Electromagnetic simulation modeling method and device for intermediate connection of high-voltage power cable

Abstract

The invention belongs to the technical field of simulation modeling, and particularly relates to an electromagnetic simulation modeling method and device for intermediate connection of high-voltage power cables, and the method comprises the steps: analyzing a damp path of the intermediate connection of the cables; a high-voltage cable intermediate connection three-dimensional model is constructed through finite element simulation software and comprises three areas, namely a cable conductor, a silicone rubber accessory and an interface, and silicone oil is smeared at the junction of the cable conductor and the silicone rubber accessory; setting simulation parameters of the three regions, adding a magnetic field model, adding an electromagnetic-thermal-mechanical coupling control equation and boundary conditions, and obtaining an electromagnetic-thermal-mechanical coupling model; and based on an electromagnetic-thermal-mechanical coupling model, establishing electromagnetic simulation models of different damp conditions at the intermediate connection interface of the cable, and using the electromagnetic simulation models to simulate and analyze the different damp conditions at the intermediate connection interface of the cable. By accurately simulating the electromagnetic field distribution of the intermediate joint of the high-voltage power cable, the damp fault is effectively predicted and diagnosed, and the reliability and safety of the cable are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of simulation modeling, and in particular relates to an electromagnetic simulation modeling method and device for an intermediate connection of a high-voltage power cable. Background Art

[0002] With the rapid development of the electric power industry, high-voltage power cables are increasingly used in power grids. As an important carrier of power transmission, the reliability and safety of high-voltage power cables are directly related to the stable operation of the entire power system. Cable intermediate joints are used to connect two sections of cables to form a continuous power transmission channel. In the long-term use of high-voltage power cables, the quality and performance of cable intermediate joints often become key factors affecting the overall performance of cable lines.

[0003] In actual operation, cables face complex working conditions and the particularity of joint materials and structures, which leads to complex distribution of electric and magnetic fields at cable joints. Traditional calculation methods often have difficulty accurately predicting the distribution of electromagnetic fields at joints under various operating conditions, resulting in greater uncertainty and risk in joint design and manufacturing.

[0004] In view of the above problems, it is possible to simulate the electromagnetic field distribution at the cable joint to evaluate and predict the joint operation status. Therefore, developing an electromagnetic simulation model method that can accurately simulate the electromagnetic field distribution of the intermediate joint of the high-voltage power cable is of great significance for improving the performance of the cable joint, reducing the design and manufacturing costs, and ensuring the stable operation of the power system. Summary of the invention

[0005] In view of the above deficiencies in the prior art, the purpose of the present invention is to provide an electromagnetic simulation modeling method and device for the intermediate connection of a high-voltage power cable, which can effectively predict and diagnose moisture faults by accurately simulating the electromagnetic field distribution of the intermediate joint of the high-voltage power cable, thereby improving the reliability and safety of the cable.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is an electromagnetic simulation modeling method for an intermediate connection of a high-voltage power cable, comprising the following steps: S1. Analyze the moisture path of the cable's intermediate connection; S2. Construct a three-dimensional model of the intermediate connection of the high-voltage cable through finite element simulation software, including three areas, namely the cable conductor, the silicone rubber accessory and the interface, and apply silicone oil at the junction of the cable conductor and the silicone rubber accessory; S3. Set the simulation parameters of the three regions, add a magnetic field model, set the electromagnetic field as a current source, set the thermal conductivity, density, and constant-pressure heat capacity to come from the material, add the control equations and boundary conditions of electromagnetic-thermal-mechanical coupling, and obtain an electromagnetic-thermal-mechanical coupling model; S4. Based on the electromagnetic-thermal-mechanical coupling model, an electromagnetic simulation model of different moisture conditions at the middle connection interface of the cable is established to simulate and analyze different moisture conditions at the middle connection interface of the cable.

[0007] As a preferred embodiment of the present invention, in the above S1, the moisture path is that due to insufficient gripping force between the cable intermediate connection and the cable body, a cavity is formed in the insulating interface of the cable intermediate connection, allowing moisture to penetrate.

[0008] As a preferred embodiment of the present invention, in the S2, the simulation process adopts Comsol finite element simulation software, the cable conductor area includes the cable conductor, insulation layer, shielding layer, aluminum sheath, outer sheath and cable intermediate connection, the cable intermediate connection includes conductor crimping tube, insulation sleeve, shielding layer connector; the interface refers to the contact surface between the layers of the cable, and the contact surface between the cable and the external environment; two domains of soil and air are set, the cable intermediate connection is located in the soil, and the interface area is the boundary area where the cable intermediate connection contacts the soil or air.

[0009] As a preferred solution of the present invention, in said S3, the setting of simulation parameters includes: Set electromagnetic parameters, including current density, voltage level, frequency of cable conductor, and dielectric constant, conductivity, and magnetic permeability of insulation and shielding layers; Set the material properties and electromagnetic characteristics of the cable conductor, insulation layer, shielding layer, aluminum sheath, outer sheath, conductor crimping tube, insulation sleeve and shielding layer connector; Set thermal parameters, including thermal conductivity, density and constant pressure heat capacity. Set thermal parameters to come from materials; Setting boundary conditions, including the electromagnetic coupling relationship between the cable intermediate connection and the external environment, and the radiation and scattering characteristics of the electromagnetic field; The setting of the control equations includes: The electromagnetic loss is coupled to the fluid temperature as the initial heat source. The electromagnetic loss includes hysteresis loss and eddy current loss. The calculation formula of the electromagnetic loss is as follows: ; In the formula, is the total electromagnetic loss; is the hysteresis loss; is the eddy current loss; Among them, hysteresis loss is caused by the hysteresis phenomenon in the magnetization process of the material. The calculation formula of hysteresis loss is: ; In the formula, is the hysteresis coefficient; f represents the frequency of change of magnetic flux density; is the maximum magnetic flux density; z is the hysteresis index; For the soil and air domains, the air domain is set as a fluid, the soil domain is set as a solid, the heat flux type is set as convective heat flux, and the initial value of solid heat transfer is set. The convective heat flux is expressed as: ; Where λ is the thermal conductivity of the insulating material; h is the heat transfer coefficient of the outer surface of the cable middle connection in contact with the air; is the cable middle connection surface area; is the middle connection surface temperature; is the ambient temperature; Represents the component of the temperature gradient in the normal direction, that is, the partial derivative of the temperature T with respect to the normal vector m; The temperature field control equation is: ; In the formula, x is the heat source; ρ is the material density; C p is the heat capacity at normal pressure; u is the electric displacement of the material under thermal stress; k is the thermal conductivity; is the gradient operator; t is the time; The heat generation rate of the conductor is: ; In the formula, Q is the heat generation rate of the conductor; I is the load current of the middle connection of the cable; R is the AC resistance of the conductor per unit length; S is the cross-sectional area of ​​the core; The heat loss of the insulating material is: ; Where P is the heat loss power of the insulating material; is the angular frequency; C is the dielectric capacitance; is the point loss angle, Indicates dielectric loss factor; is the potential of the dielectric.

[0010] As a preferred embodiment of the present invention, the value of z is between 1 and 2, and the initial value of solid heat transfer is 20°C.

[0011] As a preferred embodiment of the present invention, in the S3, adding a magnetic field model also includes setting Ampere's law in the solid, the conduction model is conductivity, and the conductivity comes from the material; the magnetization mode of the coil is set to relative magnetic permeability, and the relative magnetic permeability also comes from the material; and the current carrying capacity is set to obtain the magnetic flux density.

[0012] As a preferred embodiment of the present invention, in the magnetic field model, in order to accurately calculate the electromagnetic field distribution value caused by the loss, an assumption is made about the cable working condition: Assumption 1: The frequency of the cable during operation is 50HZ, and the displacement current generated during operation is not calculated; Assumption 2: There is no free charge in the domain field of the magnetic field model; The differential forms of the basic equations of the electromagnetic field and the medium equations are as follows: ; ; ; ; ; ; In the formula, H is the magnetic field intensity; J is the current density, that is, the current density inside the middle connection of the cable; D is the electric displacement vector; B is the magnetic induction intensity; E is the electric field intensity; is the conductivity; is the dielectric constant; Since the divergence of the vector function curl is always 0, it can be expressed as: ; Where A is any vector field; The electromagnetic loss density of the cable middle connection is , expressed as: ; ; There is the following corresponding relationship between the conductivity of the wire core connected in the middle of the cable and the temperature: ; In the formula, is the cable core conductivity at room temperature; is the temperature coefficient.

[0013] As a preferred solution of the present invention, in S4, the process of establishing the electromagnetic simulation model is: Based on the electromagnetic-thermal-mechanical coupling model, the electromagnetic field distribution, electromagnetic loss, temperature distribution and mechanical distribution of the power cable under normal operation are simulated and analyzed. Then, the interface moisture condition is set, and the moisture is taken as a variable. The influence of the damp environment on the electromagnetic performance is considered to perform mesh division. Through solving and calculating, the electromagnetic simulation results of the cable under damp conditions are processed to check the electromagnetic field distribution and electromagnetic loss, and calculate the average value; In the electromagnetic simulation model, silicone oil and water affect the physical properties of the cable through the diffusion process. Silicone oil swells into the silicone rubber in the form of free and combined states according to the Langmuir diffusion process, and water also enters through the diffusion movement of silicone oil. The weight gain rate of the silicone rubber immersed at time t is derived based on the diffusion process : ; ; In the formula, is the saturated weight gain rate; is the diffusion coefficient of the mobile molecule; is a multiple of the diffusion coefficient; b is the rate constant; is the instantaneous state function, describing the water absorption process at time t; t1 is the water absorption time; n is a summation index variable; d is the thickness of silicone rubber.

[0014] As a preferred solution of the present invention, it also includes S5, establishing a cable intermediate connection moisture test platform, testing the changes in the electromagnetic field and conductivity of the cable intermediate connection after moisture, comparing with the electromagnetic simulation model, and verifying the accuracy and feasibility of the electromagnetic simulation model comparison; The cable intermediate connection moisture test platform includes: Test platform frame, used to support and fix all components; Cable middle connection sample, fix the cable middle connection to be tested on the test platform to ensure its stability in moisture and electromagnetic field tests; Moisture simulation system, including humidity control unit and moisture penetration simulation device, used to simulate the humid environment that the cable will encounter in actual use; Electromagnetic field measurement equipment, including magnetic field intensity meters and electric field intensity meters, used to measure the electromagnetic field distribution of the cable intermediate connection after being damp; Conductivity measurement equipment, including four-probe measurement devices or other conductivity measurement tools, used to measure the change in conductivity of the cable after being exposed to moisture; A data acquisition system, including a wireless signal device, a wired signal device, and temperature sensors and current transformers arranged at multiple points in the middle of the cable connection, for collecting temperature sensor data and current transformer data; A central processing unit, used for receiving and processing data transmitted from the data acquisition system, and performing analysis and comparison; An environmental control unit, used to control the environmental conditions of the test platform; The testing process is: Sample preparation: Install the cable intermediate connection sample on the test platform; Environmental settings: Set the required temperature and humidity conditions through the environmental control unit; Moisture simulation: Start the moisture simulation system to make the middle connection of the cable wet; Data collection: Turn on the data collection system, including wireless and wired signal devices, and start collecting temperature, current transformer data, and electromagnetic field and conductivity data; Electromagnetic field and conductivity testing: Testing is performed using electromagnetic field measuring equipment and conductivity measuring equipment; Data transmission: The collected data is transmitted to the central processor through a wired signal device; Data analysis: The central processing unit analyzes the data and compares it with the electromagnetic simulation model to verify the accuracy and feasibility of the model; After completing the test, turn off all equipment and record the test results.

[0015] An electromagnetic simulation modeling device for an intermediate connection of a high-voltage power cable, comprising: a memory having a computer processing program stored thereon; The processor is used to execute the computer processing program in the memory to implement the above-mentioned electromagnetic simulation modeling method for the intermediate connection of a high-voltage power cable.

[0016] The beneficial effects of the present invention are: The present invention simulates the electromagnetic field distribution at the intermediate connection of the cable by finite element analysis technology, and particularly considers the influence of moisture on the electromagnetic characteristics. By constructing a three-dimensional model through Comsol software and setting corresponding electromagnetic-thermal-mechanical coupling model parameters, the magnetic field and temperature field distribution characteristics of the cable under different moisture conditions can be analyzed. This method helps to predict and analyze the electromagnetic field conditions of the intermediate connection of the cable before it is put into operation, thereby providing a scientific basis for the design, manufacture, installation, operation and maintenance of the cable joint.

[0017] The present invention can detect potential moisture fault problems at the middle connection of the cable at an early stage, and provide a theoretical basis for cable fault location by simulating the electromagnetic field distribution under different moisture conditions, thereby improving the reliability and safety of the power cable; it can provide technical support for the effective monitoring of the cable operation status and fault early warning, and through the evaluation of the moisture degree of the cable, it can realize real-time monitoring of the cable operation status, prevent accidents, and ensure the stable operation of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the process of embodiment 1 of the present invention; Figure 2 It is a flow diagram of embodiment 2 of the present invention. DETAILED DESCRIPTION

[0019] The embodiments of the present invention are further described below in conjunction with the accompanying drawings: Example 1: Figure 1 As shown, an electromagnetic simulation modeling method for a high-voltage power cable intermediate connection includes the following steps: S1. Analyze the moisture path of the cable's intermediate connection; S2. Construct a three-dimensional model of the intermediate connection of the high-voltage cable through finite element simulation software, including three areas, namely the cable conductor, the silicone rubber accessory and the interface, and apply silicone oil at the junction of the cable conductor and the silicone rubber accessory; S3. Set the simulation parameters of the three regions, add a magnetic field model, set the electromagnetic field as a current source, set the thermal conductivity, density, and constant-pressure heat capacity to come from the material, add the control equations and boundary conditions of electromagnetic-thermal-mechanical coupling, and obtain an electromagnetic-thermal-mechanical coupling model; S4. Based on the electromagnetic-thermal-mechanical coupling model, an electromagnetic simulation model of different moisture conditions at the middle connection interface of the cable is established to simulate and analyze different moisture conditions at the middle connection interface of the cable.

[0020] In S1, the moisture path is that due to insufficient gripping force between the cable middle connection and the cable body, a cavity is formed in the insulation interface of the cable middle connection, allowing moisture to penetrate.

[0021] In S2, the simulation process uses Comsol finite element simulation software. The cable conductor area includes the cable conductor, insulation layer, shielding layer, aluminum sheath, outer sheath and cable intermediate connection. The cable intermediate connection includes conductor crimping tube, insulation sleeve and shielding layer connector. The interface refers to the contact surface between the cable layers and the contact surface between the cable and the external environment. Two domains of soil and air are set. The cable intermediate connection is located in the soil, and the interface area is the boundary area where the cable intermediate connection contacts the soil or air.

[0022] In S3, the simulation parameter settings include: Set electromagnetic parameters, including current density, voltage level, frequency of cable conductor, and dielectric constant, conductivity, and magnetic permeability of insulation and shielding layers; Set the material properties and electromagnetic characteristics of the cable conductor, insulation layer, shielding layer, aluminum sheath, outer sheath, conductor crimping tube, insulation sleeve and shielding layer connector; Set thermal parameters, including thermal conductivity, density and constant pressure heat capacity. Set thermal parameters to come from materials; Setting boundary conditions, including the electromagnetic coupling relationship between the cable intermediate connection and the external environment, and the radiation and scattering characteristics of the electromagnetic field; The setting of the control equations includes: The electromagnetic loss is coupled to the fluid temperature as the initial heat source. The electromagnetic loss includes hysteresis loss and eddy current loss. The calculation formula of the electromagnetic loss is as follows: ; In the formula, is the total electromagnetic loss; is the hysteresis loss; is the eddy current loss; Among them, hysteresis loss is caused by the hysteresis phenomenon in the magnetization process of the material. The calculation formula of hysteresis loss is: ; In the formula, is the hysteresis coefficient; f represents the frequency of change of magnetic flux density; is the maximum magnetic flux density; z is the hysteresis index (values ​​range from 1 to 2); For the soil and air domains, the air domain is set as a fluid, the soil domain is set as a solid, the heat flux type is set as convective heat flux, and the initial value of solid heat transfer is set (20°C). The convective heat flux is expressed as: ; Where λ is the thermal conductivity of the insulating material; h is the heat transfer coefficient of the outer surface of the cable middle connection in contact with the air; is the cable middle connection surface area; is the middle connection surface temperature; is the ambient temperature; Represents the component of the temperature gradient in the normal direction, that is, the partial derivative of the temperature T with respect to the normal vector m; The temperature field control equation is: ; In the formula, x is the heat source; ρ is the material density; C p is the heat capacity at normal pressure; u is the electric displacement of the material under thermal stress; k is the thermal conductivity; is the gradient operator; t is the time; The heat generation rate of the conductor is: ; In the formula, Q is the heat generation rate of the conductor; I is the load current of the middle connection of the cable; R is the AC resistance of the conductor per unit length; S is the cross-sectional area of ​​the core; The heat loss of the insulating material is: ; Where P is the heat loss power of the insulating material; is the angular frequency; C is the dielectric capacitance; is the point loss angle, Indicates dielectric loss factor; is the potential of the dielectric.

[0023] In S3, adding a magnetic field model also includes setting Ampere's law in the solid, the conduction model is conductivity, and the conductivity comes from the material; the magnetization mode of the coil is set to relative magnetic permeability, and the relative magnetic permeability also comes from the material; the current carrying capacity is set to obtain the magnetic flux density.

[0024] In the magnetic field model, in order to accurately calculate the electromagnetic field distribution value caused by loss, assumptions are made about the cable working conditions: Assumption 1: The frequency of the cable during operation is 50HZ, and the displacement current generated during operation is not calculated; Assumption 2: There is no free charge in the domain field of the magnetic field model; The differential forms of the basic equations of the electromagnetic field and the medium equations are as follows: ; ; ; ; ; ; In the formula, H is the magnetic field intensity; J is the current density, that is, the current density inside the middle connection of the cable; D is the electric displacement vector; B is the magnetic induction intensity; E is the electric field intensity; is the conductivity; is the dielectric constant; Since the divergence of the vector function curl is always 0, it can be expressed as: ; Where A is any vector field; The electromagnetic loss density of the cable middle connection is , expressed as: ; ; There is the following corresponding relationship between the conductivity of the wire core connected in the middle of the cable and the temperature: ; In the formula, is the cable core conductivity at room temperature; is the temperature coefficient.

[0025] In S4, the process of establishing the electromagnetic simulation model is: Based on the electromagnetic-thermal-mechanical coupling model, the electromagnetic field distribution, electromagnetic loss, temperature distribution and mechanical distribution of the power cable under normal operation are simulated and analyzed. Then, the interface moisture condition is set, and the moisture is taken as a variable. The influence of the damp environment on the electromagnetic performance is considered to perform mesh division. Through solving and calculating, the electromagnetic simulation results of the cable under damp conditions are processed to check the electromagnetic field distribution and electromagnetic loss, and calculate the average value; In the electromagnetic simulation model, silicone oil and water affect the physical properties of the cable through the diffusion process. Silicone oil swells into the silicone rubber in the form of free and combined states according to the Langmuir diffusion process, and water also enters through the diffusion movement of silicone oil. The weight gain rate of the silicone rubber immersed at time t is derived based on the diffusion process : ; ; In the formula, is the saturated weight gain rate; is the diffusion coefficient of the mobile molecule; is a multiple of the diffusion coefficient; b is the rate constant; is the instantaneous state function, describing the water absorption process at time t; t1 is the water absorption time; n is a summation index variable; d is the thickness of silicone rubber.

[0026] Based on the above method, examples of simulation analysis of different damp locations and different damp degrees are as follows: Simulation analysis of different damp locations: According to the above method, a three-dimensional geometric model (three-dimensional model) of the intermediate connection of the high-voltage power cable is constructed. In the model, three different situations are set, namely, the damp area is located near the conductor, in the middle, and near the shielding layer of the cable insulation layer. For each damp location, the same electromagnetic simulation parameters are set, including an excitation source of 110kV, 50Hz AC voltage, a boundary condition of an ideal electrical boundary with air medium around the cable, adaptive meshing, fine meshing in the damp area and the connection joint, and a frequency domain solver with a frequency scanning range of 0-100Hz.

[0027] By running the simulation calculation program, the electric field intensity cloud map and partial discharge inception voltage values ​​under three different damp positions were obtained. The results show that when the damp position is close to the conductor, the concentration of the electric field intensity in the damp area is the highest and the partial discharge inception voltage is the lowest; when the damp position is close to the shielding layer, the concentration of the electric field intensity is relatively low and the partial discharge inception voltage is high; and when the damp position is in the middle of the insulating layer, the electric field intensity and the partial discharge inception voltage are between the two. Through comparative analysis, the differences in the influence of different damp positions on the electromagnetic characteristics of the cable are clarified, providing a theoretical basis for locating cable damp faults.

[0028] Simulation analysis of different moisture levels: Construct a high-voltage power cable intermediate connection model, set a damp area in the insulation layer, and simulate different degrees of dampness by changing the material parameters of the damp area, such as mild dampness (relative dielectric constant increased by 10%, conductivity increased by 5 times), moderate dampness (relative dielectric constant increased by 30%, conductivity increased by 20 times) and severe dampness (relative dielectric constant increased by 50%, conductivity increased by 50 times). Set the electromagnetic simulation parameters, the excitation source is 220kV, 50Hz AC voltage, the boundary condition is the radiation boundary condition of the cable buried in the soil, and the meshing and solver parameters are similar to those in the simulation analysis of different damp locations.

[0029] Simulation calculations were performed to obtain the electromagnetic loss and electric field concentration factor under different degrees of moisture. The analysis results show that with the increase of moisture, the electromagnetic loss increases significantly and the electric field concentration factor also gradually increases. According to the established relationship model between moisture degree and electromagnetic characteristic parameters, the moisture degree of the cable intermediate connection can be evaluated based on the actually measured electromagnetic loss or electric field concentration factor, so as to achieve effective monitoring of the cable operation status and fault warning.

[0030] It can be seen from the above simulation analysis that the method of this embodiment can effectively simulate the impact of different moisture conditions on the electromagnetic characteristics of the cable, and provides an accurate and efficient analysis method for the design, operation and maintenance, and fault diagnosis of the cable.

[0031] Example 2: Figure 2 As shown, based on Example 1, this embodiment further includes S5, establishing a cable intermediate connection moisture test platform, testing the changes in the electromagnetic field and conductivity of the cable intermediate connection after moisture, comparing with the electromagnetic simulation model, and verifying the accuracy and feasibility of the electromagnetic simulation model comparison; The cable intermediate connection moisture test platform includes: Test platform frame, used to support and fix all components; Cable middle connection sample, fix the cable middle connection to be tested on the test platform to ensure its stability in moisture and electromagnetic field tests; Moisture simulation system, including humidity control unit and moisture penetration simulation device, used to simulate the humid environment that the cable will encounter in actual use; Electromagnetic field measurement equipment, including magnetic field intensity meters and electric field intensity meters, used to measure the electromagnetic field distribution of the cable intermediate connection after being damp; Conductivity measurement equipment, including four-probe measurement devices or other conductivity measurement tools, used to measure the change in conductivity of the cable after being exposed to moisture; A data acquisition system, including a wireless signal device, a wired signal device, and temperature sensors and current transformers arranged at multiple points in the middle of the cable connection, for collecting temperature sensor data and current transformer data; A central processing unit, used for receiving and processing data transmitted from the data acquisition system, and performing analysis and comparison; An environmental control unit, used to control the environmental conditions of the test platform; The testing process is: Sample preparation: Install the cable intermediate connection sample on the test platform; Environmental settings: Set the required temperature and humidity conditions through the environmental control unit; Moisture simulation: Start the moisture simulation system to make the middle connection of the cable wet; Data collection: Turn on the data collection system, including wireless and wired signal devices, and start collecting temperature, current transformer data, and electromagnetic field and conductivity data; Electromagnetic field and conductivity testing: Testing is performed using electromagnetic field measuring equipment and conductivity measuring equipment; Data transmission: The collected data is transmitted to the central processor through a wired signal device; Data analysis: The central processing unit analyzes the data and compares it with the electromagnetic simulation model to verify the accuracy and feasibility of the model; After completing the test, turn off all equipment and record the test results.

[0032] Embodiment 3: An electromagnetic simulation modeling device for a high-voltage power cable intermediate connection, comprising: a memory having a computer processing program stored thereon; The processor is used to execute the computer processing program in the memory to implement the electromagnetic simulation modeling method of the intermediate connection of a high-voltage power cable in Example 1.

Claims

1. An electromagnetic simulation modeling method for a high-voltage power cable intermediate connection, characterized in that The following steps are involved: S1. Analyze the moisture path of the cable's intermediate connection; S2. Construct a three-dimensional model of the intermediate connection of the high-voltage cable through finite element simulation software, including three areas, namely the cable conductor, the silicone rubber accessory and the interface, and apply silicone oil at the junction of the cable conductor and the silicone rubber accessory; S3. Set the simulation parameters of the three regions, add a magnetic field model, set the electromagnetic field as a current source, set the thermal conductivity, density, and constant-pressure heat capacity to come from the material, add the control equations and boundary conditions of electromagnetic-thermal-mechanical coupling, and obtain an electromagnetic-thermal-mechanical coupling model; S4. Based on the electromagnetic-thermal-mechanical coupling model, an electromagnetic simulation model of different moisture conditions at the middle connection interface of the cable is established to simulate and analyze different moisture conditions at the middle connection interface of the cable.

2. The electromagnetic simulation modeling method for a high-voltage power cable intermediate connection according to claim 1 is characterized in that: In the above-mentioned S1, the moisture-accepting path is that due to the insufficient gripping force between the cable intermediate connection and the cable body, a cavity is formed in the insulating interface of the cable intermediate connection, allowing moisture to penetrate.

3. The electromagnetic simulation modeling method for a high-voltage power cable intermediate connection according to claim 1 is characterized in that: In the S2 described above, the simulation process adopts Comsol finite element simulation software, the cable conductor area includes the cable conductor, insulation layer, shielding layer, aluminum sheath, outer sheath and cable intermediate connection, the cable intermediate connection includes conductor crimping tube, insulation sleeve, shielding layer connector; the interface refers to the contact surface between the layers of the cable, and the contact surface between the cable and the external environment; two domains of soil and air are set, the cable intermediate connection is located in the soil, and the interface area is the boundary area where the cable intermediate connection contacts the soil or air.

4. The electromagnetic simulation modeling method for a high-voltage power cable intermediate connection according to claim 3 is characterized in that: In the above S3, the setting of simulation parameters includes: Set electromagnetic parameters, including current density, voltage level, frequency of cable conductor, and dielectric constant, conductivity, and magnetic permeability of insulation and shielding layers; Set the material properties and electromagnetic characteristics of the cable conductor, insulation layer, shielding layer, aluminum sheath, outer sheath, conductor crimping tube, insulation sleeve and shielding layer connector; Set thermal parameters, including thermal conductivity, density and constant pressure heat capacity. Set thermal parameters to come from materials; Setting boundary conditions, including the electromagnetic coupling relationship between the cable intermediate connection and the external environment, and the radiation and scattering characteristics of the electromagnetic field; The setting of the control equations includes: The electromagnetic loss is coupled to the fluid temperature as the initial heat source. The electromagnetic loss includes hysteresis loss and eddy current loss. The calculation formula of the electromagnetic loss is as follows: ； In the formula, is the total electromagnetic loss; is the hysteresis loss; is the eddy current loss; Among them, hysteresis loss is caused by the hysteresis phenomenon in the magnetization process of the material. The calculation formula of hysteresis loss is: ； In the formula, is the hysteresis coefficient; f represents the frequency of change of magnetic flux density; is the maximum magnetic flux density; z is the hysteresis index; For the soil and air domains, the air domain is set as a fluid, the soil domain is set as a solid, the heat flux type is set as convective heat flux, and the initial value of solid heat transfer is set. The convective heat flux is expressed as: ； Where λ is the thermal conductivity of the insulating material; h is the heat transfer coefficient of the outer surface of the cable middle connection in contact with the air; is the cable middle connection surface area; is the middle connection surface temperature; is the ambient temperature; Represents the component of the temperature gradient in the normal direction, that is, the partial derivative of the temperature T with respect to the normal vector m; The temperature field control equation is: ； In the formula, x is the heat source; ρ is the material density; C p is the heat capacity at normal pressure; u is the electric displacement of the material under thermal stress; k is the thermal conductivity; is the gradient operator; t is the time; The heat generation rate of the conductor is: ； In the formula, Q is the heat generation rate of the conductor; I is the load current of the middle connection of the cable; R is the AC resistance of the conductor per unit length; S is the cross-sectional area of ​​the core; The heat loss of the insulating material is: ； Where P is the heat loss power of the insulating material; is the angular frequency; C is the dielectric capacitance; is the point loss angle, Indicates dielectric loss factor; is the potential of the dielectric.

5. The electromagnetic simulation modeling method for a high-voltage power cable intermediate connection according to claim 4 is characterized in that: The value of z is between 1 and 2, and the initial value of solid heat transfer is 20℃.

6. The electromagnetic simulation modeling method for a high-voltage power cable intermediate connection according to claim 4 is characterized in that: In the S3, adding a magnetic field model also includes setting Ampere's law in the solid, the conduction model is conductivity, and the conductivity comes from the material; the magnetization mode of the coil is set to relative magnetic permeability, and the relative magnetic permeability also comes from the material; and the current carrying capacity is set to obtain the magnetic flux density.

7. The electromagnetic simulation modeling method for a high-voltage power cable intermediate connection according to claim 6 is characterized in that: In the magnetic field model, in order to accurately calculate the electromagnetic field distribution value caused by loss, assumptions are made about the cable working conditions: Assumption 1: The frequency of the cable during operation is 50HZ, and the displacement current generated during operation is not calculated; Assumption 2: There is no free charge in the domain field of the magnetic field model; The differential forms of the basic equations of the electromagnetic field and the medium equations are as follows: ； ； ； ； ； ； In the formula, H is the magnetic field intensity; J is the current density, that is, the current density inside the middle connection of the cable; D is the electric displacement vector; B is the magnetic induction intensity; E is the electric field intensity; is the conductivity; is the dielectric constant; Since the divergence of the vector function curl is always 0, it can be expressed as: ； Where A is any vector field; The electromagnetic loss density of the cable middle connection is , expressed as: ； ； There is the following corresponding relationship between the conductivity of the wire core connected in the middle of the cable and the temperature: ； In the formula, is the cable core conductivity at room temperature; is the temperature coefficient.

8. The electromagnetic simulation modeling method for a high-voltage power cable intermediate connection according to claim 1 is characterized in that: In the above-mentioned S4, the process of establishing the electromagnetic simulation model is as follows: Based on the electromagnetic-thermal-mechanical coupling model, the electromagnetic field distribution, electromagnetic loss, temperature distribution and mechanical distribution of the power cable under normal operation are simulated and analyzed. Then, the interface moisture condition is set, and the moisture is taken as a variable. The influence of the damp environment on the electromagnetic performance is considered to perform mesh division. Through solving and calculating, the electromagnetic simulation results of the cable under damp conditions are processed to check the electromagnetic field distribution and electromagnetic loss, and calculate the average value; In the electromagnetic simulation model, silicone oil and water affect the physical properties of the cable through the diffusion process. Silicone oil swells into the silicone rubber in the form of free and combined states according to the Langmuir diffusion process, and water also enters through the diffusion movement of silicone oil. The weight gain rate of the silicone rubber immersed at time t is derived based on the diffusion process : ； ； In the formula, is the saturated weight gain rate; is the diffusion coefficient of the mobile molecule; is a multiple of the diffusion coefficient; b is the rate constant; is the instantaneous state function, describing the water absorption process at time t; t1 is the water absorption time; n is an index variable for summation; d is the thickness of silicone rubber.

9. The electromagnetic simulation modeling method for a high-voltage power cable intermediate connection according to claim 1 is characterized in that: It also includes S5, establishing a cable middle connection moisture test platform, testing the changes of electromagnetic field and conductivity of the cable middle connection after moisture, comparing with the electromagnetic simulation model, and verifying the accuracy and feasibility of the electromagnetic simulation model comparison; The cable intermediate connection moisture test platform includes: Test platform frame, used to support and fix all components; Cable middle connection sample, fix the cable middle connection to be tested on the test platform to ensure its stability in moisture and electromagnetic field tests; Moisture simulation system, including humidity control unit and moisture penetration simulation device, used to simulate the humid environment that the cable will encounter in actual use; Electromagnetic field measurement equipment, including magnetic field intensity meters and electric field intensity meters, used to measure the electromagnetic field distribution of the cable intermediate connection after being damp; Conductivity measurement equipment, including four-probe measurement devices or other conductivity measurement tools, used to measure the change in conductivity of the cable after being exposed to moisture; A data acquisition system, including a wireless signal device, a wired signal device, and temperature sensors and current transformers arranged at multiple points in the middle of the cable connection, for collecting temperature sensor data and current transformer data; A central processing unit, used for receiving and processing data transmitted from the data acquisition system, and performing analysis and comparison; An environmental control unit, used to control the environmental conditions of the test platform; The testing process is: Sample preparation: Install the cable intermediate connection sample on the test platform; Environmental settings: Set the required temperature and humidity conditions through the environmental control unit; Moisture simulation: Start the moisture simulation system to make the middle connection of the cable wet; Data collection: Turn on the data collection system, including wireless and wired signal devices, and start collecting temperature, current transformer data, and electromagnetic field and conductivity data; Electromagnetic field and conductivity testing: Testing is performed using electromagnetic field measuring equipment and conductivity measuring equipment; Data transmission: The collected data is transmitted to the central processor through a wired signal device; Data analysis: The central processing unit analyzes the data and compares it with the electromagnetic simulation model to verify the accuracy and feasibility of the model; After completing the test, turn off all equipment and record the test results.

10. An electromagnetic simulation modeling device for a high-voltage power cable intermediate connection, characterized in that: include: a memory having a computer processing program stored thereon; A processor is used to execute a computer processing program in a memory to implement an electromagnetic simulation modeling method for an intermediate connection of a high-voltage power cable as described in any one of claims 1-8.

Images