CN112881318B - Method for detecting methanol content in transformer insulating paper - Google Patents
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- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 title claims abstract description 180
- 238000000034 method Methods 0.000 title claims abstract description 27
- 238000002835 absorbance Methods 0.000 claims abstract description 45
- 238000001228 spectrum Methods 0.000 claims abstract description 25
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims abstract description 22
- 239000011259 mixed solution Substances 0.000 claims abstract description 20
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 16
- 239000000243 solution Substances 0.000 claims abstract description 15
- 238000002156 mixing Methods 0.000 claims abstract description 12
- 239000012088 reference solution Substances 0.000 claims abstract description 12
- GEHJYWRUCIMESM-UHFFFAOYSA-L sodium sulfite Chemical compound [Na+].[Na+].[O-]S([O-])=O GEHJYWRUCIMESM-UHFFFAOYSA-L 0.000 claims abstract description 12
- 239000012286 potassium permanganate Substances 0.000 claims abstract description 8
- KRVSOGSZCMJSLX-UHFFFAOYSA-L chromic acid Substances O[Cr](O)(=O)=O KRVSOGSZCMJSLX-UHFFFAOYSA-L 0.000 claims abstract description 7
- AWJWCTOOIBYHON-UHFFFAOYSA-N furo[3,4-b]pyrazine-5,7-dione Chemical compound C1=CN=C2C(=O)OC(=O)C2=N1 AWJWCTOOIBYHON-UHFFFAOYSA-N 0.000 claims abstract description 7
- 235000010265 sodium sulphite Nutrition 0.000 claims abstract description 6
- 238000001816 cooling Methods 0.000 claims abstract description 5
- 239000010453 quartz Substances 0.000 claims abstract description 4
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims abstract description 4
- 238000004364 calculation method Methods 0.000 claims description 9
- 238000009413 insulation Methods 0.000 claims description 5
- 238000004611 spectroscopical analysis Methods 0.000 claims description 4
- 238000012417 linear regression Methods 0.000 claims description 3
- 238000001514 detection method Methods 0.000 abstract description 6
- HYBBIBNJHNGZAN-UHFFFAOYSA-N furfural Chemical compound O=CC1=CC=CO1 HYBBIBNJHNGZAN-UHFFFAOYSA-N 0.000 description 14
- 230000032683 aging Effects 0.000 description 9
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- WSFSSNUMVMOOMR-NJFSPNSNSA-N methanone Chemical compound O=[14CH2] WSFSSNUMVMOOMR-NJFSPNSNSA-N 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
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- 238000001237 Raman spectrum Methods 0.000 description 1
- 239000003463 adsorbent Substances 0.000 description 1
- 229920002678 cellulose Polymers 0.000 description 1
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- 239000003153 chemical reaction reagent Substances 0.000 description 1
- HLVXFWDLRHCZEI-UHFFFAOYSA-N chromotropic acid Chemical compound OS(=O)(=O)C1=CC(O)=C2C(O)=CC(S(O)(=O)=O)=CC2=C1 HLVXFWDLRHCZEI-UHFFFAOYSA-N 0.000 description 1
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- YLQBMQCUIZJEEH-UHFFFAOYSA-N tetrahydrofuran Natural products C=1C=COC=1 YLQBMQCUIZJEEH-UHFFFAOYSA-N 0.000 description 1
- 239000002351 wastewater Substances 0.000 description 1
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Abstract
The invention discloses a method for detecting the methanol content in transformer insulating paper, which comprises the following 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 the sodium sulfite solution into the first mixed solution obtained in the step S1 until the first mixed solution is just faded, dropwise adding 2 drops of chromic acid, uniformly mixing, slowly moving into 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 tested; and S4, measuring 3mL of the mixed solution to be measured into a quartz cuvette with the thickness of 10 multiplied by 10mm, taking pure water as a reference solution, detecting the absorbance of the reference solution by adopting a spectrometer, recording the spectrum of the reference solution, and calculating to obtain the concentration of the methanol. The invention obtains the methanol concentration according to the relation between the methanol concentration and the characteristic absorbance based on the spectrum principle, reduces the detection cost and increases the detection accuracy.
Description
Technical Field
The invention relates to the technical field of insulating paper detection, in particular to a method for detecting the methanol content in transformer insulating paper.
Background
Transformers are a core component in power systems, and the power grid requires that the transformer be able to operate safely for a long period of time. The state of the transformer is mainly dependent on the state of its insulation system, which is mainly composed of insulating oil and insulating paper. Because the insulating paper is difficult to replace, the service life of the transformer is directly determined, and therefore, fault diagnosis and service life assessment of the transformer are mainly realized by judging the ageing state of the insulating paper. At present, two methods for evaluating the aging of the insulating paper exist: 1) And detecting the polymerization degree of the insulating paper. 2) Furfural in transformer oil is a furan compound, can be used as a characteristic product of cellulose decomposition of insulating paper, and the content of the Furfural directly reflects the aging degree of the insulating paper.
However, the above two existing methods of evaluating the aging of insulating paper have the following disadvantages: 1) The disadvantage of the polymerization degree measurement is easily affected by the sampling points, and the results obtained according to different sampling points may have large differences. In addition, as the measurement of the average polymerization degree is to take a hanging cover sample of the transformer, the transformer is out of operation, and the corresponding method is difficult to apply to field measurement. 2) Firstly, the dispersion of measurement results can be increased by various factors such as the type of insulating paper, moisture, temperature and the like; in addition, many transformers are equipped with thermosiphon filters, with adsorbents, and a portion of the furfural in the convective circulation is lost. In this case, compensation calculation is required for the measured value, and it is difficult to ensure that an accurate result is obtained. At the same time, the treatment measure that the transformer may undergo oil change after long-term operation should be considered, which may cause a large part of furfural to be lost, so that the measurement result cannot reflect the real aging state.
Disclosure of Invention
The invention aims to provide a method for detecting the methanol content in transformer insulating paper, which is used for obtaining the methanol concentration according to the relation between the methanol concentration 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 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 the sodium sulfite solution into the first mixed solution obtained in the step S1 until the first mixed solution is just faded, dropwise adding 2 drops of chromic acid, uniformly mixing, slowly moving into 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 tested;
and S4, measuring 3mL of the mixed solution to be measured into a quartz cuvette with the thickness of 10 multiplied by 10mm, taking pure water as a reference solution, detecting the absorbance of the reference solution by adopting a spectrometer, recording the spectrum of the reference solution, and calculating to obtain the concentration of the methanol.
Preferably, in the step S4, the absorbance is detected by a spectrometer and the spectrum is recorded, and the methanol concentration is calculated, where the relationship between the methanol concentration and the absorbance is as follows:
wherein A is λ Is the characteristic absorbance, S λ Is the absorbance of the sample, D λ Absorbance in the dark, R λ Is the absorbance of the blank.
Preferably, absorbance in the wavelength range of 200-1100nm of the spectrum is obtained according to spectrometry.
Preferably, the absorbance within the 200-1100nm wavelength of the spectrum has a characteristic wavelength of 552.3nm.
Preferably, according to the spectrum 200-1100nm, the 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 chosen for further calculations, respectively.
Preferably, the partial least squares method is used for calculation according to the 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, respectively.
Preferably, the partial least squares method builds a linear regression model from the predicted and observable variables.
In the embodiment of the invention, under the acidic environment provided by sulfuric acid, potassium permanganate is used for oxidizing methanol into formaldehyde, the generated formaldehyde can react with chromic acid to generate a mauve compound under the action of concentrated sulfuric acid, pure water is used as a reference, a spectrometer is used for obtaining the spectrum of the compound, and then the concentration of the methanol can be calculated, so that the degree of polymerization of the insulating paper is obtained at the aging degree.
Drawings
In order to more clearly illustrate the technical solutions of the present invention, the drawings that are needed 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 that other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.
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 graph of ppm methanol standard curve provided by another embodiment of the present invention;
FIG. 3 is a diagram of a ppb level methanol standard curve provided by a further embodiment of the present invention;
FIG. 4 is a ppm methanol standard provided in an embodiment of the present invention;
fig. 5 is a diagram of ppb level methanol mapping provided by another embodiment of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
It should be understood that the step numbers used herein are for convenience of description only and are not limiting as to the order in which the steps are performed.
It is to be understood that the terminology used in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in this specification 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 stated 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 any and all possible combinations of one or more of the associated listed items, and includes such combinations.
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 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, the 25% dilute sulfuric acid is obtained by taking 164mL of concentrated sulfuric acid in a fume hood, slowly adding the concentrated sulfuric acid into a 1000mL beaker filled with 700mL of distilled water along a glass rod, stirring while adding, cooling, and diluting to 1000mL; potassium permanganate solution: 1.00g of potassium permanganate is weighed into a 50mL beaker, diluted with distilled water to the scale mark, cooled and transferred into a brown reagent bottle for preservation.
S2, dropwise adding the sodium sulfite solution into the first mixed solution obtained in the step S1 until the first mixed solution is just faded, dropwise adding 2 drops of chromic acid, uniformly mixing, slowly moving into 6mL of concentrated sulfuric acid along the wall of the colorimetric tube, and uniformly mixing;
specifically, a color-changing acid saturated solution: 1.00g of chromic acid is weighed and dissolved in a 50mL volumetric flask, and the mixture is shaken uniformly and stood for preparation at present; 5% sodium sulfite solution: 2.50g of sodium sulfite is weighed into a 50mL volumetric flask, shaken well for later use and prepared at present.
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 tested;
and S4, measuring 3mL of the mixed solution to be measured into a quartz cuvette with the thickness of 10 multiplied by 10mm, taking pure water as a reference solution, detecting the absorbance of the reference solution by adopting a spectrometer, recording the spectrum of the reference solution, and calculating to obtain the concentration of the methanol.
Specifically, the basic principle of detecting methanol in water by a spectrometry is as follows: under the acidic environment provided by sulfuric acid, oxidizing methanol with potassium permanganate to obtain formaldehyde, reacting the generated formaldehyde with chromic acid (1, 8-dihydroxynaphthalene-3, 6-disulfonic acid, molecular formula C10H8O8S 2) to generate a mauve compound under the action of concentrated sulfuric acid, and obtaining the spectrum of the compound by using a spectrometer with pure water as a reference to calculate the concentration of the methanol. The main chemical reaction equation is as follows:
5CH 3 OH+2KMnO 4 +4H 2 SO 4 →5CH 2 O+2MnSO 4 +2KHSO 4 +8H 2 O
CH 2 O+2C 10 S 2 O 8 H 8 →C 21 S 4 O 16 H 16 +H 2 O→C 21 S 4 O 16 H 14
the relationship between methanol concentration and characteristic absorbance is derived using beer-lambert law, expressed by the following equation:
wherein A is λ Is the characteristic absorbance, S λ Is the absorbance of the sample, D λ Absorbance in the dark, R λ The absorbance of the white space is the absorbance of the white space, the spectrometer used in the invention is a Maya 2000pro micro spectrometer, the light source is DH-20000, a 25 mu m slit grating is selected, the resolution is 1nm, and in an actual oil sample, methanol is dissolved in transformer oil, so that the methanol is extracted by water, and a standard sample is directly prepared by water, and the extraction pretreatment is not needed.
In one embodiment, spectrophotometric detection detects methanol and traditional spectrophotometry draws a standard curve from absorbance at a characteristic wavelength. The method of monitoring and analyzing water and waste water (fourth edition) indicates that the final product should have characteristic absorption wavelength at 550-570nm after full-band scanning. Thus, herein, methanol is first subjected to a series of reactions to produce a light purple compound, then its spectrum is obtained using a spectrometer, and the absorbance at the characteristic wavelength is recorded, ultimately yielding a standard curve for the conventional process.
Referring to fig. 2, a standard methanol sample with concentration of 20, 40, 60, 80 and 100ppm is prepared in ppm level methanol standard curve experiment to obtain a spectrum curve, wherein the characteristic absorption wavelength of methanol in the obtained spectrum curve is stabilized at 552.3nm, the absorbance at the place is recorded, and referring to table 1, the absorbance at 552.3nm of ppm level methanol is obtained.
TABLE 1 absorbance of methanol at 552.3nm at ppm
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 no ideal result is obtained through multiple experiments.
Referring to fig. 3, in ppb-level methanol standard experiments, methanol standard samples with concentrations of 10, 20, 40, 50, 70, 80 and 100ppb are respectively prepared, and are measured according to the experimental steps performed in steps S1 to S4, and the characteristic absorption wavelength of methanol is still 552.3nm, so that ppb-level standard curve data are obtained by tabulating and plotting the table 2:
TABLE 2 ppb level methanol absorbance at 552.3nm
In this embodiment, when only the absorbance at the characteristic absorption wavelength is used as the standard curve, the effect is still poor after multiple experiments, no matter the absorbance is at ppm level or ppb level, and the R is about 0.92-0.96. Therefore, further processing of the data is required, and calculation of the truncated spectral portion region is performed.
In another embodiment, the methanol is detected by a spectrometry method, the concentration of the methanol is detected by adopting a traditional spectrophotometry method, only the peak height value at the 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. For this purpose, the invention uses the obtained full spectrum diagram of 200-1100nm to process data by chemometric means.
Firstly, spectrum data area selection is performed, and as the absorbance in the wavelength of 200-1100nm can be obtained by the spectrum method, not only can the data at the characteristic wavelength be taken for calculation, but also the absorbance at a section of wavelength can be intercepted for data processing. By comparing the spectra of the methanol reactants at different concentrations, it can be found that: at wavelengths below 400nm, the absorbance is independent of methanol concentration. From the results, it is presumed that, when the wavelength is lower than 400nm, the absorbance may be affected by the color-changing acid. Thus, in order to eliminate the effect of the added chemical on the spectrum, this region was not selected for further analysis. And comparing the spectra tested for multiple times, and adopting the spectrum at 440-760nm to process data according to the relation between the absorbance and the methanol concentration, wherein the relation between the absorbance and the methanol concentration in the area is obvious. Methanol undergoes a series of reactions and the final product exhibits a characteristic absorption wavelength at 550-570 nm. The experimental result shows that the absorbance accords with the linear relation between the concentration in the 532.4-562.6nm region. In addition, the 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 areas, the absorbance increases 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.
The standard curve is plotted, and the Partial Least Squares (PLS) method is a statistical method, which is related to principal component analysis (regression), and establishes a linear regression model for predicted variables and observable variables. Because in PLS the X and Y data are projected to a new space, it is also called a bilinear factor model.
Referring to fig. 4 and 5, tq analysis is a multi-functional spectroscopic software that can provide extensive qualitative and quantitative analysis for mid-ir, near-ir, far-ir and raman spectra. The software has a variety of analysis methods including partial least squares. In this experiment, TQ analysis software was first run, PLS method was selected, and after inputting experiment name and test substance, various spectra and concentration data were imported into the software. Then, the 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 were selected for analysis. The principal components and factors remain default and the auto-calibration update factor number is selected. Finally, clicking the "Calibrate" option, a calculated standard curve can be obtained. After partial least square calculation is carried out on absorbance in a section of wavelength, the standard curve relationship between ppm and ppb level is obviously improved, and the correlation coefficient reaches 0.999 (0-100 ppb) and 0.99 (20-100 ppm), which shows that the method can effectively detect methanol with different concentrations.
Compared with the prior art, first, compared with the polymerization degree measurement: the methanol measurement judgment method has the advantages of convenient sampling, less consumption, no need of power failure of a transformer, convenient transportation and storage, difficult loss and the like, and has higher reliability; second, compared to furfural measurement: the furfural concentration and the polymerization degree of the insulating paper show a logarithmic linear relation, and in the primary stage of aging, the change of the polymerization degree causes the change of the furfural concentration in the oil to be small, inaccurate and sensitive, and the early and real aging trend is difficult to provide. The methanol concentration and the polymerization degree of the insulating paper show a linear relation in the initial and middle stages of aging, and are more accurate and sensitive compared with the prior art.
While the foregoing is directed to the preferred embodiments of the present invention, it will be appreciated by those skilled in the art that changes and modifications may be made without departing from the principles of the invention, such changes and modifications are also intended to be within the scope of the invention.
Claims (2)
1. A method for detecting the methanol content in insulating paper of a transformer, which is characterized by comprising the following steps:
s1, adding 1mL of methanol to be detected into a 25mL colorimetric tube, sequentially transferring 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 the sodium sulfite solution into the first mixed solution obtained in the step S1 until the first mixed solution is just faded, dropwise adding 2 drops of chromic acid, uniformly mixing, slowly moving into 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 scale marks, and uniformly mixing to obtain a mixed solution to be tested;
s4, measuring 3mL of the mixed solution to be measured into a 10 multiplied by 10mm quartz cuvette, taking pure water as a reference solution, detecting the absorbance of the reference solution by adopting a spectrometer, recording the spectrum of the reference solution, and calculating to obtain the concentration of the methanol;
in the step S4, the absorbance is detected by a spectrometer and the spectrum is recorded, and the methanol concentration is obtained by calculation, wherein the relationship between the methanol concentration and the absorbance is as follows:
wherein,,
is the characteristic absorbance,/->
Is the absorbance of the sample,/->
Absorbance in the dark, +.>
Absorbance is blank;
obtaining absorbance within 200-1100nm wavelength of spectrum according to spectrometry;
according to the spectrum 200-1100nm, the areas 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 selected, and the partial least square method is adopted for calculation.
2. The method for detecting methanol content in transformer insulation paper according to claim 1, wherein the partial least square method establishes a linear regression model according to a predicted variable and an observable variable.
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