A method and system for apparent density measurement

Abstract

The application discloses a kind of apparent density measurement method and system, applied to apparent density measurement technical field, method includes: based on the volume measured data of sample insulating paperboard in target measurement environment, the porosity influence of solid medium is determined;In first pressure environment, the first volume variation degree of solid medium under preset pressure condition is analyzed, and the compression influence condition is obtained;In second temperature environment, the second volume variation degree of solid medium under preset temperature condition is analyzed, and the temperature influence condition is obtained;In measured environment, the volume measurement data of insulating paperboard to be measured is acquired, and the measured environment condition is acquired;Based on measured environment condition, porosity influence, compression influence and temperature influence, volume measurement data is processed, and the apparent density result of insulating paperboard to be measured is obtained.The apparent density measurement method and system provided by the application effectively improve the accuracy of insulating paperboard apparent density result.

Description

Technical Field

[0001] This invention relates to the field of apparent density measurement technology, and in particular to an apparent density measurement method and system. Background Technology

[0002] In oil-immersed power transformers, insulating paperboard, as a key solid insulating material, constitutes the main insulation barrier between windings, between windings and ground, and between turns / layers. It can uniformly distribute the electric field and improve the overall breakdown strength; it also provides mechanical support to fix the winding structure and withstand short-circuit electromagnetic forces, ensuring the long-term reliability of the equipment. The apparent density of insulating paperboard refers to the mass of the insulating paperboard per unit apparent volume, which includes the volume of solid fibers and the volume of internal closed pores. Higher apparent density means fewer closed pores and higher breakdown strength; conversely, lower apparent density makes partial discharge or even breakdown more likely.

[0003] However, the surface of insulating paperboard has openings that communicate with the outside, microscopic depressions, and macroscopic warping that create voids. If these openings and voids are included in the calculation of the apparent density of the insulating paperboard, the resulting apparent density will be inaccurate.

[0004] The existing method for measuring the apparent density of insulating paperboard is a geometric measurement method. This involves measuring the length, width, and height of the insulating paperboard with a micrometer or calipers, multiplying these dimensions to obtain the volume, and then calculating the apparent density based on the volume and mass. However, micrometer or caliper measurements include voids caused by warping in the volume, leading to inaccurate apparent density. This results in paperboards with numerous closed pores being deemed acceptable due to their smooth surface. Ultimately, this leads to the use of insulating paperboard with internal defects. If the apparent density of the insulating paperboard is low, it will retain many closed pores or micropores. Under a high electric field, the gas in these gaps, with a dielectric strength much lower than that of oil-impregnated paper insulation, will ionize first, triggering partial discharge. This can ultimately lead to insulation breakdown, causing transformer failure or even serious accidents. Summary of the Invention

[0005] This invention provides a method and system for measuring apparent density, which solves the technical problem that existing techniques for measuring apparent density include the openings and voids on the surface of insulating paperboard, leading to inaccurate apparent density measurements. This invention aims to improve the accuracy of the apparent density results for insulating paperboard.

[0006] To address the aforementioned technical problems, this invention provides a method and system for measuring apparent density, the method comprising: Based on the measured volume data of the sample insulating paperboard in the target measurement environment, the influence of the porosity of the solid medium is determined. The target measurement environment is constructed by placing the sample insulating paperboard in the solid medium. Under a first pressure environment, the degree of first volume change of the solid medium under the preset pressure condition is analyzed to obtain the compression effect; In a second temperature environment, the degree of second volume change of the solid medium under the preset temperature conditions is analyzed to obtain the temperature influence. The actual test environment is determined based on the preset pressure and preset temperature conditions; Under the stated test environment, the volume measurement data of the insulating paperboard to be measured was obtained, and the test environment conditions were also obtained. The volume measurement data is processed based on the measured environmental conditions, the influence of porosity, the influence of compression, and the influence of temperature to obtain the apparent density result of the insulating paperboard to be measured.

[0007] Preferably, the determination of the influence of the porosity of the solid medium based on the measured volume data of the sample insulating paperboard in the target measurement environment, wherein the target measurement environment is constructed by placing the sample insulating paperboard in the solid medium, includes: The target measurement environment includes at least fixed pressure data and fixed temperature data; Based on the fixed pressure data and the fixed temperature data, the sample insulating paperboard is placed in the solid medium to obtain the measured volume data; The measured volume data is processed to obtain the influence of porosity.

[0008] Preferably, the step of analyzing the degree of first volume change of the solid medium under the preset pressure condition in the first pressure environment to obtain the compression effect includes: The first pressure environment includes at least the fixed temperature data; Analyze the solid medium to determine the pressure progression; Based on the pressure progression, the preset pressure condition is determined; Based on the fixed temperature data, the first volume change degree of the solid medium under the preset pressure condition is obtained; Extract the first volume measurement data corresponding to each progressive pressure under the pressure progression in the first volume change condition; The compression effect is obtained by processing the progressive pressure and the corresponding first volume measurement data.

[0009] Preferably, the step of analyzing the degree of second volume change of the solid medium under a preset temperature condition in a second temperature environment to obtain the temperature influence includes: The second temperature environment includes at least the fixed pressure data; Determine the set of measurement temperatures; Based on the measured temperature set, the preset temperature conditions are determined; Based on the fixed pressure data, the second volume change degree of the solid medium under the preset temperature condition is obtained; Extract the second volume measurement data corresponding to each measurement temperature in the measurement temperature set of the second volume change degree; The temperature measurement data and the corresponding second volume measurement data are processed to obtain the temperature influence.

[0010] Preferably, the step of processing the volume measurement data based on the measured environmental conditions, the influence of porosity, the influence of compression, and the influence of temperature to obtain the apparent density result of the insulating paperboard to be measured includes: The measured environmental conditions include at least measured pressure data and measured temperature data; Based on the aforementioned impact of porosity, the porosity correction amount is obtained; Based on the compression effect and the measured pressure data, the compression correction amount is obtained; Based on the temperature influence and the measured temperature data, the temperature correction amount is obtained; The volume measurement data is processed based on the porosity correction, the compression correction, and the temperature correction to obtain the apparent density result.

[0011] Another aspect of the present invention provides an apparent density measurement system, comprising: The porosity module is used to determine the influence of the porosity of the solid medium based on the measured volume data of the sample insulating paperboard in the target measurement environment, wherein the target measurement environment is constructed by placing the sample insulating paperboard in the solid medium. The first module is used to analyze the degree of volume change of the solid medium under the preset pressure condition under the first pressure environment, and to obtain the compression effect. The second module is used to analyze the degree of second volume change of the solid medium under the preset temperature conditions in a second temperature environment, and to obtain the temperature influence. The actual measurement module is used to determine the actual measurement environment based on the preset pressure conditions and the preset temperature conditions; The acquisition module is used to acquire volume measurement data of the insulating paperboard to be measured under the actual measurement environment, and to acquire the actual measurement environment conditions. The processing module is used to process the volume measurement data based on the measured environmental conditions, the influence of porosity, the influence of compression, and the influence of temperature to obtain the apparent density result of the insulating paperboard to be measured.

[0012] Preferably, the porosity module includes: A target measurement environment unit, wherein the target measurement environment includes at least fixed pressure data and fixed temperature data; The volume measurement data unit is used to place the sample insulating paperboard in the solid medium based on the fixed pressure data and the fixed temperature data to obtain the volume measurement data. The porosity influence unit is used to process the measured volume data to obtain the porosity influence.

[0013] Preferably, the first module includes: A first pressure environment unit is configured to include at least the fixed temperature data in the first pressure environment. The pressure progression unit is used to analyze the solid medium and determine the pressure progression. A preset pressure condition unit is used to determine the preset pressure condition based on the pressure progression. The first volume change degree unit is used to obtain the first volume change degree of the solid medium under the preset pressure condition based on the fixed temperature data. The first volume measurement data unit is used to extract the first volume measurement data corresponding to each progressive pressure under the pressure progression in the first volume change degree. The compression effect unit is used to process each of the progressive pressures and the corresponding first volume measurement data to obtain the compression effect.

[0014] Preferably, the second module includes: A second temperature environment unit is used to provide that the second temperature environment includes at least the fixed pressure data; A determination unit is used to determine the set of measured temperatures; A preset temperature condition unit is used to determine the preset temperature condition based on the measured temperature set; The second volume change degree unit is used to obtain the second volume change degree of the solid medium under the preset temperature condition based on the fixed pressure data. The second volume measurement data unit is used to extract the second volume measurement data corresponding to each measurement temperature in the measurement temperature set of the second volume change degree; The temperature influence unit is used to process the measured temperatures and the corresponding second volume measurement data to obtain the temperature influence information.

[0015] Preferably, the processing module includes: The measured environment condition unit is used to ensure that the measured environment condition includes at least measured pressure data and measured temperature data. A porosity correction unit is used to obtain a porosity correction amount based on the porosity influence. The compression correction unit is used to obtain the compression correction amount based on the compression effect and the measured pressure data; The temperature correction unit is used to obtain the temperature correction amount based on the temperature influence and the measured temperature data. The apparent density result unit is used to process the volume measurement data based on the porosity correction, the compression correction, and the temperature correction to obtain the apparent density result.

[0016] Compared with the prior art, the beneficial effects of the present invention are at least one of the following: (1) This invention constructs a target measurement environment by placing insulating paperboard in a solid medium. The solid medium particles, under pressure, squeeze and fill the openings, micro-depressions, and macro-warping voids on the surface of the insulating paperboard, thereby measuring the true apparent volume after eliminating surface interference. Specifically, when a preset pressure is applied to solid medium particles such as spherical or near-spherical particles, relative sliding and rearrangement occur between the particles, gradually forming a dense accumulation and embedding them into the openings and depressions on the surface of the insulating paperboard. Simultaneously, the rigidity of the particles allows them to support and fill the voids formed by macro-warping, ensuring that the volume occupied by the solid medium no longer includes these surface irregularities. Unlike liquid media, solid medium particles do not penetrate the fibers of the insulating paperboard, causing swelling or structural changes; therefore, the original state of the insulating paperboard is maintained before and after measurement.

[0017] (2) This invention constructs a target measurement environment in which the sample insulating paperboard is placed in a solid medium. Volume measurement data is collected in the target measurement environment to determine the influence of the porosity of the solid medium, thereby eliminating the volume measurement deviation caused by the porosity of the solid measurement medium itself in subsequent measurements. At the same time, the compression influence is obtained by analyzing the first volume change of the solid medium under the preset pressure condition in the first pressure environment, and the temperature influence is obtained by analyzing the second volume change of the solid medium under the preset temperature condition in the first pressure environment. Then, after obtaining the volume measurement data of the insulating paperboard to be measured and the actual measurement environment conditions in the actual measurement environment, the volume measurement data is processed based on the actual measurement environment conditions, the porosity influence, the compression influence, and the temperature influence to obtain the apparent density result of the insulating paperboard to be measured. This invention avoids the shortcomings of traditional geometric measurement methods that include the void space caused by warping in the volume calculation, effectively eliminates the interference of open holes and surface voids on density calculation, and compensates for the influence of pressure and temperature on the volume of the measurement medium. This significantly improves the measurement accuracy of the apparent density of insulating paperboard, and can reliably identify defective paperboard with closed air holes or micropores inside, preventing its use, reducing the risk of partial discharge and insulation breakdown in transformers, and ensuring the safe operation of equipment. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the apparent density measurement of insulating paperboard in one embodiment of the present invention; Figure 2 This is a flowchart illustrating the apparent density measurement method in one embodiment of the present invention; Figure 3 This is a schematic diagram of the apparent density measurement of the sample insulating paperboard in one embodiment of the present invention; Figure 4 This is a schematic diagram illustrating the measurement of the effect of solid medium compression under a first pressure environment in one embodiment of the present invention; Figure 5 This is a schematic diagram of the apparent density measurement system in one embodiment of the present invention; Figure label: Among them, 11. Porosity module; 12. First module; 13. Second module; 14. Measurement module; 15. Acquisition module; 16. Processing module. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] In the description of this invention, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," "third," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0021] In the description of this invention, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to communication within two components. The terms "vertical," "horizontal," "left," "right," "upper," "lower," and similar expressions used herein are for illustrative purposes only and do not indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0022] In the description of this invention, it should be noted that, unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in this specification is for the purpose of describing specific embodiments only and is not intended to limit the invention. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0023] In an oil-immersed power transformer, the apparent density of insulating cardboard directly affects its breakdown strength. In the existing geometric measurement method, the void spaces formed by the open pores, depressions, and warping on the cardboard surface are included in the volume, resulting in a low measured value of the apparent density. As a result, defective cardboard with a large number of closed pores and insufficient apparent density inside is misjudged as qualified because of its flat surface. After these defective cardboard are put into use, under the action of a high electric field, partial discharge is likely to occur in the internal air gaps, and ultimately insulation breakdown may be triggered, causing serious accidents to the transformer.

[0024] An embodiment of the present invention provides a schematic diagram for measuring the apparent density of insulating cardboard. Specifically, please refer to Figure 1 , Figure 1 which shows a schematic diagram for measuring the apparent density of insulating cardboard in one embodiment of the present invention. The insulating cardboard to be measured is completely buried in a solid medium. The solid medium surrounds the cardboard from all around and above. By applying solid pressure or gas pressure from above and combining with vibration excitation at the bottom or circumferentially, the solid medium particles flow and tightly fill the open pores, depressions, and warping voids on the cardboard surface. A spherical particle medium with high fluidity, non-wetting property, and anti-static property is used. High-strength glass microspheres or ceramic microspheres with a particle size of 0.2 - 0.3 mm are preferably used. Under the action of pressure, the particles of this medium slide and rearrange with each other, gradually embedding and filling the open pores, micro depressions, and macro warping voids on the surface of the insulating cardboard. At the same time, due to its stable physical form, it will not penetrate into the cardboard fibers to cause swelling or structural changes, so as to measure the true apparent volume after excluding surface interference. The reason why a liquid (such as oil or water) cannot be used as the medium is that the insulating cardboard, as a solid insulating material of the transformer, has a liquid-loving property and hygroscopicity. After contact with the liquid, it will infiltrate into the fiber interior, resulting in swelling of the cardboard, an increase in volume, and an irreversible change in dielectric properties, and the true apparent volume in the original state cannot be measured. The reason why a gas cannot be used as the medium is that the gas molecule scale is extremely small, and under the action of pressure, it will directly penetrate the open pores and fiber gaps of the cardboard, unable to form effective filling. At the same time, the compressibility of the gas is extremely strong, and it is difficult to establish a stable volume measurement benchmark under pressure.

[0025] However, the volume data measured only by squeezing and filling the surface voids of the insulating cardboard with a solid medium still includes the inherent gap volume between the solid medium particles, the volume compression of the medium caused by pressure fluctuations, and the volume change of the medium caused by thermal expansion and contraction due to temperature changes. If the apparent density is directly calculated using this original volume data, the above three additional volume deviations will be superimposed on the measurement result, resulting in a low or fluctuating density value.

[0026] Therefore, an embodiment of the present invention provides an apparent density measurement method. Specifically, please refer to Figure 2 , Figure 2 which shows a schematic flow diagram of the apparent density measurement method in one embodiment of the present invention, including: S1. Based on the measured volume data of the sample insulating paperboard in the target measurement environment, determine the influence of the porosity of the solid medium. The target measurement environment is constructed by placing the sample insulating paperboard in a solid medium. S2. Under the first pressure environment, analyze the degree of first volume change of the solid medium under the preset pressure conditions to obtain the compression effect. S3. Under the second temperature environment, analyze the degree of second volume change of the solid medium under the preset temperature conditions to obtain the temperature influence. S4. Determine the actual measurement environment based on preset pressure and temperature conditions; S5. Under actual testing conditions, obtain the volume measurement data of the insulating paperboard to be measured, and obtain the actual testing environment conditions; S6. Based on the actual environmental conditions, the influence of porosity, the influence of compression, and the influence of temperature, the volume measurement data is processed to obtain the apparent density result of the insulating paperboard to be measured.

[0027] First, based on the measured volume data of the sample insulating paperboard in the target measurement environment, the influence of the porosity of the solid medium is determined. The target measurement environment is constructed by placing the sample insulating paperboard in a solid medium. The target measurement environment includes at least fixed pressure data and fixed temperature data. Based on the fixed pressure and temperature data, the sample insulating paperboard is placed in the solid medium to obtain the measured volume data. The measured volume data is then processed to determine the influence of porosity.

[0028] This invention provides a schematic diagram for measuring the apparent density of a sample insulating paperboard. For details, please refer to... Figure 3 , Figure 3 The diagram illustrates the measurement of the apparent density of a sample insulating paperboard in one embodiment of the present invention. The sample insulating paperboard is embedded in a solid medium, which surrounds the paperboard from all sides and above. Solid or gas pressure is applied from above to ensure the solid medium tightly fills all exposed surface voids of the sample insulating paperboard. This step is to collect measured volume data of the sample insulating paperboard in the solid medium under the target measurement environment, which is used to subsequently determine the influence of the porosity of the solid medium. Specifically, by measuring the volume of the sample insulating paperboard in the solid medium under fixed pressure and temperature conditions, and comparing this measured volume with the true apparent volume of the sample insulating paperboard, the deviation in volume accounting for the inherent gaps between solid medium particles during the measurement can be calculated. This deviation represents the influence of porosity and is used to correct and subtract from the volume measurement data of the insulating paperboard under the actual measurement environment.

[0029] The core purpose of setting a target measurement environment is to calibrate the influence of the porosity of the solid medium itself, under the premise of completely eliminating interference from pressure and temperature fluctuations. Because there are natural gaps between solid medium particles, the volume of these gaps is included in the total measurement volume, leading to an overestimation of the apparent volume and underestimation of the density of the cardboard. Only by fixing the pressure and temperature at known and constant values ​​can we ensure that the packing state and volume of the medium particles do not change additionally, thus allowing the measured volume data to uniquely reflect the influence of the medium's porosity.

[0030] The target measurement environment must include fixed pressure and temperature data because pressure changes alter the packing density and compression between particles, while temperature changes cause thermal expansion and contraction of the particles themselves and the voids between them. Both of these directly change the total volume of the solid medium. Without these fixed values, the measured volume data will be mixed with volume changes caused by pressure and temperature fluctuations, making it impossible to separate the pure porosity effect.

[0031] In addition to fixed pressure and temperature data, the target measurement environment should also include: the type and particle size distribution of the solid medium, such as preferably 0.2~0.3 mm glass microspheres or ceramic microspheres, the size and shape of the sample insulating cardboard, the geometry of the measurement container, and the filling and compaction process, such as filling height, number of compaction times or vibration time, to ensure that the initial stacking state of the solid medium is repeatable for each measurement.

[0032] The target measurement environment refers to the specific test conditions used to measure the volume data of the sample insulating paperboard. This environment includes at least fixed temperature and fixed pressure data. The sample insulating paperboard refers to a sample with the same material and manufacturing process as the insulating paperboard to be measured. The solid medium refers to the granular material used to fill the openings, depressions, and warpage voids on the surface of the paperboard, possessing high fluidity, non-wetting, and antistatic properties. The measured volume data refers to the volume value of the sample insulating paperboard directly collected by the measuring device under the fixed pressure and temperature conditions of the target measurement environment. The fixed temperature and fixed pressure data refer to the set measurement temperature and pressure. The porosity effect refers to the quantitative parameter obtained after processing the measured volume data, used to characterize the volume deviation caused by the inherent gaps between solid medium particles and the interaction between the medium and the paperboard surface morphology. This parameter reflects the additional volume component included in the measurement process due to the porosity of the solid medium itself, and is used to correct and subtract from the volume measurement data of the insulating paperboard to be measured under the actual measurement environment.

[0033] Maintain the laboratory ambient temperature at a fixed temperature, such as 23℃ ± 0.5℃, and place the measuring device in a constant temperature chamber or temperature control platform to maintain this temperature. Simultaneously, prepare a loading device capable of applying fixed pressure data, such as a weight loading mechanism or a servo press, to ensure the pressure is stable at a preset value, such as 1 kPa ± 0.01 kPa, and that the pressure direction is perpendicular to the solid medium filling surface.

[0034] High-strength glass microspheres or ceramic microspheres with a particle size of 0.2~0.3mm were selected as the solid medium. Before use, they need to be dried at the same fixed temperature and allowed to stand for at least 2 hours to ensure that their temperature is consistent with the fixed temperature data. The insulating cardboard surface of the sample was left untreated and kept in its original state.

[0035] Place the sample insulation cardboard horizontally at the bottom of the measuring container, ensuring it is stable and not tilted. Then pour the solid medium into the container, completely covering the insulation cardboard to be measured, and fill the container to the predetermined scale line or height. At this point, the solid medium is positioned above the insulation cardboard to be measured.

[0036] Contact the pressure head of the loading device with the upper surface of the solid medium inside the container, and apply pressure according to a fixed pressure value, such as 1 kPa. Maintain stable pressure and let stand for 1 to 3 minutes to allow the solid medium particles to slide and rearrange under pressure, fully filling the openings, depressions, and warping gaps on the surface of the cardboard, while expelling excess air between the media.

[0037] Another embodiment of the present invention analyzes the characteristics of the medium to determine fixed pressure data, measures the particle size distribution of the solid medium by sieving or laser particle size analyzer to confirm whether it is within the preferred range of 0.2 to 0.3 mm; evaluates the compressive strength of the medium by single particle crushing test or hardness test to understand at what pressure it will break; and measures the natural bulk density and tapped density by filling test to understand the potential range of the medium particles that can rearrange under pressure.

[0038] Based on the above analysis, a pressure range was determined that allows the media particles to overcome static friction and slip and rearrange, but is far below the particle crushing threshold. For example, for high-strength glass or ceramic microspheres with a particle size of 0.2 to 0.3 mm, their compressive strength is typically in the tens to hundreds of MPa range, so the initial pressure can be selected between 0.05 MPa and 0.2 MPa.

[0039] Setting the fixed temperature data to room temperature is sufficient because the temperature of the insulating paperboard in the actual transformer operating environment is typically between room temperature and a certain high temperature range. Solid media (such as glass microspheres or ceramic microspheres) have a low coefficient of thermal expansion, and their volume changes are relatively stable and repeatable near room temperature (e.g., 20℃ to 25℃). Furthermore, room temperature conditions are easy to precisely control and maintain, ensuring the stability of the measurement environment without the need for additional heating or cooling devices. Therefore, setting the fixed temperature data to room temperature (e.g., 23℃ ± 0.5℃) satisfies the measurement accuracy requirements, simplifies equipment configuration and operation procedures, and ensures consistency of the temperature reference between the target measurement environment, the first pressure environment, and the second temperature environment.

[0040] Under fixed pressure and temperature conditions, measure the total volume occupied by the solid medium and the sample insulating cardboard. The volume change corresponding to the indentation depth can be calculated directly by reading the indenter displacement (a volume baseline of the empty container under different pressures needs to be pre-calibrated), or the change in the height of the solid medium's upper surface can be measured using a laser displacement sensor. This measured value is recorded as the first volume. Simultaneously, under the same container, the same medium, and the same pressure and temperature conditions without the cardboard, measure the volume of the solid medium itself separately, recording this as the second volume. The first and second volumes are the required measured volume data. Repeat all measurements 3-5 times and take the average to reduce random errors. Based on these two sets of measured volume data, the influence of the solid medium's porosity can be determined.

[0041] Under fixed pressure and temperature conditions in the target measurement environment, the volume of the sample insulating paperboard is directly measured in a solid medium. Then, the measured volume data is compared with the actual apparent volume of the same sample insulating paperboard under conditions unaffected by the solid medium. The difference or ratio between the two is calculated. This difference or ratio represents the influence of the porosity of the solid medium. It is used to characterize the fixed deviation introduced by the inherent gaps between solid medium particles being included in the volume during the measurement process. This deviation is then used to correct and deduct the volume measurement data of the insulating paperboard under the actual measurement environment.

[0042] The difference is applicable when the influence of porosity has a constant relationship with the volume of the paperboard being measured; that is, regardless of the size of the paperboard, the volume of the inherent gaps between solid media particles that are included is a fixed value. In this case, the difference can be directly used for addition or subtraction correction.

[0043] The differential ratio is applicable when the effect of porosity is approximately linearly proportional to the volume of the paperboard being measured. That is, the larger the paperboard volume, the more particles need to be displaced in the solid medium, and the total amount of inherent gaps between particles is proportionally increased. In this case, using a proportionality coefficient for multiplication and division correction is more accurate.

[0044] Because insulating paperboards of different sizes and thicknesses occupy different spaces in a solid medium, they affect the packing state of the medium particles and the total void volume. Therefore, the difference ratio is usually more universal than a fixed difference. The specific method used to characterize the impact of porosity can be determined by measuring multiple samples of insulating paperboard with different volumes under the target measurement environment and analyzing the relationship curve between the measured volume data and the true volume. If the two have a linear relationship passing through the origin, the ratio is used. If they have a linear relationship with a non-zero intercept, a composite correction using both the difference and the ratio (i.e., the linear equation) is required.

[0045] Next, under the first pressure environment, the degree of first volume change of the solid medium under the preset pressure condition is analyzed to obtain the compression effect. The first pressure environment includes at least fixed temperature data; the solid medium is analyzed to determine the pressure progression; based on the pressure progression, the preset pressure condition is determined; based on the fixed temperature data, the degree of first volume change of the solid medium under the preset pressure condition is obtained; the first volume measurement data corresponding to each pressure progression under the first volume change is extracted; and the pressure progression and the corresponding first volume measurement data are processed to obtain the compression effect.

[0046] This invention provides a schematic diagram illustrating the measurement of the effect of solid medium compression under a first pressure environment. For details, please refer to... Figure 4 , Figure 4 The diagram illustrates the measurement of the compression effect of a solid medium under a first pressure environment, as shown in one embodiment of the present invention. A container is filled with a solid medium. By applying solid or gas pressure from above, the medium is compressed. A pressure head or pressure sensor records the current pressure value, while a displacement sensor or laser sensor records changes in the position of the pressure head or the height of the medium's surface, thereby calculating the volume of the solid medium under the current pressure. Under fixed temperature conditions, multiple pressure points are applied sequentially from the initial pressure to the final pressure, and the volume data corresponding to each pressure increment is recorded. This yields a data sequence of the solid medium's volume changing with pressure, which, after processing, provides the compression effect.

[0047] The purpose of setting the first pressure environment is to separately calibrate the compressibility characteristics of the solid medium itself, and to separate the influence of pressure on volume from the total measurement deviation, so that the volume measurement data can be accurately corrected according to the actual pressure under the actual measurement environment.

[0048] The reason why the temperature must be kept constant is that solid media undergo thermal expansion and contraction when the temperature changes, resulting in volume changes. If the temperature is not kept constant, the measured volume change will include both the compression caused by pressure and the thermal expansion and contraction caused by temperature, making it impossible to distinguish the contributions of each and thus failing to obtain a pure picture of the compression effect.

[0049] The purpose of setting preset pressure conditions is to cover various pressure ranges that may occur under actual testing conditions. By applying pressure progressively from low to high, a complete pressure-volume response curve can be established, thereby obtaining the functional relationship between compression effects and pressure changes, such as whether the compressibility coefficient is constant or gradually decreases with increasing pressure. In this way, when the pressure data under actual testing conditions falls within this range, the corresponding compression correction can be accurately interpolated or calculated.

[0050] Step S3 includes only the solid medium without the insulating cardboard to eliminate the interference of the cardboard volume and its compressibility on the measurement results. If the cardboard is included, the measured volume change is the sum of the compression of the solid medium and the compression of the cardboard, making it impossible to isolate the compression effect of the solid medium. Only by measuring the pure medium can we obtain the intrinsic pressure-volume relationship that belongs solely to the medium itself, allowing for accurate deduction of volume deviations caused by medium compression during subsequent corrections.

[0051] The first pressure environment refers to the specific test conditions used to calibrate the compressibility of solid media. This environment includes at least fixed temperature data. Fixed temperature data refers to a constant temperature value maintained during calibration to eliminate interference from temperature changes on volume measurements. Solid media refers to granular material used to fill the voids on the surface of insulating cardboard. Preset pressure conditions refer to a series of pre-set pressure values ​​used to test the volume response of solid media under different pressures. Pressure progression refers to the specific sequence of gradually increasing pressure from low to high according to a set step size. First volume change degree refers to the overall trend of volume change of solid media under each preset pressure condition. First volume measurement data refers to the actual measured volume value of solid media at each progressive pressure point. Compression effect refers to the quantitative relationship between pressure and volume obtained by processing each progressive pressure and the corresponding first volume measurement data, used for subsequent compression correction of volume measurements based on measured pressure data. Progressive pressure is a series of pressure values ​​that gradually increase pressure from low to high according to a set step size or change amount.

[0052] The measuring device is placed in a constant temperature environment, with the temperature set to a fixed value within the target measurement environment. This ensures the temperature remains constant throughout the test, eliminating the interference of temperature variations on the volume of the solid medium. The measuring container, the solid medium (preferably high-strength glass or ceramic microspheres with a particle size of 0.2–0.3 mm), and the indenter all need to be allowed to stand at this temperature for an extended period to reach thermal equilibrium.

[0053] The particle size distribution of the solid medium is measured using sieving or laser particle size analyzers to confirm that it falls within the preferred range of 0.2 to 0.3 mm. The compressive strength of the medium is assessed through single-particle crushing tests or hardness tests to determine the pressure at which it will break. The natural bulk density and tapped density are measured through packing tests; the difference between the two reflects the potential for particle rearrangement under pressure.

[0054] Take 1% to 5% of the compressive strength of the medium as the initial pressure. A preliminary experiment can also be conducted: start with 0.01 MPa and gradually increase the pressure; the pressure corresponding to the volume change rate exceeding 0.05% is the initial pressure. If preliminary experimental conditions are lacking, for high-strength glass or ceramic microspheres of 0.2 to 0.3 mm, 0.05 MPa can be directly selected as the initial pressure.

[0055] By comparing the compacted density with the natural bulk density, the total volume change that may occur during full compaction is estimated. This estimate is then divided by the desired number of data points (e.g., 10 to 20 points) to obtain the expected volume change for each step size. The required pressure step size is then calculated. In practice, for high-strength spherical granular media, a fixed step size of 0.05 MPa or 0.1 MPa is sufficient to clearly capture the volume change trend with pressure.

[0056] The termination pressure is calculated by multiplying the highest possible pressure under the measured environment by 1.2 to 1.5. Simultaneously, considering the compressive strength of the medium, the termination pressure typically does not exceed 10% of the compressive strength. If the highest pressure under the measured environment is unknown, the pressure can be gradually increased until the volume change rate is consistently below 0.02% for three consecutive times per 0.1 MPa; this pressure is then taken as the termination pressure.

[0057] A constant pressure is applied, and the volume change is continuously recorded. The time when the rate of volume change is lower than the measurement resolution for 10 consecutive seconds is the required pressure holding time. For spherical glass or ceramic microspheres of 0.2 to 0.3 mm, 30 to 60 seconds is usually sufficient for the volume to stabilize.

[0058] Each pressure point in the above pressure progression scenario, starting from the initial pressure and progressing step by step until the termination pressure, is listed as a preset pressure condition.

[0059] Solid media are poured into a measuring container, filled to a fixed scale mark or with a fixed mass, and subjected to light vibration or pre-compression to achieve a repeatable initial accumulation state of the media particles. The initial position of the indenter is recorded at this point. Under fixed temperature conditions, pressure is applied starting from the initial pressure and maintained for a set time. The change in indenter position is read using an indenter displacement sensor or laser displacement sensor, and the volume of the solid media at the current pressure is calculated. This progressive pressure and its corresponding volume measurement data are recorded as the first volume measurement data. Then, the pressure is increased progressively to the next progressive pressure point, and after maintaining the same stable position for the same time, the volume is measured and recorded. This process is repeated until the measurement at the final pressure is completed. The first volume measurement data are integrated to obtain the first volume change degree.

[0060] From the above measurement results, each progressive pressure point and its corresponding first volume measurement data are extracted one by one to form a data sequence corresponding to pressure and volume. For example, the volume measured at 0.05 MPa pressure is 500.2 cm³, the volume measured at 0.10 MPa pressure is 499.8 cm³, the volume measured at 0.15 MPa pressure is 499.5 cm³, and so on until the termination pressure.

[0061] The progressively increasing pressures are analyzed in conjunction with the corresponding initial volume measurements. Typically, pressure is plotted on the x-axis and volume on the y-axis to observe the relationship between the two. If the volume decreases approximately linearly with increasing pressure, a compressibility coefficient is obtained through linear fitting. This coefficient represents the change in volume of the solid medium per unit increase in pressure. If the volume decreases curvilinearly with increasing pressure, meaning the volume change gradually decreases as pressure increases, a functional relationship between pressure and volume is obtained through curve fitting. For example, volume is equal to a constant minus a nonlinear term related to pressure. Regardless of the fitting method used, the final compressibility effect is a quantitative relationship that describes the change in volume of the solid medium with pressure.

[0062] Then, in a second temperature environment, the degree of second volume change of the solid medium under the preset temperature conditions is analyzed to obtain the temperature influence. The first pressure environment includes at least fixed temperature data; the solid medium is analyzed to determine the pressure progression; based on the pressure progression, the preset pressure conditions are determined; based on the fixed temperature data, the degree of first volume change of the solid medium under the preset pressure conditions is obtained; the first volume measurement data corresponding to each pressure progression in the first volume change degree is extracted; each pressure progression and the corresponding first volume measurement data are processed to obtain the compression influence.

[0063] The measurement steps under the second temperature environment are completely identical to those under the first pressure environment, i.e., step S2, in terms of measuring device and operating procedure, and both adopt the same method. Figure 4 The measurement diagram shown illustrates that the container is filled with a solid medium, a fixed pressure is applied through a pressure head, and the volume change of the medium is measured using a displacement sensor. The only difference between the two is that step S2 changes the pressure at a fixed temperature to obtain the compression effect, while this step changes the temperature under a fixed pressure to obtain the temperature effect. That is, the ambient temperature is gradually changed according to the preset temperature conditions by a temperature control device, and the volume of the solid medium at each temperature point is measured to obtain the temperature effect.

[0064] The purpose of setting up a second temperature environment is to separately calibrate the thermal expansion characteristics of the solid medium itself, and to separate the effect of temperature on volume from the total measurement deviation, so that the volume measurement data can be accurately corrected according to the actual temperature under the actual measurement environment.

[0065] The reason why the pressure must be kept constant is that solid media will compress or expand when the pressure changes, resulting in a change in volume. If the pressure is not kept constant, the measured volume change will include both thermal expansion and contraction caused by temperature and compression caused by pressure, making it impossible to distinguish the contributions of each and thus failing to obtain a pure picture of the temperature effect.

[0066] The purpose of setting preset temperature conditions is to cover various temperature ranges that may occur under actual testing conditions. By progressively changing the temperature from low to high, a complete temperature-volume response curve can be established, thereby obtaining the functional relationship between temperature influence and temperature changes. In this way, when the temperature data under actual testing conditions falls within this range, the corresponding temperature correction can be accurately interpolated or calculated.

[0067] This step involves only the solid medium, omitting the insulating cardboard, to eliminate the interference of the cardboard's volume and its own thermal expansion characteristics on the measurement results. If cardboard is included, the measured volume change is the sum of the thermal expansion of the solid medium and the cardboard, making it impossible to isolate the temperature effect of the solid medium. Only by measuring the pure medium can we obtain the intrinsic temperature-volume relationship belonging solely to the medium itself, allowing for accurate deduction of volume deviations caused by the medium's thermal expansion during subsequent corrections.

[0068] The second temperature environment refers to the specific test conditions used to calibrate the effect of temperature on solid media. This environment includes at least fixed pressure data. Fixed pressure data refers to a constant pressure value maintained during calibration to eliminate interference from pressure variations on volume measurements. Solid media refers to granular material used to fill the voids on the surface of insulating cardboard. The measurement temperature set refers to a pre-selected series of measurement temperature values ​​used to test the volume response of the solid media at different temperatures. Preset temperature conditions refer to a specific temperature sequence composed of various temperature points in the measurement temperature set. The degree of second volume change refers to the overall trend of volume change of the solid media under various preset temperature conditions. Second volume measurement data refers to the actual measured volume value of the solid media at each measurement temperature. Temperature influence refers to the quantitative relationship between temperature and volume obtained by processing each measurement temperature and the corresponding second volume measurement data, used for subsequent temperature correction of the volume measurement value based on the measured temperature data. The measurement temperature refers to the specific temperature value pre-set for volume measurement in the second temperature environment to calibrate the effect of temperature on solid media.

[0069] Place the measuring device in a temperature-controlled chamber or constant-temperature environment to ensure that the pressure remains constant throughout the test, matching the fixed pressure data in the target measurement environment, thus eliminating the interference of pressure changes on the volume of the solid medium. The measuring container, solid medium, and pressure head must all be allowed to settle sufficiently at their initial temperature to reach thermal equilibrium. The temperature-controlled chamber should have precise temperature adjustment and display functions, with a temperature control accuracy within ±0.5 degrees Celsius.

[0070] Based on the possible temperature range in the actual test environment, such as from the low temperature of -20℃ to the high temperature of 120℃ during transformer operation, a set of measurement temperatures is set. Specifically, starting from the lowest temperature, the temperature is gradually increased at fixed intervals (e.g., 10℃) to obtain a series of measurement temperature points. All of these measurement temperature points constitute the preset temperature conditions. Simultaneously, the holding time at each temperature point needs to be determined to ensure that the internal temperature of the solid medium is uniform and the volume is stable before measurement. Typically, each temperature point needs to be held at a constant temperature for 15 to 30 minutes.

[0071] Pour the solid medium into the measuring container, filling it to a fixed graduation mark or a fixed mass, and perform light vibration or pre-compression to bring the medium particles to a repeatable initial packing state. Apply a fixed pressure and maintain this pressure constant throughout the test, recording the initial position of the indenter.

[0072] Under fixed pressure conditions, set the temperature control chamber to the first temperature point in the measurement temperature set, such as the lowest temperature. After maintaining this temperature for the set time, read the change in pressure head position using a pressure head displacement sensor or laser displacement sensor, and calculate the volume of the solid medium at the current temperature. Record this measured temperature and its corresponding volume measurement data as the second volume measurement data. Then, set the temperature control chamber to the next temperature point, maintain this temperature for the same time again, and measure and record the volume. Repeat this process until measurements are completed under all preset temperature conditions. Note that the heating or cooling rate should be controlled during the heating or cooling process to avoid temperature overshoot or the formation of temperature gradients within the medium.

[0073] From the above measurement results, each measurement temperature point and its corresponding second volume measurement data are extracted one by one to form a set of temperature and volume corresponding data sequences. For example, the volume measured at 20℃ is 500.0 cm³, at 30℃ it is 500.1 cm³, at 40℃ it is 500.2 cm³, and so on until the highest measurement temperature. The degree of change of the second volume is obtained by integrating the various second volume measurement data.

[0074] The measured temperatures and corresponding second volume measurements are analyzed. Typically, temperature is plotted on the x-axis and volume on the y-axis to observe the relationship between the two. For most solid materials, volume increases approximately linearly with increasing temperature. In this case, a coefficient of thermal expansion can be obtained through linear fitting, representing the relative change in volume of the solid medium for every 1°C increase. If the volume changes non-linearly with temperature, a functional relationship between temperature and volume can be obtained through curve fitting. Regardless of the fitting method used, the final temperature effect is a quantitative relationship that describes the law of volume change of the solid medium with temperature.

[0075] Furthermore, the actual measurement environment is determined based on preset pressure and temperature conditions.

[0076] The actual measurement environment refers to the field conditions under which the insulating paperboard to be measured is actually measured, including the actual pressure and temperature.

[0077] First, based on the fixed pressure data in the target measurement environment and the pressure progression range covered by the compression effect calibrated under the first pressure environment, determine the target pressure control range in the actual measurement environment. This range should be centered on the fixed pressure data and fall completely between the minimum and maximum values ​​of the pressure progression (e.g., if the fixed pressure data is 0.1 MPa, the actual pressure control range is 0.05 MPa to 0.5 MPa). Simultaneously, based on the fixed temperature data in the target measurement environment and the measurement temperature set range covered by the temperature effect calibrated under the second temperature environment, determine the target temperature control range in the actual measurement environment. This range should be centered on the fixed temperature data and fall completely between the minimum and maximum values ​​of the measurement temperature set (e.g., if the fixed temperature data is 23℃, the actual temperature control range is 20℃ to 40℃). Before actual measurement, place the measuring device in a controlled environment where pressure and temperature can be adjusted simultaneously. The pressure is set and adjusted using a precision lead screw mechanism driven by a servo motor or a weight loading device, and the temperature is set and maintained using a constant temperature chamber or temperature control platform. Ensure that the pressure and temperature values ​​under the actual test environment fall within the control range centered on the fixed pressure and fixed temperature data, and that the measurement system can stably maintain and record the actual pressure and temperature values ​​in real time within this range, so that the measured pressure and temperature data can be substituted into the compression effect and temperature effect for subsequent correction.

[0078] Furthermore, under actual testing conditions, the volume measurement data of the insulating paperboard to be measured was obtained, and the actual testing environment conditions were also obtained.

[0079] The measurement system used in this step is as follows: Figure 1 As shown, the insulating paperboard to be measured is completely embedded in a solid medium, which surrounds the paperboard from all sides and above. By applying solid or gas pressure from above, combined with vibration excitation from the bottom or around the perimeter, the solid medium particles flow and tightly fill the openings, depressions, and warping gaps on the surface of the paperboard. Pressure sensors, temperature sensors, and displacement or laser measurement devices are also provided to simultaneously collect pressure and temperature data under the actual measurement environment and to measure the volume of the insulating paperboard within the solid medium.

[0080] The actual measurement environment refers to the field conditions under which the insulating paperboard to be measured is actually conducted, including the actual pressure and temperature. The insulating paperboard to be measured refers to the target insulating paperboard sample for which apparent density measurement is required. Volumetric measurement data refers to the volume values ​​obtained by placing the insulating paperboard to be measured in a solid medium under the actual measurement environment. The actual measurement environment conditions refer to the actual pressure and temperature data collected simultaneously during the measurement process, used for subsequent compression and temperature corrections to the volumetric measurement data.

[0081] Adopting such Figure 1The measurement system is shown. Ensure the measuring device is in normal working order. Place the insulating cardboard to be measured horizontally at the bottom of the measuring container, ensuring the cardboard is stable and not tilted. Then pour the solid medium into the container, completely surrounding the insulating cardboard, and fill the container to the predetermined scale line or height.

[0082] Starting with a fixed pressure data point, an initial pressure is applied from above the solid medium using an indenter or pressure loading device. Simultaneously, high-frequency electromagnetic vibration is activated, causing the solid medium particles to overcome interparticle static friction under the vibrational energy input, entering a fluid-like state. Under the influence of gravity and pressure, these particles flow downwards, fully filling every tiny wrinkle and warpage gap on the surface of the insulating cardboard being measured. The pressure is then gradually increased in small increments, with vibration maintained after each increase, until the fluidization termination criteria are met.

[0083] The system captures instantaneous pressure values ​​from the pressure head feedback at high frequency and calculates the variance of pressure data in real time over a vibration time window, such as one minute, using an algorithm. When solid media particles are still flowing and filling gaps, the resistance sensed by the pressure head fluctuates violently, resulting in a large variance. Once the particles have rearranged and reached the densest packing state under the current pressure, the medium no longer undergoes macroscopic displacement, and the pressure feedback tends to stabilize. When the calculated variance is less than a set small threshold, the system automatically determines that the fluidization process has terminated, and the solid medium has reached an ideal steady-state equilibrium. At this point, the current actual pressure value is recorded as the measured pressure data for that measurement.

[0084] The fixed pressure data in the actual measurement environment is a preset reference value. This pressure condition is manually selected and maintained constant during the calibration of the porosity effect, used to establish the correspondence between the measured volume data and the actual volume of the sample insulation paperboard under ideal conditions. The actual pressure data in the measurement environment starts from the fixed pressure data, gradually increasing the pressure and coordinating with a vibration fluidization process. The final pressure value is automatically determined and recorded by the system based on a fluidization termination judgment algorithm. Because different insulation paperboards have different thicknesses, warpages, and surface morphologies, the pressure required for the particulate medium to reach its densest packing state varies. Therefore, the measured pressure data will automatically adjust according to the sample characteristics. The determination of the measured pressure data is based on the physical criterion that the pressure variance during vibration fluidization is less than a set threshold, rather than being manually preset. This measured pressure data is then combined with the compression effect to calculate the compression correction relative to the reference pressure condition, thereby accurately compensating for the volume measurement data.

[0085] After the variance reaches the target and fluidization terminates, the system automatically triggers readings. It uses displacement or laser sensors to read changes in the pressure head position or the height of the solid medium's surface, calculating the volume measurement data of the insulating paperboard in the solid medium. This reading time is automatically determined by the algorithm, rather than using a fixed vibration time, thus eliminating random errors caused by differences in filling time and human-controlled time variations in paperboard thickness and warping.

[0086] While collecting volumetric measurement data, the current actual pressure data (i.e., the pressure value recorded at the time of fluidization termination) is read through a pressure sensor; the current actual temperature data is read through a temperature sensor. It is essential to ensure that the pressure and temperature sensors are used synchronously with the volumetric measurements to guarantee data consistency.

[0087] Record the volume measurement data, measured pressure data, and measured temperature data together. To reduce random errors, repeat the measurement 3 to 5 times, recording the results of each measurement, and take the average value as the final volume measurement data and actual measurement environment conditions. Using this method, regardless of the complexity of the sample shape (such as severe warping or burrs on the edges), the algorithm can ensure that the particles are completely filled before taking a reading, thereby eliminating volume measurement errors caused by insufficient filling.

[0088] Finally, the volume measurement data is processed based on the actual environmental conditions, the influence of porosity, the influence of compression, and the influence of temperature to obtain the apparent density result of the insulating paperboard to be measured. The actual environmental conditions include at least the actual pressure data and the actual temperature data; based on the influence of porosity, a porosity correction is obtained; based on the influence of compression and the actual pressure data, a compression correction is obtained; based on the influence of temperature and the actual temperature data, a temperature correction is obtained; the volume measurement data is processed based on the influence of porosity, the compression correction, and the temperature correction to obtain the apparent density result.

[0089] The measured environment refers to the actual pressure and temperature data collected synchronously under the actual measurement environment. Measured pressure data refers to the current actual pressure value read by the pressure sensor. Measured temperature data refers to the current actual temperature value read by the temperature sensor. Compression effect refers to the quantitative relationship between the volume of the solid medium and pressure, calibrated under the first pressure environment. The volume correction value calculated by substituting the measured pressure data as input into the compression effect is called the compression correction amount. Temperature effect refers to the quantitative relationship between the volume of the solid medium and temperature, calibrated under the second temperature environment. The volume correction value calculated by substituting the measured temperature data as input into the temperature effect is called the temperature correction amount. Porosity effect refers to the volume deviation introduced by the inherent gaps between solid medium particles calibrated under the target measurement environment. The porosity effect is processed to obtain the porosity correction amount. Volume measurement data refers to the volume value measured by placing the insulating paperboard to be measured in the solid medium under the actual measurement environment. Apparent density result refers to the final density value calculated by processing the volume measurement data after applying the porosity correction amount, compression correction amount, and temperature correction amount, combined with the mass of the insulating paperboard to be measured.

[0090] Before or after volume measurement, weigh the insulating cardboard to be measured using a high-precision electronic balance. Repeat the weighing three times and take the average value to reduce random errors.

[0091] The volume measurement data of the insulating paperboard to be measured is extracted from the measurement results under actual testing conditions. Simultaneously, the synchronously acquired measured pressure and temperature data are also extracted.

[0092] The measured pressure data is substituted into the compression effect data obtained under the first pressure environment. The compression effect is a quantitative relationship between the volume of a solid medium and pressure, such as how many cubic centimeters the volume decreases for each unit increase in pressure. Based on this relationship, the volume change of the measured pressure relative to the reference pressure, i.e., the fixed pressure data in the target measurement environment, is calculated. This change is the compression correction. If the measured pressure is higher than the reference pressure, the compression correction is positive; if the measured pressure is lower than the reference pressure, the compression correction is negative.

[0093] The measured temperature data is substituted into the temperature effect data obtained from calibration under the second temperature environment. The temperature effect is a quantitative relationship between the volume of a solid medium and temperature, such as how many cubic centimeters the volume increases per unit increase in temperature. Based on this relationship, the volume change relative to the reference temperature (i.e., the fixed temperature data in the target measurement environment) is calculated; this change is the temperature correction. If the measured temperature is higher than the reference temperature, the temperature correction is positive; if the measured temperature is lower than the reference temperature, the temperature correction is negative.

[0094] The porosity effect refers to the volume deviation introduced by the inherent gaps between solid medium particles, calibrated under the target measurement environment. This deviation is typically given as a fixed difference or a percentage of the difference. Based on the volume measurement data of the insulating paperboard to be measured, the porosity correction is calculated by substituting it into the porosity effect calculation. This correction is used to subtract the portion of the volume included in the inherent gaps of the solid medium.

[0095] The volume measurement data is subtracted sequentially by the porosity correction, compression correction, and temperature correction to obtain the true apparent volume of the insulating paperboard to be measured. The signs of the compression and temperature corrections are handled according to the rules mentioned above. The apparent density is obtained by dividing the mass of the insulating paperboard to be measured by the corrected true apparent volume.

[0096] Step S6 can also be implemented using existing artificial intelligence models. Specifically, a neural network model is constructed that takes the measured environmental conditions, porosity influence, compression influence, and temperature influence as inputs, and outputs the corrected apparent density result. The input layer contains multiple nodes, corresponding to the volume measurement data, measured pressure data, measured temperature data, and pre-calibrated porosity correction coefficient, compression influence coefficient, and temperature influence coefficient of the insulating paperboard to be measured. The output layer is a single node that outputs the final corrected apparent density value. The training process of the model is as follows: First, under the target measurement environment, the first pressure environment, and the second temperature environment, a large number of experiments are conducted to obtain the correspondence between the volume measurement data and the true apparent density under different pressure, temperature, and porosity conditions, and a training dataset is constructed. Each training sample contains the input feature vector, volume measurement data, measured pressure, measured temperature, porosity coefficient, compression coefficient, temperature coefficient, and label value, and the true apparent density obtained through destructive detection or other high-precision methods. Then, the training data is input into a multilayer perceptron or deep neural network for supervised learning. The network weights and biases are continuously adjusted using the backpropagation algorithm to minimize the mean square error between the predicted and true densities. After training, the model can learn the nonlinear combined effects of multiple factors such as pressure, temperature, and porosity on volume measurement data. In real-world testing environments, it can quickly output the comprehensively corrected apparent density result directly based on the input volume measurement data and the actual testing conditions, without needing to explicitly calculate each correction step by step.

[0097] The volume of the insulating cardboard to be measured is not calculated by directly measuring its length, width, and height, but rather indirectly using a substitution method combined with a container with a fixed cross-sectional area. Specifically, the measuring container has a uniform and known fixed cross-sectional area. The volume is calculated based on the bottom area and height by recording the height change of the solid medium's upper surface using a high-precision displacement sensor. Under this measurement principle, the core measurement parameter is the height difference, not the shape or filling state of the cardboard's sides. Therefore, it is only necessary to ensure that the solid medium can apply sufficient pressure to the cardboard surface from top to fully fill the openings, recesses, and warping gaps on the top and edge areas of the cardboard; that the upper surface of the solid medium remains horizontal and stable within the measurement area; and that the cardboard does not tilt or shift during the measurement process. Once these conditions are met, the actual apparent volume occupied by the cardboard can be accurately calculated by measuring the difference between the reference height of the medium's upper surface without cardboard and the measured height of the medium's upper surface after the cardboard is placed inside.

[0098] It should be noted that the step division and data processing logic of the target measurement environment, the first pressure environment, the second temperature environment, and the actual measurement environment in the above-mentioned apparent density measurement method are highly dependent on the physical implementation of the measuring device and the stable behavior of the particulate medium. If the device lacks effective control over the medium filling state, pressure fluctuations, and temperature drift, the calculated porosity correction, compression correction, and temperature correction will not be accurately obtained. Therefore, this embodiment, based on the explanation of the core measurement logic, further provides the physical device and engineering means to support the implementation of the method. Preferably, it provides a fiberboard apparent density detection device and method based on the constant pressure particle replacement principle. Regarding the conventional mechanical structure, general sensor selection, and basic electrical connections involved in the device, those skilled in the art can determine them according to actual measurement needs, and they will not be specifically described in this embodiment of the invention. The following section will focus on describing the device features and process algorithms that are strongly related to steps S1 to S5 above, including key means to ensure that volume measurement data can accurately reflect the true apparent density, such as vibration fluidization termination determination algorithm, dynamic porosity calibration procedure, and pressure-height correction function, thereby ensuring the integrity and feasibility of the overall technical solution.

[0099] Another embodiment of the present invention provides a device and method for detecting the apparent density of fiberboard based on the principle of constant pressure particle replacement. The device mainly consists of five subsystems: a precision measurement and containment system, including a cylindrical measuring cylinder with a hardened inner wall and an extremely low coefficient of friction, and a constant pressure piston head that can slide up and down above the cylinder; a standardized measuring medium, which uses spherical particles with high fluidity, non-wetting properties, and antistatic properties, preferably high-strength glass microspheres or ceramic microspheres with a particle size of 0.2 to 0.3 mm; a constant pressure drive and sensing system, which uses a precision lead screw mechanism driven by a servo motor to drive the vertical movement of the pressure head, and integrates a pressure sensor and a high-resolution displacement sensor; an energy input and fluidization system, in which a high-frequency electromagnetic vibrator is installed at the bottom or outer periphery of the measuring cylinder, and micro-vibration at a specific frequency of 50 to 100 Hz to induce a fluid-like state in the particle medium; and a central processing and computing system, which is used to simultaneously process the three signals of weight, pressure, and displacement, and has a built-in compensation algorithm.

[0100] In terms of measurement principle, this invention achieves medium state normalization through a dual approach of vibration fluidization and constant pressure compaction. Vibration eliminates bridging between particles, while constant pressure ensures that the porosity between particles is completely consistent in each measurement. A differential volumetric method is employed, recording the difference in indentation position under the same pressure response in two states: medium alone and medium plus sample. This offsets systematic errors such as container deformation and medium self-weight compression. Simultaneously, during volume measurement, a weighing sensor at the bottom acquires the net weight of the sample in real time, avoiding errors caused by fiber shedding or humidity changes during secondary handling.

[0101] Regarding the core calculation model and error compensation mechanism, this embodiment of the invention introduces a pressure-height correction function. The formula for calculating the actual sample volume measured under standard pressure is: the true volume equals the cross-sectional area of ​​the measuring cylinder multiplied by the indenter height difference, and then multiplied by a comprehensive correction factor. This correction factor consists of three parts: a reference value 1, a compression correction term, and a temperature correction term. The compression correction term equals the compressibility coefficient multiplied by the difference between the standard pressure and the reference atmospheric pressure, and the temperature correction term equals the temperature influence factor multiplied by the current temperature. The compressibility coefficient is obtained by recording the indenter displacement curve within the pressure range under no-load conditions in 0.01 MPa increments and performing linear regression; the temperature influence factor is obtained by adjusting the ambient temperature in a constant temperature chamber from 10 to 40 degrees Celsius and fitting the relationship curve between displacement drift and temperature change.

[0102] Regarding the dynamic porosity calibration procedure, this embodiment of the invention incorporates a built-in standard block self-calibration function. The system periodically measures a high-precision stainless steel standard block with a volume of V_std and calculates the particle density correction factor K, which is equal to V_std divided by V_std_test. For any insulating cardboard, after measuring its volume V_real, the final measurement result is corrected to V_final, which is equal to K multiplied by V_real.

[0103] Regarding the vibration fluidization termination determination algorithm, this embodiment of the invention does not employ a fixed vibration time, but instead uses a pressure sensor for real-time monitoring. When vibration is initiated, if the pressure fluctuation variance reported by the pressure sensor is less than a set threshold, it is determined that the medium has completed fluidization and reached steady-state equilibrium. This algorithm ensures that regardless of the complexity of the sample shape, the particles are fully filled before readings are taken, eliminating volume measurement errors caused by insufficient filling and random errors caused by variations in the duration of manual control.

[0104] Compared with the traditional geometric method, the embodiments of the present invention can effectively eliminate the false volume caused by the warping of insulating paperboard, and the measurement accuracy is higher; the use of dry microsphere medium does not change the moisture content of the paperboard and does not cause swelling, and the sample can be directly used for subsequent electrical tests after purging after measurement; it has a high degree of automation, eliminating random errors caused by human reading and uneven manual clamping force; it has strong universality, and is not only applicable to insulating paperboard, but also to other thin sheet porous materials that are easy to absorb water and deform.

[0105] Another embodiment of the present invention provides an apparent density measurement system; for details, please refer to [link to relevant documentation]. Figure 5 , Figure 5 The diagram shown illustrates the structure of an apparent density measurement system according to one embodiment of the present invention, comprising: The porosity module 11 is used to determine the influence of the porosity of the solid medium based on the measured volume data of the sample insulating paperboard in the target measurement environment, which is constructed by placing the sample insulating paperboard in a solid medium. The first module 12 is used to analyze the degree of first volume change of the solid medium under the preset pressure condition in the first pressure environment, and to obtain the compression effect. The second module 13 is used to analyze the degree of second volume change of the solid medium under the preset temperature conditions in the second temperature environment, and to obtain the temperature influence. The actual measurement module 14 is used to determine the actual measurement environment based on preset pressure and preset temperature conditions; The acquisition module 15 is used to acquire the volume measurement data of the insulating paperboard to be measured under the actual test environment, and to acquire the actual test environment conditions; The processing module 16 is used to process the volume measurement data based on the actual environmental conditions, the influence of porosity, the influence of compression, and the influence of temperature to obtain the apparent density result of the insulating paperboard to be measured.

[0106] Preferably, the porosity module 11 includes: The target measurement environment unit is used to ensure that the target measurement environment includes at least fixed pressure data and fixed temperature data. The volume measurement data unit is used to obtain volume measurement data by placing the sample insulating paperboard in a solid medium based on fixed pressure data and fixed temperature data. The porosity influence unit is used to process the measured volume data to obtain the porosity influence.

[0107] Preferably, the first module 12 includes: The first pressure environment unit is used to provide a first pressure environment that includes at least fixed temperature data; The pressure progression unit is used to analyze solid media and determine the pressure progression. The preset pressure condition unit is used to determine the preset pressure condition based on the pressure progression. The first volume change degree unit is used to obtain the first volume change degree of the solid medium under a preset pressure condition based on fixed temperature data; The first volume measurement data unit is used to extract the first volume measurement data corresponding to each progressive pressure under the progressive pressure condition in the first volume change degree. The compression effect unit is used to process the progressive pressure and the corresponding first volume measurement data to obtain the compression effect.

[0108] Preferably, the second module 13 includes: The second temperature environment unit, used for the second temperature environment, includes at least fixed pressure data; A determination unit is used to determine the set of measured temperatures; The preset temperature condition unit is used to determine preset temperature conditions based on the measured temperature set. The second volume change degree unit is used to obtain the second volume change degree of the solid medium under preset temperature conditions based on fixed pressure data; The second volume measurement data unit is used to extract the second volume measurement data corresponding to each measurement temperature in the measurement temperature set of the second volume change degree. The temperature influence unit is used to process the measured temperature and the corresponding second volume measurement data to obtain the temperature influence information.

[0109] Preferably, the processing module 16 includes: The measured environment condition unit is used to measure the actual environment condition, which includes at least measured pressure data and measured temperature data. The porosity correction unit is used to obtain the porosity correction amount based on the porosity influence. The compression correction unit is used to obtain the compression correction amount based on the compression effect and measured pressure data; The temperature correction unit is used to obtain the temperature correction amount based on the temperature influence and measured temperature data; The apparent density result unit is used to process volume measurement data based on porosity correction, compression correction, and temperature correction to obtain the apparent density result.

[0110] Those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. The storage medium can be a magnetic disk, optical disk, read-only memory (ROM), or random access memory (RAM), etc.

[0111] Accordingly, embodiments of the present invention provide a computer-readable storage medium comprising a stored computer program, wherein, when the computer program is executed, it controls the device containing the computer-readable storage medium to perform steps in the apparent density measurement method of the above embodiments, for example... Figure 2 Steps S1 to S6 as described above.

[0112] In this embodiment of the invention, the target measurement environment is first constructed by placing the sample insulating paperboard in a solid medium to collect actual volume measurement data and determine the influence of the porosity of the solid medium. Then, the first volume change of the solid medium under a preset pressure condition is analyzed under a first pressure condition to obtain the compression effect, and the second volume change of the solid medium under a preset temperature condition is analyzed under a second temperature condition to obtain the temperature effect. Finally, the volume measurement data of the insulating paperboard to be measured and the actual measurement environment are obtained under the actual measurement environment, and the volume measurement data are jointly processed based on the actual measurement environment, the porosity effect, the compression effect, and the temperature effect to obtain the apparent density result of the insulating paperboard to be measured. This invention eliminates the interference of surface openings and warping voids on volume measurement by considering the influence of porosity, and compensates for the additional effects of pressure and temperature fluctuations on the volume of solid media in the actual measurement environment by considering the influence of compression and temperature. This results in a corrected result that is closer to the true apparent volume of insulating paperboard, significantly improving the measurement accuracy of apparent density. It can effectively identify defective paperboard with closed pores or micropores inside, preventing its use in transformers and reducing the risk of accidents such as partial discharge and insulation breakdown.

[0113] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for measuring apparent density, characterized in that, include: Based on the measured volume data of the sample insulating paperboard in the target measurement environment, the influence of the porosity of the solid medium is determined. The target measurement environment is constructed by placing the sample insulating paperboard in the solid medium. Under a first pressure environment, the degree of first volume change of the solid medium under the preset pressure condition is analyzed to obtain the compression effect; In a second temperature environment, the degree of second volume change of the solid medium under the preset temperature conditions is analyzed to obtain the temperature influence. The actual test environment is determined based on the preset pressure and preset temperature conditions; Under the stated test environment, the volume measurement data of the insulating paperboard to be measured was obtained, and the test environment conditions were also obtained. The volume measurement data is processed based on the measured environmental conditions, the influence of porosity, the influence of compression, and the influence of temperature to obtain the apparent density result of the insulating paperboard to be measured.

2. The apparent density measurement method as described in claim 1, characterized in that, The determination of the influence of porosity on the solid medium is based on the measured volume data of the sample insulating paperboard in the target measurement environment, wherein the target measurement environment is constructed by placing the sample insulating paperboard in the solid medium, including: The target measurement environment includes at least fixed pressure data and fixed temperature data; Based on the fixed pressure data and the fixed temperature data, the sample insulating paperboard is placed in the solid medium to obtain the measured volume data; The measured volume data is processed to obtain the influence of porosity.

3. The apparent density measurement method as described in claim 2, characterized in that, In the first pressure environment, the degree of first volume change of the solid medium under the preset pressure condition is analyzed to obtain the compression effect, including: The first pressure environment includes at least the fixed temperature data; Analyze the solid medium to determine the pressure progression; Based on the pressure progression, the preset pressure condition is determined; Based on the fixed temperature data, the first volume change degree of the solid medium under the preset pressure condition is obtained; Extract the first volume measurement data corresponding to each progressive pressure under the pressure progression in the first volume change condition; The compression effect is obtained by processing the progressive pressure and the corresponding first volume measurement data.

4. The apparent density measurement method as described in claim 2, characterized in that, In the second temperature environment, the degree of second volume change of the solid medium under the preset temperature conditions is analyzed to obtain the temperature influence, including: The second temperature environment includes at least the fixed pressure data; Determine the set of measurement temperatures; Based on the measured temperature set, the preset temperature conditions are determined; Based on the fixed pressure data, the second volume change degree of the solid medium under the preset temperature condition is obtained; Extract the second volume measurement data corresponding to each measurement temperature in the measurement temperature set of the second volume change degree; The temperature measurement data and the corresponding second volume measurement data are processed to obtain the temperature influence.

5. The apparent density measurement method as described in claim 1, characterized in that, The process of processing the volume measurement data based on the measured environmental conditions, the influence of porosity, the influence of compression, and the influence of temperature to obtain the apparent density result of the insulating paperboard to be measured includes: The measured environmental conditions include at least measured pressure data and measured temperature data; Based on the aforementioned impact of porosity, the porosity correction amount is obtained; Based on the compression effect and the measured pressure data, the compression correction amount is obtained; Based on the temperature influence and the measured temperature data, the temperature correction amount is obtained; The volume measurement data is processed based on the porosity correction, the compression correction, and the temperature correction to obtain the apparent density result.

6. An apparent density measurement system, characterized in that, include: The porosity module is used to determine the influence of the porosity of the solid medium based on the measured volume data of the sample insulating paperboard in the target measurement environment, wherein the target measurement environment is constructed by placing the sample insulating paperboard in the solid medium. The first module is used to analyze the degree of volume change of the solid medium under the preset pressure condition under the first pressure environment, and to obtain the compression effect. The second module is used to analyze the degree of second volume change of the solid medium under the preset temperature conditions in a second temperature environment, and to obtain the temperature influence. The actual measurement module is used to determine the actual measurement environment based on the preset pressure conditions and the preset temperature conditions; The acquisition module is used to acquire volume measurement data of the insulating paperboard to be measured under the actual measurement environment, and to acquire the actual measurement environment conditions. The processing module is used to process the volume measurement data based on the measured environmental conditions, the influence of porosity, the influence of compression, and the influence of temperature to obtain the apparent density result of the insulating paperboard to be measured.

7. The apparent density measurement system as described in claim 6, characterized in that, The porosity module includes: A target measurement environment unit, wherein the target measurement environment includes at least fixed pressure data and fixed temperature data; The volume measurement data unit is used to place the sample insulating paperboard in the solid medium based on the fixed pressure data and the fixed temperature data to obtain the volume measurement data. The porosity influence unit is used to process the measured volume data to obtain the porosity influence.

8. The apparent density measurement system as described in claim 7, characterized in that, The first module includes: A first pressure environment unit is configured to include at least the fixed temperature data in the first pressure environment. The pressure progression unit is used to analyze the solid medium and determine the pressure progression. A preset pressure condition unit is used to determine the preset pressure condition based on the pressure progression. The first volume change degree unit is used to obtain the first volume change degree of the solid medium under the preset pressure condition based on the fixed temperature data. The first volume measurement data unit is used to extract the first volume measurement data corresponding to each progressive pressure under the pressure progression in the first volume change degree. The compression effect unit is used to process each of the progressive pressures and the corresponding first volume measurement data to obtain the compression effect.

9. The apparent density measurement system as described in claim 7, characterized in that, The second module includes: A second temperature environment unit is used to provide that the second temperature environment includes at least the fixed pressure data; A determination unit is used to determine the set of measured temperatures; A preset temperature condition unit is used to determine the preset temperature condition based on the measured temperature set; The second volume change degree unit is used to obtain the second volume change degree of the solid medium under the preset temperature condition based on the fixed pressure data. The second volume measurement data unit is used to extract the second volume measurement data corresponding to each measurement temperature in the measurement temperature set of the second volume change degree; The temperature influence unit is used to process the measured temperatures and the corresponding second volume measurement data to obtain the temperature influence information.

10. The apparent density measurement system as described in claim 6, characterized in that, The processing module includes: The measured environment condition unit is used to ensure that the measured environment condition includes at least measured pressure data and measured temperature data. A porosity correction unit is used to obtain a porosity correction amount based on the porosity influence. The compression correction unit is used to obtain the compression correction amount based on the compression effect and the measured pressure data; The temperature correction unit is used to obtain the temperature correction amount based on the temperature influence and the measured temperature data. The apparent density result unit is used to process the volume measurement data based on the porosity correction, the compression correction, and the temperature correction to obtain the apparent density result.

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