An extruded insulation low voltage power cable and a method for manufacturing the same

Abstract

The present application relates to the technical field of cable preparation, and particularly relates to an extruded insulation low-voltage power cable and a preparation method thereof, which comprises the following steps: twisting metal wires into a conductor according to preset twisting parameters, and pretreating the conductor; using a screw extruder to extrude an insulation layer on the surface of the pretreated conductor to obtain an insulated core; using a laser diameter measuring instrument to monitor the diameter of the insulated core in real time, and determining the core diameter fluctuation characteristic type under a first preset condition; obtaining the eccentricity of the insulation layer and the void fraction between the insulation layer and the conductor; determining the eligibility of the extrusion process according to an extrusion comprehensive quality index; under the condition that the extrusion process is unqualified, determining the eligibility of the extrusion process according to an insulation performance evaluation value; under the condition that the extrusion process is unqualified in the secondary determination, determining an adjustment strategy of the extrusion process; and twisting the insulated core with the qualified extrusion process into a cable and extruding an outer protective sleeve. The present application improves the production efficiency and product stability of the cable.

Description

Technical Field

[0001] This invention relates to the field of cable manufacturing technology, and in particular to an extruded insulated low-voltage power cable and its manufacturing method. Background Technology

[0002] Extruded insulated low-voltage power cables are a type of cable widely used in power distribution networks, industrial equipment, and building electrical systems. Their conductors are coated with a polymer insulation layer (such as polyvinyl chloride (PVC) or cross-linked polyethylene (XLPE)) through an extrusion process. They are characterized by simple structure, stable electrical performance, good mechanical strength, and convenient installation. With increasing demands for safety and energy efficiency in power systems, cables must meet higher standards for insulation reliability, heat resistance, and environmental protection. However, traditional extruded insulated cables still face many challenges in material selection, process control, and structural design, such as uneven insulation thickness, interface defects, and thermal stress cracking, which can easily lead to partial discharge, insulation aging, and even short-circuit faults. Furthermore, fluctuations in process parameters, material impurities, or insufficient stability of extrusion equipment during production further affect the long-term service performance of the cables.

[0003] Chinese Patent Application Publication No. CN120183781A discloses an extruded insulated low-voltage power cable and its manufacturing method. The method involves drawing and annealing copper rods to obtain copper wires, then stranding multiple copper wires to form a copper core. Insulating material is extruded around the copper core and cross-linked to form an insulating layer, thus producing a cable. An inner lining layer is wrapped around the outer surface of the cable, and finally, an outer sheath is wrapped around the outer periphery of the inner lining layer, resulting in an extruded insulated low-voltage power cable. However, the prior art has the following problems: it does not fully consider the impact of the extrusion process on the insulation layer thickness distribution, which may lead to uneven local thickness, causing electric field distortion, accelerating insulation aging, and reducing the long-term electrical performance of the cable. Summary of the Invention

[0004] Therefore, the present invention provides an extruded insulated low-voltage power cable and its preparation method, in order to overcome the problem of accelerated aging of the insulation layer caused by the failure to consider the influence of the uniformity of the insulation layer thickness on the electrical performance of the cable in the prior art.

[0005] To achieve the above objectives, the present invention provides an extruded insulated low-voltage power cable and a method for manufacturing the same, comprising:

[0006] Metal wires are twisted into a conductor according to preset twisting parameters, and the conductor is pre-treated. The twisting parameters include twisting pitch, twisting tightness, and the diameter and number of individual wires.

[0007] An insulating layer is extruded onto the surface of a pretreated conductor using a screw extruder to obtain an insulated wire core.

[0008] A laser diameter gauge is used to monitor the diameter of the insulated wire core in real time and determine the type of wire core diameter fluctuation under a first preset condition. The first preset condition is that the wire core diameter is kept within a preset diameter range and the wire core diameter is detected to exceed the preset diameter range for the first time. The type of wire core diameter fluctuation includes periodic fluctuation and non-periodic fluctuation.

[0009] The cross-sectional grayscale images of preset points in the extrusion anomaly section under non-periodic fluctuation conditions are collected to obtain the eccentricity of the insulation layer and the porosity between the insulation layer and the conductor. The extrusion anomaly section is the core segment monitored within a preset time period under the first preset condition.

[0010] The passability of the extrusion process is determined by the comprehensive extrusion quality index, which is jointly determined by eccentricity and porosity.

[0011] If the extrusion process fails, the insulation performance evaluation value is obtained through electrical performance testing, and the qualification of the extrusion process is determined a second time based on the insulation performance evaluation value.

[0012] Under the condition that the extrusion process is unqualified in the second judgment, the adjustment strategy of the extrusion process is determined according to the difference between the preset insulation performance evaluation value and the insulation performance evaluation value. This includes increasing the melt temperature of the insulating material according to the average roughness of the insulation layer surface, or reducing the extrusion speed according to the insulation layer surface defect index.

[0013] After the qualified insulated wire cores from the extrusion process are twisted into cables, an outer protective sheath is extruded.

[0014] Furthermore, the process of determining the core diameter fluctuation characteristic type under the first preset condition includes:

[0015] Based on the condition that the core diameter is detected to be outside the preset diameter range for the first time, the core diameter is monitored for a preset time and a diameter fluctuation curve is plotted.

[0016] The diameter fluctuation curves were compared with the operating cycles of the screw and traction roller, respectively.

[0017] Based on the fact that the fluctuation period of the wire core diameter coincides with any one of the cycles of the screw and the traction roller, the fluctuation characteristic of the wire core diameter is determined to be periodic fluctuation.

[0018] Based on the fact that the fluctuation period of the wire core diameter does not coincide with the operating periods of the screw and traction roller, the fluctuation characteristic of the wire core diameter is determined to be non-periodic fluctuation.

[0019] The preset duration is greater than the duration of at least three cycles of the maximum cycle in the screw and traction roller.

[0020] Furthermore, the process of determining the overall quality index of extrusion packaging includes:

[0021] The cross-sectional grayscale images of preset points in the abnormal extrusion section under non-periodic fluctuation conditions are acquired by using an industrial camera and image analysis software. The preset points include the point with the largest diameter and the point with the smallest diameter.

[0022] Obtain the maximum and minimum thickness of the insulation layer in the cross-sectional grayscale image, as well as the area of ​​the dark region between the insulation layer and the conductor in the grayscale image, where the porosity is the percentage of the dark region area to the area of ​​the conductor cross-section;

[0023] The eccentricity and porosity were obtained by calculation.

[0024] The comprehensive quality index of the extrusion bag is obtained by taking the maximum values ​​of eccentricity and void ratio at preset points and calculating them through a weighted algorithm.

[0025] Furthermore, the passability of the extrusion process is determined based on the comprehensive quality index of the extrusion process, among which,

[0026] If the overall quality index of the extrusion is less than the first preset quality index, the extrusion process is deemed unqualified, and the die core of the extruder is corrected, and the extrusion pressure is increased according to the void ratio.

[0027] If the comprehensive quality index of extrusion is greater than or equal to the first preset quality index and less than the second preset quality index, the extrusion process is deemed unqualified, and the qualification of the extrusion process is determined a second time based on the insulation performance evaluation value.

[0028] If the overall quality index of the extrusion is greater than or equal to the second preset quality index, the extrusion process is deemed qualified and proceeds to the next step of cable formation.

[0029] Furthermore, the insulation performance evaluation value is determined by both insulation resistance and dielectric loss factor.

[0030] Furthermore, the qualification of the extrusion process is determined a second time based on the insulation performance evaluation values, among which,

[0031] If the insulation performance evaluation value is less than the preset insulation performance evaluation value, the extrusion process is deemed unqualified for the second time, and an adjustment strategy for the extrusion process is determined based on the difference between the preset insulation performance evaluation value and the insulation performance evaluation value.

[0032] If the insulation performance evaluation value is greater than or equal to the preset insulation performance evaluation value, the extrusion process is deemed qualified for the second determination, and the process proceeds to the next step of cable formation.

[0033] Furthermore, adjustment strategies for the extrusion process are determined based on the insulation performance evaluation differences, among which,

[0034] If the insulation performance evaluation difference is less than the preset evaluation difference, then the adjustment strategy for the extrusion process is determined to be to increase the melt temperature of the insulating material based on the average surface roughness of the insulating layer.

[0035] If the insulation performance evaluation difference is greater than or equal to the preset evaluation difference, then the adjustment strategy for the extrusion process is determined to be to reduce the extrusion speed based on the surface defect index of the insulation layer.

[0036] The insulation performance evaluation difference is the difference between the preset insulation performance evaluation value and the insulation performance evaluation value.

[0037] Furthermore, several adjustment methods are provided for the melt temperature of the insulating material, and each adjustment method has a different adjustment range for the melt temperature.

[0038] Furthermore, the extrusion rate is negatively correlated with the surface defect index of the insulation layer, which is determined by the surface crack size.

[0039] The present invention also provides an extruded insulated low-voltage power cable, wherein the conductor material is copper, and the insulation layer material and the outer protective sheath material are polyvinyl chloride.

[0040] Compared with existing technologies, the advantages of this invention lie in its comprehensive consideration of the impact of insulation layer thickness uniformity on cable electrical performance. It utilizes a laser diameter gauge to monitor the insulation core diameter in real time, accurately determining the type of core diameter fluctuation. For non-periodic fluctuations, it acquires cross-sectional grayscale images of preset points in the extrusion anomaly section to accurately obtain the insulation layer's eccentricity and the porosity between it and the conductor, thereby determining the overall extrusion quality index. Through multi-dimensional and refined detection methods, it can promptly identify insulation layer thickness unevenness, avoiding electric field concentration or poor heat dissipation caused by excessively thin or thick local areas. This effectively delays accelerated aging of the insulation layer, improving cable lifespan and reliability.

[0041] Furthermore, this invention establishes a multi-level judgment mechanism. First, the extrusion process is preliminarily judged based on the comprehensive extrusion quality index. If the process fails to meet the standards, a second judgment is made by obtaining insulation performance evaluation values ​​through electrical performance testing. Targeted adjustment strategies are formulated based on different judgment results. This intelligent adjustment method can quickly and accurately resolve problems arising during the extrusion process, reduce scrap rates, improve production efficiency, and ensure that the extrusion quality remains consistently high.

[0042] Furthermore, the present invention has made scientific and reasonable settings for various judgment parameters. At the same time, it has set several adjustment methods for the melt temperature of the insulating material, and each adjustment method has a different adjustment range for the melt temperature. The extrusion speed is negatively correlated with the surface defect index of the insulating layer and the defect index is determined according to the surface crack size. Through flexible adjustment methods, it can adapt to different production conditions and quality requirements, further enhancing the practicality and flexibility of the preparation method of the present invention.

[0043] Furthermore, the extruded insulated low-voltage power cable provided by this invention uses copper as the conductor material, which has excellent conductivity, ensuring efficient current transmission and reducing energy loss. Both the insulation layer and the outer protective sheath material are made of polyvinyl chloride (PVC), which has good insulation properties, chemical corrosion resistance, and flame retardancy, effectively protecting the conductor and preventing leakage and fire accidents. Simultaneously, the preparation method of this invention ensures the quality of the insulation layer and the outer protective sheath, improving the overall performance of the cable. Attached Figure Description

[0044] Figure 1 This is a flowchart illustrating the preparation method of an extruded insulated low-voltage power cable according to an embodiment of the present invention;

[0045] Figure 2 This is a flowchart illustrating how the pass / fail status of the extrusion process is determined based on the comprehensive extrusion quality index, according to an embodiment of the present invention.

[0046] Figure 3 This is a flowchart illustrating the secondary determination of the extrusion process's qualification based on insulation performance evaluation values, as per an embodiment of the present invention.

[0047] Figure 4 This is a flowchart illustrating the adjustment strategy for the extrusion process based on the insulation performance evaluation difference, as described in an embodiment of the present invention. Detailed Implementation

[0048] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0049] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0050] It should be noted that the data in this embodiment are all derived from a comprehensive analysis and evaluation of historical test data and corresponding historical test results from the three months prior to this test. Those skilled in the art will understand that the determination of the above-mentioned parameters for any single item in this invention can be achieved by selecting the value with the highest percentage based on the data distribution as the preset standard parameter, using weighted summation to obtain the value as the preset standard parameter, substituting each historical data point into a specific formula and using the value obtained from that formula as the preset standard parameter, or other selection methods, as long as the invention can clearly define different specific situations in the single-item judgment process through the obtained values.

[0051] Please see Figures 1 to 4 The flowcharts shown are respectively: a flowchart of the preparation method of extruded insulated low-voltage power cable according to an embodiment of the present invention; a flowchart of determining the qualification of the extrusion process based on the comprehensive extrusion quality index according to an embodiment of the present invention; a flowchart of determining the qualification of the extrusion process a second time based on the insulation performance evaluation value according to an embodiment of the present invention; and a flowchart of determining the adjustment strategy of the extrusion process based on the insulation performance evaluation difference according to an embodiment of the present invention.

[0052] The method for preparing extruded insulated low-voltage power cables according to embodiments of the present invention includes:

[0053] Step S1: Twist the metal wires into a conductor according to preset twisting parameters, and pre-treat the conductor. The twisting parameters include twisting pitch, twisting tightness, and diameter and number of individual wires.

[0054] Step S2: Use a screw extruder to extrude an insulation layer onto the surface of the pretreated conductor to obtain an insulated wire core;

[0055] Step S3: Use a laser diameter gauge to monitor the diameter of the insulated wire core in real time and determine the type of wire core diameter fluctuation under the first preset condition. The first preset condition is that the wire core diameter is kept within the preset diameter range and the wire core diameter is detected to exceed the preset diameter range for the first time. The type of wire core diameter fluctuation includes periodic fluctuation and non-periodic fluctuation.

[0056] Step S4: Collect cross-sectional grayscale images of preset points in the extrusion anomaly section under non-periodic fluctuation conditions to obtain the eccentricity of the insulation layer and the porosity between the insulation layer and the conductor. The extrusion anomaly section is the core segment monitored within a preset time period under the first preset condition.

[0057] Step S5: Determine the qualification of the extrusion process based on the comprehensive extrusion quality index determined by eccentricity and porosity.

[0058] Step S6: If the extrusion process fails, obtain the insulation performance evaluation value through electrical performance testing, and determine the qualification of the extrusion process a second time based on the insulation performance evaluation value.

[0059] Step S7: Under the condition that the extrusion process is unqualified in the second judgment, the adjustment strategy of the extrusion process is determined according to the difference between the preset insulation performance evaluation value and the insulation performance evaluation value. The strategy includes increasing the melt temperature of the insulation material according to the average roughness of the insulation layer surface, or reducing the extrusion speed according to the insulation layer surface defect index.

[0060] Step S8: After twisting the qualified insulated wire cores into a cable, extrude an outer protective sleeve.

[0061] In this embodiment of the invention, a wire stranding machine is used to strand copper wires according to preset stranding parameters. The stranding pitch is set to 15mm, the stranding tightness is set to 85%, the diameter of a single wire is 0.5mm, and the number of single wires is 19.

[0062] Specifically, the pretreatment includes removing dust and impurities from the conductor surface by blowing with high-pressure air, increasing the surface roughness by mechanical polishing, and coating the conductor surface with an antioxidant to prevent conductor oxidation. The antioxidant may be, for example, rosin solution or silane coupling agent, and is not specifically limited.

[0063] Specifically, the initial parameters of the screw extruder include: the feed section temperature is set to 130℃, the compression section temperature is set to 160℃, the metering section temperature is set to 190℃, the die temperature is set to 200℃, the screw speed is set to 30 rpm, the extrusion pressure is set to 18 MPa, and the extrusion speed is set to 15 m / min. However, the above values ​​are not limited to these, and those skilled in the art can adjust the above values ​​according to actual needs.

[0064] Specifically, the laser diameter gauge is set 1.5m after the extruder die exit and in front of the cooling water tank. This setting can quickly capture the diameter data of the newly extruded insulated wire core and reflect the working status of the die in a timely manner. If the die is blocked or the extrusion pressure is unstable, resulting in abnormal diameter, it can quickly provide feedback so that the extruder parameters can be adjusted to ensure the initial accuracy.

[0065] Specifically, when the extruder first starts running, the diameter of the insulated wire core will be unstable for a period of time. Once the wire core diameter is kept within the preset diameter range, the situation where the wire core diameter exceeds the preset diameter range is recorded as the first preset condition. The preset diameter range is [4.85, 5.00], and the diameter unit is mm.

[0066] Specifically, the process of determining the core diameter fluctuation characteristic type under the first preset condition includes:

[0067] Based on the condition that the core diameter is detected to be outside the preset diameter range for the first time, the core diameter is monitored for a preset time and a diameter fluctuation curve is plotted.

[0068] The diameter fluctuation curves were compared with the operating cycles of the screw and traction roller, respectively.

[0069] Based on the fact that the fluctuation period of the wire core diameter coincides with any one of the cycles of the screw and the traction roller, the fluctuation characteristic of the wire core diameter is determined to be periodic fluctuation.

[0070] Based on the fact that the fluctuation period of the wire core diameter does not coincide with the operating periods of the screw and traction roller, the fluctuation characteristic of the wire core diameter is determined to be non-periodic fluctuation.

[0071] The preset duration is greater than the duration of at least three cycles of the maximum cycle in the screw and traction roller.

[0072] In this embodiment of the invention, the preset duration is 15 seconds, but this value is not limited to this. Those skilled in the art can adjust the value according to actual needs.

[0073] Specifically, for periodic fluctuations, check whether the screw and traction roller are worn or eccentric, and replace or correct the screw or traction roller.

[0074] Specifically, this invention uses continuous monitoring and curve plotting within a preset time period, combined with cross-comparison of the operating cycles of the screw and traction roller, to quickly pinpoint the root cause of fluctuations and reduce manual investigation time. The preset time period covers more than three times the maximum cycle of the equipment, ensuring that the sampled data fully includes periodic characteristics, avoiding misjudgments due to insufficient monitoring time, and improving the statistical significance of the analysis results.

[0075] Specifically, the process of determining the overall quality index of extrusion packaging includes:

[0076] The cross-sectional grayscale images of preset points in the abnormal extrusion section under non-periodic fluctuation conditions are acquired by using an industrial camera and image analysis software. The preset points include the point with the largest diameter and the point with the smallest diameter.

[0077] Obtain the maximum and minimum thickness of the insulation layer in the cross-sectional grayscale image, as well as the area of ​​the dark region between the insulation layer and the conductor in the grayscale image, where the porosity is the percentage of the dark region area to the area of ​​the conductor cross-section;

[0078] The eccentricity and porosity were obtained by calculation.

[0079] The comprehensive quality index of the extrusion bag is obtained by taking the maximum values ​​of eccentricity and void ratio at preset points and calculating them through a weighted algorithm.

[0080] Specifically, image analysis software such as Halcon, OpenCV, and MATLAB are used, without any particular limitation.

[0081] Specifically, eccentricity = (maximum thickness - minimum thickness) / (maximum thickness + minimum thickness), and the comprehensive quality index of extrusion = first weighting coefficient × eccentricity threshold / eccentricity + second weighting coefficient × porosity threshold / porosity, where the first weighting coefficient is 0.6, the eccentricity threshold is 0.16, the second weighting coefficient is 0.4, and the porosity threshold is 0.08.

[0082] Specifically, the passability of the extrusion process is determined based on the comprehensive quality index of the extrusion process, among which...

[0083] If the overall quality index of the extrusion is less than the first preset quality index, the extrusion process is deemed unqualified, and the die core of the extruder is corrected, and the extrusion pressure is increased according to the void ratio.

[0084] If the comprehensive quality index of extrusion is greater than or equal to the first preset quality index and less than the second preset quality index, the extrusion process is deemed unqualified, and the qualification of the extrusion process is determined a second time based on the insulation performance evaluation value.

[0085] If the overall quality index of the extrusion is greater than or equal to the second preset quality index, the extrusion process is deemed qualified and proceeds to the next step of cable formation.

[0086] In this embodiment of the invention, the first preset quality index is 0.8 and the second preset quality index is 0.98. However, the above values ​​are not limited to these values, and those skilled in the art can adjust the above values ​​according to actual needs.

[0087] Specifically, the extrusion pressure is positively correlated with the porosity; that is, the greater the porosity, the greater the increase in extrusion pressure. The adjustment range of the extrusion pressure is 15–25 MPa.

[0088] Specifically, the insulation performance evaluation value is determined by the insulation resistance and the dielectric loss factor. The insulation performance evaluation value = third weighting coefficient × insulation resistance / insulation resistance threshold + fourth weighting coefficient × dielectric loss factor threshold / dielectric loss factor, where the third weighting coefficient is 0.55, the insulation resistance threshold is 1000 MΩ·km, the fourth weighting coefficient is 0.45, and the dielectric loss factor threshold is 0.02.

[0089] Specifically, the insulation resistance is obtained by detecting a miniature high-resistance meter, and the dielectric loss factor is obtained by detecting an automatic dielectric loss tester. A 5mm wide segment along the length of the insulated core is selected from the above cross section, and several points are selected on the outer surface of the insulation layer of the segment for testing. There is no limit to the number of points. The lowest resistance and the highest dielectric loss factor are taken from the test data to calculate the insulation performance evaluation value.

[0090] Specifically, the qualification of the extrusion process is determined a second time based on the insulation performance evaluation value, wherein...

[0091] If the insulation performance evaluation value is less than the preset insulation performance evaluation value, the extrusion process is deemed unqualified for the second time, and an adjustment strategy for the extrusion process is determined based on the difference between the preset insulation performance evaluation value and the insulation performance evaluation value.

[0092] If the insulation performance evaluation value is greater than or equal to the preset insulation performance evaluation value, the extrusion process is deemed qualified for the second determination, and the process proceeds to the next step of cable formation.

[0093] In this embodiment of the invention, the preset insulation performance evaluation value is 0.95, but the value is not limited to this. Those skilled in the art can adjust the value according to actual needs.

[0094] Specifically, the adjustment strategy for the extrusion process is determined based on the difference in insulation performance evaluation, wherein...

[0095] If the insulation performance evaluation difference is less than the preset evaluation difference, then the adjustment strategy for the extrusion process is determined to be to increase the melt temperature of the insulating material based on the average surface roughness of the insulating layer.

[0096] If the insulation performance evaluation difference is greater than or equal to the preset evaluation difference, then the adjustment strategy for the extrusion process is determined to be to reduce the extrusion speed based on the surface defect index of the insulation layer.

[0097] The insulation performance evaluation difference is the difference between the preset insulation performance evaluation value and the insulation performance evaluation value.

[0098] In this embodiment of the invention, the preset evaluation difference is 0.15, but the above value is not limited to this. Those skilled in the art can adjust the above value according to actual needs.

[0099] Specifically, if the extrusion speed is too fast, the shear and tensile forces on the insulating material during the extrusion process will increase, which can easily lead to defects such as micropores and cracks inside the insulating layer, reducing the insulation performance. If the melt temperature is too low, the insulating material cannot melt fully, which will result in a rough surface with granular protrusions after extrusion, and there may be unmelted impurities inside, thereby reducing the insulation resistance, increasing the dielectric loss factor, and lowering the insulation performance evaluation value.

[0100] Specifically, several adjustment methods are provided for the melt temperature of the insulating material, and each method has a different adjustment range for the melt temperature.

[0101] If the average surface roughness of the insulating layer is less than the preset roughness, the melt temperature is increased to the corresponding value using the first temperature adjustment coefficient of 1.02.

[0102] If the average surface roughness of the insulating layer is greater than or equal to the preset roughness, the melt temperature is increased to the corresponding value using a second temperature adjustment coefficient of 1.05.

[0103] The melt temperature is the temperature of the metering section.

[0104] In this embodiment of the invention, the preset roughness is 1.2 μm, but the above value is not limited to this. Those skilled in the art can adjust the above value according to actual needs.

[0105] Specifically, roughness is obtained by measuring with a contact roughness tester.

[0106] Specifically, the extrusion rate is negatively correlated with the surface defect index of the insulation layer, which is determined by the surface crack size.

[0107] Specifically, if the surface defect index of the insulation layer is less than the first preset defect index, the extrusion speed is reduced to the corresponding value using the first speed adjustment coefficient of 0.98.

[0108] If the surface defect index of the insulation layer is greater than or equal to the first preset defect index and less than the second preset defect index, the extrusion speed is reduced to the corresponding value using the second speed adjustment coefficient of 0.95.

[0109] If the surface defect index of the insulation layer is greater than or equal to the second preset defect index, the extrusion speed is reduced to the corresponding value using the third speed adjustment coefficient of 0.92.

[0110] In this embodiment of the invention, the first preset defect index is 0.85 and the second preset defect index is 0.98. However, the above values ​​are not limited to these values, and those skilled in the art can adjust the above values ​​according to actual needs.

[0111] Specifically, the surface defect index of the insulation layer = depth weighting coefficient × crack depth / crack depth threshold + length weighting coefficient × crack length / crack length threshold, where the depth weighting coefficient is 0.6, the crack depth threshold is 50μm, the length weighting coefficient is 0.4, and the crack length threshold is 5mm.

[0112] Specifically, the surface crack size is obtained through industrial microscopy, and the surface crack size includes crack length and crack depth.

[0113] The extruded insulated low-voltage power cable of this invention uses copper as the conductor material and polyvinyl chloride as the insulation layer material and outer protective sheath material.

[0114] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

[0115] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing an extruded insulated low-voltage power cable, characterized in that, include: Metal wires are twisted into a conductor according to preset twisting parameters, and the conductor is pre-treated. The twisting parameters include twisting pitch, twisting tightness, and the diameter and number of individual wires. An insulating layer is extruded onto the surface of a pretreated conductor using a screw extruder to obtain an insulated wire core. A laser diameter gauge is used to monitor the diameter of the insulated wire core in real time and determine the type of wire core diameter fluctuation under a first preset condition. The first preset condition is that the wire core diameter is kept within a preset diameter range and the wire core diameter is detected to exceed the preset diameter range for the first time. The type of wire core diameter fluctuation includes periodic fluctuation and non-periodic fluctuation. The cross-sectional grayscale images of preset points in the extrusion anomaly section under non-periodic fluctuation conditions are collected to obtain the eccentricity of the insulation layer and the porosity between the insulation layer and the conductor. The extrusion anomaly section is the core segment monitored within a preset time period under the first preset condition. The passability of the extrusion process is determined by the comprehensive extrusion quality index, which is jointly determined by eccentricity and porosity. If the extrusion process fails, the insulation performance evaluation value is obtained through electrical performance testing, and the qualification of the extrusion process is determined a second time based on the insulation performance evaluation value. Under the condition that the extrusion process is unqualified in the second judgment, the adjustment strategy of the extrusion process is determined according to the difference between the preset insulation performance evaluation value and the insulation performance evaluation value. This includes increasing the melt temperature of the insulating material according to the average roughness of the insulation layer surface, or reducing the extrusion speed according to the insulation layer surface defect index. After the qualified insulated wire cores from the extrusion process are twisted into cables, an outer protective sheath is extruded.

2. The method for preparing extruded insulated low-voltage power cable according to claim 1, characterized in that, The process of determining the core diameter fluctuation characteristic type under the first preset condition includes: Based on the condition that the core diameter is detected to be outside the preset diameter range for the first time, the core diameter is monitored for a preset time and a diameter fluctuation curve is plotted. The diameter fluctuation curves were compared with the operating cycles of the screw and traction roller, respectively. Based on the fact that the fluctuation period of the wire core diameter coincides with any one of the cycles of the screw and the traction roller, the fluctuation characteristic of the wire core diameter is determined to be periodic fluctuation. Based on the fact that the fluctuation period of the wire core diameter does not coincide with the operating periods of the screw and traction roller, the fluctuation characteristic of the wire core diameter is determined to be non-periodic fluctuation. The preset duration is greater than the duration of at least three cycles of the maximum cycle in the screw and traction roller.

3. The method for preparing extruded insulated low-voltage power cable according to claim 2, characterized in that, The process of determining the overall quality index of extrusion packaging includes: The cross-sectional grayscale images of preset points in the abnormal extrusion section under non-periodic fluctuation conditions are acquired by using an industrial camera and image analysis software. The preset points include the point with the largest diameter and the point with the smallest diameter. Obtain the maximum and minimum thickness of the insulation layer in the cross-sectional grayscale image, as well as the area of ​​the dark region between the insulation layer and the conductor in the grayscale image, where the porosity is the percentage of the dark region area to the area of ​​the conductor cross-section; The eccentricity and porosity were obtained by calculation. The comprehensive quality index of the extrusion bag is obtained by taking the maximum values ​​of eccentricity and void ratio at preset points and calculating them through a weighted algorithm.

4. The method for preparing extruded insulated low-voltage power cable according to claim 3, characterized in that, The passability of the extrusion process is determined based on the comprehensive quality index of the extrusion process, among which... If the overall quality index of the extrusion is less than the first preset quality index, the extrusion process is deemed unqualified, and the die core of the extruder is corrected, and the extrusion pressure is increased according to the void ratio. If the comprehensive extrusion quality index is greater than or equal to the first preset quality index and less than the second preset quality index, the extrusion process is deemed unqualified, and the qualification of the extrusion process is determined a second time based on the insulation performance evaluation value. If the overall quality index of the extrusion is greater than or equal to the second preset quality index, the extrusion process is deemed qualified and proceeds to the next step of cable formation.

5. The method for preparing extruded insulated low-voltage power cable according to claim 4, characterized in that, The insulation performance evaluation value is determined by both insulation resistance and dielectric loss factor.

6. The method for preparing extruded insulated low-voltage power cable according to claim 5, characterized in that, The qualification of the extrusion process is determined a second time based on the insulation performance evaluation value. If the insulation performance evaluation value is less than the preset insulation performance evaluation value, the extrusion process is deemed unqualified for the second time, and an adjustment strategy for the extrusion process is determined based on the difference between the preset insulation performance evaluation value and the insulation performance evaluation value. If the insulation performance evaluation value is greater than or equal to the preset insulation performance evaluation value, the extrusion process is deemed qualified for the second time, and the process proceeds to the next step of cable formation.

7. The method for preparing an extruded insulated low-voltage power cable according to claim 6, characterized in that, The adjustment strategy for the extrusion process is determined based on the difference in insulation performance evaluation, among which, If the insulation performance evaluation difference is less than the preset evaluation difference, then the adjustment strategy for the extrusion process is determined to be to increase the melt temperature of the insulating material based on the average surface roughness of the insulating layer. If the insulation performance evaluation difference is greater than or equal to the preset evaluation difference, then the adjustment strategy for the extrusion process is determined to be to reduce the extrusion speed based on the surface defect index of the insulation layer. The insulation performance evaluation difference is the difference between the preset insulation performance evaluation value and the insulation performance evaluation value.

8. The method for preparing an extruded insulated low-voltage power cable according to claim 7, characterized in that, Several adjustment methods are available for the melt temperature of insulating materials, and each method has a different adjustment range for the melt temperature.

9. The method for preparing an extruded insulated low-voltage power cable according to claim 8, characterized in that, The extrusion rate is negatively correlated with the surface defect index of the insulation layer, which is determined by the surface crack size.

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