Optical fiber sensing system for simultaneously measuring gas pressure and decomposition product of gas insulation equipment

Abstract

The invention discloses an optical fiber sensing system for simultaneously measuring gas pressure and decomposition products of gas insulation equipment, belongs to the technical field of optical fiber sensing and measurement for operation and maintenance of power transmission and transformation equipment, and solves the problems that an optical fiber photoacoustic gas sensing system in the prior art is easily influenced by gas pressure and a photoacoustic system is complex in structure. According to the invention, an optical fiber cantilever beam in the prior art is replaced by the organic diaphragm, and the gas pressure and the concentration of an insulating gas decomposition product are detected by using the average optical path difference and the dynamic optical path difference generated by deformation of the organic diaphragm due to different gas pressures on two sides. Monitoring of the gas pressure of the insulating gas and measurement of the concentration of decomposition products of the insulating gas are achieved, the organic diaphragm can adapt to different structural deformations and can quickly respond to dynamic pressure waves, the production cost is low, excitation light and detection light are transmitted at the same time through the single multimode optical fiber, optical fiber arrangement is simplified, the complexity of the system is reduced, and the system reliability is improved. And the signal quality and the system stability are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of optical fiber sensing and measurement for operation and maintenance of power transmission and transformation equipment, and relates to an optical fiber sensing system for simultaneously measuring gas pressure and decomposition products of gas-insulated equipment. Background Art

[0002] Filling gas-insulated equipment with high-pressure SF6 gas with excellent insulation and arc-extinguishing properties can greatly reduce the size of electrical equipment and improve its transmission capacity. It is of great significance to determine whether a fault has occurred inside the gas-insulated equipment by detecting the decomposition products of SF6. When overheating or discharge failure occurs inside the gas-insulated equipment, SF6 gas will decompose to produce a variety of highly toxic and corrosive decomposition derivatives. By detecting the change in the concentration of the decomposition derivatives, it can be reflected whether there is an arc or spark discharge inside the equipment. However, the content of decomposition derivatives produced by the initial fault inside the equipment is low, which puts high demands on the sensitivity of the gas detection device.

[0003] Photoacoustic spectroscopy is gradually being applied to the field of gas-insulated equipment due to its high sensitivity, good selectivity and maintenance-free characteristics. However, the detection of decomposition products using photoacoustic spectroscopy is usually carried out under normal pressure. In practical applications, the performance of the photoacoustic system is easily affected by the gas pressure factor. In gas-insulated equipment, SF6 gas leakage will cause the internal air pressure of the equipment to drop, affecting the normal operation of the equipment. In the high-pressure gas chamber, the air pressure range is usually maintained between 2atm and 4atm. The change of the internal air pressure of the equipment will affect the detection accuracy of the photoacoustic gas sensor. Therefore, in order to detect SF6 gas leakage faults in time and perform repairs, it is particularly important to monitor the air pressure inside the gas-insulated equipment. However, when using electrical pressure sensors to monitor the air pressure inside high-voltage gas-insulated equipment, there will be problems with electromagnetic field interference, which will affect the accuracy of the monitoring results. In addition, the use of electrical pressure sensors will increase the complexity of the equipment and have high production costs.

[0004] The basic principle of fiber optic photoacoustic sensing technology based on cantilever beam is to use the fiber optic cantilever beam to detect the acoustic wave signal generated by the gas absorbing the excitation light. It has many advantages such as high sensitivity, anti-electromagnetic interference, long-distance measurement, distributed sensing and can be used in harsh environments. et al. Pressure-compensated fiber-optic photoacoustic sensor for trace SO2analysis in gas insulation equipment[J]. Analytical Chemistry, 2024, 96, 27, 10995–11001. A pressure-compensated high-sensitivity fiber-optic photoacoustic sensor is reported for analyzing the decomposition component SO2 in high-voltage gas insulation equipment. In a high-pressure environment, the excited photoacoustic signal value is enhanced, compensating for the loss of cantilever beam sensitivity. In addition, the real-time gas pressure is judged by the linear relationship between the static length of the Fabry-Perot cavity (Fabry-Perot cavity) and the gas pressure, thereby replacing the gas pressure sensor, so that the proposed fiber-optic photoacoustic sensor has the inherent advantages of being non-charged and resistant to electromagnetic interference. Although the system has a pressure compensation effect, which improves its detection performance in a high-pressure environment, it can achieve a higher gas detection sensitivity and simultaneously detect the gas pressure. However, this system requires two optical fibers to transmit the excitation light and the detection light respectively, and the required cantilever beam structure is relatively delicate and complex, requiring comprehensive consideration of multiple factors such as material selection, processing technology and dynamic characteristics, and the production cost is relatively high. Summary of the invention

[0005] The technical solution of the present invention is used to solve the problems in the prior art that the optical fiber photoacoustic gas sensing system is easily affected by air pressure and the photoacoustic system has a complex structure.

[0006] The present invention solves the above technical problems through the following technical solutions: A fiber optic sensing system for simultaneously measuring gas pressure and decomposition products of gas-insulated equipment comprises: an excitation light source (10), a wavelength division multiplexer (11), a fiber optic photoacoustic sensor probe (12), a superluminescent diode (13), a fiber optic circulator (14), a high-speed spectrometer (15), a field programmable gate array (16), and a computer (17); the output end of the excitation light source (10) is connected to an input end of the wavelength division multiplexer (11), the output end of the superluminescent diode (13) is connected to a first port of the fiber optic circulator (14), the second port of the fiber optic circulator (14) is connected to another input end of the wavelength division multiplexer (11), the output end of the wavelength division multiplexer (11) is connected to the input end of the fiber optic photoacoustic sensor probe (12), the third port of the fiber optic circulator (14) is connected to the input end of the high-speed spectrometer (15), the output end of the high-speed spectrometer (15) is connected to the input end of the field programmable gate array (16), and the output end of the field programmable gate array (16) is connected to the computer (17); The optical fiber photoacoustic sensor probe (12) comprises: a housing (121), an organic membrane (122), a multimode optical fiber (123), a photoacoustic cavity (124), an optical fiber installation cavity (125), and a diffusion hole (126); the organic membrane (122) is arranged at a middle position inside the housing (121) to divide the internal space of the housing (121) into two parts: the photoacoustic cavity (124) and the optical fiber installation cavity (125); the outer side of the photoacoustic cavity (124) is provided with a diffusion hole (126); the multimode optical fiber (123) passes through the diffusion hole (126) One end of the housing (121) enters the optical fiber installation cavity (125), the multimode optical fiber (123) is perpendicular to the organic film (122), there is a distance between the end face of the multimode optical fiber (123) and the organic film (122), and a Fabry-Perot cavity is formed between the end face of the multimode optical fiber (123) and the organic film (122); the photoacoustic excitation light emitted by the excitation light source (10) is incident on the optical fiber photoacoustic sensor probe (12) through the wavelength division multiplexer (11), and the detection light emitted by the superluminescent diode (13) is incident on the optical fiber photoacoustic sensor probe (12) through the optical fiber circulator (14) and a wavelength division multiplexer (11) are transmitted to the optical fiber photoacoustic sensor probe (12), wherein the wavelength division multiplexer (11) is used to simultaneously input the photoacoustic excitation light emitted by the excitation light source (10) and the detection light emitted by the superluminescent diode (13) into the optical fiber photoacoustic sensor probe (12) through the multimode optical fiber (123), and the photoacoustic excitation light is incident on the photoacoustic cavity (124) through the organic film (122). When the insulating gas inside the gas chamber of the gas insulation equipment enters the photoacoustic cavity (124) through the diffusion hole (126), the insulating The gas absorbs the energy of the photoacoustic excitation light, thereby generating a photoacoustic pressure wave, which pushes the organic membrane (122) to deform, and the deformation of the organic membrane (122) causes the cavity length of the Fabry-Perot cavity to change as the gas pressure in the gas insulation device changes. The high-speed spectrometer (15) receives the interference spectrum of the reflected detection light, and the interference spectrum is sent to the field programmable gate array (16) for processing, and then sent to the computer (17) to achieve simultaneous measurement of the insulating gas pressure and the decomposition product concentration through the average optical path difference and dynamic optical path difference of the Fabry-Perot cavity; Preferably, the central wavelength of the superluminescent diode (13) is 1550 nm.

[0007] Preferably, the core diameter of the multimode optical fiber (123) is 1 mm.

[0008] Furthermore, the method for simultaneously measuring the insulating gas pressure and the decomposition product concentration by using the average optical path difference and the dynamic optical path difference of the Fabry-Perot cavity is as follows: 1) The average optical path difference and dynamic optical path difference of the Fabry-Perot cavity are calculated by the interference spectrum of the detection light. The specific formula is as follows: The average optical path difference of the Fabry-Perot cavity Calculated by formula (1), formula (1) is the interference spectrum of the fiber Fabry-Perot cavity : (1) In the formula, To detect the interference spectrum of light, and are the intensity and wave number of the detection light, is the contrast of interference intensity, is the average optical path difference of the Fabry-Perot cavity, is the dynamic optical path difference of the Fabry-Perot cavity; 2) The pressure of the insulating gas inside the gas-insulated device is calculated by the relationship between the average optical path difference of the Fabry-Perot cavity and the pressure of the insulating gas. The relationship between the average optical path difference of the Fabry-Perot cavity and the pressure of the insulating gas is as follows: (2) In the formula, is the distance between the organic film (122) and the end face of the multimode optical fiber (123), is the gas refractive index related to the insulating gas pressure; 3) The concentration of the decomposition products of the insulating gas is fitted through the dynamic optical path difference of the Fabry-Perot cavity, that is, the photoacoustic signal value.

[0009] The advantages of the present invention are: The present invention replaces the optical fiber cantilever beam of the prior art with an organic diaphragm, and uses the average optical path difference and dynamic optical path difference generated by the deformation of the organic diaphragm due to the different air pressures on both sides to detect the air pressure and the concentration of the decomposition products of the insulating gas. The technical solution of the present invention realizes the monitoring of the air pressure of the insulating gas and the measurement of the concentration of the decomposition products of the insulating gas without adding an additional electrical air pressure sensor. The present invention uses an organic diaphragm to measure the air pressure, and its advantage is that compared with the cantilever beam, the organic diaphragm has better flexibility and can adapt to different structural deformations; at the same time, the thickness of the organic diaphragm is relatively thin, and it can quickly respond to dynamic pressure waves; in addition, the organic diaphragm material is easier to manufacture than the cantilever beam, and the production cost is lower. The present invention uses a single multimode optical fiber to simultaneously transmit the excitation light and the detection light, which simplifies the optical fiber arrangement and reduces the complexity of the system; at the same time, the use of a single multimode optical fiber reduces the complexity of the optical fiber structure, improves the signal quality and the stability of the system; the present invention has the advantages of simple structure, high sensitivity, and low production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a structural block diagram of an optical fiber sensing system for simultaneously measuring gas pressure and decomposition products of a gas-insulated device according to an embodiment of the present invention; Figure 2It is a schematic diagram of the structure of a fiber optic photoacoustic sensing probe of a fiber optic sensing system for simultaneously measuring gas pressure and decomposition products of a gas-insulated device according to an embodiment of the present invention; Figure 3 is a gas pressure characteristic curve diagram of the average optical path difference of the Fabry-Perot cavity of the optical fiber sensing system in which the gas pressure of the gas-insulated device and the decomposition products are measured simultaneously in an embodiment of the present invention; Figure 4 It is a linear response curve diagram of the optical fiber photoacoustic sensing probe of the optical fiber sensing system for simultaneously measuring the gas pressure and decomposition products of the gas-insulated equipment according to the embodiment of the present invention to the insulating gas to be measured. DETAILED DESCRIPTION

[0011] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0012] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and specific embodiments: Embodiment 1 like Figure 1 As shown, the optical fiber sensing system for measuring the gas pressure and decomposition products of the gas-insulated equipment according to the embodiment of the present invention comprises: an excitation light source 10, a wavelength division multiplexer 11, an optical fiber photoacoustic sensor probe 12, a super luminescent diode 13, an optical fiber circulator 14, a high-speed spectrometer 15, a field programmable gate array 16, and a computer 17; the output end of the excitation light source 10 is connected to an input end of the wavelength division multiplexer 11, the output end of the super luminescent diode 13 is connected to a first port of the optical fiber circulator 14, the second port of the optical fiber circulator 14 is connected to another input end of the wavelength division multiplexer 11, the output end of the wavelength division multiplexer 11 is connected to the input end of the optical fiber photoacoustic sensor probe 12, the third port of the optical fiber circulator 14 is connected to the input end of the high-speed spectrometer 15, the output end of the high-speed spectrometer 15 is connected to the input end of the field programmable gate array 16, and the output end of the field programmable gate array 16 is connected to the computer 17.

[0013] Preferably, the central wavelength of the superluminescent diode 13 is 1550 nm.

[0014] like Figure 2As shown, the fiber optic photoacoustic sensor probe 12 includes: a shell 121, an organic membrane 122, a multimode optical fiber 123, a photoacoustic cavity 124, a fiber installation cavity 125, and a diffusion hole 126; the organic membrane 122 is arranged in the middle position inside the shell 121, dividing the internal space of the shell 121 into two parts: the photoacoustic cavity 124 and the fiber installation cavity 125, and the diffusion hole 126 is opened on the outer side of the photoacoustic cavity 124. The multimode optical fiber 123 passes through one end of the shell 121 and enters the fiber installation cavity 125. The multimode optical fiber 123 is perpendicular to the organic membrane 122, and there is a distance between the end face of the multimode optical fiber 123 and the organic membrane 122, and a Fabry-Perot cavity (FP cavity) is formed between the end face of the multimode optical fiber 123 and the organic membrane 122.

[0015] Preferably, the core diameter of the multimode optical fiber 123 is 1 mm.

[0016] The working process of the optical fiber sensing system for simultaneously measuring the gas pressure and decomposition products of a gas-insulated device according to an embodiment of the present invention is as follows: The photoacoustic excitation light emitted by the excitation light source 10 is incident on the optical fiber photoacoustic sensor probe 12 through the wavelength division multiplexer 11, and the detection light emitted by the superluminescent diode 13 is transmitted to the optical fiber photoacoustic sensor probe 12 through the optical fiber circulator 14 and the wavelength division multiplexer 11. The wavelength division multiplexer 11 is used to simultaneously inject the photoacoustic excitation light emitted by the excitation light source 10 and the detection light emitted by the superluminescent diode 13 into the optical fiber photoacoustic sensor probe 12 through the multimode optical fiber 123, and the photoacoustic excitation light is incident on the optical fiber photoacoustic sensor probe 12 through the organic membrane 122. When the insulating gas enters the photoacoustic cavity 124 through the diffusion hole 126, the insulating gas absorbs the energy of the photoacoustic excitation light, thereby generating a photoacoustic pressure wave. The photoacoustic pressure wave pushes the organic membrane 122 to deform. The deformation of the organic membrane 122 causes the cavity length of the Fabry-Perot cavity to change as the gas pressure in the gas insulation equipment changes. The high-speed spectrometer 15 receives the interference spectrum of the reflected detection light, and the interference spectrum is sent to the field programmable gate array 16 for processing, and then sent to the computer 17 to realize the simultaneous measurement of the insulating gas pressure and the decomposition product concentration through the average optical path difference and dynamic optical path difference of the Fabry-Perot cavity.

[0017] The measurement principle of the optical fiber sensing system for simultaneously measuring the gas pressure and decomposition products of the gas-insulated equipment according to the embodiment of the present invention is as follows: The generation of photoacoustic signal value is a complex photothermal and thermoacoustic energy conversion process, and the change of air pressure will affect the accuracy and reliability of the test results. The present invention uses an organic membrane to replace the cantilever beam, and the gap between the end face of the multimode optical fiber and the plane of the organic membrane constitutes a Fabry-Perot cavity. The reflectivity of the optical fiber end face is much less than 1, which makes the intensity of the reflected light and the phase difference approximately cosine-relationship, and the multi-beam interference is equivalent to double-beam interference. The change of air pressure will change the refractive index of the gas, and then change the average optical path difference of the Fabry-Perot cavity. The average optical path difference of the Fabry-Perot cavity is calculated by formula (1).

[0018] (1) In the formula, To detect the interference spectrum of light, and are the intensity and wave number of the detection light, is the contrast of interference intensity, is the average optical path difference of the Fabry-Perot cavity, is the dynamic optical path difference of the Fabry-Perot cavity.

[0019] The real-time gas pressure inside the gas-insulated device is calculated by using the average optical path difference of the Fabry-Perot cavity obtained by formula (1). The relationship between the average optical path difference of the Fabry-Perot cavity and the gas pressure is expressed as: (2) In the formula, is the distance between the organic film (122) and the end face of the multimode optical fiber (123), is the gas refractive index related to the insulating gas pressure.

[0020] The dynamic optical path difference of the Fabry-Perot cavity, i.e., the photoacoustic signal value, is obtained by equation (1) to fit the concentration of the decomposition products of the insulating gas.

[0021] like Figure 3 As shown, this is the gas pressure characteristic curve of the average optical path difference of the Fabry-Perot cavity. It can be seen from the figure that within the range of 0.1MPa to 0.6MPa, as the gas pressure increases, the average optical path difference of the Fabry-Perot cavity increases, and there is a linear relationship between the average optical path difference and the gas pressure.

[0022] like Figure 4 As shown in the figure, it is a linear response curve of the fiber optic photoacoustic sensor probe to the insulating gas to be measured. It can be seen from the figure that in the range of 5ppm to 40ppm, as the gas concentration increases, the generated photoacoustic signal value increases, and there is an obvious linear relationship between the gas concentration and the photoacoustic signal value (dynamic optical path difference of the Fabry-Perot cavity).

[0023] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An optical fiber sensing system for simultaneously measuring gas pressure and decomposition products of gas-insulated equipment, characterized in that: The output end of the excitation light source (10) is connected to an input end of a wavelength division multiplexer (11), the output end of the superluminescent diode (13) is connected to a first port of an optical fiber circulator (14), the second port of the optical fiber circulator (14) is connected to another input end of the wavelength division multiplexer (11), the output end of the wavelength division multiplexer (11) is connected to the input end of an optical fiber photoacoustic sensor probe (12), the third port of the optical fiber circulator (14) is connected to the input end of a high-speed spectrometer (15), and the output end of the high-speed spectrometer (15) is connected to the input end of a field programmable gate array (16). The optical fiber photoacoustic sensing probe (12) is connected to the housing (121), and the output end of the field programmable gate array (16) is connected to the computer (17); the organic membrane (122) of the optical fiber photoacoustic sensing probe (12) is arranged inside the housing (121), and the internal space of the housing (121) is divided into two parts: a photoacoustic cavity (124) and a fiber installation cavity (125); a diffusion hole (126) is opened on the outside of the photoacoustic cavity (124); the multimode optical fiber (123) passes through one end of the housing (121) and enters the fiber installation cavity (125); and a Fabry-Perot cavity is formed between the end face of the multimode optical fiber (123) and the organic membrane (122).

2. The optical fiber sensing system for simultaneously measuring gas pressure and decomposition products of gas-insulated equipment according to claim 1, characterized in that: The multimode optical fiber (123) is arranged perpendicular to the organic film (122).

3. The optical fiber sensing system for simultaneously measuring gas pressure and decomposition products of gas-insulated equipment according to claim 1, characterized in that: The organic membrane (122) is arranged at a middle position inside the housing (121).

4. The optical fiber sensing system for simultaneously measuring gas pressure and decomposition products of gas-insulated equipment according to claim 1, characterized in that: The photoacoustic excitation light emitted by the excitation light source (10) is incident on the optical fiber photoacoustic sensor probe (12) through the wavelength division multiplexer (11), and the detection light emitted by the superluminescent diode (13) is transmitted to the optical fiber photoacoustic sensor probe (12) through the optical fiber circulator (14) and the wavelength division multiplexer (11). The wavelength division multiplexer (11) is used to simultaneously inject the photoacoustic excitation light emitted by the excitation light source (10) and the detection light emitted by the superluminescent diode (13) into the optical fiber photoacoustic sensor probe (12) through the multimode optical fiber (123). The photoacoustic excitation light is incident on the optical fiber photoacoustic sensor probe (12) through the organic film (122). When the gas-insulated device is gas-insulated, the photoacoustic excitation light is incident on the optical fiber photoacoustic sensor probe (12). When the insulating gas inside the chamber enters the photoacoustic cavity (124) through the diffusion hole (126), the insulating gas absorbs the energy of the photoacoustic excitation light, thereby generating a photoacoustic pressure wave. The photoacoustic pressure wave pushes the organic membrane (122) to deform. The deformation of the organic membrane (122) causes the cavity length of the Fabry-Perot cavity to change as the gas pressure in the gas insulation device changes. The high-speed spectrometer (15) receives the interference spectrum of the reflected detection light, and the interference spectrum is sent to the field programmable gate array (16) for processing, and then sent to the computer (17) to achieve simultaneous measurement of the insulating gas pressure and the concentration of the decomposition product through the average optical path difference and dynamic optical path difference of the Fabry-Perot cavity.

5. The optical fiber sensing system for simultaneously measuring gas pressure and decomposition products of gas-insulated equipment according to claim 4, characterized in that: The method for simultaneously measuring the insulating gas pressure and decomposition product concentration by using the average optical path difference and dynamic optical path difference of the Fabry-Perot cavity is as follows: 1) Calculate the average optical path difference and dynamic optical path difference of the Fabry-Perot cavity through the interference spectrum of the detection light; 2) Calculate the pressure of the insulating gas inside the gas-insulated equipment through the relationship between the average optical path difference of the Fabry-Perot cavity and the pressure of the insulating gas; 3) The concentration of the decomposition products of the insulating gas is fitted through the dynamic optical path difference of the Fabry-Perot cavity, that is, the photoacoustic signal value.

6. The optical fiber sensing system for simultaneously measuring gas pressure and decomposition products of gas-insulated equipment according to claim 5, characterized in that: The formula for calculating the average optical path difference and dynamic optical path difference of the Fabry-Perot cavity by the interference spectrum of the detection light is as follows: （1） In the formula, To detect the interference spectrum of light, and are the intensity and wave number of the detection light, is the contrast of interference intensity, is the average optical path difference of the Fabry-Perot cavity, is the dynamic optical path difference of the Fabry-Perot cavity.

7. The optical fiber sensing system for simultaneously measuring gas pressure and decomposition products of gas-insulated equipment according to claim 5, characterized in that: The relationship between the average optical path difference of the Fabry-Perot cavity and the insulating gas pressure is as follows: （2） In the formula, is the distance between the organic film (122) and the end face of the multimode optical fiber (123), is the gas refractive index related to the insulating gas pressure.

8. The optical fiber sensing system for simultaneously measuring gas pressure and decomposition products of gas-insulated equipment according to claim 1, characterized in that: The central wavelength of the superluminescent diode (13) is 1550 nm.

9. The optical fiber sensing system for simultaneously measuring gas pressure and decomposition products of gas-insulated equipment according to claim 1, characterized in that: The core diameter of the multimode optical fiber (123) is 1 mm.

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