Detection system and detection method for decomposition product of perfluoroisobutyronitrile-nitrogen mixed gas

Abstract

The invention provides a detection system and a detection method for a decomposition product of perfluoroisobutyronitrile-nitrogen mixed gas, and belongs to the technical field of gas analysis in high-voltage insulation equipment. In the detection system for the decomposition product of the perfluoroisobutyronitrile-nitrogen mixed gas, the first sample introduction device and the second sample introduction device respectively comprise the sample introduction part, the preprocessor and the quantitative tube which are connected in sequence, and the pretreated gas sample is quantitatively stored through the quantitative tube, so that the separation difficulty of a subsequent separation device can be reduced, and the detection efficiency is improved. By adopting the first separation device and the second separation device, each permanent gas in a quantitatively stored gas sample can be separated from CO2, and then a high-sensitivity signal is provided by virtue of the detection device, so that trace gas can be accurately measured; therefore, the detection sensitivity, accuracy and repeatability of each permanent gas and CO2 in the decomposition product of the perfluoroisobutyronitrile-nitrogen mixed gas are improved.

Description

Technical Field

[0001] This application relates to the field of gas analysis technology in high-voltage insulation equipment, and in particular to a detection system and method for detecting the decomposition products of perfluoroisobutyronitrile-nitrogen mixed gas. Background Technology

[0002] Perfluoroisobutyronitrile (C4F7N) is a novel environmentally friendly insulating gas with excellent insulation and arc-quenching properties. It has low toxicity and no combustion risk and is often mixed with carrier gas N2 in a certain proportion to form an insulating medium. During the operation of high-voltage electrical equipment, C4F7N in the insulating medium decomposes due to arcing, partial discharge, or overheating faults, generating permanent gases and decomposition products such as CO2. Permanent gases refer to stable small-molecule gases that are not easily condensed at normal temperature and pressure, such as hydrogen (H2), oxygen (O2), nitrogen (N2), carbon monoxide (CO), and methane (CH4). The types and amounts of these decomposition products are related to discharge and overheating faults and are important bases for assessing the operating status and fault type of gas-insulated equipment. However, traditional methods for detecting decomposition products in perfluoroisobutyronitrile-nitrogen mixtures suffer from deficiencies in sensitivity, accuracy, and repeatability.

[0003] Therefore, improving the detection methods for decomposition products in perfluoroisobutyronitrile-nitrogen mixed gas using traditional techniques to enhance the sensitivity, accuracy, and repeatability of the detection results for permanent gases and CO2 has become an urgent technical problem to be solved. Summary of the Invention

[0004] Therefore, the main objective of this application is to provide a detection system and method for the decomposition products of perfluoroisobutyronitrile-nitrogen mixed gas, so as to improve the sensitivity, accuracy and repeatability of the detection results of permanent gases and CO2.

[0005] The first aspect of this application provides a detection system for the decomposition products of a perfluoroisobutyronitrile-nitrogen mixed gas, comprising:

[0006] The first sample injection device includes a first sample injection component, a first preprocessor, and a first quantitative tube connected in sequence.

[0007] A first separation device is connected to the first metering tube to separate permanent gases from the gas sample in the first metering tube.

[0008] The second sample injection device includes a second sample injection component, a second preprocessor, and a second quantitative tube connected in sequence.

[0009] A second separation device is connected to the second quantitative tube to separate CO2 from the gas sample in the second quantitative tube;

[0010] A detection device is used to detect the content of each permanent gas separated by the first separation device and the content of CO2 separated by the second separation device.

[0011] In addition, a flow path switching valve device includes a first switching valve, which is connected to the first separation device, the second separation device and the detection device respectively.

[0012] In some embodiments, the detection device includes a plasma emission detector.

[0013] In some embodiments, the first sample injection device further includes a second switching valve, a first pressure sensor, and a first sample dispensing component;

[0014] The two ends of the first preprocessor are respectively connected to one end of the first sample injection component and the second port of the second switching valve;

[0015] The two ends of the first metering tube are respectively connected to the first port and the fourth port of the second switching valve;

[0016] The two ends of the first pressure sensor are respectively connected to the third port of the second switching valve and one end of the first sample dispensing component.

[0017] In some embodiments, the first injection device further includes a first carrier gas inlet; the first carrier gas inlet is connected to the fifth port of the second switching valve.

[0018] In some embodiments, the first injection device further includes a first venting needle valve, one end of which is connected to the ninth port of the second switching valve.

[0019] In some embodiments, the first injection device further includes a second carrier gas inlet, which is connected to the eighth port of the second switching valve.

[0020] In some embodiments, the first separation device includes a first gas chromatographic column, a second gas chromatographic column, a third switching valve, and a third gas chromatographic column;

[0021] The two ends of the first gas chromatographic column are respectively connected to the tenth port and the sixth port of the second switching valve, which are used to pre-separate C4F7N and permanent gas in the gas sample in the first quantitative tube to obtain a pre-separated product including permanent gas.

[0022] The two ends of the second gas chromatographic column are respectively connected to the seventh port of the second switching valve and the sixth port of the third switching valve, and are used to perform the first separation of permanent gases in the pre-separation product after the first gas chromatographic column pre-separation to obtain a first separation product including permanent gases.

[0023] The two ends of the third gas chromatography column are respectively connected to the first port of the third switching valve and the second port of the first switching valve, and are used to perform a second separation of the permanent gas in the first separation product of the second gas chromatography column to obtain a second separation product including the permanent gas.

[0024] In some embodiments, the first separation device further includes a third carrier gas inlet, which is connected to the second port of the third switching valve.

[0025] In some embodiments, the first separation device further includes a second venting needle valve, one end of which is connected to the third port of the third switching valve.

[0026] In some embodiments, the first separation device further includes a third venting needle valve, one end of which is connected to the fifth port of the third switching valve.

[0027] In some embodiments, the second sample injection device further includes a fourth switching valve, a second pressure sensor, and a second sample dispensing component;

[0028] The two ends of the second preprocessor are respectively connected to one end of the second sample injection component and the second port of the fourth switching valve;

[0029] The two ends of the second metering tube are respectively connected to the first port and the fourth port of the fourth switching valve;

[0030] The two ends of the second pressure sensor are respectively connected to the third port of the fourth switching valve and one end of the second sample dispensing component.

[0031] In some embodiments, the second injection device further includes a fourth carrier gas inlet, which is connected to the fifth port of the fourth switching valve.

[0032] In some embodiments, the second injection device further includes a fifth carrier gas inlet, which is connected to the eighth port of the fourth switching valve.

[0033] In some embodiments, the second injection device further includes a fourth venting needle valve, one end of which is connected to the ninth port of the fourth switching valve.

[0034] In some embodiments, the second separation device includes a fourth gas chromatography column and a fifth gas chromatography column;

[0035] The fourth gas chromatographic column is connected to the tenth port and the sixth port of the fourth switching valve at both ends, respectively, for pre-separating C4F7N and CO2 in the gas sample in the second quantitative tube (18) to obtain a pre-separated product including CO2.

[0036] The fifth gas chromatographic column is connected at both ends to the seventh port of the fourth switching valve and the sixth port of the first switching valve, respectively, and is used to separate CO2 from the pre-separation product after pre-separation by the fourth gas chromatographic column to obtain a separated product including CO2.

[0037] In some embodiments, the detection system for the decomposition products of the perfluoroisobutyronitrile-nitrogen mixed gas further includes a fifth venting needle valve and a sixth venting needle valve, one end of the fifth venting needle valve being connected to the fifth port of the first switching valve, and one end of the sixth venting needle valve being connected to the third port of the first switching valve.

[0038] A second aspect of this application provides a method for detecting the decomposition products of a perfluoroisobutyronitrile-nitrogen mixed gas, comprising the following steps:

[0039] Gas samples are fed into a first injection device and a second injection device, respectively. In the first injection device, the gas sample is pre-processed by a first preprocessor and then stored in a first quantitative tube. In the second injection device, the gas sample is pre-processed by a second preprocessor and then stored in a second quantitative tube.

[0040] The gas sample stored in the first quantitative tube is loaded into the first separation device to separate the permanent gases in the gas sample in the first quantitative tube. The permanent gases separated by the first separation device are loaded into the detection device to detect the content of each permanent gas in the gas sample.

[0041] The gas sample stored in the second quantitative tube is loaded into the second separation device to separate CO2 from the gas sample in the second quantitative tube. The CO2 separated by the second separation device is loaded into the detection device to detect the CO2 content in the gas sample.

[0042] In some embodiments, the detection device includes a plasma emission detector.

[0043] In some embodiments, loading the gas sample stored in the first metering tube into the first separation device, and separating the permanent gas from the gas sample in the first metering tube specifically includes the following steps:

[0044] The gas sample in the first quantitative tube is loaded into the first chromatographic column by a carrier gas. The C4F7N and permanent gas in the gas sample in the first quantitative tube (3) are pre-separated to obtain a pre-separated product including the permanent gas. The permanent gas in the pre-separated product is sequentially loaded into the second gas chromatographic column and the third gas chromatographic column for separation.

[0045] In some embodiments, the first chromatographic column comprises a polymer porous packed column.

[0046] In some embodiments, the second gas chromatography column comprises a 5A molecular sieve column.

[0047] In some embodiments, the third gas chromatography column comprises a 5A molecular sieve column.

[0048] In some embodiments, the gas sample stored in the second metering tube is loaded into the second separation device, and the separation of CO2 from the gas sample in the second metering tube specifically includes the following steps:

[0049] The gas sample in the second quantitative tube is loaded into the fourth gas chromatographic column using a carrier gas. The C4F7N and permanent gases in the gas sample in the second quantitative tube are pre-separated to obtain a pre-separated product including CO2. The CO2 in the pre-separated product is then loaded into the fifth gas chromatographic column for further separation.

[0050] In some embodiments, the fourth gas chromatography column comprises a polymer porous packed column.

[0051] In some embodiments, the fifth gas chromatography column includes a polymer chromatography column.

[0052] In some embodiments, the method for detecting the decomposition products of the perfluoroisobutyronitrile-nitrogen mixed gas employs the detection system for the decomposition products of the perfluoroisobutyronitrile-nitrogen mixed gas described in the first aspect.

[0053] In some embodiments, the permanent gas includes at least one of H2, O2, CH4, and CO.

[0054] Compared with traditional technologies, this application has at least the following beneficial effects:

[0055] The detection system for the decomposition products of perfluoroisobutyronitrile-nitrogen mixed gas described in this application comprises a first injection device, a first separation device, a second injection device, a second separation device, a detection device, and a flow path switching valve. The first and second injection devices each include a sample injection component, a preprocessor, and a quantitative tube connected in sequence. By quantitatively storing the pretreated gas sample, the separation difficulty of the subsequent separation device can be reduced. The first and second separation devices can be used to separate the permanent gases and CO2 from the quantitatively stored gas sample in the quantitative tube. Then, a monitoring device provides a highly sensitive signal, enabling accurate measurement of trace gases, thereby improving the detection sensitivity, accuracy, and repeatability of the permanent gases and CO2 in the decomposition products of the perfluoroisobutyronitrile-nitrogen mixed gas. Attached Figure Description

[0056] To better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, the currently described embodiments or examples, or the best mode of conduct of these applications as currently understood. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0057] Figure 1 This is a schematic diagram of the connection method of the detection system for the decomposition products of perfluoroisobutyronitrile-nitrogen mixed gas in one embodiment of this application;

[0058] Figure 2 This is a schematic diagram of the connected state of the detection system for the decomposition products of perfluoroisobutyronitrile-nitrogen mixed gas in the first state according to an embodiment of this application.

[0059] Figure 3 This is a schematic diagram of the connected state of the detection system for the decomposition products of the perfluoroisobutyronitrile-nitrogen mixed gas in a second state, according to an embodiment of this application.

[0060] Figure 4 This is a schematic diagram of the connected state of the detection system for the decomposition products of the perfluoroisobutyronitrile-nitrogen mixed gas in a third state according to an embodiment of this application.

[0061] Figure 5 This is a schematic diagram of the connected state of the detection system for the decomposition products of the perfluoroisobutyronitrile-nitrogen mixed gas in the fourth state, according to an embodiment of this application.

[0062] Figure 6 This is a schematic diagram of the connected state of the detection system for the decomposition products of the perfluoroisobutyronitrile-nitrogen mixed gas in the fifth state, according to an embodiment of this application.

[0063] Figure 7This is a schematic diagram of the connected state of the detection system for the decomposition products of the perfluoroisobutyronitrile-nitrogen mixed gas in the sixth state, according to an embodiment of this application.

[0064] Figure 8 This is a schematic diagram of the connected state of the detection system for the decomposition products of the perfluoroisobutyronitrile-nitrogen mixed gas in the seventh state, according to an embodiment of this application.

[0065] The reference numerals in the attached figures are as follows:

[0066] 1-First sample injection unit, 2-First preprocessor, 3-First quantitative tube, 4-First pressure sensor, 5-First gas chromatographic column, 6-Second switching valve, 7-First carrier gas inlet, 8-First vent needle valve, 9-Second carrier gas inlet, 10-Second gas chromatographic column, 11-Third gas chromatographic column, 12-Third switching valve, 13-Third carrier gas inlet, 14-Second vent needle valve, 15-Third vent needle valve, 16-Second sample injection unit, 17-Second preprocessor, 18-Second quantitative tube, 19-Second pressure sensor Force sensor, 20-Fourth carrier gas inlet, 21-Fifth carrier gas inlet, 22-Fourth vent needle valve, 23-Fourth gas chromatographic column, 24-Fifth gas chromatographic column, 25-Fifth vent needle valve, 26-Sixth vent needle valve, 27-First switching valve, 28-Plasma emission detector, 29-Fourth switching valve, 30-First sample outlet component, 31-Second sample outlet component; Numbers ①, ②, ③, etc., represent the first, second, and third ports of the first, second, third, and fourth switching valves, respectively. Detailed Implementation

[0067] The present application will be further described in detail below with reference to the embodiments and examples. These embodiments and examples are only for illustrating the present application and are not intended to limit the scope of the present application. The purpose of providing these embodiments and examples is to make the disclosure of the present application more thorough and comprehensive. It should also be understood that the present application can be implemented in many different forms and is not limited to the embodiments and examples described herein. Those skilled in the art can make various modifications or alterations without departing from the spirit of the present application, and the equivalent forms obtained also fall within the protection scope of the present application. In addition, numerous specific details are set forth in the following description to provide a fuller understanding of the present application. It should be understood that the present application can be implemented without one or more of these details.

[0068] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0069] When perfluoroisobutyronitrile (C4F7N)-nitrogen mixtures are used as insulating gases in high-voltage electrical equipment, the C4F7N decomposes due to arcing, partial discharge, or overheating faults during equipment operation, generating permanent gases and decomposition products such as CO2. Permanent gases are stable small-molecule gases that are not easily condensed at room temperature and pressure, including hydrogen (H2), oxygen (O2), carbon monoxide (CO), and methane (CH4). The generation of these decomposition products seriously affects the insulation performance of electrical equipment. The types and amounts of decomposition products are related to discharge and overheating faults and are important indicators for assessing the operating status and fault types of gas-insulated equipment. However, traditional methods for detecting decomposition products in perfluoroisobutyronitrile-nitrogen mixtures suffer from deficiencies in sensitivity, accuracy, and repeatability. Therefore, traditional methods for detecting permanent gases and CO2, decomposition products of perfluoroisobutyronitrile-nitrogen mixtures, suffer from insufficient sensitivity, accuracy, and repeatability. This application addresses these issues by incorporating a first injection device, a first separation device, a second injection device, a second separation device, a detection device, and a flow path switching valve. The first and second injection devices each include a sample injection component, a preprocessor, and a quantitative tube connected sequentially. By quantitatively storing the pretreated gas sample, the separation difficulty of subsequent separation devices is reduced. The first and second separation devices can separate the permanent gases and CO2 from the quantitatively stored gas sample in the quantitative tube. Then, the detection device provides a highly sensitive signal, enabling precise measurement of trace gases, thereby improving the detection sensitivity, accuracy, and repeatability of permanent gases and CO2 in the decomposition products of perfluoroisobutyronitrile-nitrogen mixtures.

[0070] It is understood that in the detection system for the decomposition products of perfluoroisobutyronitrile-nitrogen mixed gas described in this application, each component is connected through the internal flow channels of pipelines or switching valves, and each port is connected through the internal flow channels of pipelines or switching valves.

[0071] The first aspect of this application provides a detection system for the decomposition products of a perfluoroisobutyronitrile-nitrogen mixed gas, comprising a first injection device, a first separation device, a second injection device, a second separation device, a detection device, and a flow path switching valve device.

[0072] The first sample injection device includes a first sample injection component 1, a first preprocessor 2, and a first quantitative tube 3 connected in sequence.

[0073] The first separation device is connected to the first quantitative tube 3 to separate the permanent gas in the gas sample in the first quantitative tube 3.

[0074] The second sample injection device includes a second sample injection component 16, a second preprocessor 17, and a second quantitative tube 18 connected in sequence.

[0075] The second separation device is connected to the second quantitative tube 18 to separate CO2 from the gas sample in the second quantitative tube 18.

[0076] The detection device is used to detect the content of each permanent gas separated by the first separation device and the content of CO2 separated by the second separation device.

[0077] The flow path switching valve device includes a first switching valve 27, which is connected to the first separation device, the second separation device and the detection device respectively.

[0078] In this application, the first and second injection devices each include a sample inlet, a preprocessor, and a quantitative tube connected in sequence. The preprocessed gas sample is quantitatively stored through the quantitative tube, which reduces the separation difficulty of the subsequent separation device. By using the first and second separation devices, the precise separation of each permanent gas and CO2 in the quantitatively stored gas sample can be achieved. Then, the detection device provides a high-sensitivity signal, enabling the accurate measurement of trace gases, thereby improving the detection sensitivity, accuracy, and repeatability of each permanent gas and CO2 in the decomposition products of perfluoroisobutyronitrile-nitrogen mixed gas.

[0079] Traditional methods for detecting permanent gaseous decomposition products in perfluoroisobutyronitrile-nitrogen mixtures have the following drawbacks:

[0080] (1) Due to the limitations of the detection principle, the thermal conductivity detector (TCD detector) has relatively low sensitivity and is difficult to meet the detection requirements of trace gases. The optimal detection limit of conventional TCD detectors is at the level of hundreds of ppm, which is difficult to detect gases that are only produced at the level of tens of ppb in the early stage of failure. In addition, the sensitivity of TCD detectors is strongly dependent on the thermal conductivity of the carrier gas. When helium or hydrogen is used as the carrier gas, the detection of permanent gases is more sensitive. However, if argon or nitrogen is used as the carrier gas, the difference in thermal conductivity between the sample and the carrier gas decreases, and the detection sensitivity is further reduced. For the perfluoroisobutyronitrile-nitrogen mixed gas system, if inert argon is considered to be used as the carrier gas to avoid helium, the high concentration of nitrogen background will make the thermal conductivity signal generated by the TCD detector change weakly, making it difficult to distinguish trace target products. Large changes in the composition of the sample matrix (such as changes in gas composition before and after failure) may cause TCD detection baseline drift and nonlinear response, resulting in a decrease in quantitative accuracy. Therefore, traditional TCD detection methods cannot meet the detection requirements of high sensitivity and high stability.

[0081] (2) Pulse discharge helium ionization detectors (PDHID) rely heavily on high-purity helium as the discharge medium and carrier gas for normal operation. However, helium resources have been in short supply and expensive in recent years, which is not conducive to long-term field use. At the same time, when using helium carrier gas in high-nitrogen matrix samples, the large amount of nitrogen in the sample may interfere with the discharge when it encounters the helium discharge region after the column, which may increase the detection baseline noise or produce spurious peaks. The repeatability of PDHID measurement of trace oxygen is limited by the adsorption and leakage interference of oxygen in the system. Helium purging protection of valves and pipelines is required to reduce baseline noise. This indicates that when the sample matrix contains oxygen or other impurities, the baseline stability and accuracy of PDHID may be affected. In addition, PDHID detectors have a complex structure and high cost, and require high field operation and maintenance, which is not conducive to long-term online monitoring applications in environments such as high-voltage substations.

[0082] (3) Perfluoroisobutyronitrile is a relatively high molecular weight gas (molecular weight about 200). In chromatographic analysis, it may be a strongly retained component. If it cannot be effectively separated, its large presence will cause the chromatographic baseline to rise or produce tailing, submerging the signal of trace decomposition products and causing spectral interference. At the same time, the main component of the perfluoroisobutyronitrile-nitrogen mixture is nitrogen with a high concentration, which puts higher requirements on the separation of chromatographic peaks of adjacent components (such as O2 and CO). It is difficult to simultaneously take into account the analysis of high-content components and low-content products in one injection, resulting in problems such as the extension of the main component peak affecting the secondary component and the retention time of different components being too close and overlapping, which is not conducive to the accurate identification and quantification of trace gases.

[0083] In some embodiments, the detection device includes a plasma emission detector 28. The plasma emission detector used in this application provides a highly sensitive signal, which is beneficial for improving the detection sensitivity, accuracy, and repeatability of various permanent gases and CO2 in the decomposition products of the perfluoroisobutyronitrile-nitrogen mixture.

[0084] A plasma emission detector (PED detector) consists of a high-frequency radio frequency power supply, a discharge chamber, and an optical detection system. Its working principle is as follows: a carrier gas and sample form a plasma in the detector's discharge region. When excited sample molecules or atoms return to their ground state, they emit characteristic light radiation. The PED detector selects the emitted light at a specific wavelength using optical elements (lenses, bandpass filters, etc.), which is then converted into an electrical signal by a photoelectric sensor. Different gaseous products have different emission spectral characteristics. Spectral analysis is used to detect the intensity of characteristic spectral lines of each element. For example, H2 can be detected by measuring the line spectrum of atomic hydrogen (λ≈486 nm, etc.), O2 and N2 by measuring the emission of atomic oxygen (777 nm spectral line) and atomic nitrogen, CO and CO2 by detecting the emission signal of carbon atoms (247.9 nm spectral line) or molecules, and CH4 can be characterized by the emission of CH bonds produced by its cracking. Plasma emission detection is essentially a type of element-selective detection, similar to traditional atomic emission spectroscopy, except that the excitation source is miniaturized and coupled with chromatography. Since the intensity of emitted light is proportional to the concentration of the corresponding component, the PED detector can achieve quantification by calibrating the intensity of the spectral lines of each element. The advantages of PED detectors lie in the combination of sensitivity and selectivity: by selecting appropriate filters and doping strategies, only the emission light of the element of interest can be detected, while components without the target element do not generate corresponding signals, greatly reducing background noise and improving the specificity and anti-interference ability of the method; at the same time, its response sensitivity is extremely high, achieving detection limits at the ppb level or even lower under argon carrier gas conditions, enabling selective simultaneous detection of multiple components, and meeting the requirements for gas determination at concentrations of 0.05 μL / L (50 ppb) or even lower. Unlike traditional flame photometry or radioactive source detection, plasma emission detection does not require combustion gases or radioactive sources; the working gas used is only the carrier gas argon, eliminating the need for additional reagent gases, making the system simpler, safer, and with lower carrier gas costs. In particular, compared to PDHID, which relies on helium, PED detectors can directly use argon as both the carrier gas and the discharge medium while maintaining high sensitivity. Furthermore, plasma detectors are flameless and have no radioactive sources, making them environmentally friendly and eliminating the risk of using flammable gases such as hydrogen.

[0085] In some embodiments, in the first injection device, the first sample injection component 1 is used to inject a gas sample, the first preprocessor 2 is used to filter particulates and oil compounds in the gas sample entering through the first sample injection component 1, and the first quantitative tube 3 is used to quantitatively store the gas sample filtered by the first preprocessor 2. The filtration by the first preprocessor 2 protects the subsequent chromatographic column from contamination.

[0086] In some embodiments, the first preprocessor 2 consists of a housing, a stainless steel sintered filter disposed within the housing, and an activated carbon adsorption tube; the pore size of the stainless steel sintered filter is 5 μm; the activated carbon adsorption tube is filled with 20-40 mesh coconut shell activated carbon, and the amount of coconut shell activated carbon is 0.5 g.

[0087] In some embodiments, in the second injection device, the second sample injection component 16 is used to inject a gas sample, the second preprocessor 17 is used to filter particulates and oil compounds in the gas sample entering through the second sample injection component 16, and the second quantitative tube 18 is used to quantitatively store the gas sample filtered by the second preprocessor 17. The filtration by the second preprocessor 17 protects the subsequent chromatographic column from contamination.

[0088] In some embodiments, the second preprocessor 17 consists of a housing, a stainless steel sintered filter disposed within the housing, and an activated carbon adsorption tube; the pore size of the stainless steel sintered filter is 5 μm; the activated carbon adsorption tube is filled with 20-40 mesh coconut shell activated carbon, and the amount of coconut shell activated carbon is 0.5 g.

[0089] In some embodiments, the gas samples entering the first sample inlet component 1 and the second sample inlet component 16 are extracted by means of a gas-insulated switch (GIS) device using a stainless steel sampling cylinder, a gas sampling bag, or an online sampling interface.

[0090] In some embodiments, the gas samples entering the first sample injection unit 1 and the second sample injection unit 16 are extracted by the following method:

[0091] A mixture of 4% perfluoroisobutyronitrile (PFOBN) and 96% nitrogen (N) was introduced into a sealed cavity for arc discharge treatment. The conditions for arc discharge treatment were: temperature 20℃, gas pressure 0.4MPa, electrode spacing 10mm, AC current 100A, single arc duration 0.3s, number of discharges 5, and cumulative arc time 1.5s. After arc discharge treatment, the mixed gas in the cavity was extracted as a gas sample.

[0092] In some embodiments, the first metering tube 3 and the second metering tube 18 are independent loop tubes with a constant volume, which can be 0.5 mL to 1 mL.

[0093] In some embodiments, the first sample injection device further includes a second switching valve 6, a first pressure sensor 4, and a first sample dispensing component 30.

[0094] The two ends of the first preprocessor 2 are respectively connected to one end of the first sample injection component 1 and the second port of the second switching valve 6.

[0095] The two ends of the first quantitative tube 3 are connected to the first port and the fourth port of the second switching valve 6, respectively.

[0096] The two ends of the first pressure sensor 4 are respectively connected to the third port of the second switching valve 6 and one end of the first sample dispensing component 30.

[0097] In the first injection device, the first pressure sensor 4 is used to monitor and balance the pressure of the first injection device.

[0098] In some embodiments, the first injection device further includes a first carrier gas inlet 7, which is connected to the fifth port of the second switching valve 6.

[0099] In some embodiments, the first injection device further includes a first venting needle valve 8, one end of which is connected to the ninth port of the second switching valve 6.

[0100] In some embodiments, the first injection device further includes a second carrier gas inlet 9, which is connected to the eighth port of the second switching valve 6.

[0101] In some embodiments, the first separation device includes a first gas chromatographic column 5, a second gas chromatographic column 10, a third switching valve 12, and a third gas chromatographic column 11.

[0102] The two ends of the first gas chromatography column 5 are connected to the tenth port and the sixth port of the second switching valve 6, respectively, for pre-separating C4F7N and permanent gas in the gas sample in the first quantitative tube (3) to obtain a pre-separated product including permanent gas.

[0103] The two ends of the second gas chromatography column 10 are connected to the seventh port of the second switching valve 6 and the sixth port of the third switching valve 12, respectively, for the first separation of permanent gases in the pre-separation product after the first gas chromatography column 5, to obtain a first separation product including permanent gases.

[0104] The two ends of the third gas chromatography column 11 are connected to the first port of the third switching valve 12 and the second port of the first switching valve 27, respectively, for performing a second separation of the permanent gas in the first separation product after the first separation of the second gas chromatography column 10, to obtain a second separation product including the permanent gas.

[0105] In some embodiments, the first gas chromatographic column 5 is a pre-column, which can be a polymer porous packed column. By using porous polymer particles as the stationary phase, the first gas chromatographic column 5 performs preliminary separation and retention of the gas sample in the first quantitative tube 3, strongly retaining polar or high-boiling-point components (such as C4F7N), while allowing small molecules such as H2 to pass through rapidly, avoiding column contamination and baseline noise, and reducing the load on subsequent separations through coarse separation.

[0106] In some embodiments, the second gas chromatographic column 10 and the third gas chromatographic column 11 are 5A molecular sieve columns. The first separation device receives the components separated from the first gas chromatographic column 5 using the second gas chromatographic column 10 and the third gas chromatographic column 11, and further performs fine separation on the permanent gases therein, achieving efficient separation of permanent gases with similar properties. Since the 5A molecular sieve in the 5A molecular sieve column has a strong physical adsorption capacity for CO2, it is difficult to desorb CO2 from the 5A molecular sieve column. Therefore, a second separation device is used to achieve CO2 separation. The second gas chromatographic column 10 and the third gas chromatographic column 11 further efficiently separate permanent gases with similar properties by receiving the components pre-cut from the column core.

[0107] In some embodiments, the first separation device further includes a third carrier gas inlet 13, which is connected to the second port of the third switching valve 12;

[0108] In some embodiments, the first separation device further includes a second venting needle valve 14, one end of which is connected to the third port of the third switching valve 12.

[0109] In some embodiments, the first separation device further includes a third venting needle valve 15, one end of which is connected to the fifth port of the third switching valve 12.

[0110] In some embodiments, the second sample injection device further includes a fourth switching valve 29, a second pressure sensor 19, and a second sample dispensing component 31.

[0111] The two ends of the second preprocessor 17 are respectively connected to one end of the second sample injection component 16 and the second port of the fourth switching valve 29.

[0112] The two ends of the second metering tube 18 are connected to the first port and the fourth port of the fourth switching valve 29, respectively.

[0113] The two ends of the second pressure sensor 19 are respectively connected to the third port of the fourth switching valve 29 and the second sample outlet component 31.

[0114] In the second injection device, the second pressure sensor 19 is used to monitor and balance the pressure of the second injection device.

[0115] In some embodiments, the second injection device also has a fourth carrier gas inlet 20, which is connected to the fifth port of the fourth switching valve 29.

[0116] In some embodiments, the second injection device also has a fifth carrier gas inlet 21, which is connected to the eighth port of the fourth switching valve 29.

[0117] In some embodiments, the second injection device further includes a fourth venting needle valve 22, one end of which is connected to the ninth port of the fourth switching valve 29.

[0118] In some embodiments, the second separation device includes a fourth gas chromatography column 23 and a fifth gas chromatography column 24.

[0119] The two ends of the fourth gas chromatographic column 23 are connected to the tenth port and the sixth port of the fourth switching valve 29, respectively, for pre-separating C4F7N and CO2 in the gas sample in the second quantitative tube (18) to obtain a pre-separated product including CO2.

[0120] The two ends of the fifth gas chromatographic column 24 are connected to the seventh port of the fourth switching valve 29 and the sixth port of the first switching valve 27, respectively, and are used to separate CO2 in the pre-separation product after the pre-separation of the fourth gas chromatographic column 23, so as to obtain a separated product including CO2.

[0121] In some embodiments, the fourth gas chromatographic column 23 is a pre-column, which can be a polymer porous packed column. By using porous polymer particles as the stationary phase, the fourth gas chromatographic column 23 performs preliminary separation and retention of the gas sample in the second quantitative tube 18, strongly retaining polar or high-boiling-point components (such as C4F7N), while allowing small molecules such as H2 to pass through rapidly, avoiding column contamination and baseline noise, and reducing the load on subsequent separations through coarse separation.

[0122] In some embodiments, the fifth gas chromatographic column 24 is a polymer chromatographic column. The polymer chromatographic column is used to separate carbon dioxide and does not adsorb carbon dioxide, thus exhibiting good separation capability for carbon dioxide.

[0123] In some embodiments, the detection system for the decomposition products of the perfluoroisobutyronitrile-nitrogen mixed gas further includes a fifth venting needle valve 25 and a sixth venting needle valve 26, one end of the fifth venting needle valve 25 being connected to the fifth port of the first switching valve 27, and one end of the sixth venting needle valve 26 being connected to the third port of the first switching valve 27.

[0124] In some embodiments, the first switching valve 27 is a six-way valve, the second switching valve 6 is a ten-way valve, the third switching valve 12 is a six-way valve, and the fourth switching valve 29 is a ten-way valve.

[0125] In this application, the first switching valve 27, the second switching valve 6, the third switching valve 12, and the fourth switching valve 29 are automatic switching valves used for gas transmission, sample filling, and sample injection.

[0126] In this application, the first gas chromatographic column 5, the second gas chromatographic column 10, the third gas chromatographic column 11, the fourth gas chromatographic column 23, and the fifth gas chromatographic column 24 are all placed in a constant temperature column oven to ensure temperature stability, peak shape reproducibility, and separation accuracy.

[0127] In some embodiments, the detection system for the decomposition products of the perfluoroisobutyronitrile-nitrogen mixed gas includes a first injection device, a first separation device, a second injection device, a second separation device, a detection device, and a flow path switching valve device.

[0128] The first sample injection device includes a first sample injection component 1, a first preprocessor 2, a first quantitative tube 3, a second switching valve 6, a first pressure sensor 4, a first sample dispensing component 30, and a first venting needle valve 8, and also has a first carrier gas inlet 7 and a second carrier gas inlet 9.

[0129] The first separation device includes a first gas chromatographic column 5, a second gas chromatographic column 10, a third switching valve 12, a third gas chromatographic column 11, a second venting needle valve 14 and a third venting needle valve 15, and also has a third carrier gas inlet 13.

[0130] The second sample injection device includes a second sample injection component 16, a second preprocessor 17, a second quantitative tube 18, a fourth switching valve 29, a second pressure sensor 19, a second sample discharge component 31, and a fourth venting needle valve 22, and also has a fourth carrier gas inlet 20 and a fifth carrier gas inlet 21.

[0131] The second separation device includes a fourth gas chromatography column 23 and a fifth gas chromatography column 24.

[0132] The detection device includes a plasma emission detector 28.

[0133] The flow path switching valve device includes a first switching valve 27.

[0134] See Figure 1 The connection method of the detection system for the decomposition products of the perfluoroisobutyronitrile-nitrogen mixed gas is as follows:

[0135] In the first sample injection device, the two ends of the first preprocessor 2 are respectively connected to one end of the first sample injection component 1 and the second port of the second switching valve 6; the two ends of the first quantitative tube 3 are respectively connected to the first port and the fourth port of the second switching valve 6; the two ends of the first pressure sensor 4 are respectively connected to the third port of the second switching valve 6 and one end of the first sample outlet component 30; the first carrier gas inlet 7 is connected to the fifth port of the second switching valve 6; one end of the first venting needle valve 8 is connected to the ninth port of the second switching valve 6; and the second carrier gas inlet 9 is connected to the eighth port of the second switching valve 6.

[0136] In the first separation device, the two ends of the first gas chromatographic column 5 are connected to the tenth port and the sixth port of the second switching valve 6, respectively; the two ends of the second gas chromatographic column 10 are connected to the seventh port of the second switching valve 6 and the sixth port of the third switching valve 12, respectively; the two ends of the third gas chromatographic column 11 are connected to the first port of the third switching valve 12 and the second port of the first switching valve 27, respectively; the third carrier gas inlet 13 is connected to the second port of the third switching valve 12; one end of the second venting needle valve 14 is connected to the third port of the third switching valve 12; and one end of the third venting needle valve 15 is connected to the fifth port of the third switching valve 12.

[0137] In the second sample injection device, the two ends of the second preprocessor 17 are respectively connected to one end of the second sample injection component 16 and the second port of the fourth switching valve 29; the two ends of the second quantitative tube 18 are respectively connected to the first port and the fourth port of the fourth switching valve 29; the two ends of the second pressure sensor 19 are respectively connected to the third port of the fourth switching valve 29 and one end of the second sample outlet component 31; the fourth carrier gas inlet 20 is connected to the fifth port of the fourth switching valve 29; the fifth carrier gas inlet 21 is connected to the eighth port of the fourth switching valve 29; and one end of the fourth venting needle valve 22 is connected to the ninth port of the fourth switching valve 29.

[0138] In the second separation device, the two ends of the fourth gas chromatographic column 23 are connected to the tenth port and the sixth port of the fourth switching valve 29, respectively; the two ends of the fifth gas chromatographic column 24 are connected to the seventh port of the fourth switching valve 29 and the sixth port of the first switching valve 27, respectively.

[0139] The third port of the first switching valve 27 is connected to one end of the sixth venting needle valve 6;

[0140] The fifth port of the first switching valve 27 is connected to one end of the fifth venting needle valve 25;

[0141] The first port of the first switching valve 27 is connected to one end of the plasma emission detector 28.

[0142] The detection system for the decomposition products of the perfluoroisobutyronitrile-nitrogen mixed gas includes four switching valves (two ten-way valves and two six-way valves) and five gas chromatographic columns. It features column switching (center cutting) and backflushing functions. All components are connected sequentially, and multidimensional separation and precise flow path switching can be achieved through valve sequence control. This system is used for the efficient separation and detection of permanent gases and high-boiling-point matrix components in complex gas mixtures. The first separation device employs a center-cutting coupled mode and can be composed of a pre-column (first gas chromatographic column 5) and two 5A molecular sieve columns (second gas chromatographic column 10 and third gas chromatographic column 11). The pre-column is mainly used for preliminary separation and retention of the matrix gas. During the separation process of the first separation device, backflushing can be used to retain high-boiling-point matrix components. In the one-dimensional center-cutting stage, permanent gases such as H2, O2, CH4, and CO are introduced into the two-dimensional separation module for further analysis, while N2 is emitted, solving the problem of detecting trace components in high-concentration background gases. The second separation unit primarily separates CO2, while the remaining components are vented through a switching valve, achieving targeted enrichment and highly sensitive detection of the target components. During the separation process between the first and second separation units, inert gases such as N2 are directly vented and do not enter subsequent separation channels to avoid interfering with subsequent detection.

[0143] The detection system for the decomposition products of the perfluoroisobutyronitrile-nitrogen mixed gas is modularly packaged and has the ability to resist vibration and temperature fluctuations. With appropriate protection, the detection system can be connected online to the gas monitoring interface of GIS equipment for a long time, realizing unattended continuous monitoring. Once internal discharge decomposition occurs, causing the target gas level to rise, the system can detect and alarm in a timely manner. It can be deployed and applied in field environments such as power substations, providing real-time and reliable insulation status monitoring data.

[0144] A second aspect of this application provides a method for detecting the decomposition products of a perfluoroisobutyronitrile-nitrogen mixed gas, comprising the following steps:

[0145] Gas samples are fed into a first injection device and a second injection device, respectively. In the first injection device, the gas sample is pre-processed by a first preprocessor and then stored in a first quantitative tube. In the second injection device, the gas sample is pre-processed by a second preprocessor and then stored in a second quantitative tube.

[0146] The gas sample stored in the first quantitative tube is loaded into the first separation device to separate the permanent gases in the gas sample in the first quantitative tube. The permanent gases separated by the first separation device are loaded into the detection device to detect the content of each permanent gas in the gas sample.

[0147] The gas sample stored in the second quantitative tube is loaded into the second separation device to separate CO2 from the gas sample in the second quantitative tube. The CO2 separated by the second separation device is loaded into the detection device to detect the CO2 content in the gas sample.

[0148] Understandably, in this application, the gas samples input to the first and second sampling devices are laboratory simulated fault gas samples or actual GIS operating gas samples, including perfluoroisobutyronitrile (PFOS), nitrogen, permanent gases, and carbon dioxide, etc. The actual GIS operating gas sample is the insulating medium system after the perfluoroisobutyronitrile-nitrogen mixture produces decomposition products during the operation of high-voltage electrical equipment.

[0149] In some embodiments, the gas samples input to the first and second injection devices are prepared by the following method:

[0150] A mixture of 4% perfluoroisobutyronitrile (PFOBN) and 96% nitrogen (N) was introduced into a sealed cavity for arc discharge treatment. The conditions for arc discharge treatment were: temperature 20℃, gas pressure 0.4MPa, electrode spacing 10mm, AC current 100A, single arc duration 0.3s, number of discharges 5, and cumulative arc time 1.5s. After arc discharge treatment, the mixed gas in the cavity was collected as a gas sample.

[0151] In some embodiments, the detection device includes a plasma emission detector.

[0152] In some implementations, the plasma emission detector (PED detector) uses argon as both the carrier gas and the discharge medium. Argon is an inexpensive and readily available inert gas, and using argon as the carrier gas and discharge medium avoids the problem of helium supply difficulties. At the same time, the generation and maintenance of argon plasma are stable and reliable, and it has good excitation efficiency for small molecule gases. Argon also requires lower pressure from the chromatographic system, making it suitable for continuous use in on-site online analyzers.

[0153] In some implementations, the plasma emission detector maintains a constant radio frequency power and gas flow rate during operation to stabilize the baseline. After being separated by a separation device, each component sequentially enters the PED discharge region, generating corresponding optical signal peaks.

[0154] In some embodiments, loading the gas sample stored in the first metering tube into the first separation device, and separating the permanent gas from the gas sample in the first metering tube specifically includes the following steps:

[0155] The gas sample in the first quantitative tube is loaded into the first chromatographic column by a carrier gas. The C4F7N and permanent gas in the gas sample in the first quantitative tube (3) are pre-separated to obtain a pre-separated product including the permanent gas. The permanent gas in the pre-separated product is sequentially loaded into the second gas chromatographic column and the third gas chromatographic column for separation.

[0156] In some embodiments, the first chromatographic column comprises a polymer porous packed column.

[0157] In some embodiments, the second gas chromatography column comprises a 5A molecular sieve column.

[0158] In some embodiments, the third gas chromatography column comprises a 5A molecular sieve column.

[0159] In some embodiments, the gas sample stored in the second metering tube is loaded into the second separation device, and the separation of CO2 from the gas sample in the second metering tube specifically includes the following steps:

[0160] The gas sample in the second quantitative tube is loaded into the fourth gas chromatographic column using a carrier gas. The C4F7N and permanent gases in the gas sample in the second quantitative tube are pre-separated to obtain a pre-separated product including CO2. The CO2 in the pre-separated product is then loaded into the fifth gas chromatographic column for further separation.

[0161] In some embodiments, the fourth gas chromatography column comprises a polymer porous packed column.

[0162] In some embodiments, the fifth gas chromatography column includes a polymer chromatography column.

[0163] In some embodiments, the method for detecting the decomposition products of the perfluoroisobutyronitrile-nitrogen mixed gas employs the detection system for the decomposition products of the perfluoroisobutyronitrile-nitrogen mixed gas described in the first aspect.

[0164] In some embodiments, the permanent gas includes at least one of H2, O2, CH4, and CO.

[0165] In some embodiments, after loading the permanent gas in the pre-separated gas sample into the second gas chromatographic column, a backflushing step is also included. The backflushing step specifically includes: switching the second switching valve 6 to backflush the components retained by the first gas chromatographic column 5 to the first venting needle valve 8 for venting.

[0166] Backflushing refers to the operation of passing carrier gas in the opposite direction through the chromatographic column to blow away the heavy components that have not yet been eluted from the inlet end.

[0167] This application employs a sample introduction device, a gas chromatographic separation device including a first separation device and a second separation device, and a detection device including a plasma emission detector. Through a two-dimensional chromatographic process of "column core cutting + post-column backflushing," the main matrix (C4F7N, N2, and CO2, etc.) in the gas sample is separated from the target permanent gases in time and space, thereby achieving matrix elimination and target enrichment. Furthermore, the high-sensitivity signal provided by plasma emission spectroscopy allows for precise measurement of trace gases, thus improving the sensitivity, accuracy, and repeatability of the fractional detection results of permanent gases and CO2 decomposition products in perfluoroisobutyronitrile-nitrogen mixed gas. Using the detection method for decomposition products of perfluoroisobutyronitrile-nitrogen mixed gas described in this application, the chromatographic separation of each component is high, the spectra are clear, and the detection sensitivity, accuracy, and precision of each permanent gas and CO2 are significantly improved. It also exhibits strong anti-interference capabilities, providing a powerful tool for the operation and maintenance of perfluoroisobutyronitrile-nitrogen mixed gas insulation equipment. In this system, the chromatographic columns of the first separation device and the second separation device work together with the switching valves to ensure that high-concentration matrix and low-concentration target are optimally processed on different columns.

[0168] In some embodiments, the method for detecting the decomposition products of perfluoroisobutyronitrile-nitrogen mixed gas includes the following steps:

[0169] Gas samples are fed into a first injection device and a second injection device, respectively. In the first injection device, the gas sample is pre-processed by a first preprocessor and then stored in a first quantitative tube. In the second injection device, the gas sample is pre-processed by a second preprocessor and then stored in a second quantitative tube. Specifically: [The text abruptly ends here, likely due to an incomplete sentence or missing information.] Figure 2 In the first state, in the first injection device, the gas sample enters the first preprocessor 2 from the first sample injection component 1. After preprocessing by the first preprocessor 2, the gas sample enters the first quantitative tube 3 through the second port and the first port of the second switching valve 6 for quantitative storage. Excess gas enters the first sample outlet 30 through the first pressure sensor 4 for discharge. In the second injection device, the gas sample enters the second preprocessor 17 from the second sample injection component 16. After preprocessing by the second preprocessor 17, the gas sample enters the second quantitative tube 18 through the second port and the first port of the fourth switching valve 29 for quantitative storage. Excess gas enters the second sample outlet component 31 through the second pressure sensor 19 for discharge.

[0170] See Figures 3-5 The gas sample stored in the first quantitative tube is loaded into the first separation device to separate the permanent gases in the gas sample. The permanent gases separated by the first separation device are then loaded into the detection device to detect the content of each permanent gas in the gas sample. Specifically, the second switching valve 6 is switched (see [reference]). Figure 3In the second state, the first carrier gas is introduced through the first carrier gas inlet 7. The first carrier gas enters the first quantitative tube 3 through the fifth and fourth ports of the second switching valve 6, and the gas sample stored in the first quantitative tube 3 is loaded into the first gas chromatographic column 5 for pre-separation. After all the permanent gases in the gas sample have flowed into the second gas chromatographic column 10, the second switching valve 6 is switched. See [link to relevant documentation]. Figure 4 In the third state, the first carrier gas is introduced through the first carrier gas inlet 7, backflushing the components retained by the first gas chromatographic column 5 to the first vent needle valve 8 for venting. Simultaneously, the second carrier gas is introduced through the second carrier gas inlet 9, carrying the permanent gases flowing through the second gas chromatographic column 10 into the third gas chromatographic column 11 for a second separation. The permanent gases after the second separation enter the plasma emission detector 28 through the second and first ports of the first switching valve 27, realizing the detection of the content of permanent gases in the gas sample. When other components (such as nitrogen) besides permanent gases are detected flowing out of the second gas chromatographic column 10, the third switching valve 12 is switched for venting. See [link to relevant documentation]. Figure 5 In the fourth state, components other than the permanent gas flowing out of the second gas chromatographic column 10 are vented through the sixth and fifth ports of the third switching valve 12 into the third vent needle valve 15. At the same time, the third carrier gas is introduced through the third carrier gas inlet 13, and the permanent gas flowing through the third gas chromatographic column 11 is vented into the plasma emission detector 28 for content detection. It can be understood that the third and fourth states can be automatically switched according to the types of components flowing out of the second gas chromatographic column 10.

[0171] See Figures 6-8 The gas sample stored in the second quantitative tube is loaded into the second separation device to separate CO2 from the gas sample in the second quantitative tube. The separated CO2 is then loaded into the detection device to detect the CO2 content in the gas sample. Specifically, the fourth switching valve 29 is switched (see [reference]). Figure 6 In the fifth state, the fourth carrier gas is introduced through the fourth carrier gas inlet 20. The fourth carrier gas enters the second quantitative tube 18 through the fifth port and the fourth port of the fourth switching valve 29, loading the gas sample stored in the second quantitative tube 18 into the fourth gas chromatographic column 23 for pre-separation. After all the carbon dioxide in the gas sample has flowed into the fifth gas chromatographic column 24, the fourth switching valve 29 is switched. See [link to relevant documentation]. Figure 7In the sixth state, the fourth carrier gas is introduced through the fourth carrier gas inlet 20, backflushing the components retained by the fourth gas chromatographic column 23 to the fourth vent needle valve 22 for venting. Simultaneously, the fifth carrier gas is introduced through the fifth carrier gas inlet 21. CO2 separated by the fifth gas chromatographic column 24 is loaded into the plasma emission detector 28 through the sixth and first ports of the first switching valve 27, realizing the detection of CO2 content in the gas sample. When other components besides CO2 are detected flowing out of the fifth gas chromatographic column 24, the first switching valve 27 is switched. (See [link to relevant documentation]). Figure 8 In the seventh state, components other than CO2 flowing out of the fifth gas chromatographic column 24 are loaded into the fifth vent needle valve 25 for venting through the sixth and fifth ports of the first switching valve 27. Understandably, the sixth and seventh states can be automatically switched according to the types of components flowing out of the fifth gas chromatographic column 24.

[0172] In some embodiments, the first, second, third, fourth, and fifth carrier gases are independently argon. The argon is high-purity argon (purity ≥ 99.999%). This application uses high-purity argon as both the carrier gas and the PED discharge gas, which has the following advantages: First, argon is an inexpensive and readily available inert gas, avoiding the problem of helium supply difficulties; second, the generation and maintenance of argon plasma are stable and reliable, and it has good excitation efficiency for small molecule gases; third, argon requires lower pressure for the chromatographic system, making it suitable for continuous use in on-site online analyzers. Simultaneously, using argon as the carrier gas also eliminates the background peak problem that may be caused by trace impurities (such as neon and argon) in helium, and the on-site gas source is convenient, using argon cylinders or even on-site argon generation devices.

[0173] It is understood that, unless otherwise specified, in the embodiments of this application, the flow rate of the same carrier gas remains constant under different conditions.

[0174] This application combines a center-cutting and backflushing technology controlled by a dual ten-way valve and a six-way valve, with each component connected sequentially, achieving high separation and low interference in gas chromatography for various permanent gases and CO2. The detection limits for permanent gases and CO2 in the decomposition products of the perfluoroisobutyronitrile-nitrogen mixture of this application reach or exceed 0.05 μL / L. Under typical conditions, the lowest detection concentration for each component can reach the tens of ppb level, with the detection limits for H2, O2, N2, and CH4 in the range of 0.01-0.1 ppm, and slightly higher limits for CO and CO2 due to adsorption or background issues, but still better than 0.05 ppm. Compared to the detection capability of traditional TCD at the hundred ppm level, the sensitivity of this method is improved by more than two orders of magnitude. After processing with two-dimensional separation and center-cutting technology, baseline separation of all permanent gases and CO2 is achieved in the chromatogram. There is no tailing or overlay between the gases, and they are well separated with symmetrical and sharp peaks. This enables efficient separation and high-sensitivity detection of trace components, making it more suitable for field engineering applications and overcoming the shortcomings of existing technologies in terms of spectral interference, carrier gas dependence, and equipment complexity. The backflushing principle reverses the flow direction after center-cutting, blowing the heavy components remaining at the end of the pre-column out of the column. This not only prevents the delayed diffusion of heavy components into the analytical column and causing background interference, but also significantly shortens the overall analysis cycle (without waiting for all heavy components to be eluted). By appropriately selecting the valve switching timing, perfluoroisobutyronitrile (PFO) has zero efflux on the gas chromatography column, is completely intercepted and backflushed, and will not appear in the chromatogram. Simultaneously, it ensures that permanent gases such as H2 and CH4 are transferred to the analytical column after only slight separation in the pre-column. In the first separation device, CO2 is adsorbed by the 5A molecular sieve column, thus avoiding mutual interference between CO2 and permanent gases such as O2 and CO. CO2 peaks are delayed through a special channel, avoiding overlap with O2 and other components. This separation and backflushing process design ensures good peak shape and separation for each target gas, resulting in a concise final spectrum, avoiding interfering peaks, significantly improving signal-to-noise ratio and readability, facilitating qualitative and integral analysis, and laying the foundation for subsequent high-sensitivity detection. This method is characterized by its ingenious structure and advanced principle. Thanks to the backflushing technology removing heavy components, the analysis time for a single analysis in this application can be controlled within 15-30 minutes.

[0175] In some embodiments, considering the problem of O2 adsorption loss in the pipeline, this application reduces O2 adsorption retention and improves the accuracy of O2 quantification by inerting the detection system, adding a certain amount of argon gas to the gas sample for balancing, and using a high-temperature valve.

[0176] In some implementations, the content of each permanent gas decomposition product in a gas sample is detected by the following methods:

[0177] A standard curve for permanent gases was established using a plasma emission detector, with concentration on the x-axis and emission intensity on the y-axis. The content of permanent gas decomposition products in the gas sample was calculated based on the emission intensity detected by the detector.

[0178] In some implementations, the CO2 content in a gas sample is detected by the following method:

[0179] A standard curve for CO2 was established using a plasma emission detector, with concentration on the x-axis and emission intensity on the y-axis. The content of CO2 decomposition products in the gas sample was calculated based on the emission intensity detected by the detector.

[0180] After being separated by the chromatographic column, CO2 and the various permanent gas components sequentially enter the discharge region of the PED detector. In the high-energy argon plasma, they can be effectively excited to produce atomic spectral lines, generating corresponding light signal emission intensities. By using pre-calibrated standard sample gases, calibration curves are established for CO2 and the permanent gases H2, O2, N2, CO, and CH4, respectively, which enables the identification and concentration determination of each component.

[0181] In this embodiment of the application, during the combined analysis of gas chromatography and plasma optical emission detector (PED), the decomposition products CO2 and permanent gases in the perfluoroisobutyronitrile-nitrogen mixture are presented as sequentially separated spectral peaks. Component identification and concentration determination can be achieved using the external standard method. Regarding retention time, the types of compounds corresponding to each peak are identified by comparison with standard samples. In terms of spectral selectivity, the PED detector only responds to the emission of specific elements, exhibiting strong anti-interference capabilities and avoiding interference from most non-target impurities, thus reducing the possibility of misidentification. Furthermore, since external standard quantification is used, the emission intensity of each component's optical signal satisfies a linear relationship with its concentration, allowing the content of each gas in the sample to be determined based on a pre-established standard curve.

[0182] The quantitative methods for detecting the content of various permanent gases and CO2, employing the external standard method and a highly stable PED detector, demonstrate good linearity and high precision. This application establishes a standard curve by repeatedly detecting the emission intensity of the standard gases. Measurements show that the peak area / height of each component is linearly correlated with its concentration (correlation coefficient R0). 2 Typically >0.999). All permanent gases and CO2 exhibit good linearity in the range of 0.1–50 μL / L. The repeatability of the method (based on relative standard deviation (RSD)) is better than 3%. This application achieves excellent quantitative reproducibility while ensuring high sensitivity. For example, for samples at the 1 μL / L level, the RSD of multiple parallel determinations of H2, CO, etc., is around 2%, indicating that the system is stable and reliable. In contrast, the TCD method requires high concentrations for determination due to low sensitivity, and its repeatability is often limited; while the PDHID method is sensitive, its baseline is prone to drift and O2 quantification is difficult, also affecting repeatability.

[0183] For data processing, dual-channel signal acquisition can be used (under the condition that the PED detector is configured with different filter channels) or different element signals can be synthesized into a single chromatogram for output. The final output result is the concentration value (volume fraction, μL / L) of each permanent gas.

[0184] The embodiments of this application will be described in detail below with reference to examples. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of this application. For experimental methods in the following embodiments where specific conditions are not specified, please refer to the guidelines given in this application, or follow experimental manuals or conventional conditions in the art, or follow the conditions recommended by the manufacturer, or refer to experimental methods known in the art.

[0185] Example 1

[0186] The insulating medium, a mixture of perfluoroisobutyronitrile (PFOB) and nitrogen, was used as a gas sample after the decomposition of the insulating medium during the operation of high-voltage electrical equipment. Specifically, the gas sample was obtained by the following method: a mixture of 4% (v / v) PFOB and 96% (v / v) nitrogen was injected into a sealed cavity for arc discharge treatment. The arc discharge treatment conditions were: temperature 20℃, gas pressure 0.4 MPa, electrode spacing 10 mm, AC current 100 A, single arc duration 0.3 s, number of discharges 5, and cumulative arc time 1.5 s. After arc discharge treatment, the mixed gas in the cavity was collected as the gas sample.

[0187] pass Figure 1 The detection system for the decomposition products of perfluoroisobutyronitrile-nitrogen mixed gas shown is used to detect the content of each permanent gas (H2, O2, CH4, and CO) and the content of carbon dioxide in the gas sample. Specifically:

[0188] See Figure 2In the first state, within the first injection device, the gas sample is continuously introduced into the first pre-processor 2 at a flow rate of 50 mL / min through the first sample injection component 1 for pretreatment. The first pre-processor 2 consists of a housing, a stainless steel sintered filter (5 μm pore size) disposed within the housing, and an activated carbon adsorption tube (filled with 20-40 mesh coconut shell activated carbon, with a filling amount of 0.5 g). After being introduced into the first pre-processor 2, the gas sample is first filtered by the stainless steel sintered filter, and then filtered again by the activated carbon adsorption tube. The gas sample, pretreated by the first preprocessor 2, enters the first quantitative tube 3 with a constant volume of 1 mL through the second port and the first port of the second switching valve 6 for quantitative storage. Excess gas is discharged through the first sample outlet 30 via the first pressure sensor 4. In the second injection device, the gas sample is continuously introduced into the second preprocessor 17 at a flow rate of 50 mL / min through the second sample injection component 16 for pretreatment. The second preprocessor 17 consists of a shell, a stainless steel sintered filter (5 μm pore size) disposed within the shell, and an activated carbon adsorption tube (filled with 20-40 mesh coconut shell activated carbon, with a filling amount of 0.5 g). After entering the second preprocessor 17, the gas sample is first filtered by the stainless steel sintered filter (5 μm pore size) and then filtered again by the activated carbon adsorption tube. The gas sample pretreated by the second preprocessor 17 enters the second quantitative tube 18 with a constant volume of 1 mL through the second port and the first port of the fourth switching valve 29 for quantitative storage. Excess gas is discharged through the second sample outlet 31 via the second pressure sensor 19.

[0189] See Figures 3-5 The gas sample stored in the first quantitative tube is loaded into the first separation device to separate the permanent gases in the gas sample. The permanent gases separated by the first separation device are then loaded into the detection device to detect the content of each permanent gas in the gas sample, as follows:

[0190] Switch to the second switching valve 6, see [link / reference] Figure 3 In the second state, the first carrier gas (argon) is continuously introduced from the first carrier gas inlet 7 at a flow rate of 30 mL / min (from the start of the first carrier gas meter, T1 = 0 min). The first carrier gas enters the first quantitative tube 3 through the fifth and fourth ports of the second switching valve 6, and the gas sample stored in the first quantitative tube 3 is loaded into the first gas chromatography column 5 for pre-separation. The pre-separation conditions of the first gas chromatography column 5 include: the first gas chromatography column 5 is a polymer porous packed column (model HayeSep D, column length 2 m, inner diameter 3 mm), and the column temperature is 60℃. After pre-separation by the first gas chromatography column 5, when all the permanent gases in the gas sample flow into the second gas chromatography column 10, the second switching valve 6 is switched (from the start of the first carrier gas meter, T1 = 2.5 min), see [link to relevant documentation]. Figure 4 In the third state, the first carrier gas backflushs the components (including perfluoroisobutyronitrile) retained by the first gas chromatographic column 5 to the first venting needle valve 8 for venting. Simultaneously, the second carrier gas (argon) is continuously introduced through the second carrier gas inlet 9 at a flow rate of 30 mL / min. The permanent gases in the gas sample undergo a first separation on the second gas chromatographic column 10. The conditions for the first separation on the second gas chromatographic column 10 include: the second gas chromatographic column 10 is a 5A molecular sieve column (Hayesep MS5A, column length 2 m, inner diameter 3 mm), and the column temperature is 60℃. Then, the permanent gases in the gas sample after the first separation on the second gas chromatographic column 10 are carried into the third gas chromatographic column 11 for a second separation. The conditions for the second separation on the third gas chromatographic column 11 include: the third gas chromatographic column 11 is a 5A molecular sieve column (Hayesep MS5A, column length 2 m, inner diameter 3 mm), and the column temperature is 60℃. The permanent gases, after secondary separation by the third gas chromatograph column 11, enter the plasma emission detector 28 through the second and first ports of the first switching valve 27 to detect the content of permanent gases in the gas sample. The detection conditions of the plasma emission detector 28 include: a plasma emission detector with an operating frequency of 2450 MHz, a power of 50 W, a wavelength range of 170–800 nm, and a temperature of 200°C. When other components (such as nitrogen) besides permanent gases are detected escaping from the second gas chromatograph column 10 (from the start of the first carrier gas meter, within the range of T1 = 8.0–15.0 min and 20.0–30.0 min), the third switching valve 12 is switched to vent. See [link to relevant documentation]. Figure 5 In the fourth state, components other than permanent gases flowing out of the second gas chromatograph column 10 are vented through the sixth and fifth ports of the third switching valve 12 into the third venting needle valve 15. At the same time, the third carrier gas (argon) is continuously introduced through the third carrier gas inlet 13 at a flow rate of 30 mL / min to provide a carrier gas environment for the separation of permanent gases in the third gas chromatograph column 11 and subsequent detection by the plasma emission detector 28.

[0191] See Figures 6-8 The gas sample stored in the second quantitative tube is loaded into the second separation device to separate CO2 from the gas sample in the second quantitative tube. The separated CO2 is then loaded into the detection device to detect the CO2 content in the gas sample, as detailed below:

[0192] Switch to the fourth switching valve 29, see [link / reference] Figure 6In the fifth state, the fourth carrier gas (argon) is continuously introduced through the fourth carrier gas inlet 20 at a flow rate of 30 mL / min (from the start of the fourth carrier gas meter, T2 = 0 min). The fourth carrier gas enters the second quantitative tube 18 through the fifth and fourth ports of the fourth switching valve 29. The gas sample stored in the second quantitative tube 18 is loaded into the fourth gas chromatography column 23 for pre-separation. The pre-separation conditions of the fourth gas chromatography column 23 include: the fourth gas chromatography column 23 is a polymer porous packed column (model HayeSep D, column length 2 m, inner diameter 3 mm), and the column temperature is 60℃. After pre-separation by the fourth gas chromatography column 23, when all the carbon dioxide in the gas sample flows into the fifth gas chromatography column 24, the fourth switching valve 29 is switched (from the start of the fourth carrier gas meter, T2 = 2.5 min), see [link to relevant documentation]. Figure 7 In the sixth state, the fourth carrier gas is introduced through the fourth carrier gas inlet 20, backflushing the components retained by the fourth gas chromatographic column 23 to the fourth venting needle valve 22 for venting. Simultaneously, the fifth carrier gas (argon) is continuously introduced through the fifth carrier gas inlet 21 at a flow rate of 30 mL / min. CO2 in the gas sample is separated in the fifth gas chromatographic column 24. The separation conditions for the fifth gas chromatographic column 24 include: the fifth gas chromatographic column 24 is a polymer column (model HayeSep Q, column length 2m, inner diameter 3mm), and the column temperature is 60℃. The CO2 separated by the fifth gas chromatographic column 24 is loaded into the plasma emission detector 28 through the sixth port and the first port of the first switching valve 27 to detect the CO2 content in the gas sample. The detection conditions for the plasma emission detector 28 include: the plasma emission detector is a plasma emission detector with an operating frequency of 2450MHz, a power of 50W, a wavelength range of 170-800 nm, and a temperature of 200℃. When elution of components other than CO2 is detected in the fifth gas chromatographic column 24, switch the first switching valve 27 (from the start of the fourth carrier gas meter, within the range of T2 = 3.0-8.0 min and 12.0-20.0 min), see [link to relevant documentation]. Figure 8 In the seventh state, components other than CO2 flowing out of the fifth gas chromatographic column 24 are loaded into the fifth venting needle valve 25 for venting through the sixth and fifth ports of the first switching valve 27.

[0193] The results of the detection of the contents of each permanent gas (H2, O2, CH4, and CO) and carbon dioxide are as follows:

[0194] In the gas sample: the content of H2 was 8.38 μL / L, the content of O2 was 5.26 μL / L, the content of CH4 was 3.14 μL / L, the content of CO was 12.35 μL / L, and the content of CO2 was 35.46 μL / L.

[0195] The detection limits for H2 were 0.05 μL / L (50 ppb), O2, CH4, CO, and CO2 were 0.05 μL / L. The linear correlation coefficients for each component were not less than 0.999, and the relative standard deviations (RSDs) for repeated determinations of each permanent gas and carbon dioxide were ≤3% (n=6).

[0196] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0197] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A detection system for the decomposition products of a perfluoroisobutyronitrile-nitrogen mixed gas, characterized in that, include: The first sample injection device includes a first sample injection component (1), a first preprocessor (2), and a first quantitative tube (3) connected in sequence. A first separation device is connected to the first quantitative tube (3) to separate permanent gases in the gas sample in the first quantitative tube (3); The second sample injection device includes a second sample injection component (16), a second preprocessor (17), and a second quantitative tube (18) connected in sequence. The second separation device is connected to the second quantitative tube (18) to separate CO2 from the gas sample in the second quantitative tube (18); A detection device is used to detect the content of each permanent gas separated by the first separation device and the content of CO2 separated by the second separation device. In addition, the flow path switching valve device includes a first switching valve (27), which is connected to the first separation device, the second separation device and the detection device respectively.

2. The detection system for the decomposition products of perfluoroisobutyronitrile-nitrogen mixed gas according to claim 1, characterized in that, The detection device includes a plasma emission detector (28).

3. The detection system for the decomposition products of perfluoroisobutyronitrile-nitrogen mixed gas according to claim 1, characterized in that, The first sample injection device also includes a second switching valve (6), a first pressure sensor (4), and a first sample dispensing component (30). The two ends of the first preprocessor (2) are respectively connected to one end of the first sample injection component (1) and the second port of the second switching valve (6); The two ends of the first quantitative tube (3) are respectively connected to the first port and the fourth port of the second switching valve (6); The two ends of the first pressure sensor (4) are respectively connected to the third port of the second switching valve (6) and one end of the first sample outlet component (30); Optionally, the first injection device further includes a first carrier gas inlet (7); the first carrier gas inlet (7) is connected to the fifth port of the second switching valve (6); Optionally, the first injection device further includes a first venting needle valve (8), one end of which is connected to the ninth port of the second switching valve (6); Optionally, the first injection device also has a second carrier gas inlet (9), which is connected to the eighth port of the second switching valve (6).

4. The detection system for the decomposition products of perfluoroisobutyronitrile-nitrogen mixed gas according to claim 3, characterized in that, The first separation device includes a first gas chromatography column (5), a second gas chromatography column (10), a third switching valve (12), and a third gas chromatography column (11). The two ends of the first gas chromatography column (5) are connected to the tenth port and the sixth port of the second switching valve (6) respectively, for pre-separating C4F7N and permanent gas in the gas sample in the first quantitative tube (3) to obtain a pre-separated product including permanent gas; The two ends of the second gas chromatography column (10) are connected to the seventh port of the second switching valve (6) and the sixth port of the third switching valve (12), respectively, for the first separation of permanent gases in the pre-separation product after the first gas chromatography column (5) is pre-separated, to obtain a first separation product including permanent gases; The two ends of the third gas chromatography column (11) are respectively connected to the first port of the third switching valve (12) and the second port of the first switching valve (27), and are used to perform a second separation of the permanent gas in the first separation product after the first separation of the second gas chromatography column (10) to obtain a second separation product including the permanent gas. Optionally, the first separation device also has a third carrier gas inlet (13), which is connected to the second port of the third switching valve (12); Optionally, the first separation device further includes a second venting needle valve (14), one end of which is connected to the third port of the third switching valve (12); Optionally, the first separation device further includes a third venting needle valve (15), one end of which is connected to the fifth port of the third switching valve (12).

5. The detection system for the decomposition products of perfluoroisobutyronitrile-nitrogen mixed gas according to any one of claims 1-4, characterized in that, The second sample injection device also includes a fourth switching valve (29), a second pressure sensor (19), and a second sample dispensing component (31); The two ends of the second preprocessor (17) are respectively connected to one end of the second sample injection component (16) and the second port of the fourth switching valve (29); The two ends of the second metering tube (18) are respectively connected to the first port and the fourth port of the fourth switching valve (29); The two ends of the second pressure sensor (19) are respectively connected to the third port of the fourth switching valve (29) and one end of the second sample outlet component (31); Optionally, the second injection device also has a fourth carrier gas inlet (20), which is connected to the fifth port of the fourth switching valve (29); Optionally, the second injection device also has a fifth carrier gas inlet (21), which is connected to the eighth port of the fourth switching valve (29); Optionally, the second injection device further includes a fourth venting needle valve (22), one end of which is connected to the ninth port of the fourth switching valve (29).

6. The detection system for the decomposition products of perfluoroisobutyronitrile-nitrogen mixed gas according to claim 5, characterized in that, The second separation device includes a fourth gas chromatography column (23) and a fifth gas chromatography column (24); The two ends of the fourth gas chromatographic column (23) are connected to the tenth port and the sixth port of the fourth switching valve (29) respectively, and are used to pre-separate C4F7N and CO2 in the gas sample in the second quantitative tube (18) to obtain a pre-separated product including CO2. The two ends of the fifth gas chromatography column (24) are connected to the seventh port of the fourth switching valve (29) and the sixth port of the first switching valve (27), respectively, to separate CO2 in the pre-separated product after the pre-separation of the fourth gas chromatography column (23) to obtain a separated product including CO2.

7. The detection system for the decomposition products of perfluoroisobutyronitrile-nitrogen mixed gas according to any one of claims 1-4, 6, is characterized in that, It also includes a fifth venting needle valve (25) and a sixth venting needle valve (26), one end of the fifth venting needle valve (25) being connected to the fifth port of the first switching valve (27), and one end of the sixth venting needle valve (26) being connected to the third port of the first switching valve (27).

8. A method for detecting the decomposition products of a perfluoroisobutyronitrile-nitrogen mixed gas, characterized in that, Includes the following steps: Gas samples are fed into the first and second injection devices, respectively. In the first injection device, the gas sample is pre-processed by the first preprocessor and then stored in the first quantitative tube; In the second injection device, the gas sample is pre-processed by the second preprocessor and then stored in the second quantitative tube; The gas sample stored in the first quantitative tube is loaded into the first separation device to separate the permanent gases in the gas sample in the first quantitative tube. The permanent gases separated by the first separation device are loaded into the detection device to detect the content of each permanent gas in the gas sample. The gas sample stored in the second quantitative tube is loaded into the second separation device to separate CO2 from the gas sample in the second quantitative tube. The CO2 separated by the second separation device is loaded into the detection device to detect the CO2 content in the gas sample.

9. The method for detecting the decomposition products of perfluoroisobutyronitrile-nitrogen mixed gas according to claim 8, characterized in that, The detection device includes a plasma emission detector.

10. The method for detecting the decomposition products of perfluoroisobutyronitrile-nitrogen mixed gas according to claim 8 or 9, characterized in that, It meets at least one of the following characteristics: (1) Loading the gas sample stored in the first quantitative tube into the first separation device, and separating the permanent gas in the gas sample in the first quantitative tube specifically includes the following steps: The gas sample in the first quantitative tube is loaded into the first chromatographic column by the carrier gas. The C4F7N and permanent gas in the gas sample in the first quantitative tube (3) are pre-separated to obtain a pre-separated product including permanent gas. The permanent gas in the pre-separated product is sequentially loaded into the second gas chromatographic column and the third gas chromatographic column for separation. Optionally, the first chromatographic column comprises a polymer porous packed column; Optionally, the second gas chromatography column includes a 5A molecular sieve column; Optionally, the third gas chromatography column includes a 5A molecular sieve column; (2) Loading the gas sample stored in the second quantitative tube into the second separation device, and separating CO2 from the gas sample in the second quantitative tube specifically includes the following steps: The gas sample in the second quantitative tube is loaded into the fourth gas chromatographic column by a carrier gas. The C4F7N and permanent gases in the gas sample in the second quantitative tube are pre-separated to obtain a pre-separated product including CO2. The CO2 in the pre-separated product is loaded into the fifth gas chromatographic column for separation. Optionally, the fourth gas chromatography column comprises a polymer porous packed column; Optionally, the fifth gas chromatography column includes a polymer chromatography column; (3) The method for detecting the decomposition products of the perfluoroisobutyronitrile-nitrogen mixed gas uses the detection system for the decomposition products of the perfluoroisobutyronitrile-nitrogen mixed gas as described in any one of claims 1-8; (4) The permanent gas includes at least one of H2, O2, CH4 and CO.

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