CN114062274A - Optical fiber photoacoustic sensing system and method for detecting dissolved gas in oil - Google Patents
Optical fiber photoacoustic sensing system and method for detecting dissolved gas in oil Download PDFInfo
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- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
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- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/1702—Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids
- G01N2021/1704—Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids in gases
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2201/00—Features of devices classified in G01N21/00
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- G01N2201/088—Using a sensor fibre
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Abstract
The invention discloses an optical fiber photoacoustic sensing system for detecting gas dissolved in oil, which comprises a laser light source, a sensing channel, a detection light source, an optical fiber coupler, a reference channel, a high-speed spectrometer and a signal acquisition and processing module, wherein the sensing channel is provided with a sensing optical fiber, the side surface of the sensing optical fiber is provided with a hole and is immersed in transformer oil, and laser emitted by the laser light source is incident to the sensing optical fiber of the sensing channel; the signal acquisition and processing module acquires a spectrum signal of the high-speed spectrometer, calculates an optical path difference between the reference channel and the sensing channel, obtains the amplitude of an optical acoustic signal in the sensing optical fiber according to the change of the optical path difference, and obtains the concentration of the dissolved gas in the oil according to the corresponding relation between the amplitude of the optical acoustic signal and the concentration of the dissolved gas in the oil; the invention has the advantages that: the anti-interference performance is better, can directly measure oil gas dissolved gas, and the sensing optical fiber who adopts can arrange inside transformer this type of insulating apparatus in.
Description
Technical Field
The invention relates to the technical field of high-voltage electrical equipment online monitoring, in particular to an optical fiber photoacoustic sensing system and method for detecting dissolved gas in oil.
Background
During the operation of the oil-immersed power transformer, faults such as overheating or discharging enable insulating oil molecules to be cracked to generate gases with small molecular characteristics, such as methane, ethane, ethylene, acetylene and the like. In the analysis of these fault-characteristic gases, gas chromatography and photoacoustic spectroscopy techniques are commonly employed. Among them, the photoacoustic spectroscopy is gradually replacing gas chromatography because of its high sensitivity and maintenance-free characteristics.
In 2003, Kelman corporation in England has first developed photoacoustic spectroscopy oil dissolved gas analysis equipment based on blackbody radiation infrared broad spectrum light source, and can perform online monitoring on various characteristic gases in oil. However, the strong electromagnetic environment near the high voltage electrical insulation equipment makes the conventional photoacoustic spectroscopy apparatus susceptible to interference, affecting the stability and reliability of the measurement of the concentration of dissolved gas in the transformer oil. In addition, need utilize the oil pump to draw the oil sample into analytical instrument in, the inside complicated oil circuit pipeline of analytical instrument has brought the potential safety hazard that transformer oil spills over. The optical fiber photoacoustic sensing is a new trace gas detection technology, the basic principle of the optical fiber photoacoustic sensing is to detect photoacoustic pressure wave signals generated by gas absorption by using an optical fiber acoustic wave sensing device, and the optical fiber photoacoustic sensing has the advantages of electromagnetic interference resistance, remote measurement, distributable sensing and the like. The photoacoustic excitation light and the photoacoustic detection light are transmitted by optical fibers, so that the passivity and the miniaturization of the photoacoustic probe are realized. The document Chen Ke, Guo Min, Liu Shuai, et al fiber-optical photoacoustic sensor for remote monitoring of gas micro-leak [ J ] Optics express,2019,27(4): 4648) 4659 reports a miniature fiber optic photoacoustic gas sensor, the laser light is transmitted through the fiber into the photoacoustic probe, and the laser light energy is absorbed by the target gas diffused into the probe to generate a photoacoustic signal. However, the cantilever beam is also very sensitive to the vibration of the transformer, resulting in poor interference rejection. In addition, the sensor cannot directly measure the oil gas dissolved gas, and the metal sensor adopted in the scheme cannot be arranged inside insulating equipment such as a transformer.
Disclosure of Invention
The invention aims to solve the technical problems that the optical fiber photoacoustic sensor in the prior art has poor anti-interference performance, cannot directly measure oil gas dissolved gas, and cannot be arranged in insulating equipment such as a transformer by adopting a metal sensor.
The invention solves the technical problems through the following technical means: an optical fiber photoacoustic sensing system for detecting gas dissolved in oil comprises a laser light source, a sensing channel, a detection light source, an optical fiber coupler, a reference channel, a high-speed spectrometer and a signal acquisition and processing module, wherein the sensing channel is provided with a sensing optical fiber, the side surface of the sensing optical fiber is provided with a hole and is immersed in transformer oil, and laser emitted by the laser light source is incident to the sensing optical fiber of the sensing channel; wide spectrum light emitted by a detection light source is divided into two beams after passing through an optical fiber coupler, wherein one beam of light is incident into a sensing optical fiber through a sensing channel and is incident into a high-speed spectrometer after being reflected; the other beam of light emitted from the optical fiber coupler is reflected after passing through the reference channel and enters the high-speed spectrometer; the signal acquisition and processing module acquires the spectrum signal of the high-speed spectrometer, then calculates the optical path difference between the reference channel and the sensing channel, obtains the amplitude of the photoacoustic signal in the sensing optical fiber according to the change of the optical path difference, and obtains the concentration of the dissolved gas in the oil according to the corresponding relation between the amplitude of the photoacoustic signal and the concentration of the dissolved gas in the oil.
The sensing optical fiber with the hole is directly immersed in transformer oil to directly measure dissolved gas in oil gas, the adopted sensing optical fiber can be placed in insulating equipment such as a transformer, the optical path difference between the reference channel and the sensing channel is calculated, the optical path difference between the two channels can counteract interference signals in the two channels, only photoacoustic signals in the sensing optical fiber are reserved, the amplitude of the photoacoustic signals in the sensing optical fiber is obtained according to the change of the optical path difference, the concentration of the dissolved gas in the oil is obtained according to the corresponding relation between the amplitude of the photoacoustic signals and the concentration of the dissolved gas in the oil, and the whole system is good in anti-interference performance.
Furthermore, the sensing channel comprises a wavelength division multiplexer, a transmission optical fiber and a sensing channel optical fiber reflector, the reference channel comprises a reference optical fiber and a reference channel optical fiber reflector, laser emitted by the laser source sequentially passes through the wavelength division multiplexer and the transmission optical fiber to be incident into the sensing optical fiber, and is reflected by the sensing channel optical fiber reflector to be incident into the sensing optical fiber again; wide spectrum light emitted by a detection light source is divided into two beams after passing through an optical fiber coupler, wherein one beam of light is incident into a sensing optical fiber after passing through a wavelength division multiplexer and a conducting optical fiber in sequence, and then is incident into a high-speed spectrometer after being reflected by a sensing channel optical fiber reflector and passing through the sensing optical fiber, the conducting optical fiber, the wavelength division multiplexer and the optical fiber coupler in sequence; and the other beam of light emitted from the optical fiber coupler is reflected by the reference channel optical fiber reflector after passing through the reference optical fiber, and then is incident to the high-speed spectrometer after passing through the reference optical fiber and the optical fiber coupler.
Further, the laser light source is a near-infrared narrow linewidth tunable semiconductor laser.
Furthermore, the working wavelength range of the reflection port of the wavelength division multiplexer covers the central wavelength of the laser light source, and the working wavelength range of the transmission port of the wavelength division multiplexer covers the emission spectrum range of the detection light source.
Furthermore, the sensing optical fiber is a hollow optical fiber, and the aperture of the hole formed in the side surface is less than 100 nm.
Further, the detection light source is a wide spectrum light source, and the spectrum width is more than 20 nm.
Further, the central wavelength of the detection light source and the central wavelength of the laser light source are different by more than 50 nm.
Further, the optical coupling ratio of the optical fiber coupler is 50: 50.
Further, the operating wavelength range of the high-speed spectrometer is covered by the emission spectrum range of the detection light source.
The invention also provides a method for detecting the optical fiber photoacoustic sensing system for detecting the gas dissolved in the oil, wherein laser emitted by the laser source is incident to the sensing optical fiber of the sensing channel, is incident to the sensing optical fiber again after being reflected, and is used for enhancing photoacoustic signals by utilizing two-way absorption, and the gas to be detected in the sensing optical fiber generates photoacoustic signals after absorbing laser energy so as to enable the length of the sensing optical fiber to generate periodic change; the signal acquisition and processing module acquires the spectrum signal of the high-speed spectrometer, then calculates the optical path difference between the reference channel and the sensing channel, obtains the amplitude of the photoacoustic signal in the sensing optical fiber according to the change of the optical path difference, and obtains the concentration of the dissolved gas in the oil according to the corresponding relation between the amplitude of the photoacoustic signal and the concentration of the dissolved gas in the oil.
The invention has the advantages that:
(1) the sensing optical fiber with the hole is directly immersed in transformer oil to directly measure dissolved gas in oil gas, the adopted sensing optical fiber can be placed in insulating equipment such as a transformer, the optical path difference between the reference channel and the sensing channel is calculated, the optical path difference between the two channels can counteract interference signals in the two channels, only photoacoustic signals in the sensing optical fiber are reserved, the amplitude of the photoacoustic signals in the sensing optical fiber is obtained according to the change of the optical path difference, the concentration of the dissolved gas in the oil is obtained according to the corresponding relation between the amplitude of the photoacoustic signals and the concentration of the dissolved gas in the oil, and the whole system is good in anti-interference performance.
(2) The hollow optical fiber is used as a sensing element and an oil-gas separation element at the same time, and the sensor does not need an additional oil-gas separation membrane.
(3) The invention fully utilizes the characteristics of ultralow conductivity, small volume, long absorption range and long sensing distance of the hollow optical fiber, reduces the volume of the optical fiber photoacoustic sensor and improves the detection sensitivity and the insulation performance.
Drawings
FIG. 1 is a schematic structural diagram of an optical fiber photoacoustic sensing system for detecting dissolved gas in oil according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of an interference spectrum detected by a high-speed spectrometer in an optical fiber photoacoustic sensing system for detecting dissolved gas in oil according to an embodiment of the present invention;
in the figure: 1, a laser light source; 2 a wavelength division multiplexer; 3 a conducting optical fiber; 4, a sensing optical fiber;
5 sensing channel fiber reflector; 6, detecting a light source; 7 a fiber coupler; 8 a reference fiber;
9 a reference channel fiber optic mirror; 10, a high-speed spectrometer; 11 signal collecting and processing module.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1, an optical fiber photoacoustic sensing system for detecting dissolved gas in oil includes a laser light source 1, a wavelength division multiplexer 2, a transmission optical fiber 3, a sensing optical fiber 4, a sensing channel fiber mirror 5, a detection light source 6, an optical fiber coupler 7, a reference optical fiber 8, a reference channel fiber mirror 9, a high-speed spectrometer 10, and a signal acquisition and processing module 11. Laser emitted by a laser source 1 is incident into a sensing optical fiber 4 through a wavelength division multiplexer 2 and a conducting optical fiber 3, a sensing channel optical fiber reflector 5 is connected with the other end of the sensing optical fiber 4, and the laser is reflected by the sensing channel optical fiber reflector 5 and then is incident into the sensing optical fiber 4 again; wide spectrum light emitted by a detection light source 6 is divided into two beams after passing through an optical fiber coupler 7, wherein one beam of light is incident into a sensing optical fiber 4 after passing through a wavelength division multiplexer 2 and a conducting optical fiber 3, and then is incident into a high-speed spectrometer 10 after being reflected by a sensing channel optical fiber reflector 5 and then sequentially passing through the sensing optical fiber 4, the conducting optical fiber 3, the wavelength division multiplexer 2 and the optical fiber coupler 7; the other beam of light emitted from the optical fiber coupler 7 passes through the reference optical fiber 8, is reflected by the reference channel optical fiber reflector 9, and then is incident to the high-speed spectrometer 10 through the reference optical fiber 8 and the optical fiber coupler 7; the signal collecting and processing module 11 collects the spectrum signal of the high-speed spectrometer 10 and then processes the spectrum signal in real time.
Wherein, the laser light source 1 is a near infrared semiconductor laser with the central wavelength of 1653.7nm, and the power is more than 10 mW. The working wavelength range of the reflection port of the wavelength division multiplexer 2 is 1630-. The conducting fiber 3 is a G652 single mode silica fiber. The sensing optical fiber 4 is a hollow optical fiber, and the side surface is provided with micropores with the aperture of 50 nm.
The detection light source 6 is a superluminescent light emitting diode, the central wavelength is 1550nm, and the spectral width is 50 nm. The optical coupling ratio of the fiber coupler 7 is 50: 50. The operating wavelength range of the high-speed spectrometer 10 is 1510-1590 nm. The core of the signal acquisition and processing module 11 is an FPGA chip, the data acquisition rate is 5MHz, and the signal of the high-speed spectrometer 10 is subjected to real-time data acquisition and photoacoustic signal demodulation.
Dissolved gas in the oil is diffused into the hollow sensing optical fiber 4 through the micropores, laser and probe light are simultaneously incident into the sensing optical fiber 4, and a photoacoustic signal generated in the sensing optical fiber 4 is detected by using an optical fiber Michelson interference method. The detailed process is as follows: firstly, dissolved gas in transformer oil diffuses into the hollow sensing optical fiber 4 through the micropores; laser emitted by a laser source 1 enters a public port from a reflection port of a wavelength division multiplexer 2 and then is incident into a sensing optical fiber 4 through a conducting optical fiber 3, a sensing channel optical fiber reflector 5 is connected with the other end of the sensing optical fiber 4, the laser is reflected by the sensing channel optical fiber reflector 5 and then is incident into the sensing optical fiber 4 again, and the photoacoustic signal is enhanced by double-pass absorption, so that the measurement precision is improved; the gas to be measured in the sensing optical fiber 4 generates a photoacoustic signal after absorbing laser energy, so that the length of the sensing optical fiber 4 generates periodic change.
Then, the photoacoustic signal is detected by an optical fiber Michelson interferometer composed of a sensing optical fiber 4, a sensing channel optical fiber reflector 5, a reference channel optical fiber reflector 9, a reference optical fiber 8 and an optical fiber coupler 7; wide spectrum light emitted by a detection light source 6 is divided into two beams after passing through an optical fiber coupler 7, wherein one beam of light enters a sensing optical fiber 4 after passing through a wavelength division multiplexer 2 and a conducting optical fiber 3, and then enters a high-speed spectrometer 10 after being reflected by an optical fiber reflector 5 and sequentially passing through the sensing optical fiber 4, the conducting optical fiber 3, the wavelength division multiplexer 2 and the optical fiber coupler 7; another beam of light emitted from the optical fiber coupler 7 passes through the reference optical fiber 8, is reflected by the reference channel optical fiber reflector 9, and then passes through the reference optical fiber 8 and the optical fiber coupler 7 to enter the high-speed spectrometer 10, and fig. 2 is the interference spectrum detected by the high-speed spectrometer.
Finally, the signal collecting and processing module 11 collects the interference spectrum signal of the high-speed spectrometer 10 and then dynamically demodulates the signal, calculates the optical path difference between the reference channel (the wavelength division multiplexer 2, the transmission fiber 3, the sensing fiber 4 and the sensing channel fiber reflector 5) and the sensing channel (the reference fiber 8 and the reference channel fiber reflector 9), normally the optical path difference should be fixed, but since the gas to be measured in the sensing fiber 4 generates photoacoustic signals after absorbing laser energy to cause the length of the sensing fiber 4 to change periodically, therefore, the optical path difference can be changed, the amplitude of the photoacoustic signal in the sensing optical fiber 4 can be obtained according to the change of the optical path difference, a calibration coefficient is arranged between the amplitude of the photoacoustic signal and the concentration of the dissolved gas in the oil, namely, the amplitude of the photoacoustic signal has a corresponding relation with the concentration of the dissolved gas in the oil, and obtaining the concentration of the dissolved gas in the oil according to the corresponding relation between the amplitude of the photoacoustic signal and the concentration of the dissolved gas in the oil.
The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (10)
1. An optical fiber photoacoustic sensing system for detecting gas dissolved in oil is characterized by comprising a laser light source, a sensing channel, a detection light source, an optical fiber coupler, a reference channel, a high-speed spectrometer and a signal acquisition and processing module, wherein the sensing channel is provided with a sensing optical fiber, the side surface of the sensing optical fiber is provided with a hole and is immersed in transformer oil, and laser emitted by the laser light source is incident to the sensing optical fiber of the sensing channel; wide spectrum light emitted by a detection light source is divided into two beams after passing through an optical fiber coupler, wherein one beam of light is incident into a sensing optical fiber through a sensing channel and is incident into a high-speed spectrometer after being reflected; the other beam of light emitted from the optical fiber coupler is reflected after passing through the reference channel and enters the high-speed spectrometer; the signal acquisition and processing module acquires the spectrum signal of the high-speed spectrometer, then calculates the optical path difference between the reference channel and the sensing channel, obtains the amplitude of the photoacoustic signal in the sensing optical fiber according to the change of the optical path difference, and obtains the concentration of the dissolved gas in the oil according to the corresponding relation between the amplitude of the photoacoustic signal and the concentration of the dissolved gas in the oil.
2. The optical fiber photoacoustic sensing system for detecting dissolved gas in oil according to claim 1, wherein the sensing channel comprises a wavelength division multiplexer, a transmission optical fiber and a sensing channel optical fiber reflector, the reference channel comprises a reference optical fiber and a reference channel optical fiber reflector, the laser emitted by the laser source sequentially passes through the wavelength division multiplexer and the transmission optical fiber to be incident into the sensing optical fiber, and is reflected by the sensing channel optical fiber reflector to be incident into the sensing optical fiber again; wide spectrum light emitted by a detection light source is divided into two beams after passing through an optical fiber coupler, wherein one beam of light is incident into a sensing optical fiber after passing through a wavelength division multiplexer and a conducting optical fiber in sequence, and then is incident into a high-speed spectrometer after being reflected by a sensing channel optical fiber reflector and passing through the sensing optical fiber, the conducting optical fiber, the wavelength division multiplexer and the optical fiber coupler in sequence; and the other beam of light emitted from the optical fiber coupler is reflected by the reference channel optical fiber reflector after passing through the reference optical fiber, and then is incident to the high-speed spectrometer after passing through the reference optical fiber and the optical fiber coupler.
3. The fiber optic photoacoustic sensing system for the detection of dissolved gases in oil of claim 1, wherein the laser light source is a near-infrared narrow linewidth tunable semiconductor laser.
4. The fiber optic photoacoustic sensing system for the detection of dissolved gases in oil of claim 2, wherein the wavelength division multiplexer has a reflection port with an operating wavelength range covering the center wavelength of the laser light source and a transmission port with an operating wavelength range covering the emission spectrum of the probe light source.
5. The fiber optic photoacoustic sensing system for the detection of dissolved gases in oil of claim 1, wherein the sensing fiber is a hollow fiber with a hole opened in the side surface with a diameter of less than 100 nm.
6. The fiber optic photoacoustic sensing system for the detection of dissolved gases in oil of claim 1, wherein the probe light source is a broad spectrum light source with a spectral width greater than 20 nm.
7. The fiber optic photoacoustic sensing system for the detection of dissolved gases in oil of claim 1, wherein the center wavelength of the probe light source and the center wavelength of the laser light source differ by more than 50 nm.
8. The fiber optic photoacoustic sensing system for the detection of dissolved gases in oil of claim 1, wherein the optical coupling ratio of the fiber optic coupler is 50: 50.
9. The fiber optic photoacoustic sensing system for the detection of dissolved gases in oil of claim 1, wherein the operating wavelength range of the high speed spectrometer is covered by the emission spectral range of the probe light source.
10. The method for the fiber optic photoacoustic sensing system for detecting the dissolved gas in the oil according to any one of claims 1 to 9, wherein the laser emitted from the laser source is incident to the sensing fiber of the sensing channel, reflected and then incident to the sensing fiber again, the photoacoustic signal is enhanced by using two-way absorption, and the gas to be detected in the sensing fiber absorbs the laser energy to generate the photoacoustic signal, so that the length of the sensing fiber changes periodically; the signal acquisition and processing module acquires the spectrum signal of the high-speed spectrometer, then calculates the optical path difference between the reference channel and the sensing channel, obtains the amplitude of the photoacoustic signal in the sensing optical fiber according to the change of the optical path difference, and obtains the concentration of the dissolved gas in the oil according to the corresponding relation between the amplitude of the photoacoustic signal and the concentration of the dissolved gas in the oil.
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