Infrared spectrum-based mixed gas decomposition product detection method

Abstract

The invention provides an infrared spectrum-based mixed gas decomposition product detection method, which comprises the following steps: based on the detection principles of hybrid functional B3LYP and photoacoustic spectrometry technology, calculating the theoretical infrared spectrum of a C4F7N / CO2 / O2 mixed gas decomposition product theoretically, and analyzing and comparing the mixed gas after a local overheating experiment to determine the decomposition product of the C4F7N / CO2 / O2 mixed gas decomposition product. The specific wave bands for detecting the three characteristic decomposition products of CO, C3F6 and COF2 are accurately obtained, the feasibility of using the Fourier infrared spectrum as a detection method is determined, and the method can be used for detecting the type and severity of faults occurring in the electrical insulation equipment.

Description

Technical Field

[0001] The invention relates to the field of state evaluation and fault diagnosis of mixed gas insulation equipment, and in particular to a mixed gas decomposition product detection method based on infrared spectroscopy. Background Art

[0002] Application research related to C4F7N gas has become a hot topic in the high-voltage field at home and abroad. At present, a large number of researchers from universities, research institutes, equipment manufacturers, power companies and other industries in my country have carried out a series of research on its application issues. The application prospects of C4F7N / CO2 / O2 mixed gas insulation equipment have gradually become clear, and the corresponding electrical equipment is also accelerating into practical application on site. Due to certain differences from existing SF6 gas insulation equipment, in the future application process, operation and maintenance technologies such as status assessment and fault diagnosis of C4F7N / CO2 / O2 mixed gas insulation equipment will become a new research direction. The power industry's demand for detection equipment generally includes rapid detection, easy operation, and online monitoring or portable detection capabilities. Existing technologies such as gas chromatography and semiconductor sensors for detecting decomposition products such as CO, C3F6 and COF2 have defects such as complex operation, slow response, great environmental impact and serious cross-interference.

[0003] Spectral detection technology has the advantages of fast response speed, high sensitivity, and convenient operation. Compared with chemical detection methods such as semiconductor sensors that are easily affected by environmental factors, spectral detection technology has less cross-interference and will not damage gas samples. However, the problem of overlapping gas absorption bands when detecting the decomposition products of C4F7N mixed gas has not been solved. Therefore, the present invention points out the detectable band of specific decomposition products, making it possible to develop portable devices and online monitoring devices based on spectral detection technology. Summary of the invention

[0004] The present invention provides a mixed gas decomposition product detection method based on infrared spectroscopy. The content of CO, C3F6 and COF2 in the decomposition product can be determined based on the detection method, so as to monitor the degree of fault inside the electrical insulation equipment.

[0005] A method for detecting decomposition products of mixed gases based on infrared spectroscopy comprises the following steps:

[0006] Step 1, calculating the infrared spectrum of the decomposition products of the C4F7N / CO2 / O2 mixed gas, and determining the infrared detection band of the decomposition products calculated by the analysis theory according to the infrared spectrum of the decomposition products of the C4F7N / CO2 / O2 mixed gas;

[0007] Step 2, obtaining an actual infrared spectrum distribution diagram of decomposition products of the C4F7N / CO2 / O2 mixed gas through a local overheating experiment, and obtaining an infrared detection band of the decomposition products obtained in the experiment according to the actual infrared spectrum distribution diagram of decomposition products of the C4F7N / CO2 / O2 mixed gas;

[0008] Step 3: By comparing the infrared detection band of the decomposition products theoretically calculated in step 1 with the infrared detection band of the actual decomposition products obtained experimentally in step 2, verify that the theoretical calculation method is applicable to the infrared spectrum detection of C4F7N and its decomposition gas; by comparing and observing the peaks of different decomposition products in different bands in the theoretical infrared spectrum, further analyze the detection bands of C4F7N and its decomposition gas in the infrared spectrum, so as to obtain the specific distribution bands of the three characteristic decomposition products of CO, C3F6 and COF2 that can be stably detected in the infrared spectrum.

[0009] Furthermore, step 1 specifically includes:

[0010] Step 1.1, construct a molecular model of the decomposition products of C4F7N / CO2 / O2 mixed gas;

[0011] Step 1.2, select the B3LYP method, calculate the theoretical infrared spectrum of the decomposition product of the C4F7N / CO2 / O2 mixed gas, and search for its accurate geometric structure parameter information through the CCCBDB database to verify the accuracy of the B3LYP method in calculation;

[0012] Step 1.3, by comparing the infrared spectra of C4F7N and each decomposition product, determine the band suitable for detection, so as to obtain the infrared detection band of the decomposition product calculated by analytical theory.

[0013] Furthermore, step 2 specifically includes:

[0014] Step 2.1, a 4% C4F7N / 92% CO2 / 4% O2 mixed gas is filled into the heating chamber of the superheated decomposition experimental platform, and a C4F7N / CO2 / O2 mixed gas superheated decomposition experiment is carried out, and a certain amount of original gas is taken as a mixed gas sample before superheating, and infrared spectrum detection is performed using a long optical path gas cell, and the background gas during the detection is N2;

[0015] Step 2.2, in the experiment, 500°C and 70 kPa are used as the temperature and pressure in the heating tank in the superheated decomposition experiment, and the heating time is set to 12 h. The mixed gas after superheated decomposition is detected by infrared spectroscopy to obtain the actual infrared spectral distribution diagram of the decomposition products of the C4F7N / CO2 / O2 mixed gas, and it is compared and analyzed section by section with the original infrared spectrum to obtain the infrared detection band of the decomposition products obtained in the experiment.

[0016] Furthermore, step 3 specifically includes:

[0017] Step 3.1, by analyzing the infrared spectrum detection bands of the decomposition products obtained in step 1, the bands with less peak overlap influence are screened out to obtain the infrared spectrum bands that need to be analyzed in focus in actual detection;

[0018] Step 3.2: In the bands with less overlap, the three characteristic decomposition products of CO, C3F6 and COF2 are distributed in the infrared spectrum at 2080-2220 cm -1 and 1500~2600cm -1 The infrared spectra of the mixed gas before and after superheat decomposition were calculated by using the difference spectrum calculation method, and the difference factor was adjusted to obtain the CO at 2080~2220cm -1 The infrared spectrum absorption appears in the band, at 2400cm -1 Near the band, the infrared intensity of C4F7N is very weak, and the interference effect on the detection is small, so the specific distribution bands of C3F6 and COF2 that can be stably detected in the infrared spectrum are obtained, thereby obtaining the specific distribution bands of the three characteristic decomposition products of CO, C3F6 and COF2 that can be stably detected in the infrared spectrum.

[0019] The present invention detects the concentration of trace CO, C3F6 and COF2 gases under the background of C4F7N / CO2 / O2, obtains the infrared distribution bands of various decomposition products based on Fourier infrared spectrometer through theoretical calculation and experimental verification, determines the specific distribution wavenumbers of CO, C3F6 and COF2 in the decomposition products in the infrared spectrum, and determines their contents by comparing the absorbance, verifying the feasibility of the method. The method is used to determine the contents of CO, C3F6 and COF2 in the decomposition products, so as to detect the degree of fault inside the electrical insulation equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a flow chart of the mixed gas decomposition product detection method based on infrared spectroscopy of the present invention;

[0021] Figure 2 It is the molecular configuration diagram of the decomposition products of C4F7N / CO2 / O2 mixed gas;

[0022] Figure 3 This is the theoretical infrared spectrum of C4F7N and its decomposition products;

[0023] Figure 4 It is the difference spectrum of C4F7N / CO2 / O2 mixed gas before and after overheating and the standard infrared spectrum of decomposition products. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] See also Figure 1 The embodiment of the present invention provides a method for detecting mixed gas decomposition products based on infrared spectroscopy, comprising:

[0026] Step 1: Calculate the infrared spectrum of the decomposition product of the C4F7N / CO2 / O2 mixed gas, and determine the infrared detection band of the decomposition product calculated by the analysis theory according to the infrared spectrum of the decomposition product of the C4F7N / CO2 / O2 mixed gas. Step 1 specifically includes:

[0027] Step 1.1, build Figure 2 The molecular model of the decomposition products of the C4F7N / CO2 / O2 mixed gas shown;

[0028] Step 1.2, select the B3LYP method with smaller deviation, calculate the theoretical infrared spectrum of the decomposition products of the C4F7N / CO2 / O2 mixed gas, and search for its accurate geometric structure parameter information through the CCCBDB (Computational Chemistry Comparison and Benchmark DataBase) database to verify the calculation accuracy of the B3LYP method.

[0029] Step 1.3: Due to the broadening of the infrared spectrum of high-concentration C4F7N, the spectra of most decomposition products may be submerged. By comparing the infrared spectra of C4F7N and each decomposition product, the band suitable for detection is determined, thereby obtaining the infrared detection band of the decomposition product calculated by the analysis theory.

[0030] Step 2: Obtain the actual infrared spectrum distribution diagram of the decomposition products of the C4F7N / CO2 / O2 mixed gas through a local overheating experiment, and obtain the infrared detection band of the decomposition products obtained in the experiment according to the actual infrared spectrum distribution diagram of the decomposition products of the C4F7N / CO2 / O2 mixed gas. Step 2 specifically includes:

[0031] Step 2.1, fill the heating chamber of the superheat decomposition experimental platform with a mixed gas of 4% C4F7N / 92% CO2 / 4% O2 by volume, carry out a superheat decomposition experiment of the C4F7N / CO2 / O2 mixed gas, take a certain amount of original gas as the mixed gas sample before superheating, and use a long optical path gas cell to perform infrared spectroscopy detection, and the background gas during the detection is N2.

[0032] Step 2.2, in the experiment, 500°C and 70 kPa are used as the temperature and pressure in the heating tank in the superheated decomposition experiment, and the heating time is set to 12 h. The mixed gas after superheated decomposition is detected by infrared spectroscopy to obtain the actual infrared spectral distribution diagram of the decomposition products of the C4F7N / CO2 / O2 mixed gas, and it is compared and analyzed section by section with the original infrared spectrum to obtain the infrared detection band of the decomposition products obtained in the experiment.

[0033] Step 3: By comparing the infrared spectrum detection band of the decomposition product theoretically calculated in step 1 with the infrared spectrum detection band of the actual decomposition product obtained experimentally in step 2, the accuracy of the theoretical calculation is verified, and the distribution of C4F7N and its decomposition gas in the infrared spectrum is further analyzed to obtain the specific distribution wavenumbers of the three characteristic decomposition products of CO, C3F6 and COF2 that can be stably detected in the infrared spectrum, so as to prove the feasibility of using infrared spectrum detection. Step 3 specifically includes:

[0034] Step 3.1: By analyzing the infrared spectrum detection bands of the decomposition products obtained in step 1, the bands with less peak overlap are screened out to obtain the infrared spectrum bands that need to be analyzed in actual detection. Since the infrared intensity difference in different bands is large, the infrared spectrum is divided into 400-900cm -1 , 900~1500cm -1 and 1500~2600cm -1 ,like Figure 3 (a), (b) and (c). Figure 3 In (a), we can get C4F7N at 700cm -1 The infrared intensity nearby is strong, and at high concentrations it will cause the spectrum to be saturated within a certain range, making the area around 700cm -1 The infrared spectrum of the decomposition products nearby cannot be analyzed. In addition, for the C4F7N / CO2 / O2 mixed gas, CO2 is between 600 and 700 cm -1 There is absorption in this band, which will also lead to spectrum saturation in this band. Although some decomposition products are in the range of 400-500cm -1 There is absorption in this band, and the interference is small, but its infrared intensity is weak. At the same time, the light source energy in this band is weak, and the transmittance of the gas pool lens is low, so the detection difficulty is also greater. Figure 3 (b) Found between 900 and 1500 cm-1 Band, C4F7N infrared spectrum distribution in this band is relatively wide, and the intensity is relatively high, overlapping with most of the decomposition product spectra. 1000cm -1 and 1400cm -1 There is no infrared spectrum of C4F7N nearby and it is far away from the infrared spectrum of C4F7N, so these two bands have the possibility of detecting decomposition products. Figure 3 In (c), it is found that the infrared spectrum of C4F7N only appears at 2400cm -1 Nearby, and the infrared intensity is very weak, the interference effect on detection is small. However, 1500 ~ 2600cm -1 There are fewer decomposition products with infrared spectra, only C3F6 and COF2.

[0035] In general, the infrared spectrum of C4F7N is between 400 and 1500 cm -1 The distribution between them is relatively wide. Due to the broadening of the infrared spectrum of high-concentration C4F7N, the spectra of most decomposition products may be submerged, which makes detection difficult. However, in some weaker bands of the infrared spectrum of C4F7N, some decomposition products may be detected. Through the above analysis, we finally found that in the range of 1500-2600cm -1 It is basically not affected by the infrared spectrum of C4F7N.

[0036] Step 3.2: In the bands with less overlap, the three characteristic decomposition products of CO, C3F6 and COF2 are distributed in the infrared spectrum at 2080-2220 cm -1 and 1500~2600cm -1 The infrared spectra of the mixed gas before and after superheat decomposition were calculated by using the difference spectrum calculation method, and the difference reduction factor was adjusted until the infrared spectrum was between 2080 and 2220 cm -1 The complete CO infrared spectrum absorption appears in the band to ensure that the infrared absorption of the mixed gas before superheat decomposition is basically subtracted. The difference spectrum calculation results are as follows Figure 4 shown. Figure 4 The standard spectra of the decomposition products at the corresponding positions are also given. It can be seen that although there is a certain detection interference in the difference spectrum, the three decomposition products of CO, C3F6 and COF2 can still be clearly judged from the peak shape and peak position, which is close to the results of the above theoretical analysis. -1 The infrared spectrum of C4F7N is less affected by it, and it is feasible to detect the decomposition products. The final results show that the long optical path gas cell combined with infrared spectrometer can effectively perform qualitative detection of decomposition products.

[0037] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for detecting decomposition products of mixed gases based on infrared spectroscopy, characterized in that: The steps include: Step 1, calculating the infrared spectrum of the decomposition products of the C4F7N / CO2 / O2 mixed gas, and determining the infrared detection band of the decomposition products calculated by the analysis theory according to the infrared spectrum of the decomposition products of the C4F7N / CO2 / O2 mixed gas; Step 2, obtaining an actual infrared spectrum distribution diagram of decomposition products of the C4F7N / CO2 / O2 mixed gas through a local overheating experiment, and obtaining an infrared detection band of the decomposition products obtained in the experiment according to the actual infrared spectrum distribution diagram of decomposition products of the C4F7N / CO2 / O2 mixed gas; Step 3: By comparing the infrared detection band of the decomposition products theoretically calculated in step 1 with the infrared detection band of the actual decomposition products obtained experimentally in step 2, verify that the theoretical calculation method is applicable to the infrared spectrum detection of C4F7N and its decomposition gas; by comparing and observing the peaks of different decomposition products in different bands in the theoretical infrared spectrum, further analyze the detection bands of C4F7N and its decomposition gas in the infrared spectrum, so as to obtain the specific distribution bands of the three characteristic decomposition products of CO, C3F6 and COF2 that can be stably detected in the infrared spectrum.

2. The method for detecting mixed gas decomposition products based on infrared spectroscopy according to claim 1, characterized in that: Step 1 specifically includes: Step 1.1, construct a molecular model of the decomposition products of C4F7N / CO2 / O2 mixed gas; Step 1.2, select the B3LYP method, calculate the theoretical infrared spectrum of the decomposition product of the C4F7N / CO2 / O2 mixed gas, and search for its accurate geometric structure parameter information through the CCCBDB database to verify the accuracy of the B3LYP method in calculation; Step 1.3, by comparing the infrared spectra of C4F7N and each decomposition product, determine the band suitable for detection, so as to obtain the infrared detection band of the decomposition product calculated by analytical theory.

3. The method for detecting mixed gas decomposition products based on infrared spectroscopy according to claim 1, characterized in that: Step 2 specifically includes: Step 2.1, a 4% C4F7N / 92% CO2 / 4% O2 mixed gas is filled into the heating chamber of the superheated decomposition experimental platform, and a C4F7N / CO2 / O2 mixed gas superheated decomposition experiment is carried out, and a certain amount of original gas is taken as a mixed gas sample before superheating, and infrared spectrum detection is performed using a long optical path gas cell, and the background gas during the detection is N2; Step 2.2, in the experiment, 500°C and 70 kPa are used as the temperature and pressure in the heating tank in the superheated decomposition experiment, and the heating time is set to 12 h. The mixed gas after superheated decomposition is detected by infrared spectroscopy to obtain the actual infrared spectral distribution diagram of the decomposition products of the C4F7N / CO2 / O2 mixed gas, and it is compared and analyzed section by section with the original infrared spectrum to obtain the infrared detection band of the decomposition products obtained in the experiment.

4. The method for detecting mixed gas decomposition products based on infrared spectroscopy according to claim 1, characterized in that: Step 3 specifically includes: Step 3.1, by analyzing the infrared spectrum detection bands of the decomposition products obtained in step 1, the bands with less peak overlap influence are screened out to obtain the infrared spectrum bands that need to be analyzed in focus in actual detection; Step 3.2: In the bands with less overlap, the three characteristic decomposition products of CO, C3F6 and COF2 are distributed in the infrared spectrum at 2080-2220 cm -1 and 1500~2600cm -1 The infrared spectra of the mixed gas before and after superheat decomposition were calculated by using the difference spectrum calculation method, and the difference factor was adjusted to obtain the CO at 2080~2220cm -1 The infrared spectrum absorption appears in the band, at 2400cm -1 Near the band, the infrared intensity of C4F7N is very weak, and the interference effect on the detection is small, so the specific distribution bands of C3F6 and COF2 that can be stably detected in the infrared spectrum are obtained, thereby obtaining the specific distribution bands of the three characteristic decomposition products of CO, C3F6 and COF2 that can be stably detected in the infrared spectrum.

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