A method for improving the mechanical properties of the electrical insulation layer of a medium voltage cross-linked cable

Abstract

The application provides a method for improving mechanical properties of an electrical insulation layer of a medium-voltage crosslinked cable and relates to the technical field of medium-voltage crosslinked cable production processes.Under the condition that the electrical insulation material extrusion speed is kept unchanged, 1-2 heating sections located at the end of a crosslinking section are closed, and the medium-voltage crosslinked cable electrical insulation layer is produced according to the original production condition.The application closes 1-2 heating sections located at the end of the crosslinking section, which is equivalent to reducing the crosslinking section and increasing the pre-cooling section.The application improves the mechanical properties of the medium-voltage crosslinked cable electrical insulation layer by artificially increasing the pre-cooling section without equipment modification, reducing the production efficiency and ensuring that the crosslinking degree meets the national standards.

Description

Technical Field

[0001] This invention relates to the field of medium-voltage cross-linked cable manufacturing technology, and in particular to a method for improving the mechanical properties of the electrical insulation layer of medium-voltage cross-linked cables. Background Technology

[0002] Currently, the production method for the electrical insulation layer of medium-voltage cross-linked cables is as follows: the electrical insulation material is melted by heating and then... Figure 1 The three-layer co-extrusion die head shown encapsulates the metal conductor, then passes through a cross-linking section to complete the cross-linking process of the electrical insulation material. It then enters a pre-cooling section for transitional cooling of the electrical insulation layer, and finally enters a cooling section for cooling and shaping before being coiled for the next processing step. Currently, cable manufacturers all use this method for producing the electrical insulation layer of medium-voltage cross-linked cables. The only difference lies in the length of the cross-linking and cooling sections, and the layout of the cross-linking and pre-cooling sections is either 6 sections + 2 sections, 7 sections + 2 sections, or 9 sections + 2 sections. Initially, the cross-linking equipment for medium-voltage cross-linked cables used a 6-section + 2-section layout, but later, due to the need to improve production efficiency, the layout of the cross-linking equipment changed to 7 sections + 2 sections or 9 sections + 2 sections.

[0003] While increasing the length of the cross-linking tube increases production speed and efficiency during the extrusion process, the pre-cooling section of the cross-linking equipment, regardless of whether it's a 7- or 9-segment cross-linking heating section, remains at 2 segments and 12m in length (each cross-linking and cooling section is 6m long). This leads to various manufacturers increasing production speed to varying degrees based on the cross-linking tube length ratio during cable insulation production, while ensuring the cross-linking degree of medium-voltage cross-linked cable insulation meets national standards. Consequently, while the cross-linking degree of the electrical insulation layer meets national standards, the mechanical performance indicators of the electrical insulation layer (the rate of change in insulation tensile strength before and after aging) frequently exceed the standards, affecting the cable's service life.

[0004] To address the drawbacks of increased production speed—specifically, the severe exceedance of tensile strength variation before and after aging—the common industry practice is to reduce production speed without modifying equipment. This delays the cooling and setting time of the hot medium-voltage cross-linked cable insulation layer in the cooling section, reducing stress concentration caused by rapid cooling and resulting in excessive tensile strength variation before and after aging. However, this solution sacrifices production efficiency to ensure the mechanical properties of the electrical insulation layer meet requirements. Therefore, effectively resolving the issue of excessive insulation mechanical properties caused by mismatched process parameters during the extrusion of medium-voltage cable electrical insulation layers, without modifying equipment, altering production efficiency, or ensuring the degree of cross-linking meets national standards, has become a pressing technical challenge. Summary of the Invention

[0005] The purpose of this invention is to provide a method for improving the mechanical properties of the electrical insulation layer of medium-voltage cross-linked cables. This invention improves the mechanical properties of the electrical insulation layer of medium-voltage cross-linked cables without modifying equipment, reducing production efficiency, or ensuring that the degree of cross-linking meets national standards.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for improving the mechanical properties of the electrical insulation layer of medium-voltage cross-linked cables. While keeping the extrusion speed of the electrical insulation material constant, the heating of the 1st to 2nd sections at the end of the cross-linking section is turned off, and the electrical insulation layer of the medium-voltage cross-linked cable is produced according to the original production conditions.

[0008] Preferably, for the original layout of 7 crosslinking sections and 2 precooling sections, the heating of the last section of the crosslinking section is turned off, so that the layout of the crosslinking sections and precooling sections becomes 6 sections and 3 sections.

[0009] Preferably, for the original cross-linking section and pre-cooling section with a layout of 9 sections + 2 sections, the production rated voltage is 35kV, and the specifications are 25~800mm. 2 When cross-linking cables, turn off the heating of the end section of the cross-linking section, so that the layout of the cross-linking section and the pre-cooling section becomes 8 sections + 3 sections.

[0010] Preferably, for the original cross-linking section and pre-cooling section with a layout of 9 sections + 2 sections, the production rated voltage is 10kV, and the diameter is 25~800mm. 2 When cross-linking cables, the heating of the two sections at the end of the cross-linking section is turned off, so that the layout of the cross-linking section and the pre-cooling section becomes 7 sections + 4 sections.

[0011] This invention provides a method for improving the mechanical properties of the electrical insulation layer of medium-voltage cross-linked cables. While keeping the extrusion speed of the electrical insulation material constant, the heating of the 1st to 2nd sections at the end of the cross-linking section is turned off, and the electrical insulation layer of the medium-voltage cross-linked cable is produced according to the original production conditions.

[0012] This invention shuts off the heating of the 1st and 2nd sections at the end of the cross-linking section, which is equivalent to reducing the number of cross-linking sections and increasing the pre-cooling section. By artificially adding the pre-cooling section, this invention effectively solves the problem of excessive change rate of tensile strength before and after aging caused by stress concentration during the extrusion process of electrical insulation layer of medium voltage cable without changing the original production efficiency.

[0013] This invention does not require equipment modification, the introduction of relevant calculation software, or changes to the original production efficiency. While ensuring that the degree of crosslinking meets national standards, it improves the mechanical properties of the electrical insulation layer of medium-voltage crosslinked cables. Attached Figure Description

[0014] Figure 1 A schematic diagram of equipment for co-extruding the electrical insulation layer of medium-voltage cross-linked cables. Detailed Implementation

[0015] This invention provides a method for improving the mechanical properties of the electrical insulation layer of medium-voltage cross-linked cables. While keeping the extrusion speed of the electrical insulation material constant, the heating of the 1st to 2nd sections at the end of the cross-linking section is turned off, and the electrical insulation layer of the medium-voltage cross-linked cable is produced according to the original production conditions.

[0016] In this invention, for the original layout of 7 segments + 2 segments for the crosslinking segment and the precooling segment, it is preferable to turn off the heating of the 1 segment at the end of the crosslinking segment, so that the layout of the crosslinking segment and the precooling segment becomes 6 segments + 3 segments.

[0017] In the case of the original layout of 9 cross-linking sections and 2 pre-cooling sections, when producing cross-linked cables with a rated voltage of 35kV, the present invention preferably shuts off the heating of the 1st section at the end of the cross-linking section, so that the layout of the cross-linking section and pre-cooling section becomes 8 sections and 3 sections.

[0018] In the case of the original layout of 9 sections + 2 sections for cross-linking and pre-cooling, when producing cross-linked cables with a rated voltage of 10kV, the present invention preferably shuts off the heating of the two sections at the end of the cross-linking section, so that the layout of the cross-linking and pre-cooling sections becomes 7 sections + 4 sections.

[0019] This invention shuts off the heating of the 1st and 2nd sections at the end of the cross-linking section, which is equivalent to reducing the number of cross-linking sections and increasing the pre-cooling section. By artificially adding the pre-cooling section, this invention effectively solves the problem of excessive change rate of tensile strength before and after aging caused by stress concentration during the extrusion process of electrical insulation layer of medium voltage cable without changing the original production efficiency.

[0020] The following detailed description of the method for improving the mechanical properties of the electrical insulation layer of medium-voltage cross-linked cables provided by the present invention, with reference to specific embodiments, should not be construed as limiting the scope of protection of the present invention.

[0021] Example 1

[0022] The above scheme was verified using the applicant company's (Kunming Cable Group Kunming Electric Cable Co., Ltd.) 9-segment + 2-segment cross-linking unit:

[0023] The original company's rated voltage was 10kV and the nominal cross-sectional area was 185mm². 2 Copper core cross-linked polyethylene insulated cable core (YJV-10kV-185) 2The production speed was 7.0 m / min, and the cross-linking tube temperatures were as follows (°C): 390 / 390 / 370 / 370 / 350 / 320 / 320 / 310 / 285. Even with the cross-linking section temperature unchanged, when the production speed was adjusted to 3.5 m / min (production efficiency halved), the tensile strength change rate before and after aging still exceeded the national standard by ±25%, with some even reaching 35%. However, by adding a pre-cooling section (changing the original 9-section heating to 7-section heating, with the last two heating tubes closed and not heated, resulting in an actual heat transfer temperature of around 200°C), while maintaining the original production speed of 7.0 m / min, the tensile strength of the electrical insulation layer of the produced medium-voltage cross-linked cables remained below 20% before aging (all other properties met national standard requirements, including the degree of cross-linking), achieving the expected target.

[0024] Example 2

[0025] The above scheme was validated using the applicant company's 9-stage + 2-stage crosslinking unit:

[0026] The original company's rated voltage was 35kV and the nominal cross-sectional area was 150mm². 2 Copper core cross-linked polyethylene insulated cable core (YJV-35kV-150) 2 The production speed was 4.6 m / min, and the cross-linking tube temperatures (°C) were as follows: 200 / 330 / 370 / 370 / 350 / 320 / 320 / 310 / 285. When the production speed was adjusted to 3.4 m / min while keeping the cross-linking section temperature constant, the change rate of tensile strength before and after aging still exceeded the national standard of ±25%. By adding a pre-cooling section (changing the original 9-section heating to 8-section heating, with the last section of heating tube turned off and not heated, the actual heat transfer temperature was around 200°C), while maintaining the original production speed of 4.6 m / min, the tensile strength of the electrical insulation layer of the produced medium-voltage cross-linked cables before aging remained below 15%, achieving the expected target.

[0027] Example 3

[0028] The above scheme was validated using the applicant company's 7-stage + 2-stage crosslinking unit:

[0029] The original company's rated voltage was 10kV and the nominal cross-sectional area was 120mm². 2 Copper core cross-linked polyethylene insulated cable core (YJV-10kV-120) 2The production speed was 8.2 m / min, and the cross-linking tube temperatures (°C) were as follows: 390 / 380 / 370 / 360 / 350 / 330 / 320. When the production speed was adjusted to 6 m / min while keeping the cross-linking section temperature constant, the change rate of tensile strength before and after aging still exceeded the national standard of ±25%. By adding a pre-cooling section (changing the original 7-section heating to 5-section heating, with the last 2 heating tubes turned off and not heated, the actual heat transfer temperature was around 200°C), while maintaining the original production speed of 8.2 m / min, the tensile strength of the electrical insulation layer of the produced medium-voltage cross-linked cables before aging remained below 15%, achieving the expected target.

[0030] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for improving the mechanical properties of the electrical insulation layer of a medium-voltage cross-linked cable, characterized in that, While keeping the extrusion speed of the electrical insulation material constant, turn off the heating of the 1st and 2nd sections at the end of the cross-linking section, and produce the electrical insulation layer of the medium-voltage cross-linked cable according to the original production conditions; For the original layout of 7 sections + 2 sections for the crosslinking section and the precooling section, the heating of the last section of the crosslinking section is turned off, so that the layout of the crosslinking section and the precooling section becomes 6 sections + 3 sections. For the original cross-linking section and pre-cooling section for 9 sections + 2 sections of layout, the rated voltage is 35kV, and the specification is 25-800mm 2 When cross-linking the cable, the last section of the cross-linking section is closed, and the layout of the cross-linking section and the pre-cooling section is changed to 8 sections + 3 sections. For the original cross-linking section and pre-cooling section for 9 sections + 2 sections of layout, the production rated voltage is 10kV, 25~800mm 2 When cross-linking the cable, the last two sections of heating in the cross-linking section are closed, and the layout of the cross-linking section and the pre-cooling section is changed to 7 sections + 4 sections.

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