Epoxy insulating material for a transformer and method for producing same

Abstract

The application provides an epoxy insulating material for a mutual inductor and a preparation method thereof. The epoxy insulating material comprises the following raw materials in parts by mass: 100 parts of epoxy resin, 30-60 parts of modified alumina, 80-85 parts of anhydride curing agent, and 0.3-0.5 parts of curing accelerator. The modified alumina comprises an alumina matrix and a urea-based organic silicon structure on the surface of the alumina matrix. The modified alumina is further modified by a silane modifier, and the silane modifier comprises fluorine-containing silane. The obtained epoxy insulating material has high breakdown strength and electrical performance stability, and can still maintain good electrical insulation performance in a complex environment, and is suitable for the insulation packaging and structural support of electrical equipment such as mutual inductors.

Description

Technical Field

[0001] This application relates to the field of epoxy materials technology, specifically to an epoxy insulation material for instrument transformers and its preparation method. Background Technology

[0002] Instrument transformers, as key electrical equipment in power systems, are widely used for voltage and current measurement and protection. Their long-term operational safety and stability are of great significance to the power grid system. In actual operation, instrument transformers are typically subjected to high electric field strength and complex environmental conditions, placing high demands on the electrical performance, environmental adaptability, and long-term reliability of their internal insulation materials.

[0003] Epoxy resin, due to its excellent mechanical properties, electrical insulation properties, and molding and processing performance, has been widely used in the insulation encapsulation and structural support of electrical equipment such as instrument transformers. To further improve the electrical properties of epoxy insulation materials, inorganic fillers are typically introduced into the epoxy resin system. Among these, alumina is widely used due to its stable dielectric properties, high thermal conductivity, and relatively moderate cost.

[0004] However, the significant differences in interfacial properties between alumina filler and epoxy resin matrix can lead to uneven filler dispersion and weak interfacial bonding. Under complex environments, microscopic defects can easily form at the interface, affecting the electrical insulation performance of the material, especially potentially causing a decrease in breakdown strength under high electric fields. Therefore, improving the interfacial compatibility between alumina and epoxy resin while ensuring sufficient filler content, and enhancing the dielectric strength and electrical performance stability of the material, is one of the problems that needs to be solved in the field of epoxy insulation materials. In existing technologies, silane coupling agent treatment is typically used to improve the dispersion and interfacial bonding of alumina in epoxy resin. However, the single silane modification method still has limitations in improving interfacial stability under complex service environments. Especially after long-term service, the interfacial structure may still deteriorate, thus affecting the electrical performance stability and long-term insulation reliability of the material.

[0005] Therefore, there is an urgent need to provide an epoxy insulation material suitable for instrument transformers, which has good breakdown strength and electrical performance stability to meet the requirements of electrical equipment such as instrument transformers for insulation materials. Summary of the Invention

[0006] This application provides an epoxy insulation material for instrument transformers and its preparation method, aiming to solve the problem of insufficient interfacial compatibility between inorganic fillers and epoxy resin in the prior art, which affects insulation performance and long-term stability.

[0007] In a first aspect, this application provides an epoxy insulation material for instrument transformers, comprising the following raw materials in parts by weight:

[0008] The mixture comprises 100 parts epoxy resin, 30-60 parts modified alumina, 80-85 parts acid anhydride curing agent, and 0.3-0.5 parts curing accelerator; the modified alumina includes an alumina matrix and a urea-based organosilicon structure on the surface of the alumina matrix; the modified alumina is further modified by a silane modifier, the silane modifier including fluorinated silanes.

[0009] According to this application, by introducing alumina filler with "urea-based organosilicon structure-fluorinated silane" dual modification into the epoxy resin system through the above formulation design, it is helpful to build a synergistic system for interface charge regulation and electric field optimization suitable for the service scenarios of instrument transformers, thereby improving the breakdown strength and electrical performance stability of the material and meeting the insulation requirements of high electric field and complex environment.

[0010] Specifically, the modified alumina uses alumina as the inorganic matrix. Alumina has high dielectric strength and stability, and can form a relatively continuous inorganic phase support structure within the material. However, unmodified alumina is prone to electric field concentration or performance degradation in the interface region under long-term electric field. By introducing urea-based organosilicon structures onto the alumina surface, the urea-based structures may form a certain degree of local correlation structure through hydrogen bonding, thereby forming an organic functional layer with a certain polarity at the filler interface. This interface layer may regulate the charge migration behavior at the interface, causing some charges to be temporarily retained and redistributed in the interface region, thereby reducing the space charge migration rate and weakening the local electric field distortion to a certain extent. This has a positive effect on mitigating interface polarization and slowing down the increase in dielectric loss. However, since the urea matrix has a certain polarity overall, under long-term electric field, if some retained charges are difficult to release in time, a certain degree of charge accumulation may still occur in the interface region.

[0011] Therefore, this application further introduces fluorinated silanes to comprehensively regulate the interfacial region of the filler surface. The fluorinated alkyl chains introduced by the fluorinated silanes have low polarizability and low dielectric constant, which can reduce dielectric abrupt changes in the interfacial region. Under the action of an electric field, the dispersed fluorinated siloxane microregions may weaken the interfacial polarization and help to homogenize the electric field distribution, which helps to further regulate the overall polarization response of the interfacial region and reduce the electric field distortion caused by the abrupt change in dielectric properties between the filler and the resin matrix. On the other hand, under humid heat or electrothermal coupling stress conditions, the hydrogen bond network in the urea-based interfacial layer can buffer the interfacial stress through reversible binding and dissociation processes, while the fluorinated silanes may provide dielectric regulation and structural auxiliary stabilization for the organic interfacial layer. Its chemical inertness helps to suppress the structural relaxation or performance degradation of the interfacial layer under long-term environmental stress.

[0012] In summary, by synergistically constructing a composite interface structure on the surface of an alumina matrix, which is formed by a urea-based organosilicon structure and a fluorinated silane dispersion microregion, the interfacial charge behavior can be guided and regulated, and the accumulation of space charge and electric field distortion can be suppressed, thereby meeting the long-term reliability requirements of epoxy insulation materials for high-voltage electrical equipment.

[0013] In some embodiments, the method for preparing the modified alumina includes the following steps:

[0014] S1: Activated alumina and γ-aminopropyltriethoxysilane are dispersed in toluene, and γ-aminopropyltriethoxysilane is fixed on the surface of activated alumina by silane coupling to obtain amino-alumina;

[0015] S2: Amino-alumina and hexamethylene diisocyanate are dispersed in toluene, and the amino groups on the surface of amino-alumina react with the isocyanate groups in hexamethylene diisocyanate to generate urea groups, thus obtaining urea-based organosilicon-alumina.

[0016] S3: Disperse urea-based organosilicon-alumina and silane modifier in an ethanol-water solution, and fix the silane modifier on the surface of urea-based organosilicon-alumina through silane coupling to obtain modified alumina.

[0017] In some of the above embodiments, γ-aminopropyltriethoxysilane can undergo hydrolysis to generate silanol structures under the action of water adsorbed on the surface of activated alumina or trace amounts of water in the system. The silanol groups formed can undergo condensation reactions with hydroxyl groups on the surface of activated alumina, introducing an amino functional layer on the alumina surface, which helps to provide chemical reaction sites for the subsequent construction of organic interface structures on the filler surface.

[0018] In step S2, hexamethylene diisocyanate undergoes an addition reaction with the primary amine groups on the surface of amino-alumina, introducing the urea group structure covalently to construct an organic layer containing urea bonds. The hydrogen bond network formed in the interface region can buffer the charge migrating to the interface.

[0019] In step S3, after the silane modifier is hydrolyzed to generate a silanol structure, it can undergo a condensation reaction with the residual hydroxyl sites on the surface of the modified alumina and the incompletely condensed silanol sites that may exist in the preceding silicon structure, forming a silane structure anchored by Si-O-Al or Si-O-Si bonds. Dispersed silane structural units are introduced around the urea-based organosilicon functional layer, so that a composite interface environment composed of urea-based functional regions and silane functional regions is formed on the filler surface.

[0020] In some embodiments, the activated alumina in step S1 is prepared by the following steps:

[0021] Alumina, glacial acetic acid, and water are dispersed in ethanol and treated at 60-80℃ for 2-3 hours to form hydroxyl-activated structures on the surface of alumina, thus obtaining activated alumina.

[0022] In some of the above embodiments, the alumina is surface-activated by glacial acetic acid. Ethanol, as a dispersion medium, can suppress local over-reaction to a certain extent, promoting the formation of a more uniform hydroxyl functional structure on the alumina surface, thereby obtaining activated alumina. This activation treatment can provide reaction sites for subsequent silane coupling reactions, which is beneficial for the anchoring of silanes on the alumina surface.

[0023] In some embodiments, step S1 includes:

[0024] 100 parts of activated alumina and 1-2 parts of γ-aminopropyltriethoxysilane were dispersed in 300-500 parts of toluene and reacted at 90-150℃ for 2-6 hours to obtain amino-alumina.

[0025] In some of the above embodiments, under the given mass ratio conditions, the amount of γ-aminopropyltriethoxysilane is relatively low, which is beneficial for forming an anchoring structure mainly composed of Al-O-Si covalent bonds on the surface of alumina. Due to the low water content in the reaction system, the self-condensation and multilayer aggregation of silane in the bulk phase can be suppressed.

[0026] In some embodiments, step S2 further includes 2-amino-6-chlorobenzothiazole, wherein the mass ratio of amino-alumina to 2-amino-6-chlorobenzothiazole is 100:1.1~1.4.

[0027] In some of the above embodiments, the primary amino group in the 2-amino-6-chlorobenzothiazole molecule can undergo an addition reaction with the isocyanate group in hexamethylene diisocyanate, thereby covalently fixing the benzothiazole structural unit in the urea-based organic layer constructed on the filler surface. The benzothiazole structural unit has a conjugated aromatic ring skeleton and heteroatom structure, and its high electronic polarization ability helps to regulate the electronic distribution state of the interface region, thereby having a certain influence on the migration path of charge carriers at the interface and mitigating the phenomenon of uneven local electric field distribution to a certain extent. In addition, the introduction of the rigid benzothiazole structural unit helps to form a certain steric hindrance effect in the urea-based hydrogen bond network, thereby limiting the migration of interface chain segments while maintaining the dynamic regulation ability of hydrogen bonds, which is beneficial to improving the stability of the interface structure under long-term electric field. Controlling the mass ratio of amino-alumina to 2-amino-6-chlorobenzothiazole within the range of 100:1.1~1.4 is beneficial for embedding benzothiazole structural units into the urea interface layer in an appropriate proportion, thereby achieving the synergistic effect between the hydrogen bond regulation network and the conjugated heterocyclic unit, and thus improving the stability and insulation reliability of the interface structure under long-term electric field.

[0028] In some implementations, step S2 includes:

[0029] 100 parts of amino-alumina, 2-3 parts of hexamethylene diisocyanate, and 1.1-1.4 parts of 2-amino-6-chlorobenzothiazole are dispersed in 300-500 parts of toluene and reacted at 50-100℃ for 2-6 hours to obtain urea-based organosilicon-alumina.

[0030] In some of the above embodiments, under the specified mass ratio, hexamethylene diisocyanate reacts with the primary amine groups on the surface of amino-alumina to construct an organic layer framework containing urea bonds; 2-amino-6-chlorobenzothiazole is covalently introduced into the framework by participating in the reaction, and its 6-chloro substituent, as an electron-withdrawing group, can improve the molecular polarization ability of the benzothiazole structural unit, thereby regulating the electronic distribution state of the interface region.

[0031] In some embodiments, the silane modifier in step S3 further includes alkylsilanes, wherein the alkylsilanes include methyltriethoxysilanes, the fluorinated silanes include trifluoropropyltrimethoxysilanes, and the mass ratio of the trifluoropropyltrimethoxysilanes to the methyltriethoxysilanes is 1:2~5.

[0032] In some of the above embodiments, alkylsilanes and fluorinated silanes can construct a composite siloxane network structure around the filler particles. Due to differences in hydrolysis rate, condensation activity, and steric hindrance between the two types of silanes, methyltriethoxysilane can serve as the main building block of the composite siloxane network. Its hydrolysis and condensation behavior helps form a continuous and controllable siloxane framework, providing a relatively uniform dielectric environment for the interface region. Trifluoropropyltrimethoxysilane, on the other hand, tends to embed itself in the siloxane network in a confined and dispersed manner, participating in the interface structure construction as a local dielectric regulation unit. This composite siloxane structure, together with the urea structure, constitutes a complete interface functional body. The relatively stable siloxane framework constructed by the alkylsilane provides a controlled interface constraint environment for the dynamic urea hydrogen bond network, helping to maintain its structural integrity. The fluorinated silane helps to regulate the polarity and dielectric properties of the interface region, creating a smoother transition in the interface dielectric environment between the filler surface and the urea substrate, thus mitigating the uneven distribution of the local electric field to some extent. When the mass ratio of trifluoropropyltrimethoxysilane to methyltriethoxysilane is controlled at 1:2~5, the excessive enrichment of fluorine-containing groups at the interface can be reduced, thereby helping to maintain the uniformity of the dielectric environment at the interface.

[0033] In some implementations, step S3 includes:

[0034] 100 parts of urea-based organosilicon-alumina, 0.5-2 parts of methyltriethoxysilane, and 0.25-0.4 parts of trifluoropropyltrimethoxysilane were dispersed in 100-200 parts of ethanol-water solution and reacted at 20-70℃ for 1-3 hours to obtain modified alumina.

[0035] In some of the above embodiments, alkylsilanes and fluorinated silanes are chemically co-condensed under the above ratios and reaction conditions to construct a composite outer layer structure. Based on the prior organic interface regulation, the interface electrical behavior of this outer layer structure can be further optimized to improve the insulation performance.

[0036] In some embodiments, the anhydride curing agent includes methyltetrahydrophthalic anhydride; the curing accelerator includes 2-methylimidazole. Based on the above embodiments, by selecting an anhydride curing system composed of methyltetrahydrophthalic anhydride and 2-methylimidazole, epoxy resin can be cured more fully and uniformly.

[0037] Secondly, this application provides a method for preparing an epoxy insulation material for instrument transformers, comprising:

[0038] Provide raw materials for the epoxy insulating material according to any embodiment of the first aspect;

[0039] The raw materials are mixed, degassed, cast into molds, and cured to obtain epoxy insulation material for instrument transformers.

[0040] According to this application, by using the raw materials of the epoxy insulating material described in the first aspect, and sequentially mixing and dispersing, vacuum degassing, casting molding, and segmented curing, the epoxy resin, modified alumina, anhydride curing agent, curing accelerator, and other components can be uniformly dispersed during the mixing process; vacuum degassing removes air bubbles from the mixture, reducing the formation of microscopic leakage channels; segmented curing promotes uniform and sufficient cross-linking of the epoxy system, reducing internal stress and microscopic cracks. This preparation method can produce the epoxy insulating material described in the first aspect, thus possessing the beneficial effects of the first aspect, and the resulting material exhibits good electrical insulation strength and electrical performance stability.

[0041] Compared with the prior art, the beneficial effects of this application are at least as follows:

[0042] This application utilizes a composite interface regulation structure formed by the synergistic construction of a urea-based organosilicon structure and a fluorinated silane on the surface of an alumina matrix. The hydrogen bond network formed by the urea-based organosilicon structure can transiently regulate the interfacial charge migration, helping to buffer local electric field fluctuations. The synergistic effect of the fluorinated silane and the urea-based structure helps to mitigate differences in interfacial polarization response and homogenize the local electric field distribution. Under complex service conditions, the interfacial region is prone to structural relaxation and electrical response instability. The synergistic effect of the chemical bonding structure constructed by the fluorinated silane in the interfacial region and the dynamic charge regulation function of the urea-based organosilicon structure helps to maintain the stability of the interfacial structure, thereby achieving a simultaneous improvement in the breakdown strength and long-term electrical reliability of the epoxy insulation material. Detailed Implementation

[0043] The various embodiments or implementation schemes in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments.

[0044] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0045] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0046] In this specification, unless otherwise specified, "parts" refers to "parts by weight".

[0047] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0048] Alumina: Spherical, with an average particle size of approximately 3 μm;

[0049] Epoxy resin; model number E-51;

[0050] Methyltetrahydrophthalic anhydride: CAS number 11070-44-3;

[0051] γ-aminopropyltriethoxysilane: CAS number 919-30-2;

[0052] Hexamethylene diisocyanate: CAS No. 822-06-0;

[0053] Trifluoropropyltrimethoxysilane: CAS number 429-60-7;

[0054] Methyltriethoxysilane: CAS number 2031-67-6;

[0055] 2-Amino-6-chlorobenzothiazole: CAS number 95-24-9.

[0056] Preparation Example 1

[0057] Preparation of activated alumina:

[0058] 100 parts alumina, 15 parts glacial acetic acid, and 80 parts deionized water were dispersed in 300 parts anhydrous ethanol. The mixture was stirred at a constant temperature of 70°C for 2 hours. After filtration, the filter cake was washed with deionized water and dried to obtain activated alumina.

[0059] Preparation Example 2

[0060] Preparation of modified alumina:

[0061] S1: 100 parts of activated alumina were dispersed in 400 parts of anhydrous toluene. Under nitrogen protection, 1.5 parts of γ-aminopropyltriethoxysilane were added and reacted at 110°C for 4 hours. After filtration, the filter cake was washed with anhydrous toluene and dried under vacuum to obtain amino-alumina.

[0062] S2: 100 parts of amino-alumina were dispersed in 400 parts by mass of anhydrous toluene. Under nitrogen protection, 2.5 parts of hexamethylene diisocyanate were added and reacted at 80°C for 1.5 h. Then, 1.2 parts of 2-amino-6-chlorobenzothiazole were added and reacted at 85°C for 3 h. After filtration, the filter cake was washed with anhydrous toluene and dried under vacuum to obtain urea-based organosilicon-alumina.

[0063] S3: 100 parts of urea-based organosilicon-alumina, 0.25 parts of trifluoropropyltrimethoxysilane, and 1 part of methyltriethoxysilane were dispersed in 150 parts of ethanol-water solution (145 parts of anhydrous ethanol and 5 parts of deionized water). 0.2 parts of glacial acetic acid were added, and the mixture was reacted at 50°C for 2 hours. After filtration, the filter cake was washed with anhydrous ethanol and dried under vacuum to obtain modified alumina A.

[0064] Preparation Example 3

[0065] Preparation of modified alumina:

[0066] The preparation method is largely the same as in Example 2, except that the mass ratio of trifluoropropyltrimethoxysilane and methyltriethoxysilane is different in step S3. Specifically, the difference is as follows:

[0067] S3: 100 parts of urea-based organosilicon-alumina, 1 part of trifluoropropyltrimethoxysilane, and 0.25 parts of methyltriethoxysilane were dispersed in 150 parts of ethanol-water solution (145 parts of anhydrous ethanol and 5 parts of deionized water). 0.2 parts of glacial acetic acid were added, and the mixture was reacted at 50°C for 2 hours. After filtration, the filter cake was washed with anhydrous ethanol and dried under vacuum to obtain modified alumina B.

[0068] Preparation Example 4

[0069] Preparation of modified alumina:

[0070] The preparation method is largely the same as in Example 2, except that the mass ratio of trifluoropropyltrimethoxysilane and methyltriethoxysilane is different in step S3. Specifically, the difference is as follows:

[0071] S3: 100 parts of urea-based organosilicon-alumina, 0.05 parts of trifluoropropyltrimethoxysilane, and 1.2 parts of methyltriethoxysilane were dispersed in 150 parts of ethanol-water solution (145 parts of anhydrous ethanol and 5 parts of deionized water). 0.2 parts of glacial acetic acid were added, and the mixture was reacted at 50°C for 2 hours. After filtration, the filter cake was washed with anhydrous ethanol and dried under vacuum to obtain modified alumina C.

[0072] Preparation Example 5

[0073] Preparation of modified alumina:

[0074] The preparation method is largely the same as in Example 2, except that the mass ratio of urea-based organosilicon-alumina and silane modifier is different in step S3. Specifically, the difference is as follows:

[0075] S3: 100 parts of urea-based organosilicon-alumina, 1 part of trifluoropropyltrimethoxysilane, and 4 parts of methyltriethoxysilane were dispersed in 150 parts of ethanol-water solution (145 parts of anhydrous ethanol and 5 parts of deionized water). 0.2 parts of glacial acetic acid were added, and the mixture was reacted at 50°C for 2 hours. After filtration, the filter cake was washed with anhydrous ethanol and dried under vacuum to obtain modified alumina D.

[0076] Preparation Example 6

[0077] Preparation of modified alumina:

[0078] The preparation method is largely the same as in Example 2, except that the mass ratio of urea-based organosilicon-alumina and silane modifier is different in step S3. Specifically, the difference is as follows:

[0079] S3: 100 parts of urea-based organosilicon-alumina, 0.1 parts of trifluoropropyltrimethoxysilane, and 0.4 parts of methyltriethoxysilane were dispersed in 150 parts of ethanol-water solution (145 parts of anhydrous ethanol and 5 parts of deionized water). 0.2 parts of glacial acetic acid were added, and the mixture was reacted at 50°C for 2 hours. After filtration, the filter cake was washed with anhydrous ethanol and dried under vacuum to obtain modified alumina E.

[0080] Preparation Example 7

[0081] Preparation of modified alumina:

[0082] The preparation method is largely the same as in Example 2, except that the mass ratio of amino-alumina and 2-amino-6-chlorobenzothiazole is different in step S2. Specifically, the difference is as follows:

[0083] S2: 100 parts of amino-alumina were dispersed in 400 parts by mass of anhydrous toluene. Under nitrogen protection, 2.5 parts of hexamethylene diisocyanate were added and reacted at 80°C for 1.5 h. Then, 0.8 parts of 2-amino-6-chlorobenzothiazole were added and reacted at 85°C for 3 h. After filtration, the filter cake was washed with anhydrous toluene and dried under vacuum to obtain urea-based organosilicon-alumina.

[0084] The other steps are the same, and modified alumina I is obtained.

[0085] Preparation Example 8

[0086] Preparation of modified alumina:

[0087] The preparation method is largely the same as in Example 2, except that the mass ratio of amino-alumina and 2-amino-6-chlorobenzothiazole is different in step S2. Specifically, the difference is as follows:

[0088] S2: 100 parts of amino-alumina were dispersed in 400 parts by mass of anhydrous toluene. Under nitrogen protection, 2.5 parts of hexamethylene diisocyanate were added and reacted at 80°C for 1.5 h. Then, 1.6 parts of 2-amino-6-chlorobenzothiazole were added and reacted at 85°C for 3 h. After filtration, the filter cake was washed with anhydrous toluene and dried under vacuum to obtain urea-based organosilicon-alumina.

[0089] The other steps are the same, and modified alumina J is obtained.

[0090] Comparative Preparation Example 1

[0091] Preparation of modified alumina:

[0092] S1: 100 parts of activated alumina were dispersed in 400 parts of anhydrous toluene. Under nitrogen protection, 1.5 parts of γ-aminopropyltriethoxysilane were added and reacted at 110°C for 4 hours. After filtration, the filter cake was washed with anhydrous toluene and dried under vacuum to obtain amino-alumina.

[0093] S2: 100 parts of amino-alumina were dispersed in 400 parts by mass of anhydrous toluene. Under nitrogen protection, 2.5 parts of hexamethylene diisocyanate were added and reacted at 80°C for 1.5 h. Then, 1.2 parts of 2-amino-6-chlorobenzothiazole were added and reacted at 85°C for 3 h. After filtration, the filter cake was washed with anhydrous toluene and dried under vacuum to obtain urea-based organosilicon-alumina.

[0094] S3: 100 parts of urea-based organosilicon-alumina and 1.25 parts of methyltriethoxysilane were dispersed in 150 parts of ethanol-water solution (145 parts of anhydrous ethanol and 5 parts of deionized water). 0.2 parts of glacial acetic acid were added, and the mixture was reacted at 50°C for 2 hours. After filtration, the filter cake was washed with anhydrous ethanol and dried under vacuum to obtain modified alumina F.

[0095] Comparative Preparation Example 2

[0096] Preparation of modified alumina:

[0097] S1: 100 parts of activated alumina were dispersed in 400 parts of anhydrous toluene. Under nitrogen protection, 1.5 parts of γ-aminopropyltriethoxysilane were added and reacted at 110°C for 4 hours. After filtration, the filter cake was washed with anhydrous toluene and dried under vacuum to obtain amino-alumina.

[0098] S2: 100 parts of amino-alumina were dispersed in 400 parts by mass of anhydrous toluene. Under nitrogen protection, 2.5 parts of hexamethylene diisocyanate were added and reacted at 80°C for 1.5 h. Then, 1.2 parts of 2-amino-6-chlorobenzothiazole were added and reacted at 85°C for 3 h. After filtration, the filter cake was washed with anhydrous toluene and dried under vacuum to obtain modified alumina G.

[0099] Comparative preparation example 3

[0100] Preparation of modified alumina:

[0101] S1: 100 parts activated alumina, 0.25 parts trifluoropropyltrimethoxysilane, and 1 part methyltriethoxysilane were dispersed in 150 parts ethanol-water solution (145 parts anhydrous ethanol and 5 parts deionized water). 0.2 parts glacial acetic acid were added, and the mixture was reacted at 50°C for 2 hours. After filtration, the filter cake was washed with anhydrous ethanol and dried under vacuum to obtain modified alumina H.

[0102] Example 1

[0103] Preparation of epoxy insulation materials:

[0104] 100 parts of epoxy resin and 50 parts of modified alumina A were mixed and stirred at 500 rpm for 15 min. 80 parts of methyltetrahydrophthalic anhydride were added and stirred at 500 rpm for 20 min. 0.4 parts of 2-methylimidazole were added and stirred at 500 rpm for 10 min. Vacuum degassing was performed (40℃, -0.09 MPa) to obtain an epoxy mixture. The epoxy mixture was injected into a mold preheated to 80℃ and kept at 80℃ for 4 h, 120℃ for 10 h, and 140℃ for 6 h. After curing, it was allowed to cool naturally to room temperature, demolded, and trimmed to obtain an epoxy insulation material for instrument transformers.

[0105] Example 2

[0106] Preparation of epoxy insulation materials:

[0107] It is largely the same as Example 1, except that modified alumina A is replaced with modified alumina B.

[0108] Example 3

[0109] Preparation of epoxy insulation materials:

[0110] It is largely the same as Example 1, except that modified alumina A is replaced with modified alumina C.

[0111] Example 4

[0112] Preparation of epoxy insulation materials:

[0113] It is largely the same as Example 1, except that modified alumina A is replaced with modified alumina D.

[0114] Example 5

[0115] Preparation of epoxy insulation materials:

[0116] It is largely the same as Example 1, except that modified alumina A is replaced with modified alumina E.

[0117] Example 6

[0118] Preparation of epoxy insulation materials:

[0119] It is largely the same as Example 1, except that modified alumina A is replaced with modified alumina I.

[0120] Example 7

[0121] Preparation of epoxy insulation materials:

[0122] It is largely the same as Example 1, except that modified alumina A is replaced with modified alumina J.

[0123] Comparative Example 1

[0124] Preparation of epoxy insulation materials:

[0125] It is largely the same as Example 1, except that modified alumina A is replaced with modified alumina F.

[0126] Comparative Example 2

[0127] Preparation of epoxy insulation materials:

[0128] It is largely the same as Example 1, except that modified alumina A is replaced with modified alumina G.

[0129] Comparative Example 3

[0130] Preparation of epoxy insulation materials:

[0131] It is largely the same as Example 1, except that modified alumina A is replaced with modified alumina H.

[0132] Comparative Example 4

[0133] Preparation of epoxy insulation materials:

[0134] It is largely the same as Example 1, except that modified alumina A is replaced with alumina.

[0135] Test section

[0136] The epoxy insulation materials prepared in the examples and comparative examples were subjected to performance tests.

[0137] Breakdown strength test: Epoxy insulation material is prepared into circular specimens with a diameter of 100 mm and a thickness of 1 mm. Referring to national standard GB / T1408.1-2016, the breakdown strength E of the specimen under a short-time electric field is measured at 25℃, with a voltage increase rate of 2000 V / s and a test voltage frequency of 50 Hz. b0 (kV / mm), the test was performed 5 times at different locations on the sample, and the median value of the test results was taken as the E of the sample. b0 If the deviation of the five test results from the median does not exceed ±10%, the test results are used for subsequent breakdown strength analysis.

[0138] Breakdown strength retention test after aging: The epoxy insulation material was placed in an aging test chamber, the temperature was set at 50℃ and the relative humidity at 90%RH, and after aging for 1000 hours, it was cooled to room temperature and left for 48 hours. Then, the breakdown strength E was tested again using the same method as above. b1 (kV / mm), calculate the breakdown strength retention rate R=E after aging. b1 / E b0 ×100%.

[0139] The test results are shown in Table 1.

[0140] Table 1

[0141]

[0142] As shown in Table 1, the epoxy insulation materials obtained in each embodiment have higher breakdown strength and breakdown strength retention rate after aging compared to the comparative examples. This may be because Comparative Example 1 only uses alkylsilane for modification, and the resulting interface structure mainly provides basic chemical bonding. Its ability to regulate interface response behavior under electric field and thermal / humid environment is insufficient, thus limiting the improvement of the material's breakdown strength and stability to some extent. Comparative Example 2 only constructs a urea-based organosilicon functional layer structure, and the interface structure stability is easily disturbed under the coupling of damp heat and electric field, and it is difficult to mitigate the impact. The difference in dielectric response between the filler and the epoxy resin may lead to local electric field inhomogeneity, which in turn affects the insulation reliability. In Comparative Example 3, the alumina surface was modified with silane. The interface structure mainly relied on a limited number of chemical bonding points and lacked dynamic functional units that could participate in charge regulation and stress buffering. Under long-term electrothermal stress, the interface electrical response stability was insufficient, and local weak areas were easily formed. In Comparative Example 4, the interface compatibility between the unmodified alumina and the epoxy resin was poor. Under the action of an external electric field, local stress concentration was more likely to form in the interface area, thereby accelerating the deterioration of electrical performance.

[0143] As can be seen from Examples 1-3, the mass ratio of trifluoropropyltrimethoxysilane to methyltriethoxysilane has a certain influence on the breakdown strength and the breakdown strength retention rate after aging of epoxy insulation materials. When the mass ratio of trifluoropropyltrimethoxysilane to methyltriethoxysilane is 1:2-5, the breakdown strength and the breakdown strength retention rate after aging of the material are relatively high.

[0144] As shown in Examples 1, 4, and 5, the mass ratio of urea-based organosilicon-alumina to silane modifier has a certain influence on the breakdown strength and the breakdown strength retention rate after aging of epoxy insulation materials. When the mass ratio of urea-based organosilicon-alumina to silane modifier is 100:1~2, the breakdown strength and the breakdown strength retention rate after aging of the material are relatively high.

[0145] As shown in Examples 1, 6, and 7, the mass ratio of amino-alumina to 2-amino-6-chlorobenzothiazole has a certain influence on the breakdown strength and the breakdown strength retention rate after aging of epoxy insulation materials. When the mass ratio of amino-alumina to 2-amino-6-chlorobenzothiazole is 100:1.1~1.4, the breakdown strength and the breakdown strength retention rate after aging of the material are relatively high.

[0146] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. An epoxy insulation material for instrument transformers, characterized in that, Includes the following quantities of raw materials: 100 parts epoxy resin, 30-60 parts modified alumina, 80-85 parts acid anhydride curing agent, and 0.3-0.5 parts curing accelerator; The method for preparing the modified alumina includes the following steps: S1: 100 parts activated alumina and 1-2 parts γ-aminopropyltriethoxysilane are dispersed in 300-500 parts toluene and reacted at 90-150℃ for 2-6 hours to obtain amino-alumina; S2: Amino-alumina and hexamethylene diisocyanate are dispersed in toluene, and the amino groups on the surface of amino-alumina react with the isocyanate groups in hexamethylene diisocyanate to generate urea groups, thus obtaining urea-based organosilicon-alumina. S3: Disperse 100 parts of urea-based organosilicon-alumina, 0.5-2 parts of methyltriethoxysilane, and 0.25-0.4 parts of trifluoropropyltrimethoxysilane in 100-200 parts of ethanol-water solution, and react at 20-70℃ for 1-3 hours to obtain modified alumina.

2. The epoxy insulation material according to claim 1, characterized in that, The activated alumina described in step S1 is prepared through the following steps: Alumina, glacial acetic acid, and water are dispersed in ethanol and treated at 60-80℃ for 2-3 hours to form hydroxyl-activated structures on the surface of alumina, thus obtaining activated alumina.

3. The epoxy insulation material according to claim 1, characterized in that, In step S2, 2-amino-6-chlorobenzothiazole is also added, wherein the mass ratio of amino-alumina to 2-amino-6-chlorobenzothiazole is 100:1.1~1.

4.

4. The epoxy insulation material according to claim 3, characterized in that, Step S2 includes: 100 parts of amino-alumina, 2-3 parts of hexamethylene diisocyanate, and 1.1-1.4 parts of 2-amino-6-chlorobenzothiazole are dispersed in 300-500 parts of toluene and reacted at 50-100℃ for 2-6 hours to obtain urea-based organosilicon-alumina.

5. The epoxy insulation material according to claim 1, characterized in that, The anhydride curing agent includes methyltetrahydrophthalic anhydride; the curing accelerator includes 2-methylimidazole.

6. A method for preparing epoxy insulation material for instrument transformers, characterized in that, include: Provide the raw materials for the epoxy insulating material according to any one of claims 1 to 5; The raw materials are mixed, degassed, cast into molds, and cured to obtain epoxy insulation material for instrument transformers.

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