Method and system for detecting concentration of ethane gas dissolved in transformer oil

Abstract

The invention discloses a method and system for detecting the gas concentration of ethane dissolved in transformer oil, and the method comprises the following steps: carrying out TDLAS detection on pure ethylene with known concentration at a first wavelength which is maximally absorbed by ethane to obtain a second harmonic X1; respectively determining the calibration coefficients of ethane and ethylene under the first wavelength and the second wavelength which only absorbs ethylene; acquiring an ethane-ethylene mixed gas removed from the transformer oil, performing TDLAS detection under a second wavelength to obtain a second harmonic X2, and calculating the ethylene concentration according to an ethylene calibration coefficient; adjusting the second harmonic X1 according to the concentration ratio of ethylene to pure ethylene; performing TDLAS detection on the mixed gas under the first wavelength to obtain a second harmonic X3, subtracting the second harmonic X3 from the adjusted second harmonic X1'to obtain a second harmonic X4 of ethane, and calculating the concentration of ethane according to an ethane calibration coefficient. The method can effectively remove cross interference of ethylene in the ethane-ethylene mixed gas on ethane concentration detection.

Description

Technical Field

[0001] The present invention relates to a transformer oil spectrum online monitoring technology, and in particular to a method and system for detecting the concentration of dissolved ethane gas in transformer oil. Background Art

[0002] The transformer oil spectroscopy online monitoring system heats the transformer oil to separate the dissolved gases. It then uses tunable diode laser absorption spectroscopy (TDLAS) to measure the gas concentration, thereby inferring potential hidden transformer faults. The main gases dissolved in transformer oil are carbon monoxide, carbon dioxide, methane, ethane, ethylene, and acetylene. TDLAS technology uses a tuning signal applied to a diode laser to scan the wavelength, obtaining absorption lines of gaseous substances and inferring their composition and state. It is widely used for gas detection in industrial and environmental fields.

[0003] Because dissolved gases in transformer oil typically form a mixed gas after release, cross-interference is unavoidable when using TDLAS technology to detect dissolved gases in transformer oil. For example, a mixture of ethane and ethylene may be released from transformer oil. While ethane has a near-infrared absorption peak at 1683.1 nm, ethylene also exhibits significant absorption near this wavelength, indicating ethane-ethylene cross-interference at this wavelength. Using other ethane wavelengths in the near-infrared region would result in absorption intensities below 1683.1 nm, failing to meet the required detection limit.

[0004] Therefore, an effective method is needed to separate cross-interference. Summary of the Invention

[0005] The technical problem to be solved by the present invention is as follows: In view of the above-mentioned problems in the prior art, a method and system for detecting the concentration of dissolved ethane gas in transformer oil are provided, which can effectively eliminate the cross interference of ethylene gas when detecting the ethane concentration in the mixed gas of ethane and ethylene released from the transformer oil.

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

[0007] A method for detecting the concentration of dissolved ethane gas in transformer oil comprises the following steps:

[0008] Performing TDLAS detection on pure ethylene gas of known concentration A at a first wavelength to obtain the second harmonic X1 of the pure ethylene gas, where the first wavelength is the wavelength of maximum absorption by ethane;

[0009] determining an ethane calibration factor at a first wavelength and determining an ethylene calibration factor at a second wavelength, the second wavelength being a wavelength absorbed only by ethylene;

[0010] Obtaining a mixed gas containing ethane and ethylene released from transformer oil, performing TDLAS detection at a second wavelength to obtain the second harmonic X2 of ethylene in the mixed gas, and calculating the concentration B of ethylene in the mixed gas based on the second harmonic X2 of ethylene and an ethylene calibration coefficient;

[0011] According to the ratio of concentration B to concentration A, the second harmonic X1 of pure ethylene gas is adjusted to obtain an adjusted second harmonic X1';

[0012] Performing TDLAS detection on the mixed gas at a first wavelength to obtain a corresponding second harmonic X3, and subtracting the second harmonic X3 from the second harmonic X1' to obtain a second harmonic X4 of ethane in the mixed gas;

[0013] The concentration C of ethane in the mixed gas is calculated based on the second harmonic X4 of ethane and the ethane calibration coefficient.

[0014] Furthermore, determining the ethane calibration coefficient at the first wavelength and determining the ethylene calibration coefficient at the second wavelength both include:

[0015] At a specified wavelength, TDLAS detection is performed on target gases with different known concentrations to obtain the corresponding second harmonics;

[0016] Look for gas absorption peaks in the second harmonic corresponding to each known concentration;

[0017] Perform data fitting on each known concentration and the peak-to-valley value of the corresponding gas absorption peak to obtain a linear relationship between the peak-to-valley value of the second harmonic gas absorption peak and the concentration;

[0018] The coefficient of the linear relationship is used as the calibration coefficient of the target gas at the specified wavelength.

[0019] Furthermore, when calculating the concentration B of ethylene in the mixed gas based on the second harmonic X2 of ethylene and the ethylene calibration coefficient, and when calculating the concentration C of ethane in the mixed gas based on the second harmonic X4 of ethane and the ethane calibration coefficient, both include:

[0020] Find the gas absorption peak in the second harmonic, substitute the peak-to-valley value and calibration coefficient of the gas absorption peak into the corresponding linear relationship, and then solve the concentration variable in the linear relationship to obtain the corresponding gas concentration.

[0021] Furthermore, when searching for the gas absorption peak, the first-order derivative and the second-order derivative of the second harmonic are calculated in sequence, and then each point of the second harmonic is traversed, and the point where the sign of the first-order derivative changes is selected as the candidate point, and the point where the sign of the second-order derivative among the candidate points is less than 0 is selected as the maximum point, and the point where the sign of the second-order derivative among the candidate points is greater than 0 is selected as the minimum point. Finally, the point with the maximum value is selected from the maximum points as the peak point of the gas absorption peak, and the minimum point adjacent to the peak point of the gas absorption peak is selected as the peak-valley point of the gas absorption peak.

[0022] Furthermore, when adjusting the second harmonic X1 of the pure ethylene gas according to the ratio of the concentration B to the concentration A, specifically, the values of all points in the second harmonic X1 of the pure ethylene gas are multiplied by the ratio.

[0023] Furthermore, the first wavelength is 1683.1 nm

[0024] Furthermore, the second wavelength is 1626nm-1627nm.

[0025] The present invention also proposes a system for detecting the concentration of dissolved ethane gas in transformer oil, comprising a memory, a processor, and a computer program stored in the memory. The processor executes the computer program to implement the steps of the method for detecting the concentration of dissolved ethane gas in transformer oil.

[0026] The present invention also provides a computer-readable storage medium having a computer program / instruction stored thereon. When the computer program / instruction is executed by a processor, the steps of the method for detecting the concentration of dissolved ethane gas in transformer oil are implemented.

[0027] The present invention also provides a computer program product, comprising a computer program / instruction, which implements the steps of the method for detecting the concentration of dissolved ethane gas in transformer oil when executed by a processor.

[0028] Compared with the prior art, the advantages of the present invention are:

[0029] The present invention first obtains and records the second harmonic of pure ethylene gas with a known first concentration at the maximum absorption wavelength of ethane, then measures a mixed gas containing ethane and ethylene at a wavelength that can only be absorbed by ethylene to calculate the second concentration of ethylene therein, and adjusts the second harmonic of the pure ethylene gas according to the ratio of the calculated second concentration to the first concentration. Finally, the mixed gas containing ethane and ethylene is measured at the maximum absorption wavelength of ethane to obtain a corresponding second harmonic, and the second harmonic is subtracted from the adjusted second harmonic to obtain the second harmonic of ethane in the mixed gas, and the concentration of ethane in the mixed gas is calculated based on the second harmonic. When the ethane concentration of the mixed gas containing ethane and ethylene is detected at the maximum absorption wavelength of ethane, the cross interference of ethylene on ethane is effectively resolved, and the detection accuracy of near-infrared ethane is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Flowchart of a method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0031] The present invention will be further described below in conjunction with the accompanying drawings and specific preferred embodiments, but the scope of protection of the present invention is not limited thereby.

[0032] Before introducing the specific embodiments of the present invention, the relevant concepts are first explained.

[0033] TDLAS:

[0034] The Lambert-Beer theorem is the core theory of TDLAS, which states that a monochromatic laser with an intensity of I0 and a frequency of v has an intensity of I after passing through an absorbing medium with a length of L. The basic form is:

[0035] I(v)=I0 exp(-α(v)CL)

[0036] Where C is the concentration of the gas being measured, that is, the number of molecules per unit volume; α(v) is the absorption cross section of the medium at frequency v, which is related to the temperature and pressure during the test. The absorbance A of the gas at frequency v can be expressed by the incident light intensity and the initial light intensity:

[0037] A=In(I / I0)

[0038] From the formula, we can see that when monochromatic light passes vertically through a uniform, non-scattering, absorbing medium, its absorbance A is proportional to the concentration C of the absorbing substance and the thickness L of the absorbing layer. If the thickness of the absorbing layer is known, the gas concentration can be calculated from the output light intensity.

[0039] Another foundation of TDLAS is harmonic detection theory, which uses a high-frequency cosine signal to add to the current and modulate the output of the semiconductor laser by controlling the current.

[0040] i ic (t) = i c +i a cosωt

[0041] Where i c and i a Represent the center current value and the modulation amplitude of the injection current respectively, and ω is the modulation frequency. It can be concluded that the instantaneous output frequency of the semiconductor laser is

[0042] v=v c +v a cosωt

[0043] v c and v a The intensity of the laser after absorption by the White cell is expanded into the Fourier series of I(v):

[0044]

[0045] Each harmonic component A n It can be measured by a lock-in amplifier:

[0046]

[0047] Where θ = ωt. When the light absorption intensity of the trace gas in the White cell is α(v)CL << 1, the above formula can be simplified as

[0048]

[0049] Therefore, each harmonic component A n (v c ) is proportional to the trace gas. a When it is much smaller than the absorption line width, Taylor expansion is performed on the above formula:

[0050]

[0051] It can be seen that the nth harmonic component is proportional to the nth derivative of α(v). Due to the factorial in the denominator of the above formula, the amplitude of the absorption spectrum will decrease rapidly as the harmonic order increases. Therefore, when selecting a harmonic to calculate concentration, do not choose a harmonic with too high an order. At the same time, odd harmonics are odd-symmetrical about the central absorption position, and the amplitude is 0 at the absorption center position, but if there is baseline interference, it is not conducive to finding the central absorption position. Even harmonics are even-symmetrical about the central absorption position, and the amplitude is maximum at the central absorption position, which is more conducive to searching for the central absorption position. Usually, the second harmonic is selected for concentration calculation based on factors such as anti-interference ability and amplitude size.

[0052] In practice, the peak-to-valley values of the gas absorption peak in the second harmonic are often used as the basis for concentration calculation. By introducing a known concentration of gas into the White cell in advance, a linear relationship between the peak-to-valley values of the second harmonic gas absorption peak and the concentration is calculated. When measuring a gas of unknown concentration, the concentration can be inferred by calculating the peak-to-valley values of the second harmonic and this relationship.

[0053] Example 1

[0054] This embodiment proposes a method for detecting the concentration of dissolved ethane gas in transformer oil. By using the concept of background subtraction, pure ethylene gas of known concentration is measured at a wavelength of 1683.1 nm, and the second harmonic waveform of pure ethylene at this wavelength is recorded. During actual measurement, the second harmonic waveform of pure ethylene is amplified or reduced according to the actual concentration of ethylene, and the amplified and reduced second harmonic waveform of pure ethylene is subtracted from the measured waveform of the ethane-ethylene mixed gas at 1683.1 nm to obtain the second harmonic waveform of pure ethane in the ethane-ethylene mixed gas. The actual concentration of ethane is obtained based on the second harmonic waveform of pure ethane. Figure 1 As shown, the following steps are included:

[0055] S1) performing TDLAS detection on pure ethylene gas of known concentration A at the wavelength of maximum absorption by ethane (referred to as the first wavelength in this embodiment for differentiation), to obtain the second harmonic X1 of the pure ethylene gas;

[0056] S2) determining an ethane calibration factor at a first wavelength, and determining an ethylene calibration factor at a wavelength that is absorbed only by ethylene (referred to in this embodiment as a second wavelength for differentiation);

[0057] S3) obtaining the mixed gas comprising ethane and ethylene deviated from in the transformer oil, and carrying out TDLAS detection at a second wavelength to obtain the second harmonic X2 of ethylene in the mixed gas, and calculating the concentration B of ethylene in the mixed gas according to the second harmonic X2 of ethylene and the ethylene calibration coefficient;

[0058] S4) adjusting the second harmonic X1 of the pure ethylene gas according to the ratio of the concentration B to the concentration A to obtain an adjusted second harmonic X1';

[0059] S5) performing TDLAS detection on the mixed gas at a first wavelength to obtain a corresponding second harmonic X3, and subtracting the second harmonic X3 from the second harmonic X1′ to obtain a second harmonic X4 of ethane in the mixed gas;

[0060] S6) Calculating the concentration C of ethane in the mixed gas based on the second harmonic X4 of ethane and the ethane calibration coefficient.

[0061] Through the above steps, a simulated second harmonic waveform is generated according to the ethylene concentration, and the simulated second harmonic is subtracted from the second harmonic of the measured mixed gas, thereby removing the interference of ethylene on ethane and improving the detection accuracy of near-infrared ethane.

[0062] In this embodiment, the first wavelength is 1683.1 nm and the second wavelength is 1626.1 nm. Each step is described in detail below.

[0063] In this embodiment, in step S1 , pure ethylene gas of known concentration is introduced into the gas chamber during the field test phase, and the second harmonic waveform of the pure ethylene gas at the wavelength of maximum absorption by ethane is recorded.

[0064] For example, 100 ppm pure ethylene gas is introduced into the gas chamber, and TDLAS detection is performed at a wavelength of 1683.1 nm, and the corresponding second harmonic waveform is recorded.

[0065] In this embodiment, in step S2, during the calibration phase, pure ethane gas is calibrated at a wavelength of 1683.1 nm, and pure ethylene gas is calibrated at a wavelength of 1626.1 nm to determine corresponding ethane calibration coefficients and ethylene calibration coefficients.

[0066] Specifically, in step S2 of this embodiment, when determining the ethane calibration coefficient at the first wavelength and determining the ethylene calibration coefficient at the second wavelength, the following steps are included:

[0067] S21) performing TDLAS detection on a plurality of target gases of different known concentrations at a specified wavelength to obtain corresponding second harmonics, specifically performing TDLAS detection on a plurality of ethanes of different known concentrations at a first wavelength, and performing TDLAS detection on a plurality of ethylenes of different known concentrations at a second wavelength;

[0068] S22) searching for a gas absorption peak in the second harmonic corresponding to each known concentration. In this embodiment, a peak detection algorithm is used to search for the gas absorption peak in the second harmonic. Specifically, the first-order derivative and the second-order derivative of the second harmonic are calculated in sequence. Then, each point of the second harmonic is traversed, and a point where the sign of the first-order derivative changes is selected as a candidate point. The sign change point of the first-order derivative is specifically a data point in the second harmonic where the sign of the first-order derivative of the previous point is opposite to that of the first-order derivative of the next point. The point where the sign of the second-order derivative among the candidate points is less than 0 is selected as a maximum point, and the point where the sign of the second-order derivative among the candidate points is greater than 0 is selected as a minimum point. Finally, the point with the maximum value is selected from the maximum points as the peak point of the gas absorption peak, and the minimum point adjacent to the peak point of the gas absorption peak is selected as the peak-valley point of the gas absorption peak.

[0069] S23) performing data fitting on each concentration of the same target gas and the peak-to-valley value of the corresponding gas absorption peak to obtain a linear relationship between the peak-to-valley value of the gas absorption peak of the second harmonic of the target gas at a specified wavelength and the concentration, as shown in the following expression:

[0070] R=k·c+b

[0071] Wherein, the variable R represents the peak-to-valley value of the gas absorption peak of the second harmonic, the variable c represents the concentration of the target gas, and k and b represent the coefficients obtained by fitting;

[0072] S24) The coefficients of the linear relationship are used as calibration coefficients of the target gas at the specified wavelength, that is, according to the object of data fitting, k and b in the above expression are used as the ethane calibration coefficient at the first wavelength, or the ethylene calibration coefficient at the second wavelength.

[0073] In this embodiment, in step S3, the ethylene concentration in the mixed gas is measured at the second wavelength that is absorbed only by ethylene. When calculating the ethylene concentration B in the mixed gas based on the second harmonic X2 of ethylene and the ethylene calibration coefficient, a peak detection algorithm is used to find the gas absorption peak in the second harmonic X2. The peak-to-valley value of the gas absorption peak and the ethylene calibration coefficient at the second wavelength are substituted into the corresponding linear relationship R = k·c + b. Then, the concentration variable c in the linear relationship is solved to obtain the corresponding ethylene concentration.

[0074] In this embodiment, in step S4 , the second harmonic X1 of the pure ethylene gas with concentration A at the first wavelength of ethane maximum absorption is adjusted to deduce the second harmonic X1 ′ of the pure ethylene gas with concentration B at the first wavelength.

[0075] Specifically, in step S4 of this embodiment, when the second harmonic X1 of the pure ethylene gas is adjusted according to the ratio of the concentration B to the concentration A, the values of all points in the second harmonic X1 of the pure ethylene gas are multiplied by the ratio of the concentration B to the concentration A, thereby amplifying or reducing the waveform of the second harmonic X1 as a whole, and inferring the waveform of the second harmonic X1' of the absorption of ethylene at the first wavelength of 1683.1 nm at the concentration B.

[0076] In this embodiment, in step S5, the second harmonic X3 of the mixed gas at the first wavelength of ethane maximum absorption is measured, and then the ethylene component in the second harmonic X3 is eliminated, thereby eliminating the cross interference of ethylene on ethane, and obtaining the waveform of the second harmonic X4 of the pure ethane gas at the first wavelength of 1683.1 nm for concentration calculation.

[0077] Specifically, in step S5 of this embodiment, when the second harmonic X3 is subtracted from the second harmonic X1', based on the one-to-one correspondence between the data points in the second harmonic X3 and the second harmonic X1', each data point of the second harmonic X3 is traversed, the value of the current data point is subtracted from the corresponding value in the second harmonic X1', and the difference between the two is used as the value of the corresponding data point in the second harmonic X4.

[0078] In step S6 of this embodiment, when calculating the ethane concentration C in the mixed gas based on the second harmonic X4 of ethane and the calibration coefficient of ethane, a peak detection algorithm is used to find the gas absorption peak in the second harmonic X4. The peak-to-valley value of the gas absorption peak and the ethane calibration coefficient at the first wavelength are substituted into the corresponding linear relationship R=k·c+b. The concentration variable c in the linear relationship is then solved to obtain the corresponding ethane concentration.

[0079] Example 2

[0080] This embodiment provides a system for detecting the concentration of dissolved ethane gas in transformer oil, including a memory, a processor, and a computer program stored in the memory. The processor executes the computer program to implement the steps of the method for detecting the concentration of dissolved ethane gas in transformer oil described in Example 1.

[0081] This embodiment further provides a computer-readable storage medium having a computer program / instruction stored thereon. When the computer program / instruction is executed by a processor, the steps of the method for detecting the concentration of dissolved ethane gas in transformer oil described in the first embodiment are implemented.

[0082] This embodiment further provides a computer program product, including a computer program / instruction, which, when executed by a processor, implements the steps of the method for detecting the concentration of dissolved ethane gas in transformer oil described in the first embodiment.

[0083] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiment. All technical solutions based on the concept of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for detecting the concentration of dissolved ethane gas in transformer oil, characterized in that: The following steps are involved: Performing TDLAS detection on pure ethylene gas of known concentration A at a first wavelength to obtain the second harmonic X1 of the pure ethylene gas, where the first wavelength is the wavelength of maximum absorption by ethane; determining an ethane calibration factor at a first wavelength and determining an ethylene calibration factor at a second wavelength, the second wavelength being a wavelength absorbed only by ethylene; Obtaining a mixed gas containing ethane and ethylene released from transformer oil, performing TDLAS detection at a second wavelength to obtain the second harmonic X2 of ethylene in the mixed gas, and calculating the concentration B of ethylene in the mixed gas based on the second harmonic X2 of ethylene and an ethylene calibration coefficient; According to the ratio of concentration B to concentration A, the second harmonic X1 of pure ethylene gas is adjusted to obtain an adjusted second harmonic X1'; Performing TDLAS detection on the mixed gas at a first wavelength to obtain a corresponding second harmonic X3, and subtracting the second harmonic X3 from the second harmonic X1' to obtain a second harmonic X4 of ethane in the mixed gas; The concentration C of ethane in the mixed gas is calculated based on the second harmonic X4 of ethane and the ethane calibration coefficient.

2. The method for detecting dissolved ethane gas concentration in transformer oil according to claim 1, wherein When determining the ethane calibration factor at the first wavelength, and when determining the ethylene calibration factor at the second wavelength, both include: At a specified wavelength, TDLAS detection is performed on target gases with different known concentrations to obtain the corresponding second harmonics; Look for gas absorption peaks in the second harmonic corresponding to each known concentration; Perform data fitting on each known concentration and the peak-to-valley value of the corresponding gas absorption peak to obtain a linear relationship between the peak-to-valley value of the second harmonic gas absorption peak and the concentration; The coefficient of the linear relationship is used as the calibration coefficient of the target gas at the specified wavelength.

3. The method for detecting dissolved ethane gas concentration in transformer oil according to claim 2, wherein: When calculating the concentration B of ethylene in a mixed gas based on the second harmonic X2 of ethylene and the ethylene calibration coefficient, and when calculating the concentration C of ethane in a mixed gas based on the second harmonic X4 of ethane and the ethane calibration coefficient, both include: Find the gas absorption peak in the second harmonic, substitute the peak-to-valley value and calibration coefficient of the gas absorption peak into the corresponding linear relationship, and then solve the concentration variable in the linear relationship to obtain the corresponding gas concentration.

4. The method for detecting dissolved ethane gas concentration in transformer oil according to claim 2 or 3, wherein: When searching for the gas absorption peak, the first-order derivative and the second-order derivative of the second harmonic are calculated in sequence, and then each point of the second harmonic is traversed, and the point where the sign of the first-order derivative changes is selected as the candidate point, and the point where the sign of the second-order derivative among the candidate points is less than 0 is selected as the maximum point, and the point where the sign of the second-order derivative among the candidate points is greater than 0 is selected as the minimum point. Finally, the point with the maximum value is selected from the maximum points as the peak point of the gas absorption peak, and the minimum point adjacent to the peak point of the gas absorption peak is selected as the peak-valley point of the gas absorption peak.

5. The method for detecting dissolved ethane gas concentration in transformer oil according to claim 1, wherein: When the second harmonic X1 of the pure ethylene gas is adjusted according to the ratio of the concentration B to the concentration A, specifically, the values of all points in the second harmonic X1 of the pure ethylene gas are multiplied by the ratio.

6. The method for detecting dissolved ethane gas concentration in transformer oil according to claim 1, wherein: The first wavelength is 1683.1 nm.

7. The method for detecting dissolved ethane gas concentration in transformer oil according to claim 1, wherein: The second wavelength is 1626 nm to 1627 nm.

8. A system for detecting the concentration of dissolved ethane gas in transformer oil, comprising a memory, a processor, and a computer program stored in the memory, wherein: The processor executes the computer program to implement the steps of the method for detecting the concentration of dissolved ethane gas in transformer oil according to any one of claims 1 to 7.

9. A computer-readable storage medium having a computer program / instruction stored thereon, characterized in that: When the computer program / instruction is executed by a processor, the steps of the method for detecting the concentration of dissolved ethane gas in transformer oil according to any one of claims 1 to 7 are implemented.

10. A computer program product comprising a computer program / instructions, characterized in that When the computer program / instruction is executed by a processor, the steps of the method for detecting the concentration of dissolved ethane gas in transformer oil according to any one of claims 1 to 7 are implemented.

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