A test method for reliability of C4F7N / CO2 / O2 ternary mixed gas after charging

Abstract

The application provides a kind of C4F7N / CO2 / O2 ternary mixed gas filling reliability test method after filling, belongs to electrical equipment field, according to the mole fraction of each gas component in C4F7N / CO2 / O2, liquefaction temperature-saturation vapor pressure relationship and insulation strength, a certain standard proportion of C4F7N / CO2 / O2 ternary mixed gas is calculated to obtain the liquefaction temperature and insulation strength under target pressure, and in the consideration of correction coefficient, two parameters are used as constraint condition to obtain C4F7N / CO2 / O2 filling reliability criterion.The method of the application avoids the cumbersome operation of conventional gas chromatography for C4F7N / CO2 / O2 ternary mixed gas proportion detection, realizes the convenient check of filling reliability based on liquefaction temperature and insulation strength, and provides help for the research and application of C4F7N / CO2 / O2 ternary mixed gas.

Description

Technical Field

[0001] This invention belongs to the field of electrical equipment, and in particular relates to a method for testing the inflation reliability of a C4F7N / CO2 / O2 ternary mixed gas. Background Technology

[0002] Sulfur hexafluoride (SF6) is widely used in the power industry, accounting for up to 80% of global SF6 consumption, approximately 8,000 tons annually. Its application in high-voltage electrical equipment accounts for over 80% of this usage. However, SF6 is a stable gas and is currently known as the most potent greenhouse gas. Since the 1960s, the power industry has continuously researched alternatives to SF6, and researching environmentally friendly and insulating SF6 substitutes has become a hot topic in the power sector.

[0003] As a potential environmentally friendly alternative to SF6 for insulation, C4F7N and its mixed gases have been extensively studied by scholars both domestically and internationally. Current research on binary C4F7N mixed gases mainly focuses on two schemes: C4F7N / CO2 and C4F7N / N2. However, these schemes cannot meet the requirement of achieving insulation performance close to or exceeding 0.5MPa SF6 at a minimum operating temperature of -25℃. Since replacing an appropriate amount of buffer gas with a strong insulating gas can improve the insulation strength of the mixed gas, a ternary C4F7N mixed gas scheme has been proposed. Adding O2 to C4F7N / CO2 / O2 can effectively inhibit the discharge decomposition of C4F7N gas and extend equipment lifespan; therefore, more and more equipment is beginning to adopt the C4F7N / CO2 / O2 ternary mixed gas formulation.

[0004] Currently, research on ternary mixed insulating gases is still in its early stages both domestically and internationally. Compared to binary mixed gases, ternary mixed gases have more complex compositions and higher requirements for the reliability of the filling ratio. Therefore, it is necessary to verify the filling reliability of C4F7N / CO2 / O2 after filling. Summary of the Invention

[0005] The purpose of this invention is to provide a method for verifying the filling reliability of a C4F7N / CO2 / O2 ternary gas mixture. Based on the mole fraction of each gas component in C4F7N / CO2 / O2, the liquefaction temperature-saturated vapor pressure relationship, and the insulation strength, the liquefaction temperature and insulation strength of a C4F7N / CO2 / O2 ternary gas mixture in a certain standard ratio are calculated at a target pressure. These two parameters are then used as constraints, with correction coefficients considered, to derive the filling reliability criteria for C4F7N / CO2 / O2. This method avoids the cumbersome operation of conventional gas chromatography for detecting the proportion of C4F7N / CO2 / O2 ternary gas mixtures. It provides a convenient verification of filling reliability based on liquefaction temperature and insulation strength, thus aiding in the research and application of C4F7N / CO2 / O2 ternary gas mixtures.

[0006] To achieve the above objectives, this invention provides a method for testing the inflation reliability of a C4F7N / CO2 / O2 ternary compound gas, comprising the following steps: S1. Select the required C4F7N / CO2 / O2 ternary mixed gas component ratio scheme according to the project needs, and let the gas stand after the filling is completed; S2. Based on the liquefaction temperatures of each component in the C4F7N / CO2 / O2 ternary gas mixture. T bi And the volume fraction of component i in the ternary gas mixture. k i The liquefaction temperature of the gas mixture under a set pressure is calculated and denoted as the critical standard liquefaction temperature. T c ; S3. Based on the expected insulation performance of the C4F7N / CO2 / O2 ternary mixed gas at the target ratio, the insulation performance is characterized by the power frequency breakdown voltage, and the obtained data is recorded as the critical standard power frequency breakdown voltage. U c ; S4. Based on the critical standard liquefaction temperature T c and critical standard power frequency breakdown voltage U c Thus, an ideal inflation reliability criterion without margin is obtained that meets engineering requirements; S5. Perform liquefaction temperature detection and insulation strength testing on the actual C4F7N / CO2 / O2 ternary mixed gas, and obtain the actual values, including the actual liquefaction temperature. T b and actual power frequency breakdown voltage U b ; S6. Based on the ideal inflation reliability criterion obtained in S4, analyze the actual value obtained in S5 and select an appropriate correction coefficient. Q A reliability criterion considering margin is constructed, and based on the reliability criterion considering margin, the filling reliability of the prepared C4F7N / CO2 / O2 ternary mixed gas is verified.

[0007] The preferred calculation process for the critical standard liquefaction temperature is as follows: Estimate the liquefaction temperature of the gas mixture: ; In the formula, p v The vapor pressure of the mixed gas. T bi This refers to the liquefaction temperature of a gaseous component at atmospheric pressure. R It is the ideal gas constant, which is 8.314 J·mol⁻¹. -1 ·K -1 , A This is the Trouton constant, which is 85-88 J·K. T mb Let be the liquefaction temperature of the gas mixture, corresponding to the critical proportion of C4F7N gas in practical applications. T mb This is denoted as the critical standard liquefaction temperature. T c .

[0008] Preferably, the vapor pressure of the mixed gas p v : Combining the Clausius-Clapeyron equation and Truden's rule, and assuming that the gas mixture obeys the ideal gas law, the equation for calculating the saturated vapor pressure of the gas mixture is obtained: ; In the formula, T The ambient temperature.

[0009] Preferably, the insulation strength of the C4F7N / CO2 / O2 ternary gas mixture is: ; In the formula, E mix The insulation strength of the ternary gas mixture. k j gaseous components j volume fraction, β ij Components i and components j The synergistic effect coefficient between them; Ei Components i insulation strength, E j Components j The insulation strength; C4F7N has higher insulation properties than CO2 and O2, therefore, equation (3) simplifies to: ; In the formula, E mix The breakdown field strength of the gas mixture. The breakdown field strength of C4F7N gas. , , These represent the volume fractions of C4F7N gas, CO2 gas, and O2 gas, respectively. The coefficient representing the synergistic effect between C4F7N gas and CO2 gas. The coefficient representing the synergistic effect between C4F7N gas and O2 gas.

[0010] Preferably, the calculation of the ideal reliability criterion without considering margin includes the following steps: Using the critical standard liquefaction temperature T c and critical standard power frequency breakdown voltage U c By reverse reasoning about the proportion of C4F7N, we can obtain the following results: T c The corresponding volume fraction of C4F7N as well as U c The corresponding volume fraction of C4F7N This yields an ideal reliability criterion without considering margin.

[0011] The preferred reliability criterion, considering margin, is: Ideally Should be with , Equal, for T c as well as U c Perform coefficient correction, consider margin, and select an appropriate insulation correction coefficient. Q U and liquefaction temperature correction factor Q T The reliability criterion considering margin is constructed as follows: , ],in The minimum C4F7N volume fraction considering margin, corresponding to the power frequency breakdown voltage.Q U U c , Q U The value is greater than 1; To account for the highest C4F7N volume fraction with margin, the corresponding liquefaction temperature Q is... T T c , Q T The value is less than 1.

[0012] Preferably, the verification of the charging reliability of the C4F7N / CO2 / O2 ternary gas mixture specifically includes: The liquefaction temperature and insulation strength of the prepared gases were tested to obtain the actual liquefaction temperature. T b and actual power frequency breakdown voltage U b ; Using a reliability criterion that takes margin into account, when T b T T c and U b > Q U U c At that time, it was considered that the prepared C4F7N / CO2 / O2 ternary gas mixture met the requirements.

[0013] Therefore, the present invention employs the above-mentioned method for testing the inflation reliability of a C4F7N / CO2 / O2 ternary hybrid gas, and the technical effects are as follows: (1) The liquefaction temperature of the C4F7N / CO2 / O2 ternary mixed gas was calculated based on the liquefaction temperature and mole fraction of each gas component. The insulation strength of the mixed gas was obtained by consulting the literature. The gas filling reliability criterion was obtained by considering the correction coefficient.

[0014] (2) A convenient method for verifying the reliability of C4F7N / CO2 / O2 ternary mixed gas filling is given, which avoids the cumbersome gas chromatography detection operation without sacrificing the accuracy of verification. Attached Figure Description

[0015] Figure 1 This is a flowchart illustrating a method for testing the inflation reliability of a C4F7N / CO2 / O2 ternary hybrid gas according to the present invention. Detailed Implementation

[0016] ​The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0017] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0018] Example 1 like Figure 1 As shown, a method for testing the inflation reliability of a C4F7N / CO2 / O2 ternary compound gas includes the following steps: S1. Select the required C4F7N / CO2 / O2 ternary mixed gas component ratio scheme according to the project requirements, and let the gas stand after the filling is completed; the C4F7N / CO2 / O2 ternary mixed gas component ratio scheme should be determined according to actual needs, and judged in combination with the requirements of the use environment and voltage level.

[0019] S2. Based on the liquefaction temperatures of each component in the C4F7N / CO2 / O2 ternary gas mixture. T bi and the mole fraction of each component k i The liquefaction temperature of the gas mixture under a certain pressure is calculated and denoted as the critical standard liquefaction temperature. T c ; The specific calculation process for the liquefaction temperature of the C4F7N / CO2 / O2 ternary gas mixture is as follows: First, combining the Clausius-Clapeyron equation and the Trudeau rule, and assuming that the gas mixture obeys the ideal gas law, the equation for calculating the saturated vapor pressure of the gas mixture can be obtained: ; In the formula, p v It is the vapor pressure of the mixed gas, and the unit is MPa; k i It is the volume fraction of a certain gaseous component; T This is the ambient temperature, expressed in Kelvin (K). T bi This is the liquefaction temperature of the gas component at atmospheric pressure, expressed in Kelvin (K); R is the ideal gas constant, which is 8.314 J·mol⁻¹. -1 ·K -1 A is Trouton's constant, which is 85-88 J·K. In the calculation, A is taken as 85 J·K.

[0020] Therefore, the liquefaction temperature of the gas mixture is estimated as follows: ; In the formula, T mbThis is the liquefaction temperature of the gas mixture, expressed in Kelvin (K).

[0021] In a ternary gas mixture, due to differences in partial pressure and liquefaction temperature, one component will reach its saturated vapor pressure and liquefy when the ambient pressure increases. Therefore, the liquefaction temperature of the gas mixture should be the maximum value of the liquefaction temperatures of each component calculated under ambient pressure. Since C4F7N has a relatively high liquefaction temperature, it is generally easier to reach liquefaction conditions. Therefore, the liquefaction temperature of the gas mixture calculated based on the proportion of C4F7N and the liquefaction temperature parameters under normal pressure is used as the standard value, denoted as the critical standard liquefaction temperature. T c .

[0022] S3. Consult literature or existing engineering data to obtain the required insulation performance of the target proportion of C4F7N / CO2 / O2 ternary mixed gas. Characterize the insulation performance using the power frequency breakdown voltage and record the obtained data as the critical standard power frequency breakdown voltage U. c ; The insulation performance of the C4F7N / CO2 / O2 ternary gas mixture should be obtained from literature review or existing engineering data, and the obtained data should be denoted as the critical standard power frequency breakdown voltage U. c Considering a simple synergistic effect, the insulation strength of the ternary gas mixture can be described by equation (3): ; In the formula, E mix The insulation strength of a ternary gas mixture; k i It is the volume fraction of a certain gaseous component; β ij Components i and components j The synergistic effect coefficient between them; E i Components i The insulation strength.

[0023] Considering that the insulation performance of the C4F7N / CO2 / O2 ternary gas mixture is mainly contributed by C4F7N, equation (3) can be simplified to: ; S4. Select appropriate correction coefficients Q Critical standard liquefaction temperature T c and critical standard power frequency breakdown voltage U c The calibration was performed to obtain an inflation reliability criterion that meets the engineering requirements; According to the formula for calculating liquefaction temperature, the liquefaction temperature of the ternary gas mixture C4F7N / CO2 / O2 is... T mb mole fraction of C4F7N Positive correlation; the insulation strength of the C4F7N / CO2 / O2 ternary gas mixture is related to... Positive correlation, that is, with Positive correlation. Therefore, the critical standard liquefaction temperature can be used. T c and critical standard power frequency breakdown voltage U c Let's reverse-engineer the proportion of C4F7N. Ideally... Should be with as well as In order to construct a suitable inflatability reliability criterion, the following should be considered: T c And U c Perform coefficient correction and select appropriate correction coefficients. Q The reliability criterion is constructed as follows: , ].in Corresponding power frequency breakdown voltage Q U U c Q U The value is greater than 1; Corresponding liquefaction temperature Q T T c Q T The value is less than 1.

[0024] S5. Perform liquefaction temperature detection and insulation strength testing on the actual C4F7N / CO2 / O2 ternary mixed gas to obtain the actual liquefaction temperature. T b And the actual power frequency breakdown voltage U b ; S6. Based on the inflation reliability criteria obtained in S4, analyze the actual value obtained in S5 to verify whether the prepared C4F7N / CO2 / O2 ternary mixed gas has reliability.

[0025] The reliability of the C4F7N / CO2 / O2 ternary gas filling process was verified by comparing experimental results. The liquefaction temperature and insulation strength of the prepared gases were tested to obtain the actual liquefaction temperature. T b And the actual power frequency breakdown voltage U b Using reliability criteria, when T b T T c And U​b Q U U c At that time, it was considered that the prepared C4F7N / CO2 / O2 ternary gas mixture met the requirements.

[0026] Taking a ternary gas mixture of 10% C4F7N / 85% CO2 / 5% O2 as an example, the liquefaction temperature of C4F7N at atmospheric pressure is -4.7℃. Calculations show that the liquefaction temperature of the 10% C4F7N / 85% CO2 / 5% O2 ternary gas mixture at 0.1 MPa is -53.8℃. Existing experimental results indicate that the power frequency breakdown voltage of 10% C4F7N / 85% CO2 / 5% O2 at 0.1 MPa is 14.683 kV. A liquefaction temperature correction factor Q is set. T The insulation strength correction factor is 95%, and the insulation strength correction factor is Q. U If the value is 105%, then the liquefaction temperature criterion threshold Q is... T T c The insulation strength criterion threshold is -51.11℃, and the threshold is Q. U U c The voltage is 15.417 kV. Experiments were conducted on the prepared ternary gas mixture to obtain its actual liquefaction temperature T. b and actual insulation strength U b Then, the inflation reliability criterion is used: inflation reliability criterion is applied if and only if T is satisfied simultaneously. b <-51.11℃, U b At a voltage >15.417kV, the prepared ternary gas mixture ratio of 10%C4F7N / 85%CO2 / 5%O2 is considered reliable and passes the reliability verification.

[0027] Therefore, the present invention adopts the above-mentioned method for testing the filling reliability of C4F7N / CO2 / O2 ternary mixed gas, avoiding the cumbersome operation of conventional gas chromatography for detecting the proportion of C4F7N / CO2 / O2 ternary mixed gas. Based on liquefaction temperature and insulation strength, it realizes convenient verification of filling reliability, which helps the research and application of C4F7N / CO2 / O2 ternary mixed gas.

[0028] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for testing the inflation reliability of a C4F7N / CO2 / O2 ternary compound gas, characterized in that, Includes the following steps: S1. Select the required C4F7N / CO2 / O2 ternary mixed gas component ratio scheme according to the project needs, and let the gas stand after the filling is completed; S2. Based on the liquefaction temperatures of each component in the C4F7N / CO2 / O2 ternary gas mixture. T bi And the volume fraction of component i in the ternary gas mixture. k i The liquefaction temperature of the gas mixture under a set pressure is calculated and denoted as the critical standard liquefaction temperature. T c ; S3. Based on the expected insulation performance of the C4F7N / CO2 / O2 ternary mixed gas at the target ratio, the insulation performance is characterized by the power frequency breakdown voltage, and the obtained data is recorded as the critical standard power frequency breakdown voltage. U c ; S4. Based on the critical standard liquefaction temperature T c and critical standard power frequency breakdown voltage U c Thus, an ideal inflation reliability criterion without margin is obtained that meets engineering requirements; S5. Perform liquefaction temperature detection and insulation strength testing on the actual C4F7N / CO2 / O2 ternary mixed gas, and obtain the actual values, including the actual liquefaction temperature. T b and actual power frequency breakdown voltage U b ; S6. Based on the ideal inflation reliability criterion obtained in S4, analyze the actual value obtained in S5 and select an appropriate correction coefficient. Q A reliability criterion considering margin is constructed, and based on the reliability criterion considering margin, the filling reliability of the prepared C4F7N / CO2 / O2 ternary mixed gas is verified.

2. The method for testing the inflation reliability of a C4F7N / CO2 / O2 ternary hybrid gas according to claim 1, characterized in that, The specific calculation process for the critical standard liquefaction temperature: Estimate the liquefaction temperature of the gas mixture: ； In the formula, p v The vapor pressure of the mixed gas. T bi This refers to the liquefaction temperature of a gaseous component at atmospheric pressure. R It is the ideal gas constant, which is 8.314 J·mol⁻¹. -1 ·K -1 , A This is the Trouton constant, which is 85-88 J·K. T mb Let be the liquefaction temperature of the gas mixture, corresponding to the critical proportion of C4F7N gas in practical applications. T mb This is denoted as the critical standard liquefaction temperature. T c .

3. The method for testing the inflation reliability of a C4F7N / CO2 / O2 ternary hybrid gas according to claim 2, characterized in that, Vapor pressure of the mixed gas p v : Combining the Clausius-Clapeyron equation and Truden's rule, and assuming that the gas mixture obeys the ideal gas law, the equation for calculating the saturated vapor pressure of the gas mixture is obtained: ； In the formula, T The ambient temperature.

4. The method for testing the inflation reliability of a C4F7N / CO2 / O2 ternary gas mixture according to claim 1, characterized in that the insulation strength of the C4F7N / CO2 / O2 ternary gas mixture is: ； In the formula, E mix The insulation strength of the ternary gas mixture. k j gaseous components j volume fraction, β ij Components i and components j The synergistic effect coefficient between them; E i Components i insulation strength, E j Components j The insulation strength; C4F7N has higher insulation properties than CO2 and O2, therefore, equation (3) simplifies to: ； In the formula, E mix The breakdown field strength of the gas mixture. The breakdown field strength of C4F7N gas. , , These represent the volume fractions of C4F7N gas, CO2 gas, and O2 gas, respectively. The coefficient representing the synergistic effect between C4F7N gas and CO2 gas. The coefficient representing the synergistic effect between C4F7N gas and O2 gas.

5. The method for testing the inflation reliability of a C4F7N / CO2 / O2 ternary hybrid gas according to claim 1, characterized in that, The calculation of the ideal reliability criterion without considering margin includes the following steps: Using the critical standard liquefaction temperature T c and critical standard power frequency breakdown voltage U c By reverse reasoning about the proportion of C4F7N, we can obtain the following results: T c The corresponding volume fraction of C4F7N as well as U c The corresponding volume fraction of C4F7N This yields an ideal reliability criterion without considering margin.

6. The method for testing the inflation reliability of a C4F7N / CO2 / O2 ternary hybrid gas according to claim 1, characterized in that, The reliability criterion considering margin is: Ideally Should be with , Equal, for T c as well as U c Perform coefficient correction, consider margin, and select an appropriate insulation correction coefficient. Q U and liquefaction temperature correction factor Q T The reliability criterion considering margin is constructed as follows: , ],in The minimum C4F7N volume fraction considering margin, corresponding to the power frequency breakdown voltage. Q U U c , Q U The value is greater than 1; To account for the highest C4F7N volume fraction with margin, the corresponding liquefaction temperature Q is... T T c , Q T The value is less than 1.

7. The method for testing the inflation reliability of a C4F7N / CO2 / O2 ternary hybrid gas according to claim 1, characterized in that, The verification of the charging reliability of the C4F7N / CO2 / O2 ternary gas mixture specifically includes: The liquefaction temperature and insulation strength of the prepared gases were tested to obtain the actual liquefaction temperature. T b and actual power frequency breakdown voltage U b ; Using a reliability criterion that takes margin into account, when T b T T c and U b > Q U U c At that time, it was considered that the prepared C4F7N / CO2 / O2 ternary gas mixture met the requirements.​

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