Method and system for detecting concentration of ethylene dissolved in transformer oil

Abstract

The invention discloses a method and system for detecting the concentration of ethylene dissolved in transformer oil, and the method comprises the following steps: carrying out oil-gas separation on the transformer oil to obtain mixed gas containing ethylene and ethane, feeding the mixed gas into a to-be-detected gas chamber, and feeding pure ethane gas as reference gas into a reference gas chamber; performing TDLAS measurement on the gas in the to-be-measured gas chamber and the reference gas chamber at the same time by using laser with ethylene absorption wavelength to respectively obtain second harmonic signals of the mixed gas and the reference gas; and correcting the absorption peak information in the second harmonic signal of the mixed gas by using the absorption peak information in the second harmonic signal of the reference gas, and calculating the ethylene concentration according to the corrected absorption peak information. According to the method, the peak position of the absorption peak of the ethane pure gas under the laser with the ethylene absorption wavelength is found to realize cross interference correction, so that the ethylene measurement accuracy is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of transformer fault diagnosis, and particularly to a method and system for detecting the concentration of dissolved ethylene in transformer oil. Background Art

[0002] The Dissolved Gas Analysis (DGA) technology in transformer oil is an effective method for identifying the state of transformers. The DGA technology evaluates the operating state of transformers by real-time monitoring of multi-component gases dissolved in transformer insulating oil, such as hydrogen (H2), carbon monoxide (CO), carbon dioxide (CO2), methane (CH4), ethane (C2H6), ethylene (C2H4), acetylene (C2H2), etc. Existing methods for monitoring dissolved gases in oil, such as gas chromatography and photoacoustic spectroscopy, have problems such as high maintenance costs and low detection sensitivity. The Tunable Diode Laser Absorption Spectroscopy (TDLAS) technology has advantages such as non-contact measurement and anti-electromagnetic interference, and has very good applicability in the monitoring of dissolved gases in transformer oil.

[0003] The TDLAS technology is a technology that realizes wavelength scanning by applying a tuning signal to a diode laser, obtains the absorption spectrum line of gaseous substances, and thus infers their composition and state information. Currently, when detecting dissolved ethylene gas in transformer oil based on the TDLAS technology, there is inevitably an influence of cross-interference of ethane gas. Especially when detecting a mixed gas with an ethane content significantly greater than the ethylene content, the measurement accuracy of ethylene is difficult to meet the requirements. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: aiming at the technical problems existing in the prior art, the present invention provides a method and system for detecting the concentration of dissolved ethylene in transformer oil, finds the peak position of the absorption peak of pure ethane gas under the laser with the ethylene absorption wavelength, so as to realize cross-interference correction, and thus improve the measurement accuracy of ethylene.

[0005] To solve the above technical problems, the technical solution proposed by the present invention is:

[0006] A method for detecting the concentration of dissolved ethylene in transformer oil, comprising the following steps:

[0007] Perform oil-gas separation on the transformer oil to obtain a mixed gas containing ethylene and ethane, send the mixed gas into the gas chamber to be measured, and send pure ethane gas into the reference gas chamber as a reference gas;

[0008] Use a laser with the ethylene absorption wavelength to perform TDLAS measurement on the gases in the gas chamber to be measured and the reference gas chamber at the same time, and obtain the second harmonic signals of the mixed gas to be measured and the reference gas respectively;

[0009] The absorption peak information in the second harmonic signal of the mixed gas is corrected using the absorption peak information in the second harmonic signal of the reference gas, and the ethylene concentration is calculated based on the corrected absorption peak information.

[0010] Further, when correcting the absorption peak information in the second harmonic signal of the mixed gas using the absorption peak information in the second harmonic signal of the reference gas, it includes:

[0011] Finding the peak and the positions of the left and right valleys of the absorption peak in the second harmonic signal of the mixed gas, and finding the peak position of the absorption peak in the second harmonic signal of the reference gas. The characteristic value of ethylene gas in the mixed gas is calculated based on the peak and the positions of the left and right valleys of the absorption peak in the second harmonic signal of the mixed gas and the peak position of the absorption peak in the second harmonic signal of the reference gas.

[0012] Further, the expression of the characteristic value of ethylene gas is as follows:

[0013] Y 乙烯 =2*[X 待 (b)-X 待 (a)]*|sin[(p - b)*π / (c - a)]|

[0014] Wherein, X 待 (b) and X 待 (a) respectively represent the amplitudes of the second harmonic signal of the mixed gas at the peak position b and the left valley position a of the absorption peak. "||" represents taking the absolute value. p represents the peak position of the absorption peak in the second harmonic signal of the reference gas, and c represents the right valley position in the second harmonic signal of the mixed gas.

[0015] Further, when calculating the ethylene concentration based on the corrected absorption peak information, specifically, the characteristic value of ethylene gas is matched with the fitting function of ethylene concentration and ethylene characteristic value to obtain the corresponding ethylene concentration.

[0016] Further, the laser with the ethylene absorption wavelength is specifically a laser with a wavelength range of 1683.55 - 1683.65 nm.

[0017] Further, the pure ethane gas is specifically a high - concentration pure ethane gas with an ethane concentration greater than 1000 μL / L.

[0018] The present invention also provides a detection system for the dissolved ethylene concentration in transformer oil, including a central control unit, and the central control unit is programmed or configured to execute the detection method for the dissolved ethylene concentration in transformer oil described above.

[0019] The present invention also provides a detection system for the dissolved ethylene concentration in transformer oil, including:

[0020] An oil-gas separation module for separating oil and gas from transformer oil;

[0021] A laser driver module for changing the output laser wavelength of the laser module;

[0022] A laser module for emitting a laser beam;

[0023] A laser splitter for separately sending the laser into the gas chamber to be measured and the reference gas chamber;

[0024] A reference gas chamber for storing pure ethane gas;

[0025] A gas chamber to be measured for storing the mixed gas of ethylene and ethane after oil-gas separation;

[0026] A gas detection module for obtaining the absorption signals of the laser after being absorbed by the gas in the gas chamber to be measured and the reference gas chamber, performing demodulation analysis to obtain the second harmonic signals corresponding to the gas in the gas chamber to be measured and the reference gas chamber, and then using the absorption peak information in the second harmonic signal of the reference gas to correct the absorption peak information in the second harmonic signal of the mixed gas, and calculating the ethylene concentration according to the corrected absorption peak information.

[0027] Further, when the gas detection module uses the absorption peak information in the second harmonic signal of the reference gas to correct the absorption peak information in the second harmonic signal of the mixed gas and calculates the ethylene concentration according to the corrected absorption peak information, it specifically includes:

[0028] Finding the peak and the positions of the left and right valleys of the absorption peak in the second harmonic signal of the mixed gas, and finding the peak position of the absorption peak in the second harmonic signal of the reference gas, and calculating the ethylene gas characteristic value in the mixed gas according to the peak and the positions of the left and right valleys of the absorption peak in the second harmonic signal of the mixed gas and the peak position of the absorption peak in the second harmonic signal of the reference gas;

[0029] Matching the ethylene gas characteristic value with the fitting function of ethylene concentration and ethylene characteristic value to obtain the corresponding ethylene concentration.

[0030] Further, the central wavelength of the laser module is 1683 nm, and the wavelength range is 1682 - 1684 nm.

[0031] Compared with the prior art, the advantages of the present invention are:

[0032] The present invention sends high-concentration pure ethane gas as the reference gas into the reference gas chamber, and at the same time sends the mixed gas of ethylene and ethane into the gas chamber to be measured, uses the laser with the ethylene absorption wavelength to perform TDLAS measurement on the gas in both the gas chamber to be measured and the reference gas chamber, and corrects the measurement result of ethylene in the mixed gas according to the measurement result of the reference gas, realizing cross-interference correction, thereby improving the accuracy of ethylene measurement. Description of the Drawings

[0033] Figure 1 It is a flowchart of the method according to an embodiment of the present invention.

[0034] Figure 2 It is a schematic diagram of the waveforms of the second harmonic signals of the gases in the gas chamber to be measured and the reference gas chamber according to an embodiment of the present invention.

[0035] Figure 3 It is a schematic diagram for comparing the ethylene concentration detection results between the method according to an embodiment of the present invention and the existing method.

[0036] Figure 4 It is a schematic diagram of the system structure according to an embodiment of the present invention. Detailed Embodiments

[0037] The present invention will be further described below in conjunction with the accompanying drawings of the specification and specific preferred embodiments, but the protection scope of the present invention is not limited thereby.

[0038] Embodiment 1

[0039] The existing State Grid enterprise standard Q / GDW 10536-2021 "Technical Specification for On-line Monitoring Devices of Dissolved Gases in Transformer Oil" is the basis for the type appraisal of on-line monitoring devices for DGA transformers. In the cross-sensitivity test item of this standard, when the ethane content > 150 μL / L and the ethylene content < 10 μL / L, the ethylene detection error needs to meet the relevant requirements. For Class A devices, under the above ethane and ethylene contents, the absolute error of ethylene measurement is less than ±0.5 μL / L or the relative error is less than 30%.

[0040] In view of the situation that when the ethane gas in the dissolved gases in transformer insulating oil is significantly greater than the ethylene gas, it is difficult for the TDLAS technology to separate the cross-interference of ethane in the detection of ethylene gas, resulting in the inability to meet the requirements of the standard Q / GDW 10536-2021 for the measurement accuracy of ethylene. This embodiment proposes a method for detecting the concentration of dissolved ethylene in transformer oil, which realizes the cross-interference correction through the peak position of the absorption peak of pure ethane gas at the ethylene wavelength, so as to meet the ethylene measurement requirements in Q / GDW 10536-2021. As Figure 1 shown, the method of this embodiment includes the following steps:

[0041] S1) Separate the oil and gas from the transformer oil to obtain a mixed gas containing ethylene and ethane, send the mixed gas into the gas chamber to be measured, and send pure ethane gas as the reference gas into the reference gas chamber. In this embodiment, the structures, optical paths, photodetectors, etc. of the gas chamber to be measured and the reference gas chamber are all the same, and the only difference is the stored gases;

[0042] S2) Use a laser with an ethylene absorption wavelength to perform TDLAS measurements on the gases in the gas chamber to be measured and the reference gas chamber simultaneously, and obtain the second harmonic signals of the mixed gas to be measured and the reference gas respectively, which are denoted as X 待 , X 参 ;

[0043] S3) Use the absorption peak information in the second harmonic signal of the reference gas to correct the absorption peak information in the second harmonic signal of the mixed gas, and calculate the ethylene concentration based on the corrected absorption peak information.

[0044] Through the above steps, the method of this embodiment realizes cross-interference correction through the absorption peak information of pure ethane gas at the ethylene wavelength, and can improve the accuracy of ethylene concentration detection. In addition, in practical engineering applications, laser wavelength drift is relatively common. For example, temperature changes during the measurement process, DC level drift of the current scan signal, drift of the drive current and temperature, incomplete coupling of the thermistor and the laser chip, aging of the optical path and circuit, etc. will all cause laser wavelength drift. The method of this embodiment can avoid the reduction of detection accuracy in the actual engineering application of the ethylene detection method proposed in this embodiment due to laser wavelength drift by using an additional reference gas chamber.

[0045] The following specifically describes the relevant content of each step.

[0046] In step S1 of this embodiment, the pure ethane gas is specifically high-concentration pure ethane gas with an ethane concentration greater than 1000 μL / L.

[0047] In step S2 of this embodiment, the laser with an ethylene absorption wavelength is specifically a laser with a wavelength range of 1683.55 - 1683.65 nm.

[0048] The specific steps of step S3 of this embodiment are as follows:

[0049] S31) Use the absorption peak information in the second harmonic signal of the reference gas to correct the absorption peak information in the second harmonic signal of the mixed gas. According to the two second harmonic signals X 待 , X 参 , after completing the cross-interference correction, the ethylene eigenvalue Y 乙烯 can be obtained, including the following steps:

[0050] Step 1: According to the second harmonic signal X 参 of the reference gas (high-concentration pure ethane gas) in the reference gas chamber at the ethylene wavelength, find its absorption peak, and record the position p where the peak is located. The second harmonic signal X 参 is as shown by the red curve in Figure 2 ;

[0051] Step 2: According to the second harmonic signal X of the mixed gas in the gas chamber to be measured at the ethylene wavelength 待 , find its absorption peak, and record the position of the left trough of the absorption peak as a, the position of the peak as b, and the position of the right trough as c. The second harmonic signal X 待 is as shown by the blue curve in Figure 2 ;

[0052] Step 3: Calculate the characteristic value of ethylene gas in the mixed gas based on the peak and the positions of the left and right troughs of the absorption peak in the second harmonic signal of the mixed gas, and the peak position of the absorption peak in the second harmonic signal of the reference gas. The expression is as follows:

[0053] Y 乙烯 = 2 * [X 待 (b) - X 待 (a)] * |sin[(p - b) * π / (c - a)]|

[0054] where, X 待 (b) and X 待 (a) respectively represent the amplitudes of the second harmonic signal of the mixed gas at the peak position b and the left trough position a of the absorption peak. "||" represents taking the absolute value. p represents the peak position of the absorption peak in the second harmonic signal of the reference gas, and c represents the position of the right trough in the second harmonic signal of the mixed gas.

[0055] S32) Obtain the ethylene characteristic value Y 乙烯 After that, based on the fitting function of ethylene concentration and ethylene characteristic value, the detection of ethylene concentration can be completed. Specifically, the ethylene gas characteristic value is matched with the fitting function of ethylene concentration and ethylene characteristic value to obtain the corresponding ethylene concentration.

[0056] In this embodiment, the fitting function of ethylene concentration and ethylene characteristic value is obtained by using a laser with an ethylene absorption wavelength to perform TDLAS measurement on the mixed gas of ethylene and ethane with different ethylene content concentrations in advance, obtaining the peak in the corresponding second harmonic signal as the ethylene characteristic value, and then performing data fitting on the array composed of different ethylene concentrations and the corresponding ethylene characteristic values to obtain the fitting function of ethylene concentration and ethylene characteristic value.

[0057] Next, the effect of the method in this embodiment is verified through experiments. For the dissolved gases in transformer oil where the ethane gas is significantly greater than the ethylene gas in multiple groups, the method in this embodiment is used to calculate the ethylene concentration after cross-interference correction, and the TDLAS technology is used to directly calculate the ethylene concentration. The results are as Figure 3 shown. It can be seen that the error of the ethylene concentration obtained by the method in this embodiment is much smaller than the error of the ethylene concentration directly calculated by the TDLAS technology, significantly improving the accuracy of ethylene concentration detection and meeting the requirements of standard Q / GDW 10536 - 2021 at the same time.

[0058] Example Two

[0059] This example proposes a detection system for the concentration of dissolved ethylene in transformer oil. As Figure 4 shown, it includes:

[0060] An oil-gas separation module, which is used to separate oil and gas from the transformer oil to complete the extraction of dissolved gases in the transformer insulating oil;

[0061] A laser driver module, which is used to change the output laser wavelength of the laser module by changing the temperature and current;

[0062] A laser module, which is used to emit a laser beam. In this example, a laser with a central wavelength of 1683 nm is selected for the laser module to scan. This laser can excite a laser beam in the wavelength range of 1682 - 1684 nm, which can cover the absorption range of ethylene;

[0063] A laser splitter, which is used to send the laser into the gas chamber to be measured and the reference gas chamber respectively;

[0064] The gas chamber to be measured, which is used to store the mixed gas of ethylene and ethane extracted after oil-gas separation to complete the detection of ethylene concentration;

[0065] The reference gas chamber, which is used to store pure ethane gas. In this example, the structure, optical path, photodetector, etc. of the reference gas chamber and the gas chamber to be measured are the same;

[0066] A gas detection module, which is used to obtain the absorption signals of the laser after being absorbed by the gas in the gas chamber to be measured and the reference gas chamber, and perform demodulation analysis to obtain the second harmonic signals corresponding to the gases in the gas chamber to be measured and the reference gas chamber. Then, the absorption peak information in the second harmonic signal of the mixed gas is corrected using the absorption peak information in the second harmonic signal of the reference gas, and the ethylene concentration is calculated based on the corrected absorption peak information, so as to complete the calculation and analysis of the ethylene concentration in the gas chamber to be measured.

[0067] As Figure 4 shown, the detection system for the concentration of dissolved ethylene in transformer oil in this example further includes a central control unit, which is used for system control, data processing, sending, displaying, storing, etc.

[0068] For system control, the central control unit in this example is programmed or configured to execute the method for detecting the concentration of dissolved ethylene in transformer oil described in Example One, and the steps are as follows:

[0069] S101: The central control unit enables the oil-gas separation module to complete the extraction of the gas to be measured in the transformer insulating oil and send it into the gas chamber to be measured;

[0070] S102: The central control unit enables the laser driver module to drive the laser to generate laser light with the wavelength absorbed by ethylene. The generated laser light enters the gas chamber to be measured and the reference gas chamber respectively after passing through the laser beam splitter. After being absorbed by the gases in the gas chamber to be measured and the reference gas chamber, photoelectric conversion is completed to obtain corresponding absorption signals;

[0071] S103: The gas detection module respectively demodulates and analyzes the absorption signals of the gas chamber to be measured and the reference gas chamber to obtain the second harmonic signals of the mixed gas and the reference gas corresponding to the gas chamber to be measured and the reference gas chamber, which are respectively denoted as X 待 , X 参 ;

[0072] S104: The gas detection module uses the absorption peak information in the second harmonic signal of the reference gas to correct the absorption peak information in the second harmonic signal of the mixed gas. Specifically, according to the two second harmonic signals X 待 , X 参 , after completing the cross-interference correction, the ethylene eigenvalue Y 乙烯 is obtained. The steps include:

[0073] Find the peak and the positions of the left and right valleys of the absorption peak in the second harmonic signal X 待 of the mixed gas, and find the peak position of the absorption peak in the second harmonic signal X 参 of the reference gas. According to the peak and the positions of the left and right valleys of the absorption peak in the second harmonic signal X 待 of the mixed gas, and the peak position of the absorption peak in the second harmonic signal X 参 of the reference gas, calculate the ethylene gas eigenvalue Y 乙烯 in the mixed gas. The expression is as follows:

[0074] Y 乙烯 = 2 * [X 待 (b) - X 待 (a)] * |sin[(p - b) * π / (c - a)]|

[0075] where X 待 (b), X 待 (a) respectively represent the amplitudes of the second harmonic signal of the mixed gas at the peak position b and the left valley position a of the absorption peak. "||" represents taking the absolute value. p represents the peak position of the absorption peak in the second harmonic signal of the reference gas, and c represents the right valley position in the second harmonic signal of the mixed gas;

[0076] S5: The central control unit calculates the ethylene concentration based on the corrected absorption peak information. Specifically, on the basis of the fitting function of the ethylene concentration and the ethylene eigenvalue, the ethylene concentration detection is completed. The steps include: Substitute the ethylene gas eigenvalue Y 乙烯Match the fitting function of ethylene concentration and ethylene characteristic value to obtain the corresponding ethylene concentration.

[0077] In summary, the present invention proposes a method for detecting the dissolved ethylene concentration in transformer oil, and a corresponding detection system for the dissolved ethylene concentration in transformer oil. The cross-interference correction is realized by the peak position of the absorption peak of pure ethane gas at the ethylene wavelength, which can significantly improve the detection accuracy of ethylene concentration. It effectively solves the problem that when the ethane gas in the dissolved gas in transformer insulating oil is significantly greater than the ethylene gas, it is difficult to separate the cross-interference of ethane in the detection of ethylene gas by the TDLAS technology, resulting in the measurement accuracy of ethylene not meeting the requirements of the standard Q / GDW 10536-2021.

[0078] The above is only a preferred embodiment of the present invention and does not impose any form of limitation on the present invention. Although the present invention has been disclosed above with the preferred embodiment, it is not intended to limit the present invention. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the scope of the protection of the technical solution of the present invention.

Claims

1. A method for detecting the concentration of dissolved ethylene in transformer oil, characterized in that: The following steps are involved: Transformer oil is subjected to oil-gas separation to obtain a mixed gas containing ethylene and ethane, the mixed gas is sent into a gas chamber to be tested, and pure ethane gas is sent into a reference gas chamber as a reference gas; Use laser light with ethylene absorption wavelength to perform TDLAS measurement on the gases in the test gas chamber and the reference gas chamber at the same time, and obtain the second harmonic signals of the mixed gas and the reference gas respectively; The absorption peak information in the second harmonic signal of the mixed gas is corrected using the absorption peak information in the second harmonic signal of the reference gas, and the ethylene concentration is calculated based on the corrected absorption peak information.

2. The method for detecting dissolved ethylene concentration in transformer oil according to claim 1, characterized in that: When the absorption peak information in the second harmonic signal of the reference gas is used to correct the absorption peak information in the second harmonic signal of the mixed gas, it includes: The peak and left and right trough positions of the absorption peak in the second harmonic signal of the mixed gas are found, and the peak position of the absorption peak in the second harmonic signal of the reference gas is found. The characteristic value of ethylene gas in the mixed gas is calculated based on the peak and left and right trough positions of the absorption peak in the second harmonic signal of the mixed gas and the peak position of the absorption peak in the second harmonic signal of the reference gas.

3. The method for detecting the concentration of dissolved ethylene in transformer oil according to claim 2, wherein: The expression of the characteristic value of ethylene gas is as follows: Y 乙烯 =2*[X 待 (b)-X 待 (a)]*|sin[(pb)*π / (ca)]| Among them, X 待 (b) X 待 (a) represents the amplitude of the second harmonic signal of the mixed gas at the absorption peak position b and the left trough position a, respectively. "||" represents the absolute value. p represents the peak position of the absorption peak in the second harmonic signal of the reference gas. c represents the right trough position in the second harmonic signal of the mixed gas.

4. The method for detecting the concentration of dissolved ethylene in transformer oil according to claim 2, wherein: When the ethylene concentration is calculated based on the corrected absorption peak information, specifically, the ethylene gas characteristic value is matched with the ethylene concentration and the ethylene characteristic value fitting function to obtain the corresponding ethylene concentration.

5. The method for detecting the concentration of dissolved ethylene in transformer oil according to claim 1, wherein: The laser with the ethylene absorption wavelength is specifically a laser with a wavelength range of 1683.55 to 1683.65 nm.

6. The method for detecting the concentration of dissolved ethylene in transformer oil according to claim 1, wherein: The pure ethane gas is specifically a high-concentration pure ethane gas with an ethane concentration greater than 1000 μL / L.

7. A system for detecting the concentration of dissolved ethylene in transformer oil, characterized in that: It comprises a central control unit, which is programmed or configured to execute the method for detecting dissolved ethylene concentration in transformer oil according to any one of claims 1 to 6.

8. A system for detecting the concentration of dissolved ethylene in transformer oil, characterized in that: include: Oil-gas separation module, used to separate oil and gas from transformer oil; A laser driving module, used to change the output laser wavelength of the laser module; A laser module, used for emitting a laser beam; A laser divider, used for sending laser light into the gas chamber to be tested and the reference gas chamber respectively; Reference gas chamber, used to store pure ethane gas; The gas chamber to be tested is used to store the mixed gas of ethylene and ethane after oil and gas separation; The gas detection module is used to obtain the absorption signal of the laser in the test gas chamber and the reference gas chamber after being absorbed by the gas, and perform demodulation analysis to obtain the second harmonic signal corresponding to the gas in the test gas chamber and the reference gas chamber, and then use the absorption peak information in the second harmonic signal of the reference gas to correct the absorption peak information in the second harmonic signal of the mixed gas, and calculate the ethylene concentration based on the corrected absorption peak information.

9. The system for detecting dissolved ethylene concentration in transformer oil according to claim 8, characterized in that: The gas detection module uses the absorption peak information in the second harmonic signal of the reference gas to correct the absorption peak information in the second harmonic signal of the mixed gas, and calculates the ethylene concentration according to the corrected absorption peak information, specifically including: Find the peak and left and right trough positions of the absorption peak in the second harmonic signal of the mixed gas, and find the peak position of the absorption peak in the second harmonic signal of the reference gas, and calculate the characteristic value of ethylene gas in the mixed gas according to the peak and left and right trough positions of the absorption peak in the second harmonic signal of the mixed gas and the peak position of the absorption peak in the second harmonic signal of the reference gas; The ethylene gas characteristic value is matched with the ethylene concentration and the ethylene characteristic value fitting function to obtain the corresponding ethylene concentration.

10. The system for detecting dissolved ethylene concentration in transformer oil according to claim 8, characterized in that: The central wavelength of the laser module is 1683 nm, and the wavelength range is 1682-1684 nm.

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