A device and method for measuring characteristic gas diffusion coefficient in insulating oil

Abstract

The present application discloses a device and method for measuring characteristic gas diffusion coefficient in insulating oil, including an experimental platform, a constant temperature and humidity chamber, a gas delivery device, an observation device and a terminal device; the experimental platform is arranged in the constant temperature and humidity chamber, including a main area and a secondary area; the gas delivery device is used to deliver the experimental gas into the main area through the secondary area; the main area includes a main tank provided with an electrode plate, which is used to realize the measurement of characteristic gas diffusion coefficient under different electric field strengths; the observation device is connected to the terminal device, which is used to observe the experimental process in real time and upload the generated experimental data to the terminal device. The device realizes the measurement of gas diffusion coefficient under different temperatures or electric field strengths through a constant temperature and humidity chamber and an electrode plate, and has a wide range of applications. When measuring based on the device, the measurement accuracy of the gas diffusion coefficient in insulating oil is improved by iterative correction of experiments and simulations, the experimental cycle is short, the gas consumption is small, the operation is simple, and the safety of the experimental platform is improved.

Description

Technical Field

[0001] The present application relates to the field of gas diffusion coefficient testing, and in particular to a device and method for measuring characteristic gas diffusion coefficient in insulating oil. Background Art

[0002] Diffusion phenomenon is an important molecular transport mechanism. For example, when there is a concentration gradient of a component inside a fluid, the molecular thermal motion causes the component to be transported in the opposite direction of the concentration gradient. Usually, the diffusion flux is proportional to the concentration gradient, and the proportional coefficient is called the diffusion coefficient, which characterizes the diffusion ability of the molecules of the substance and is one of the basic physical properties of the substance. During the thermal aging process or when a local failure occurs in an oil-immersed transformer, the characteristic gas generated will migrate to other parts of the transformer through diffusion and convection. Characteristic gas is an important factor affecting the safe and stable operation of oil-immersed transformers. Mastering the diffusion coefficient of characteristic gas in insulating oil can help understand the distribution of characteristic gas in transformer oil, thereby accurately judging the operating status of the transformer and further optimizing the transformer structural design and online monitoring and detection scheme, which is of great significance to ensuring and promoting the safe and stable operation of the transformer.

[0003] At present, the methods for measuring gas diffusion coefficient mainly include capillary method, pressure drop method and bubble dissolution method. Among them, the volume of the capillary used in the capillary method is small, and the volume of the bubble and liquid column during the test is also small. Therefore, it is easily affected by the temperature and pressure fluctuations of the system during the test, which leads to a large error in the measured diffusion coefficient; the disadvantage of the pressure drop method is that the experimental cycle is long. For gases with slow pressure drop, its accuracy will decrease and the error will increase. For example, the diffusion coefficient of characteristic gases C2H4, C2H6, etc. at room temperature is on the order of 10-9m2 / s. Because the diffusion coefficient is small, the use of the pressure drop method will produce a large error. The traditional bubble dissolution method is a method of determining the gas diffusion coefficient by optical recording of pure bubbles dissolving in degassed liquid, but it does not take into account the convective movement of the liquid as the bubble size decreases during the dissolution process. The convective movement will cause the bubble dissolution process to accelerate, which may cause the measured value to be greater than the actual value. Summary of the invention

[0004] The purpose of the present application is to provide a device and method for measuring the characteristic gas diffusion coefficient in insulating oil, so as to solve the problems of low measurement accuracy, long measurement cycle and limited application scope in the existing method for measuring the characteristic gas diffusion coefficient of insulating oil.

[0005] To achieve the above object, the present application provides a device for measuring the characteristic gas diffusion coefficient in insulating oil, comprising:

[0006] Experimental platform, constant temperature and humidity chamber, gas delivery device, observation device and terminal equipment;

[0007] The experimental platform is arranged in the constant temperature and humidity chamber, and includes a main area and a secondary area;

[0008] The gas introduction device is used to introduce the experimental gas into the main zone through the secondary zone;

[0009] The main area includes a main tank, in which an electrode plate is arranged for measuring the characteristic gas diffusion coefficient in the insulating oil under different electric field strengths;

[0010] The observation device is connected to the terminal device and is used to observe the experimental process of the experimental platform in real time and upload the generated experimental data to the terminal device.

[0011] Furthermore, a grid is provided in the main tank for absorbing bubbles generated by the characteristic gas in the liquid.

[0012] Furthermore, the grid is a polytetrafluoroethylene grid with low dielectric constant filler added.

[0013] Furthermore, the adjustable temperature range of the constant temperature and humidity chamber is 25°C to 100°C; the adjustable electric field strength range of the electrode plate is 0 to 40 kV / mm.

[0014] Furthermore, the main area also includes:

[0015] Main tank cover, located on the top of the main tank;

[0016] At least two insulators are arranged on the outer tank wall of the main tank and are respectively connected to two groups of high-voltage cables; one group of high-voltage cables is used to apply positive high voltage, and the other group of high-voltage cables is used to apply negative high voltage.

[0017] Further, the auxiliary zone is arranged beside the main zone, and includes an auxiliary tank and an auxiliary tank cover;

[0018] The auxiliary tank cover is arranged on the top of the auxiliary tank;

[0019] The tube walls of the auxiliary tank and the main tank are provided with through holes that can communicate with each other, and the through holes are provided with rubber gaskets.

[0020] Furthermore, the gas feeding device comprises:

[0021] Gas cylinders, valves and syringes;

[0022] The gas tank is filled with experimental gas; one end of the valve is connected to the gas tank outlet, and the other end is connected to the needle tube; the needle tube sends the experimental gas into the main tank through the auxiliary tank via a rubber gasket.

[0023] Furthermore, the device for measuring characteristic gas diffusion coefficient in insulating oil also includes a glass sheet, a bracket and a lighting device;

[0024] The glass sheet is arranged on the through hole of the constant temperature and humidity chamber, and is used to enable the observation device to observe the experimental process in the main area in real time;

[0025] The main tank and the auxiliary tank are placed on the bracket;

[0026] The lighting device is arranged below the bracket, and the normal working temperature range is 25°C to 90°C.

[0027] The present application also provides a method for measuring characteristic gas diffusion coefficient in insulating oil, which is applied to the device for measuring characteristic gas diffusion coefficient in insulating oil as described in any one of the above items, and the method comprises:

[0028] Determine the diffusion coefficient reference value of the characteristic gas in the tested insulating oil, simulate the diffusion coefficient reference value, and obtain the bubble dissolution curve of the characteristic size of the bubble of the characteristic gas in the insulating oil changing with time;

[0029] The bubble dissolution curve is compared with the fitting curve obtained according to the experimental data, and the bubble dissolution curve is iteratively corrected using fluid simulation and measurement results so that the relative error between the bubble dissolution curve and the fitting curve reaches a preset value, and the characteristic gas diffusion coefficient at this time is used as the target measurement result.

[0030] Furthermore, the iterative correction of the bubble dissolution curve using the fluid simulation and the measurement results so that the relative error between the bubble dissolution curve and the fitting curve reaches a preset value includes:

[0031] The diffusion coefficient reference value is reduced by one order of magnitude to obtain a diffusion coefficient sub-reference value;

[0032] updating the bubble dissolution curve according to the diffusion coefficient sub-reference value, and determining the positional relationship between the updated bubble dissolution curve and the fitting curve;

[0033] If the updated bubble dissolution curve is above the fitting curve, the relative error between the bubble dissolution curve and the fitting curve is calculated using the dichotomy method until the relative error reaches a preset value;

[0034] If the updated bubble dissolution curve is below the fitting curve, the step of reducing the diffusion coefficient reference value by one order of magnitude is returned.

[0035] Compared with the prior art, the beneficial effects of this application are:

[0036] 1) The measuring device of the present application uses a special thermostat to control the temperature of the insulating oil, thereby realizing the measurement of the diffusion coefficient of the gas in the insulating oil at different temperatures;

[0037] 2) Two adjustable spacing electrode plates are installed in the measuring device of the present application, so that the electric field strength can be adjusted within 0-40 kV, realizing the measurement of the diffusion coefficient of gas in insulating oil under different electric field strengths;

[0038] 3) In order to facilitate the observation of the characteristic size of the bubbles, the measuring device of the present application uses a special polytetrafluoroethylene grid to fix the bubbles. At the same time, in order to eliminate the influence of the grid on the electric field distribution, a special polytetrafluoroethylene grid with the same dielectric constant as the insulating oil is obtained by controlling the degree of polymerization or adding fillers with low dielectric constants;

[0039] 4) The measurement method of the present application uses fluid simulation and iterative correction of the effects of bubble dissolution on oil flow and electric field-induced bubble deformation on the measured value of the diffusion coefficient, and can accurately measure the diffusion coefficient of gas in insulating oil under a certain field strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solution of the present application, the drawings required for use in the implementation manner will be briefly introduced below. Obviously, the drawings described below are only some implementation manners of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0041] Figure 1 It is a structural schematic diagram of a device for measuring the characteristic gas diffusion coefficient in insulating oil provided in a certain embodiment of the present application;

[0042] Figure 2 It is a structural schematic diagram of a device for measuring characteristic gas diffusion coefficient in insulating oil provided by another embodiment of the present application;

[0043] Figure 3 It is a structural schematic diagram of a device for measuring characteristic gas diffusion coefficient in insulating oil provided by another embodiment of the present application;

[0044] Figure 4 It is a flow chart of a method for measuring characteristic gas diffusion coefficient in insulating oil provided in a certain embodiment of the present application. DETAILED DESCRIPTION

[0045] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0046] It should be understood that the step numbers used in this document are only for convenience of description and are not intended to limit the order in which the steps are executed.

[0047] It should be understood that the terms used in this application specification are only for the purpose of describing specific embodiments and are not intended to limit the application. As used in this application specification and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0048] The terms “include” and “comprising” indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0049] The term "and / or" means and includes any and all possible combinations of one or more of the associated listed items.

[0050] It should be noted that diffusion is a common molecular transport mechanism. During the thermal aging process or when a local fault occurs in an oil-immersed transformer, the characteristic gas generated will migrate to other parts of the transformer through diffusion and convection. Since the dissolved gas content in the oil measured by the DGA (dissolved gas analysis in oil) method is transported through the flow field to the sampling position, the transformer fault diagnosis method based on DGA is inseparable from the gas diffusion process. At the same time, the characteristic gas is usually generated in the form of bubbles, and the diffusion coefficient also has an important influence on the behavior of the bubbles in the transformer oil flow field. Under different operating conditions, the diffusion coefficient of the gas in the insulating oil is different, so it is necessary to establish a characteristic gas diffusion coefficient database covering the general operating parameter range of the transformer to provide key data for the numerical calculation of the dissolved gas transport behavior.

[0051] In order to timely grasp the diffusion coefficient of characteristic gas in insulating oil, so as to understand the distribution of characteristic gas in transformer oil, accurately judge the operating status of transformer, and further optimize the transformer structure design and online monitoring and detection scheme, the common methods for measuring gas diffusion coefficient mainly include capillary method, pressure drop method and bubble dissolution method.

[0052] The capillary method determines the molecular diffusion coefficient of gas in liquid by monitoring the movement of the interface. Before the experiment, the tube is filled with experimental liquid, and gas is injected into the tube to form a bubble. After the gas-liquid system reaches equilibrium under constant pressure, the diffusion experiment is carried out. The system is pressurized by a high-pressure container. The increase in pressure will cause the solubility of the gas in the experimental liquid to increase, and mass transfer will occur through the gas-liquid interface. The bubble becomes smaller due to dissolution, and the interface on both sides of the bubble moves toward the middle. The entire process is observed and the movement of the interface is recorded under a microscope, and finally the solubility of the components in each phase and the movement data of the interface are used to calculate the diffusion coefficient. Since this method uses a small capillary volume, the volume of the bubble and the liquid column during the test is also small. Therefore, it is easily affected by the temperature and pressure fluctuations of the system during the test, which leads to a large error in the measured diffusion coefficient.

[0053] The pressure drop method is that when gas diffuses into liquid in a closed container, the pressure of the gas phase decreases as the diffusion proceeds until the gas in the liquid phase is completely saturated. By recording the pressure change data during the diffusion process, the diffusion equation and the law of conservation of mass are used to calculate the diffusion coefficient. The disadvantage of this method is that the experimental cycle is long. For gases with slow pressure drop, its accuracy will decrease and the error will increase. For example, the diffusion coefficient of characteristic gases C2H4, C2H6, etc. is on the order of 10-9m2 / s at room temperature. Because the diffusion coefficient is small, the use of the pressure drop method will produce a large error.

[0054] The traditional bubble dissolution method is to inject bubbles into a container filled with insulating oil, observe the change of bubble radius over time, and derive the diffusion coefficient of gas in liquid using the formula describing the change of radius of isolated static bubbles in infinite volume of liquid over time. This method is a method to determine the gas diffusion coefficient using optical records of pure bubbles dissolving in degassed liquid, but it does not take into account the convection movement of liquid as the bubble size decreases during the dissolution process. Convection movement will cause the bubble dissolution process to accelerate, which may cause the measured value to be greater than the actual value.

[0055] In summary, in view of the shortcomings of the existing methods, this embodiment aims to provide a device for measuring the diffusion coefficient of characteristic gas in insulating oil, which can study the diffusion coefficient of gas in insulating oil under different temperatures, pressures, and electric field strengths, improve the measurement accuracy of the diffusion coefficient, and shorten the test cycle.

[0056] See also Figure 1 A certain embodiment of the present application provides a device for measuring characteristic gas diffusion coefficient in insulating oil, comprising:

[0057] Experimental platform 03, constant temperature and humidity chamber 2, gas delivery device 04, observation device 01 and terminal equipment 05;

[0058] The experimental platform 03 is set in the constant temperature and humidity chamber 2, including a main area and a secondary area;

[0059] The gas delivery device 04 is used to deliver the experimental gas into the main zone through the secondary zone;

[0060] The main area includes a main tank 6, in which an electrode plate 8 is arranged for measuring the characteristic gas diffusion coefficient in the insulating oil under different electric field strengths;

[0061] The observation device 01 is connected to the terminal device 05 and is used to observe the experimental process of the experimental platform 03 in real time and upload the generated experimental data to the terminal device 05 .

[0062] In this embodiment, it can be understood that the experimental platform 03 is mainly arranged in the constant temperature and humidity chamber 2, and includes a main area and a secondary area. During measurement, the gas delivery device 04 is used to first deliver the experimental gas into the secondary area, and the secondary area can be connected to the main area, so the gas will enter the main tank 6 of the main area from the secondary area, and then the experimental process in the main tank 6 is observed through the observation device 01. Among them, the data generated during the observation will be uploaded to the terminal device 05 for subsequent analysis.

[0063] It should be noted that the core of this embodiment is that an electrode plate 8 is provided in the main tank 6. As a preferred embodiment, the adjustable electric field strength range of the electrode plate 8 is 0 to 40 kV / mm. It is used to study the influence of the electric field on the diffusion coefficient. At the same time, the electrode plate 8 preferably adopts a circular metal flat plate electrode with a diameter of 40 mm, and the edge shape of the electrode is designed according to the Rogowski formula to ensure that the inter-electrode field strength is uniformly distributed as much as possible and the electric field distortion is minimized at the edge. Preferably, the adjustable temperature range of the constant temperature and humidity chamber 2 is 25°C to 100°C, so that the diffusion coefficient of gas in insulating oil at different temperatures and electric field strengths can be measured.

[0064] See also Figure 2 In a specific embodiment, the observation device 01 of the characteristic gas diffusion coefficient measurement device in the insulating oil is mainly a camera, and observation is performed through the telephoto lens 1 of the camera. The terminal device 05 is preferably a computer, and can also be other terminals such as a host computer that can display and analyze data. In this embodiment, positive high voltage and negative high voltage are also applied to both ends of the experimental platform 03, respectively, to adjust the pressure of the main tank 6, that is, the main tank 6 is required to have a certain pressure resistance and the internal pressure is adjustable. In this way, the device can not only realize the measurement of the diffusion coefficient of gas in insulating oil at different temperatures and electric field strengths, but also measure the diffusion coefficient of gas in insulating oil at different pressures.

[0065] See also Figure 3 , Figure 3A schematic diagram of the specific internal structure of the device for measuring the characteristic gas diffusion coefficient in insulating oil is provided. Figure 3 As shown, in a specific embodiment, a grid 9 is further provided in the main tank 6 for absorbing bubbles generated by the characteristic gas in the liquid. Preferably, the grid 9 is a polytetrafluoroethylene grid 9 with a low dielectric constant filler added.

[0066] It should be noted that the grid 9 is a key element of the experimental platform 03 in this embodiment, because the grid 9 fixes the dissolved bubbles in order to observe the characteristic size changes of the bubbles. By changing the degree of polymerization of polytetrafluoroethylene or adding fillers with low dielectric constants, the special polytetrafluoroethylene grid 9 has a dielectric constant close to that of the insulating oil, which can better adsorb the bubbles of characteristic gases in the insulating oil.

[0067] Please continue reading Figure 3 Specifically, the main area also includes:

[0068] A main tank cover 7 is provided on the top of the main tank 6;

[0069] At least two insulators 5 are arranged on the outer tank wall of the main tank 6 and are respectively connected to two groups of high-voltage cables 3; wherein, one group of high-voltage cables 3 is used to apply positive high voltage, and the other group of high-voltage cables 3 is used to apply negative high voltage.

[0070] Furthermore, the auxiliary zone is arranged beside the main zone, and includes an auxiliary tank 10 and an auxiliary tank cover 11; wherein,

[0071] The auxiliary tank cover 11 is arranged on the top of the auxiliary tank 10;

[0072] The walls of the auxiliary tank 10 and the main tank 6 are provided with through holes that can communicate with each other, and a rubber gasket 12 is provided on the through holes.

[0073] In a preferred embodiment, the gas feeding device 04 comprises:

[0074] Gas tank 17, valve 16 and needle tube 13;

[0075] The gas tank 17 is filled with experimental gas; one end of the valve 16 is connected to the outlet of the gas tank 17, and the other end is connected to the needle tube 13; the needle tube 13 delivers the experimental gas to the main tank 6 through the auxiliary tank 10 through the rubber gasket 12. Among them, a small hole is also provided in the middle of the rubber gasket 12, and the needle tube 13 mainly delivers gas through the small hole. When there is no needle tube 13 passing through, the small hole is closed.

[0076] In a preferred embodiment, the device for measuring characteristic gas diffusion coefficient in insulating oil further includes a glass sheet 4, a bracket 14 and a lighting device 15;

[0077] The glass sheet 4 is arranged on the through hole of the constant temperature and humidity chamber 2, and is used to enable the observation device 01 to observe the experimental process in the main area in real time;

[0078] The main tank 6 and the auxiliary tank 10 are placed on the bracket 14;

[0079] The lighting device 15 is disposed below the bracket 14 and has a normal operating temperature range of 25°C to 90°C.

[0080] It can be understood that the characteristic gas diffusion coefficient measuring device in insulating oil constructed by the above structure has an operating temperature adjustment range of 10 to 90°C, and the external electric field can be continuously adjusted between 0 and 40 kV / mm.

[0081] Usually, the simplest way to compare experimental data and calculations is to use the geometry directly. To achieve this, dissolved bubbles are placed on a grid 9 inside the liquid. The bottom and cover of the pool are made of glass so that the dissolution of tiny bubbles, about 1 mm in diameter, can be observed under a microscope. The bubbles are introduced into the container using a syringe and needle. The bubbles float upwards and are adsorbed on the grid 9.

[0082] Furthermore, in this embodiment, a camera connected to a special telephoto lens 1 is used to record the changes of characteristic dimensions of bubbles in the oil, such as the major axis and the minor axis of the ellipsoid, over time.

[0083] Preferably, the glass sheet 4 is a transparent glass sheet 4 with a thickness of 5 mm. The main tank 6 and the main tank cover 7, the auxiliary tank 10 and the auxiliary tank cover 11 are all made of organic glass, and the wall thickness of the main tank 6, the wall thickness of the auxiliary tank 10, the main tank cover 7 and the auxiliary tank cover 11 are all 10 mm.

[0084] In a specific embodiment, based on the above-mentioned characteristic gas diffusion coefficient measuring device in insulating oil, the steps of performing a characteristic gas diffusion coefficient measurement experiment specifically include:

[0085] 1) Open the lids of the main tank 6 and the auxiliary tank 10, rotate the adjustment knob of the electrode plate 8, and adjust the distance between the electrode plates 8 to the required distance (the adjustable range of the distance d between the electrode plates 8 is 0 to 20 mm, and the voltage U applied to the electrode plates 8 is 0 to 100 kV using a positive and negative high-voltage DC power supply). The calculation formula of the electric field strength E is:

[0086]

[0087] Wherein, U is the voltage between the two electrode plates 8 , and d is the distance between the electrode plates 8 .

[0088] 2) Add oil to the tanks until the oil levels in the main tank 6 and the auxiliary tank 10 are close to the tank openings, and then cover the main tank 6 and the auxiliary tank 10 with lids and seal them;

[0089] 3) Place the can on the shelf in the constant temperature and humidity chamber 2 and turn on the experimental light bulb;

[0090] 4) Lead the high-voltage cable 3 from outside the box and connect it to the terminal on the side wall of the main tank 6;

[0091] 5) Connect the gas tank 17 filled with experimental gas to the gas inlet of the gas delivery device, and connect its gas outlet to the metal needle tube 13;

[0092] 6) Insert the metal needle tube 13 from outside the box through the small hole on the side wall of the box, and then insert it into the rubber small hole on the side wall of the auxiliary tank 10 to approximately the midpoint of the auxiliary tank 10;

[0093] 7) Adjust the vacuum T-valve to a state that connects the air inlet and the outside gas, open the gas tank 17 and start injecting gas until the air in the gas transmission device is completely discharged, adjust the vacuum T-valve to a state that connects the air inlet and the air outlet, and continue injecting gas until the air in the metal needle tube 13 is completely discharged into the transformer oil in the auxiliary tank 10, stop injecting the gas to be tested, and continue to insert the metal needle tube 13 forward into the rubber hole on the side wall of the main tank 6 to the center of the field of view of the main tank 6 observation hole;

[0094] 8) Close the door, start adjusting the temperature, and turn on the power;

[0095] 9) When both the temperature and voltage reach the predetermined values, start gas injection and conduct the experiment;

[0096] 10) After the experiment, stop the gas injection, disconnect the power supply, and open the door when the temperature in the box drops to the normal range;

[0097] 11) Slowly pull the metal needle tube 13 out of the box, remove it from the gas outlet of the gas delivery device, clean it and wipe it dry;

[0098] 12) Separate the gas tank 17 containing the experimental gas from the gas delivery device;

[0099] 13) Disconnect the high-voltage cable 3 from the terminal on the side wall of the main tank 6, take the tank out of the box, and turn off the experimental light bulb;

[0100] 14) Open the lid of the auxiliary tank 10, pour out the oil in the tank, and clean the auxiliary tank 10;

[0101] 15) Open the lid of the main tank 6, pour out the oil in the tank, and clean the main tank 6;

[0102] 16) Wipe the inner walls of the main tank 6 and the auxiliary tank 10 dry and then cover them with lids;

[0103] 17) Process the experimental data and the experiment ends.

[0104] See also Figure 4 In one embodiment, a method for measuring characteristic gas diffusion coefficient in insulating oil is provided, which is applied to the device for measuring characteristic gas diffusion coefficient in insulating oil as described in any of the above embodiments. Specifically, the method comprises:

[0105] S10, determining a diffusion coefficient reference value of a characteristic gas in the measured insulating oil, simulating the diffusion coefficient reference value, and obtaining a bubble dissolution curve of a bubble characteristic size of the characteristic gas in the insulating oil changing with time;

[0106] S20, comparing the bubble dissolution curve with the fitting curve obtained according to the experimental data, and iteratively correcting the bubble dissolution curve using fluid simulation and measurement results so that the relative error between the bubble dissolution curve and the fitting curve reaches a preset value, and taking the characteristic gas diffusion coefficient at this time as the target measurement result.

[0107] It should be noted that, in order to improve the measurement accuracy, this embodiment adopts an improved bubble dissolution method to measure the diffusion coefficient of the characteristic gas in the insulating oil.

[0108] First, the value obtained by formula (2) is used as the reference value D. Specifically, considering the dissolution of bubbles in liquid, an expression describing the change of the radius of an isolated static bubble in an infinite volume of liquid with time is obtained, assuming that the liquid is not saturated with gas:

[0109]

[0110] Where R is the current value of the dissolved bubble radius, D is the diffusion coefficient of the gas in the liquid, and tt 0 is the time elapsed after the start of dissolution and k is the gas solubility coefficient.

[0111] Furthermore, the calculated curve is compared with the curve fitted by the experimental data, and the influence of the oil flow caused by bubble dissolution and the bubble deformation caused by the electric field on the measured value of the diffusion coefficient is corrected by iterative correction of the fluid simulation and measurement results. If the error between the experimental curve and the curve simulated by the nth iteration value Dn is less than the preset value after calculation, it is taken as the final measured value of the diffusion coefficient.

[0112] In a specific embodiment, in step S20, the bubble dissolution curve is iteratively corrected using the fluid simulation and measurement results so that the relative error between the bubble dissolution curve and the fitting curve reaches a preset value, including:

[0113] The diffusion coefficient reference value is reduced by one order of magnitude to obtain a diffusion coefficient sub-reference value;

[0114] updating the bubble dissolution curve according to the diffusion coefficient sub-reference value, and determining the positional relationship between the updated bubble dissolution curve and the fitting curve;

[0115] If the updated bubble dissolution curve is above the fitting curve, the relative error between the bubble dissolution curve and the fitting curve is calculated using the dichotomy method until the relative error reaches a preset value;

[0116] If the updated bubble dissolution curve is below the fitting curve, the step of reducing the diffusion coefficient reference value by one order of magnitude is returned.

[0117] It should be noted that the actual size of the bubble is determined by comparing the image of the bubble with that of a spherical etalon with a diameter of D = 1 mm, and the magnification factor is calculated by comparing the bubble image with the etalon image. Due to the different dielectric constants of the bubble and the insulating oil, the uneven distribution of the field intensity on the bubble surface causes the electric stress distribution on the bubble to be uneven, which causes the bubble to deform. The simulation calculation is used to simulate the convection motion caused by the bubble dissolution process and the bubble deformation process under the action of the electric field, so as to obtain a more accurate and reliable diffusion coefficient value.

[0118] In this embodiment, the initial size of the bubble is first selected to be equal to the experimental measurement value of each bubble, and the diffusion coefficient calculated by formula (2) is used as the initial reference value. The curve of the change of the characteristic size of the bubble over time is obtained by simulation calculation, and then the bubble dissolution curve obtained by simulation calculation is compared with the fitting curve recorded in the experiment. Because the reference value D is larger than the actual diffusion coefficient value, the curve of the change of the characteristic size over time obtained by substituting the reference value D is located below the experimental curve.

[0119] Specifically, the diffusion coefficient D is first reduced by one order of magnitude to obtain D1. If the simulation curve obtained by substituting D1 into the calculation is above the experimental curve, it can be determined that D<Dactual value<D1. Then the binary method is used to continuously approximate until -5%≤δ≤5%;

[0120] If the simulation curve is still below the experimental curve after D1 is substituted, continue to reduce it by one order of magnitude until the actual value D is found. Then use the dichotomy method to keep approximating until -5% ≤ δ ≤ 5%. If the difference between the experimental curve and the calculated curve in each case exceeds 5%, the diffusion coefficient is re-estimated. After several steps of coefficient fitting, the curves are basically consistent, and the diffusion coefficient finally calculated is considered to be accurate. Among them, the characteristic size data of the bubble obtained at different times in the experiment constitute vector A, and the corresponding data obtained by simulation constitute vector B. The relative error δ is shown in formula (3):

[0121]

[0122] In summary, the measurement method provided in this embodiment combines experiments with simulations, and iteratively corrects the effects of oil flow caused by bubble dissolution and bubble deformation caused by the electric field on the measured value of the diffusion coefficient based on fluid simulation and measurement results, thereby greatly improving the measurement accuracy of the diffusion coefficient and shortening the test cycle.

[0123] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0124] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0125] In this application, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0126] In the present application, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0127] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A device for measuring the diffusion coefficient of characteristic gases in insulating oil, It is characterized in that include: Experimental platform, constant temperature and humidity chamber, gas delivery device, observation device and terminal equipment; The experimental platform is arranged in the constant temperature and humidity chamber, and includes a main area and a secondary area; The gas introduction device is used to introduce the experimental gas into the main zone through the secondary zone; The main area includes a main tank, and an electrode plate is arranged in the main tank for measuring the diffusion coefficient of characteristic gas in insulating oil under different electric field strengths; a grid is also arranged in the main tank for absorbing bubbles generated by characteristic gas in liquid; the secondary area is arranged beside the main area, and includes a secondary tank and a secondary tank cover; the secondary tank cover is arranged on the top of the secondary tank; the tube walls of the secondary tank and the main tank are provided with a through hole that can be connected, and a rubber gasket is arranged on the through hole; The gas delivery device comprises: a gas tank, a valve and a needle tube; the gas tank is filled with experimental gas; one end of the valve is connected to the gas tank outlet, and the other end is connected to the needle tube; The needle tube delivers the experimental gas into the main tank through the auxiliary tank via the rubber gasket; The observation device is connected to the terminal device and is used to observe the experimental process of the experimental platform in real time and upload the generated experimental data to the terminal device.

2. The device for measuring characteristic gas diffusion coefficient in insulating oil according to claim 1, It is characterized in that The grid is a polytetrafluoroethylene grid with low dielectric constant fillers added.

3. The device for measuring characteristic gas diffusion coefficient in insulating oil according to claim 1, It is characterized in that The adjustable temperature range of the constant temperature and humidity box is 25° C. to 100° C.; the adjustable electric field strength range of the electrode plate is 0 to 40 kV / mm.

4. The device for measuring characteristic gas diffusion coefficient in insulating oil according to claim 1, It is characterized in that The main area also includes: Main tank cover, located on the top of the main tank; At least two insulators are arranged on the outer tank wall of the main tank and are respectively connected to two groups of high-voltage cables; one group of high-voltage cables is used to apply positive high voltage, and the other group of high-voltage cables is used to apply negative high voltage.

5. The device for measuring characteristic gas diffusion coefficient in insulating oil according to claim 1, It is characterized in that It also includes glass pieces, brackets and lighting fixtures; The glass sheet is arranged on the through hole of the constant temperature and humidity chamber, and is used to enable the observation device to observe the experimental process in the main area in real time; The main tank and the auxiliary tank are placed on the bracket; The lighting device is arranged below the bracket, and the normal working temperature range is 25°C to 90°C.

6. A method for measuring characteristic gas diffusion coefficient in insulating oil, applied to the device for measuring characteristic gas diffusion coefficient in insulating oil as claimed in any one of claims 1 to 5, It is characterized in that The method comprises: Determine the diffusion coefficient reference value of the characteristic gas in the tested insulating oil, simulate the diffusion coefficient reference value, and obtain the bubble dissolution curve of the characteristic size of the bubble of the characteristic gas in the insulating oil changing with time; The bubble dissolution curve is compared with the fitting curve obtained according to the experimental data, and the bubble dissolution curve is iteratively corrected using fluid simulation and measurement results so that the relative error between the bubble dissolution curve and the fitting curve reaches a preset value, and the characteristic gas diffusion coefficient at this time is used as the target measurement result.

7. The method for measuring characteristic gas diffusion coefficient in insulating oil according to claim 6, It is characterized in that The iterative correction of the bubble dissolution curve using the fluid simulation and the measurement results so that the relative error between the bubble dissolution curve and the fitting curve reaches a preset value includes: The diffusion coefficient reference value is reduced by one order of magnitude to obtain a diffusion coefficient sub-reference value; updating the bubble dissolution curve according to the diffusion coefficient sub-reference value, and determining the positional relationship between the updated bubble dissolution curve and the fitting curve; If the updated bubble dissolution curve is above the fitting curve, the relative error between the bubble dissolution curve and the fitting curve is calculated using the dichotomy method until the relative error reaches a preset value; If the updated bubble dissolution curve is below the fitting curve, the step of reducing the diffusion coefficient reference value by one order of magnitude is returned.

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