Dry and wet transformer separated gas online detection system and method based on double-enhanced photoacoustic spectroscopy

Abstract

The invention discloses a dry and wet transformer separated gas online detection system and method based on a double-enhanced photoacoustic spectrometry, and the system comprises an air intake and exhaust module which obtains the dissolved gas of the oil of a liquid transformer or the decomposed gas of the insulating gas of a dry type transformer; the laser module is used for providing laser for gas absorption to generate sound waves; the movable annular light path mechanism is used for providing a light path and adjusting the length of a light cavity so as to realize optical enhancement; the photoacoustic cell is used for receiving the gas output by the intake and exhaust module and constructing a photoacoustic cavity; the tuning fork type quartz crystal oscillator is arranged in the photoacoustic cell and is matched with the modulation frequency of the laser and the resonant frequency of the photoacoustic cavity to realize acoustic enhancement; and the control and signal processing module is used for setting and controlling other modules of the system, processing a signal, and outputting and displaying a detection result. According to the invention, continuous online detection of the content of fault gas and micro water dissolved in the transformer oil can be realized, and comprehensive real-time monitoring and early warning are provided for the transformer.

Description

Technical Field

[0001] This invention belongs to the field of transformers and relates to gas detection technology for dry and wet transformers. Specifically, it relates to an online gas detection system and method for dry and wet transformers based on dual-enhanced photoacoustic spectroscopy. Background Technology

[0002] When an internal fault exists in SF6 electrical equipment, the SF6 gas and solid insulating material in the fault area will decompose under the influence of heat and electricity, producing characteristic components such as SO2, SOF2, H2S, CO, HF, and CF4. Therefore, detecting the content of these characteristic components can diagnose the internal fault. However, because the content of characteristic gases in latent internal faults is relatively small, and the mobility of SF6 gas is very poor, the decomposition products mainly dissolve slowly into the SF6 gas through dissolution, diffusion, and weak convection caused by changes in ambient temperature. Therefore, it is essential to select detection methods and instruments with high sensitivity, good stability, and fast response speed.

[0003] However, existing detection methods and instruments suffer from many problems, such as poor equipment compatibility, limited types of test gases, unstable measurements, inaccurate low-concentration tests, weak signals, and large equipment size, making it difficult to achieve ideal detection results. Summary of the Invention

[0004] Purpose of the invention: In order to overcome the shortcomings of the existing technology, this invention provides an online gas detection system and method for dry and wet transformers based on dual-enhanced photoacoustic spectroscopy. It can realize continuous online detection of fault gases such as H2, CO, CO2, CH4, C2H2, C2H4, and C2H6 dissolved in transformer oil, as well as trace moisture content, providing comprehensive real-time monitoring and early warning for transformers.

[0005] Technical Solution: To achieve the above objectives, this invention provides an online gas detection system for dry and wet transformers based on dual-enhanced photoacoustic spectroscopy, comprising:

[0006] The intake and exhaust module obtains dissolved gases from liquid transformer oil or decomposed gases from insulating gases in dry-type transformers.

[0007] Laser module, used to provide laser light, which is absorbed by the gas to generate sound waves;

[0008] A movable annular optical path mechanism is used to provide an optical path and adjust the length of the optical cavity, so that the laser resonates within the optical cavity to achieve optical enhancement.

[0009] The photoacoustic cell is used to receive the gas output from the intake and exhaust modules and forms the photoacoustic cavity;

[0010] A tuning fork quartz crystal oscillator (QTF) is placed inside the photoacoustic cell and achieves acoustic enhancement by matching the modulation frequency of the laser with the resonant frequency of the photoacoustic cavity.

[0011] The control and signal processing module is used to set and control other modules of the system, process signals, and output and display detection results.

[0012] Furthermore, the laser module includes a laser array composed of multiple lasers and corresponding output collimators. The laser wavelength corresponds to the absorption wavelength of the detection gas. The laser module is a quick-change module, which integrates a narrow-linewidth laser that matches the absorption spectrum of the detection gas. This module includes a high-precision temperature control system for stabilizing and adjusting the laser wavelength. The collimator is used to shape and collimate the laser beam so that the light spot matches the spacing between the photoacoustic cell and the tuning fork quartz crystal oscillator.

[0013] Furthermore, the movable annular optical path mechanism constructs two sets of annular optical paths in both horizontal and vertical directions. Each set of annular optical paths includes two pairs of reflector groups. Each pair of reflector groups is symmetrically arranged on both sides of the photoacoustic cell, and each pair of reflector groups is equipped with a motion mechanism. The optical cavity length is adjusted by moving relative to each other along the optical axis through the motion mechanism.

[0014] Furthermore, the movable annular optical path mechanism includes two orthogonal plane mirrors in the mirror group. Each mirror in the mirror group can both reflect and transmit the laser beam. Each collimator corresponds to a plane mirror to couple the laser beam into the optical cavity. Each mirror group can be connected to two lasers of different wavelengths, and can connect and couple eight different wavelength lasers to achieve high-precision testing of eight different gases.

[0015] Furthermore, in the movable annular optical path mechanism, the direct spacing between the mirrors in each set of mirrors matches the annular optical path, that is, the light spot spacing (horizontal and vertical) of the annular optical path in the acousto-optic system falls within the T-type tuning fork quartz crystal oscillator, and the midpoint of the two light spots in each annular optical path falls within the resonant point (maximum torque point) of the T-type tuning fork quartz crystal oscillator. In addition, the horizontal distance between the two light spots is not greater than 4 / 5 of the tuning fork spacing, and the vertical distance between the two light spots is greater than twice the horizontal light spot spacing and less than 1 / 2 of the tuning fork length (excluding the T-type head).

[0016] Furthermore, the photoacoustic cell includes a resonator, a buffer chamber, and a pair of optical windows; a tuning fork quartz crystal is disposed in the middle of the photoacoustic cell, and the gap of the tuning fork quartz crystal is parallel to the resonant cavity surface of the photoacoustic cell, allowing for fine-tuning of the angle to achieve optimal response intensity; the two light spots of the horizontal mirror group do not interfere with the tuning fork arms of the tuning fork quartz crystal, but fall between the two tuning fork arms.

[0017] Furthermore, the tuning fork quartz crystal oscillator adopts a T-shaped structure design, and the formula for the center resonant frequency of the quartz tuning fork is as follows:

[0018]

[0019] In the formula, ρ and L p T and T represent the density, length, and width of the fork arm, respectively.

[0020] Furthermore, the control and signal processing module includes a drive component, a phase-locked amplifier component, an ADC component, a feedback and control component, and a display and wireless communication component, as detailed below:

[0021] The driving component is used to drive the laser, control and regulate its current and temperature, and modulate it; drive the mirror assembly; drive the tuning fork quartz crystal oscillator, and output a reference signal to the lock-in amplifier for signal demodulation. The driving component's laser driving includes constant current driving and temperature control. Laser modulation includes a low-frequency scanning current and a slightly higher-frequency modulation current. The low-frequency scanning current has a triangular or sawtooth waveform. The slightly higher-frequency modulation signal is a sinusoidal signal with a frequency half that of a certain order longitudinal resonant frequency of the H-type photoacoustic cavity and also half that of the T-type tuning fork quartz crystal oscillator.

[0022] Lock-in amplifier: Used to demodulate the tuning fork quartz crystal oscillator signal. The modulation signal of the modulating laser and the signal of the T-type tuning fork quartz crystal oscillator are input into the lock-in amplifier, and the first harmonic, second harmonic and third harmonic are output.

[0023] Feedback and Control Components: This is the core of the entire control and signal processing module. It is used to implement the functions of the control module, including control drive, lock-in amplification, ADC, concentration inversion and display, etc. It outputs signals to control the intake and exhaust systems, and processes the output signals of the lock-in amplification to use the feedback network PID to precisely control the laser and the reflector assembly. The algorithm in the feedback and control components contains multiple closed-loop control logics, such as: scanning relevant drive parameters, using harmonic signals as error signals to input to the PID, and feedback modulation of relevant drive parameters until the system reaches the predetermined steady state.

[0024] Display and wireless communication components are used for displaying and storing gas composition and concentration.

[0025] Based on the above system, the present invention provides an online gas detection method for dry and wet transformers based on dual-enhanced photoacoustic spectroscopy, comprising the following steps:

[0026] S1: The control and signal processing module controls the intake and exhaust module to obtain dissolved gas from liquid transformer oil or decomposed insulating gas from dry transformer. The intake and exhaust module injects gas into the photoacoustic cell through the inlet of the photoacoustic cell. Once the photoacoustic cell is full of gas, the intake and exhaust module stops working.

[0027] S2: The driving component performs temperature control, current tuning, and modulation signal superposition on a laser according to the initial settings; at the same time, it controls the mirror group to stabilize it.

[0028] S3: Input the T-type tuning fork quartz crystal oscillator and the reference signal into the normalized third harmonic signal output of the lock-in amplifier module. The third harmonic is used as an error feedback signal input to the PID controller in the control module. The output of the PID controller controls the laser current bias in the driver, realizing closed-loop control of the laser output center frequency. When the third harmonic signal output signal is 0 and the slope is at its maximum, the current is the optimal current.

[0029] S4: The scanning voltage of the mirror group in the ring optical path is adjusted by the drive component. The collected T-type tuning fork quartz crystal oscillator signal and the reference signal are input to the normalized third harmonic signal output by the lock-in amplifier module. The third harmonic is used as an error feedback signal and is input to the PID controller in the control module. The output of the PID controller controls the scanning voltage of the mirror group. When the third harmonic signal output signal is 0 and the slope is at its maximum, the voltage value is the optimal voltage for the drive component to drive the mirror group.

[0030] S5: The obtained driving current temperature, optimal current, and optimal voltage are used as the laser operating temperature, current, and driving voltage of the mirror group, respectively. After a certain integration time, the first harmonic signal and the second harmonic signal output by the lock-in amplifier are extracted. After denoising and filtering, the second harmonic is normalized with the amplitude of the first harmonic. The amplitude of the normalized second harmonic is extracted and then inverted to output the gas concentration.

[0031] S6: The control and signal processing module controls the drive components to light up the remaining lasers in sequence, repeating steps S2-S5 until all lasers have been cycled through.

[0032] Based on the above, the innovative points of this invention can be summarized as follows:

[0033] 1. Optical enhancement: A tunable optical cavity is used, and the cavity length can be adjusted for different gas measurements, so that the laser resonates within the optical cavity.

[0034] 2. Tunable optical cavity: It adopts a non-interference four-reflective annular optical path constructed in both the horizontal and vertical directions. The two pairs of reflected optical paths are symmetrically placed on both sides of the photoacoustic cell, and the mirrors in each pair can move relative to each other along the optical axis to achieve the adjustment of the optical cavity length. Combined with the laser's own frequency stabilization drive system, the laser resonates in the cavity. At the same time, the presence of the annular optical path increases the effective optical path length, enhances the effective absorption of the laser by the gas, and generates higher intensity sound waves.

[0035] 3. Acoustic enhancement: The modulation frequency of the laser is set to half of the QTF resonant frequency. At the same time, the tuning fork quartz crystal oscillator (QTF) is matched with the resonant frequency of the photoacoustic cavity and installed at the center of the photoacoustic cavity. Through COMSOL multiphysics simulation, the photoacoustic cavity is constructed using an H-shaped photoacoustic cell to achieve resonance enhancement between the gas absorption laser-generated sound wave and the photoacoustic cavity, which also falls on the resonant frequency of the QTF.

[0036] 4. Select the time-division laser, start the frequency stabilization system, adjust the optical cavity to make the laser resonate and enhance the absorption of the laser by the gas; extract the signal, and after phase-locked amplification test, cycle through all lasers.

[0037] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0038] 1. It solves the problem of inaccurate detection of ultra-low concentration trace gases, effectively improving the overall detection effect;

[0039] 2. It can detect multiple gases simultaneously, which not only improves detection efficiency but also enhances detection functionality;

[0040] 3. It is applicable to gas detection of both dry and wet transformers and protection devices, solving the problems of poor equipment compatibility and limited types of test gases;

[0041] 4. The detection integration is high, the equipment is convenient, and the problem of large equipment size has been solved. Attached Figure Description

[0042] Figure 1 This is a front view of the online gas detection system for dry and wet transformers.

[0043] Figure 2 This is a top view of the online gas detection system for dry and wet transformers;

[0044] Figure 3 This is a structural diagram of a T-type tuning fork quartz crystal oscillator;

[0045] Figure 4 This is a detection status diagram of the gas online detection system for dry and wet transformers;

[0046] Figure 5 This is a diagram of the third harmonic signal;

[0047] Figure 6 This is a graph showing the concentration detection data of CF4 gas.

[0048] Figure 7 This is a graph showing the concentration detection data of CS2 gas.

[0049] Figure 8 This is a graph showing the concentration detection data of H2S gas.

[0050] Figure 9 This is a graph showing the concentration detection data of SO2F2 gas. Detailed Implementation

[0051] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. After reading this invention, any modifications of the invention in various equivalent forms by those skilled in the art will fall within the scope defined by the appended claims.

[0052] Example 1:

[0053] like Figure 1 and Figure 2 As shown, this embodiment provides an online gas detection system for dry and wet transformers based on dual-enhanced photoacoustic spectroscopy, including:

[0054] The intake and exhaust module obtains dissolved gases from liquid transformer oil or decomposed gases from insulating gases in dry-type transformers.

[0055] Laser module, used to provide laser light, which is absorbed by the gas to generate sound waves;

[0056] A movable annular optical path mechanism is used to provide an optical path and adjust the length of the optical cavity, so that the laser resonates within the optical cavity to achieve optical enhancement.

[0057] The photoacoustic cell is used to receive the gas output from the intake and exhaust modules and forms the photoacoustic cavity;

[0058] A tuning fork quartz crystal oscillator (QTF) is placed inside the photoacoustic cell and achieves acoustic enhancement by matching the modulation frequency of the laser with the resonant frequency of the photoacoustic cavity.

[0059] The control and signal processing module is used to set and control other modules of the system, process signals, and output and display detection results.

[0060] The laser module includes a laser array composed of various lasers and corresponding output collimators. The laser wavelength corresponds to the absorption wavelength of the detection gas. In this embodiment, the linewidth is less than 5MHz and the power is 2-10mW. The laser module is a quick-change module, which integrates a narrow-linewidth laser that matches the absorption spectrum of the detection gas. This module includes a high-precision temperature control system for stabilizing and adjusting the laser wavelength. The collimator is used to shape and collimate the laser beam so that the beam spot matches the spacing between the photoacoustic cell and the tuning fork quartz crystal oscillator. In this embodiment, the size of the collimated beam spot is set to 1 / 3 of the tuning fork spacing, and the relationship between the beam spot and the tuning fork spacing is: D≤1 / 2*tuning fork spacing. The connection method between the laser and the collimator is not limited to a specific connection method. For example, fiber optic collimation or spatial light collimation can be used.

[0061] The movable annular optical path mechanism constructs two sets of annular optical paths in both horizontal and vertical directions. Each set of annular optical paths includes two pairs of reflectors, each pair of reflectors being symmetrically arranged on both sides of the photoacoustic cell. Each pair of reflectors is equipped with a motion mechanism, which moves relative to each other along the optical axis to adjust the length of the optical cavity. In this embodiment, the motion mechanism can be a high-precision piezoelectric ceramic, or a servo, stepper, linear displacement, or other closed-loop control mechanism.

[0062] The movable annular optical path mechanism includes a mirror assembly comprising two orthogonal plane mirrors. Each mirror in the assembly can both reflect and transmit a laser beam. Each collimator corresponds one-to-one with a plane mirror, coupling the laser beam into the optical cavity. Each mirror assembly can be connected to two lasers of different wavelengths, allowing for the coupling of eight different wavelength lasers to achieve high-precision testing of eight different gases. In this embodiment, the mirror material is not limited, but the transmittance of the laser light band corresponding to the gas under test is 5-10%, and the surface profile is 1 / 4-1 / 10λ (@632.8nm).

[0063] In the movable annular optical path mechanism, the direct spacing between the mirrors in each group of reflectors matches the annular optical path. This ensures that the beam spacing (horizontal and vertical) of the annular optical path in the acousto-optic system falls within the T-type tuning fork quartz crystal oscillator. Furthermore, the midpoint of the two beams in each annular optical path falls at the resonant point (maximum torque point) of the T-type tuning fork quartz crystal oscillator. Horizontally, the distance between the two beams is no greater than 4 / 5 of the tuning fork spacing, and vertically, the distance is greater than twice the horizontal beam spacing but less than 1 / 2 of the tuning fork length (excluding the T-head). (This design is based on the fact that the beams in the tuning fork do not overlap and do not contact the tuning fork wall, allowing for sufficient space; the vertical distribution being less than 1 / 2 of the length is because this position has a stronger resonance effect.) The resonant position differs for T-type QTF tuning forks with different parameters. The beam spacing can be determined based on the parameters of the T-type tuning fork and the acousto-optic cell, and then the spacing of the mirrors in the reflector group can be determined based on the position of the incident light from the collimator.

[0064] The photoacoustic cell includes a resonator, a buffer chamber, and a pair of optical windows. The resonator, buffer chamber, and optical windows are constructed of materials resistant to strong acids and alkalis, such as NS3301. The windows can transmit the absorption spectrum of the gas to be detected and have some corrosion resistance, such as calcium fluoride. A tuning fork quartz crystal is placed in the middle of the photoacoustic cell. The gap of the tuning fork quartz crystal is parallel to the resonant cavity surface of the photoacoustic cell, and the angle can be finely adjusted to achieve optimal response intensity. The two light spots of the horizontal mirror group do not interfere with the tuning fork arms of the tuning fork quartz crystal and fall between the two tuning fork arms.

[0065] like Figure 3As shown, the tuning fork quartz crystal oscillator adopts a T-shaped structure design. In this embodiment, the fundamental resonant frequency is selected to be between 2-10kHz. The resonant frequency of the H cell coincides with the fundamental frequency of the T-shaped QTF. The parameters of the quartz tuning fork are as follows: tuning fork spacing 6-10mm, length 12-15mm; width 1.5mm, thickness 0.5mm, T-shaped head 3*3.6mm; resonant frequency is 2869.97Hz.

[0066] The formula for the center resonant frequency of a quartz tuning fork is as follows:

[0067]

[0068] In the formula, ρ = 2650 kg / m³, E = 72 GPa, ν (n＝0) =1.194, ν (n＝1) =2.988; ρ, L p T and T represent the density, length, and width of the fork arm, respectively.

[0069] In this embodiment, the resonant cavity (acoustic resonator) is made of NS3301, and the window is sealed with a calcium fluoride window with a transmittance greater than 90%. The resonant cavity has a radius of 12mm and a length of 60mm. The two buffer cavities each have a radius of 40mm and a length of 25mm. When the gas to be tested is methane with a volume concentration of 100×10⁻⁶ and a laser power of 4.5mW, its fourth longitudinal mode frequency is 2872.5Hz, and the Q of the H-type photoacoustic cell is 62.2. It can have good frequency matching with the T-type QTF.

[0070] The control and signal processing module includes a drive component, a phase-locked amplifier component, an ADC component, a feedback and control component, and a display and wireless communication component, as detailed below:

[0071] Driving components: used to drive the laser, control and regulate the laser's current and temperature, and modulate the laser; drive the mirror assembly; drive the tuning fork quartz crystal oscillator, and output a reference signal to the lock-in amplifier for signal demodulation output; wherein the driving components drive the laser including constant current driving and temperature control, and modulate the laser including a low-frequency scanning current and a slightly higher frequency modulation current. The waveform of the low-frequency scanning current is a triangular wave or a sawtooth wave; the slightly higher frequency modulation signal is a sine wave, with a frequency that is half of the longitudinal resonance frequency of a certain order of the H-type photoacoustic cavity, and also half of the T-type tuning fork quartz crystal oscillator. In this embodiment, it is half of 2869.97Hz, which is 1,434.985Hz;

[0072] Lock-in amplifier: Used to demodulate the tuning fork quartz crystal oscillator signal. The modulation signal of the modulating laser and the signal of the T-type tuning fork quartz crystal oscillator are input into the lock-in amplifier, and the first harmonic, second harmonic and third harmonic are output.

[0073] Feedback and Control Components: This is the core of the entire control and signal processing module. It is used to implement the functions of the control module, including control drive, lock-in amplification, ADC, concentration inversion and display, etc. It outputs signals to control the intake and exhaust systems, and processes the output signals of the lock-in amplification to use the feedback network PID to precisely control the laser and the reflector assembly. The algorithm in the feedback and control components contains multiple closed-loop control logics, such as: scanning relevant drive parameters, using harmonic signals as error signals to input to the PID, and feedback modulation of relevant drive parameters until the system reaches the predetermined steady state.

[0074] ADC component: used to acquire data information;

[0075] Display and wireless communication components are used for displaying and storing gas composition and concentration. The collected data is uploaded to a cloud platform via wireless communication. On the cloud platform, artificial intelligence algorithms are used to analyze the concentration of dissolved gases in the oil or SF6 decomposition gases, diagnose transformer condition, and predict transformer lifespan.

[0076] Because the device of this invention is portable, equipped with a wireless module, can be deployed in a distributed manner, and can be compatible with different equipment types by changing the laser array, it is small in size; it provides a feasible solution for real-time monitoring of the status of large-scale outdoor power equipment and transformer equipment containing SF6, and can provide accurate and real-time status data to an intelligent power big data platform.

[0077] Example 2:

[0078] This embodiment utilizes the system of Embodiment 1 to continuously and online detect fault gases such as H2, CO, CO2, CH4, C2H2, C2H4, and C2H6, as well as trace amounts of water, in liquid transformer oil. It provides a method for online gas detection in dry and wet transformers based on dual-enhanced photoacoustic spectroscopy, referring to... Figure 4 It includes the following steps:

[0079] S1: The control and signal processing module controls the intake and exhaust module to obtain dissolved gas from liquid transformer oil or decomposed insulating gas from dry transformer. The intake and exhaust module injects gas into the photoacoustic cell through the inlet of the photoacoustic cell. Once the photoacoustic cell is full of gas, the intake and exhaust module stops working.

[0080] S2: The driving component performs temperature control, current tuning, and modulation signal superposition on a laser according to the initial settings; at the same time, it controls the mirror group to stabilize it.

[0081] S3: Input the T-type tuning fork quartz crystal oscillator and the reference signal into the lock-in amplifier module to normalize the waveform of the third harmonic signal. The third harmonic signal is as follows: Figure 5As shown. The third harmonic is used as the error feedback signal input to the PID controller in the feedback and control module. The output of the PID controller controls the laser current bias in the driver, realizing closed-loop control of the laser output center frequency; when the third harmonic signal output signal is 0 and the slope is at its maximum, the current is the optimal current.

[0082] S4: By controlling the scanning voltage through the drive component, the reflector group in the ring optical path is adjusted. The acquired T-type tuning fork quartz crystal oscillator signal and the reference signal are input to the normalized third harmonic signal output by the lock-in amplifier module. The third harmonic signal is as follows: Figure 5 As shown. The third harmonic is used as an error feedback signal input to the PID controller in the feedback and control module. The output of the PID controller controls the scanning voltage of the driving mirror group. When the third harmonic signal output signal is 0 and the slope is at its maximum, the voltage value at this time is the optimal voltage for the driving component to drive the mirror group.

[0083] S5: The optimal temperature (obtained in step S2), optimal current, and optimal voltage are used as the laser operating temperature, current, and driving voltage of the mirror assembly, respectively. After a certain integration time, the first and second harmonic signals output by the lock-in amplifier are extracted. After denoising and filtering, the second harmonic is normalized using the amplitude of the first harmonic. The amplitude of the normalized second harmonic is extracted and then inverted to output the gas concentration. The amplitude of the second harmonic signal after normalization of the first harmonic amplitude and the gas concentration have an approximately linear relationship under low absorption. This conclusion is already an industry consensus. The calibration process of the function relating the amplitude of the normalized second harmonic to the gas concentration is also a standard procedure in the industry, so it will not be elaborated here.

[0084] S6: The control and signal processing module controls the drive components to light up the remaining lasers in sequence, repeating steps S2-S5 until all lasers have been cycled through.

[0085] Example 3:

[0086] To verify the effectiveness and efficacy of the present invention, the following fault gas detection data were obtained through experiments in this embodiment:

[0087] Figures 6-9 The concentration detection data for four fault gases, namely CF4, CS2, H2S, and SO2F2, show that the present invention can effectively achieve high-accuracy detection of fault gases in dry and wet transformers.

Claims

1. An online gas detection system for dry and wet transformers based on dual-enhanced photoacoustic spectroscopy, characterized in that, include: The intake and exhaust module obtains dissolved gases from liquid transformer oil or decomposed gases from insulating gases in dry-type transformers. Laser module, used to provide laser light, which is absorbed by the gas to generate sound waves; A movable annular optical path mechanism is used to provide an optical path and adjust the length of the optical cavity, so that the laser resonates within the optical cavity to achieve optical enhancement. The photoacoustic cell is used to receive the gas output from the intake and exhaust modules and forms the photoacoustic cavity; A tuning fork quartz crystal oscillator is placed inside the photoacoustic cell. Acoustic enhancement is achieved by matching the modulation frequency of the laser with the resonant frequency of the photoacoustic cavity. The control and signal processing module is used to set and control other modules of the system, process signals, and output and display detection results.

2. The online gas detection system for dry and wet transformers based on dual-enhanced photoacoustic spectroscopy according to claim 1, characterized in that, The laser module includes a laser array composed of multiple lasers and corresponding output collimators. The laser wavelength corresponds to the absorption wavelength of the detection gas. The laser module is a quick-change module, which integrates a narrow-linewidth laser that matches the absorption spectrum of the detection gas. This module includes a high-precision temperature control system for stabilizing and adjusting the laser wavelength. The collimator is used to shape and collimate the laser beam so that the light spot matches the spacing between the photoacoustic cell and the tuning fork quartz crystal oscillator.

3. The online gas detection system for dry and wet transformers based on dual-enhanced photoacoustic spectroscopy according to claim 1, characterized in that, The movable annular optical path mechanism constructs two sets of annular optical paths in the horizontal and vertical directions. Each set of annular optical paths includes two pairs of reflector groups. Each pair of reflector groups is symmetrically arranged on both sides of the photoacoustic cell, and each pair of reflector groups is equipped with a motion mechanism. The optical cavity length can be adjusted by moving relative to each other along the optical axis through the motion mechanism.

4. The online gas detection system for dry and wet transformers based on dual-enhanced photoacoustic spectroscopy according to claim 3, characterized in that, The movable annular optical path mechanism includes a reflector group comprising two orthogonal plane reflectors. Each reflector in the reflector group can both reflect and transmit the laser beam. Each collimator corresponds one-to-one with the plane reflector to couple the laser beam into the optical cavity.

5. The online gas detection system for dry and wet transformers based on dual-enhanced photoacoustic spectroscopy according to claim 4, characterized in that, In the movable annular optical path mechanism, the direct spacing between the mirrors in each set of mirrors matches the annular optical path, that is, the spacing between the light spots of the annular optical path in the acousto-optic system falls within the T-type tuning fork quartz crystal oscillator, and the midpoint of the two light spots in each annular optical path falls at the resonant point in the T-type tuning fork quartz crystal oscillator. Furthermore, the horizontal distance between the two light spots is no greater than 4 / 5 of the tuning fork spacing, and the vertical distance between the two light spots is greater than twice the horizontal light spot spacing and less than 1 / 2 of the tuning fork length.

6. The online gas detection system for dry and wet transformers based on dual-enhanced photoacoustic spectroscopy according to claim 1, characterized in that, The photoacoustic cell includes a resonator, a buffer chamber, and a pair of optical windows; a tuning fork quartz crystal is placed in the middle of the photoacoustic cell, and the gap of the tuning fork quartz crystal is parallel to the resonant cavity surface of the photoacoustic cell; the two light spots of the horizontal mirror group do not interfere with the tuning fork arms of the tuning fork quartz crystal, and fall between the two tuning fork arms.

7. The online gas detection system for dry and wet transformers based on dual-enhanced photoacoustic spectroscopy according to claim 1, characterized in that, The tuning fork quartz crystal oscillator adopts a T-shaped structure design, and the formula for the center resonant frequency of the quartz tuning fork is as follows: In the formula, ρ and L p T and T represent the density, length, and width of the fork arm, respectively.

8. The online gas detection system for dry and wet transformers based on dual-enhanced photoacoustic spectroscopy according to claim 7, characterized in that, The control and signal processing module includes a drive component, a phase-locked amplifier component, an ADC component, a feedback and control component, and a display and wireless communication component, as detailed below: The driving component is used to drive the laser, control and regulate its current and temperature, and modulate it; drive the mirror assembly; drive the tuning fork quartz crystal oscillator, and output a reference signal to the lock-in amplifier for signal demodulation. The driving component's laser driving includes constant current driving and temperature control. Laser modulation includes a low-frequency scanning current and a slightly higher-frequency modulation current. The low-frequency scanning current has a triangular or sawtooth waveform. The slightly higher-frequency modulation signal is a sinusoidal signal with a frequency half that of a certain order longitudinal resonant frequency of the H-type photoacoustic cavity and also half that of the T-type tuning fork quartz crystal oscillator. Lock-in amplifier: Used to demodulate the tuning fork quartz crystal oscillator signal. The modulation signal of the modulating laser and the signal of the T-type tuning fork quartz crystal oscillator are input into the lock-in amplifier, and the first harmonic, second harmonic and third harmonic are output. Feedback and control components: used to implement the functions of the control module, output signals to control the intake and exhaust system, and process the lock-in amplifier output signals to use the feedback network PID to precisely control the laser and the mirror assembly; Display and wireless communication components are used for displaying and storing gas composition and concentration.

9. A method for online gas detection in dry and wet transformers based on dual-enhanced photoacoustic spectroscopy according to claim 8, characterized in that, Includes the following steps: S1: The control and signal processing module controls the intake and exhaust module to obtain dissolved gas from liquid transformer oil or decomposed insulating gas from dry transformer. The intake and exhaust module injects gas into the photoacoustic cell through the inlet of the photoacoustic cell. Once the photoacoustic cell is full of gas, the intake and exhaust module stops working. S2: The driving component performs temperature control, current tuning, and modulation signal superposition on a laser according to the initial settings; at the same time, it controls the mirror group to stabilize it. S3: Input the T-type tuning fork quartz crystal oscillator and the reference signal into the normalized third harmonic signal output of the lock-in amplifier module. The third harmonic is used as an error feedback signal input to the PID controller in the control module. The output of the PID controller controls the laser current bias in the driver, realizing closed-loop control of the laser output center frequency. When the third harmonic signal output signal is 0 and the slope is at its maximum, the current is the optimal current. S4: The scanning voltage of the mirror group in the ring optical path is adjusted by the drive component. The collected T-type tuning fork quartz crystal oscillator signal and the reference signal are input to the normalized third harmonic signal output by the lock-in amplifier module. The third harmonic is used as an error feedback signal and is input to the PID controller in the control module. The output of the PID controller controls the scanning voltage of the mirror group. When the third harmonic signal output signal is 0 and the slope is at its maximum, the voltage value is the optimal voltage for the drive component to drive the mirror group. S5: The obtained driving current temperature, optimal current, and optimal voltage are used as the laser operating temperature, current, and driving voltage of the mirror group, respectively. After a certain integration time, the first harmonic signal and the second harmonic signal output by the lock-in amplifier are extracted. After denoising and filtering, the second harmonic is normalized with the amplitude of the first harmonic. The amplitude of the normalized second harmonic is extracted and then inverted to output the gas concentration. S6: The control and signal processing module controls the drive components to light up the remaining lasers in sequence, repeating steps S2-S5 until all lasers have been cycled through.

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