A 1.5kV DC cable and its preparation method

Abstract

The present invention discloses a 1.5kV DC cable and a preparation method thereof; the cable comprises a single-strand or multi-strand cable core, a sheath layer, and a filling layer for filling the gap between the cable core and the sheath layer; the cable core comprises a conductor, and an inner insulating layer, a charge dispersion layer, an outer insulating layer, a charge elimination layer, and an auxiliary elimination layer arranged outside the conductor in sequence from the inside to the outside; the charge elimination layer is extruded outside the outer insulating layer, and its cross-sectional shape is composed of a number of regular basin-shaped saw teeth evenly distributed along the circumference of the cable core, the ratio of the height of the basin top to the length of the basin bottom of the basin-shaped saw teeth is 1:1, and each connection between the basin top and the basin bottom is an arc angle transition. The outer side surface of the basin-shaped saw teeth of the charge elimination layer of the present invention can reduce the normal component of the electric field intensity on the surface of the outer insulating layer, and effectively inhibit the surface charge accumulation of the outer insulating layer. The cable core is made of a multilayer material 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 realize the reliable transmission of electric energy.

Description

Technical Field

[0001] The invention relates to a cable, in particular to a 1.5kV DC cable and a preparation method thereof. Background Art

[0002] With the development of power transmission technology, large-scale interconnected power grids pay more and more attention to the efficiency and safety of power transmission. At present, DC transmission technology is widely used due to its advantages such as small footprint, low line loss and simple line structure. In actual operation, the insulation of DC cable system is in a unipolar high voltage environment for a long time, which is easy to cause insulation aging, breakdown and other problems, especially for DC cable accessories with complex structures, where the space charge accumulation and local electric field distortion are particularly serious.

[0003] In an AC electric field, the migration of positive and negative charges in materials cannot keep up with the rapid changes in the power frequency electric field, so there is no space charge effect. Under the action of DC power, the insulation layer of a DC cable must be able to withstand rapid polarity changes. Under load, polarity changes will actually cause an increase in the electric field strength inside the cable insulation, usually up to 50% to 70%. The presence of space charge will cause the electric field inside the cable insulation layer to be distorted and other electrical properties to be reduced. Especially in actual operation, the temperature gradient effect will aggravate the severe distortion of the outer insulation layer of the cable and reduce the service life of the cable. At the same time, the existing technology has a thin insulation layer, a single material, and a small number of insulation layers, which makes the insulation effect of the cable unreliable, thereby reducing the service life of the cable.

[0004] At the same time, there are a large number of local states in the commonly used polyethylene insulation materials, and the space charge effect is particularly serious. The cross-linked polyethylene insulation layer is chemically cross-linked, which is an integral cross-linked structure and belongs to a non-polar polymer. From the perspective of the entire cable structure, the cable itself is like a large capacitor. After the DC power transmission stops, it is equivalent to charging a capacitor. Although the conductor core is grounded, it cannot be effectively discharged. A large amount of DC power still exists in the cable, which is the so-called space charge. These space charges will not be consumed with dielectric loss like AC power cables, but will gather at cable defects. With the extension of use time or frequent interruptions and changes in current strength, more and more space charges will gather, accelerating the aging of the insulation layer, thereby affecting the service life. Summary of the invention

[0005] The technical purpose of the present invention is to provide a DC cable with good insulation performance, capable of preventing charge accumulation and capable of long-term safe operation under a DC voltage of 1.5kV in view of the deficiencies of the above-mentioned prior art.

[0006] The technical purpose of the present invention is achieved by the following technical solutions:

[0007] A 1.5kV DC cable comprises a single-strand or multi-strand cable core, a sheath layer and a filling layer for filling the gap between the cable core and the sheath layer; the cable core comprises a conductor, and an inner insulating layer, a charge dispersion layer, an outer insulating layer, a charge elimination layer and an auxiliary elimination layer which are sequentially arranged outside the conductor from the inside to the outside; the charge elimination layer is extruded outside the outer insulating layer, and its cross-sectional shape consists of a plurality of regular basin-shaped saw teeth evenly distributed along the circumference of the cable core, the ratio of the basin top height to the basin bottom length of the basin-shaped saw teeth is 1:1, and each connection between the basin top and the basin bottom is an arc angle transition.

[0008] The charge elimination layer is made of polymethyl methacrylate, epoxy resin or silicone rubber.

[0009] The auxiliary dissipation layer is alkali-free glass cloth, and its wrapping overlap rate is 15-25%.

[0010] The charge dispersion layer is a cotton thread layer, and its weaving density is 80% to 85%.

[0011] The filling layer is made of filling strips or mesh filling ropes made of polypropylene material.

[0012] The sheath layer is one or a combination of a metal shielding layer, a metal armor layer, a PVC sheath layer, a PE sheath layer or a low-smoke halogen-free polyolefin sheath layer.

[0013] The conductor is a copper conductor, an aluminum conductor or an aluminum alloy conductor.

[0014] The inner insulating layer and the outer insulating layer are made of modified polypropylene insulating material; the modified polypropylene insulating material is made of the following components in parts by weight: 86-90 parts of polypropylene base material, 2-5 parts of antistatic agent, and 5-10 parts of maleic anhydride.

[0015] A method for preparing a 1.5 kV DC cable, the method comprising the following process steps:

[0016] S1. Make conductors;

[0017] S2. Extrude a layer of modified polypropylene insulation material on the outside of the conductor. The temperature of the feeding section of the extruder is set at 100-180℃, the compression section is set at 200-250℃, the homogenization section is set at 260-300℃, and the die head is heated to 300-350℃ using a mold temperature controller. The extrusion speed is 10-15 m / min, and the conductor is cooled by constant temperature hot water cooling, water cooling, and air cooling to form an inner insulation layer;

[0018] S3. Weaving a cotton thread layer outside the inner insulating layer, the cotton thread weaving density is controlled at 80% to 85%, to form the charge dispersion layer;

[0019] S4. Extrude a layer of modified polypropylene insulation material outside the charge dispersion layer. The temperature of the feeding section of the extruder is set at 100-180℃, the compression section is set at 200-250℃, the homogenization section is set at 260-300℃, and the die head is heated to 300-350℃ by a mold temperature controller. The extrusion speed is 10-15 m / min, and the outer insulation layer is formed by three cooling steps: constant temperature hot water cooling, water cooling, and air cooling;

[0020] S5. Extruding a charge elimination layer made of polymethyl methacrylate, epoxy resin or silicone rubber outside the outer insulating layer through a die having a cross-sectional shape of a plurality of regular basin-shaped saw teeth evenly distributed along the circumference of the cable core;

[0021] S6. Wrap a layer of wrapping tape around the charge elimination layer, the wrapping tape is made of alkali-free glass cloth, and the wrapping overlap rate is 15-25% to form an auxiliary charge elimination layer;

[0022] S7. The two strands of the cable core made by steps S1 to S6 are twisted according to a certain twist rate, and the outer core is filled with filler strips or mesh filler ropes to form a filling layer;

[0023] S8. A metal shielding layer, a metal armor layer, a PVC sheath layer, a PE sheath layer or a low-smoke halogen-free polyolefin sheath layer or a combination of these structures is coated on the outside of the filling layer to form a sheath layer.

[0024] The preparation method of the modified polypropylene insulating material in step S2 and the modified polypropylene insulating material in step S4 is as follows:

[0025] 1) First, 86-93 parts of polypropylene and 5-10 parts of maleic anhydride are mixed at a low speed, heated and stirred for 20-30 minutes, and the temperature is controlled at 120-150°C to react and prepare a polypropylene-maleic anhydride copolymer;

[0026] 2) Add 2-5 parts of antistatic agent in step 1) and mix at 90-110°C for 5-10 minutes; then mix in a plasticizer for about 30-35 minutes to plasticize into sheets;

[0027] 3) Put the plasticized flakes in step 2) into the mold at a temperature of 120-150°C and a pressure of 0.3-0.8Mpa. After 10-12 minutes, cool and take out the blanks, and crush them into pellets.

[0028] 4) The pellets crushed in step 3) are put into an extruder, the head temperature is controlled at 300-350° C., and are extruded outside the conductor and the charge dispersion layer.

[0029] The beneficial technical effects of the present invention are:

[0030] 1. The outer side surface of the basin-shaped sawtooth of the charge elimination layer of the present invention can reduce the normal component of the electric field intensity on the surface of the outer insulating layer, and effectively inhibit the surface charge accumulation of the outer insulating layer. The ratio of the height of the basin top to the length of the basin bottom of the basin-shaped sawtooth is used as a structure to minimize the normal component of the electric field intensity on the surface of the outer insulating layer, and reduce the surface charge accumulation as much as possible. At the same time, the inner insulating layer, charge dispersion layer, outer insulating layer, charge elimination layer and auxiliary elimination layer outside the conductor of the cable core are all made of materials with good insulating properties; its filling layer is also made of materials with good insulating properties to further improve the insulation effect. The use of this technical measure can effectively improve the insulation effect, extend the service life of the cable, ensure the long-term stable operation of the cable, and realize the reliable transmission of electric energy.

[0031] 2. The insulating layer of the present invention is designed as a double-layer structure, and a cotton thread layer woven with cotton threads is used between the inner insulating layer and the outer insulating layer as a charge dispersion layer, which can effectively prevent local charge accumulation.

[0032] 3. The charge elimination layer of the present invention is wrapped with an auxiliary elimination layer made of alkali-free glass cloth material, which cooperates with the charge elimination layer to eliminate charge accumulation.

[0033] 4. The charge elimination layer of the present invention is made of polymethyl methacrylate, epoxy resin or silicone rubber, which effectively improves the insulation capacity of the cable.

[0034] 5. The filling layer of the present invention is made of filling strips or mesh filling ropes made of polypropylene, which further effectively improves the insulation capacity of the cable.

[0035] 6. The inner insulating layer and the outer insulating layer of the present invention are made of modified polypropylene insulating material, which is a non-cross-linked material, environmentally friendly and reusable.

[0036] 7. The cable manufactured by the cable manufacturing process of the present invention has the technical advantages of simple structure, low manufacturing cost, good insulation effect, ability to prevent charge accumulation, strong ability to resist external electromagnetic interference, high compressive strength, high tensile strength, light weight, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A structural schematic diagram of the present invention;

[0038] Figure 2 It is a schematic diagram of a basin-shaped sawtooth 151 of the charge elimination layer 15;

[0039] The meaning of the codes in the figure are: 1—cable core; 11—conductor; 12—inner insulation layer; 13—charge dispersion layer; 14—outer insulation layer; 15—charge elimination layer; 151—basin-type serrations; 1511—basin top; 1512—basin bottom; 1513—arc angle; 16—auxiliary elimination layer; 2—sheath layer; 3—filling layer. DETAILED DESCRIPTION

[0040] The present invention relates to a cable, which is a 1.5kV DC cable. The main technical content of the present invention is described in detail with multiple embodiments. Figure 1 , Figure 2 The technical solution of the present invention is explained clearly and in detail.

[0041] It should be particularly noted that the drawings of the present invention are schematic, and unnecessary details have been simplified to clarify the technical purpose of the present invention so as to avoid blurring the technical solution that the present invention contributes to the prior art.

[0042] Example 1

[0043] like Figure 1 , Figure 2 As shown, a 1.5kV DC cable comprises two cable cores 1, a sheath layer 2, and a filling layer 3 filling the gap between the cable core 1 and the sheath layer 2. The filling layer 3 is made of a filling strip made of a material with good insulation performance, such as polypropylene. The sheath layer 2 is a metal shielding layer. The anti-interference ability of the cable can be improved by setting the metal shielding layer.

[0044] Specifically, the cable core 1 includes a conductor 11 , and an inner insulating layer 12 , a charge dispersion layer 13 , an outer insulating layer 14 , a charge elimination layer 15 and an auxiliary elimination layer 16 which are sequentially arranged outside the conductor 11 from the inside to the outside.

[0045] The conductor 11 is a copper conductor with good conductivity. In actual use, the conductor 11 can be a conductor made of other metal materials. For example, the conductor 11 is made of multiple copper wires, soft aluminum alloy wires or soft aluminum wires that are twisted together.

[0046] The inner insulating layer 12 and the outer insulating layer 14 are made of polypropylene insulating material with good insulation performance. In order to be reusable and reduce the impact on the environment, the existing polypropylene insulating material is modified. The modified polypropylene insulating material is made of the following components by mass: 86 parts of polypropylene base material, 4 parts of antistatic agent, and 10 parts of maleic anhydride. By adding the antistatic agent, the inner insulating layer 12 and the outer insulating layer 14 have a certain antistatic ability. By adding maleic anhydride, the tensile and impact strength of the filled polypropylene is improved, thereby increasing the tensile and impact strength of the inner insulating layer 12 and the outer insulating layer 14.

[0047] The preparation method of modified polypropylene insulation material is as follows:

[0048] 1) First, 86 parts of polypropylene and 10 parts of maleic anhydride were mixed at a low speed, heated and stirred for 20 to 30 minutes, and the temperature was controlled at 120 to 150°C to prepare a polypropylene-maleic anhydride copolymer;

[0049] 2) Add 4 parts of antistatic agent in step 1) and mix at 90-110°C for 5-10 minutes; then mix in a plasticizer for about 30-35 minutes to plasticize into sheets;

[0050] 3) Put the plasticized flakes in step 2) into the mold at a temperature of 120-150°C and a pressure of 0.3-0.8Mpa. After 10-12 minutes, cool and take out the blanks, and crush them into pellets.

[0051] 4) The pellets crushed in step 3) are put into an extruder, the die temperature is controlled at 300-350° C., and are extruded around the conductor 11 and the charge dispersion layer 3 .

[0052] The charge dispersion layer 13 is a cotton thread layer woven with cotton threads having good insulation performance, and its weaving density is 80%. The charge dispersion layer 13 is arranged between the inner insulating layer 12 and the outer insulating layer 14 as a charge dispersion layer, which can effectively prevent local charge accumulation.

[0053] The charge elimination layer 15 is made of polymethyl methacrylate with good insulation and weather resistance. It is extruded with the outer insulating layer 14 through a mold. Its cross-sectional shape is composed of a number of regular basin-shaped saw teeth 151 evenly distributed along the circumference of the cable core 1. The ratio of the height of the basin top 1511 of the basin-shaped saw teeth 151 to the length of the basin bottom 1512 is 1:1, and each connection between the basin top 1511 and the basin bottom 1512 is a transition of an arc angle 1513.

[0054] In actual use, the outer side of the basin-shaped sawtooth of the charge elimination layer 15 can reduce the normal component of the electric field intensity on the surface of the outer insulating layer 14, effectively inhibiting the surface charge accumulation of the outer insulating layer 14. The ratio of the height of the basin top 1511 to the length of the basin bottom 1512 of the basin-shaped sawtooth 151 is 1:1, so that the normal component of the electric field intensity on the surface of the outer insulating layer 14 is minimized, and the surface charge accumulation is reduced as much as possible.

[0055] The auxiliary elimination layer 16 is made of alkali-free glass cloth with good insulation, strong heat resistance and good corrosion resistance, and its wrapping overlap rate is 15%. The elimination layer adopts alkali-free glass cloth with high relative dielectric constant, which cooperates with the charge elimination layer 15 to eliminate charge accumulation. The inner insulation layer 12, charge dispersion layer 13, outer insulation layer 14, charge elimination layer 15 and auxiliary elimination layer 16 outside the conductor 11 of the present invention are all made of materials with good insulation performance; at the same time, the filling layer 3 is also made of materials with good insulation performance; the use of this technical measure can effectively improve the insulation effect, extend the service life of the cable, ensure the long-term stable operation of the cable, and realize the reliable transmission of electric energy; at the same time, through the charge dispersion layer 13, the charge elimination layer 15 and the auxiliary elimination layer 16, it can effectively prevent local charge accumulation, further ensure the long-term stable operation of the cable, and realize the reliable transmission of electric energy.

[0056] The 1.5kV DC cable preparation method includes the following process steps:

[0057] S1. Making conductor 11;

[0058] S2. Extrude a layer of modified polypropylene insulation material on the conductor 11, set the temperature of the feeding section of the extruder to 100-180°C, the compression section to 200-250°C, the homogenization section to 260-300°C, and heat the die head to 300-350°C using a mold temperature controller. Extrusion speed 10-15 m / min, after constant temperature hot water cooling, water cooling, air cooling 3 stages of cooling, to form an inner insulation layer 12;

[0059] S3. A cotton thread layer is woven outside the inner insulating layer 12, and the cotton thread weaving density is controlled at 80% to form a charge dispersion layer 13;

[0060] S4. Extruding a layer of modified polypropylene insulation material outside the charge dispersion layer 13, the feeding section of the extruder is set to a temperature of 100-180°C, the compression section is set to a temperature of 200-250°C, the homogenization section is set to a temperature of 260-300°C, and the die head is heated to 300-350°C using a mold temperature controller. The extrusion speed is 10-15 m / min, and the outer insulation layer 14 is formed by cooling in three stages: constant temperature hot water cooling, water cooling, and air cooling;

[0061] S5. A layer of charge elimination layer 15 of polymethyl methacrylate is extruded outside the outer insulating layer 14 through a die having a cross-sectional shape of several regular basin-shaped serrations 151 evenly distributed along the circumference of the cable core;

[0062] S6. A layer of wrapping tape is wrapped around the charge elimination layer 15, and the wrapping tape is made of alkali-free glass cloth, and the wrapping overlap rate is 15%, forming an auxiliary elimination layer 16;

[0063] S7. The two strands of the cable core 1 made by steps S1 to S6 are twisted according to a certain twist rate, and the outer cable core 1 is rounded with a filler strip to form a filling layer 3;

[0064] S8. Cover the filling layer 3 with a metal shielding layer to form a sheath layer 2.

[0065] The cables made using this process have the technical advantages of simple structure, low manufacturing cost, good insulation effect, ability to prevent charge accumulation, and strong ability to resist external electromagnetic interference.

[0066] The present invention can withstand the long-term operating voltage of a 1.5kV DC power transmission line, the industrial frequency AC voltage superimposed on the DC, the polarity reversal voltage generated by the voltage and current commutation in the system, the operating impulse voltage generated by the switching action, and the atmospheric overvoltage caused by lightning impulse, meet the electrical performance requirements for cable insulation, ensure the long-term stable operation of the cable, and realize the reliable transmission of electric energy.

[0067] Example 2

[0068] like Figure 1 , Figure 2 As shown, a 1.5kV DC cable comprises two cable cores 1, a sheath layer 2 and a filling layer 3 filling the gap between the cable core 1 and the sheath layer 2. In actual use, the cable core 1 can be one or more strands. The filling layer 3 is a mesh filling rope made of a material with good insulation performance, such as polypropylene. The sheath layer 2 adopts a metal armor layer. The metal armor layer not only strengthens the mechanical protection of the cable such as compressive strength and tensile strength, and increases the service life, but also has a certain resistance to external forces and can prevent animals from tearing. The bending radius of the metal armor layer should be large, and the metal armor layer can be grounded to protect the cable.

[0069] Specifically, the cable core 1 includes a conductor 11 , and an inner insulating layer 12 , a charge dispersion layer 13 , an outer insulating layer 14 , a charge elimination layer 15 and an auxiliary elimination layer 16 which are sequentially arranged outside the conductor 11 from the inside to the outside.

[0070] The conductor 11 is made of aluminum conductor with good conductivity and low cost. The inner insulating layer 12 and the outer insulating layer 14 are made of polypropylene insulating material with good insulation performance. In order to be reusable and reduce the impact on the environment, the existing polypropylene insulating material is modified. The modified polypropylene insulating material is made of the following components by mass: 89 parts of polypropylene base material, 5 parts of antistatic agent, and 6 parts of maleic anhydride. By adding the antistatic agent, the inner insulating layer 12 and the outer insulating layer 14 have a certain antistatic ability.

[0071] The preparation method of modified polypropylene insulation material is as follows:

[0072] 1) First, 89 parts by weight of polypropylene and 6 parts by weight of maleic anhydride are mixed at a low speed, heated and stirred for 20 to 30 minutes, and the temperature is controlled at 120 to 150° C. to react and prepare a polypropylene-maleic anhydride copolymer;

[0073] 2) Add 5 parts by weight of antistatic agent in step 1) and mix at 90-110°C for 5-10 minutes; then mix in a plasticizer for about 30-35 minutes to plasticize into sheets;

[0074] 3) Put the plasticized flakes in step 2) into the mold at a temperature of 120-150°C and a pressure of 0.3-0.8Mpa. After 10-12 minutes, cool and take out the blanks, and crush them into pellets.

[0075] 4) The pellets crushed in step 3) are put into an extruder, the die temperature is controlled at 300-350° C., and are extruded around the conductor 11 and the charge dispersion layer 13 .

[0076] The charge dispersion layer 13 is a cotton thread layer woven with cotton threads having good insulation performance, and its weaving density is 83%. The charge dispersion layer 13 is arranged between the inner insulating layer 12 and the outer insulating layer 14 as a charge dispersion layer, which can effectively prevent local charge accumulation.

[0077] The charge elimination layer 15 is made of a material having excellent chemical resistance, especially alkali resistance, heat resistance and insulation.

[0078] It is made of epoxy resin and is extruded with an outer insulating layer 14 through a mold. Its cross-sectional shape is composed of a number of regular basin-shaped serrations 151 evenly distributed along the circumference of the cable core 1. The ratio of the height of the basin top 1511 of the basin-shaped serration 151 to the length of the basin bottom 1512 is 1:1, and each connection between the basin top 1511 and the basin bottom 1512 is a transition of an arc angle 1513.

[0079] In actual use, the outer side of the basin-shaped sawtooth of the charge elimination layer 15 can reduce the normal component of the electric field intensity on the surface of the outer insulating layer 14, effectively inhibiting the surface charge accumulation of the outer insulating layer 14. The ratio of the height of the basin top 1511 to the length of the basin bottom 1512 of the basin-shaped sawtooth 151 is 1:1, so that the normal component of the electric field intensity on the surface of the outer insulating layer 14 is minimized, and the surface charge accumulation is reduced as much as possible.

[0080] The auxiliary elimination layer 16 is made of alkali-free glass cloth with good insulation, strong heat resistance and good corrosion resistance, and its wrapping overlap rate is 20%. The elimination layer adopts alkali-free glass cloth with high relative dielectric constant, which cooperates with the charge elimination layer 15 to eliminate charge accumulation. The inner insulation layer 12, charge dispersion layer 13, outer insulation layer 14, charge elimination layer 15 and auxiliary elimination layer 16 outside the conductor 11 of the present invention are all made of materials with good insulation performance; at the same time, the filling layer 3 is made of materials with good insulation performance; the adoption of this technical measure can effectively improve the insulation effect, extend the service life of the cable, ensure the long-term stable operation of the cable, and realize the reliable transmission of electric energy; at the same time, through the charge dispersion layer 13, the charge elimination layer 15 and the auxiliary elimination layer 16, it can effectively prevent local charge accumulation, further ensure the long-term stable operation of the cable, and realize the reliable transmission of electric energy.

[0081] The 1.5kV DC cable preparation method includes the following process steps:

[0082] S1. Making conductor 11;

[0083] S2. Extrude a layer of modified polypropylene insulation material on the conductor 11, set the temperature of the feeding section of the extruder to 100-180°C, the compression section to 200-250°C, the homogenization section to 260-300°C, and heat the die head to 300-350°C using a mold temperature controller. Extrusion speed 10-15 m / min, after constant temperature hot water cooling, water cooling, air cooling 3 stages of cooling, to form an inner insulation layer 12;

[0084] S3. A cotton thread layer is woven outside the inner insulating layer 12, and the cotton thread weaving density is controlled at 83% to form a charge dispersion layer 13;

[0085] S4. Extruding a layer of modified polypropylene insulation material outside the charge dispersion layer 13, the feeding section of the extruder is set to a temperature of 100-180°C, the compression section is set to a temperature of 200-250°C, the homogenization section is set to a temperature of 260-300°C, and the die head is heated to 300-350°C using a mold temperature controller. The extrusion speed is 10-15 m / min, and the outer insulation layer 14 is formed by cooling in three stages: constant temperature hot water cooling, water cooling, and air cooling;

[0086] S5. A charge elimination layer 15 of epoxy resin is extruded outside the outer insulating layer 14 through a die having a cross-sectional shape of several regular basin-shaped serrations 151 evenly distributed along the circumference of the cable core (1);

[0087] S6. A layer of wrapping tape is wrapped around the charge elimination layer 15, and the wrapping tape is made of alkali-free glass cloth, and the wrapping overlap rate is 20%, forming an auxiliary elimination layer 16;

[0088] S7. The two strands of the cable core 1 made by steps S1 to S6 are twisted according to a certain twist rate, and the outer cable core 1 is filled with a mesh filling rope to form a filling layer 3;

[0089] S8. Wrap a metal armor layer outside the filling layer 3 to form a sheath layer 2.

[0090] The cable made by this process has the technical advantages of simple structure, low manufacturing cost, good insulation effect, high compressive strength and high tensile strength. At the same time, in addition to increasing the service life, it effectively improves the scope of use.

[0091] The present invention can withstand the long-term operating voltage of a 1.5kV DC power transmission line, the industrial frequency AC voltage superimposed on the DC, the polarity reversal voltage generated by the voltage and current commutation in the system, the operating impulse voltage generated by the switching action, and the atmospheric overvoltage caused by lightning impulse, meet the electrical performance requirements for cable insulation, ensure the long-term stable operation of the cable, and realize the reliable transmission of electric energy.

[0092] Example 3

[0093] like Figure 1 , Figure 2 As shown, a 1.5kV DC cable comprises two cable cores 1, a sheath layer 2, and a filling layer 3 filling the gap between the cable core 1 and the sheath layer 2. The filling layer 3 is a mesh filling rope made of a material with good insulation performance, such as polypropylene. The sheath layer 2 is made of one or a combination of PVC, PE or low-smoke halogen-free polyolefin. Specifically, the sheath layer 2 can be a PVC sheath layer, a PE sheath layer or a low-smoke halogen-free polyolefin sheath layer. The sheath layer 2 is made of non-metallic materials such as PVC, PE or low-smoke halogen-free polyolefin, and has the advantages of light weight and good insulation effect.

[0094] Specifically, the cable core 1 includes a conductor 11 , and an inner insulating layer 12 , a charge dispersion layer 13 , an outer insulating layer 14 , a charge elimination layer 15 and an auxiliary elimination layer 16 which are sequentially arranged outside the conductor 11 from the inside to the outside.

[0095] The conductor 11 is made of an aluminum alloy conductor with good corrosion resistance, tensile strength, elongation and bending performance. The inner insulating layer 12 and the outer insulating layer 14 are made of polypropylene insulating material with good insulation performance. In order to be reusable and reduce the impact on the environment, the existing polypropylene insulating material is modified. The modified polypropylene insulating material is made of the following mass parts: 93 parts of polypropylene base material, 2 parts of antistatic agent, and 5 parts of maleic anhydride. By adding the antistatic agent, the inner insulating layer 12 and the outer insulating layer 14 have a certain antistatic ability.

[0096] The preparation method of modified polypropylene insulation material is as follows:

[0097] 1) First, 93 parts by weight of polypropylene and 5 parts by weight of maleic anhydride are mixed at a low speed, heated and stirred for 20 to 30 minutes, and the temperature is controlled at 120 to 150° C. to react and prepare a polypropylene-maleic anhydride copolymer;

[0098] 2) Add 2 parts by weight of antistatic agent in step 1) and mix at 90-110°C for 5-10 minutes; then mix in a plasticizer for about 30-35 minutes to plasticize into sheets;

[0099] 3) Put the plasticized flakes in step 2) into the mold at a temperature of 120-150°C and a pressure of 0.3-0.8Mpa. After 10-12 minutes, cool and take out the blanks, and crush them into pellets.

[0100] 4) The pellets crushed in step 3) are put into an extruder, the die temperature is controlled at 300-350° C., and are extruded around the conductor 11 and the charge dispersion layer 13 .

[0101] The charge dispersion layer 13 is a cotton thread layer woven with cotton threads having good insulation performance, and its weaving density is 85%. The charge dispersion layer 13 is arranged between the inner insulating layer 12 and the outer insulating layer 14 as a charge dispersion layer, which can effectively prevent local charge accumulation.

[0102] The charge elimination layer 15 is made of silicone rubber that is resistant to high and low temperatures and has good insulation performance. It is extruded with the outer insulating layer 14 through a mold. Its cross-sectional shape is composed of a number of regular basin-shaped saw teeth 151 evenly distributed along the circumference of the cable core 1. The ratio of the height of the basin top 1511 of the basin-shaped saw teeth 151 to the length of the basin bottom 1512 is 1:1, and each connection between the basin top 1511 and the basin bottom 1512 is a transition of an arc angle 1513.

[0103] In actual use, the outer side of the basin-shaped sawtooth of the charge elimination layer 15 can reduce the normal component of the electric field intensity on the surface of the outer insulating layer 14, effectively inhibiting the surface charge accumulation of the outer insulating layer 14. The ratio of the height of the basin top 1511 to the length of the basin bottom 1512 of the basin-shaped sawtooth 151 is 1:1, so that the normal component of the electric field intensity on the surface of the outer insulating layer 14 is minimized, and the surface charge accumulation is reduced as much as possible.

[0104] The auxiliary elimination layer 16 is made of alkali-free glass cloth with good insulation, strong heat resistance and good corrosion resistance, and its wrapping overlap rate is 25%. The elimination layer adopts alkali-free glass cloth with high relative dielectric constant, which cooperates with the charge elimination layer 15 to eliminate charge accumulation. The inner insulation layer 12, charge dispersion layer 13, outer insulation layer 14, charge elimination layer 15 and auxiliary elimination layer 16 outside the conductor 11 of the present invention are all made of materials with good insulation performance; at the same time, the filling layer 3 is made of materials with good insulation performance; the use of this technical measure can effectively improve the insulation effect and extend the service life of the cable. At the same time, the charge dispersion layer 13, charge elimination layer 15 and auxiliary elimination layer 16 can effectively prevent local charge accumulation.

[0105] The 1.5kV DC cable preparation method includes the following process steps:

[0106] S1. Making conductor 11;

[0107] S2. Extrude a layer of modified polypropylene insulation material on the conductor 11, set the temperature of the feeding section of the extruder to 100-180°C, the compression section to 200-250°C, the homogenization section to 260-300°C, and heat the die head to 300-350°C using a mold temperature controller. Extrusion speed 10-15 m / min, after constant temperature hot water cooling, water cooling, air cooling 3 stages of cooling, to form an inner insulation layer 12;

[0108] S3. A cotton thread layer is woven outside the inner insulating layer 12, and the cotton thread weaving density is controlled at 85% to form a charge dispersion layer 13;

[0109] S4. Extruding a layer of modified polypropylene insulation material outside the charge dispersion layer 13, the feeding section of the extruder is set to a temperature of 100-180°C, the compression section is set to a temperature of 200-250°C, the homogenization section is set to a temperature of 260-300°C, and the die head is heated to 300-350°C using a mold temperature controller. The extrusion speed is 10-15 m / min, and the outer insulation layer 14 is formed by cooling in three stages: constant temperature hot water cooling, water cooling, and air cooling;

[0110] S5. A charge elimination layer 15 of silicone rubber is extruded outside the outer insulating layer 14 through a mold having a cross-sectional shape of a plurality of regular basin-shaped saw teeth 151 evenly distributed along the circumference of the cable core (1);

[0111] S6. A layer of wrapping tape is wrapped around the charge elimination layer 15, and the wrapping tape is made of alkali-free glass cloth, and the wrapping overlap rate is 25%, forming an auxiliary elimination layer 16;

[0112] S7. The two strands of the cable core 1 made by steps S1 to S6 are twisted according to a certain twisting rate, and the outer surface of the cable core 1 is filled with a mesh filling rope to form a filling layer 3;

[0113] S8. Cover the filling layer 3 with one or a combination of a PVC sheath layer, a PE sheath layer or a low-smoke halogen-free polyolefin sheath layer to form a sheath layer 2.

[0114] The cable made by this process has the advantages of simple structure, low manufacturing cost, good insulation effect, light weight and good insulation effect.

[0115] The present invention can withstand the long-term operating voltage of a 1.5kV DC power transmission line, the industrial frequency AC voltage superimposed on the DC, the polarity reversal voltage generated by the voltage and current commutation in the system, the operating impulse voltage generated by the switching action, and the atmospheric overvoltage caused by lightning impulse, meet the electrical performance requirements for cable insulation, ensure the long-term stable operation of the cable, and realize the reliable transmission of electric energy.

[0116] Example 4

[0117] The other contents of this embodiment are the same as those of Embodiment 1, except that the sheath layer 2 is a composite structure of a metal shielding layer and a non-metallic layer. Specifically, the sheath layer 2 is a composite structure of a copper tape shielding layer and a halogen-free, low-smoke, flame-retardant polyolefin sheath layer. The overlap rate of the copper tape shielding layer is controlled at 15-25%. By providing a copper tape shielding layer, the ability to resist external electromagnetic interference can be improved, and the electromagnetic field generated by itself during use can be prevented from interfering with the surrounding environment and causing fault currents. The use of this technical measure can further improve the insulation effect and anti-electromagnetic interference ability of the cable. It can meet the electrical performance requirements for cable insulation, ensure the long-term stable operation of the cable, and realize the reliable transmission of electric energy.

[0118] The above embodiments are only used to illustrate the present invention, but not to limit it. Although the present invention is described in detail with reference to the above embodiments, it should be understood by those skilled in the art that the above embodiments can still be modified, or some of the technical features thereof can be replaced by equivalents, and these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the present invention.

Claims

1. A 1.5kV DC cable, characterized in that: It comprises a single-strand or multi-strand cable core (1), a sheath layer (2), and a filling layer (3) filling the gap between the cable core (1) and the sheath layer (2); The cable core (1) comprises a conductor (11), and an inner insulating layer (12), a charge dispersion layer (13), an outer insulating layer (14), a charge elimination layer (15), and an auxiliary elimination layer (16) which are arranged outside the conductor (11) in order from the inside to the outside; The charge elimination layer (15) is extruded outside the outer insulating layer (14), and its cross-sectional shape is composed of a plurality of regular basin-shaped saw teeth (151) evenly distributed along the circumference of the cable core (1), the ratio of the height of the basin top (1511) to the length of the basin bottom (1512) of the basin-shaped saw teeth (151) is 1:1, and each connection between the basin top (1511) and the basin bottom (1512) is a transition of an arc angle (1513); The charge elimination layer (15) is made of polymethyl methacrylate, epoxy resin or silicone rubber; The auxiliary dissipation layer (16) is an alkali-free glass cloth, and its wrapping overlap rate is 15-25%; The charge dispersion layer (13) is a cotton thread layer, and its weaving density is 80% to 85%.

2. The 1.5 kV DC cable according to claim 1, characterized in that: The filling layer (3) is made of filling strips or mesh filling ropes made of polypropylene.

3. The 1.5 kV DC cable according to claim 1, characterized in that: The sheath layer (2) is one or a combination of a metal shielding layer, a metal armor layer, a PVC sheath layer, a PE sheath layer or a low-smoke halogen-free polyolefin sheath layer.

4. The 1.5 kV DC cable according to claim 1, characterized in that: The conductor (11) is a copper conductor, an aluminum conductor or an aluminum alloy conductor.

5. The 1.5 kV DC cable according to claim 1, characterized in that: The inner insulating layer (12) and the outer insulating layer (14) are made of modified polypropylene insulating material; the modified polypropylene insulating material is made of the following components in parts by mass: 86-90 parts of polypropylene base material, 2-5 parts of antistatic agent, and 5-10 parts of maleic anhydride.

6. A method for preparing a 1.5 kV DC cable according to any one of claims 1 to 5, characterized in that: The preparation method comprises the following process steps: S1. Make a conductor (11); S2. A layer of modified polypropylene insulation material is extruded outside the conductor (11), the feeding section of the extruder is set to a temperature of 100-180°C, the compression section is set to a temperature of 200-250°C, the homogenization section is set to a temperature of 260-300°C, and the die head is heated to 300-350°C using a mold temperature controller; The extrusion speed is 10-15 m / min, and the inner insulation layer (12) is formed by three cooling steps: constant temperature hot water cooling, water cooling, and air cooling; S3. Weaving a cotton thread layer outside the inner insulating layer (12), wherein the cotton thread weaving density is controlled at 80% to 85%, to form the charge dispersion layer (13); S4. A layer of modified polypropylene insulating material is extruded outside the charge dispersion layer (13), the feeding section of the extruder is set to a temperature of 100-180 ℃, the compression section is set to a temperature of 200-250 ℃, the homogenization section is set to a temperature of 260-300 ℃, and the die head is heated to 300-350 ℃ by a mold temperature controller; The extrusion speed is 10-15 m / min, and the cooling is performed through three stages of constant temperature hot water cooling, water cooling, and air cooling to form an outer insulating layer (14); S5. Extruding a charge elimination layer (15) made of polymethyl methacrylate, epoxy resin or silicone rubber outside the outer insulating layer (14) through a die having a cross-sectional shape of a plurality of regular basin-shaped saw teeth (151) evenly distributed along the circumference of the cable core (1); S6. Wrapping a layer of wrapping tape around the charge elimination layer (15), the wrapping tape is made of alkali-free glass cloth, and the wrapping overlap rate is 15 to 25%, forming an auxiliary elimination layer (16); S7. The two strands of the cable core (1) prepared in steps S1 to S6 are twisted at a certain twist rate, and the cable core (1) is rounded with a filler strip or a mesh filler rope to form a filling layer (3); S8. A metal shielding layer, a metal armor layer, a PVC sheath layer, a PE sheath layer or a low-smoke halogen-free polyolefin sheath layer or a combination of these is coated on the outside of the filling layer (3) to form a sheath layer (2).

7. The method for preparing a 1.5 kV DC cable according to claim 6, characterized in that: The preparation method of the modified polypropylene insulating material in step S2 and the modified polypropylene insulating material in step S4 is as follows: 1) First, 86-93 parts of polypropylene and 5-10 parts of maleic anhydride are mixed at a low speed, heated and stirred for 20-30 minutes, and the temperature is controlled at 120-150°C to react and prepare a polypropylene-maleic anhydride copolymer; 2) Add 2-5 parts of antistatic agent in step 1) and mix at 90-110°C for 5-10 minutes; then mix in a plasticizer for about 30-35 minutes to plasticize into sheets; 3) Put the plasticized flakes in step 2) into the mold at a temperature of 120-150°C and a pressure of 0.3-0.8Mpa. After 10-12 minutes, cool and take out the blanks, and crush them into pellets. 4) The pellets crushed in step 3) are fed into an extruder, the die temperature is controlled at 300-350° C., and extruded outside the conductor (11) and the charge dispersion layer (13).

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