Transformer insulation pull plate, preparation method and transformer

Abstract

The application discloses a transformer insulation pull plate, a preparation method and a transformer, and belongs to the technical field of transformers. The transformer insulation pull plate is obtained by injection molding or hot press molding of a blended material, and the blended material is formed by mixing BN, PMMA and ZnS, wherein the incorporation amount of the BN is 1wt%-5wt%, and the incorporation amount of the ZnS is 1wt%-10wt%. In the application, the ZnS and the BN cooperate to form a heterojunction interface polarization effect, to improve the dielectric constant while inhibiting the leakage current, and the two can form a rigid-tough balance system to improve the comprehensive mechanical properties. The PMMA, as a transparent polymer matrix, can not only effectively disperse the ZnS nanoparticles and reduce the non-radiation recombination caused by the agglomeration of the ZnS nanoparticles, but also can enhance the radiation light-emitting efficiency of the ZnS. The application can meet the mechanical stability requirements of large-capacity transformers under high-temperature operation conditions, does not have the problem of eddy current loss existing in the steel pull plate, and has a fault visualization function.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of transformers, in particular to a transformer insulation pull plate, a preparation method and a transformer. BACKGROUND

[0002] The transformer insulation pull plate is a key support structure inside the transformer, and its performance directly affects the mechanical stability, insulation reliability and operating efficiency of the transformer. At present, the traditional transformer insulation pull plate mainly adopts epoxy resin or steel material. The epoxy resin material has poor impact resistance and insufficient thermal performance, and its thermal deformation temperature is usually lower than 80℃, which is difficult to meet the mechanical stability requirements of large-capacity transformers under high-temperature (>100℃) operating conditions. The steel pull plate has the problem of eddy current loss, which affects the service life of the insulation system. In addition, the steel pull plate needs to be additionally provided with an insulation layer, which increases the structural complexity and potential failure points.

[0003] Since the transformer is operated in a high-voltage, large-current and complex electromagnetic environment for a long time, the internal insulation system may be deteriorated or failed due to various factors, resulting in the insulation pull plate being electrified. For example, when there are defects in the inter-turn, inter-layer or ground insulation of the winding, partial discharge or even short circuit failure may occur under the action of operating voltage or overvoltage, resulting in strong electric arc and electromagnetic disturbance. Such a fault can form an abnormal electric field near the insulation pull plate. If there is a conductive channel between the fault point and the insulation pull plate, the high potential may be directly conducted to the insulation pull plate. In addition, external shocks such as lightning or operating overvoltage may instantaneously raise the potential at the position of the pull plate, especially when the insulation pull plate is poorly grounded, and the induced voltage cannot be released in time, which will also cause the insulation pull plate to be continuously electrified.

[0004] The existence of the electrified insulation pull plate constitutes a serious operation safety hazard. On the one hand, it may cause discharge, accelerate insulation deterioration, and even evolve into a more serious fault; on the other hand, it poses a high-voltage electric shock risk to subsequent maintenance and repair personnel. However, the existing detection methods have significant defects. The mainstream method is contact detection, which relies on manual contact or close-range detection of the pull plate surface using a high-voltage electroscope under the condition that the equipment is powered off or electrified, which poses a great risk of electric shock and even death and is inefficient. In the non-contact detection method, the sensor is placed outside the tank, and the detection signal needs to penetrate the metal tank wall and the insulation medium, resulting in serious signal attenuation and being strongly affected by external environmental electromagnetic noise and the electromagnetic interference of the transformer body, which leads to low signal-to-noise ratio, poor detection sensitivity and high false alarm rate. Therefore, the present application proposes a transformer insulation pull plate that can meet the mechanical stability of large-capacity transformers under high-temperature operating conditions and has a fault visualization function. SUMMARY

[0005] The application aims to overcome the problems in the prior art, and provides a transformer insulation pull plate, a preparation method and a transformer, which can meet the mechanical stability requirement of a large-capacity transformer under high-temperature operation conditions, does not have the problem of eddy current loss of a steel pull plate, and has a fault visualization function.

[0006] The application provides a transformer insulation pull plate, which is obtained by injection molding or hot-pressing molding of a blended material, wherein the blended material is mixed by BN (boron nitride), PMMA (polymethyl methacrylate) and ZnS (zinc sulfide), the incorporation amount of BN is 1wt%-5wt%, the incorporation amount of ZnS is 1wt%-10wt%, and the rest is PMMA, and as a preferred mode, the BN particles are hexagonal boron nitride with a sheet structure.

[0007] In the application, the high dielectric constant of ZnS can enhance the overall dielectric constant of the composite material through interface polarization, and the wide band gap and high resistivity of h-BN can block the conduction path between ZnS particles and inhibit the leakage current. The two synergistically form a heterojunction interface polarization effect, which can improve the dielectric constant while inhibiting the leakage current, and disperse the electric field through the layered structure of BN to optimize the dielectric stability under high frequency. Under high frequency (kHz-MHz), the dielectric constant (ε r ) of the transformer and the composite material significantly decreases (by 20%-40%) due to polarization hysteresis, and the dielectric loss (tanδ) increases several times due to dipole friction and ion migration; after the addition of BN particles, the dielectric constant of the composite material under high frequency is increased.

[0008] In the application, the ZnS nanoparticles improve the rigidity and compressive strength of the material through the load transfer effect, and at the same time, inhibit the polymer chain slippage to improve the yield strength; and the h-BN sheet layer enhances the toughness through crack deflection, interlayer slippage energy absorption and lubrication effect to improve the impact performance and processing fluidity. After the combination of the two, a rigid-tough balanced system is formed, so as to synergistically improve the comprehensive mechanical properties of the material. In the application, the ZnS improves the rigidity through the load transfer effect and anchors the PMMA molecular chain to inhibit slippage, and the h-BN improves the processing fluidity through sheet layer slippage induced crack deflection and lubrication effect; the two together construct a "rigid domain-flexible interface" interpenetrating network, the ZnS disperses the stress concentration point, the h-BN absorbs the crack propagation energy, and the brittle fracture tendency of PMMA is synergistically inhibited, so as to realize the triple optimization of strength, toughness and processability.

[0009] In the application, ZnS is a direct band gap semiconductor, under ultraviolet light or electric field excitation, the valence band electrons of ZnS jump to the conduction band, and then release energy through radiative recombination to produce characteristic luminescence. PMMA is a transparent polymer matrix, which can not only effectively disperse ZnS nanoparticles and reduce the non-radiative recombination caused by the agglomeration of ZnS nanoparticles, but also can limit the carrier migration through its insulating property to enhance the radiative luminescence efficiency of ZnS.

[0010] As a preferred mode, the PMMA purity is ≥ 99%; the particle size of the BN particles is 1-30 μm; the particle size of the ZnS particles is ≤ 20 nm, and the BN particles and the ZnS particles are uniformly dispersed in the blended material.

[0011] The BN particles and the BN particles of the present application are both small in particle size, which promotes uniform dispersion of the particles in the matrix and strong interface bonding, significantly improves dielectric performance, enhances breakdown performance due to uniform dispersion, and optimizes mechanical performance.

[0012] As a preferred mode, the thickness of the transformer insulation pull plate structure is 20-50 mm.

[0013] The second object of the present application is to provide a preparation method of a transformer insulation pull plate, comprising the following steps:

[0014] The BN particles, ZnS particles and PMMA particles are dried at 80-120℃ for 2-6 h;

[0015] After the dried PMMA particles are dissolved in DMF, the BN particles and the ZnS particles are added in sequence, and mechanical stirring and mixing are performed to form a blended material; the blended material is injection molded or hot-pressed into a transformer insulation pull plate.

[0016] The purpose of the drying treatment of the BN particles, ZnS particles and PMMA particles of the present application is to completely remove moisture and organic solvent residues adsorbed on the surfaces of the BN particles, ZnS particles and PMMA particles, so as to avoid the generation of bubbles, pores or interface delamination in the material due to water vaporization during subsequent processing.

[0017] As a preferred mode, the mechanical stirring and mixing is first stirred at a low speed of 100 rpm for 30 min, and then the stirring speed is increased to 300 rpm for high-speed stirring for 1 h.

[0018] The third object of the present application is to provide a transformer comprising any one of the above transformer insulation pull plates.

[0019] As a preferred mode, the transformer is a dry-type transformer.

[0020] As a preferred mode, the working temperature range of the transformer insulation pull plate is -40-128℃, and the deformation rate under long-term load is < 1%.

[0021] Compared with the prior art, the present application has the following beneficial effects:

[0022] This invention prepares a PMMA-based composite material by doping micron-sized BN particles (1μm-30μm) and nano-sized ZnS particles (≤20nm). This PMMA-based composite material is then injection-molded or hot-pressed into transformer insulation tabs. The ZnS and BN particles combine to create a heterogeneous interfacial polarization effect, which improves the dielectric constant while suppressing leakage current. The BN layered structure disperses the electric field, optimizing dielectric stability at high frequencies. The two together form a rigid-tough balance, enhancing the material's overall mechanical properties. PMMA, as a transparent polymer matrix, not only effectively disperses the ZnS nanoparticles, reducing their agglomeration-induced non-radiative recombination, but also limits carrier migration through its insulating properties, enhancing the radiative luminescence efficiency of the ZnS. The PMMA-based composite material, when used in transformer tabs, produces lower losses than conventional steel tabs and, compared to conventional epoxy resin tabs, meets the mechanical stability requirements of large-capacity transformers operating under high-temperature (>100°C) conditions.

[0023] The thermal deformation temperature of the transformer insulation pull plate of the present invention is increased to ≥100° C., and the dielectric constant is ≥5, thereby improving the charge storage capacity per unit volume and avoiding a surge in loss caused by an excessively high dielectric constant.

[0024] The transformer insulation pull plate of the present invention has added a fault visualization detection function. When the transformer insulation pull plate is electrified due to various factors, the zinc ions or sulfur vacancies in the ZnS crystal undergo directionally migration due to the electrical stress, causing local lattice distortion and band structure changes, thereby changing its optical band gap, causing the material to change color and emit light, thereby causing the corresponding part of the transformer insulation pull plate to emit light and change color, realizing visual fault detection.

[0025] The transformer insulation pull plate of the present invention can be directly injection molded or hot-pressed into a transformer insulation pull plate with a thickness of 20 mm to 50 mm. The overall structure is integrally molded, which can better adapt to the transformer winding support requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a diagram showing the dielectric constant data of pure PMMA material according to an embodiment of the present invention.

[0027] Figure 2 This is a graph showing the dielectric constant data of a composite material of PMMA doped with 1 wt% BN according to an embodiment of the present invention.

[0028] Figure 3 This is a graph showing the dielectric constant data of a composite material of PMMA doped with 1 wt% BN and 1 wt% ZnS according to an embodiment of the present invention.

[0029] Figure 4Weibull distribution diagram of AC breakdown field strength of PMMA composite material doped with BN of different concentrations according to an embodiment of the present application.

[0030] Figure 5 Weibull distribution diagram of AC breakdown field strength of PMMA composite material doped with BN and ZnS of different concentrations according to an embodiment of the present application.

[0031] Figure 6 Tensile data result diagram of PMMA composite material doped with BN of different concentrations according to an embodiment of the present application.

[0032] Figure 7 Tensile data result diagram of PMMA composite material doped with BN and ZnS of different concentrations according to an embodiment of the present application.

[0033] Figure 8 Thermal deformation temperature of PMMA composite material doped with BN and ZnS of different concentrations compared with thermal deformation temperatures of other materials according to an embodiment of the present application.

[0034] Figure 9 Loss simulation result diagram of PMMA composite material as a transformer tension plate according to an embodiment of the present application.

[0035] Figure 10 Loss simulation result diagram of traditional steel tension plate according to an embodiment of the present application.

[0036] Figure 11 Appearance of PMMA sample doped with ZnS before power-on according to an embodiment of the present application.

[0037] Figure 12 Appearance of PMMA sample doped with ZnS after power-on according to an embodiment of the present application.

[0038] Figure 13 Chroma diagram of light emission of PMMA composite material before and after power-on according to an embodiment of the present application. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions of the embodiments of the present application will be described clearly and completely below with reference to the drawings of the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the described embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without any creative effort fall within the scope of protection of the present application. In the description of the present application, if not specifically stated, the used reagents are commercially available, and the used methods are conventional techniques in the art.

[0040] At present, the transformer insulation pull plate made of insulating material may cause the surface insulation resistance to decrease due to long-term damp, dust or oil stain, especially in a humid environment, water infiltration may form a conductive channel. The aging or mechanical damage of the insulating material may also destroy its insulation capacity, so that the transformer insulation pull plate is induced to be charged under the action of an electric field or directly contacts a charged component to be conducted. If the transformer suffers from a sudden short-circuit fault during operation, a strong electrodynamic force may be generated by a huge short-circuit current, which may cause the transformer insulation pull plate to be mechanically displaced or deformed, so that the insulation distance between the transformer insulation pull plate and the charged component is reduced or even directly contacted, thereby conducting high voltage. The transient overvoltage during short-circuit may charge the transformer insulation pull plate through capacitive coupling, and if the insulating material is damaged due to mechanical impact, the discharge risk will be further aggravated, finally leading to abnormal charging of the transformer insulation pull plate, which threatens the safety of equipment and people. As a kind of polymer material with excellent dielectric properties and mechanical strength, polymethyl methacrylate (PMMA) can be theoretically applied to the transformer insulation pull plate. However, pure PMMA has the following technical bottlenecks: 1. Insufficient heat resistance, the heat distortion temperature is only 80-85℃, which cannot meet the long-term high-temperature operation requirement of large-capacity transformers; 2. Limited mechanical and electrical properties, the fracture toughness, bending strength and breakdown field strength of pure PMMA are low, which is difficult to withstand the mechanical and electrical stress under the complex working conditions inside the transformer. 3. No visual detection function, the detection of the charged insulation pull plate relies on contact detection or non-contact detection method, which has the problems of low detection efficiency and poor sensitivity.

[0041] In view of the above problems, the present application provides a PMMA composite material based on ZnS microparticles and BN nanoparticles synergistic enhancement, which can significantly improve the heat resistance, mechanical strength and insulation performance of the material by optimizing the dispersion and interface combination of the fillers, and can visually detect some transformer faults, so as to meet the comprehensive performance requirements of the insulation pull plate for high-voltage and large-capacity transformers.

[0042] Embodiment 1

[0043] The transformer insulation pull plate of the present embodiment is obtained by injection molding or hot pressing molding of a blended material, which is obtained by mixing BN, PMMA and ZnS, wherein the incorporation amount of BN is 1wt%, the incorporation amount of ZnS is 2wt%, and the rest is PMMA; the PMMA selected in the present embodiment has a purity of ≥99%; the particle size of the BN particles is 5μm; the particle size of the ZnS particles is ≤20nm; and the BN particles are hexagonal boron nitride with a sheet structure.

[0044] The preparation method of the transformer insulation pull plate of the present embodiment comprises the following steps:

[0045] The BN particles, ZnS particles and PMMA (polymethyl methacrylate) particles are dried at 100℃ for 2h;

[0046] After the dried PMMA particles are dissolved in DMF (N, N-dimethylformamide), the BN particles and the ZnS particles are sequentially added, and mechanical stirring and mixing are performed to form a blended material; the mechanical stirring and mixing is first performed at a low speed of 100 rpm for 30 min, and then the stirring speed is increased to 300 rpm for high-speed stirring for 1 h; the blended material is injection molded or hot-pressed into a transformer insulation pull plate.

[0047] In all the embodiments of the present application, the thickness of the transformer insulation pull plate is 20 mm to 50 mm.

[0048] Embodiment 2

[0049] The transformer insulation pull plate of the present embodiment is obtained by injection molding or hot-pressing a blended material composed of BN, PMMA and ZnS, wherein the incorporation amount of BN is 3 wt%, the incorporation amount of ZnS is 10 wt%, and the rest is PMMA; the PMMA selected in the present embodiment has a purity of ≥ 99%; the particle size of the BN particles is 20 μm; the particle size of the ZnS particles is ≤ 20 nm; and the BN particles are hexagonal boron nitride with a sheet structure.

[0050] The preparation method of the above-mentioned transformer insulation pull plate of the present embodiment comprises the following steps:

[0051] The BN particles, the ZnS particles and the PMMA (polymethyl methacrylate) particles are dried at 80°C for 5 h;

[0052] After the dried PMMA particles are dissolved in DMF (N, N-dimethylformamide), the BN particles and the ZnS particles are sequentially added, and mechanical stirring and mixing are performed to form a blended material; the mechanical stirring and mixing is first performed at a low speed of 100 rpm for 30 min, and then the stirring speed is increased to 300 rpm for high-speed stirring for 1 h; the blended material is injection molded or hot-pressed into a transformer insulation pull plate.

[0053] Embodiment 3

[0054] The transformer insulation pull plate of the present embodiment is obtained by injection molding or hot-pressing a blended material composed of BN, PMMA and ZnS, wherein the incorporation amount of BN is 5 wt%, the incorporation amount of ZnS is 7 wt%, and the rest is PMMA; the PMMA selected in the present embodiment has a purity of ≥ 99%; the particle size of the BN particles is 10 μm; the particle size of the ZnS particles is ≤ 20 nm; and the BN particles are hexagonal boron nitride with a sheet structure.

[0055] The preparation method of the above-mentioned transformer insulation pull plate of the present embodiment comprises the following steps:

[0056] The BN particles, the ZnS particles and the PMMA (polymethyl methacrylate) particles are dried at 100°C for 4 h;

[0057] After the dried PMMA particles are dissolved in DMF (N,N-dimethylformamide), the BN particles and the ZnS particles are sequentially added, and mechanical stirring and mixing are performed to form a blended material; the mechanical stirring and mixing is first performed at a low speed of 100 rpm for 30 min, and then the stirring speed is increased to 300 rpm for high speed stirring for 1 h; the blended material is injection molded or hot pressed into a transformer insulation pull plate.

[0058] Example 4

[0059] The transformer insulation pull plate of the present example is obtained by injection molding or hot pressing of a blended material composed of BN, PMMA and ZnS, wherein the incorporation amount of BN is 3 wt%, the incorporation amount of ZnS is 8 wt%, and the rest is PMMA; the PMMA selected in the present example has a purity of ≥99%; the particle size of the BN particles is 15 μm; the particle size of the ZnS particles is ≤20 nm; and the BN particles are hexagonal boron nitride with a sheet structure.

[0060] The preparation method of the transformer insulation pull plate of the present example comprises the following steps:

[0061] The BN particles, the ZnS particles and the PMMA (polymethyl methacrylate) particles are dried at 120°C for 5 h;

[0062] After the dried PMMA particles are dissolved in DMF (N,N-dimethylformamide), the BN particles and the ZnS particles are sequentially added, and mechanical stirring and mixing are performed to form a blended material; the mechanical stirring and mixing is first performed at a low speed of 100 rpm for 30 min, and then the stirring speed is increased to 300 rpm for high speed stirring for 1 h; the blended material is injection molded or hot pressed into a transformer insulation pull plate.

[0063] In order to further demonstrate the advantages of the transformer insulation pull plate in the above examples in terms of temperature resistance, dielectric properties, tensile properties, breakdown field strength and luminous efficiency, the present application will be described in detail in combination with experimental examples, as follows:

[0064] Experimental Example

[0065] The preparation method of the PMMA composite functional film doped with BN of different concentrations in the present experimental example is as follows:

[0066] PMMA particles with a purity of ≥99% are selected, hexagonal boron nitride (h-BN) with a particle size of 1 μm-30 μm and a purity of ≥99.5% is selected, and analytical pure DMF (N,N-dimethylformamide) is selected as the solvent;

[0067] 1 g of h-BN particles was added into 100 mL of isopropyl alcohol, and a probe-type ultrasonic instrument was used for treatment for 30 minutes, and then water bath ultrasonic treatment was performed for 1 hour, to finally obtain a uniform and stable BN composite dispersion liquid with a concentration of 10 mg / mL.

[0068] 10 g of PMMA particles were dissolved in 100 mL of DMF, and magnetic stirring was performed at 60 °C under oil bath conditions for 2 hours until complete dissolution. BN dispersion liquid was added in proportions of 1 wt%, 2 wt%, 3 wt% and 4 wt% of BN based on the mass of PMMA, and stirring was continued for 1 hour, followed by ultrasonic treatment for 30 minutes.

[0069] A casting film forming method was used, the composite solution was poured onto a polished glass plate placed horizontally, an automatic film scraper was used to control the wet film thickness, and the film was first pre-dried in a 80 °C air oven for 1 hour, and then transferred into a 120 °C vacuum oven for curing for 2 hours. After natural cooling to room temperature, the film was demolded, and composite films with 1 wt%, 2 wt%, 3 wt% and 4 wt% of BN based on the mass of PMMA were obtained, respectively.

[0070] The preparation method of the PMMA composite functional film with uniform BN-ZnS distribution in the experimental example is as follows:

[0071] 1 g of h-BN particles was added into 100 mL of isopropyl alcohol for dispersion, and 1 g of ZnS particles (particle size 20 nm, purity 99.5%) was simultaneously added, and then a three-stage dispersion method was used for treatment;

[0072] First, 500 W probe ultrasonic treatment was performed for 15 minutes to fully break up the ZnS agglomerates;

[0073] Then, 0.1 g of sodium dodecyl sulfate (SDS) was added as a dispersant to improve the stability of the system;

[0074] Then, 60 °C water bath ultrasonic treatment was performed for 2 hours, to finally obtain a uniform and stable BN-ZnS composite dispersion liquid. The PMMA base liquid was still prepared by dissolving 10.0 g of PMMA particles in 100 mL of DMF and performing magnetic stirring at 60 °C under oil bath conditions for 2 hours until complete dissolution.

[0075] The obtained uniform and stable BN-ZnS composite dispersion liquid was added into the PMMA base liquid to obtain a two-component doped composite dispersion liquid. It should be understood that, on the basis of obtaining a uniform and stable BN-ZnS composite dispersion liquid, different doping concentrations of PMMA composite dispersion liquid can be obtained by adjusting the addition amount of BN and ZnS;

[0076] The PMMA composite dispersion liquid is then mixed by gradient stirring method. First, low-speed stirring at 100 rpm is performed for 30 minutes to prevent the ZnS nanoparticles from settling, and then the stirring speed is increased to 300 rpm for high-speed stirring for 1 hour to ensure uniform dispersion of the components. Finally, the uniformly mixed composite solution is poured onto a polished glass substrate treated by plasma through a flow casting process, an automatic film scraper is used to control the wet film thickness, the filler distribution is first locked by UV pre-curing, and then curing is performed by a stepwise temperature program. After demolding, the film is treated by Ar plasma on both sides to obtain a composite functional film with uniform BN-ZnS distribution.

[0077] The preparation method of the pure PMMA composite functional film in the experimental example is as follows:

[0078] PMMA particles with a purity of ≥99% are selected, and analytical pure DMF (N,N-dimethylformamide) is selected as the solvent. 10 g of PMMA particles are dissolved in 100 mL of DMF, and magnetic stirring is performed at 60°C for 2 hours until complete dissolution. A flow casting method is used to pour the PMMA solution onto a horizontally placed polished glass plate, an automatic film scraper is used to control the wet film thickness, and then pre-drying is performed at 80°C in a blowing oven for 1 hour, followed by curing in a 120°C vacuum oven for 2 hours. After natural cooling to room temperature, the film is demolded to obtain a pure PMMA composite functional film.

[0079] The preparation method of the PMMA composite functional film with uniform ZnS distribution in the experimental example is as follows:

[0080] First, ZnS nanoparticles with a particle size of 20 nm are surface modified by a silane coupling agent (such as KH-550) to improve dispersibility, and then dissolved in DMF solvent together with PMMA by magnetic stirring for 2-4 hours to form a uniformly mixed solution. Then, a flow casting method is used to pour the PMMA solution onto a horizontally placed polished glass plate, an automatic film scraper is used to control the wet film thickness, and finally the solvent is removed and the density is enhanced by a stepwise curing process. It should be understood that PMMA composite functional films with different doping concentrations can be obtained by adjusting the amount of ZnS nanoparticles added.

[0081] The performance of each PMMA composite film obtained above is also tested in the experimental example, wherein, Figures 1-3is the embodiment of broadband dielectric impedance spectroscopy technology, using the concept of 80 type broadband dielectric impedance spectrometer (manufactured by Germany Novocontrol technologies company) for PMMA composite film sample dielectric constant and dielectric loss measurement, including the frequency response at room temperature and the temperature response at a specific frequency. In order to ensure the accuracy of the measurement results, 0.1 mm thick PMMA film sample is selected for testing, and the sample is pretreated, including measuring and recording the thickness, using anhydrous ethanol cleaning and drying in a vacuum oven at 60 DEG C for 12 hours. Then the ion sputtering technology is used to coat the silver electrode with a diameter of 30 mm and 40 mm on both sides of the film. In the test process, an additional electrode is added on both sides of the sample to ensure good contact with the instrument electrode. The test conditions of frequency response at room temperature are: 1V voltage, frequency range is 1Hz to 106Hz: the temperature test conditions of specific frequency are: 1V voltage, frequency is fixed at 1kHz, temperature rises from 20 DEG C to 100 DEG C, and the temperature rising rate is 5K / min. After the measurement, a point of data is collected from the continuous temperature spectrum every 5 DEG C for chart analysis.

[0082] Figures 4-5 The electric breakdown test device manufactured by Huayang mechanical and electrical equipment Co., Ltd. is used to test the DC AC breakdown strength of PMMA composite film under different doping ratios. The 25 mu m thick sample is used for electric breakdown test, and the sample with smooth surface and uniform thickness is selected before the experiment. The sample is cleaned with anhydrous ethanol and then dried in a vacuum oven at 60 DEG C for 12h to eliminate the possible influence of humidity on electric breakdown strength. The experimental parameters such as voltage rising speed and range can be directly set by software. Ensure that the electrode is connected correctly and grounded, the sample is placed between the two copper ball electrodes, the electrodes are aligned to reduce deviation, and the electrodes are completely immersed in transformer oil to eliminate the electric breakdown effect in the air. Ensure that the operation area is free of people before starting the test, and immediately turn off the power after breakdown, use the discharge rod to eliminate residual charge, and record the breakdown voltage value displayed on the computer. At least 20 times of breakdown test is carried out on different positions of the sample to ensure the accuracy of the data. Use heat insulation gloves when replacing the sample, and the rest of the steps are similar to the normal temperature test.

[0083] Figures 6-7 is cut into 210 mm x 20 mm tensile test piece according to GB / T1447-2005, and the tensile mechanical property test is carried out under the microcomputer control electronic universal testing machine with 5mm / min loading rate, and the average value is obtained by repeating test 4 times for each group.

[0084] Figure 8The material to be tested is processed into a long strip specimen with a standard size of 125mm×10mm. Under the microcomputer-controlled heat deformation temperature tester, a constant bending load of 0.45MPa is applied, and the oil bath temperature is increased at a uniform rate of 120℃ / h. The temperature when the bending deformation of the specimen reaches the specified value is recorded. Each group of tests is repeated 4 times and the average value is taken to obtain the heat deformation temperature of the material.

[0085] in, Figure 1 This is the dielectric constant data diagram of pure PMMA material. Figure 2 The dielectric constant data of PMMA doped with 1wt% BN composite material is shown in Figure 2. Figure 1 and Figure 2 It can be seen that at a specific frequency, such as 10 -1 At 10 Hz, it can be seen that with increasing temperature, the dielectric constant of pure PMMA films gradually increases from 4.5 to 5.5, while that of PMMA composite films doped with 1 wt% BN increases from 6.0 to 8.0. As the temperature rises, the mobility of the polymer chain segments increases, and the highly polar ester groups (-COOCH) on the side chains gain greater rotational freedom due to thermal fluctuations, significantly enhancing the dipole rotation polarization. Simultaneously, the expansion of the material's internal free volume reduces intermolecular constraints, promoting the accumulation of space charge at the amorphous interface. The dynamic dissociation of the hydrogen bond network also releases more polar groups to participate in the polarization response. Especially below the glass transition temperature, the rigidity of the main chain hinders dipole motion at low temperatures. However, increasing temperature activates localized segmental cooperative orientation, resulting in a unique positive temperature dependence of the dielectric constant. At a specific temperature, such as 20°C, the dielectric constant of pure PMMA films gradually decreases from 4.5 to 3.0 with increasing frequency, while the dielectric constant of the PMMA composite film doped with 1 wt% BN increases from 6.0 to 4.0. As the electric field frequency increases, dipole steering needs to overcome intermolecular forces and the viscous resistance of chain segment motion. Its steering speed cannot keep up with the rapidly changing electric field, resulting in a delayed or even frozen dipole polarization response. At the same time, the high-frequency electric field shortens the time window for space charge accumulation at the amorphous interface, hindering the full establishment of interfacial polarization. Furthermore, the dynamic response of the hydrogen bond network within the material is suppressed at high frequencies, further weakening the polarization contribution. This ultimately manifests as a relaxation phenomenon in which the dielectric constant decreases significantly with increasing frequency.

[0086] At a specific temperature and frequency, such as 10 -1Hz, 20℃, the relative dielectric constant of the composite material rises from 4.5 to 6.0 with the incorporation of BN particles. This change is mainly due to the interface polarization and dipole synergy effect. BN nanosheet has a two-dimensional layered structure, its introduction will form a large number of heterogeneous interfaces in the PMMA matrix. Due to the difference in dielectric constant between BN and polymer and the interface energy barrier, the migration of charge carriers (such as ions and electrons) is hindered under alternating electric field, resulting in strong interface polarization, and a macroscopic dipole layer is formed at the interface. At the same time, the unsaturated dangling bonds on the surface of BN and the strong polar ester groups of PMMA side chains form a localized dipole network through hydrogen bonding or dipole-dipole interaction. These dynamic dipoles are more likely to be oriented under an external electric field, significantly enhancing the dipole polarization response. In addition, the two-dimensional confinement effect of BN forces adjacent polymer chains to arrange in the interface region, exposing more polar groups and reducing their rotation barrier. The wide band gap characteristics of BN inhibit the leakage loss, so that the polarization contribution dominates the dielectric response. The above-mentioned multiple coupling mechanisms of interface polarization, dipole synergy and structural ordering ultimately lead to a significant increase in the dielectric constant of the composite material at low doping levels.

[0087] Figure 3 The dielectric constant data graph of the composite material of PMMA doped with 1wt% BN and 1wt% ZnS is shown in FIG. 2. Through Figure 3 It can be seen that at a certain frequency, such as 10 -1 Hz, it can be found that the dielectric constant of the composite film gradually increases with the increase of temperature. At a certain temperature, such as 20℃, the dielectric constant of the composite film gradually decreases with the increase of frequency. Compared with the dielectric constant of pure PMMA and the dielectric constant of the composite film doped with BN particles only, the dielectric constant of the composite film doped with BN+ZnS particles is the largest at the same temperature and frequency. This is because BN as an insulating filler can improve the dielectric constant of the matrix, and ZnS as a wide band gap semiconductor induces interface charge migration under alternating electric field, forming a strong local electric field at the PMMA / ZnS and BN / ZnS interfaces through Maxwell-Wagner-Sillars interface polarization; at the same time, BN sheet and ZnS particles construct a micro-capacitance network structure, which significantly enhances the space charge polarization strength.

[0088] Figure 4 The weibull distribution graph of the AC breakdown field strength of the composite material of PMMA doped with different concentrations of BN is shown in FIG. 4. Through Figure 4It can be found that with the incorporation of BN microparticles, the breakdown field strength of the PMMA composite film presents a non-monotonic change trend of first increasing and then decreasing, and the essence of this phenomenon is the synergistic regulation of BN doping concentration on the microstructure and dielectric properties of the composite material. In the stage of incorporating low concentration BN, the BN two-dimensional sheet structure forms a physical barrier network through uniform dispersion, effectively inhibits the growth path of electrical treeing, and dissipates local Joule heat quickly through high thermal conductivity, delaying the thermal breakdown process. At the same time, the polar groups on the surface of BN form interface dipole interaction with the ester groups of PMMA molecular chain, homogenize the electric field distribution and introduce deep trap energy level, significantly inhibit the Schottky emission or Frenkel-Poole transition of carriers, thereby improving the intrinsic breakdown field strength.

[0089] Figure 5 The Weibull distribution diagram of the AC breakdown field strength of the PMMA composite material doped with different concentrations of BN and ZnS is shown in Figure 2. Figure 5 It can be seen that the breakdown field strength of the composite film after incorporating BN and ZnS particles is significantly improved compared with that of the pure PMMA film. This is because the BN nanosheet prolongs the breakdown path and inhibits the development of electrical treeing through physical barrier effect, and the ZnS particles form deep energy level traps at the interface to capture high-energy carriers, relieve electric field distortion, and at the same time, the high thermal conductivity of BN quickly dissipates Joule heat, combined with the enhanced interfacial bonding force of ZnS / PMMA interface chemical bond, which synergistically blocks the initiation channels of electrical breakdown and thermal breakdown, so that the breakdown field strength of the composite film is improved.

[0090] Figure 6 The tensile data result graph of the PMMA composite material doped with different concentrations of BN according to the embodiment of the application is shown in Figure 3. Figure 6 The horizontal coordinate represents the fraction, 1 fraction means the content of 1wt% BN, and the vertical coordinate represents the tensile strength and elastic modulus of the composite film. Figure 6 It can be seen that with the increase of BN content, the tensile strength and elastic modulus of the PMMA composite film gradually increase, and the moderate increase of tensile strength and elastic modulus can significantly improve the material's resistance to deformation and fracture, while maintaining the structural stability.

[0091] Figure 7 The tensile data result graph of the PMMA composite material doped with different concentrations of BN and ZnS is shown in Figure 4. Figure 7 The horizontal coordinate represents the fraction, 1 fraction means the content of 1wt% BN and 1wt% ZnS, and 2 fraction means the content of 2wt% BN and 2wt% ZnS. The vertical coordinate represents the tensile strength and elongation at break of the composite film. Figure 7 It can be seen that with the increase of BN and ZnS content, the tensile strength of the PMMA composite film gradually increases, and the elongation at break gradually decreases. The moderate increase of tensile strength can significantly improve the material's resistance to deformation and fracture, while maintaining the structural stability, and the moderate decrease of elongation at break can effectively inhibit the plastic deformation of the material under stress.

[0092] Figure 8 The thermal deformation temperature of the PMMA composite material doped with different concentrations of BN and ZnS is compared with other materials, and it can be found from the figure that the thermal deformation temperature of the epoxy resin material is 72 DEG C, the thermal deformation temperature of the pure PMMA material is 88 DEG C, the thermal deformation temperature of the PMMA composite material after adding 5wt% BN is 109 DEG C, and the thermal deformation temperature of the PMMA composite material after adding 5wt% BN and 10wt% ZnS is 128 DEG C, and the experimental results show that doping BN and ZnS significantly improves the thermal deformation temperature of the PMMA composite material, from 88 DEG C of the pure PMMA to 128 DEG C, which is much higher than 72 DEG C of the epoxy resin, and the composite material has more excellent thermal performance than the traditional epoxy resin material.

[0093] The loss generated by the PMMA composite material doped with BN and ZnS of the application as a transformer pull plate is as shown in Figure 9 The loss generated by the ordinary steel pull plate as a transformer pull plate is as shown in Figure 10 As can be seen from the simulation, the loss generated by the ordinary steel pull plate is much larger than the loss generated by the PMMA composite material doped with BN and ZnS of the application. This is because PMMA is an insulating material and almost no eddy current loss is generated, while steel as a conductor will form significant eddy current loss and hysteresis loss in a high-frequency alternating magnetic field.

[0094] The luminescence and color change before and after applying an electric field in the embodiment are as shown in Figure 11 and Figure 12 The chromaticity diagram of the luminescence before and after power-on is as shown in Figure 13 As can be seen from the chromaticity diagram, the color of the film changes from white to blue-green before and after luminescence, which reflects the luminescence and color change phenomenon.

[0095] Through testing, the power frequency dielectric loss of the PMMA composite material doped with BN and ZnS in the embodiment is 0.058, the power frequency dielectric constant is 6.7, and the alternating current breakdown field strength is 226kV / mm.

[0096] Although the embodiments of the application have been shown and described, it can be understood by those skilled in the art that various changes, modifications, replacements and variations can be made to the embodiments without departing from the principles and spirits of the application, and the scope of the application is defined by the appended claims and their equivalents.

Claims

1. A transformer insulation pull plate, characterized by: The composite material is obtained by injection molding or hot pressing, wherein the composite material is a mixture of BN particles, PMMA particles and ZnS particles, wherein the amount of BN particles added is 1wt% to 5wt%, the amount of ZnS particles added is 1wt% to 10wt%, and the rest are PMMA particles, wherein the BN particles are lamellar hexagonal boron nitride.

2. The transformer insulation pull plate according to claim 1, characterized in that: The PMMA particles have a purity of ≥99%; the BN particles have a particle size of 1 μm-30 μm; the ZnS particles have a particle size of ≤20 nm, and the BN particles and the ZnS particles are uniformly dispersed in the blended material.

3. The transformer insulation pull plate according to claim 1, characterized in that: The thickness of the transformer insulation pull plate is 20mm-50mm.

4. The method for preparing a transformer insulating plate according to any one of claims 1 to 3, characterized in that: The following steps are involved: Drying the BN particles, ZnS particles and PMMA particles at 80°C-120°C for 2h-6h; After the dried PMMA particles are dissolved in DMF, BN particles and ZnS particles are added in sequence, and mechanically stirred and mixed to form a blended material; the blended material is injection molded or hot-pressed into a transformer insulation pull plate.

5. The method for preparing the transformer insulating plate according to claim 4, wherein: The mechanical stirring and mixing was performed by first stirring at a low speed of 100 rpm for 30 minutes, and then increasing the stirring speed to 300 rpm and continuing high-speed stirring for 1 hour.

6. A transformer, characterized in that: A transformer insulating pull plate comprising the method according to any one of claims 1 to 4.

7. The transformer according to claim 6, characterized in that The transformer is a dry-type transformer.

8. The transformer according to claim 6, characterized in that The operating temperature range of the transformer insulation pull plate is -40°C to 128°C, and the deformation rate under long-term load is less than 1%.

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