Composite insulating oil paper as well as preparation method and application thereof

Abstract

The invention discloses composite insulating oil paper as well as a preparation method and application thereof, and relates to the technical field of electrical engineering insulation. The composite insulation oil paper sequentially comprises a dielectric transition layer, a cellulose insulation paper matrix and a conductive slow release layer, the dielectric transition layer comprises BaTiO3 and TiO2 according to the mass ratio of (0.3-3): 1, and the conductive slow release layer comprises alpha-SiC. Different functional layers are introduced to the two sides of a cellulose insulation paper substrate respectively, so that the interface bonding between the insulation paper and ester insulation oil can be improved by virtue of the synergistic effect of mechanisms such as dielectric constant gradient mitigation and local electric field peak diffusion; therefore, the dielectric loss of the oil-paper insulation system is reduced while the partial discharge capacity of the oil-paper insulation system is reduced and the insulation breakdown strength is improved.

Description

Technical Field

[0001] This invention relates to the field of electrical engineering insulation technology, specifically to a composite insulating paper, its preparation method, and its application. Background Technology

[0002] With the rapid development of the power industry, the transmission capacity of the power grid system is constantly increasing, and the voltage level is also continuously breaking through and improving. While this further expands the range and efficiency of power transmission, it also puts forward higher requirements for the reliability and stability of the power transmission and distribution system. Oil-immersed transformers are the central hub for power transmission and distribution in the power system. Their function is to flexibly switch the transmission voltage: the voltage of the electricity produced by power plants is usually low (such as 35kV and below), which cannot meet the needs of long-distance power transmission. This is because long-distance transmission of low voltage will lead to a sharp increase in power loss and a significant decrease in transmission efficiency. Therefore, when the power grid system transmits current from the power plant to the power terminal, it usually first uses transformers to step up the current to ultra-high voltage or extra-high voltage levels (such as 500kV or 1000kV) to reduce energy loss during transmission and achieve efficient long-distance power transmission. After the power is transmitted to the power consumption area, the high voltage power is stepped down by transformers to voltage levels suitable for industrial production (such as 10kV) and residential life (such as 220V or 380V) to ensure that the power can be safely adapted to various electrical equipment. Given the crucial role of transformers and their critical position in the power grid system, their function directly impacts the current utilization efficiency of the power grid, and their safety directly determines the safe and stable operation of the power grid. Therefore, to ensure the normal operation of transformers and the effective functioning of their transformer capabilities, the high-voltage components within the transformer must be insulated to resist voltage surges, prevent insulation breakdown, and simultaneously prevent leakage current and eddy current generation, thereby reducing energy loss.

[0003] Currently, power systems typically use oil-paper insulation systems to insulate transformers. This system is a combination of transformer oil and insulating paper. The core function of the insulating paper is as a solid insulating substrate, wrapping around the surface of the transformer windings. It acts as an insulating medium separating the winding conductors, windings, and core, preventing localized electric field concentration and leakage between conductors and between windings and the core. The core function of the transformer oil is as a more fluid liquid insulating medium, filling the interior and gaps of the insulating paper. On one hand, it enhances the overall insulation performance, fills the gaps that the insulating paper cannot cover, and improves the breakdown strength of the composite insulation unit. On the other hand, it also has a heat dissipation function, conducting the heat generated during transformer operation to the outside. Furthermore, it absorbs impurities produced by the aging of the insulating paper, slowing down the deterioration of the insulation system. Currently, the industry mainly uses mineral oil and ester oils for transformers, with mineral oil being the earlier and most currently used in operating transformers as the liquid insulating medium. However, mineral oil is a non-renewable resource; after insulation aging, it can only be extracted and discarded. Therefore, the utilization of mineral oil greatly limits the environmentally friendly development of the power grid system. To address this issue, the industry has begun to gradually replace traditional mineral oil with more environmentally friendly ester-based insulating oil. However, due to its unique molecular structure containing ester groups, ester-based insulating oil has a weak interface bond with insulating paper, resulting in dielectric discontinuity at the oil-paper interface. This can easily lead to charge traps and electric field distortion, thereby reducing partial discharge and causing insulation breakdown, which affects the safe operation of transformers. At the same time, this weak interface bond can lead to insufficient oil impregnation in the paper, resulting in increased dielectric loss and a shortened lifespan of the insulation system. Summary of the Invention

[0004] To address the problems of high partial discharge, low insulation breakdown voltage, and high dielectric loss in existing oil-paper insulation systems using ester-based insulating oil as the liquid insulating medium, this invention provides a composite insulating oil-paper. Different functional layers are introduced on both sides of the cellulose insulating paper matrix. Through the synergistic effect of mechanisms such as mitigating the dielectric constant gradient and diffusing local electric field peaks, the interfacial bonding between the insulating paper and the ester-based insulating oil is improved. This reduces the partial discharge of the oil-paper insulation system, improves the insulation breakdown strength, and simultaneously reduces its dielectric loss.

[0005] Another object of the present invention is to provide a method for preparing the above-mentioned composite insulating paper.

[0006] Another object of the present invention is to provide an oil-paper insulation system.

[0007] Another object of the present invention is to provide the application of the composite insulating paper or the paper insulation system in transformers.

[0008] The above-mentioned objective of this invention is achieved through the following technical solution: A composite insulating oil paper comprises, in sequence, a dielectric transition layer, a cellulose insulating paper matrix, and a conductive slow-release layer, wherein: the dielectric transition layer comprises BaTiO3 and TiO2 in a mass ratio of (0.3-3):1, and the conductive slow-release layer comprises α-SiC.

[0009] The composite insulating paper provided by this invention introduces different functional layers on both sides of the cellulose insulating paper matrix. The dielectric transition layer, composed of BaTiO3 and TiO2, primarily serves to provide a dielectric constant buffer gradient transition. Of the two fillers in the dielectric transition layer, BaTiO3 has a higher dielectric constant. Therefore, this invention combines BaTiO3 and TiO2 fillers and coats them onto the surface of the insulating paper matrix, forming a dielectric constant gradient from the cellulose insulating paper matrix to TiO2 to BaTiO3 (the dielectric constant increases sequentially from the matrix to BaTiO3). This significantly improves the surface dielectric constant of the resulting composite insulating paper while making the dielectric constant gradient transition between the insulating paper and the insulating oil smoother, reducing Maxwell-Wagner interface polarization caused by dielectric mismatch, thereby reducing electric field distortion at the insulating oil-insulating paper interface. The inventors of this application, through experimental research, discovered that directly compounding BaTiO3 and TiO2 filler particles to form a single-layer dielectric transition layer, compared to sequentially coating two layers (TiO2 and BaTiO3) onto the substrate surface, provides a better dielectric constant buffering effect, reduces electric field distortion in the oil-paper insulation system, lowers partial discharge, and increases breakdown voltage. The reasons are speculated to be as follows: firstly, the introduction of a multilayer structure introduces additional macroscopic interfaces, increasing the risk of electric field distortion at these interfaces; secondly, the functional layer formed by the stacking of filler particles... The component contains a porous structure. When the composite oil paper is immersed in insulating oil, the insulating oil will penetrate into the dielectric transition layer and the internal pores of the insulating paper. When the dielectric transition layer is a single layer formed by BaTiO3 and TiO2, the insulating oil can simultaneously achieve full wetting and bonding of the surfaces of the two filler particles. However, if TiO2 layer and BaTiO3 layer are coated on the substrate surface in sequence, the wetting time of the insulating oil on TiO2 will not match the wetting time of BaTiO3, affecting the establishment of the interfacial electric field and the conduction of charge carriers, thus leading to a decrease in the uniformity of the interfacial electric field.

[0010] The composite insulating paper provided by this invention also incorporates a conductive slow-release layer on the other side of the substrate relative to the dielectric transition layer. This layer mainly comprises α-SiC. The conductive slow-release layer in the paper of this invention also serves to homogenize the electric field at the oil-paper interface. This is mainly because the α-SiC in this layer has nonlinear conductivity characteristics, which can promote charge dissipation: when the local electric field is too high, the conductivity of the SiC layer increases rapidly, causing the charge accumulated at the interface to dissipate quickly along the surface, thereby smoothing out electric field spikes, preventing the generation of partial discharge, reducing the amount of partial discharge, and improving the insulation breakdown strength.

[0011] The inventors of this application discovered through experiments that forming two layers of α-SiC and BaTiO3 / TiO2 on both sides of the substrate, compared to directly combining α-SiC, BaTiO3, and TiO2 filler particles into a single layer, or sequentially forming a dielectric transition layer and a conductive slow-release layer on one side of the insulating paper substrate, can more fully utilize the advantages of each of the three fillers. This is mainly because the intrinsic dielectric constant of α-SiC does not significantly increase compared to the insulating paper substrate. Directly combining α-SiC, BaTiO3, and TiO2 filler particles into a single layer, or sequentially forming a dielectric transition layer and a conductive slow-release layer on one side of the insulating paper substrate... The dielectric transition layer and the conductive buffer layer are formed sequentially on one side of the body. Both of these layers introduce an additional dielectric constant transition gradient in the insulating paper matrix-SiC-TiO2. However, they do not significantly improve the dielectric constant of the oil-paper insulation system. At the same time, the nonlinear conductivity of α-SiC will affect the carrier transport direction based on the change in dielectric constant (generally speaking, the larger the dielectric constant, the easier the carrier transition / conduction. Therefore, the introduction of the dielectric transition layer can make the composite insulating paper form a trend of decreasing carrier transport speed from insulating oil to BaTiO3, TiO2 and then to the insulating paper matrix. The introduction of α-SiC will break this trend).

[0012] Based on the above principles and mechanisms, the composite insulating oil paper provided in this application can improve the interfacial bonding between the insulating paper and the ester-based insulating oil, thereby reducing the partial discharge of the oil paper insulation system and improving the insulation breakdown strength while reducing its dielectric loss.

[0013] In a preferred embodiment of the composite insulating paper of the present invention, the thickness of the dielectric transition layer is 5-20 μm.

[0014] In a preferred embodiment of the composite insulating paper of the present invention, the thickness of the cellulose insulating paper matrix is ​​100-300 μm.

[0015] In a preferred embodiment of the composite insulating paper of the present invention, the thickness of the conductive slow-release layer is 1-3 μm.

[0016] In a preferred embodiment of the composite insulating paper of the present invention, the average particle size of the BaTiO3 is 50-100 nm.

[0017] In a preferred embodiment of the composite insulating paper of the present invention, the average particle size of the TiO2 is 20-50 nm.

[0018] In a preferred embodiment of the composite insulating paper of the present invention, the average particle size of the α-SiC is 100-500 nm.

[0019] In a preferred embodiment of the composite insulating paper of the present invention, the basis weight of the cellulose insulating paper matrix is ​​150-250 g / m². 2 .

[0020] As a preferred embodiment of the composite insulating paper of the present invention, at least one of BaTiO3, TiO2, and α-SiC is surface-treated with a silane coupling agent.

[0021] This invention also protects a method for preparing composite insulating paper, comprising the following steps: S1. Disperse BaTiO3, TiO2 and silane coupling agent in a solvent and react. After the reaction, separate the solid and liquid to obtain the solid. After washing and drying, disperse the obtained solid in ester insulating oil to obtain slurry A. Coat slurry A on the surface of cellulose insulating paper substrate. After curing, the insulating paper with a dielectric transition layer on the surface is obtained. S2. Disperse α-SiC and silane coupling agent in ester insulating oil to obtain slurry B. Coat slurry B on the other side of the insulating paper obtained in step S1, opposite to the dielectric transition layer. After curing, composite insulating oil paper is obtained.

[0022] In a preferred embodiment of the method for preparing the composite insulating oil paper of the present invention, the mass ratio of the silane coupling agent to BaTiO3 in step S1 is (0.01-0.05):1.

[0023] In a preferred embodiment of the method for preparing the composite insulating oil paper of the present invention, the silane coupling agent in step S1 includes γ-aminopropyltriethoxysilane.

[0024] In a preferred embodiment of the method for preparing the composite insulating oil paper of the present invention, the reaction temperature in step S1 is 40-80℃ and the time is 2-6 h.

[0025] In a preferred embodiment of the method for preparing the composite insulating oil paper of the present invention, the solvent in step S1 includes ethanol.

[0026] In a preferred embodiment of the method for preparing the composite insulating oil paper of the present invention, the mass percentage of solids in the slurry A in step S1 is 2%-10%.

[0027] In a preferred embodiment of the method for preparing the composite insulating oil paper of the present invention, the curing in step S1 is carried out at 60-100°C for 1-3 hours.

[0028] In a preferred embodiment of the method for preparing the composite insulating oil paper of the present invention, the mass ratio of the silane coupling agent to α-SiC in step S2 is (0.01-0.03):1.

[0029] In a preferred embodiment of the method for preparing the composite insulating oil paper of the present invention, the silane coupling agent in step S2 includes γ-aminopropyltriethoxysilane.

[0030] In a preferred embodiment of the method for preparing the composite insulating paper of the present invention, the mass percentage of α-SiC in the slurry B in step S2 (the mass percentage of α-SiC in the slurry) is 2%-8%.

[0031] In a preferred embodiment of the method for preparing the composite insulating oil paper of the present invention, the curing in step S2 is carried out at 60-100°C for 1-3 hours.

[0032] The present invention also protects an oil-paper insulation system comprising the composite insulating oil paper and an ester-based insulating oil.

[0033] In a preferred embodiment of the oil-paper insulation system of the present invention, the oil-paper insulation system further includes an additive, wherein the mass of the additive accounts for 0.1%-1% of the total mass of the additive and the ester insulating oil, and the additive includes SiO2.

[0034] In a preferred embodiment of the oil-paper insulation system of the present invention, the average particle size of the SiO2 is 10-40 nm.

[0035] This invention also protects the application of the composite insulating paper or paper insulation system in transformers.

[0036] Compared with the prior art, the present invention has the following beneficial effects: The composite insulating oil paper provided by this invention introduces different functional layers on both sides of the cellulose insulating paper matrix. Through the synergistic effect of mechanisms such as mitigating the dielectric constant gradient and diffusing local electric field spikes, the interfacial bonding between the insulating paper and the ester insulating oil is improved. As a result, while reducing the partial discharge of the oil paper insulation system to above 66.24 pC and increasing the insulation breakdown strength to above 77.42 kV, its dielectric loss is also reduced. The dielectric loss of the resulting oil paper insulation system is as low as below 0.38%. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0038] <Terminology Definition> The term "α-SiC" refers to α-silicon carbide (SiC), which has a hexagonal or rhombohedral crystal structure.

[0039] The term "paper basis weight" refers to the mass of paper per unit area, expressed in grams per square meter (g / m²). 2 )express.

[0040] The term "cellulose insulating paper" refers to insulating paper formed by cross-linking cellulose fibers. Paper that meets at least one of the following standards can be used as cellulose insulating paper in this application: GB / T20628.1-2006 "Cellulose paper for electrical use - Part 1: Definitions and general requirements", GB / T 20628.2-2006 "Cellulose paper for electrical use - Part 2: Test methods", and JB / T 12166-2015 "Cellulose paper for power capacitors".

[0041] The embodiments of this application may omit unnecessary detailed descriptions. For example, detailed descriptions of well-known matters and repetitive descriptions of actually identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art.

[0042] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0043] In this application, a list of items connected by the term "at least one of" can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another instance, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C.

[0044] In the following description, all figures disclosed in this application are approximate values, regardless of whether the terms "about" or "approximately" are used in conjunction. They may vary by 1%, 2%, 5%, or sometimes 10% to 20%. Whenever a range of values ​​with a lower limit (RL) and an upper limit (RU) is disclosed, any values ​​falling within that range are specifically disclosed. Specifically, the following values ​​within this range are specifically disclosed: R = RL + k * (RU - RL), where k is a variable with a 1% increment from 1% to 100%, i.e., k is 1%, 2%, 3%, 4%, 5%, ..., 50%, 51%, 52%, ..., 95%, 96%, 97%, 98%, 99%, or 100%. Furthermore, any range of values ​​defined by the two R values ​​as defined above are also specifically disclosed.

[0045] In this application, numerical ranges are involved. Unless otherwise specified, the numerical ranges mentioned above are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Any lower limit can be combined with any upper limit to form a range not explicitly stated; and any lower limit can be combined with other lower limits to form a range not explicitly stated, just as any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form a range not explicitly stated.

[0046] Throughout this specification, references to "implementation," "partial implementation," "one implementation," "some implementations," "another enumerated method," "specific method," or "partial method" mean that at least one implementation or embodiment in this application includes the specific features, structures, materials, or characteristics described in that implementation or embodiment.

[0047] I. Composite insulating paper To address the problems of high partial discharge, easy insulation breakdown, and large dielectric loss in existing oil-paper insulation systems that use ester-based insulating oil as the liquid insulating medium, this invention provides a composite insulating oil paper, which sequentially comprises a dielectric transition layer, a cellulose insulating paper matrix, and a conductive slow-release layer, wherein: the dielectric transition layer comprises BaTiO3 and TiO2 in a mass ratio of (0.3-3):1, and the conductive slow-release layer comprises α-SiC.

[0048] The composite insulating paper provided by this invention introduces different functional layers on both sides of the cellulose insulating paper matrix. The dielectric transition layer, composed of BaTiO3 and TiO2, primarily serves to provide a dielectric constant buffer gradient transition. Of the two fillers in the dielectric transition layer, BaTiO3 has a higher dielectric constant. Therefore, this invention combines BaTiO3 and TiO2 fillers and coats them onto the surface of the insulating paper matrix, forming a dielectric constant gradient from the cellulose insulating paper matrix to TiO2 to BaTiO3 (the dielectric constant increases sequentially from the matrix to BaTiO3). This significantly improves the surface dielectric constant of the resulting composite insulating paper while making the dielectric constant gradient transition between the insulating paper and the insulating oil smoother, reducing Maxwell-Wagner interface polarization caused by dielectric mismatch, thereby reducing electric field distortion at the insulating oil-insulating paper interface. The inventors of this application, through experimental research, discovered that directly compounding BaTiO3 and TiO2 filler particles to form a single-layer dielectric transition layer, compared to sequentially coating two layers (TiO2 and BaTiO3) onto the substrate surface, provides a better dielectric constant buffering effect, reduces electric field distortion in the oil-paper insulation system, lowers partial discharge, and increases breakdown voltage. The reasons are speculated to be as follows: firstly, the introduction of a multilayer structure introduces additional macroscopic interfaces, increasing the risk of electric field distortion at these interfaces; secondly, the functional layer formed by the stacking of filler particles... The component contains a porous structure. When the composite oil paper is immersed in insulating oil, the insulating oil will penetrate into the dielectric transition layer and the internal pores of the insulating paper. When the dielectric transition layer is a single layer formed by BaTiO3 and TiO2, the insulating oil can simultaneously achieve full wetting and bonding of the surfaces of the two filler particles. However, if TiO2 layer and BaTiO3 layer are coated on the substrate surface in sequence, the wetting time of the insulating oil on TiO2 will not match the wetting time of BaTiO3, affecting the establishment of the interfacial electric field and the conduction of charge carriers, thus leading to a decrease in the uniformity of the interfacial electric field.

[0049] The composite insulating paper provided by this invention also incorporates a conductive slow-release layer on the other side of the substrate relative to the dielectric transition layer. This layer mainly comprises α-SiC. The conductive slow-release layer in the paper of this invention also serves to homogenize the electric field at the oil-paper interface. This is mainly because the α-SiC in this layer has nonlinear conductivity characteristics, which can promote charge dissipation: when the local electric field is too high, the conductivity of the SiC layer increases rapidly, causing the charge accumulated at the interface to dissipate quickly along the surface, thereby smoothing out electric field spikes, preventing the generation of partial discharge, reducing the amount of partial discharge, and improving the insulation breakdown strength.

[0050] The inventors of this application discovered through experiments that forming two layers of α-SiC and BaTiO3 / TiO2 on both sides of the substrate, compared to directly combining α-SiC, BaTiO3, and TiO2 filler particles into a single layer, or sequentially forming a dielectric transition layer and a conductive slow-release layer on one side of the insulating paper substrate, can more fully utilize the advantages of each of the three fillers. This is mainly because the intrinsic dielectric constant of α-SiC does not significantly increase compared to the insulating paper substrate. Directly combining α-SiC, BaTiO3, and TiO2 filler particles into a single layer, or sequentially forming a dielectric transition layer and a conductive slow-release layer on one side of the insulating paper substrate... The sequential formation of a dielectric transition layer and a conductive buffer layer on one side of the insulating paper matrix introduces an additional dielectric constant gradient into the insulating paper matrix-SiC-TiO2. However, this has little effect on the buffering improvement of the dielectric constant in the oil-paper insulation system. Furthermore, the nonlinear conductivity of α-SiC affects the carrier transport direction based on the dielectric constant variation (generally, a higher dielectric constant facilitates carrier transition / conduction; therefore, the introduction of the dielectric transition layer can cause the composite insulating paper to exhibit a decreasing trend in carrier transport velocity from insulating oil to BaTiO3, TiO2, and then to the insulating paper matrix, but the introduction of α-SiC disrupts this trend). In practical applications, the insulating paper in an oil-paper insulation system is in contact with oil on both sides. Placing the high-dielectric layer (BaTiO3 / TiO2) on one side utilizes its high polarization characteristics to optimize the overall electric field distribution, while placing the nonlinear conductivity layer (SiC) on the other side is responsible for leaking and accumulating charge. This asymmetric structure utilizes the insulating paper itself as a buffer, achieving independent functional control without mutual interference.

[0051] Based on the above principles and mechanisms, the composite insulating oil paper provided in this application can improve the interfacial bonding between the insulating paper and the ester-based insulating oil, thereby reducing the partial discharge of the oil paper insulation system and improving the insulation breakdown strength while reducing its dielectric loss.

[0052] In a preferred embodiment of the composite insulating paper of the present invention, the mass ratio of BaTiO3 to TiO2 in the dielectric transition layer can be 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1, or 3:1, or fall within the range of any two of the above values. In a preferred embodiment of the composite insulating paper of the present invention, the mass ratio of BaTiO3 to TiO2 in the dielectric transition layer is (0.5-2):1.

[0053] In a preferred embodiment of the composite insulating paper of the present invention, the thickness of the dielectric transition layer is 5-20 μm. Exemplarily, the thickness of the dielectric transition layer can be 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, 18 μm, 18.5 μm, 19 μm, 19.5 μm, or 20 μm, or fall within the range of any two of the above values.

[0054] In a preferred embodiment of the composite insulating paper of the present invention, the thickness of the cellulose insulating paper matrix is ​​100-300 μm. Exemplarily, the thickness of the cellulose insulating paper matrix can be 100 μm, 105 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, 200 μm, 210 μm, 220 μm, 230 μm, 240 μm, 250 μm, 260 μm, 270 μm, 280 μm, 290 μm, 300 μm, or within any two of the above values.

[0055] In a preferred embodiment of the composite insulating paper of the present invention, the cellulose insulating paper matrix can be obtained through commercial channels.

[0056] In a preferred embodiment of the composite insulating paper of the present invention, the thickness of the conductive slow-release layer is 1-3 μm. Exemplarily, the thickness of the conductive slow-release layer can be 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, or 3 μm, or fall within the range of any two of the above values.

[0057] In a preferred embodiment of the composite insulating paper of the present invention, the average particle size of the BaTiO3 is 50-100 nm. For example, the average particle size of the BaTiO3 can be 50nm, 51nm, 52nm, 53nm, 54nm, 55nm, 56nm, 57nm, 58nm, 59nm, 60nm, 61nm, 62nm, 63nm, 64nm, 65nm, 66nm, 67nm, 68nm, 69nm, 70nm, 71nm, 72nm, 73nm, 74nm, 75nm, 76nm, 77nm, 78nm, 79nm, 80nm, 81nm, 82nm, 83nm, 84nm, 85nm, 86nm, 87nm, 88nm, 89nm, 90nm, 91nm, 92nm, 93nm, 94nm, 95nm, 96nm, 97nm, 98nm, 99nm, or 100nm, or fall within the range of any two of the above values.

[0058] In a preferred embodiment of the composite insulating paper of the present invention, the average particle size of the TiO2 is 20-50 nm. Exemplarily, the average particle size of the TiO2 can be 20 nm, 21 nm, 22 nm, 23 nm, 24 nm, 25 nm, 26 nm, 27 nm, 28 nm, 29 nm, 30 nm, 31 nm, 32 nm, 33 nm, 34 nm, 35 nm, 36 nm, 37 nm, 38 nm, 39 nm, 40 nm, 41 nm, 42 nm, 43 nm, 44 nm, 45 nm, 46 nm, 47 nm, 48 nm, 49 nm, or 50 nm, or fall within the range of any two of the above values.

[0059] In a preferred embodiment of the composite insulating paper of the present invention, the average particle size of the α-SiC is 100-500 nm. Exemplarily, the average particle size of the α-SiC can be 100 nm, 105 nm, 110 nm, 115 nm, 120 nm, 125 nm, 130 nm, 135 nm, 140 nm, 145 nm, 150 nm, 155 nm, 160 nm, 165 nm, 170 nm, 175 nm, 180 nm, 185 nm, 190 nm, 195 nm, 200 nm, 205 nm, 210 nm, 215 nm, 220 nm, 225 nm, 230 nm, 235 nm, 240 nm, 245 nm, 250 nm, 255 nm, 260 nm, 265 nm, 270 nm, 275 nm, 280 nm, 285 nm, 290 nm, 295 nm, 300 nm, etc. nm, 305nm, 310nm, 315nm, 320nm, 325nm, 330nm, 335nm, 340nm, 345nm, 350nm, 355nm, 360nm, 365nm, 370nm, 375nm, 380nm, 385nm, 390nm, 395nm, 400nm, 405nm, 410nm, 415nm, 420nm, 425nm, 430nm, 435nm, 440nm, 445nm, 450nm, 455nm, 460nm, 465nm, 470nm, 475nm, 480nm, 485nm, 490nm, 495nm, 500nm, or within the range of any two of the above values.

[0060] In a preferred embodiment of the composite insulating paper of the present invention, the basis weight of the cellulose insulating paper matrix is ​​150-250 g / m². 2 .

[0061] As a preferred embodiment of the composite insulating paper of the present invention, at least one of BaTiO3, TiO2, and α-SiC is surface-treated with a silane coupling agent.

[0062] This invention also protects a method for preparing composite insulating paper, comprising the following steps: S1. Disperse BaTiO3, TiO2 and silane coupling agent in a solvent and react. After the reaction, separate the solid and liquid to obtain the solid. After washing and drying, disperse the obtained solid in ester insulating oil to obtain slurry A. Coat slurry A on the surface of cellulose insulating paper substrate. After curing, the insulating paper with a dielectric transition layer on the surface is obtained. S2. Disperse α-SiC and silane coupling agent in ester insulating oil to obtain slurry B. Coat slurry B on the other side of the insulating paper obtained in step S1, opposite to the dielectric transition layer. After curing, composite insulating oil paper is obtained.

[0063] In a preferred embodiment of the method for preparing the composite insulating oil paper of the present invention, the mass ratio of the silane coupling agent to BaTiO3 in step S1 is (0.01-0.05):1.

[0064] As a preferred embodiment of the method for preparing the composite insulating oil paper of the present invention, the silane coupling agent in step S1 includes at least one of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, and n-octyltriethoxysilane.

[0065] In a preferred embodiment of the method for preparing the composite insulating paper of the present invention, the reaction temperature in step S1 is 40-80℃, and the reaction time is 2-6 h. Exemplarily, the reaction temperature in step S1 can be 40℃, 41℃, 42℃, 43℃, 44℃, 45℃, 46℃, 47℃, 48℃, 49℃, 50℃, 51℃, 52℃, 53℃, 54℃, 55℃, 56℃, 57℃, 58℃, 59℃, 60℃, 61℃, 62℃, 63℃, 64℃, 65℃, 66℃, 67℃, 68℃, 69℃, 70℃, 71℃, 72℃, 73℃, 74℃, 75℃, 76℃, 77℃, 78℃, 79℃, or 80℃, or fall within the range of any two of the above values. For example, the reaction time in step S1 can be 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, or within any two of the above values.

[0066] In a preferred embodiment of the method for preparing the composite insulating oil paper of the present invention, the solvent in step S1 includes ethanol.

[0067] In a preferred embodiment of the method for preparing the composite insulating oil paper of the present invention, the mass percentage of solids in slurry A in step S1 is 2%-10%. Exemplarily, the mass percentage of solids in slurry A in step S1 can be 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, or fall within any two of the above values.

[0068] In a preferred embodiment of the method for preparing the composite insulating paper of the present invention, the curing in step S1 is carried out at 60-100°C for 1-3 hours. Exemplarily, the curing in step S1 can be carried out at 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, or within any two of the above values. Exemplarily, the curing time in step S1 can be 1 hour, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours, 1.5 hours, 1.6 hours, 1.7 hours, 1.8 hours, 1.9 hours, 2 hours, 2.1 hours, 2.2 hours, 2.3 hours, 2.4 hours, 2.5 hours, 2.6 hours, 2.7 hours, 2.8 hours, 2.9 hours, 3 hours, or within any two of the above values.

[0069] In a preferred embodiment of the method for preparing the composite insulating oil paper of the present invention, the mass ratio of the silane coupling agent to α-SiC in step S2 is (0.01-0.03):1.

[0070] In a preferred embodiment of the method for preparing the composite insulating paper of the present invention, the silane coupling agent in step S2 includes at least one of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, and n-octyltriethoxysilane.

[0071] In a preferred embodiment of the method for preparing the composite insulating paper of the present invention, the mass percentage of α-SiC in the slurry B in step S2 is 2%-8%.

[0072] In a preferred embodiment of the method for preparing the composite insulating paper of the present invention, the curing in step S2 is carried out at 60-100°C for 1-3 hours. Exemplarily, the curing in step S2 can be carried out at 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, or within any two of the above values. Exemplarily, the curing time in step S2 can be 1 hour, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours, 1.5 hours, 1.6 hours, 1.7 hours, 1.8 hours, 1.9 hours, 2 hours, 2.1 hours, 2.2 hours, 2.3 hours, 2.4 hours, 2.5 hours, 2.6 hours, 2.7 hours, 2.8 hours, 2.9 hours, 3 hours, or within any two of the above values.

[0073] II. Oil-paper insulation systems and their applications The present invention also protects an oil-paper insulation system comprising the composite insulating oil paper and an ester-based insulating oil.

[0074] In a preferred embodiment of the oil-paper insulation system of the present invention, the oil-paper insulation system further includes an additive, the mass of which accounts for 0.1%-1% of the total mass of the additive and the ester insulating oil, and the additive includes SiO2. Exemplarily, the mass of the additive may be 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, or 1% of the total mass of the additive and the ester insulating oil, or fall within the range of any two of the above values.

[0075] In a preferred embodiment of the oil-paper insulation system of the present invention, the average particle size of the SiO2 is 10-40 nm. Exemplarily, the average particle size of the SiO2 can be 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm, 21 nm, 22 nm, 23 nm, 24 nm, 25 nm, 26 nm, 27 nm, 28 nm, 29 nm, 30 nm, 31 nm, 32 nm, 33 nm, 34 nm, 35 nm, 36 nm, 37 nm, 38 nm, 39 nm, or 40 nm, or fall within the range of any two of the above values.

[0076] With an average particle size of 10-40nm, SiO2 has a huge specific surface area, forming a large number of deep-level electron traps in the oil, capturing free electrons and ions in the oil flow, reducing carrier mobility, reducing the number of high-energy electrons impacting the paper surface, and further dissipating residual charges on the paper surface in conjunction with the functional layer on the paper surface. The combination of the two can form a multi-level protection system, further improving the performance of the oil-paper insulation system.

[0077] In a preferred embodiment of the oil-paper insulation system of the present invention, the SiO2 is surface-treated with a silane coupling agent.

[0078] In a preferred embodiment of the oil-paper insulation system of the present invention, the silane coupling agent includes γ-aminopropyltriethoxysilane.

[0079] In a preferred embodiment of the oil-paper insulation system of the present invention, the surface treatment includes the following steps: SiO2 and silane coupling agent are dispersed in a solvent at a mass ratio of (1-2):1 and reacted. After the reaction, the solid is separated from the liquid and washed and dried to obtain the final product.

[0080] In a preferred embodiment of the oil-paper insulation system of the present invention, the solvent used in the surface treatment includes ethanol.

[0081] In a preferred embodiment of the oil-paper insulation system of the present invention, the reaction temperature during surface treatment is 40-80°C, and the time is 1-10 h. Exemplarily, the reaction temperature during surface treatment can be 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C, 49°C, 50°C, 51°C, 52°C, 53°C, 54°C, 55°C, 56°C, 57°C, 58°C, 59°C, 60°C, 61°C, 62°C, 63°C, 64°C, 65°C, 66°C, 67°C, 68°C, 69°C, 70°C, 71°C, 72°C, 73°C, 74°C, 75°C, 76°C, 77°C, 78°C, 79°C, or 80°C, or fall within the range of any two of the above values. For example, the reaction time during the surface treatment can be 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h, 10h, or within any two of the above values.

[0082] In a preferred embodiment of the oil-paper insulation system of the present invention, the mass ratio of the composite insulating oil paper to the ester insulating oil is (1-2):10.

[0083] In a preferred embodiment of the oil-paper insulation system of the present invention, the ester insulating oil includes synthetic ester insulating oil.

[0084] In a preferred embodiment of the oil-paper insulation system of the present invention, the preparation method of the oil-paper insulation system includes the following steps: The additive is dispersed in ester-based insulating oil to obtain insulating oil containing the additive. Then, composite insulating paper is impregnated in the insulating oil containing the additive to obtain the final product.

[0085] This invention also protects the application of the composite insulating paper or paper insulation system in transformers.

[0086] III. Examples Unless otherwise specified, all reagents, materials, and instruments used in the following examples and comparative examples are commercially available. Furthermore, unless otherwise specified, "parts" and "%" refer to mass measurements.

[0087] The following is some information about the raw materials involved in the embodiments and comparative examples in this application: BaTiO3-1: Prepared using conventional methods in the field or purchased from commercial sources and then ground and sieved to an average particle size of 75 nm.

[0088] BaTiO3-2: Prepared using conventional methods in the field or purchased from commercial sources and then ground and sieved to an average particle size of 100 nm.

[0089] BaTiO3-3: Prepared using conventional methods in the field or purchased from commercial sources and then ground and sieved to an average particle size of 40 nm.

[0090] BaTiO3-4: Prepared using conventional methods in the field or purchased from commercial sources and then ground and sieved to an average particle size of 125 nm.

[0091] SrTiO3: Prepared using conventional methods in the field or purchased from commercial sources and then ground and sieved to an average particle size of 75 nm.

[0092] TiO2-1: Prepared using conventional methods in the field or purchased from commercial channels and then ground and sieved to an average particle size of 35 nm.

[0093] TiO2-2: Prepared using conventional methods in the field or purchased from commercial channels and then ground and sieved to an average particle size of 20 nm.

[0094] TiO2-3: Prepared using conventional methods in the field or purchased from commercial channels and then ground and sieved to an average particle size of 10 nm.

[0095] TiO2-4: Prepared using conventional methods in the field or purchased from commercial channels and then ground and sieved to an average particle size of 75nm.

[0096] Al2O3: Prepared using conventional methods in the field or purchased from commercial sources and then ground and sieved to an average particle size of 35 nm.

[0097] α-SiC-1: Prepared using conventional methods in the field or purchased from commercial sources and then ground and sieved to an average particle size of 300 nm.

[0098] α-SiC-2: Prepared using conventional methods in the field or purchased from commercial sources and then ground and sieved to an average particle size of 450 nm.

[0099] α-SiC-3: Prepared using conventional methods in the field or purchased from commercial sources and then ground and sieved to an average particle size of 75 nm.

[0100] α-SiC-4: Prepared using conventional methods in the field or purchased from commercial sources and then ground and sieved to an average particle size of 600 nm.

[0101] β-SiC: Prepared using conventional methods in the field or purchased from commercial sources and then ground and sieved to an average particle size of 300 nm.

[0102] SiO2-1: Prepared using conventional methods in the art or purchased from commercial channels, then ground and sieved to an average particle size of 25 nm, followed by surface treatment with a silane coupling agent. The surface treatment includes the following steps: SiO2 and γ-aminopropyltriethoxysilane were dispersed in ethanol at a mass ratio of 1.5:1. After reacting at 60°C for 4 hours, the solid was separated from the liquid and washed and dried to obtain the final product.

[0103] SiO2-2: Prepared using conventional methods in the art or purchased from commercial channels, then ground and sieved to an average particle size of 10 nm, followed by surface treatment with a silane coupling agent. The surface treatment operation is consistent with the surface treatment operation of SiO2-1.

[0104] SiO2-3: Prepared using conventional methods in the art or purchased from commercial channels, then ground and sieved to an average particle size of 50 nm, followed by surface treatment with a silane coupling agent. The surface treatment operation is consistent with the surface treatment operation of SiO2-1.

[0105] SiO2-4: Prepared using conventional methods in the art or purchased from commercial channels, then ground and sieved to an average particle size of 5 nm, followed by surface treatment with a silane coupling agent. The surface treatment operation is consistent with the surface treatment operation of SiO2-1.

[0106] MgO: Prepared using conventional methods in the art or purchased from commercial channels, then ground and sieved to an average particle size of 25 nm, followed by surface treatment with a silane coupling agent. The surface treatment operation is consistent with the surface treatment operation of SiO2-1.

[0107] Ester insulating oil: Miedel 7131 synthetic ester insulating oil.

[0108] Cellulose insulating paper matrix: purchased from Yangzhou Fikete Electric Co., Ltd., brand name NHN 6650, paper basis weight 218g / m³. 2 Thickness 200μm.

[0109] Example 1 An oil-paper insulation system includes composite insulating oil paper, ester-based insulating oil, and additive SiO2-1, wherein the mass ratio of composite insulating oil paper to ester-based insulating oil is 1:10, and the mass of the additive accounts for 0.5% of the total mass of the additive and ester-based insulating oil. The composite insulating oil paper sequentially comprises a dielectric transition layer with a thickness of 10 μm, a cellulose insulating paper matrix, and a conductive slow-release layer with a thickness of 2 μm. The dielectric transition layer comprises BaTiO3-1 and TiO2-1 in a mass ratio of 1:1, and the conductive slow-release layer comprises α-SiC-1. BaTiO3-1, TiO2-1, and α-SiC-1 are all surface-treated with a silane coupling agent. The method for preparing the composite insulating paper includes the following steps: S1. BaTiO3-1, TiO2-1 and γ-aminopropyltriethoxysilane were dispersed in ethanol at a mass ratio of 1:1:0.03. After reacting at 70°C for 4 hours, the solid was separated from the liquid and the solid was washed with ethanol and dried at 60°C to constant weight. The obtained solid was dispersed in ester insulating oil at a dosage of 5 wt (insulating oil)% to obtain slurry A. Slurry A was coated on the surface of cellulose insulating paper substrate and cured at 80°C for 2 hours to obtain insulating paper with a dielectric transition layer on the surface. S2. Disperse α-SiC-1 and γ-aminopropyltriethoxysilane in ester insulating oil at a mass ratio of 1:0.02 to obtain slurry B, in which the mass percentage of α-SiC is 5%; coat slurry B onto the other side of the insulating paper obtained in step S1 opposite to the dielectric transition layer, and cure at 80°C for 2 h to obtain composite insulating oil paper. The preparation method of the oil-paper insulation system includes the following steps: Additives were added to the ester insulating oil at a mass ratio of 5% of the total mass of additives and ester insulating oil. The mixture was then ultrasonically dispersed at 40 kHz for 60 min to obtain a pre-dispersion. Subsequently, ester insulating oil was added to the pre-dispersion at a mass ratio of 0.5% of the total mass of additives and ester insulating oil. The mixture was stirred at 400 rpm for 30 min. Then, an ultrasonic homogenizer (power 500 W, frequency 40 kHz) was started and processed for 15 min. Finally, the mixture was vacuum degassed at 60℃ for 10 min to obtain insulating oil containing additives. The composite insulating paper is obtained by immersing it in insulating oil containing additives for 48 hours.

[0110] Example 2 An oil-paper insulation system includes composite insulating oil paper, ester-based insulating oil, and additive SiO2-2, wherein the mass ratio of composite insulating oil paper to ester-based insulating oil is 2:10, and the mass of the additive accounts for 0.9% of the total mass of the additive and ester-based insulating oil. The composite insulating oil paper sequentially comprises a dielectric transition layer with a thickness of 15 μm, a cellulose insulating paper matrix, and a conductive slow-release layer with a thickness of 1 μm. The dielectric transition layer comprises BaTiO3-2 and TiO2-2 in a mass ratio of 0.5:1, and the conductive slow-release layer comprises α-SiC-2. BaTiO3-2, TiO2-2, and α-SiC-2 are all surface-treated with a silane coupling agent. The method for preparing the composite insulating paper includes the following steps: S1. BaTiO3-2, TiO2-2 and γ-aminopropyltriethoxysilane were dispersed in ethanol at a mass ratio of 0.5:1:0.025. After reacting at 80℃ for 5 h, the solid was separated from the liquid and the solid was washed with ethanol and dried at 60℃ to constant weight. The obtained solid was dispersed in ester insulating oil at an amount of 8 wt (insulating oil)% to obtain slurry A. Slurry A was coated on the surface of cellulose insulating paper substrate and cured at 100℃ for 1 h to obtain insulating paper with a dielectric transition layer on the surface. S2. Disperse α-SiC-2 and γ-aminopropyltriethoxysilane in ester insulating oil at a mass ratio of 1:0.03 to obtain slurry B, in which the mass percentage of α-SiC is 6%; coat slurry B onto the other side of the insulating paper obtained in step S1 opposite to the dielectric transition layer, and cure at 70°C for 3 h to obtain composite insulating oil paper. The preparation method of the oil-paper insulation system is the same as that in Example 1.

[0111] Examples 3-10 Examples 3-10 differ from Example 1 only in the fillers and additives used in each layer, as shown in Table 1. All other aspects are the same as in Example 1.

[0112] Table 1. Examples 11-14 Examples 11-14 differ from Example 1 only in the thickness of each layer, as shown in Table 2; all other aspects are the same as in Example 1. By changing the amount of coating paste (e.g., by applying multiple coats), the thickness of each layer in Examples 11-14 can be made as shown in Table 2.

[0113] Table 2. Example 15 An oil-paper insulation system, wherein the only difference from Example 1 is: The additives account for 1.5% of the total mass of the additives and ester-based insulating oil; The preparation method of the oil-paper insulation system includes the following steps: Additives were added to the ester insulating oil at a mass ratio of 15% of the total mass of additives and ester insulating oil. The mixture was then ultrasonically dispersed at 40 kHz for 60 min to obtain a pre-dispersion. Subsequently, ester insulating oil was added to the pre-dispersion at a mass ratio of 1.5% of the total mass of additives and ester insulating oil. The mixture was stirred at 400 rpm for 30 min. Then, an ultrasonic homogenizer (500 W power, 40 kHz frequency) was started and processed for 15 min. Finally, the mixture was vacuum degassed at 60℃ for 10 min to obtain insulating oil containing additives. The composite insulating paper is obtained by immersing it in insulating oil containing additives for 48 hours.

[0114] Example 16 An oil-paper insulation system, wherein the only difference from Example 1 is: The mass of the additives accounts for 0.05% of the total mass of the additives and ester insulating oil; The preparation method of the oil-paper insulation system includes the following steps: Additives were added to the ester insulating oil at a mass ratio of 0.5% of the total mass of additives and ester insulating oil. The mixture was then ultrasonically dispersed at 40 kHz for 60 min to obtain a pre-dispersion. Subsequently, ester insulating oil was added to the pre-dispersion at a mass ratio of 0.05% of the total mass of additives and ester insulating oil. The mixture was stirred at 400 rpm for 30 min. Then, an ultrasonic homogenizer (500 W power, 40 kHz frequency) was started and processed for 15 min. Finally, the mixture was vacuum degassed at 60℃ for 10 min to obtain insulating oil containing additives. The composite insulating paper is obtained by immersing it in insulating oil containing additives for 48 hours.

[0115] Example 17 An oil-paper insulation system, wherein the only difference from Example 1 is: The dielectric transition layer of the composite insulating oil paper includes BaTiO3-1 and TiO2-1 in a mass ratio of 3:1; in the preparation method of the composite insulating oil paper, the mass ratio of BaTiO3-1, TiO2-1 and γ-aminopropyltriethoxysilane in step S1 is 3:1:0.09.

[0116] Example 18 An oil-paper insulation system, wherein the only difference from Example 1 is: The dielectric transition layer of the composite insulating oil paper includes BaTiO3-1 and TiO2-1 in a mass ratio of 0.3:1; in the preparation method of the composite insulating oil paper, the mass ratio of BaTiO3-1, TiO2-1 and γ-aminopropyltriethoxysilane in step S1 is 0.3:1:0.009.

[0117] Example 19 An oil-paper insulation system, wherein the only difference from Example 1 is: It contains no additives.

[0118] Examples 20-21 An oil-paper insulation system, wherein the only difference from Example 1 is that in Examples 20-21, the additive SiO2-1 is replaced with an equal mass of MgO and TiO2-1, respectively.

[0119] Comparative Example 1 An oil-paper insulation system, differing from Example 1 only in that: The composite insulating paper comprises, in sequence, a cellulose insulating paper matrix, a conductive slow-release layer with a thickness of 2 μm, and a dielectric transition layer with a thickness of 10 μm. The method for preparing the composite insulating paper includes the following steps: S1. Disperse α-SiC-1 and γ-aminopropyltriethoxysilane in ester insulating oil at a mass ratio of 1:0.02 to obtain slurry A, in which the mass percentage of α-SiC is 5%; coat slurry A onto the surface of cellulose insulating paper substrate and cure at 80℃ for 2 h to obtain insulating paper with a conductive slow-release layer on the surface. S2. BaTiO3-1, TiO2-1 and γ-aminopropyltriethoxysilane are dispersed in ethanol at a mass ratio of 1:1:0.03. After reacting at 70°C for 4 hours, the solid is separated from the liquid and the solid is washed with ethanol and dried at 60°C to constant weight. The obtained solid is then dispersed in ester insulating oil at a dosage of 5 wt (insulating oil)% to obtain slurry B. Slurry B is coated on the surface of the conductive slow-release layer in the insulating paper obtained in step S1. After curing at 80°C for 2 hours, the composite insulating oil paper is obtained.

[0120] Comparative Example 2 An oil-paper insulation system, differing from Example 1 only in that: The composite insulating paper comprises, in sequence, a cellulose insulating paper matrix, a dielectric transition layer with a thickness of 10 μm, and a conductive slow-release layer with a thickness of 2 μm. The method for preparing the composite insulating paper includes the following steps: S1. BaTiO3-1, TiO2-1 and γ-aminopropyltriethoxysilane were dispersed in ethanol at a mass ratio of 1:1:0.03. After reacting at 70°C for 4 hours, the solid was separated from the liquid and the solid was washed with ethanol and dried at 60°C to constant weight. The obtained solid was dispersed in ester insulating oil at a dosage of 5 wt (insulating oil)% to obtain slurry A. Slurry A was coated on the surface of cellulose insulating paper substrate and cured at 80°C for 2 hours to obtain insulating paper with a dielectric transition layer on the surface. S2. Disperse α-SiC-1 and γ-aminopropyltriethoxysilane in ester insulating oil at a mass ratio of 1:0.02 to obtain slurry B, in which the mass percentage of α-SiC is 5%; coat slurry B onto the surface of the dielectric transition layer of the insulating paper obtained in step S1, and cure at 80°C for 2 h to obtain composite insulating oil paper.

[0121] Comparative Example 3 An oil-paper insulation system, differing from Example 1 only in that: The composite insulating oil paper comprises, in sequence, a conductive slow-release layer with a thickness of 2 μm, a cellulose insulating paper matrix, a TiO2 layer with a thickness of 5 μm, and a BaTiO3 layer with a thickness of 5 μm. The method for preparing the composite insulating paper includes the following steps: S1. TiO2-1 and γ-aminopropyltriethoxysilane were dispersed in ethanol at a mass ratio of 1:0.015. After reacting at 70°C for 4 hours, the solid was separated from the liquid and the solid was washed with ethanol and dried at 60°C to constant weight. The obtained solid was dispersed in ester insulating oil at a dosage of 5 wt (insulating oil)% to obtain slurry A. Slurry A was coated on the surface of cellulose insulating paper substrate and cured at 80°C for 2 hours to obtain insulating paper with TiO2 layer on the surface. S2. Disperse BaTiO3-1 and γ-aminopropyltriethoxysilane in ethanol at a mass ratio of 1:0.015. After reacting at 70°C for 4 hours, separate the solid and liquid to obtain the solid. Wash with ethanol and dry at 60°C to constant weight. Disperse the obtained solid in ester insulating oil at a dosage of 5 wt (insulating oil)% to obtain slurry B. Coat the TiO2 layer surface of the insulating paper obtained in step S1 with slurry B. After curing at 80°C for 2 hours, the insulating paper with BaTiO3 layer on the surface is obtained. S3. Disperse α-SiC-1 and γ-aminopropyltriethoxysilane in ester insulating oil at a mass ratio of 1:0.02 to obtain slurry C, in which the mass percentage of α-SiC is 5%; coat slurry C onto the other side of the insulating paper obtained in step S2, opposite to the TiO2 layer and BaTiO3 layer, and cure at 80°C for 2 h to obtain composite insulating oil paper.

[0122] Comparative Example 4 An oil-paper insulation system, wherein the only difference from Example 1 is: The composite insulating paper does not include a dielectric transition layer; The method for preparing the composite insulating paper includes the following steps: α-SiC-1 and γ-aminopropyltriethoxysilane were dispersed in ester insulating oil at a mass ratio of 1:0.02 to obtain a slurry, in which the mass percentage of α-SiC was 5%. The slurry was coated on the surface of a cellulose insulating paper substrate and cured at 80°C for 2 h to obtain composite insulating oil paper.

[0123] Comparative Example 5 An oil-paper insulation system, wherein the only difference from Example 1 is: The composite insulating oil paper does not include a conductive slow-release layer; The method for preparing the composite insulating paper includes the following steps: BaTiO3-1, TiO2-1 and γ-aminopropyltriethoxysilane were dispersed in ethanol at a mass ratio of 1:1:0.03. After reacting at 70°C for 4 hours, the solid was separated from the liquid and the solid was washed with ethanol and dried at 60°C to constant weight. The obtained solid was then dispersed in ester insulating oil at a dosage of 5 wt (insulating oil)% to obtain a slurry. The slurry was coated on the surface of cellulose insulating paper substrate and cured at 80°C for 2 hours to obtain composite insulating oil paper.

[0124] Comparative Examples 6-8 An oil-paper insulation system, wherein the only difference from Example 1 is that in Comparative Examples 6-8, BaTiO3-1, TiO2-1 and α-SiC-1 are replaced with equal masses of SrTiO3, Al2O3 and β-SiC, respectively.

[0125] Performance testing Partial discharge quantity test: The test was conducted using the pulse current method, referring to IEC 60270-2000 "High Voltage Test Techniques - Partial Discharge Measurement". The test voltage was applied to 1.2 times the rated power frequency voltage, and the steady-state partial discharge quantity (unit: pC) was recorded. Each group of samples was tested 5 times, and the average value was taken.

[0126] Power frequency breakdown voltage test: Referring to GB / T 1408.1-2016 "Test Method for Electrical Strength of Insulating Materials" and GB / T507 "Determination of Breakdown Voltage of Insulating Oil", a continuous uniform voltage increase method was adopted, with a voltage increase rate of 2 kV / s. The voltage value (unit: kV) at which the sample breaks down was measured. Each group of samples was tested 10 times, and the average value was taken as the power frequency breakdown voltage.

[0127] Dielectric loss test: Referring to GB / T 5654 "Method for Determination of Dielectric Loss Factor of Insulating Oil", the dielectric loss factor (%) was measured using an automatic dielectric loss meter at a power frequency of 50 Hz and a temperature of 90℃. Before testing, the oil-paper insulation system was kept at 90℃ for 30 min. Each group of samples was tested three times, and the average value was taken.

[0128] The results of the above performance tests are shown in Table 3 below: Table 3. As can be seen from the data in Table 3 above, the oil-paper insulation system provided by the present invention improves the interfacial bonding between the insulating paper and the ester-based insulating oil, thereby reducing the partial discharge of the oil-paper insulation system to below 82pC, increasing the insulation breakdown strength to above 64.25kV, and reducing its dielectric loss to below 0.62%.

[0129] According to Examples 3-10, the different particle sizes of specific fillers in the two functional layers of this application can affect the interfacial bonding between the insulating oil and the paper. Simultaneously, SiO2, as an additive in the insulating oil, can further dissipate residual charges on the paper surface, but its dissipation effect also requires specific particle sizes to be effective. Therefore, the overall effect of the paper insulation system is optimal when the average particle sizes of BaTiO3, TiO2, α-SiC, and SiO2 are 50-100 nm, 20-50 nm, 100-500 nm, and 10-40 nm, respectively, as preferred in this invention.

[0130] According to Examples 11-14, the layer thickness affects the effectiveness of each layer. When the thicknesses of the dielectric transition layer and the conductive slow-release layer are 5-20 μm and 1-3 μm, respectively, which are preferred by this invention, the overall effect is optimal.

[0131] According to Examples 15-16 and 19, the absence of additives or the inappropriate amount of additives in the insulating oil also affects the bonding between the oil and paper. The effect is optimal when the amount of additives in the oil is 0.1%-1%, which is preferred in this invention.

[0132] According to Examples 17-18, the effect is better when the ratio of the two components BaTiO3 and TiO2 in the dielectric transition layer is (0.5-2):1, which is the preferred ratio of the present invention.

[0133] According to Examples 20-21, the effect is better when SiO2 is added to the oil as an additive.

[0134] According to Comparative Examples 1-2, when the dielectric transition layer and the conductive slow-release layer are both on the same side of the insulating paper substrate, their respective functions are affected.

[0135] According to Comparative Example 3, introducing BaTiO3 and TiO2 into the dielectric transition layer as two separate layers leads to a decrease in performance.

[0136] According to Comparative Examples 4-5, the introduction of two functional layers is the key to the good results achieved in this application.

[0137] According to Comparative Examples 6-8, the functional layer in this application needs to be composed of specific fillers.

[0138] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A composite insulating paper, characterized in that, It comprises, in sequence, a dielectric transition layer, a cellulose insulating paper matrix, and a conductive slow-release layer, wherein: the dielectric transition layer comprises BaTiO3 and TiO2 in a mass ratio of (0.3-3):1, and the conductive slow-release layer comprises α-SiC.

2. The composite insulating paper as described in claim 1, characterized in that, Includes at least one of the following (1)-(3): (1) The thickness of the dielectric transition layer is 5-20 μm; (2) The thickness of the cellulose insulating paper matrix is ​​100-300 μm; (3) The thickness of the conductive slow-release layer is 1-3 μm.

3. The composite insulating paper as described in claim 1 or 2, characterized in that, Includes at least one of the following (1)-(3): (1) The average particle size of the BaTiO3 is 50-100 nm; (2) The average particle size of the TiO2 is 20-50 nm; (3) The average particle size of the α-SiC is 100-500 nm.

4. The composite insulating paper as described in claim 1, characterized in that, Includes at least one of the following (1)-(2): (1) The basis weight of the cellulose insulating paper matrix is ​​150-250 g / m³. 2 ; (2) At least one of BaTiO3, TiO2, and α-SiC is surface-treated with a silane coupling agent.

5. The method for preparing the composite insulating paper according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Disperse BaTiO3, TiO2 and silane coupling agent in a solvent and react. After the reaction, separate the solid and liquid to obtain the solid. After washing and drying, disperse the obtained solid in ester insulating oil to obtain slurry A. Coat slurry A on the surface of cellulose insulating paper substrate. After curing, the insulating paper with a dielectric transition layer on the surface is obtained. S2. Disperse α-SiC and silane coupling agent in ester insulating oil to obtain slurry B. Coat slurry B on the other side of the insulating paper obtained in step S1, opposite to the dielectric transition layer. After curing, composite insulating oil paper is obtained.

6. The method for preparing the composite insulating paper as described in claim 5, characterized in that, Includes at least one of the following (1)-(10): (1) The mass ratio of the silane coupling agent to BaTiO3 in step S1 is (0.01-0.05):1; (2) The silane coupling agent in step S1 includes at least one of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, and n-octyltriethoxysilane; (3) The reaction temperature in step S1 is 40-80℃ and the reaction time is 2-6 h; (4) The solvent in step S1 includes ethanol; (5) The mass percentage of solids in slurry A in step S1 is 2%-10%; (6) The curing in step S1 is carried out at 60-100℃ for 1-3 hours; (7) The mass ratio of the silane coupling agent to α-SiC in step S2 is (0.01-0.03):1; (8) The silane coupling agent in step S2 includes at least one of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, and n-octyltriethoxysilane; (9) The mass percentage of α-SiC in slurry B described in step S2 is 2%-8%; (10) The curing in step S2 is carried out at 60-100℃ for 1-3 hours.

7. An oil-paper insulation system, characterized in that, Includes the composite insulating paper and ester-based insulating oil as described in any one of claims 1-4.

8. The oil-paper insulation system as described in claim 7, characterized in that, It also includes additives, the mass of which accounts for 0.1%-1% of the total mass of the additives and ester insulating oil, and the additives include SiO2.

9. The oil-paper insulation system as described in claim 8, characterized in that, The average particle size of the SiO2 is 10-40 nm.

10. The application of the composite insulating paper according to any one of claims 1-4 or the paper insulation system according to any one of claims 7-9 in a transformer.

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