Nuclear power winding wire special insulating material and its preparation method

Abstract

The application discloses a kind of nuclear power winding wire special insulating material and preparation method thereof, the insulating material is made of raw materials including the following components by mass fraction: ethylene-vinyl acetate copolymer 5~8 parts, metallocene linear low density polyethylene 75~85 parts, high density polyethylene 0~5 parts, maleic anhydride grafted metallocene polyethylene-vinyl acetate copolymer 3~7 parts, high-temperature antioxidant 1~3 parts, tris (methacrylic acid) trimethylolpropane ester 2~4 parts, condensed ring aromatic nucleating agent 0.1~0.3 parts, absorption type light stabilizer 0.5~1.2 parts, succinic acid and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinol polymer 0.3~0.8 parts;Condensed ring aromatic nucleating agent is pyrazolo 1,3,5-triazine and / or 6,8-diamino-7-nitro-tetrazolo [1,5-b] pyridazine.The application has excellent high-temperature aging resistance, insulation, radiation resistance and water tree resistance, can meet the performance requirements of nuclear power winding wire.

Description

Technical Field

[0001] This invention relates to insulating materials, and more specifically, to an insulating material specifically for nuclear power plant winding wires. Background Technology

[0002] In nuclear power plants, the reactor coolant pump (i.e., the main pump) is the heart of the nuclear island, classified as nuclear safety level 1. Its main function is to supply coolant to the reactor and circulate it within the coolant loop system. Shielded main pumps offer advantages such as leak-free operation and ease of decontamination; however, with the increasing development of commercial nuclear power, their low efficiency makes them unsuitable for the coasting requirements of main pump motors in medium and large-scale nuclear power plants. While shaft-sealed main pumps offer high efficiency, their high technical requirements, operational difficulties, short seal lifespan, and the need for periodic shutdowns for maintenance make them unsuitable for commercial nuclear power. Therefore, wet-wound pumps, with their advantages of light weight, low input power, no need for voltage reduction, high overall efficiency, and low eddy current losses, are gradually becoming the preferred choice for main pumps.

[0003] The windings of wet-wound pumps are made from a single, continuous winding wire. Due to their unique operating environment, the performance requirements for this winding wire are extremely high. When moisture, electrical stress, and other inducing factors such as impurities, protrusions, space charges, or ions are present in the insulation layer of the winding wire, microchannels resembling tree branches can form, a phenomenon known as water treeing, which significantly impacts the cable's lifespan. The insulation material used to create the insulation layer must be able to withstand various harsh conditions, including radiation, high temperatures, and water treeing, to ensure the cable's long-term safe operation in wet-wound pumps. To meet the future development needs of nuclear power, there is an urgent need to develop an insulation material that can withstand the environment of wet-wound pumps. Summary of the Invention

[0004] To address the issues of high temperature, high radiation, and water treeing in cables of wet-winding pumps, this invention provides a special insulating material for nuclear power windings and its preparation method. This special insulating material for nuclear power windings has the advantages of high mechanical strength, high temperature aging resistance, radiation resistance, water treeing resistance, and high insulation, which can protect the cable to work normally in wet-winding main pumps.

[0005] To achieve the above objectives, the present invention provides a special insulating material for nuclear power plant windings, which, by weight, is made from raw materials comprising the following components:

[0006] The composition includes 5-8 parts of ethylene-vinyl acetate copolymer, 75-85 parts of metallocene linear low-density polyethylene, 0-5 parts of high-density polyethylene, 3-7 parts of maleic anhydride-grafted metallocene polyethylene-vinyl acetate copolymer, 1-3 parts of high-temperature antioxidant, 2-4 parts of tri(methacrylate)trimethylolpropane ester, 0.1-0.3 parts of polycyclic aromatic hydrocarbon nucleating agent, 0.5-1.2 parts of absorption-type light stabilizer, and 0.3-0.8 parts of polymer of succinic acid and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinol; wherein the polycyclic aromatic hydrocarbon nucleating agent is pyrazolo-1,3,5-triazine and / or 6,8-diamino-7-nitro-tetrazo[1,5-b]pyridazine.

[0007] This invention achieves high-temperature aging resistance through the compounding of ethylene-vinyl acetate copolymer, metallocene linear low-density polyethylene, high-density polyethylene, maleic anhydride-grafted metallocene polyethylene-vinyl acetate copolymer, and a high-temperature antioxidant. Tris(methacrylate)trimethylolpropane ester crosslinking sensitizer transforms the linear molecular structure of the polymer insulating material into a three-dimensional network structure, converting the thermoplastic material into a thermosetting insulating material, thereby further improving the high-temperature aging resistance and mechanical properties of the insulating material. Under the action of the polycyclic aromatic hydrocarbon nucleating agent, the crystal particles in the insulating material are finer, resulting in better inhibition of water tree growth and greater high-temperature resistance. The compounding of an absorption-type light stabilizer and a hindered amine light stabilizer (polymer of succinic acid and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinol) provides excellent radiation resistance. Furthermore, the polymerization of various ethylene components significantly improves the insulation properties of the insulating material. The coordinated composition of the components in this invention enables it to maintain stable performance in the harsh environment of wet-wound pumps.

[0008] Preferably, the mass fraction of vinyl acetate in the ethylene-vinyl acetate copolymer is 40-60%.

[0009] The beneficial effect of this preferred method is that ethylene-vinyl acetate copolymers with high vinyl acetate content have excellent aging resistance.

[0010] Preferably, the metallocene linear low-density polyethylene has a branched structure, a crystallinity of 35-75%, a molecular weight of 20,000-50,000, a tensile strength of 29-35 MPa, an elongation at break of 650-800%, and a melt index greater than or equal to 1 g / 10 min.

[0011] Preferably, the high-density polyethylene has a linear molecular structure with a crystallinity of 60-90%, a molecular weight of 70,000-350,000, a tensile strength of 30-38 MPa, an elongation at break of 500-700%, and a melt index greater than or equal to 0.9 g / 10 min.

[0012] Preferably, the maleic anhydride-grafted metallocene polyethylene-vinyl acetate copolymer is prepared by in-situ polymerization of ethylene, vinyl acetate and maleic anhydride under the catalysis of metallocene; the content of maleic anhydride groups in the maleic anhydride-grafted metallocene polyethylene-vinyl acetate copolymer is 0.6~0.8%.

[0013] Preferably, the high-temperature resistant antioxidant is selected from one or more of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], dilauryl thiodipropionate, tris[2,4-di-tert-butylphenyl]phosphite, N,N'-bis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hydrazine, and β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate n-octadecyl alcohol ester.

[0014] Preferably, the absorbent light stabilizer is selected from one or more of phenyl benzoate, 2-hydroxy-4-n-octyloxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-(2-hydroxy-5-methylphenyl)benzotriazole and 2-(2-hydroxy-5-tert-octylphenyl)benzotriazole.

[0015] Another aspect of the present invention provides a method for preparing the above-mentioned insulation material for nuclear power winding wires, the method comprising the following steps:

[0016] The ethylene-vinyl acetate copolymer, metallocene linear polyethylene, high-density polyethylene, maleic anhydride-grafted metallocene polyethylene-vinyl acetate copolymer, high-temperature antioxidant, tri(methacrylate)trimethylolpropane ester, polycyclic aromatic hydrocarbon nucleating agent, absorption-type light stabilizer, and succinic acid and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinol polymer are mixed by frequency up-mixing, heated to 160~170℃ and kneaded for 15~20 minutes, then extruded through a twin-screw extruder and granulated to obtain the special insulation material for nuclear power winding wires.

[0017] Preferably, the frequency upsampling method is as follows: mixing at 15~20Hz for 45~60s, then mixing at 30~35Hz for 100~120s, and finally mixing at 45~50Hz for 280~300s.

[0018] The advantages of this preferred method are: the step-by-step frequency increase can protect the motor of the high-frequency mixing equipment, prevent the high-frequency mixing device from losing balance and tipping over due to excessive shaking frequency, and enable the resin to be mixed more thoroughly.

[0019] Preferably, the machine parameters of the twin-screw extruder are set as follows: upper barrel temperature 123~135℃, lower barrel temperature 136~153℃.

[0020] Through the above technical solution, the present invention achieves the following beneficial effects:

[0021] This invention achieves high-temperature aging resistance by compounding various ethylene and ethylene derivatives, adding high-temperature resistant antioxidants and trimethylolpropane (trimethylolpropane) (methacrylate), and controlling the mass fraction of vinyl acetate in the ethylene-vinyl acetate copolymer; it also achieves water-resistant properties by adding polycyclic aromatic hydrocarbon nucleating agents; it achieves radiation resistance by compounding absorbent light stabilizers and polymers of succinic acid and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinol; and it provides insulation through the polymerization of the matrix components, resulting in excellent overall performance that meets the performance requirements of nuclear power winding wires. Detailed Implementation

[0022] The specific embodiments of the present invention will be described in detail below with reference to examples. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0023] The ethylene-vinyl acetate copolymer used in the following examples and comparative examples was purchased from Arkema, model 42-60; the high-density polyethylene was purchased from SCG Chemicals, model H511W; the maleic anhydride-grafted metallocene polyethylene-vinyl acetate copolymer was prepared by in-situ polymerization of ethylene, vinyl acetate and maleic anhydride under metallocene catalysis, with a maleic anhydride group content of 0.6~0.8%.

[0024] Example 1:

[0025] The preparation method of special insulation material for nuclear power plant winding wires is as follows:

[0026] The following ingredients were added: 8g of ethylene-vinyl acetate copolymer, 85g of metallocene linear low-density polyethylene, 5g of high-density polyethylene, 7g of maleic anhydride-grafted metallocene polyethylene-vinyl acetate copolymer, 3g of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 4g of tris(methacrylate) trimethylolpropane ester, 0.3g of pyrazolo-1,3,5-triazine, 1.2g of phenyl o-hydroxybenzoate, and 0g of a polymer of succinic acid and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinol. 0.8g was mixed using the following frequency ramping method: 20Hz for 45s, then 35Hz for 100s, and finally 50Hz for 280s; after mixing, the mixture was heated to 170℃ and kneaded for 15min; the kneaded material was extruded through a twin-screw extruder with the extruder parameters set as follows: upper barrel 135℃, lower barrel 153℃; after the extruded material was cooled in a 20℃ cooling water bath and dried in a 50℃ hot air dryer to remove surface moisture, it was placed in a rotary pelletizer for granulation to obtain a special insulating material for nuclear power winding wires.

[0027] Example 2:

[0028] The preparation method of special insulation material for nuclear power plant winding wires is as follows:

[0029] The following ingredients were added: 6.5g of ethylene-vinyl acetate copolymer, 80g of metallocene linear low-density polyethylene, 2.5g of high-density polyethylene, 5g of maleic anhydride-grafted metallocene polyethylene-vinyl acetate copolymer, 1g of dilaurate thiodipropionate, 1g of tris[2,4-di-tert-butylphenyl]phosphite, 3g of tris(methacrylic acid)trimethylolpropane, 0.1g of pyrazolo-1,3,5-triazine, 0.1g of 6,8-diamino-7-nitro-tetrazo[1,5-b]pyridazine, 0.45g of 2-hydroxy-4-n-octyloxybenzophenone, 0.4g of 2-hydroxy-4-methoxybenzophenone, and butyl... 0.55g of the polymer of diacid and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinol was mixed by frequency increase as follows: 18Hz for 52s, then 33Hz for 110s, and finally 52Hz for 290s. After mixing, the mixture was heated to 165℃ and kneaded for 18min. The mixture was then extruded through a twin-screw extruder with the machine parameters set as follows: upper barrel 130℃ and lower barrel 145℃. After the extruded material was cooled in a 20℃ cooling water bath and dried in a 50℃ hot air dryer to remove surface moisture, it was then placed in a rotary pelletizer for granulation to obtain a special insulating material for nuclear power winding wires.

[0030] Example 3:

[0031] The preparation method of special insulation material for nuclear power plant winding wires is as follows:

[0032] The following ingredients were added: 5g of ethylene-vinyl acetate copolymer, 75g of metallocene linear low-density polyethylene, 3g of maleic anhydride-grafted metallocene polyethylene-vinyl acetate copolymer, 0.5g of N,N'-bis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hydrazine, 0.5g of β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate n-octadecyl alcohol ester, 2g of tris(methacrylate) trimethylolpropane ester, 0.1g of 6,8-diamino-7-nitro-tetrazo[1,5-b]pyridazine, 0.25g of 2-(2-hydroxy-5-methylphenyl)benzotriazole, and 2-(2-hydroxy-5-tert-octylphenyl)benzene 0.25g of triazole and 0.3g of a polymer of succinic acid and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinol were mixed by frequency increase as follows: 15Hz for 60s, then 30Hz for 120s, and finally 45Hz for 300s. The mixture was heated to 160℃ and kneaded for 20min. The mixture was extruded through a twin-screw extruder with the machine parameters set as follows: upper barrel 135℃ and lower barrel 153℃. After the extruded material was cooled in a 20℃ cooling water bath and dried in a 50℃ hot air dryer to remove surface moisture, it was granulated in a rotary pelletizer to obtain a special insulating material for nuclear power winding wires.

[0033] Comparative Example 1: Other conditions are the same as in Example 1, except that it does not contain ethylene-vinyl acetate copolymer.

[0034] Comparative Example 2: Other conditions were the same as in Example 1, except that it did not contain maleic anhydride-grafted metallocene polyethylene-vinyl acetate copolymer.

[0035] Comparative Example 3: Other conditions were the same as in Example 1, except that tri(methacrylate) trimethylolpropane ester was replaced with N,N-methylenebisacrylamide.

[0036] Comparative Example 4: Other conditions are the same as in Example 1, except that the mass fraction of vinyl acetate in the ethylene-vinyl acetate copolymer is changed to 10~20%.

[0037] Comparative Example 5: Other conditions were the same as in Example 1, except that pyrazolo-1,3,5-triazine was replaced with 1,3:2,4-bis(p-methylbenzyl)sorbitol.

[0038] Comparative Example 6: Other conditions were the same as in Example 1, except that it did not contain the polymer of succinic acid and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinol.

[0039] The performance of the nuclear power winding insulation material obtained in the examples and comparative examples was tested. The test methods and standards are as follows:

[0040] Tensile strength and elongation at break: GT / T 1040.3;

[0041] Thermal aging test: GB / T 2951.12;

[0042] Resistivity: GB / T 1410;

[0043] Step withstand voltage test: IECA S-94-649-2004 Sec 10.1.3;

[0044] UV resistance: HD 605.

[0045] The results of the performance test are shown in Table 1.

[0046] Table 1: Performance test results of the special insulation material for nuclear power windings obtained in the examples and comparative examples

[0047]

[0048] As shown in Table 1, the tensile strength change rate (change rate = difference between data before and after the thermal aging test / data before the thermal aging test) of the nuclear power winding insulation material obtained in the examples was between 5.1% and 7.9%, and the elongation at break change rate was between -2.7% and 3.8%, indicating good heat resistance and high thermal stability. Comparative Example 1, due to the absence of ethylene-vinyl acetate copolymer, exhibited a tensile strength change rate of 45.9% and an elongation at break change rate of 40.0%, failing to maintain stability at high temperatures. Comparative Example 2, lacking maleic anhydride-grafted metallocene polyethylene-vinyl acetate copolymer, had significantly lower tensile strength and elongation at break compared to Example 1. Tris(methacrylate)trimethylolpropane is a crosslinking agent that can increase the material's high-temperature resistance and mechanical properties. Replacing it with the common crosslinking agent N,N-methylenebisacrylamide resulted in a certain degree of decrease in the tensile strength and elongation at break of the insulation material, and a significant increase in the change rate, all of which can be analyzed from the data of Comparative Example 3 and Example 1. On the other hand, the mass fraction of vinyl acetate in the ethylene-vinyl acetate copolymer also affects the high-temperature aging resistance. Comparative Example 4 shows that when the mass fraction of vinyl acetate is only 20%, the tensile strength change rate is 24.9%, and the elongation at break is 39.2%. Comparative Example 5 uses pyrazolo-1,3,5-triazine as a nucleating agent. This nucleating agent affects the water-tree resistance of the insulation material by influencing the crystal size. The step withstand voltage test can quantitatively reflect this property; a higher value indicates better water-tree resistance. However, the step withstand voltage test result of Comparative Example 5 is only 9.7 kV / mm, indicating that its water-tree resistance is even worse. In Comparative Example 6, because only one light stabilizer was used, without adding the polymer of succinic acid and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinol, its radiation resistance effect did not meet the standard, and cracks appeared in the UV aging test. Besides these differences, Comparative Examples 1-4, due to changes in the matrix composition, resulted in lower resistivity of the insulating material at 20°C and 90°C compared to Example 1, while Comparative Examples 5 and 6, without changes in the matrix composition, showed no significant change in resistivity.

[0049] As can be seen from the above description, the present invention has the following advantages: excellent resistance to high temperature aging, insulation, water resistance and radiation resistance.

[0050] The preferred embodiments of the present invention have been described in detail above with reference to the examples. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0051] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0052] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A special insulating material for nuclear power plant winding wires, characterized in that, The product, by weight, is prepared from raw materials comprising the following components: 5-8 parts of ethylene-vinyl acetate copolymer, 75-85 parts of metallocene linear low-density polyethylene, 0-5 parts of high-density polyethylene, 3-7 parts of maleic anhydride-grafted metallocene polyethylene-vinyl acetate copolymer, 1-3 parts of high-temperature resistant antioxidant, 2-4 parts of trimethylolpropane tris(methacrylate), 0.1-0.3 parts of polycyclic aromatic hydrocarbon nucleating agent, 0.5-1.2 parts of absorption-type light stabilizer, and 0.3-0.8 parts of a polymer of succinic acid and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinol; wherein the polycyclic aromatic hydrocarbon nucleating agent is pyridine. The copolymer contains zozo[1,3,5-triazine] and / or 6,8-diamino-7-nitro-tetrazozo[1,5-b]pyridazine, wherein the mass fraction of vinyl acetate in the ethylene-vinyl acetate copolymer is 40-60%; the high-temperature resistant antioxidant is selected from one or more of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], dilauryl thiodipropionate, tris[2,4-di-tert-butylphenyl]phosphite, N,N'-bis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hydrazine and β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate n-octadecyl alcohol ester.

2. The special insulating material for nuclear power winding wires according to claim 1, characterized in that, The metallocene linear low-density polyethylene has a branched structure, a crystallinity of 35-75%, a molecular weight of 20,000-50,000, a tensile strength of 29-35 MPa, an elongation at break of 650-800%, and a melt index greater than or equal to 1 g / 10 min.

3. The special insulating material for nuclear power winding wires according to claim 1, characterized in that, The high-density polyethylene has a linear molecular structure with a crystallinity of 60-90%, a molecular weight of 70,000-350,000, a tensile strength of 30-38 MPa, an elongation at break of 500-700%, and a melt index greater than or equal to 0.9 g / 10 min.

4. The special insulating material for nuclear power winding wires according to claim 1, characterized in that, The maleic anhydride-grafted metallocene polyethylene-vinyl acetate copolymer is prepared by in-situ polymerization of ethylene, vinyl acetate and maleic anhydride under the catalysis of metallocene; the content of maleic anhydride groups in the maleic anhydride-grafted metallocene polyethylene-vinyl acetate copolymer is 0.6~0.8%.

5. The special insulating material for nuclear power winding wires according to claim 1, characterized in that, The absorbent light stabilizer is selected from one or more of phenyl benzoate, 2-hydroxy-4-n-octyloxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-(2-hydroxy-5-methylphenyl)benzotriazole and 2-(2-hydroxy-5-tert-octylphenyl)benzotriazole.

6. A method for preparing a special insulating material for nuclear power plant winding wires according to any one of claims 1 to 5, characterized in that, Includes the following steps: The ethylene-vinyl acetate copolymer, metallocene linear polyethylene, high-density polyethylene, maleic anhydride-grafted metallocene polyethylene-vinyl acetate copolymer, high-temperature antioxidant, tri(methacrylate)trimethylolpropane ester, polycyclic aromatic hydrocarbon nucleating agent, absorption-type light stabilizer, and succinic acid and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinol polymer are mixed by frequency up-mixing, heated to 160~170℃ and kneaded for 15~20 minutes, then extruded through a twin-screw extruder and granulated to obtain the special insulation material for nuclear power winding wires.

7. The preparation method according to claim 6, characterized in that, The frequency upsampling and mixing method is as follows: mix 15~20Hz for 45~60s, then mix 30~35Hz for 100~120s, and finally mix 45~50Hz for 280~300s.

8. The preparation method according to claim 6, characterized in that, The machine parameters of the twin-screw extruder are set as follows: upper barrel temperature 123~135℃, lower barrel temperature 136~153℃.

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