CN115201069A - Device and method for measuring diffusion coefficient of characteristic gas in insulating oil - Google Patents
Device and method for measuring diffusion coefficient of characteristic gas in insulating oil Download PDFInfo
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Abstract
The application discloses a device and a method for measuring a characteristic gas diffusion coefficient in insulating oil, wherein the device comprises an experiment platform, a constant temperature and humidity box, a gas feeding device, an observation device and terminal equipment; the experiment platform is arranged in the constant temperature and humidity box and comprises a main area and an auxiliary area; the gas feeding device is used for feeding the experimental gas into the main zone through the secondary zone; the main zone comprises a main tank provided with an electrode plate and is used for measuring the characteristic gas diffusion coefficients under different electric field strengths; the observation device is connected with the terminal equipment and is used for observing the experimental process in real time and uploading the generated experimental data to the terminal equipment. The device realizes the measurement of gas diffusion coefficients under different temperatures or electric field strengths through the constant temperature and humidity box and the electrode plate, and has wide application range. When the device is used for measurement, the measurement precision of the gas diffusion coefficient in the insulating oil is improved in a mutual iteration correction mode of experiment and simulation, the experiment period is short, the gas consumption is small, the operation is simple, and the safety of an experiment platform is improved.
Description
Technical Field
The application relates to the field of gas diffusion coefficient testing, in particular to a device and a method for measuring a characteristic gas diffusion coefficient in insulating oil.
Background
Diffusion is an important molecular transport mechanism, for example, when a concentration gradient exists in a component in a fluid, the thermal motion of molecules causes the component to be transported in the opposite direction of the concentration gradient. Generally, the flux of diffusion is proportional to the concentration gradient, and the proportionality coefficient is called diffusion coefficient, characterizes the diffusion capacity of the substance molecules, and is one of the basic physical properties of the substance. When the oil-immersed transformer fails in the thermal aging process or locally, the generated characteristic gas can migrate to other parts of the transformer through diffusion and convection. The characteristic gas is an important factor influencing the safe and stable operation of the oil-immersed transformer, and the diffusion coefficient of the characteristic gas in the insulating oil is mastered so as to know the distribution condition of the characteristic gas in the transformer oil, thereby accurately judging the operation state of the transformer, further optimizing the structural design and the online monitoring and detecting scheme of the transformer, and having very important significance for guaranteeing and promoting the safe and stable operation of the transformer.
The current methods for measuring the gas diffusion coefficient mainly comprise a capillary method, a pressure drop method and a bubble dissolution method. The capillary used in the capillary method has small volume, and the volumes of bubbles and a liquid column are small in the test process, so that the capillary is easily influenced by system temperature and pressure fluctuation in the test process, and further the measured diffusion coefficient has large error; the pressure drop method has the disadvantages that the experimental period is long, the precision of the gas with slow pressure drop is reduced, the error is increased, for example, the characteristic gases C2H4, C2H6 and the like, the diffusion coefficient under the room temperature condition is in the order of 10-9m2/s, and the pressure drop method can generate larger error due to the smaller diffusion coefficient. The conventional bubble dissolution method is a method for determining the gas diffusion coefficient by using optical recording of pure bubbles dissolved in degassed liquid, but it does not take into account the convective movement of the liquid during dissolution as the bubble size decreases, which would lead to a faster bubble dissolution process, which may lead to measured values larger than the actual values.
Disclosure of Invention
The application aims to provide a device and a method for measuring a characteristic gas diffusion coefficient in insulating oil, and aims to solve the problems of low measurement precision, long measurement period and limited application range in the existing method for measuring the characteristic gas diffusion coefficient of the insulating oil.
In order to achieve the above object, the present application provides an apparatus for measuring a characteristic gas diffusion coefficient in insulating oil, comprising:
the device comprises an experiment platform, a constant temperature and humidity box, a gas feeding device, an observation device and terminal equipment;
the experiment platform is arranged in the constant temperature and humidity box and comprises a main area and an auxiliary area;
the gas feeding device is used for feeding experimental gas into the primary zone through the secondary zone;
the main zone comprises a main tank, and an electrode plate is arranged in the main tank and used for measuring the characteristic gas diffusion coefficient in the insulating oil under different electric field strengths;
the observation device is connected with the terminal equipment and used for observing the experimental process of the experimental platform in real time and uploading generated experimental data to the terminal equipment.
Furthermore, a grid is arranged in the main tank and used for adsorbing bubbles generated by characteristic gas in liquid.
Further, the grid is a polytetrafluoroethylene grid added with a low dielectric constant filler.
Further, the adjustable temperature range of the constant temperature and humidity box is 25-100 ℃; the adjustable electric field intensity range of the electrode plate is 0-40 kV/mm.
Further, the primary zone further includes:
the main tank cover is arranged at the top of the main tank;
the at least two insulators are arranged on the outer tank wall of the main tank and are respectively connected with the two groups of high-voltage cables; one group of high-voltage cables is used for applying positive high voltage, and the other group of high-voltage cables is used for applying negative high voltage.
Furthermore, the auxiliary area is arranged beside the main area and comprises an auxiliary tank and an auxiliary tank cover;
the auxiliary tank cover is arranged at the top of the auxiliary tank;
the pipe wall of vice jar with main jar is equipped with the through-hole that can communicate, be equipped with the rubber packing ring on the through-hole.
Further, the gas feeding device includes:
a gas tank, a valve and a needle tube;
experimental gas is filled in the gas tank; one end of the valve is connected with the outlet of the gas tank, and the other end of the valve is connected with the needle tube; the needle tube sends experimental gas into the main tank through the auxiliary tank through the rubber gasket.
Further, the device for measuring the characteristic gas diffusion coefficient in the insulating oil further comprises a glass sheet, a bracket and a lighting device;
the glass sheet is arranged on the through hole of the constant temperature and humidity box and is used for enabling 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 temperature range of normal work is 25-90 ℃.
The application also provides a method for measuring the characteristic gas diffusion coefficient in the insulating oil, which is applied to the device for measuring the characteristic gas diffusion coefficient in the insulating oil, and the method comprises the following steps:
determining a diffusion coefficient reference value of the characteristic gas in the measured insulating oil, and simulating the diffusion coefficient reference value to obtain a bubble dissolution curve of the characteristic size of the characteristic gas in the insulating oil along with the change of time;
and comparing the bubble dissolution curve with a fitting curve obtained according to experimental data, and iteratively correcting the bubble dissolution curve by using a fluid simulation and measurement result so as to enable the relative error of the bubble dissolution curve and the fitting curve to reach a preset value, and taking the characteristic gas diffusion coefficient at the moment as a target measurement result.
Further, the iteratively correcting the bubble dissolution curve by using the fluid simulation and measurement results to enable the relative error between the bubble dissolution curve and the fitted curve to reach a preset value includes:
reducing the diffusion coefficient reference value 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 judging the position relation between the updated bubble dissolution curve and the fitting curve;
if the updated bubble dissolution curve is above the fitting curve, calculating the relative error between the bubble dissolution curve and the fitting curve by adopting a dichotomy until the relative error reaches a preset value;
and if the updated bubble dissolution curve is below the fitting curve, returning to execute the step of reducing the reference value of the diffusion coefficient by one order of magnitude.
Compared with the prior art, the beneficial effects of this application lie in:
1) The measuring device of the application adopts the special constant temperature box to control the temperature of the insulating oil, and realizes the measurement of diffusion coefficients of gas in the insulating oil at different temperatures;
2) Two electrode plates capable of adjusting the distance are additionally arranged in the measuring device, so that the electric field intensity can be adjusted within 0-40 kV, and the measurement of diffusion coefficients of gas in insulating oil under different electric field intensities is realized;
3) In order to conveniently observe the characteristic size of the bubbles, the measuring device fixes the bubbles by using a special polytetrafluoroethylene grid, and simultaneously obtains the special polytetrafluoroethylene grid with the same dielectric constant as that of the insulating oil by controlling the polymerization degree or adding a filler with low dielectric constant in order to eliminate the influence of the grid on the electric field distribution;
4) According to the measuring method, the influence of oil flow caused by bubble dissolution and bubble deformation caused by an electric field on the diffusion coefficient measured value is corrected through iteration of fluid simulation and a measuring result, and the diffusion coefficient of the gas in the insulating oil under a certain field intensity can be accurately measured.
Drawings
In order to more clearly illustrate the technical solution of the present application, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
FIG. 1 is a schematic structural diagram of an apparatus for measuring a characteristic gas diffusion coefficient in insulating oil according to an embodiment of the present application;
FIG. 2 is a schematic structural diagram of a device for measuring a characteristic gas diffusion coefficient in insulating oil according to yet another embodiment of the present application;
FIG. 3 is a schematic structural diagram of an apparatus for measuring a characteristic gas diffusion coefficient in insulating oil according to yet another embodiment of the present application;
fig. 4 is a schematic flowchart of a method for measuring a characteristic gas diffusion coefficient in insulating oil according to an embodiment of the present application.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments in the present application without making any creative effort belong to the protection scope of the present application.
It should be understood that the step numbers used herein are for convenience of description only and are not intended as limitations on the order in which the steps are performed.
It is to be understood that the terminology used in the description of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in the specification of the present application and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.
The terms "comprises" and "comprising" indicate the presence of the described features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
The term "and/or" refers to any and all possible combinations of one or more of the associated listed items and includes such combinations.
It should be noted that diffusion is a common molecular transport mechanism. When the oil-immersed transformer fails in the thermal aging process or locally, the generated characteristic gas can migrate to other parts of the transformer through diffusion and convection. Since the content of dissolved gas in oil measured by a DGA (dissolved gas in oil analysis) method is transported through a flow field to a sampling location, a DGA-based transformer fault diagnosis method is inseparable from a diffusion process of gas. Meanwhile, 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 working conditions, the diffusion coefficients of gas in insulating oil are different, so that a characteristic gas diffusion coefficient database covering the general working condition parameter range of the transformer needs to be established, and key data are provided for the calculation of dissolved gas transport behavior numerical values.
In order to grasp the diffusion coefficient of the characteristic gas in the insulating oil in time so as to know the distribution condition of the characteristic gas in the transformer oil, accurately judge the running state of the transformer and further optimize the structural design and the online monitoring and detecting scheme of the transformer, the common methods for measuring the diffusion coefficient of the gas at present mainly comprise a capillary method, a pressure drop method and a bubble dissolution method. Wherein,
the capillary method determines the molecular diffusion coefficient of a gas in a liquid by monitoring the interfacial movement. Experiment liquid is filled in the experiment front pipe, gas is injected into the pipe to form a bubble, and a diffusion experiment is carried out after the gas-liquid system reaches balance under constant pressure. The system is pressurized by a high pressure vessel, and the increase in pressure will result in an increase in the solubility of the gas in the test liquid, with a consequent mass transfer through the gas-liquid interface. The bubbles are reduced in size by the dissolution, and the interface between both sides of the bubbles moves toward the center. And observing and recording the movement of the interface in the whole process through a microscope, and finally, solving the diffusion coefficient by utilizing the solubility of the components in each phase and the movement data of the interface. The method has the advantages that the volume of the capillary used is small, and the volumes of the air bubbles and the liquid column are small in the test process, so that the method is easily influenced by system temperature and pressure fluctuation in the test process, and further the measured diffusion coefficient has large errors;
in the pressure drop method, when gas diffuses into a 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. The diffusion coefficient is obtained by recording pressure change data in the diffusion process and utilizing a diffusion equation and a mass conservation law. The method has the disadvantages that the experimental period is long, the precision of the gas with slow pressure drop is reduced, the error is increased, for example, the characteristic gases C2H4, C2H6 and the like have diffusion coefficients of 10-9m < 2 >/s at room temperature, and the pressure drop method is used to generate larger error because the diffusion coefficients are smaller.
The traditional bubble dissolution method is to inject bubbles into a container filled with insulating oil, and by observing the change of the radius of the bubbles along with time, the diffusion coefficient of gas in the liquid is deduced by using a formula describing the change of the radius of an isolated static bubble in an infinite volume of liquid along with time. This method is a method for determining the gas diffusion coefficient by means of optical recording of the dissolution of pure gas bubbles in degassed liquid, but it does not take into account the convective movements of the liquid during dissolution which occur as the size of the bubbles decreases, which would lead to a faster bubble dissolution process, which may lead to measured values that are greater than the actual values.
In summary, in view of the defects of the existing method, the present embodiment aims to provide a device for measuring a characteristic gas diffusion coefficient in insulating oil, which is capable of studying the diffusion coefficient of gas in insulating oil under different temperatures, pressures and electric field strengths, improving the measurement accuracy of the diffusion coefficient, and shortening the test period.
Referring to fig. 1, an embodiment of the present application provides an apparatus for measuring a characteristic gas diffusion coefficient in insulating oil, including:
the system comprises an experiment platform 03, a constant temperature and humidity box 2, a gas feeding device 04, an observation device 01 and terminal equipment 05;
the experiment platform 03 is arranged in the constant temperature and humidity box 2 and comprises a main area and an auxiliary area;
the gas feeding device 04 is used for feeding the experimental gas into the main zone through the secondary zone;
the main area comprises a main tank 6, and an electrode plate 8 is arranged in the main tank 6 and used for measuring the characteristic gas diffusion coefficient in the insulating oil under different electric field strengths;
the observation device 01 is connected with the terminal equipment 05 and is used for observing the experiment process of the experiment platform 03 in real time and uploading the generated experiment data to the terminal equipment 05.
In this embodiment, can understand that experiment platform 03 mainly sets up in constant temperature and humidity case 2, and includes main district and accessory region, and when measuring, gaseous feeding device 04 is used for sending experimental gas into the accessory region earlier, and the accessory region can communicate with the main district, therefore gaseous can follow the accessory region and get into the main jar 6 of main district in, then observes the experimental process in the main jar 6 through observation device 01. Wherein, the data generated in the observation can be uploaded to the terminal device 05 for subsequent analysis.
The core of the present embodiment is that the electrode plate 8 is provided in the main tank 6. In a preferred embodiment, the adjustable electric field strength of the electrode plate 8 is in the range of 0 to 40kV/mm. Used for researching the influence of the electric field action on the diffusion coefficient. Meanwhile, the electrode plate 8 is preferably a circular metal plate electrode with a diameter of 40mm, and the shape of the edge of the electrode is designed according to the Rogowski formula, so as to ensure that the field intensity between electrodes is uniformly distributed as much as possible and the distortion of the electric field at the edge is minimum. Preferably, the adjustable temperature range of the constant temperature and humidity box 2 is 25-100 ℃, so that the measurement of the diffusion coefficient of gas in insulating oil under different temperatures and electric field strengths can be realized.
Referring to fig. 2, in one specific embodiment, the observation device 01 of the apparatus for measuring diffusion coefficient of characteristic gas in insulating oil is mainly a camera, and the observation is performed through a telephoto lens 1 of the camera. The terminal device 05 is preferably a computer, and may be other terminals capable of displaying and analyzing data, such as an upper computer. In this embodiment, positive high pressure and negative high pressure are respectively applied to two ends of the experiment platform 03, and are used for adjusting 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. Therefore, the device not only can realize the measurement of the diffusion coefficient of the gas in the insulating oil under different temperatures and electric field intensities, but also can measure the diffusion coefficient of the gas in the insulating oil under different pressures.
Referring to fig. 3, fig. 3 provides a specific internal structure diagram of the apparatus for measuring characteristic gas diffusivity in insulating oil. In a specific embodiment, as shown in fig. 3, a grid 9 is further provided in the main tank 6 for adsorbing bubbles generated in the liquid by the characteristic gas. Preferably, the mesh 9 is a polytetrafluoroethylene mesh 9 to which a low dielectric constant filler is added.
It should be noted that the grid 9 is a key element of the experiment platform 03 in this embodiment, because the grid 9 fixes the dissolved bubbles so as to observe the characteristic size change of the bubbles, and the specially-made teflon grid 9 has a dielectric constant similar to that of the insulating oil by changing the polymerization degree of the teflon or adding a filler with a low dielectric constant, so that the bubbles of the characteristic gas in the insulating oil can be better adsorbed.
Continuing to refer to fig. 3, the main area further includes:
the main tank cover 7 is arranged at the top of the main tank 6;
the at least two insulators 5 are arranged on the outer tank wall of the main tank 6 and are respectively connected with the two groups of high-voltage cables 3; one group of high voltage cables 3 is used for applying a positive high voltage, and the other group of high voltage cables 3 is used for applying a negative high voltage.
Further, the auxiliary area is arranged beside the main area and comprises an auxiliary tank 10 and an auxiliary tank cover 11; wherein,
the auxiliary tank cover 11 is arranged at the top of the auxiliary tank 10;
the pipe walls of the auxiliary tank 10 and the main tank 6 are provided with through holes which can be communicated, and rubber gaskets 12 are arranged on the through holes.
In a preferred embodiment, the gas feeding means 04 comprises:
a gas tank 17, a valve 16 and a needle tube 13;
experimental gas is filled in the gas tank 17; one end of the valve 16 is connected with the outlet of the gas tank 17, and the other end is connected with the needle tube 13; the needle tube 13 sends the test gas into the main tank 6 through the sub-tank 10 via the rubber packing 12. Wherein, the middle of the rubber gasket 12 is also provided with a small hole, and the needle tube 13 mainly sends gas through the small hole. The orifice is closed when the needle-free tube 13 passes through it.
In a preferred embodiment, the device for measuring the characteristic gas diffusion coefficient in the insulating oil further comprises a glass sheet 4, a bracket 14 and a lighting device 15;
the glass sheet 4 is arranged on the through hole of the constant temperature and humidity box 2 and is used for enabling the observation device 01 to observe the experiment process in the main area in real time;
the main tank 6 and the auxiliary tank 10 are placed on the bracket 14;
the lighting device 15 is arranged below the bracket 14, and the temperature range of normal work is 25-90 ℃.
It can be understood that the working temperature of the device for measuring the characteristic gas diffusion coefficient in the insulating oil built by the structure is adjusted within the range of 10-90 ℃, and the external electric field can be continuously adjusted between 0 and 40kV/mm.
Generally, the simplest way to compare experimental data and calculations is to directly use geometry. To achieve this, dissolved gas bubbles are placed on the grid 9 inside the liquid. The tank bottom and the tank cover are both made of glass, so that the dissolution condition of the micro bubbles can be observed by using a microscope, and the diameters of the bubbles are about 1 mm. The bubbles are delivered into the container using a syringe and needle. The bubbles float upward and are adsorbed on the mesh 9.
Further, in the present embodiment, the change with time of the characteristic size of the bubble in the oil, such as the major axis and the minor axis of the ellipsoid, is recorded by using a camera connected to the special telephoto lens 1.
Preferably, the glass sheet 4 is a transparent glass sheet 4 having a thickness of 5mm. The main tank 6, the main tank cover 7, the auxiliary tank 10 and the auxiliary tank cover 11 are made of organic glass materials, and the wall thickness of the main tank 6, the wall thickness of the auxiliary tank 10, the thickness of the main tank cover 7 and the thickness of the auxiliary tank cover 11 are all 10mm.
In a specific embodiment, the step of performing a measurement experiment of the characteristic gas diffusion coefficient based on the apparatus for measuring the characteristic gas diffusion coefficient in insulating oil specifically includes:
1) The covers of the main tank 6 and the auxiliary tank 10 are opened, the adjusting knob of the electrode plate 8 is rotated, the distance between the electrode plates 8 is adjusted to the required distance (the adjustable range of the distance d between the electrode plates 8 is 0-20 mm, the adjustable range of the voltage U between the electrode plates 8 is 0-100 kV by adopting high-voltage direct-current power supplies with positive and negative polarities), and the calculation formula of the electric field intensity E is as follows:
where U is the voltage between the two electrode plates 8 and d is the distance between the electrode plates 8.
2) Filling oil into the tank until the oil level in the main tank 6 and the auxiliary tank 10 is close to the tank opening, and covering and sealing the main tank 6 and the auxiliary tank 10;
3) Putting the tank body on a frame in a constant temperature and humidity box 2, and turning on a small experimental bulb;
4) Introducing the high-voltage cable 3 from the outside of the tank, connecting to a terminal on the side wall of the main tank 6;
5) Connecting a gas tank 17 filled with experimental gas to a gas inlet of a gas transmission device, wherein a gas outlet of the gas tank is connected to the metal needle tube 13;
6) A metal needle tube 13 is led in from the outside of the tank through a small hole on the side wall of the tank body, and then is inserted into a rubber small hole on the side wall of the auxiliary tank 10 to approximately the midpoint of the auxiliary tank 10;
7) Adjusting the vacuum T-shaped valve to a state of communicating an air inlet and external air, opening the air tank 17 to start air injection until air in the air transmission device is completely discharged, adjusting the vacuum T-shaped valve to a state of communicating the air inlet and an air outlet, continuing to inject air until the air in the metal needle tube 13 is completely discharged into transformer oil in the auxiliary tank 10, stopping injecting the gas to be detected, and continuing to insert the metal needle tube 13 forwards into a rubber small hole on the side wall of the main tank 6 to the center of the visual field of an observation hole of the main tank 6;
8) Closing the box door, starting to regulate the temperature, and switching on a power supply;
9) When the temperature and the voltage reach preset values, gas injection is started to perform an experiment;
10 After the experiment is finished, stopping gas injection, cutting off the power supply, and opening the box door when the temperature in the box is reduced to a normal range;
11 The metal needle tube 13 is slowly pulled out of the box body and is unloaded from the air outlet of the air conveying device, cleaned and wiped dry;
12 Separate the gas tank 17 containing the test gas from the gas transport means;
13 Disconnect the high voltage cable 3 from the main tank 6 side wall terminal, take the tank out of the box, close the experimental small bulb;
14 Opening the lid of the sub-tank 10, pouring out the oil in the tank, and washing the sub-tank 10;
15 Opening the lid of the main tank 6, pouring out the oil in the tank, and washing the main tank 6;
16 The inner walls of the main tank 6 and the auxiliary tank 10 are wiped dry and then covered with a cover;
17 Processing experimental data and ending the experiment.
Referring to fig. 4, in an embodiment, there is further provided a method for measuring a characteristic gas diffusion coefficient in insulating oil, applied to the apparatus for measuring a characteristic gas diffusion coefficient in insulating oil according to any of the embodiments above, specifically, the method includes:
s10, determining a diffusion coefficient reference value of the characteristic gas in the measured insulating oil, and simulating the diffusion coefficient reference value to obtain a bubble dissolution curve of the characteristic size of the characteristic gas in the insulating oil along with the change of time;
s20, comparing the bubble dissolution curve with a fitting curve obtained according to experimental data, and iteratively correcting the bubble dissolution curve by using a fluid simulation and measurement result so as to enable the relative error between the bubble dissolution curve and the fitting curve to reach a preset value, and taking the characteristic gas diffusion coefficient at the moment as a target measurement result.
It should be noted that, in order to improve the measurement accuracy, the present embodiment adopts a modified bubble dissolution method to determine the diffusion coefficient of the characteristic gas in the insulating oil.
First, the numerical value obtained by the formula (2) is used as the reference value D. Specifically, considering the dissolution of bubbles in a liquid, an expression is obtained describing the variation over time of the radius of an isolated stationary bubble in an infinitely large volume of liquid, assuming that the gas in the liquid is not saturated:
where R is the current value of the dissolved bubble radius, D is the diffusion coefficient of the gas in the liquid, t-t 0 Is the time elapsed after the start of dissolution, and k is the gas solubility coefficient.
And further, comparing the calculated curve with a curve fitted by experimental data, and iteratively correcting the influence of bubble deformation caused by oil flow and an electric field on the diffusion coefficient measured value through fluid simulation and a measurement result. And if the error between the experimental curve and the curve simulated by the nth iteration value Dn is smaller than a preset value through calculation, taking the experimental curve and the curve simulated by the nth iteration value Dn as a final measurement value of the diffusion coefficient.
In one embodiment, the iteratively correcting the bubble dissolution curve by using the fluid simulation and measurement result in step S20 to make the relative error between the bubble dissolution curve and the fitting curve reach a preset value includes:
reducing the diffusion coefficient reference value 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 judging the position relation between the updated bubble dissolution curve and the fitting curve;
if the updated bubble dissolution curve is above the fitting curve, calculating the relative error between the bubble dissolution curve and the fitting curve by adopting a dichotomy until the relative error reaches a preset value;
and if the updated bubble dissolution curve is below the fitting curve, returning to execute the step of reducing the reference value of the diffusion coefficient by one order of magnitude.
The actual size of the bubble is determined by comparing the image of the bubble with the image of the spherical etalon having a diameter of D =1mm, and the magnification factor is calculated by comparing the image of the bubble with the image of the etalon. Because the dielectric constants of the bubbles and the insulating oil are different, the distribution of the electric stress borne by the bubbles is also uneven due to the unevenness of the field intensity distribution on the surfaces of the bubbles, so that the bubbles are deformed, and the convection motion caused by the bubble deformation process under the action of the bubble dissolution process and the electric field is simulated through simulation calculation so as to obtain a more accurate and reliable diffusion coefficient value.
In this embodiment, the initial size of the bubble is selected to be equal to the experimental measurement value of each bubble, the diffusion coefficient calculated by the formula (2) is used as the initial reference value, the change curve of the characteristic size of the bubble with time is obtained through simulation calculation, and then the bubble dissolution curve obtained through 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, a curve of the characteristic size changing along with time obtained by substituting the reference value D in simulation is positioned below the experimental curve.
Specifically, the diffusion coefficient D is reduced by one order of magnitude to obtain D1, if the simulation curve obtained by substituting D1 into the calculation is positioned above the experimental curve, the actual value of D is more than D and less than D1, and then the dichotomy is adopted for continuous approximation until delta is more than or equal to minus 5% and less than or equal to 5%;
if the simulation curve is still positioned below the experimental curve after the D1 is substituted, continuing to reduce by one order of magnitude until an interval where the actual value D is located is found out, and then continuously approximating by adopting a dichotomy until delta is more than or equal to minus 5% and less than or equal to 5%. If the difference between the experimental curve and the calculated curve in each case exceeds 5%, the diffusion coefficient is re-estimated, and after several steps of coefficient fitting, the curves are substantially consistent, and the finally calculated diffusion coefficient is considered to be accurate. The characteristic size data of the bubble obtained through the experiment at different moments form a vector A, the corresponding data obtained through simulation form a vector B, and the relative error delta is shown as a formula (3):
in summary, the measurement method provided in this embodiment combines the experiment and the simulation, and iteratively corrects the influence of the bubble deformation caused by the oil flow and the electric field due to the bubble dissolution on the diffusion coefficient measurement value based on the fluid simulation and the measurement result, thereby greatly improving the measurement accuracy of the diffusion coefficient and shortening the test period.
In the description of the present application, it is to be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," and the like are used in the orientations and positional relationships indicated in the drawings for convenience in describing the present application and for simplicity in description, and are not intended to indicate or imply that the referenced devices or elements must have a particular orientation, be constructed in a particular orientation, and be operated in a particular manner, and thus should not be considered limiting.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present application, "a plurality" means two or more unless specifically limited otherwise.
In this application, unless expressly stated or limited otherwise, the terms "mounted," "connected," "secured," and the like are to be construed broadly and encompass, for example, both fixed and removable connections or integral parts thereof; can be mechanically or electrically connected; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meaning of the above terms in the present application can be understood by those of ordinary skill in the art as appropriate.
In this application, unless expressly stated or limited otherwise, the recitation of a first feature "on" or "under" a second feature may include the recitation of the first and second features being in direct contact, and may also include the recitation of the first and second features not being in direct contact, but being in contact with another feature between them. Also, the first feature being "on," "above" and "over" the second feature includes the first feature being directly on and obliquely above the second feature, or merely indicating that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature includes the first feature being directly under and obliquely below the second feature, or simply meaning that the first feature is at a lesser elevation than the second feature.
Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present application, and not for limiting the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions in the embodiments of the present application.
Claims (10)
1. A device for measuring a characteristic gas diffusion coefficient in insulating oil, comprising:
the device comprises an experiment platform, a constant temperature and humidity box, a gas feeding device, an observation device and terminal equipment;
the experiment platform is arranged in the constant temperature and humidity box and comprises a main area and an auxiliary area;
the gas feeding device is used for feeding experimental gas into the primary zone through the secondary zone;
the main zone comprises a main tank, and an electrode plate is arranged in the main tank and used for measuring the characteristic gas diffusion coefficient in the insulating oil under different electric field strengths;
the observation device is connected with the terminal equipment and used for observing the experimental process of the experimental platform in real time and uploading generated experimental data to the terminal equipment.
2. The apparatus of claim 1, wherein a grid is further provided in the main tank for adsorbing bubbles generated by the characteristic gas in the liquid.
3. The apparatus of claim 2, wherein the grid is a polytetrafluoroethylene grid incorporating a low dielectric constant filler.
4. The apparatus for measuring the characteristic gas diffusion coefficient in the insulating oil according to claim 1, wherein the adjustable temperature range of the constant temperature and humidity chamber is 25 ℃ to 100 ℃; the adjustable electric field intensity range of the electrode plate is 0-40 kV/mm.
5. The apparatus of claim 1, wherein the primary zone further comprises:
the main tank cover is arranged at the top of the main tank;
the at least two insulators are arranged on the outer tank wall of the main tank and are respectively connected with the two groups of high-voltage cables; one group of high-voltage cables is used for applying positive high voltage, and the other group of high-voltage cables is used for applying negative high voltage.
6. The apparatus of claim 1, wherein the secondary region is provided beside the primary region and includes a secondary tank and a secondary cover;
the auxiliary tank cover is arranged at the top of the auxiliary tank;
the pipe wall of the auxiliary tank and the pipe wall of the main tank are provided with through holes which can be communicated, and rubber gaskets are arranged on the through holes.
7. The apparatus of claim 6, wherein the gas feed means comprises:
a gas tank, a valve and a needle tube;
experiment gas is filled in the gas tank; one end of the valve is connected with the outlet of the gas tank, and the other end of the valve is connected with the needle tube; the needle tube sends experimental gas into the main tank through the auxiliary tank through the rubber gasket.
8. The apparatus of claim 7, further comprising a glass sheet, a holder, and an illumination device;
the glass sheet is arranged on the through hole of the constant temperature and humidity box and is used for enabling the observation device to observe the experiment 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 temperature range of normal work is 25-90 ℃.
9. A method for measuring a characteristic gas diffusivity in insulating oil, applied to the apparatus for measuring a characteristic gas diffusivity in insulating oil according to any one of claims 1 to 8, comprising:
determining a diffusion coefficient reference value of the characteristic gas in the measured insulating oil, and simulating the diffusion coefficient reference value to obtain a bubble dissolution curve of the characteristic size of the characteristic gas in the insulating oil along with the change of time;
and comparing the bubble dissolution curve with a fitting curve obtained according to experimental data, and iteratively correcting the bubble dissolution curve by using a fluid simulation and measurement result so as to enable the relative error of the bubble dissolution curve and the fitting curve to reach a preset value, and taking the characteristic gas diffusion coefficient at the moment as a target measurement result.
10. The method of claim 9, wherein the iteratively correcting the bubble dissolution curve using the fluid simulation and measurement results to make the relative error between the bubble dissolution curve and the fitted curve reach a preset value comprises:
reducing the diffusion coefficient reference value 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 judging the position relation between the updated bubble dissolution curve and the fitting curve;
if the updated bubble dissolution curve is above the fitting curve, calculating the relative error between the bubble dissolution curve and the fitting curve by adopting a dichotomy until the relative error reaches a preset value;
and if the updated bubble dissolution curve is below the fitting curve, returning to execute the step of reducing the reference value of the diffusion coefficient by one order of magnitude.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202210923226.3A CN115201069A (en) | 2022-08-02 | 2022-08-02 | Device and method for measuring diffusion coefficient of characteristic gas in insulating oil |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202210923226.3A CN115201069A (en) | 2022-08-02 | 2022-08-02 | Device and method for measuring diffusion coefficient of characteristic gas in insulating oil |
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| CN202210923226.3A Pending CN115201069A (en) | 2022-08-02 | 2022-08-02 | Device and method for measuring diffusion coefficient of characteristic gas in insulating oil |
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| CN (1) | CN115201069A (en) |
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