Gas Concentration Monitoring Device and Method for Transformers Based on Optical Interference Demodulation

Abstract

The present invention relates to the technical field of optical interference demodulation, and discloses a gas concentration monitoring device and method for a transformer based on optical interference demodulation, which includes generating a narrowband laser with a preset wavelength and dividing it into two paths for output. One path is modulated by an acousto-optic modulator to generate a frequency-shifted optical signal, and the other path is modulated by a low-frequency phase modulation signal sensed by a fiber optic gas sensor to generate a sensing optical signal with a further low-frequency phase change; the frequency-shifted optical signal and the sensing optical signal are subjected to photoelectric conversion to output an optical interference beat signal; the optical interference beat signal and a difference frequency signal that differs from the optical interference beat signal by a preset low-frequency carrier frequency are mixed and fused to output first and second fused down-converted signals; the first fused down-conversion module is filtered to serve as a reference signal; a lock-in amplifier is used to demodulate the second fused down-converted signal based on the reference signal to obtain a low-frequency phase modulation signal characterizing the gas concentration inside the transformer to be monitored.

Description

Technical Field

[0001] The present invention relates to the technical field of optical interference demodulation, and in particular to a gas concentration monitoring device and method for a transformer based on optical interference demodulation. Background Art

[0002] As a key operating equipment for power transmission and distribution in the power system, the transformer is one of the most important components in the power system. Once a fault occurs, it will pose a great threat to the stable operation of the power system and social production. Therefore, the safe and stable operation state of the transformer is of great significance for ensuring the safety of the power grid. Traditional transformer condition monitoring methods mainly rely on electrical sensors and electronic devices, which may be affected by electromagnetic interference and may have reliability problems during long-term operation. Due to its advantages such as anti-electromagnetic interference, high reliability, and the ability to achieve distributed measurement, fiber optic sensing technology has gradually become an important means for transformer condition monitoring.

[0003] Common fiber optic sensing technologies include Fiber Bragg Grating (FBG) sensor technology and Brillouin Optical Time Domain Reflectometry (BOTDR) technology.

[0004] In the Fiber Bragg Grating (FBG) sensor technology, the FBG sensor is based on the grating structure in the optical fiber. When light waves pass through the grating, light of a specific wavelength is reflected, and the rest is transmitted. The reflected wavelength is directly related to the strain and temperature changes in the optical fiber and is widely used in monitoring the temperature and strain of transformers. By embedding FBG sensors in transformer oil or fixing them on transformer windings, the internal temperature changes and mechanical strain of the transformer can be monitored in real time. However, the demodulation and processing of FBG sensor signals require high-precision optical equipment and complex signal processing algorithms.

[0005] Brillouin Optical Time Domain Reflectometry (BOTDR) technology is based on the Brillouin scattering principle and obtains the strain and temperature information distributed along the optical fiber by measuring the Brillouin scattering frequency shift in the optical fiber. The BOTDR technology can achieve distributed measurement of the internal temperature and strain of the transformer. By arranging optical fibers inside the transformer, continuous monitoring can be carried out for long-distance transformer windings and the inside of the oil tank. However, BOTDR systems usually require expensive optical equipment and complex signal processing algorithms, with a relatively high system cost and a relatively long measurement time, which is not suitable for real-time and fast-changing monitoring requirements.

[0006] In summary, for the existing transformer internal gas concentration detection devices based on fiber optic sensing technology, when demodulating the signals collected from inside the transformer, the signal processing method is complex, the device cost is high, and the measurement time is relatively long, which is not suitable for real-time monitoring, resulting in the problems of low detection efficiency and high cost. Summary of the Invention

[0007] To this end, the technical problem to be solved by the present invention is to overcome the problems of low detection efficiency and high cost when the existing technology demodulates the internal signals of the transformer collected to obtain the corresponding detection results.

[0008] To solve the above technical problems, the present invention provides a gas concentration monitoring device in a transformer based on optical interference demodulation, including:

[0009] A light source module, configured to generate narrowband laser with a preset wavelength and output it in two paths;

[0010] An acousto-optic modulator, whose input end is connected to the output end of the light source module, and frequency-shifts one path of narrowband laser to obtain a frequency-shifted optical signal;

[0011] An optical fiber gas sensor, whose sensing probe is placed inside the transformer to be monitored to obtain a low-frequency phase modulation signal; the input end of its sensing optical fiber is connected to the sensing probe and the output end of the light source module, and uses the low-frequency phase modulation signal to modulate the other path of narrowband laser output by the light source module, and outputs a sensing optical signal carrying a low-frequency phase change through the output end of the sensing optical fiber;

[0012] A balanced photodetector, whose input end is connected to the output end of the acousto-optic modulator and the output end of the sensing optical fiber of the optical fiber gas sensor, performs photoelectric conversion on the frequency-shifted optical signal and the sensing optical signal, and outputs an optical interference beat signal;

[0013] A signal generation module, configured to generate a difference frequency signal that differs from the optical interference beat signal by a preset low-frequency carrier frequency;

[0014] A mixing module, whose input end is connected to the output end of the balanced photodetector and the output end of the signal generation module, mixes and fuses the optical interference beat signal and the difference frequency signal, and outputs a first fused down-converted signal and a second fused down-converted signal;

[0015] A filtering module, whose input end is connected to the output end of the mixing module, filters the first fused down-conversion module and outputs it as a reference signal;

[0016] A lock-in amplifier, whose input end is connected to the output end of the mixing module and the output end of the filtering module, demodulates the second fused down-converted signal based on the reference signal, and obtains a low-frequency phase modulation signal characterizing the gas concentration inside the transformer to be monitored.

[0017] Preferably, the mixing module includes:

[0018] A first power splitter, whose input end is connected to the output end of the balanced photodetector, and divides the optical interference beat signal into two paths for output;

[0019] The second power splitter, whose input end is connected to the output end of the signal generating module, divides the difference frequency signal into two paths for output;

[0020] The first mixer, whose input end is connected to the first output end of the first power splitter and the first output end of the second power splitter, mixes an optical interference beat frequency signal and a difference frequency signal, and outputs it as a first fusion down-converted signal;

[0021] The second mixer, whose input end is connected to the second output end of the first power splitter and the second output end of the second power splitter, mixes the other optical interference beat frequency signal and the other difference frequency signal, and outputs it as a second fusion down-converted signal.

[0022] Preferably, the mixing module includes:

[0023] The mixer, whose input end is connected to the output end of the balanced photodetector and the output end of the signal generating module, mixes the optical interference beat frequency signal and the difference frequency signal, and outputs it as a fusion down-converted signal;

[0024] The power splitter, whose input end is connected to the output end of the mixer, divides the fusion down-converted signal into a first fusion down-converted signal and a second fusion down-converted signal for output.

[0025] Preferably, the light source module includes:

[0026] The narrowband laser, which is used to output narrowband laser with a preset wavelength;

[0027] The optical coupler, whose input end is connected to the output end of the narrowband laser, divides the narrowband laser with the preset wavelength into two paths for output.

[0028] Preferably, the fiber optic gas sensor includes:

[0029] The sensing probe is placed inside the transformer to be monitored. The gas sensing layer inside it generates a low-frequency phase modulation signal by interacting with the gas inside the transformer to be monitored;

[0030] The sensing optical fiber modulates the narrowband laser based on the low-frequency phase modulation signal and outputs a sensing optical signal carrying the low-frequency phase change.

[0031] Preferably, the preset low-frequency carrier frequency is greater than 80KHz.

[0032] This embodiment provides a monitoring method applied to the monitoring device for gas concentration in a transformer based on optical interference demodulation as described above, including:

[0033] Obtain a low-frequency phase modulation signal containing the gas concentration to be measured in the transformer to be monitored;

[0034] Divide the narrowband laser with a preset wavelength into two paths. One path is frequency-shifted through acousto-optic modulation to obtain a frequency-shifted optical signal, and the other path is modulated based on the low-frequency phase modulation signal to obtain a sensing optical signal carrying low-frequency phase changes;

[0035] Perform photoelectric conversion on the frequency-shifted optical signal and the sensing optical signal to generate an optical interference beat signal;

[0036] Obtain a difference frequency signal that differs from the optical interference beat signal by a preset low-frequency carrier frequency;

[0037] Mix and fuse the optical interference beat signal and the difference frequency signal, and output a first fused down-converted signal and a second fused down-converted signal;

[0038] Filter the first fused down-converted signal to obtain a reference signal;

[0039] Based on the reference signal, perform a phase-locked amplification operation on the second fused down-converted signal, and demodulate to obtain the phase amplitude of the low-frequency phase modulation signal in the second fused down-converted signal, so as to obtain the gas concentration in the transformer to be monitored based on the phase amplitude.

[0040] Preferably, the phase amplitude of the low-frequency phase modulation signal in the second fused down-converted signal is proportional to the concentration of the corresponding gas in the transformer to be monitored.

[0041] Preferably, the mixing and fusing of the optical interference beat signal and the difference frequency signal to output a first fused down-converted signal and a second fused down-converted signal includes:

[0042] Divide the optical interference beat signal into a first optical interference beat signal and a second optical interference beat signal;

[0043] Divide the difference frequency signal into a first difference frequency signal and a second difference frequency signal;

[0044] Mix the first optical interference beat signal and the first difference frequency signal, and output it as the first fused down-converted signal;

[0045] Mix the second optical interference beat signal and the second difference frequency signal, and output it as the second fused down-converted signal.

[0046] Preferably, the mixing and fusing of the optical interference beat signal and the difference frequency signal to output a first fused down-converted signal and a second fused down-converted signal includes:

[0047] Mix the optical interference beat signal and the difference frequency signal as the fused down-converted signal;

[0048] Divide the fused down-converted signal into a first fused down-converted signal and a second fused down-converted signal and output them.

[0049] The above technical solution of the present invention has the following beneficial effects compared with the prior art:

[0050] For the gas concentration monitoring device and method in a transformer based on optical interference demodulation provided by the present invention, an optical fiber gas sensor is used to sense the gas concentration inside the transformer to be monitored, generate a corresponding low-frequency phase modulation signal, modulate a narrow-band laser, and obtain a sensing optical signal carrying the low-frequency phase change; the sensing optical signal and the frequency-shifted optical signal generated by frequency shifting are subjected to photoelectric conversion to generate an optical interference beat signal; the optical interference beat signal is mixed and fused to generate two identical signals; one of them is filtered to remove the influence brought by the low-frequency phase modulation signal and used as a reference signal, and the other is used as a signal to be measured. A phase-locked amplifier is used for demodulation to obtain the low-frequency phase modulation signal characterizing the gas concentration inside the transformer to be monitored. Based on the relationship that the phase amplitude of the low-frequency phase modulation signal is proportional to the gas concentration, the gas concentration inside the transformer to be monitored is analyzed, and no complex processing algorithm is required. The present invention uses optical interference means to obtain the low-frequency phase modulation signal that senses the gas concentration inside the transformer to be monitored, and at the same time uses a mixer to down-convert the optical interference beat signal, reducing the frequency of the signal, greatly reducing the time required for signal processing and demodulation, and realizing the rapid detection of the gas concentration inside the transformer to be monitored. Description of the Drawings

[0051] In order to make the content of the present invention easier to be clearly understood, the following further details the present invention according to the specific embodiments of the present invention in conjunction with the drawings, where:

[0052] Figure 1 is a schematic structural diagram of the gas concentration monitoring device in a transformer based on optical interference demodulation provided by the present invention;

[0053] Figure 2 is a schematic diagram of the mixing module that first performs power splitting and then mixing provided by the present invention;

[0054] Figure 3 is a schematic diagram of the mixing module that first performs mixing and then power splitting provided by the present invention;

[0055] Figure 4 is a flowchart of the steps of the gas concentration monitoring method in a transformer based on optical interference demodulation provided by the present invention. Detailed Embodiments

[0056] The following further describes the present invention in conjunction with the drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the embodiments cited do not limit the present invention.

[0057] Refer toFigure 1 As shown in Figure 1 , the structural schematic diagram of the gas concentration monitoring device in the transformer based on optical interference demodulation provided by the present invention. The specific device includes:

[0058] A light source module, which is used to generate narrow-band laser with a preset wavelength and output it in two paths;

[0059] An acousto-optic modulator, whose input end is connected to the output end of the light source module, and frequency-shifts one path of narrow-band laser to obtain a frequency-shifted optical signal;

[0060] An optical fiber gas sensor, whose sensing probe is placed inside the transformer to be monitored to obtain a low-frequency phase modulation signal; the input end of its sensing optical fiber is connected to the sensing probe and the output end of the light source module, and uses the low-frequency phase modulation signal to modulate the other path of narrow-band laser output by the light source module, and outputs a sensing optical signal carrying low-frequency phase change through the output end of the sensing optical fiber;

[0061] A balanced photodetector, whose input end is connected to the output end of the acousto-optic modulator and the output end of the sensing optical fiber of the optical fiber gas sensor, performs photoelectric conversion on the frequency-shifted optical signal and the sensing optical signal, and outputs an optical interference beat signal;

[0062] A signal generating module, which is used to generate a difference frequency signal that differs from the optical interference beat signal by a preset low-frequency carrier frequency;

[0063] A mixing module, whose input end is connected to the output end of the balanced photodetector and the output end of the signal generating module, mixes and fuses the optical interference beat signal and the difference frequency signal, and outputs a first fused down-converted signal and a second fused down-converted signal;

[0064] A filtering module, whose input end is connected to the output end of the mixing module, filters the first fused down-conversion module and outputs it as a reference signal;

[0065] A lock-in amplifier, whose input end is connected to the output end of the mixing module and the output end of the filtering module, demodulates the second fused down-converted signal based on the reference signal to obtain a low-frequency phase modulation signal characterizing the gas concentration inside the transformer to be monitored.

[0066] Specifically, in the embodiment of the present invention, according to the attenuation effects of the mixer and power divider used, two connection methods of the mixing module are provided; since the power divider attenuates high frequencies more than low frequencies, power dividing first and then mixing will attenuate the signal amplitude and reduce the sensitivity. At this time, the method of mixing first and then power dividing needs to be adopted; but when the performance of the power divider is good enough and does not attenuate the target frequency, both connection methods are applicable.

[0067] ① Refer to Figure 2As shown in the figure, it is a schematic diagram of a mixing module that first divides the signal and then mixes it. At this time, the mixing module includes:

[0068] A first power splitter, whose input end is connected to the output end of the balanced photodetector, and divides the optical interference beat signal into two paths for output;

[0069] A second power splitter, whose input end is connected to the output end of the signal generation module, and divides the difference frequency signal into two paths for output;

[0070] A first mixer, whose input end is connected to the first output end of the first power splitter and the first output end of the second power splitter, mixes one path of optical interference beat signal with one path of difference frequency signal, and outputs it as a first fusion down-converted signal;

[0071] A second mixer, whose input end is connected to the second output end of the first power splitter and the second output end of the second power splitter, mixes the other path of optical interference beat signal with the other path of difference frequency signal, and outputs it as a second fusion down-converted signal.

[0072] ② Refer to Figure 3 As shown in the figure, it is a schematic diagram of a mixing module that first mixes the signal and then divides it. At this time, the mixing module includes:

[0073] A mixer, whose input end is connected to the output end of the balanced photodetector and the output end of the signal generation module, mixes the optical interference beat signal with the difference frequency signal, and outputs it as a fusion down-converted signal;

[0074] A power splitter, whose input end is connected to the output end of the mixer, and divides the fusion down-converted signal into a first fusion down-converted signal and a second fusion down-converted signal for output.

[0075] Specifically, the light source module includes:

[0076] A narrowband laser, which is used to output narrowband laser with a preset wavelength;

[0077] An optical coupler, whose input end is connected to the output end of the narrowband laser, and divides the narrowband laser with a preset wavelength into two paths for output.

[0078] Specifically, the fiber optic gas sensor includes:

[0079] A sensing probe, which is placed inside the transformer to be monitored. The gas sensing layer inside it generates a low-frequency phase modulation signal through interaction with the gas inside the transformer to be monitored;

[0080] A sensing optical fiber, which modulates the narrowband laser based on the low-frequency phase modulation signal, and outputs a sensing optical signal carrying low-frequency phase changes.

[0081] In an embodiment of the present invention, the preset low-frequency carrier frequency by which the difference frequency signal differs from the optical interference beat frequency signal is greater than 80 KHz, which can avoid low-frequency noise interference and effectively implement phase carrier at the same time.

[0082] Based on the above description, the gas concentration monitoring device in the transformer based on optical interference demodulation provided by the present invention can be divided into two parts. The first part is used to generate an optical interference beat frequency signal, and the second part is used to demodulate the optical interference beat frequency signal to obtain the corresponding parameter to be measured. In the first part, the source module emits narrowband laser with a specific wavelength through an optical fiber. Using an optical coupler, the generated laser is respectively transmitted to an acousto-optic modulation module and an optical fiber gas sensor; the optical signal is frequency-shifted in the acousto-optic modulation module, and the parameter to be measured inside the transformer is measured in the optical fiber gas sensor, which has a relatively low-frequency change compared with the frequency shift amount in the acousto-optic modulation module. Finally, the two beams of light are transmitted into a balanced photodetector module; the balanced photodetector module processes the two input optical signals to obtain a beat frequency signal carrying the low-frequency change in the optical fiber gas sensor at the frequency of the frequency shift amount in the acousto-optic modulation module, that is, the optical interference beat frequency signal; in the second part, the generated optical interference beat frequency signal is input into the first power splitter module, and at the same time, a signal generated by the signal generation module with a low-frequency carrier frequency that differs from the interference beat frequency signal is input into the second power splitter module; after the first power splitter module and the second power splitter module distribute the input signals, they are respectively output to the first mixer module and the second mixer module for mixing; the signal output by the first mixer module is input into the filtering module to filter out the low-frequency change amount in the interference signal, and only the signal with the required low-frequency carrier frequency is retained as the reference signal, which is jointly input into the lock-in amplifier module with the signal to be measured output by the second mixer module, and the real-time demodulation processing of the low-frequency change amount in the optical interference signal is realized by using the lock-in amplification function. The optical interference demodulation system based on mixer frequency down-conversion proposed by the present invention solves the problem that it is difficult to perform real-time demodulation processing on optical interference signals and requires complex signal processing algorithms.

[0083] The present invention performs optical interference demodulation based on mixer frequency down-conversion. By using the method of mixer frequency down-conversion for the low-frequency information contained in the high-frequency optical interference beat frequency signal, the function of real-time demodulation of the low-frequency change amount generated by the internal state monitoring of the transformer is realized, and the real-time performance of state monitoring is improved.

[0084] In this embodiment, after obtaining the low-frequency phase modulation signal characterizing the gas concentration inside the transformer to be monitored by using the gas concentration monitoring device in the transformer based on optical interference demodulation provided by the present invention, the lock-in amplifier transmits the demodulated signal to the acquisition card through a BNC data cable for storage and analysis. The gas concentration inside the transformer to be monitored includes the concentrations of hydrocarbon gases (methane, ethane, ethylene, acetylene) dissolved in the oil of the transformer to be monitored.

[0085] Based on the above embodiments, in the embodiments of the present invention, there is also provided a monitoring method applied to the gas concentration monitoring device in the transformer based on optical interference demodulation as described above. Referring to Figure 4 As shown, it is a step flowchart of the gas concentration monitoring method in the transformer based on optical interference demodulation. The specific steps include:

[0086] S101: Obtain a low-frequency phase modulation signal containing the gas concentration to be measured in the transformer to be monitored;

[0087] S102: Divide a narrowband laser with a preset wavelength into two paths. One path is frequency-shifted through acousto-optic modulation to obtain a frequency-shifted optical signal, and the other path is modulated based on the low-frequency phase modulation signal to obtain a sensing optical signal carrying low-frequency phase changes;

[0088] S103: Perform photoelectric conversion on the frequency-shifted optical signal and the sensing optical signal to generate an optical interference beat signal;

[0089] S104: Obtain a difference frequency signal that is different from the optical interference beat signal by a preset low-frequency carrier frequency;

[0090] S105: Mix and fuse the optical interference beat signal and the difference frequency signal, and output a first fused down-converted signal and a second fused down-converted signal;

[0091] S106: Filter the first fused down-converted signal to obtain a reference signal;

[0092] S107: Perform a phase-locked amplification operation on the second fused down-converted signal based on the reference signal, and demodulate to obtain the phase amplitude of the low-frequency phase modulation signal in the second fused down-converted signal, so as to obtain the gas concentration in the transformer to be monitored based on the phase amplitude.

[0093] Among them, the phase amplitude of the low-frequency phase modulation signal in the second fused down-converted signal is proportional to the concentration of the corresponding gas in the transformer to be monitored.

[0094] Specifically, in step S105, mixing and fusing the optical interference beat signal and the difference frequency signal includes two methods: mixing first and then splitting equally, and splitting equally first and then mixing. They are respectively:

[0095] ① Splitting equally first and then mixing:

[0096] Divide the optical interference beat signal into a first optical interference beat signal and a second optical interference beat signal;

[0097] Divide the difference frequency signal into a first difference frequency signal and a second difference frequency signal;

[0098] Mix the first optical interference beat signal and the first difference frequency signal, and output it as the first fused down-converted signal;

[0099] Mix the second optical interference beat frequency signal with the second difference frequency signal and output it as the second fused down-converted signal.

[0100] ② Mixing first and then power splitting:

[0101] Mix the optical interference beat frequency signal with the difference frequency signal and output it as the fused down-converted signal;

[0102] Divide the fused down-converted signal into a first fused down-converted signal and a second fused down-converted signal and output them.

[0103] In the gas concentration monitoring device and method for a transformer based on optical interference demodulation according to the present invention, a fiber optic gas sensor is used to sense the gas concentration inside the transformer to be monitored, generate a corresponding low-frequency phase modulation signal, modulate a narrowband laser, and obtain a sensing optical signal carrying a low-frequency phase change; perform photoelectric conversion on the sensing optical signal and the frequency-shifted optical signal generated by frequency shifting to generate an optical interference beat frequency signal; mix and fuse the optical interference beat frequency signal to generate two identical signals; filter one of the signals to remove the influence brought by the low-frequency phase modulation signal and use it as a reference signal, and use the other as a signal to be measured, and perform demodulation using a lock-in amplifier to obtain a low-frequency phase modulation signal characterizing the gas concentration inside the transformer to be monitored. Based on the relationship that the phase amplitude of the low-frequency phase modulation signal is proportional to the gas concentration, analyze the gas concentration inside the transformer to be monitored, and do not require a complex processing algorithm. The present invention uses optical interference means to obtain a low-frequency phase modulation signal that senses the gas concentration inside the transformer to be monitored, and at the same time uses a mixer to down-convert the optical interference beat frequency signal, reducing the frequency of the signal, greatly reducing the time required for signal processing and demodulation, and realizing the rapid detection of the gas concentration inside the transformer to be monitored.

[0104] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0105] This application is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to embodiments of the present application. It should be understood that each flow and / or block in the flowchart and / or block diagram, and the combination of flows and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, such that the instructions executed by the processor of the computer or other programmable data processing devices produce a means for implementing the functions specified in the Figure 1 one or more flows and / or blocks Figure 1 means for implementing the functions specified in one or more blocks or multiple blocks.

[0106] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, such that the instructions stored in the computer-readable memory produce a manufactured article including an instruction means that implements the functions specified in the Figure 1 one or more flows and / or blocks Figure 1 means for implementing the functions specified in one or more blocks or multiple blocks.

[0107] These computer program instructions can also be loaded onto a computer or other programmable data processing device, such that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process, and thus the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in the Figure 1 one or more flows and / or blocks Figure 1 means for implementing the functions specified in one or more blocks or multiple blocks.

[0108] Obviously, the above embodiments are merely examples for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is not necessary and impossible to exhaustively list all implementation manners here. And the obvious changes or variations derived therefrom are still within the protection scope of the present invention.

Claims

1. A gas concentration monitoring device for a transformer based on optical interference demodulation, characterized in that Comprising: A light source module for generating narrowband laser of a preset wavelength and splitting it into two paths for output; An acousto-optic modulator, whose input end is connected to the output end of the light source module, to shift the frequency of one path of narrowband laser to obtain a frequency-shifted optical signal; An optical fiber gas sensor, whose sensing probe is placed inside the transformer to be monitored to obtain a low-frequency phase modulation signal; Its sensing optical fiber input end is connected to the sensing probe and the output end of the light source module, using the low-frequency phase modulation signal to modulate the other path of narrowband laser output by the light source module, and outputting a sensing optical signal carrying low-frequency phase change through the output end of the sensing optical fiber; A balanced photodetector, whose input end is connected to the output end of the acousto-optic modulator and the output end of the sensing optical fiber of the optical fiber gas sensor, performing photoelectric conversion on the frequency-shifted optical signal and the sensing optical signal, and outputting an optical interference beat frequency signal; A signal generation module for generating a difference frequency signal that differs from the optical interference beat frequency signal by a preset low-frequency carrier frequency; A mixing module, whose input end is connected to the output end of the balanced photodetector and the output end of the signal generation module, mixing and fusing the optical interference beat frequency signal and the difference frequency signal, and outputting a first fused down-converted signal and a second fused down-converted signal; A filtering module, whose input end is connected to the output end of the mixing module, filtering the first fused down-conversion module and outputting it as a reference signal; A lock-in amplifier, whose input end is connected to the output end of the mixing module and the output end of the filtering module, demodulating the second fused down-converted signal based on the reference signal to obtain a low-frequency phase modulation signal characterizing the gas concentration inside the transformer to be monitored.

2. The gas concentration monitoring device for a transformer based on optical interference demodulation according to claim 1, characterized in that The mixing module includes: A first power splitter, whose input end is connected to the output end of the balanced photodetector, dividing the optical interference beat frequency signal into two paths for output; A second power splitter, whose input end is connected to the output end of the signal generation module, dividing the difference frequency signal into two paths for output; A first mixer, whose input end is connected to the first output end of the first power splitter and the first output end of the second power splitter, mixing one path of optical interference beat frequency signal and one path of difference frequency signal, and outputting it as a first fused down-converted signal; A second mixer, whose input end is connected to the second output end of the first power splitter and the second output end of the second power splitter, mixing the other path of optical interference beat frequency signal and the other path of difference frequency signal, and outputting it as a second fused down-converted signal.

3. The gas concentration monitoring device for a transformer based on optical interference demodulation according to claim 1, characterized in that The mixing module includes: A mixer, whose input end is connected to the output end of the balanced photodetector and the output end of the signal generation module, mixing the optical interference beat frequency signal and the difference frequency signal, and outputting it as a fused down-converted signal; A power splitter, whose input end is connected to the output end of the mixer, dividing the fused down-converted signal into a first fused down-converted signal and a second fused down-converted signal for output.

4. The gas concentration monitoring device for a transformer based on optical interference demodulation according to claim 1, wherein The light source module includes: A narrowband laser for outputting narrowband laser of a preset wavelength; An optical coupler, whose input end is connected to the output end of the narrowband laser, dividing the narrowband laser of the preset wavelength into two paths for output.

5. The gas concentration monitoring device for a transformer based on optical interference demodulation according to claim 1, characterized in that, The optical fiber gas sensor includes: The sensing probe is placed inside the transformer to be monitored. The gas sensing layer inside it generates a low-frequency phase modulation signal through interaction with the gas inside the transformer to be monitored. The sensing optical fiber modulates the narrowband laser based on the low-frequency phase modulation signal and outputs a sensing optical signal carrying the low-frequency phase change.

6. The method for monitoring the gas concentration in a transformer based on optical interference demodulation according to claim 1, wherein The preset low-frequency carrier frequency is greater than 80 KHz.

7. A monitoring method applied to the gas concentration monitoring device of the transformer based on optical interference demodulation as described in any one of claims 1 to 6, characterized in that, It includes: Obtain a low-frequency phase modulation signal containing the concentration of the gas to be measured in the transformer to be monitored. Divide the narrowband laser with a preset wavelength into two paths. One path is frequency-shifted through acousto-optic modulation to obtain a frequency-shifted optical signal, and the other path is modulated based on the low-frequency phase modulation signal to obtain a sensing optical signal carrying the low-frequency phase change. Perform photoelectric conversion on the frequency-shifted optical signal and the sensing optical signal to generate an optical interference beat frequency signal. Obtain a difference frequency signal that differs from the optical interference beat frequency signal by a preset low-frequency carrier frequency. Mix and fuse the optical interference beat frequency signal and the difference frequency signal, and output a first fused down-converted signal and a second fused down-converted signal. Filter the first fused down-converted signal to obtain a reference signal. Based on the reference signal, perform a phase-locked amplification operation on the second fused down-converted signal, demodulate and obtain the phase amplitude of the low-frequency phase modulation signal in the second fused down-converted signal, so as to obtain the gas concentration in the transformer to be monitored based on the phase amplitude.

8. The gas concentration monitoring method for a transformer based on optical interference demodulation according to claim 7, characterized in that, The phase amplitude of the low-frequency phase modulation signal in the second fused down-converted signal is proportional to the concentration of the corresponding gas in the transformer to be monitored.

9. The method for monitoring the gas concentration in a transformer based on optical interference demodulation according to claim 7, characterized in that, The step of mixing and fusing the optical interference beat frequency signal and the difference frequency signal to output a first fused down-converted signal and a second fused down-converted signal includes: Divide the optical interference beat frequency signal into a first optical interference beat frequency signal and a second optical interference beat frequency signal. Divide the difference frequency signal into a first difference frequency signal and a second difference frequency signal. Mix the first optical interference beat frequency signal and the first difference frequency signal and output it as the first fused down-converted signal. Mix the second optical interference beat frequency signal and the second difference frequency signal and output it as the second fused down-converted signal.

10. The gas concentration monitoring method for a transformer based on optical interference demodulation according to claim 7, wherein The step of mixing and fusing the optical interference beat frequency signal and the difference frequency signal to output a first fused down-converted signal and a second fused down-converted signal includes: Mix the optical interference beat frequency signal and the difference frequency signal as the fused down-converted signal. Divide the fused down-converted signal into a first fused down-converted signal and a second fused down-converted signal and output them.

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