CN112881318A - Method for detecting content of methanol in transformer insulation paper - Google Patents
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Abstract
The invention discloses a method for detecting the content of methanol in transformer insulation paper, which comprises the steps of S1, adding 1mL of methanol to be detected into a 25mL colorimetric tube, sequentially transferring into 2.5mL of 25% sulfuric acid solution and 0.5mL of potassium permanganate solution, shaking uniformly and standing for 10min to obtain a first mixed solution; s2, dropwise adding a sodium sulfite solution into the first mixed solution obtained in the step S1 until the solution just fades, dropwise adding 2 drops of discoloring acid, uniformly mixing, slowly transferring 6mL of concentrated sulfuric acid along the wall of the colorimetric tube, and uniformly mixing; s3, standing and cooling to room temperature, adding water to dilute to 25mL of scale marks, and uniformly mixing to obtain a mixed solution to be detected; s4, measuring 3mL of the mixed solution to be detected into a 10 x 10mm quartz cuvette, detecting the absorbance of the mixed solution by using pure water as a reference solution and recording the spectrum of the mixed solution by using a spectrometer, and calculating to obtain the concentration of the methanol. The method is based on the spectrum principle, and the methanol concentration is obtained according to the relation between the methanol concentration and the characteristic absorbance, so that the detection cost is reduced, and the detection accuracy is increased.
Description
Technical Field
The invention relates to the technical field of insulating paper detection, in particular to a method for detecting the content of methanol in transformer insulating paper.
Background
Transformers are a core component in power systems, and power grids require transformers to be able to operate safely for long periods of time. The state of the transformer depends mainly on the state of its insulation system, which is mainly composed of insulating oil and insulating paper. Since the insulating paper is difficult to replace and the service life of the insulating paper directly determines the service life of the transformer, fault diagnosis and service life evaluation of the transformer are mainly realized by judging the aging state of the insulating paper. At present, the aging evaluation methods of the insulating paper have two types: 1) and (5) detecting the polymerization degree of the insulating paper. 2) The furfural in the transformer oil is a furan compound and can be used as a characteristic product for decomposing the insulating paper cellulose, and the content of the furfural directly reflects the aging degree of the insulating paper.
However, the above two existing insulation paper aging evaluation methods have the following disadvantages: 1) the disadvantage of the measurement of the degree of polymerization is easily influenced by sampling points, and results obtained according to different sampling points may have great difference. In addition, because the measurement of the average polymerization degree needs to carry out hanging cover sampling on the transformer, the transformer is quitted from running, and the corresponding method is difficult to be applied to field measurement. 2) The disadvantages of furfural measurement, firstly, the dispersion of the measurement results is increased by various factors such as the type of insulating paper, moisture, temperature and the like; in addition, many transformers are equipped with thermosyphon filters, with adsorbents inside, and some furfural is lost from the convectively circulated oil. In this case, compensation calculation is required for the measured value, and it is difficult to ensure an accurate result. Meanwhile, a treatment measure that the transformer may undergo oil change after long-term operation is considered, so that a large part of furfural is lost, and a measurement result cannot reflect a real aging state.
Disclosure of Invention
The invention aims to provide a method for detecting the content of methanol in transformer insulation paper, which is used for obtaining the concentration of the methanol according to the relation between the concentration of the methanol and the characteristic absorbance, reducing the detection cost and increasing the detection accuracy.
In order to achieve the above object, an embodiment of the present invention provides a method for detecting a methanol content in transformer insulation paper, including:
s1, adding 1mL of methanol to be detected into a 25mL colorimetric tube, sequentially transferring into 2.5mL of 25% sulfuric acid solution and 0.5mL of potassium permanganate solution, shaking uniformly and standing for 10min to obtain a first mixed solution;
s2, dropwise adding a sodium sulfite solution into the first mixed solution obtained in the step S1 until the solution just fades, dropwise adding 2 drops of discoloring acid, uniformly mixing, slowly transferring 6mL of concentrated sulfuric acid along the wall of the colorimetric tube, and uniformly mixing;
s3, standing and cooling to room temperature, adding water to dilute to 25mL of scale marks, and uniformly mixing to obtain a mixed solution to be detected;
s4, measuring 3mL of the mixed solution to be detected into a 10 x 10mm quartz cuvette, detecting the absorbance of the mixed solution by using pure water as a reference solution and recording the spectrum of the mixed solution by using a spectrometer, and calculating to obtain the concentration of the methanol.
Preferably, in step S4, the absorbance is detected by using a spectrometer and the spectrum is recorded, and the methanol concentration is calculated, wherein the relationship between the methanol concentration and the absorbance is as follows:
wherein A isλIs the characteristic absorbance, SλIs the absorbance of the sample, DλIs the absorbance in the dark, RλIs the absorbance of the blank.
Preferably, the absorbance within the wavelength of 200-1100nm of the spectrum is obtained from spectroscopy.
Preferably, the characteristic wavelength of the absorbance within the wavelength range of 200-1100nm of the spectrum is 552.3 nm.
Preferably, based on the spectrum 200-1100nm, regions 532.4-562.6nm, 443.4-482.9nm, 505.4-541.8nm, 620.6-654.9nm, 654.9-679.9nm and 731.2-759.0nm are selected for further calculations.
Preferably, the calculation is performed by partial least squares according to the 532.4-562.6nm, 443.4-482.9nm, 505.4-541.8nm, 620.6-654.9nm, 654.9-679.9nm and 731.2-759.0nm regions, respectively.
Preferably, the partial least squares method builds a linear regression model from the predicted variables and the observable variables.
In the embodiment of the invention, under an acid environment provided by sulfuric acid, potassium permanganate is used for oxidizing methanol to form formaldehyde, the generated formaldehyde can react with discoloring acid to form a mauve compound under the action of concentrated sulfuric acid, pure water is used as a reference, and a spectrum of the compound is obtained by a spectrometer, so that the concentration of the methanol can be calculated, and further the polymerization degree of the insulating paper is obtained at the aging degree.
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In order to more clearly illustrate the technical solution of the present invention, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic flow chart of a method for detecting methanol content in transformer insulation paper according to an embodiment of the present invention;
FIG. 2 is a plot of ppm methanol calibration provided by another embodiment of the present invention;
FIG. 3 is a plot of a ppb level methanol calibration provided by yet another embodiment of the present invention;
FIG. 4 is a ppm methanol standard curve provided by an embodiment of the present invention;
fig. 5 is a plot of ppb level methanol as provided by another embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be understood that the step numbers used herein are for convenience of description only and are not intended as limitations on the order in which the steps are performed.
It is to be understood that the terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the specification of the present invention and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.
The terms "comprises" and "comprising" indicate the presence of the described features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
The term "and/or" refers to and includes any and all possible combinations of one or more of the associated listed items.
Referring to fig. 1, an embodiment of the present invention provides a method for detecting a methanol content in transformer insulation paper, including:
s1, adding 1mL of methanol to be detected into a 25mL colorimetric tube, sequentially transferring into 2.5mL of 25% sulfuric acid solution and 0.5mL of potassium permanganate solution, shaking uniformly and standing for 10min to obtain a first mixed solution;
specifically, 164mL of concentrated sulfuric acid is measured in a fume hood, and is slowly added into a 1000mL beaker filled with 700mL of distilled water along a glass rod, stirring is carried out while adding, and the diluted sulfuric acid is diluted to 1000mL after cooling; potassium permanganate solution: weighing 1.00g of potassium permanganate into a 50mL beaker, diluting the potassium permanganate to a scale mark with distilled water, cooling the solution, and transferring the solution into a brown reagent bottle for storage.
S2, dropwise adding a sodium sulfite solution into the first mixed solution obtained in the step S1 until the solution just fades, dropwise adding 2 drops of discoloring acid, uniformly mixing, slowly transferring 6mL of concentrated sulfuric acid along the wall of the colorimetric tube, and uniformly mixing;
specifically, the saturated solution of discoloring acid: weighing 1.00g of metachromatic acid, dissolving in a 50mL volumetric flask, shaking up and standing, and preparing in situ when in use; 5% sodium sulfite solution: 2.50g of sodium sulfite is weighed to a 50mL volumetric flask, and the volumetric flask is shaken up for standby application and prepared on site.
S3, standing and cooling to room temperature, adding water to dilute to 25mL of scale marks, and uniformly mixing to obtain a mixed solution to be detected;
s4, measuring 3mL of the mixed solution to be detected into a 10 x 10mm quartz cuvette, detecting the absorbance of the mixed solution by using pure water as a reference solution and recording the spectrum of the mixed solution by using a spectrometer, and calculating to obtain the concentration of the methanol.
Specifically, the basic principle of spectroscopy for detecting methanol in water is as follows: under the acidic environment provided by sulfuric acid, methanol is oxidized by potassium permanganate to form formaldehyde, the generated formaldehyde can react with chromotropic acid (1, 8-dihydroxynaphthalene-3, 6-disulfonic acid, molecular formula C10H8O8S2) to form a mauve compound under the action of concentrated sulfuric acid, pure water is used as reference, and a spectrum of the compound is obtained by a spectrometer, so that the methanol concentration can be calculated. The main chemical reaction equation is as follows:
5CH3OH+2KMnO4+4H2SO4→5CH2O+2MnSO4+2KHSO4+8H2O
CH2O+2C10S2O8H8→C21S4O16H16+H2O→C21S4O16H14
the relationship between methanol concentration and characteristic absorbance is derived using beer-lambert law, and is represented by the following equation:
wherein A isλIs the characteristic absorbance, SλIs the absorbance of the sample, DλIs the absorbance in the dark, RλThe optical spectrum is blank absorbance, the optical spectrum used by the invention is a Maya 2000pro micro-optical spectrum, the light source is DH-20000, a 25-micron slit grating is selected, the resolution is 1nm, and methanol is dissolved in transformer oil in an actual oil sample, so that the methanol needs to be extracted by water, and a standard sample is directly prepared by water, so that the extraction pretreatment is not needed.
In one embodiment, methanol is detected by spectrophotometry, which is a standard curve drawn by absorbance at characteristic wavelengths. Methods for monitoring and analyzing water and wastewater (fourth edition) indicated that the final product should have a characteristic absorption wavelength at 550-570nm by full-band scanning. Therefore, the methanol is firstly subjected to a series of reactions to generate a light purple compound, then a spectrum of the light purple compound is obtained by using a spectrometer, and the absorbance at a characteristic wavelength is recorded, so that the standard curve of the traditional method is finally obtained.
Referring to fig. 2, in the ppm-level methanol calibration experiment, 20 ppm, 40 ppm, 60 ppm, 80 ppm and 100ppm methanol calibration samples were prepared, and a spectral curve was obtained, wherein the characteristic absorption wavelength of methanol in the obtained spectral curve was stabilized at 552.3nm, and the absorbance at 552.3nm was recorded, referring to table 1.
TABLE 1 ppm methanol Absorbance at 552.3nm
The traditional spectrophotometry only establishes a standard curve according to the absorbance at the characteristic wavelength, the linear relation at the ppm level is not good, and an ideal result is not obtained in multiple experiments.
Referring to fig. 3, in the ppb level methanol labeling experiment, 10, 20, 40, 50, 70, 80, and 100ppb methanol standards were prepared, and the measurement was performed according to the experimental procedures from step S1 to S4, and the characteristic absorption wavelength of methanol was still 552.3nm, so that they are tabulated and plotted, and the ppb level labeling data are shown in table 2:
TABLE 2 ppb methanol Absorbance at 552.3nm
In this embodiment, when only the absorbance at the characteristic absorption wavelength is used as the calibration curve, the R is about 0.92 to 0.96 no matter in the ppm level or the ppb level, and the effect is still not good after many experiments. Therefore, further processing is required to intercept the spectral portion for calculation.
In another embodiment, the methanol is detected by a spectrum method, the concentration of the methanol is detected by a traditional spectrophotometry method, only the peak height value at a characteristic peak is read, the peak height value is greatly influenced by a plurality of interference factors, and the obtained standard curve is not ideal. Therefore, the invention adopts the obtained 200-1100nm full spectrogram and utilizes a chemometrics section to perform data processing.
Firstly, the spectral data area is selected, and the optical absorption in the wavelength of 200-1100nm can be obtained by the optical spectrum method, so that not only can the data at the characteristic wavelength be taken for calculation, but also the optical absorption at a section of wavelength can be intercepted for data processing. By comparing the spectra of different concentrations of methanol reactant, it can be found that: when the wavelength is less than 400nm, the absorbance is independent of the methanol concentration. It is presumed from the results that, when the wavelength is less than 400nm, the absorbance may be affected by the discoloring acid. Therefore, to eliminate the effect of the added chemical reagent on the spectrum, this region was not selected for further analysis. And comparing the spectra obtained by multiple tests, and processing data by adopting the spectrum at the position of 440-760nm according to the relation between the absorbance and the methanol concentration, wherein the relation between the absorbance and the methanol concentration in the region is obvious. Methanol undergoes a series of reactions, and the final product has characteristic absorption wavelength at 550-570 nm. The experimental result shows that the absorbance accords with the linear relation with the concentration in the 532.4-562.6nm region. In addition, regions 443.4-482.9nm, 505.4-541.8nm, 620.6-654.9nm, 654.9-679.9nm and 731.2-759.0nm were selected for analysis. In these regions, the absorbance increased with increasing methanol concentration. Based on the above analysis, regions of 532.4-562.6nm, 443.4-482.9nm, 505.4-541.8nm, 620.6-654.9nm, 654.9-679.9nm and 731.2-759.0nm were selected for further calculations.
Normalized, Partial Least Squares (PLS) is a statistical method that is related to principal component analysis (regression) and that builds a linear regression model for predicted variables and observable variables. Since in PLS the X and Y data are projected into a new space, it is also called bilinear factor model.
Referring to fig. 4 and 5, TQ analysts are a multifunctional spectroscopy software that can provide extensive qualitative and quantitative analysis for mid-infrared, near-infrared, far-infrared and raman spectra. The software has a variety of analytical methods, including partial least squares. In this experiment, TQ Analyst software was run first, the PLS method was selected, the name of the experiment and the test substance were entered, and the data for various spectra and concentrations were imported into the software. Then, regions of 532.4-562.6nm, 443.4-482.9nm, 505.4-541.8nm, 620.6-654.9nm, 654.9-679.9nm and 731.2-759.0nm were selected for analysis. The principal components and factors remain default and the auto-calibration update factor number is selected. And finally, clicking the Calibrate option to obtain a calculated standard curve. After partial least square calculation is carried out on the absorbance in a section of wavelength, the ppm and ppb level standard curve relations are obviously improved, the correlation coefficients reach 0.999(0-100ppb) and 0.99(20-100ppm), and the results show that the method can effectively detect the methanol with different concentrations.
Compared to the prior art, firstly, compared to the degree of polymerization measurement: the methanol measurement judgment method has the advantages of convenient sampling, less consumption, no need of transformer power failure, convenient transportation and storage, difficult loss and the like, and has higher reliability; second, compared to furfural measurements: the concentration of furfural and the polymerization degree of insulating paper present a log-linear relationship, and the change of the polymerization degree causes the change of the concentration of furfural in oil in the primary stage of aging, which is not accurate and sensitive enough and is difficult to provide early real aging trend. The methanol concentration and the polymerization degree of the insulating paper present a linear relation in the initial and middle stage of aging, and are more accurate and sensitive than each other.
While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention.
Claims (7)
1. A method for detecting the content of methanol in transformer insulation paper is characterized by comprising the following steps:
s1, adding 1mL of methanol to be detected into a 25mL colorimetric tube, sequentially transferring into 2.5mL of 25% sulfuric acid solution and 0.5mL of potassium permanganate solution, shaking uniformly and standing for 10min to obtain a first mixed solution;
s2, dropwise adding a sodium sulfite solution into the first mixed solution obtained in the step S1 until the solution just fades, dropwise adding 2 drops of discoloring acid, uniformly mixing, slowly transferring 6mL of concentrated sulfuric acid along the wall of the colorimetric tube, and uniformly mixing;
s3, standing and cooling to room temperature, adding water to dilute to 25mL of scale marks, and uniformly mixing to obtain a mixed solution to be detected;
s4, measuring 3mL of the mixed solution to be detected into a 10 x 10mm quartz cuvette, detecting the absorbance of the mixed solution by using pure water as a reference solution and recording the spectrum of the mixed solution by using a spectrometer, and calculating to obtain the concentration of the methanol.
2. The method for detecting the content of methanol in transformer insulation paper according to claim 1, wherein in step S4, the absorbance of the paper is detected by a spectrometer, the spectrum of the paper is recorded, and the concentration of methanol is obtained by calculation, wherein the relationship between the concentration of methanol and the absorbance is as follows:
wherein A isλIs the characteristic absorbance, SλIs the absorbance of the sample, DλIs the absorbance in the dark, RλIs the absorbance of the blank.
3. The method for detecting the methanol content in the transformer insulation paper as claimed in claim 2, wherein the absorbance within the wavelength of 200-1100nm of the spectrum is obtained according to a spectroscopic method.
4. The method as claimed in claim 3, wherein the characteristic wavelength of the absorbance within the wavelength range of 200-1100nm of the spectrum is 552.3 nm.
5. The method for detecting the methanol content in the insulation paper of the transformer as claimed in claim 4, wherein the regions of 532.4-562.6nm, 443.4-482.9nm, 505.4-541.8nm, 620.6-654.9nm, 654.9-679.9nm and 731.2-759.0nm are respectively selected for further calculation according to the spectrum of 200-1100 nm.
6. The method for detecting the content of methanol in the insulation paper of the transformer as claimed in claim 5, wherein the calculation is performed by using partial least squares method according to the regions of 532.4-562.6nm, 443.4-482.9nm, 505.4-541.8nm, 620.6-654.9nm, 654.9-679.9nm and 731.2-759.0nm, respectively.
7. The method for detecting the content of methanol in the insulation paper of the transformer as claimed in claim 6, wherein the partial least squares method establishes a linear regression model according to a predicted variable and an observable variable.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN113418911A (en) * | 2021-06-17 | 2021-09-21 | 中国石化销售股份有限公司油品技术研究所 | Device for rapidly detecting methanol content and preparation and detection methods thereof |
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| CN108872101A (en) * | 2018-05-10 | 2018-11-23 | 广东电网有限责任公司电力科学研究院 | A kind of appraisal procedure and detection system of transformer degree of aging |
| CN111157518A (en) * | 2020-01-03 | 2020-05-15 | 云南电网有限责任公司电力科学研究院 | Method for detecting aging degree of insulating paper based on methanol content |
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| CN108872101A (en) * | 2018-05-10 | 2018-11-23 | 广东电网有限责任公司电力科学研究院 | A kind of appraisal procedure and detection system of transformer degree of aging |
| CN111157518A (en) * | 2020-01-03 | 2020-05-15 | 云南电网有限责任公司电力科学研究院 | Method for detecting aging degree of insulating paper based on methanol content |
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| CN113418911A (en) * | 2021-06-17 | 2021-09-21 | 中国石化销售股份有限公司油品技术研究所 | Device for rapidly detecting methanol content and preparation and detection methods thereof |
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