CN111239100A - Gas detection device in transformer oil - Google Patents
Gas detection device in transformer oil Download PDFInfo
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- CN111239100A CN111239100A CN202010106127.7A CN202010106127A CN111239100A CN 111239100 A CN111239100 A CN 111239100A CN 202010106127 A CN202010106127 A CN 202010106127A CN 111239100 A CN111239100 A CN 111239100A
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- 238000001514 detection method Methods 0.000 title claims abstract description 37
- 238000001069 Raman spectroscopy Methods 0.000 claims abstract description 37
- 238000001228 spectrum Methods 0.000 claims abstract description 13
- 230000010287 polarization Effects 0.000 claims description 60
- 230000005540 biological transmission Effects 0.000 claims description 10
- 238000001914 filtration Methods 0.000 claims description 5
- 230000002708 enhancing effect Effects 0.000 claims description 3
- 239000000835 fiber Substances 0.000 claims description 3
- 230000003287 optical effect Effects 0.000 claims description 3
- 230000003595 spectral effect Effects 0.000 claims description 2
- 230000005611 electricity Effects 0.000 abstract description 2
- 238000011065 in-situ storage Methods 0.000 abstract description 2
- 239000007789 gas Substances 0.000 description 66
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 9
- 229910002092 carbon dioxide Inorganic materials 0.000 description 5
- 239000001569 carbon dioxide Substances 0.000 description 4
- 238000012544 monitoring process Methods 0.000 description 4
- 238000001237 Raman spectrum Methods 0.000 description 3
- 230000009471 action Effects 0.000 description 3
- 230000032683 aging Effects 0.000 description 3
- 238000000034 method Methods 0.000 description 3
- 230000035945 sensitivity Effects 0.000 description 3
- 238000004566 IR spectroscopy Methods 0.000 description 1
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- 230000008033 biological extinction Effects 0.000 description 1
- 230000033228 biological regulation Effects 0.000 description 1
- 230000000903 blocking effect Effects 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000006012 detection of carbon dioxide Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000004817 gas chromatography Methods 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 238000009413 insulation Methods 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 238000004949 mass spectrometry Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000004867 photoacoustic spectroscopy Methods 0.000 description 1
- 230000000750 progressive effect Effects 0.000 description 1
- 238000002310 reflectometry Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000002834 transmittance Methods 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
- G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
- G01N21/65—Raman scattering
Abstract
A gas detection device in transformer oil comprises a laser unit, an acoustoelectric combined modulation unit, a gas chamber unit, a PDH frequency locking unit and a spectrum acquisition unit. The laser unit is used for providing a light source required by detection; the sound and electricity combined modulation unit is used for modulating the laser generated by the laser unit so as to realize the frequency locking of the resonant cavity; the gas chamber unit is used for placing the FP resonant cavity unit and filling gas to be detected, wherein the FP resonant cavity is used for improving the intensity of Raman scattering light and realizing high-sensitivity Raman detection of the gas dissolved in the transformer oil; the PDH frequency locking unit is used for adjusting the cavity length of the FP resonant cavity so as to realize the frequency locking of the resonant cavity; the spectrum acquisition unit is used for acquiring and detecting Raman scattering light. The invention can realize the in-situ detection of the fault gas in the transformer oil, enhance the Raman scattering light by the acoustoelectric combined modulation frequency, improve the Raman scattering intensity of trace gas and realize the high-sensitivity detection of the dissolved gas in the transformer oil.
Description
Technical Field
The application relates to the technical field of gas detection, in particular to a gas detection device in transformer oil.
Background
The power transformer undertakes the tasks of voltage conversion, electric energy distribution and the like in the power system, is the most important pivotal equipment in the power system, and the operation reliability of the power transformer is related to the safety and the stability of the power system. Once a power transformer fails during operation, the power transformer is damaged or even scrapped, and a large-area power failure accident can be caused, so that huge economic loss is caused. During the fault and aging process of the oil-immersed power transformer, the oil-paper insulation system of the oil-immersed power transformer is cracked and generates various characteristic gases (such as H) reflecting the fault type and the aging degree2、CO、CO2、CH4、C2H6、C2H4、C2H2Etc.) these characteristic gases are dissolved in the insulating oil. Therefore, monitoring dissolved gas in oil is one of the most convenient and effective methods for determining early latent faults of the oil-immersed power transformer.
For detecting dissolved gas in transformer oil, gas detection methods such as gas chromatography, mass spectrometry, a chemical sensor method, an infrared absorption spectrometry, a photoacoustic spectrometry and the like are commonly used at present, but the methods have the problems of easy aging of a chromatographic column, cross sensitivity of mixed gas, low stability and the like, in-situ detection of the gas in the oil cannot be realized, and the long-term stable on-line monitoring requirement of electrical equipment cannot be met. In view of the above problems, raman spectroscopy is generally adopted to detect the dissolved gas in the transformer oil at present, but the detection mode is limited by extremely low raman scattering intensity of the gas, so that the minimum detection concentration of the gas cannot meet the actual requirement.
Therefore, it is desirable to provide a novel device for detecting dissolved gas in transformer oil, so as to realize high-sensitivity detection of dissolved gas in transformer oil.
Disclosure of Invention
The invention provides a gas detection device in transformer oil, aiming at solving the problem of the traditional detection method of dissolved gas in transformer oil.
The embodiment of the invention provides a gas detection device in transformer oil, which comprises:
a laser unit for emitting laser light;
the sound and electricity combined modulation unit comprises a sound and light modulator, is arranged on the light emergent side of the laser unit and is used for performing sound and light modulation on the laser and enhancing the intensity of the laser; the electro-optical modulator is arranged on the light emitting side of the acousto-optical modulator and is used for modulating the phase, the amplitude, the intensity and the polarization state of an optical signal output by the acousto-optical modulator;
the gas chamber unit is arranged on the light emitting side of the acoustoelectric combined modulation unit and used for placing the FP resonant cavity and filling gas to be detected;
the FP resonant cavity consists of a first high reflecting mirror and a second high reflecting mirror and is used for improving the power of laser entering the cavity, and the laser in the FP resonant cavity penetrates through the gas to be detected and enables the gas to be detected to generate Raman scattering light;
the PDH frequency locking unit is used for adjusting the cavity length of the FP resonant cavity according to the laser signal fed back by the FP resonant cavity;
and the spectrum acquisition unit is used for acquiring and detecting the Raman scattering light emitted by the FP resonant cavity.
Further, the laser unit includes:
a laser for emitting laser light;
the collimating mirror is arranged on the light-emitting side of the laser and is used for collimating the laser into parallel light;
and the band-pass filter mirror is arranged on the light-emitting side of the collimating mirror and used for filtering stray light so as to reduce spectral noise.
Further, the acoustoelectric joint modulation unit further includes:
the first half-wave plate is arranged on the light-emitting side of the band-pass filter and used for adjusting the polarization direction of the laser emitted by the laser unit;
the first polarization beam splitter is arranged on the light emergent side of the first half-wave plate and used for splitting the laser to form two orthogonal beams of laser, wherein one beam of laser enters the acousto-optic modulator after transmitting through the first polarization beam splitter, and the other beam of laser enters the second half-wave plate;
the first quarter-wave plate is arranged on the light emitting side of the acousto-optic modulator and used for adjusting the polarization state of the laser;
the third reflector is arranged on the light outgoing side of the first quarter wave plate and used for reflecting the laser light, so that the laser light passes through the first quarter wave plate and the acousto-optic modulator again and then reaches the second half wave plate through the first polarization beam splitter;
and the polaroid is arranged between the second half-wave plate and the electro-optical modulator and used for improving the polarization of the laser.
Further, the air chamber unit further comprises an air chamber, and the air chamber is provided with:
the first window mirror is arranged on the laser emitting side of the acoustoelectric combined modulation unit and used for enabling the laser to enter and exit the air chamber;
the second window mirror is arranged on one side of the spectrum acquisition unit and is used for collecting the Raman scattered light;
the airtight data interface is used for enabling a negative feedback control signal output by the PDH frequency locking unit to enter the air chamber;
and the air inlet and the air outlet are used for the gas to be detected to enter and exit the air chamber.
Further, the PDH frequency locking unit includes:
the second polarization beam splitter is arranged on the light emergent side of the electro-optic modulator and used for splitting the laser to form two orthogonal beams of laser, wherein one beam of laser enters the second quarter wave plate after transmitting through the second polarization beam splitter, and the other beam of laser enters the photoelectric detector;
the second quarter-wave plate is arranged between the second polarization beam splitter and the gas chamber unit and used for adjusting the polarization state of the laser;
the photoelectric detector is used for detecting the laser intensity fed back by the FP resonant cavity and outputting a laser transmission signal of the FP resonant cavity;
the PDH frequency locker receives the FP resonant cavity laser transmission signal, performs frequency mixing comparison on the laser frequency emitted by the laser and the FP resonant cavity laser transmission signal, and outputs the negative feedback control signal;
and the piezoelectric displacer is connected with the first high-reflection mirror or the second high-reflection mirror and is used for driving the first high-reflection mirror or the second high-reflection mirror to move according to the negative feedback control signal.
Further, the spectrum collection unit includes:
the high-pass filter mirror is arranged on one side of the gas chamber and is used for filtering stray light signals in the Raman scattering light so as to improve the signal-to-noise ratio of the Raman scattering light;
the collecting lens is arranged on the light outlet side of the high-pass filter mirror and used for focusing the gas Raman scattering light and improving the collecting efficiency of the gas Raman scattering light;
and the spectrometer and the CCD are arranged on the light emergent side of the collecting lens and are used for collecting the gas Raman scattering light.
Furthermore, the working wavelength of the acousto-optic modulator is 1064nm, the central frequency is 25MHz, and the bandwidth is 1 MHz.
Further, the working wavelength of the electro-optical modulator is 1064nm, and the modulation frequency is 12.5 MHz.
Further, the first high-reflection mirror and the second high-reflection mirror are both plano-concave mirrors, and the curvature radius is 1 m.
Further, the laser is a fiber laser.
Based on the above embodiments, it can be seen that the gas detection device for transformer oil provided by the embodiments of the present invention. The device carries out acousto-optic modulation to laser through the acousto-optic modulator, and the electro-optic modulator carries out phase, amplitude, intensity and polarization state's modulation to the light signal to and PDH frequency locking unit is to the regulation of FP resonant cavity chamber length, has realized the matching of incident laser and the laser in the FP resonant cavity, and laser after the matching forms multibeam constructive interference in the FP resonant cavity, improves intracavity laser power, and then has improved the raman scattering signal intensity of trace gas, realizes that the dissolved gas high sensitivity detects in the transformer oil.
Drawings
In order to more clearly explain the technical solution of the present application, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious to those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a diagram of a gas detection device for transformer oil according to an embodiment of the present invention;
fig. 2 is a relative raman intensity graph of carbon dioxide dissolved in transformer oil according to an embodiment of the present invention.
FIG. 1 illustrates by reference numerals:
1-laser unit 11-laser
12-collimator 13-first mirror
14-second mirror 15-band-pass filter mirror
2-acoustoelectric combined modulation unit 21-first half wave plate
22-first polarizing beam splitter 23-acousto-optic modulator
24-first quarter-wave plate 25-third mirror
26-fourth mirror 27-fifth mirror
28-sixth mirror 29-second half-wave plate
210-polarizer 211-electro-optic modulator
3-gas cell unit 31-first high-reflection mirror
32-second high-reflection mirror 33-first window mirror
34-second Window mirror 35-hermetic data interface
36-inlet 37-outlet
4-PDH frequency locking unit 41-second polarization beam splitter
42-second quarter-wave plate 43-seventh mirror
44-electro-optical detector 45-PDH frequency locker
46-piezoelectric shifter 5-spectrum acquisition unit
51-high pass filter mirror 52-collecting lens
53-spectrometer and CCD
Detailed Description
In order to make those skilled in the art better understand the technical solutions in the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. It is to be understood that the embodiments described are only a few embodiments of the present application and 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 application.
Fig. 1 shows a gas detection device in transformer oil based on acoustoelectric combined modulation frequency enhanced raman spectroscopy. As shown in fig. 1, the device includes a laser unit 1, an acoustoelectric joint modulation unit 2, a gas chamber unit 3, a PDH frequency locking unit 4, and a spectrum acquisition unit 5. Wherein, the laser unit 1 comprises a laser 11, a collimator 12, a first reflector 13, a second reflector 14 and a band-pass filter 15; the acoustoelectric joint modulation unit 2 comprises a first half wave plate 21, a first polarization beam splitter 22, an acoustooptic modulator 23, a first quarter wave plate 24, a third mirror 25, a fourth mirror 26, a fifth mirror 27, a sixth mirror 28, a second half wave plate 29, a polarizing plate 210 and an electro-optical modulator 211; the gas chamber unit 3 comprises a first high reflection mirror 31, a second high reflection mirror 32, a first window mirror 33, a second window mirror 34, a gas-tight data interface 35, a gas inlet 36 and a gas outlet 37; the PDH frequency locker unit 4 comprises a second polarization beam splitter 41, a second quarter wave plate 42, a seventh mirror 43, an electro-optical detector 44, a PDH frequency locker 45 and a piezoelectric displacer; the spectrum collection unit 5 includes a high-pass filter mirror 51, a collection lens 52, and a spectrometer and CCD 53.
Specifically, the laser unit 1 is used to emit laser light. The laser 11 may be a fiber laser, and emits laser light with wavelength of 1064nm, line width of less than 5KHz, and power of 3.7mW, and is used to provide a light source required for gas raman spectrum detection. Laser that laser 11 sent will disperse laser collimation through collimating mirror 12 and be parallel laser, wherein, the collimating mirror of selecting for use can be plano-convex lens, and the focus is 3.6mm, and diameter 6.35mm, and the facula of laser behind the collimating mirror is 2 mm. The laser collimated by the collimating mirror 12 reaches the band-pass filter 15 through the guidance of the first reflecting mirror 13 and the second reflecting mirror 14, wherein the selected first reflecting mirror 13 and the selected second reflecting mirror 14 can be plane reflecting mirrors, and the diameter of the selected first reflecting mirror 13 and the selected second reflecting mirror 14 is 25.4mm, and the selected first reflecting mirror and the selected second reflecting mirror are used for guiding and adjusting a laser light path. The center wavelength of the band-pass filter 15 is 1064nm, the bandwidth is 10nm, and the diameter of the lens is 25.4mm, so that the band-pass filter is used for blocking 980nm stray light emitted by the laser. The laser enters the acoustoelectric combined modulation unit 2 after passing through the band-pass filter 15. The laser unit 1 emits laser, collimates the laser and filters stray light, and provides a high-quality light source for gas Raman spectrum detection.
And the acoustoelectric combined modulation unit 2 is arranged on the light emitting side of the laser unit 1 and is used for modulating the laser generated by the laser unit 1 so as to realize the frequency locking of the resonant cavity. The laser emitted by the laser unit 1 reaches the acoustoelectric combined modulation unit 2, firstly, the polarization direction of the laser is modulated by the first half-wave plate 21, and the polarization direction of the laser is modulated into the polarization direction which can transmit the laser through the first polarization beam splitter 22 by the first half-wave plate 21; wherein, the working wavelength of the first half wave plate 21 is 1064nm, and the diameter of the lens is 25.4 mm. The laser modulated by the first half-wave plate 21 enters a first polarization beam splitter 22, the working wavelength of the first polarization beam splitter 22 is 1064nm, the shape of the first polarization beam splitter can be a cube, the side length of the first polarization beam splitter can be 30mm, and the first polarization beam splitter is used for splitting the laser to form two orthogonal beams of laser; one of the laser beams is transmitted through the first polarization beam splitter 22 and then enters the acousto-optic modulator 23, and the other laser beam reaches the second half-wave plate 29. The acousto-optic modulator 23 has a working wavelength of 1064nm, a center frequency of 25MHz, and a bandwidth of 1MHz, and is used for performing acousto-optic modulation on laser and enhancing the intensity of the laser. The laser light emitted from the acousto-optic modulator 23 passes through the first quarter wave plate 24 to reach the third mirror 25, and is reflected by the third mirror 25 so that the laser light passes through the first quarter wave plate 24 and the acousto-optic modulator 23 again, and then passes through the first polarization beam splitter 22 to reach the second half wave plate 29. The working wavelength of the first quarter-wave plate 24 is 1064nm, the diameter of the lens is 25.4mm, and the first quarter-wave plate is used for adjusting the polarization state of the laser; the third reflector 25 has a working wavelength of 1064nm and a lens diameter of 25.4mm, and is used for reflecting the laser light so that the laser light passes through the first quarter-wave plate 24 and the acousto-optic modulator 23 again. The laser passes through the acousto-optic modulator 23 twice, so that the acousto-optic modulator 23 is used for acousto-optic modulation twice, the use amount of elements is saved, and the modulation effect on the laser is enhanced; the laser passing through the first quarter-wave plate 24 twice changes the polarization direction of the laser twice, and the laser with the changed polarization direction can only change the transmission direction to reach the second half-wave plate 29 when passing through the first polarization beam splitter 21 again, but cannot transmit through the first polarization beam splitter 21 and return to the laser unit 1, so that the influence of the laser reflection on the laser emitted by the laser 11 is avoided. In addition, a fourth mirror 26, a fifth mirror 27 and a sixth mirror 28 are disposed between the first polarization beam splitter 22 and the second half-wave plate 29, the operating wavelength is 1064nm, the diameter of the mirror is 25.4mm, and the mirror is used for guiding the laser light, and the optical path can be finely adjusted by a plurality of mirrors. The second half-wave plate 29 has a working wavelength of 1064nm and a lens diameter of 25.4mm and is used to modulate the polarization direction of the laser again so that the exiting laser can better match the polarizer 210. The laser is modulated by the second half-wave plate 29 and reaches the matching polarizing plate 210, the working wavelength of the polarizing plate 210 is 1064nm, the extinction ratio is greater than 10000, and the diameter of the lens is 25.4mm, so that the polarization of the laser is further improved. After passing through the polarizing plate 210, the laser light reaches the electro-optical modulator 211, and the used electro-optical modulator 211 has an operating wavelength of 1064nm and a modulation frequency of 12.5MHz, and is used for modulating the phase, amplitude, intensity and polarization state of the laser light. The laser light emitted from the electro-optical modulator 211 is split by the second polarization beam splitter 41 to form two orthogonal laser beams, the laser light transmitted through the second polarization beam splitter 41 enters the gas chamber unit 3, and the other laser beam enters the PDH frequency locking unit 4.
The acousto-electric combined modulation unit 2 modulates the phase, amplitude and intensity of the laser through the acousto-optical modulator 23 and the electro-optical modulator 211, and modulates the polarization direction, polarization state and the like of the laser through the half-wave plate, the quarter-wave plate and the polarizing plate, so that the frequency locking can be better realized when the laser enters the FP resonant cavity.
The laser light is emitted from the second polarization beam splitter 41 and then passes through the second quarter wave plate 42 before entering the gas chamber unit 3, wherein the working wavelength of the second polarization beam splitter 41 is 1064nm, the shape of the second polarization beam splitter can be a cube, and the side length of the second polarization beam splitter can be 30 mm; the second quarter-wave plate 42 has an operating wavelength of 1064nm and a lens diameter of 25.4mm, and is used for adjusting the polarization state of the laser. Then, the laser light enters the gas chamber through the first window mirror 33 provided in the gas chamber of the gas chamber unit 3. The laser entering the gas chamber first reaches the first high reflecting mirror 31, part of the laser transmits through the first high reflecting mirror 31 and enters the FP resonator formed by the first high reflecting mirror 31 and the second high reflecting mirror 32, and the laser is reflected multiple times in the FP resonator and forms multiple beam constructive interference, thereby increasing the laser power in the cavity. The gas chamber is filled with gas to be detected, and laser in the FP resonant cavity penetrates through the gas to be detected, so that the gas generates Raman scattering light. The gas chamber is also provided with a second window mirror 34 for emitting the Raman scattered light from the gas chamber to the spectrum acquisition unit 5; an airtight data interface 35, which is used for the negative feedback control signal output by the PDH frequency locking unit 4 to enter the air chamber; and the gas inlet 36 and the gas outlet 37 are used for the gas to be measured to enter and exit the gas chamber. The first window mirror 33 and the second window mirror 34 are plane mirrors, each of which has a diameter of 25.4mm and is coated with an antireflection film suitable for laser with a wavelength of 1000 nm-1600 nm to increase the transmittance of the laser. The first high-reflection mirror and the second high-reflection mirror can be plano-concave mirrors, the curvature radius is 1m, the reflectivity of the mirror at the wavelength of 1064nm is 99.98%, and the diameter of the mirror is 25.4 mm; the first high-reflection mirror and the second high-reflection mirror are arranged in parallel and are 50cm away from each other.
And the PDH frequency locking unit 4 is used for monitoring and processing the laser signal fed back by the FP resonant cavity in real time and adjusting the cavity length of the FP resonant cavity so as to meet the requirement that the laser frequency of the FP resonant cavity is locked by a laser and further contribute to the improvement of the power in the cavity. The laser light transmitted by the first high-reflection mirror 31 and the laser light reflected by the high-reflection mirror in the FP resonant cavity pass through the second quarter-wave plate 42 again, and the laser light reaches the second polarization beam splitter 41 after the polarization state of the laser light is adjusted again by the second quarter-wave plate 42. The laser light with the polarization state adjusted twice cannot be transmitted back when passing through the second polarization beam splitter 41, and can only enter the PDH frequency locking unit 4, so that both the laser light emitted by the laser and the laser light transmitted by the FP resonant cavity can enter the PDH frequency locking unit 4. The laser entering the PDH frequency locking unit 4 first passes through the photodetector 44, and the photodetector 44 is configured to detect the laser reflection intensity of the FP cavity and output the FP cavity laser transmission signal to the PDH frequency locking unit. A PDH frequency locker 45, receiving the FP cavity laser transmission signal, performing frequency mixing comparison between the frequency of the laser emitted from the laser 11 and the obtained FP cavity laser transmission signal, filtering and amplifying to obtain an error signal, performing proportional-integral processing on the error signal to obtain a negative feedback control signal, and applying the negative feedback control signal to the piezoelectric shifter 46; and the piezoelectric displacer 46 is connected with the first high-reflection mirror 31 or the second high-reflection mirror 32, receives a negative feedback control signal sent by the PDH frequency locker 45, and drives the first high-reflection mirror 31 or the second high-reflection mirror 32 to move, so that the cavity length is accurately controlled. The laser frequency of the FP resonant cavity is locked by the laser frequency of the laser to emit laser frequency by monitoring and processing the laser signal fed back by the FP resonant cavity through the PDH frequency locking unit 4 and adjusting the cavity length of the FP resonant cavity, so that the resonance performance of the laser in the FP resonant cavity is improved.
And the spectrum acquisition unit 5 is arranged on one side of the gas chamber unit 3 and is used for acquiring and detecting the Raman scattering light. The raman scattered light coming out of the second window mirror 34 of the closed gas chamber passes through the high-pass filter mirror 51 at first, the cut-off wavelength of the high-pass filter mirror 51 is 1065nm, the laser light smaller than the wavelength is reflected, and the laser light larger than the wavelength is transmitted, so as to filter stray light and improve the signal-to-noise ratio of the raman scattered light; then the light reaches a collecting lens 52, the focal length of the collecting lens 52 is 50.4mm, the diameter of the lens is 25.4mm, and the collecting lens is used for focusing the gas Raman scattering light in the light path into a spectrometer slit and improving the collecting efficiency of the gas Raman scattering light; finally, the gas Raman scattered light is collected by a spectrometer and a CCD 53. The working wavelength of the spectrometer and the CCD53 is 1000nm-2000 nm.
According to the gas detection device in the transformer oil, the phase, amplitude, intensity and polarization state of laser are modulated by the acoustoelectric combined modulation unit on the laser emitted by the laser unit, and the PDH frequency locking unit accurately controls the length of the FP resonant cavity, so that the locking of the laser frequency emitted by the laser and the laser frequency fed back by the FP resonant cavity unit is realized, and the resonance of the laser in the FP resonant cavity is enhanced; the laser with stronger resonance is reflected for many times in the FP resonant cavity and forms multiple beam constructive interference, thereby improving the laser power in the cavity. Finally, the Raman scattering intensity of trace gas is improved, and high-sensitivity detection of the dissolved gas in the transformer oil is realized.
Fig. 2 is a relative raman intensity graph of carbon dioxide dissolved in transformer oil according to an embodiment of the present invention. The raman scattering intensity of the dissolved carbon dioxide in the transformer oil is obtained by detection of the gas detection device in the transformer oil provided by the embodiment. The device can enable the laser intensity in the cavity to reach 22W, and the corresponding laser intensity enhancement multiple is 5900 times. Taking carbon dioxide dissolved in transformer oil as an example, a raman spectrum measured by the device is shown in fig. 2. The lower limit of the detection of carbon dioxide by the device is 5 ppm. The detection device is proved to have higher sensitivity for detecting the dissolved gas in the transformer oil.
The embodiments in this specification are described in a progressive manner. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.
It should be noted that, unless otherwise specified and limited, the terms "connected" and "connected" are to be interpreted broadly, and may be, for example, mechanically or electrically connected, or may be communicated between two elements, directly or indirectly through an intermediate medium, and specific meanings of the terms may be understood by those skilled in the relevant art according to specific situations. The terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a circuit structure, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such article or apparatus, and the phrase "including an … …" does not exclude the presence of other like elements in the article or apparatus including the elements. Relational terms such as "first" and "second," and the like, may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions.
It will be understood that the invention is not limited to the precise arrangements described above and shown in the drawings and that various modifications and changes may be made without departing from the scope thereof. The scope of the invention is limited only by the appended claims.
Claims (10)
1. A gas detection device in transformer oil, comprising:
a laser unit (1) for emitting laser light;
the acoustoelectric combined modulation unit (2) comprises an acousto-optic modulator (23) which is arranged on the light outgoing side of the laser unit (1) and is used for carrying out acousto-optic modulation on the laser and enhancing the intensity of the laser; the electro-optical modulator (211) is arranged on the light emitting side of the acousto-optical modulator (23) and is used for modulating the phase, the amplitude, the intensity and the polarization state of an optical signal output by the acousto-optical modulator (23);
the gas chamber unit (3) is arranged on the light-emitting side of the acoustoelectric combined modulation unit (2) and is used for placing the FP resonant cavity and filling gas to be measured;
the FP resonant cavity consists of a first high reflecting mirror (31) and a second high reflecting mirror (32) and is used for improving the power of laser entering the cavity, and the laser in the FP resonant cavity penetrates through the gas to be detected and enables the gas to be detected to generate Raman scattering light;
a PDH frequency locking unit (4) for adjusting the cavity length of the FP resonant cavity according to the laser signal fed back by the FP resonant cavity;
and the spectrum acquisition unit (5) is used for acquiring and detecting the Raman scattering light emitted by the FP resonant cavity.
2. The transformer oil gas detection apparatus according to claim 1, wherein the laser unit (1) comprises:
a laser (11) for emitting laser light;
the collimating mirror (12) is arranged on the light-emitting side of the laser (11) and is used for collimating the laser light into parallel light;
and the band-pass filter mirror (15) is arranged on the light outlet side of the collimating mirror (12) and is used for filtering stray light so as to reduce spectral noise.
3. The transformer oil gas detection apparatus according to claim 2, wherein the acoustoelectric combination modulation unit (2) further comprises:
the first half-wave plate (21) is arranged on the light outgoing side of the band-pass filter (15) and used for adjusting the polarization direction of laser emitted by the laser unit (1);
the first polarization beam splitter (22) is arranged on the light outgoing side of the first half wave plate (21) and is used for splitting the laser to form two orthogonal laser beams, wherein one laser beam penetrates through the first polarization beam splitter (22) and then enters the acousto-optic modulator (23), and the other laser beam enters the second half wave plate (29);
the first quarter wave plate (24) is arranged on the light outlet side of the acousto-optic modulator (23) and used for adjusting the polarization state of the laser light;
a third mirror (25) disposed on the light exit side of the first quarter wave plate (24) for reflecting the laser light so that the laser light passes through the first quarter wave plate (24) and the acousto-optic modulator (23) again and then reaches the second half wave plate (29) through the first polarization beam splitter (22);
a polarizer (210) disposed between the second half-wave plate (29) and the electro-optic modulator (211) for improving the polarization of the laser light.
4. A transformer oil gas detection arrangement according to claim 3, characterized in that the gas cell unit (3) further comprises a gas cell, which is equipped with:
the first window mirror (33) is arranged on the laser emitting side of the acoustoelectric combination modulation unit (2) and is used for enabling the laser to enter and exit the gas chamber;
a second window mirror (34) arranged on one side of the spectrum collection unit (5) and used for collecting the Raman scattered light;
an airtight data interface (35) for negative feedback control signals output by the PDH frequency locking unit (4) to enter the gas chamber;
and the gas inlet (36) and the gas outlet (37) are used for the gas to be measured to enter and exit the gas chamber.
5. The transformer oil gas detection apparatus according to claim 4, wherein the PDH frequency locking unit (4) comprises:
the second polarization beam splitter (41) is arranged on the light outgoing side of the electro-optical modulator (211) and is used for splitting the laser to form two orthogonal beams of laser, wherein one beam of laser enters the second quarter wave plate (42) after transmitting through the second polarization beam splitter (41), and the other beam of laser enters the photoelectric detector (44);
the second quarter wave plate (42) is arranged between the second polarization beam splitter (41) and the gas chamber unit (3) and is used for adjusting the polarization state of the laser light;
the photoelectric detector (44) is used for detecting the laser intensity fed back by the FP resonant cavity and outputting a laser transmission signal of the FP resonant cavity;
a PDH frequency locker (45) for receiving the FP resonant cavity laser transmission signal, performing frequency mixing comparison on the laser frequency emitted by the laser and the FP resonant cavity laser transmission signal, and outputting the negative feedback control signal;
and the piezoelectric displacer (46) is connected with the first high-reflection mirror (31) or the second high-reflection mirror (32) and is used for driving the first high-reflection mirror (31) or the second high-reflection mirror (32) to move according to the negative feedback control signal.
6. The transformer oil gas detection apparatus according to claim 4, wherein the spectrum collection unit (5) comprises:
the high-pass filter mirror (51) is arranged on one side of the gas chamber and is used for filtering stray light signals in the Raman scattering light so as to improve the signal-to-noise ratio of the Raman scattering light;
a collecting lens (52) arranged on the light outlet side of the high-pass filter mirror (51) and used for focusing the gas Raman scattered light and improving the collecting efficiency of the gas Raman scattered light;
and the spectrometer and the CCD (53) are arranged at the light outgoing side of the collecting lens (52) and are used for collecting the gas Raman scattered light.
7. The transformer oil gas detection device according to claim 1, wherein the acousto-optic modulator (23) has an operating wavelength of 1064nm, a center frequency of 25MHz, and a bandwidth of 1 MHz.
8. The transformer oil gas detection device according to claim 1, wherein the electro-optical modulator (211) has an operating wavelength of 1064nm and a modulation frequency of 12.5 MHz.
9. The transformer oil gas detection apparatus according to claim 1, wherein the first high-reflection mirror (31) and the second high-reflection mirror (32) are each a plano-concave mirror having a radius of curvature of 1 m.
10. The transformer oil gas detection apparatus according to claim 2, wherein the laser (11) is a fiber laser.
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