A high current copper core conductor polypropylene insulated medium voltage power cable

Abstract

The application discloses a large-current copper core conductor polypropylene insulation medium-voltage power cable and belongs to the technical field of cable processing, which is used to solve the technical problem that the insulation and heat aging resistance of the polypropylene insulation medium-voltage power cable in the prior art need to be further improved, and specifically comprises a copper conductor, a conductor shielding layer and an insulation layer arranged in sequence from inside to outside. The application effectively improves the electrical strength, mechanical strength and heat aging resistance of the polypropylene insulation layer by optimizing the composition of the polypropylene insulation layer, and introduces the conductor shielding layer, the metal shielding layer and the flame-retardant wrapping layer in the multilayer structure outside the high-purity round-corner copper conductor, thereby significantly improving the comprehensive performance of the medium-voltage power cable, and achieving the technical effects of enhancing current carrying capacity, prolonging the service life of the cable and improving the operation safety.

Description

Technical Field

[0001] This invention relates to the field of insulated cable processing technology, specifically to a high-current copper core conductor polypropylene insulated medium-voltage power cable. Background Technology

[0002] High-current copper core conductor polypropylene insulated medium-voltage power cable is a high-performance cable made of copper core conductor and polypropylene insulation material, specially designed for rated voltage of 35kV and below, and designed to carry large current for power transmission and distribution. Its core advantage lies in significantly improving current carrying capacity through material and structural innovation, while taking into account environmental protection and operational safety.

[0003] Currently, cross-linked polyethylene is widely used as insulation material in medium-voltage power cables. Its long-term operating temperature is limited to below 90℃. In high-temperature environments, the cross-linked polyethylene insulation layer is prone to water treeing and aging, which leads to deterioration of insulation performance and causes partial discharge or even breakdown accidents.

[0004] Polypropylene, as a thermoplastic material, has good electrical insulation properties, low dielectric loss, excellent thermal stability, and environmentally friendly recyclability, and has gradually become an important candidate for next-generation cable insulation materials. However, polypropylene has a low degree of cross-linking and many interface defects, which makes it prone to partial discharge, electrical breakdown, or electrical treeing under high voltage, resulting in limited improvement in insulation performance. In addition, polypropylene lacks an efficient free radical stabilization mechanism, and its strength decays rapidly and its lifespan is short in a thermo-oxidative aging environment. It also has insufficient heat aging resistance, and there is an interfacial incompatibility problem between the conductor and the insulation layer. The electric field tends to concentrate at the interface or micro-defects, inducing breakdown. The uneven electric field distribution limits its practical application in medium-voltage cables.

[0005] Therefore, there is an urgent need to develop a new type of polypropylene-based insulation material with adjustable structure, optimized interface, and synergistic performance enhancement. This material should retain the environmental protection and electrical insulation advantages of polypropylene itself, while overcoming its shortcomings in flexibility, thermal stability, and space charge suppression capabilities. This would meet the comprehensive requirements of high-current medium-voltage cables in terms of long-term operation, voltage withstand capability, and laying performance. Summary of the Invention

[0006] The purpose of this invention is to provide a high-current copper core conductor polypropylene insulated medium-voltage power cable to solve the technical problem that the insulation and heat aging resistance of polypropylene insulated medium-voltage power cables in the prior art need to be further improved.

[0007] The objective of this invention can be achieved through the following technical solution: a high-current copper core conductor polypropylene insulated medium-voltage power cable, comprising a copper conductor, a conductor shielding layer, and an insulation layer arranged sequentially from the inside out;

[0008] The copper conductor is a long conductor with a rounded corner cross-section;

[0009] The method for forming the insulating layer is as follows: 100 parts by weight of polypropylene, 60-70 parts of composite polypropylene, 1.6-2 parts by weight of epoxy-modified zinc oxide and 2-3 parts by weight of additives are added to a twin-screw extruder and melt-mixed for 3-5 minutes. The mixture is then extruded and coated onto the outside of the conductor shielding layer. After cooling and curing, an insulating layer is formed on the outside of the conductor shielding layer.

[0010] Furthermore, the copper conductor has a copper content greater than 99.95%, and the conductor shielding layer is composed of polyethylene and conductive carbon black with a resistivity of 650-750 Ω·m.

[0011] Furthermore, the additives are composed of dispersant, lubricant, plasticizer and antioxidant in a ratio of 5:2:4:2. The dispersant is stearate, the lubricant is ethylene bis-stearamide, the plasticizer is phthalate, and the antioxidant is any one of antioxidant AW, antioxidant DNP and antioxidant CPPD. The temperatures of the six temperature zones of the twin-screw extruder from the feed end to the discharge end are 170℃, 175℃, 175℃, 180℃, 180℃ and 185℃ respectively.

[0012] Furthermore, the composite polypropylene is obtained by the following steps:

[0013] A1. Mix PP-g-MAH and chlorobenzene and stir. Raise the temperature of the reaction system to 75-85℃ and stir until the system is dissolved. Add 4-penten-1-amine to the reaction system and keep it at the temperature for 60-80 min. After post-treatment, unsaturated modified polypropylene is obtained.

[0014] A2. Heat unsaturated modified polypropylene, modified polysiloxane and initiator to 160-170℃ and mix for 20-30 minutes to obtain composite polypropylene.

[0015] Further, in step A1, the ratio of PP-g-MAH, chlorobenzene, and 4-penten-1-amine is 10g:150mL:0.9-1.2g. The post-treatment includes: after the reaction is complete, the temperature of the reaction system is lowered to room temperature, the reaction solution is slowly added to anhydrous methanol, stirred and dispersed for 20-30 minutes, filtered, the filter cake is washed with methanol 3 times and dried, the filter cake is transferred to a drying oven at 60-70℃ and dried to constant weight to obtain unsaturated modified polypropylene.

[0016] Furthermore, in step A2, the weight ratio of the unsaturated modified polypropylene, the modified polysiloxane, and the initiator is 100:65-75:1-2, and the initiator is dicumyl peroxide.

[0017] Furthermore, the modified polysiloxane is obtained by the following steps:

[0018] B1. Under an inert gas atmosphere, 2-amino-4-methyl-6-methoxy-1,3,5-triazine and acetonitrile are mixed, the temperature of the reaction system is raised to 60-70℃, and the mixture is stirred until the system is dissolved. 3-propyl isocyanate methyl diethoxysilane is added to the reaction system, and the reaction is kept at the temperature for 60-80 min. After post-treatment, diethoxysilane-modified triazine is obtained.

[0019] The reaction equation for the synthesis of triazine modified with diethoxysilane is:

[0020]

[0021] B2. Under an inert gas atmosphere, 4-aminomethyl-2,2,6,6-tetramethylpiperidine and tetrahydrofuran are mixed, the temperature of the reaction system is raised to 60-70℃, and the mixture is stirred until the system is dissolved. Propyltriethoxysilane isocyanate is added to the reaction system, and the reaction is kept at the temperature for 60-80 min. After post-treatment, triethoxysilane-modified piperidine is obtained.

[0022] The synthesis reaction equation for triethoxysilane-modified piperidine is:

[0023]

[0024] B3. Mix octamethylcyclotetrasiloxane, diethoxysilane-modified triazine, triethoxysilane-modified piperidine, aminopropylmethyldimethoxysilane and catalyst, raise the temperature of the reaction system to 85-95℃, keep the reaction at this temperature for 50-60 min, add end-capping agent to the reaction system, keep the reaction at this temperature for 100-120 min, and then perform post-treatment to obtain modified polysiloxane.

[0025] The synthesis reaction equation for modified polysiloxanes is as follows:

[0026]

[0027] In the formula:

[0028] ;

[0029] .

[0030] Further, in step B1, the ratio of 2-amino-4-methyl-6-methoxy-1,3,5-triazine to acetonitrile is 1 g: 20 mL, and the ratio of 2-amino-4-methyl-6-methoxy-1,3,5-triazine to 3-isocyanate-methyldiethoxysilane is 1 mol: 1 mol. The post-treatment includes: after the reaction is complete, maintaining the temperature of the reaction system at 60-70 °C, drawing a negative pressure to -0.1 MPa, and removing low-boiling substances by vacuum evaporation to obtain diethoxysilane-modified triazine.

[0031] Further, in step B2, the ratio of 4-aminomethyl-2,2,6,6-tetramethylpiperidine to tetrahydrofuran is 1 g:10 mL, and the ratio of 4-aminomethyl-2,2,6,6-tetramethylpiperidine to propyltriethoxysilane isocyanate is 1 mol:1 mol. The post-treatment includes: after the reaction is complete, maintaining the temperature of the reaction system at 60-70°C, drawing a negative pressure to -0.1 MPa, and removing low-boiling substances under reduced pressure to obtain triethoxysilane-modified piperidine.

[0032] Further, in step B3, the ratio of octamethylcyclotetrasiloxane, diethoxysilane-modified triazine, triethoxysilane-modified piperidine, aminopropylmethyldimethoxysilane, catalyst, and end-capping agent is 15g:4-5g:1.8-2.2g:1.6-1.8g:4-6mL:2.3-2.5g. The end-capping agent is diallyltetramethyldisiloxane, and the catalyst is 50-60wt% sulfuric acid. The post-treatment includes: after the reaction is complete, the reaction system temperature is lowered to room temperature, 3-5wt% sodium bicarbonate aqueous solution is added to the reaction system to adjust the pH of the system to 7, the system is allowed to stand and separated, the upper oil phase is washed with purified water until neutral, and then transferred to a rotary evaporator with a water bath temperature of 80-90℃ to remove low-boiling substances under reduced pressure to obtain modified polysiloxane.

[0033] Furthermore, the preparation method of epoxy-modified zinc oxide is as follows: nano zinc oxide, anhydrous ethanol, tetraethyl orthosilicate and KH-560 are mixed and ultrasonically dispersed for 30-50 min. The temperature of the reaction system is raised to 50-60℃, sodium hydroxide solution is added to the reaction system, and the reaction is kept at the temperature for 60-80 min. After post-treatment, epoxy-modified zinc oxide is obtained.

[0034] The reaction formulas involved in the synthesis of epoxy-modified zinc oxide are as follows:

[0035]

[0036] Furthermore, the ratio of nano zinc oxide, anhydrous ethanol, tetraethyl orthosilicate, KH-560, and sodium hydroxide solution is 7g:100mL:1.8-2.2g:1.2-1.4g:15mL, and the concentration of the sodium hydroxide solution is 1-2mol / L. The post-treatment includes: after the reaction is complete, the reaction system temperature is lowered to room temperature, filtered, the filter cake is washed with purified water until neutral, dried, and the filter cake is transferred to a drying oven at 60-70℃ and dried to constant weight to obtain epoxy-modified zinc oxide.

[0037] Furthermore, the outer surface of the insulating layer may also be provided with an insulating shielding layer, a metal shielding layer, a wrapping layer, and an outer sheath layer.

[0038] Furthermore, the insulating shielding layer is obtained by wrapping Mylar tape around the outside of the insulating layer, the metal shielding layer is obtained by covering the outside of the insulating shielding layer with woven copper mesh, the wrapping layer is obtained by wrapping refractory mica wrapping tape around the outside of the metal shielding layer, and the outer sheath layer is obtained by melt extrusion of thermoplastic elastomer TPE around the outside of the outer sheath layer.

[0039] The present invention has the following beneficial effects:

[0040] 1. This invention utilizes high-purity copper conductors to reduce resistance loss and ensure high current carrying capacity. Rounded corners reduce electric field concentration and lower the risk of partial discharge. A conductor shielding layer composed of polyethylene and conductive carbon black eliminates electric field distortion on the copper conductor surface, ensuring a uniform electric field within the insulation layer, improving interface adhesion, preventing "interface treeing discharge," and maintaining a certain resistivity. It balances conductivity and processability. Composite siloxane phases and nano-zinc oxide reinforce the PP matrix, forming an insulation layer outside the conductor shielding layer, improving the electrical insulation performance of the insulation material. Depending on the application scenario, an outer layer structure can be set outside the insulation layer, using Mylar tape to form an insulating shielding layer, achieving a uniform electric field and preventing partial discharge. The metal shielding layer provides a stable potential, discharges leakage current, and enhances the cable's mechanical strength and flexibility. The wrapping layer improves flame retardancy and fire resistance, meeting fire-resistant cable requirements. The TPE outer sheath layer provides good mechanical protection and weather resistance, while also offering flexibility for easy installation.

[0041] 2. This invention introduces unsaturated bonds through the reaction of PP-g-MAH with 4-penten-1-amine, providing active sites for subsequent crosslinking reactions with modified polysiloxanes. Dicumyl peroxide acts as an initiator, triggering crosslinking between the unsaturated modified polypropylene and the modified polysiloxane to form a three-dimensional network structure in the composite polypropylene. This crosslinking structure significantly improves the tensile strength and heat aging resistance of the insulation layer. Nano-zinc oxide undergoes surface modification with tetraethyl orthosilicate using KH-560 coupling agent, improving its dispersibility and interfacial bonding strength in the polymer matrix and significantly inhibiting the formation of crosslinks due to oxidation. The electric field distortion and electrical treeing effect caused by interface defects improve the overall dielectric strength. At the same time, the introduction of modified polysiloxane not only enhances the flexibility and toughness of the material chain segments, but its Si-O-Si bond structure itself has high electrical insulation and strong resistance to electrical breakdown, further improving the breakdown voltage level of the material. In addition, unsaturated modified polypropylene undergoes a free radical cross-linking reaction with polysiloxane under the action of peroxide initiator, forming a uniform three-dimensional cross-linked network structure, which effectively blocks electron migration channels and enhances the overall electrical stability of the insulation layer.

[0042] 3. This invention prepares diethoxysilane-modified triazine and trithoxysilane-modified piperidine. Multiple siloxane monomers react under sulfuric acid catalysis to form modified polysiloxanes with complex structures. Octamethylcyclotetrasiloxane serves as the basic structural unit, imparting good flexibility and heat resistance to the material. The introduction of trithoxysilane-modified piperidine increases the crosslinking points of the molecular chain, forming a crosslinked structure in the modified polysiloxane, improving the tensile strength and heat aging resistance of the insulating layer. The triazine ring has high conjugation and symmetry, and its high decomposition temperature can improve the structure of the material under high-temperature electrical stress environments. The structure enhances the integrity of the material, reduces the causes of electrical breakdown, and the triazine structure can stabilize free radicals, reducing chain degradation reactions under high electric field excitation. It has a good effect on inhibiting electrical treeing and improving breakdown voltage. The piperidine ring structure is a classic hindered amine stabilizer, which can play a truncation role in free radical chain reactions induced by electric field or high temperature, significantly delaying electrical aging and improving electrical lifetime. At the same time, the piperidine structure has a "trap" effect on charge migration, which can delay the accumulation and migration rate of space charge. In combination with modified zinc oxide, it improves the stability of the material under DC or pulsed electric fields. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 This is a three-dimensional structural diagram of the entire invention.

[0045] In the diagram: 1. Copper conductor; 2. Conductor shielding layer; 3. Insulation layer; 4. Insulation shielding layer; 5. Metal shielding layer; 6. Wrapping layer; 7. Outer sheath layer. Detailed Implementation

[0046] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] In this invention, PP-g-MAH is commercially available maleic anhydride-grafted polypropylene with a maleic anhydride grafting rate of 1-1.2% and a melt index of 90-110 g / 10 min.

[0048] In this invention, polypropylene is a commercially available material, manufactured (originating from) by Sinopec Maoming, with the grade PPH-T03 and the processing level being injection molding grade;

[0049] In this invention, the nano zinc oxide is a commercially available material with an average particle size of 50 nm;

[0050] In this invention, KH-560 is commercially available 3-glycidyl etheroxypropyltrimethoxysilane, CAS number 2530-83-8.

[0051] Example 1

[0052] This embodiment provides a method for preparing composite polypropylene, including the following steps:

[0053] Step 1: Preparation of diethoxysilane-modified triazine

[0054] Weigh 28.0 g of 2-amino-4-methyl-6-methoxy-1,3,5-triazine and 560 mL of acetonitrile into an argon-protected reaction flask and stir. Raise the temperature of the reaction flask to 60 °C and stir until the system dissolves. Add 43.5 g of 3-propyl isocyanate-methyldiethoxysilane to the reaction flask and keep the reaction at this temperature for 60 min. Then, evacuate the reaction flask to -0.1 MPa and remove low-boiling substances by vacuum distillation to obtain diethoxysilane-modified triazine.

[0055] During the reaction, after dissolving 2-amino-4-methyl-6-methoxy-1,3,5-triazine, the amino group on the 2-amino-4-methyl-6-methoxy-1,3,5-triazine molecule condenses with the isocyanate group on the 3-isocyanate-propylmethyldiethoxysilane molecule, thereby modifying 6-methoxy-1,3,5-triazine with diethoxysilane to prepare diethoxysilane-modified triazine. The mass spectrometry analysis data of the diethoxysilane-modified triazine are as follows: m / z: 357.18 (100.0%), 358.19 (15.6%), 358.18 (6.9%), 359.18 (3.7%), 359.19 (2.8%).

[0056] Step 2: Preparation of triethoxysilane-modified piperidine

[0057] Weigh 17.0 g of 4-aminomethyl-2,2,6,6-tetramethylpiperidine and 170 mL of tetrahydrofuran into an argon-protected reaction flask and stir. Raise the temperature of the reaction flask to 60 °C and stir until the system dissolves. Add 24.7 g of propyltriethoxysilane isocyanate to the reaction flask and keep the reaction at this temperature for 60 min. Then, evacuate the reaction flask to -0.1 MPa and remove low-boiling substances by vacuum distillation to obtain triethoxysilane-modified piperidine.

[0058] During the reaction, the amino group on the 4-aminomethyl-2,2,6,6-tetramethylpiperidine molecule undergoes condensation with the isocyanate group on the propyltriethoxysilane molecule, thus modifying 2,2,6,6-tetramethylpiperidine with triethoxysilane to prepare triethoxysilane-modified piperidine. The mass spectrometry analysis data of the triethoxysilane-modified piperidine are as follows: m / z: 417.30 (100.0%), 418.31 (22.3%), 418.30 (6.2%), 419.31 (4.3%), 419.30 (3.7%).

[0059] Step 3: Preparation of modified polysiloxane

[0060] Weigh out 150g of octamethylcyclotetrasiloxane, 40g of diethoxysilane-modified triazine, 18g of triethoxysilane-modified piperidine, 16g of aminopropylmethyldimethoxysilane, and 40mL of 50wt% sulfuric acid and add them to a reaction flask. Stir the mixture and raise the temperature of the reaction flask to 85℃. Maintain the temperature for 50min. Add 23g of diallyltetramethyldisiloxane to the reaction flask and maintain the temperature for 100min. Lower the temperature of the reaction flask to room temperature and add 3wt% sodium bicarbonate aqueous solution to adjust the pH of the system to 7. Allow the mixture to stand and separate the layers. Wash the upper oil phase with purified water until neutral and transfer it to a rotary evaporator with a water bath temperature of 80℃. Apply a negative pressure to -0.1MPa and remove low-boiling substances by vacuum evaporation to obtain modified polysiloxane.

[0061] During the reaction, sulfuric acid catalyzes the hydrolysis of octamethylcyclotetrasiloxane, triethoxysilane-modified piperidine, and aminopropylmethyldimethoxysilane molecules to form siloxane segments with silanol activity. Then, the silanols on the siloxane segments undergo condensation to form polysiloxane. Diallyltetramethyldisiloxane serves as a capping group to form unsaturated olefins on the polysiloxane chain, thus preparing the modified polysiloxane.

[0062] Step 4: Preparation of unsaturated modified polypropylene

[0063] Weigh out 500g of PP-g-MAH and 7500mL of chlorobenzene and add them to the reaction flask. Stir the mixture and raise the temperature of the reaction flask to 75℃. Keep the mixture warm and stir until the system is dissolved. Add 45g of 4-penten-1-amine to the reaction flask and keep the mixture warm for 60min. Then lower the temperature of the reaction flask to room temperature to obtain a low-temperature reaction solution.

[0064] Add 4 times the volume of anhydrous methanol to another reaction flask and stir. Then slowly add the low-temperature reaction solution to the anhydrous methanol and stir to disperse for 20 minutes. Filter the mixture and wash the filter cake three times with methanol. Dry the filter cake and transfer it to a drying oven at 60°C. Dry the mixture to constant weight to obtain unsaturated modified polypropylene.

[0065] During the reaction, PP-g-MAH is polypropylene grafted with maleic anhydride. The anhydride rings distributed on the molecular chain serve as active reaction sites. The 4-penten-1-amine molecule contains an amino group, which acts as a nucleophile to attack the carbonyl group of the anhydride ring and cause a ring-opening reaction, forming an unsaturated olefin end cap on the polypropylene molecular chain, thus preparing unsaturated modified polypropylene.

[0066] Step 5: Preparation of composite polypropylene

[0067] Weigh out 100 parts by weight of unsaturated modified polypropylene, 65 parts by weight of modified polysiloxane and 1 part by weight of diisopropylbenzene peroxide, add them to a torque rheometer at 160℃, mix for 20 minutes to obtain composite polypropylene.

[0068] Example 2

[0069] This embodiment provides a method for preparing composite polypropylene, including the following steps:

[0070] Step 1: Preparation of diethoxysilane-modified triazine

[0071] Weigh 28.0 g of 2-amino-4-methyl-6-methoxy-1,3,5-triazine and 560 mL of acetonitrile into an argon-protected reaction flask and stir. Raise the temperature of the reaction flask to 65 °C and stir until the system dissolves. Add 43.5 g of 3-propyl isocyanate-methyldiethoxysilane to the reaction flask and keep the reaction at this temperature for 70 min. Then, evacuate the reaction flask to -0.1 MPa and remove low-boiling substances by vacuum distillation to obtain diethoxysilane-modified triazine.

[0072] Step 2: Preparation of triethoxysilane-modified piperidine

[0073] Weigh 17.0 g of 4-aminomethyl-2,2,6,6-tetramethylpiperidine and 170 mL of tetrahydrofuran into an argon-protected reaction flask and stir. Raise the temperature of the reaction flask to 65 °C and stir until the system dissolves. Add 24.7 g of propyltriethoxysilane isocyanate to the reaction flask and keep the reaction at this temperature for 70 min. Then, evacuate the reaction flask to -0.1 MPa and remove low-boiling substances by vacuum distillation to obtain triethoxysilane-modified piperidine.

[0074] Step 3: Preparation of modified polysiloxane

[0075] Weigh out 150g of octamethylcyclotetrasiloxane, 45g of diethoxysilane-modified triazine, 20g of triethoxysilane-modified piperidine, 17g of aminopropylmethyldimethoxysilane, and 50mL of 55wt% sulfuric acid and add them to a reaction flask. Stir the mixture and raise the temperature of the reaction flask to 90℃. Maintain the temperature for 55min. Add 24g of diallyltetramethyldisiloxane to the reaction flask and maintain the temperature for 110min. Lower the temperature of the reaction flask to room temperature and add 4wt% sodium bicarbonate aqueous solution to adjust the pH of the system to 7. Allow the mixture to stand and separate the layers. Wash the upper oil phase with purified water until neutral and transfer it to a rotary evaporator with a water bath temperature of 85℃. Remove low-boiling substances under reduced pressure and then apply negative pressure to -0.1MPa to obtain modified polysiloxane.

[0076] Step 4: Preparation of unsaturated modified polypropylene

[0077] Weigh out 500g of PP-g-MAH and 7500mL of chlorobenzene and add them to the reaction flask. Stir the mixture and raise the temperature of the reaction flask to 80℃. Keep the mixture warm and stir until the system is dissolved. Add 52g of 4-penten-1-amine to the reaction flask and keep the mixture warm for 70min. Then lower the temperature of the reaction flask to room temperature to obtain a low-temperature reaction solution.

[0078] Add 4 times the volume of anhydrous methanol to another reaction flask and stir. Then slowly add the low-temperature reaction solution to the anhydrous methanol and stir to disperse for 25 minutes. Filter the mixture and wash the filter cake three times with methanol. Dry the filter cake and transfer it to a drying oven at 65°C. Dry the mixture to constant weight to obtain unsaturated modified polypropylene.

[0079] Step 5: Preparation of composite polypropylene

[0080] Weigh out 100 parts by weight of unsaturated modified polypropylene, 70 parts by weight of modified polysiloxane and 1.5 parts by weight of diisopropylbenzene peroxide, add them to a torque rheometer at a temperature of 165℃, mix for 25 minutes to obtain composite polypropylene.

[0081] Example 3

[0082] This embodiment provides a method for preparing composite polypropylene, including the following steps:

[0083] Step 1: Preparation of diethoxysilane-modified triazine

[0084] Weigh 28.0 g of 2-amino-4-methyl-6-methoxy-1,3,5-triazine and 560 mL of acetonitrile into an argon-protected reaction flask and stir. Raise the temperature of the reaction flask to 70 °C and stir until the system dissolves. Add 43.5 g of 3-propyl isocyanate-methyldiethoxysilane to the reaction flask and keep the reaction at this temperature for 80 min. Then, evacuate the reaction flask to -0.1 MPa and remove low-boiling substances by vacuum distillation to obtain diethoxysilane-modified triazine.

[0085] Step 2: Preparation of triethoxysilane-modified piperidine

[0086] Weigh 17.0 g of 4-aminomethyl-2,2,6,6-tetramethylpiperidine and 170 mL of tetrahydrofuran into an argon-protected reaction flask and stir. Raise the temperature of the reaction flask to 70 °C and stir until the system dissolves. Add 24.7 g of propyltriethoxysilane isocyanate to the reaction flask and keep the reaction at this temperature for 80 min. Then, evacuate the reaction flask to -0.1 MPa and remove low-boiling substances by vacuum distillation to obtain triethoxysilane-modified piperidine.

[0087] Step 3: Preparation of modified polysiloxane

[0088] Weigh out 150g of octamethylcyclotetrasiloxane, 50g of diethoxysilane-modified triazine, 22g of triethoxysilane-modified piperidine, 18g of aminopropylmethyldimethoxysilane, and 60mL of 60wt% sulfuric acid and add them to a reaction flask. Stir the mixture and raise the temperature of the reaction flask to 95℃. Maintain the temperature for 60min. Add 25g of diallyltetramethyldisiloxane to the reaction flask and maintain the temperature for 120min. Lower the temperature of the reaction flask to room temperature and add 5wt% sodium bicarbonate aqueous solution to adjust the pH of the system to 7. Allow the mixture to stand and separate the layers. Wash the upper oil phase with purified water until neutral and transfer it to a rotary evaporator with a water bath temperature of 90℃. Apply a negative pressure to -0.1MPa and remove low-boiling substances by vacuum evaporation to obtain modified polysiloxane.

[0089] Step 4: Preparation of unsaturated modified polypropylene

[0090] Weigh out 500g of PP-g-MAH and 7500mL of chlorobenzene and add them to the reaction flask. Stir the mixture and raise the temperature of the reaction flask to 85℃. Keep the mixture warm and stir until the system is dissolved. Add 60g of 4-penten-1-amine to the reaction flask and keep the mixture warm for 80min. Then lower the temperature of the reaction flask to room temperature to obtain a low-temperature reaction solution.

[0091] Add 4 times the volume of anhydrous methanol to another reaction flask and stir. Then slowly add the low-temperature reaction solution to the anhydrous methanol and stir to disperse for 30 minutes. Filter the mixture and wash the filter cake three times with methanol. Dry the filter cake and transfer it to a drying oven at 70°C. Dry the mixture to constant weight to obtain unsaturated modified polypropylene.

[0092] Step 5: Preparation of composite polypropylene

[0093] Weigh out 100 parts by weight of unsaturated modified polypropylene, 75 parts by weight of modified polysiloxane and 2 parts by weight of diisopropylbenzene peroxide, add them to a torque rheometer at a temperature of 170℃, mix for 30 minutes to obtain composite polypropylene.

[0094] Example 4

[0095] Please see Figure 1 This embodiment provides a method for preparing a high-current copper core conductor polypropylene insulated medium-voltage power cable, including the following steps:

[0096] Step 1: Forming the conductor shielding layer

[0097] A long conductor with a copper content of 99.95% and a rounded cross-section is used as copper conductor 1. Then, a conductor shielding layer 2 with a resistivity of 650 Ω·m composed of polyethylene and conductive carbon black is wrapped around the outside of copper conductor 1.

[0098] Step 3: Insulation layer forming

[0099] Weigh out 70g of nano zinc oxide, 1000mL of anhydrous ethanol, 18g of tetraethyl orthosilicate and 12g of KH-560 and add them to the reaction flask. Mix and ultrasonically disperse for 30min. Fix the reaction flask in an oil bath with mechanical stirring and stir. Raise the temperature of the reaction flask to 50℃. Add 150mL of 1mol / L sodium hydroxide solution to the reaction flask and keep it at this temperature for 60min. Lower the temperature of the reaction flask to room temperature, filter, wash the filter cake with purified water until neutral and then dry it. Transfer the filter cake to a drying oven at 60℃ and dry it to constant weight to obtain epoxy-modified zinc oxide.

[0100] Zinc stearate, ethylene bis-stearamide, diisobutyl phthalate and antioxidant AW were mixed evenly in a ratio of 5:2:4:2 to obtain the additive.

[0101] Weigh out the following by weight: 100 parts of polypropylene, 60 parts of the composite polypropylene prepared in Example 1, 1.6 parts of epoxy-modified zinc oxide, and 2 parts of additives. Add them to a twin-screw extruder. The temperatures of the six temperature zones of the twin-screw extruder from the feed end to the discharge end are 170°C, 175°C, 175°C, 180°C, 180°C, and 185°C, respectively. After melting and mixing for 3 minutes, the mixture is extruded and coated onto the outside of the conductor shielding layer 2. After cooling and curing, an insulating layer 3 with a thickness of 5 mm is formed on the outside of the conductor shielding layer 2.

[0102] Step 4: Add an external shielding layer

[0103] Mylar tape is wrapped around the outside of the insulation layer 3 to form an insulating shielding layer 4 on the outside of the insulation layer 3;

[0104] A metal shielding layer 5 is formed by wrapping a mesh woven from copper wire around the outside of the insulating shielding layer 4;

[0105] A refractory mica wrapping tape is wrapped around the outside of the metal shielding layer 5 to form a wrapping layer 6.

[0106] Step 5: Add an outer sheath layer

[0107] Thermoplastic elastomer (TPE) is melt-extruded and coated onto the outside of the wrapping layer 6, then cooled and cured to form the outer sheath layer 7, thus preparing a medium-voltage power cable.

[0108] Example 5

[0109] Please see Figure 1 This embodiment provides a method for preparing a high-current copper core conductor polypropylene insulated medium-voltage power cable, including the following steps:

[0110] Step 1: Forming the conductor shielding layer

[0111] A long conductor with a copper content of 99.96% and a rounded cross-section is used as copper conductor 1. Then, a conductor shielding layer 2 with a resistivity of 700 Ω·m composed of polyethylene and conductive carbon black is wrapped around the outside of copper conductor 1.

[0112] Step 3: Insulation layer forming

[0113] Weigh out 70g of nano zinc oxide, 1000mL of anhydrous ethanol, 20g of tetraethyl orthosilicate and 13g of KH-560 and add them to a reaction flask. Mix and ultrasonically disperse for 40min. Fix the reaction flask in an oil bath with mechanical stirring and stir. Raise the temperature of the reaction flask to 55℃. Add 150mL of 1.5mol / L sodium hydroxide solution to the reaction flask and keep it at this temperature for 70min. Lower the temperature of the reaction flask to room temperature, filter, wash the filter cake with purified water until neutral and then dry it. Transfer the filter cake to a drying oven at 65℃ and dry it to constant weight to obtain epoxy-modified zinc oxide.

[0114] Calcium stearate, ethylene bis-stearamide, diisooctyl phthalate and antioxidant DNP were mixed evenly in a ratio of 5:2:4:2 to obtain the additive.

[0115] Weigh out the following by weight: 100 parts of polypropylene, 65 parts of the composite polypropylene prepared in Example 3, 1.8 parts of epoxy-modified zinc oxide, and 2.5 parts of additives, and add them to a twin-screw extruder. The temperatures of the six temperature zones of the twin-screw extruder from the feed end to the discharge end are 170°C, 175°C, 175°C, 180°C, 180°C, and 185°C, respectively. After melting and mixing for 4 minutes, the mixture is extruded and coated on the outside of the conductor shielding layer 2. After cooling and curing, an insulating layer 3 with a thickness of 5.5 mm is formed on the outside of the conductor shielding layer 2.

[0116] Step 4: Add an external shielding layer

[0117] Mylar tape is wrapped around the outside of the insulation layer 3 to form an insulating shielding layer 4 on the outside of the insulation layer 3;

[0118] A metal shielding layer 5 is formed by wrapping a mesh woven from copper wire around the outside of the insulating shielding layer 4;

[0119] A refractory mica wrapping tape is wrapped around the outside of the metal shielding layer 5 to form a wrapping layer 6.

[0120] Step 5: Add an outer sheath layer

[0121] Thermoplastic elastomer (TPE) is melt-extruded and coated onto the outside of the wrapping layer 6, then cooled and cured to form the outer sheath layer 7, thus preparing a medium-voltage power cable.

[0122] Example 6

[0123] Please see Figure 1 This embodiment provides a method for preparing a high-current copper core conductor polypropylene insulated medium-voltage power cable, including the following steps:

[0124] Step 1: Forming the conductor shielding layer

[0125] A long conductor with a copper content of 99.97% and a rounded cross-section is used as copper conductor 1. Then, a conductor shielding layer 2 with a resistivity of 750 Ω·m composed of polyethylene and conductive carbon black is wrapped around the outside of copper conductor 1.

[0126] Step 3: Insulation layer forming

[0127] Weigh out 70g of nano zinc oxide, 1000mL of anhydrous ethanol, 22g of tetraethyl orthosilicate and 14g of KH-560 and add them to a reaction flask. Mix and ultrasonically disperse for 50min. Fix the reaction flask in an oil bath with mechanical stirring and stir. Raise the temperature of the reaction flask to 60℃. Add 150mL of 2mol / L sodium hydroxide solution to the reaction flask and keep it at this temperature for 80min. Lower the temperature of the reaction flask to room temperature, filter, wash the filter cake with purified water until neutral and then dry it. Transfer the filter cake to a drying oven at 70℃ and dry it to constant weight to obtain epoxy-modified zinc oxide.

[0128] Sodium stearate, ethylene bis-stearamide, diisopropyl phthalate and antioxidant CPPD were mixed evenly in a ratio of 5:2:4:2 to obtain the additive.

[0129] Weigh out the following by weight: 100 parts of polypropylene, 70 parts of the composite polypropylene prepared in Example 3, 2 parts of epoxy-modified zinc oxide, and 3 parts of additives. Add them to a twin-screw extruder. The temperatures of the six temperature zones of the twin-screw extruder from the feed end to the discharge end are 170°C, 175°C, 175°C, 180°C, 180°C, and 185°C, respectively. After melting and mixing for 5 minutes, the mixture is extruded and coated on the outside of the conductor shielding layer 2. After cooling and curing, an insulating layer 3 with a thickness of 6 mm is formed on the outside of the conductor shielding layer 2.

[0130] Step 4: Add an external shielding layer

[0131] Mylar tape is wrapped around the outside of the insulation layer 3 to form an insulating shielding layer 4 on the outside of the insulation layer 3;

[0132] A metal shielding layer 5 is formed by wrapping a mesh woven from copper wire around the outside of the insulating shielding layer 4;

[0133] A refractory mica wrapping tape is wrapped around the outside of the metal shielding layer 5 to form a wrapping layer 6.

[0134] Step 5: Add an outer sheath layer

[0135] Thermoplastic elastomer (TPE) is melt-extruded and coated onto the outside of the wrapping layer 6, then cooled and cured to form the outer sheath layer 7, thus preparing a medium-voltage power cable.

[0136] Comparative Example 1

[0137] The difference between this comparative example and Example 6 is that, in the preparation of the composite polypropylene, step 1 was omitted, and diethoxysilane-modified triazine was not added in step 3.

[0138] Comparative Example 2

[0139] The difference between this comparative example and Example 6 is that, in the preparation of the composite polypropylene, step 2 was omitted, and triethoxysilane-modified piperidine was not added in step 3.

[0140] Comparative Example 3

[0141] The difference between this comparative example and Example 6 is that nano zinc oxide in step three is used instead of epoxy-modified zinc oxide in the preparation of the insulating layer.

[0142] Performance testing:

[0143] The tensile strength and elongation at break of the insulation layers of the medium-voltage power cables prepared in Examples 4-6 and Comparative Examples 1-3 were determined in accordance with the standard GB / T 2951.11-2008 "General Test Methods for Insulation and Sheath Materials of Cables and Optical Fibers - Part 11: General Test Methods - Thickness and Dimensional Measurements - Mechanical Properties Tests".

[0144] The electrical strength of the insulation layers of the medium-voltage power cables prepared in Examples 4-6 and Comparative Examples 1-3 was determined in accordance with the standard GB / T 1408.1-2016 "Electrical strength test method for insulating materials - Part 1: Test at power frequency".

[0145] The medium-voltage power cable samples prepared in Examples 4-6 and Comparative Examples 1-3 were placed in an oven at 110°C and kept at that temperature for 100 hours. The tensile strength, elongation at break, and electrical strength of the medium-voltage power cable samples were then measured. The specific test results are shown in Table 1 below.

[0146] Table 1 - Performance Test Data of Samples

[0147]

[0148] Data Analysis:

[0149] Comparative analysis of the data in Table 1 shows that the insulation layer of the high-current copper core conductor polypropylene insulated medium-voltage power cable prepared by this invention has a tensile strength of 27.7 MPa, an elongation at break of 360%, and an electrical strength of 32.8 kV / mm before thermal aging. After thermal aging, the tensile strength reaches 25.9 MPa with a retention rate of 93.5%, the elongation at break reaches 310% with a retention rate of 86.1%, and the electrical strength reaches 31.2 kV / mm with a retention rate of 95.1%. All performance test data are superior to those of the comparative example.

[0150] This invention describes a composite polypropylene prepared by constructing a modified polysiloxane containing triazine, piperidine, and amino structures and combining it with unsaturated modified polypropylene. Then, epoxy-modified nano-zinc oxide and the composite polypropylene are used to complement and enhance the polypropylene, forming an insulating layer. This effectively improves the electrical and mechanical strength of the polypropylene insulation layer, as well as its heat aging resistance, thus enhancing the reliability and safety of the medium-voltage cable insulation layer during long-term operation. Furthermore, the multi-layered structure, including a conductor shielding layer, a metal shielding layer, and a flame-retardant wrapping layer, designed outside the high-purity rounded copper conductor, significantly improves the overall performance of the medium-voltage power cable, achieving the technical effects of enhanced current carrying capacity, extended cable life, and improved operational safety.

[0151] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A high-current copper core conductor polypropylene insulated medium-voltage power cable, characterized in that, It includes a copper conductor (1), a conductor shielding layer (2), and an insulating layer (3) arranged sequentially from the inside out. The copper conductor (1) is a long conductor with a rounded corner cross-section; The molding method of the insulating layer (3) is as follows: 100 parts by weight of polypropylene, 60-70 parts of composite polypropylene, 1.6-2 parts of epoxy modified zinc oxide and 2-3 parts of additives are added to a twin-screw extruder and melt-mixed for 3-5 minutes. The mixture is then extruded and coated on the outside of the conductor shielding layer (2). The mixture is then cooled and cured to form an insulating layer (3) on the outside of the conductor shielding layer (2). Composite polypropylene is obtained by the following steps: A1. Mix PP-g-MAH and chlorobenzene and stir. Raise the temperature of the reaction system to 75-85℃ and stir until the system is dissolved. Add 4-penten-1-amine to the reaction system and keep it at the temperature for 60-80 min. After post-treatment, unsaturated modified polypropylene is obtained. A2. Heat unsaturated modified polypropylene, modified polysiloxane and initiator to 160-170℃ and mix for 20-30 minutes to obtain composite polypropylene; The modified polysiloxane is prepared by mixing octamethylcyclotetrasiloxane, diethoxysilane-modified triazine, triethoxysilane-modified piperidine, aminopropylmethyldimethoxysilane and catalyst, raising the temperature of the reaction system to 85-95℃, maintaining the temperature for 50-60 min, adding an end-capping agent to the reaction system, maintaining the temperature for 100-120 min, and then performing post-treatment to obtain the modified polysiloxane.

2. The high-current copper core conductor polypropylene insulated medium-voltage power cable according to claim 1, characterized in that, The copper conductor (1) has a copper content greater than 99.95%, and the conductor shielding layer (2) is composed of polyethylene and conductive carbon black with a resistivity of 650-750 Ω·m.

3. The high-current copper core conductor polypropylene insulated medium-voltage power cable according to claim 1, characterized in that, In step A1, the ratio of PP-g-MAH, chlorobenzene, and 4-penten-1-amine is 10g:150mL:0.9-1.2g; in step A2, the weight ratio of unsaturated modified polypropylene, modified polysiloxane, and initiator is 100:65-75:1-2, and the initiator is dicumyl peroxide.

4. A high-current copper core conductor polypropylene insulated medium-voltage power cable according to claim 1, characterized in that, The preparation method of diethoxysilane-modified triazine is as follows: Under an inert gas atmosphere, 2-amino-4-methyl-6-methoxy-1,3,5-triazine and acetonitrile are mixed, the temperature of the reaction system is raised to 60-70℃, and the mixture is stirred until the system is dissolved. 3-propyl isocyanate-methyldiethoxysilane is added to the reaction system, and the reaction is maintained at this temperature for 60-80 min. After post-treatment, diethoxysilane-modified triazine is obtained. The ratio of 2-amino-4-methyl-6-methoxy-1,3,5-triazine to acetonitrile is 1 g: 20 mL, and the ratio of 2-amino-4-methyl-6-methoxy-1,3,5-triazine to 3-propyl isocyanate-methyldiethoxysilane is 1 mol: 1 mol.

5. A high-current copper core conductor polypropylene insulated medium-voltage power cable according to claim 1, characterized in that, The preparation method of triethoxysilane-modified piperidine is as follows: Under an inert gas atmosphere, 4-aminomethyl-2,2,6,6-tetramethylpiperidine and tetrahydrofuran are mixed, the temperature of the reaction system is raised to 60-70℃, and the mixture is stirred until the system is dissolved. Propyltriethoxysilane isocyanate is added to the reaction system, and the reaction is maintained at this temperature for 60-80 min. After post-treatment, triethoxysilane-modified piperidine is obtained. The ratio of 4-aminomethyl-2,2,6,6-tetramethylpiperidine to tetrahydrofuran is 1 g:10 mL, and the ratio of 4-aminomethyl-2,2,6,6-tetramethylpiperidine to propyltriethoxysilane is 1 mol:1 mol.

6. A high-current copper core conductor polypropylene insulated medium-voltage power cable according to claim 1, characterized in that, The ratio of octamethylcyclotetrasiloxane, diethoxysilane-modified triazine, triethoxysilane-modified piperidine, aminopropylmethyldimethoxysilane, catalyst, and end-capping agent is 15g:4-5g:1.8-2.2g:1.6-1.8g:4-6mL:2.3-2.5g, wherein the end-capping agent is diallyltetramethyldisiloxane, and the catalyst is 50-60wt% sulfuric acid.

7. A high-current copper core conductor polypropylene insulated medium-voltage power cable according to claim 1, characterized in that, The preparation method of epoxy-modified zinc oxide is as follows: nano zinc oxide, anhydrous ethanol, tetraethyl orthosilicate and KH-560 are mixed and ultrasonically dispersed for 30-50 min. The temperature of the reaction system is raised to 50-60℃, sodium hydroxide solution is added to the reaction system, and the reaction is kept at the temperature for 60-80 min. After post-treatment, epoxy-modified zinc oxide is obtained.

8. A high-current copper core conductor polypropylene insulated medium-voltage power cable according to claim 7, characterized in that, The ratio of nano zinc oxide, anhydrous ethanol, tetraethyl orthosilicate, KH-560, and sodium hydroxide solution is 7g:100mL:1.8-2.2g:1.2-1.4g:15mL, and the concentration of the sodium hydroxide solution is 1-2mol / L.

9. A high-current copper core conductor polypropylene insulated medium-voltage power cable according to claim 1, characterized in that, The outer side of the insulating layer (3) may also be provided with an insulating shielding layer (4), a metal shielding layer (5), a wrapping layer (6), and an outer sheath layer (7).

10. A high-current copper core conductor polypropylene insulated medium-voltage power cable according to claim 9, characterized in that, The insulating shielding layer (4) is obtained by wrapping Mylar tape around the outside of the insulating layer (3), the metal shielding layer (5) is obtained by covering the outside of the insulating shielding layer (4) with woven copper mesh, the wrapping layer (6) is obtained by wrapping refractory mica wrapping tape around the outside of the metal shielding layer (5), and the outer sheath layer (7) is obtained by melt extrusion of thermoplastic elastomer TPE around the outside of the outer sheath layer (7).

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