A cold-resistant power cable based on a modified elastomer sheath and a method for producing the same

Abstract

The application relates to the technical field of power cables, and discloses a cold-resistant power cable based on a modified elastomer sheath and a preparation method thereof, and aims to solve the interface failure problem caused by the different step of the dielectric properties of an insulation layer and a sheath layer with temperature change when the existing cold-resistant cable is operated for a long time in a low-temperature environment. The cable insulation layer adopts a rubber composite material containing cyanoethylated pentaerythritol, a polar group is anchored in a crosslinked network in a chemical bonding mode, the rate of the dielectric constant with temperature drop is slowed down, the outer sheath layer adopts a modified elastomer material composed of chlorinated polyethylene, specific polyester and a low-temperature plasticizer, the temperature response behavior of the dielectric constant is actively controlled by adjusting the flexibility of the molecular chain, the dielectric matching of the insulation layer is realized at low temperature, the electric field distortion at the interface between the insulation and the sheath at low temperature is inhibited, and the interface electrical stability and long-term operation reliability of the cable in an extremely low-temperature environment are improved.

Description

Technical Field

[0001] This invention relates to the field of power cable technology, and in particular to a cold-resistant power cable based on a modified elastomer sheath and its preparation method. Background Technology

[0002] In power transmission networks in high-latitude, frigid regions, cold-resistant power cables are a key infrastructure for ensuring the reliability of power supply systems. As the outermost protective and mechanical support structure of the cable, the sheath layer needs to maintain excellent flexibility, mechanical strength, and environmental tolerance in extreme low-temperature environments for a long time. To this end, the industry generally uses elastomers such as chloroprene rubber, styrene-butadiene rubber, and silicone rubber as base materials, and improves their cold resistance through chemical grafting modification, polymer blending, or functional filler composites. The core purpose is to suppress the tendency of elastomer materials to become brittle and crack at low temperatures.

[0003] Existing technologies have explored this area extensively. For example, Chinese patent application CN118725433A discloses a cold-resistant sheath material for cables, which balances the cold resistance and mechanical properties of the material by modifying neoprene rubber with side-linking and grafting, and combining it with specific modified plasticizers. Another Chinese patent application CN119331321A discloses an antifreeze power cable, whose outer sheath uses a blend system of styrene rubber and silicone rubber, and adds surface-modified illite powder, aiming to simultaneously improve the low-temperature resistance and physical strength of the sheath.

[0004] The dielectric constant (ε) of polymer dielectrics is not a fixed value. In their article "Analysis of the Influence of Temperature on the Dielectric Parameters of Two Cable Insulation Materials" published in Volume 55, Issue 12 of the Journal of Polymer Science in 2024, Li Yan et al. pointed out that the dielectric constants of both cross-linked polyethylene (XLPE) and oil paper insulation showed a regular decrease with decreasing temperature. This is due to the weakening of the orientation polarization ability of the polar groups inside the material at low temperatures.

[0005] Different types of polymer materials exhibit varying degrees and rates of decrease in dielectric constant. Experimental data from the same paper mentioned above show that the dielectric constant curves of XLPE and paper insulation do not change parallel with temperature. This means that when the insulation and sheath layers of a cable undergo the same low-temperature process, the difference in the rate of change of their dielectric constants will cause their ratio to deviate from the room-temperature design value, resulting in dielectric mismatch.

[0006] This dielectric mismatch directly interferes with the electric field distribution at the interface between the cable insulation and sheath. In the paper "Simulation Study on the Effect of Interface Morphology of Main Insulation and Shielding Layer of DC Cable on Electric Field Distortion" published in the Journal of Electrical Engineering, Vol. 13, No. 11, 2018, Yin Yi et al. confirmed through modeling that when the electric field distribution at the interface between the two media is inversely proportional to its dielectric constant, the electric field near the interface will be distorted and twisted, and a region with a significantly increased local electric field intensity will be formed on the side with a relatively higher dielectric constant.

[0007] This electric field distortion can induce additional Maxwell electro-induced stress at the interface. In the article "The Material Properties of XLPE / SIR for High Voltage DC Cable Accessories and the Influence of Interface Charge Accumulation on Electric Field Distribution" published in the Journal of Electrical Engineering Technology, Vol. 36, No. 14, 2021, Li Guochang et al. pointed out that in low-temperature environments, the polymer material of the cable itself becomes brittle due to the reduced mobility of molecular chain segments, and its crack resistance decreases. At this time, the periodic electro-induced stress will have a synergistic effect with the brittleness of the material, thereby increasing the risk of microcrack initiation and propagation at the interface.

[0008] Current technologies and industry practices do not consider the inherent electric field characteristics of power cables during operation and neglect the dielectric matching requirements of the insulation and sheath layers. The insulation and sheath layers of cables are polymer materials with different polarities and molecular chain structures. When the ambient temperature drops sharply, the dielectric constants of both will decrease, but at significantly different rates. The asynchronous change of dielectric constants will cause distortion of the interfacial electric field, resulting in electric field concentration on the side with a relatively higher dielectric constant. Consequently, this non-uniform electric field will generate periodic Maxwell electrostress, which will induce and accelerate the initiation and propagation of interfacial microcracks, ultimately affecting the long-term dielectric strength and mechanical integrity of the cable. Summary of the Invention

[0009] The technical problem to be solved by this invention is that the existing technology has the problem of low-temperature embrittlement caused by dielectric property mismatch. To this end, we propose a cold-resistant power cable based on a modified elastomer sheath and its preparation method.

[0010] To achieve the above objectives, this application adopts the following technical solution: a cold-resistant power cable based on a modified elastomer sheath, comprising, from the inside out, a conductor, an insulation layer, a wrapping layer, a filling layer, an armor layer, and an outer sheath layer. The insulation layer is formed of an insulating composite material, which includes a rubber matrix, a thermoplastic polyurethane elastomer, and pentaerythritol cyanoethylated. The pentaerythritol cyanoethylated is chemically bonded to the crosslinking network of the insulating composite material through its hydroxyl groups. The outer sheath layer is formed of a sheath material, which includes chlorinated polyethylene, poly(1,2-propanediol adipate), and dibutyl diglyceride adipate. The poly(1,2-propanediol adipate) and dibutyl diglyceride adipate together constitute a modification system to adjust the molecular chain flexibility of chlorinated polyethylene.

[0011] Preferably, the insulating composite material comprises, by weight, 50-65 parts rubber matrix, 15-25 parts thermoplastic polyurethane elastomer, 3.0-5.0 parts cyanoethylated pentaerythritol, 4.0-7.0 parts modified nano silica, 12-20 parts dioctyl sebacate, 1.5-2.5 parts dicumyl peroxide, 1.0-1.8 parts triallyl isocyanurate, and 0.5-1.0 parts antioxidant 1010.

[0012] Preferably, the sheath material comprises, by weight, 55-70 parts of chlorinated polyethylene, 8.0-15.0 parts of poly(1,2-propanediol adipate), 15-25 parts of dibutyl diglyceride adipate, 20-30 parts of carbon black N550, 2-4 parts of epoxidized soybean oil, and 3-5 parts of composite lead salt stabilizer.

[0013] Preferably, the rubber matrix is ​​hydrogenated nitrile butadiene rubber, wherein the acrylonitrile content of the hydrogenated nitrile butadiene rubber is 34%-36%, and the degree of hydrogenation is ≥98%.

[0014] Preferably, the cyanoethylated pentaerythritol has an average cyanoethyl substitution degree of ≥3.5 and a hydroxyl value of ≤50mgKOH / g.

[0015] Preferably, the modified nano-silica is nano-silica with a surface treated with γ-aminopropyltriethoxysilane.

[0016] Preferably, the chlorine content of the chlorinated polyethylene is 35%-38%.

[0017] Preferably, the poly(1,2-propanediol adipate) has a number-average molecular weight of 1800-2200 and an acid value ≤1.0 mgKOH / g.

[0018] A method for preparing a cold-resistant power cable based on a modified elastomer sheath includes the following steps: S1: preparing a conductor core; S2: mixing an insulating compound containing a rubber matrix, thermoplastic polyurethane elastomer, and pentaerythritol cyanoethylate, and extruding it around the conductor core to form an insulation layer; S3: performing segmented vulcanization on the insulation layer, including microwave preheating and subsequent multi-stage hot air vulcanization; S4: twisting the vulcanized insulated core with filler material into a cable, and sequentially covering it with a wrapping layer and an armor layer; S5: mixing a sheathing compound containing chlorinated polyethylene, poly(1,2-propanediol adipate), and dibutyl diglyceride adipate, and extruding it around the armor layer to form an outer sheath layer; S6: vulcanizing the outer sheath layer to obtain the finished cable.

[0019] Preferably, the multi-stage hot air vulcanization in S3 specifically includes vulcanization at 156-160°C for 8-10 minutes in the first zone, followed by vulcanization at 166-170°C for 10-12 minutes in the second zone, and finally vulcanization at 142-148°C for 18-22 minutes in the third zone.

[0020] The technical effects and advantages of this invention are as follows: In this invention, by introducing pentaerythritol cyanoethylated as a functional additive into the insulation layer, the strongly polar cyanoethyl group in its molecule undergoes covalent bonding with the cross-linking network through the hydroxyl group, thereby anchoring the polar group in the cross-linking network and suppressing the rapid decrease in dielectric constant caused by the freezing of polar group orientation at low temperatures, thus achieving active low-temperature stability of the dielectric properties of the insulation material. In the sheath layer, a composite modification system composed of a specific polyester and a low-temperature plasticizer is used to flexibly regulate the chlorinated polyethylene matrix, aiming to actively regulate the response rate of the dielectric constant of the sheath material with temperature, so that it forms dielectric matching with the insulation layer at low temperatures, thereby fundamentally alleviating the interfacial electric field distortion, optimizing the interfacial electric field distribution of the cable at low temperatures, and thus improving the long-term operational reliability and electrical life of the cable in extreme low-temperature environments. Attached Figure Description

[0021] The disclosure of this invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings, the same reference numerals are used to refer to the same parts:

[0022] Figure 1 This is a graph showing the change in dielectric constant of the insulating layer material of the present invention with temperature. Figure 2 This is a graph showing the change in dielectric constant of the sheath material of the present invention with temperature. Detailed Implementation

[0023] It is readily understood that, based on the technical solution of this invention, those skilled in the art can propose various interchangeable structural methods and implementations without altering the essential spirit of the invention. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative examples of the technical solution of this invention and should not be considered as the entirety of the invention or as limitations or restrictions on the technical solution of this invention.

[0024] This invention provides a cold-resistant power cable based on a modified elastomer sheath and its preparation method, aiming to solve the interface failure problem caused by the asynchronous change of dielectric properties between the insulation layer and the sheath layer with temperature when existing cold-resistant cables operate in low-temperature environments for a long time.

[0025] This invention provides a cold-resistant power cable based on a modified elastomer sheath, which, from the inside out, consists of a conductor, an insulation layer, a wrapping layer, a filler layer, an armor layer, and an outer sheath layer.

[0026] The conductor is made of Class 2 annealed soft copper wire conforming to GB / T 3956-2008 "Conductors of Cables" standard, or a copper-aluminum composite conductor structure can be used. Its cross-sectional area is determined according to the cable's rated current carrying capacity. The insulation layer is tightly extruded around the conductor and is the main insulation layer of the cable. The wrapping layer uses semi-conductive water-resistant tape, wrapped in an overlapping manner around the insulated cores, with a thickness between 0.2-0.5 mm. Its main functions are to uniformly distribute the electric field, buffer thermomechanical stress, and provide longitudinal water resistance. When multiple insulated cores are stranded into a cable, the gaps are filled with the filling layer, which is made of low-density... The cable is constructed of high-strength, closed-cell cross-linked polyolefin foam rope to ensure the roundness of the cable cross-section and provide cushioning during mechanical deformation. The armor layer, located outside the filler layer, is wrapped with galvanized or painted steel strip in a single or double-layer gap manner to provide radial protection against external mechanical impact and pressure. It should be noted that not all layers are used to solve the dielectric mismatch problem to the same extent. The electrical properties of the metal conductor and armor layer are basically unchanged with temperature in the low-temperature range, while the wrapping layer and filler layer mainly serve the functions of mechanical cushioning, water blocking, and maintaining roundness.

[0027] To achieve relatively stable dielectric properties of the insulation layer at low temperatures, this invention employs an insulating composite material with the following specific composition; the insulating composite material, by weight, comprises the following components: 50-65 parts hydrogenated nitrile rubber, 15-25 parts thermoplastic polyurethane elastomer, 3.0-5.0 parts pentaerythritol cyanoethylate, 4.0-7.0 parts modified nano-silica, 12-20 parts dioctyl sebacate, 1.5-2.5 parts dicumyl peroxide, 1.0-1.8 parts triallyl isocyanurate, and 0.5-1.0 parts antioxidant 1010; wherein, the hydrogenated nitrile rubber serves as the matrix, and its acrylonitrile content is preferably 3%. The thermoplastic polyurethane elastomer has a Shore hardness of 4%-36%, a hydrogenation degree ≥98%, and an ML(1+4) value of 75-85 measured at 100℃ using a Mooney viscometer. The preferred Shore hardness is 90A-95A. Blending it with hydrogenated nitrile rubber improves the flexibility and tear resistance of the composite material at low temperatures. The cyanoethylated pentaerythritol is prepared by cyanoethylation of pentaerythritol and acrylonitrile. Specifically, after adding an alkaline catalyst, the hydroxyl group in the pentaerythritol molecule undergoes a Michael addition reaction with acrylonitrile, where the hydrogen atom on the hydroxyl group is replaced by a cyanoethyl group (-CH2CH2CN), generating cyanoethylated pentaerythritol, with the following structural formula: The cyanoethyl group has a degree of substitution x ≥ 3.5 and a residual hydroxyl value ≤ 50 mg KOH / g. The strongly polar cyanoethyl (-CH2CH2CN) group in the molecule maintains the material's polarity. Furthermore, the hydroxyl group (-OH) undergoes an addition reaction with the unsaturated bond of triallyl isocyanurate during vulcanization, covalently bonding to the hydrogenated nitrile rubber crosslinking network. This prevents the precipitation of polar groups at low temperatures, maintaining an effective polar concentration over a long period, thereby slowing down the rate at which the dielectric constant decreases with temperature. The modified nano-silica has an average primary particle size of 10-20 nm and a specific surface area of ​​150-200 m². 2 / g, the surface of which is treated with γ-aminopropyltriethoxysilane to improve dispersibility and interfacial bonding; the purity of the dioctyl sebacate is ≥99.5% and the acid value is ≤0.1mgKOH / g; the purity of the dicumyl peroxide is ≥98%.

[0028] The sheath material, by weight, comprises the following components: 55-70 parts chlorinated polyethylene, 8.0-15.0 parts poly(1,2-propanediol adipate), 15-25 parts dibutyl diglyceride adipate, 20-30 parts carbon black N550, 2-4 parts epoxidized soybean oil, and 3-5 parts composite lead salt stabilizer; wherein, the chlorinated polyethylene serves as the sheath matrix, with a chlorine content of 35-38%, and an ML(1+4) value of 60-80 measured by a Mooney viscometer at 121°C; The poly(1,2-propanediol adipate) is a polyester with a number-average molecular weight of 1800-2200 and an acid value ≤1.0 mgKOH / g; the dibutyl diglyceride adipate serves as a low-temperature plasticizer, and together the two constitute a modification system for chlorinated polyethylene, adjusting the flexibility of the chlorinated polyethylene molecular chain and simultaneously regulating its dielectric constant temperature response rate, thus forming a dielectric match with the insulating layer; the epoxidized soybean oil has an epoxy value ≥6.0%, and synergistically improves the thermal stability and processability of the material with the composite lead salt stabilizer.

[0029] This invention also provides a method for preparing a cold-resistant power cable based on a modified elastomer sheath, specifically including the following steps: S1: Annealed soft copper monofilaments are concentrically stranded on a frame-type stranding machine or a tubular stranding machine at a pitch ratio of 14-18 to obtain a conductor core; S2: Hydrogenated nitrile rubber and thermoplastic polyurethane elastomer are first put into a mixer preheated to 75±5℃ and plasticized for 2-3 minutes; then, modified nano-silica and cyanoethyl pentaerythritol are added and mixed for 3-4 minutes; dioctyl sebacate, dicumyl peroxide, triallyl isocyanurate and antioxidant 1010 are added and mixed for 2- After 3 minutes of homogenization, an insulating compound is obtained. The insulating compound is fed into an extruder, with the feeding section set at 50-60℃, the plasticizing section at 70-80℃, and the homogenizing section and die head at 80-90℃, and the screw speed at 18-22 r / min. It is then extruded onto the conductor core to form an insulating compound layer. S3: The insulating compound layer is preheated using microwave at a frequency of 2450MHz and a power density of 3.0±0.2W / g for 75-85 seconds, allowing the insulation layer to heat up uniformly from the inside out and initiating initial cross-linking. Subsequently, it is introduced into a hot air vulcanization pipe, with the first zone temperature set at 158±2℃ and held for 9±1 minutes. Zone 2 temperature 168±2℃, held for 11±1 min; Zone 3 temperature 145±3℃, held for 20±2 min; after vulcanization, the wire core is cooled to room temperature in a cooling water bath to obtain the vulcanized insulated wire core; S4: The insulated wire core and cross-linked polyolefin foamed rope are twisted together on a disc cabling machine, and the cabling pitch ratio is controlled at 16±2. At the same time, a semi-conductive resistive water buffer strip is wrapped in an overlapping wrapping manner. A galvanized steel strip with a thickness of 0.20±0.02mm is used to wrap the outside of the cable core in a single or double layer gap to form a metal armor layer; S5: Chlorinated polyethylene, high abrasion-resistant carbon black N550, and ring Oxygenated soybean oil and compound lead salt stabilizer are added to a mixer preheated to 80±5℃ and mixed for 4-5 minutes. Then, poly(1,2-propanediol adipate) and dibutyl diglyceride adipate are added and mixed for another 2-3 minutes until homogeneous to obtain the sheathing compound. The sheathing compound is fed into an extruder, and the die head temperature is set to 80-85℃. It is extruded over the armor layer to form the sheathing compound layer. S6: The cable is introduced into a hot air continuous vulcanization pipeline and vulcanized at a temperature of 160±2℃. The vulcanization time is maintained at 18±2 minutes by controlling the line speed. After vulcanization, the cable is cooled, inspected, and printed to obtain the finished cable.

[0030] To verify the technical effects of the present invention, the following series of embodiments and comparative examples were designed. Except for the insulation layer, sheath layer materials and processes specifically mentioned, all cable samples maintained the same structure and general production steps.

[0031] Example 1: This example provides a cold-resistant power cable based on a modified elastomer sheath. The insulation material formulation, by weight, includes 60 parts hydrogenated nitrile rubber, 20 parts thermoplastic polyurethane elastomer, 4 parts cyanoethylated pentaerythritol, 5.5 parts modified nano-silica, 16 parts dioctyl sebacate, 2.0 parts dicumyl peroxide, 1.5 parts triallyl isocyanurate, and 0.8 parts antioxidant 1010. The sheath material formulation, by weight, includes 62 parts chlorinated polyethylene, 12 parts poly(1,2-propanediol adipate), 20 parts dibutyl diglyceride adipate, 28 parts carbon black N550, 3 parts epoxidized soybean oil, and 4 parts composite lead salt stabilizer. This embodiment also provides a method for preparing a cold-resistant power cable based on a modified elastomer sheath, specifically including the following steps: S1: Annealed soft copper monofilaments are concentrically stranded at a pitch ratio of 16 using a tubular stranding machine to obtain a conductor core; S2: Hydrogenated nitrile rubber and thermoplastic polyurethane elastomer are first put into a mixer preheated to 75°C and plasticized for 3 minutes; modified nano-silica and cyanoethyl pentaerythritol are added and mixed for 4 minutes; dioctyl sebacate, dicumyl peroxide, triallyl isocyanurate and antioxidant 1010 are added and mixed for 3 minutes until uniform to obtain an insulating compound; the insulating compound is fed into an extruder and the feeding section is set to 55°C. S1: The plasticizing section is 75℃, the homogenization section and die head are 85℃, and the screw speed is 20r / min. The material is extruded onto the conductor core to form an insulating rubber layer. S2: The material is treated for 80s at a frequency of 2450MHz and a power density of 3.0W / g. Then it is introduced into the hot air vulcanization pipeline. The temperature of the first zone is set at 158℃ for 9min, the temperature of the second zone is set at 168℃ for 11min, and the temperature of the third zone is set at 145℃ for 20min. After vulcanization, it is cooled to room temperature to obtain the vulcanized insulated wire core. S3: The insulated wire core is stranded with cross-linked polyolefin foam rope on a disc cabling machine. A 0.20mm thick galvanized steel strip is used for single-layer bonding. S5: Chlorinated polyethylene, high abrasion-resistant carbon black N550, epoxidized soybean oil, and composite lead salt stabilizer are added to a mixer preheated to 80°C and mixed for 5 minutes. Poly(1,2-propanediol adipate) and dibutyl diglyceride adipate are added and mixed for another 3 minutes until homogeneous to obtain the sheathing compound. The sheathing compound is fed into an extruder, the die head temperature is set to 85°C, and it is extruded over the armor layer to form the sheathing compound layer. S6: The cable is introduced into a hot air continuous vulcanization pipeline and vulcanized at 160°C. The vulcanization time is maintained at 18 minutes by controlling the line speed. After vulcanization, the cable is cooled, inspected, and printed to obtain the finished cable.

[0032] Example 2: This example provides a cold-resistant power cable based on a modified elastomer sheath and its preparation method. The difference from Example 1 is that the amount of pentaerythritol cyanoethylated is 3.0 parts, the amount of modified nano-silica is 4.0 parts, and the amount of dioctyl sebacate is 12 parts in the insulation layer.

[0033] Example 3: This example provides a cold-resistant power cable based on a modified elastomer sheath and its preparation method. The difference from Example 1 is that the amount of cyanoethylated pentaerythritol in the insulation layer is 5.0 parts, and the amount of surface-modified nano-silica is 7.0 parts.

[0034] Example 4: This example provides a cold-resistant power cable based on a modified elastomer sheath and its preparation method. The difference from Example 1 is that the amount of poly(1,2-propanediol adipate) in the sheath layer is 15 parts and the amount of dibutyl diglyceride adipate is 25 parts.

[0035] Comparative Example 1: This comparative example provides a cold-resistant power cable based on a modified elastomer sheath and its preparation method. The difference from Example 1 is that no cyanoethylated pentaerythritol is added to the insulation layer, and its amount is replaced by an equal mass of hydrogenated nitrile rubber.

[0036] Comparative Example 2: This comparative example provides a cold-resistant power cable based on a modified elastomer sheath and its preparation method. The difference from Example 1 is that no poly(1,2-propanediol adipate) is added to the sheath layer, and its amount is replaced by an equal mass of DBEEA plasticizer.

[0037] Comparative Example 3: This comparative example provides a cold-resistant power cable based on a modified elastomer sheath and its preparation method. The difference from Example 1 is that, in the insulation layer, dioctyl phthalate is used instead of pentaerythritol cyanoethylated by an equal mass.

[0038] Comparative Example 4: This comparative example provides a cold-resistant power cable based on a modified elastomer sheath and its preparation method. The difference from Example 1 is that, in the sheath layer, dioctyl sebacate is used instead of poly(1,2-propanediol adipate) of equal mass.

[0039] Comparative Example 5: This embodiment provides a cold-resistant power cable based on a modified elastomer sheath and its preparation method. The difference from Example 1 is that the third zone of the insulation layer vulcanization is eliminated, and the residence time of the wire core in the second zone is extended to 25 minutes. The total hot air vulcanization time is similar to that of Example 1.

[0040] Comparative Example 6: This embodiment provides a cold-resistant power cable based on a modified elastomer sheath and its preparation method. The difference from Example 1 is that the vulcanization conditions of the sheath layer are changed to vulcanization at 170°C for 12 minutes.

[0041] Comparative Example 7: This comparative example provides a cold-resistant power cable based on a modified elastomer sheath and its preparation method. The insulation layer uses commercially available cold-resistant ethylene propylene rubber insulation material. The sheath layer composition, by weight, includes 35 parts styrene-butadiene rubber, 30 parts phenyl silicone rubber, 20 parts modified illite powder, 22 parts ammonium polyphosphate, 2 parts ethylene wax, 2 parts dioctyl terephthalate, and 1 part 1,1-dithiodicaprolactam. The components of the sheath material are mixed evenly in a mixer or open mill to form a sheath compound. The sheath compound is then extruded onto the cable core using an extruder, with the extruder head temperature controlled at 95°C. Finally, the cable is vulcanized in a hot air vulcanization pipe at 160°C for 18 minutes to form the outer sheath layer.

[0042] To verify the technical effect of the present invention, we conducted systematic and rigorous performance tests on the cable samples prepared in the above embodiments and comparative examples. The specific test plan is as follows.

[0043] Test Example 1: This test aims to quantitatively measure the change of dielectric constant of the insulation layer and sheath layer materials with temperature, so as to evaluate the effectiveness of the technical solution of the present invention in achieving low-temperature dielectric matching.

[0044] From the finished cables of Examples 1 and 1-7, longitudinal sections were carefully cut and peeled off to obtain pure insulation and sheath vulcanized rubber sheets. These samples were punched with a standard dumbbell cutter and then precision ground to form smooth circular samples with a diameter of Φ100±0.5mm and a thickness of 2.0±0.1mm. Three parallel samples were prepared for each sample, and the average value of the test results was taken. The samples were placed in a three-electrode fixture and placed in a temperature chamber. An impedance analyzer was connected for open-circuit and short-circuit calibration. The frequency point was set at 50Hz, and the test signal voltage was 1.0Vrms. When the temperature chamber reached 20°C and stabilized, the first measurement was started, and the capacitance value (C) was recorded. The relative permittivity at this temperature was calculated according to the formula. Where d is the thickness, A is the effective area of ​​the electrode, and ε0 is the vacuum permittivity; starting from 20℃, the temperature was decreased to -50℃ in 10℃ increments, for a total of 8 temperature points. At each target temperature point, the sample was held at a constant temperature without an electric field for at least 60 minutes to ensure the equilibrium of the internal and external temperatures and polarization states of the sample. Measurements were then performed, and the results are shown in […]. Figure 1 and Figure 2 As shown.

[0045] according to Figure 1The results showed that the dielectric constant of Example 1 decreased gradually from 5.82 at 20°C to 5.12 at -50°C, with the curve being the flattest among all examples and comparative examples. This verified the key role of pentaerythritol cyanoethylated as a dielectric stabilizer. Multiple cyanoethyl groups in its molecule provide strong polarity, and the polar groups are anchored by chemical bonding with the cross-linking network through hydroxyl groups. As the temperature decreases, these fixed polar points can still effectively respond to the electric field, thereby significantly suppressing the decay of orientation polarization ability and achieving low-temperature stabilization of the dielectric constant. The curves of Comparative Example 1 and Comparative Example 3 are highly similar and steep. At -50°C, the dielectric constants decreased to 3.18 and 3.33, respectively. The curve of Comparative Example 5 is between that of Example 1 and Comparative Example 1. Because it omits the third-zone vulcanization step, the internal stress of the cross-linking network is not fully released, and the stable conformation of the functional molecule is not fully formed. As a result, although its low-temperature dielectric stability is better than that of Comparative Example 1, it is worse than that of Example 1.

[0046] according to Figure 2 The results showed that the dielectric constant of Example 1 decreased from 4.48 at 20℃ to 3.62 at -50℃, with a relatively gentle downward trend. This verified the synergistic modification effect of poly(1,2-propanediol adipate) and dibutyl diglyceride adipate. The segments of the flexible polyester still have a certain degree of mobility at low temperatures, and its ester bond dipoles can provide additional induced polarization, compensating for the polarizability lost by the matrix itself due to low-temperature freezing, thereby increasing the dielectric constant in the low-temperature region and making the curve flatter. The curves of Comparative Examples 2 and 4 were extremely steep, indicating that the lack of polymer... The active compensation effect of the ester cannot achieve dielectric matching with the insulation layer; the decrease in the curve of Comparative Example 6 is slightly greater than that of Example 1, because it uses a higher temperature for vulcanization, which may cause some polypropylene adipate to undergo thermal degradation or excessive volatilization, weakening its polarity compensation ability and thus affecting the final low-temperature dielectric properties; the initial dielectric constant values ​​of the insulation layer and the sheath layer of Comparative Example 7 are both low, and the curves with decreasing temperature also show a significant decreasing trend. More importantly, the dielectric constants of its insulation and sheath are low and mismatched throughout the entire temperature range.

[0047] Test Example 2: This test aims to evaluate the electrical stability of the interface between the cable insulation layer and the modified elastomer sheath layer under extreme low temperature operating conditions.

[0048] A 1.5-meter section of the finished cable prepared in the examples and comparative examples was selected as the sample. To accurately simulate and test the insulation and sheath interface, about 20 cm of the outer sheath, armor, and part of the insulation were stripped from both ends of the cable sample to expose the conductor and insulation layer. Terminal stress cones were installed to eliminate end discharge interference. Subsequently, the prepared sample was placed in a high and low temperature test chamber pre-cooled to -50℃ and kept at a constant temperature for at least 12 hours to ensure that the overall temperature of the cable was uniform and stable to reach the test temperature. The partial discharge test was carried out according to GB / T 3048.12-2007, using a calibrated pulse current method partial discharge detection system. During the test, a power frequency AC voltage starting from 5kV was applied to the sample and the voltage was increased uniformly at a rate of 1kV / s. The discharge signal was monitored and recorded in real time. The voltage value corresponding to the generation of the first discharge pulse with a stable amplitude greater than 5pC was defined as the -50℃ PDIV of the sample. Each sample was tested 3 times, and the average value was taken as the final result. The results are shown in Table 1 below.

[0049] Table 1. Electrical stability test results at extreme low temperatures

[0050]

[0051] According to the data in Table 1, Examples 1-4 all showed higher PDIV values ​​than any comparative example, indicating that through the material co-design and process of the present invention, the electric field distribution at the interface between the cable insulation and sheath is optimized, and local electric field concentration is effectively suppressed, thereby improving the discharge resistance of the interface at low temperatures.

[0052] The technical scope of this invention is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the protection scope of this invention.

Claims

1. A cold-resistant power cable based on a modified elastomer sheath, characterized in that, The device comprises, from the inside out, a conductor, an insulating layer, a wrapping layer, a filling layer, an armor layer, and an outer sheath layer. The insulating layer is formed of an insulating composite material, which includes a rubber matrix, a thermoplastic polyurethane elastomer, and pentaerythritol cyanoethylated. The pentaerythritol cyanoethylated is chemically bonded to the cross-linked network of the insulating composite material through its hydroxyl groups. The outer sheath layer is formed of a sheath material, which includes chlorinated polyethylene, poly(1,2-propanediol adipate), and dibutyl diglyceride adipate. The poly(1,2-propanediol adipate) and dibutyl diglyceride adipate together constitute a modification system to adjust the flexibility of the molecular chain of chlorinated polyethylene.

2. The cold-resistant power cable based on a modified elastomer sheath according to claim 1, characterized in that: The insulating composite material comprises, by weight, 50-65 parts rubber matrix, 15-25 parts thermoplastic polyurethane elastomer, 3.0-5.0 parts cyanoethylated pentaerythritol, 4.0-7.0 parts modified nano silica, 12-20 parts dioctyl sebacate, 1.5-2.5 parts dicumyl peroxide, 1.0-1.8 parts triallyl isocyanurate, and 0.5-1.0 parts antioxidant 1010.

3. A cold-resistant power cable based on a modified elastomer sheath according to claim 2, characterized in that: The sheath material comprises, by weight, 55-70 parts of chlorinated polyethylene, 8.0-15.0 parts of poly(1,2-propanediol adipate), 15-25 parts of dibutyl diglyceride adipate, 20-30 parts of carbon black N550, 2-4 parts of epoxidized soybean oil, and 3-5 parts of composite lead salt stabilizer.

4. A cold-resistant power cable based on a modified elastomer sheath according to claim 2, characterized in that: The rubber matrix is ​​hydrogenated nitrile butadiene rubber, and the acrylonitrile content of the hydrogenated nitrile butadiene rubber is 34%-36%, and the degree of hydrogenation is ≥98%.

5. A cold-resistant power cable based on a modified elastomer sheath according to claim 2, characterized in that: The cyanoethylated pentaerythritol has an average degree of cyanoethyl substitution ≥3.5 and a hydroxyl value ≤50mgKOH / g.

6. A cold-resistant power cable based on a modified elastomer sheath according to claim 2, characterized in that: The modified nano-silica is nano-silica with a surface treated with γ-aminopropyltriethoxysilane.

7. A cold-resistant power cable based on a modified elastomer sheath according to claim 3, characterized in that: The chlorinated polyethylene has a chlorine content of 35%-38%.

8. A cold-resistant power cable based on a modified elastomer sheath according to claim 3, characterized in that: The poly(1,2-propanediol adipate) has a number-average molecular weight of 1800-2200 and an acid value ≤1.0 mgKOH / g.

9. A method for preparing a cold-resistant power cable based on a modified elastomer sheath, used to prepare the cold-resistant power cable based on a modified elastomer sheath as described in any one of claims 1-8, characterized in that, Includes the following steps: S1: Prepare conductor core; S2: Mix an insulating compound containing a rubber matrix, thermoplastic polyurethane elastomer, and cyanoethylated pentaerythritol, and extrude it over the conductor core to form an insulation layer; S3: Perform segmented vulcanization on the insulation layer, including microwave preheating and subsequent multi-stage hot air vulcanization; S4: Twist the vulcanized insulated core with filler material to form a cable, and then cover it with a wrapping layer and an armor layer in sequence; S5: Mix a sheathing compound containing chlorinated polyethylene, poly(1,2-propanediol adipate), and dibutyl diglyceride adipate, and extrude it over the armor layer to form an outer sheath layer; S6: Vulcanize the outer sheath layer to obtain the finished cable.

10. A method for preparing a cold-resistant power cable based on a modified elastomer sheath according to claim 9, characterized in that: The multi-stage hot air vulcanization in S3 specifically includes vulcanization for 8-10 minutes at 156-160℃ in the first zone, followed by vulcanization for 10-12 minutes at 166-170℃ in the second zone, and finally vulcanization for 18-22 minutes at 142-148℃ in the third zone.

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