Method for detecting aromatic hydrocarbon concentration in transformer oil based on fluorescence spectrum correction

Abstract

The method for detecting the aromatic hydrocarbon concentration of transformer oil based on fluorescence spectrum correction belongs to the technical field of transformer fault diagnosis, solves the problem of how to correct the measured aromatic hydrocarbon concentration of transformer oil under the current condition, and improves the detection accuracy of the aromatic hydrocarbon concentration of transformer oil.The method excites the fluorescence spectrum of transformer oil through monochromatic excitation light of the optimal excitation wavelength, establishes the mapping relationship between the fluorescence spectrum of transformer oil and the aromatic hydrocarbon compound concentration by adopting the multivariate regression correction method, designs a multivariate correction filter to calculate the aromatic hydrocarbon concentration of transformer oil under the current condition, corrects the measured aromatic hydrocarbon concentration of transformer oil under the current condition by adopting the calibration coefficient, and thus the real aromatic hydrocarbon concentration of transformer oil is obtained, the influence of external factors under the current condition on the detection accuracy of the aromatic hydrocarbon concentration of transformer oil is eliminated, and the detection accuracy of the aromatic hydrocarbon concentration of transformer oil is improved.

Description

Technical Field

[0001] This invention belongs to the field of transformer fault diagnosis technology, and relates to a method for detecting aromatic hydrocarbon concentration in transformer oil based on fluorescence spectroscopy correction. Background Technology

[0002] Transformers are the core of energy conversion in the process of power generation and distribution. They are numerous and have a wide impact. Their operating status directly affects the safe and reliable operation of the power system. Once a transformer has an accident, it will not only damage expensive electrical equipment (the price of a single transformer can be as high as 50 million yuan), but also cause large-scale power outages, and even cause casualties, environmental pollution, and huge economic and social losses. Therefore, monitoring the operating status of transformers has become particularly important.

[0003] Transformer oil refers to a type of insulating oil used in oil-filled electrical equipment such as transformers, reactors, instrument transformers, bushings, and oil switches, serving as insulation, cooling, and arc-extinguishing agents. Transformer oil is a fractionation product of petroleum, and its main components are alkanes, cycloalkanes, aromatic unsaturated hydrocarbons, and non-hydrocarbon compounds. Transformer oil can fluoresce under ultraviolet or X-ray irradiation. Fluorescence refers to a photoluminescence phenomenon. When a substance at room temperature is irradiated with incident light of a certain wavelength (usually ultraviolet or X-rays), it absorbs the light energy, enters an excited state, and immediately de-excites, emitting outgoing light with a wavelength longer than the incident light (usually in the visible light range); and once the incident light stops, the luminescence disappears immediately. This property of outgoing light is called fluorescence.

[0004] Fluorescent detection technology (FMS) for transformer operation status analyzes changes in the optical signal of the transformer insulating oil through a fluorescent detection device, thereby achieving the purpose of monitoring the transformer. For example, the Chinese invention patent document "An Online Fluorescent Detection Device for Transformer Insulating Oil" (application publication date: July 13, 2021, application publication number: CN113109682A) discloses an online fluorescent detection device for transformer insulating oil that features high sensitivity, short analysis time, immunity to interference from surrounding magnetic and electric fields, and good stability and reproducibility, thus meeting the online fault detection requirements of transformers under operating conditions.

[0005] When the properties of transformer oil remain unchanged, the factors affecting the fluorescence intensity of transformer oil are mainly external factors under the current conditions, such as light source intensity attenuation, temperature, and device response. These external factors under the current conditions lead to a decrease in the detection accuracy of aromatic hydrocarbon concentration in transformer oil, which cannot meet the requirements of accurate quantitative detection. Therefore, it is necessary to eliminate the influence of external factors. Summary of the Invention

[0006] The technical problem to be solved by the present invention is how to design a method for detecting aromatic hydrocarbon concentration in transformer oil based on fluorescence spectroscopy correction, so as to correct the aromatic hydrocarbon concentration in transformer oil measured under the current conditions, thereby improving the detection accuracy of aromatic hydrocarbon concentration in transformer oil.

[0007] The present invention solves the above-mentioned technical problems through the following technical solutions:

[0008] A method for detecting aromatic hydrocarbon concentration in transformer oil based on fluorescence spectroscopy correction includes the following steps:

[0009] S1. Select the optimal excitation wavelength of monochromatic excitation light to excite the transformer oil to generate a fluorescence spectrum;

[0010] S2. The mapping relationship between the fluorescence spectrum of transformer oil and the concentration of aromatic hydrocarbon compounds is established by using the multiple regression correction method, thereby obtaining the multiple regression correction coefficient;

[0011] S3. The positive and negative coefficients after standardization of the multivariate regression correction coefficients are used as the transmittance of the filter. Based on the transmittance, positive multivariate correction filters and negative multivariate correction filters are designed to calculate the aromatic hydrocarbon concentration of transformer oil under the current conditions.

[0012] S4. Calculate the calibration coefficient to correct the aromatic hydrocarbon concentration of the transformer oil measured under the current conditions, so as to obtain the true aromatic hydrocarbon concentration of the transformer oil.

[0013] Further, the method for selecting the optimal excitation wavelength in step S1 is as follows: Collect three-dimensional fluorescence spectral data of different types of transformer oil; determine the optimal excitation wavelength range based on the distribution range of fluorescence characteristic values ​​in the transformer oil fluorescence spectrum; compare the main peak intensity of sample characteristics under different excitation wavelengths using the excitation wavelength as the abscissa and the main peak intensity as the ordinate; compare the dispersion of sample characteristics under different excitation wavelengths using the excitation wavelength as the abscissa and the coefficient of variation as the ordinate; select the excitation wavelength that maximizes both the main peak intensity and the coefficient of variation as the excitation wavelength of the monochromatic optimal wavelength LED excitation light source (121); the formula for calculating the coefficient of variation is as follows: Among them, c v δ is the coefficient of variation, μ is the standard deviation, and μ is the mean. The larger the coefficient of variation, the greater the dispersion.

[0014] Furthermore, the mapping relationship described in step S2 is as follows:

[0015] The fluorescence spectrum of transformer oil is directly related to the concentration of aromatic hydrocarbons. The formula for calculating the concentration of aromatic hydrocarbons is derived using multiple linear regression:

[0016] c = a1s1 + a2s2 + ... + a n s n +b

[0017] Where c is the concentration of aromatic hydrocarbons, and a1~a n The multivariate regression correction coefficients for the fluorescence spectra obtained in bands 1 to n are s1 to s2. n Here, represents the fluorescence spectrum of the first to nth bands, and b is the bias coefficient.

[0018] The vector form of the formula for calculating the concentration of aromatic hydrocarbon compounds using multiple linear regression correction is as follows:

[0019] c = s·a + b

[0020] Where, a = (a1, a2, ... a n ), where a is the regression correction coefficient vector; s = (s1, s2…s n ) T s is the fluorescence spectral vector.

[0021] Furthermore, the calculation process for transmittance described in step S3 is as follows:

[0022] Define half coefficient and and a i The positive and negative parts, that is:

[0023]

[0024] Find the maximum value of the half coefficient:

[0025]

[0026] Therefore, the transmittances of the positive and negative filters are obtained as follows:

[0027] t i + =a i + / m;t i - =a i - / m

[0028] Where i = 1, 2, ..., n, n is a natural number, a i t is the i-th element of the regression correction coefficient vector a. i + For vector t + The i-th element, t i - For vector t - The i-th element.

[0029] Furthermore, the process for calculating the aromatic hydrocarbon concentration of transformer oil under the current conditions described in step S3 is as follows:

[0030] Assume the fluorescence spectrum of the target being detected is s i Then, the energy received by the detector after passing through the positive multivariate correction filter and the negative multivariate correction filter is expressed as:

[0031] P + =s i ·t + ;P - =s i ·t -

[0032] According to P measured by the detector + and P - The concentration of aromatic hydrocarbons (c) in the transformer oil under the current conditions is calculated as follows:

[0033] c = c + -c - +b=(P + -P - )m+b

[0034] Among them, c + =(P + m; c - =(P - m; i = 1, 2…n, where n is a natural number, a i Let be the i-th element of the regression correction coefficient vector a.

[0035] Furthermore, the process of calculating the scaling coefficients described in step S4 is as follows:

[0036] The fluorescence intensity values ​​of the standard solution measured under standard conditions are as follows:

[0037] P s_s =s s_s ·t

[0038] The fluorescence intensity values ​​of the standard solution measured under the current conditions are:

[0039] P s_c =s s_c ·t

[0040] Therefore, the scaling factor is:

[0041] R = P s_s / P s_c

[0042] Among them, s s_s The fluorescence spectrum of the standard solution measured under standard conditions is represented by s. s_cThis represents the fluorescence spectrum of the standard solution measured under the current conditions, and t represents the transmittance of the filter of the fluorescence detector.

[0043] Furthermore, the calculation process for the actual aromatic hydrocarbon concentration of the transformer oil mentioned in step S4 is as follows:

[0044] The aromatic hydrocarbon concentration of the transformer oil measured under the current conditions is corrected using the calibration factor R, thus obtaining the true aromatic hydrocarbon concentration of the transformer oil as follows:

[0045] c=((P + -P - )m+b)*R=((P + -P - )m+b)*P s_s / P s_c

[0046] Where R is the scaling factor.

[0047] The advantages of this invention are:

[0048] The method of this invention excites transformer oil to generate a fluorescence spectrum using monochromatic excitation light with the optimal excitation wavelength. A multivariate regression correction method is used to establish a mapping relationship between the fluorescence spectrum of transformer oil and the concentration of aromatic hydrocarbons. A multivariate correction filter is designed to calculate the concentration of aromatic hydrocarbons in transformer oil under the current conditions. A calibration coefficient is used to correct the concentration of aromatic hydrocarbons in transformer oil measured under the current conditions, thereby obtaining the true concentration of aromatic hydrocarbons in transformer oil. This method eliminates the influence of external factors under the current conditions on the detection accuracy of aromatic hydrocarbon concentration in transformer oil, and improves the detection accuracy of aromatic hydrocarbon concentration in transformer oil. Attached Figure Description

[0049] Figure 1 This is a flowchart of a method for detecting aromatic hydrocarbon concentration in transformer oil based on fluorescence spectroscopy correction;

[0050] Figure 2 This is a flowchart of the optimal excitation wavelength selection method for monochromatic excitation light in a transformer oil aromatic hydrocarbon concentration detection method based on fluorescence spectroscopy correction.

[0051] Figure 3 It is a fluorescence spectrum scanned at the excitation wavelength of a new oil sample;

[0052] Figure 4 It is a graph showing the relationship between the main peak intensity and different excitation wavelengths when determining the optimal excitation wavelength for Karamay oil;

[0053] Figure 5 This is a graph showing the relationship between the coefficient of variation and different excitation wavelengths when determining the optimal excitation wavelength for Karamay oil.

[0054] Figure 6This is a schematic diagram illustrating the transmittance calculation principle of a multi-element correction filter for a transformer oil aromatic hydrocarbon concentration detection method based on fluorescence spectroscopy correction. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0056] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0057] Example 1

[0058] like Figure 1 As shown, the method for detecting aromatic hydrocarbon concentration in transformer oil based on fluorescence spectroscopy correction includes the following steps:

[0059] Step 1: Select the optimal excitation wavelength of monochromatic excitation light to excite the transformer oil to generate a fluorescence spectrum.

[0060] like Figure 2 As shown, the method for selecting the optimal excitation wavelength is as follows:

[0061] First, three-dimensional fluorescence spectral data of different types of transformer oil were collected, such as... Figure 3 As shown, scanning the fluorescence spectrum of the new oil sample at the excitation wavelength reveals that the fluorescence characteristic values ​​of the transformer oil fluorescence spectrum are distributed in the 350nm to 500nm band. Within this range, the fluorescence spectrum can most significantly show the characteristics of the sample, that is, the characteristic peaks are clearly distinguishable and regular. The excitation wavelength range is 270nm to 310nm.

[0062] Secondly, using excitation wavelength as the x-axis and peak intensity as the y-axis, the peak intensity of sample features under different excitation wavelengths is compared. Then, using excitation wavelength as the x-axis and coefficient of variation as the y-axis, the dispersion of sample features under different excitation wavelengths is compared. The formula for calculating the coefficient of variation is as follows: Among them, c v denoted as coefficient of variation, δ as standard deviation, and μ as mean. A larger coefficient of variation indicates a greater degree of dispersion.

[0063] The optimal excitation wavelength should maximize both peak intensity and coefficient of variation.

[0064] like Figure 4 and Figure 5 As shown, a three-dimensional fluorescence spectroscopy analysis experiment was conducted on Karamay oil. The excitation wavelengths were selected from 270 nm to 310 nm. The peak intensity and coefficient of variation were compared. It was found that both were the largest at an excitation wavelength of 270 nm. Therefore, the optimal excitation wavelength is 270 nm.

[0065] Step 2: Establish the mapping relationship between the fluorescence spectrum of transformer oil and the concentration of aromatic hydrocarbon compounds using the multiple regression correction method, thereby obtaining the multiple regression correction coefficients.

[0066] The fluorescence spectrum of transformer oil is directly related to the concentration of aromatic hydrocarbons. The formula for calculating the concentration of aromatic hydrocarbons is derived using multiple linear regression:

[0067] c = a1s1 + a2s2 + ... + a n s n +b

[0068] Where c is the concentration of aromatic hydrocarbons, and a1~a n The regression correction coefficients for the fluorescence spectra obtained in bands 1 to n are s1 to s2. n Here, represents the fluorescence spectrum of the first to nth bands, and b is the bias coefficient.

[0069] The vector form of the formula for calculating the concentration of aromatic hydrocarbon compounds using multiple linear regression correction is as follows:

[0070] c = a + b

[0071] Where, a = (a1, a2, ... a n ), where a is the regression correction coefficient vector; s = (s1, s2…s n ) T s is the fluorescence spectral vector.

[0072] Step 3: Standardize the positive and negative coefficients of the multivariate regression correction coefficients and use them as the transmittance of the filter. Based on the transmittance, design positive and negative multivariate correction filters to calculate the aromatic hydrocarbon concentration of transformer oil under current conditions.

[0073] like Figure 6As shown, the positive and negative parts of the regression correction coefficient vector a are made into two correction filters, that is, the positive and negative coefficients after the regression correction coefficient vector a is standardized are used as the transmittance of the filter.

[0074] Define half coefficient and and a i The positive and negative parts, that is:

[0075]

[0076] Find the maximum value of the half coefficient:

[0077]

[0078] Therefore, the transmittances of the positive and negative filters are obtained as follows:

[0079] t i + =a i + / m;t i - =a i - / m

[0080] Assume the fluorescence spectrum of the target being detected is s i Then, the energy received by the detector after passing through the positive multivariate correction filter and the negative multivariate correction filter is expressed as:

[0081] P + =s i ·t + ;P - =s i ·t -

[0082] According to P measured by the detector + and P - The concentration of aromatic hydrocarbons (c) in the transformer oil under the current conditions is calculated as follows:

[0083] c = c + -c - +b=(P + -P - )m+b

[0084] Among them, c + =(P + m; c - =(P - m; i = 1, 2…n, where n is a natural number, a i t is the i-th element of the regression correction coefficient vector a.i + For vector t + The i-th element, t i - For vector t - The i-th element.

[0085] Step 4: Calculate the calibration factor to correct the aromatic hydrocarbon concentration of the transformer oil measured under the current conditions, thereby obtaining the true aromatic hydrocarbon concentration of the transformer oil.

[0086] The calibration coefficients are calculated, and the fluorescence spectral intensity values ​​of the transformer oil under the current conditions are corrected using these calibration coefficients to obtain the true fluorescence spectral intensity values ​​of the transformer oil. The calculation process for the calibration coefficients is as follows:

[0087] The fluorescence intensity values ​​of the standard solutions (such as quinine sulfate or rhodamine solution) measured under standard conditions are as follows:

[0088] P s_s =s s_s ·t

[0089] The fluorescence intensity values ​​of the standard solution measured under the current conditions are:

[0090] P s_c =s s_c ·t

[0091] Therefore, the scaling factor is:

[0092] R = P s_s / P s_c

[0093] The aromatic hydrocarbon concentration of the transformer oil measured under the current conditions is corrected using the calibration factor R, thus obtaining the true aromatic hydrocarbon concentration of the transformer oil as follows:

[0094] c=((P + -P - )m+b)*R=((P + -P - )m+b)*P s_s / P s_c

[0095] Among them, s s_s The fluorescence spectrum of the standard solution measured under standard conditions is represented by s. s_c This represents the fluorescence spectrum of the standard solution measured under the current conditions, and t represents the transmittance of the filter of the fluorescence detector.

[0096] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for detecting aromatic hydrocarbon concentration in transformer oil based on fluorescence spectroscopy correction, characterized in that, Includes the following steps: S1. Select the optimal excitation wavelength of monochromatic excitation light to excite the transformer oil to generate a fluorescence spectrum; S2. The mapping relationship between the fluorescence spectrum of transformer oil and the concentration of aromatic hydrocarbon compounds is established by using the multiple regression correction method, thereby obtaining the multiple regression correction coefficient; The mapping relationship is as follows: The fluorescence spectrum of transformer oil is directly related to the concentration of aromatic hydrocarbons. The formula for calculating the concentration of aromatic hydrocarbons is derived using multiple linear regression: Where c is the concentration of aromatic hydrocarbons. The multivariate regression correction coefficients for the fluorescence spectra obtained in bands 1 to n are given. Here, represents the fluorescence spectrum of the first to nth bands, and b is the bias coefficient. The vector form of the formula for calculating the concentration of aromatic hydrocarbon compounds using multiple linear regression correction is as follows: in, This is the vector of regression correction coefficients; = , T , This is the fluorescence spectrum vector; S3. The positive and negative coefficients after standardization of the multivariate regression correction coefficients are used as the transmittance of the filter. Based on the transmittance, positive multivariate correction filters and negative multivariate correction filters are designed to calculate the aromatic hydrocarbon concentration of transformer oil under the current conditions. The calculation process for the transmittance is as follows: Define half coefficient and , and They are respectively The positive and negative parts, that is: ； Find the maximum value of the half coefficient: Therefore, the transmittances of the positive and negative filters are obtained as follows: ； Where i = 1, 2, ..., n, and n is a natural number. The regression correction coefficient vector The i-th element; The process for calculating the aromatic hydrocarbon concentration of transformer oil under the current conditions is as follows: Assuming the current target fluorescence spectrum is Then, the energy received by the detector after passing through the positive multivariate correction filter and the negative multivariate correction filter is expressed as: ； According to the detector measurements and Calculate the aromatic hydrocarbon concentration in transformer oil under the current conditions. as follows: in, ; i = 1, 2, ..., n, where n is a natural number. The regression correction coefficient vector The i-th element; S4. Calculate the calibration coefficient to correct the aromatic hydrocarbon concentration of the transformer oil measured under the current conditions, so as to obtain the true aromatic hydrocarbon concentration of the transformer oil. The process of calculating the scaling coefficients is as follows: The fluorescence intensity values ​​of the standard solution measured under standard conditions are as follows: The fluorescence intensity values ​​of the standard solution measured under the current conditions are: Therefore, the scaling factor is: in, This represents the fluorescence spectrum of the standard solution measured under standard conditions. This represents the fluorescence spectrum of the standard solution measured under the current conditions. This indicates the transmittance of the filter in the fluorescence detector.

2. The method for detecting aromatic hydrocarbon concentration in transformer oil based on fluorescence spectroscopy correction according to claim 1, characterized in that, The method for selecting the optimal excitation wavelength in step S1 is as follows: Collect three-dimensional fluorescence spectral data of different types of transformer oil, and determine the optimal excitation wavelength range based on the distribution range of fluorescence characteristic values ​​of the transformer oil fluorescence spectrum; compare the main peak intensity of the sample characteristics under different excitation wavelengths with the excitation wavelength as the abscissa and the main peak intensity as the ordinate. Using the excitation wavelength as the abscissa and the coefficient of variation as the ordinate, the dispersion of sample characteristics under different excitation wavelengths is compared; the excitation wavelength that maximizes both the main peak intensity and the coefficient of variation is selected as the optimal wavelength for the monochromatic LED excitation light source (121); the formula for calculating the coefficient of variation is as follows: ;in, δ is the coefficient of variation, μ is the standard deviation, and μ is the mean. The larger the coefficient of variation, the greater the dispersion.

3. The method for detecting aromatic hydrocarbon concentration in transformer oil based on fluorescence spectroscopy correction according to claim 2, characterized in that, The calculation process for the actual aromatic hydrocarbon concentration of the transformer oil mentioned in step S4 is as follows: The aromatic hydrocarbon concentration of the transformer oil measured under the current conditions is corrected using the calibration factor R, thus obtaining the true aromatic hydrocarbon concentration of the transformer oil as follows: Where R is the scaling factor.

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