A self-calibrating device for a C4F7N / CO2 / O2 ternary mixed gas density relay

Abstract

This invention relates to a self-calibration device for a C4F7N / CO2 / O2 ternary gas density relay, belonging to the field of density relay calibration technology. It solves the problem of unreliable and inaccurate data caused by the inability of existing ternary gas density relays to verify their own sensor status. The device includes a calibration chamber comprising a temperature control component and an optical monitoring component, used to regulate temperature and form a light beam and monitor the light energy intensity of the beam after passing through the calibration chamber, respectively. The pressure and temperature sensors of the density relay are both connected to the interior of the calibration chamber. The control component calibrates the temperature sensor status by controlling the temperature control component to lower the temperature. After determining the liquefaction point of C4F7N gas based on the optical monitoring component, multiple sets of temperature and pressure measurements from the pressure and temperature sensors are collected to verify the linear relationship between the pressure value and temperature of the CO2 and O2 mixed gas, thus calibrating the pressure sensor status. Online self-calibration is achieved.

Description

Technical Field

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

[0002] With increasingly stringent environmental protection requirements, environmentally friendly C4F7N / CO2 / O2 ternary gas mixtures are being gradually adopted in the power industry. To ensure the insulation and arc-extinguishing performance of electrical equipment using this gas mixture, density relays must be installed on the equipment to monitor the gas density online. The basic principle is that the density relay monitors the gas pressure and temperature in real time using internal pressure and temperature sensors, and utilizes 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 and alarm purposes.

[0003] After prolonged use, the pressure and temperature sensors of existing density relays may drift or malfunction. The current practice is to rely on maintenance personnel to conduct periodic on-site calibration with external calibration equipment. However, due to the large number of electrical equipment chambers within substations, this manual calibration method is labor-intensive, costly, and inefficient. More seriously, during calibration cycles that can last for several years, the health status of the equipment itself cannot be monitored in real time, and any failure poses a safety hazard.

[0004] Moreover, existing devices cannot detect changes in gas composition. In actual operation, if the actual mixing ratio of the ternary gas may deviate from the rated ratio due to factors such as improper gas replenishment operation or slow gas leakage, it will directly reduce the insulation performance of the gas. At this time, even if the sensor of the density relay device itself is intact, its monitoring results will be distorted and cannot truly reflect the density state of the equipment's gas chamber, thus losing its effective monitoring significance. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a self-calibration device for a C4F7N / CO2 / O2 ternary mixed gas density relay, in order to solve the problem that existing ternary mixed gas density relays cannot verify the status of their own sensors, resulting in a lack of data reliability and accuracy.

[0006] This invention provides a self-calibrating device for a C4F7N / CO2 / O2 ternary mixed gas density relay, comprising: The calibration chamber is connected to the gas chamber of the electrical equipment via an air inlet pipe with a valve. The pressure sensor and temperature sensor of the density relay are both connected to the interior of the calibration chamber to detect the pressure and temperature of the gas inside the calibration chamber. The calibration chamber includes a temperature control component and an optical monitoring component. The temperature control component is used to regulate the temperature inside the calibration chamber. 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 the temperature sensor 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 the pressure sensor and temperature sensor to 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.

[0007] Based on further improvements to the above-mentioned device, the temperature control component 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 the outer surface of the calibration chamber.

[0008] Based on further improvements to the above device, the optical monitoring component includes: a light emitter, a light receiver, and a reflector; the light emitter and the light receiver are installed on the top wall of the calibration chamber, and the reflector is installed on the upper side of the semiconductor cooler at the bottom of the inner surface of the calibration chamber, reflecting the light emitted by the light emitter to the light receiver to form a folded optical path.

[0009] Based on further improvements to the above-mentioned device, the control component determines the liquefaction point of C4F7N gas 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 a preset decrease per unit time. If it does, the temperature in the current verification chamber is the liquefaction point of C4F7N gas.

[0010] Based on further improvements to the above-mentioned device, the control component controls the temperature control component to perform differentiated cooling, which means controlling the cooling temperature of the semiconductor cooler installed at the bottom of the inner surface of the calibration chamber to be lower than the cooling temperature of the semiconductor cooler installed on the outer surface.

[0011] Based on further improvements to the above-mentioned device, the control component verifies the linear relationship between the pressure value and temperature of the CO2 and O2 mixed gas to check the pressure sensor status, including: Calculate the corresponding C4F7N gas pressure value based on the measured value of each temperature; establish a linear equation between the pressure value of the CO2 and O2 mixture and the temperature; wherein the pressure value of the CO2 and O2 mixture is obtained by subtracting the C4F7N gas pressure value from the measured pressure value; 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. Substitute the measured temperature values ​​from the remaining data sets into the linear equation to obtain the theoretical pressure values. 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 device, the corresponding C4F7N gas pressure value is calculated according to the measured value of each temperature. This calculation is based on 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.

[0013] Based on a further improvement of the above device, the control component verifies the temperature sensor status by controlling the temperature control component to cool down, including: By controlling the temperature control component to set multiple target temperatures, the temperature measurement value obtained by the temperature sensor each time is compared with each target temperature. If all comparison results are within the corresponding deviation range, the temperature sensor is normal; otherwise, the temperature sensor is abnormal.

[0014] Based on further improvements to the above device, the control component is also used to obtain 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 normal; control the temperature control component to raise the temperature in the calibration chamber to 0°C, and calculate the actual mixing ratio of the ternary mixed gas based on the measured pressure value and slope in the calibration chamber at 0°C, so as to verify the gas state.

[0015] Based on further improvements to the above device, the actual mixing ratio of the ternary gas mixture is calculated according to the measured pressure and slope at 0°C in the calibration chamber, 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.

[0016] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: 1. By verifying the temperature control and optical monitoring components in the calibration chamber, a complete self-calibration system was constructed, enabling multi-point temperature comparison and calibration of the density sensor's temperature sensor. By actively liquefying C4F7N and utilizing its gas-liquid balance characteristics, combined with the ideal gas behavior of CO2 and O2, the linearity of the pressure sensor was calculated and verified. A periodic self-calibration mechanism was implemented, ensuring the long-term accuracy and reliability of the core sensing unit data of the device, and eliminating the risk of false alarms or missed alarms caused by sensor drift from the source.

[0017] 2. The control component uses the data obtained during the calibration process to accurately calculate the volume mixing ratio of the ternary gas mixture, and constructs an "intelligent" device that can sense changes in gas composition. It can promptly detect mixing ratio imbalances caused by leaks or improper gas replenishment, and determine from the root cause whether the currently built-in density compensation algorithm is still effective, thereby ensuring the authenticity and accuracy of density monitoring results and providing a reliable basis for assessing the insulation status of the equipment.

[0018] 3. It has achieved fully automated online self-verification, completely overcoming the reliance on manual on-site verification, significantly reducing the workload and cost of operation and maintenance, realizing the transformation from "periodic preventive maintenance" to "continuous condition-based operation and maintenance", and greatly improving the intelligence level of electrical equipment condition monitoring and the operation safety of the power grid.

[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 1This is a schematic diagram of a self-calibrating device for a C4F7N / CO2 / O2 ternary mixed gas density relay in an embodiment of the present invention; Figure label: 1-Intake pipe; 2-Valve; 3-Calibration 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] A specific embodiment of the present invention discloses a self-calibration device for a C4F7N / CO2 / O2 ternary mixed gas density relay, such as... Figure 1 As shown, it includes: The calibration chamber 3 is connected to the gas chamber of the electrical equipment via an air inlet pipe 1 with a 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 3; 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 3. 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.

[0023] 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.

[0024] Preferably, valve 2 is a solenoid valve.

[0025] Furthermore, the temperature control component 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 the outer surface of the calibration chamber.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] The control component is connected to the temperature control component, optical monitoring component, valve 2, pressure sensor 6 of density relay, and 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.

[0030] The control component stores a verification program to coordinate the actions of other components, collect sensor data, perform data calculations, make logical judgments, and output verification results or alarm signals to complete the verification of the density relay's own status and the gas status.

[0031] During self-calibration, the control component verifies the temperature sensor's status by controlling the temperature control component to lower the temperature, including: By controlling the temperature control component to set multiple target temperatures, the temperature measurement value obtained by the temperature sensor each time is compared with each target temperature. If all comparison results are within the corresponding deviation range, the temperature sensor is normal.

[0032] Specifically, the control component opens valve 2, connecting the calibration chamber 3 to the gas chamber of the electrical equipment, and fills it with a ternary mixed gas of C4F7N / CO2 / O2. The control component then activates the temperature control component and controls the temperature of each thermoelectric cooler to reach multiple set temperatures, which must be higher than the liquefaction temperature of C4F7N gas, such as 5°C, 0°C, and -5°C.

[0033] It should be noted that C4F7N has a relatively high liquefaction temperature. For example, the rated pressure of the C4F7N / CO2 / O2 ternary gas mixture in electrical equipment is generally 0.8MPa. When the C4F7N content is around 8%, the liquefaction temperature is around -15℃.

[0034] After each temperature setting, wait for the temperature control component to display that the temperature has dropped to the set temperature, then let it stand for 10 minutes to allow the gas temperature in the calibration chamber to stabilize. After that, collect the reading of the temperature sensor 7 as the temperature measurement value.

[0035] 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 fault alarm for temperature sensor 7 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.

[0036] 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.

[0037] If temperature sensor 7 is functioning normally, continue with the calibration of pressure sensor 6.

[0038] At this time, the temperature inside the calibration chamber 3 remains at the last temperature set during the temperature sensor calibration. The control component starts the light emitter 4 and the light receiver 5. At this time, the ternary mixed gas inside the calibration chamber 3 is still in a pure gaseous state, and the light path is unobstructed. The light receiver 5 will receive a stable, high-intensity light signal and record the stable light energy intensity as a reference.

[0039] 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.

[0040] 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.

[0041] 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. , The gas liquefaction point is C4F7N, and valve 2 is closed to isolate the connection between the calibration chamber 3 and the gas chamber of the electrical equipment, ensuring that subsequent calibrations are carried out under closed conditions with constant gas mass.

[0042] 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 represented as follows: , ; The thermodynamic temperature represents the converted value of a temperature measurement; preferably, Take 10.

[0043] As the amount of C4F7N liquid gradually increases, the C4F7N in calibration chamber 3 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.

[0044] By converting the measured temperature values ​​and substituting them into the above equation, the corresponding C4F7N gas pressure values ​​can be obtained. .

[0045] 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 . .

[0046] 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.

[0047] Since the air intake in test chamber 3 has stopped, 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.

[0048] 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.

[0049] 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 6 is normal; otherwise, a pressure sensor fault alarm is issued and the subsequent verification process is terminated.

[0050] For example, the pressure deviation threshold is 0.01 MPa, when it meets the requirements. When, it conforms to a linear relationship.

[0051] It should be noted that the control component is also used to obtain the slope of the linear relationship between the pressure value of the CO2 and O2 mixed gas and the temperature when the pressure sensor 6 is normal; control the temperature control component to raise the temperature in the calibration chamber 3 to 0℃, and calculate the actual mixing ratio of the ternary mixed gas based on the measured pressure value and slope at 0℃ in the calibration chamber, so as to verify the gas state and determine whether the gas composition has changed due to leakage or improper gas replenishment.

[0052] It should be noted that the mixing ratio refers to the ratio of the gas volumes of different components in the gas mixture under standard conditions, where standard conditions refer to 0°C and standard atmospheric pressure. Therefore, the control component controls all the semiconductor coolers in the temperature control component to reverse-energize and heat the gas in the calibration chamber 3 uniformly to 0°C. Heating stops when the temperature sensor 7 detects a temperature of 0°C. At this point, C4F7N is in a gaseous state, and the pressure measured by the pressure sensor 6 is recorded. .

[0053] 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.

[0054] 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).

[0055] 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.

[0056] 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).

[0057] Furthermore, given the known slope, calculate... Under these conditions, the relationship between the densities of CO2 and O2 is as follows: (7).

[0058] 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 .

[0059] Combining formulas (7) and (8), we can obtain: (9).

[0060] 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: .

[0061] 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).

[0062] 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). .

[0063] 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.

[0064] Specifically, the actual mixing ratio of a three-way gas mixture is calculated using the following formula: (14).

[0065] 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.

[0066] After the verification is completed, the control component opens valve 2 to restore the connection between the verification chamber and the air chamber of the electrical equipment.

[0067] Compared with existing technologies, this embodiment provides a self-calibration device for a C4F7N / CO2 / O2 ternary mixed gas density relay. Through a temperature control component and an optical monitoring component in the calibration chamber, a complete self-calibration system is constructed, enabling multi-point temperature comparison calibration of the density sensor's temperature sensor. By actively liquefying C4F7N and utilizing its gas-liquid balance characteristics, combined with the ideal gas behavior of CO2 and O2, the linearity of the pressure sensor is calculated and verified. A periodic self-calibration mechanism is implemented, ensuring the long-term accuracy and reliability of the core sensing unit data, eliminating the risk of false alarms or missed alarms caused by sensor drift. The control component uses the data acquired during the calibration process to accurately calculate the volume mixing ratio of the ternary mixed gas, constructing an "intelligent" device capable of sensing changes in gas composition. This device promptly detects mixing ratio imbalances caused by leaks or improper gas replenishment and determines whether the currently built-in density compensation algorithm is still effective, thereby ensuring the authenticity and accuracy of the density monitoring results and providing a reliable basis for assessing the insulation status of the equipment. It has achieved fully automated online self-verification, completely overcoming the reliance on manual on-site verification, significantly reducing the workload and cost of operation and maintenance, realizing the transformation from "periodic preventive maintenance" to "continuous condition-based operation and maintenance", and greatly improving the intelligence level of electrical equipment condition monitoring and the operation safety of the power grid.

[0068] 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.

[0069] 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 self-calibrating device for a C4F7N / CO2 / O2 ternary mixed gas density relay, characterized in that, include: The calibration chamber is connected to the gas chamber of the electrical equipment via an air inlet pipe with a valve. The pressure sensor and temperature sensor of the density relay are both connected to the interior of the calibration chamber to detect the pressure and temperature of the gas inside. The calibration chamber includes a temperature control component and an optical monitoring component. The temperature control component is used to regulate the temperature inside the calibration chamber. The optical monitoring component is used to generate light and monitor the light energy intensity of the light after it has passed through the calibration chamber. The control component is used to control the temperature control component to cool down in order to verify the state of the temperature sensor, and after determining the liquefaction point of C4F7N gas based on the optical monitoring component, close the valve to isolate the connection between the verification chamber and the gas chamber of the electrical equipment; continue to cool down in a gradient, collect multiple sets of temperature and pressure measurements output by the pressure sensor and temperature sensor, and verify the linear relationship between the pressure value and temperature of the CO2 and O2 mixed gas to verify the state of the pressure sensor. The control component is also used to obtain 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 normal; control the temperature control component to raise the temperature in the calibration chamber to 0°C, and calculate the actual mixing ratio of the ternary mixed gas based on the measured pressure value at 0°C in the calibration chamber and the slope, so as to verify the gas state.

2. The self-calibration device for the C4F7N / CO2 / O2 ternary mixed gas density relay according to claim 1, characterized in that, 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 the outer surface of the calibration chamber.

3. The self-calibrating device for the C4F7N / CO2 / O2 ternary mixed gas density relay according to claim 2, characterized in that, The optical monitoring component includes a light emitter, a light receiver, and a reflective mirror. The light emitter and the light receiver are installed on the top wall of the calibration chamber, and the reflective mirror is installed on the upper side of the semiconductor cooler at the bottom of the inner surface of the calibration chamber, reflecting the light emitted by the light emitter to the light receiver to form a folded optical path.

4. The self-calibration device for the C4F7N / CO2 / O2 ternary mixed gas density relay according to claim 3, characterized in that, 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 a preset decrease per unit time. If it does, the temperature in the current verification chamber is the C4F7N gas liquefaction point.

5. The self-calibration device for the C4F7N / CO2 / O2 ternary mixed gas density relay according to claim 4, characterized in that, The control component controls the temperature control component to perform differentiated cooling, which means controlling the cooling temperature of the semiconductor cooler installed at the bottom of the inner surface of the calibration chamber to be lower than the cooling temperature of the semiconductor cooler installed on the outer surface.

6. The self-calibration device for the C4F7N / CO2 / O2 ternary mixed gas density relay according to claim 1, characterized in that, The control component verifies the linear relationship between the pressure value and temperature of the CO2 and O2 mixture to check the pressure sensor status, including: Calculate the corresponding C4F7N gas pressure value based on the measured value of each temperature; establish a linear equation between the pressure value of the CO2 and O2 mixture and the temperature; wherein the pressure value of the CO2 and O2 mixture is obtained by subtracting the C4F7N gas pressure value from the measured pressure value; 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. Substitute the measured temperature values ​​from the remaining data sets into the linear equation to obtain the theoretical pressure values. 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 self-calibration device for the C4F7N / CO2 / O2 ternary mixed gas density relay according to claim 6, characterized in that, The calculation of the corresponding C4F7N gas pressure value based on the measured value of each 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.

8. The self-calibration device for the C4F7N / CO2 / O2 ternary mixed gas density relay according to claim 1, characterized in that, The control component verifies the temperature sensor status by controlling the temperature control component to cool down, including: By controlling the temperature control component to set multiple target temperatures, the measured temperature value obtained by the temperature sensor each time is compared with each target temperature. If all comparison results are within the corresponding deviation range, the temperature sensor is normal; otherwise, the temperature sensor is abnormal.

9. The self-calibration device for the C4F7N / CO2 / O2 ternary mixed gas density relay according to claim 1, characterized in that, The step of calculating the actual mixing ratio of the ternary gas mixture based on the measured pressure at 0°C in the calibration chamber 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.

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