Crosslinked polyethylene cable insulation layer by-product detection method

Abstract

The invention belongs to the technical field of cable detection, and particularly relates to a crosslinked polyethylene cable insulation layer by-product detection method, which comprises the following steps: adding n-hexane and isopropanol according to a preset proportion before dilution, combining ultrasonic elution and filtration separation under a low temperature condition, and dissolving small molecule by-products by using the strong polarity of the isopropanol, so as to obtain the crosslinked polyethylene cable insulation layer by-product. N-hexane is used for promoting swelling of polyethylene, and low-temperature ultrasound is used for synergistically reducing viscosity, so that complete extraction of cumyl alcohol and other by-products at low temperature is realized, and the detection precision of the corresponding by-products is improved; meanwhile, the ionization effect can be improved by adopting an ionic liquid injection mode, so that the electrification effect of the supernate is improved, the activeness of the supernate is further improved, byproducts are enabled to be more active in the detection process, and the purpose of improving the detection sensitivity is achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of cable detection, and particularly relates to a method for detecting by-products of an insulation layer of a cross-linked polyethylene cable. BACKGROUND

[0002] Polar or small molecular compounds such as cumyl alcohol, acetophenone and alpha-methylstyrene are generated in the production process of a cross-linked polyethylene (XLPE) cable. Unlike AC cables, these residues continuously generate charge traps and accumulate space charges during the operation of DC cables at high voltage levels, thereby significantly affecting the electrical performance and long-term operation safety of the cable, and thus the content thereof needs to be controlled through a degassing process, and the content is detected after the degassing process is completed.

[0003] There are the following several traditional detection methods: 1. Gas chromatography-mass spectrometry, which can realize quantitative analysis, but since the boiling points of cumyl alcohol, acetophenone and alpha-methylstyrene are relatively high, the original component system in the sample will be damaged in the volatilization process, resulting in distortion of the test content; 2. Fourier infrared spectroscopy, which is simple to operate, but can only detect the total content of by-products and cannot realize accurate quantitative analysis of single components; 3. Thermogravimetric method, which can only calculate the total content through the weight difference and cannot meet the demand for accurate quantitative detection of single components; 4. Liquid chromatograph-photoelectric diode array detector combined with a conventional C18 chromatographic column and an acetonitrile-water system, which can avoid the shortcomings of the above three methods, but it is difficult to completely extract the target substances at a lower temperature, and since the molecular structure and molecular weight of cumyl alcohol and acetophenone are similar, it is difficult to separate the two by traditional methods, and it is impossible to accurately quantify all single components.

[0004] Therefore, a new detection method is needed to overcome the shortcomings of the prior art, to accurately and sensitively quantify the by-products such as cumyl alcohol, acetophenone and alpha-methylstyrene in the insulation layer of the cross-linked polyethylene cable, and to provide a basis for optimizing the cable degassing process.

[0005] It should be noted that this part of the application only provides background technology related to the application, and does not necessarily constitute prior art or known technology. SUMMARY

[0006] The purpose of the application is to provide a method for detecting by-products of an insulation layer of a cross-linked polyethylene cable, which can more accurately and sensitively quantify the by-products of the insulation layer.

[0007] In order to achieve the above purpose, the application provides a method for detecting by-products of an insulation layer of a cross-linked polyethylene cable, comprising: S100: taking a preset region of the crosslinked polyethylene cable insulation layer to be measured as a sample; S200: using n-hexane and isopropyl alcohol as solvents in a proportion of (0.5-2):1 to ultrasonically elute the sample at 40-60°C for a preset time, and obtaining a filtrate after filtering solid impurities; S300: diluting the filtrate with a mixture of acetonitrile and water, and injecting 0.4-0.6wt% of a solution of 18F- in the dilution mixture, and then mixing and standing and extracting the supernatant; S300: diluting the filtrate with a mixture of acetonitrile and water, and injecting 0.4-0.6wt% of a solution of 18F- in the dilution mixture, and then mixing and standing and extracting the supernatant; S400: performing gradient elution separation of the extracted supernatant by using a charged surface chromatographic column; S500: setting different detection wavelengths corresponding to different by-products; S600: quantitatively analyzing the mass concentrations of different by-products.

[0008] In one possible embodiment, in S100, a preset region of the crosslinked polyethylene cable insulation layer to be measured is taken as a sample, specifically including: S110: freezing the crosslinked polyethylene cable to be measured under conditions of -35 to -45°C; S120: after removing the conductor, the crosslinked polyethylene cable to be measured is sliced along the radial direction; S130: a layered rectangular cross-section is cut along the radial direction to obtain a sample of the crosslinked by-product gradient at different positions in the insulation layer; S140: after freezing the sample using liquid nitrogen for a preset time, the sample is placed in an ultracentrifugal grinder for grinding and sieving.

[0009] In one possible embodiment, in step S200, the ratio of n-hexane to isopropyl alcohol is 1:1, the ultrasonic elution temperature is 50°C, and the elution preset time is 50-70 min.

[0010] In one possible embodiment, in step S300, the ratio of acetonitrile to water in the mixture of acetonitrile and water is (1-4):2.

[0011] In one possible embodiment, in step S400, when the extracted supernatant is eluted and separated by gradient elution by using a charged surface chromatographic column, multiple gradient elution is performed by using multiple elution mixtures with different acetonitrile-water ratios, so that the supernatant sequentially flows through multiple elution mixtures with different acetonitrile-water ratios to elute and separate different by-products.

[0012] In one possible embodiment, the multiple gradient elution includes first gradient elution and second gradient elution, the acetonitrile-water ratio of the first gradient elution is 35:65, and the acetonitrile ratio of the second gradient elution is 100%.

[0013] In a possible embodiment, the multi-gradient elution further comprises a third gradient elution, and the acetonitrile-water ratio of the third gradient elution is 35:65.

[0014] In a possible embodiment, in step S400, the column temperature of the chromatographic column is 30-40 DEG C.

[0015] In a possible embodiment, in step S400, the first mobile phase of the chromatographic column adopts 0.08%-0.12% formic acid aqueous solution, and the pH is 2.5-3; and the second mobile phase of the chromatographic column adopts acetonitrile containing 0.08%-0.12% formic acid.

[0016] In a possible embodiment, in step S500, the detection wavelength of the by-product cumyl alcohol is set to 210 nm, and the detection wavelength of phenylacetone and alpha-methylstyrene is 245 nm.

[0017] The present application has at least the following beneficial effects: The cross-linked polyethylene cable insulation layer by-product detection method provided by the present application uses the strong polarity of isopropyl alcohol to dissolve small molecule by-products, and promotes polyethylene swelling through n-hexane, while cooperating with low-temperature ultrasonic to reduce viscosity, so that the by-products such as cumyl alcohol are completely extracted at low temperature, which is beneficial to improve the detection accuracy of the corresponding by-products; and the ionization effect is improved by using the ion liquid injection method, so as to improve the charging effect of the supernatant, and then improve the activity of the supernatant, so that the by-products are more active in the detection process, and the detection sensitivity is improved.

[0018] Further, the present application uses multi-gradient elution to realize complete separation of three types of by-products by accurately controlling the elution strength, and can avoid cross contamination, and realizes synchronous and accurate quantification of different by-product components in combination with the gradient elution time window.

[0019] Further, by using low-temperature freezing combined with liquid nitrogen quick freezing, the volatilization of by-products can be significantly inhibited, and by radial layered slicing and rectangular mold stamping, the gradient distribution analysis of by-products in the insulation layer is realized for the first time, which provides spatial distribution data for degassing process optimization; and after liquid nitrogen freezing, ultracentrifugal grinding and sieving can better ensure the sufficiency and uniformity of sample grinding, avoid the situation that the grinding particle size is not uniform in the grinding process due to the toughness of the insulation layer, and then in the dissolving process, the uniformity of the solute distribution after dissolving can be better guaranteed, so as to reduce the error of subsequent detection and ensure the accuracy of detection.

[0020] Further, by setting different detection wavelengths for different by-products, the graded detection of different by-products can be realized, which is beneficial to improve the detection accuracy of different by-products. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the specific embodiments of the present application or the prior art, the accompanying drawings required by the specific embodiments or prior art description will be briefly introduced below. Obviously, the accompanying drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative effort.

[0022] Figure 1 is a flow chart of a cross-linked polyethylene cable insulation layer by-product detection method provided by an embodiment of the present application; Figure 2 is a specific flow chart of step S100 provided by an embodiment of the present application; Figure 3 is a chromatogram schematic diagram of the detection of by-products in the cross-linked polyethylene cable insulation layer by the detection method of the embodiment of the present application; Figure 4 is a chromatogram schematic diagram of the detection of by-products in the cross-linked polyethylene cable insulation layer by the prior art method. DETAILED DESCRIPTION

[0023] The technical solutions of the present application will be described below in conjunction with the embodiments. Obviously, the described embodiments are some of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of the present application.

[0024] Those skilled in the art can understand that, unless otherwise defined, all terms (including technical terms and scientific terms) used herein have the same meaning as generally understood by those skilled in the art to which the present application belongs. It should also be understood that terms such as those defined in a general dictionary should be understood as having meanings consistent with those in the context of the prior art, and unless specifically defined as such herein, should not be interpreted in an idealized or overly formal sense.

[0025] It should be further understood that the phrase "comprising" used in the specification of the present application means that the described features, integers, steps, operations, elements and / or components exist, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or their combinations. The phrase "and / or" used herein includes all or any single unit and all combinations of the associated listed items.

[0026] As shown in Figure 1 The present application provides a cross-linked polyethylene cable insulation layer by-product detection method, which comprises: S100: Take the preset area of the crosslinked polyethylene cable insulation layer to be tested as a sample.

[0027] Optionally, as shown in the specific process of making the sample includes: Figure 2 S110: Freeze the crosslinked polyethylene cable to be tested at -35~ -45℃.

[0028] Specifically, by using -40℃ freezing combined with liquid nitrogen quick freezing, the by-product volatilization can be significantly inhibited, and aluminum foil can be used to wrap the sample to further reduce the loss of substances.

[0029] S120: After removing the conductor, the crosslinked polyethylene cable to be tested is sliced radially, and the slice thickness is generally 2mm.

[0030] S130: Take a layered rectangular section along the radial direction to obtain a sample of the gradient of crosslinking by-products at different positions in the insulation layer.

[0031] Specifically, a rectangular die is used to punch a layered rectangular section along the radial direction to obtain a sample of the gradient of crosslinking by-products at different positions in the cable, specifically, rectangular areas of the outer layer (close to the metal shielding layer), the middle layer and the inner layer (close to the conductive layer) of the insulation layer are taken as samples for subsequent detection.

[0032] Through radial layered slicing and rectangular die punching, the gradient distribution analysis of by-products in the insulation layer is realized for the first time, providing spatial distribution data for degassing process optimization.

[0033] S140: After freezing the sample for a preset time using liquid nitrogen, put it into an ultra-centrifugal grinder for grinding and sieving.

[0034] Specifically, the sample is frozen for 1min using liquid nitrogen, and then put into an ultra-centrifugal grinder for grinding and sieving after freezing to improve the surface area of the sample and further improve the extraction recovery rate.

[0035] By liquid nitrogen freezing, ultra-centrifugal grinding and sieving, the sample grinding can be better guaranteed to be sufficient and uniform, and the size of the grinding particles can be avoided due to the toughness of the insulation layer itself during the grinding process. In the dissolving process of S200, the uniformity of the solute distribution after dissolving can be better guaranteed to reduce the error of subsequent detection and ensure the accuracy of detection.

[0036] S200: Use n-hexane and isopropyl alcohol with a ratio of (0.5~2):1 as solvent to ultrasonically elute the sample at 40~60℃ for a preset time, and filter the solid impurities to obtain the filtrate.

[0037] ​The inventors find that by using a mixed solvent of n-hexane and isopropyl alcohol with a ratio of (0.5-2):1 as the elution solvent of the insulating layer, the strong polarity of isopropyl alcohol can dissolve small molecular by-products, and n-hexane can promote the swelling of polyethylene, while the low-temperature ultrasonic wave can synergistically reduce the viscosity, so that the by-products such as cumyl alcohol can be completely extracted at low temperature. If the ratio is too high, the solubility of cumyl alcohol and phenylethanone will be insufficient, and in severe cases, it will cause stratification. If the ratio is too low, the extraction of alpha-methylstyrene will be insufficient. The ratio of n-hexane to isopropyl alcohol is preferably 1:1.

[0038] Optionally, the temperature of the ultrasonic elution is 50°C, and the preset elution time is 50-70 min (preferably 60 min). If the temperature of the supplementary ultrasonic elution is too high, the cumyl alcohol will be further converted into alpha-methylstyrene, resulting in distortion. If the temperature is too low, the elution will not be complete. If the elution time is too long, the phenylethanone will be converted into methane, resulting in distortion and increasing the risk of leakage of the headspace bottle. If the elution time is too short, the elution will not be complete.

[0039] Specifically, the solution after ultrasonic elution is filtered by using a vacuum filtration device (the sample after ultrasonic elution is a ground particulate matter), mainly to filter the solid impurities after ultrasonic crushing, so as to obtain a filtrate with high purity, which is conducive to improving the final detection result.

[0040] S300: The filtrate is diluted with a mixed solution of acetonitrile and water, and 0.4-0.6wt% of the ionic liquid is injected into the diluted mixed solution. After mixing, the supernatant is extracted.

[0041] The inventors find that the main material of the insulating layer and the by-products are all insulating materials, which do not have conductivity and are difficult to be charged by using the charge loading method for surface mixing technology. By injecting 0.4-0.6wt% of the ionic liquid, the ionization effect of cumyl alcohol and phenylethanone can be improved, the charging effect of the supernatant can be improved, and the activity of the supernatant can be improved, so as to make the by-products more active during the detection process, and the detection sensitivity can be improved. If the injection concentration is too high, the cations will form a strong ion pair with the silanol groups (-SiOH) of the C18 bonded phase silica gel, which will destroy the hydrophobic layer of the chromatographic column and is difficult to clean. If the injection concentration is too low, the effect will not be obvious.

[0042] Optionally, the ratio of acetonitrile to water in the mixed solution of acetonitrile and water is (1-4):2, preferably 3:2. If the ratio is too high, the polarity will be reduced, and alpha-methylstyrene will be precipitated. If the ratio is too low, the polarity will be too strong, and cumyl alcohol will be precipitated. Preferably, the mass percentage of the solution is 0.5wt%, and the mixing and standing time is 8-12 min, preferably 10 min. ​

[0043] S400: The extracted supernatant is subjected to an attached electric gradient elution separation by using a charged surface chromatographic column.

[0044] Specifically, when the extracted supernatant is subjected to an attached electric gradient elution separation by using a charged surface chromatographic column (the chromatographic column used in the embodiment of the present application is CSH C18), a plurality of elution mixtures with different acetonitrile-water ratios are used for multi-gradient elution, so that the supernatant sequentially flows through the plurality of elution mixtures with different acetonitrile-water ratios for elution separation of different by-products.

[0045] Since the ionic liquid is injected into the extracted supernatant, the weak coordination bond is formed between the anions and cations in the supernatant and the by-products, and the molecular polarity is enhanced; during the chromatographic separation, the ionic liquid acts as a "charge carrier" to amplify the electrostatic difference between cumyl alcohol and acetophenone, and further improve the separation degree and detection sensitivity.

[0046] Alternatively, the multi-gradient elution includes first gradient elution and second gradient elution, the acetonitrile-water ratio of the first gradient elution is 35:65, and the acetonitrile ratio of the second gradient elution is 100%. Through the improvement, the acetonitrile-water ratio of the first gradient elution is set to realize the elution separation of cumyl alcohol and acetophenone. If the ratio is too high, the separation degree of cumyl alcohol and acetophenone will be reduced, and the quantitative accuracy will be decreased. If the ratio is too low, the peak tailing phenomenon will be intensified, and the quantitative accuracy will be decreased. The acetonitrile-water ratio of the second gradient elution is set to realize the elution separation of α-methylstyrene. If the ratio is too low, the efficiency will be low, and the peak time of α-methylstyrene will be seriously delayed.

[0047] Alternatively, in addition to the first gradient elution and the second gradient elution, the multi-gradient elution further includes third gradient elution, the acetonitrile-water ratio of the first gradient elution is 35:65, the acetonitrile ratio of the second gradient elution is 100%, and the acetonitrile-water ratio of the third gradient elution is 35:65.

[0048] It should be noted that after the elution separation of cumyl alcohol, acetophenone and α-methylstyrene is completed, there will be other by-products. In order to avoid the deposition of other by-products in the elution separation copper pipe, the acetonitrile-water ratio of the third gradient elution is set to completely take out the remaining substances to avoid affecting the test results of the next time. If the acetonitrile-water ratio of the third gradient elution is 100:0, the general applicability is poor, and the remaining substances are not completely taken out. Therefore, the acetonitrile-water ratio of 35:65 is set. If the ratio is too high, the cleaning efficiency will be reduced. If the ratio is too low, the baseline balance of the next sample will be affected.

[0049] The three-stage gradient elution is adopted in the embodiment, complete separation of three types of by-products is realized by precisely controlling the elution strength, the third gradient avoids cross contamination, and the synchronous precise quantification of different by-product components is realized by combining the gradient elution time window. The parameters of the multi-gradient elution are shown in Table 1. Table 1 Comparison of multi-gradient elution parameters

[0050] Optionally, the column temperature of the chromatographic column is 30-40℃, which is beneficial to optimize mass transfer, reduce peak tailing, and thus improve the detection accuracy of the chromatograph.

[0051] Optionally, the first mobile phase of the chromatographic column adopts 0.08%-0.12% formic acid (preferably 0.1% formic acid) aqueous solution, and the pH is 2.5-3 (preferably pH 2.8), which is used for protonating cumyl alcohol and enhancing electrostatic repulsion. The pH control is 2.5-3, which is beneficial to improve the separation degree. If the pH value is too low, the chromatographic column will be damaged. If the pH value is too high, the separation degree will decrease significantly. The second mobile phase of the chromatographic column is acetonitrile containing 0.08%-0.12% formic acid (preferably 0.1% formic acid), which is beneficial to maintain an acidic environment and avoid hydrophobic collapse. In combination with the acidic environment, the adsorption of silanol groups can be inhibited, the mass transfer path is shortened by gradient elution, and the peak symmetry is improved.

[0052] Optionally, 0.1% formic acid is added to the elution mixture with various proportions of acetonitrile-water. By adding formic acid, the problem of peak tailing can be alleviated during detection and analysis, especially when the detection wavelengths of cumyl alcohol and phenylacetone are similar. The peak tailing problem easily causes interference in analysis, which is beneficial to improve the detection accuracy of by-products.

[0053] S500: Set the detection wavelengths corresponding to different by-products to detect multiple by-products.

[0054] Optionally, in step S500, the detection wavelength of cumyl alcohol is set to 210 nm, and the detection wavelengths of phenylacetone and a-methylstyrene are set to 245 nm. That is, the contents of cumyl alcohol, phenylacetone and a-methylstyrene can be detected at a detection wavelength of 210 nm, and the contents of phenylacetone and a-methylstyrene can be detected at a detection wavelength of 245 nm. Therefore, by setting different detection wavelengths for different by-products, the detection accuracy of different by-products can be improved.

[0055] As Figure 3As shown, under the conditions of detection wavelengths 210nm and 245nm, wherein the black curve is the detection curve of the detection wavelength 210nm, the purple curve is the detection curve of the detection wavelength 245nm, the abscissa is time, and the ordinate is the output electric signal of the detection device, with the progress of the multi-gradient elution process, cumyl alcohol, acetophenone and alpha-methylstyrene are detected under the condition of detection wavelength 210nm, and acetophenone and alpha-methylstyrene are detected under the condition of detection wavelength 245nm, wherein 2-phenyl-2-propanol is cumyl alcohol, and the peak area of the detection wave of each curve represents the content of the detection substance, and the content converted from the peak area of different substances is independent, that is, the contents of two detection substances cannot be judged to be the same according to the same peak area.

[0056] S600: quantitative analysis of the mass concentration of different by-products.

[0057] Specifically, the supernatant after elution and separation is detected by chromatography by using a gas chromatograph, the concentrations of the corresponding by-products are obtained by checking the chromatogram, and the amounts of the three target substances are determined by the standard concentration curve determined by the external standard method, and finally the contents of cumyl alcohol, acetophenone and alpha-methylstyrene in the insulating sample are calculated according to the mass of the solid sample taken.

[0058] The crosslinked polyethylene cable insulation layer by-product detection method provided by the application uses isopropanol to dissolve small molecular by-products due to its strong polarity, and uses n-hexane to promote polyethylene swelling, while cooperating with low-temperature ultrasonic to reduce viscosity, so that complete extraction of by-products such as cumyl alcohol at low temperature is realized, which is conducive to improving the detection accuracy of the corresponding by-products; and the ion liquid injection method can improve the ionization effect, thereby improving the charging effect of the supernatant, and further improving the activity of the supernatant, so that the by-products are more active in the detection process, and the purpose of improving the detection sensitivity is achieved.

[0059] Further, the application adopts multi-gradient elution, accurately controls the elution strength, realizes complete separation of the three types of by-products, and can avoid cross contamination, combines with the gradient elution time window, realizes synchronous and accurate quantification of different by-product components.

[0060] Further, by using low-temperature freezing combined with liquid nitrogen quick freezing, the volatilization of by-products can be significantly inhibited, and by radial layered slicing and rectangular mold stamping, the gradient distribution analysis of by-products in the insulation layer is realized for the first time, providing spatial distribution data for degassing process optimization; and after liquid nitrogen freezing, ultracentrifugal grinding and sieving can better ensure the sufficiency and uniformity of sample grinding, avoid the situation that the grinding particle size is not uniform in the grinding process due to the toughness of the insulation layer, and better ensure the uniformity of the solute distribution after melting, so as to reduce the error in the subsequent detection and ensure the accuracy of the detection.

[0061] The following detailed description of the embodiments of the present application is exemplary only and is not to be understood in a limiting sense.

[0062] Embodiment 1 This embodiment uses two groups of samples (sample 1 and sample 2) for testing, each group of samples including an inner layer, a middle layer and an outer layer. The specific cross-linked polyethylene cable insulation layer by-product detection method comprises: S100: Take a preset area of the cross-linked polyethylene cable insulation layer to be tested as a sample.

[0063] Specifically: S110: Freeze the cross-linked polyethylene cable to be tested at -40°C, then slice and use centrifugation.

[0064] S120: After removing the conductor, slice the cross-linked polyethylene cable to be tested along the radial direction, and the slice thickness is 2mm.

[0065] S130: Take a layered rectangular section along the radial direction to obtain a sample of the gradient of the cross-linked by-product at different positions in the insulation layer. Specifically, take the rectangular area of the outer layer (close to the metal shielding layer), the middle layer and the inner layer (close to the conductive layer) of the insulation layer as a sample for subsequent detection. S140: Freeze the sample in liquid nitrogen for 1 min, then put it into an ultra-centrifugal grinder for grinding and sieving.

[0066] S200: Use n-hexane and isopropyl alcohol with a ratio of 1:1 as solvents to ultrasonically elute the sample at 50°C for 60 min, and then filter the solid impurities to obtain a filtrate. S300: Dilute the filtrate with a mixture of acetonitrile and water in a ratio of 3:2, and inject 0.5wt% of the solution into the diluted mixture. After mixing, stand and extract the supernatant.

[0067] S400: Use a charged surface chromatographic column to separate the extracted supernatant by three-stage gradient elution. Specifically, the temperature of the charged chromatographic column is 35°C; the first mobile phase of the chromatographic column uses 0.1% formic acid aqueous solution with a pH of 2.8; the first gradient elution of the second mobile phase of the chromatographic column uses acetonitrile-water with a ratio of 35:65; the second gradient elution uses acetonitrile with a ratio of 100%; and the third gradient elution uses acetonitrile-water with a ratio of 35:65.

[0068] S500: Set different detection wavelengths corresponding to different by-products.

[0069] Specifically, the detection wavelength of cumyl alcohol in the by-product is set to 210nm, and the detection wavelength of phenylacetone and a-methylstyrene is set to 245nm. ​

[0070] S600: quantitative analysis of the mass concentration of different by-products.

[0071] The test results of by-products obtained by using the scheme of Example 1 are shown in Table 2 below: Table 2: Test results of by-products in the insulation layer in Example 1

[0072] As can be seen from Table 2, after degassing, the removal effect of polar substances in different regions of the cross-linked polyethylene cable is significantly different, and the overall trend from the inner layer to the outer layer is gradually decreasing, which is presumably related to the degree of air contact.

[0073] Example 2 The sample is the same as Example 1, except that in step S110, when the sample is prepared, the cross-linked polyethylene cable to be tested is frozen at -35°C; in step S200, n-hexane and isopropyl alcohol with a ratio of 0.5:1 are used as solvents to ultrasonically elute the sample at 60°C for 60 min; in step S300, 0.6wt% of the solution is injected into the dilution mixture; in step S400, the temperature of the charged chromatographic column is 40°C; and other process parameters are the same.

[0074] The test results are shown in Table 3 below: Table 3: Test results of by-products in the insulation layer in Example 2

[0075] As can be seen from Table 4, the test results under this condition have no significant changes.

[0076] Example 3 The sample is the same as Example 1, except that in step S110, when the sample is prepared, the cross-linked polyethylene cable to be tested is frozen at -45°C; in step S200, n-hexane and isopropyl alcohol with a ratio of 2:1 are used as solvents to ultrasonically elute the sample at 40°C for 60 min; in step S300, 0.4wt% of the solution is injected into the dilution mixture; in step S400, the temperature of the charged chromatographic column is 30°C; and other process parameters are the same.

[0077] The test results are shown in Table 4 below: Table 4: Test results of by-products in the insulation layer in Example 3

[0078] As can be seen from Table 4, the test results under this condition have no significant changes.

[0079] Example 4 ​​The sample is the same as that in Example 1, except that in step S140, liquid nitrogen is not used for freezing after slicing; other process parameters are the same.

[0080] The test results are shown in Table 5 below: Table 5 Detection content of insulating layer byproducts in Example 4

[0081] As can be seen from Table 5, since liquid nitrogen was not used for freezing after slicing, the content of each cross-linked by-product in the test results decreased significantly, especially in the outer layer.

[0082] Comparative Example 1 Conventional testing method, specifically, without freezing or grinding, only using a 1:1 mixture of n-hexane and isopropanol to ultrasonically extract the specimen at 60°C, without injecting 0.4wt% The solution was analyzed without adding formic acid and using only a conventional Bridge column.

[0083] like Figure 4 As shown in the figure, it shows a conventional detection method. The horizontal axis is time and the vertical axis is the output electrical signal of the detection equipment. Detection is performed by increasing the output electrical signal. In the absence of charged surface mixing technology, 0.1% formic acid, and multi-gradient elution, problems such as overlapping peak curves of different detection objects, more interference peaks, and poor peak symmetry occur. It is difficult to convert the content of the detection object and the accuracy is low, which seriously affects the detection quality and the judgment of the detection results. This is consistent with the Figure 3 The test results showed a large difference.

[0084] Comparative Example 2 The sample is the same as that in Example 1. The difference from Example 1 is that only isopropyl alcohol is used as the solvent in step S200. Other parameters are the same as those in Example 1.

[0085] The test results are shown in Table 6 below: Table 6 Detection content of insulating layer by-products in comparative example 2

[0086] As can be seen from Table 6, since the solvent does not contain n-hexane, the α-methylstyrene content in the test results is significantly reduced, which is not in line with reality.

[0087] Comparative Example 3 The sample is the same as Example 1, except that no injection is performed in step S300. solution.

[0088] The test results are shown in Table 7 below: Table 7 Detection content of by-products in the insulating layer of Comparative Example 3

[0089] As can be seen from Table 7, due to no injection of the ionic liquid, the substance separation degree is reduced, the waveforms are coincided, and the proportion of cumyl alcohol to phenylacetone in each layer is obviously too low, leading to quantitative distortion.

[0090] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not limited to them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for detecting byproducts in the insulation layer of a cross-linked polyethylene cable, characterized in that: include: S100: Take a preset area of ​​the insulation layer of the cross-linked polyethylene cable to be tested as a sample; S200: Using n-hexane and isopropanol in a ratio of (0.5-2):1 as solvent, ultrasonically elute the sample at 40-60°C for a preset time, and filter out solid impurities to obtain a filtrate; S300: Dilute the filtrate with a mixture of acetonitrile and water, and inject 0.4~0.6wt% The solution was mixed, allowed to stand and the supernatant was extracted; S400: The extracted supernatant is separated by electrostatic gradient elution using a charged surface chromatography column; S500: Setting the detection wavelength corresponding to different by-products; S600: Quantitative analysis to obtain the mass concentration of different by-products.

2. The method for detecting byproducts in the insulation layer of a cross-linked polyethylene cable according to claim 1, characterized in that: In S100, a predetermined area of ​​the insulation layer of the cross-linked polyethylene cable to be tested is taken as a sample, specifically including: S110: Freeze the cross-linked polyethylene cable to be tested at -35~-45℃; S120: After removing the conductor, slice the cross-linked polyethylene cable to be tested along the radial direction; S130: cutting a layered rectangular cross section along the radial direction to obtain a sample with a gradient of the cross-linked byproduct at different positions in the insulating layer; S140: After freezing the sample with liquid nitrogen for a preset time, place it in an ultracentrifugal grinder for grinding and sieving.

3. The method for detecting byproducts in the insulation layer of a cross-linked polyethylene cable according to claim 1, characterized in that: In step S200 , the ratio of n-hexane to isopropanol is 1:1, the temperature of ultrasonic elution is 50° C., and the preset elution time is 50 to 70 minutes.

4. The method for detecting byproducts in the insulation layer of a cross-linked polyethylene cable according to claim 1, characterized in that: In step S300, the ratio of acetonitrile to water in the mixture of acetonitrile and water is (1-4):

2.

5. The method for detecting byproducts in the insulation layer of a cross-linked polyethylene cable according to claim 4, characterized in that: In step S400, when the extracted supernatant is subjected to electrostatic gradient elution separation using a charged surface chromatography column, multiple gradient elutions are performed using elution mixtures with different acetonitrile-water ratios, so that the supernatant flows through the elution mixtures with different acetonitrile-water ratios in sequence to elute and separate different by-products.

6. The method for detecting byproducts in the insulation layer of a cross-linked polyethylene cable according to claim 5, characterized in that: The multi-gradient elution includes a first gradient elution and a second gradient elution, wherein the ratio of acetonitrile to water in the first gradient elution is 35:65, and the ratio of acetonitrile to water in the second gradient elution is 100%.

7. The method for detecting byproducts in the insulation layer of a cross-linked polyethylene cable according to claim 6, characterized in that: The multi-gradient elution further includes a third gradient elution, and the acetonitrile-water ratio of the third gradient elution is 35:

65.

8. The method for detecting byproducts in the insulation layer of a cross-linked polyethylene cable according to claim 1, characterized in that: In step S400, the column temperature of the chromatographic column is 30-40°C.

9. The method for detecting byproducts in the insulation layer of a cross-linked polyethylene cable according to claim 1, characterized in that: In step S400 , the first mobile phase of the chromatographic column is a 0.08% to 0.12% formic acid aqueous solution with a pH of 2.5 to 3; the second mobile phase of the chromatographic column is acetonitrile containing 0.08% to 0.12% formic acid.

10. The method for detecting byproducts in the insulation layer of a cross-linked polyethylene cable according to claim 1, characterized in that: In step S500, the detection wavelength of cumyl alcohol in the by-product is set to 210 nm, and the detection wavelength of acetophenone and α-methylstyrene is set to 245 nm.

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