Microfluidic technology-based microcosmic simulation method for oil-paper insulation dampness

Abstract

The application relates to an oil-paper insulation damp microcosmic simulation method based on microfluidic technology and belongs to the electrical technical field. Based on the microfluidic technology, a microfluidic chip with a microfluid channel is prepared to simulate the micron-level capillary channel environment in insulation paper, and in combination with external pressure pumps, heating tables, microscopes and other equipment, the macroscopic preparation process of the existing oil-paper insulation damp simulation method, namely, vacuum drying, vacuum oil immersion and moisture absorption treatment processes of insulation oil and insulation paper, is changed into corresponding microcosmic operations suitable for being carried out on the microfluidic chip, so that an oil-paper insulation damp microcosmic simulation method is formed, and the method has the advantages of less oil sample consumption, rapid treatment, micron-scale precision controllability and observability.

Description

Technical Field

[0001] This invention belongs to the field of electrical technology and relates to a microscopic simulation method for moisture absorption of oil-paper insulation based on microfluidic technology. Background Technology

[0002] Oil-paper insulation is a major component of the insulation in electrical equipment such as oil-immersed transformers, oil-immersed high-voltage bushings, and oil-immersed instrument transformers. Oil-paper insulation equipment accounts for a large proportion of power grid equipment and plays a vital role. Oil-paper insulation is a form of insulation formed by impregnating insulating paper in insulating oil. The insulating paper is composed of cellulose fibers, which are interwoven, creating unfilled cavities that form a porous structure with pore sizes ranging from tens to hundreds of micrometers. After impregnation, the capillary channels in the paper are fully filled with insulating oil, forming oil-paper insulation. Due to the combined effects of prolonged mechanical pressure, chemical corrosion, operating voltage, and moisture, the performance of oil-paper insulation gradually deteriorates, potentially leading to insulation breakdown and equipment failure. In particular, improper maintenance can cause external moisture to enter the high-voltage electrical equipment, resulting in dampness in the oil-paper insulation. This moisture is absorbed into the capillaries between the insulating paper fibers, causing a significant decrease in the macroscopic electrical performance of the oil-paper insulation, becoming a primary cause of equipment failure.

[0003] Therefore, studying the moisture absorption process of oil-paper insulation, the changes in electrical strength after moisture absorption, and diagnostic methods for the degree of moisture absorption in oil-paper insulation are hot engineering issues and important needs in this field. The fundamental premise is to use appropriate methods in the laboratory to artificially simulate the moisture absorption conditions of oil-paper insulation under controllable conditions, thereby preparing oil-paper insulation samples with different degrees of moisture absorption for subsequent experimental and theoretical research. Existing artificial moisture absorption simulation methods for oil-paper insulation all use oil-impregnated insulating paperboard of a certain size and shape. By exposing the paperboard to a humid space, it is allowed to naturally absorb moisture, and the weight difference before and after moisture absorption is obtained by weighing, thus preparing oil-impregnated insulating paperboard samples with different trace moisture contents. However, the macroscopic moisture absorption phenomenon of oil-paper insulation and the other macroscopic electrical performance changes it causes are all rooted in the physical processes occurring within the capillary space of the insulating paper. Existing methods for simulating moisture absorption in oil-paper insulation are macroscopic experiments, which cannot directly and precisely control or visualize the behavior of moisture at the micrometer scale in the capillaries of the insulating paper. This prevents experimental research on moisture absorption in oil-paper insulation at the micropore scale, thus hindering further theoretical understanding of the problem. To address this issue, this invention, based on microfluidic technology, uses a microfluidic chip with microchannels to simulate the micrometer-scale capillary environment in insulating paper. Combined with external pressure pumps, heating stages, microscopes, and other equipment, the macroscopic preparation process of existing oil-paper insulation moisture absorption simulation methods—vacuum drying of insulating oil and insulating paper, vacuum impregnation, and moisture absorption—is modified to be suitable for corresponding microscopic operations on a microfluidic chip. This forms a microscopic simulation method for oil-paper insulation moisture absorption, which has the advantages of low oil sample consumption, rapid processing, and precise control and observation at the micrometer scale. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a microscopic simulation method for moisture absorption in oil-paper insulation based on microfluidic technology. Addressing the issue that existing methods for simulating moisture absorption in oil-paper insulation are macroscopic experimental methods, unable to directly and precisely control or visually observe the moisture behavior at the micrometer scale of the capillary pores in the damp oil-paper insulation, this invention, based on microfluidic technology, simulates the micrometer-scale capillary pore environment in the insulating paper by fabricating a microfluidic chip with microchannels. Combined with external pressure pumps, heating stages, microscopes, and other equipment, the macroscopic preparation process of existing oil-paper insulation moisture absorption simulation methods—vacuum drying of insulating oil and insulating paper, vacuum impregnation, and moisture absorption treatment—is modified to be suitable for corresponding microscopic operations performed on a microfluidic chip. This forms a complete microscopic simulation method for moisture absorption in oil-paper insulation, with advantages such as low oil sample consumption, rapid processing, and precise control and observation at the micrometer scale.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A microscopic simulation method for moisture absorption in oil-paper insulation based on microfluidics technology, comprising the following steps:

[0007] S1 uses polydimethylsiloxane as the fluid layer of the microfluidic chip. Microchannels with rectangular cross-sections are fabricated on the fluid layer, with a width and depth ranging from 0 to 100 μm. After fabrication, a plasma cleaner is used to perform plasma cleaning on the inner surface of the channels and the surface of the fluid layer to make the channel walls hydrophilic. The channels are then sealed with a glass cover to complete the fabrication of the microfluidic chip.

[0008] S2 uses a pressure pump to generate a positive pressure of 2000 mbar, injects deionized water into the microchannel to rinse for 5 minutes, and then injects anhydrous ethanol to rinse for 5 minutes. The above cleaning process is repeated 2 to 3 times until the residual oil and impurities in the channel are cleaned. After cleaning, the above pressure is maintained, air is injected into the microchannel, and the microchannel is observed simultaneously through a microscope until the residual cleaning reagent on the channel wall is dried.

[0009] S3 measures 10 ml of insulating oil and places it in a capped centrifuge tube. Use a pressure pump to remove excess air from the centrifuge tube, maintaining the pressure inside the centrifuge tube at 50 Pa. Place the centrifuge tube in a water bath and set the temperature to 90 ℃ to vacuum dry the insulating oil for 20 min.

[0010] S4 Weigh 10g of microcrystalline cellulose and add it to 10ml of 64% H2SO4 w / w solution (w / w is the mass ratio concentration). Stir to disperse the cellulose evenly, then stir in a 45℃ water bath for 3min. Add a large amount of deionized water to terminate the reaction. Then, centrifuge and wash three times to remove residual sulfuric acid. Then, use dialysis to completely remove sulfuric acid and other excess ions. Sonicate the acid-hydrolyzed cellulose using a cell disruptor at 50W for 1min to obtain a microcellulose suspension. Disperse the suspension in deionized water at 100mg / L to prepare a cellulose solution.

[0011] S5 uses a pressure pump to introduce the cellulose solution into the microchannel, controls the pressure of the pressure pump, and makes the cellulose solution flow in the channel at a rate of 5 μL / min for 10 to 30 minutes, so that the fibers in the solution are fully adsorbed to the wall of the microchannel, forming a microcapillary environment between the insulating paper fibers; then drains the liquid in the channel.

[0012] S6 closes the liquid outlet end of the microchannel, controls the gas pressure in the channel to 5Pa through a pressure pump, and places the chip on a constant temperature heating stage, controlling the temperature of the heating stage to 50℃, to vacuum dry the cellulose adsorption layer on the wall of the microchannel. At the same time, it is observed simultaneously through a microscope.

[0013] S7 takes deionized water according to the required simulated moisture level of the oil-paper insulation, adds 10ml of dried insulating oil from S3, and then disperses the two by ultrasonication to make an oil-water emulsion.

[0014] S8 uses a pressure pump to inject the oil-water emulsion into the dried microchannel of S6. Then, the microfluidic chip is left to stand for 12 hours to allow the micron-sized water droplets dispersed in the emulsion to be gradually adsorbed onto the cellulose layer on the channel wall. During this period, observation and recording are performed using a microscope.

[0015] After S9 has settled, the stable distribution of water on the surface of the cellulose layer on the channel wall is observed using a microscope; the oil-water two-phase distribution in the channel is also observed using a microscope.

[0016] Under a microscope, the size distribution of water droplets and the wetting angle distribution of water droplets on the channel wall were measured using S10.

[0017] By changing the amount of deionized water added to the insulating oil in step S7, and repeating steps S8 to S10, different microscopic moisture states of the insulating paper capillaries were simulated. The corresponding moisture content in the microchannels was studied by microscopic observation.

[0018] Optionally, the deionized water is 1-10 μL.

[0019] The beneficial effects of this invention are as follows: Existing methods for absorbing moisture from oil-paper insulation are macroscopic experimental methods, which cannot directly and precisely control or visualize the moisture behavior at the micron-scale capillary structure of the insulating paper. Compared with the prior art, this invention proposes a microfluidic technology-based method that uses microchannels on a microfluidic chip to simulate the micron-scale capillary environment in the insulating paper. Combined with external pressure pumps, heating stages, and other equipment, the macroscopic processes of preparation, vacuum drying, vacuum oil impregnation, and moisture absorption are transformed into corresponding microscopic processing techniques, thus forming a microscopic simulation method for absorbing moisture from oil-paper insulation. This method has the advantages of being fast, accurate, and providing micron-scale visualization.

[0020] The method proposed in this invention can deduce the individual dielectric variables of each dielectric material from the overall dielectric response of multi-dielectric composite insulation, which can overcome the problem that existing dielectric response techniques can only obtain the overall dielectric response and cannot know the individual dielectric properties of each part.

[0021] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0022] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein:

[0023] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0024] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0025] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0026] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0027] like Figure 1 As shown, the present invention includes the following steps:

[0028] S1 uses polydimethylsiloxane as the fluid layer of the microfluidic chip. Microchannels with rectangular cross-sections are fabricated on the fluid layer, with a width and depth ranging from 0 to 100 μm. After fabrication, a plasma cleaner is used to perform plasma cleaning on the inner surface of the channels and the surface of the fluid layer, making the channel walls hydrophilic. The channels are then sealed with a glass cover to complete the fabrication of the microfluidic chip.

[0029] S2 uses a pressure pump to generate a positive pressure of 2000 mbar, injects deionized water into the microchannel to rinse for 5 minutes, and then injects anhydrous ethanol to rinse for 5 minutes. The above cleaning process is repeated 2 to 3 times until the residual oil and impurities in the channel are cleaned. After cleaning, the above pressure is maintained, air is injected into the microchannel, and the microchannel is observed simultaneously through a microscope until the residual cleaning reagent on the channel wall is dried.

[0030] S3 measures 10 ml of insulating oil and places it in a capped centrifuge tube. Use a pressure pump to remove excess air from the centrifuge tube, maintaining the pressure inside the centrifuge tube at 50 Pa. Place the centrifuge tube in a water bath and set the temperature to 90 °C to vacuum dry the insulating oil for 20 minutes.

[0031] S4 Weigh 10g of microcrystalline cellulose and add it to 10ml of 64% H2SO4 (w / w) solution. Stir to disperse the cellulose evenly, then stir in a 45℃ water bath for 3min. Add a large amount of deionized water to terminate the reaction. Then, centrifuge and wash three times to remove residual sulfuric acid. Then, use dialysis to completely remove sulfuric acid and other excess ions. Sonicate the acid-hydrolyzed cellulose using a cell disruptor at 50W for 1min to obtain a microcellulose suspension. Further disperse it in deionized water at 100mg / L to prepare a cellulose solution.

[0032] S5 uses a pressure pump to introduce the cellulose solution into the microchannel, and controls the pressure of the pressure pump to make the cellulose solution flow through the channel at a rate of 5 μL / min for 10-30 min, so that the fibers in the solution are fully adsorbed onto the wall of the microchannel, forming a microcapillary environment similar to that between the fibers of insulating paper; then, the liquid in the channel is drained.

[0033] S6 closes the liquid outlet end of the microchannel, controls the gas pressure inside the channel to 5Pa using a pressure pump, and places the chip on a constant temperature heating stage, controlling the temperature of the heating stage to 50℃, to vacuum dry the cellulose adsorption layer on the wall of the microchannel. At the same time, it is observed simultaneously using a microscope.

[0034] S7 takes a small amount of deionized water (1-10 μL) according to the required simulated moisture level of the oil-paper insulation, adds it to 10 ml of the dried insulating oil in S3, and then disperses the two by ultrasonication to make an oil-water emulsion.

[0035] S8 uses a pressure pump to inject the oil-water emulsion into the dried microchannel of S6. Then, the microfluidic chip is left to stand for 12 hours, allowing the micron-sized water droplets dispersed in the emulsion to be gradually adsorbed onto the cellulose layer on the channel wall. During this period, observation and recording are performed using a microscope.

[0036] After S9 has settled, the stable distribution of water on the surface of the cellulose layer on the channel wall is observed using a microscope; the oil-water two-phase distribution in the channel is also observed using a microscope.

[0037] Under a microscope, the size distribution of water droplets and the wetting angle distribution of water droplets on the channel wall were measured using the S10.

[0038] By changing the amount of deionized water added to the insulating oil in step S7, and repeating steps S8-S10, different microscopic moisture states of the insulating paper capillaries were simulated. The corresponding moisture content in the microchannels was studied by microscopic observation.

[0039] 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 it. 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 spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A microscopic simulation method for moisture absorption in oil-paper insulation based on microfluidic technology, characterized in that: The method includes the following steps: S1 uses polydimethylsiloxane as the fluid layer of the microfluidic chip. Microchannels with rectangular cross-sections are fabricated on the fluid layer, with a width and depth ranging from 0 to 100 μm. After fabrication, a plasma cleaner is used to perform plasma cleaning on the inner surface of the channels and the surface of the fluid layer to make the channel walls hydrophilic. The channels are then sealed with a glass cover to complete the fabrication of the microfluidic chip. S2 uses a pressure pump to generate a positive pressure of 2000 mbar, injects deionized water into the microchannel to rinse for 5 minutes, and then injects anhydrous ethanol to rinse for 5 minutes. The above cleaning process is repeated 2 to 3 times until the residual oil and impurities in the channel are cleaned. After cleaning, the above pressure is maintained, air is injected into the microchannel, and the microchannel is observed simultaneously through a microscope until the residual cleaning reagent on the channel wall is dried. S3 measures 10 ml of insulating oil and places it in a capped centrifuge tube. Use a pressure pump to remove excess air from the centrifuge tube, maintaining the pressure inside the centrifuge tube at 50 Pa. Place the centrifuge tube in a water bath and set the temperature to 90 ℃ to vacuum dry the insulating oil for 20 min. S4 Weigh 10g of microcrystalline cellulose and add it to 10ml of 64% H2SO4 w / w solution (w / w is the mass ratio concentration). Stir to disperse the cellulose evenly, then stir in a 45℃ water bath for 3min. Add a large amount of deionized water to terminate the reaction. Then, centrifuge and wash three times to remove residual sulfuric acid. Then, use dialysis to completely remove sulfuric acid and other excess ions. Sonicate the acid-hydrolyzed cellulose using a cell disruptor at 50W for 1min to obtain a microcellulose suspension. Disperse the suspension in deionized water at 100mg / L to prepare a cellulose solution. S5 uses a pressure pump to introduce the cellulose solution into the microchannel, controls the pressure of the pressure pump, and makes the cellulose solution flow in the channel at a rate of 5 μL / min for 10 to 30 minutes, so that the fibers in the solution are fully adsorbed to the wall of the microchannel, forming a microcapillary environment between the insulating paper fibers; then drains the liquid in the channel. S6 closes the liquid outlet end of the microchannel, controls the gas pressure in the channel to 5Pa through a pressure pump, and places the chip on a constant temperature heating stage, controlling the temperature of the heating stage to 50℃, to vacuum dry the cellulose adsorption layer on the wall of the microchannel. At the same time, it is observed simultaneously through a microscope. S7 takes deionized water according to the required simulated moisture level of the oil-paper insulation, adds 10ml of dried insulating oil from S3, and then disperses the two by ultrasonication to make an oil-water emulsion. S8 uses a pressure pump to inject the oil-water emulsion into the dried microchannel of S6. Then, the microfluidic chip is left to stand for 12 hours to allow the micron-sized water droplets dispersed in the emulsion to be gradually adsorbed onto the cellulose layer on the channel wall. During this period, observation and recording are performed using a microscope. After S9 has settled, the stable distribution of water on the surface of the cellulose layer on the channel wall is observed using a microscope; the oil-water two-phase distribution in the channel is also observed using a microscope. Under a microscope, the size distribution of water droplets and the wetting angle distribution of water droplets on the channel wall were measured using S10. By changing the amount of deionized water added to the insulating oil in step S7, and repeating steps S8 to S10, different microscopic moisture states of the insulating paper capillaries were simulated. The corresponding moisture content in the microchannels was studied by microscopic observation.

2. The method for simulating moisture absorption in oil-paper insulation based on microfluidic technology according to claim 1, characterized in that: The amount of deionized water is 1-10 μL.

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