Oil-gas separation membrane for on-line detection of transformer and preparation method thereof

Abstract

This invention discloses a method for preparing an oil-gas separation membrane for online transformer testing, comprising: Step 1, spreading liquid fluorosilicone rubber on a flat plate and curing it to form a thin film; Step 2, mixing and dispersing Hyflon AD60 with a perfluoropolyether thermally conductive liquid, adding α-phase nano-alumina powder, and dispersing it evenly to obtain a casting solution; Step 3, coating the casting solution onto the thin film, allowing it to stand, covering it with a pressure plate, and heating it to 180–220°C in a drying oven for 3–10 hours; Step 4, allowing it to stand under high pressure for 24–48 hours, then placing it again in a preheated drying oven for 6–12 hours, and cooling it to obtain the final product. The preparation method of this invention is mild, resulting in an oil-gas separation membrane with high mechanical strength and a short oil-gas separation time. This invention discloses an oil-gas separation membrane with a short oil-gas separation time, which can significantly improve the efficiency of online transformer testing and shorten the testing cycle.

Description

Technical Field

[0001] This invention relates to the field of online transformer testing technology. More specifically, this invention relates to an oil-gas separation membrane for online transformer testing and its preparation method. Background Technology

[0002] Transformers are crucial operating equipment in power systems, and their proper functioning significantly impacts the safe operation of the power grid. The insulating oil inside a transformer decomposes under heat and electricity, producing seven characteristic gases: H2, CO, CO2, CH4, C2H2, C2H4, and C2H6, which dissolve in the oil. The presence of latent overheating or discharge faults accelerates the production of these gases. By detecting the dissolved gas content in the insulating oil, the type and severity of transformer faults can be analyzed promptly. Current methods for oil-gas separation include dynamic headspace degassing, vacuum degassing, and permeate membrane degassing.

[0003] The principle of dynamic headspace degassing is as follows: a certain volume of sample oil containing dissolved gas is injected into the degassing chamber. An inert gas (N2) is passed into the transformer oil to purge the gas, allowing it to pass through an adsorbent for enrichment. The adsorbent is then heated, causing the adsorbed components to desorb and enter the gas chromatograph with the carrier gas for analysis. A single analysis takes only 30 minutes. The Zhongfen 3000 online chromatographic monitoring system from Henan Zhongfen Instrument Co., Ltd. uses chromatographic analysis principles, applying dynamic headspace (purge-and-trap) degassing technology and a high-sensitivity microbridge detector to detect seven components in transformer oil. Its drawbacks include the instrument's complexity and the potential loss of sample components due to adsorption and desorption.

[0004] The vacuum complete degassing method involves the following oil-gas separation process: a certain volume of sample oil containing dissolved gas is injected into the degassing chamber. Under vacuum conditions, the gas released from the oil is transferred from the degassing chamber to the gas collecting chamber by a piston. After several degassing and gas collecting processes, the gas in the collecting chamber is transmitted to a chromatographic analysis system for analysis via an injector. The vacuum degassing method has a simple process and a short equilibrium time; with the aid of stirring, equilibrium is generally reached in about ten minutes. The NS801B online monitoring system from Nanjing Nanzhi Electric Technology Co., Ltd. uses chromatographic analysis principles, vacuum degassing technology, and a high-sensitivity gas sensor to detect seven components in transformer oil. Its drawbacks include a large device size, complex structure, and high requirements for the stability of the degassing machine.

[0005] Membrane degassing is a simple method that simplifies online monitoring devices and is widely welcomed by the power sector. Utilizing the permeability of polymer membranes, gases can be directly separated from oil, easily meeting the requirements of continuous online monitoring. For example, polymer membranes such as PTFE membranes, PTFE-nylon tubing, and polyimide membranes have been successfully used in transformer online monitoring systems. However, these polymer membranes typically require tens of hours or even days to complete separation, which may prevent timely detection of transformer faults.

[0006] The permeation mechanism of polymer membranes follows a dissolution-diffusion pathway. When a gas chamber containing a polymer membrane is installed on a sealed container filled with transformer oil (containing a certain concentration of the target gas), the diffusion process of the target gas molecules in the oil through the membrane, oil, and gas chamber is as follows: First, the gas contacts the membrane; second, the gas dissolves on the membrane surface; the gas volume fraction gradient created by the dissolution causes the gas to diffuse forward within the membrane; subsequently, the gas reaches the other side of the membrane. This process remains unstable until the gas volume fraction in the membrane becomes linear along the membrane thickness, at which point a stable state is reached, i.e., the diffusion rates in both directions reach dynamic equilibrium. Therefore, improving the dissolution-diffusion rate of the characteristic gas in the oil-gas separation membrane and shortening the time to reach oil-gas equilibrium is a key research focus. Summary of the Invention

[0007] One object of the present invention is to solve at least the above-mentioned problems and to provide at least the advantages that will be described later.

[0008] To achieve these objectives and other advantages according to the present invention, a method for preparing an oil-gas separation membrane for online transformer testing is provided, comprising the following steps:

[0009] Step 1: Lay the liquid fluorosilicone rubber flat on a smooth plate and allow it to cure to form a film;

[0010] Step 2: Mix Hyflon AD60 with perfluoropolyether thermal conductive liquid until uniformly dispersed, degas by ultrasonication, then add α-phase nano alumina powder, mix and disperse until uniformly dispersed, degas by ultrasonication, and obtain casting solution.

[0011] Step 3: Coat the casting solution onto the film from Step 1, let it stand for a certain period of time, cover it with a pressure plate, place it in a drying oven, heat it to 180-220℃ at a certain heating rate, and keep it at a constant temperature for 3-10 hours.

[0012] Step 4: Allow the mixture to cool under high pressure for 24-48 hours. Then, place it in a drying oven preheated to 150-180°C and maintain the temperature for 6-12 hours. After cooling, the oil-gas separation membrane is obtained.

[0013] Preferably, the thickness of the film in step one is 10–25 μm, and the thickness of the film coated in step three is 10–15 μm.

[0014] Preferably, the mass ratio of Hyflon AD60, perfluoropolyether thermal conductive liquid, and α-phase nano-alumina powder in step two is 100:10-15:3-5.

[0015] Preferably, the high pressure condition in step four is 1.5 to 1.8 kPa.

[0016] Preferably, the heating rate in step three is 0.5–1 °C / min.

[0017] Preferably, the perfluoropolyether thermal conductive fluid in step two is Galden HT170.

[0018] Preferably, the α-phase nano-alumina powder in step two has an average particle size of 30 nm and a specific surface area greater than 60 m². 2 / g.

[0019] Preferably, the temperature during ultrasonic degassing in step two is not less than 60°C.

[0020] An oil-gas separation membrane prepared by the above method is provided.

[0021] The present invention has at least the following beneficial effects: the oil-gas separation membrane prepared by composite of four raw materials, namely fluorosilicone rubber, Hyflon AD60, perfluoropolyether thermal conductive liquid and α-phase nano alumina powder, has good air permeability and mechanical strength, which can meet the usage environment of transformer online detection, namely high voltage resistance, oil resistance, and the time for characteristic gases to reach oil-gas equilibrium is significantly shortened.

[0022] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Detailed Implementation

[0023] The present invention will now be described in further detail with reference to experiments, so that those skilled in the art can implement it based on the description.

[0024] It should be noted that, unless otherwise specified, the experimental methods described in the following embodiments are all conventional methods, and the reagents and materials described are all commercially available unless otherwise specified. In the description of this invention, the orientation or positional relationship indicated by the terms is only for the convenience of describing this invention and simplifying the description, and does 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, and therefore should not be construed as a limitation of this invention.

[0025] <Equipment, Instruments and Test Materials>

[0026] The equipment and instruments include: ultrasonic cleaner, stirrer, fully automatic drying oven, gas cylinder, high-pressure permeation platform, gas permeation performance testing platform, gas chromatograph, etc.

[0027] The experimental materials are shown in the table below:

[0028] Table 1 Detailed list of test materials

[0029]

[0030]

[0031] <Experiment 1>

[0032] The method for preparing an oil-gas separation membrane includes the following steps:

[0033] Step 1: Spread the liquid fluorosilicone rubber evenly in a smooth and flat ceramic container. A glass container can also be used instead of a ceramic container. The fluorosilicone rubber will automatically level at room temperature. After standing at room temperature and completely curing, it will form a film. Store it in a desiccator for later use. The film thickness is 25μm.

[0034] Step 2: Weigh Hyflon AD60 and place it in a glass bottle. Add perfluoropolyether thermal conductive liquid (Galden HT170), and mix and disperse evenly using a stirrer (300 r / min, dispersion for 30 min). Then, place it in an ultrasonic cleaner (60℃, frequency 60 kHz, time 60 min) for ultrasonic degassing. Next, add α-phase nano-alumina powder, and mix and disperse evenly again using a stirrer (300 r / min, dispersion for 60 min). Then, place it in an ultrasonic cleaner (60℃, frequency 60 kHz, time 60 min) for ultrasonic degassing to obtain the casting solution. Prepare two groups of casting solutions with different mass ratios. The mass ratios of the raw materials for each group of casting solutions are shown in Table 2.

[0035] Table 2 Raw material usage of casting solution

[0036] Group Hyflon AD60 Galden HT170 α-phase nano alumina powder 1 50g 5g 1.5g 2 50g 7.5g 2.5g

[0037] Step 3: Take out the film prepared in Step 1, then add 2.5 ml of the casting solution prepared in Step 2 to the surface of the film, slowly rotate the container to spread the casting solution evenly on the surface of the film, let it stand for 10 seconds and then pour it out. After waiting for 10 seconds, add 2.5 ml of the casting solution to the surface of the film again, repeat several times, for a total of 5 coatings.

[0038] After standing for 1 hour, place it in a fully automatic drying oven. Adjust the heating rate of the fully automatic drying oven to 1℃ / min. After heating to 220℃, bake at a constant temperature for 10 hours.

[0039] Step 4: Remove the membrane and allow it to cool under high pressure of 1.8 MPa for 48 hours. Then, place it in a fully automatic drying oven preheated to 180°C for 12 hours. After cooling, the oil-gas separation membrane is obtained. It is a composite membrane. The thicknesses of the oil-gas separation membranes obtained are 32 μm for group 1 and 33 μm for group 2.

[0040] In the experiment, the oil-gas separation membrane was placed in a sealed container, and a nitrogen gas cylinder was used to seal the container. The pressure valve of the gas cylinder was opened and adjusted to 1.8 MPa.

[0041] <Experiment 2>

[0042] The method for preparing an oil-gas separation membrane includes the following steps:

[0043] Step 1: Spread the liquid fluorosilicone rubber evenly in a smooth and flat ceramic container. A glass container can also be used instead of a ceramic container. The fluorosilicone rubber will automatically level at room temperature. After standing at room temperature and completely curing, it will form a film. Store it in a desiccator for later use. The film thickness is 10μm.

[0044] Step 2: Weigh Hyflon AD60 and place it in a glass bottle. Add perfluoropolyether thermal conductive liquid (Galden HT170), and mix and disperse evenly using a stirrer (300 r / min, dispersion for 30 min). Then, place it in an ultrasonic cleaner (60℃, frequency 60 kHz, time 60 min) for ultrasonic degassing. Next, add α-phase nano-alumina powder, and mix and disperse evenly again using a stirrer (300 r / min, dispersion for 60 min). Then, place it in an ultrasonic cleaner (60℃, frequency 60 kHz, time 60 min) for ultrasonic degassing to obtain the casting solution. Prepare two groups of casting solutions with different mass ratios. The mass ratios of the raw materials for each group of casting solutions are shown in Table 3.

[0045] Table 3 Raw material usage of casting solution

[0046] Group Hyflon AD60 Galden HT170 α-phase nano alumina powder 1 50g 5g 1.5g 2 50g 7.5g 2.5g

[0047] Step 3: Take out the film prepared in Step 1, then add 2.5 ml of the casting solution prepared in Step 2 to the surface of the film, slowly rotate the container to spread the casting solution evenly on the surface of the film, let it stand for 10 seconds and then pour it out. After waiting for 10 seconds, add 2.5 ml of the casting solution to the surface of the film again, repeat several times, and coat a total of 3 times.

[0048] After standing for 1 hour, place it in a fully automatic drying oven. Adjust the heating rate of the fully automatic drying oven to 0.5℃ / min. After heating to 180℃, bake at a constant temperature for 3 hours.

[0049] Step 4: Remove the membrane and allow it to cool under high pressure of 1.5 MPa for 24 hours. Then, place it in a fully automatic drying oven preheated to 150°C for 6 hours. After cooling, the oil-gas separation membrane is obtained. It is a composite membrane. The thicknesses of the oil-gas separation membranes obtained in Group 1 and Group 2 are 18 μm and 19 μm, respectively.

[0050] <Experiment 3>

[0051] The method for preparing an oil-gas separation membrane includes the following steps:

[0052] Step 1: Spread the liquid fluorosilicone rubber evenly in a smooth and flat ceramic container. A glass container can also be used instead of a ceramic container. The fluorosilicone rubber will automatically level at room temperature. After standing at room temperature and completely curing, it will form a film. Store it in a desiccator for later use. The film thickness is 18μm.

[0053] Step 2: Weigh Hyflon AD60 and place it in a glass bottle. Add perfluoropolyether thermal conductive liquid (Galden HT170), and mix and disperse evenly using a stirrer (300 r / min, dispersion for 30 min). Then, place it in an ultrasonic cleaner (60℃, frequency 60 kHz, time 60 min) for ultrasonic degassing. Next, add α-phase nano-alumina powder, and mix and disperse evenly again using a stirrer (300 r / min, dispersion for 60 min). Then, place it in an ultrasonic cleaner (60℃, frequency 60 kHz, time 60 min) for ultrasonic degassing to obtain the casting solution. Prepare two groups of casting solutions with different mass ratios. The mass ratios of the raw materials for each group of casting solutions are shown in Table 4.

[0054] Table 4 Raw material usage of casting solution

[0055] Group Hyflon AD60 Galden HT170 α-phase nano alumina powder 1 50g 5g 1.5g 2 50g 7.5g 2.5g

[0056] Step 3: Take out the film prepared in Step 1, then add 2.5 ml of the casting solution prepared in Step 2 to the surface of the film, slowly rotate the container to spread the casting solution evenly on the surface of the film, let it stand for 10 seconds and then pour it out. After waiting for 10 seconds, add 2.5 ml of the casting solution to the surface of the film again, repeat several times, for a total of 4 coatings.

[0057] After standing for 1 hour, place it in a fully automatic drying oven. Adjust the heating rate of the fully automatic drying oven to 1℃ / min. After heating to 200℃, bake at a constant temperature for 3 hours.

[0058] Step 4: Remove the membrane and allow it to cool under high pressure of 1.5 MPa for 36 hours. Then, place it in a fully automatic drying oven preheated to 180°C for 10 hours. After cooling, the oil-gas separation membrane is obtained. It is a composite membrane. The thicknesses of the oil-gas separation membranes obtained in Group 1 and Group 2 are 28 μm and 30 μm, respectively.

[0059] <Comparative Example 1>

[0060] The preparation method of the oil-gas separation membrane is the same as that of Group 2 in Experiment 3. The difference is that in step two, α-phase nano-alumina powder was not added, but an equal amount of fumed silica prepared by the gas phase method was added.

[0061] <Comparative Example 2>

[0062] The preparation method of the oil-gas separation membrane is the same as that of Group 2 in Experiment 3, except that in step four, the membrane is allowed to stand and cool under normal pressure.

[0063] <Comparative Example 3>

[0064] The preparation method of the oil-gas separation membrane is the same as that of Group 2 in Experiment 3, except that a second fully automatic drying oven treatment was not performed in step four.

[0065] Performance Testing

[0066] 1. Mechanical strength test

[0067] The oil-gas separation membrane under test was fixed in a metal perforated frame and sealed circumferentially to the side wall of the oil chamber headspace. The oil-gas separation membrane and the oil chamber headspace formed a gas chamber. Insulating oil was filled into the oil chamber below the metal perforated frame. The front port of the oil chamber was sealed to a gas cylinder. The pressure valve of the gas cylinder was adjusted to 500 kPa and maintained for 48 hours. The oil-gas separation membrane was then checked for ruptures and oil leakage. The test results are shown in the table below:

[0068] Table 5. Mechanical strength test results of oil-gas separators in each group.

[0069] Group rupture Oil seepage Composite membrane separation Experiment 1 Group 1 none none none Experiment 1 Group 2 none none none Experiment 2 group 1 none none none Experiment 2 group 2 none none none Experiment 3 Group 1 none none none Experiment 3 Group 2 none none none Comparative Example 1 none none none Comparative Example 2 none have have Comparative Example 3 none have have

[0070] The mechanical strength test results in the table above show that the oil-gas separation membranes prepared in tests 1-3 and Comparative Example 1 have good compressive strength and no rupture, oil leakage or membrane separation occurred, which can meet the testing requirements of insulating oil in transformers.

[0071] Comparative Example 1 used silica, a reinforcing agent commonly used in the prior art, in order to enhance the mechanical strength of the oil-gas separation membrane. Silica had strong interaction with each component (no membrane separation occurred).

[0072] Comparative Examples 2 and 3 both used the new material reinforcing agent α-phase nano alumina powder. However, without high-pressure static cooling and secondary high-temperature reheating treatment, the film layers were prone to separation, which affected the adhesion between the two layers and led to oil seepage.

[0073] 2. Breathability test

[0074] The gas permeability of the oil-gas separation membrane was tested using a gas permeation performance testing platform. Insulating oil was injected into a 5L oil tank and circulated at a flow rate of 300ml / min. The oil temperature in the tank was heated to 90℃, and a vacuum was drawn to below 5kPa, maintained for 24 hours. After the oil temperature cooled to room temperature, standard gas was injected into the oil at a flow rate of 200ml / min. When the pressure in the headspace of the oil chamber reached 101.3kPa, the pressure relief valve was opened to ensure that the headspace pressure remained at 101.3kPa. Gas was circulated for 6 hours to prepare the standard oil.

[0075] At room temperature, the oil in the tank is circulated and passes through an oil-gas separation membrane. Before the experiment, the gas chamber is purged with high-purity nitrogen for 5 minutes to ensure that the concentration of the characteristic gas in the gas chamber is close to zero. After purging, the valve is sealed.

[0076] Samples were taken from the gas collection chamber at regular intervals, with 1 ml of sample taken each time, and then the gas was detected by a gas chromatograph.

[0077] According to existing equilibrium theory, when the gas concentration reaches 90% of the equilibrium concentration, it is considered that oil and gas equilibrium has been achieved. The oil and gas equilibrium time for various gases is shown in the table below:

[0078] Table 6 shows the time it takes for each group of oil-gas separation membranes to reach oil-gas equilibrium.

[0079] Gas types <![CDATA[CO2]]> <![CDATA[C2H4]]> <![CDATA[C2H2]]> <![CDATA[C2H6]]> <![CDATA[H2]]> <![CDATA[CH4]]> CO Experiment 1 Group 1 1h 3h 3h 3h 2h 3h 2h Experiment 1 Group 2 1h 3h 3h 3h 2h 3h 2h Experiment 2 group 1 1h 3h 3h 3h 2h 3h 2h Experiment 2 group 2 1h 3h 3h 3h 2h 3h 2h Experiment 3 Group 1 1h 3h 3h 3h 2h 3h 2h Experiment 3 Group 2 1h 3h 3h 3h 2h 3h 2h Comparative Example 1 8 h 12h 11h 10h 6h 4h 8h

[0080] As can be seen from the table above, the oil-gas separation membranes prepared by the methods in Experiments 1 to 3 reached oil-gas equilibrium within 3 hours. Among them, CO and H2 reached oil-gas equilibrium within an average of 2 hours, CO2 reached oil-gas equilibrium within an average of 1 hour, and the other four gases C2H4, C2H2, C2H6, and CH4 reached oil-gas equilibrium within 3 hours.

[0081] In Comparative Example 1, the addition of reinforcing agent silica enhanced the mechanical strength of the composite membrane, but severely affected its permeability, resulting in a slow oil-gas separation speed.

[0082] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and embodiments shown and described herein.

Claims

1. A method for preparing an oil-gas separation membrane for online transformer testing, characterized in that, Includes the following steps: Step 1: Lay the liquid fluorosilicone rubber flat on a smooth plate and allow it to cure to form a film; Step 2: Mix Hyflon AD60 with perfluoropolyether thermal conductive liquid until uniformly dispersed, degas by ultrasonication, then add α-phase nano alumina powder, mix and disperse until uniformly dispersed, degas by ultrasonication, and obtain casting solution. Step 3: Coat the casting solution onto the film from Step 1, let it stand for a certain period of time, cover it with a pressure plate, place it in a drying oven, heat it to 180~220℃ at a certain heating rate, and keep it at a constant temperature for 3~10 hours. Step 4: Allow the mixture to cool under high pressure for 24 to 48 hours. Then, place it in a drying oven preheated to 150 to 180°C and maintain the temperature for 6 to 12 hours. After cooling, the oil-gas separation membrane is obtained. In step two, the mass ratio of Hyflon AD60, perfluoropolyether thermal conductive liquid, and α-phase nano alumina powder is 100:10~15:3~5. The high-pressure condition in step four is 1.5~1.8 MPa; The perfluoropolyether thermal conductive fluid used in step two is Galden HT170; The α-phase nano-alumina powder in step two has an average particle size of 30 nm and a specific surface area greater than 60 m². 2 / g.

2. The method for preparing the oil-gas separation membrane for online transformer testing as described in claim 1, characterized in that, In step one, the thickness of the film is 10~25 μm, and in step three, the thickness of the film coated is 10~15 μm.

3. The method for preparing the oil-gas separation membrane for online transformer testing as described in claim 1, characterized in that, The heating rate in step three is 0.5~1℃ / min.

4. The method for preparing the oil-gas separation membrane for online transformer testing as described in claim 1, characterized in that, The temperature during ultrasonic degassing in step two shall not be less than 60℃.

5. The oil-gas separation membrane prepared by the method according to any one of claims 1 to 4.

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