Method for manufacturing high-voltage cable and high-voltage cable manufactured thereby

Abstract

The present invention relates to a method for manufacturing a high-voltage cable. The method for manufacturing a high-voltage cable comprises the steps of: (a) introducing a cable into a vulcanization tube, the cable being extrusion-coated with an insulation layer to which a crosslinking agent has been added; (b) performing a crosslinking process on the insulating layer by increasing the temperature of the front end of the vulcanization tube into which the cable is introduced, and adjusting the speed at which the cable passes through the vulcanization tube; and (c) degassing crosslinking by-products resulting from the crosslinking process at the rear end of the vulcanization tube.

Description

Method for manufacturing high-voltage cables and high-voltage cables manufactured according to the same

[0001] The present invention relates to a method for manufacturing a high-voltage cable and a high-voltage cable manufactured according to the same. More specifically, the present invention relates to a method for manufacturing a high-voltage cable capable of improving the electrical characteristics of the cable and improving production and manufacturing efficiency, and a high-voltage cable manufactured according to the same.

[0002]

[0003] Recently, due to high power demand, the demand for high-voltage cables of approximately 66kV or higher is increasing, and cables with thicker insulation layers than medium-voltage cables are required to transmit a larger amount of power and operate at high temperatures.

[0004] Meanwhile, cross-linked polyethylene (XLPE) is used as a resin in the insulation layer of high-voltage cables. Cross-linked polyethylene is a mixture of polyethylene (PE) to which organic hydrogen peroxide is added, and cross-linking proceeds through a chemical reaction caused by heat. Cross-linked polyethylene possesses thermosetting and viscoelastic properties, allowing it to be used as an insulator. However, cross-linking byproducts generated after the cross-linking reaction have a negative effect on the electrical properties of the insulator, so they are released through a degassing process.

[0005] High-voltage cables require a lengthy degassing process because the thick insulation layer makes it difficult to release internal cross-linking byproducts, which leads to reduced productivity. To increase productivity, wire manufacturers are producing cables at higher speeds than before.

[0006] Meanwhile, concentric bands may form in the insulation layer depending on the crosslinking process, and an average degassing time of more than 12 days is required to remove the concentric bands, which significantly reduces the production efficiency of high-voltage cables.

[0007] It is known that the halo phenomenon, in which concentric bands are formed, occurs when cumyl alcohol, one of the byproducts of crosslinking, decomposes into α-methyl styrene and water when subjected to high heat, and abnormal bands can form due to the water generated at that time; however, the clear reason for the formation of concentric bands within the insulator has not yet been confirmed.

[0008] Therefore, it is urgent to develop a method for manufacturing high-voltage cables that can reduce the degassing process by maintaining the crosslinking degree at a standard value while preventing concentric bands from forming on the insulation layer during the crosslinking process.

[0009] Korean Patent No. 10-2082674 is disclosed as background technology for the present invention.

[0010]

[0011] The objective of the present invention is to provide a method for manufacturing a high-voltage cable that can improve the electrical characteristics of the cable and improve production and manufacturing efficiency.

[0012] The above and other objectives of the present invention can all be achieved by the present invention described below.

[0013]

[0014] 1. One aspect of the present invention relates to a method for manufacturing a high-voltage cable comprising an insulating layer in which a round band is not formed on the insulating layer.

[0015] The above method for manufacturing a high-voltage cable comprises: (a) a step of introducing a cable extruded with an insulating layer to which a crosslinking agent has been added into a vulcanization tube;

[0016] (b) a step of increasing the temperature of the leading portion of the vulcanization tube into which the cable is introduced to perform a crosslinking process in the insulating layer and controlling the speed at which the cable passes through the vulcanization tube; and

[0017] (c) a step of degassing a portion of the crosslinking byproduct resulting from the crosslinking process at the rear end of the vulcanization tube; includes.

[0018] 2. In the above 1 embodiment, the temperature of the vulcanization tube shear section is about 390 to 600°C, and the surface temperature of the insulator may be about 400°C or lower.

[0019] 3. In the above 1 or 2 embodiments, the overall temperature distribution of the vulcanization tube can be determined according to the following Equation 1.

[0020] [Equation 1]

[0021] Ta > Tb

[0022] In the above Equation 1, Ta is the temperature at the front end of the vulcanization tube, and Tb is the temperature at the rear end of the vulcanization tube.

[0023] 4. In any one of the embodiments 1 to 3 above, the overall temperature distribution of the vulcanization tube can be controlled according to the surface temperature of the insulating layer and the degree of crosslinking.

[0024] 5. In any one of the embodiments 1 to 4 above, the crosslinking process in (b) above maintains the degree of crosslinking of the insulating layer within a certain range, and the range of the hot-set may be about 80 to 85%.

[0025] 6. In any one of the embodiments 1 to 5 above, the crosslinking byproduct removed in (c) above may be methane.

[0026] 7. In any one of the 6 embodiments of 1 to 6 above, the concentration of methane degassed in (c) may be about 200 ppm or less.

[0027] 8. In any one of the embodiments of 1 to 7 above, the step of forming a conductor and an internal semiconducting layer in the center of the cable prior to (a) may be further included.

[0028] 9. In any one of the embodiments 1 to 8 above, the method may further include the step of forming an outer semiconducting layer surrounding the insulating layer and forming a sheath layer surrounding the outer semiconducting layer after (c).

[0029] 10. In any one of the embodiments 1 to 9 above, the insulating layer may comprise cross-linked polyethylene (XLPE).

[0030] 11. Another aspect of the present invention provides a high-voltage cable manufactured by the high-voltage cable manufacturing method described above.

[0031]

[0032] According to the high-voltage cable manufacturing method of the present invention, by preventing the occurrence of round bands caused by crosslinking by-products in the insulation layer of a high-voltage cable of 66 kV or higher, the degassing time after forming the insulation layer can be reduced, thereby significantly increasing the manufacturing efficiency of the high-voltage cable.

[0033] The high-voltage cable manufactured according to the present invention has the round band formed in the insulation layer removed, which not only increases cable production and manufacturing efficiency but also significantly improves electrical characteristics, and prevents insulation breakdown that may occur during underground laying, thereby ensuring long-term durability.

[0034]

[0035] FIG. 1 is a process flowchart of a method for manufacturing a high-voltage cable according to one embodiment of the present invention.

[0036] FIG. 2 is a cross-sectional view of a high-voltage cable according to one embodiment of the present invention.

[0037] FIG. 3 is a graph showing the temperature profile of a cure tube in a method for manufacturing a high-voltage cable according to one embodiment of the present invention.

[0038]

[0039] The present invention will be described in more detail below with reference to the attached drawings. However, the following drawings are provided merely to aid in understanding the present invention, and the present invention is not limited by the drawings. Furthermore, the shapes, sizes, ratios, angles, numbers, etc. disclosed in the drawings are exemplary, and the present invention is not limited to the depicted details.

[0040] Throughout the specification, the same reference numerals refer to the same components. Additionally, in describing the present invention, detailed descriptions of related prior art are omitted if it is determined that such detailed descriptions would unnecessarily obscure the essence of the invention.

[0041] Where terms such as 'includes,' 'have,' and 'consists of' are used in this specification, other parts may be added unless 'only' is used. Where a component is expressed in the singular, it includes cases where it includes the plural unless specifically stated otherwise.

[0042] In interpreting the components, they are interpreted to include a margin of error even in the absence of a separate explicit statement.

[0043] In this specification, "a to b" indicating a numerical range is defined as "≥a and ≤b".

[0044] In this specification, all numerical ranges include a 95% standard error range.

[0045]

[0046] The inventors confirmed that when cross-linked polyethylene (XLPE) is formed as an insulation layer in the process of forming an insulation layer for high-voltage cables of 66 kV or higher, if a white band known as the halo phenomenon is formed within the insulation layer, the time required for the degassing process increases, thereby reducing the efficiency of the high-voltage cable production process. During research to prevent this halo phenomenon and increase the manufacturing efficiency of high-voltage cables, they confirmed that methane, not cumyl alcohol, is the direct cause of the halo phenomenon among the cross-linking byproducts of the cross-linking process. Conventionally, the crosslinking process is performed by lowering the temperature of the vulcanizing tube as much as possible to prevent the generation of water due to cumyl alcohol. However, when producing high-voltage cables at high line speeds, it was confirmed that the crosslinking temperature of the front end of the vulcanizing tube is increased to induce the crosslinking reaction to start as quickly as possible at the front end of the vulcanizing tube, thereby preventing the formation of a round band within the insulation layer by maximally removing methane from the crosslinking byproducts at the rear end of the vulcanizing tube. Additionally, it was confirmed that the degassing time, which is typically 17 days or more, can be reduced to within 7 days, thereby completing the present invention.

[0047] The present invention may include a method for forming a high-voltage cable insulation layer.

[0048] The above method for forming an insulation layer of a high-voltage cable is a method for forming an insulation layer of a high-voltage cable, wherein the formation of crosslinking by-products is suppressed by controlling the crosslinking temperature of the vulcanizing tube during the insulation layer crosslinking process through the vulcanizing tube, thereby preventing a halo phenomenon in the insulation layer.

[0049] The above method for forming a high-voltage cable insulation layer selects cross-linked polyethylene (hereinafter 'XLPE') as the insulation layer and, by controlling the cross-linking temperature of the vulcanizing tube during the cross-linking process of the insulation layer through the vulcanizing tube, can degas the cross-linking by-products, thereby preventing the formation of a halo phenomenon in the insulation layer caused by cross-linking by-products.

[0050] The above-mentioned halo phenomenon may be the formation of concentric white bands in some parts of the insulation layer during the degassing process of the vulcanization tube, and in particular, may be the formation of concentric round bands in high-voltage cables using cross-linked polyethylene as the insulation layer.

[0051] Since the aforementioned halo phenomenon reduces the electrical properties of the insulating layer and, in particular, can induce dielectric breakdown of the insulating layer, a sufficient degassing process is required after the formation of the insulating layer to prevent the halo phenomenon from occurring.

[0052] The above white band may include pores with an average diameter of 1 to 3 μm.

[0053] The above white band contains pores within the above range, and if pores within the above range are formed, they are abnormal pores that adversely affect the electrical properties of the insulating layer, so they need to be removed.

[0054] The above insulating layer may include cross-linked polyethylene (XLPE).

[0055] The above insulation layer may be XLPE, which is mainly selected as an insulation layer for high-voltage cables of about 66 kV or higher. The XLPE is a polyethylene mixture with added organic hydrogen peroxide that is cross-linked by a chemical reaction caused by heat, and it exhibits thermosetting viscoelasticity and can be used as an insulation layer for high-voltage cables, but cross-linking by-products are generated during the cross-linking process, which may reduce the electrical properties of the insulation layer.

[0056] The above-mentioned crosslinking byproduct may be methane.

[0057] For example, the crosslinking byproduct may include one or more of acetophenone, cumyl alcohol, α-methylstyrene, and methane.

[0058] Conventional halo phenomena are influenced by the formation of the crosslinking byproducts, and in particular, when cumyl alcohol is subjected to high heat, it decomposes into alpha-methylstyrene and water, and it is known that an abnormal white band is formed by the water produced at this time. However, the method for forming an insulating layer according to the embodiment of the present invention can prevent the occurrence of halo phenomena in an insulating layer formed of XLPE by controlling the content of methane rather than cumyl alcohol.

[0059] The above method for forming an insulating layer can effectively prevent the occurrence of a halo phenomenon in the insulating layer by controlling the temperature of the vulcanization tube during the insulating layer crosslinking process through the vulcanization tube to remove methane among the crosslinking byproducts.

[0060]

[0061] One aspect of the present invention relates to a method for manufacturing a high-voltage cable comprising an insulating layer in which a white band is not formed on the insulating layer.

[0062] FIG. 1 is a process flowchart of a method for manufacturing a high-voltage cable according to one embodiment of the present invention.

[0063] Referring to FIG. 1, the method for manufacturing a high-voltage cable comprises: (a) introducing a cable extruded with an insulating layer to which a crosslinking agent is added into a vulcanization tube;

[0064] (b) a step of increasing the temperature of the shear section in the vulcanization tube into which the cable is introduced to perform a crosslinking process in the insulation layer and controlling the speed at which the cable passes through the vulcanization tube; and

[0065] (c) a step of degassing a portion of the crosslinking byproduct resulting from the crosslinking process at the rear end of the vulcanization tube;

[0066] First, a cable with an extruded insulating layer containing a crosslinking agent is introduced into a vulcanization tube (S100).

[0067] A method for manufacturing a high-voltage cable according to one embodiment of the present invention includes a chemical crosslinking process in which a cable extruded with an insulating layer to which a crosslinking agent has been added is passed through a high-temperature vulcanization tube to crosslink the polymer constituting the insulating layer.

[0068] In the above insulating layer, the crosslinking agent induces crosslinking of polyethylene.

[0069] The above XLPE may include one or more of acetophenone, cumyl alcohol, α-methyl styrene, and methane in the crosslinking process.

[0070] Among the above crosslinking by-products, methane can cause a halo phenomenon in which concentric circular bands are formed in the insulation layer.

[0071] In one embodiment, the step of forming a conductor and an internal semiconducting layer in the center prior to S100 may be further included.

[0072] The above method for manufacturing a high-voltage cable can be performed in a continuous cross-linking device, for example, by winding the conductor at a constant speed from a first bobbin on which the conductor is wound and supplying it to an extruder. At this time, an internal semiconducting layer surrounding the conductor can be formed.

[0073] Polyethylene with a crosslinking agent added is continuously extruded from the above extruder, and a coated cable including an insulation layer can be introduced into a cure tube.

[0074] The temperature of the shear section in the vulcanization tube into which the above cable is introduced is increased to perform a cross-linking process in the insulation layer, and the passing speed of the cable vulcanization tube can be controlled (S200).

[0075] The continuous cross-linking device includes a second bobbin that maintains the tension of the cable and winds it at a constant speed, and the second bobbin can control the speed at which the cable passes through the vulcanization tube by winding the cable at a constant speed.

[0076] In this case, if the cable passes through the vulcanization tube at a very slow speed, no crosslinking byproducts are formed during the crosslinking process; however, if the cable's line speed is increased to increase the speed of passage through the vulcanization tube, the crosslinking process proceeds to the rear end of the vulcanization tube, and the generated crosslinking byproducts remain inside the vulcanization tube, making it difficult to effectively remove the crosslinking byproducts.

[0077] When the temperature of the front section of the vulcanization tube is increased to perform the crosslinking process in the insulation layer, the crosslinking process occurs as much as possible at the front section of the vulcanization tube, allowing the crosslinking byproducts to be sufficiently degassed at the rear section of the vulcanization tube.

[0078] In one embodiment, the temperature of the shear section of the vulcanization tube may be about 400 to 600°C (e.g., 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500, 510, 520, 530, 540, 550, 560, 570, 580, 590, or 600°C).

[0079] The above vulcanization tube can induce a cross-linking reaction by applying heat to the insulator, and can control the temperature of the front portion of the vulcanization tube to within the above range by increasing the temperature.

[0080] At this time, the surface temperature of the insulating layer may be about 400°C or lower, and preferably about 390°C or lower (e.g., 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, or 390°C).

[0081] By determining the temperature of the leading portion of the vulcanization tube within the above range, the cable flux within the vulcanization tube can be increased to increase manufacturing and production efficiency, and cross-linking can be induced at the leading portion of the vulcanization tube to allow cross-linking to be initiated rapidly.

[0082] Typically, the temperature of the vulcanization tube forming XLPE as an insulating layer is limited to about 370°C, but in the embodiment of the present invention, the temperature of the vulcanization tube front section is set to about 390°C to increase the vulcanization tube temperature by more than 10°C, thereby allowing the cross-linking reaction to be initiated rapidly at the vulcanization tube front section.

[0083] In the temperature range of the shear section of the vulcanization tube above, the surface temperature of the insulating layer can be controlled to within about 400°C to prevent deformation of the insulating layer. The surface temperature of the insulating layer is determined to be within about 400°C, and, for example, can be determined by considering the thermal decomposition temperature of EBA included in the semiconducting layer, about 410 to 450°C (e.g., 410, 420, 430, or 450°C).

[0084] The above vulcanization tube performs the cross-linking reaction of the insulation layer, and when the line speed, which is the cable production speed, increases, complete cross-linking must be performed during the process of passing through the vulcanization tube.

[0085] Since the above cross-linking reaction is proportional to the temperature of the vulcanization tube and the passage time, the temperature of the vulcanization tube increases when the line flux increases. However, if the temperature of the vulcanization tube is increased overall, the surface temperature of the insulation layer also increases, which may degrade the degradation characteristics of the cable.

[0086] In one embodiment, the overall temperature distribution of the vulcanization tube can be determined according to the following Equation 1.

[0087] [Equation 1]

[0088] Ta > Tb

[0089] In the above Equation 1, Ta is the temperature at the front end of the vulcanization tube, and Tb is the temperature at the rear end of the vulcanization tube.

[0090] According to Equation 1 above, the temperature distribution of the entire vulcanization tube can be controlled so that the temperature of the front end of the vulcanization tube is higher than the temperature of the rear end of the vulcanization tube. In this case, the front end of the vulcanization tube can be defined as the part where the cross-linking reaction is initiated in the insulating layer.

[0091] FIG. 3 is a graph showing the temperature profile of a cure tube in a method for manufacturing a high-voltage cable according to one embodiment of the present invention.

[0092] Referring to FIG. 3, as the temperature of the front zone of the vulcanization tube is increased, the crosslinking reaction is initiated more rapidly and the generation of crosslinking by-products can be suppressed, and as the temperature of the back zone is decreased, the occurrence of a halo phenomenon can be effectively prevented.

[0093] In the conventional process of forming an XLPE insulation layer through a vulcanizing tube, the cross-linking reaction proceeds to the end of the vulcanizing tube, making it difficult to remove cross-linking by-products. However, by increasing the temperature of the front end of the vulcanizing tube, the cross-linking reaction is rapidly induced at the front end of the vulcanizing tube, and methane among the cross-linking by-products can be removed within the vulcanizing tube.

[0094] By increasing the temperature of the front end of the vulcanization tube, the starting point of the crosslinking reaction can be moved as far forward as possible. In this case, the point at which crosslinking begins within the vulcanization tube is moved forward, and space can be secured to sufficiently remove crosslinking byproducts from the rear end of the vulcanization tube.

[0095] In one embodiment, the overall temperature distribution of the vulcanization tube can be controlled according to the surface temperature of the insulating layer and the degree of crosslinking.

[0096] The overall temperature distribution of the above vulcanization tube can be determined according to the surface temperature of the insulating layer due to the crosslinking reaction and the degree of crosslinking of the insulating layer, for example, the surface temperature can be controlled to be about 400°C or lower, and the temperature of the front end of the vulcanization tube can be high and decrease toward the rear end.

[0097] The temperature of the shear section of the vulcanization tube may vary depending on the speed at which the cable passes through the vulcanization tube, and can be determined through simulation at a temperature at which the surface temperature of the insulation layer does not cause deformation of the insulation layer.

[0098] In one embodiment, the crosslinking process in S200 maintains the degree of crosslinking of the insulating layer within a certain range, and the range of the hot-set may be about 80 to 85% (e.g., 80, 81, 82, 83, 84, or 85%).

[0099] The overall temperature distribution of the above vulcanization tube is controlled to maintain the degree of crosslinking of the insulating layer within a certain range, and finally, the insulating layer is formed to have a hot-set within the said range and can exhibit a certain degree of crosslinking.

[0100] The crosslinking byproduct resulting from the crosslinking process is degassing at the rear end of the above vulcanization tube (S300).

[0101] The crosslinking by-products resulting from the crosslinking process can be removed by degassing at the rear end of the above vulcanization tube.

[0102] In one embodiment, the crosslinking byproduct removed from the S300 may be methane.

[0103] By controlling the overall temperature distribution of the above vulcanization tube, a crosslinking reaction is performed at the front end of the vulcanization tube, and crosslinking byproducts generated during the crosslinking reaction process can be removed at the rear end of the vulcanization tube. In particular, if methane among the crosslinking byproducts is sufficiently removed, the occurrence of a halo phenomenon in the insulation layer can be very effectively prevented, thereby significantly shortening the degassing process time in the high-voltage cable manufacturing process.

[0104] In one embodiment, the concentration of methane degassed in the S300 may be about 200 ppm or less.

[0105] In the above degassing process, the concentration of methane is controlled to about 200 ppm or less, preferably about 195 ppm or less (e.g., 150, 155, 160, 165, 170, 175, 180, 185, 190, or 195 ppm), and when removed so that it remains within the above content range at the rear end of the vulcanization tube, the halo phenomenon occurring in the insulation layer can be effectively prevented, thereby significantly improving the efficiency of the high-voltage cable manufacturing process.

[0106] In one embodiment, after S300, the method may further include the step of forming an outer semiconducting layer surrounding the insulating layer and forming a sheath layer surrounding the outer semiconducting layer.

[0107] After the above S300, the cable is cooled and an outer semiconducting layer and a sheath layer are formed to manufacture a high-voltage cable of approximately 66kV or higher.

[0108]

[0109] Another aspect of the present invention provides a high-voltage cable manufactured by the above high-voltage cable manufacturing method.

[0110] FIG. 2 is a cross-sectional view of a high-voltage cable according to one embodiment of the present invention.

[0111] Referring to FIG. 2, the high-voltage cable may include a conductor (100) at the center and an inner semiconducting layer (200), an insulating layer (300), an outer semiconducting layer (400), and a sheath layer (500) surrounding the conductor (100).

[0112] The above inner semiconducting layer (200) and outer semiconducting layer (400) are used to fill the gap between the conductor and the insulating layer, suppress partial discharge, and alleviate electric field concentration. In particular, the inner semiconducting layer (conductor screen) can smoothly fill the surface of the conductor to make the electric field distribution between the conductor and the insulating layer uniform, thereby suppressing partial discharge and increasing the dielectric strength of the insulator. The above outer semiconducting layer (insulation screen) can suppress electric field inequality caused by thickness variation of the insulating layer.

[0113] The above insulating layer (300) is formed according to the high-voltage cable manufacturing method described above, is made of XLPE, prevents the halo phenomenon, and may have improved electrical characteristics by removing concentric circular bands (310) within the insulating layer.

[0114] The sheath layer (500) is formed to surround the outer semiconducting layer (400), and can secure the mechanical strength of the wire, prevent damage, and suppress inductive interference.

[0115] A cable outer sheath (600) may finally be provided outside the sheath layer.

[0116] Accordingly, the high-voltage cable according to another aspect of the present invention is a high-voltage cable manufactured according to the high-voltage cable manufacturing method described above, and since no halo phenomenon occurs within the XLPE insulation layer, the electrical characteristics of the insulation layer are improved, and in particular, since no insulation breakdown occurs during underground installation, the performance of the high-voltage cable is greatly improved, the degassing process is greatly shortened, manufacturing costs are reduced, and manufacturing efficiency is also very high.

[0117]

[0118] Hereinafter, preferred embodiments are presented to aid in understanding the present invention; however, the following embodiments are merely illustrative of the invention and the scope of the invention is not limited to the following embodiments.

[0119]

[0120] Example 1

[0121] A continuous crosslinking device that performs a chemical crosslinking process to crosslink a polymer constituting an insulating layer by adding a crosslinking agent is equipped to control the overall temperature distribution by measuring the temperature at a total of 9 points of the vulcanization tube, and the temperature distribution of the vulcanization tube was controlled according to Table 1 below.

[0122]

[0123] Experimental Examples 1 ~ 3

[0124] The crosslinking reaction of the insulating layer in the vulcanization tube was carried out in the same manner as in Example 1, except that the temperature distribution of the vulcanization tube was changed according to Table 1 below.

[0125] Experimental Example 1 above is a cross-linking process performed according to the temperature distribution of a vulcanizing tube used in the manufacture of commercial high-voltage cables using XLPE as an insulating layer.

[0126] Vulcanization Tube Temperature (°C) Hot-set (%) Experimental Example 1 370 370 350 340 330 320 320 320 31580~85 Experimental Example 2 380 380 350 310 300 290 280 280 280 100~110 Experimental Example 3 386 386 380 350 340 340 330 330 330 80~85 Example 3 90 390 375 360 340 330 320 320 320 80~85

[0127]

[0128] Referring to Table 1 above, in Examples and Experimental Examples 1 to 3, an insulating layer was extruded onto the same conductor and passed through a vulcanization tube with the same linear velocity, and the temperature of the leading edge of the vulcanization tube and the overall temperature distribution were controlled according to Table 1.

[0129] In the example, the temperature of the front section was increased to approximately 390°C to rapidly induce the crosslinking reaction, whereas in Experimental Example 1, the temperature of the front section of the vulcanization tube was maintained at 370°C. The overall temperature distribution was maintained so that the temperature of the rear section was lower than that of the front section, and the temperature distribution was controlled by checking the degree of crosslinking within the hot-set range.

[0130] It was confirmed that the hot-set in the overall temperature distribution of the vulcanization tube according to the example was at the same level as in Experimental Examples 1 and 3, confirming that a similar degree of crosslinking can be exhibited even if the temperature of the shear section is increased.

[0131] Degassing (day) White band Appearance Crosslinking byproducts (ppm) Methane Acetophenone Cumyl Alcohol Alpha-Methylstyrene Total Experiment Example 1 17 Thick 63 15 29 49 15 03 11 14 75 5 Experiment Example 2 17 Thick 62 85 21 19 20 12 95 14 52 7 Experiment Example 3 12 Thin 37 95 16 19 07 62 08 14 44 5 Example 7 Removal 19 3 45 62 80 9 35 02 13 15 7

[0132] Table 2 above confirms the degassing date and halo phenomenon of the insulating layer according to the example and analyzes the crosslinking by-products in the vulcanization tube.

[0133] Methane in the vulcanization tube was analyzed by GC-MS, and the remaining crosslinking by-products were sampled from the vulcanization tube, placed in a mixture of isopropanol (IPA):n-hexane (n-Hexane) = 1:1, pretreated at high temperature, and then measured by HPLC to check the peak size and analyze the crosslinking by-product content to have an error of about 100 ppm or less.

[0134] Referring to Table 2 above, in the example, when the temperature of the shear section of the vulcanization tube was increased and the overall temperature was controlled to control the degree of crosslinking, it was confirmed that methane was reduced to about 193 ppm and the concentric white bands indicating the halo phenomenon were removed, and it was confirmed that the time taken to degas was 7 days, which was reduced by 10 days compared to Experimental Example 1.

[0135] Scanning electron microscope (SEM) measurements were taken to analyze the surface of the insulating layer. As a result, it was confirmed that in Experimental Examples 1 to 3, where abnormal white bands appeared, small voids with a diameter of 1 to 3 μm were concentratedly distributed in the insulating layer. In contrast, in the insulating layer according to the example, the white bands were completely removed, and it was confirmed that the electrical properties of the insulating layer could be significantly improved because no voids existed within the insulating layer.

[0136] Therefore, if the temperature of the front end is maintained higher than that of the rear end within a surface temperature that does not deform the insulation layer, and the overall temperature distribution of the vulcanization tube is controlled to maintain the degree of crosslinking within a certain hot-set range, methane among the crosslinking byproducts can be removed very effectively. When the methane is removed, the halo phenomenon occurring within the insulation layer can be prevented, thereby improving the electrical characteristics of the high-voltage cable. Furthermore, when manufacturing a high-voltage cable containing an XLPE insulation layer, the degassing process can be significantly reduced, thereby reducing manufacturing costs and greatly increasing overall manufacturing efficiency.

[0137]

[0138] The present invention has been described above with reference to embodiments. Those skilled in the art will understand that the present invention may be embodied in modified forms without departing from the essential characteristics of the invention. Therefore, the disclosed embodiments should be considered in an illustrative rather than a restrictive sense. The scope of the invention is defined by the claims, not by the foregoing description, and all variations within the scope of equivalents should be interpreted as being included in the invention.

Claims

1. (a) A step of introducing a cable extruded with an insulating layer containing a crosslinking agent into a vulcanization tube; (b) a step of increasing the temperature of the leading portion of the vulcanization tube into which the cable is introduced to perform a crosslinking process in the insulating layer and controlling the speed at which the cable passes through the vulcanization tube; and (c) a step of degassing a portion of the crosslinking byproduct resulting from the crosslinking process at the rear end of the vulcanization tube; comprising, Method for manufacturing high-voltage cables.

2. A method for manufacturing a high-voltage cable according to claim 1, wherein the temperature of the vulcanization tube shear section is about 390 to 600℃ and the temperature of the surface of the insulation layer is about 400℃ or less.

3. A method for manufacturing a high-voltage cable according to claim 1, wherein the total temperature distribution of the vulcanization tube is determined according to the following Equation 1: [Equation 1] Ta > Tb In the above Equation 1, Ta is the temperature at the front end of the vulcanization tube, and Tb is the temperature at the rear end of the vulcanization tube.

4. A method for manufacturing a high-voltage cable according to paragraph 3, wherein the overall temperature distribution of the vulcanization tube is controlled according to the surface temperature of the insulation layer and the degree of crosslinking.

5. A method for manufacturing a high-voltage cable according to claim 1, wherein the crosslinking process in (b) above maintains the degree of crosslinking of the insulating layer within a certain range, and the hot-set range is approximately 80 to 85%.

6. A method for manufacturing a high-voltage cable according to claim 1, wherein the crosslinking byproduct removed in (c) is methane.

7. A method for manufacturing a high-voltage cable according to claim 6, wherein the concentration of methane degassed in (c) is about 200 ppm or less.

8. A method for manufacturing a high-voltage cable according to claim 1, further comprising the step of forming a conductor and an internal semiconducting layer in the center of the cable prior to (a).

9. A method for manufacturing a high-voltage cable according to claim 1, further comprising the step of forming an outer semiconducting layer surrounding the insulating layer and forming a sheath layer surrounding the outer semiconducting layer after (c).

10. A method for manufacturing a high-voltage cable according to claim 1, wherein the insulating layer comprises cross-linked polyethylene (XLPE).

11. Manufactured by a high-voltage cable manufacturing method according to any one of paragraphs 1 to 10, High-voltage cable.

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