CN118777459A - A method for testing the content of cross-linked byproducts in high-voltage XLPE cable insulation under different degassing temperatures and times - Google Patents

Abstract

The invention discloses a method for testing the content of cross-linked byproducts in the insulation of a high-voltage XLPE cable under different air-removal temperature and time conditions. The test method comprises the following steps: s1, reserving three parts of conductor shielding, XLPE insulation and insulation shielding for a cable sample; s2, performing heat treatment on the cable sample; s3, cutting a cable integral sample and XLPE insulating inner layer, middle layer and outer layer samples; s4, carrying out heat treatment on the sample; s5, preparing standard solutions with different concentrations by using cumyl alcohol, acetophenone and alpha-methylstyrene, and performing analysis and test by using a gas chromatography-mass spectrometry method to obtain the linear relation between the peak areas and the mass of the three crosslinking byproducts; s6, analyzing and testing the heat-treated sample, and bringing the peak areas of the three crosslinking byproducts into a linear relationship to obtain the concentration of the three crosslinking byproducts in the insulating sample. The invention reflects the air removal effect of the high-voltage XLPE cable by detecting the contents of three crosslinking byproducts in the air-removed sample.

Description

A method for testing the content of cross-linked byproducts in high-voltage XLPE cable insulation under different degassing temperatures and times

Technical field:

The invention relates to the technical field of high-voltage XLPE cable degassing production process, and in particular to a method for testing the content of cross-linked byproducts inside the insulation of a high-voltage XLPE cable under different degassing temperature and time conditions.

Background technology:

For high-voltage XLPE cables, the insulating material undergoes a cross-linking reaction during the production process, and the insulating material is transformed from a linear thermoplastic material to a mesh thermosetting material, which increases the operating temperature of the cable. For high-voltage cables, peroxide cross-linking is mainly used, and the most commonly used cross-linking agent is diisopropylbenzene peroxide (DCP). During the cross-linking reaction, the main by-products are cumyl alcohol, acetophenone, α-methylstyrene, and methane. These cross-linking by-products mainly exist in the amorphous region of XLPE in the form of small molecules, causing insulation defects that affect the safe operation of the cable. Therefore, it is necessary to degas the high-voltage cross-linked polyethylene insulated cable. At present, the main degassing method of cable manufacturers is to place the cable insulation core in a special degassing chamber at 65℃~70℃ to eliminate the by-products produced by the cross-linking reaction.

The insulation thickness of cables of different voltage levels is different, so the degassing time of the cables is also different. However, the current cable degassing time is mostly determined based on experience, and there is a lack of evaluation indicators for the degree of cable degassing. Therefore, an effective method for detecting the content of cross-linked by-products in the insulation of high-voltage XLPE cables is needed to accurately quantify the concentration of cross-linked by-products inside XLPE, so as to establish an evaluation index for the degree of degassing on this basis. The existing methods for detecting the degassing effect of high-voltage XLPE cables mainly include detecting the internal space charge characteristics of the insulation core and detecting the residual amount of cross-linked by-products. The methods include weighing and using a thermogravimetric analyzer to detect the cross-linked by-products, and using a gas chromatograph to detect the gas composition and content in the degassing chamber. Although these methods can determine the approximate residual amount of cross-linked by-products, they cannot be accurately quantified. The gas chromatography-mass spectrometry (GC-MS) instrument can provide a mass spectrum that can be used to identify compounds with known or unknown identities, and also provides a chromatogram that can be used for qualitative and quantitative analysis. The specific residual amount of cross-linked by-products can be obtained, which is conducive to evaluating the degassing effect of high-voltage cables. Therefore, it is necessary to propose an efficient and accurate test method for the content of internal cross-linking by-products in high-voltage XLPE cable insulation under different degassing temperatures and time conditions based on liquid chromatography-mass spectrometry.

Summary of the invention:

The present invention solves the problems existing in the prior art and provides a method for testing the content of cross-linked by-products in the insulation of a high-voltage XLPE cable under different degassing temperature and time conditions. The testing method proposed by the present invention can accurately detect the concentrations of three cross-linked by-products, namely, cumyl alcohol, acetophenone and alpha-methylstyrene, in the XLPE insulation, thereby establishing an evaluation index for the degassing effect of the high-voltage cable, and can more effectively guide the production of the high-voltage XLPE cable.

The object of the present invention is to provide a method for testing the content of cross-linked byproducts in the insulation of a high-voltage XLPE cable under different degassing temperatures and time conditions, comprising the following steps:

S1. Remove the conductor, semi-conductive nylon tape and semi-conductive multi-tape parts from the cable sample, and keep the conductor shield, XLPE insulation and insulation shield;

S2. Divide the cable samples into two groups and perform heat treatment on the cable samples respectively;

S3, further cutting the heat-treated cable sample to obtain the whole cable sample including the conductor shield, XLPE insulation, insulation shield, and the inner layer, middle layer and outer layer samples of the XLPE insulation;

S4, heat treating the whole cable sample, the inner layer of XLPE insulation, the middle layer of XLPE insulation and the outer layer of XLPE insulation;

S5. Using three analytical test standards, namely, cumyl alcohol, acetophenone and α-methylstyrene, standard solutions of different concentrations are prepared, and the standard solutions of different concentrations are analyzed and tested by gas chromatography-mass spectrometry to obtain a linear relationship between the peak area and mass of the three cross-linking byproducts of cumyl alcohol, acetophenone and α-methylstyrene in the standard solution;

S6. Using gas chromatography-mass spectrometry, the whole cable sample, the inner layer of XLPE insulation, the middle layer of XLPE insulation and the outer layer of XLPE insulation after the heat treatment in step S4 are analyzed and tested respectively, and the peak areas of the three cross-linked by-products measured in the sample test are brought into this linear relationship to obtain the concentrations of the three cross-linked by-products in the insulation sample.

The present invention simulates the cable degassing process by heat treatment to obtain the variation law of crosslinked byproducts in the sample with heating time. The present invention reflects the degassing effect of the high-voltage XLPE cable by detecting the contents of three crosslinked byproducts, namely cumyl alcohol, acetophenone and α-methylstyrene, in the degassing sample.

Preferably, step S2 specifically includes the following steps:

S21, divide the samples into two groups, each group has several sections of samples, labeled A and B respectively;

One sample was retained from each of the two groups S22, A, and B, and the other samples were placed in a constant temperature box for simulated degassing. The heat treatment temperatures of the two groups A and B were set at 65°C and 70°C, respectively. Sampling was taken every 12 hours, and the degassing cycle was 144 hours.

Preferably, the specific steps of step S3 are: using a cable cutter to cut a fan-shaped whole cable sample including a conductor shield, XLPE insulation, and an insulation shield to obtain a whole cable sample; when preparing the inner, middle, and outer layer samples of the XLPE insulation, on the basis of the whole cable sample, remove the conductor shield and the insulation shield, leaving the XLPE insulation part, and then cut it into three equal parts parallel to the arc surface, which are the inner layer of the XLPE insulation, the middle layer of the XLPE insulation, and the outer layer of the XLPE insulation from the inside to the outside.

Preferably, the specific steps of step S4 are: packing the whole cable sample, the inner layer of XLPE insulation, the middle layer of XLPE insulation and the outer layer of XLPE insulation in headspace bottles, and heat treating them in a constant temperature oven, and the heat treatment conditions are: heating temperature 120° C., heating time 5 h.

Preferably, in step S5: cumyl alcohol is respectively configured into 6 standard solutions of different concentrations of 0.2 mg/mL, 0.4 mg/mL, 1.0 mg/mL, 2.0 mg/mL, 4.0 mg/mL, and 20.0 mg/mL; acetophenone is respectively configured into 6 standard solutions of different concentrations of 0.3 mg/mL, 0.6 mg/mL, 1.5 mg/mL, 3.0 mg/mL, 6.0 mg/mL, and 30.0 mg/mL; α-methylstyrene is respectively configured into 6 standard solutions of different concentrations of 0.02 mg/mL, 0.04 mg/mL, 0.1 mg/mL, 0.2 mg/mL, 0.4 mg/mL, and 2.0 mg/mL.

Preferably, step S5 specifically includes the following steps:

S51. Use gas chromatography-mass spectrometry to detect the sample and 6 standard solutions of different concentrations, obtain the peak area of each cross-linked by-product at 6 different concentrations, record the 6 test data and the origin on the coordinate plane, and fit the regression equation y=kx+b corresponding to each cross-linked by-product, where the ordinate y represents the mass of the cross-linked by-product, and the abscissa x represents the peak area of the cross-linked by-product. The regression equation parameter solution formula is as follows:

Preferably, step S6 specifically includes the following steps:

S61. Using the external standard method, the concentration of various cross-linking by-products in the sample is calculated based on the relationship curve between the peak area and mass of the cross-linking by-products. The formula is as follows:

Wherein, _ci represents the concentration of cross-linked by-product i, i includes α-methylstyrene, acetophenone and cumyl alcohol, and the unit is mg/g; _ki represents the slope of the standard curve of cross-linked by-product i, and the unit is mg; _mj represents the mass of the j-th sample, and the unit is g; _Aji represents the peak area of cross-linked by-product i in the j-th sample, and the unit is unitless.

Preferably, the gas chromatography-tandem mass spectrometry detection conditions described in step S5 or S6 are: the chromatographic column is HP-INNOWax, with specifications of 30m×0.25mm×0.25μm; the injection port temperature is 250°C;

Heating program: initial temperature 40°C, hold for 3 min, increase to 250°C at 10°C/min, hold for 5 min;

The carrier gas used was helium with a purity of 99.9995% and a helium flow rate of 1 mL/min; the injection method was split injection with a split ratio of 30:1 and an injection volume of 100 μL; the mass spectrometry acquisition method was scan mode with an m/z range of 33-500.

The present invention also protects the application of the test method in testing the content of cross-linked byproducts inside the insulation of a high-voltage XLPE cable under different degassing temperature and time conditions.

Compared with the prior art, the present invention has the following advantages: the present invention uses a gas chromatography-mass spectrometer to detect and analyze the cross-linked by-product components and contents of XLPE samples, and can accurately quantify and obtain the concentrations of three cross-linked by-products, namely, alpha-methylstyrene, acetophenone, and cumyl alcohol, in XLPE insulation, so that the evaluation is more accurate and efficient; the present invention analyzes the contents of cross-linked by-products at different degassing temperatures and degassing times, and obtains the law of content changes of cross-linked by-products during the degassing process.

Description of the drawings:

FIG1 is a flow chart of the testing method proposed by the present invention;

Figure 2 shows the sampling method and specifications of the samples;

Fig. 3 is a headspace bottle test sample preparation method;

Fig. 4 is a schematic diagram of a gas chromatography-mass spectrometer;

Fig. 5 is a schematic diagram of configuring a standard solution;

Fig. 6 is the peak area-mass relationship of the standard solution in Example 1;

FIG7 is a test result of samples with different degassing times;

Explanation of the reference numerals: 1. conductor; 2. semiconductor nylon tape + semiconductor terylene tape layer; 3. conductor shielding layer; 4. XLPE insulation layer; 41. insulation inner layer; 42. insulation middle layer; 43. insulation outer layer; 5. insulation shielding layer.

Specific implementation method:

The following examples are provided to further illustrate the present invention, rather than to limit the present invention.

Unless otherwise defined, all professional terms used hereinafter have the same meaning as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the experimental materials and reagents herein are conventional commercial products in the art.

As shown in FIGS. 1-5 , the cable sample includes, from the inside to the outside, a conductor 1, a semiconductor nylon tape + a semiconductor terylene tape layer 2; a conductor shielding layer 3, an XLPE insulation layer 4 and an insulation shielding layer 5. The XLPE insulation layer 4 includes, from the inside to the outside, an insulation inner layer 41, an insulation middle layer 42 and an insulation outer layer 43.

A method for testing the content of cross-linked byproducts in the insulation of a high-voltage XLPE cable under different degassing temperatures and time conditions, which reflects the degassing effect of the high-voltage XLPE cable by detecting the contents of three cross-linked byproducts, namely, cumyl alcohol, acetophenone and α-methylstyrene, in the degassing sample. The testing method comprises the following steps:

S1. Use a cable cutter to cut a 20 mm long cable sample, remove the conductor and semi-conductive nylon tape, and semi-conductive multi-tape, and keep the conductor shield, XLPE insulation, and insulation shield.

S2. Divide the cable samples into two groups, and heat the cable insulation samples in a constant temperature oven. Set the heating temperature to 65℃ and 70℃, take samples every 12h, and the degassing cycle is 144h;

S3, further cutting the insulation samples taken out of the constant temperature oven, cutting out the whole cable samples including the conductor shield, XLPE insulation, insulation shield, and the inner layer, middle layer and outer layer samples of the XLPE insulation, and weighing the sample masses;

S4. Different insulation samples were packed into 20 mL headspace bottles and heat treated in a constant temperature oven at 120 °C for 5 h.

S5. Using three analytical test standards of cumyl alcohol, acetophenone and α-methylstyrene with a concentration greater than 99%, 6 standard solutions of different concentrations were prepared, and 50 μL of each solution was dispensed into a 20 mL headspace bottle; using gas chromatography-mass spectrometry, the standard solutions of different concentrations were analyzed and tested to obtain the linear relationship between the peak area and mass of the three cross-linking byproducts of cumyl alcohol, acetophenone and α-methylstyrene in the standard solution;

S6. Using gas chromatography-mass spectrometry, the whole cable sample, the inner layer of XLPE insulation, the middle layer of XLPE insulation and the outer layer of XLPE insulation after the heat treatment in step S4 are analyzed and tested respectively, and the peak areas of the three cross-linked by-products measured in the sample test are brought into this linear relationship to obtain the concentrations of the three cross-linked by-products in the insulation sample.

The specific steps of step S1 are:

S11. Cut a 20 mm XLPE sample with a cable cutter, fix the sample horizontally, and use a hammer to hit the conductor inside for several times until the conductor falls off. Then tear off the semi-conductive nylon tape and semi-conductive terylene tape on the inner surface. Make the sample only contain the three-layer structure of conductor shielding, XLPE insulation and insulation shielding, and prepare 26 samples in total.

The specific steps of step S2 are:

S21. Divide the samples into two groups, each with 13 samples, labeled A and B respectively.

One sample was kept in each of the two groups S22, A, and B, and the other samples were placed in a constant temperature box for simulated degassing. The two groups were set at 65℃ and 70℃ respectively.

S23. Arrange the samples evenly on the bottom layer of the constant temperature box, with all samples located on the same horizontal plane to ensure that the samples are heated evenly.

The specific steps of step S3 are:

S31. Cut a fan-shaped cable sample including conductor shielding, XLPE insulation, and insulation shielding with a cable cutter to obtain a cable sample. When preparing the inner, middle, and outer layer samples of XLPE insulation, remove the conductor shielding and insulation shielding on the basis of the cable sample, leaving the XLPE insulation part. Then cut it into three equal parts parallel to the arc surface, from the inside to the outside, respectively, the inner layer of XLPE insulation, the middle layer of XLPE insulation, and the outer layer of XLPE insulation.

S32. Use an electronic balance to weigh the sample. Clean the sample surface first, then set the electronic balance to zero to avoid system errors. Then place the sample on the electronic balance and weigh it. Close the glass window of the electronic balance during weighing to avoid interference.

The specific steps of step S4 are:

S41. During heating, all headspace bottles are placed on a stainless steel sample bottle rack and neatly arranged on the bottom layer of the oven to ensure uniform heating temperature.

The specific steps of step S5 are:

S51. Prepare standard solutions: first use a pipette to sample α-methylstyrene, acetophenone, and cumyl alcohol, pipette them into a 5mL volumetric flask 1, and weigh the masses. The masses of the three standards are 10mg, 150mg, and 100mg, respectively. Then add methanol solution to the scale line of the volumetric flask to obtain standard sample 1, which is used as the mother solution for dilution. Use a pipette to take 1mL of the mother solution to a 5mL volumetric flask 2, add methanol solution to dilute to the scale line of the volumetric flask, and obtain standard sample 2. Use a pipette to take 1mL of the mother solution to a 10mL volumetric flask 3, add methanol solution to dilute to the scale line of the volumetric flask, and obtain standard sample 3. Use a pipette to take 0.5mL of the mother solution to a 10mL volumetric flask 4, add methanol solution to dilute to the scale line of the volumetric flask, and obtain standard sample 4. Use a pipette to take 1mL of standard sample 2 to a 10mL volumetric flask, add methanol solution to dilute to the scale line of the volumetric flask, and obtain standard sample 5. Use a pipette to transfer 1 mL of standard sample 3 to a 10 mL volumetric flask, add methanol solution and dilute to the mark on the volumetric flask to obtain standard sample 6.

S52. Use gas chromatography-mass spectrometry to detect the sample and 6 standard solutions of different concentrations, obtain the peak area of each cross-linked by-product at 6 different concentrations, record the 6 test data and the origin on the coordinate plane, and fit the regression equation y=kx+b corresponding to each cross-linked by-product, where the ordinate y represents the mass of the cross-linked by-product, and the abscissa x represents the peak area of the cross-linked by-product. The regression equation parameter solution formula is as follows:

The specific steps of step S6 are:

S61. Using the external standard method, the concentration of various cross-linking by-products in the sample is calculated based on the relationship curve between the peak area and mass of the cross-linking by-products. The formula is as follows:

Wherein, _ci represents the concentration of cross-linked by-product i (including α-methylstyrene, acetophenone and cumyl alcohol), in mg/g; _ki represents the slope of the standard curve of cross-linked by-product i, in mg; _mj represents the mass of the j-th sample, in g; _Aji represents the peak area of cross-linked by-product i in the j-th sample, without unit.

Example 1

A method for testing the content of cross-linked byproducts in the insulation of a high-voltage XLPE cable under different degassing temperatures and time conditions comprises the following specific steps:

S1. Use a cable cutter to cut a 20mm long 110kV XLPE insulated cable sample that has not been degassed. The cable specifications are shown in Table 1. Fix the cable sample horizontally, hit the central conductor part repeatedly with a hammer until the conductor falls off, and then tear off the inner semi-conductive nylon tape and semi-conductive terylene tape, so that the sample only contains the three-layer structure of conductor shield, XLPE insulation and insulation shield. The sampling method is shown in Figure 2. A total of 26 samples were taken.

S2. Subject the samples to simulated degassing treatment. In the laboratory simulated degassing test, the 26 sections of samples were divided into two groups, A and B, with 13 sections in each group. One section was retained in each group as a control, and then the remaining 12 sections of samples in group A were placed in a 65°C constant temperature oven for heating, while the remaining 12 sections of samples in group B were placed in a 70°C constant temperature oven for heating to simulate the degassing process. When placing the samples, arrange the samples evenly on the bottom layer of the constant temperature oven, with the 12 sections of samples on the same horizontal plane to ensure that each section of the sample is heated evenly. Samples were taken from each group of samples once every 12 hours. The first sampling time for both groups was 12 hours, and the degassing cycle was 144 hours.

S3. Prepare the sample again after simulated degassing. The previously reserved undegassed samples and the two groups of samples A and B after simulated degassing are further cut. Each section of the sample is cut into four samples: the whole insulation sample with a three-layer structure of conductor shielding, XLPE insulation and insulation shielding, and the inner insulation layer, middle insulation layer and outer insulation layer. Specific sample preparation method: Use a cable cutter to cut a fan-shaped insulation whole with a three-layer structure of conductor shielding, XLPE insulation and insulation shielding from each section of the sample to obtain a whole sample. When preparing the inner insulation layer, middle insulation layer and outer insulation layer, the conductor shielding and insulation shielding are cut off based on the whole insulation sample, leaving only the XLPE insulation part, and then cut into three equal parts parallel to the arc surface, with a layer interval of 5mm, from the inside to the outside, they are the inner layer, middle layer and outer layer samples of XLPE insulation. The sample preparation method is shown in Figure 3. After the sample preparation is completed, weigh it with an electronic balance. Clean the sample surface first, then set the electronic balance to zero to avoid system errors. Then place the sample on the electronic balance for weighing, and close the glass window of the electronic balance during weighing to avoid interference. The sample mass is controlled at 1.5 to 3 g. If the mass is too large, the peak area detected by the gas chromatograph mass spectrometer will be too large, and too many cross-linked byproducts will be adsorbed on the inner wall of the instrument during detection, making the data of the next detection larger, affecting the accuracy of the experiment. If the mass is too small, the peak area will be small during detection, which will be confused with the miscellaneous peaks and difficult to distinguish. Therefore, the mass of the sample to be tested must be controlled to ensure the accuracy of the data. After recording the mass of the prepared strip sample, it is placed in a 20 mL threaded headspace bottle and numbered, for a total of 104 samples.

S4, detect the composition and content of cross-linked by-products. First, use the analytical test standards of three substances, α-methylstyrene, acetophenone and cumyl alcohol, as solutes, and use methanol solution as solvent to prepare 6 standard solutions of different concentrations. The concentrations of the standard solutions are shown in Table 2. The specific configuration process is as follows: First, use a pipette to sample α-methylstyrene, acetophenone, and cumyl alcohol, pipette them into a 5mL volumetric flask 1 and weigh the mass. The masses of the three standards are 10mg, 150mg, and 100mg, respectively. Then add methanol solution to the scale line of the volumetric flask to obtain standard sample 1, which is used as the mother liquor for dilution. Use a pipette to take 1mL of mother liquor to a 5mL volumetric flask 2, add methanol solution and dilute to the scale line of the volumetric flask to obtain standard sample 2. Use a pipette to take 1mL of mother liquor to a 10mL volumetric flask 3, add methanol solution and dilute to the scale line of the volumetric flask to obtain standard sample 3. Use a pipette to take 0.5mL of the mother solution to a 10mL volumetric flask 4, add methanol solution to dilute to the scale line of the volumetric flask, and obtain standard sample 4. Use a pipette to take 1mL of standard sample 2 to a 10mL volumetric flask, add methanol solution to dilute to the scale line of the volumetric flask, and obtain standard sample 5. Use a pipette to take 1mL of standard sample 3 to a 10mL volumetric flask, add methanol solution to dilute to the scale line of the volumetric flask, and obtain standard sample 6. The configuration flow chart is shown in Figure 4 below, and the standard concentration solutions are shown in Table 2. Take 50μL from each of the 6 standard solutions, dispense them into headspace bottles and number them for testing.

S5. Agilent GCMS 7890B-7000C gas chromatograph-mass spectrometer, whose operating principle is shown in Figure 5, was used to analyze and test the standard solution sample and 104 test samples. The detection conditions of gas chromatography-tandem mass spectrometry were as follows: the chromatographic column was HP-INNOWax with a specification of 30m×0.25mm×0.25μm; the injection port temperature was 250°C; the heating program was as follows: the initial temperature was 40°C, maintained for 3min, and then heated to 250°C at a rate of 10°C/min and maintained for 5min; the carrier gas used was helium with a purity of 99.9995%, and the helium flow rate was 1mL/min; the injection mode was split injection with a split ratio of 30:1 and an injection volume of 100μL; the mass spectrometry acquisition mode was scan mode, and the m/z range was 33-500. The relationship between the mass and peak area of the three cross-linked by-products in the six standard solutions was obtained (as shown in FIG6 ), and the six peak areas and the origin were recorded in a coordinate graph, and the regression equation y=kx+b corresponding to each cross-linked by-product was fitted, where the ordinate y represents the mass of the cross-linked by-product, and the abscissa x represents the peak area of the cross-linked by-product. The regression equation parameter solution formula is as follows:

Then, the external standard method is used to calculate the concentrations of α-methylstyrene, acetophenone and cumyl alcohol in the sample according to the standard sample curve. The formula is as follows:

Wherein, _ci represents the concentration of cross-linked by-product i (including α-methylstyrene, acetophenone and cumyl alcohol), in mg/g; _ki represents the slope of the standard curve of cross-linked by-product i, in mg; _mj represents the mass of the j-th sample, in g; _Aji represents the peak area of cross-linked by-product i in the j-th sample, without unit.

Table 1110kV XLPE insulated cable specifications

Table 2 Standard concentration solutions

The test results of samples with different degassing times are shown in FIG7 . The present invention can accurately quantify the composition and content of the cross-linked by-products of the XLPE sample, and obtain the concentrations of the three cross-linked by-products, namely, α-methylstyrene, acetophenone, and cumyl alcohol, in the XLPE insulation, so that the evaluation of the degassing effect of the high-voltage cable is more accurate and efficient.

The description of the above embodiments is only used to help understand the technical solution and core ideas of the present invention. It should be pointed out that for technicians in this technical field, several improvements and modifications can be made to the present invention without departing from the principles of the present invention. These improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims (9)

1. A method for testing the content of cross-linked byproducts in high-voltage XLPE cable insulation under different degassing temperatures and time conditions, characterized in that it comprises the following steps: S1. Remove the conductor, semi-conductive nylon tape and semi-conductive multi-tape parts from the cable sample, and keep the conductor shield, XLPE insulation and insulation shield; S2. Divide the cable samples into two groups and perform heat treatment on the cable samples respectively; S3, further cutting the heat-treated cable sample to obtain the whole cable sample including the conductor shield, XLPE insulation, insulation shield, and the inner layer, middle layer and outer layer samples of the XLPE insulation; S4, heat treating the whole cable sample, the inner layer of XLPE insulation, the middle layer of XLPE insulation and the outer layer of XLPE insulation; S5. Using three analytical test standards, namely, cumyl alcohol, acetophenone and α-methylstyrene, standard solutions of different concentrations are prepared, and the standard solutions of different concentrations are analyzed and tested by gas chromatography-mass spectrometry to obtain a linear relationship between the peak area and mass of the three cross-linking byproducts of cumyl alcohol, acetophenone and α-methylstyrene in the standard solution; S6. Using gas chromatography-mass spectrometry, the whole cable sample, the inner layer of XLPE insulation, the middle layer of XLPE insulation and the outer layer of XLPE insulation after the heat treatment in step S4 are analyzed and tested respectively, and the peak areas of the three cross-linked by-products measured in the sample test are brought into this linear relationship to obtain the concentrations of the three cross-linked by-products in the insulation sample. 2. The testing method according to claim 1, characterized in that step S2 specifically comprises the following steps: S21, divide the samples into two groups, each group has several sections of samples, labeled A and B respectively; One sample was retained from each of the two groups S22, A, and B, and the other samples were placed in a constant temperature box for simulated degassing. The heat treatment temperatures of the two groups A and B were set at 65°C and 70°C, respectively. Sampling was taken every 12 hours, and the degassing cycle was 144 hours. 3. The testing method according to claim 1 is characterized in that the specific steps of step S3 are: using a cable cutter to cut a fan-shaped cable sample including a conductor shield, XLPE insulation, and insulation shield to obtain a cable sample; when preparing the inner, middle and outer layer samples of XLPE insulation, on the basis of the cable sample, the conductor shield and insulation shield are removed, leaving the XLPE insulation part, and then cut into three equal parts parallel to the arc surface, which are the inner layer of XLPE insulation, the middle layer of XLPE insulation and the outer layer of XLPE insulation from the inside to the outside. 4. The testing method according to claim 1 is characterized in that the specific steps of step S4 are: the whole cable sample, the inner layer of XLPE insulation, the middle layer of XLPE insulation and the outer layer of XLPE insulation are packed in headspace bottles, and heat-treated in a constant temperature oven, and the heat treatment conditions are: heating temperature 120° C., heating time 5 h. 5. The test method according to claim 1, characterized in that in step S5: cumyl alcohol is respectively configured into 6 standard solutions of different concentrations of 0.2 mg/mL, 0.4 mg/mL, 1.0 mg/mL, 2.0 mg/mL, 4.0 mg/mL, and 20.0 mg/mL, acetophenone is respectively configured into 6 standard solutions of different concentrations of 0.3 mg/mL, 0.6 mg/mL, 1.5 mg/mL, 3.0 mg/mL, 6.0 mg/mL, and 30.0 mg/mL, and α-methylstyrene is respectively configured into 6 standard solutions of different concentrations of 0.02 mg/mL, 0.04 mg/mL, 0.1 mg/mL, 0.2 mg/mL, 0.4 mg/mL, and 2.0 mg/mL. 6. The testing method according to claim 1 or 5, characterized in that step S5 specifically comprises the following steps: S51. Use gas chromatography-mass spectrometry to detect the sample and 6 standard solutions of different concentrations, obtain the peak area of each cross-linked by-product at 6 different concentrations, record the 6 test data and the origin on the coordinate plane, and fit the regression equation y=kx+b corresponding to each cross-linked by-product, where the ordinate y represents the mass of the cross-linked by-product, and the abscissa x represents the peak area of the cross-linked by-product. The regression equation parameter solution formula is as follows: 7. The testing method according to claim 1, characterized in that step S6 specifically comprises the following steps: S61. Using the external standard method, the concentration of various cross-linking by-products in the sample is calculated based on the relationship curve between the peak area and mass of the cross-linking by-products. The formula is as follows: Wherein, _ci represents the concentration of cross-linked by-product i, i includes α-methylstyrene, acetophenone and cumyl alcohol, and the unit is mg/g; _ki represents the slope of the standard curve of cross-linked by-product i, and the unit is mg; _mj represents the mass of the j-th sample, and the unit is g; _Aji represents the peak area of cross-linked by-product i in the j-th sample, and the unit is unitless. 8. The test method according to claim 1, characterized in that the gas chromatography-tandem mass spectrometry detection conditions described in step S5 or S6 are: the chromatographic column is HP-INNOWax, with a specification of 30m×0.25mm×0.25μm; the injection port temperature is 250°C; the heating program is: initial temperature 40°C, maintained for 3min, heated to 250°C at 10°C/min, and maintained for 5min; The carrier gas used was helium with a purity of 99.9995% and a helium flow rate of 1 mL/min; the injection method was split injection with a split ratio of 30:1 and an injection volume of 100 μL; the mass spectrometry acquisition method was scan mode with an m/z range of 33-500. 9. Application of the test method described in claim 1 in testing the content of cross-linking byproducts inside the insulation of high-voltage XLPE cables under different degassing temperature and time conditions.