1E-grade medium-voltage variable-frequency cable with good heat aging resistance for ships and warships

Abstract

The invention relates to the field of cables, and particularly discloses a ship 1E-grade medium-voltage variable frequency cable with good heat aging resistance, the ship 1E-grade medium-voltage variable frequency cable comprises a conductor, an insulating layer and a sheath layer, the insulating layer comprises the following raw materials: 100-120 parts of ethylene propylene diene monomer; 70 to 90 parts of aluminum hydroxide; 70 to 90 parts of magnesium hydroxide; 10 to 15 parts of pottery clay; 5-10 parts of zinc oxide; 5-10 parts of a stabilizer; 4-6.5 parts of an anti-aging agent; 4-5 parts of microcrystalline wax; 4-5 parts of a vulcanizing agent; 1.5-2 parts of a crosslinking auxiliary agent; 1 to 1.5 parts of a coupling agent; 1-1.5 parts of a light stabilizer; 0.5 to 1 part of stearic acid; the compaction stacking density of the aluminum hydroxide is 0.5-0.8 g / cm < 3 >, the compaction stacking density of the magnesium hydroxide is 0.7-1.0 g / cm < 3 >, and the compaction stacking density of the argil is 0.7-1.0 g / cm < 3 >. The product provided by the invention has good thermal aging resistance, electrical property, flame retardant property and processing technology property.

Description

Technical Field

[0001] The present application relates to the technical field of cables, and in particular to a Class 1E medium-voltage frequency-converting cable for ships with good heat-aging resistance. Background Art

[0002] As modern shipboard power systems evolve toward higher power and greater integration, traditional low-voltage cables are no longer sufficient. Furthermore, nuclear power, with its high efficiency, stability, low carbon footprint, and economical nature, has become a core pillar of energy transformation. Class 1E medium-voltage variable-frequency cables for ships are primarily used for medium-voltage power transmission between reactor cooling systems and propulsion motors. (Class 1E cables are cables used in safety-grade electrical systems in nuclear power plants and must continuously perform safety functions under normal operating conditions, design basis events, and subsequent phases.) Due to their inherent advantages of high-power, efficient transmission, reduced losses, and reduced cable size, they have become a core component of shipboard power systems.

[0003] During long-term thermal aging, the cross-linked network of EPDM undergoes de-crosslinking reactions at high temperatures, resulting in a decrease in the material's mechanical properties (such as tensile strength and elasticity) and even embrittlement. High temperatures accelerate the oxidation reaction between oxygen and polymer chains, generating polar groups such as carbonyl and hydroxyl groups, which increase dielectric loss and reduce insulation performance. The oxidation products may trigger partial discharge or electrical treeing, which can easily cause cable breakdown and other problems during use at high voltage terminals, leading to failure of supporting equipment.

[0004] High-energy radiation (e.g., gamma rays, electron beams) can cause molecular chain breakage (degradation) or excessive cross-linking, making the material hard and brittle. Radiation decomposes the material, releasing gases (e.g., H2, CH4), which can cause internal micropores or holes, reducing insulation strength and triggering partial discharge.

[0005] Existing land-based nuclear-grade medium-voltage cables have complex structures and poor bending resistance. Ship-based nuclear-grade medium-voltage variable-frequency cables have strict requirements on product weight and outer diameter. In addition, due to the small nuclear reaction space in the cabin, if an accident occurs, the temperature and pressure generated will far exceed those of land-based nuclear power plants. Therefore, there are more stringent requirements on the cable's resistance to high temperature, high pressure, nuclear radiation, electromagnetic shielding and other special environmental performance. Summary of the Invention

[0006] In order to solve the above technical problems, the present application provides a Class 1E medium-voltage frequency conversion cable for ships with good heat aging resistance.

[0007] The present application provides a 1E-class medium-voltage frequency conversion cable for ship use with good heat aging resistance, comprising a conductor, an insulation layer, and a sheath layer arranged in sequence along the axial direction. The raw materials used for the insulation layer include the following components, by weight: 100-120 parts of EPDM; 70-90 parts of aluminum hydroxide; 70-90 parts of magnesium hydroxide; 10-15 parts of clay; 5-10 parts of zinc oxide; 5-10 parts of stabilizer; 4-6.5 parts of antioxidant; 4-5 parts of microcrystalline wax; 4-5 parts of vulcanizing agent; 1.5-2 parts of cross-linking agent; 1-1.5 parts of coupling agent; 1-1.5 parts of light stabilizer; 0.5-1 part of stearic acid; the compacted bulk density of the aluminum hydroxide is 0.5-0.8 g / cm 3 The compacted bulk density of magnesium hydroxide is 0.7-1.0g / cm 3 The compacted bulk density of clay is 0.7-1.0g / cm 3 .

[0008] By adopting the above technical solution, the present application uses EPDM as the main insulating material. Since EPDM will generate a large number of active groups when it is irradiated by radiation or high-energy electron beams, which accelerates the oxidative degradation of the material, the present application also adds a light stabilizer to capture the free radicals generated by ultraviolet rays and ionizing radiation, blocking the chain reaction of EPDM molecular chains, and reducing the generation of cross-linking or degradation products; and uses the synergistic effect of the vulcanizing agent and the cross-linking auxiliary agent to induce EPDM to form a three-dimensional cross-linked network structure. The cross-linked structure can limit the movement of the molecular chains, improve the material's resistance to radiation-induced chain breakage, and enhance the thermal stability to improve the material's radiation resistance; the present application also adds an antioxidant and a stabilizer for use in combination, by capturing the free radicals (such as O2 - , ·OH), inhibiting the oxidative degradation and cross-linking of the EPDM main chain, maintaining the mechanical properties and dielectric properties of the material. When the antioxidant is compounded with the stabilizer, multiple antioxidant defense lines can be formed to delay the molecular chain breakage and carbonyl formation caused by thermal oxidative aging; stearic acid as an auxiliary antioxidant can react with metal oxides (such as zinc oxide) to form soap compounds, reducing the risk of metal catalytic oxidation and further extending thermal life. Magnesium hydroxide, aluminum hydroxide and clay are also added to the compound. The lattice structure of magnesium hydroxide can absorb free radicals generated by high-energy radiation, inhibit the chain degradation reaction of the EPDM main chain, and at the same time decompose the hydroxide (OH -) can neutralize free radicals and delay radiation aging. Aluminum hydroxide will dehydrate and absorb heat after heating, reduce the surface temperature of the material, and slow down the combustion rate. At the same time, the water vapor and aluminum oxide produced by its decomposition will also play a certain protective effect, improving the overall thermal stability. Clay has high thermal conductivity, which can disperse local heat and reduce the temperature rise inside the material. At the same time, its layered structure can adsorb EPDM degradation products (such as volatile acids) and reduce thermal aging side reactions. More importantly, this application strictly controls the compacted bulk density of the three, optimizes the filler dispersion through density differences, and greatly weakens the electrical performance defects caused by agglomeration.

[0009] To sum up, the insulation layer of the 1E-class medium-voltage frequency conversion cable for ships in the present application is obtained by combining EPDM rubber, aluminum hydroxide, magnesium hydroxide, clay, zinc oxide, stabilizer, antioxidant, microcrystalline wax, vulcanizing agent, cross-linking aid, coupling agent, light stabilizer and stearic acid in a certain proportion. It has good heat aging resistance, electrical properties, flame retardant properties, etc. as well as processing technology performance. The experimental results show that the insulation layer has a tensile strength change rate of no more than 5% and a break elongation change rate of no more than 7% in a 168h heat aging test at 135°C. The thermal elongation at a temperature of 250°C and a duration of 15min does not exceed 25%. The insulation resistance constant at 20°C is 32800-39850. The carbonization height of the overall 1E-class medium-voltage frequency conversion cable for ships in the bundled flame retardant Class A test does not exceed 1.2m.

[0010] Preferably, the raw materials used for the insulating layer further include boron-cyclophosphazene anti-aging additive, the amount of which is 15-25 wt% of the total amount of aluminum hydroxide and magnesium hydroxide.

[0011] Preferably, the amount of the boron-cyclophosphazene anti-aging additive is 18-22 wt % of the total amount of aluminum hydroxide and magnesium hydroxide.

[0012] Preferably, the boron-cyclophosphazene anti-aging additive is prepared by the following method: ① dispersing 4-bromophenol and sodium hydroxide in an organic solvent, stirring and refluxing under the protection of inert gas, then adding hexachlorocyclotriphosphazene, stirring and refluxing under the protection of inert gas, removing the organic solvent and then adsorbing and desorbing to obtain an intermediate product, wherein the molar ratio of 4-bromophenol, sodium hydroxide and hexachlorocyclotriphosphazene is (6.5-7):7.75:(0.85-0.9); ② under the protection of inert gas, The intermediate product obtained in step ① and n-butyl lithium are blended and dispersed in an organic solvent at a temperature of -80°C to -70°C, the mixture is kept warm and stirred, triisopropyl borate is added, and the mixture is continued to be kept warm and stirred, and then the mixture is naturally warmed to room temperature and left overnight. After the organic solvent is removed, acid hydrolysis is added, and the solid is filtered, washed, and dried to obtain a boron-cyclophosphazene anti-aging additive. The molar ratio of the intermediate product obtained in step ①, n-butyl lithium, and triisopropyl borate is (4-4.5):38:(50-53).

[0013] Preferably, in step ①, the molar ratio of 4-bromophenol, sodium hydroxide and hexachlorocyclotriphosphazene is 6.9:7.75:0.86.

[0014] Preferably, in step ②, the molar ratio of the intermediate product obtained in step ①, n-butyl lithium and triisopropyl borate is 4.3:38:52.

[0015] By adopting the above technical solution, the present application prepared a boron-cyclophosphazene anti-aging additive and added it to the system in an amount of 15-25wt% of the total amount of aluminum hydroxide and magnesium hydroxide. It can have a significant synergistic effect with the aluminum hydroxide and magnesium hydroxide in the system, thereby significantly improving the flame retardant properties of the insulation layer with a relatively low addition amount, thereby improving the flame retardancy of the entire cable. The results show that after adding the boron-cyclophosphazene anti-aging additive, the carbonization height in the bundled flame retardant Class A test is reduced. More importantly, the present application strictly controls the dosage of the boron-cyclophosphazene anti-aging additive, maximizing the flame retardant properties without affecting the mechanical properties of the insulation layer.

[0016] Preferably, the magnesium hydroxide is further subjected to a modification treatment, specifically: the dried magnesium hydroxide, silane coupling agent and sodium oleate are blended in a weight ratio of 100:(0.5-2):(1-2), stirred at a temperature of 50-70°C for 8-15 minutes, cooled, filtered, washed and dried to obtain modified magnesium hydroxide.

[0017] By adopting the above technical scheme, the present application prepares modified magnesium hydroxide by blending magnesium hydroxide, silane coupling agent and sodium oleate. Sodium oleate will cover the surface of the magnesium hydroxide during the blending process, and the hydrophilic groups in its organic long chains will combine with the hydrophilic groups on the surface of the magnesium hydroxide. The hydrophobic long chains will diffuse into the interface area of ​​the macromolecular fiber and react with the macromolecular long chains, thereby changing the surface polarity of the magnesium hydroxide, improving the compatibility between magnesium hydroxide and EPDM rubber, making the combination between the two closer, and the flame retardant distribution more uniform, which is conducive to the magnesium hydroxide achieving better flame retardant effect. The silanol bond in the silane coupling agent dehydrates and condenses with the OH on the surface of the magnesium hydroxide to form a silane organic lipophilic group on the surface of the modified magnesium hydroxide, thereby improving the hydrophobic properties of the magnesium hydroxide and further enhancing the compatibility between the magnesium hydroxide and EPDM rubber.

[0018] Preferably, the dried magnesium hydroxide, silane coupling agent and sodium oleate are blended in a weight ratio of 100:1.2:1.8.

[0019] By adopting the above technical solution, the present application strictly controls the weight ratio of the three, thereby maximizing the compatibility between magnesium hydroxide and EPDM rubber.

[0020] Preferably, the insulating layer is prepared by the following method: all raw materials except the vulcanizing agent are blended, kneaded at a temperature of 130-140°C for 3-5 minutes, unloaded at a temperature of <140°C after kneading, then the vulcanizing agent is added, kneaded at a temperature of 100-110°C for 1-1.5 minutes, debonded at a temperature of <120°C after kneading, cooled, sliced, and extruded to obtain the insulating layer.

[0021] By adopting the above technical solution, the preparation method can fully and evenly mix the raw materials of the insulation layer, avoid performance defects caused by uneven mixing, and is conducive to forming a stable and uniform insulation layer structure, thereby ensuring the heat aging resistance, electrical properties, flame retardant properties, etc. and processing technology performance of the 1E-level medium-voltage frequency conversion cable for ships.

[0022] Preferably, the extrusion temperature is 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 80°C, 80°C.

[0023] By adopting the above technical solution and precisely controlling the temperature at each stage of extrusion, the raw materials of the insulation layer can be fully integrated and the physical and chemical properties can be stable, thus ensuring the molding quality and performance of the insulation layer and improving the overall quality of Class 1E medium-voltage variable-frequency cables for ships.

[0024] In summary, this application has the following beneficial technical effects: The insulation layer of the 1E-class medium-voltage frequency conversion cable for ships in the present application is obtained by combining EPDM rubber, aluminum hydroxide, magnesium hydroxide, clay, zinc oxide, stabilizer, antioxidant, microcrystalline wax, vulcanizing agent, cross-linking aid, coupling agent, light stabilizer and stearic acid in a certain proportion. It has good heat aging resistance, electrical properties, flame retardant properties, etc. as well as processing technology performance. Experimental results show that in the 168h heat aging test at 135°C, the tensile strength change rate of the insulation layer does not exceed 5%, the elongation at break does not exceed 7%, the thermal elongation at a temperature of 250°C and a duration of 15min does not exceed 25%, and the insulation resistance constant at 20°C is 32800-39850. The carbonization height of the overall 1E-class medium-voltage frequency conversion cable for ships in the bundled flame retardant Class A test does not exceed 1.2m. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a cross-sectional view of the Class 1E medium-voltage frequency conversion cable for ships of this application. DETAILED DESCRIPTION

[0026] Material Source Unless otherwise specified, the raw materials used in this application are all commercially available products, specifically: EPDM rubber was purchased from Dow Chemical with the brand number 3722; Aluminum hydroxide was purchased from Albemarle Chemical with the brand name 104LEO; Magnesium hydroxide was purchased from Shanghai Qike Fluorosilicon Materials Co., Ltd.; The clay was purchased from KaMin LLC, USA, with the brand name P-80; The curing agent DCP was purchased from Nouryon Chemicals; Cross-linking aid TAIC was purchased from Hangzhou Keli Chemical Co., Ltd. Light stabilizer UV944 was purchased from BASF, Germany; Microcrystalline wax was purchased from Cangzhou Tuofeng Wax Industry Co., Ltd., brand 80#; Coupling agent A-172 was purchased from Momentive Silicone Materials Co., Ltd. Antioxidant Naugard 445 was purchased from SI Group Chemical (Shanghai) Co., Ltd. Antioxidant Vulkanox ZMB2 / C5 was purchased from LANXESS Chemical (China) Co., Ltd. Zinc oxide was purchased from Suzhou Tengtai Chemical Technology Co., Ltd.; The stabilizer was purchased from LANXESS Chemical (China) Co., Ltd. Stearic acid was purchased from Guangdong Xinrunhao Chemical Co., Ltd.; Silane coupling agent was purchased from Dinghai Plastic Chemical Co., Ltd., KH-550; Sodium oleate was purchased from Sinopharm Chemical Reagent Co., Ltd. 4-Bromophenol, hexachlorocyclotriphosphazene, n-butyllithium, and triisopropyl borate were purchased from Beijing Huawei Ruike Chemical Co., Ltd.

[0027] The present application is further described in detail below with reference to preparation examples, embodiments and comparative examples.

[0028] Preparation Example 1.1 The preparation method of the boron-cyclophosphazene anti-aging additive comprises the following steps: ① 4-bromophenol and sodium hydroxide were dispersed in anhydrous THF, stirred and refluxed under nitrogen for 1 hour, and then hexachlorocyclotriphosphazene was dispersed in anhydrous THF to obtain a hexachlorocyclotriphosphazene solution, which was added to the aforementioned solution and stirred and refluxed under nitrogen for 18 hours. After stopping the reaction, THF was removed by rotary evaporation to obtain a yellow solid, which was adsorbed and desorbed using a silica gel column (DCM / petroleum ether = 1:3, v / v) to obtain an intermediate product, wherein the molar ratio of 4-bromophenol, sodium hydroxide and hexachlorocyclotriphosphazene was 6.5:7.75:0.9; ② In a sealed container, the intermediate product obtained in step ① was dispersed in anhydrous THF, and the nitrogen was repeatedly evacuated and flushed, and then a nitrogen bag was connected. The sealed container was placed in an acetone / dry ice bath and stirred to completely dissolve the intermediate product. The system was cooled to -80 ° C, and then n-butyl lithium was slowly added dropwise thereto, maintaining a nitrogen atmosphere and temperature, and stirred for 2h. After adding triisopropyl borate, the nitrogen atmosphere and temperature were continued to be maintained and stirred for 2h, and then naturally warmed to room temperature overnight. After stopping the reaction, the THF was removed by rotary evaporation to obtain a yellow solid, which was added to deionized water, and a small amount of hydrochloric acid was added dropwise and stirred for hydrolysis for 1h. The solid was collected by filtration, washed three times in deionized water, and washed three times in DCM to obtain a boron-cyclophosphazene aging-resistant additive. The molar ratio of the intermediate product obtained in step ①, n-butyl lithium and triisopropyl borate was 4:38:53.

[0029] Preparation Example 1.2 The preparation method of the boron-cyclophosphazene anti-aging additive comprises the following steps: ① 4-bromophenol and sodium hydroxide were dispersed in anhydrous THF, stirred and refluxed under nitrogen for 1 hour, and then hexachlorocyclotriphosphazene was dispersed in anhydrous THF to obtain a hexachlorocyclotriphosphazene solution, which was added to the aforementioned solution and stirred and refluxed under nitrogen for 18 hours. After stopping the reaction, THF was removed by rotary evaporation to obtain a yellow solid, which was adsorbed and desorbed using a silica gel column (DCM / petroleum ether = 1:3, v / v) to obtain an intermediate product, wherein the molar ratio of 4-bromophenol, sodium hydroxide and hexachlorocyclotriphosphazene was 7:7.75:0.85; ② In a sealed container, the intermediate product obtained in step ① was dispersed in anhydrous THF, and the nitrogen was repeatedly evacuated and flushed, and then a nitrogen bag was connected. The sealed container was placed in an acetone / dry ice bath and stirred to completely dissolve the intermediate product. The system was cooled to -80 ° C, and then n-butyl lithium was slowly added dropwise thereto, maintaining a nitrogen atmosphere and temperature, and stirred for 2h. After adding triisopropyl borate, the nitrogen atmosphere and temperature were continued to be maintained and stirred for 2h, and then naturally warmed to room temperature overnight. After stopping the reaction, the THF was removed by rotary evaporation to obtain a yellow solid, which was added to deionized water, and a small amount of hydrochloric acid was added dropwise and stirred for hydrolysis for 1h. The solid was collected by filtration, washed three times in deionized water, and washed three times in DCM to obtain a boron-cyclophosphazene aging-resistant additive. The molar ratio of the intermediate product obtained in step ①, n-butyl lithium and triisopropyl borate was 4.5:38:50.

[0030] Preparation Example 2.1 The preparation method of the boron-cyclophosphazene anti-aging additive is different from that of Preparation Example 1.1 in that: in step ①, the molar ratio of 4-bromophenol, sodium hydroxide and hexachlorocyclotriphosphazene is 6.9:7.75:0.86, and the rest is the same as Preparation Example 1.1.

[0031] Preparation Example 2.2 The preparation method of the boron-cyclophosphazene anti-aging additive is different from that of Preparation Example 1.1 in that: in step ①, the molar ratio of 4-bromophenol, sodium hydroxide and hexachlorocyclotriphosphazene is 6.7:7.75:0.88, and the rest is the same as Preparation Example 1.1.

[0032] Preparation Example 3.1 The preparation method of the boron-cyclophosphazene anti-aging additive is different from that of Preparation Example 2.1 in that: in step ②, the molar ratio of the intermediate product obtained in step ①, n-butyl lithium and triisopropyl borate is 4.3:38:52, and the rest is the same as Preparation Example 2.1.

[0033] Preparation Example 3.2 The preparation method of the boron-cyclophosphazene anti-aging additive is different from that of Preparation Example 2.1 in that: in step ②, the molar ratio of the intermediate product obtained in step ①, n-butyl lithium and triisopropyl borate is 4.4:38:51, and the rest is the same as Preparation Example 2.1.

[0034] Example 1.1 A method for preparing a Class 1E medium-voltage frequency conversion cable for ship use having good heat aging resistance comprises the following steps: S1, such as Figure 1 As shown, the conductor is made of tinned copper wire using a hot-dip coating process. The conductor strands have a bundled pitch-diameter ratio of 30 times, the bundle direction is left-handed, and the strand outer diameter is 2.3mm. The inner conductor has a twisted pitch-diameter ratio of 20 times, and the outer conductor has a twisted pitch-diameter ratio of 16 times. The inner and outer layers are twisted in a left-handed direction, and the outer diameter of the twisted conductor is 16.2mm. The conductor is bundled and twisted in the same direction, reducing the gaps between the conductor filaments. If bending occurs, the inner and outer conductors will move simultaneously without relative displacement, resulting in less bending stress. In addition, a large-pitch production process is used for twisting. To prevent loosening and floating threads due to the increased pitch, the conductor is wrapped with a layer of reinforced non-woven fabric, which can be wrapped evenly. The conductor is also wrapped with a layer of semi-conductive polytetramethylene tape with a nominal thickness of 0.2mm, and the overlap rate should be no less than 25%. S2, all raw materials except the vulcanizing agent are blended (specific components and amounts are shown in Table 1, wherein the compacted bulk density of aluminum hydroxide is 0.5-0.8 g / cm 3 The compacted bulk density of magnesium hydroxide is 0.7-1.0g / cm 3 The compacted bulk density of clay is 0.7-1.0g / cm 3), kneading at a temperature of 140°C for 3 minutes, unloading at a temperature of less than 140°C after kneading, then adding a vulcanizing agent, kneading at a temperature of 110°C for 1 minute, debonding at a temperature of less than 120°C after kneading, cooling, slicing, and extrusion. The conductor shielding layer, the insulating layer, and the insulating shielding layer are co-extruded on the outside of the conductor. The thickness of the conductor shielding layer and the insulating shielding layer at the thinnest part is not less than 0.5mm. They are all composed of extruded semi-conductive shielding material and a layer of overlapping semi-conductive tape. The nominal thickness of the insulating layer is controlled to be 4.5mm. The insulation extrusion temperature is 55°C, 60°C, 65°C, 7 0℃, 75℃, 80℃, 80℃, 80℃, the production water level is 15%, the air pressure is 8.5bar, the outer diameter after three-layer co-extrusion is 30.0mm, after preparation, put it into the degassing chamber for parking and degassing, the degassing chamber temperature is (40-50)℃, the degassing time is not less than 12h, the wire core is wrapped with a layer of semi-conductive terylene tape with a nominal thickness of 0.2mm, the wrapping coverage rate should be not less than 25%, and then a tinned copper wire is used to weave a metal shielding layer, the tinned copper wire nominal diameter is 0.25mm, and the braiding coverage rate is not less than 88% to obtain an insulated wire core, and a total of three groups of identical insulated wire cores are made; S3. Twist three groups of identical insulated cores together, use a vulcanized inner arc triangular filling strip in the center, and "one large and two small" circular filling strips on the sides. The filling strips are made of aramid and semi-conductive shielding material. After the cable is formed, wrap it with two layers of low-smoke halogen-free flame retardant tape with a nominal thickness of 0.2mm. The outer diameter after the cable is wrapped is 69.5mm. Then, cross-linked polyolefin is extruded on the outer layer of the cable wrapping to obtain an inner sheath layer with a nominal thickness of 3.5mm. The mold core / mold sleeve is 70.5mm / 77.0mm, and the extrusion temperature is: 110℃, 120℃, 130℃, 140℃, 145℃, 150℃, 160℃, 160℃, 160℃, 160℃. After extrusion, segmented cooling is used (using different sections of cooling water tanks, the first section of the cooling water tank temperature is 40-60℃, and the second section is room temperature water) to ensure that the sheath material has good crystallinity. The outer diameter of the sheath after extrusion is 77.5mm. During the production process, the processing temperature is controlled, and the processing speed and screw speed are correspondingly controlled (the pulling speed is 5m / min and the screw speed is 15r / min) to avoid excessive temperature and excessive time, which may cause material degradation. In addition, radiation cross-linking is adopted. The irradiation process is as follows: 4 passes, beam current 30mA, speed 12m / min, energy 2.7Mev, and thermal extension is controlled at 20%-30%. The armor layer is then prepared, using a layer of copper plastic tape (inner) + tinned copper wire (outer) braided armor. The nominal thickness of the copper plastic tape is 0.05mm, the copper surface of the copper plastic tape faces inward, and the wrapping coverage rate is not less than 15%. The nominal diameter of the tinned copper wire is 0.4mm, and the braiding coverage rate is not less than 88%. One layer of reinforced non-woven fabric with a nominal thickness of 0.16 mm is allowed to be wrapped around the braided cable core, and the wrapping coverage rate is not less than 15%. The outer layer of the armor layer is extruded with cross-linked polyolefin to obtain the outer sheath layer. The nominal thickness of the outer sheath layer is 2.8 mm, the mold core / mold sleeve: 79.5 mm / 86.0 mm, and the extrusion temperature: 110°C, 120°C, 130°C, 140°C, 145°C, 150°C, 160°C, 160°C, 160°C, 160°C. After extrusion, segmented cooling is adopted to ensure that the sheath material has good crystallinity. The outer diameter of the sheath after extrusion is 86.5mm. The processing temperature is controlled during the production process, and the processing speed and screw speed are correspondingly controlled (the traction speed is 5m / min and the screw speed is 18r / min) to avoid excessive temperature and excessive time, which may cause material degradation. Irradiation cross-linking is adopted. The irradiation process is as follows: 4 passes, 30mA beam current, 12m / min speed, and 2.7Mev energy. The inner sheath layer, armor layer, and outer sheath layer constitute the sheath layer, and finally a Class 1E medium-voltage variable-frequency cable for ships is obtained.

[0035] Example 1.2 A method for preparing a Class 1E medium-voltage frequency conversion cable for ship use having good heat aging resistance comprises the following steps: S1, such as Figure 1As shown, the conductor is made of tinned copper wire using a hot-dip coating process. The conductor strands have a bundled pitch-diameter ratio of 30 times, the bundle direction is left-handed, and the strand outer diameter is 2.3mm. The inner conductor has a twisted pitch-diameter ratio of 20 times, and the outer conductor has a twisted pitch-diameter ratio of 16 times. The inner and outer layers are twisted in a left-handed direction, and the outer diameter of the twisted conductor is 16.2mm. The conductor is bundled and twisted in the same direction, reducing the gaps between the conductor filaments. If bending occurs, the inner and outer conductors will move simultaneously without relative displacement, resulting in less bending stress. In addition, a large-pitch production process is used for twisting. To prevent loosening and floating threads due to the increased pitch, the conductor is wrapped with a layer of reinforced non-woven fabric, which can be wrapped evenly. The conductor is also wrapped with a layer of semi-conductive polytetramethylene tape with a nominal thickness of 0.2mm, and the overlap rate should be no less than 25%. S2, all raw materials except the vulcanizing agent are blended (specific components and amounts are shown in Table 1, wherein the compacted bulk density of aluminum hydroxide is 0.5-0.8 g / cm 3 The compacted bulk density of magnesium hydroxide is 0.7-1.0g / cm 3 The compacted bulk density of clay is 0.7-1.0g / cm 3 ), kneading at a temperature of 130°C for 5 minutes, unloading at a temperature of <140°C after the kneading is completed, and then adding a vulcanizing agent, kneading at a temperature of 100°C for 1.5 minutes, and removing the glue at a temperature of <120°C after the kneading is completed, cooling, slicing, and extrusion. The conductor shielding layer, the insulating layer, and the insulating shielding layer are co-extruded on the outside of the conductor. The thickness of the conductor shielding layer and the insulating shielding layer at the thinnest part is not less than 0.5mm. They are all composed of extruded semi-conductive shielding material and a layer of overlapping semi-conductive tape. The nominal thickness of the insulating layer is controlled to be 4.5mm. The insulation extrusion temperature is 55°C, 60°C, 65°C, 70℃, 75℃, 80℃, 80℃, 80℃, the production water level is 15%, the air pressure is 8.5bar, the outer diameter after three-layer co-extrusion is 30.0mm, after preparation, put it into the degassing chamber for parking and degassing, the degassing chamber temperature is (40-50)℃, the degassing time is not less than 12h, the wire core is wrapped with a layer of semi-conductive terylene tape with a nominal thickness of 0.2mm, the wrapping coverage rate should be not less than 25%, and then a tinned copper wire is used to weave a metal shielding layer, the tinned copper wire nominal diameter is 0.25mm, and the braiding coverage rate is not less than 88% to obtain an insulated wire core, and a total of three groups of identical insulated wire cores are made; S3. Twist three groups of identical insulated cores together, use a vulcanized inner arc triangular filling strip in the center, and "one large and two small" circular filling strips on the sides. The filling strips are made of aramid and semi-conductive shielding material. After the cable is formed, wrap it with two layers of low-smoke halogen-free flame retardant tape with a nominal thickness of 0.2mm. The outer diameter after the cable is wrapped is 69.5mm. Then, cross-linked polyolefin is extruded on the outer layer of the cable wrapping to obtain an inner sheath layer with a nominal thickness of 3.5mm. The mold core / mold sleeve is 70.5mm / 77.0mm, and the extrusion temperature is: 110℃, 120℃, 130℃, 140℃, 145℃, 150℃, 160℃, 160℃, 160℃, 160℃. After extrusion, segmented cooling is used (using different sections of cooling water tanks, the first section of the cooling water tank temperature is 40-60℃, and the second section is room temperature water) to ensure that the sheath material has good crystallinity. The outer diameter of the sheath after extrusion is 77.5mm. During the production process, the processing temperature is controlled, and the processing speed and screw speed are correspondingly controlled (the pulling speed is 5m / min and the screw speed is 15r / min) to avoid excessive temperature and excessive time, which may cause material degradation. In addition, radiation cross-linking is adopted. The irradiation process is as follows: 4 passes, beam current 30mA, speed 12m / min, energy 2.7Mev, and thermal extension is controlled at 20%-30%. The armor layer is then prepared, using a layer of copper plastic tape (inner) + tinned copper wire (outer) braided armor. The nominal thickness of the copper plastic tape is 0.05mm, the copper surface of the copper plastic tape faces inward, and the wrapping coverage rate is not less than 15%. The nominal diameter of the tinned copper wire is 0.4mm, and the braiding coverage rate is not less than 88%. One layer of reinforced non-woven fabric with a nominal thickness of 0.16 mm is allowed to be wrapped around the braided cable core, and the wrapping coverage rate is not less than 15%. The outer layer of the armor layer is extruded with cross-linked polyolefin to obtain the outer sheath layer. The nominal thickness of the outer sheath layer is 2.8 mm, the mold core / mold sleeve: 79.5 mm / 86.0 mm, and the extrusion temperature: 110°C, 120°C, 130°C, 140°C, 145°C, 150°C, 160°C, 160°C, 160°C, 160°C. After extrusion, segmented cooling is adopted to ensure that the sheath material has good crystallinity. The outer diameter of the sheath after extrusion is 86.5mm. The processing temperature is controlled during the production process, and the processing speed and screw speed are correspondingly controlled (the traction speed is 5m / min and the screw speed is 18r / min) to avoid excessive temperature and excessive time, which may cause material degradation. Irradiation cross-linking is adopted. The irradiation process is as follows: 4 passes, 30mA beam current, 12m / min speed, and 2.7Mev energy. The inner sheath layer, armor layer, and outer sheath layer constitute the sheath layer, and finally a Class 1E medium-voltage variable-frequency cable for ships is obtained.

[0036] Table 1 Details of raw materials and dosage of Examples 1.1-1.2 (kg) Components Example 1.1 Dosage Example 1.2 Dosage EPDM 10 12 aluminum hydroxide 9 7 magnesium hydroxide 7 9 clay 1 1.5 zinc oxide 1 0.5 stabilizer 0.5 1 Antioxidant Naugard445 0.15 0.1 Antioxidant Vulkanox ZMB2 / C5 0.5 0.3 microcrystalline wax 0.4 0.5 vulcanizing agent 0.05 0.04 Crosslinking aids 0.15 0.2 coupling agent 0.15 0.1 Light stabilizers 0.1 0.15 stearic acid 0.1 0.05 Example 2.1 A method for preparing a Class 1E medium-voltage variable-frequency cable for ships with good heat aging resistance is different from that of Example 1.1 in that, in step S2, 2.4 kg of the boron-cyclophosphazene anti-aging additive prepared in Preparation Example 1.1 is also added and blended with all raw materials except the vulcanizing agent, and the rest are the same as in Example 1.1.

[0037] Example 2.2 A method for preparing a Class 1E medium-voltage variable-frequency cable for ships with good heat-aging resistance is different from that of Example 1.1 in that, in step S2, 4 kg of the boron-cyclophosphazene anti-aging additive prepared in Preparation Example 1.2 is also added and blended with all raw materials except the vulcanizing agent. The rest is the same as in Example 1.1.

[0038] Example 2.3 A method for preparing a Class 1E medium-voltage frequency conversion cable for ships with good heat aging resistance is different from that of Example 2.1 in that, in step S2, the amount of the boron-cyclophosphazene anti-aging additive prepared in Preparation Example 1.1 added is 2.6 kg, and the rest is the same as Example 2.1.

[0039] Example 2.4 A method for preparing a Class 1E medium-voltage variable-frequency cable for ships with good heat aging resistance is different from that of Example 2.1 in that, in step S2, the amount of the boron-cyclophosphazene anti-aging agent prepared in Preparation Example 1.1 added is 2.9 kg, and the rest is the same as Example 2.1.

[0040] Example 2.5 A method for preparing a Class 1E medium-voltage frequency conversion cable for ships with good heat aging resistance is different from that of Example 2.1 in that, in step S2, the amount of the boron-cyclophosphazene anti-aging additive prepared in Preparation Example 1.1 added is 3.1 kg, and the rest is the same as Example 2.1.

[0041] Example 2.6 A method for preparing a Class 1E medium-voltage variable-frequency cable for ships with good heat aging resistance is different from that of Example 2.1 in that, in step S2, the amount of the boron-cyclophosphazene anti-aging additive prepared in Preparation Example 1.1 added is 3.5 kg, and the rest is the same as Example 2.1.

[0042] Example 2.7 A method for preparing a Class 1E medium-voltage frequency conversion cable for ships with good heat aging resistance is different from Example 2.1 in that, in step S2, the amount of the boron-cyclophosphazene anti-aging additive prepared in Preparation Example 1.1 added is 3.75 kg, and the rest is the same as Example 2.1.

[0043] Example 3.1 A method for preparing a Class 1E medium-voltage frequency conversion cable for ships with good heat aging resistance is different from that of Example 2.5 in that, in step S2, the boron-cyclophosphazene anti-aging agent prepared in Preparation Example 1.1 is replaced by the boron-cyclophosphazene anti-aging agent prepared in Preparation Example 2.1, and the rest is the same as Example 2.5.

[0044] Example 3.2 A method for preparing a Class 1E medium-voltage frequency-converter cable for ships with good heat-aging resistance is different from that of Example 2.5 in that, in step S2, the boron-cyclophosphazene anti-aging agent prepared in Preparation Example 1.1 is replaced by the boron-cyclophosphazene anti-aging agent prepared in Preparation Example 2.2, and the rest is the same as Example 2.5.

[0045] Example 4.1 A method for preparing a Class 1E medium-voltage frequency-converter cable for ships with good heat-aging resistance is different from that of Example 3.1 in that, in step S2, the boron-cyclophosphazene anti-aging agent prepared in Preparation Example 2.1 is replaced by the boron-cyclophosphazene anti-aging agent prepared in Preparation Example 3.1, and the rest is the same as Example 3.1.

[0046] Example 4.2 A method for preparing a Class 1E medium-voltage frequency conversion cable for ships with good heat aging resistance is different from that of Example 3.1 in that, in step S2, the boron-cyclophosphazene anti-aging agent prepared in Preparation Example 2.1 is replaced by the boron-cyclophosphazene anti-aging agent prepared in Preparation Example 3.2, and the rest is the same as Example 3.1.

[0047] Example 5.1 A method for preparing a 1E-class medium-voltage frequency conversion cable for ships with good heat aging resistance, which differs from Example 1.1 in that, in step S2, the magnesium hydroxide is further modified, specifically: the magnesium hydroxide is dried at 80°C for 10 hours, cooled for standby use, the silane coupling agent and sodium oleate are dispersed in anhydrous ethanol, stirred for 30 minutes for standby use, the dried magnesium hydroxide is added to the aforementioned silane coupling agent and sodium oleate solution three times, ultrasonically stirred at 50°C for 15 minutes, cooled to room temperature, filtered, washed twice with anhydrous ethanol, and dried at 80°C until the system has a constant weight to obtain modified magnesium hydroxide, and the weight ratio of the dried magnesium hydroxide, silane coupling agent and sodium oleate is controlled at 100:0.5:2.

[0048] Example 5.2 A method for preparing a 1E-class medium-voltage frequency conversion cable for ships with good heat aging resistance, which differs from Example 1.1 in that, in step S2, the magnesium hydroxide is further modified, specifically: the magnesium hydroxide is dried at 80°C for 10 hours, cooled for standby use, the silane coupling agent and sodium oleate are dispersed in anhydrous ethanol, stirred for 30 minutes for standby use, the dried magnesium hydroxide is added to the aforementioned silane coupling agent and sodium oleate solution three times, ultrasonically stirred at 70°C for 8 minutes, cooled to room temperature, filtered, washed twice with anhydrous ethanol, and dried at 80°C until the system reaches constant weight to obtain modified magnesium hydroxide, and the weight ratio of the dried magnesium hydroxide, silane coupling agent and sodium oleate is controlled at 100:2:1.

[0049] Example 5.3 A method for preparing a Class 1E medium-voltage frequency conversion cable for ships with good heat aging resistance is different from Example 5.1 in that the weight ratio of the dried magnesium hydroxide, silane coupling agent, and sodium oleate is controlled at 100:1.5:1.5, and the rest is the same as Example 5.1.

[0050] Example 5.4 A method for preparing a Class 1E medium-voltage frequency conversion cable for ships with good heat aging resistance is different from Example 5.1 in that the weight ratio of the dried magnesium hydroxide, silane coupling agent, and sodium oleate is controlled at 100:1.2:1.8, and the rest is the same as Example 5.1.

[0051] Comparative Example 1.1 The difference from Example 1.1 is that in step S2, magnesium hydroxide is removed, the amount of aluminum hydroxide used is 14.8 kg, the amount of pottery clay used is 2.2 kg, and the rest is the same as Example 1.1.

[0052] Comparative Example 1.2 The difference from Example 1.1 is that in step S2, aluminum hydroxide is removed, the amount of magnesium hydroxide used is 14.8 kg, the amount of pottery clay used is 2.2 kg, and the rest is the same as Example 1.1.

[0053] Comparative Example 1.3 The difference from Example 1.1 is that in step S2, the clay is removed, the amount of aluminum hydroxide used is 9.56 kg, and the amount of magnesium hydroxide used is 7.44 kg. The rest is the same as Example 1.1.

[0054] Comparative Example 2.1 The difference from Example 1.1 is that in step S2, magnesium hydroxide and aluminum hydroxide are removed, the amount of clay used is 17 kg, and the rest is the same as Example 1.1.

[0055] Comparative Example 2.2 The difference from Example 1.1 is that in step S2, the clay and aluminum hydroxide are removed, the amount of magnesium hydroxide used is 17 kg, and the rest is the same as Example 1.1.

[0056] Comparative Example 2.3 The difference from Example 1.1 is that in step S2, magnesium hydroxide and clay are removed, the amount of aluminum hydroxide used is 17 kg, and the rest is the same as Example 1.1.

[0057] Comparative Example 3.1 The difference from Example 2.5 is that in step S2, magnesium hydroxide is removed, the amount of aluminum hydroxide used is 14.8 kg, the amount of clay used is 2.2 kg, and the rest is the same as Example 2.5.

[0058] Comparative Example 3.2 The difference from Example 2.5 is that in step S2, aluminum hydroxide is removed, the amount of magnesium hydroxide used is 14.8 kg, the amount of clay used is 2.2 kg, and the rest is the same as Example 2.5.

[0059] Performance testing 1. The cables were subjected to a 50-year heat aging test (155°C, 895h) and an irradiation aging test (550kGy). The sheath appearance and withstand voltage (3.5kV / 5min) of Examples 1.1-5.4 were found to be acceptable. The cables were of good apparent quality, free of cracks and exhibited no breakdown at 3.5kV / 5min. The insulation resistance constant (MΩ·km) at 20°C after immersion in water after heat aging and irradiation aging, as well as the charring height (m) in the bundled Class A test after irradiation aging, are detailed in Table 2.1. 2. After heat aging and radiation aging, place the cables in air for gamma irradiation with a cumulative dose of 935 kGy. Perform an accidental radiation aging test and record the passing results in Table 2.1. 3. Subject the cable to a high-temperature, high-pressure accident environment test (360 hours, 230°C, 2.2MPa) and record the passing results in Table 2.1; 4. According to standards GJB 1916-1994 and GJB 774-2020, the tensile strength (MPa) and elongation at break of the insulation layer were tested, as well as the change rate of tensile strength (%) and elongation at break (%) in a 168h thermal aging test at 135°C, the thermal elongation at 250°C for 15min (the value was found to be stable between 15% and 25% after testing), and the insulation resistance constant at 20°C (the value was found to be stable between 32800 and 39850 after testing). The results of tensile strength and its change rate (%), and elongation at break and its change rate (%) are recorded in Table 2.2.

[0060] Table 2.1 Special performance test table (optimization test) Table 2.2 Insulation performance test table (routine test) Data Analysis: It can be seen from Tables 2.1-2.2 that the thermal aging insulation resistance constant of Examples 1.1-1.2 is 14900-15000 MΩ·km, the radiation aging insulation resistance constant is 8670 MΩ·km, the carbonization height of the bundled Class A test after radiation aging is 1.78-1.79m, the tensile strength of the insulation layer of Examples 1.1-1.2 is 9.5-9.6 MPa, the elongation at break is 350-360%, the tensile strength change rate after the thermal aging test is -4.9 to -5.0%, and the elongation change rate is -12.0% to -13.0%, which proves that the insulation layer of the 1E-class medium-voltage frequency conversion cable for ships in this application is obtained by combining EPDM rubber, aluminum hydroxide, magnesium hydroxide, clay, zinc oxide, stabilizer, antioxidant, microcrystalline wax, vulcanizing agent, cross-linking aid, coupling agent, light stabilizer and stearic acid in a certain proportion, and has good heat aging resistance, electrical properties and processing performance.

[0061] The difference between Examples 2.1-4.2 and Example 1.1 is that a certain amount of boron-cyclophosphazene anti-aging additive is also added in the present application. The results show that the thermal aging insulation resistance constant and the radiation aging insulation resistance constant are improved, the carbonization height of the bundled Class A test after radiation aging is reduced, and the tensile strength change rate, elongation at break change rate and carbonization height of the entire cable after the thermal aging test of the insulation layer are significantly reduced, proving that the boron-cyclophosphazene anti-aging additive of the present application can have a significant synergistic effect with the aluminum hydroxide and magnesium hydroxide in the system, thereby greatly improving the flame retardant properties of the insulation layer with a lower addition amount, thereby improving the flame retardancy of the entire cable.

[0062] Among the many embodiments of the present application, only Examples 3.1-4.2 can pass the accident radiation aging test and the high-temperature and high-pressure accident environment resistance test. This is because the present application adjusts the amount of boron-cyclophosphazene anti-aging additive added to make it more suitable, and strictly controls the proportion of each substance during preparation, so that the heat resistance, radiation resistance, high-voltage resistance and flame retardancy of the overall cable are further improved. In addition, in-depth tests were conducted on Examples 3.1-4.2, and it was found that they still have good mechanical properties after undergoing 50 years of life aging, and can meet the conditions of radiation aging, high temperature and high pressure, and still have good electrical properties under the premise that the insulation layer has been aged and damaged.

[0063] The difference between Examples 5.1-5.4 and Example 1.1 is that the present application modified the magnesium hydroxide, and the results showed that the thermal aging insulation resistance constant and the radiation aging insulation resistance constant were improved, and the carbonization height of the bundled Class A test after radiation aging was reduced, and the tensile strength change rate and elongation at break change rate of the insulation layer after thermal aging test and the carbonization height of the entire cable were significantly optimized. At the same time, the tensile strength before the thermal aging test was also improved to a certain extent, proving that the present application prepared modified magnesium hydroxide by blending magnesium hydroxide, silane coupling agent and sodium oleate. Sodium oleate will cover the surface of magnesium hydroxide during the blending process, and the hydrophilicity in its organic long chain is The groups will combine with the hydrophilic groups on the surface of magnesium hydroxide, and the hydrophobic long chains will diffuse into the interface area of ​​the macromolecular fibers and interact with the macromolecular long chains, thereby changing the surface polarity of magnesium hydroxide, improving the compatibility between magnesium hydroxide and EPDM rubber, making the combination between the two closer, and the flame retardant distribution more uniform, which is conducive to magnesium hydroxide achieving better flame retardant effect. The silanol bond in the silane coupling agent dehydrates and condenses with the OH on the surface of magnesium hydroxide to form a silane organic lipophilic group on the surface of the modified magnesium hydroxide, thereby improving the hydrophobic properties of magnesium hydroxide and further enhancing the compatibility between magnesium hydroxide and EPDM rubber.

[0064] In comparative examples 1.1-1.3, the present application removed aluminum hydroxide, magnesium hydroxide, and clay respectively. In comparative examples 2.1-2.3, the present application only used clay, magnesium hydroxide, and aluminum hydroxide respectively. The results showed that the thermal aging insulation resistance constant and the radiation aging insulation resistance constant decreased, and the carbonization height of the bundled Class A test after radiation aging was improved. The change rate of tensile strength, the change rate of elongation at break, and the carbonization height of the entire cable after the thermal aging test of the insulation layer were significantly improved, proving that the present application added magnesium hydroxide, aluminum hydroxide and clay as a composite, wherein the lattice structure of magnesium hydroxide can absorb free radicals generated by high-energy radiation, inhibit the chain degradation reaction of the EPDM main chain, and decompose the generated hydroxide (OH - ) can neutralize free radicals and delay radiation aging. Aluminum hydroxide will dehydrate and absorb heat after heating, reduce the surface temperature of the material, and slow down the combustion rate. At the same time, the water vapor and aluminum oxide produced by its decomposition will also play a certain protective effect, improving the overall thermal stability. Clay has high thermal conductivity, which can disperse local heat and reduce the temperature rise inside the material. At the same time, its layered structure can adsorb EPDM degradation products (such as volatile acids) and reduce thermal aging side reactions. More importantly, this application strictly controls the compacted bulk density of the three, optimizes the filler dispersion through density differences, and greatly weakens the electrical performance defects caused by agglomeration.

[0065] In Comparative Examples 3.1-3.2, the present application removed magnesium hydroxide and aluminum hydroxide respectively on the basis of Example 2.5. The results showed that the thermal aging insulation resistance constant and the radiation aging insulation resistance constant were reduced, and the carbonization height of the bundled Class A test was improved after radiation aging. In addition, the tensile strength change rate, elongation at break change rate and carbonization height of the entire cable after the thermal aging test of the insulation layer were poor, and some data were even worse than Example 1.1, proving that the boron-cyclophosphazene anti-aging additive can have a significant synergistic effect with the aluminum hydroxide and magnesium hydroxide in the system, thereby greatly improving the flame retardant properties of the insulation layer with a lower addition amount, thereby improving the flame retardancy of the entire cable.

[0066] The embodiments of this specific implementation method are all preferred embodiments of the present application and are not intended to limit the scope of protection of the present application. Therefore, any equivalent changes made based on the structure, shape, and principle of the present application should be included in the scope of protection of the present application.

Claims

1. A Class 1E medium voltage variable frequency cable for ship use with good heat aging resistance, comprising a conductor, an insulation layer and a sheath layer arranged in sequence along the axial direction, characterized in that: The raw materials used for the insulating layer include the following components by weight: 100-120 parts of EPDM; 70-90 parts of aluminum hydroxide; 70-90 parts of magnesium hydroxide; 10-15 parts of clay; 5-10 parts of zinc oxide; and 5-10 parts of stabilizer. 4-6.5 parts of antioxidant; 4-5 parts of microcrystalline wax; 4-5 parts of vulcanizing agent; 1.5-2 parts of crosslinking agent; 1-1.5 parts of coupling agent; 1-1.5 parts of light stabilizer; 0.5-1 part of stearic acid; the compacted bulk density of the aluminum hydroxide is 0.5-0.8 g / cm 3 The compacted bulk density of magnesium hydroxide is 0.7-1.0g / cm 3 The compacted bulk density of clay is 0.7-1.0g / cm 3 .

2. A Class 1E medium voltage frequency conversion cable for ships with good heat aging resistance according to claim 1, characterized in that: The raw materials used for the insulating layer also include boron-cyclophosphazene anti-aging additive, the amount of which is 15-25wt% of the total amount of aluminum hydroxide and magnesium hydroxide.

3. A Class 1E medium voltage frequency conversion cable for ships with good heat aging resistance according to claim 2, characterized in that: The amount of the boron-cyclophosphazene anti-aging additive is 18-22 wt % of the total amount of aluminum hydroxide and magnesium hydroxide.

4. A Class 1E medium voltage frequency conversion cable for ships with good heat aging resistance according to claim 2, characterized in that: The boron-cyclophosphazene aging-resistant additive is prepared by the following method: ① Dispersing 4-bromophenol and sodium hydroxide in an organic solvent, stirring and refluxing under the protection of an inert gas, then adding hexachlorocyclotriphosphazene, stirring and refluxing under the protection of an inert gas, removing the organic solvent, and then adsorbing and desorbing to obtain an intermediate product, wherein the molar ratio of the 4-bromophenol, sodium hydroxide, and hexachlorocyclotriphosphazene is (6.5-7):7.75:(0.85-0.9); ② Under the protection of inert gas, the intermediate product obtained in step ① and n-butyl lithium are blended and dispersed in an organic solvent at a temperature of -80°C to -70°C, and the mixture is kept warm and stirred. After adding triisopropyl borate, the mixture is continued to be kept warm and stirred. The mixture is then naturally warmed to room temperature and left overnight. After removing the organic solvent, acid hydrolysis is added, and the solid is filtered, washed, and dried to obtain a boron-cyclophosphazene anti-aging additive. The molar ratio of the intermediate product obtained in step ①, n-butyl lithium, and triisopropyl borate is (4-4.5):38:(50-53).

5. A Class 1E medium voltage frequency conversion cable for ships with good heat aging resistance according to claim 4, characterized in that: In the step ①, the molar ratio of 4-bromophenol, sodium hydroxide and hexachlorocyclotriphosphazene is 6.9:7.75:0.

86.

6. A Class 1E medium voltage frequency conversion cable for ships with good heat aging resistance according to claim 4, characterized in that: In step ②, the molar ratio of the intermediate product obtained in step ①, n-butyl lithium and triisopropyl borate is 4.3:38:

52.

7. The 1E-class medium voltage frequency conversion cable for ships with good heat aging resistance according to claim 1, characterized in that: The magnesium hydroxide is further subjected to a modification treatment, specifically: the dried magnesium hydroxide, a silane coupling agent and sodium oleate are blended in a weight ratio of 100:(0.5-2):(1-2), stirred at a temperature of 50-70°C for 8-15 minutes, cooled, filtered, washed and dried to obtain modified magnesium hydroxide.

8. The 1E-class medium voltage frequency conversion cable for ships with good heat aging resistance according to claim 7, characterized in that: The dried magnesium hydroxide, silane coupling agent and sodium oleate were blended in a weight ratio of 100:1.2:1.

8.

9. The 1E-class medium voltage frequency conversion cable for ships with good heat aging resistance according to claim 1, characterized in that: The insulating layer is prepared by the following method: all raw materials except the vulcanizing agent are blended, kneaded at a temperature of 130-140°C for 3-5 minutes, unloaded at a temperature of less than 140°C after the kneading, then the vulcanizing agent is added, kneaded at a temperature of 100-110°C for 1-1.5 minutes, debonded at a temperature of less than 120°C after the kneading, cooled, sliced, and extruded to obtain the insulating layer.

10. A Class 1E medium voltage frequency conversion cable for ships with good heat aging resistance according to claim 9, characterized in that: The extrusion temperature is 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 80°C, and 80°C.

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