Catenary secondary cross-linking method of medium-voltage cross-linked polyethylene cable and cable

Abstract

The invention belongs to the technical field of medium-voltage cross-linked polyethylene cable production, and particularly relates to a catenary secondary cross-linking method of a medium-voltage cross-linked polyethylene cable and the cable, and the method comprises the following steps: determining a production mold according to the attribute of a primary cross-linked unqualified product; the determined production mold is installed, and the temperature of a machine head and the pressure of a pipeline are adjusted; placing the primary cross-linked unqualified product in a production mold and a pipeline, connecting the secondary cross-linked pull wire and the primary cross-linked unqualified product insulated wire core, and performing sealed multi-layer strip coating treatment at a joint; 3 / 4 of the primary cross-linking production speed serves as the secondary cross-linking production speed, nitrogen supply is started in a pipeline, the pipeline pressure and the pipeline four-section gradient temperature are adjusted, and a nitrogen protection dynamic thermodynamic equilibrium system is constructed; and processing the primary cross-linked unqualified insulated wire core in the constructed nitrogen protection dynamic thermodynamic equilibrium system to complete secondary cross-linking.

Description

Technical Field

[0001] The present invention belongs to the technical field of medium-voltage cross-linked polyethylene cable production, and particularly relates to a suspension-type secondary cross-linking method and cable for medium-voltage cross-linked polyethylene cables. Background Art

[0002] The statements in this section merely provide background technical information related to the present invention and do not necessarily constitute prior art.

[0003] The manufacture of medium-voltage cross-linked polyethylene (XLPE) power cables of 35 kV and below generally adopts a three-layer co-extrusion semi-dry suspension production line. Through three-layer co-extrusion, an insulating layer with excellent structural integrity can be prepared in this production process, and the production efficiency is relatively high, which has become the mainstream process in the industry; this process realizes the synchronous extrusion molding of the conductor shielding layer, insulating layer, and insulating shielding layer through pendant control, and cooperates with the nitrogen-pressurized peroxide cross-linking process. The entire feeding, extrusion, and cross-linking processes are fully enclosed without impurity interference. The produced insulating layer has good compactness, avoiding the entry of water molecules and other impurities in the air from causing defects in the insulating layer, conductor, and insulating shielding layer during the production process and affecting the electrical properties, and can effectively avoid the micropore defects of traditional wet cross-linking.

[0004] The semi-dry suspension line adopts the peroxide cross-linking process. After the main cross-linking reaction is completed in the high-temperature zone of the cross-linking tube, it is quickly cooled and shaped through the water-cooling section. However, limited by the dynamic production characteristics of the suspension line and the thermodynamic gradient limitation, the actual cross-linking degree may be affected by reasons such as production speed and pipeline temperature, and the equipment complexity is relatively high. It may not meet the standard specification requirements of ≤175% for the thermal elongation rate in IEC60502-2 due to human or equipment reasons; especially for large cross-sections (≥500 mm 2 ) and thick insulation (≥10.5 mm) wire cores.

[0005] Due to the relatively thick extrusion layer and large conductor outer diameter, the situation of unqualified primary cross-linking is likely to occur. There is currently no content related to secondary cross-linking treatment. For the unqualified cross-linking degree of the insulated wire core after primary cross-linking and the failure of the thermal elongation test, it is necessary to strip the insulation and re-extrude the insulation. This not only wastes raw materials and consumes too much energy, but also there is a risk of easily damaging the conductor during the stripping process. The conductor cost accounts for 70-80% of the cable cost structure. If the conductor is damaged, it cannot be repaired, and the cost loss will increase significantly. Therefore, how to achieve efficient secondary cross-linking in the suspension production line has become the key technical bottleneck for improving the reliability of medium-voltage XLPE cables. Summary of the Invention

[0006] To solve the above problems, the present invention proposes a suspension-type secondary cross-linking method and cable for medium-voltage cross-linked polyethylene cables. By constructing a nitrogen protection dynamic thermodynamic equilibrium system, stable control of the thermal elongation rate of the core is achieved on the premise of ensuring the integrity of the insulation structure, and the unqualified products of the primary cross-linking thermal elongation are subjected to secondary pipe cross-linking to make their various performances meet the standards.

[0007] According to some embodiments, the first solution of the present invention provides a suspension-type secondary cross-linking method for medium-voltage cross-linked polyethylene cables, adopting the following technical solutions:

[0008] A suspension-type secondary cross-linking method for medium-voltage cross-linked polyethylene cables, comprising:

[0009] Determine the production mold according to the attributes of the unqualified products of the primary cross-linking;

[0010] Install the determined production mold and adjust the head temperature and pipe pressure;

[0011] Place the unqualified products of the primary cross-linking in the production mold and the pipe, connect the secondary cross-linking traction line and the insulating core of the unqualified products of the primary cross-linking, and perform sealed multi-layer strip wrapping treatment at the joint;

[0012] Take three-quarters of the primary cross-linking production speed as the secondary cross-linking production speed, turn on the nitrogen supply in the pipe, adjust the pipe pressure and the four-section gradient temperature of the pipe, and construct a nitrogen protection dynamic thermodynamic equilibrium system;

[0013] Process the insulating core of the unqualified products of the primary cross-linking in the constructed nitrogen protection dynamic thermodynamic equilibrium system to complete the secondary cross-linking.

[0014] As a further technical limitation, the constructed nitrogen protection dynamic thermodynamic equilibrium system is in a secondary cross-linking pipe provided with a four-section gradient temperature and the pressure maintained at the pressure threshold. According to the primary cross-linking production speed, control the secondary cross-linking production speed of the insulating core of the unqualified products of the primary cross-linking and maintain a constant secondary cross-linking production speed.

[0015] Furthermore, during the process of processing the insulating core of the unqualified products of the primary cross-linking in the constructed nitrogen protection dynamic thermodynamic equilibrium system, the sealing condition of the production mold mouth and the nitrogen pressure in the pipe are detected in real time, and secondary cross-linking is performed according to the preset four-section gradient temperature and pressure threshold of the pipe.

[0016] As a further technical limitation, inject nitrogen into the pipe before secondary cross-linking to isolate the influence of air on secondary cross-linking during the secondary cross-linking process and inhibit oxidation side reactions; maintain the nitrogen pressure in the pipe within the pressure threshold during the secondary cross-linking process.

[0017] As a further technical limitation, the core inner diameter and outer mold inner diameter of the secondary cross-linking production mold are selected in turn according to the insulation core diameter of the unqualified product of the first cross-linking, the secondary cross-linking production mold is cleaned and inspected, the production mold is installed and the catenary production line equipment is debugged.

[0018] As a further technical limitation, the temperatures of the conductor preheater, rubber hose and machine head in the catenary production line equipment are set, and the conductor preheater temperature, production mold mouth temperature, rubber hose temperature and machine head temperature are set in sequence from low to high; then the temperatures of the conductor preheater, rubber hose and machine head in the catenary production line equipment are debugged and calibrated.

[0019] As a further technical limitation, a catenary secondary cross-linking method for a medium-voltage cross-linked polyethylene cable also includes a performance test on the finished cable product after the secondary cross-linking, and the performance test includes at least insulation thermal extension, insulation thermal shrinkage, tensile strength before and after aging, and elongation at break before and after aging.

[0020] As a further technical limitation, the multi-layer tapes used are, from inside to outside, non-woven fabrics, polyethylene tape, polytetrafluoroethylene tape, polyethylene tape and silicone rubber sleeve.

[0021] As a further technical limitation, the preheating zone, cross-linking zone, pre-cooling zone and cooling zone of the pipeline are set in sequence according to the gradient temperature of the four sections of the pipeline; the temperature of the cross-linking zone is higher than the temperature of the preheating zone and the temperature of the pre-cooling zone, the cooling zone is water-cooled, and the temperature of the cooling zone is lower than the temperature of the pre-cooling zone.

[0022] According to some embodiments, a second solution of the present invention provides a cable, adopting the following technical solution:

[0023] A cable adopts the catenary secondary cross-linking method of the medium-voltage cross-linked polyethylene cable in the first solution during its preparation.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention constructs a nitrogen protection dynamic thermodynamic equilibrium system to achieve stable control of the thermal elongation of the wire core under the premise of ensuring the integrity of the insulation structure, and performs secondary pipeline cross-linking on the primary cross-linked thermal elongation unqualified products to make their various performances meet the standards. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings in the specification that constitute a part of this embodiment are used to provide a further understanding of this embodiment. The schematic embodiments of this embodiment and their descriptions are used to explain this embodiment and do not constitute improper limitations on this embodiment.

[0027] Figure 1It is a flowchart of the suspension type secondary cross - linking method for medium - voltage cross - linked polyethylene cables in the first embodiment of the present invention. Detailed implementation manners

[0028] The present invention will be further described below in conjunction with the drawings and embodiments.

[0029] It should be noted that the following detailed description is exemplary and is intended to provide further illustration of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0030] It should be noted that the terms used herein are only for describing specific implementation manners and are not intended to limit the exemplary embodiments of the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0031] In the present invention, terms such as "upper", "lower", "left", "right", "front", "rear", "vertical", "horizontal", "side", "bottom", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. They are only relational terms determined for the convenience of describing the structural relationship of each component or element of the present invention and do not specifically refer to any component or element of the present invention and should not be construed as a limitation of the present invention.

[0032] In the present invention, terms such as "fixed connection", "connected", "joined" should be understood in a broad sense, which may mean a fixed connection, an integral connection or a detachable connection; it may be directly connected or indirectly connected through an intermediate medium. For those related scientific research or technical personnel in this field, the specific meaning of the above terms in the present invention can be determined according to specific circumstances and should not be construed as a limitation of the present invention.

[0033] Without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0034] Embodiment 1

[0035] Embodiment 1 of the present invention introduces a suspension type secondary cross - linking method for medium - voltage cross - linked polyethylene cables.

[0036] As Figure 1 shown, a suspension type secondary cross - linking method for medium - voltage cross - linked polyethylene cables includes:

[0037] Determine the production mold according to the attributes of the unqualified products of the first cross - linking.

[0038] Install the determined production mold, and adjust the head temperature and pipeline pressure;

[0039] Place the unqualified products of the first cross-linking in the production mold and pipeline, connect the traction wire of the second cross-linking and the insulating core of the unqualified product of the first cross-linking, and conduct a multi-layer strip wrapping treatment for sealing at the joint;

[0040] Take three-quarters of the production speed of the first cross-linking as the production speed of the second cross-linking, turn on the nitrogen supply in the pipeline, adjust the pipeline pressure and the four-section gradient temperature of the pipeline, and construct a nitrogen protection dynamic thermodynamic equilibrium system;

[0041] Process the insulating core of the unqualified product of the first cross-linking in the constructed nitrogen protection dynamic thermodynamic equilibrium system to complete the second cross-linking.

[0042] In this embodiment, the suspension-type second cross-linking method of medium-voltage cross-linked polyethylene cables is elaborated through two examples.

[0043] Example 1

[0044] Example 1 conducts tests on cables with the specification of YJY22-8.7 / 15kV-3*300, and five reels (each reel section is 550m long) of unqualified samples of the first cross-linking are used for testing.

[0045] Measure the outer diameter D of the insulating core of the unqualified product of the first cross-linking with a cross-section of 300mm 2 to be 31.54mm to ensure matching with the subsequent process requirements. Prepare strip materials such as non-woven fabric, polyethylene tape, polytetrafluoro tape, and silicone rubber sleeve for sealing treatment; at the same time, check the nitrogen supply system to ensure that the nitrogen purity and pressure meet the production requirements.

[0046] According to the outer diameter D of the insulating core of the unqualified product of the first cross-linking being 31.54mm, select the inner diameter D1 of the die core = D + 1.2mm, and in this embodiment, take the inner diameter D1 of the die core as 33mm; the outer diameter D2 of the outer die = D1 + 0.5mm, and in this embodiment, take the outer diameter D2 of the outer die as 33.5mm. Before installing the production mold, it is necessary to check and clean the production mold to ensure no impurities and defects. After installation, debug the equipment to ensure that the production mold is firmly installed and in the correct position. At the same time, debug the temperature control systems of the conductor preheater, the rubber guiding tube, and the head, set the temperature of the conductor preheater to 85°C, the temperature of the rubber guiding tube to 105°C, the temperature of the head to 115°C, and the temperature of the die orifice to 95°C, and conduct temperature calibration to ensure the temperature control accuracy.

[0047] After the insulating core is connected to the traction wire, conduct multi-layer strip wrapping in strict accordance with the order from the inside to the outside, that is, tightly wind the non-woven fabric around the joint, then wind the polyethylene tape, then wrap the polytetrafluoro tape, then wind another layer of polyethylene tape, and finally put on the silicone rubber sleeve to ensure good sealing of the joint and prevent water ingress.

[0048] According to the total length L of the heating pipeline and the original primary cross-linking production speed v0 of 6.0 m / min, calculate the secondary cross-linking production speed v as 4.5 m / min according to the empirical formula v = 0.75v0, and prepare a production speed closed-loop control system; traction the insulated wire core at a set speed of 4.5 m / min to ensure reasonable residence time of the wire core in each area and guarantee the cross-linking quality; turn on the nitrogen supply system and adjust the pipeline pressure to 0.75 MPa. Debug the temperature control system of the heating and cooling areas, and set the preheating area to be maintained at 280 ± 10 °C; the temperature of the eight-section pipeline in the cross-linking area is controlled to decrease in a gradient from 350 to 300 °C; the pre-cooling area decreases from 290 °C to 270 °C; the cooling area adopts a water-cooling method and sets a reasonable gradient cooling program.

[0049] The insulated wire core is preheated by a conductor preheater, heated through a conductive rubber tube, a die head, and a die orifice temperature zone, the outer diameter expands, and a certain sealing function at the die orifice is maintained. Check the nitrogen pressure situation for leakage. After checking and finding no change, proceed with normal traction; the insulated wire core enters the heating pipeline in a nitrogen environment and is processed according to the set temperature gradient; it is heated to 280 °C in the preheating area, the temperature in the cross-linking area is maintained at 350 °C - 300 °C, the temperature is decreased to 270 °C in the pre-cooling area, and finally it enters the cooling area for water-cooling gradient cooling; at the same time, the speed of the traction device remains stable, and finally a sample after secondary cross-linking is obtained.

[0050] Conduct a comprehensive inspection on the ZA-YJV28.7 / 15kV-3*300 cable completed by secondary cross-linking production, including indicators such as insulation resistance, withstand voltage performance, outer diameter size, insulation layer thickness, and mechanical properties after aging. After inspection, all indicators meet the requirements of relevant standards, proving that this production process can stably produce high-quality cable products.

[0051] It is stipulated in GB / T12706.2-2020 that the maximum elongation at load ≤ 175%, and the maximum permanent elongation after cooling ≤ 15%. The test results are shown in Table 1, and the thermal elongation is qualified.

[0052] Table 1 Insulation Thermal Elongation Test (GB / T2951.21-2008)

[0053]

[0054] It is stipulated in GB / T12706.2-2020 that the maximum allowable shrinkage rate ≤ 4%. The test results are shown in Table 2, and the thermal shrinkage is qualified.

[0055] Table 2 Insulation Thermal Shrinkage (GB / T2951.13-2008)

[0056]

[0057] GB / T 12706.2-2020 stipulates that the tensile strength before aging ≥ 12.5 N / mm 2 , the elongation at break ≥ 200%, the maximum change rate of tensile strength after aging is ±25%, and the maximum change rate of elongation at break is ±25%. The test results are shown in Table 3, and the mechanical properties before and after aging meet the standards.

[0058] Table 3 Mechanical properties before and after aging (GB / T - 2951.11 - 2008, GB / T - 2951.12 - 2008)

[0059]

[0060] For partial discharge test equipment, the test sensitivity should be above 10 pC, and the test is carried out according to GB / T 3048.12 - 2008; a complete copper tape shield is carried out outside the insulated conductor core, the test voltage should be gradually increased to 2U0 and maintained for 10 s, and then slowly decreased to 1.73U0. At the voltage of 1.73U0, there should be no detectable discharge exceeding the declared test sensitivity generated by the cable under test. Then, an AC voltage withstand test is carried out. During the test, a voltage of 30.5 kV is applied and maintained for 5 min.

[0061] The test results show that: when testing five samples of shielded conductor cores with a loading quantity of 550 m per reel, no detectable discharge exceeding the declared test sensitivity was found during the partial discharge process, and no insulation breakdown occurred during the voltage withstand process. According to the provisions of GB / T 3048.12 - 2008 and GB / T 12706.2 - 2020, it meets the standards.

[0062] Example 2

[0063] Tests were carried out on YJY22 - 8.7 / 15 kV - 3*300 cables with the same specifications as in Example 1. Five samples of unqualified products after the first cross - linking (each section is 550 m long) were selected for testing.

[0064] Measure the outer diameter D of the insulated conductor core of the unqualified product after the first cross - linking with a cross - section of 300 mm 2 to be 31.60 mm to ensure matching with subsequent process requirements. Prepare tapes such as non - woven fabric, polyethylene tape, polytetrafluoroethylene tape, and silicone rubber sleeves for sealing treatment. At the same time, check the nitrogen supply system to ensure that the nitrogen purity and pressure meet the production requirements.

[0065] Based on the outer diameter D of the insulating wire core of the unqualified product after the first cross-linking being 31.60 mm, the inner diameter D1 of the die core is selected as D + 1.2 mm. In this embodiment, the inner diameter D1 of the die core is taken as 33 mm; the inner diameter D2 of the outer die is D1 + 0.5 mm. In this embodiment, the inner diameter D2 of the outer die is taken as 33.5 mm. Before installing the production die, clean and inspect the production die to ensure there are no impurities and defects. After installation, debug the equipment to ensure that the die is firmly installed and in the correct position. At the same time, debug the temperature control systems of the conductor preheater, the glue guide tube, and the head. Set the temperature of the conductor preheater to 85 °C, the temperature of the glue guide tube to 105 °C, the temperature of the head to 115 °C, and the temperature of the die orifice to 95 °C, and perform temperature calibration to ensure the temperature control accuracy.

[0066] After the insulating wire core is connected to the traction wire, perform multi-layer tape wrapping in strict order from the inside to the outside, that is, tightly wrap the joint with non-woven fabric, then wrap the polyethylene tape, then wrap the polytetrafluoroethylene tape, then wrap another layer of polyethylene tape, and finally put on a silicone rubber sleeve to ensure good sealing of the joint and prevent water ingress.

[0067] At the original speed of the first cross-linking (6.0 m / min in this embodiment), turn on the nitrogen supply system and adjust the pipeline pressure to 0.75 MPa. Debug the temperature control systems of the heating and cooling areas. Set the preheating area to be maintained at 280 ± 10 °C; the temperature control of the eight-section pipeline in the cross-linking area drops in a gradient from 350 °C to 300 °C; the pre-cooling area drops from 290 °C to 270 °C; the cooling area uses water cooling, and a reasonable gradient cooling program is set.

[0068] The insulating wire core is preheated by the conductor preheater, heated through the glue guide tube, the head, and the die orifice temperature zones, the outer diameter expands, maintaining a certain sealing function at the die orifice. Check the nitrogen pressure situation for any leakage. After checking and finding no change, proceed with normal traction; the insulating wire core enters the heating pipeline in the nitrogen environment and is processed according to the set temperature gradient. It is heated to 280 °C in the preheating area, the temperature in the cross-linking area is maintained at 350 - 300 °C, cooled to 270 °C in the pre-cooling area, and finally enters the cooling area for water-cooling gradient cooling; at the same time, the speed of the traction device remains stable, and finally a sample after the second cross-linking is obtained.

[0069] Conduct a comprehensive inspection on the ZA-YJV28.7 / 15kV-3*300 cable completed by the second cross-linking production, including indicators such as insulation resistance, withstand voltage performance, outer diameter size, insulation layer thickness, and mechanical properties after aging. After inspection, all indicators meet the relevant standard requirements, proving that this production process can stably produce high-quality cable products.

[0070] As shown in Table 4, the post-inspection hot elongation data shows that the samples produced at this production speed are unqualified, and the hot elongation data does not reach the lower limit of the national standard (≤175%).

[0071] By reducing the production speed, the sample can be fully heated, the inner layer can be heated more evenly, and sufficient reaction time can be provided for the cross-linking process. Although reducing the production speed increases energy consumption, it reduces the unqualified rate of cross-linking. On the other hand, it reduces greater losses, proving that the insulated wire core should have sufficient heating time in the pipeline to achieve a sufficient cross-linking effect.

[0072] Table 4 Insulation Thermal Elongation Test (GB / T 2951.21 - 2008)

[0073]

[0074]

[0075] In this embodiment, a comparative analysis of Example 1 and Example 2 and a study on the influence of production speed are carried out, and the comparison of key process parameters as shown in Table 5 can be obtained.

[0076] Table 5 Comparison of Key Process Parameters

[0077]

[0078] The speed reduction of Example 1 (4.5 m / min) extends the residence time of the wire core in the cross-linking zone by 33%, that is, the residence time t is The extended time window ensures the full progress of the cross-linking reaction, enabling the molecular chains to form a more complete three-dimensional network structure.

[0079] The speed reduction makes the temperature decay curve of the insulated wire core in the high-temperature zone of 350°C - 300°C smoother, avoiding the cross-linking termination phenomenon caused by rapid cooling. The test data shows that the temperature difference between the surface and the core of the wire core reaches 18°C at 6.0 m / min, while it is reduced to 12°C at 4.5 m / min.

[0080] Regarding the thermal elongation performance, the elongation rate of Example 1 is stable at 60 - 66% (far lower than the upper limit of 175%), and the permanent elongation rate is 0 / -1%; in Example 2, 50% of the samples are fractured, and the remaining elongation rate is out of tolerance (the actual measured value > 200%).

[0081] Regarding the thermal shrinkage performance, the shrinkage rate of Example 1 is stable at -1% to -3% (meeting the requirement of ≤ 4%); in Example 2, due to excessive residual stress, the actual shrinkage rate exceeds the standard limit value (the measured value reaches -5.2%).

[0082] Combining the relationship between the cross-linking degree (X) and the production speed (v) X = X0·e -k·v (k = 0.12 min / m), we get:

[0083] Example 1: X = 89.5% (meeting the cross-linking qualification requirements);

[0084] Example 2: X = 72.3% (below the 85% qualified threshold).

[0085] This embodiment combines Example 1 and Example 2 to verify the core of this solution - the coupling control technology of the three elements of "speed - temperature - pressure", verifies the rationality of the speed correction coefficient α = 0.75 (determined based on the rheological properties of the material), the matching relationship between gradient cooling and speed (dT / dt = 15°C / min), and the application of the nitrogen permeation kinetic equation P = Lv·D·ΔC; where D = nitrogen diffusion coefficient, by reducing the v value, the permeation efficiency is improved without changing the nitrogen pressure.

[0086] Example 1 achieved the kinetic balance of the cross - linking reaction by optimizing the secondary cross - linking production speed (reducing the speed by 25%), making the secondary cross - linked products meet the requirements of GB / T12706.2 - 2020 standard. Example 2 proves that relying solely on the original speed cannot overcome the thermodynamic limitations, verifying the necessity of the speed regulation technology of the present invention. This embodiment provides a basis for optimizing the key parameters of the cable secondary cross - linking process and has significant engineering application value.

[0087] This embodiment sets a multi - end temperature gradient at the head. Utilizing the principle that the molecular volume of uncross - linked polyethylene expands and the outer diameter increases when heated, a high - pressure sealed environment is achieved during the secondary cross - linking process, avoiding the existence of media (such as oxygen in the air that easily causes thermal oxidation of the insulation layer and water molecules that easily generate water trees, affecting the insulation performance of the product, etc.) that are likely to react unfavorably with the insulation raw material except for inert gases during the cross - linking environment;

[0088] This embodiment controls the nitrogen pressure (0.7MPa - 0.8MPa), isolates the influence of water molecules and oxygen molecules in the air during the cross - linking process, inhibits the oxidation side reaction, sets a four - section gradient temperature control model, avoids the elastic recovery lag caused by sudden cooling through the cooling rate limit, and optimizes the heat transfer efficiency to establish a dynamic mapping relationship between the nitrogen partial pressure and the temperature field, increasing the diffusion coefficient of cross - linking by - products by 3 - 5 times and reducing the volatility of the dielectric loss factor;

[0089] This embodiment adopts a five - layer coating protection system (non - woven fabric → PE tape → PTFE tape → PE tape → silicone rubber sleeve) and a material temperature - resistance gradient design (inner layer moisture - absorbing + middle layer pressure - resistant + outer layer waterproof) to achieve the sealing reliability under multiple working conditions of high temperature / high pressure / water cooling;

[0090] This embodiment constructs a complete closed - loop control system for core processing through multi - dimensional technological innovations (structural design - process parameters - material combination), focuses on solving industry pain points such as cross - linking uniformity, deformation control, stress elimination, and joint sealing, provides a powerful remedial measure for unqualified primary cross - linking of cross - linked polyethylene, and reduces the cost loss by nearly 50% compared with peeling and remanufacturing unqualified products after primary cross - linking.

[0091] Example 2

[0092] Example 2 of the present invention introduces a cable.

[0093] A cable, in the preparation process, adopts the suspension secondary cross-linking method of the medium-voltage cross-linked polyethylene cable introduced in Example 1.

[0094] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and its equivalent technologies, the present invention also intends to include these changes and modifications.

[0095] The above are only the preferred embodiments of this example and are not used to limit this example. For those skilled in the art, this example can have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this example shall be included within the protection scope of this example.

Claims

1. A catenary secondary cross-linking method for a medium voltage cross-linked polyethylene cable, characterized in that: include: Determine the production mold based on the properties of the unqualified products of the primary cross-linking; Install the determined production mold, adjust the die head temperature and pipeline pressure; Place the first cross-linked unqualified products in the production mold and pipeline, connect the secondary cross-linked traction wire and the insulated wire core of the first cross-linked unqualified products, and perform sealing multi-layer tape coating treatment at the joint; The secondary cross-linking production speed is three-quarters of the primary cross-linking production speed, the nitrogen supply is turned on in the pipeline, the pipeline pressure and the gradient temperature of the four sections of the pipeline are adjusted, and a nitrogen protection dynamic thermodynamic equilibrium system is established; The insulated wire cores that failed the primary cross-linking were treated in the constructed nitrogen-protected dynamic thermodynamic equilibrium system to complete the secondary cross-linking.

2. A catenary secondary cross-linking method for a medium voltage cross-linked polyethylene cable as claimed in claim 1, characterized in that: The constructed nitrogen protection dynamic thermodynamic equilibrium system is a secondary cross-linking pipeline with four-section gradient temperature and pressure maintained at a pressure threshold. The secondary cross-linking production speed of the insulated wire core of the primary cross-linking unqualified product is controlled according to the primary cross-linking production speed to maintain a constant secondary cross-linking production speed.

3. A catenary secondary cross-linking method for a medium voltage cross-linked polyethylene cable as claimed in claim 2, characterized in that: In the process of handling defective insulated wire cores that have undergone primary cross-linking in the constructed nitrogen-protected dynamic thermodynamic equilibrium system, the sealing condition of the production mold mouth and the nitrogen pressure in the pipeline are detected in real time, and secondary cross-linking is performed based on the preset gradient temperature and pressure thresholds of the four sections of the pipeline.

4. A catenary secondary cross-linking method for a medium voltage cross-linked polyethylene cable as claimed in claim 1, characterized in that: Nitrogen is injected into the pipeline before the secondary cross-linking to isolate the influence of air on the secondary cross-linking during the secondary cross-linking process and inhibit oxidation side reactions; during the secondary cross-linking process, the nitrogen pressure in the pipeline is maintained within the pressure threshold.

5. A catenary secondary cross-linking method for a medium voltage cross-linked polyethylene cable as claimed in claim 1, characterized in that: According to the insulation core diameter of the unqualified product of the first cross-linking, the core inner diameter and outer mold inner diameter of the secondary cross-linking production mold are selected in turn, the secondary cross-linking production mold is cleaned and inspected, the production mold is installed and the catenary production line equipment is debugged.

6. A catenary secondary cross-linking method for a medium voltage cross-linked polyethylene cable as claimed in claim 1, characterized in that: Set the temperature of the conductor preheater, rubber hose and machine head in the catenary production line equipment, and set the conductor preheater temperature, production mold mouth temperature, rubber hose temperature and machine head temperature from low to high; then debug and calibrate the temperature of the conductor preheater, rubber hose and machine head in the catenary production line equipment.

7. A catenary secondary cross-linking method for a medium voltage cross-linked polyethylene cable as claimed in claim 1, characterized in that: It also includes a performance test on the finished cable after secondary cross-linking, and the performance test at least includes insulation thermal extension, insulation thermal shrinkage, tensile strength before and after aging, and elongation at break before and after aging.

8. A catenary secondary cross-linking method for a medium voltage cross-linked polyethylene cable as claimed in claim 1, characterized in that: The multi-layer belt materials used are non-woven fabric, polyethylene belt, polytetrafluoro belt, polyethylene belt and silicone rubber sleeve from inside to outside.

9. A catenary secondary cross-linking method for a medium voltage cross-linked polyethylene cable as claimed in claim 1, characterized in that: The preheating zone, cross-linking zone, pre-cooling zone and cooling zone of the pipeline are sequentially set according to the gradient temperature of the four sections of the pipeline; the temperature of the cross-linking zone is higher than the temperature of the preheating zone and the temperature of the pre-cooling zone, the cooling zone is water-cooled, and the temperature of the cooling zone is lower than the temperature of the pre-cooling zone.

10. A cable, characterized in that: During the preparation process, a catenary secondary cross-linking method for a medium voltage cross-linked polyethylene cable as described in any one of claims 1 to 9 is adopted.

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