Calibration method and device for mixed gas density relay with humidity detection function

Abstract

The present application relates to a kind of verification method and device of mixed gas density relay with humidity detection function, belong to density relay verification technical field, solve the problem that humidity and gas mixing ratio cannot be detected simultaneously when carrying out density relay verification in existing.The method comprises: in the verification chamber, fill mixed gas to pressure balance;The verification chamber is cooled by refrigeration, the actual pressure in the verification chamber, actual temperature, the light energy value of light after the action of the verification chamber, and the measured pressure read by the pressure sensor of density relay;During the cooling process, the pressure sensor of density relay is verified by comparing actual pressure and measured pressure;The humidity detection and mixing ratio detection of mixed gas in the verification chamber are carried out in turn by monitoring the multiple change rates of light energy value.Various tasks are integrated, and the comprehensive operation and maintenance efficiency is improved.

Description

Technical Field

[0001] This invention relates to the field of density relay calibration technology, and in particular to a calibration method and apparatus for a mixed-gas density relay with humidity detection function. Background Technology

[0002] C4F7N / CO2 / O2 ternary gas mixture is a new type of environmentally friendly insulating medium, and its density is a key parameter for ensuring the insulation performance of electrical equipment. Currently, the industry mainly monitors the density of this ternary gas mixture online by installing density relays on electrical equipment. The basic principle is to convert the monitored gas temperature and pressure data into an equivalent pressure value at 20°C through a built-in temperature-pressure characteristic curve based on the rated mixing ratio for display and judgment.

[0003] However, density relays may experience performance drift or malfunction after long-term operation, causing deviations between the monitored gas density value (pressure at 20°C) and the actual value. Regular calibration is necessary to ensure accuracy, but current calibrations typically target the alarm and lockout points of the density relay. Furthermore, the humidity of the ternary gas mixture also affects its insulation performance. Currently, dew point meters are commonly used for offline sampling at the equipment's gas inlet or outlet to obtain humidity values ​​at atmospheric pressure.

[0004] Current technology lacks online monitoring methods for gas humidity, relying solely on offline detection using dew point meters during periodic inspections. This fails to capture humidity levels during inspection intervals, posing a safety hazard. Furthermore, the current maintenance process requires the use of three different instruments and three separate operations for calibrating density relays, confirming gas mixing ratios, and detecting humidity. This cumbersome and time-consuming process significantly impacts the efficiency of power equipment maintenance. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a calibration method and apparatus for a gas density relay with humidity detection function, so as to solve the problem that existing density relays cannot simultaneously detect humidity and gas mixing ratio during calibration.

[0006] On one hand, embodiments of the present invention provide a calibration method for a mixed-gas density relay with humidity detection function, comprising the following steps:

[0007] Fill the calibration chamber with a mixed gas until the pressure is balanced;

[0008] The calibration chamber is cooled down, and the actual pressure, actual temperature, light energy value of light after passing through the calibration chamber, and the measured pressure read by the pressure sensor of the density relay are monitored in real time.

[0009] During the cooling process, the pressure sensor of the density relay is calibrated by comparing the actual pressure and the measured pressure; the humidity and mixing ratio of the mixed gas in the calibration chamber are detected sequentially by monitoring multiple rates of change of light energy value.

[0010] Based on the further improvement of the above method, the mixed gas is a ternary mixed gas of C4F7N / CO2 / O2; the light energy value is obtained by monitoring the folded optical path set in the calibration chamber, and the condensate of the C4F7N / CO2 / O2 ternary mixed gas condenses on the reflective surface in the folded optical path.

[0011] Based on further improvements to the above method, by monitoring multiple rates of change in light energy values, the humidity and mixing ratio of the mixed gas in the calibration chamber are sequentially detected, including:

[0012] When a decrease in light energy value is detected and the absolute value of the rate of change is less than or equal to the preset threshold for judging water condensation, the condensate is determined to be water and humidity is detected.

[0013] Continue cooling the calibration chamber; when the absolute value of the rate of change of the detected light energy value is greater than the liquefaction judgment threshold, the condensate is determined to be C4F7N liquid, and the mixing ratio is detected.

[0014] Based on further improvements to the above method, humidity detection is performed, including:

[0015] When the condensate is determined to be water, the actual temperature and actual pressure in the current calibration chamber are obtained, and the current actual temperature is used as the dew point temperature under the current actual pressure. Then, the water volume fraction is obtained by looking up the water dew point-volume fraction comparison table.

[0016] The humidity value under standard pressure is calculated based on the water volume fraction and the actual pressure.

[0017] If the humidity value under standard pressure is less than or equal to the standard humidity limit, the humidity of the air chamber is deemed to be within acceptable limits; otherwise, an alarm is issued to indicate that the humidity of the air chamber exceeds the limit.

[0018] Based on further improvements to the above method, the mixing ratio is detected, including:

[0019] When the condensate is determined to be C4F7N liquid, the actual temperature and actual pressure in the current calibration chamber are obtained, and the current actual temperature is used as the liquefaction temperature of C4F7N. Then, based on the built-in temperature-pressure-mixing ratio relationship data, the actual mixing ratio is obtained by querying or linear interpolation.

[0020] If the comparison between the actual mixing ratio and the rated mixing ratio is within the set deviation range, the gas chamber mixing ratio is determined to be normal; otherwise, an alarm for abnormal gas chamber mixing ratio is issued.

[0021] Based on further improvements to the above method, the verification method also includes: heating the verification chamber; during the heating process, comparing the actual pressure inside the verification chamber with the measured pressure read by the pressure sensor of the density relay in real time, and performing pressure boosting verification on the density relay.

[0022] On the other hand, embodiments of the present invention provide a calibration device for a mixed-gas density relay with humidity detection function, comprising:

[0023] The calibration chamber includes: a first temperature sensor, a first pressure sensor, a semiconductor cooler, and an optical monitoring component; the first temperature sensor and the first pressure sensor are used to detect the actual temperature and actual pressure inside the calibration chamber; the semiconductor cooler is used to regulate the temperature inside the calibration chamber; the optical monitoring component is used to generate light and monitor the light energy value of the light after it passes through the calibration chamber; the calibration chamber is connected to a density relay.

[0024] The control component is used to control the semiconductor cooler to cool down the calibration chamber. It performs pressure reduction calibration by collecting the pressure values ​​of the first pressure sensor and the second pressure sensor of the density relay in the calibration chamber. It also performs humidity detection and mixing ratio detection on the mixed gas in the calibration chamber by monitoring multiple change rates of the light energy value of the optical monitoring component.

[0025] Based on further improvements to the above device, the optical monitoring component includes: a light emitting tube, a light receiving tube, and a reflective mirror; the light emitting tube and the light receiving tube are horizontally mounted facing each other on the inner walls of both sides of the calibration chamber, and the reflective mirror is mounted on the bottom of the inner surface of the calibration chamber to reflect the light emitted by the light emitting tube to the light receiving tube to form a folded optical path.

[0026] Based on further improvements to the above-mentioned device, the first temperature sensor of the calibration chamber is installed below and in close contact with the reflective mirror.

[0027] Based on further improvements to the above-mentioned device, the calibration chamber has a frustum-shaped structure with its cross-section gradually decreasing from top to bottom; the outer wall of the calibration chamber is made of metal; and the semiconductor cooler is installed on the outer wall at the bottom of the calibration chamber.

[0028] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0029] 1. Without adding detection sensors, the system completes density relay calibration while adding mixing ratio and humidity detection functions. This integrates the three separate tasks of density relay calibration, humidity detection, and mixing ratio detection, which originally required three separate operations using three different instruments (density calibrator, dew point meter, and gas chromatograph), into a single continuous automated operation. This completely changes the traditional operation and maintenance model, combining multiple equipment shutdowns and multiple manual interventions into one operation, greatly shortening the operation and maintenance time window, reducing manpower and skill requirements, and improving overall operation and maintenance efficiency.

[0030] 2. By capturing the gradual change rate of the light energy value during the condensation of moisture in the mixed gas, the dew point is calculated in real time and converted into standard humidity, realizing "quasi-online" humidity monitoring. This facilitates the immediate detection and alarm of excessive humidity during inspection intervals, significantly improving the real-time performance and safety of equipment insulation status monitoring.

[0031] 3. By identifying the steep rate of change of light energy value during C4F7N liquefaction and combining it with temperature-pressure-mixing ratio data, the actual gas mixing ratio can be deduced. This enables effective monitoring of the gas mixing ratio without relying on additional, expensive gas chromatographs, providing a low-cost and high-efficiency technical means for judging gas leaks, stratification, or abnormal decomposition.

[0032] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0033] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0034] Figure 1 This is a flowchart of the calibration method for the mixed gas density relay with humidity detection function in Embodiment 1 of the present invention;

[0035] Figure 2 This is a schematic diagram of the calibration device for the mixed gas density relay with humidity detection function in Embodiment 2 of the present invention;

[0036] Figure label:

[0037] 1-Verification chamber; 2-First temperature sensor; 3-First pressure sensor; 4-Light emitting tube; 5-Light receiving tube; 6-Reflecting mirror; 7-Semiconductor cooler; 8-Density relay; 9-Second pressure sensor; 10-Second temperature sensor; 11-Test gas chamber; 12-Valve; 13-First three-way valve; 14-Second three-way valve. Detailed Implementation

[0038] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0039] Example 1

[0040] A specific embodiment of the present invention discloses a calibration method for a mixed-gas density relay with humidity detection function, such as... Figure 1 As shown, it includes the following steps:

[0041] S1. Fill the calibration chamber with a mixed gas until the pressure is balanced;

[0042] S2. Cool down the calibration chamber and monitor in real time the actual pressure, actual temperature, light energy value of light after passing through the calibration chamber, and the pressure reading of the density relay pressure sensor.

[0043] S3. During the cooling process, the pressure sensor of the density relay is calibrated by comparing the actual pressure and the measured pressure; the humidity and mixing ratio of the mixed gas in the calibration chamber are detected sequentially by monitoring multiple rates of change of light energy value.

[0044] It should be noted that the term "mixed gas" in this embodiment is short for mixed gas, specifically referring to a C4F7N / CO2 / O2 ternary mixed gas. The method in this embodiment is an integrated verification method that simultaneously verifies the performance of the C4F7N / CO2 / O2 ternary mixed gas density relay and diagnoses the humidity and mixing ratio of the gas itself in a single operation.

[0045] Specifically, in step S1, firstly, ensure that the calibration chamber and its connecting pipelines have been evacuated to a vacuum using a vacuum pump. Then, open the isolation valve on the electrical equipment to connect the test chamber, density relay, and calibration chamber. The C4F7N / CO2 / O2 ternary mixed gas from the test chamber is then introduced into the calibration chamber until the actual pressure collected in real-time by the pressure sensor in the calibration chamber reaches equilibrium with the pressure in the test chamber (i.e., the pressure read by the pressure sensor of the density relay). This step ensures that the gas sample in the calibration chamber is consistent with the gas state in the test chamber, providing a reliable sample for subsequent calibration.

[0046] Further, the valve is closed to isolate the gas chamber under test, and step S2 is executed to cool down the calibration chamber.

[0047] For example, a semiconductor cooler is installed in the calibration chamber. When the semiconductor cooler is activated, the temperature of the calibration chamber gradually decreases.

[0048] As the temperature decreases, the actual pressure of the ternary gas mixture within the calibration chamber also decreases. During this process, real-time monitoring is performed, including: real-time monitoring of the actual pressure by a pressure sensor within the calibration chamber, and real-time monitoring of the actual temperature by a temperature sensor within the calibration chamber. The calibration chamber measures the light energy after it passes through the chamber, and the pressure measured by the pressure sensor of the density relay. The light energy is obtained by monitoring the folded optical path within the calibration chamber, where condensates of the C4F7N / CO2 / O2 ternary gas mixture condense on the reflective surface. The actual temperature within the calibration chamber is the temperature of the reflective surface.

[0049] It should be noted that the folded optical path significantly increases the interaction distance between the beam and the reflective surface region where condensation may form. Compared to the direct optical path, it is more sensitive to the light scattering effect caused by the very early and minute amounts of condensation (whether water frost or liquid film) on the reflective surface, thus significantly improving the detection sensitivity and response speed for minute changes in the gas state.

[0050] For example, an optical system consisting of a light emitting tube, a light receiving tube, and a reflective mirror is constructed within the calibration chamber. The light emitting tube continuously emits light, which is reflected by the reflective mirror to the light receiving tube to form a folded optical path. A temperature sensor within the calibration chamber is attached to the reflective mirror to collect the actual temperature. This refers to the temperature of the reflective surface.

[0051] When the emitting surface is smooth and free of condensation, the folded optical path is in a state of total internal reflection, and the monitored light energy value is... Initial value The calibration is set at 100%.

[0052] During the real-time monitoring process in step S2, step S3 is executed simultaneously to compare the actual pressure at different time points. and measuring pressure If the absolute value of the difference between the two satisfies ( The set pressure difference threshold varies depending on the accuracy class of the density relay. Taking a density relay with an accuracy class of 1.0 as an example... ,in If "full scale" is short for "full scale" (meaning full range), it indicates that the pressure sensor's reading accuracy is qualified during the pressure reduction process, and the pressure detection of the density relay is deemed qualified, thus completing the pressure reduction calibration of the C4F7N / CO2 / O2 ternary mixed gas density relay.

[0053] Furthermore, as cooling continues, the actual temperature within the calibration chamber decreases, causing some components in the ternary gas mixture to reach saturation and begin to condense. The condensate deposits on the reflective surface, scattering light and causing a decrease in the monitored light energy value. The rate of change is calculated and recorded in real time. .

[0054] By monitoring multiple rates of change in light energy, the humidity and mixing ratio of the mixed gas in the calibration chamber are sequentially measured, including:

[0055] ① When a decrease in light energy value is detected and the absolute value of the rate of change is less than or equal to the preset threshold for judging water condensation, the condensate is determined to be water, and humidity is detected.

[0056] It should be noted that when the light energy value is detected to undergo its first sudden change (i.e., a significant decrease from the initial value), the absolute value of the rate of change is judged to be less than or equal to the preset threshold for judging water condensation. If it is less than or equal to, it is determined that water (frost) is condensed on the reflective surface at this time. The actual temperature and actual pressure in the current calibration chamber are obtained, and the current actual temperature is taken as the dew point temperature under the current actual pressure. This dew point temperature is higher than the liquefaction temperature of the C4F7N / CO2 / O2 ternary mixed gas.

[0057] Based on the dew point temperature, the water volume fraction is obtained by consulting the water volume fraction conversion table for dew point. Specifically, the water volume fraction corresponding to the dew point temperature is obtained by referring to Appendix A, "Water Volume Fraction Conversion Table," in GB / T 5832.2-2016 "Determination of Trace Moisture in Gas Analysis - Part 2: Dew Point Method."

[0058] Furthermore, the water volume fraction is expressed using the following formula. Humidity value converted to standard pressure:

[0059] (1),

[0060] in, This indicates the humidity value under standard pressure. This indicates the current actual pressure. This represents the standard pressure, with a value of 0.1013 MPa.

[0061] The humidity value under standard pressure is compared with the standard humidity limit (e.g., set to 500 μL / L). If it is less than or equal to the standard humidity limit, the humidity of the air chamber is deemed to be qualified; otherwise, an alarm is issued to indicate that the humidity of the air chamber exceeds the limit.

[0062] Compared with existing technologies, this embodiment realizes the transformation of humidity from offline sampling to online near real-time diagnosis, which facilitates the timely detection of potential humidity problems during inspection intervals.

[0063] ② Continue to cool the calibration chamber; when the absolute value of the rate of change of the detected light energy value is greater than the liquefaction judgment threshold, the condensate is determined to be C4F7N liquid, and the mixing ratio is detected.

[0064] After the water liquefies, the temperature continues to drop. The second abrupt change point of the light energy value will be monitored. It will be determined whether the absolute value of the rate of change of the light energy value is greater than the liquefaction judgment threshold. If it is greater, it will be determined that the liquid condensed on the reflective surface is C4F7N. The actual temperature and actual pressure in the current verification chamber will be obtained, and the current actual temperature will be used as the C4F7N liquefaction temperature.

[0065] Furthermore, based on the C4F7N liquefaction temperature and the current actual pressure, and using the built-in temperature-pressure-mixing ratio data, the actual mixing ratio is obtained through querying or linear interpolation.

[0066] It should be noted that the temperature-pressure-mixing ratio data were obtained through experiments. Table 1 lists the values ​​of different pressures and C4F7N liquefaction temperatures for ternary gas mixtures under four mixing ratio conditions. The actual mixing ratio can be deduced based on this table.

[0067] Table 1 Liquefaction Temperature of C4F7N / CO2 / O2 Mixed Gas

[0068]

[0069] If the comparison result between the actual mixing ratio and the rated mixing ratio (i.e., the difference) is within the set deviation range, such as the absolute value of the difference being less than or equal to 1%, then the gas chamber mixing ratio is determined to be normal; otherwise, an abnormal gas chamber mixing ratio alarm is issued.

[0070] Compared with existing technologies, this embodiment achieves effective monitoring of gas mixing ratio without adding specialized equipment such as gas chromatographs, providing a key basis for judging gas leakage or decomposition.

[0071] After completing pressure verification, humidity detection, and mixing ratio detection during the refrigeration and depressurization process described above, the verification chamber is heated by controlling the semiconductor cooler. During the heating process, the liquefied gas re-vaporizes, and the pressure inside the verification chamber rises. The actual pressure inside the verification chamber is compared in real time. The pressure measured by the pressure sensor read by the density relay If the absolute value of the difference between the two satisfies If the reading is within acceptable limits, it indicates that the pressure sensor's reading accuracy is qualified during the pressurization process. The pressure detection of the density relay is deemed qualified, and the pressurization verification of the C4F7N / CO2 / O2 ternary mixed gas density relay is completed, thus realizing the bidirectional full-stroke verification of the density relay's pressure sensing function.

[0072] It should be noted that the water condensation judgment threshold and liquefaction judgment threshold used in step S2 to identify whether the condensate is water or C4F7N liquid are the key to achieving accurate identification. This embodiment provides the following two methods for pre-calibration.

[0073] (1) Theoretical modeling method

[0074] It should be noted that, ideally, the condensate forms a uniform, transparent frost layer (moisture) or thin film (C4F7N liquid film) on the reflective surface, the thickness of which is proportional to the condensation mass. In the initial condensation stage, the light energy value... Attenuation and condensation layer thickness They form an approximately linear relationship, that is The condensation rate depends on the speed at which water molecules or C4F7N molecules diffuse to the reflective surface.

[0075] ①Based on Fick's diffusion law, a mass condensation rate model is established for the diffusion and condensation of condensate towards the reflective surface in the calibration chamber, and the first functional relationship between the condensate layer thickness growth rate and the gas state parameters and the physical parameters of the condensate is obtained.

[0076] Specifically, the formula for the mass condensation rate model is as follows:

[0077] (2),

[0078] in, The mass condensation rate of the condensate is expressed in units of 1. ; This represents the diffusion coefficient, with units of 1000 m / s. This indicates the diffusion capacity of water vapor or C4F7N gas in the background gas (CO2 / O2); This indicates the mass concentration of condensate in the mainstream gas near the reflector, in units of... ; This indicates the mass concentration of condensate on the reflector surface, in units of... When it is completely solidified, ; This represents the effective condensation area on the reflecting surface, in units of... ; This represents the thickness of the diffusion boundary layer near the reflecting surface, in units of... It is related to the gas flow state.

[0079] It should be noted that in formula (2) This is the key to the calculation, as it is directly related to the state of the gas being measured, and is calculated using the following formula:

[0080] (3),

[0081] in, This indicates the partial pressure of the condensate (water or C4F7N); Represents the universal gas constant. ; The molar mass of the condensate is expressed in units of 1. ; This indicates the absolute temperature of the gas.

[0082] It should be noted that the quality of the condensate It is calculated using the following formula:

[0083] (4),

[0084] in, The density of a condensate in liquid or solid form is expressed in units of 1. ; This indicates the thickness of the condensed layer, in units of... .

[0085] The mass of condensate in formula (4) Differentiating with respect to time, we obtain the following formula representing the mass condensation rate:

[0086] (5).

[0087] In formula (2) Substituting into formula (5), the simplified result is the growth rate of the condensed layer thickness. The first functional relationship between the gas state parameters and the physical parameters of the condensate:

[0088] (6).

[0089] ②Based on the relationship between the attenuation of light energy value and the thickness of the condensate layer, and the first functional relationship, the second functional relationship between the rate of change of light energy and the physical parameters of the condensate is obtained.

[0090] Specifically, based on the optical attenuation model, the relationship between the attenuation of light energy and the thickness of the condensation layer is expressed by the following formula:

[0091] (7),

[0092] in, This represents the attenuated light energy value. This represents the initial light energy value; This represents the attenuation coefficient, which is measured in advance through calibration experiments.

[0093] Furthermore, according to Combining formulas (6) and (7), the second functional relationship is obtained as follows:

[0094] (8).

[0095] ③ Substitute the physical property parameters of water and C4F7N into the second function relationship respectively to calculate the theoretical reference values ​​for water condensation and liquefaction. Then, based on their respective safety margins, obtain the water condensation judgment threshold and liquefaction judgment threshold.

[0096] It should be noted that the physical properties include: the molar mass of the condensate. Density of condensate and diffusion coefficient Correspondingly, the physical properties of water condensation are as follows: , (ice), The physical properties of C4F7N liquefaction and condensation are as follows: , (liquid), .

[0097] With a C4F7N / CO2 / O2 ternary gas mixture ratio of 8.56%:86.03%:5.41%, a rated pressure of 0.8 MPa, and a humidity of 500 μL / L, the thickness of the diffusion boundary layer near the reflective surface is set. If the thickness is 1 mm, then calculate the mass concentration of water condensation. Approximately The mass concentration of C4F7N liquefaction condensation Approximately .

[0098] Finally, according to formula (8), the liquefaction condensation rate of C4F7N is calculated to be 273 times that of water condensation rate, that is... This indicates that the absolute value of the rate of change in light energy during the liquefaction and condensation of C4F7N is approximately 273 times that during the condensation of water. The signal characteristics of the two condensates are significantly different, resulting in an extremely low risk of misjudgment.

[0099] Based on the attenuation coefficient measured in actual application scenarios, the theoretical reference values ​​for water condensation and liquefaction can be calculated.

[0100] To compensate for errors introduced by model simplification and ensure reliability, safety margins are typically set based on theoretical reference values ​​to obtain condensation and liquefaction thresholds. The condensation threshold is usually set to 10 to 30 times the theoretical reference value for condensation, and the liquefaction threshold is set to 1 / 5 to 1 / 20 of the theoretical reference value for liquefaction.

[0101] Preferably, in this embodiment, the threshold for judging water condensation is set to 20 times the theoretical reference value for water condensation, and the threshold for judging liquefaction is set to 1 / 10 of the theoretical reference value for liquefaction.

[0102] (2) Experimental calibration method

[0103] To simulate field application conditions, a similar test platform was built.

[0104] The test chamber was filled with C4F7N / CO2 / O2 at a standard humidity of 500 μL / L and a rated mixing ratio until the absolute pressure reached 0.8 MPa. Following the method of this embodiment, the chamber was cooled at a rate of 0.5 °C / min (to avoid supercooling), and the actual temperature was collected in real time. Actual pressure The maximum slope of the light energy value curve during the water condensation stage is measured, and its upper limit is taken as the threshold for judging water condensation.

[0105] Dry C4F7N / CO2 / O2 with a rated mixing ratio is introduced into the test chamber until the absolute pressure is 0.8 MPa. According to the method of this embodiment, the temperature is reduced at a rate of 0.5 °C / min, and the initial slope of the light energy value curve during the large-scale condensation stage of C4F7N is measured. The lower limit of the slope is taken as the liquefaction judgment threshold.

[0106] The two methods for determining the thresholds described above are parallel and equivalent. In practical applications, either method can be used depending on the different requirements for accuracy, cost, and development stage, or the threshold can be initially determined through theoretical calculations and then precisely calibrated through experimental calibration. Regardless of the method used, as long as the final determined liquefaction judgment threshold is significantly greater than the water condensation judgment threshold, the reliable implementation of the diagnostic logic described in this invention can be guaranteed.

[0107] It should be noted that although there is currently no humidity standard for C4F7N / CO2 / O2 ternary gas mixed-gas electrical equipment, most of these devices are gas chambers without arc decomposition products. Referring to the SF6 gas standard, if the humidity value under standard pressure... A humidity level of 500 μL / L or less indicates that the humidity in the gas chamber is within acceptable limits; otherwise, an alarm for excessive humidity in the gas chamber will be issued. The judgment criterion for SF6 gas (Q / GDW 10471-2022 "Supervision and Management Standard for Sulfur Hexafluoride Gas in Operating Electrical Equipment") is typically 20℃. The humidity value under pressure, therefore according to formula (1), the electrical equipment of C4F7N / CO2 / O2 ternary mixed gas operates under pressure. The corresponding humidity volume fraction Consulting the moisture dew point-volume fraction conversion table, the dew point value corresponding to this volume fraction is approximately -5°C. This means that for electrical equipment with a rated pressure of 0.8 MPa, the method in this embodiment needs to be able to measure a dew point of at least -5°C to cover the standard requirements. Furthermore, it is necessary to ensure that the proportion of C4F7N in the ternary gas mixture does not exceed a certain limit, so that the liquefaction temperature of C4F7N is below -5°C, allowing moisture to condense first.

[0108] This embodiment calculates the critical ratio to be approximately 13.67% based on Wagner-type equations and Dalton's law of partial pressures. Currently, commonly used mixing ratios in engineering (as shown in Table 1) are all lower than this value; therefore, this method has broad engineering applicability.

[0109] It should be noted that the C4F7N gas pressure value is calculated based on the Wagner type equation below:

[0110] (9),

[0111] in, This refers to the gas pressure value of C4F7N. The critical pressure of C4F7N gas. ; The reference temperature is the temperature at which C4F7N gas is compared. Given the current thermodynamic temperature, This is the critical temperature of C4F7N gas. ; This is a dimensionless intermediate variable, representing the ratio of the difference from the critical temperature; All are fitting coefficients: a = -6.84, b = -1.65, c = 9.26, d = -165.39.

[0112] After converting -5℃ to a thermodynamic temperature, substituting it into formula (9) yields the gas pressure of C4F7N gas at that temperature. .

[0113] Since C4F7N gas is easier to liquefy than CO2 and O2, the liquefaction temperature of the C4F7N gas mixture depends only on the liquefaction temperature of C4F7N.

[0114] The van der Waals empirical equation is adopted as the equation of state for C4F7N gas:

[0115] (10),

[0116] in, This indicates the pressure value, and the unit is Pa. It represents thermodynamic temperature, and its unit is K; This represents the molar volume of a gas, and the unit is _____. ; This represents the gas pressure correction factor; This represents the gas volume correction factor.

[0117] Will Substituting T = 268.15 K (-5℃) into formula (10), the molar volume of the gas is calculated. Since molar volume is independent of temperature, and mass remains constant, molar volume also remains constant. Therefore, according to molar volume... Substituting T=293.15K (20℃) into formula (10), the corresponding C4F7N gas pressure at 20℃ is calculated. .

[0118] For a C4F7N gas mixture with a total pressure of 0.8 MPa at 20°C, the partial pressures of each component at 20°C are calculated using the following formula based on Dalton's law of partial pressures:

[0119] (11),

[0120] in, This represents the pressure value of C4F7N gas in a ternary gas mixture, in MPa. This indicates the proportion of C4F7N gas in the ternary gas mixture, which, through calculation, is 13.67%.

[0121] Compared with existing technologies, this embodiment provides a calibration method for a gas density relay with humidity detection function. Without adding a detection sensor, it completes density relay calibration while simultaneously adding mixing ratio and humidity detection functions. This integrates the three separate tasks—density relay calibration, humidity detection, and mixing ratio detection—that originally required three separate operations using three different instruments (density calibrator, dew point meter, and gas chromatograph) into a single, continuous automated operation. This completely changes the traditional operation and maintenance model, combining multiple equipment shutdowns and manual interventions into a single process, significantly shortening the maintenance time window, reducing labor and skill requirements, and improving overall operation and maintenance efficiency. By capturing the gradual change rate of the light energy value during moisture condensation in the mixed gas, the dew point is calculated in real time and converted to standard humidity, achieving "near-online" humidity monitoring. This facilitates immediate detection and alarm of excessive humidity during inspection intervals, significantly improving the real-time performance and security of equipment insulation status monitoring. By identifying the steep rate of change of light energy value during C4F7N liquefaction and combining it with temperature-pressure-mixing ratio data, the actual gas mixing ratio can be deduced. This enables effective monitoring of the gas mixing ratio without relying on additional, expensive gas chromatographs, providing a low-cost and high-efficiency technical means for judging gas leaks, stratification, or abnormal decomposition.

[0122] Example 2

[0123] Another embodiment of the present invention discloses a calibration device for a mixed-gas density relay with humidity detection function, thereby implementing the calibration method for the mixed-gas density relay with humidity detection function in Embodiment 1. The specific implementation of each component in the device is described in the corresponding description in Embodiment 1. Figure 2 As shown, the device includes:

[0124] The calibration chamber 1 includes: a first temperature sensor 2, a first pressure sensor 3, a semiconductor cooler 7, and an optical monitoring component; the first temperature sensor 2 and the first pressure sensor 3 are used to detect the actual temperature and actual pressure inside the calibration chamber 1; the semiconductor cooler 7 is used to regulate the temperature inside the calibration chamber 1; the optical monitoring component is used to generate light and monitor the light energy value of the light after it passes through the calibration chamber 1; the calibration chamber 1 is connected to a density relay 8.

[0125] The control component is used to control the semiconductor cooler 7 to cool down the calibration chamber 1, and to perform pressure reduction calibration by collecting the pressure values ​​of the first pressure sensor 3 and the second pressure sensor 9 of the density relay 8 in the calibration chamber 1; and to perform humidity detection and mixing ratio detection on the mixed gas in the calibration chamber 1 by monitoring multiple change rates of the light energy value of the optical monitoring component.

[0126] It should be noted that the first pressure sensor 3 in the calibration chamber 1 is installed at the top of the calibration chamber 1 to directly measure the gas pressure, thus avoiding the influence of condensate that may exist at the bottom on the measurement accuracy.

[0127] The optical monitoring assembly includes a light emitting tube 4, a light receiving tube 5, and a reflective mirror 6. The light emitting tube 4 and the light receiving tube 5 are horizontally mounted facing each other on the inner walls of the calibration chamber 1. The reflective mirror 6 is mounted on the bottom of the inner surface of the calibration chamber 1 and is used to reflect the light emitted by the light emitting tube 4 to the light receiving tube 5 to form a folded optical path. The mounting angle and height of the light emitting tube 4 and the light receiving tube 5 ensure that the light can illuminate the reflective mirror 6 and be reflected to the light receiving tube 5.

[0128] The light path is folded by reflecting once through the reflective mirror 6, which greatly increases the interaction distance between the light and the condensate and improves the detection sensitivity of trace condensate.

[0129] The first temperature sensor 2 of the calibration chamber 1 is installed below and close to the reflective mirror 6, which facilitates real-time and accurate measurement of the mirror temperature, i.e. the mirror temperature at which condensation occurs. This is the key to obtaining the dew point temperature and liquefaction temperature.

[0130] It should be noted that the calibration chamber 1 has a frustum-shaped structure, with its cross-section gradually decreasing from top to bottom, i.e., a frustum-shaped structure that is wider at the top and narrower at the bottom. Correspondingly, the reflective mirror 6 is circular.

[0131] The frustum-shaped structure facilitates natural convection of gas during the cooling process, concentrating the low-temperature region at the bottom and promoting the uniform formation of condensate on the reflective surface at the bottom. At the same time, it reduces thermal interference in the upper space, ensuring the controllability and consistency of the temperature field and the condensation process.

[0132] The outer wall of the calibration chamber 1 is made of metal; the semiconductor cooler 7 is installed on the metal outer wall at the bottom periphery of the calibration chamber 1. The metal outer wall (such as aluminum alloy) has good thermal conductivity, which can ensure that the cooling / heating power is quickly and evenly transferred to the entire bottom of the chamber, thereby accurately controlling the rate of temperature change of the reflective mirror.

[0133] The semiconductor cooler 7 is placed at the bottom and combined with the frustum-shaped structure to form a temperature gradient from top to bottom, which facilitates pressure monitoring at the top and induction and monitoring of condensation at the bottom.

[0134] The control component is connected to the first temperature sensor 2, the first pressure sensor 3, the semiconductor cooler 7, the optical monitoring component, the second pressure sensor 9, and the second temperature sensor 10 of the density relay 8 in the calibration chamber 1 via signal connection or data line connection; the control component includes an operation unit, which includes a touch screen for displaying, setting data, and sending instructions.

[0135] The calibration chamber 1 is connected to the valve 12 and density relay 8 of the gas chamber 11 under test via the second three-way valve 14 and the first three-way valve 13 in sequence.

[0136] Specifically, the three ports of the first three-way valve 13 are respectively connected to the valve 12 of the gas chamber 11 under test, the density relay 8, and one end of the second three-way valve 14; the other two ports of the second three-way valve 14 are respectively connected to the calibration chamber 1 and the vacuum pump or gas supply port.

[0137] During calibration, start the vacuum pump to ensure that the calibration chamber 1 and its connecting pipelines have been evacuated to a vacuum. Then, open valve 12 to connect the gas chamber under test 11, density relay 8, and calibration chamber 1.

[0138] The control component internally stores a verification program, which is used to coordinate the actions of other components, collect sensor data, look up tables, perform data calculations, make logical judgments, and output verification results or alarm signals, so as to execute all comparisons, calculations, table lookups, logical judgments, and alarm outputs in the method of Embodiment 1.

[0139] Since the calibration device for a mixed-gas density relay with humidity detection function in this embodiment and the calibration method for a mixed-gas density relay with humidity detection function mentioned above are related and can be referenced from each other, this is a repetition of the description, so it will not be repeated here.

[0140] Compared with existing technologies, the device in this embodiment, through its unique structural design, integrates pressure monitoring, optical monitoring, and precise temperature control into a compact chamber. This not only provides a reliable hardware platform for the implementation of the integrated verification method, but its frustum-shaped structure, optimized sensor layout, and thermally conductive metal outer wall create an ideal physical environment for high-precision pressure measurement, accurate condensation temperature capture, and controllable condensation process, fundamentally ensuring the accuracy of the data and the reliability of the results of the entire method. Since this device embodiment shares the same principle as the aforementioned method embodiment, it also possesses the corresponding technical effects of the aforementioned method embodiment.

[0141] Those skilled in the art will understand that all or part of the processes of the methods described in the above embodiments can be implemented by a computer program instructing related hardware, and the program can be stored in a computer-readable storage medium. The computer-readable storage medium may be a disk, optical disk, read-only memory, or random access memory, etc.

[0142] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A calibration method for a mixed-gas density relay with humidity detection function, characterized in that, Includes the following steps: Fill the calibration chamber with a mixed gas until the pressure is balanced; The calibration chamber is cooled down, and the actual pressure, actual temperature, light energy value of light after passing through the calibration chamber, and the measured pressure read by the pressure sensor of the density relay are monitored in real time. During the cooling process, the pressure sensor of the density relay is calibrated by comparing the actual pressure and the measured pressure; the humidity and mixing ratio of the mixed gas in the calibration chamber are detected sequentially by monitoring multiple rates of change of the light energy value.

2. The calibration method for the mixed-gas density relay with humidity detection function according to claim 1, characterized in that, The mixed gas is a ternary mixed gas of C4F7N / CO2 / O2; the light energy value is obtained by monitoring the folded optical path set in the calibration chamber, and the condensate of the C4F7N / CO2 / O2 ternary mixed gas is condensed on the reflective surface of the folded optical path.

3. The calibration method for the mixed-gas density relay with humidity detection function according to claim 2, characterized in that, The method of monitoring multiple rates of change of the light energy value to sequentially perform humidity detection and mixing ratio detection on the mixed gas in the calibration chamber includes: When the light energy value decreases and the absolute value of the rate of change is less than or equal to the preset water condensation judgment threshold, the condensate is determined to be water and humidity is detected. Continue cooling the calibration chamber; when the absolute value of the rate of change of the light energy value is greater than the liquefaction judgment threshold, the condensate is determined to be C4F7N liquid, and the mixing ratio is detected.

4. The calibration method for the mixed-gas density relay with humidity detection function according to claim 3, characterized in that, The humidity detection includes: When the condensate is determined to be water, the actual temperature and actual pressure in the current calibration chamber are obtained, and the current actual temperature is used as the dew point temperature under the current actual pressure. Then, the water volume fraction is obtained by looking up the water dew point-volume fraction comparison table. The humidity value under standard pressure is calculated based on the stated water volume fraction and the actual pressure. If the humidity value under standard pressure is less than or equal to the standard humidity limit, the humidity of the air chamber is deemed to be within acceptable limits; otherwise, an alarm is issued to indicate that the humidity of the air chamber exceeds the limit.

5. The calibration method for the mixed-gas density relay with humidity detection function according to claim 3, characterized in that, The mixing ratio detection includes: When the condensate is determined to be C4F7N liquid, the actual temperature and actual pressure in the current calibration chamber are obtained, and the current actual temperature is used as the liquefaction temperature of C4F7N. Then, based on the built-in temperature-pressure-mixing ratio relationship data, the actual mixing ratio is obtained by querying or linear interpolation. If the comparison between the actual mixing ratio and the rated mixing ratio is within the set deviation range, the gas chamber mixing ratio is determined to be normal; otherwise, an alarm for abnormal gas chamber mixing ratio is issued.

6. The calibration method for the mixed-gas density relay with humidity detection function according to claim 1, characterized in that, The verification method further includes: heating the verification chamber; during the heating process, comparing the actual pressure inside the verification chamber with the measured pressure read by the pressure sensor of the density relay in real time, and performing pressure boosting verification on the density relay.

7. A calibration device for a mixed-gas density relay with humidity detection function, characterized in that, include: The calibration chamber includes: a first temperature sensor, a first pressure sensor, a semiconductor cooler, and an optical monitoring component; The first temperature sensor and the first pressure sensor are used to detect the actual temperature and actual pressure inside the calibration chamber; the semiconductor cooler is used to regulate the temperature inside the calibration chamber; the optical monitoring component is used to generate light and monitor the light energy value of the light after it passes through the calibration chamber; the calibration chamber is connected to a density relay. The control component is used to control the semiconductor cooler to cool down the calibration chamber, and to perform pressure reduction calibration by collecting the pressure values ​​of the first pressure sensor of the calibration chamber and the second pressure sensor of the density relay; and to perform humidity detection and mixing ratio detection on the mixed gas in the calibration chamber by monitoring multiple change rates of the light energy value of the optical monitoring component.

8. The calibration device for the mixed-gas density relay with humidity detection function according to claim 7, characterized in that, The optical monitoring component includes: a light emitting tube, a light receiving tube, and a reflective mirror; the light emitting tube and the light receiving tube are horizontally mounted facing each other on the inner walls of the two sides of the calibration chamber, and the reflective mirror is mounted on the bottom of the inner surface of the calibration chamber to reflect the light emitted by the light emitting tube to the light receiving tube to form a folded optical path.

9. The calibration device for a mixed-gas density relay with humidity detection function according to claim 8, characterized in that, The first temperature sensor of the calibration chamber is installed below and in close contact with the reflective mirror.

10. The calibration device for the mixed-gas density relay with humidity detection function according to claim 7, characterized in that, The verification chamber has a frustum-shaped structure with its cross-section gradually decreasing from top to bottom; the outer wall of the verification chamber is made of metal; and the semiconductor cooler is installed on the outer wall at the bottom of the verification chamber.

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