TDLAS-based detection system and method for dissolved gas in oil

Abstract

The invention discloses a TDLAS-based system and method for detecting gas dissolved in oil, and the method comprises the steps: selecting four lasers with different central wavelengths to detect six different gases dissolved in oil, controlling the light-emitting time sequence and light-emitting time of the lasers through an optical switch, and setting a characteristic absorption cell and a reference absorption cell, weak useful signals are obtained through two-way phase-locked amplification, and parameters of a gas detection system are dynamically adjusted to obtain an optimal second harmonic peak value for concentration inversion. According to the TDLAS-based dissolved gas in oil detection system provided by the invention, the detection precision of the system after long-term operation is ensured, the economical efficiency and long-term stability of the system are improved, and an auxiliary decision is provided for health condition monitoring of a transformer.

Description

Technical Field

[0001] The present invention relates to the technical field of on-line monitoring of electrical equipment in intelligent substations, and particularly to a dissolved gas in oil detection system based on TDLAS. Background Art

[0002] As an important device in the power grid transmission, transformation, and distribution process, power transformers undertake the key work of voltage conversion and power distribution at different levels, and their normal operation is the core to ensure the safety and stability of the power system. At present, large power transformers at home and abroad are mainly oil-immersed transformers, and their internal composite insulation structure is composed of insulating oil and insulating paper. Since faults such as overheating of transformer oil, spark discharge in oil, and arc discharge in oil will occur during the long-term operation of the transformer, it will accelerate the cracking of materials such as insulating oil and insulating paper and generate gases. By monitoring the concentration of gases such as alkanes, the current health status of the transformer can be effectively reflected.

[0003] Currently, common methods for detecting dissolved gases in transformer oil include: electrochemical detection method, gas chromatography method, photoacoustic spectroscopy method, and tunable diode laser absorption spectroscopy (TDLAS). The electrochemical detection method detects gases based on chemical reactions, with low cost and high sensitivity, but it is limited by the response time and lifespan. The gas chromatography method uses the different adsorption capacities of chromatographic columns for different samples to separate and detect gases. It can achieve the simultaneous detection of multi-component gases, but the carrier gas and chromatographic column need to be frequently replaced. The photoacoustic spectroscopy method realizes the detection of gases based on the photoacoustic effect, with a fast response speed and high measurement accuracy, but the system is complex and vulnerable to environmental noise. TDLAS detects the spectral characteristics of gases by detecting the change in the intensity of transmitted light absorbed by the gases, thereby detecting the gas content. It has the advantages of high sensitivity and non-contact measurement, and has a wide range of applications in the field of gas detection.

[0004] However, when using TDLAS technology to detect dissolved multi-component gases in oil at present, it often needs to be equipped with multiple corresponding lasers. For example, when measuring N different dissolved gases in oil, N lasers need to be configured in equal amounts, resulting in a complex optical path, poor flexibility, and low economic efficiency. In addition, after long-term operation of the system, due to the drift of the central wavelength of the laser, the corresponding signal waveform cannot be obtained in the case of low concentration, resulting in poor gas detection accuracy. Summary of the Invention

[0005] Aiming at the defects of the prior art, the purpose of the present invention is to provide an oil-dissolved gas detection system based on TDLAS, which realizes the rapid detection of 6 different oil-dissolved gases by using lasers with 4 different central wavelengths, ensures the detection accuracy after the long-term operation of the system, improves the economy and long-term stability of the system, and provides an auxiliary decision for the health condition monitoring of transformers.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] The first aspect of the present invention provides an oil-dissolved gas detection system based on TDLAS, including: N2 lasers with different central wavelengths, a reference absorption cell 7, a characteristic absorption cell 8, a photodetector, a lock-in amplifier 11, a signal processing circuit 12 and a control module;

[0008] The reference absorption cell 7 is filled with N1 kinds of known oil-dissolved gases with set concentrations, and the characteristic absorption cell 8 is filled with a to-be-detected gas with an unknown concentration and an unknown type, and the to-be-detected gas is at least one of the N1 kinds of known oil-dissolved gases; the N1 kinds of known oil-dissolved gases are divided into N2 groups, and each group contains one or two oil-dissolved gases. If the difference between the gas absorption spectra of two oil-dissolved gases is less than a set value, they are divided into one group;

[0009] The N2 lasers with different central wavelengths are used to emit laser light to detect N1 different oil-dissolved gases, where N1 > N2; the gas absorption spectra of the N2 groups of to-be-detected gases respectively correspond to the central wavelengths of the N2 lasers;

[0010] The control module controls the light emission timing and light emission time of the N2 lasers with different central wavelengths. After the transmitted light is split, it enters the characteristic absorption cell 8 and the reference absorption cell 7 respectively. The photodetector performs photoelectric conversion to obtain the electrical signal after gas molecule absorption; the electrical signal is input into the lock-in amplifier and the signal processing circuit 12 for extracting the weak useful signal in the electrical signal and performing concentration inversion.

[0011] Preferably, if there is only one oil-dissolved gas in the group, after rounding the gas absorption spectrum to the nearest integer, it is used as the central wavelength of the corresponding laser; if there are two oil-dissolved gases in the group, when selecting a laser, it is necessary to consider the measurement of both gases. After averaging the two gas absorption spectra and rounding to the nearest integer, it is used as the central wavelength of the corresponding laser.

[0012] Preferably, for the gas absorption spectral lines of six different dissolved gases in oil in the near-infrared region, four lasers with different central wavelengths are selected to emit light. The gas absorption spectral lines of six different dissolved gases in oil, namely C2H2, CH4, C2H4, C2H6, CO, and CO2, in the near-infrared region are 1522.0 nm, 1653.1 nm, 1681.8 nm, 1680.2 nm, 1580.8 nm, and 1579.1 nm respectively;

[0013] C2H2 is classified into the first group, CH4 is classified into the second group, C2H4 and C2H6 are classified into the third group, and CO and CO2 are classified into the fourth group. Furthermore, four distributed feedback lasers with different central wavelengths of 1522 nm, 1653 nm, 1680 nm, and 1579 nm are selected.

[0014] Preferably, the dissolved gas in oil detection system further includes: the optical switch 5, which switches N2 lasers with different central wavelengths, and the switching time is less than or equal to 15 ms, and the number of switching channels is greater than or equal to 4 channels.

[0015] Preferably, the characteristic absorption cell and the reference absorption cell are White cells, the effective optical path range is 3 - 20 m, and the cell volume range is 50 - 300 ml.

[0016] The second aspect of the present invention provides a method for detecting dissolved gases in oil based on TDLAS. Based on the above-mentioned dissolved gas in oil detection system based on TDLAS, it includes the following steps:

[0017] Step 1, according to the gas absorption spectral lines of N1 dissolved gases in oil in the near-infrared region, combine them into N2 groups, where N2 < N1, and determine the different central wavelengths of N2 lasers;

[0018] Step 2, control the emission timing and emission time of N2 lasers with different central wavelengths, use the fiber optic coupler 6 to split the transmitted light, and the transmitted light enters the reference absorption cell 7 and the characteristic absorption cell 8 of the gas detection system in two equal parts. The first photodetector 9 and the second photodetector 10 detect the laser passing through the reference absorption cell 7 and the characteristic absorption cell 8, perform photoelectric conversion, and obtain the electrical signal after gas molecule absorption; input the electrical signal into the lock-in amplifier;

[0019] Step 3, dynamically adjust the parameters of the gas detection system to make the peak value of the waveform after lock-in amplification output by the reference absorption cell 7 the largest;

[0020] Step 4, fix the parameters of the gas detection system when the waveform peak value in Step 3 is the largest, obtain the corresponding waveform of the characteristic absorption cell, and perform peak-to-concentration inversion.

[0021] Preferably, Step 1 includes:

[0022] Step 1.1: Obtain the gas absorption spectral lines of the dissolved gases in N1 kinds of oils in the near-infrared region.

[0023] Step 1.2: Sort the gas absorption spectral lines of each dissolved gas in the oil obtained in Step 1.1 in the near-infrared region. If the adjacent gas absorption spectral lines are less than the set value, they are divided into one group. If the adjacent gas absorption spectral lines are not less than the set value, they are each in a separate group, and a total of N2 groups are divided.

[0024] Step 1.3: Determine the center wavelength of the laser for each group of dissolved gases in the oil. If there is only one kind of dissolved gas in the group, after rounding the gas absorption spectral line to the nearest integer, it is used as the center wavelength of the laser. If there are two kinds of dissolved gases in the group, when selecting a laser, it is necessary to consider the measurement of both gases. After averaging the two gas absorption spectral lines and rounding to the nearest integer, it is used as the center wavelength of the laser.

[0025] Preferably, obtain the gas absorption spectral lines of 6 kinds of dissolved gases in the oil, namely C2H2, CH4, C2H4, C2H6, CO, and CO2, in the near-infrared region, which are 1522.0 nm, 1653.1 nm, 1681.8 nm, 1680.2 nm, 1580.8 nm, and 1579.1 nm respectively. Divide C2H2 into the first group, CH4 into the second group, C2H4 and C2H6 into the third group, and CO and CO2 into the fourth group. Select 4 distributed feedback lasers with different center wavelengths, and the center wavelengths are 1522 nm, 1653 nm, 1680 nm, and 1579 nm respectively.

[0026] Preferably, Step 2 includes: Using an optical switch 5 to switch N2 lasers with different center wavelengths, the switching time is less than or equal to 15 ms, and the switching channels are greater than or equal to 4 channels, so that the lasers are connected to the gas detection system to emit light in sequence, and the light emission time lasts for 10 - 60 s.

[0027] Preferably, Step 3 includes: Dynamically adjusting the working temperature, minimum drive current, and maximum drive current of the laser so that the waveform peak value generated after the high-concentration gas in the reference absorption cell 7 absorbs light is the largest, and the waveform peak value is the second harmonic peak value generated by gas absorption.

[0028] Preferably, in Step 3, two reference signals with the same frequency as the signal to be measured are used to perform cross-correlation operations with the signal to be measured respectively; after passing through a low-pass filter to filter out the high-frequency components, the DC component containing the amplitude of the signal to be measured is retained, and the final signal is obtained by summing, and the waveform peak is extracted.

[0029] The beneficial effects of the present invention are as follows: by using the TDLAS-based dissolved gas detection system in oil, rapid detection of six different dissolved gases in oil can be achieved using lasers with four different central wavelengths, thereby ensuring the detection accuracy after long-term operation of the system, improving the economy and long-term stability of the system, and providing auxiliary decision-making for transformer health status monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a schematic structural diagram of a TDLAS-based dissolved gas detection system in oil provided in an embodiment of the present invention;

[0031] Figure 1 Middle: 1-1522nm central wavelength laser, 2-1653nm central wavelength laser, 3-1680nm central wavelength laser, 4-1579nm central wavelength laser, 5-optical switch, 6-fiber coupler, 7-reference absorption cell, 8-characteristic absorption cell, 9-first photodetector, 10-second photodetector, 11-lock-in amplifier, 12-signal processing circuit. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0033] In view of the defects or improvement needs of the prior art, the present invention provides a TDLAS-based dissolved gas detection system in oil, which realizes the rapid detection of six different dissolved gases in oil using lasers with four different central wavelengths, ensures the detection accuracy after long-term operation of the system, improves the economy and long-term stability of the system, and provides auxiliary decision-making for transformer health status monitoring.

[0034] Embodiment 1 of the present invention provides a TDLAS-based dissolved gas detection system in oil, comprising: N2 lasers with different central wavelengths, an optical switch 5, an optical fiber coupler 6, a reference absorption cell 7, a characteristic absorption cell 8, a first photodetector 9, a second photodetector 10, a phase-locked amplifier 11, a signal processing circuit 12 and a control module.

[0035] The N2 lasers with different central wavelengths are used to emit lasers to detect N1 different gases dissolved in oil, N1>N2. Specifically, the N1 known gases dissolved in oil can be divided into N2 groups, each group containing one or two gases dissolved in oil, and if the difference between the gas absorption spectra of the two gases dissolved in oil is less than a set value, they are divided into one group; the gas absorption spectra of the N2 groups of gases to be tested correspond to the central wavelengths of the N2 lasers respectively.

[0036] Preferably, the gas absorption spectral lines of N1 kinds of known dissolved gases in oil in the near-infrared region are sorted, and it is determined whether to divide adjacent gas absorption spectral lines into a group according to the following formula. If formula (1) holds, the adjacent gas absorption spectral lines are divided into a group; otherwise, each single gas forms a group.

[0037] δ i+1 =|s i -s i+1 |≤S TH (1)

[0038] In the formula:

[0039] δ i+1 represents the relative difference between the (i + 1)-th gas absorption spectral line and the i-th gas absorption spectral line in the gas absorption spectral line sequence;

[0040] s i represents the i-th gas absorption spectral line, where i ∈ [1, N1];

[0041] S TH represents the set grouping threshold. Preferably but not limited to, S TH ≤2 nm.

[0042] Determine the center wavelength of the laser for each group of dissolved gases in oil. If there is only one kind of dissolved gas in oil in a group, after rounding the gas absorption spectral line to an integer, it is used as the corresponding laser center wavelength; if there are two kinds of dissolved gases in oil in a group, when selecting a laser, it is necessary to take both gases into account. After averaging the two gas absorption spectral lines and rounding to an integer, it is used as the corresponding laser center wavelength.

[0043] The N2 lasers with different center wavelengths are distributed feedback lasers, and the operating temperature range is 25 - 35 °C, and the drive current range is 20 - 110 mA

[0044] In a preferred but non-limiting embodiment of the present invention, for the gas absorption spectral lines of 6 different dissolved gases in oil in the near-infrared region, 4 lasers with different center wavelengths are selected to emit light for gas molecule absorption, that is, N1 = 6 and N2 = 4. Specifically, the 4 lasers with different center wavelengths include: laser 1 with a center wavelength of 1522 nm, laser 2 with a center wavelength of 1653 nm, laser 3 with a center wavelength of 1680 nm, and laser 4 with a center wavelength of 1579 nm, which are respectively used for C2H2, CH4, C2H4, and C2H6, CO, and CO2 gas molecule absorption.

[0045] Among them, the gas absorption spectral lines of C2H2, CH4, C2H4, C2H6, CO, and CO2 in six different oils in the near-infrared region are 1522.0 nm, 1653.1 nm, 1681.8 nm, 1680.2 nm, 1580.8 nm, and 1579.1 nm respectively; according to formula (1), C2H2 is classified into the first group, CH4 is classified into the second group, C2H4 and C2H6 are classified into the third group, and CO and CO2 are classified into the fourth group. Furthermore, distributed feedback lasers with four different central wavelengths of 1522 nm, 1653 nm, 1680 nm, and 1579 nm are selected.

[0046] The optical switch 5 is used to control the emission timing and emission time of lasers with N2 different central wavelengths. Specifically, the control module uses the optical switch 5 to switch lasers with N2 different central wavelengths, the switching time is less than or equal to 15 ms, and the switching channels are greater than or equal to 4 channels, so that the lasers are connected to the gas detection system to emit light according to the timing, and the emission time lasts for 10 - 60 s.

[0047] The optical fiber coupler 6 is used to split the transmitted light, and the transmitted light enters the reference absorption cell 7 and the characteristic absorption cell 8 of the gas detection system in a one-to-two manner. Preferably, the splitting ratio of the optical fiber coupler is 1:1.

[0048] The reference absorption cell 7 is used to compare and find the signal waveform and determine the parameters of the gas detection system, which is filled with N1 kinds of known dissolved gases in oil with set concentrations, and N1 > N2. The characteristic absorption cell 8 is used to detect the concentration of dissolved gases in oil, which is filled with a to-be-detected gas with an unknown concentration and an unknown type, and the to-be-detected gas is at least one of the N1 kinds of known dissolved gases in oil. The transmitted light enters the characteristic absorption cell 8 and the reference absorption cell 7 after passing through the optical fiber coupler 6, and gas molecule absorption occurs in the cells, causing the light intensity signal to attenuate weakly and being converted into a useful electrical signal by the photodetector.

[0049] In a preferred but non-limiting embodiment of the present invention, the characteristic absorption cell and the reference absorption cell of the gas detection system are White cells, the effective optical path range is 3 - 20 m, and the cell volume range is 50 - 300 ml.

[0050] The first photodetector 9 and the second photodetector 10 are used to detect the laser passing through the reference absorption cell 7 and the characteristic absorption cell 8, perform photoelectric conversion, and obtain the electrical signal after gas molecule absorption.

[0051] The lock-in amplifier 11 is used to receive the electrical signals obtained by the first photodetector 9 and the second photodetector 10, and perform lock-in amplification using two reference signals with the same frequency as the to-be-detected signal.

[0052] The signal processing circuit 12 is used to receive the signal amplified by phase-locked amplifier 11, and two reference signals with the same frequency as the signal to be measured are adopted to perform cross-correlation operations with the signal to be measured respectively. Subsequently, the high-frequency components are filtered out through a low-pass filter, and the DC component containing the amplitude of the signal to be measured is retained, and the final signal is obtained by summation. Preferably, the frequencies of the two reference signals are twice the high-frequency driving frequency of the laser, and the phases of the two reference signals differ by 90°. The cut-off frequency of the low-pass filter is 100 Hz.

[0053] The control module is used to dynamically adjust the parameters of the gas detection system, including: switching the optical switch 5, adjusting the working temperature of the laser, the minimum driving current and the maximum driving current to maximize the waveform peak value of the final signal generated by the reference absorption cell 7. The waveform peak value is the second harmonic peak value generated by gas absorption, which is used for inversion with the concentration.

[0054] Embodiment 2 of the present invention provides a method for detecting dissolved gases in oil based on TDLAS, including the following steps:

[0055] Step 1, according to the gas absorption spectra of N1 kinds of dissolved gases in oil in the near-infrared region, merge them into N2 groups, N2 < N1, and determine the different central wavelengths of N2 lasers.

[0056] In a preferred but non-limiting embodiment of the present invention, Step 1 specifically includes:

[0057] Step 1.1, obtain the gas absorption spectra of N1 kinds of dissolved gases in oil in the near-infrared region.

[0058] In a preferred but non-limiting embodiment of the present invention, the gas absorption spectra of 6 kinds of dissolved gases in oil, namely C2H2, CH4, C2H4, C2H6, CO and CO2, in the near-infrared region are obtained, which are 1522.0 nm, 1653.1 nm, 1681.8 nm, 1680.2 nm, 1580.8 nm, and 1579.1 nm respectively.

[0059] Step 1.2, sort the gas absorption spectra of each dissolved gas in oil obtained in Step 1.1. If the adjacent gas absorption spectra are less than the set value, they are divided into one group. If the adjacent gas absorption spectra are not less than the set value, they are separately divided into one group, and a total of N2 groups are divided.

[0060] It should be noted that among the N1 kinds of dissolved gases in oil of the present invention, the gas absorption spectra of at least two gases are less than the set value, so N2 < N1.

[0061] Preferably, it is determined whether to divide adjacent gas absorption spectral lines into a group according to the following formula (1). If formula (1) holds, the adjacent gas absorption spectral lines are divided into a group; otherwise, each gas is a separate group.

[0062] δ i+1 =|s i -s i+1 |≤S TH (1)

[0063] In the formula:

[0064] δ i+1 represents the relative difference between the (i + 1)-th gas absorption spectral line and the i-th gas absorption spectral line in the gas absorption spectral line sequence;

[0065] s i represents the i-th gas absorption spectral line, where i ∈ [1, N1];

[0066] S TH represents the set grouping threshold. Preferably but not limited to, S TH ≤2 nm.

[0067] Similarly preferably, it is determined whether to divide adjacent gas absorption spectral lines into a group according to the following formula. If formula (2) holds, the adjacent gas absorption spectral lines are divided into a group; otherwise, each gas is a separate group.

[0068]

[0069] In the formula:

[0070] δ i+1 represents the relative difference between the (i + 1)-th gas absorption spectral line and the i-th gas absorption spectral line in the gas absorption spectral line sequence;

[0071] s i represents the i-th gas absorption spectral line, where i ∈ [1, N1];

[0072] S TH represents the set grouping threshold.

[0073] For the above 6 kinds of gases to be measured, C2H2 is classified into the first group, CH4 is classified into the second group, C2H4 and C2H6 are classified into the third group, and CO and CO2 are classified into the fourth group.

[0074] Step 1.3: Determine the center wavelength of the laser for each group of dissolved gases in oil. If there is only one type of dissolved gas in the group, round the gas absorption spectral line to the nearest integer, which will be used as the center wavelength of the laser. If there are two types of dissolved gases in the group, when selecting a laser, it is necessary to consider the measurement of both gases. After averaging the absorption spectral lines of the two gases and rounding to the nearest integer, it will be used as the center wavelength of the laser. It can be understood that N2 different center wavelengths will be obtained in Step 1.3.

[0075] For the gas absorption spectral lines of the above six different dissolved gases in oil in the near-infrared region, four distributed feedback lasers with different center wavelengths are selected, and the center wavelengths are 1522nm, 1653nm, 1680nm, and 1579nm respectively.

[0076] Step 2: Using the N2 different center wavelengths obtained in Step 1, select lasers with N2 different center wavelengths to emit light. Control the emission timing and emission time of the lasers with N2 different center wavelengths. The optical fiber coupler 6 splits the transmitted light, and the transmitted light enters the reference absorption cell 7 and the characteristic absorption cell 8 of the gas detection system in two equal parts. The first photodetector 9 and the second photodetector 10 detect the laser passing through the reference absorption cell 7 and the characteristic absorption cell 8, perform photoelectric conversion, and obtain the electrical signal after the gas molecules absorb. Input the electrical signal into the lock-in amplifier to extract the weak useful signal in the electrical signal.

[0077] In a preferred but non-limiting embodiment of the present invention, Step 2 specifically includes: The control module uses the optical switch 5 to switch the lasers with N2 different center wavelengths, the switching time is less than or equal to 15ms, and the switching channels are greater than or equal to 4 channels, so that the lasers are connected to the gas detection system to emit light in sequence, and the emission time lasts for 10 - 60S.

[0078] Step 3: Dynamically adjust the parameters of the gas detection system to make the peak value of the waveform output from the reference absorption cell 7 after lock-in amplification the largest.

[0079] In a preferred but non-limiting embodiment of the present invention, Step 3 includes: Dynamically adjusting the working temperature, minimum drive current, and maximum drive current of the laser to make the peak value of the waveform generated after the high-concentration gas in the reference absorption cell 7 absorbs light the largest, and the waveform peak value is the second harmonic peak value generated by gas absorption.

[0080] Specifically, the lock-in amplifier 11 receives the electrical signals obtained by the first photodetector 9 and the second photodetector 10, and performs lock-in amplification using two reference signals with the same frequency as the signal to be measured. More preferably, two reference signals with the same frequency as the signal to be measured are used to perform cross-correlation operations with the signal to be measured respectively. Subsequently, the high-frequency components are filtered out by a low-pass filter, the DC component containing the amplitude of the signal to be measured is retained, and the final signal is obtained by summation. Preferably, the frequencies of the two reference signals are twice the high-frequency driving frequency of the laser, and the phases of the two reference signals differ by 90°. The cut-off frequency of the low-pass filter is 100 Hz.

[0081] Step 4: Fix the parameters of the gas detection system when the waveform peak value in Step 3 is the largest, obtain the corresponding waveform of the characteristic absorption cell, and perform peak-concentration inversion.

[0082] In a preferred but non-limiting embodiment of the present invention, Step 4 includes:

[0083] Fix the working temperature, minimum driving current, and maximum driving current of the laser at this time in Step 3, obtain the waveform peak value generated after the gas with the concentration to be measured absorbs light, and perform inversion with the concentration.

[0084] It should be noted that the present invention provides a reference absorption cell 7, which contains six known high-concentration gases. If only the characteristic absorption cell 8 exists, when the concentration of the gas to be measured is very low and the central wavelength drifts, it is impossible to obtain a useful waveform or the waveform deteriorates under the set working temperature and driving current of the laser, resulting in poor or abnormal gas detection accuracy; by providing a reference absorption cell containing six known high-concentration gases, one path of the transmitted light will enter it after passing through the fiber optic coupler. Since the gas concentration in the reference absorption cell is high, the absorption waveform and the corresponding position of its peak value can be clearly seen. Therefore, by recording the peak position and its change rule for program correction, adjusting the laser temperature and driving current, the waveform peak value can be restored to the initial position. Thus, the influence caused by the central wavelength drift is solved.

[0085] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and the descriptions in the specification only illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A dissolved gas in oil detection system based on TDLAS, characterized in that, Including: N2 lasers with different central wavelengths, a reference absorption cell (7), a characteristic absorption cell (8), a photodetector, a lock-in amplifier (11), a signal processing circuit (12) and a control module; The reference absorption cell (7) is filled with N1 kinds of known dissolved gases in oil with set concentrations, and the characteristic absorption cell (8) is filled with the to-be-detected gas with unknown concentration and unknown type, and the to-be-detected gas is at least one of the N1 kinds of known dissolved gases in oil; the N1 kinds of known dissolved gases in oil are divided into N2 groups, and each group contains one or two dissolved gases in oil. If the difference between the gas absorption spectra of two dissolved gases in oil is less than the set value, they are divided into one group; The N2 lasers with different central wavelengths are used to emit laser light to detect N1 different dissolved gases in oil, where N1 > N2; the gas absorption spectra of the N2 groups of to-be-detected gases respectively correspond to the central wavelengths of the N2 lasers; The control module controls the light emission timing and light emission time of the N2 lasers with different central wavelengths. After the transmitted light is split, it enters the characteristic absorption cell (8) and the reference absorption cell (7) respectively. The photodetector performs photoelectric conversion to obtain the electrical signal after gas molecule absorption; The electrical signal is input into the lock-in amplifier and the signal processing circuit (12) to extract the weak useful signal in the electrical signal and perform concentration inversion.

2. The dissolved gas in oil detection system based on TDLAS according to claim 1, characterized in that: If there is only one dissolved gas in oil in a group, after rounding the gas absorption spectrum to the nearest integer, it is used as the central wavelength of the corresponding laser; if there are two dissolved gases in oil in a group, when selecting a laser, the measurement of both gases needs to be considered. After averaging the two gas absorption spectra and rounding to the nearest integer, it is used as the central wavelength of the corresponding laser.

3. The dissolved gas in oil detection system based on TDLAS according to claim 3, characterized in that: For the gas absorption spectra of 6 different dissolved gases in oil in the near-infrared region, 4 lasers with different central wavelengths are selected to emit light. The gas absorption spectra of 6 different dissolved gases in oil, namely C2H2, CH4, C2H4, C2H6, CO and CO2, in the near-infrared region are 1522.0nm, 1653.1nm, 1681.8nm, 1680.2nm, 1580.8nm, 1579.1nm respectively; C2H2 is classified into the first group, CH4 is classified into the second group, C2H4 and C2H6 are classified into the third group, and CO and CO2 are classified into the fourth group. Furthermore, 4 distributed feedback lasers with different central wavelengths of 1522nm, 1653nm, 1680nm, and 1579nm are selected.

4. The dissolved gas in oil detection system based on TDLAS according to any one of claims 1 to 3, characterized in that: The dissolved gas in oil detection system further includes: the optical switch (5), and the optical switch (5) switches the N2 lasers with different central wavelengths, and the switching time is less than or equal to 15ms, and the switching channels are greater than or equal to 4 channels.

5. A dissolved gas detection system in oil based on TDLAS according to any one of claims 1 to 3, characterized in that: The characteristic absorption cell and the reference absorption cell are White cells, with an effective optical path range of 3 to 20 m and a cell volume range of 50 to 300 ml.

6. A method for detecting dissolved gases in oil based on TDLAS, based on a system for detecting dissolved gases in oil based on TDLAS according to any one of claims 1-5, characterized in that, It includes the following steps: Step 1, according to the gas absorption spectral lines of N1 kinds of dissolved gases in oil in the near-infrared region, merge them into N2 groups, N2 < N1, and determine the different central wavelengths of N2 lasers; Step 2, control the emission timing and emission time of N2 lasers with different central wavelengths, use an optical fiber coupler (6) to split the transmitted light, and the transmitted light enters the reference absorption cell (7) and the characteristic absorption cell (8) of the gas detection system in two equal parts. The first photodetector (9) and the second photodetector (10) detect the laser passing through the reference absorption cell (7) and the characteristic absorption cell (8), perform photoelectric conversion, and obtain the electrical signal after gas molecule absorption; input the electrical signal into a lock-in amplifier; Step 3, dynamically adjust the parameters of the gas detection system to make the peak value of the waveform output from the reference absorption cell (7) after lock-in amplification the largest; Step 4, fix the parameters of the gas detection system when the waveform peak value in Step 3 is the largest, obtain the corresponding waveform of the characteristic absorption cell, and perform peak and concentration inversion.

7. A dissolved gas detection method in oil based on TDLAS according to claim 6, characterized in that: Step 1 includes: Step 1.1, obtain the gas absorption spectral lines of N1 kinds of dissolved gases in oil in the near-infrared region; Step 1.2, sort the gas absorption spectral lines of each dissolved gas in oil obtained in Step 1.1 in the near-infrared region. If the adjacent gas absorption spectral lines are less than the set value, divide them into one group. If the adjacent gas absorption spectral lines are not less than the set value, make them into a separate group, and a total of N2 groups are divided; Step 1.3, determine the laser center wavelength for each group of dissolved gases in oil. If there is only one kind of dissolved gas in oil in the group, round the gas absorption spectral line to the nearest integer as the laser center wavelength; if there are two kinds of dissolved gases in oil in the group, when selecting a laser, it is necessary to take both gases into account. After averaging the two gas absorption spectral lines and rounding to the nearest integer, it is used as the laser center wavelength.

8. A dissolved gas detection method in oil based on TDLAS according to claim 7, characterized in that: Obtain the gas absorption spectral lines of 6 kinds of dissolved gases in oil, namely C2H2, CH4, C2H4, C2H6, CO, and CO2, in the near-infrared region, which are 1522.0 nm, 1653.1 nm, 1681.8 nm, 1680.2 nm, 1580.8 nm, and 1579.1 nm respectively; divide C2H2 into the first group, CH4 into the second group, C2H4 and C2H6 into the third group, and CO and CO2 into the fourth group; select 4 distributed feedback lasers with different central wavelengths, and the central wavelengths are 1522 nm, 1653 nm, 1680 nm, and 1579 nm respectively.

9. A dissolved gas detection method in oil based on TDLAS according to claim 6 or 7, characterized in that: Step 2 includes: using an optical switch (5) to switch N2 lasers with different central wavelengths, the switching time is less than or equal to 15 ms, and the number of switching channels is greater than or equal to 4 channels, so that the lasers access the gas detection system to emit light in sequence, and the light emission time lasts for 10 to 60 s.

10. A method for detecting dissolved gases in oil based on TDLAS according to claim 6 or 7, characterized in that: Step 3 includes: dynamically adjusting the working temperature, minimum drive current and maximum drive current of the laser so that the peak value of the waveform generated after the high-concentration gas in the reference absorption cell (7) absorbs light is the largest, and the waveform peak value is the peak value of the second harmonic generated by gas absorption.

11. A method for detecting dissolved gases in oil based on TDLAS according to claim 10, characterized in that: In step 3, two reference signals with the same frequency as the signal to be measured are used to perform cross-correlation operations with the signal to be measured respectively; the high-frequency components are filtered out through a low-pass filter, and the DC component containing the amplitude of the signal to be measured is retained, and then summed to obtain the final signal, and the waveform peak is extracted.

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