Silicone rubber for dry-type transformer and dry-type transformer

Abstract

The invention provides silicone rubber for a dry-type transformer and the dry-type transformer. The silicon rubber comprises raw silicon rubber, and fumed silica, a heat-conducting filler, a flame-retardant filler, a coupling agent and a vulcanizing agent which are uniformly dispersed in the raw silicon rubber, wherein the raw silicone rubber is methyl vinyl silicone rubber, the heat-conducting filler is magnesium oxide, and the flame-retardant filler is aluminum hydroxide; the particle size of the magnesium oxide is 1-2 mu m and / or 5-10 mu m, the particle size of the aluminum hydroxide is 1-2 mu m and / or 5-10 mu m, the particle size of one of the magnesium oxide and the aluminum hydroxide is at least 1-2 mu m, and the particle size of the other one of the magnesium oxide and the aluminum hydroxide is at least 5-10 mu m; the silicon rubber comprises the following components in parts by weight: 100 parts of silicon rubber, 25-40 parts of fumed silica, 50-150 parts of magnesium oxide, 50-150 parts of aluminum hydroxide, 5-15 parts of a coupling agent and 1-2 parts of a vulcanizing agent. The silicone rubber disclosed by the invention has excellent heat resistance, heat conduction, flame retardance, tracking resistance and electric erosion resistance.

Description

Technical Field

[0001] This application relates to the field of dry-type transformer technology, specifically to a silicone rubber for dry-type transformers and a dry-type transformer. Background Technology

[0002] Dry-type transformers have become key equipment in modern power systems due to their environmental friendliness, high safety, and strong environmental adaptability. Compared to oil-immersed transformers, their external insulation uses a solid insulating medium, completely avoiding the risks of insulating oil leakage and fire, and meeting the safety regulations for densely populated urban areas.

[0003] Traditional dry-type transformers mainly have two technical routes: epoxy resin casting and encapsulation type and varnish impregnation type. Their inherent defects are becoming increasingly prominent: (1) Varnish impregnation type dry-type transformers have poor moisture and dust resistance, are easily contaminated by dust, leading to surface discharge, and have weak environmental adaptability, requiring strict control of temperature and humidity; (2) Epoxy resin casting type dry-type transformers have the risk of cracking under large temperature difference due to the difference in thermal expansion coefficients between epoxy resin and copper windings, and the recycling of wires inside retired transformers is difficult and energy consumption is high; (3) Traditional dry-type transformers have high noise levels, insufficient flame retardancy rating, and release toxic gases such as HF and CO and dense smoke when burning, seriously endangering the safety of people indoors.

[0004] Currently, one of the main technical routes for new dry-type transformers is injection-molded silicone rubber-coated dry-type transformers. Silicone rubber, as a non-petroleum-based polymer material, possesses excellent damping characteristics (loss factor greater than 0.2) and good processability. It can withstand harsh operating conditions such as high humidity and high altitude, and significantly reduces operation and maintenance costs through natural convection cooling. However, its intrinsic thermal conductivity is low (approximately 0.2 W·m). -1 ·K -1 This results in defects in silicone rubber in dry-type transformers, such as low thermal conductivity, poor flame retardancy, weak resistance to tracking and electrical erosion, which severely restricts the application of silicone rubber in the external insulation of dry-type transformers. Therefore, it is usually necessary to modify silicone rubber using thermally conductive fillers.

[0005] Currently, the most commonly used thermally conductive filler is alumina, which is low in cost and has a thermal conductivity of approximately 35 W·m. -1 ·K -1However, alumina has a high Mohs hardness (approximately 9), higher than that of steel (approximately 8), making it highly susceptible to wear and tear on kneading and injection molding machines during production. The resulting metal filings from this wear remain inside the material, shortening equipment lifespan and significantly reducing the material's insulation and aging resistance. Furthermore, unmodified alumina dispersed in silicone rubber leads to a sharp increase in system viscosity, which is detrimental to injection molding, and results in poor mechanical properties of the molded material. Novel thermally conductive fillers such as boron nitride, aluminum nitride, graphene, and carbon nanotubes can achieve thermal conductivity up to 200 W·m. -1 ·K -1 However, due to its high price (approximately 8 to 10 times that of alumina) and anisotropy, as well as the low degree of industrialization of the modification process, its application in the external insulation silicone rubber of dry-type transformers faces problems such as excessively high cost, complex modification process, and poor mechanical properties.

[0006] The content of the background section is merely the technology known to the inventor and does not necessarily represent the prior art in this field. Summary of the Invention

[0007] In order to solve at least one of the technical problems in the prior art, the first aspect of this application provides a silicone rubber for dry-type transformers, comprising raw silicone rubber and fumed silica, thermally conductive filler, flame-retardant filler, coupling agent and vulcanizing agent uniformly dispersed in the raw silicone rubber;

[0008] Wherein, the raw silicone rubber is methyl vinyl silicone rubber, the thermally conductive filler is magnesium oxide, and the flame-retardant filler is aluminum hydroxide; the particle size of the magnesium oxide includes 1~2μm and / or 5~10μm, the particle size of the aluminum hydroxide includes 1~2μm and / or 5~10μm, and the particle size of one of the magnesium oxide and the aluminum hydroxide is at least 1~2μm, and the particle size of the other is at least 5~10μm;

[0009] The raw silica gel is 100 parts, the fumed silica is 25-40 parts, the magnesium oxide is 50-150 parts, the aluminum hydroxide is 50-150 parts, the coupling agent is 5-15 parts, and the vulcanizing agent is 1-2 parts.

[0010] In some embodiments of this application, the fumed silica is selected from one or more of hydrophilic fumed silica 150, hydrophilic fumed silica 200, hydrophobic fumed silica 150, and hydrophobic fumed silica 200.

[0011] In some embodiments of this application, the coupling agent is selected from one or more of silane 151, silane 171, silane KH-550, silane KH-560, hydroxyl silicone oil, dimethyl silicone oil, and vinyl silicone oil.

[0012] In some embodiments of this application, the vulcanizing agent is selected from one or more of dicumyl peroxide, bis(2,4-dichlorobenzoyl peroxide) and 2,5-dimethyl-2,5-bis(tert-butadiene)hexane.

[0013] In some embodiments of this application, the thermal decomposition temperature of the silicone rubber is 508~510℃.

[0014] In some embodiments of this application, the thermal conductivity of the silicone rubber is 0.84~1.18 W·m. -1 ·K -1 .

[0015] In some embodiments of this application, the tensile strength of the silicone rubber is 3.7~4.5MPa and the elongation at break is 250~320%.

[0016] In some embodiments of this application, the flame retardancy of the silicone rubber meets the FV-0 rating.

[0017] In some embodiments of this application, the silicone rubber has a tracking and electrical erosion resistance rating of 1A4.5.

[0018] A second aspect of this application provides a dry-type transformer comprising a solid insulating medium made of any of the aforementioned silicone rubber.

[0019] The silicone rubber provided in this application uses a method of compounding large-particle-size and small-particle-size magnesium oxide and aluminum hydroxide. By utilizing the high thermal conductivity and free radical quenching ability of magnesium oxide and the endothermic decomposition characteristics of aluminum hydroxide, the heat accumulation of silicone rubber during electro-ablation is reduced, the local temperature of the material is lowered, and the electro-ablation resistance of silicone rubber is improved. Ultimately, silicone rubber is endowed with excellent heat resistance, thermal conductivity, flame retardancy, resistance to tracking and electro-erosion.

[0020] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0021] The accompanying drawings, which form part of this disclosure, are used to provide a further understanding of this disclosure. The illustrative embodiments of this disclosure and their descriptions are used to explain this disclosure and do not constitute an undue limitation of this disclosure.

[0022] Figure 1 The process flow for preparing silicone rubber for dry-type transformers provided in one embodiment of this application is shown.

[0023] Figure 2 This illustration shows a schematic diagram of the distribution of filler in silicone rubber for dry-type transformers according to an embodiment of this application. Detailed Implementation

[0024] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0025] The following disclosure provides many different embodiments or examples for implementing the invention. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. In addition, examples of various specific processes and materials are provided in this invention, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0026] Furthermore, unless otherwise specified, all terms used herein (including technical and scientific terms) shall have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It will also be understood that terms, such as those defined in common dictionaries, shall be interpreted as having the same meaning as they have in the context of the relevant technology and the invention, and shall not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0027] Taking into account the measurements discussed and the errors associated with the measurement of a particular quantity (i.e., limitations of the measurement system), as used herein, “about” or “approximately” includes the stated value and means within an acceptable range of deviation from the particular value as determined by a person skilled in the art. For example, “about” may mean within one or more standard deviations, or within ±30%, ±20%, ±10%, or ±5% of the stated value.

[0028] The specific embodiments of the present invention will be described in more detail below with reference to the accompanying drawings and examples, so as to better understand the solution of the present invention and its advantages in various aspects. However, the specific embodiments and examples described below are for illustrative purposes only and are not intended to limit the present invention.

[0029] The silicone rubber for the external insulation of dry-type transformers must simultaneously meet several key performance requirements: high thermal conductivity to enhance winding heat dissipation and improve load capacity; excellent mechanical properties to support internal windings and resist vibration; excellent flame retardancy, without releasing toxic gases during combustion to ensure the safety of personnel and equipment inside; good resistance to electrical erosion; and high heat resistance to ensure a long product lifespan. This application provides a silicone rubber solution for dry-type transformers that meets the above requirements.

[0030] Figure 1 This application illustrates a method for preparing silicone rubber for dry-type transformers, comprising steps S1 to S4. This method is mature, inexpensive, and the modification process is simple and controllable, providing an effective solution for developing high-performance thermally conductive and flame-retardant silicone rubber suitable for dry-type transformers.

[0031] S1: The raw silica rubber is first mixed, and fumed silica and the first coupling agent are added in sequence. After the mixture is further mixed into a ball, vacuum is applied for the first kneading to obtain the first product.

[0032] This step involves mixing fumed silica and a coupling agent with raw silicone rubber, followed by vacuum kneading. Fumed silica, with its nanoscale particle size and large specific surface area, can form a three-dimensional network structure with silicone rubber molecular chains through physical adsorption and chemical bonding, acting as a "bridge" and "anchor." The coupling agent improves the interfacial bonding performance between silicone rubber and inorganic fillers through chemical bonding.

[0033] Optionally, the first coupling agent is selected from one or more of silane 151, silane 171, silane KH-550, silane KH-560, hydroxyl silicone oil, dimethyl silicone oil, and vinyl silicone oil.

[0034] Optionally, the raw silicone rubber is selected from one or more of type 110-1 methyl vinyl silicone rubber, type 110-2 methyl vinyl silicone rubber, and type 110-3 methyl vinyl silicone rubber.

[0035] Optionally, the fumed silica is selected from one or more of hydrophilic fumed silica 150, hydrophilic fumed silica 200, hydrophobic fumed silica 150, and hydrophobic fumed silica 200.

[0036] Optionally, the temperature of the first mixing step is 120~180℃, and the time is 90~180 min. In some embodiments of this application, the temperature of the first mixing step can be 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, or 180℃. In some embodiments of this application, the time of the first mixing step can be 90 min, 100 min, 110 min, 120 min, 130 min, 140 min, 160 min, 170 min, or 180 min.

[0037] Optionally, the temperature of the first kneading is 120~180℃, and the time is 20~30 minutes. In some embodiments of this application, the temperature of the first kneading can be 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, or 180℃. In some embodiments of this application, the time of the first kneading can be 20 minutes, 22 minutes, 24 minutes, 26 minutes, 28 minutes, or 30 minutes.

[0038] S2: Add flame-retardant filler to the first product and perform a second mixing process to obtain the second product.

[0039] This step involves mixing a flame-retardant filler with the first product obtained in step S1. The flame-retardant filler used in this application is aluminum hydroxide. When aluminum hydroxide decomposes upon heating, it releases water of crystallization and absorbs heat, lowering the surface temperature of the material. Simultaneously, its decomposition products can form a dense alumina protective layer on the material surface, effectively blocking oxygen and heat transfer, blocking conductive channels, preventing further expansion of combustion and electro-ablation, and improving flame-retardant performance.

[0040] Optionally, the temperature of the second mixing step is 100~160℃, and the time is 30~60 minutes. In some embodiments of this application, the temperature of the second mixing step can be 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, or 160℃. In some embodiments of this application, the time of the second mixing step can be 30 minutes, 40 minutes, 50 minutes, or 60 minutes.

[0041] S3: Add thermally conductive filler and second coupling agent to the second product in sequence, and perform third mixing to obtain compound rubber.

[0042] This step involves mixing a thermally conductive filler and a coupling agent with the second product obtained in step S2. The thermally conductive filler used in this application is magnesium oxide. Magnesium oxide has high thermal conductivity, which can improve the thermal conductivity efficiency of silicone rubber and enhance its thermal performance. Furthermore, its free radical quenching properties allow it to quickly disperse heat and capture active free radicals when the material faces combustion or electro-ablation, inhibiting the reaction process, improving the heat resistance of silicone rubber, and reducing localized temperatures.

[0043] Optionally, the second coupling agent is selected from one or more of silane 151, silane 171, silane KH-550, silane KH-560, hydroxyl silicone oil, dimethyl silicone oil, and vinyl silicone oil.

[0044] Optionally, the temperature of the third mixing step is 60~120℃, and the time is 30~60 minutes. In some embodiments of this application, the temperature of the third mixing step can be 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, or 120℃. In some embodiments of this application, the time of the third mixing step can be 30 minutes, 40 minutes, 50 minutes, or 60 minutes.

[0045] S4: Cool the rubber compound to room temperature, add vulcanizing agent to the rubber compound, and perform a second kneading to obtain silicone rubber.

[0046] This step involves using a vulcanizing agent to vulcanize the compound obtained in step S3. The vulcanizing agent causes the silicone rubber molecular chains to crosslink through a crosslinking reaction, forming a stable three-dimensional network structure and improving the material's mechanical properties.

[0047] Optionally, the vulcanizing agent is selected from one or more of dicumyl peroxide (DCP), bis(2,4-dichlorobenzoyl peroxide) (DCBP) and 2,5-dimethyl-2,5-bis(tert-butoxy)hexane (bis-dipentane).

[0048] Optionally, the compound can be cooled at room temperature for 4 to 48 hours, or simply cooled to room temperature. For example, it can be cooled for 4 hours, 6 hours, 8 hours, 10 hours, 15 hours, 20 hours, 25 hours, 30 hours, 35 hours, 40 hours, or 48 hours.

[0049] Optionally, the temperature of the second kneading is 20~50℃, and the time is 20~40 minutes. In some embodiments of this application, the temperature of the second kneading can be 20℃, 30℃, 40℃, or 50℃. In some embodiments of this application, the time of the second kneading can be 20 minutes, 30 minutes, or 40 minutes.

[0050] This application uses magnesium oxide instead of alumina as the main thermally conductive filler, which can effectively solve the problem of severe equipment wear caused by the high hardness of alumina; moreover, magnesium oxide can be directly modified in situ during the mixing process, and its modification process is simpler and more efficient than boron nitride and the like; at the same time, the addition of magnesium oxide can significantly increase the thermal decomposition temperature of silicone rubber and greatly enhance the heat resistance of the material.

[0051] This application utilizes the high thermal conductivity of magnesium oxide and the endothermic decomposition properties of aluminum hydroxide to fully leverage their synergistic flame-retardant effects, endowing silicone rubber with excellent thermal conductivity, resistance to electrical erosion, and flame-retardant properties, thus meeting the performance requirements of high-performance external insulating silicone rubber for new dry-type transformers.

[0052] In addition, this application ensures uniform dispersion of fillers through a segmented mixing process, enabling the silicone rubber product to exhibit excellent properties such as high tensile strength, high elongation at break, and high thermal conductivity.

[0053] Furthermore, the magnesium oxide used in this application has a particle size of 1-2 μm and / or 5-10 μm, and the aluminum hydroxide has a particle size of 1-2 μm and / or 5-10 μm, wherein the particle size of one of the magnesium oxide and aluminum hydroxide is at least 1-2 μm, and the particle size of the other is at least 5-10 μm. For example, when the particle size of magnesium oxide is 1-2 μm, the particle size of aluminum hydroxide may be 5-10 μm, or include 1-2 μm and 5-10 μm; when the particle size of magnesium oxide is 5-10 μm, the particle size of aluminum hydroxide may be 1-2 μm, or include 1-2 μm and 5-10 μm; when the particle size of magnesium oxide includes 1-2 μm and 5-10 μm, the particle size of aluminum hydroxide may be 1-2 μm, or 5-10 μm, or include 1-2 μm and 5-10 μm.

[0054] This application uses a composite of large-particle-size (5~10μm) and small-particle-size (1~2μm) magnesium oxide and aluminum hydroxide powders as a thermally conductive / flame-retardant filler for silicone rubber. Through segmented kneading and in-situ modification processes, the filler is uniformly dispersed in the silicone rubber, with the small-particle-size filler filling the voids between the large-particle-size filler, synergistically constructing a highly efficient three-dimensional continuous thermally conductive network (e.g., ...). Figure 2 As shown in the figure, this method can significantly improve the internal thermal conductivity of silicone rubber. Furthermore, by using coupling agents to enhance the chemical bonding force between aluminum hydroxide and magnesium oxide and the silicone rubber matrix, the interfacial thermal resistance is effectively reduced, thereby simultaneously improving thermal conductivity and mechanical properties. Simultaneously, on the one hand, the inherent high thermal conductivity and free radical quenching properties of magnesium oxide allow it to rapidly disperse heat and capture active free radicals when the material faces combustion or electro-ablation, inhibiting the reaction process, improving the heat resistance of silicone rubber, and reducing local temperatures. On the other hand, the characteristic of aluminum hydroxide to absorb a large amount of heat during thermal decomposition removes heat from the material surface during combustion, and its decomposition products can form a dense alumina protective layer on the material surface, effectively blocking oxygen and heat transfer and preventing further expansion of combustion and electro-ablation.

[0055] Optionally, the raw silicone rubber used is 100 parts, fumed silica is 25-40 parts, magnesium oxide is 50-150 parts, aluminum hydroxide is 50-150 parts, the first coupling agent and the second coupling agent together are 5-15 parts, and the vulcanizing agent is 1-2 parts. All the above parts are by weight. The performance of the silicone rubber can be optimized by adjusting the ratio of magnesium oxide and aluminum hydroxide. In some embodiments of this application, the fumed silica can be 25 parts, 30 parts, 35 parts, or 40 parts. In some embodiments of this application, the magnesium oxide can be 50 parts, 60 parts, 70 parts, 80 parts, 90 parts, 100 parts, 110 parts, 120 parts, 130 parts, 140 parts, or 150 parts. In some embodiments of this application, the aluminum hydroxide can be 50 parts, 60 parts, 70 parts, 80 parts, 90 parts, 100 parts, 110 parts, 120 parts, 130 parts, 140 parts, or 150 parts. In some embodiments of this application, the first coupling agent and the second coupling agent may be in a total of 5 parts, 7 parts, 9 parts, 11 parts, 13 parts, or 15 parts. In some embodiments of this application, the vulcanizing agent may be 1 part, 1.5 parts, or 2 parts.

[0056] This application provides a silicone rubber for dry-type transformers prepared by the above method, which has excellent heat resistance, thermal conductivity, flame retardancy, resistance to tracking and electrical erosion.

[0057] The silicone rubber for dry-type transformers provided in this application includes raw silicone rubber and fumed silica, thermally conductive filler, flame-retardant filler, coupling agent and vulcanizing agent uniformly dispersed in the raw silicone rubber.

[0058] As mentioned above, the thermally conductive filler is magnesium oxide, and the flame-retardant filler is aluminum hydroxide. The particle size of magnesium oxide includes 1~2μm and / or 5~10μm, and the particle size of aluminum hydroxide includes 1~2μm and / or 5~10μm, and the particle size of one of magnesium oxide and aluminum hydroxide is at least 1~2μm, and the particle size of the other is at least 5~10μm.

[0059] The composition includes 100 parts of raw silica, 25-40 parts of fumed silica, 50-150 parts of magnesium oxide, 50-150 parts of aluminum hydroxide, 5-15 parts of coupling agent, and 1-2 parts of vulcanizing agent.

[0060] As mentioned above, the raw silicone rubber can be selected from one or more of type 110-1 methyl vinyl silicone rubber, type 110-2 methyl vinyl silicone rubber, and type 110-3 methyl vinyl silicone rubber.

[0061] The fumed silica can be selected from one or more of hydrophilic fumed silica 150, hydrophilic fumed silica 200, hydrophobic fumed silica 150, and hydrophobic fumed silica 200.

[0062] The coupling agent may be selected from one or more of silane 151, silane 171, silane KH-550, silane KH-560, hydroxyl silicone oil, dimethyl silicone oil, and vinyl silicone oil.

[0063] The vulcanizing agent may be selected from one or more of dicumyl peroxide (DCP), bis(2,4-dichlorobenzoyl peroxide) (DCBP) and 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane (bis-dipentane).

[0064] The silicone rubber for dry-type transformers provided in this application has a thermal decomposition temperature of 508~510℃ and a thermal conductivity of 0.84~1.18 W·m. -1 ·K -1 The tensile strength can reach 3.7~4.5MPa, the elongation at break can reach 250~320%, the flame retardancy can meet the FV-0 level, and the resistance to tracking and electro-erosion can meet the 1A4.5 level.

[0065] This application further provides a dry-type transformer comprising a solid insulating medium made of the aforementioned silicone rubber. Therefore, the dry-type transformer exhibits excellent overall performance.

[0066] The present invention will now be described with reference to specific embodiments. The process conditions and values ​​used in the following embodiments and comparative examples are exemplary, and their possible ranges are as shown in the foregoing description of the invention. For process parameters not specifically noted, conventional techniques can be used. Unless otherwise specified, the reagents and instruments used in the technical solutions provided by the present invention can all be purchased from conventional channels or the market. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0067] Example 1

[0068] This embodiment prepares a silicone rubber for dry-type transformers, and the specific steps are as follows:

[0069] S1: Mix 50 parts of type 110-1 methyl vinyl silicone rubber and 50 parts of type 110-3 methyl vinyl silicone rubber in a kneader at about 150°C for about 150 min. Then add 35 parts of hydrophilic fumed silica 200, 3 parts of hydroxyl silicone oil and 3 parts of dimethyl silicone oil in sequence. After mixing into a ball, knead under vacuum at about 150°C for about 25 min to obtain the first product.

[0070] S2: Add 80 parts of aluminum hydroxide with a particle size of 5~10μm to the first product and mix at about 140℃ for about 40 minutes to obtain the second product.

[0071] S3: Add 120 parts of magnesium oxide with a particle size of 1~2μm, 3 parts of hydroxyl silicone oil and 3 parts of dimethyl silicone oil to the second product, and mix at about 100°C for about 50 minutes to obtain the compound.

[0072] S4: Place the compound at room temperature for about 24 hours, then put it into a kneader, add 1.5 parts of 2,5-dimethyl-2,5-bis(tert-butadiene)hexane, and knead at about 30°C for about 30 minutes to obtain silicone rubber.

[0073] The tensile strength, elongation at break, thermal decomposition temperature, thermal conductivity, flame retardancy (UL94), resistance to tracking and electrolytic corrosion of silicone rubber were tested. Please refer to Table 1 for details.

[0074] Example 2

[0075] The difference between this embodiment and Embodiment 1 is that the aluminum hydroxide used in step S2 has a particle size of 1~2 μm, and the magnesium oxide used in step S3 has a particle size of 5~10 μm. The properties of the obtained silicone rubber are shown in Table 1.

[0076] Example 3

[0077] The difference between this embodiment and Embodiment 1 is that step S3 uses 3 parts hydroxyl silicone oil, 1 part dimethyl silicone oil, and 3 parts silane KH-550. The properties of the obtained silicone rubber are shown in Table 1.

[0078] Example 4

[0079] The difference between this embodiment and Embodiment 3 is that in step S2, 30 parts of aluminum hydroxide with a particle size of 1-2 μm and 50 parts of aluminum hydroxide with a particle size of 5-10 μm were used, while in step S3, 90 parts of magnesium oxide with a particle size of 1-2 μm and 30 parts of magnesium oxide with a particle size of 5-10 μm were used. The properties of the obtained silicone rubber are shown in Table 1.

[0080] Example 5

[0081] The difference between this embodiment and Embodiment 3 is that step S2 uses 40 parts of aluminum hydroxide with a particle size of 1-2 μm and 40 parts of aluminum hydroxide with a particle size of 5-10 μm, while step S3 uses 60 parts of magnesium oxide with a particle size of 1-2 μm and 60 parts of magnesium oxide with a particle size of 5-10 μm. The properties of the obtained silicone rubber are shown in Table 1.

[0082] Comparative Example 1

[0083] The difference between this comparative example and Example 1 is that step S2 used 30 parts of aluminum hydroxide with a particle size of 1-2 μm and 120 parts of aluminum hydroxide with a particle size of 5-10 μm, and step S3 did not use magnesium oxide. The properties of the obtained silicone rubber are shown in Table 1.

[0084] Comparative Example 2

[0085] The difference between this comparative example and Example 1 is that step S2 used 75 parts of aluminum hydroxide with a particle size of 1-2 μm and 75 parts of aluminum hydroxide with a particle size of 5-10 μm, while step S3 did not use magnesium oxide. The properties of the obtained silicone rubber are shown in Table 1.

[0086] Comparative Example 3

[0087] The difference between this comparative example and Example 4 is that aluminum hydroxide with a particle size of 20-30 μm was used in step S2. The properties of the obtained silicone rubber are shown in Table 1.

[0088] Comparative Example 4

[0089] The difference between this comparative example and Example 1 is that alumina was used in step S2. The properties of the obtained silicone rubber are shown in Table 1.

[0090] Comparative Example 5

[0091] The difference between this comparative example and Example 4 is that magnesium oxide, hydroxyl silicone oil, dimethyl silicone oil, and silane KH-550 were added in step S2, and aluminum hydroxide was added in step S3. The properties of the obtained silicone rubber are shown in Table 1.

[0092] Table 1

[0093] Tensile strength / MPa Elongation at break / % Thermal decomposition temperature / °C <![CDATA[Thermal conductivity / W·m -1 ·K -1 > Flame retardancy (UL94) Resistance to tracking and electrolytic corrosion (1A 4.5 grade) Example 1 3.9 250 506 0.95 FV-0 pass Example 2 3.7 264 508 0.84 FV-0 pass Example 3 4.2 287 509 1.04 FV-0 pass Example 4 4.4 312 510 1.18 FV-0 pass Example 5 4.5 320 508 1.09 FV-0 pass Comparative Example 1 3.8 325 473 0.42 FV-0 pass Comparative Example 2 4.1 306 475 0.51 FV-0 pass Comparative Example 3 2.7 198 506 0.80 FV-0 Not approved Comparative Example 4 3.1 210 510 1.12 FV-0 Not approved Comparative Example 5 3.2 204 508 0.73 FV-0 pass

[0094] As can be seen from Table 1, the thermal conductivity and mechanical properties (tensile strength and elongation at break) of the silicone rubbers prepared in Examples 3 to 5 are better than those in Examples 1 and 2. This is because the use of silane KH-550 can modify magnesium oxide during the mixing process, improve the dispersibility of magnesium oxide in silicone rubber, enhance the chemical bonding between magnesium oxide and silicone rubber, reduce the interfacial thermal resistance, and thus improve the thermal conductivity and mechanical properties of silicone rubber.

[0095] The thermal decomposition temperature and thermal conductivity of the silicone rubbers prepared in Examples 1-5 are significantly higher than those in Comparative Examples 1-2. This is because the intrinsic thermal conductivity of magnesium oxide is higher than that of aluminum hydroxide, which can improve the overall thermal conductivity of the material. At the same time, magnesium oxide has free radical quenching properties, which can quickly disperse heat and capture active free radicals during material combustion, inhibit the thermal decomposition reaction process, and increase the thermal decomposition temperature of silicone rubber.

[0096] The silicone rubbers prepared in Examples 1-5 exhibit significantly higher mechanical and insulation properties than those in Comparative Example 4. This is because Comparative Example 4 uses alumina as a thermally conductive filler, which has a high Mohs hardness. During production, alumina can wear down the kneading and injection molding machines, resulting in iron filings that remain inside the material and weaken its insulation and mechanical properties. Using magnesium oxide as a thermally conductive filler effectively avoids these problems and improves the mechanical and insulation properties of the silicone rubber. The silicone rubber prepared in Example 4 has a higher thermal conductivity than that in Examples 3 and 5. This is because the preferential mixing and filling of easily dispersible aluminum hydroxide with varying particle sizes, followed by the use of magnesium oxide with varying particle sizes, results in a denser filling of the material's internal pores, which is more conducive to building a thermally conductive network.

[0097] The mechanical properties and thermal conductivity of the silicone rubber prepared in Example 4 are significantly better than those in Comparative Example 3. This is because compared with aluminum hydroxide with ultra-large particle size (20~30μm), aluminum hydroxide with small particle size (1~2μm, 5~10μm) has a larger specific surface area. After being compounded, it has a stronger interfacial bonding and stress transfer efficiency with the silicone rubber matrix, and a higher reinforcing ability. In addition, the small particle size compounded silicone rubber can form a denser thermally conductive network and has a higher thermal conductivity.

[0098] The silicone rubber prepared in Example 4 exhibits significantly better mechanical properties and thermal conductivity than that in Comparative Example 5. This is because silane KH550 readily hydrolyzes and self-polymerizes at higher temperatures. The lower temperature during mixing and modification in step S3 maximizes the modification degree of magnesium oxide, improving its dispersibility in the matrix and thus enhancing the performance of the silicone rubber. In Comparative Example 4, magnesium oxide was mixed at a high temperature in step S2, causing the KH550 self-polymerization to fail, resulting in a decreased modification degree of magnesium oxide, poorer dispersibility in the matrix, and increased matrix viscosity. Consequently, the dispersibility of aluminum hydroxide in the low-temperature, high-viscosity matrix deteriorated, thus weakening the performance of the silicone rubber.

[0099] The silicone rubber for dry-type transformers in this application employs a method of compounding large-particle-size and small-particle-size magnesium oxide with aluminum hydroxide. By utilizing the high thermal conductivity and free radical quenching ability of magnesium oxide and the endothermic decomposition characteristics of aluminum hydroxide, the heat accumulation of silicone rubber during electro-ablation is reduced, the local temperature of the material is lowered, and the electro-ablation resistance of silicone rubber is improved. Ultimately, this endows silicone rubber with excellent heat resistance, thermal conductivity, flame retardancy, resistance to tracking and electro-erosion.

[0100] Obviously, the above embodiments are merely examples for clearly illustrating the present invention and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A silicone rubber for dry-type transformers, characterized by, It includes raw silica gel and fumed silica, thermally conductive filler, flame-retardant filler, coupling agent and vulcanizing agent uniformly dispersed in the raw silica gel; Wherein, the raw silicone rubber is methyl vinyl silicone rubber, the thermally conductive filler is magnesium oxide, and the flame-retardant filler is aluminum hydroxide; the particle size of the magnesium oxide includes 1~2μm and / or 5~10μm, the particle size of the aluminum hydroxide includes 1~2μm and / or 5~10μm, and the particle size of one of the magnesium oxide and the aluminum hydroxide is at least 1~2μm, and the particle size of the other is at least 5~10μm; The raw silica gel is 100 parts, the fumed silica is 25-40 parts, the magnesium oxide is 50-150 parts, the aluminum hydroxide is 50-150 parts, the coupling agent is 5-15 parts, and the vulcanizing agent is 1-2 parts.

2. The silicone rubber according to claim 1, characterized in that, The fumed silica is selected from one or more of hydrophilic fumed silica 150, hydrophilic fumed silica 200, hydrophobic fumed silica 150, and hydrophobic fumed silica 200.

3. The silicone rubber according to claim 1, characterized in that, The coupling agent is selected from one or more of silane 151, silane 171, silane KH-550, silane KH-560, hydroxyl silicone oil, dimethyl silicone oil, and vinyl silicone oil.

4. The silicone rubber according to claim 1, characterized in that, The vulcanizing agent is selected from one or more of dicumyl peroxide, bis(2,4-dichlorobenzoyl peroxide) and 2,5-dimethyl-2,5-bis(tert-butoxy)hexane.

5. The silicone rubber according to claim 1, characterized in that, The thermal decomposition temperature of the silicone rubber is 508~510℃.

6. The silicone rubber according to claim 1, characterized in that, The thermal conductivity of the silicone rubber is 0.84-1.18 W·m -1 ·K -1 .

7. The silicone rubber according to claim 1, characterized in that, The tensile strength of the silicone rubber is 3.7~4.5MPa, and the elongation at break is 250~320%.

8. The silicone rubber according to claim 1, characterized in that, The flame retardancy of the silicone rubber meets the FV-0 standard.

9. The silicone rubber according to claim 1, characterized in that, The silicone rubber exhibits resistance to tracking and electrical erosion at level 1A4.

5.

10. A dry-type transformer, characterized in that, Includes a solid insulating medium made of silicone rubber as described in any one of claims 1 to 9.

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