Polypropylene insulated high-voltage direct-current cable and production method thereof

Abstract

The invention discloses a polypropylene insulation high-voltage direct-current cable and a production method thereof, and relates to the technical field of cables, the polypropylene insulation high-voltage direct-current cable comprises an insulation layer, the insulation layer comprises an insulation part arranged between a conductor shielding layer and an insulation shielding layer, the insulation part is provided with a plurality of limiting holes communicated with the insulation shielding layer, the limiting holes are filled with phase change parts, and the phase change parts can transmit heat on the inner side of the insulation layer to the outer side of the insulation layer; and the cable can be converted between solid and liquid along with the temperature of the cable so as to fill an air gap between the insulating layer and the insulating shielding layer. The plurality of limiting holes are formed in the insulating part, the limiting holes are filled with the phase change parts capable of generating phase change at low temperature, and the temperature difference between the two sides of the insulating part is reduced through the heat conduction capability of the phase change parts, so that the problem of charge accumulation caused by the overlarge temperature difference between the two sides of the insulating part is avoided; and meanwhile, separation or air gaps between the insulating part and the insulating shielding layer are filled through phase change of the phase change part.

Description

Technical Field

[0001] The present invention relates to the technical field of cables, and particularly relates to a polypropylene insulated high-voltage DC cable and a production method thereof. Background Art

[0002] The global demand for clean energy is increasing, and flexible DC transmission technology is an important direction for future power transmission. It is used in fields such as long-distance power transmission and offshore wind power. It uses DC transmission, which has advantages such as high transmission efficiency, low power loss, and small land occupation compared with AC transmission, and can solve problems such as power loss and voltage stability. At present, cross-linked polyethylene insulated cables are commonly used for medium and high-voltage power transmission, but their cross-linking process is complex, energy consumption is large, difficult to recycle, and the thermal stability is not ideal, which limits the improvement of the power capacity of DC cables. Therefore, it is of great significance to develop an environmentally friendly DC cable with high voltage, large capacity, and high thermal stability.

[0003] Chinese Patent with application number 2022106304433 discloses a 1.5 kV DC cable and its preparation method; it includes a single-strand or multi-strand cable core, a sheath layer, and a filling layer that fills the gap between the cable core and the sheath layer; the cable core includes a conductor, and an inner insulation layer, a charge dispersion layer, an outer insulation layer, a charge elimination layer, and an auxiliary elimination layer are sequentially arranged outside the conductor from the inside out; the charge elimination layer is extruded outside the outer insulation layer, and its cross-sectional shape is composed of several regular basin-shaped sawteeth evenly distributed along the circumference of the cable core. The ratio of the height of the basin top of the basin-shaped sawtooth to the length of the basin bottom is 1:1, and each connection between the basin top and the basin bottom is a circular arc angle transition. The outer side of the basin-shaped sawtooth of the charge elimination layer of the above invention can reduce the normal component of the electric field strength on the surface of the outer insulation layer, and effectively inhibit the surface charge accumulation of the outer insulation layer. The cable core is made of multiple materials with good insulation performance; it can effectively improve the insulation effect, extend the service life of the cable, ensure the long-term stable operation of the cable, and achieve reliable power transmission.

[0004] Similar to the above prior art, when solving the problem of space charge accumulation during the use of polypropylene insulated high-voltage DC cables, a charge elimination layer composed of several regular basin-shaped sawteeth is used to eliminate the accumulated charges. However, due to the heat generated by the resistance loss of the conductor (cable core), the temperature inside the insulation layer is significantly higher than that outside, and the conductivity of the insulation material increases exponentially with the increase in temperature. The charge migration on the high-temperature side is fast, and the charge retention on the low-temperature side forms an accumulation, which still leads to charge accumulation.

[0005] Moreover, since high-voltage DC cables are usually buried underground or underwater during long-distance power transmission, the protective layer outside the cable core will deform under long-term stress, resulting in an increase in the air gap between multiple insulation layers inside, which causes the overall dielectric constant of the insulation layer to be uneven, increases the dielectric loss, and accelerates the insulation aging due to heat accumulation during long-term operation.

[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 the present invention is to provide a polypropylene-insulated high-voltage DC cable and its production method to solve the problems raised in the above background technology.

[0008] To achieve the above purpose, the present invention provides the following technical solution: a polypropylene-insulated high-voltage DC cable, including a cable core, and a conductor shielding layer, an insulating layer, an insulating shielding layer, and a protective layer are sequentially sleeved outside the cable core; The insulating layer includes an insulating member disposed between the conductor shielding layer and the insulating shielding layer. The insulating member is provided with a plurality of limiting holes communicating with the insulating shielding layer. A phase change member is filled in the limiting holes, which can transfer the heat inside the insulating layer to the outside, and can change between solid and liquid phases with the temperature of the cable to fill the air gap between the insulating layer and the insulating shielding layer.

[0009] Preferably, one end of the limiting hole away from the insulating shielding layer extends into the insulating member and does not penetrate the insulating member to ensure that the connection strength between the insulating member and the conductor shielding layer is not damaged.

[0010] Preferably, the phase change member is composed of an insulating substance that can change from a solid phase to a liquid phase and increase in volume after the temperature rises. The cable core is a stranded conductor formed by stranding a plurality of oxygen-free copper single wires according to a certain rule, with opposite lay directions in adjacent layers.

[0011] Preferably, the conductor shielding layer is extruded from a semi-conductive material, and the conductor shielding layer tightly wraps outside the cable core, fills the stranding gaps of the cable core, and forms an inner semi-conductive layer.

[0012] Preferably, the insulating member is composed of a nano-modified polypropylene composite material.

[0013] Preferably, the insulating shielding layer is extruded from a semi-conductive material, which can evenly disperse the surface charges of the cable insulation and reduce the surface electric field strength of the insulation.

[0014] Preferably, the protective layer includes a semi-conductive water-blocking tape, an aluminum-plastic composite tape, a sheath, an electromagnetic shielding layer, and an armor layer sequentially sleeved outside the insulating shielding layer. The semi-conductive water-blocking tape, the aluminum-plastic composite tape, and the sheath together form a comprehensive waterproof layer.

[0015] Preferably, the electromagnetic shielding layer includes copper wires and a copper tape shielding layer. A plurality of the copper wires are wound outside the sheath, and the copper tape shielding layer is wrapped outside the copper wires.

[0016] The present invention also provides a production method of a polypropylene-insulated high-voltage DC cable, which is used to manufacture the above high-voltage DC cable, and includes the following steps: S1. Prepare the cable core by stranding multiple single-strand oxygen-free copper wires in a certain rule with opposite stranding directions for adjacent layers to obtain the cable core. S2. Extrude a conductor shield layer, an insulating layer, and an insulation shield layer in sequence outside the cable core obtained in S1. S3. Wind the semiconductive water-resistant tape around the insulation shield layer in sequence, longitudinally wrap the aluminum-plastic composite tape, and extrude the sheath to form a comprehensive waterproof layer. S4. Sheath an electromagnetic shielding layer and an armor layer in sequence outside the comprehensive waterproof layer.

[0017] Preferably, in S2, before fixing the insulating layer outside the cable core, first fill multiple phase change components into the limiting holes, and then extrude a conductor shield layer, an insulating layer, and an insulation shield layer in sequence outside the cable core.

[0018] Technical effects and advantages of the present invention: 1. By opening multiple limiting holes in the insulating part and filling phase change components that can undergo phase change at low temperature in the limiting holes, on the one hand, during the laying and installation of the cable, the flexible phase change components provide buffering for the insulating layer of the cable, thus avoiding the problem that the insulating layers of the cable are separated or have air gaps, which affects the use; on the other hand, the heat conduction ability of the phase change components reduces the temperature difference between both sides of the insulating part, thus avoiding the problem that charge accumulation occurs in the insulating part due to too large temperature difference between both sides. At the same time, the separation or air gap between the insulating part and the insulation shield layer is filled by the phase change of the phase change components. Brief description of the drawings

[0019] Figure 1 It is a schematic diagram of the overall structure of the present invention.

[0020] Figure 2 It is a schematic diagram of the insulating layer structure of the present invention.

[0021] Figure 3 It is a partial cross-sectional view of the cable structure of the present invention.

[0022] Figure 4 It is a partial cross-sectional view of the cable structure in another state of the present invention.

[0023] Figure 5 For the present invention Figure 4 The schematic diagram of the structure of the mechanism at position A.

[0024] In the figure: 1. Cable core; 2. Conductor shield layer; 3. Insulating layer; 31. Insulating part; 32. Limiting hole; 33. Phase change component; 4. Insulation shield layer; 5. Semiconductive water-resistant tape; 6. Aluminum-plastic composite tape; 7. Sheath; 8. Electromagnetic shielding layer; 9. Armor layer. Specific embodiments

[0025] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0026] To overcome the problems that existing polyethylene cable products cannot meet the requirements of stable operation under high temperature and high electric field strength, and the problem that polyethylene materials are difficult to recycle and reuse.

[0027] Figures 1 to 5 As shown, in the first embodiment of the present invention, a polypropylene-insulated high-voltage DC cable is provided, which includes a cable core 1. A conductor shielding layer 2, an insulating layer 3, an insulation shielding layer 4, and a protective layer are sequentially sleeved outside the cable core 1.

[0028] In this embodiment, the cable core 1 is a stranded conductor formed by stranding multiple oxygen-free copper single wires according to a certain rule with opposite lay directions for adjacent layers.

[0029] In this embodiment, the conductor shielding layer 2 is extruded from a semi-conductive material. The conductor shielding layer 2 tightly wraps outside the cable core 1, fills the stranding gaps of the cable core 1 and forms an inner semi-conductive layer, which can effectively prevent electric field concentration caused by uneven conductor surfaces or air gaps generated by wire core stranding, thereby reducing the withstand voltage level of the cable insulation and affecting the service life of the cable.

[0030] In this embodiment, the main body of the insulating layer 3 uses a nano-modified polypropylene composite material, retaining the excellent insulating properties of polypropylene such as breakdown field strength and volume resistivity, while improving the deficiencies of low rigidity and modulus and easy aging of polypropylene.

[0031] In this embodiment, the insulation shielding layer 4 is extruded from a semi-conductive material, which can evenly disperse the surface charges of the cable insulation, reduce the surface electric field strength of the insulation, and reduce the risk of partial discharge.

[0032] In this embodiment, the protective layer includes a semi-conductive water-blocking tape 5, an aluminum-plastic composite tape 6, a sheath 7, an electromagnetic shielding layer 8, and an armor layer 9 that are sequentially sleeved outside the insulation shielding layer 4. The semi-conductive water-blocking tape 5, the aluminum-plastic composite tape 6, and the sheath 7 together form a comprehensive waterproof layer.

[0033] In this embodiment, the semi-conductive water-blocking tape 5 is specifically a wrapped water-blocking semi-conductive tape. The aluminum-plastic composite tape 6 is wound around the cable in a longitudinal wrapping manner. The semi-conductive water-blocking tape 5 can prevent the internal insulation from being damaged; and the aluminum-plastic composite tape 6 is bonded to the sheath 7 made of high-density polyethylene, thereby improving the longitudinal water-blocking effect of the cable.

[0034] In this embodiment, the electromagnetic shielding layer 8 includes copper wires and a copper tape shielding layer. A plurality of copper wires are wound around the outer side of the sheath 7, and the copper tape shielding layer is wrapped around the outer side of the copper wires, which can not only isolate the interference from outside the cable, but also play the role of a fault current, improve the safety of the cable, and can also withstand tension and pressure, playing a protective role for the cable core.

[0035] However, during actual use, technicians found that although replacing traditional polyethylene with modified polypropylene as the main insulating material of the cable can overcome the problems that existing cables cannot operate stably under high temperature and high electric field strength requirements, and the problem that polyethylene materials are difficult to recycle and reuse, since this cable is a high-voltage DC cable, during use, the cable core 1 generates heat due to resistance loss, and due to the heat insulation characteristics of polypropylene, the temperature inside the insulating layer 3 is significantly higher than that outside. And the conductivity of polypropylene increases exponentially with the increase in temperature. The charge migration is fast on the high-temperature side, and charge accumulation forms due to charge retention on the low-temperature side, still resulting in charge aggregation; moreover, since high-voltage DC cables are usually buried underground or underwater during long-distance power transmission, the protective layer outside the cable core will deform under long-term stress, resulting in an increase in the air gap between multiple insulating layers inside, and the air gap causes the overall dielectric constant of the insulating layer 3 to be uneven, increasing the dielectric loss, and the heat accumulation during long-term operation accelerates the insulation aging.

[0036] Therefore, to solve the above problems, in another embodiment of the present invention, the device further 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, and a phase change member 33 is filled in the limiting holes 32, which can transfer the heat inside the insulating layer 3 to the outside, and can change between solid and liquid phases with the temperature of the cable to fill the air gap between the insulating layer 3 and the insulating shielding layer 4.

[0037] It should be noted that the material of the phase change member 33 can be an insulating material such as paraffin that can change from a solid phase to a liquid phase at a low temperature and whose volume increases when changing from a solid phase to a liquid phase.

[0038] In this embodiment, one end of the limiting hole 32 away from the insulating shielding layer 4 extends into the insulating member 31 and does not penetrate the insulating member 31 to ensure that the connection strength between the insulating member 31 and the conductor shielding layer 2 is not damaged. The phase change member 33 is composed of an insulating substance that can change from a solid phase to a liquid phase and whose volume increases after the temperature rises.

[0039] For ease of explanation, paraffin or modified paraffin is taken as an example of the main constituent material of the phase change member 33 here. During use, when the conductor shielding layer 2, the insulating layer 3, and the insulation shielding layer 4 are sequentially installed outside the cable core 1, since the cable core 1 is not in the power transmission state at this time, the temperature of the cable core 1 is the same as the ambient temperature. At this temperature, the phase change member 33 remains in a solid state. And because the hardness of the phase change member 33 is lower than that of the insulating member 31, during the cable installation and laying process, if the cable needs to be bent or dragged, the phase change member 33 in this part can conform to the dragging force or bending force to provide a flexible buffer for the insulating layer 3, thus avoiding the problem of the insulating layer 3 being separated from the conductor shielding layer 2 or the insulation shielding layer 4 to generate air gaps.

[0040] When the cable is assembled and put into use, the cable core 1 is in the power transmission state at this time. The cable core 1 generates heat due to resistance loss and transfers the heat to the insulating layer 3 through the conductor shielding layer 2. In this state, since the phase change member 33 is arranged in the insulating member 31 and the thermal conductivity of paraffin is higher than that of polypropylene, the phase change member 33 can absorb the heat of the insulating member 31 on the side close to the cable core 1 and transfer it to the side far from the cable core 1. On the one hand, the heat dissipation effect of the device is improved, and on the other hand, the temperature difference between both sides of the insulating member 31 is improved through the heat transfer of paraffin, thus avoiding the problem that the temperature difference between both sides of the insulating member 31 is too large, resulting in electric field distortion and charge accumulation.

[0041] As Figure 4 shown, during the heat absorption process of the phase change member 33, since the phase change member 33 is composed of a material similar to paraffin and its phase change temperature is relatively low, during the heat absorption process of the phase change member 33, it can change from a solid state to a liquid state and the volume increases. At this time, if there is no air gap or the air gap is too small between the insulation shielding layer 4 and the insulating member 31 and they are still in close contact, the liquid phase change member 33 will be compressed. And if there is an air gap or separation between the insulation shielding layer 4 and the insulating member 31 at this time, the liquid phase change member 33 can move towards the place with a larger air gap or the separation, thus ensuring the degree of fit between the insulation shielding layer 4 and the insulating member 31, effectively avoiding the problems of uneven overall dielectric constant of the insulating member 31, increased dielectric loss, and accelerated aging of the insulating member 31 due to heat accumulation during long-term operation.

[0042] And by arranging a plurality of limiting holes 32 on the insulating member 31 and filling the phase change member 33 in the limiting holes 32, the overall insulating member 31 is in a basin-shaped sawtooth, and the normal component of the electric field strength on its outer surface can be reduced, effectively suppressing the surface charge accumulation on the outer insulating member 31, making the normal component of the electric field strength on the surface of the insulating member 31 reach the minimum, and minimizing the surface charge accumulation as much as possible.

[0043] In another embodiment of the present invention, a production method of a polypropylene-insulated high-voltage DC cable is further provided. This method is used to manufacture the above-mentioned high-voltage DC cable and includes the following steps: S1. Prepare the cable core 1. Strands of oxygen-free copper single wires are stranded in accordance with a certain rule, with the lay direction of adjacent layers being opposite, to obtain the cable core 1.

[0044] S2. Extrude a conductor shielding layer 2, an insulating layer 3, and an insulation shielding layer 4 in sequence outside the cable core 1 obtained in S1.

[0045] S3. Wrap a semiconductive water-blocking tape 5, longitudinally wrap an aluminum-plastic composite tape 6, and extrude a sheath 7 in sequence outside the insulation shielding layer 4 to form a comprehensive waterproof layer.

[0046] S4. Sheath an electromagnetic shielding layer 8 and an armor layer 9 in sequence outside the comprehensive waterproof layer.

[0047] In S2 of this embodiment, before fixing the insulating layer 3 outside the cable core 1, a plurality of phase change elements 33 are first filled in the limiting holes 32, and then a conductor shielding layer 2, an insulating layer 3, and an insulation shielding layer 4 are extruded in sequence outside the cable core 1.

[0048] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used 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 perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A polypropylene-insulated high-voltage DC cable, comprising a cable core, characterized in that, A conductor shielding layer, an insulating layer, an insulation shielding layer and a protective layer are sequentially sleeved outside the cable core; The insulating layer includes an insulating member disposed between the conductor shielding layer and the insulation shielding layer. The insulating member is provided with a plurality of limiting holes communicating with the insulation shielding layer. A phase change member is filled in the limiting holes, which can transfer the heat inside the insulating layer to the outside, and can change between solid and liquid phases according to the cable temperature to fill the air gap between the insulating layer and the insulation shielding layer.

2. The high-voltage DC cable according to claim 1, wherein, One end of the limiting hole away from the insulation shielding layer extends into the insulating member and does not penetrate the insulating member, so as to ensure that the connection strength between the insulating member and the conductor shielding layer is not damaged.

3. The high-voltage DC cable according to claim 2, wherein, The phase change member is composed of an insulating substance that can change from solid phase to liquid phase and increase in volume after the temperature rises. The cable core is a stranded conductor formed by stranding multiple oxygen-free copper single wires according to a certain rule, with opposite lay directions for adjacent layers.

4. The high-voltage DC cable according to claim 3, wherein The conductor shielding layer is extruded from a semi-conductive material and tightly wraps outside the cable core to fill the stranding gaps of the cable core and form an inner semi-conductive layer.

5. The high-voltage DC cable according to claim 4, wherein, The insulating member is made of a nano-modified polypropylene composite material.

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

7. The high-voltage DC cable according to claim 6, wherein The protective layer includes a semi-conductive water-resistant tape, an aluminum-plastic composite tape, a sheath, an electromagnetic shielding layer and an armor layer sequentially sleeved outside the insulation shielding layer. The semi-conductive water-resistant tape, the aluminum-plastic composite tape and the sheath together form a comprehensive waterproof layer.

8. The high-voltage DC cable according to claim 7, characterized in that The electromagnetic shielding layer includes copper wires and a copper tape shielding layer. A plurality of the copper wires are wound outside the sheath, and the copper tape shielding layer is wrapped outside the copper wires.

9. A production method of a polypropylene-insulated high-voltage DC cable, which is used to manufacture the high-voltage DC cable as claimed in claim 8, characterized in that, It includes the following steps: S1. Prepare the cable core by stranding multiple oxygen-free copper single wires according to a certain rule with opposite lay directions for adjacent layers to obtain the cable core; S2. Extrude a conductor shielding layer, an insulating layer and an insulation shielding layer outside the cable core obtained in S1 in sequence; S3. Wind the semi-conductive water-resistant tape outside the insulation shielding layer in sequence, longitudinally wrap the aluminum-plastic composite tape, and extrude the sheath to form a comprehensive waterproof layer; S4. Sleeve an electromagnetic shielding layer and an armor layer outside the comprehensive waterproof layer in sequence.

10. The production method of the high-voltage DC cable according to claim 9, characterized in that, In S2, before fixing the insulating layer outside the cable core, first fill a plurality of phase change members in the limiting holes, and then extrude a conductor shielding layer, an insulating layer and an insulation shielding layer outside the cable core in sequence.

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