Self-calibration method for C4F7N / CO2 / O2 ternary gas mixture density relay and mixing ratio monitoring method

Abstract

This invention relates to a self-calibration method and a mixing ratio monitoring method for a C4F7N / CO2 / O2 ternary gas density relay, belonging to the field of density relay calibration technology. It solves the problem of low reliability in density monitoring results caused by the inability to verify the sensor status of the density relay itself and the inability to monitor changes in the gas mixing ratio. The method includes: real-time acquisition of temperature and pressure measurements within the calibration chamber by the density relay's temperature and pressure sensors; calibration of the temperature sensor status based on the measured temperature and a set temperature within the calibration chamber; if the temperature sensor is normal, lowering the temperature within the calibration chamber to the liquefaction point of C4F7N gas, acquiring multiple sets of temperature and pressure measurements, calculating the corresponding C4F7N gas pressure value, and then verifying the linear relationship between the pressure value and temperature of the CO2 and O2 gas mixture to calibrate the pressure sensor status. This ensures the reliability of the density relay's sensor data.

Description

Technical Field

[0001] This invention relates to the field of density relay calibration technology, and in particular to a self-calibration method and a mixing ratio monitoring method for a C4F7N / CO2 / O2 ternary mixed gas density relay. Background Technology

[0002] With increasingly stringent environmental protection requirements, the use of environmentally friendly C4F7N / CO2 / O2 ternary gas mixtures in various electrical equipment is currently being promoted. To ensure the insulation and arc-extinguishing performance of these devices, density relays must be installed to monitor the density of the gas mixture online. The basic principle is to monitor the gas temperature and pressure in real time, using a built-in temperature-pressure compensation algorithm to convert the measured pressure value to an equivalent pressure value at a standard temperature of 20°C for monitoring.

[0003] Density relays may drift or fail after long-term use. Current methods for verifying density relays typically involve periodic manual verification. However, due to the large number of electrical equipment chambers in substations, relying on maintenance personnel to perform verification on-site at each chamber with a verification instrument is extremely labor-intensive and costly. More importantly, the operational status of density relays cannot be guaranteed in real time over verification cycles that can last for several years. If a failure occurs, it will pose a threat to the safe operation of the power grid.

[0004] Furthermore, in actual operation, due to factors such as improper gas replenishment operations or gas leaks, the actual mixing ratio of the C4F7N / CO2 / O2 ternary gas mixture may deviate from the rated ratio. Changes in the mixing ratio directly affect the gas's insulation performance, and the existing temperature-pressure compensation algorithm built into the density relay is calibrated under the rated mixing ratio. When the mixing ratio changes, the original compensation algorithm becomes inaccurate, resulting in a significant error between the calculated 20℃ standard pressure value and the actual value. This makes the density monitoring results unreliable and unable to accurately reflect the gas state calibrated by the density relay. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a self-calibration method and device for a C4F7N / CO2 / O2 ternary mixed gas density relay, in order to solve the problem that existing C4F7N / CO2 / O2 ternary mixed gas density relays cannot verify their own sensor status and cannot monitor changes in the gas mixing ratio, resulting in low reliability of density monitoring results.

[0006] On one hand, embodiments of the present invention provide a self-calibration method for a C4F7N / CO2 / O2 ternary mixed gas density relay, comprising the following steps: The temperature and pressure of the ternary gas mixture in the calibration chamber are measured in real time using temperature and pressure sensors from a density relay; the temperature sensor status is then verified based on the measured temperature and the set temperature in the calibration chamber. If the temperature sensor is normal, the temperature in the calibration chamber is lowered to the liquefaction point of C4F7N gas, and multiple sets of temperature and pressure measurements are obtained. The corresponding C4F7N gas pressure value is calculated based on the temperature measurement value, thereby verifying the linear relationship between the pressure value of the CO2 and O2 mixed gas and the temperature to verify the status of the pressure sensor.

[0007] Based on a further improvement to the above method, the temperature sensor status is verified according to the measured temperature value and the set temperature in the calibration chamber, including: The temperature of the ternary mixed gas in the calibration chamber is controlled to multiple set temperatures. The measured temperature value is compared with each set temperature. If all comparison results are within the corresponding deviation range, the temperature sensor is normal; otherwise, the temperature sensor is abnormal.

[0008] Further improvements to the above method, including lowering the temperature within the calibration chamber to the liquefaction point of C4F7N gas, include: During the gradual cooling process, when the decrease in light energy intensity per unit time exceeds the preset decrease, the measured value of the current temperature is taken as the liquefaction point of C4F7N gas. The light energy intensity is obtained by monitoring the folded optical path set in the calibration chamber, and the droplets formed when C4F7N gas liquefies condense on the reflective surface in the folded optical path.

[0009] Based on a further improvement of the above method, the corresponding C4F7N gas pressure value is calculated according to the measured temperature value. This is done using the saturated vapor pressure equation for C4F7N gas, as shown in the following formula: , in, For the first The corresponding C4F7N gas pressure value at each temperature. The critical pressure of C4F7N gas; The reference temperature is the temperature at which C4F7N gas is compared. For the first The thermodynamic temperature is converted from the measured temperature value. 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.

[0010] Based on a further improvement of the above method, the pressure value of the CO2 and O2 mixture is obtained by subtracting the C4F7N gas pressure value from the measured pressure value corresponding to the same temperature, based on Dalton's law of partial pressures.

[0011] Further improvements to the above method are made to verify the linear relationship between the pressure of the CO2 and O2 mixture and temperature to validate the pressure sensor status, including: Establish a linear equation relating the pressure and temperature of a CO2 and O2 mixture; The slope of the linear equation is calculated by taking the first and last sets of data from multiple sets of temperature and pressure measurements. Substitute the measured temperature values ​​from the remaining data sets into the linear equation to obtain the theoretical pressure value of the ternary gas mixture. If the absolute difference between all theoretical pressure values ​​and the corresponding measured pressure values ​​is less than the set pressure deviation threshold, it is determined that the linear relationship is met and the pressure sensor is normal; otherwise, the pressure sensor is abnormal.

[0012] Based on further improvements to the above method, the linear equation between the pressure and temperature of the CO2 and O2 mixture is expressed by the following formula: , in, For the first The measured value of the temperature. For the first The measured value of the pressure. To and The corresponding C4F7N gas pressure value, For the first The pressure value of a mixture of CO2 and O2 gas; The slope represents the linear relationship.

[0013] On the other hand, embodiments of the present invention provide a method for monitoring the mixing ratio of a C4F7N / CO2 / O2 ternary mixed gas, comprising the following steps: The self-calibration method for the C4F7N / CO2 / O2 ternary mixed gas density relay, which executes any of the above, obtains the slope of the linear relationship between the pressure value of the CO2 and O2 mixed gas and the temperature when the pressure sensor is determined to be normal. Raise the temperature in the calibration chamber to 0℃. Calculate the actual mixing ratio of the ternary gas mixture based on the measured pressure and slope at 0℃. If the deviation between the actual mixing ratio and the rated mixing ratio is within the set range, the gas mixing ratio is normal; otherwise, the gas mixing ratio is abnormal.

[0014] Based on further improvements to the above method, the actual mixing ratio of the ternary gas mixture is calculated using the measured pressure and slope at 0°C, including: Based on the measured pressure and slope at 0℃, the pressure value of C4F7N gas at 0℃ is calculated, and then the pressure value of the CO2 and O2 mixture at 0℃ is obtained by the difference. Based on Dalton's law of partial pressures, the pressure values ​​of the CO2 and O2 mixture at 0℃ are calculated by solving the slope; Calculate the ratio of the pressure values ​​of C4F7N gas, CO2 and O2 at 0℃ to the measured pressure values ​​at 0℃, obtain the volume fraction of C4F7N gas, CO2 gas and O2 gas at 0℃, and then obtain the actual mixing ratio of the ternary gas mixture.

[0015] Based on further improvements to the above method, the actual mixing ratio of the ternary gas mixture is obtained through the following formula: , in, , and These represent the volume fractions of C4F7N gas, CO2 gas, and O2 gas at 0℃. This represents the pressure of C4F7N gas at 0℃. This represents the pressure of a CO2 and O2 mixture at 0°C. This is the measured pressure value at 0℃. The slope represents the linear relationship.

[0016] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: 1. By controlling the temperature of the calibration chamber, the temperature sensor of the density relay is calibrated; by liquefying C4F7N gas and utilizing its gas-liquid balance characteristics to perform separation calculations with the ideal gas behavior of CO2 and O2, the pressure sensor is calibrated; thus ensuring the long-term reliability of the density relay's sensor data.

[0017] 2. By cleverly utilizing the linear relationship between the pressure and temperature of the remaining CO2 and O2 in the calibration chamber after C4F7N liquefaction, the slope is calculated. Combined with the measured value of the total pressure at 0℃, the volume mixing ratio of the three components is accurately deduced through Dalton's law of partial pressure. This allows for the timely detection of mixing ratio imbalances caused by leakage or improper gas replenishment, thus ensuring the accuracy of density monitoring and insulation performance evaluation from the root cause.

[0018] 3. By integrating the self-calibration of the density relay with the gas mixing ratio monitoring function, it possesses the self-diagnostic capability of the density relay and the deep sensing capability of the gas state, which greatly improves the intelligence level and operational safety of electrical equipment condition monitoring; it realizes fully automated online self-calibration, completely overcomes the dependence on manual on-site calibration, significantly reduces the workload and cost of operation and maintenance, and eliminates monitoring blind spots between calibration cycles.

[0019] 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

[0020] 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. Figure 1 This is a flowchart of the self-calibration method for the C4F7N / CO2 / O2 ternary mixed gas density relay in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the self-calibration device for the C4F7N / CO2 / O2 ternary mixed gas density relay in Embodiment 3 of the present invention; Figure label: 1-Intake pipe; 2-Solenoid valve; 3-Verification chamber; 4-Light emitter; 5-Light receiver; 6-Pressure sensor; 7-Temperature sensor; 8-Reflector; 9-Pressure sensor interface; 10-Temperature sensor interface. Detailed Implementation

[0021] 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.

[0022] Example 1 A specific embodiment of the present invention discloses a self-calibration method for a C4F7N / CO2 / O2 ternary mixed gas density relay, such as... Figure 1 As shown, it includes the following steps: S1. The temperature and pressure of the ternary gas mixture in the calibration chamber are measured in real time using the temperature sensor and pressure sensor of the density relay; the temperature sensor status is checked based on the measured temperature value and the set temperature in the calibration chamber. S2. If the temperature sensor is normal, lower the temperature in the calibration chamber to the liquefaction point of C4F7N gas, obtain multiple sets of temperature and pressure measurements, and calculate the corresponding C4F7N gas pressure value based on the temperature measurement value. Then, verify the linear relationship between the pressure value and temperature of the CO2 and O2 mixed gas to verify the status of the pressure sensor.

[0023] During implementation, the calibration chamber is a sealed container connected to the gas chamber of the electrical equipment via a pipeline with valves, and filled with a ternary gas mixture of C4F7N / CO2 / O2. The valves can be controlled to open and close automatically. The temperature and pressure sensors of the density relay are connected to the interior of the calibration chamber through interfaces on the calibration chamber to measure the temperature and pressure of the gas inside the calibration chamber. By actively controlling the temperature of the calibration chamber to liquefy the C4F7N gas in the ternary gas mixture, and combining optical monitoring with theoretical calculations, the automatic calibration of the temperature and pressure sensors of the density relay is achieved.

[0024] Preferably, the sensing parts of the temperature sensor and the pressure sensor extend into the interior of the calibration chamber.

[0025] Specifically, in step S1, the temperature sensor status is verified based on the measured temperature value and the set temperature inside the verification chamber, including: The temperature of the ternary mixed gas in the calibration chamber is controlled to multiple set temperatures. The measured temperature value is compared with each set temperature. If all comparison results are within the corresponding deviation range, the temperature sensor is normal; otherwise, the temperature sensor is abnormal.

[0026] It should be noted that the temperature of the ternary gas mixture in the calibration chamber is controlled and stabilized at multiple set temperatures by a semiconductor cooler (which can both control and detect the gas temperature). In this embodiment, since C4F7N gas in the ternary gas mixture is easily liquefied, the set temperature during calibration is usually higher than the liquefaction temperature of C4F7N gas. For example, the rated pressure of the C4F7N / CO2 / O2 ternary gas mixture in electrical equipment is generally 0.8 MPa, and when the C4F7N content is about 8%, the liquefaction temperature is about -15°C. The three set points are 5°C, 0°C, and -5°C.

[0027] After each temperature setting, wait for the thermoelectric cooler to display a temperature drop to the set temperature, then let it stand for 10 minutes to allow the gas temperature in the calibration chamber to stabilize. Record the temperature sensor reading as the measured temperature value.

[0028] Furthermore, if the measured temperature value is within the corresponding deviation range at each set temperature, it indicates that the temperature sensor is normal and subsequent calibration can be performed; if any value exceeds the deviation range, a temperature sensor fault alarm will be issued immediately, and the subsequent calibration process will be terminated to avoid systematic deviations in all subsequent density and mixing ratio calculations due to inaccurate temperature sensing.

[0029] For example, if the deviation range corresponding to each set temperature is ±1℃, then at the three set temperatures of 5℃, 0℃ and -5℃, the measured temperature values ​​should be within the ranges of [4℃, 6℃], [-1℃, 1℃] and [-6℃, -4℃] respectively for the temperature sensor to function normally; otherwise, the temperature sensor is not functioning properly.

[0030] After confirming that the temperature sensor is working properly, proceed to step S2 to verify the pressure sensor.

[0031] It should be noted that, since C4F7N is a macromolecule, unlike CO2 and O2, it is not subject to the ideal gas law. The temperature and pressure of C4F7N gas are not linearly related. Therefore, the temperature and pressure of the C4F7N / CO2 / O2 ternary gas mixture are not linearly related.

[0032] In step S2, the liquefaction point of C4F7N gas is accurately determined by monitoring the light energy intensity. The light energy signal is obtained by monitoring a folded optical path located within the calibration chamber, and droplets formed during C4F7N gas liquefaction condense on the reflective surface of the folded optical path. In other words, when the ternary gas mixture in the calibration chamber is not liquefied, the monitored light energy signal is relatively strong. Once C4F7N gas begins to liquefy, the formed droplets condense on the reflective surface, and the light energy signal drops sharply. When the drop exceeds a preset decrease, the temperature is determined to have dropped to the C4F7N liquefaction point.

[0033] Specifically, the light energy intensity at the point of entry into step S2 is used as a reference, and then the gas temperature in the verification chamber is further reduced by the semiconductor cooler in the verification chamber. In order to ensure that the droplets formed by liquefaction condense on the reflective surface first, the temperature of the area where the reflective surface is located can be controlled to be lower than that of other areas.

[0034] During the gradual cooling process, when the decrease in light energy intensity reflected by the reflective surface exceeds a preset decrease per unit time, the readings of the temperature and pressure sensors are recorded at this point, yielding an initial set of temperature and pressure measurements. , It is the liquefaction point of C4F7N gas.

[0035] It should be noted that once the C4F7N gas begins to liquefy, the ternary gas mixture is no longer introduced into the calibration chamber to ensure that subsequent calibrations are performed under closed conditions with constant gas mass. The temperature continues to decrease gradually. Based on the readings of the temperature and pressure sensors, a set of temperature and pressure measurements is recorded for every 1°C decrease in temperature, resulting in multiple sets of temperature and pressure measurements. Each set of temperature and pressure measurements is expressed as follows: , ; The thermodynamic temperature represents the converted value of a temperature measurement; preferably, Take 10.

[0036] As the amount of C4F7N liquid gradually increases, the C4F7N in the calibration chamber remains in a state of vapor-liquid equilibrium. The temperature and pressure values ​​of the C4F7N gas conform to the saturated vapor pressure equation. The C4F7N gas pressure values ​​at each temperature are calculated based on this equation, as shown in the following formula: (1), in, For the first The corresponding C4F7N gas pressure value at each temperature. The critical pressure of C4F7N gas is taken as 2.5028 MPa. The reference temperature is the temperature at which C4F7N gas is compared. For the first The thermodynamic temperature converted from a measured temperature value, in Kelvin (K). The critical temperature of C4F7N gas is taken as 385.928 K; This is a dimensionless intermediate variable, representing the ratio of the difference from the critical temperature; All are fitting coefficients: a=6.84453, b=1.64783, c=9.26244, d=165.39152.

[0037] By converting the measured temperature values ​​and substituting them into the above equation, the corresponding C4F7N gas pressure values ​​can be obtained. .

[0038] Furthermore, since CO2 and O2 are ideal gases, they conform to the following ideal gas law: (2), in, , T and M are the pressure (Pa), density (kg / m3), thermodynamic temperature (K), and relative molecular mass of the CO2 and O2 mixture, respectively. Let be the molar gas constant, and take the value of . .

[0039] It should be noted that CO2 and O2 are at the same temperature. The temperature and pressure of the CO2 and O2 mixture conform to the following formula: (3), in, and The densities of CO2 and O2 are respectively. and These are the relative molecular masses of CO2 and O2, respectively.

[0040] Since the calibration chamber has stopped receiving air, the ratio and density of CO2 and O2 are constant. If the pressure is a fixed value, then, assuming the pressure sensor is functioning normally and the mass and volume of the CO2 and O2 mixture are fixed, its pressure should be a direct function of thermodynamic temperature.

[0041] According to Dalton's law of partial pressures, the measured pressure values ​​corresponding to the same temperature are... Subtract the C4F7N gas pressure value The pressure values ​​of the CO2 and O2 mixture were obtained corresponding to multiple sets of temperature and pressure measurements. Therefore, the following linear equation is established between the pressure and temperature of the CO2 and O2 mixture: (4), in, The slope represents the linear relationship.

[0042] The slope of the linear equation is calculated by taking the first and last sets of data from multiple sets of temperature and pressure measurements and the corresponding C4F7N gas pressure values. Substituting the measured temperature values ​​from the remaining data sets into the linear equation, we obtain the theoretical pressure value of the ternary gas mixture. If all theoretical pressure values ​​match the corresponding measured pressure values... If the absolute difference is less than the set pressure deviation threshold, it is determined that the linear relationship is met and the pressure sensor is normal; otherwise, a pressure sensor fault alarm is issued and the subsequent verification process is terminated.

[0043] For example, the pressure deviation threshold is 0.01 MPa, when it meets the requirements. When, it conforms to a linear relationship.

[0044] Compared with the prior art, this embodiment provides a self-calibration method for a C4F7N / CO2 / O2 ternary mixed gas density relay. By controlling the temperature of the calibration chamber, the temperature sensor of the density relay is calibrated; by liquefying the C4F7N gas and using its gas-liquid balance characteristics to perform separation calculations with the ideal gas behavior of CO2 and O2, the pressure sensor is calibrated; thus ensuring the long-term reliability of the density relay's sensor data.

[0045] Example 2 Another embodiment of the present invention discloses a method for monitoring the mixing ratio of a C4F7N / CO2 / O2 ternary gas mixture to determine whether the gas composition has changed due to leakage or improper gas replenishment. The method of this embodiment includes the following steps: The self-calibration method of the C4F7N / CO2 / O2 ternary mixed gas density relay in Example 1 is implemented. When the pressure sensor is determined to be normal, the slope of the linear relationship between the pressure value of the CO2 and O2 mixed gas and the temperature is obtained. Raise the temperature in the calibration chamber to 0℃. Calculate the actual mixing ratio of the ternary gas mixture based on the measured pressure and slope at 0℃. If the deviation between the actual mixing ratio and the rated mixing ratio is within the set range, the gas mixing ratio is normal; otherwise, the gas mixing ratio is abnormal.

[0046] It should be noted that the mixing ratio refers to the ratio of the gas volumes of different components in a gas mixture under standard conditions, where standard conditions refer to 0°C and standard atmospheric pressure. Therefore, by using a semiconductor cooler in the calibration chamber to raise the gas temperature to 0°C, heating is stopped when the temperature sensor detects a temperature of 0°C. At this point, C4F7N is in a gaseous state, and the pressure measured by the pressure sensor is recorded. .

[0047] Furthermore, the actual mixing ratio of the ternary gas mixture is calculated through the following steps: ①Based on the measured pressure and slope at 0℃, the partial pressure of C4F7N gas at 0℃ is calculated, and then the pressure of the CO2 and O2 mixture at 0℃ is obtained by the difference.

[0048] Specifically, according to formula (4), The value is taken as the thermodynamic temperature at which 0℃ is converted, combined with the measured pressure at 0℃. and slope Calculate the pressure of the C4F7N gas at this time. Due to the pressure of the mixed gas Since the pressure of each component gas is the sum of its pressure values, the pressure of the CO2 and O2 mixture at 0℃ can be calculated. for: (5).

[0049] ②Based on Dalton's law of partial pressures, the pressure values ​​of the CO2 and O2 mixture at 0℃ are calculated by solving the slope. The pressure values ​​of CO2 and O2 gas at 0℃ are then calculated.

[0050] It should be noted that the relative molecular masses of CO2 and O2 are known to be 44 and 32, respectively. According to formulas (3) and (4), we can obtain: (6).

[0051] Furthermore, given the known slope, calculate... Under these conditions, the relationship between the densities of CO2 and O2 is as follows: (7).

[0052] The effective volume of the calibration chamber is V (unit: m³). 3 Then, the quasi-state volumes of CO2 and O2 in the verification chamber are: (8), in, and These represent the volume and density of CO2 in the calibration chamber under standard conditions. Take 1.98 kg / m 3 ; and These represent the volume and density of O2 in the calibration chamber under standard conditions. Take 1.43 kg / m 3 .

[0053] Combining formulas (7) and (8), we can obtain: (9).

[0054] Since the density ratio of an ideal gas is equal to its pressure ratio, that is: (10), in, For standard atmospheric pressure, take 0.1 MPa, then Take 1.43 kg / m 3 At that time, we can obtain: .

[0055] Furthermore, based on Dalton's law of partial pressures, the pressure of CO2 under standard conditions is: (11), If the pressure ratio of each component is equal to the volume ratio, then formula (9) can be converted to: (12), Simplifying formula (12), we get: (13).

[0056] Formula (13) does not contain any unknowns, so the pressure value of O2 under standard conditions can be calculated. The pressure value of CO2 under standard conditions is further calculated according to formula (11). .

[0057] ③ Calculate the ratio of the pressure values ​​of C4F7N gas, CO2 gas, and O2 at 0℃ to the measured pressure values ​​at 0℃, and obtain the volume fraction of C4F7N gas, CO2 gas, and O2 gas at 0℃. , and This allows us to obtain the actual mixing ratio of the ternary gas mixture.

[0058] Specifically, the actual mixing ratio of a three-way gas mixture is calculated using the following formula: (14).

[0059] Furthermore, to verify whether the deviation between the actual mixing ratio and the rated mixing ratio is within the set range, it is necessary to determine whether the deviation between the volume fraction of any component in the ternary gas mixture and the corresponding rated volume fraction exceeds the set range, such as ±0.5%. If none of them exceed the set range, the actual mixing ratio meets the requirements; otherwise, a density relay fault alarm signal is issued.

[0060] Compared with existing technologies, this embodiment provides a C4F7N / CO2 / O2 ternary gas mixing ratio monitoring method. It cleverly utilizes the linear relationship between the pressure and temperature of the remaining CO2 and O2 in the calibration chamber after C4F7N liquefaction to calculate the slope. Combined with the measured total pressure at 0°C, the volume mixing ratio of the three components is accurately deduced using Dalton's law of partial pressures. This allows for timely detection of mixing ratio imbalances caused by leaks or improper gas replenishment, fundamentally ensuring the accuracy of density monitoring and insulation performance assessment. By integrating the self-calibration of the density relay with the gas mixing ratio monitoring function, it possesses the self-diagnostic capability of the density relay and deep gas state perception capability, greatly improving the intelligence level and operational safety of electrical equipment condition monitoring. It achieves fully automated online self-calibration, completely overcoming the reliance on manual on-site calibration, significantly reducing maintenance workload and costs, and eliminating monitoring blind spots between calibration cycles.

[0061] Example 3 Another embodiment of the present invention discloses a self-calibration device for a C4F7N / CO2 / O2 ternary mixed gas density relay, thereby realizing the self-calibration method for a C4F7N / CO2 / O2 ternary mixed gas density relay in Embodiment 1, and the method for monitoring the mixing ratio of a C4F7N / CO2 / O2 ternary mixed gas in Embodiment 2. Figure 2 As shown, the device includes: The calibration chamber 3 is connected to the gas chamber of the electrical equipment via an air inlet pipe 1 equipped with a solenoid valve 2; the pressure sensor 6 and temperature sensor 7 of the density relay are both connected to the interior of the calibration chamber 3 to detect the pressure and temperature of the gas inside the calibration chamber; the calibration chamber 3 includes a temperature control component and an optical monitoring component; the temperature control component is used to regulate the temperature inside the calibration chamber 3; the optical monitoring component is used to generate light and monitor the light energy intensity of the light after it passes through the calibration chamber. The control component is used to verify the status of temperature sensor 7 by controlling the temperature control component to cool down, and after determining the liquefaction point of C4F7N gas based on the optical monitoring component, it collects multiple sets of temperature and pressure measurements output by pressure sensor 6 and temperature sensor 7 to verify the linear relationship between the pressure value and temperature of the CO2 and O2 mixed gas to verify the status of pressure sensor 6; when the pressure sensor is normal, it obtains the slope of the linear relationship, and calculates the actual mixing ratio of the ternary mixed gas based on the slope and the pressure measurement value at 0℃ in the verification chamber to verify the gas state.

[0062] It should be noted that the calibration chamber 3 is a sealed container, equipped with a pressure sensor interface 9 and a temperature sensor interface 10. The pressure sensor 6 and the temperature sensor 7 are respectively installed on the corresponding interfaces to measure the pressure and temperature of the gas inside the calibration chamber 3.

[0063] Furthermore, the temperature control assembly includes: multiple semiconductor coolers; wherein, one semiconductor cooler is installed at the bottom of the inner surface of the calibration chamber, and the remaining semiconductor coolers are respectively installed on each outer surface of the calibration chamber.

[0064] Preferably, the calibration chamber 3 is cubic in shape, with one thermoelectric cooler installed on the bottom of the inner surface of the calibration chamber 3, and the remaining thermoelectric coolers installed on the top, front, back, left, and right outer surfaces of the calibration chamber. The size of the thermoelectric coolers is customized according to the size of each face of the calibration chamber 3.

[0065] Furthermore, the optical monitoring component includes: a light emitter 4, a light receiver 5, and a reflector 8; the light emitter 4 and the light receiver 5 are installed on the top wall of the calibration chamber 3, and the reflector 8 is installed on the upper side of the semiconductor cooler at the bottom of the inner surface of the calibration chamber 3, reflecting the light emitted by the light emitter 4 to the light receiver 5 to form a folded optical path; the control component determines the C4F7N gas liquefaction point based on the optical monitoring component. During the process of controlling the temperature control component to perform differentiated cooling, it identifies whether the decrease in light energy intensity of the light received by the light receiver exceeds the preset decrease within a unit time. If it does, the current temperature in the calibration chamber is the C4F7N gas liquefaction point.

[0066] Preferably, the pressure sensing part of the pressure sensor 6 extends into the calibration chamber 3 through the pressure sensor interface 9; the temperature sensing part of the temperature sensor 7 extends into the calibration chamber 3 through the temperature sensor interface 10, with its end positioned near the reflector surface 8 to accurately measure the gas temperature inside the calibration chamber 3. The semiconductor cooler on the top wall of the calibration chamber 3 is designed with a dedicated clearance area to ensure that the areas of the pressure sensor interface 9 and the temperature sensor interface 10 are not covered.

[0067] The control component is connected to the temperature control component, the optical monitoring component, the solenoid valve 2, the pressure sensor 6 of the density relay, and the temperature sensor 7 via signal or data cable; the control component includes an operating unit, which includes a touch screen for displaying, setting data, and sending commands.

[0068] The control component internally stores a verification program, which is used to coordinate the actions of each component, collect sensor data, perform data calculations, make logical judgments, and output verification results or alarm signals, thus completing the self-verification method in Example 1 and the mixing ratio monitoring method in Example 2.

[0069] Specifically, when performing step S1 of the method in embodiment 1, the control component opens the solenoid valve 2, starts the temperature control component and controls the temperature of each semiconductor cooler to reach multiple set temperatures, such as 5°C, 0°C and -5°C, respectively collects data from the pressure sensor 6 and the temperature sensor 7, obtains the measured values ​​of temperature and pressure, and verifies the state of the temperature sensor 7 according to the verification method in step S1.

[0070] When the temperature sensor 7 is normal, when executing step S2, the light transmitter 4 and the light receiver 5 are started first. At this time, the ternary mixed gas in the calibration chamber 3 is still in a pure gaseous state, the light path is unobstructed, and the light receiver 5 will receive a stable light signal with a relatively high intensity. The stable light energy intensity is recorded as a reference.

[0071] During the continued cooling process, in order to ensure that C4F7N liquefies on the reflector surface 8, the control component controls the temperature control component to perform differentiated cooling, that is, to control the cooling temperature of the semiconductor cooler installed at the bottom of the inner surface of the calibration chamber 3 to be lower than the cooling temperature of the semiconductor cooler installed on the outer surface.

[0072] Specifically, let the current reading of temperature sensor 7 be... The set temperature of the semiconductor coolers on the five sides (top, front, back, left, and right) of the calibration chamber is then controlled. The control unit, a semiconductor cooler mounted on the bottom surface of the calibration chamber, is set to a lower value. The purpose of this design is to make area 8 of the reflective mirror the coldest point in the calibration chamber, ensuring that the C4F7N liquid preferentially condenses here, thus being effectively monitored by the optical path above, and avoiding the liquid condensing on the side walls and affecting the detection.

[0073] Furthermore, as the temperature continues to decrease, the control component monitors the light energy intensity received by the optical monitoring component in real time. When the decrease in light energy intensity exceeds a preset decrease rate per unit time, it indicates that the C4F7N gas has begun to liquefy, and droplets condense on the reflecting mirror 8, causing the light path to be scattered and absorbed. At this point, the current temperature and pressure measurements are immediately recorded. Then, close the solenoid valve 2 to isolate the connection between the calibration chamber 3 and the gas chamber of the electrical equipment, ensuring that subsequent calibration is carried out under closed conditions with constant gas mass, and calibrate the state of the pressure sensor 6 according to the method in step S2.

[0074] When pressure sensor 6 is functioning normally, and the method of Example 2 is executed, the control component controls all semiconductor coolers in the temperature control component to be energized in reverse to generate heat, uniformly heating the gas in the calibration chamber 3 to 0°C, and recording the pressure measurement value monitored by pressure sensor 6. Then, the actual mixing ratio of the ternary gas mixture is calculated according to the method of Example 2 to verify the gas state; after verification, the control component opens solenoid valve 2 to restore communication between the calibration chamber and the gas chamber of the electrical equipment.

[0075] Since the self-calibration device for a C4F7N / CO2 / O2 ternary mixed gas density relay in this embodiment is related to the methods in the two aforementioned embodiments and can be mutually referenced, this description is redundant and will not be repeated here. Because this device embodiment shares the same principle as the two aforementioned method embodiments, it also possesses the corresponding technical effects of the two aforementioned method embodiments.

[0076] 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.

[0077] 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 method for monitoring the mixing ratio of a C4F7N / CO2 / O2 ternary gas mixture, characterized in that, Includes the following steps: The temperature and pressure of the ternary gas mixture in the calibration chamber are measured in real time using temperature and pressure sensors from a density relay; the temperature sensor status is verified based on the measured temperature and the set temperature in the calibration chamber. If the temperature sensor is normal, the temperature in the calibration chamber is lowered to the liquefaction point of C4F7N gas, and multiple sets of temperature and pressure measurements are obtained. The corresponding C4F7N gas pressure value is calculated based on the temperature measurement value, thereby verifying the linear relationship between the pressure value of the CO2 and O2 mixed gas and the temperature to verify the status of the pressure sensor. When the pressure sensor is determined to be normal, the slope of the linear relationship between the pressure value of the CO2 and O2 mixed gas and the temperature is obtained; the temperature in the calibration chamber is raised to 0°C, and the actual mixing ratio of the ternary mixed gas is calculated based on the measured pressure value at 0°C and the slope. If the deviation between the actual mixing ratio and the rated mixing ratio is within the set range, the gas mixing ratio is normal; otherwise, the gas mixing ratio is abnormal.

2. The method for monitoring the mixing ratio of a C4F7N / CO2 / O2 ternary mixed gas according to claim 1, characterized in that, The step of verifying the temperature sensor status based on the measured temperature value and the set temperature within the verification chamber includes: The temperature of the ternary mixed gas in the calibration chamber is controlled to multiple set temperatures. The measured temperature value obtained each time is compared with each set temperature. If all comparison results are within the corresponding deviation range, the temperature sensor is normal; otherwise, the temperature sensor is abnormal.

3. The method for monitoring the mixing ratio of a C4F7N / CO2 / O2 ternary mixed gas according to claim 1, characterized in that, Lowering the temperature inside the calibration chamber to the liquefaction point of C4F7N gas includes: During the gradual cooling process, when the decrease in light energy intensity per unit time exceeds the preset decrease, the measured value of the current temperature is taken as the liquefaction point of C4F7N gas. The light energy intensity is obtained by monitoring the folded optical path set in the calibration chamber, and the droplets formed when the C4F7N gas liquefies are condensed on the reflective surface of the folded optical path.

4. The method for monitoring the mixing ratio of a C4F7N / CO2 / O2 ternary mixed gas according to claim 1, characterized in that, The calculation of the corresponding C4F7N gas pressure value based on the measured temperature is obtained according to the saturated vapor pressure equation of C4F7N gas, as shown in the following formula: ， in, For the first The corresponding C4F7N gas pressure value at each temperature. The critical pressure of C4F7N gas; The reference temperature is the temperature at which C4F7N gas is compared. For the first The thermodynamic temperature is converted from the measured temperature value. 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.

5. The method for monitoring the mixing ratio of a C4F7N / CO2 / O2 ternary mixed gas according to claim 1, characterized in that, The pressure value of the CO2 and O2 mixture is obtained by subtracting the C4F7N gas pressure value from the measured pressure value corresponding to the same temperature, based on Dalton's law of partial pressure.

6. The method for monitoring the mixing ratio of a C4F7N / CO2 / O2 ternary mixed gas according to claim 5, characterized in that, The verification of the linear relationship between the pressure value and temperature of the CO2 and O2 mixed gas to check the pressure sensor status includes: Establish a linear equation relating the pressure and temperature of a CO2 and O2 mixture; The slope of the linear equation is calculated by taking the first and last sets of data from multiple sets of temperature and pressure measurements. Substitute the measured temperature values ​​from the remaining data sets into the linear equation to obtain the theoretical pressure value of the ternary gas mixture. If the absolute difference between all theoretical pressure values ​​and the corresponding measured pressure values ​​is less than the set pressure deviation threshold, it is determined that the linear relationship is met and the pressure sensor is normal; otherwise, the pressure sensor is abnormal.

7. The method for monitoring the mixing ratio of a C4F7N / CO2 / O2 ternary mixed gas according to claim 6, characterized in that, The linear equation relating the pressure and temperature of the CO2 and O2 mixture is expressed by the following formula: ， in, For the first The measured value of the temperature. For the first The measured value of the pressure. To and The corresponding C4F7N gas pressure value, For the first The pressure value of a mixture of CO2 and O2 gas; The slope represents the linear relationship.

8. The method for monitoring the mixing ratio of a C4F7N / CO2 / O2 ternary mixed gas according to claim 1, characterized in that, The calculation of the actual mixing ratio of the ternary gas mixture based on the measured pressure at 0°C and the slope includes: Based on the measured pressure at 0℃ and the slope, the pressure value of C4F7N gas at 0℃ is calculated, and then the pressure value of the CO2 and O2 mixture at 0℃ is obtained by the difference. Based on Dalton's law of partial pressures, the pressure values ​​of the CO2 and O2 mixture at 0℃ are calculated by using the slope, and the individual pressure values ​​of CO2 and O2 at 0℃ are obtained. Calculate the ratio of the pressure values ​​of C4F7N gas, CO2 and O2 at 0℃ to the measured pressure values ​​at 0℃, obtain the volume fraction of C4F7N gas, CO2 gas and O2 gas at 0℃, and then obtain the actual mixing ratio of the ternary gas mixture.

9. The method for monitoring the mixing ratio of a C4F7N / CO2 / O2 ternary mixed gas according to claim 8, characterized in that, The actual mixing ratio of a ternary gas mixture can be obtained using the following formula: ， in, , and These represent the volume fractions of C4F7N gas, CO2 gas, and O2 gas at 0℃. This represents the pressure of C4F7N gas at 0℃. This represents the pressure of a CO2 and O2 mixture at 0°C. This is the measured pressure value at 0℃. The slope represents the linear relationship.

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