Dry-type transformer insulating material and method for producing the same

Abstract

The application discloses dry-type transformer insulating material and a preparation method thereof, and belongs to electrical equipment insulating material, which comprises the following raw materials by mass: 55-65 parts of epoxy resin matrix, 20-40 parts of organic acid anhydride curing agent, 20-50 parts of insulating filler, 2-10 parts of meta-aramid pulp and 0.3-1.5 parts of tri-substituted imidazole tetrafluoroborate. The preparation method of the dry-type transformer insulating material comprises the following steps: mixing the raw materials, vacuum defoaming, pouring into a transformer coil mold and solidifying. The insulating material system adopts 1-alkyl-2,3-dimethyl imidazole tetrafluoroborate with long-chain alkyl substitution as a latent curing accelerator and combines a composite insulating filler system, so that the mechanical properties and dielectric characteristics of the material are optimized. The insulating material prepared by the method has high volume resistivity, high power frequency electrical strength, low dielectric loss factor and excellent tensile strength and impact toughness.

Description

Technical Field

[0001] This invention belongs to the technical field of electrical equipment insulation materials, specifically dry-type transformer insulation materials and their preparation methods. Background Technology

[0002] Dry-type transformers are widely used in urban power grids, rail transit, and new energy power generation due to their advantages such as safety, environmental friendliness, and ease of maintenance. As their core insulating component, the performance of epoxy resin cast insulation material directly determines the reliability, service life, and capacity rating of the transformer.

[0003] In existing technologies, several approaches are typically used to improve the performance of epoxy resin insulation materials: One approach is to add functional fillers. For example, patent CN111892749A discloses a boron nitride high thermal conductivity insulating filler with surface-adsorbed imidazole-copper complexes. This aims to significantly improve the thermal conductivity of the composite material by bridging boron nitride with nano-copper sintered in situ generated on the filler surface, forming a thermally conductive pathway. However, this technical solution primarily focuses on heat dissipation performance. The imidazole-copper complex used decomposes during curing to produce traditional imidazole compounds as accelerators. While these accelerators have high activity, their latency is poor, resulting in a narrow process window for the resin system. This makes it unsuitable for the vacuum casting process of large or complex transformer coils requiring long-term operation. Simultaneously, while the introduction of boron nitride filler improves thermal conductivity, its overall mechanical strengthening effect on the material is limited, and the viscosity of the system increases sharply at high filler concentrations, posing difficulties for casting and degassing. Secondly, reinforcing fibers, such as glass fibers or aramid fibers, are added to improve the mechanical properties of the material. However, conventional chopped fibers are prone to sedimentation, orientation, or agglomeration in the resin, affecting the uniformity and isotropy of the casting. Thirdly, an anhydride-accelerator curing system is used. However, traditional small-molecule tertiary amines or unsubstituted imidazole accelerators have problems such as high volatility, poor storage stability, and insufficient thermal stability of the cured product. Summary of the Invention

[0004] To overcome the aforementioned technical problems, this invention provides an insulating material for dry-type transformers and its preparation method. This insulating material system uses long-chain alkyl-substituted 1-alkyl-2,3-dimethylimidazolium tetrafluoroborate as a latent curing accelerator, combined with a composite insulating filler system, thereby optimizing the material's mechanical properties and improving its dielectric characteristics. The resulting insulating material possesses high volume resistivity, high power frequency electrical strength, low dielectric loss factor, and excellent tensile strength and impact toughness.

[0005] The present invention solves the above-mentioned technical problems through the following technical solutions.

[0006] This invention discloses an insulating material for dry-type transformers, comprising the following raw materials in parts by weight: 55-65 parts epoxy resin matrix, 20-40 parts organic acid anhydride curing agent, 20-50 parts insulating filler, 2-10 parts meta-aramid pulp, and 0.3-1.5 parts trisubstituted imidazole tetrafluoroborate. The trisubstituted imidazole tetrafluoroborate is 1-alkyl-2,3-dimethylimidazolium tetrafluoroborate, wherein the alkyl group is a straight-chain alkyl group with 10 to 16 carbon atoms; preferably, it is at least one of 1-decyl-2,3-dimethylimidazolium tetrafluoroborate (CAS No.: 640282-11-7), 1-dodecyl-2,3-dimethylimidazolium tetrafluoroborate (CAS No.: 676607-47-9), 1-tetradecyl-2,3-dimethylimidazolium tetrafluoroborate (CAS No.: 1636918-90-5), and 1-hexadecyl-2,3-dimethylimidazolium tetrafluoroborate (CAS No.: 467443-06-7).

[0007] The cationic moiety of this type of trisubstituted imidazole tetrafluoroborate consists of an imidazole ring substituted with methyl groups at positions 2 and 3, and a long-chain alkyl group attached to position 1. The methyl substitution at positions 2 and 3 protects the highly reactive nitrogen atom on the imidazole ring, making it difficult for it to attack epoxy groups or acid anhydrides at room temperature, exhibiting excellent latency. The introduction of the long-chain alkyl group significantly improves the solubility and compatibility of the trisubstituted imidazole tetrafluoroborate in nonpolar and weakly polar epoxy resins, preventing the precipitation or aggregation of accelerators. Under heating conditions, the tetrafluoroborate anion is activated, effectively initiating ring-opening of the acid anhydride, thereby triggering the curing reaction of the epoxy resin. In addition, it forms extremely weak ionic conductive channels, homogenizes the electric field distribution, and inhibits the accumulation of space charge; furthermore, the long-chain alkyl group may play a certain internal plasticizing role in the cured network, slightly improving toughness.

[0008] Preferably, the dry-type transformer insulation material comprises the following raw materials in parts by weight: 58-62 parts epoxy resin matrix, 25-35 parts organic acid anhydride curing agent, 25-40 parts insulating filler, 4-8 parts meta-aramid pulp and 0.5-1.2 parts trisubstituted imidazole tetrafluoroborate.

[0009] According to some embodiments of the present invention, the epoxy resin matrix comprises 50 parts of bisphenol A type epoxy resin and 5 to 15 parts of alicyclic epoxy resin; preferably, the epoxy resin matrix comprises 50 parts of bisphenol A type epoxy resin and 8 to 12 parts of alicyclic epoxy resin. Furthermore, the alicyclic epoxy resin is selected from hydrogenated bisphenol A type epoxy resin or epoxy cyclohexane carboxylic acid ester epoxy resin.

[0010] According to some embodiments of the present invention, the organic acid anhydride curing agent is at least one of methylhexahydrophthalic anhydride, methylnadic anhydride, and methyltetrahydrophthalic anhydride.

[0011] According to some embodiments of the present invention, the density of the meta-aramid pulp is 1.35~1.40 g / cm³. 3 The preferred concentration is 1.37~1.38 g / cm³. 3 .

[0012] According to some embodiments of the present invention, the specific surface area of ​​the meta-aramid pulp is 5-15 m². 2 / g, preferably 6~12m 2 / g.

[0013] According to some embodiments of the present invention, the insulating filler is 5-20 wt% barium titanate and the balance silica filler, preferably 7-14 wt% barium titanate and the balance silica filler. Barium titanate is a high dielectric constant ceramic filler, but excessive content will lead to an excessively high dielectric constant of the system, which may cause local electric field distortion; barium titanate adjusts the dielectric constant to suit transformer operating conditions, nano-silica improves mechanical strength and insulation, and fumed silica inhibits filler sedimentation through thixotropic effect.

[0014] The silica filler is 18-45 wt% nano silica and the balance fumed silica, preferably 20-38 wt% nano silica and the balance fumed silica.

[0015] According to some embodiments of the present invention, the average particle size of the barium titanate is 1~5 μm.

[0016] According to some embodiments of the present invention, the particle size of the nano-silica is 30~60nm.

[0017] According to some embodiments of the present invention, the D50 of the fumed silica is 1~10μm, preferably 5~10μm.

[0018] According to some embodiments of the present invention, the raw materials for preparation further include 1.5 to 3.0 parts of organosilicon core-shell toughened epoxy resin; wherein, the core-shell structure in the organosilicon core-shell toughened epoxy resin is formed by emulsion polymerization, the organosilicon core-shell content accounts for 20 to 40 wt%, and the balance is bisphenol A type epoxy resin.

[0019] The silicone core-shell particles have an epoxy resin shell and a silicone rubber core. When the material is under stress, the softer silicone rubber core acts as a stress concentration point, inducing the surrounding epoxy matrix to generate a large number of crazes and shear bands, consuming a large amount of energy. At the same time, the epoxy resin shell ensures its good compatibility with the matrix epoxy.

[0020] According to some embodiments of the present invention, the raw materials for preparation further include 0.5 to 2 parts of coupling agent, 0.1 to 0.15 parts of defoamer and 0.05 to 0.5 parts of wetting and dispersing agent.

[0021] According to some embodiments of the present invention, the coupling agent is KH-560 or KH-570.

[0022] According to some embodiments of the present invention, the defoamer is BYK. A530, BYK 141 and Tego At least one of 800.

[0023] According to some embodiments of the present invention, the wetting and dispersing agent is BYK. 110. BYK 163 and Tego At least one of 750W.

[0024] The present invention also discloses a method for preparing the aforementioned dry-type transformer insulation material, comprising the following steps: mixing the raw materials, degassing them under vacuum, pouring them into a transformer coil mold, and then curing them.

[0025] According to some embodiments of the present invention, the mixing process is as follows: S01. Heating the epoxy resin matrix to 50~70°C, adding meta-aramid pulp and trisubstituted imidazole tetrafluoroborate, and stirring to disperse; S02. Adding insulating filler, coupling agent, and wetting and dispersing agent, and continuing to stir and disperse; S03. Adding defoamer and vacuum degassing; S04. Adding organic acid anhydride curing agent, mixing evenly, and vacuum degassing again.

[0026] According to some embodiments of the present invention, the mold is preheated to 100~130°C before casting.

[0027] According to some embodiments of the present invention, the curing is carried out by holding at 90~110°C for 1~3 hours, then holding at 130~150°C for 2~5 hours, and then cooling to below 50°C for demolding.

[0028] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0029] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention uses long-alkyl-chain trisubstituted imidazole tetrafluoroborate as a latent curing accelerator to synergistically improve insulating materials with the insulating filler system and an anhydride curing agent. On the one hand, the long-chain alkyl groups of the trisubstituted imidazole tetrafluoroborate endow it with excellent compatibility with epoxy resin and extremely low room-temperature reactivity, while it can efficiently catalyze the ring-opening curing of anhydrides at high temperatures. On the other hand, the trisubstituted imidazole tetrafluoroborate forms extremely weak ion-conducting channels, which can homogenize the electric field distribution and suppress space charge accumulation. The insulating filler adopts a composite filler system of barium titanate / nano silica / fumed silica. Barium titanate is used to adjust the dielectric constant of the composite material to match it with other materials inside the transformer and optimize the electric field distribution; nano silica provides the main reinforcement and reduces the coefficient of thermal expansion; fumed silica plays a role in preventing sedimentation, thixotropy, and auxiliary reinforcement.

[0030] 2. The insulating material of this invention has high volume resistivity and power frequency electrical strength, and a low dielectric loss factor, ensuring excellent electrical insulation reliability and efficiency. In terms of mechanical properties, the material simultaneously possesses high tensile strength and impact toughness, enabling it to effectively resist electromagnetic impacts, thermal stress, and mechanical vibrations during transformer operation, reducing the risk of insulation cracking.

[0031] 3. The insulating material of the present invention is not only suitable for conventional dry-type transformers, but its high heat resistance, high toughness and high reliability also make it have broad application prospects in the field of high-requirement special transformers such as offshore wind power, rail transit traction and shipbuilding. Detailed Implementation

[0032] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0033] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0034] The raw material information used in the following examples is as follows: Bisphenol A type epoxy resin grade: Dow DER331; Hydrogenated bisphenol A type epoxy resin grade: Mitsubishi YX8000; The meta-aramid pulp was sourced from Zhongfang New Materials Co., Ltd., and its density was 1.35~1.40 g / cm³. 3 Specific surface area is 6~12m² 2 / g, average fiber length is 0.7~1.2mm; The para-aramid pulp, sourced from Hubei Tengdi New Materials Co., Ltd., has a density of 1.44~1.46 g / cm³. 3 Specific surface area is 5~11m² 2 / g, average fiber length is 1mm; The average particle size of barium titanate is 3 μm; The chopped glass fiber filaments are alkali-free chopped glass fiber yarns with a chopped length of 3~4.5mm and a fiber diameter of 9~13μm; The particle size of nano-silica is 50 nm; Fumed silica is hydrophobic, with a density of 8.6 μm and a nitrogen adsorption surface area of ​​59 m². 2 / g; The silicone core-shell toughened epoxy resin comes from Shanghai Zhuzi New Materials Co., Ltd. Its core-shell structure (size 200nm) is formed by emulsion polymerization, containing 25wt% silicone core-shell and 75wt% bisphenol A type epoxy resin, with an epoxy equivalent of 250~260g / eq. This includes, but is not limited to, the models from the above manufacturers.

[0035] Example 1 The dry-type transformer insulation material of this embodiment is composed of the following raw materials in parts by weight: 60 parts epoxy resin matrix (50 parts bisphenol A type epoxy resin and 10 parts hydrogenated bisphenol A type epoxy resin), 30 parts organic acid anhydride curing agent (methylhexahydrophthalic anhydride), 6 parts meta-aramid pulp, 0.8 parts trisubstituted imidazole tetrafluoroborate (1-dodecyl-2,3-dimethylimidazolium tetrafluoroborate), 36 parts insulating filler (4 parts barium titanate, 12 parts nano silica and 20 parts fumed silica), 2 parts organosilicon core-shell toughened epoxy resin, 1.3 parts coupling agent (KH-560), and 0.11 parts defoamer (BYK). A530) and 0.26 parts wetting and dispersing agent (Tego) 750W).

[0036] The preparation method is as follows: Step 1: Preparation of the mixture S01. Add trisubstituted imidazole tetrafluoroborate and meta-aramid pulp sequentially to the preheated epoxy resin matrix (60℃) and stir at 800 rpm for 20 min to form a uniform emulsion. S02. Add insulating filler, coupling agent and wetting and dispersing agent, and stir under -0.09MPa vacuum for 30 minutes to form a paste; S03. Increase the vacuum in the mixing tank to -0.097MPa, maintain this vacuum and stir for 15 minutes to remove most of the air bubbles introduced during the stirring process; break the vacuum, add the silicone core-shell toughened epoxy resin, and then stir at 600 rpm for 20 minutes. S04. After adding the organic acid anhydride curing agent, stir at 400 rpm for 20 min, stop stirring and let the mixture stand for 1 min to allow the material on the tank wall to flow level, then stir at 50 rpm for 20 min under a vacuum degree ≤ -0.099 MPa to obtain the mixture. Step 2: Pouring Preheat the dry-type transformer coil mold to 115±5℃ before casting. The degassed mixture is then poured into a preheated transformer coil mold through a pipeline under vacuum.

[0037] Step 3: Curing The mold after casting is kept at 100±2℃ for 2 hours, then at 140±2℃ for 4 hours, and then cooled to below 50℃ for demolding.

[0038] Example 2 The difference between this embodiment and Embodiment 1 is as follows: The trisubstituted imidazole tetrafluoroborate is 1-hexadecyl-2,3-dimethylimidazole tetrafluoroborate; The other raw materials, steps and parameters are the same as in Example 1.

[0039] Example 3 The difference between this embodiment and Embodiment 1 is as follows: 1-Ethyl-2,3-dimethylimidazolium tetrafluoroborate was used in place of 1-dodecyl-2,3-dimethylimidazolium tetrafluoroborate in Example 1. The other raw materials, steps and parameters are the same as in Example 1.

[0040] Example 4 The difference between this embodiment and Embodiment 1 is as follows: The addition weight of trisubstituted imidazole tetrafluoroborate was increased to 2.0 parts; The other raw materials, steps and parameters are the same as in Example 1.

[0041] Example 5 The difference between this embodiment and Embodiment 1 is as follows: The insulating filler contains only 36 parts of fumed silica and no barium titanate or nano silica. The other raw materials, steps and parameters are the same as in Example 1.

[0042] Example 6 The difference between this embodiment and Embodiment 1 is as follows: The added insulating filler is 38 parts by weight, including 8 parts barium titanate, 10 parts nano silica and 20 parts fumed silica; The other raw materials, steps and parameters are the same as in Example 1.

[0043] Example 7 The difference between this embodiment and Embodiment 1 is as follows: In this embodiment, no silicone core-shell toughened epoxy resin was added to the preparation materials. The other raw materials, steps and parameters are the same as in Example 1.

[0044] Comparative Example 1 The difference between this comparative example and Example 1 is as follows: 2-Ethyl-4-methylimidazolium was used to replace 1-dodecyl-2,3-dimethylimidazolium tetrafluoroborate in Example 1; The other raw materials, steps and parameters are the same as in Example 1.

[0045] Comparative Example 2 The difference between this comparative example and Example 1 is as follows: Replace the barium titanate in Example 1 with chopped glass fibers; The other raw materials, steps and parameters are the same as in Example 1.

[0046] Comparative Example 3 The difference between this comparative example and Example 1 is as follows: Replace the meta-aramid pulp in Example 1 with para-aramid pulp; The other raw materials, steps and parameters are the same as in Example 1.

[0047] The dry-type transformer insulation materials prepared in the above embodiments and comparative examples were subjected to the following tests, and the test results are shown in Table 1 and Table 2, respectively: Test Example 1—Electrical Performance Test Volume resistivity: The test method refers to GB / T 1410-2006; DC voltage is applied to the sample at room temperature (23℃) and high temperature (130℃) respectively, the leakage current through the volume is measured, and the resistivity is calculated. Power frequency electrical strength: The test method refers to GB / T 1408.1-2016; in oil medium, power frequency AC voltage is applied to the sample in a continuous and uniform manner until breakdown, and the average value of 3 tests is taken; Dielectric loss factor: The test method refers to GB / T 1409-2006; the capacitance and loss of the sample are measured at 50Hz using a precision impedance analyzer.

[0048]

[0049] Test Example 2—Mechanical Property Test The test methods for tensile strength and elongation at break shall refer to GB / T 1040.1-2025; the test methods for impact strength shall refer to GB / T 1043.1-2008.

[0050]

[0051] The following points should be noted when referring to Tables 1 and 2: Example Group: Example 3 uses short-chain trisubstituted imidazole tetrafluoroborate. On the one hand, excessively short alkyl chains lead to compatibility issues, internal micro-defects, and decreased mechanical properties; on the other hand, the promoting effect is not better, and the resistivity and breakdown strength of the final cured insulation material are slightly inferior. Example 4 has an excessively high proportion of trisubstituted imidazole tetrafluoroborate, introducing weak conductive channels, increasing losses and reducing electrical strength; the plasticizing effect is too strong, reducing stiffness and strength. Example 5 lacks nano-silica reinforcement and barium titanate to regulate dielectrics, resulting in a non-dense structure, poor dielectric matching, and the worst electrical performance; furthermore, the insulation filler system lacks density and toughness. Example 6 has a relatively high proportion of barium titanate, which causes a slight distortion of the electric field and a slight increase in leakage current.

[0052] Comparative Examples: Comparative Example 1 uses a traditional imidazole accelerator, which exhibits high activity at room temperature, uneven curing, significant high-temperature losses, and low breakdown strength. Using traditional imidazole as an accelerator leads to a brittle cured network with poor elongation at break and impact strength. Comparative Example 2 uses glass fiber, which easily causes interface defects and stress concentration, resulting in decreased toughness and electrical properties. Comparative Example 3 uses para-aramid pulp, which has high rigidity, but its fibrillation degree and wettability may be inferior to meta-aramid, and its toughness is inferior to Example 1.

[0053] Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in this invention can be purchased commercially or prepared using existing methods. The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this invention. It should be understood that the above descriptions are merely specific embodiments of this invention and are not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. Insulation material for dry-type transformers, characterized in that, The preparation raw materials include the following parts by weight: 55-65 parts epoxy resin matrix, 20-40 parts organic acid anhydride curing agent, 20-50 parts insulating filler, 2-10 parts meta-aramid pulp and 0.3-1.5 parts trisubstituted imidazole tetrafluoroborate; The trisubstituted imidazole tetrafluoroborate is 1-alkyl-2,3-dimethylimidazolium tetrafluoroborate, wherein the alkyl group is a straight-chain alkyl group with 10 to 16 carbon atoms.

2. The dry-type transformer insulation material as described in claim 1, characterized in that, The epoxy resin matrix comprises 50 parts of bisphenol A type epoxy resin and 5-15 parts of alicyclic epoxy resin; And / or, the organic acid anhydride curing agent is at least one of methylhexahydrophthalic anhydride, methylnadic anhydride, and methyltetrahydrophthalic anhydride.

3. The dry-type transformer insulation material as described in claim 1, characterized in that, The trisubstituted imidazole tetrafluoroborate is at least one selected from 1-decyl-2,3-dimethylimidazolium tetrafluoroborate, 1-dodecyl-2,3-dimethylimidazolium tetrafluoroborate, 1-tetradecyl-2,3-dimethylimidazolium tetrafluoroborate, and 1-hexadecyl-2,3-dimethylimidazolium tetrafluoroborate.

4. The dry-type transformer insulation material as described in claim 1, characterized in that, The density of the meta-aramid pulp is 1.35~1.40 g / cm³. 3 ; And / or, the specific surface area of ​​the meta-aramid pulp is 5~15m². 2 / g.

5. The dry-type transformer insulation material as described in claim 1, characterized in that, The insulating filler is 5-20 wt% barium titanate and the balance is silica filler; The silica filler consists of 18-45 wt% nano-silica and the balance being fumed silica.

6. The dry-type transformer insulation material as described in claim 5, characterized in that, The average particle size of the barium titanate is 1~5μm; And / or, the particle size of the nano-silica is 30~60nm; And / or, the D50 of the fumed silica is 1~10μm.

7. The dry-type transformer insulation material as described in claim 1, characterized in that, The raw materials for preparation also include 1.5 to 3.0 parts of organosilicon core-shell toughened epoxy resin; The core-shell structure in the organosilicon core-shell toughened epoxy resin is formed by emulsion polymerization, and the organosilicon core-shell content accounts for 20~40wt%.

8. The dry-type transformer insulation material as described in claim 1, characterized in that, The raw materials for preparation also include 0.5 to 2 parts of coupling agent, 0.1 to 0.15 parts of defoamer and 0.05 to 0.5 parts of wetting and dispersing agent.

9. The method for preparing the insulating material of a dry-type transformer as described in any one of claims 1 to 8, characterized in that, Includes the following steps: The raw materials are mixed, degassed under vacuum, poured into a transformer coil mold, and then cured.

10. The method for preparing the insulating material of a dry-type transformer as described in claim 9, characterized in that, The mixing process is as follows: S01. Heat the epoxy resin matrix to 50~70℃, add meta-aramid pulp and trisubstituted imidazole tetrafluoroborate, and stir to disperse; S02. Add insulating filler, coupling agent, and wetting and dispersing agent, and continue to stir and disperse; S03. Add defoamer and degas under vacuum; S04. Add organic acid anhydride curing agent, mix evenly, and degas under vacuum again. And / or, the mold is preheated to 100~130℃ before casting; And / or, the curing is performed by holding at 90~110℃ for 1~3 hours, then holding at 130~150℃ for 2~5 hours, followed by cooling to below 50℃ for demolding.

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