CN114136923A - Online measurement system for dissolved methane in transformer oil - Google Patents
Online measurement system for dissolved methane in transformer oil Download PDFInfo
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- CN114136923A CN114136923A CN202111430735.4A CN202111430735A CN114136923A CN 114136923 A CN114136923 A CN 114136923A CN 202111430735 A CN202111430735 A CN 202111430735A CN 114136923 A CN114136923 A CN 114136923A
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Classifications
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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
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/41—Refractivity; Phase-affecting properties, e.g. optical path length
- G01N21/45—Refractivity; Phase-affecting properties, e.g. optical path length using interferometric methods; using Schlieren methods
-
- 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
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/41—Refractivity; Phase-affecting properties, e.g. optical path length
- G01N21/45—Refractivity; Phase-affecting properties, e.g. optical path length using interferometric methods; using Schlieren methods
- G01N2021/458—Refractivity; Phase-affecting properties, e.g. optical path length using interferometric methods; using Schlieren methods using interferential sensor, e.g. sensor fibre, possibly on optical waveguide
Abstract
The invention discloses an online measurement system and method for dissolved methane in transformer oil. Wherein, dissolve methane measurement system in this transformer oil includes: the broadband light source is used for generating broadband light with the wavelength range of 1528 and 1605 nm; the tapered optical fiber methane sensor coated with the methane sensitive film is used for measuring the concentration of methane in the transformer oil; a spectrum analyzer and a computer for reading the spectrum and demodulating the data. The tapered structure optical fiber sensor is manufactured by melting and tapering a single-mode optical fiber, a methane sensitive film is coated on the surface of the tapered optical fiber after tapering, and the sensitive film is an ultraviolet curing fluorosilicone (UVCFS) porous methane sensitive film containing cage-shaped molecule Cryptophane-A. The conical optical fiber methane sensor can be directly placed in transformer oil, when methane molecules in the transformer oil to be measured and cage-shaped molecules Cryptophane-A in the sensitive film act, the refractive index of the sensitive film is rapidly changed, so that interference spectrum formed by broadband light passing through the conical optical fiber is shifted, and wavelength shift of the interference spectrum is measured
And then the concentration of the methane gas in the transformer oil to be detected can be obtained. The invention has the characteristics of no need of oil-gas separation, transformer oil corrosion resistance, high sensitivity, good stability and the like.
Description
Technical Field
The invention provides an online measurement system for dissolved methane in transformer oil, which is used for measuring the concentration of dissolved methane in the transformer oil and belongs to the technical field of online monitoring of high-voltage electrical equipment.
Background
With the steady promotion of national economy and quality of life, the scale of an intelligent power grid is gradually enlarged, and the requirements on the power supply quality and safe and reliable operation of the power grid are higher and higher. The power transformer is used as a core device for power transmission and distribution of a power grid, and the normal supply of electric energy of a power system is directly influenced by the safe and reliable operation of the power transformer. The failure of the power transformer can cause large-area power failure accidents, and huge economic loss and social influence can be caused.
At present, most of power transformers in a power grid are oil-immersed power transformers, an insulating medium of the oil-immersed transformer mainly adopts an oil-paper insulation mode, insulating oil and insulating paper can not be aged gradually under the influence of electricity, heat, oxygen and various environmental factors in the daily operation process, the insulating oil and organic insulating materials of the transformer can be cracked gradually under the thermoelectric action to generate hydrogen, methane, ethane, ethylene, acetylene, carbon monoxide, carbon dioxide and other gases, the gases are dissolved in transformer oil, particularly, the oil-immersed transformer with long service life can have the problems of internal oil degradation, insulating property degradation and the like in long-term operation, serious accidents such as damage or burnout of transformer equipment can be caused in serious cases, and the safe and reliable operation of the whole power supply system is damaged. Analysis (DGA) of dissolved gas in oil is the most convenient and effective method for diagnosing early faults of the oil-immersed transformer at the present stage, and most of the early faults of discharge and overheating can generate methane gas, so that the content of the dissolved methane in the transformer oil is detected so as to judge the early latent faults of the oil-immersed transformer in time, and the method has great significance for ensuring safe and stable operation of the transformer.
At present, methods for detecting the dissolved gas in the transformer oil by the power system mainly include a gas chromatography method and a conventional method for monitoring the dissolved gas in the oil on line, but both the methods rely on oil-gas separation, and the mixed gas needs to be separated and detected, so that the detection period is long, the electromagnetic compatibility is poor, and the dissolved gas and carrier gas are consumed, therefore, the research on the method for monitoring the gas in the transformer oil without oil-gas separation is an important means for simplifying a detection device for the gas in the oil and shortening the detection period. The tapered optical fiber methane sensor surface sensitive film contains cage-shaped molecule Cryptophane-A, can complex methane and small halogenated methane, does not need oil-gas separation, is oil-resistant and high-temperature-resistant, and can be placed in transformer oil for on-line monitoring of methane concentration.
Disclosure of Invention
The invention provides a system for measuring dissolved methane in tapered optical fiber transformer oil based on a coated methane sensitive film, solves the problems of oil-gas separation, long detection period and the like in the prior art, and realizes the rapid online monitoring of the dissolved methane in the transformer oil.
In order to achieve the purpose, the invention provides the following technical scheme: an on-line monitoring system for dissolved methane in transformer oil comprises a broadband light source, a single-mode optical fiber, a tapered optical fiber methane sensor, a spectrum analyzer and a computer. The input end of the conical optical fiber methane sensor is connected with a broadband light source through a single-mode optical fiber to receive broadband light signals, and the output end of the conical optical fiber methane sensor is connected with a spectrum analyzer through the single-mode optical fiber; the testing oil tank is provided with an oil inlet and an oil outlet and is externally connected with a circulating pump, and the testing oil tank is provided with an air inlet and is externally connected with a methane flow controller; the surface of the tapered optical fiber is coated with a methane sensitive film.
Further, the methane sensitive film is an ultraviolet curing fluorosilicone siloxane (UVCFS) porous methane sensitive film containing caged molecules Cryptophane-A. Cryptophanes are semi-closed cage-shaped compounds, and cavities in certain spaces in molecules of the compounds can adsorb neutral small molecules or ions to form host-guest complexes. The clathrate molecule Cryptophane-A can complex methane and small halogenated methane. The refractive index of the complex changes after the methane molecules enter the cavity of the cage-shaped molecule Cryptophane-A, and due to the fact that the complex of the methane and the Cryptophane-A is unstable, when the concentration of the methane is reduced, the methane molecules can be desorbed from the cavity, and therefore the Cryptophane-A can be used for the conical optical fiber methane sensor based on refractive index change.
Optionally, the ultraviolet curing fluorosilicone (UVCFS) is a fluorine-containing optical fiber coating, is oil-resistant and high-temperature resistant, and can be directly placed in transformer oil as the optical fiber coating; the refractive index of the ultraviolet curing fluorosilicone is 1.353, and the mixture of the ultraviolet curing fluorosilicone and Cryptophane-A can be regulated and controlled, so that the refractive index of the sensitive film reaches the designed target of 1.42; the ultraviolet curing fluorosilicone has small heat conduction coefficient, and can reduce the temperature cross sensitivity to a certain extent.
Alternatively, the solvent for preparing the methane sensitive film is dichloromethane which is an ultraviolet curing fluorosilicone (UVCFS) material containing caged molecule Cryptophane-A, and the dichloromethane solution is volatile and can be used for regulating and controlling the thickness of the sensitive film. During preparation, Cryptophane-A and ultraviolet curing fluorosilicone are dissolved by dichloromethane, are oscillated and mixed uniformly, and then the mixed solution is stirred to volatilize the dichloromethane.
Furthermore, the ultraviolet curing fluorosilicone siloxane (UVCFS) porous methane sensitive film containing the caged molecule Cryptophane-A only complexes with methane molecules and responds to methane gas, and hardly responds to non-methane gases such as hydrogen, ethane, ethylene, acetylene, carbon monoxide and the like dissolved in transformer oil, so that the selectivity is good.
Furthermore, the diameter of the single-mode optical fiber is 125 micrometers, the tapered transition region is required to be uniformly transitioned after tapering, the taper angle is 45-60 degrees, the diameter of the waist region is required to be 8-12 micrometers, and the length of the tapered optical fiber is 5 millimeters. The broadband light generates mode interference and coupling processes when passing through the tapered optical fiber, generates an interference spectrum and is very sensitive to the change of the refractive index of the surrounding environment, so that the sensor has very high precision and sensitivity. And the porous methane sensitive film on the surface of the tapered optical fiber is combined, so that the high-sensitivity, high-response-speed and high-selectivity detection of the methane gas dissolved in the transformer oil can be realized.
Further, the broadband light source is an Amplified Spontaneous Emission (ASE) broadband light source with the wavelength range of 1528-1605nm and the bandwidth is 77 nm.
Further, the optical spectrum analyzer is a Yokogawa AQ6370D optical spectrum analyzer in the wavelength range of 600-1700 nm.
Furthermore, the conical optical fiber methane sensor is directly placed in the transformer oil, oil-gas separation is not needed, and the response speed is high; the interference spectrum wavelength offset is measured in real time through a spectrum analyzer and a computer, online monitoring of dissolved methane in transformer oil is achieved, early latent faults of the oil-immersed transformer are judged in time, and safe and stable operation of the transformer is guaranteed.
The working principle of the sensor is as follows:
the light emitted from a broadband light source has only a fundamental mode (HE) when propagating in a single-mode optical fiber11Mode), when the incident light of the fundamental mode passes through the first tapered transition region of the tapered fiber, the normalized frequency changes drastically due to the steep transition region, and the fundamental mode (HE) is partially11Mode) will couple to higher order modes in the transition region, where it will interact with HE12The coupling efficiency of the mode is highest. The higher order modes and the fundamental mode propagate forward along the uniform waist region and interfere to produce a periodic intensity distribution, and these higher order modes are coupled back into the fundamental mode in a second tapered transition region. The calculation formula of the total light intensity after interference is as follows:
in the formula (I), the compound is shown in the specification,I 1 、I 2 is HE11Modulo sum HE12The intensity of the light in the two modes modulo,
is the phase difference between the two modes. The phase difference between the two modes is:
in the formula (I), the compound is shown in the specification,
is HE11Modulo sum HE12The difference between the effective refractive indices of the two modes of the mode,
the waist length.
The phase difference between the interference spectrum and the two modes is a sine relation, the interference spectrum is composed of a series of maximum values (wave crests) and minimum values (wave troughs), and when the phase difference is larger than the phase difference, the interference spectrum is subjected to phase inversion
(k is an integer), interference spectrumIReaches a maximum value when
Time, interference spectrumIReaching a minimum value. First, themThe wave length corresponding to the wave crest or the wave trough of the order interference fringe is as follows:
in the formula (I), the compound is shown in the specification,
is HE11Modulo sum HE12Optical path difference of two modes. When the external environment changes, the offset of the interference spectrum wavelength
Only with respect to the change of the refractive index of the external environment.
Therefore, when the concentration of dissolved methane in transformer oil is changed, the refractive index of a methane molecular complex in a Cryptophane-A cavity in the methane sensitive film on the surface of the tapered optical fiber is changed, and the wavelength shift corresponding to the peak or the trough of the interference fringe is measured
And the concentration of the dissolved methane gas in the transformer oil can be measured.
The invention has the following technical effects:
the system for measuring the dissolved methane in the tapered optical fiber transformer oil based on the coating of the methane sensitive film does not need oil-gas separation, is oil-resistant and high-temperature resistant, and can be placed in the transformer oil for on-line monitoring of the methane concentration; compared with the existing gas chromatography and the conventional online monitoring of the dissolved gas in the oil, the method has the advantages of short detection period, strong electromagnetic compatibility, no consumption of the dissolved gas and carrier gas, substantial simplification of a gas detection device in the oil, and substantial shortening of the measurement time of the dissolved methane in the oil.
Drawings
Fig. 1 is a schematic diagram of a method for measuring the concentration of dissolved methane gas in transformer oil according to the present invention.
FIG. 2 is a schematic structural diagram of a methane sensor with a tapered optical fiber coated with a methane sensitive membrane according to the present invention.
Fig. 3 is a schematic cross-sectional view of a test fuel tank according to the present invention.
Detailed Description
The present invention will be described in further detail below with reference to fig. 1, 2 and 3.
Fig. 1 is a schematic diagram of a method for measuring the concentration of dissolved methane gas in transformer oil, according to the invention, two ends of a tapered optical fiber methane sensor 2 coated with a methane sensitive film are connected with a single mode optical fiber 6, and the sensor 2 is placed in a test oil tank 5 and sealed. The input end of the tapered optical fiber methane sensor 2 is connected to an Amplified Spontaneous Emission (ASE) broadband light source 1 through a single mode fiber 6, the output end of the tapered optical fiber methane sensor 2 is connected to a Yokogawa AQ6370D spectrum analyzer 3 through the single mode fiber 6, and the spectrum analyzer 3 is connected to a computer 4 through a network cable 7.
Specifically, the broadband light source 1 is used for generating broadband light with the wavelength range of 1528 and 1605 nm; the test oil tank 5 provides a closed environment for storing the test transformer oil; the device comprises a conical optical fiber methane sensor 2, a broadband light source 1 and a transformer oil tank, wherein the conical optical fiber methane sensor 2 is acted with methane molecules in the transformer oil and used for measuring the concentration of the methane molecules in the transformer oil, the conical optical fiber methane sensor 2 is placed in a test oil tank 5 and is immersed in the transformer oil for test, and the broadband light emitted by the broadband light source 1 generates mode interference through the conical optical fiber methane sensor 2; the spectrum analyzer 3 is used for reading the mode interference spectrum which is emitted by the broadband light source 1 and obtained by the conical optical fiber methane sensor 2, and transmitting the spectrum data to the computer 4, and the computer 4 is connected with the spectrum analyzer 3 and used for demodulating the spectrum data, obtaining the interference wavelength offset and calculating the concentration of dissolved methane in the transformer oil.
Fig. 2 is a schematic structural diagram of a tapered fiber methane sensor coated with a methane sensitive film according to the present invention, in which the tapered fiber methane sensor 2 includes a single-mode fiber 201, a tapered transition region 202 connecting the single-mode fiber and the waist region, a very fine uniform waist region 203, and a methane sensitive film 204 coated on the surface of the tapered fiber. The single-mode fiber 201 is a Corning SMF-28 fiber, the diameter of a cladding is 125 mu m, and the diameter of a fiber core is 9 mu m. The tapered optical fiber is prepared by a melting tapering method for a single mode optical fiber, the tapered transition region 202 is required to be uniformly transitioned, the taper angle is 45-60 degrees, the diameter of the uniform waist region 203 is required to be 8-12 mu m, and the length of the uniform waist region 203 is 3 mm. The porous methane sensitive film 204 is required to be coated by a glass slide dispensing method and cured by irradiation with an ultraviolet high-pressure mercury lamp (UV mercury lamp) in an inert gas environment; the porous methane sensitive film 204 is an ultraviolet curing fluorosilicone siloxane (UVCFS) porous methane sensitive film containing caged molecule Cryptophane-A, the film thickness is required to be 1.1-1.3 mu m, and the refractive index is 1.42; the caged molecule Cryptophane-A is a specific material with direct photosensitive response to methane, and is required to be prepared by adopting a CTV coupling method, and the purity of the caged molecule Cryptophane-A is 95 percent as measured by nuclear magnetic resonance spectroscopy; the ultraviolet curing fluorosilicone (UVCFS) is fluorine-containing optical fiber coating, and the refractive index of the coating is required to be 1.353, and the coating is oil stain resistant and high temperature resistant.
Specifically, the preparation process of the tapered optical fiber methane sensor comprises the steps of drawing the tapered optical fiber, preparing an ultraviolet curing fluorosilicone (UVCFS) solution containing cage-shaped molecule Cryptophane-A, and coating and curing a methane sensitive film. The method comprises the following specific steps:
(1) taking a section of single-mode optical fiber, stripping a coating layer of the middle section of the single-mode optical fiber by using a wire stripper, stretching two ends of the single-mode optical fiber to be straight and clamping the single-mode optical fiber on a clamp holder, wherein the clamp holder is fixed on a precise electric moving platform. The step motor is arranged for two-step stretching, the moving distance of the first step is 2mm, the moving speed is 0.5mm/s, the moving distance of the second step is 6mm, and the moving speed is 1 mm/s.
(2) And heating the optical fiber stripped of the coating layer to a molten state by using a butane flame generator, starting a stepping motor, driving the precise electric moving platform to move towards two ends by using the stepping motor, stretching the single-mode optical fiber in the molten state to form uniform transition, and enabling parameters to reach the required tapered optical fiber.
(3) 0.1mL of analytically pure dichloromethane was sampled with a microsyringe and placed in a centrifuge tube with a capacity of 0.5mL, and the centrifuge tube was rapidly closed to prevent dichloromethane from volatilizing. The caged molecule Cryptophane-A is dug by a medicine spoon, 10mg is weighed on a high-precision milligram electronic scale, and the weighed mixture is poured into a centrifuge tube for mixing. Will the centrifuging tube oscillation 10 minutes, then add ultraviolet curing fluorosilicone (UVCFS) 0.1mL in the centrifuging tube, will the centrifuging tube oscillation ten minutes makes the intensive mixing of solution even, opens the centrifuging tube, and stirring solution makes dichloromethane wherein volatilize fast, will the centrifuging tube is arranged in vacuum drying oven and is evacuated, makes the dichloromethane in the solution take out completely, makes even transparent ultraviolet curing fluorosilicone (UVCFS) solution that contains cage molecule Cryptophane-A.
(4) Fixing a tapered optical fiber on a glass slide, taking a small amount of prepared ultraviolet curing fluorosilicone siloxane (UVCFS) solution containing caged molecule Cryptophane-A by using a micro medicine spoon, dripping the solution on one end of the tapered optical fiber, vertically placing the glass slide, enabling the solution to slowly flow down along the tapered optical fiber, and forming a layer of uniform film on the surface of the tapered optical fiber.
(5) The glass slide is placed in a transparent cover, the transparent cover is provided with a vent hole, nitrogen is introduced into the transparent cover from the vent hole, an inert gas environment is created, and the purpose is to overcome the phenomenon of oxygen inhibition in the ultraviolet curing fluorosilicone (UVCFS) curing process. And after ten minutes of ventilation, irradiating and curing by using an ultraviolet high-pressure mercury lamp (UV mercury lamp), closing the high-pressure mercury lamp after ten minutes of irradiation, and finishing the preparation of the tapered optical fiber methane sensor coated with the methane sensitive film.
Fig. 3 is a schematic view of a section of a test oil tank according to the present invention, the test oil tank 5 is a special airtight container made of stainless steel, a tapered fiber methane sensor package structure 501 is provided inside the test oil tank, single-mode fiber channels 502 are provided on two sides of the test oil tank, a barometer 503 and an observation window 504 are provided on the top of the test oil tank 3, and three valves are provided on the top and the bottom of the test oil tank.
Specifically, a first valve 505 at the top of the test oil tank 5 is externally connected with a circulating pump, and is internally connected with a through hole of the packaging structure 501 and used for conveying transformer oil into the test oil tank 5; a second valve 506 at the top of the test oil tank 5 is externally connected with a vacuum pump and is used for vacuumizing to extract methane dissolved in the transformer oil; and a third valve 507 at the top of the test oil tank 5 is externally connected with a nitrogen gas circuit and used for introducing nitrogen to protect the transformer oil after vacuum pumping. A first valve 508 at the bottom of the test oil tank 5 is externally connected with a circulating pump and used for pumping transformer oil from the test oil tank; a second valve 509 at the bottom of the test oil tank 5 is an oil taking port, and an oil sample is extracted from the oil taking port by using a needle tube to measure the methane concentration; the third valve 510 at the bottom of the test tank 5 was used for aeration.
Further, during testing, the conical optical fiber methane sensor 2 is packaged on a packaging structure 501 in the testing oil tank 5, a methane flow controller is opened, and methane gas is introduced into the transformer oil through a valve 510; and opening a circulating pump to uniformly mix the methane gas in the transformer oil. When the concentration of the dissolved methane in the transformer oil is changed, the refractive index of a methane molecular complex in a cavity of a Cryptophane-A in the methane sensitive film on the surface of the tapered optical fiber is changed, an interference spectrum is read on the spectrometer 3, data is transmitted to the computer 4, and the concentration of the dissolved methane in the transformer oil can be measured by measuring the wavelength shift delta lambda m corresponding to the wave crest or the wave trough of the interference fringe.
The above-mentioned embodiments only express the embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (8)
1. The utility model provides a dissolve methane on-line measuring system in transformer oil which characterized in that includes:
the broadband light source is used for generating broadband light with the wavelength range of 1528 and 1605 nm;
the device comprises a conical optical fiber methane sensor, a broadband light source and a control unit, wherein the conical optical fiber methane sensor is used for acting with methane molecules in transformer oil to measure the concentration of the methane molecules in the transformer oil, is placed in a test oil tank and is immersed in the transformer oil for test, is connected with the broadband light source through a single-mode optical fiber, and generates mode interference when the broadband light emitted by the broadband light source passes through the conical optical fiber methane sensor;
the spectrum analyzer is connected with the tapered optical fiber methane sensor and used for reading a mode interference spectrum emitted by the broadband light source and obtained through the tapered optical fiber methane sensor and transmitting the spectrum data to the computer, and the computer is connected with the spectrum analyzer and used for demodulating the spectrum data, obtaining interference wavelength offset and calculating the concentration of dissolved methane in the transformer oil.
2. The system for on-line measurement of dissolved methane in transformer oil according to claim 1, wherein the tapered fiber methane sensor comprises a tapered fiber and a porous methane sensitive film coated on the surface of the tapered fiber, wherein:
the tapered optical fiber is prepared by a melting tapering method for a single-mode optical fiber; the tapered structure of the tapered optical fiber has specific requirements, and the structure of the tapered optical fiber comprises an extremely fine waist part and a tapered transition region, wherein the two ends of the waist part are connected with the standard single-mode optical fiber, the tapered transition region is required to be uniformly transitioned, the taper angle is 35-45 degrees, the diameter of the waist part is required to be 8-12 micrometers, and the length of the waist part is 3 millimeters;
the porous methane sensitive film is required to be coated by a glass slide drop coating method and irradiated and cured by an ultraviolet high-pressure mercury lamp (UV mercury lamp) in an inert gas environment; the porous methane sensitive film is an ultraviolet curing fluorosilicone siloxane (UVCFS) porous methane sensitive film containing caged molecule Cryptophane-A, the film thickness is required to be 1.1-1.3 micrometers, and the refractive index is 1.42; the caged molecule Cryptophane-A is a specific material with direct photosensitive response to methane, and is required to be prepared by adopting a CTV coupling method, and the purity of the caged molecule Cryptophane-A is 95 percent as measured by nuclear magnetic resonance spectroscopy; the ultraviolet curing fluorosilicone (UVCFS) is fluorine-containing optical fiber coating, and the refractive index of the coating is required to be 1.353, and the coating is oil stain resistant and high temperature resistant.
3. The system of claim 1, wherein the testing tank is a special sealed container made of stainless steel, the testing tank has the tapered fiber methane sensor package structure inside, and has single-mode fiber channels on both sides, the top of the testing tank is equipped with a barometer and an observation window, the side of the testing tank is connected with a thermocouple and a heating rod, and the top and the bottom of the testing tank are respectively provided with three valves, wherein:
the first valve at the top of the test oil tank is externally connected with a circulating pump and internally connected with a through hole of a packaging structure and used for feeding oil into the test oil tank; the second valve at the top of the test oil tank is externally connected with a vacuum pump and is used for vacuumizing to extract methane dissolved in the transformer oil; a third valve at the top of the test oil tank is externally connected with a nitrogen gas circuit and used for introducing nitrogen to protect the transformer oil after vacuum pumping;
the first valve at the bottom of the test oil tank is externally connected with a circulating pump and used for pumping transformer oil from the test oil tank; the second valve at the bottom of the test oil tank is an oil taking port, and an oil sample is extracted from the oil taking port by adopting a needle tube to measure the methane concentration; and a third valve at the bottom of the test oil tank is used for aeration.
4. The system for on-line measurement of dissolved methane in transformer oil according to claim 1, wherein the tapered fiber methane sensor is connected in an optical path topology by a single mode fiber, and a methane sensing measurement signal is transmitted through the single mode fiber; the single-mode optical fiber core material is a high-refractive-index glass fiber core (germanium-doped silica), and the single-mode optical fiber cladding material is a low-refractive-index silica glass cladding (pure silica) which is not easy to react with the transformer oil; the porous methane sensitive film coated on the tapered optical fiber is resistant to oil stain and high temperature and is not easy to react with transformer oil; the tapered fiber methane sensor can be placed in transformer oil for methane concentration measurement.
5. The system for on-line measurement of dissolved methane in transformer oil according to claim 2, wherein the tapered optical fiber is prepared by a fused biconical taper method, and the method for preparing the tapered optical fiber by the fused biconical taper method comprises the following steps:
taking a section of single-mode optical fiber, stripping a coating layer from a middle section of the single-mode optical fiber by using a wire stripper, stretching two ends of the single-mode optical fiber to be straight and clamping the two ends of the single-mode optical fiber on a clamp holder, fixing the clamp holder on a precise electric moving platform, heating the optical fiber stripped of the coating layer to a molten state by using a butane flame generator, starting a stepping motor at the same time, driving the precise electric moving platform to move towards the two ends by using the stepping motor, and stretching the single-mode optical fiber in the molten state to form a tapered optical fiber with uniform transition;
the stepping motor is connected with a computer, and the moving distance and the moving speed of the stepping motor are controlled by the computer, so that structural parameters such as the waist diameter, the length and the like of the tapered optical fiber are controlled.
6. The system for on-line measurement of dissolved methane in transformer oil according to claim 2, wherein the coating method of the porous methane sensitive film is a glass slide dripping method, and the glass slide dripping method comprises the following steps:
firstly fixing the tapered optical fiber on a glass slide, then taking a small amount of prepared ultraviolet curing fluorosilicone (UVCFS) solution containing cage-shaped molecule Cryptophane-A by using a micro medicine spoon, dripping the solution on one end of the tapered optical fiber, vertically placing the glass slide, enabling the solution to slowly flow down along the tapered optical fiber to form a layer of film on the surface of the tapered optical fiber, and finally curing the methane sensitive film.
7. The system for on-line measurement of dissolved methane in transformer oil according to claim 2, wherein the porous methane sensitive film coated on the surface of the tapered optical fiber is cured by irradiation with an ultraviolet high-pressure mercury lamp (UV mercury lamp), and nitrogen is introduced to cure the methane sensitive film in an inert gas environment, so as to overcome the oxygen inhibition phenomenon during the curing process of ultraviolet curing fluorosilicone (UVCFS).
8. The on-line measurement system for dissolved methane in transformer oil according to claim 6, wherein the ultraviolet curing fluorosilicone (UVCFS) solution containing caged molecule Cryptophane-A is prepared by the following steps:
taking dichloromethane 0.1ml and clathrate molecule Cryptophane-A10 mg to mix in the centrifuging tube, will the centrifuging tube oscillation 10 minutes, then add ultraviolet curing fluorosilicone (UVCFS) 0.1ml in the centrifuging tube, will the centrifuging tube oscillation ten minutes makes solution intensive mixing even, opens the centrifuging tube, and stirring solution makes dichloromethane wherein volatilize rapidly, will the centrifuging tube is arranged in vacuum drying oven and is taken out the vacuum, makes the ultraviolet curing fluorosilicone (UVCFS) solution that contains clathrate molecule Cryptophane-A.
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