Density detection method for C4F7N / CO2 mixed gas

Abstract

The invention discloses a density detection method for C4F7N / CO2 mixed gas, which comprises the following steps: leading the C4F7N / CO2 mixed gas into a gas tank, vacuumizing, and stabilizing the pressure value at 0.12 Mpa; determining a characteristic absorption spectrum of the C4F7N / CO2 in the C4F7N / CO2 mixed gas; detecting the mixing ratio of the C4F7N / CO2 mixed gas by utilizing a spectrum detection technology; determining the dew point of the C4F7N / CO2 mixed gas according to the mixing ratio, and determining the humidity of the C4F7N / CO2 mixed gas to be measured according to the dew point; and calculating the density of the C4F7N / CO2 mixed gas according to the mixing ratio. According to the density detection method for the C4F7N / CO2 mixed gas, an advanced sensing technology and a data processing algorithm are combined, the density change of the C4F7N / CO2 mixed gas can be detected, abnormal conditions can be found in time and accidents can be prevented when the density detection method is applied to insulating gas detection, and the density detection method has the advantages of being easy and convenient to operate, low in cost and the like.

Description

Technical Field

[0001] The present invention relates to a C 4 F 7 N / CO 2 Density detection method for mixed gases. Background Art

[0002] Sulfur hexafluoride (SF 6 ) gas, as a strongly electronegative gas, is easy to combine with free electrons to form negative ions, thereby weakening the collision ionization process in the gas, which leads to a significant reduction in the number of free electrons in space. The negative ions combine with the positive ions generated during the arc discharge process to form electrically neutral particles. Globally, SF 6 Gas is mainly used for gas-insulated electrical equipment, degassing and purification of active metals (such as magnesium or aluminum) and their alloy melts, and tracers for atmospheric diffusion research. 6 As an excellent insulating medium, SF 6 It has always been a major consumer of the global electricity industry, and its demand for SF 6 The demand is about SF 6 The power industry accounts for 80% of the total output and is also the largest SF 6 The largest contributor to emissions. The power industry SF 6 Emissions may occur in the manufacturing, installation, maintenance and testing of gas-insulated electrical equipment. The Intergovernmental Panel on Climate Change 2013 report shows that SF 6 The atmospheric life cycle of the gas is 3,200 years, and its global warming potential (GWP) is 23,500 times that of CO2. In 1997, it was included in the Kyoto Protocol to the United Nations Framework Convention on Climate Change as one of the six types of greenhouse gases with emission restrictions.

[0003] At present, environmental protection departments, power companies and gas producers in various countries around the world have taken certain emission reduction measures in various aspects to deal with the SF 6 Emission issues. Reduce the emission risk caused by leakage failure through regular equipment leak detection and maintenance; 6 Gas is recycled; through SF 6 Gas decomposition and conversion treatment can reduce its harm to the atmospheric environment. Although these measures can play a certain role, if we want to fundamentally solve the SF 6 To solve the environmental problems caused by gas emissions, it is necessary to reduce SF 6 The amount of gas used in electrical equipment, the use of more environmentally friendly gas as the insulating medium in electrical equipment.

[0004] Currently C 4 F 7 N / CO 2 Mixed gas environmentally friendly GIS equipment has been initially demonstrated and applied, and the operation effect is good. However, as the operation time of GIS equipment increases, due to equipment aging and other problems, gas leakage is very likely to occur, which may cause the pressure of insulating gas in the equipment to decrease, affecting the insulation and arc extinguishing ability of the gas, bringing serious safety hazards to the operation of the equipment and shortening the service life of the equipment. Therefore, a suitable detection method is needed to detect C 4 F 7 N / CO 2 The density change of the mixed gas is detected to find abnormal conditions in time and prevent accidents. However, the current detection method has low detection accuracy and complex operation. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide a C 4 F 7 N / CO 2 The density detection method of mixed gas combines advanced sensing technology and data processing algorithms to detect C 4 F 7 N / CO 2 The change in the density of the mixed gas can be used in the detection of insulating gas to detect abnormal conditions in time and prevent accidents. It has the advantages of simple operation and low cost.

[0006] The technical solution to achieve the above purpose is: a C 4 F 7 N / CO 2 The method for detecting the density of a mixed gas comprises the following steps:

[0007] S1, C 4 F 7 N / CO 2 The mixed gas is led out to the gas pool, evacuated, and the pressure value is stabilized at 0.12Mpa;

[0008] S2, determine C 4 F 7 N / CO 2 C in mixed gas 4 F 7 N / CO 2 Characteristic absorption spectrum of

[0009] S3, using spectral detection technology to detect C 4 F 7 N / CO 2 Mixing ratio of the mixed gas;

[0010] S4, determine C according to the mixing ratio4 F 7 N / CO 2 The dew point of the mixed gas is determined based on the dew point. 4 F 7 N / CO 2 Humidity of the gas mixture;

[0011] S5, calculate C according to the mixing ratio 4 F 7 N / CO 2 Density of the gas mixture.

[0012] One of the above C 4 F 7 N / CO 2 The density detection method of the mixed gas, in step S2, uses the spectrum theoretical calculation software and the hybrid functional B3LYP to perform C 4 F 7 The geometry optimization and excited state calculation of N molecule were carried out with TZP as the basis set, single point calculation was selected, and the number of excited states was set to 60. According to TDDFT calculation, C 4 F 7 The excitation energy and oscillator strength of N molecules from the ground state to the excited state are fitted by Gaussian function, and the ultraviolet spectrum in the 80-200nm band is simulated;

[0013] With C 4 F 7 N / CO 2 C in mixed gas 4 F 7 As the proportion of N increases, the ultraviolet absorption peak of the mixed gas gradually increases, which has a linear law. The mixing ratio detection method of ultraviolet spectrum is used to determine C 4 F 7 N / CO 2 C in mixed gas 4 F 7 N / CO 2 Characteristic absorption spectrum.

[0014] One of the above C 4 F 7 N / CO 2 In the method for detecting the density of a mixed gas, in step S2, select C 4 F 7 N / CO 2 The experiment was conducted with standard samples of mixed gas with a mixing ratio of 1 to 10% to cover the conventional use range of mixed gas insulating media, and the absorption spectrum data of mixed gases with different mixing ratios were obtained, and the ultraviolet absorption spectrum diagram in the 180 to 220 nm band was obtained.

[0015] One of the above C4 F 7 N / CO 2 In the mixed gas density detection method, in step S2, the spectrum theory calculation software is Amsterdam Density Functional, and the version number is 2017.111.

[0016] One of the above C 4 F 7 N / CO 2 In the method for detecting the density of mixed gas, in step S3, the average value of 10 groups of original absorption spectrum data is taken as the measurement value to obtain the ultraviolet absorption spectrum of the mixed gas with different mixing ratios. 4 F 7 N / CO 2 C in mixed gas 4 F 7 With the increase of N proportion, the absorption peak of the UV absorption spectrum gradually increases, while the peak shoulder caused by interference factors gradually decreases and the peak value becomes more and more prominent.

[0017] One of the above C 4 F 7 N / CO 2 A method for detecting the density of a mixed gas, wherein the absorption peak of the ultraviolet absorption spectrum appears at 186.8 nm.

[0018] One of the above C 4 F 7 N / CO 2 A method for detecting the density of a mixed gas, wherein according to C 4 F 7 N / CO 2 The UV absorption spectrum of the mixed gas is obtained by drawing a vertical line from the peak point to the horizontal axis, selecting the characteristic value, and determining the linear fitting algorithm to calculate C 4 F 7 N / CO 2 Mixing ratio of mixed gases.

[0019] One of the above C 4 F 7 N / CO 2 A density detection method for a mixed gas, wherein when selecting characteristic values ​​for linear fitting, four quantitative schemes, namely, peak value Peak, area A to the left of the peak vertical line, area B to the right of the peak vertical line, and area C of the total absorption peak area, are selected as characteristic values, and the optimal linear fitting algorithm is determined.

[0020] One of the above C 4 F 7 N / CO 2Density detection method of mixed gas, wherein the linear fitting results obtained by using four quantitative schemes are shown in Table 1, where y is the characteristic value and x is the mixing ratio:

[0021] Table 1. Linear fitting results obtained by four quantitative schemes

[0022]

[0023] The fitting effect of selecting the peak vertical line and taking the left area Area A as the characteristic value is poor. 2 is 0.985, and the best fitting effect is obtained by using Area B to the right of the peak vertical line. 2 It reaches 0.999, which means that the area Area A to the left of the peak vertical line is indeed affected by interference factors such as light source truncation and spectrometer grating, and cannot present a complete absorption peak. If only the area Area B to the right of the peak vertical line is taken as the characteristic value, a very good fitting effect can be obtained; the absorption peak full area Area C selects the full area of ​​the entire absorption peak, which is affected by the area Area A to the left of the peak vertical line and cannot achieve the fitting effect of Area B to the right of the peak vertical line. 2 is 0.997.

[0024] One of the above C 4 F 7 N / CO 2 A method for detecting the density of a mixed gas, wherein the peak vertical line in the ultraviolet absorption spectrum is finally determined to use the right area Area B as the characteristic value to determine the optimal linear fitting algorithm.

[0025] C of the present invention 4 F 7 N / CO 2 The density detection method of mixed gas combines advanced sensing technology and data processing algorithms to detect C 4 F 7 N / CO 2 The change in the density of the mixed gas can be used in the detection of insulating gas to detect abnormal conditions in time and prevent accidents. It has the advantages of simple operation and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 C 4 F 7 Ultraviolet spectrum of N molecule in the 80-200nm band;

[0027] Figure 2 10% mixing ratio C 4 F 7 N / CO 2Ultraviolet absorption spectrum of mixed gas;

[0028] Figure 3 C under different mixing ratios 4 F 7 N / CO 2 Ultraviolet absorption spectrum of mixed gas (mixing ratio from bottom to top is 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%);

[0029] Figure 4 C 4 F 7 N / CO 2 C in mixed gas 4 F 7 Schematic diagram of the N mixing ratio detection scheme. DETAILED DESCRIPTION

[0030] In order to enable those skilled in the art to better understand the technical solution of the present invention, the specific implementation methods thereof are described in detail below in conjunction with the accompanying drawings:

[0031] See also Figure 1 , Figure 2 , Figure 3 and Figure 4 , an embodiment of the present invention, a C 4 F 7 N / CO 2 The method for detecting the density of a mixed gas comprises the following steps:

[0032] S1, C 4 F 7 N / CO 2 The mixed gas is led out to the gas pool, evacuated, and the pressure value is stabilized at 0.12Mpa;

[0033] S2, determine C 4 F 7 N / CO 2 C in mixed gas 4 F 7 N / CO 2 Characteristic absorption spectrum of

[0034] S3, using spectral detection technology to detect C 4 F 7 N / CO 2 Mixing ratio of the mixed gas;

[0035] S4, determine C according to the mixing ratio 4 F 7 N / CO 2 The dew point of the mixed gas is determined based on the dew point. 4 F 7N / CO 2 Humidity of the gas mixture;

[0036] S5, calculate C according to the mixing ratio 4 F 7 N / CO 2 Density of the gas mixture.

[0037] In step S2, the spectrum theoretical calculation software used in this embodiment is Amsterdam Density Functional (ADF), version number 2017.111. It is generally believed that hybrid functional can obtain relatively good results, at least in terms of energy calculation, and the results of calculating the ultraviolet spectrum of small molecules using the B3LYP method are closer to the experimental value. Therefore, this embodiment selects the hybrid functional B3LYP for C 4 F 7 The geometry optimization and excited state calculation of the N molecule are shown in Figure 2. The basis set is TZP, single point calculation is selected, and the number of excited states is set to 60 to better show the C 4 F 7 UV spectral characteristics of N molecules. According to TDDFT calculation, C 4 F 7 The excitation energy and oscillator strength of the N molecule from the ground state to the excited state are fitted by a Gaussian function, and the simulated ultraviolet spectrum in the 80-200nm band is as follows: Figure 1 , Figure 1 C is shown in 4 F 7 Ultraviolet spectrum of N molecules in the 80-200nm band.

[0038] With C 4 F 7 N / CO 2 C in mixed gas 4 F 7 As the proportion of N increases, the UV absorption peak measured by the detection platform gradually increases, showing a certain linear law. It is possible to consider studying the mixing ratio detection method of UV spectrum. 1-10% standard samples were selected for experiments to cover the conventional use range of mixed gas insulating media. The absorption spectrum data of 10% mixing ratio obtained in the experiment are as follows: Figure 2 As shown, Figure 2The absorption spectrum of the 180-220nm band is given in the figure, and the dotted line is the peak vertical line a from the peak point to the horizontal axis. It can be seen that the absorption peak detected by the detection platform is not complete. This is because the light source band used by the experimental platform is distributed in the range of 185-400nm, so there is a truncation at 185nm. Compared with the calculated results, the experimental results cannot reflect the complete absorption spectrum. In addition, there is a peak shoulder to the left of the vertical line, as shown in the dotted circle b in the figure. This may be because this is the initial band of the spectrometer, and the grating stability of the spectrometer is low, which will cause some interference. Combined with the peak shape characteristics here in the calculation results, the part to the right of the peak vertical line a is closer to the calculated results and may be closer to the actual situation. Therefore, when conducting a study on the detection of the mixing ratio, the area to the right of the peak vertical line of the absorption spectrum can be considered as the characteristic value to determine the fitting algorithm.

[0039] In step S3, the average value of 10 groups of original absorption spectrum data is taken as the measurement value to obtain the ultraviolet absorption spectrum of the mixed gas with different mixing ratios (see Figure 3 ),according to Figure 3 It can be seen that with the C 4 F 7 N / CO 2 C in mixed gas 4 F 7 As the proportion of N increases, the absorption peak of the UV absorption spectrum gradually increases, while the peak shoulder caused by interference factors gradually decreases, and the peak becomes more and more prominent. In the experiment, the absorption peak of the UV absorption spectrum appears at 186.8nm.

[0040] According to C 4 F 7 N / CO 2 The UV absorption spectrum of the mixed gas is obtained by drawing a vertical line from the peak point to the horizontal axis, selecting the characteristic value, and determining the linear fitting algorithm to calculate C 4 F 7 N / CO 2 Mixing ratio of mixed gases.

[0041] See also Figure 4 When selecting characteristic values ​​for linear fitting, four quantitative schemes, namely, peak value Peak, area A to the left of the peak vertical line, area B to the right of the peak vertical line, and area C of the absorption peak, are selected as characteristic values, and the optimal linear fitting algorithm is determined. In step S2, it is analyzed that selecting area B to the right of the peak as the characteristic value for fitting may achieve better results, and four schemes are selected in step S3 to verify it.

[0042] The linear fitting results obtained using the four quantitative schemes are shown in Table 1, where y is the characteristic value and x is the mixing ratio:

[0043] Table 1. Linear fitting results obtained by four quantitative schemes

[0044]

[0045] The fitting effect of selecting the peak vertical line and taking the left area Area A as the characteristic value is poor. 2 is 0.985, and the best fitting effect is obtained by using Area B to the right of the peak vertical line. 2 It reaches 0.999, which means that the area Area A to the left of the peak vertical line is indeed affected by interference factors such as light source truncation and spectrometer grating, and cannot present a complete absorption peak. If only the area Area B to the right of the peak vertical line is taken as the characteristic value, a very good fitting effect can be obtained; the absorption peak full area Area C selects the full area of ​​the entire absorption peak, which is affected by the area Area A to the left of the peak vertical line and cannot achieve the fitting effect of Area B to the right of the peak vertical line. 2 is 0.997.

[0046] Finally, it is determined that the peak vertical line in the ultraviolet absorption spectrum is used as the characteristic value, the right area Area B is used to determine the optimal linear fitting algorithm, and the mixing ratio is calculated based on the peak value. After obtaining the mixing ratio, C is determined based on the mixing ratio. 4 F 7 N / CO 2 The dew point of the mixed gas is determined based on the dew point. 4 F 7 N / CO 2 The humidity of the mixed gas; and calculate C according to the mixing ratio 4 F 7 N / CO 2 Density of the gas mixture.

[0047] C of the present invention 4 F 7 N / CO 2 The density detection method of mixed gas is as follows: in the ultraviolet spectrum, when a high concentration of C 4 F 7 After N gas was injected, a significant absorption peak appeared at 185-200nm, which is very close to the starting band of the light source. There are two absorption peaks in the 170-200nm band, both of which are weaker in intensity and far away from each other. The ultraviolet spectrum near 170nm has little effect on the absorption spectrum detected in the experiment. It can be determined that 170nm is the lowest absorption spectrum. In infrared spectrum detection, C 4 F 7 N / CO 2 Mixed gas leak detection, you can choose 900 ~ 1400cm-1 However, as a gas insulating medium, C 4 F 7 C in N mixed gas 4 F 7 The N concentration is high, so choose 900~1400cm -1 The band is likely to be saturated due to the strong absorption spectrum, making it impossible to detect the mixing ratio. -1 Band pair C 4 F 7 N was used for quantitative analysis.

[0048] In summary, the C of the present invention 4 F 7 N / CO 2 The density detection method of mixed gas is used to reveal C 4 F 7 Based on the spectral characteristics of N gas, a mixing ratio detection method that can be used for the evaluation of the insulation status of mixed gases in the future is proposed; combining advanced sensing technology and data processing algorithms, it is possible to detect C 4 F 7 N / CO 2 The change in the density of the mixed gas can be used in the detection of insulating gas to detect abnormal conditions in time and prevent accidents. It has the advantages of simple operation and low cost.

[0049] Those skilled in the art should recognize that the above embodiments are only used to illustrate the present invention, and are not intended to limit the present invention. As long as they are within the spirit of the present invention, any changes or modifications to the above embodiments will fall within the scope of the claims of the present invention.

Claims

1. A method for detecting the density of a C4F7N / CO2 mixed gas, characterized in that: The steps include: S1, guide the C4F7N / CO2 mixed gas to the gas pool, evacuate it, and stabilize the pressure value at 0.12Mpa; S2, determining the characteristic absorption spectrum of C4F7N / CO2 in the C4F7N / CO2 mixed gas; S3, using spectrum detection technology to detect the mixing ratio of C4F7N / CO2 mixed gas; S4, determining the dew point of the C4F7N / CO2 mixed gas according to the mixing ratio, and determining the humidity of the C4F7N / CO2 mixed gas to be measured according to the dew point; S5, calculating the density of the C4F7N / CO2 mixed gas according to the mixing ratio.

2. The method for detecting density of a C4F7N / CO2 mixed gas according to claim 1, characterized in that: In step S2, the hybrid functional B3LYP is used to perform geometric structure optimization and excited state calculation of the C4F7N molecule using spectral theoretical calculation software, the basis set is TZP, single-point calculation is selected, the number of excited states is set to 60, and the excitation energy and oscillator strength of the C4F7N molecule from the ground state to the excited state are obtained according to TDDFT calculation, and the Gaussian function is used to fit it to simulate the ultraviolet spectrum in the 80-200 nm band; As the proportion of C4F7N in the C4F7N / CO2 mixed gas increases, the ultraviolet absorption peak of the mixed gas gradually increases with a linear law. The mixing ratio detection method of ultraviolet spectrum is used to determine the characteristic absorption spectrum of C4F7N / CO2 in the C4F7N / CO2 mixed gas.

3. The method for detecting density of a C4F7N / CO2 mixed gas according to claim 2, characterized in that: In step S2, a standard sample with a C4F7N / CO2 mixed gas ratio of 1 to 10% is selected for experiment to cover the conventional use range of mixed gas insulating media, obtain absorption spectrum data of mixed gases with different mixing ratios, and obtain an ultraviolet absorption spectrum diagram in the 180 to 220 nm band.

4. The method for detecting density of a C4F7N / CO2 mixed gas according to claim 2, characterized in that: In step S2, the spectral theoretical calculation software is Amsterdam Density Functional, and the version number is 2017.

111.

5. The method for detecting density of a C4F7N / CO2 mixed gas according to claim 3, characterized in that: In step S3, the average value of 10 groups of original absorption spectrum data is taken as the measurement value to obtain the ultraviolet absorption spectrum of the mixed gas with different mixing ratios. As the proportion of C4F7N in the C4F7N / CO2 mixed gas increases, the absorption peak of the ultraviolet absorption spectrum gradually increases, while the peak shoulder caused by the interference factor gradually decreases, and the peak value becomes more and more prominent.

6. The method for detecting density of a C4F7N / CO2 mixed gas according to claim 5, characterized in that: The absorption peak of the ultraviolet absorption spectrum appears at 186.8 nm.

7. The method for detecting density of a C4F7N / CO2 mixed gas according to claim 5, characterized in that: According to the ultraviolet absorption spectrum of the C4F7N / CO2 mixed gas, a vertical line is drawn from the peak point to the horizontal axis to obtain a peak vertical line, characteristic values ​​are selected, and a linear fitting algorithm is determined to calculate the mixing ratio of the C4F7N / CO2 mixed gas.

8. The method for detecting density of a C4F7N / CO2 mixed gas according to claim 7, characterized in that: When selecting characteristic values ​​for linear fitting, four quantitative schemes, namely, peak value Peak, area A to the left of the peak vertical line, area B to the right of the peak vertical line, and area C of the total absorption peak area, are selected as characteristic values, and the optimal linear fitting algorithm is determined.

9. The method for detecting density of a C4F7N / CO2 mixed gas according to claim 8, characterized in that: The linear fitting results obtained using the four quantitative schemes are shown in Table 1, where y is the characteristic value and x is the mixing ratio: Table 1. Linear fitting results obtained by four quantitative schemes The fitting effect of selecting the peak vertical line and taking the left area Area A as the characteristic value is poor. 2 is 0.985, and the best fitting effect is obtained by using Area B to the right of the peak vertical line. 2 It reaches 0.999, which means that the area Area A to the left of the peak vertical line is indeed affected by interference factors such as light source truncation and spectrometer grating, and cannot present a complete absorption peak. If only the area Area B to the right of the peak vertical line is taken as the characteristic value, a very good fitting effect can be obtained; the absorption peak full area Area C selects the full area of ​​the entire absorption peak, which is affected by the area Area A to the left of the peak vertical line and cannot achieve the fitting effect of Area B to the right of the peak vertical line. 2 is 0.

997.

10. The method for detecting density of a C4F7N / CO2 mixed gas according to claim 9, characterized in that: Finally, it was determined that the peak vertical line in the ultraviolet absorption spectrum was used with the right area Area B as the characteristic value to determine the optimal linear fitting algorithm.

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