/mm, so that the power frequency voltage breakdown field strength of the crosslinked polyethylene insulating layer 14 meets the design requirements.

And then, performing a lightning impulse breakdown voltage test on the three model cable samples by adopting a step-by-step boosting lightning impulse breakdown mode, setting the initial voltage to be 125kV, increasing the impulse test voltage step by step according to the amplitude of 100kV, and performing 10 times of positive impulse tests and 10 times of negative impulse tests in each step until the three model cable samples are broken down.

Table 2 shows the intensity of lightning impulse breakdown electric field of the core of the insulation layer in the three-core 500kV crosslinked polyethylene insulation optical fiber composite submarine cable according to this embodiment, and the following three model cable samples are named as # 1, # 2 and # 3, respectively.

As can be seen from the observation of the table 2, the average breakdown field strength of the lightning impulse of the model cable sample is greater than 130kV/mm, and the maximum breakdown field strength is greater than 170kV/mm, so that the lightning impulse performance of the crosslinked polyethylene insulating layer 14 meets the design requirements.

When the thickness of the crosslinked polyethylene insulating layer 14 is checked and determined, the thickness of the crosslinked polyethylene insulating layer 14 corresponding to the power frequency voltage breakdown needs to be compared with the thickness of the crosslinked polyethylene insulating layer 14 corresponding to the lightning impulse, and the larger thickness value of the two is the thickness value required in the actual design process.

Table 2 table of strength of lightning impulse breakdown electric field of core of insulation layer in three-core 500kV crosslinked polyethylene insulation optical fiber composite submarine cable according to this embodiment

Model cable sample	Maximum breakdown field strength kV/mm	Average breakdown field strength kV/mm
			1#	173.0	131.8
2#	173.0	131.8
			3#	196.8	150.5

Specifically, the thickness of the crosslinked polyethylene insulating layer 14 is checked and determined according to the average electric field strength at the power frequency voltage by using the following formula.

（6）

In the above formula (6), d_acThe thickness of the crosslinked polyethylene insulating layer 14 corresponding to the power frequency impulse voltage is in mm; u shape_mThe highest line voltage of the system; k is a radical of₁The temperature coefficient of the breakdown strength under the power frequency voltage; k is a radical of₂An aging system of breakdown strength under power frequency voltage; k is a radical of₃The safety factor of the breakdown strength under the power frequency voltage; e_LacFor power frequency impactMinimum breakdown strength determined by the breakdown voltage;

illustratively, take U_mIs 525kV, k₁Is 1.1, k₂Is 2.89, k₃Is 1.1, E_LacIs 40kV/mm, d can be calculated according to the formula (6)_ac=27.8mm。

Further, the thickness of the crosslinked polyethylene insulation layer 14 is checked and determined according to the minimum breakdown strength at the lightning breakdown voltage using the following formula.

（7）

In the above formula (7), d_impThe thickness of the cross-linked polyethylene insulation layer 14 corresponding to the lightning impulse voltage of the system is in mm; u shape_LmThe lightning impulse withstand voltage level of the system is set; k is a radical of₁Is the temperature coefficient of the breakdown strength under the lightning impulse voltage; k is a radical of₂Is the aging coefficient of the breakdown strength under the lightning impulse voltage; k is a radical of₃The' is the safety coefficient of the breakdown strength under the lightning impulse voltage; e_LimpA minimum breakdown strength determined for the breakdown voltage of the lightning impulse.

Illustratively, take U_LmIs 1550kV, k₁Is 1.25, k₂Is 1.1, k₃Is 1.1, E_LimpAt 60kV/mm, d is calculated according to the formula (7)_imp=29.3mm, at this time, since 29.3 is larger than 27.8, the thickness of the crosslinked polyethylene insulation layer 14 should be 29.3mm in the present example.

Further, the water-blocking tape 16 is wrapped on the insulating shielding layer 15 by a double-sided semi-conductive water-blocking tape material in a gap lapping manner, and the volume resistivity is less than 1 × 10³Omega cm, and the water blocking tape 16 can play a role in buffering and longitudinally blocking water, so as to prevent the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable 10 of the present embodiment from breaking or being damaged by water immersion, and thus, the service life of the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable 10 of the present embodiment can be prolonged; the metal sleeve 17 adopts a continuous sealing structure and adopts an alloy vertical extrusion coating resistor with excellent processing performanceThe water belt 16 can be used as a radial waterproof layer; the split-phase protection layer 18 is directly extruded on the metal sleeve 17 by using semi-conductive polyethylene or insulating polyethylene thermoplastic sheath material, and further serves as a radial waterproof layer and a protection layer.

In some other embodiments, the metal sheath 17 may also be made of E-alloy lead or lead-tellurium-copper alloy, which may improve corrosion resistance, wear resistance and strength.

In order to provide the filling unit 3 with a better damping effect, in this embodiment, the filling unit 3 is provided with a cavity, and the cavity extends in the same direction as the axial direction of the submarine cable. Thus, when the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable 10 is impacted, the deformation of the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable 10 can be increased due to the arrangement of the concave cavity, and the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable is prevented from being broken.

The filling unit 3 in the present embodiment will be described in detail below.

Fig. 4 is a schematic diagram illustrating a positional relationship between a first filling unit and an optical fiber unit in a three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable according to an embodiment of the present application.

As shown in fig. 1 and 4, in a specific embodiment of this embodiment, the gap 5 includes a first gap 51 and a second gap 52, the first gap 51 is formed between two adjacent cable cores 1 and the protection unit 2, and the second gap 52 is formed by three cable cores 1; the filling unit 3 comprises a first filling unit 31 and a second filling unit 32, the first filling unit 31 and the optical fiber unit 4 are positioned in the first gap 51, and the second filling unit 32 is positioned in the second gap 52; the first filling unit 31 has two side surfaces 311 abutting against two adjacent cable cores 1, respectively, and the shape of the side surfaces 311 matches the shape of the outer peripheral surface of the cable core 1; the first filling unit 31 has an outer peripheral surface abutting against the inner wall of the protection unit 2; the second filling unit 32 is provided with a first concave cavity 321, the first concave cavity 321 is coaxially arranged with the submarine cable, specifically, the second filling unit 32 is a cylindrical body, and the first concave cavity 321 is also a cylindrical cavity; the first filling unit 31 is provided with a plurality of second cavities 312, the plurality of second cavities 312 are arranged along the circumferential direction of the submarine cable, in the specific implementation manner of the embodiment, the plurality of second cavities 312 have the same opening shape, the first filling unit 31 is internally provided with an installation space 313 for the optical fiber unit 4 to be embedded, the axial direction of the installation space 313 is consistent with the axial direction of the submarine cable, and the cross section of the installation space 313 is circular. In this embodiment, the first filling unit 31 and the second filling unit 32 both adopt a hollow design, and after the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable of this embodiment is laid, seawater is filled in the first cavity 321 and the second cavity 312, so that the filling thermal resistance of the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable can be reduced, and the current-carrying capacity of the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable is increased; in addition, in this embodiment, the optical fiber unit 4 is embedded in the installation space 313, which can effectively protect the optical fiber unit 4, and the impact resistance of the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable 10 provided in this embodiment can be improved by 200%.

In order to form the installation space 313, in a specific embodiment of the present embodiment, the first filling unit 31 includes a first filling portion 314 and a second filling portion 315 distributed along the circumferential direction of the protection unit 2, the first filling portion 314 and the second filling portion 315 are both provided with a second cavity 312, and a first surrounding portion 316 is provided on a side of the first filling portion 314 facing the second filling portion 315; a second surrounding portion 317 is disposed on a side of the second filling portion 315 facing the first filling portion 314, the second surrounding portion 317 is disposed opposite to the first surrounding portion 316, and the second surrounding portion 317 and the first surrounding portion 316 surround the installation space 313.

To further protect the optical fiber unit 4, in some embodiments, a side of the first filling part 314 facing the second filling part 315 is further provided with at least two first protrusions 318, the at least two first protrusions 318 are located on two sides of the first surrounding part 316 in a radial direction of the submarine cable, and the first protrusions 318 protrude toward the second filling part 315; the side of the second filling part 315 facing the first filling part 314 is further provided with at least two second protrusions 319, the at least two second protrusions 319 are located on two sides of the second surrounding part 317 in the radial direction of the submarine cable, and the second protrusions 319 protrude toward the first filling part 314; the at least two second protrusions 319 are engaged with the at least two first protrusions 318 to lock the first filling part 314 and the second filling part 315. In this way, by providing the first protrusion 318 and the second protrusion 319, the locking of the first filling part 314 and the second filling part 315 can be realized, so that the structure of the first filling unit 31 is more stable, and the optical fiber unit 4 is further protected; further, the flexibility of the first filling unit 31 is increased, and the first filling unit 31 can transmit more force to the cable core 1 after being stressed, and transmit the force to the optical fiber unit 4 as little as possible, so that the optical fiber unit 4 is protected in a buffering way.

In order to achieve a fixed connection of the first filler part 314 and the second filler part 315, in some embodiments, the first filler part 314 has a first end 3141 facing the cable core 1 in a radial direction of the submarine cable, the second filler part 315 has a second end 3151 facing the cable core 1 in the radial direction of the submarine cable, and the first end 3141 and the second end 3151 are integrally connected such that the first filler part 314 and the second filler part 315 constitute a first filler unit 31.

In a specific embodiment of this embodiment, the diameter of the installation space 313 is 5 to 10mm larger than the diameter of the optical fiber unit.

It should be noted that, when the transmission power is not high, in order to make the processing of the first filling unit 31 simpler, the second cavity 312 may not be provided on the first filling unit 31, and the shape of the first filling unit 31 will not be further described herein.

Further, the first filling unit 31 and the second filling unit 32 are formed by continuously extruding high-strength thermoplastic materials.

In a specific design process, the material of the filling unit 3 can be controlled according to the transmission capacity, the thermal resistance coefficient of the filling unit 3 is designed, the thermal resistance of the filling unit 3 is reduced, and the thermal resistance coefficient of the filling unit 3 can be designed by adopting the following two schemes.

The first scheme is as follows: one part of the filling unit 3 is made of normal polyethylene material, the other part is made of low-heat-resistance material, the ratio of the two parts is different, and the comprehensive thermal resistance coefficient of the filling unit 3 can be calculated by the following formula:

（8）

in the above formula (8), ρ₁Is the thermal resistivity, S, of the polyethylene material₁The cross-sectional area, rho, of the corresponding part of the filling unit 3 is made of polyethylene material₂Is the thermal resistivity, S, of the polyethylene material₂The cross-sectional area of the corresponding part of the filling unit 3 is made of polyethylene material.

Illustratively, p may be taken₁Is 3.5 ℃ cm/W, S₁Is 360mm²，ρ₂0.5 ℃ cm/W, S₂Is 640mm²Calculating rho according to the formula_{Synthesis of}It was found that the thermal resistivity of the filling unit 3 using a part of the low thermal resistance material was smaller than that of the filling unit 3 using only the polyethylene material, since the thermal resistivity was 1.58. degreeCcm/W.

Scheme II: the method is characterized in that a flowable high-heat-capacity low-heat-resistance liquid medium is arranged in the cavity to reduce the heat resistance coefficient, a high-pressure pump is adopted to circularly take out heat, the temperature of the surface of the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable 10 is reduced, the current-carrying capacity of the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable 10 is increased, and the specific design is carried out according to the following formula:

（9）

（10）

（11）

in the above formulae (9), (10) and (11), I is the rated current (A) of the cable and DeltaθThe allowable working temperature (DEG C) for the cable;θ _po is the temperature (deg.C) at the coolant medium inlet;θ _a ambient temperature (deg.C);lis the length (cm) of the cooling section of the cable;W _d dielectric loss per phase (W/cm) per cm of cable;Rthe alternating current resistance (omega/cm) of each phase conductor of each centimeter of cable at the working temperature;λ ₁the loss factor of the metal sleeve 17;λ ₂is the armor 22 loss factor;Q ₀the flow rate (g/s) of the cooling medium; c is the heat capacity coefficient of the cooling medium [ J/(g. DEG C)]；T ₀Thermal resistance around the coolant medium (C.cm/W);T ₁insulation thermal resistance (DEG C cm/W);T ₂the liner thermal resistance (DEG C cm/W);T ₃the thermal resistance of the protective layer (DEG C cm/W);T ₄the external thermal resistance (. degree.C. cm/W) was obtained.

In some alternative embodiments, the number of the optical fiber units 4 is one to three; in a specific embodiment of this embodiment, there are three first filling units 31 and three optical fiber units 4, the first filling units 31 correspond to the first gaps 51 one by one, and the optical fiber units 4 correspond to the first filling units 31 one by one.

Fig. 5 is a schematic structural diagram of an optical fiber unit in a three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable provided by an embodiment of the present application.

As shown in fig. 5, in the present embodiment, the optical fiber unit 4 includes a plurality of optical fibers 41, and a metal layer 42 and a protective layer 43 sequentially covering the outer sides of the optical fibers 41, and in order to improve the water blocking effect of the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable 10 of the present embodiment, water blocking ointments are filled between the optical fibers 41 and the metal layer 42.

The number of the optical fibers 41 is 1 to 192, the optical fibers 41 are all-color-spectrum optical fibers special for submarine cables with high screening stress, the metal layer 42 is formed by twisting a plurality of stainless steel tubes, the stainless steel tubes are processed by a trimming protection welding process and an online excess length control process, the protective layer 43 is a plastic protective layer, and the plastic protective layer is formed by extruding and wrapping a high-strength anti-corrosion thermoplastic material.

As shown in fig. 1, in this embodiment, the protection unit 2 includes an inner liner 21, an armor layer 22 and an outer layer 23 sequentially coated from inside to outside, the cable core 1, the filling unit 3 and the optical fiber unit 4 are all located in a space surrounded by the inner liner 21, wherein the inner liner 21 is formed by wrapping a high strength polypropylene (PP) fiber rope with an outer diameter of 2-4 mm, in order to improve the processability of the armor layer 22, the armor layer 22 includes an inner steel wire armor layer 221 and an outer steel wire armor layer 222 sequentially distributed from inside to outside along the radial direction of the submarine cable, the strength of the inner steel wire armor layer 221 is greater than that of the outer steel wire armor layer 222, and the diameter of a steel wire in the inner steel wire armor layer 221 is smaller than that of the outer steel wire armor layer 222, in a specific embodiment of this embodiment, the strength of the inner steel wire armor layer 221 is greater than or equal to 1970MPa, the strength of the outer steel wire armor layer 222 is greater than or equal to 345MPa, steel wires in the inner steel wire armor layer 221 and the outer steel wire armor layer 222 are round steel wires or flat steel wires, the cross section of the steel wires under the same tension load is reduced by 82.5%, the using amount of the armor layer 22 can be greatly reduced, the weight of the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable 10 is reduced, and the cost is reduced; the outer layer 23 is coated with asphalt and directly wrapped on the armor layer 22 by a PP fiber rope, wherein the asphalt is special asphalt with high melting point, high adhesion and brittle fracture resistance, and the PP fiber rope is made of high-strength materials with wear resistance, corrosion resistance and the like.

When the armor layer 22 is designed, the inner steel wires mainly bear the tensile working load of the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable 10, and the outer steel wires mainly bear the compression-resistant working load.

Specifically, the armor 22 needs to be designed in two ways, namely, the deformation calculation of the steel wire per unit length on the one hand, and the tension calculation of the armor 22 on the other hand.

Fig. 6a is a state diagram of a steel wire armor in an armor layer of a three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable according to an embodiment of the present application. Fig. 6b is an expanded view of steel wires in an armor layer in a three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable according to an embodiment of the present application.

As shown in FIGS. 6a and 6b, when untwisted, one wire-armored pitch line is deformed intoA is a twist angle, and the amount of deformation per unit length of the armor wire is

（12）

In the above formula (12), L is the core length on the cabling pitch, if L is usedAnd replacing, then:

（13）

if h in the above formula (13) is replaced with mD, where m is the pitch to diameter ratio, then:

（14）

in the above formula (14), if m is replaced with π tga:

（15）

it was calculated that the amount of wire deformation per unit length was the greatest when the twist angle a =45 °.

Further, when the wires are not untwisted, a sheathing pitch wire deformation angle is 2 πAnd, and:

（16）

（17）

（18）

in the above formulas (16), (17) and (18), h is the armor pitch, and m is the pitch-diameter ratio.

For example, for 10 of the embodiment, the armor pitch diameter ratio m1 of the inner layer steel wire is 12 to 18, the torsion angle is 304.8 to 339.9 degrees, and in order to ensure that no torsion stress exists in the steel wire, the steel wire should be reversely rotated by 304.8 to 339.9 degrees within one armor pitch; the armor joint diameter ratio m2 of the outer layer steel wire is 5-9, the torsion angle is 348.3-355.6 degrees, and in order to ensure that no torsion stress exists in the steel wire, the steel wire is reversely rotated by 348.3-355.6 degrees within one armor pitch.

Fig. 7 is a stress-strain curve diagram of an armor layer in a three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable provided by an embodiment of the present application. The first curve is a thin solid line and corresponds to a curve that the steel wire armor grade is G34, the diameter of the cable core 1 is 6.0mm, and the stress value of the armor layer 22 in the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable 10 changes along with strain; the second curve is a broken line with higher density, and corresponds to a curve that the armor layer 22 in the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable 10 with the steel wire armor grade of G34 and the diameter of the cable core 1 of 6.0mm changes along with the strain; the third curve is a thick solid line, and corresponds to a curve that the stress value of the armor layer 22 in the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable 10 with the steel wire armor grade of G85 and the diameter of the cable core 1 of 5.0mm changes along with strain; the fourth curve is a dotted line with lower concentration, and corresponds to a curve that the steel wire armor grade is G85, and the diameter of the cable core 1 is 5.0mm, and the stress value of the armor layer 22 in the three-core 500kV cross-linked polyethylene insulated optical fiber composite submarine cable 10 changes along with strain.

As shown in fig. 7, specifically, the strength of the steel wire at 0.5% strain is extracted, for example, the stress value at 0.5% strain is 10000N, and the working tension is calculated according to the weight of the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable 10 at the designed water depth, for example, when the wave height is less than 2m and the water depth is less than 500m, the maximum tension of the tension bending test of the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable 10 of the embodiment is calculated as follows:

（19）

（20）

in the above formulae (19) and (20), T₁Is a loading test tensile force; w_{Water (W)}The underwater weight of the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable 10 with the length of 1 m; d is the maximum water depth; h is the maximum allowable residual subsea tension.

Assuming that the working tension of the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable 10 is completely borne by the armored steel wires, the maximum working tension allowed by the armored steel wires is calculated according to the following formula:

（21）

in the above formula (21), n is the number of the sheathed wires; σ is the stress when a single armor wire is 0.5% strained (e.g., Φ6.0mm, G34 grade wire armor, σ = 10000N); k is a safety factor.

In addition to designing the structures of the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable according to the present embodiment, the equipment for manufacturing the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable according to the present embodiment needs to be selected.

Specifically, the capacity and the bearing weight of a single cabled rotating disc in the cabling device need to be calculated, further, the outer diameter of the single rotating disc of the cabling device is D, the inner diameter is D, the height is H, the diameter of the cable core 1 is phi, and the weight of the insulated wire core in unit length is X.

Further, the number of layers of the flat cable is as follows:

p=0.95×H÷Ф （22）

in the above formula (22), 0.95 is a factor considering the degree of closeness;

the number of turns of the single-layer flat cable is as follows:

n=(D-d)÷Ф （23）

in the above formula (23), n is an integer;

the length of the wire installation is as follows:

L=π×（D+d）÷2×p×n （24）

the total weight is as follows:

T=X×π×（D+d）÷2×p×n （25）

taking the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable 10 of the present embodiment as an example, the diameter of the single wire of the submarine cable is 155 mm; the weight per unit length is 58.9T/km; the design of the vertical cabling steel wire armouring equipment is 3 x [ phi 16000mm (diameter) x phi 3000mm (cylinder diameter) x 4600mm (height) ], the single rotary disc is designed to carry 2000 tons, the joint-free production can reach 32km, and the total bearing weight is 1890 tons; the net bearing capacity of the rotary support of the whole vertical cabling equipment is 6000 tons.

It should be noted that the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable 10 provided by the embodiment is suitable for important equipment such as large-capacity island interconnection, large-scale offshore wind farm, interconnection transmission of offshore booster station and land station, and has the advantages of low construction cost, mature technology and the like when compared with the transmission distance of 20-50km for normal high voltage direct current transmission, and the transmission capacity can be increased compared with a 220kV submarine cable transmission system; the three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable 10 provided by the embodiment can be used for connecting two large-scale power grid loops, can be directly applied to the existing 500kV ring network interconnection, is mature in networking technology and low in difficulty, and can enhance the stability of a power grid.

The three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable provided by this embodiment comprises three cable cores, a protection unit, a filling unit and an optical fiber unit, wherein the three cable cores are all located in the protection unit, and the three cable cores are uniformly distributed at intervals in the circumferential direction of the protection unit, so as to form gaps for accommodating the filling unit and the optical fiber unit between each cable core and between the protection unit and the cable core; the gaps comprise first gaps, and first gaps are formed between two adjacent cable cores and the protection units; the filling unit comprises a first filling unit, the first filling unit and the optical fiber unit are both positioned in the first gap, the first filling unit is provided with two side surfaces which are respectively abutted with two adjacent cable cores, and the shape of each side surface is matched with the shape of the outer peripheral surface of each cable core; the first filling unit has an outer peripheral surface abutting against the inner wall of the protection unit; the first filling unit is internally provided with an installation space for embedding the optical fiber unit, the axial direction of the installation space is consistent with the axial direction of the submarine cable, and the cross section of the installation space is circular; the protection unit includes the armor, and the armor includes radially from inside to outside inner steel wire armor and the outer steel wire armor that distributes in proper order along submarine cable, and the intensity of inner steel wire armor is greater than the intensity of outer steel wire armor, and the steel wire diameter in the inner steel wire armor is less than the steel wire diameter in the outer steel wire armor. The three-core 500kV crosslinked polyethylene insulated optical fiber composite submarine cable provided by the application has the advantages that the manufacturing cost is low, the optical fiber unit is not easy to damage, and the tensile property and the compressive property of the submarine cable are strong.

Finally, it should be noted that: the above embodiments are only used for illustrating the technical solutions of the present application, and not for limiting the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present application.