Polypropylene insulated high voltage dc cable and method of production thereof

Abstract

The application discloses a kind of polypropylene insulation high-voltage direct current cable and its production method, it is related to cable technical field, including insulating layer, which contains the insulating piece between conductor shielding layer and insulating shielding layer, the insulating piece is equipped with multiple limit holes connected with insulating shielding layer, the limit hole is filled with phase change piece, it can pass inside heat of insulating layer to outside, and can be transformed between solid-liquid phase with cable temperature to fill up air gap between insulating layer and insulating shielding layer.The application is equipped with multiple limit holes on the insulating piece and filled with phase change piece that can be phase changed at low temperature in limit hole, the temperature difference on both sides of insulating piece is reduced by the heat conduction capacity of phase change piece, to avoid the problem that charge aggregation appears due to too large temperature difference on both sides of insulating piece, and the separation or air gap between insulating piece and insulating shielding layer is filled up by phase change of phase change piece.

Description

Technical Field

[0001] This invention relates to the field of cable technology, and in particular to a polypropylene insulated high-voltage DC cable and its manufacturing method. Background Technology

[0002] With increasing global demand for clean energy, flexible direct current (DC) transmission technology is a crucial direction for future power transmission. It is used in long-distance power transmission, offshore wind power, and other fields. Compared to alternating current (AC) transmission, DC transmission offers advantages such as higher transmission efficiency, lower energy loss, and smaller footprint, and can solve problems related to energy loss and voltage stability. Currently, cross-linked polyethylene (XLPE) insulated cables are commonly used for medium and high voltage power transmission, but their cross-linking process is complex, energy-intensive, difficult to recycle, and has unsatisfactory thermal stability, limiting the increase in DC cable power capacity. Therefore, the development of high-voltage, high-capacity, and thermally stable environmentally friendly DC cables is of great significance.

[0003] Chinese Patent Application No. 2022106304433 discloses a 1.5kV DC cable and its manufacturing method. The cable includes a single or multi-strand core, a sheath layer, and a filling layer to fill the gap between the core and the sheath layer. The core includes a conductor and, from the inside out, an inner insulation layer, a charge dispersion layer, an outer insulation layer, a charge elimination layer, and an auxiliary charge elimination layer, sequentially disposed outside the conductor. The charge elimination layer is extruded outside the outer insulation layer, and its cross-sectional shape consists of several regular basin-shaped serrations evenly distributed along the circumference of the core. The ratio of the height of the basin top to the length of the basin bottom is 1:1, and each connection between the basin top and the basin bottom is a rounded corner transition. The outer surface of the basin-shaped serrations of the charge elimination layer of the above invention can reduce the normal component of the surface electric field intensity of the outer insulation layer, effectively suppressing the accumulation of surface charge in the outer insulation layer. The core is made of multiple layers of materials with good insulation performance; this effectively improves the insulation effect, extends the service life of the cable, ensures the long-term stable operation of the cable, and realizes reliable power transmission.

[0004] Similar to the existing technologies described above, when addressing the problem of space charge accumulation during the use of polypropylene insulated high-voltage DC cables, a charge elimination layer consisting of several regular basin-shaped sawtooth layers is used to eliminate the accumulated charge. However, due to the heating caused by resistance loss in the conductor core, the temperature inside the insulation layer is significantly higher than that outside. Furthermore, the conductivity of the insulation material increases exponentially with increasing temperature. Charge migrates quickly on the high-temperature side, while charge remains and accumulates on the low-temperature side, which still leads to charge accumulation.

[0005] Furthermore, since high-voltage DC cables are usually buried underground or underwater when transmitting power over long distances, the outer protective layer of the cable core will deform under long-term stress, which will increase the air gap between multiple insulation layers. The air gap will cause the overall dielectric constant of the insulation layer to be uneven, the dielectric loss will increase, and the heat accumulation during long-term operation will accelerate the aging of the insulation.

[0006] Therefore, it is necessary to invent a polypropylene insulated high-voltage DC cable and its production method to solve the above problems. Summary of the Invention

[0007] The purpose of this invention is to provide a polypropylene insulated high-voltage DC cable and its manufacturing method to solve the problems mentioned in the background art.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a polypropylene insulated high-voltage DC cable, comprising a cable core, wherein a conductor shielding layer, an insulation layer, an insulation shielding layer, and a protective layer are sequentially sleeved on the outside of the cable core;

[0009] The insulating layer includes an insulating component disposed between the conductor shielding layer and the insulating shielding layer. The insulating component has multiple limiting holes that connect to the insulating shielding layer. The limiting holes are filled with phase change components, which can transfer heat from the inside of the insulating layer to the outside and can change between solid and liquid phases with the cable temperature to fill the air gap between the insulating layer and the insulating shielding layer.

[0010] Preferably, the end of the limiting hole away from the insulating shielding layer extends into the insulating component but does not penetrate the insulating component, so as to ensure that the connection strength between the insulating component and the conductor shielding layer is not damaged.

[0011] Preferably, the phase change element is composed of an insulating material that can change from a solid phase to a liquid phase and increase in volume when the temperature rises, and the cable core is a stranded conductor formed by stranding multiple oxygen-free copper single wires in a certain pattern with adjacent layers stranded in opposite directions.

[0012] Preferably, the conductor shielding layer is extruded from a semiconductive material, and the conductor shielding layer is tightly wrapped around the outside of the cable core, filling the stranding gaps of the cable core and forming an inner semiconductive layer.

[0013] Preferably, the insulating component is composed of nano-modified polypropylene composite material.

[0014] Preferably, the insulating shielding layer is extruded from a semi-conductive material, which can uniformly disperse the charge on the cable insulation surface and reduce the electric field strength on the insulation surface.

[0015] Preferably, the protective layer includes a semiconducting water-blocking tape, an aluminum-plastic composite tape, a sheath, an electromagnetic shielding layer, and an armor layer sequentially fitted outside the insulating shielding layer, wherein the semiconductor water-blocking tape, the aluminum-plastic composite tape, and the sheath together form a comprehensive waterproof layer.

[0016] Preferably, the electromagnetic shielding layer includes copper wires and copper strip shielding layers, with multiple copper wires wound around the outside of the sheath and the copper strip shielding layer wrapped around the outside of the copper wires.

[0017] The present invention also provides a method for producing a polypropylene insulated high-voltage DC cable, the method being used to manufacture the aforementioned high-voltage DC cable, comprising the following steps:

[0018] S1. Prepare the cable core by twisting multiple oxygen-free copper single wires together in a certain pattern with adjacent layers in opposite directions to obtain the cable core.

[0019] S2. The conductor shielding layer, the insulation layer, and the insulation shielding layer are sequentially extruded onto the outside of the cable core obtained in S1.

[0020] S3. Wrap the semi-conductive resistive water tape around the outside of the insulating shielding layer, wrap the aluminum-plastic composite tape longitudinally, and extrude the sheath to form a comprehensive waterproof layer;

[0021] S4. An electromagnetic shielding layer and an armor layer are sequentially fitted on the outside of the comprehensive waterproof layer.

[0022] Preferably, in S2, before fixing the insulation layer to the outside of the cable core, multiple phase change elements are first filled into the limiting hole, and then the conductor shielding layer, the insulation layer and the insulation shielding layer are sequentially extruded on the outside of the cable core.

[0023] The technical effects and advantages of this invention are as follows:

[0024] 1. This invention, by opening multiple limiting holes on the insulating component and filling the limiting holes with a phase change element capable of undergoing a phase change at low temperatures, provides a buffer for the cable insulation layer during cable laying and installation through the flexible phase change element, thereby preventing separation or air gaps between the cable insulation layers and affecting its use. On the other hand, the thermal conductivity of the phase change element reduces the temperature difference between the two sides of the insulating component, thereby preventing the problem of charge accumulation due to excessive temperature difference between the two sides of the insulating component. At the same time, the phase change of the phase change element fills the separation or air gaps between the insulating component and the insulating shielding layer. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the overall structure of the present invention.

[0026] Figure 2 This is a schematic diagram of the insulating layer structure of the present invention.

[0027] Figure 3 This is a partial cross-sectional view of the cable structure of the present invention.

[0028] Figure 4 This is a cross-sectional view of another partial state of the cable structure of the present invention.

[0029] Figure 5 For the present invention Figure 4 Schematic diagram of the mechanism at point A.

[0030] In the diagram: 1. Cable core; 2. Conductor shielding layer; 3. Insulation layer; 31. Insulation component; 32. Limiting hole; 33. Phase change component; 4. Insulation shielding layer; 5. Semiconductor resistive water tape; 6. Aluminum-plastic composite tape; 7. Sheath; 8. Electromagnetic shielding layer; 9. Armoring layer. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] To overcome the problem that existing polyethylene cable products cannot operate stably under high temperature and high field strength, and the problem that polyethylene materials are difficult to recycle and reuse.

[0033] Figures 1 to 5 As shown, in the first embodiment of the present invention, a polypropylene insulated high-voltage DC cable is provided, including a cable core 1, and a conductor shielding layer 2, an insulation layer 3, an insulation shielding layer 4 and a protective layer are sequentially sleeved on the outside of the cable core 1.

[0034] In this embodiment, the cable core 1 is a stranded conductor formed by stranding multiple oxygen-free copper single wires according to certain rules, with adjacent layers stranded in opposite directions.

[0035] In this embodiment, the conductor shielding layer 2 is extruded from a semi-conductive material. The conductor shielding layer 2 tightly wraps around the outside of the cable core 1, filling the stranding gaps of the cable core 1 and forming an inner semi-conductive layer. It can effectively prevent electric field concentration caused by uneven conductor surface or air gaps generated by wire stranding, thereby reducing the withstand voltage level of the cable insulation and affecting the service life of the cable.

[0036] In this embodiment, the main body of the insulation layer 3 is made of nano-modified polypropylene composite material, which retains the excellent insulation properties of polypropylene such as breakdown field strength and volume resistivity, while improving the rigidity of polypropylene and the shortcomings of low modulus and easy aging.

[0037] In this embodiment, the insulating shielding layer 4 is extruded from a semi-conductive material, which can uniformly disperse the charge on the surface of the cable insulation, reduce the electric field strength on the insulation surface, and reduce the risk of partial discharge.

[0038] In this embodiment, the protective layer includes a semi-conductive resistive water tape 5, an aluminum-plastic composite tape 6, a sheath 7, an electromagnetic shielding layer 8, and an armor layer 9, which are sequentially sleeved on the outside of the insulating shielding layer 4. The semi-conductive resistive water tape 5, the aluminum-plastic composite tape 6, and the sheath 7 together form a comprehensive waterproof layer.

[0039] In this embodiment, the semiconducting water-blocking tape 5 is specifically a wrapped water-blocking semiconducting tape. The aluminum-plastic composite tape 6 is wrapped around the cable in a longitudinal manner. The semiconducting water-blocking tape 5 can prevent damage to the internal insulation. The aluminum-plastic composite tape 6 is bonded together with the sheath 7 made of high-density polyethylene, thereby improving the longitudinal water-blocking effect of the cable.

[0040] In this embodiment, the electromagnetic shielding layer 8 includes copper wire and copper tape shielding layers. Multiple copper wires are wound around the outside of the sheath 7, and the copper tape shielding layer is wrapped around the outside of the copper wires. It can not only isolate the cable from external interference, but also provide fault current protection, improve the cable's safety, and withstand tension and pressure, thus protecting the cable core.

[0041] However, in actual use, technicians found that although replacing traditional polyethylene with modified polypropylene as the main insulation material of the cable can overcome the problems of existing cables not being able to operate stably under high temperature and high field strength, and the difficulty of recycling polyethylene materials, since this cable is a high-voltage DC cable, during use, the cable core 1 heats up due to resistance loss, and due to the heat insulation properties of polypropylene, the temperature inside the insulation layer 3 is significantly higher than that outside. The conductivity of polypropylene increases exponentially with increasing temperature. Charge migrates quickly on the high-temperature side, while charge accumulates on the low-temperature side, which still leads to charge accumulation. Furthermore, since high-voltage DC cables are usually buried underground or underwater when transmitting power over long distances, the outer protective layer of the cable core will deform under long-term stress, resulting in an increase in the air gap between multiple insulation layers inside. The air gap causes the overall dielectric constant of the insulation layer 3 to be uneven, increasing dielectric loss. During long-term operation, heat accumulation accelerates insulation aging.

[0042] Therefore, in order to solve the above problems, in another embodiment of the present invention, the device further includes: the insulating layer 3 includes an insulating member 31 disposed between the conductor shielding layer 2 and the insulating shielding layer 4, the insulating member 31 is provided with a plurality of limiting holes 32 communicating with the insulating shielding layer 4, the limiting holes 32 are filled with a phase change member 33, which can transfer the heat inside the insulating layer 3 to the outside, and can change between solid and liquid phases with the cable temperature to fill the air gap between the insulating layer 3 and the insulating shielding layer 4.

[0043] It should be noted that the phase change element 33 can be made of insulating materials such as paraffin wax, which can change from a solid phase to a liquid phase at low temperatures and increase in volume when changing from a solid phase to a liquid phase.

[0044] In this embodiment, the end of the limiting hole 32 away from the insulating shielding layer 4 extends into the insulating component 31 but does not penetrate the insulating component 31, so as to ensure that the connection strength between the insulating component 31 and the conductor shielding layer 2 is not damaged. The phase change component 33 is composed of an insulating material that can change from a solid phase to a liquid phase and increase in volume after the temperature rises.

[0045] For ease of explanation, paraffin wax or modified paraffin wax is used as the main component material of the phase change element 33 as an example. In use, when the conductor shielding layer 2, the insulation layer 3, and the insulation shielding layer 4 are installed sequentially on the outside of the cable core 1, the cable core 1 is not in a power transmission state, so the temperature of the cable core 1 is the same as the ambient temperature. At this temperature, the phase change element 33 remains in a solid state. Since the hardness of the phase change element 33 is lower than that of the insulation element 31, if the cable needs to be bent or dragged during the cable installation and laying process, this part of the phase change element 33 can adapt to the dragging or bending force to provide a flexible buffer for the insulation layer 3, thereby avoiding the problem of air gaps caused by the separation of the insulation layer 3 from the conductor shielding layer 2 or the insulation shielding layer 4.

[0046] When the cable is assembled and put into use, the cable core 1 is in the power transmission state. The cable core 1 generates heat due to resistance loss and transfers the heat to the insulation layer 3 through the conductor shielding layer 2. In this state, since the phase change element 33 is set inside the insulation element 31, and the thermal conductivity of paraffin is higher than that of polypropylene, the phase change element 33 can absorb the heat of the insulation element 31 on the side close to the cable core 1 and transfer it to the side away from the cable core 1. On the one hand, it improves the heat dissipation effect of the device, and on the other hand, it improves the temperature difference on both sides of the insulation element 31 through the heat transfer of paraffin, thereby avoiding the problem of excessive temperature difference on both sides of the insulation element 31, which would lead to electric field distortion and charge accumulation.

[0047] like Figure 4 As shown, during the heat absorption process of the phase change element 33, since the phase change element 33 is composed of a material similar to paraffin wax, its phase change temperature is relatively low. Therefore, during the heat absorption process, the phase change element 33 can change from a solid phase to a liquid phase and its volume increases. At this time, if the insulating shield layer 4 and the insulating element 31 are still in a tight fit without an air gap or the air gap is too small, the liquid phase change element 33 will be compressed. However, if there is an air gap or separation between the insulating shield layer 4 and the insulating element 31, the liquid phase change element 33 can move to the area with a larger air gap or the separation area, thereby ensuring the fit between the insulating shield layer 4 and the insulating element 31. This effectively avoids the problem of uneven dielectric constant of the insulating element 31, increased dielectric loss, and accelerated aging of the insulating element 31 due to heat accumulation during long-term operation.

[0048] Furthermore, by setting multiple limiting holes 32 on the insulating component 31 and filling the limiting holes 32 with phase change components 33, the insulating component 31 is made to have a basin-shaped sawtooth shape. Its outer surface can reduce the normal component of the electric field intensity on the surface of the outer insulating component 31, effectively suppressing the accumulation of surface charge on the outer insulating component 31, minimizing the normal component of the electric field intensity on the surface of the insulating component 31, and minimizing the accumulation of surface charge as much as possible.

[0049] In another embodiment of the present invention, a method for producing a polypropylene insulated high-voltage DC cable is also provided. This method, used to manufacture the aforementioned high-voltage DC cable, includes the following steps:

[0050] S1. Prepare cable core 1 by twisting multiple oxygen-free copper single wires in opposite directions according to certain rules to obtain cable core 1.

[0051] S2. The conductor shielding layer 2, the insulation layer 3 and the insulation shielding layer 4 are extruded sequentially around the cable core 1 obtained in S1.

[0052] S3. After wrapping the insulating shielding layer 4 with semi-conductive resistive water tape 5, longitudinally wrapping aluminum-plastic composite tape 6, and extruding sheath 7, a comprehensive waterproof layer is formed.

[0053] S4. An electromagnetic shielding layer 8 and an armor layer 9 are sequentially applied to the outside of the comprehensive waterproof layer.

[0054] In S2 of this embodiment, before fixing the insulation layer 3 to the outside of the cable core 1, multiple phase change elements 33 are filled into the limiting hole 32, and then the conductor shielding layer 2, the insulation layer 3 and the insulation shielding layer 4 are extruded sequentially on the outside of the cable core 1.

[0055] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A polypropylene insulated high-voltage DC cable, comprising a cable core (1), characterized in that, The outer side of the cable core (1) is sequentially fitted with a conductor shielding layer (2), an insulation layer (3), an insulation shielding layer (4), and a protective layer; The insulating layer (3) includes an insulating component (31) disposed between the conductor shielding layer (2) and the insulating shielding layer (4). The insulating component (31) is provided with a plurality of limiting holes (32) communicating with the insulating shielding layer (4). The limiting holes (32) are filled with a phase change component (33), which can transfer heat from the inside of the insulating layer (3) to the outside and can change between solid and liquid phases with the cable temperature to fill the air gap between the insulating layer (3) and the insulating shielding layer (4). The phase change element (33) is composed of an insulating material that can change from a solid phase to a liquid phase and increase in volume when the temperature rises.

2. The high-voltage DC cable according to claim 1, characterized in that, The end of the limiting hole (32) away from the insulating shield layer (4) extends into the insulating component (31) but does not penetrate the insulating component (31) to ensure that the connection strength between the insulating component (31) and the conductor shield layer (2) is not damaged.

3. The high-voltage DC cable according to claim 2, characterized in that, The cable core (1) is a stranded conductor made of multiple oxygen-free copper single wires stranded in opposite directions in adjacent layers.

4. The high-voltage DC cable according to claim 3, characterized in that, The conductor shielding layer (2) is extruded from a semi-conductive material. The conductor shielding layer (2) is tightly wrapped around the outside of the cable core (1), filling the twisted gaps of the cable core (1) and forming an inner semi-conductive layer.

5. The high-voltage DC cable according to claim 4, characterized in that, The insulating component (31) is made of nano-modified polypropylene composite material.

6. The high-voltage DC cable according to claim 5, characterized in that, The insulating shielding layer (4) is extruded from a semi-conductive material, which can evenly disperse the charge on the cable insulation surface and reduce the electric field strength on the insulation surface.

7. The high-voltage DC cable according to claim 6, characterized in that, The protective layer includes a semi-conductive resistive water tape (5), an aluminum-plastic composite tape (6), a sheath (7), an electromagnetic shielding layer (8), and an armor layer (9) sequentially fitted on the outside of the insulating shielding layer (4). The semi-conductive resistive water tape (5), the aluminum-plastic composite tape (6), and the sheath (7) together form a comprehensive waterproof layer.

8. The high-voltage DC cable according to claim 7, characterized in that, The electromagnetic shielding layer (8) includes copper wire and copper strip shielding layer, with multiple copper wires wrapped around the outside of the sheath (7) and the copper strip shielding layer wrapped around the outside of the copper wires.

9. A method for producing a polypropylene insulated high-voltage DC cable, the method being used to manufacture the high-voltage DC cable as described in claim 8, characterized in that, Includes the following steps: S1. Prepare the cable core (1): Multiple oxygen-free copper single wires are twisted together according to the rule of opposite twisting directions of adjacent layers to obtain the cable core (1). S2. The conductor shielding layer (2), insulation layer (3) and insulation shielding layer (4) are extruded sequentially around the cable core (1) obtained in S1. S3. Wrap the semi-conductive resistive water tape (5) around the outside of the insulating shielding layer (4), wrap the aluminum-plastic composite tape (6) longitudinally, and extrude the sheath (7) to form a comprehensive waterproof layer; S4. An electromagnetic shielding layer (8) and an armor layer (9) are sequentially fitted on the outside of the comprehensive waterproof layer.

10. The method for producing a high-voltage DC cable according to claim 9, characterized in that, In S2, before fixing the insulation layer (3) to the outside of the cable core (1), multiple phase change elements (33) are filled into the limiting hole (32), and then the conductor shielding layer (2), insulation layer (3) and insulation shielding layer (4) are extruded in sequence on the outside of the cable core (1).

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