Method and special equipment for simultaneously detecting sulfur hexafluoride and decomposed gas thereof based on liquid core optical fiber enhancement

Abstract

The invention relates to a method and special equipment for simultaneously detecting sulfur hexafluoride and decomposition gas thereof based on liquid core optical fiber enhancement. The method comprises the following steps: preparing detection equipment; preparing standard gas; filling the mixed gas to be detected and the standard gas into the optical fiber liquid core in batches, and carrying out Raman spectrum detection to obtain a corresponding Raman spectrogram; acquiring characteristic Raman shift corresponding to the standard gas according to the standard Raman spectrogram of the standard gas; comparing the Raman spectrogram of the mixed gas to be detected with the characteristic Raman displacement of the standard gas, and carrying out qualitative calibration on each component of the mixed gas to be detected; constructing a standard curve of the standard gas by taking an ethanol Raman spectrum characteristic peak as an internal standard peak according to the standard Raman spectrogram of each standard gas under different concentrations; according to the standard curve and the Raman spectrogram of the mixed gas to be detected, performing quantitative calibration on each component of the mixed gas to be detected. The Raman scattering intensity of trace SF6 and decomposed gas thereof is greatly improved, and the detection accuracy is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of monitoring sulfur hexafluoride and decomposition gas in power systems, and in particular to a method and special equipment for simultaneously detecting sulfur hexafluoride and its decomposition gas based on liquid core optical fiber enhancement. Background Art

[0002] Sulfur hexafluoride (SF6) gas is widely used in electrical equipment such as gas-insulated switchgear (GIS) and circuit breakers. Determining the internal insulation state of gas-insulated equipment still presents significant technical challenges, making it particularly important to find effective methods for evaluating its internal state. Detection of SF6 gas decomposition products offers advantages such as minimal interference from the external environment, high sensitivity, and excellent accuracy for diagnosing latent faults within gas-insulated equipment and locating faults after equipment accidents. SF6 gas is used extensively in the high-voltage electrical equipment manufacturing industry. Accurately and rapidly detecting SF6 decomposition in power equipment can monitor the internal state of the equipment, allowing for timely determination of equipment faults and the type of fault based on the decomposition products, providing technical support for operations and maintenance personnel. Therefore, research on SF6 and decomposition product detection technology during on-site operation and maintenance of power equipment is highly necessary.

[0003] Raman spectroscopy is a detection technology based on the scattering effect of light. It has the advantages of short measurement time, simple sample preparation, and no interference from the measured components. Due to the extremely low gas scattering cross section and weak Raman signal, traditional Raman spectroscopy technology is difficult to measure trace gases. At present, the most important gas Raman sensing enhancement technologies for SF6 and its decomposition products include cavity enhancement technology and fiber enhancement technology. Among them, the rapid development of fiber enhancement technology has made it possible to detect trace amounts of SF6 decomposition products. For example, patent CN109445020A proposes a method for detecting SF6 gas and decomposition components based on hollow-core fiber enhancement. The Raman scattering signal is enhanced by improving the collection efficiency of spherical scattered light, so that most of the Raman scattered light can enter the spectral detector. However, since the refractive index of air is lower than that of the cladding, the hollow-core fiber will not undergo total reflection, and the Raman enhancement ability is limited. The fiber enhancement technology based on the surface-enhanced Raman scattering (SERS) theory is achieved by coating a layer of specially treated precious metals such as silver, gold, and copper on the quartz cladding. On the roughened metal surface, the scattering cross section of the adsorbed gas molecules increases by 10 4 ~10 7times, and the Raman signal is significantly enhanced. Since precious metals such as Ag and Cu are easily oxidized in the air, Au is generally used as a quartz coating to detect gas samples. However, the cost of Au coating is relatively high and it is easy to react with sulfur-containing gases (SO2, H2S) when it contains impurities. In addition, a synergistic Raman enhancement effect can be produced by nano-Au composite metal-organic framework materials (MOF), and the enrichment characteristics of MOF can further improve the SERS performance. For example, patent CN117517252A discloses a method for MOF-coated nano-Au enhanced Raman spectroscopy detection of VOCs gas. However, the preparation process of MOF materials is complicated, the uniformity and thickness of crystal growth are difficult to control, the coating is likely to fall off or be damaged during use, and the functionalized modified molecules bonded to the surface of metal nanoparticles (i.e., the substrate material) generally have specific adsorption to the target gas molecules, which is not suitable for the simultaneous detection of multiple gas components such as SF6 and its decomposition products. Therefore, this greatly limits the application of MOF materials in the field of SERS optical fiber gas detection.

[0004] In addition, during the detection of trace gas molecules, the laser incident wavelength, continuous measurement time, and ambient temperature will all affect the Raman peak intensity, resulting in poor repeatability of Raman detection results. Summary of the Invention

[0005] The purpose of the present invention is to solve the problems existing in the above-mentioned prior art, and further proposes a method and special equipment for simultaneous detection of sulfur hexafluoride and its decomposition gases based on liquid core optical fiber enhancement, which is suitable for simultaneous detection of SF6 and its main decomposition gas molecules CO, H2S, SO2 and other inorganic gas molecules.

[0006] A method for simultaneously detecting sulfur hexafluoride and its decomposition gas based on liquid core optical fiber enhancement comprises the following steps:

[0007] Step 1: Prepare the testing equipment

[0008] Injecting an ethanol aqueous solution with a volume fraction of 1 to 80% into the optical fiber through the inlet connector to serve as the optical fiber liquid core;

[0009] Step 2: Prepare standard gas

[0010] Prepare n single standard gases with different concentrations, the single standard gas includes SF6 and its decomposition gas;

[0011] Step 3: The mixed gas to be tested and the prepared single standard gases in the gas insulated switchgear are filled into the optical fiber liquid core in batches, and Raman spectrum detection is performed to obtain the corresponding Raman spectrum;

[0012] Step 4: Obtain the characteristic Raman shift corresponding to each single standard gas according to the standard Raman spectrum of each single standard gas;

[0013] Step 5: Compare the Raman spectrum of the mixed gas to be tested with the characteristic Raman shifts of each single standard gas to perform qualitative calibration on each component of the mixed gas to be tested;

[0014] Step 6: Based on the standard Raman spectra of each single standard gas at different concentrations, a standard curve of each single standard gas is constructed using the characteristic peak of the ethanol Raman spectrum as the internal standard peak;

[0015] Step 7: Quantitatively calibrate each component of the mixed gas to be tested according to the standard curve and the Raman spectrum of the mixed gas to be tested.

[0016] In step 1, the volume fraction of the ethanol aqueous solution is 20 to 60%.

[0017] The volume fraction of the ethanol aqueous solution is 40%.

[0018] Raman spectroscopy detection includes the following steps:

[0019] The test gas is pumped into the optical fiber liquid core at a certain pressure through a booster pump connected to the inlet connector, and the internal pressure of the liquid core is monitored in real time by a pressure sensor. When the pressure increases to 1MPa, the inlet connector is closed and the gas pumping is stopped;

[0020] When the pressure sensor readings are stable, the detection gas is fully absorbed by the ethanol-water solution and the Raman spectrum measurement begins;

[0021] The laser passes through the first lens and fiber coupler on the light inlet side and enters the high-pressure liquid-core fiber. The outgoing light is focused by the second lens on the light outlet side to the spectrometer. After being received by the charge-coupled amplifier (CCD), it enters the computer for signal processing, and finally obtains the Raman spectrum corresponding to the detected gas.

[0022] After the measurement is completed, open the drain valve and the test gas and ethanol aqueous solution are discharged together.

[0023] The ethanol-water solution in the optical fiber liquid core must be replaced before each test, and the certain pressure is <2MPa.

[0024] The characteristic Raman shifts of each single standard gas and ethanol are: ν1(SF6) = 774 cm -1 、ν1(SO2)=1152cm -1 ν1(CO)=2140cm -1 、ν1(H2S)=2610cm -1 and ν1(ethanol)=887cm -1 .

[0025] Step 6 is as follows:

[0026] According to the standard Raman spectrum of a single standard gas, the characteristic Raman peak intensity value I corresponding to the single standard gas of different concentrations is obtained. A,1 ,…,I A,n and the characteristic Raman peak intensity of ethanol I 乙醇,1 ,…,I 乙醇,n ;

[0027] Using the characteristic peak of ethanol Raman spectrum as the internal standard peak, calculate the relative peak intensity y′ of a single standard gas at different concentrations A and relative content x′ A :

[0028] y′ A =I A,n / I 乙醇,n

[0029] x′ A =X A,n / X 乙醇

[0030] Where A is the type of standard gas, n is the number of single standard gases with different concentrations, X 乙醇 is the concentration of ethanol aqueous solution;

[0031] The relative peak intensity y′ of a single standard gas A is the vertical axis, relative concentration x′ A As the horizontal axis, the standard curve of standard gas A was drawn using the internal standard method;

[0032] Perform a one-dimensional linear fit on the standard curve to establish the standard curve equation y′ A =ax′ A +b, where a and b are fitting constants.

[0033] Step 7 includes specifically:

[0034] Read the characteristic Raman peak intensity value I of a component A in the Raman spectrum of the mixed gas to be tested A and the characteristic Raman peak intensity of ethanol I 乙醇 , according to y′ A =I A / I 乙醇 , calculate the relative peak intensity y′ of a component A to be measured A , change y′ A Substitute into the standard curve equation to calculate the relative content x' of a certain component A in the mixed gas to be tested A , then according to the formula X A =x′ A *X 乙醇 , calculate the concentration X of a component A to be tested A .

[0035] A dedicated device for the method of simultaneously detecting sulfur hexafluoride and its decomposition gas based on liquid core optical fiber enhancement, comprising:

[0036] An optical fiber body, comprising a hollow core with two open ends, wherein the two open ends of the hollow core are provided with lenses and a closed cavity is filled with an ethanol-water solution;

[0037] An inlet connector, the inlet connector being arranged on one end of the light inlet of the hollow fiber core;

[0038] The inlet connector is a three-way valve, one port of which is connected to the gas to be tested via a booster air pump, another port is connected to a liquid storage bottle for storing ethanol and water solution, and the last port is vertically connected to the hollow fiber core via a pipe, and the pipe is provided with a pressure sensor for detecting the pressure in the pipe;

[0039] and an exhaust pipe, which is vertically arranged on one side of the light outlet of the hollow fiber core and is equipped with an exhaust valve.

[0040] The maximum boost ratio of the booster pump is 50:1;

[0041] A temperature sensor for detecting the real-time temperature of the ethanol-water solution is also provided on the exhaust pipe between the booster air pump and the hollow fiber core;

[0042] The hollow fiber core is covered with a cladding and a coating in sequence. The cladding is a low-refractive-index fluorine-doped quartz material, and the coating is a metallic copper material.

[0043] (1) Liquid core fiber is a fiber composed of a transparent liquid with a high refractive index filled into a quartz cladding with a low refractive index. Both ends are blocked by transparent hard material windows. The light is transmitted forward by total internal reflection in the fiber. Since the refractive index of the liquid sample is higher than that of the liquid core fiber, the laser can be totally reflected in the liquid core fiber. The laser can be reflected multiple times in the liquid core fiber without being transmitted, and the power loss is lower. Therefore, the laser can pass through the liquid sample multiple times, so that the effective optical path of the excitation light through the sample is much longer than the geometric length of the liquid core fiber, thereby significantly improving the Raman signal intensity and sensitivity.

[0044] (2) Due to the resonance Raman effect, when the excitation frequency is close to or equal to the electronic absorption band of the scattering molecule, the intensity of certain Raman bands will increase dramatically. Different incident lasers will result in very different relative intensities of each spectral line. Therefore, choosing the appropriate incident laser wavelength can increase the intensity of the Raman signal. Hollow-core optical fibers generally have a short wavelength range, use single light, and cannot adjust the wavelength. Liquid-core optical fibers transmit light in a wide wavelength range, from 200nm in the ultraviolet region to 3000nm in the near-infrared region, and can perform multi-wavelength detection.

[0045] (3) By finely adjusting the gas pressure in the pipeline (<2MPa), the solubility of SF6 and the main decomposition gas molecules (CO, H2S, SO2) in the liquid core can be significantly increased, thereby increasing the molecular scattering cross section and further enhancing the Raman signal.

[0046] (4) Adding a certain amount of organic solvent with a known content to the liquid core not only increases the absorption of the target gas molecules, but more importantly, it can serve as an internal standard for peak intensity correction of the target component. This method can effectively eliminate the influence of the detection environment (ambient temperature, pressure, and continuous measurement time) and human factors on the Raman characteristic peak intensity of the object being measured, thus solving the problem of poor repeatability of Raman spectroscopy.

[0047] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0048] The incident laser can meet the total reflection condition, with a longer effective optical path and lower power loss. It can select a wider wavelength range (200nm-3000nm) and can perform multi-wavelength detection.

[0049] It can simultaneously detect SF6 and its decomposition products (CO, H2S, SO2) qualitatively and quantitatively, and the measurement results are highly repeatable;

[0050] The device has a simple structure and flexible design. Different types of liquid-core optical fibers can be customized according to the properties of the target gas molecules to be measured. It is low-cost and can significantly enhance the Raman signal by finely adjusting the device pressure.

[0051] The method provided by the present invention can greatly improve the Raman scattering intensity of trace SF6 and decomposition gases. Compared with the traditional hollow-core fiber detection method, the high-pressure liquid-core fiber enhanced detection method provided by the present invention can improve the signal-to-noise ratio of SF6 and decomposition gases by at least 50 times, and its sensitivity (detection limit: 2.5-25.4μL / L) and repeatability (RSD<5%) are good.

[0052] Ethanol is not present in insulating gases or gas-insulated equipment, yet it meets the Raman characteristics required for use as an internal standard. Water has limited solubility for the component to be measured, SF6, but the addition of ethanol significantly increases this solubility. The present invention incorporates ethanol as a liquid core internal standard for multi-component quantification of gas molecules. Compared to other conventional additives, ethanol is environmentally friendly, pollution-free, and low-cost.

[0053] This invention eliminates the need for complex chemical modification of the inner surface of the liquid-core optical fiber. Instead, it directly applies pressure within the core to fully dissolve the gas molecules being measured in a specific liquid core (an ethanol-water solution is used in this invention). This transition from gaseous to solution molecules increases the scattering cross section of the molecules, significantly boosting their Raman signal intensity.

[0054] To address the issue of poor repeatability in gas Raman detection, the present invention proposes adding a known amount of ethanol to the liquid core as an internal calibration standard. This ensures that the relative standard deviation (RSD) of repeated measurements of the same sample is within 5%. This effectively eliminates the influence of the detection environment (ambient temperature, pressure, and continuous measurement time) and human factors on the Raman characteristic peak intensity of the analyte, thus resolving the issue of poor repeatability in gas Raman spectroscopy. Furthermore, ethanol can also serve as a modifier for the liquid core, further enhancing its absorption capacity for sulfur hexafluoride molecules. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 It is a high-pressure liquid core optical fiber gas detection device;

[0056] Figure 2 The Raman spectra of SF6 with a content of 500 μL / L were detected using hollow-core fiber and high-pressure water-ethanol liquid-core fiber;

[0057] Figure 3 Raman spectra of SO2 with a content of 500μL / L after detection using hollow-core fiber and high-pressure water-ethanol liquid-core fiber;

[0058] Figure 4 Raman spectra of H2S with a concentration of 500μL / L detected using hollow-core fiber and high-pressure water-ethanol liquid-core fiber;

[0059] Figure 5 Raman spectra of CO at a concentration of 500 μL / L after detection using hollow-core fiber and high-pressure water-ethanol liquid-core fiber. DETAILED DESCRIPTION

[0060] The technical problem to be solved in the present invention is achieved by a pressurized liquid core optical fiber device, such as Figure 1 As shown, the device consists of a fiber optic body and auxiliary structures. The fiber optic body consists of a hollow core 6 with two open ends, a cladding 7, and a metal coating 8. The auxiliary structures include a booster pump 2, an inlet connector 3, a pressure sensor, a temperature sensor 5, a drain valve 12, a light inlet 9, and a light outlet 10. After the two open ends of the hollow core 6 are fitted with lenses, the sealed cavity is filled with an ethanol-water solution.

[0061] The inlet connector 3 is located at the optical inlet 9 of the hollow fiber core 6. This connector 3 is a three-way valve. One horizontal end of the inlet connector 3 is connected to a booster pump 2, which collects and pressurizes gas samples, increasing the solubility of target gas molecules such as SF6, CO, H2S, and SO2 in the liquid core. The maximum pressure increase ratio is 50:1. The other end is connected to a liquid storage bottle 4, which stores an ethanol-water solution. The vertical end connects to a pressure sensor 5 and the fiber body. The pressure sensor 5 detects the pressure in the pipeline. The fiber body structure is used for optical transmission and gas absorption. The hollow fiber core 6 is filled with an ethanol-water solution, which has a strong absorption capacity for target gas molecules such as SF6, CO, H2S, and SO2. Ethanol serves as an internal standard to correct the peak intensity of the target component. The liquid core ensures that the refractive index of the laser in the liquid core is greater than that of the cladding, resulting in total internal reflection. The cladding 7 is a low-refractive-index fluorine-doped quartz material, and the coating 8 is made of metallic copper. It protects the fiber, improves its pressure resistance, and allows for welding of auxiliary structures. The optical fiber's horizontal ends are the light inlet 9 and light outlet 10, each equipped with a light window sealed by a sealing ring. The light window is primarily made of sapphire. A drain pipe connects to the hollow fiber core 6 on one side of the light outlet 10. The drain pipe is equipped with a temperature sensor 11 and a drain valve 12. The temperature sensor 11 detects the real-time temperature of the liquid core within the optical fiber, and the drain valve 12 is used to discharge the gas sample and liquid core after testing. The main optical fiber structure is fixed to the V-groove substrate.

[0062] use Figure 1 The liquid core fiber device designed in this paper is used to build a liquid core fiber enhanced Raman spectroscopy detection system. The specific steps of the SF6 and decomposition gas detection method based on this system are as follows:

[0063] Step 1: Inject ethanol water solution (volume fraction is 1-80%) into the optical fiber through the inlet connector 3 as the optical fiber liquid core; a new liquid core solution must be replaced before each measurement to ensure the accuracy of the measurement results.

[0064] Step 2: Prepare n single standard gases of different concentrations, the single standard gas includes SF6 and its decomposition gas, and the decomposition gas includes CO, H2S, and SO2;

[0065] Step 2 is as follows: prepare SF6, CO, H2S and SO2 with concentrations of 10L / L, 50L / L, 100L / L, 200L / L, 500L / L and 1000L / L;

[0066] Step 3: The mixed gas to be tested and the prepared single standard gases in the gas insulated switchgear are filled into the optical fiber liquid core in batches, and Raman spectrum detection is performed to obtain the corresponding Raman spectrum;

[0067] Place all single standard gases (SF6, CO, H2S and SO2) prepared in step 2 and the mixed gas to be tested in the gas-insulated switchgear in the optical fiber liquid core, perform Raman spectroscopy detection, and obtain the corresponding Raman spectra;

[0068] Raman spectroscopy detection includes the following steps:

[0069] The test gas is pumped into the optical fiber liquid core at a certain pressure (<2MPa) through the booster pump 2 connected to the inlet connector 3, and the internal pressure of the liquid core is monitored in real time by the pressure sensor. When the pressure increases to 1MPa, the inlet connector is closed and the pumping is stopped;

[0070] When the pressure sensor readings are stable, the detection gas is fully absorbed by the ethanol-water solution and the Raman spectrum measurement begins;

[0071] The laser passes through the first lens and fiber coupler and enters the high-pressure liquid-core fiber. The outgoing light is focused by the second lens to the spectrometer, received by the charge-coupled amplifier (CCD), and then sent to the computer for signal processing, ultimately obtaining the Raman spectrum corresponding to the detected gas.

[0072] After the test is completed, the drain valve 12 is opened and the test gas and ethanol water solution are discharged together. The pressure in the liquid core is about 10 times higher than the external atmospheric pressure and can be discharged directly.

[0073] When the SF6 content in the gas sample is high, SF6 can be fully dissolved by increasing the pipeline pressure and the ethanol content in the liquid core.

[0074] Step 4: Obtain the characteristic Raman shift corresponding to each single standard gas based on the standard Raman spectrum of each single standard gas, and determine that the characteristic Raman shifts of SF6 and its decomposition products (CO, H2S, SO2) are ν1(SF6) = 774 cm -1 、ν1(SO2)=1152cm -1 ν1(CO)=2140cm -1 、ν1(H2S)=2610cm -1 ;

[0075] Step 5: Compare the Raman spectrum of the mixed gas to be tested with the characteristic Raman shifts of each single standard gas to perform qualitative calibration on each component of the mixed gas to be tested;

[0076] Step 6: Based on the standard Raman spectra of each single standard gas at different concentrations, the characteristic peak of the ethanol Raman spectrum is used as the internal standard peak to construct the standard curve of each single standard gas; specifically:

[0077] According to the standard Raman spectrum of a single standard gas, the characteristic Raman peak intensity value I corresponding to the single standard gas of different concentrations is obtained.A,2 ,…,I A,n and the characteristic Raman peak intensity of ethanol I 乙醇,2 ,…,I 乙醇,n ;

[0078] The characteristic peak of ethanol Raman spectrum was used as internal standard peak to calculate the relative peak intensity (y′) of standard gas A at different concentrations. A ) and relative content (x′ A ).

[0079] y′ A =I A,n / I 乙醇,n

[0080] x′ A =X A,n / X 乙醇

[0081] Where A is the type of standard gas, n is the number of single standard gases with different concentrations, X 乙醇 is the concentration of ethanol aqueous solution;

[0082] According to the rule that the Raman peak intensity is proportional to the concentration of the standard gas A, the relative peak intensity y′ of the standard gas A is A is the vertical axis, relative concentration x′ A As the horizontal axis, the internal standard method is used to draw the standard curve of standard gas A, and a one-dimensional linear fitting is performed on the standard curve to establish the standard curve equation y′ A =ax′ A +b (where a and b are fitting constants).

[0083] Step 7: Quantitatively calibrate each component of the mixed gas to be tested according to the standard curve and the Raman spectrum of the mixed gas to be tested, specifically:

[0084] Read the characteristic Raman peak intensity value I of a component A in the Raman spectrum of the mixed gas to be tested A and the characteristic Raman peak intensity of ethanol I 乙醇 , according to y′ A =I A / I 乙醇 , calculate the relative peak intensity y′ of a component A to be measured A , change y′ A Substitute into the standard curve equation to calculate the relative content x' of a certain component A in the mixed gas to be tested A , then according to the formula X A =x′ A *X 乙醇 , calculate the concentration X of a component A to be tested A .

[0085] Example:

[0086] The liquid core fiber enhanced Raman spectroscopy detection system constructed above was used to perform Raman detection on trace target gas molecules. The laser light source was a Nd:YAG pulsed semiconductor laser (wavelength of 532nm, energy continuously adjustable from 0 to 3mJ), the laser power was 300mW, the exposure time was 2000ms, the inlet pressure was controlled at 1.0MPa, and a 40% volume fraction of ethanol aqueous solution was introduced as the optical fiber liquid core. Each sample was tested three times, and the average spectrum of the three times was used as the original Raman spectrum of the sample. The continuous wavelet transform penalty and partial least squares (PLS) method were used to perform Savitzky-Golay 5-point smoothing noise reduction and Baseline baseline subtraction background preprocessing on the original Raman spectrum curve, and finally the stimulated Raman scattering spectra of SF6 with a content of 500μL / L and its decomposition products (CO, H2S, SO2) were obtained. The results show that the measurement results of SF6, SO2, H2S and CO using the high-pressure water-ethanol liquid core fiber method increased by 85 times ( Figure 2 ), 72 times ( Figure 3 ), 64 times ( Figure 4 ) and 57 times ( Figure 5 Based on a 3x signal-to-noise ratio criterion, the detection limits for SF6, SO2, H2S, and CO were calculated to be 8.2 μL / L, 2.5 μL / L, 17.9 μL / L, and 25.4 μL / L, respectively. These results demonstrate that the high-pressure water-ethanol liquid-core fiber device proposed in this invention can significantly enhance the Raman peak intensities of SF6 and its decomposition products.

[0087] In order to eliminate the influence of the continuous working time of the Raman spectrometer and the ambient temperature on the Raman characteristic peak intensity of the gas to be measured, 500 μL / L of SF6 single standard gas was introduced into the above-mentioned optical fiber device, and the Raman spectra of SF6 were measured at different ambient temperatures (23℃, 28℃, 32℃) and different operating times (0h, 1h, 2h). The Raman spectrum characteristic peak (887cm -1 ) as the internal standard peak, and calculate the relative ratio of its characteristic peak intensity to that of ethanol under other conditions, and use the relative ratio to calibrate the SF6 at 774 cm in the corresponding samples. -1 The results are shown in Table 1. The characteristic peak intensity of SF6 in the same sample decreased significantly with increasing ambient temperature and instrument measurement time, resulting in poor instrument measurement repeatability, with a relative standard deviation (RSD) of 27.6%. After ethanol calibration, the relative standard deviation (RSD) of the SF6 measurement results (4.9%) was significantly reduced. This demonstrates that using ethanol as an internal standard to calibrate the Raman characteristic peak intensity of the analyte is highly effective.

[0088] Table 1 SF6 (500 μL / L) under different conditions using ethanol 887 cm-1 Characteristic peak intensity and repeatability test before and after peak intensity internal standard correction

[0089]

Claims

1. A method for simultaneous detection of sulfur hexafluoride and its decomposition gas based on liquid core optical fiber enhancement, characterized in that: The following steps are involved: Step 1: Prepare the testing equipment Injecting an ethanol aqueous solution with a volume fraction of 1 to 80% into the optical fiber through the inlet connector to serve as the optical fiber liquid core; Step 2: Prepare standard gas Prepare n single standard gases with different concentrations, the single standard gas includes SF6 and its decomposition gas; Step 3: The mixed gas to be tested and the prepared single standard gases in the gas insulated switchgear are filled into the optical fiber liquid core in batches, and Raman spectrum detection is performed to obtain the corresponding Raman spectrum; Step 4: Obtain the characteristic Raman shift corresponding to each single standard gas according to the standard Raman spectrum of each single standard gas; Step 5: Compare the Raman spectrum of the mixed gas to be tested with the characteristic Raman shifts of each single standard gas to perform qualitative calibration on each component of the mixed gas to be tested; Step 6: Based on the standard Raman spectra of each single standard gas at different concentrations, a standard curve of each single standard gas is constructed using the characteristic peak of the ethanol Raman spectrum as the internal standard peak; Step 7: Quantitatively calibrate each component of the mixed gas to be tested according to the standard curve and the Raman spectrum of the mixed gas to be tested.

2. The method for simultaneous detection of sulfur hexafluoride and its decomposition gas based on liquid core optical fiber enhancement according to claim 1, characterized in that: In step 1, the volume fraction of the ethanol aqueous solution is 20 to 60%.

3. The method for simultaneous detection of sulfur hexafluoride and its decomposition gas based on liquid core optical fiber enhancement according to claim 1, characterized in that: The volume fraction of the ethanol aqueous solution is 40%.

4. The method for simultaneous detection of sulfur hexafluoride and its decomposition gas based on liquid core optical fiber enhancement according to claim 1, characterized in that: Raman spectroscopy detection includes the following steps: The test gas is pumped into the optical fiber liquid core at a certain pressure through a booster pump (2) connected to an inlet connector (3), and the internal pressure of the liquid core is monitored in real time by a pressure sensor. When the pressure increases to 1 MPa, the inlet connector is closed and the gas pumping is stopped; When the pressure sensor readings are stable, the detection gas is fully absorbed by the ethanol-water solution and the Raman spectrum measurement begins; The laser light passes through the first lens and the fiber coupler on the side of the light inlet (9) and enters the high-pressure liquid core fiber. The outgoing light is converged to the spectrometer through the second lens on the side of the light outlet (10). The light is received by the charge coupled amplifier (CCD) and then enters the computer for signal processing, and finally a Raman spectrum corresponding to the detected gas is obtained. After the measurement is completed, the drain valve (12) is opened and the detection gas and the ethanol aqueous solution are discharged together.

5. The method for simultaneous detection of sulfur hexafluoride and its decomposition gas based on liquid core optical fiber enhancement according to claim 4, characterized in that: The ethanol-water solution in the optical fiber liquid core must be replaced before each test, and the certain pressure is <2MPa.

6. The method for simultaneous detection of sulfur hexafluoride and its decomposition gas based on liquid core optical fiber enhancement according to claim 1, characterized in that: The characteristic Raman shifts of each single standard gas and ethanol are: ν1(SF6) = 774 cm -1 、ν1(SO2)=1152cm -1 ν1(CO)=2140cm -1 、ν1(H2S)=2610cm -1 and ν1(ethanol)=887cm -1 .

7. The method for simultaneous detection of sulfur hexafluoride and its decomposition gas based on liquid core optical fiber enhancement according to claim 1, characterized in that: Step 6 is as follows: According to the standard Raman spectrum of a single standard gas, the characteristic Raman peak intensity value I corresponding to the single standard gas of different concentrations is obtained. A,1 ,…,I A,n and the characteristic Raman peak intensity of ethanol I 乙醇,1 ,…,I 乙醇,n ; Using the characteristic peak of ethanol Raman spectrum as the internal standard peak, calculate the relative peak intensity y′ of a single standard gas at different concentrations A and relative content x′ A : y′ A =I A,n / I 乙醇,n x′ A =X A,n / X 乙醇 Where A is the type of standard gas, n is the number of single standard gases with different concentrations, X 乙醇 is the concentration of ethanol aqueous solution; The relative peak intensity y′ of a single standard gas A is the vertical axis, relative concentration x′ A As the horizontal axis, the standard curve of standard gas A was drawn using the internal standard method; Perform a one-dimensional linear fit on the standard curve to establish the standard curve equation y′ A =ax′ A +b, where a and b are fitting constants.

8. The method for simultaneous detection of sulfur hexafluoride and its decomposition gas based on liquid core optical fiber enhancement according to claim 1, characterized in that: Step 7 includes specifically: Read the characteristic Raman peak intensity value I of a component A in the Raman spectrum of the mixed gas to be tested A and the characteristic Raman peak intensity of ethanol I 乙醇 , according to y′ A =I A / I 乙醇 , calculate the relative peak intensity y′ of a component A to be measured A , change y′ A Substitute into the standard curve equation to calculate the relative content x' of a certain component A in the mixed gas to be tested A , then according to the formula X A =x′ A *X 乙醇 , calculate the concentration X of a component A to be tested A .

9. A special device for the method of simultaneous detection of sulfur hexafluoride and its decomposition gas based on liquid core optical fiber enhancement according to claim 1-8, characterized in that: include: An optical fiber body, the optical fiber body comprising a hollow fiber core (6) with two open ends, wherein the closed cavity of the hollow fiber core (6) after the two open ends are equipped with lenses is filled with an ethanol aqueous solution; An inlet connector (3), the inlet connector (3) being arranged on one end of the light inlet (9) of the hollow fiber core (6); The inlet connector (3) is a three-way valve, one port of which is connected to the gas to be measured via a booster air pump (2), another port is connected to a liquid storage bottle (4) for storing an ethanol-water solution, and the last port is vertically connected to the hollow fiber core (6) via a pipeline, and a pressure sensor (5) for detecting the pressure in the pipeline is provided on the pipeline; and an exhaust pipe, which is vertically arranged on one side of the light outlet (10) of the hollow fiber core (6) and is equipped with an exhaust valve (12).

10. The special equipment according to claim 9, characterized in that: The maximum boost ratio of the boost air pump (2) is 50:1; A temperature sensor (11) for detecting the real-time temperature of the ethanol aqueous solution is also provided on the exhaust pipe between the booster air pump (2) and the hollow fiber core (6); The hollow fiber core (6) is sequentially covered with a cladding (7) and a coating (8); the cladding (7) is a fluorine-doped quartz material with a low refractive index, and the coating (8) is a metallic copper material.

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