Determination method for degassing time of high-voltage direct-current cable based on cross-linked by-product migration and application

Abstract

The invention relates to the technical field of power cables, and particularly discloses a high-voltage direct-current cable degassing time judgment method based on cross-linked by-product migration and application. According to the method, a degassing time prediction model containing a specific coefficient is constructed according to external specific surface area parameters of a cross-linked high-voltage direct-current cable insulating layer, and the degassing time prediction model can be obtained only by acquiring geometric parameters of the inner diameter and the outer diameter of the cable insulating layer through the model after the external specific surface area of the insulating layer is obtained through calculation. And the shortest degassing time required by the high-voltage direct-current cable can be directly deduced. The determination method provided by the invention simplifies the calculation process of the degassing time, does not need to introduce complex interference parameters such as material components and process environments, has good adaptability to direct-current cables with different radial dimensions, can realize unified determination of the degassing time of cross-specification cables, and is high in practicability. The technical bottlenecks that the existing degassing time judgment technology is complicated and the degassing time is difficult to accurately judge are solved.

Description

Technical Field

[0001] This application relates to the field of power cable technology, and in particular to a method and application for determining the degassing time of high-voltage DC cables based on the migration of cross-linking byproducts. Background Technology

[0002] Cross-linked polyethylene (XLPE) insulated high-voltage direct current (HVDC) cables are key power equipment for new energy development. Industrially, they are mainly produced by chemically cross-linking linear low-density polyethylene (LLDPE) initiated by dicumyl peroxide (DCP). DCP has a low decomposition temperature and high cross-linking efficiency, and can form a uniform cross-linked network structure, making it an ideal chemical cross-linking agent. During the cross-linking reaction, DCP produces polar byproducts such as acetophenone, cumyl alcohol, and α-methylstyrene. The residue of these byproducts in the cable insulation layer can significantly affect the space charge distribution, potentially leading to electric field distortion under high-voltage direct current, inducing electrical tree growth and partial discharge, threatening the long-term operational reliability of the cable. Therefore, during cable manufacturing, a heating degassing process is required to reduce or remove these cross-linking byproducts.

[0003] Currently, the determination of degassing process time in industrial production generally relies on empirical settings or extensive experimentation. This method has the following main shortcomings: First, it lacks a unified and quantitative judgment standard, making it difficult to accurately determine the degassing endpoint, which may lead to insufficient or excessive degassing; second, the degassing time is closely related to the geometric dimensions of the cable insulation layer, and existing methods cannot establish a universal degassing time prediction model applicable to different cable specifications, resulting in repeated experiments for each new specification product development, which is inefficient.

[0004] How to establish a universal method that can accurately and efficiently determine the degassing time of high-voltage DC cables and is applicable to different cable specifications has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] In view of this, the purpose of this application is to provide a method and application for determining the degassing time of high-voltage DC cables based on the migration of cross-linking byproducts, in order to solve the technical bottleneck of existing degassing time determination technology being complex and difficult to accurately determine the degassing time.

[0006] To achieve the above technical objectives, this application provides a method for determining the degassing time of high-voltage DC cables based on the migration of cross-linking byproducts, comprising the following steps:

[0007] Step S1: Construct a migration and diffusion model of crosslinking byproducts in the radial direction of the high-voltage DC cable based on Fick's diffusion law;

[0008] Step S2: Degas the high-voltage DC cable and simultaneously detect the following parameters: initial concentration of cross-linking byproducts, arc length of electrical trees in the radial direction of the high-voltage DC cable, and concentration of cross-linking byproducts when electrical trees stop growing. The concentration of cross-linking byproducts when electrical trees stop growing is used as the threshold concentration.

[0009] Step S3: Substitute the degassing time, the initial concentration of crosslinking byproducts, the threshold concentration of crosslinking byproducts, and the arc length of the electrical tree in the radial direction of the high-voltage DC cable into the migration and diffusion model constructed in step S1 to obtain the diffusion coefficient of crosslinking byproducts.

[0010] Step S4: Combining the diffusion coefficient of crosslinking byproducts, the initial concentration of crosslinking byproducts, and the threshold concentration of crosslinking byproducts, a degassing simulation experiment was conducted on the high-voltage DC cable using finite element simulation software to obtain the relationship curve between degassing time and the specific surface area of ​​the outer insulation layer. The Levenberg-Marquardt fitting was used to calculate the relationship curve to obtain a degassing time prediction model.

[0011] Furthermore, the migration and diffusion model of crosslinking byproducts in the radial direction of the high-voltage DC cable is as follows:

[0012] Equation (1);

[0013] In equation (1), C represents the concentration of crosslinking byproducts at radius r at time t; D represents the diffusion coefficient; r represents the radial coordinate; and t represents the diffusion time.

[0014] Furthermore, the rated voltage of the high-voltage DC cable is 100kV~500kV; the inner diameter of the insulation layer of the high-voltage DC cable is 25mm~70mm, and the outer diameter is 35mm~100mm;

[0015] Crosslinking byproducts include at least one of acetophenone, α-methylstyrene, and cumyl alcohol.

[0016] Furthermore, in the degassing simulation experiment, the physical field model selected was the rare matter transport model, and the simulation temperature was set to 30~70℃; the simulation termination condition was: the concentration of cross-linking byproducts in the radial direction of the insulation layer was lower than the threshold concentration.

[0017] Furthermore, in the degassing simulation experiment, a simulation model was established using finite element simulation software. The simulation model includes an insulation layer and an air layer, where the air layer is a cylindrical region extending outward from the outer surface of the insulation layer by 8mm to 12mm. The insulation layer is divided into free triangular meshes, with the largest cell size less than or equal to 1.2mm and the smallest cell size greater than or equal to 0.03mm. The air layer is also divided into free triangular meshes, with the largest cell size less than or equal to 140mm and the smallest cell size greater than or equal to 0.5mm.

[0018] Furthermore, the degassing time prediction model is shown in equation (2). The degassing time of the high-voltage DC cable is calculated using the degassing time prediction model shown in equation (2):

[0019] Equation (2);

[0020] In equation (2), T1 represents the shortest degassing time required when the concentration of crosslinking byproducts is below the threshold concentration; S' represents the outer surface area of ​​the insulation layer.

[0021] Furthermore, the outer specific surface area of ​​the insulation layer is the ratio of the surface area of ​​the outer insulation layer to the volume of the insulation layer per unit length of a DC cable. The formula for calculating the outer specific surface area of ​​the insulation layer is as follows:

[0022] Equation (3);

[0023] In equation (3), S' represents the outer surface area of ​​the insulation layer; D represents the outer diameter of the insulation layer; and d represents the inner diameter of the insulation layer.

[0024] This application provides a system for determining the degassing time of a high-voltage DC cable, including a data input module, a data processing module, and a data output module;

[0025] The data input module is used to input the outer diameter and inner diameter of the insulation layer of the high-voltage DC cable;

[0026] The data processing module includes a degassing time prediction model. The data processing module receives parameters of the outer diameter and inner diameter of the insulation layer, performs calculations using the degassing time prediction model, and obtains the shortest degassing time.

[0027] The data output module is used to display or transmit the shortest degassing time.

[0028] This application provides a high-voltage DC cable degassing system, including a degassing time prediction model or a high-voltage DC cable degassing time determination system.

[0029] In summary, this application proposes a method for determining the degassing time of high-voltage DC cables based on the migration characteristics of cross-linking byproducts. This method constructs a degassing time prediction model with specific coefficients, focusing on the external specific surface area parameter of the cross-linked high-voltage DC cable insulation layer. Using this model, only the inner and outer diameter geometric parameters of the cable insulation layer need to be obtained. After calculating the external specific surface area of ​​the insulation layer, the minimum degassing time required for the high-voltage DC cable can be directly derived. The method proposed in this application simplifies the calculation process of degassing time, eliminates the need to introduce complex interfering parameters such as material composition and process environment, and has good adaptability to DC cables of different radial dimensions, enabling a unified determination of degassing time for cables of different specifications.

[0030] Compared with existing technologies, the outstanding innovation of this solution lies in the fact that it is the first time to use the outer surface area of ​​the insulation layer as the core indicator for determining the degassing time, which simplifies the degassing time calculation process and improves the reliability of the results, providing a new technical path for the standardization and efficiency of the degassing process of high voltage DC cables. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 The method for determining the degassing time of high-voltage DC cables based on the migration of crosslinking byproducts is provided in the embodiments.

[0033] Figure 2 A schematic diagram illustrating the mechanism by which DCP-initiated crosslinking reactions generate XLPE and produce crosslinking byproducts;

[0034] Figure 3 A model diagram illustrating the migration and diffusion of matter along the x-axis in accordance with Fick's second law;

[0035] Figure 4 This is a schematic diagram showing the change in the concentration of crosslinking byproducts in the radial direction of a 320kV DC cable with degassing time.

[0036] Figure 5 This is a schematic diagram showing the change in the concentration of crosslinking byproducts in the radial direction of a 200kV DC cable with degassing time.

[0037] Figure 6 This is a schematic diagram showing the change in the concentration of crosslinking byproducts in the radial direction of a 100kV DC cable with degassing time.

[0038] Figure 7 This graph shows the relationship between degassing time and the specific surface area of ​​the cable insulation layer under different voltages. Detailed Implementation

[0039] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments in this application specification, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection claimed in this application.

[0040] In the description of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0041] Unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0042] The raw materials used in this invention are not particularly restricted in their source; they can be purchased on the market or prepared using conventional methods known to those skilled in the art.

[0043] This application provides a method for determining the degassing time of a high-voltage DC cable based on the migration of crosslinking byproducts, including the following steps:

[0044] Step S1: Construct a migration and diffusion model of crosslinking byproducts in the radial direction of the high-voltage DC cable based on Fick's diffusion law;

[0045] Step S2: Degas the high-voltage DC cable and simultaneously detect the following parameters: initial concentration of cross-linking byproducts, arc length of electrical trees in the radial direction of the high-voltage DC cable, and concentration of cross-linking byproducts when electrical trees stop growing. The concentration of cross-linking byproducts when electrical trees stop growing is used as the threshold concentration.

[0046] Step S3: Substitute the degassing time, the initial concentration of crosslinking byproducts, the threshold concentration of crosslinking byproducts, and the arc length of the electrical tree in the radial direction of the high-voltage DC cable into the migration and diffusion model constructed in step S1 to obtain the diffusion coefficient of crosslinking byproducts.

[0047] Step S4: Combining the diffusion coefficient of crosslinking byproducts, the initial concentration of crosslinking byproducts and the threshold concentration of crosslinking byproducts, a degassing simulation experiment was conducted on the high-voltage DC cable using finite element simulation software to obtain the relationship curve between degassing time and the specific surface area of ​​the outer insulation layer. The Levenberg-Marquardt fitting was used to calculate the relationship curve to obtain the degassing time prediction model shown in Equation (2).

[0048] In some embodiments, the migration and diffusion model of crosslinking byproducts in the radial direction of the high-voltage DC cable is as follows:

[0049] Equation (1);

[0050] In equation (1), C represents the concentration of crosslinking byproducts at radius r at time t; D represents the diffusion coefficient; r represents the radial coordinate; and t represents the diffusion time.

[0051] It should be noted that when t is 0d, C represents the initial concentration of cross-linking byproducts at radius r; when t is the shortest degassing time, C represents the threshold concentration of cross-linking byproducts at radius r.

[0052] In some embodiments, the evolution of the migration and diffusion model for crosslinking byproducts in DC cables is calculated as follows:

[0053] (1) When cross-linking byproducts are dispersed in XLPE in the form of small molecules, their molecular motion is random. This motion process follows the diffusion process described by Fick's first law. Therefore, by introducing the local concentration C of the cross-linking byproducts as the core input variable into Fick's first law, we obtain the following equation:

[0054] Equation (4); In Equation (4), D—diffusion coefficient, m 2 / s; C—diffuse concentration, g / m³ 3 x—the spatial coordinate perpendicular to the cross section.

[0055] (2) Since the cross-linking byproducts diffuse along the x, y, and z axes, the diffusion rate concentration C(x, y, z, t) in these three axes changes with time t according to Fick's second law as shown in equation (5); where Figure 3 The migration equation is only for the diffusion of matter along the x-axis;

[0056] Equation (5); In Equation (5), D is the diffusion coefficient (m² / s); C is the local concentration of crosslinking byproducts (g / m³); ∇2 is the Laplace operator.

[0057] (3) Since DC cables are standard cylindrical structures, under ideal conditions (i.e., the initial distribution of byproducts is uniform and the diffusion process is axisymmetric), the concentration C of crosslinking byproducts is only related to the radial distance r and time t, and is independent of the axial position z and the circumferential angle θ. Therefore, the three-dimensional diffusion equation of crosslinking byproducts can be simplified to the following one-dimensional form with respect to radius r:

[0058] Equation (1); In Equation (1), C—the concentration of crosslinking byproducts at radius r at time t (g / m 3D—Diffusion coefficient (m) 2 / s), is a constant; r—radial coordinate, radius (m); t—diffusion time (s).

[0059] In some embodiments, the rated voltage of the high-voltage DC cable is 100kV~500kV; the inner diameter of the insulation layer of the high-voltage DC cable is 25mm~70mm, and the outer diameter is 35mm~100mm; the crosslinking byproducts include at least one of acetophenone, α-methylstyrene, and cumyl alcohol.

[0060] It should be noted that crosslinking byproducts are generated during the DCP-initiated crosslinking reaction to form XLPE, and their specific formation pathway is as follows: Figure 2 As shown.

[0061] In some embodiments, in the degassing simulation experiment, the physical field model is selected as "dilute mass transport model", and the simulation temperature is set to 30~70℃; the simulation termination condition is: the concentration of cross-linked by-products in the radial direction of the insulating layer is lower than the threshold concentration.

[0062] In some embodiments, in the degassing simulation experiment, a simulation model is established using finite element simulation software. The simulation model includes an insulation layer and an air layer, wherein the air layer is a cylindrical region extending outward from the outer surface of the insulation layer by 8mm to 12mm. The insulation layer is divided into free triangular meshes, with the largest cell size less than or equal to 1.2mm and the smallest cell size greater than or equal to 0.03mm. The air layer is divided into free triangular meshes, with the largest cell size less than or equal to 140mm and the smallest cell size greater than or equal to 0.5mm.

[0063] In some embodiments, the degassing time prediction model is as shown in equation (2), and the degassing time of the high-voltage DC cable is calculated using the degassing time prediction model shown in equation (2):

[0064] Equation (2);

[0065] In equation (1), T1 represents the shortest degassing time required when the concentration of crosslinking byproducts is below the threshold concentration; S' represents the outer surface area of ​​the insulation layer.

[0066] In some embodiments, the outer specific surface area of ​​the insulation layer is the ratio of the surface area of ​​the outer insulation layer to the volume of the insulation layer per unit length of the DC cable. The formula for calculating the outer specific surface area of ​​the insulation layer is as follows:

[0067] Equation (3);

[0068] In equation (3), S' represents the outer surface area of ​​the insulation layer; D represents the outer diameter of the insulation layer; and d represents the inner diameter of the insulation layer.

[0069] This application provides an application of a method for determining the degassing time of high-voltage DC cables based on the migration of crosslinking byproducts, used to calculate the shortest degassing time of high-voltage DC cables.

[0070] This application provides a high-voltage DC cable degassing time determination system, including a data input module, a data processing module, and a data output module;

[0071] The data input module is used to input the outer diameter and inner diameter of the insulation layer of the high-voltage DC cable;

[0072] The data processing module includes a degassing time prediction model. The data processing module receives parameters of the outer diameter and inner diameter of the insulation layer, performs calculations using the degassing time prediction model, and obtains the shortest degassing time.

[0073] The data output module is used to display or transmit the shortest degassing time.

[0074] This application provides a high-voltage DC cable degassing system, including a degassing time prediction model or a high-voltage DC cable degassing time determination system.

[0075] The applicant further provides the following specific embodiments to describe the present invention. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0076] Example 1

[0077] This embodiment provides a method for determining the degassing time of high-voltage DC cables based on the migration of crosslinking byproducts. The specific steps are as follows:

[0078] Step S1: Select the four specifications of DC cables shown in Table 1 (their structural parameters are shown in Table 1) and calculate the specific surface area of ​​the insulation layer of the DC cable.

[0079] Table 1. Parameter Comparison Table for Four Types of DC Cables

[0080]

[0081] Step S2: The four different specifications of DC cables in Table 1 were placed in the same degassing environment for degassing experiments. At four time points—day 1, day 7, day 30, and day 60 of the degassing treatment—the concentration of crosslinking byproducts and the arc length of electrical trees in the radial direction were measured for each type of cable. The crosslinking byproducts included acetophenone, α-methylstyrene, and cumyl alcohol. Finally, the changes in the radial arc length of electrical trees and the concentration of the three crosslinking byproducts at different degassing times were obtained. For detailed data and curves, please refer to [link to relevant documentation]. Figures 4-6Finally, the concentration of cross-linking byproducts corresponding to the point when electrical tree growth completely stops was taken as the threshold concentration, and the degassing time corresponding to the point when electrical tree growth completely stops was taken as the shortest degassing time. The initial concentration and threshold concentration of cross-linking byproducts obtained are shown in Table 2.

[0082] Table 2. Initial and threshold concentrations of crosslinking byproducts in the degassing experiment

[0083]

[0084] Step S3: Based on the initial concentration and threshold concentration of crosslinking byproducts in Table 2, and the shortest degassing time, the migration and diffusion coefficient of crosslinking byproducts as shown in Table 3 is calculated according to the migration and diffusion model of crosslinking byproducts in the radial direction of the high voltage DC cable.

[0085] Table 3. Diffusion coefficient and decomposition reaction rate constant of crosslinking byproducts at different temperatures

[0086]

[0087] Step S4: Combining the initial and threshold concentrations of crosslinking byproducts shown in Table 2 and the diffusion coefficients of crosslinking byproducts at different temperatures shown in Table 3, a degassing simulation experiment of the high-voltage DC cable was conducted using finite element simulation software. The basic parameters of the finite element simulation software were set as follows: A simulation model of the high-voltage DC cable was established, consisting of an insulation layer and an outer air layer. The size of the insulation layer was set according to the data shown in Table 1, and the outer air layer was set to extend 10m outward from the outer surface of the insulation layer. After the model was established, a mesh was generated. The insulation layer used a free triangular mesh with a maximum cell size of 1mm, a minimum cell size of 0.04mm, and a maximum cell growth rate of 1.05. The outer air layer used a free triangular mesh with a maximum cell size of 134mm, a minimum cell size of 0.6mm, and a maximum cell growth rate of 1.3. In the physical field model, a rare matter transport model was selected, with the temperature set to 70℃. The diffusion coefficients of the three crosslinking byproducts were set according to the data shown in Table 3. The termination condition of the degassing simulation experiment was that the concentration of crosslinking byproducts in the radial direction of the insulation layer was lower than the threshold concentration measured in the degassing experiment. At this point, the shortest degassing time obtained from the degassing simulation experiment is approximately the shortest degassing time in actual engineering, and the results are obtained simultaneously as follows: Figure 7 The graph shows the relationship between the outer specific surface area of ​​the insulation layer and the degassing time. Finally, by combining the Levenberg-Marquardt fitting of the relationship between degassing time and outer specific surface area, the following formula is derived: the relationship between the number of days required for degassing of the high-voltage DC cable and the outer specific surface area of ​​the insulation layer (i.e., the degassing time prediction model):

[0088] In the formula, T1 is the shortest degassing time required when the concentration of crosslinking byproducts is below the threshold concentration, in days; S' is the specific surface area outside the insulation layer, in mm. -1 e is a natural constant that performs an exponential fit between degassing time and external surface area.

[0089] The above are merely preferred embodiments of this application and are not intended to limit the present invention. Although this application has been described in detail with reference to examples, those skilled in the art can still modify the technical solutions described in the foregoing examples or make equivalent substitutions for some of the technical features. However, any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for determining the degassing time of high-voltage DC cables based on the migration of cross-linking byproducts, characterized in that, Includes the following steps: Step S1: Construct a migration and diffusion model of crosslinking byproducts in the radial direction of the high-voltage DC cable based on Fick's diffusion law; Step S2: Degas the high-voltage DC cable and simultaneously detect the following parameters: initial concentration of cross-linking byproducts, arc length of electrical trees in the radial direction of the high-voltage DC cable, and concentration of cross-linking byproducts when electrical trees stop growing, with the concentration of cross-linking byproducts when electrical trees stop growing being the threshold concentration. Step S3: Substitute the degassing time, the initial concentration of crosslinking byproducts, the threshold concentration of crosslinking byproducts, and the arc length of the electrical tree in the radial direction of the high-voltage DC cable into the migration and diffusion model constructed in step S1 to obtain the diffusion coefficient of crosslinking byproducts. Step S4: Combining the diffusion coefficient of crosslinking byproducts, the initial concentration of crosslinking byproducts, and the threshold concentration of crosslinking byproducts, a degassing simulation experiment was conducted on the high-voltage DC cable using finite element simulation software to obtain the relationship curve between the degassing time and the specific surface area of ​​the outer insulation layer. The Levenberg-Marquardt fitting was used to calculate the relationship curve to obtain a degassing time prediction model.

2. The method for determining the degassing time of high-voltage DC cables based on the migration of cross-linking byproducts according to claim 1, characterized in that: The migration and diffusion model of the crosslinking byproducts in the radial direction of the high-voltage DC cable is as follows: Equation (1); In equation (1), C represents the concentration of crosslinking byproducts at radius r at time t; D represents the diffusion coefficient; r represents the radial coordinate; and t represents the diffusion time.

3. The method for determining the degassing time of high-voltage DC cables based on the migration of cross-linking byproducts according to any one of claims 1 to 2, characterized in that: The rated voltage of the high-voltage DC cable is 100kV~500kV; the inner diameter of the insulation layer of the high-voltage DC cable is 25mm~70mm, and the outer diameter is 35mm~100mm. The cross-linking byproducts include at least one of acetophenone, α-methylstyrene, and cumyl alcohol.

4. The method for determining the degassing time of high-voltage DC cables based on the migration of cross-linking byproducts according to any one of claims 1 to 3, characterized in that: In the degassing simulation experiment, the rare matter transport model was selected as the physical field model, and the simulation temperature was set to 30~70℃. The simulation termination condition was that the concentration of cross-linked by-products in the radial direction of the insulating layer was lower than the threshold concentration.

5. The method for determining the degassing time of high-voltage DC cables based on the migration of cross-linking byproducts according to claim 4, characterized in that: In the degassing simulation experiment, a simulation model was established using finite element simulation software. The simulation model includes an insulation layer and an air layer, wherein the air layer is a cylindrical region extending outward from the outer surface of the insulation layer by 8mm to 12mm. The insulation layer is divided into free triangular meshes, with the largest cell size less than or equal to 1.2mm and the smallest cell size greater than or equal to 0.03mm. The air layer is divided into free triangular meshes, with the largest cell size less than or equal to 140mm and the smallest cell size greater than or equal to 0.5mm.

6. The method for determining the degassing time of high-voltage DC cables based on the migration of cross-linking byproducts according to claim 1, characterized in that: In the degassing simulation experiment, the rare matter transport model was selected as the physical field model, and the simulation temperature was set to 30~70℃. The simulation termination condition was that the concentration of cross-linked by-products in the radial direction of the insulating layer was lower than the threshold concentration.

7. The method for determining the degassing time of high-voltage DC cables based on the migration of cross-linking byproducts according to claim 1, characterized in that, The degassing time prediction model is shown in Equation (2). The degassing time of the high-voltage DC cable is calculated using the degassing time prediction model shown in Equation (2). Equation (2); In equation (2), T1 represents the shortest degassing time required when the concentration of crosslinking byproducts is below the threshold concentration; S' represents the outer surface area of ​​the insulation layer.

8. The method for determining the degassing time of high-voltage DC cables based on the migration of cross-linking byproducts according to claim 7, characterized in that, The specific surface area of ​​the insulation layer is the ratio of the surface area of ​​the outer insulation layer to the volume of the insulation layer per unit length of a DC cable. The formula for calculating the specific surface area of ​​the insulation layer is as follows: Equation (3); In equation (3), S' represents the outer surface area of ​​the insulation layer; D represents the outer diameter of the insulation layer; and d represents the inner diameter of the insulation layer.

9. A system for determining the degassing time of a high-voltage DC cable, characterized in that, It includes a data input module, a data processing module, and a data output module; The data input module is used to input the outer diameter and inner diameter of the insulation layer of the high-voltage DC cable; The data processing module includes the degassing time prediction model according to any one of claims 7 to 8. The data processing module is used to receive parameters of the outer diameter and inner diameter of the insulation layer, and to perform calculations using the degassing time prediction model to obtain the shortest degassing time. The data output module is used to display or transmit the shortest degassing time.

10. A degassing treatment system for high-voltage DC cables, characterized in that, This includes the degassing time prediction model as described in any one of claims 7 to 8 or the high-voltage DC cable degassing time determination system as described in claim 9.

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