Medium-voltage cable for supplying power to underwater direct-current equipment and underwater transmission system

Abstract

The utility model relates to a medium-voltage cable for supplying power to underwater direct-current equipment and an underwater transmission system, and the cable comprises a conductor which is arranged at the center of the cable; the insulating layer is coated on the outer surface of the conductor; the at least two metal shielding layers are coated on the outer surface of the insulating layer, and the shielding layers are adjacently coated; the wrapping tape is wrapped outside the metal shielding layer; and the double-layer sheath is wrapped outside the wrapping tape. The single-core cable is simple in structure, green and environment-friendly. No inner and outer shielding layer structure exists, the outer diameter and the bending radius of the cable are reduced, the weight is light, and underwater sleeve laying is facilitated. And the two adjacent metal shielding layers are adopted, so that an anti-surge effect can be effectively achieved. And the flame-retardant nylon outer sheath is adopted, so that the effects of radial water resistance, flame retardance and rat and ant prevention can be effectively achieved.

Description

Technical Field

[0001] The present application relates to the field of cable technology, and in particular to a medium-voltage cable for powering underwater DC equipment and an underwater transmission system. Background Art

[0002] With the continuous development of underwater communication technology, more and more underwater DC equipment has been used in deep water. DC cables for powering underwater DC equipment have come into being. Cables used to power underwater DC equipment usually need to be used in casings. It is difficult to lay underwater casings, so the outer diameter should not be too large. The use of cable underwater casings needs to ensure that they are moisture-proof, flame-retardant, and rat-proof. In addition, underwater power supply equipment usually has the characteristics of high voltage and low current, so it needs to have surge protection function.

[0003] Compared with AC cables, DC cables have the advantages of large transmission capacity and low loss, and their DC resistance is 2-3 times higher than that of AC. Therefore, cables with the same insulation thickness have greater advantages in DC transmission and have a larger DC transmission capacity. In related medium-voltage DC cable technology, the cable structure from inside to outside is mostly conductor, conductive shield, insulation layer, insulation shield, metal shield, filling layer, armor layer and outer sheath. This type of medium-voltage DC cable is similar to the structure of traditional AC cables, with thick insulation core, large cable outer diameter, high cost, and is not suitable for use in casing when powering underwater constant current equipment. Summary of the invention

[0004] Based on this, it is necessary to provide a medium-voltage cable and underwater transmission system for powering underwater DC equipment with a simple structure and environmental protection in order to solve the above technical problems.

[0005] A medium voltage cable for powering underwater DC equipment, the cable comprising:

[0006] A conductor, the conductor has a circular cross section and is arranged at the center of the cable;

[0007] An insulating layer, covering the outer surface of the conductor;

[0008] A double-layer metal shielding layer is coated on the outer surface of the insulating layer, and each layer of the shielding layer is adjacently coated.

[0009] The cable has a simple structure and is green and environmentally friendly. It has no inner and outer shielding layer structure, which reduces the outer diameter of the cable and the bending radius, and can reduce the outer diameter of the cable by about 8-20%. It is lightweight and convenient for underwater casing laying. The adjacent double-layer metal shielding layer is used to effectively prevent surges.

[0010] In one embodiment, the conductor is made of copper rod, aluminum rod or aluminum alloy rod. The conductor monofilament made of the above materials is easy to stretch, so the cable is easier to bend.

[0011] In one embodiment, the insulating layer is made of environmentally friendly polypropylene. The insulating layer is extruded from polypropylene insulation material, which is green, environmentally friendly and recyclable; polypropylene insulation material has a higher temperature resistance level, thinner insulation thickness and excellent electrical performance.

[0012] Polypropylene insulation does not require the use of cross-linking technology to enhance the insulation's temperature resistance level, and can easily reach the conductor's long-term operating temperature of 90°C; it does not require high-temperature vulcanization, and will not produce cross-linked byproducts. It is a green and environmentally friendly production process and is suitable for underwater work; thermoplastic materials can be recycled, avoiding the insulation treatment problem of cross-linked polyethylene cables after their service life expires, reducing environmental pressure and being more green and environmentally friendly. Compared with traditional cross-linked polyethylene insulation cable materials, polypropylene insulation materials have a higher temperature resistance level, up to 105°C, better electrical properties, and a thinner insulation layer.

[0013] In one embodiment, the conductor is a stranded conductor, which is a compact round stranded conductor or a profile stranded conductor. The stranded conductor has a compact structure, a smooth surface without burrs, and a high roundness of the core.

[0014] In one of the embodiments, the shielding layer is made of soft metal tape, and the soft metal tape is stacked and wrapped with an overlap rate of 10-20%.

[0015] In one of the embodiments, the cable further includes a tape layer, and the tape layer is coated on the outer surface of the shielding layer.

[0016] In one embodiment, the cable further includes an inner sheath layer, and the inner sheath layer is coated on the outer surface of the shielding layer.

[0017] In one embodiment, the inner sheath layer is made of high-density polyethylene, which can effectively prevent moisture.

[0018] In one embodiment, the cable further includes an outer sheath layer, which is coated on the outer surface of the inner sheath layer. The material of the outer sheath layer is flame-retardant nylon, which can effectively play the role of radial water blocking, rat and ant prevention, and flame retardancy.

[0019] An underwater transmission system is provided, which is connected to a DC device arranged underwater. The underwater transmission system comprises the above-mentioned medium-voltage cable for powering the underwater DC device. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG1 is a schematic cross-sectional view of a medium voltage cable for powering underwater DC equipment of the present application;

[0021] Figure 2 It is a schematic cross-sectional view of a cable with a T-shaped conductor line in one embodiment of the present application. DETAILED DESCRIPTION

[0022] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present application, so the present application is not limited by the specific embodiments disclosed below.

[0023] In the description of the present application, it should be understood that if the terms "center", "longitudinal", "lateral", "length", "width" and "thickness" appear, the orientation or position relationship indicated by these terms is based on the orientation or position relationship shown in the drawings. It is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be understood as a limitation on the present application.

[0024] In addition, if the terms "first" or "second" appear, these terms are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features.

[0025] With the development and utilization of hydropower and marine resources, the application of offshore platforms such as offshore oil and gas production platforms, offshore wind turbines, wave energy generators, tidal energy generators, etc. has gradually increased, and underwater production systems have also developed. Various underwater equipment needs to be equipped with supporting power supply systems. The underwater power supply system is a key component of the underwater production system, providing the necessary power transmission and conversion for deep-sea long-distance underwater production systems. The underwater power supply system mainly includes umbilical cables, underwater transformers, underwater frequency converters, underwater electrical connectors, underwater switches, electrical equipment, etc. The underwater power supply system is closely related to the power supply distance. There are currently four underwater power supply methods, namely direct power supply, underwater transformer power supply, underwater AC power supply, and underwater DC power supply. The underwater DC power supply method is suitable for systems with a power supply distance greater than 200km and where AC power transmission cannot meet production requirements. Its biggest advantage over the AC power transmission method is that the line loss is small, there is no skin effect, and the cost of submarine cables is low.

[0026] The communication optical cable supporting equipment of underwater equipment needs to use a DC power supply system to operate normally. In addition, underwater power supply equipment usually has the characteristics of high voltage and low current, so it needs to have surge protection function. In the relevant medium-voltage DC cable technology, the cable structure from the inside to the outside is mostly conductor, conductive shield, insulation layer, insulation shield, metal shield, filling layer, armor layer and outer sheath. This type of medium-voltage DC cable is similar to the structure of traditional AC cable. The insulation core is thick, the outer diameter of the cable is large, and the cost is high, which is not suitable for use in casing when powering underwater constant current equipment.

[0027] Referring to FIG1 , FIG1 shows a cross-sectional schematic diagram of a medium voltage cable for powering underwater DC equipment of the present application. The cable 100 provided by the present application includes a conductor 1, an insulating layer, and at least two shielding layers. The cable 100 is used in an underwater transmission system, and the underwater transmission system is connected to the DC equipment located underwater.

[0028] The present application provides a medium voltage power supply cable 100 for underwater use. More preferably, the medium voltage cable described in the present application has a voltage level of 15 kV and below.

[0029] The conductor 1 is arranged at the center of the cable 100. The insulating layer 2 is coated on the outer surface of the conductor 1. At least two shielding layers 3 are coated on the outer surface of the insulating layer 2, and each shielding layer 3 is disposed adjacent to each other; the shielding layer 3 is made of metal.

[0030] The cable 100 is designed with a single-core conductor 1, which is simple in structure and environmentally friendly. The cable 100 is designed without inner and outer shielding layers, which reduces the outer diameter and bending radius of the cable 100, is lightweight, and is convenient for underwater casing laying, installation and joint laying. The adjacent double-layer shielding layer 3 is used, which can effectively prevent surges. The outer diameter of the cable 100 of the present application is 10-30 mm, for example, 19.2 mm, which can reduce the outer diameter of the cable by about 8-20% compared with the traditional 10kV medium voltage cable.

[0031] In one embodiment, the conductor 1 is made of a copper rod, an aluminum rod or an aluminum alloy rod. For example, the conductor 1 is made of oxygen-free copper rods that are drawn and twisted.

[0032] The conductor is a stranded conductor, which can be a compact round stranded conductor or a profile stranded conductor. In one embodiment, the conductor is preferably a profile stranded conductor. In the embodiment shown in FIG1 , the conductor single wire is round. Figure 2 In the embodiment shown, the conductor single wire is T-shaped, and each single wire is a T-shaped sub-wire group, which are arranged layer by layer to form a busbar group. The wire twisted conductor has a tight structure and a smooth surface without burrs. Compared with the traditional round compressed conductor, the outer diameter of the wire core can be reduced, the roundness of the wire core can be improved, and the material consumption can be reduced.

[0033] Specifically, the conductor 1 can be twisted in the following manner: The conductor 1 is formed by simply twisting multiple strands of monofilaments of the same material and equal wire diameter. The conductor 1 includes a central layer located at the central axis of the entire conductor 1 and multiple outer layers wrapped and twisted outside the central layer.

[0034] In the embodiment shown in FIG1 , the center layer of the conductor 1 is a single filament, and each additional outer layer increases 4-6 filaments. The first outer layer is wrapped and twisted outside the center layer, and 4-6 filaments are added relative to the center layer. The second outer layer is wrapped and twisted outside the first outer layer, and 4-6 filaments are added relative to the first outer layer. The twisting directions of each adjacent outer layer are opposite.

[0035] Specifically, the conductor 1 can also be twisted in the following manner. The conductor 1 is formed by twisting a plurality of strands of monofilaments into a sub-wire group, which is further twisted into a plurality of strands to form a busbar group. Hereinafter, the number of strands of the sub-wire group constituting the busbar group (i.e., the conductor 1) is referred to as the number of strands of the main twist, and the number of strands of the monofilaments constituting the sub-wire group is referred to as the number of strands of the sub-twisted wire.

[0036] The number of parent twisted strands in conductor 1 is greater than the number of child twisted strands, and the twisting direction of the child wire group is the same as that of the parent wire group (conductor 1). This is because if the number of child twisted strands is greater than the number of parent twisted strands, the outer diameter of the child wire group increases (becomes thicker), and larger gaps are easily formed between the monofilaments when performing parent twisting.

[0037] That is, by making the number of mother twisted strands greater than the number of child twisted strands, and the twisting direction of the child wire group and the mother wire group (conductor 1) is the same direction, it is not easy to produce useless gaps between the monofilaments, and the monofilaments can be arranged more closely. As a result, compared with the case where the number of mother twisted strands is less than the number of child twisted strands, and the twisting directions of the child wire group and the mother wire group (conductor 1) are opposite, even if the number of monofilaments is the same, the outer diameter of the conductor 1 can be reduced, and the overall outer diameter of the cable 100 can be reduced, so that the cable 100 that is easy to bend (highly flexible) can be realized, and the outer diameter of the cable 100 is reduced, which is more conducive to laying, installation and matching use.

[0038] As the conductor 1 of the single-core cable 100, an oxygen-free copper rod is preferably used, and TPC (Tough-Pitch Copper) and soft copper wire with low yield strength can be used. If soft copper wire with low yield strength is used compared to TPC, the single wire is easy to stretch, so the cable 100 is easier to bend. Combined with the structure without inner and outer shielding layers 3, the outer diameter and bending radius of the cable 100 are reduced, which is convenient for laying, installation and connection.

[0039] In one embodiment, the insulating layer 2 is made of polypropylene. Polypropylene insulating material is green, environmentally friendly and recyclable; it has a higher temperature resistance level, a thinner insulation thickness and excellent electrical properties.

[0040] Polypropylene insulation does not need to use cross-linking technology to enhance the insulation temperature resistance level, and can easily reach the conductor's long-term working temperature of 90°C; it does not require high-temperature vulcanization and will not produce cross-linked byproducts. It is a green and environmentally friendly production process and is suitable for underwater working environments; thermoplastic materials can be recycled, avoiding the insulation treatment problem after the service life of cross-linked polyethylene cables expires, reducing environmental pressure, and being more green and environmentally friendly. Compared with traditional cross-linked polyethylene insulation cable materials, polypropylene insulation has a higher temperature resistance level, up to 105°C, better electrical properties, and a thinner insulation layer 2.

[0041] The insulating layer 2 is extruded into a whole by a multi-layer co-extrusion method. Preferably, a three-layer co-extrusion catenary production line is used, and a corresponding extrusion temperature is selected for each layer. The three-layer co-extrusion production ensures the cleanliness of the cable 100 insulation, reduces impurities and pores in the insulation, and ensures the effectiveness of the long-term operation of the cable 100 insulation. In addition, the eccentricity of the insulating core can be better guaranteed.

[0042] In one embodiment, the shielding layer 3 includes a first shielding layer and a second shielding layer arranged close to each other, the first shielding layer is coated on the outer surface of the insulating layer 2, and the second shielding layer is coated on the outer surface of the first shielding layer. The material and manufacturing process of the first shielding layer and the second shielding layer can be the same, or the material and manufacturing process of the first shielding layer and the second shielding layer can be different.

[0043] In one embodiment, each layer of the shielding layer 3 is made of soft metal tape, which is stacked and wrapped with an overlap rate of 10-20%. Preferably, the shielding layer 3 is made of a double layer of general high-purity annealed soft copper tape with an overlap rate of 15%. The use of double-layer copper tape shielding can effectively prevent surges.

[0044] That is, at least one of the first shielding layer and the second shielding layer is made of a soft metal tape, and the soft metal tape used in at least one of the first shielding layer and the second shielding layer is stacked and wrapped, with an overlap rate of 10-20%. The first shielding layer and the second shielding layer can also be formed by stacking and wrapping two layers of the same soft metal tape.

[0045] The soft metal tape used in at least one of the first shielding layer and the second shielding layer has a structure in which a base material and a metal foil are stacked. Therefore, the shielding layer 3 including the metal foil can be formed by spirally winding the soft metal tape around the outer periphery of the insulating layer 2 etc. along the long dimension direction of the insulating layer 2. It should be noted that in order to form the shielding layer 3 around the entire outer periphery of the insulating layer 2, the soft metal tape is preferably wound around the outer periphery of the insulating layer 2 etc. in a manner that a portion overlaps each other.

[0046] The soft metal tape may also have an adhesive layer on the side of the base material where the metal foil is not provided. When the soft metal tape has an adhesive layer, when the soft metal tape is spirally wound around the outer periphery of the insulating layer 2 along the long dimension direction of the insulating layer 2, the soft metal tapes can be bonded to each other via the adhesive layer at the overlapping portions of the soft metal tapes. Therefore, the shape of the shielding layer 3 can be stabilized.

[0047] When the shield layer 3 is formed using a soft metal tape, it is preferably wound around the outer periphery of the insulating layer 2 etc. so that the surface B on the metal foil side is located on the integrated shield layer 3 side. In this case, the surface A on the base material side is located on the insulating layer 2 side.

[0048] In other embodiments, the metal tape used in forming the shielding layer 3 is not limited to the above structure. Specifically, the metal tape used in forming the shielding layer 3 may be a double-sided metal tape having an upper metal foil and a lower metal foil on both sides of the base material, i.e., the upper and lower surfaces.

[0049] In one embodiment, the cable 100 further includes a tape layer 4, and the tape layer 4 is coated on the outer surface of the shielding layer 3. Further, the tape layer 4 is formed by overlapping and wrapping non-woven fabrics. The tape layer 4 made of non-woven fabric has good insulation performance, and a certain thickness of wrapping can also provide a buffering effect. The non-woven fabric material has high strength and good heat-resistant deformation performance, which can prevent the cable core from loosening or deforming when bending, so as to ensure the roundness and tightness of the cable core.

[0050] In one embodiment, the cable 100 further includes an inner sheath layer 5, and the inner sheath layer 5 is coated on the outer surface of the shielding layer 3. Further, the inner sheath layer 5 is coated on the outer surface of the tape layer 4. The material of the inner sheath layer 5 is polyethylene, and preferably, the inner sheath layer 5 is extruded from a high-density polyethylene sheath material. The inner sheath layer 5 fills the gap outside the cable core by extrusion, and the inner wall of the inner sheath layer 5 is in close contact with the internal structure, and can be peeled off without damaging each other, which can greatly improve the bending performance of the cable 100.

[0051] In one embodiment, the cable 100 further includes an outer sheath layer 6, which is coated on the outer surface of the inner sheath layer 5, and the material of the outer sheath layer 6 is a flame retardant material. The material of the outer sheath layer 6 is nylon, and preferably, the outer sheath layer 6 is made of flame retardant nylon sheath material extruded by a general extruder, or can be made of ceramic silicone rubber and other materials with excellent fireproof, flame retardant, low smoke, non-toxic and other properties.

[0052] The inner sheath layer 5 or the outer sheath layer 6 is selected to be a water-blocking and flame-retardant material, which can effectively play a radial water-blocking effect and is conducive to the use of underwater DC power supply. Even if a pipeline is provided outside the cable to isolate the cable and the water body, water flow cannot be avoided. The water-blocking and flame-retardant sheath layer can block underwater safety hazards and improve the safety of power supply.

[0053] The high-density polyethylene sheath material is used as the inner sheath layer 5, and a flame-retardant nylon sheath is wrapped outside the inner sheath layer 5 to form effective radial water-blocking, flame-retardant, rat-proof, ant-proof, wear-resistant, corrosion-resistant, and weather-resistant properties.

[0054] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0055] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent application shall be subject to the attached claims.

Claims

1. A medium voltage cable for powering underwater DC equipment, characterized in that: The cable comprises: A conductor, the conductor has a circular cross section and is arranged at the center of the cable; an insulating layer, covering the outer surface of the conductor; and A double-layer metal shielding layer is coated on the outer surface of the insulating layer, and each layer of the shielding layer is adjacently coated.

2. The medium voltage cable for powering underwater DC equipment according to claim 1, characterized in that: The conductor is made of a copper rod, an aluminum rod or an aluminum alloy rod.

3. The medium voltage cable for powering underwater DC equipment according to claim 1, characterized in that: The insulating layer is made of environmentally friendly polypropylene material.

4. The medium voltage cable for powering underwater DC equipment according to claim 1, characterized in that: The conductor is a stranded conductor, which is a compressed circular stranded conductor or a profiled stranded conductor.

5. The medium voltage cable for powering underwater DC equipment according to claim 1, characterized in that: The shielding layer is made of soft metal tape, which is stacked and wrapped in layers with an overlap rate of 10-20%.

6. The medium voltage cable for powering underwater DC equipment according to claim 1, characterized in that: The cable also includes a tape layer, which is coated on the outer surface of the shielding layer.

7. The medium voltage cable for powering underwater DC equipment according to claim 6, characterized in that: The cable also includes an inner sheath layer, which is coated on the outer surface of the tape layer.

8. The medium voltage cable for powering underwater DC equipment according to claim 7, characterized in that: The material of the inner sheath layer is high-density polyethylene.

9. The medium voltage cable for powering underwater DC equipment according to claim 7, characterized in that: The cable also includes an outer sheath layer, which is coated on the outer surface of the inner sheath layer, and the material of the outer sheath layer is flame-retardant nylon material.

10. An underwater transmission system, characterized in that: The underwater transmission system is connected to a low-current DC device installed underwater, and comprises a medium-voltage cable for powering the underwater DC device according to any one of claims 1 to 9.

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