Modeling analysis method and device for intermediate connection thermal circuit fault of high-voltage power cable

Abstract

The invention belongs to the technical field of thermal circuit model construction, and particularly relates to a high-voltage power cable intermediate connection thermal circuit fault modeling analysis method and device, and the method comprises the steps: building a high-voltage power cable intermediate connection thermal circuit fault circuit model through analyzing a cable intermediate connection temperature inversion principle; the method comprises the following steps: establishing a geometric model for multi-physics field analysis of the intermediate connection of the high-voltage power cable by utilizing Comsol finite element simulation software, setting material parameters of each component, and setting field domain parameters; an electromagnetic field module is added, boundary conditions of electromagnetic field analysis are set, and a cable intermediate connection electromagnetic field simulation model is obtained; adding a solid heat transfer module to obtain a solid temperature field simulation model; obtaining an electromagnetic-thermal coupling model, and solving to obtain the temperature, current and loss of the cable middle connection wire core and the outer surface in different insulation states. According to the method, the cable intermediate connection fault problem can be found and predicted, and the reliability and the safety of the power cable are improved.

Description

Technical Field

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

[0002] High-voltage power cables are important equipment in urban transmission networks. At present, most cable failures occur at the intermediate connection. If the intermediate connection of the cable is in poor contact or is affected by external force, the cable joint will generate a lot of heat. The accumulated heat will cause the temperature of the cable joint to rise. Over time, it will cause insulation aging and cause partial discharge, and in severe cases, it will cause fire and explosion accidents. The cable conductor is at a high potential, and its temperature cannot generally be measured directly. Therefore, there is a lack of effective methods for detecting hot spot fault temperatures in the intermediate connection of power cables. In addition, the intermediate connection of power cables has strict requirements on the sealing of the outer shell in actual operation, so it is difficult to use effective equipment to detect and analyze the temperature distribution characteristics of the intermediate connection of power cables.

[0003] In existing research, in theory, optical fiber, temperature sensing cable or thermocouple sensors can be used to monitor the cable surface temperature and ambient temperature, and then the cable conductor temperature can be indirectly calculated using a thermal circuit model or temperature field analysis. However, unlike the cable body, the cable joint has a complex structure that is difficult to simplify into a one-dimensional model, and the parameters such as the size and material properties of the on-site manual structure fluctuate greatly. Therefore, it is particularly important to establish a new transient thermal circuit model and conduct real-time analysis of its temperature change characteristics during the development process. Summary of the invention

[0004] In view of the above deficiencies in the prior art, the purpose of the present invention is to provide a modeling and analysis method and device for high-voltage power cable intermediate connection thermal circuit faults, which helps to discover and predict cable intermediate connection faults and improve the reliability and safety of power cables.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is a modeling and analysis method for a high-voltage power cable intermediate connection thermal circuit fault, comprising the following steps: S1. By analyzing the temperature inversion principle of the cable intermediate connection, setting the cable intermediate connection equivalent circuit, establishing the high-voltage power cable intermediate connection thermal path fault circuit model including the cable core current, convection heat transfer coefficient and main insulation thermal conductivity, completing the setting of the high-voltage power cable intermediate connection insulation degradation fault; S2. Use Comsol finite element simulation software to establish a geometric model for multi-physical field analysis of the intermediate connection of high-voltage power cables. The components in the geometric model include cable core, inner shielding layer, cross-linked polyethylene, outer shielding layer, aluminum sheath and outer sheath. Set the material parameters of each component and set the field parameters. The cable core is a single core and cross-linked polyethylene is the insulation material of the intermediate connection part of the cable. S3, add the electromagnetic field module, set the field component to be solved as the out-of-plane vector potential, set the background field to solve the whole field, set the boundary conditions of the electromagnetic field analysis, construct the electromagnetic field solution area, divide the electromagnetic field grid, and obtain the electromagnetic field simulation model of the cable middle connection; S4. Add a solid heat transfer module, add a temperature monitoring position, perform steady-state field calculation, obtain the steady-state temperature of the cable under normal working conditions, use it as the initial temperature for the solid temperature field calculation of the cable intermediate connection insulation degradation, apply the resistance loss of the cable intermediate connection as a heat source to the solid temperature field, set the boundary conditions for the solid temperature field calculation, divide the calculation grids for each component of the cable intermediate connection, and obtain a solid temperature field simulation model; S5. Couple the electromagnetic field simulation model of the cable intermediate connection to the solid temperature field simulation model to obtain the electromagnetic-thermal coupling model, add transient research to the physical field interface, numerically solve the electromagnetic-thermal coupling model of the cable intermediate connection under rated operating conditions, and obtain the temperature, current, and loss of the cable intermediate connection core (that is, the full name of the cable core) and the outer surface in different insulation states; S6. Perform post-processing of the solution results.

[0006] As a preferred embodiment of the present invention, in said S1, the principle of analyzing the temperature inversion of the intermediate connection of the cable is to obtain the temperature of the core of the intermediate connection of the cable by inverting the temperature measuring point. , expressed as: ; In the formula, is the temperature of the measuring point, and β is the inversion coefficient.

[0007] As a preferred embodiment of the present invention, in said S2, the material parameters include thickness, thermal conductivity, density and specific heat capacity.

[0008] As a preferred solution of the present invention, in said S3, when establishing the electromagnetic field simulation model of the cable intermediate connection, the following assumptions are made: the cable core current is an AC current of 50Hz, and the influence of displacement current is not considered; except for the cable core material, the materials of other cable components are isotropic, and the material parameters are regarded as constants; there is no free charge in the field; According to the above assumptions, based on Maxwell's equations, the vector magnetic potential is introduced. In the presence of an external excitation source, its control equation is: ; For the non-current region without external excitation source, the control equation is: ; In the formula, is the gradient operator; is the magnetic permeability; A is the vector magnetic potential; is the external source current density; j is the imaginary unit; is the angular frequency; is the conductivity.

[0009] As a preferred embodiment of the present invention, in said S4, when establishing the solid temperature field simulation model, the following assumptions are made: the radiation of the internal parts of the cable intermediate connection is not considered, and it is assumed that the cable intermediate connection radiates energy to the surrounding environment only through the outer surface, and the heat transfer process is equivalently expressed by the radiation heat transfer coefficient; when calculating the heat transfer, the temperature change characteristics of the multilayer structure of the power cable intermediate connection are considered; Due to the uneven distribution of the thermal field in the cable intermediate connection, it is assumed that the relative velocity between the outer surface of the cable intermediate connection and the cable core is 0, and the outer surface temperature is consistent with the ambient fluid temperature; the heat conduction and heat convection of each part inside the cable are fully considered, and the outer surface of the cable intermediate connection is simplified to a smooth plane, that is, the heat dissipation process of the outer surface of the cable intermediate connection is considered to be longitudinal flat plate convection heat transfer, and the convection heat transfer coefficient is used to equivalently express the heat transfer process between the power cable intermediate connection and the outside world.

[0010] As a preferred embodiment of the present invention, in the solid temperature field simulation model, the influence of temperature gradient is considered, the direction is radially transferred, and the heat balance equation is followed in solid heat transfer, indicating that the sum of the heat energy transferred from the outside to the inside of the object and the energy generated by the object itself is equal to the heat energy consumed by the temperature change of the object; the temperature field problem of the middle connection of the cable satisfies the three-dimensional control equation, and its expression is as follows: ; In the formula, is the material density; c is the material specific heat capacity; T is the temperature to be determined; t is the time; , , are the thermal conductivities of the object in the X, Y, and Z directions respectively; is the internal heat energy of the object; x, y, z are the components of the object in the X, Y, and Z directions, respectively, indicating spatial coordinates; the object is the component in the geometric model; In finite element analysis, boundary conditions are a set of constraints that regulate the behavior of the physics at the boundaries of the model. Boundary conditions are essential for solving partial differential equations because they provide the necessary information on the boundaries of the solution region. Boundary conditions can specify the value or rate of change of a physical quantity at the boundary, depending on the physics being simulated and the nature of the problem.

[0011] When calculating heat transfer, boundary conditions include the following three categories: The first type: Boundary conditions with known temperature distribution on the boundary. When the temperature on the boundary is a fixed value, the control equation is: ; In the formula, To solve the domain boundary; is the boundary temperature; The second category: The boundary conditions of the convective heat transfer and the fluid temperature on the known boundary are applicable to the boundary heat transfer process where the solid and the gas intersect. The control equation is: ; In the formula, is the thermal conductivity; h is the convective heat transfer coefficient; is the fluid temperature; n is the normal vector on the boundary; is the mark of the boundary, indicating a point on the boundary; The third category: The boundary conditions of the ambient temperature and the convection heat transfer coefficient are known, and the heat dissipation has reached a balanced thermal insulation boundary condition. The control equation is: ; In the formula, is the ambient temperature.

[0012] As a preferred embodiment of the present invention, in the solid temperature field simulation model, the outer surface of the cable is exposed to the air in the middle of the cable connection, and its outer surface also transfers heat with the external environment through thermal radiation, and its control equation is: ; In the formula, is the Stefan-Boltzmann constant; is the external surface emissivity.

[0013] As a preferred embodiment of the present invention, in S5, the electromagnetic loss of the intermediate connection of the power cable is obtained by numerically solving the electromagnetic-thermal coupling model under the rated operating conditions of the intermediate connection of the power cable, and the electromagnetic loss is coupled to the fluid temperature field as an initial heat source; Taking resistance loss and load loss as heat sources, the weighted interpolation method is used to map heterogeneous grids, and the loss value in the grid of the electromagnetic field calculation result is applied to the corresponding grid node of the cable fluid temperature field; comprehensively considering the heat dissipation intensity of the outer surface of the cable intermediate connection and the internal heat transfer characteristics, the mass, momentum, and energy conservation equations of the cable intermediate connection are numerically solved and calculated to obtain the temperature values ​​of each part of the cable intermediate connection under rated operating conditions; The short-circuit method is used to conduct a temperature rise test on the cable intermediate connection. The electromagnetic-thermal coupling model of the cable intermediate connection under different operating conditions is calibrated based on the test data of the temperature rise of the cable intermediate connection and the temperature rise of the surrounding environment to ensure that the calculation error is within a reasonable range. After the electromagnetic-thermal coupling model is calibrated, a short-circuit fault is set at the intermediate connection of the cable. The electromagnetic losses of the faulty cable and the normal cable are obtained by solving the short-circuit fault equivalent circuit equation (i.e., the equivalent circuit of the thermal circuit fault circuit model of the intermediate connection of the high-voltage power cable after the fault is set, and the equivalent circuit equation can be obtained based on the known technology) and the electromagnetic field mathematical model (i.e., the electromagnetic field simulation model of the intermediate connection of the cable). The losses of each part are coupled to the corresponding part of the intermediate connection of the cable by using the heterogeneous grid mapping of the weighted interpolation method. According to the calculation conditions under the rated operating conditions of the intermediate connection of the cable, the temperature distribution characteristics of the short-circuit fault of the intermediate connection of the cable are calculated, including the temperature of the intermediate connection of the high-voltage cable, the temperature at the short-circuit position, and the temperature distribution of the outer surface of the intermediate connection of the cable.

[0014] As a preferred embodiment of the present invention, in S6, based on the results obtained by solving, temperature curves under different insulation conditions are drawn, the intermediate connection state of the cable corresponding to the temperature distribution characteristics is analyzed, and a cable intermediate connection temperature test platform is built using distributed optical fiber temperature measurement to verify the accuracy between the simulation calculation and the actual measured temperature.

[0015] The modeling and analysis device for the thermal circuit fault of the intermediate connection of the high-voltage power cable includes: 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 modeling and analysis method for the thermal path fault of the intermediate connection of the high-voltage power cable.

[0016] The beneficial effects of the present invention are: The present invention provides an effective method to monitor and analyze the temperature change of the cable intermediate connection by establishing a thermal circuit fault analysis model of the high-voltage power cable intermediate connection. Comsol multi-physics field analysis software is used to combine the simulation of electromagnetic field and temperature field to simulate the temperature distribution of the cable under different operating conditions, and the model is corrected by the short-circuit method temperature rise test to ensure the accuracy of the analysis results.

[0017] The present invention can inversely calculate the temperature of the cable conductor by monitoring the cable surface temperature, which is very useful for actual situations where the temperature of the high-potential cable conductor cannot be directly measured. Through this method, thermal circuit faults at the intermediate connection of the cable can be discovered in time, insulation aging and potential fire risks can be prevented, thereby improving the reliability and safety of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the process of the present invention; Figure 2 Schematic diagram of the inversion principle in an embodiment 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, the modeling and analysis method for the thermal path fault of the intermediate connection of the high-voltage power cable includes the following steps: S1. By analyzing the temperature inversion principle of the cable intermediate connection, setting the cable intermediate connection equivalent circuit, establishing the high-voltage power cable intermediate connection thermal path fault circuit model including the cable core current, convection heat transfer coefficient and main insulation thermal conductivity, completing the setting of the high-voltage power cable intermediate connection insulation degradation fault; S2. Use Comsol finite element simulation software to establish a geometric model for multi-physical field analysis of the intermediate connection of high-voltage power cables. The components in the geometric model include cable core, inner shielding layer, cross-linked polyethylene, outer shielding layer, aluminum sheath and outer sheath. Set the material parameters of each component and set the field parameters. The cable core is a single core and cross-linked polyethylene is the insulation material of the intermediate connection part of the cable. S3, add the electromagnetic field module, set the field component to be solved as the out-of-plane vector potential, set the background field to solve the whole field, set the boundary conditions of the electromagnetic field analysis, construct the electromagnetic field solution area, divide the electromagnetic field grid, and obtain the electromagnetic field simulation model of the cable middle connection; S4. Add a solid heat transfer module, add a temperature monitoring position, perform steady-state field calculation, obtain the steady-state temperature of the cable under normal working conditions, use it as the initial temperature for the solid temperature field calculation of the cable intermediate connection insulation degradation, apply the resistance loss of the cable intermediate connection as a heat source to the solid temperature field, set the boundary conditions for the solid temperature field calculation, divide the calculation grids for each component of the cable intermediate connection, and obtain a solid temperature field simulation model; S5. Couple the electromagnetic field simulation model of the cable intermediate connection to the solid temperature field simulation model to obtain an electromagnetic-thermal coupling model, add transient research to the physical field interface, numerically solve the electromagnetic-thermal coupling model of the cable intermediate connection under rated operating conditions, and obtain the temperature, current, and loss of the cable intermediate connection core and outer surface in different insulation states; S6. Perform post-processing of the solution results.

[0020] Comsol finite element simulation software solves engineering and scientific problems based on the finite element method (FEM), and can simulate the interaction between multiple physical fields, such as electromagnetic fields, fluid dynamics, heat conduction, chemical reactions, structural mechanics, etc. You can build models, define material properties, set boundary conditions and initial conditions, run simulations, and visualize results through a graphical user interface (GUI).

[0021] In Comsol, the electromagnetic field module can simulate and analyze various electromagnetic phenomena, including but not limited to: Electrostatic Field: Simulate the distribution of charge and electric field; Current and Resistance: Analyze current flow and the effects of resistance; Magnetic Field: simulates magnetic fields generated by electric currents or permanent magnets; Electromagnetic waves: analysis of the propagation and scattering of electromagnetic waves; Radio Frequency (RFEM) Module: Specialized for high-frequency electromagnetic field problems such as antenna design, microwave devices, and RFID tags; Low Frequency Module: Used to simulate low-frequency electromagnetic field problems such as motors, transformers, and electromagnetic compatibility (EMC) analysis.

[0022] The Heat Transfer in Solids Module is used to simulate and analyze heat transfer processes, including but not limited to: Heat conduction: simulates the transfer of heat in solid materials; Convection: Analysis of heat exchange between fluids and solid surfaces; Radiation: simulates the transfer of thermal radiation, suitable for high temperature or vacuum environment; Phase change: simulate the heat exchange between different phases of the material; Thermal Stress: Analyze thermal stress and material deformation due to temperature changes.

[0023] A notable feature of COMSOL is its multi-physics coupling analysis capability, which means that multiple physical phenomena can be considered simultaneously in the same model. That is, the electromagnetic-thermal coupling in this embodiment can be realized. In COMSOL, the physical field interface refers to the module used to define and simulate specific physical phenomena. These interfaces provide a way to set up and solve partial differential equations related to specific physical fields, thereby simulating various physical processes. Each physical field interface usually corresponds to one or a class of physical phenomena.

[0024] In S1, the principle of cable middle connection temperature inversion is to obtain the cable middle connection wire core temperature by inverting the temperature measuring point. , expressed as: ; In the formula, is the temperature of the measuring point, and β is the inversion coefficient.

[0025] The inversion principle is to collect parameters such as cable skin temperature and current, and use the above empirical formula to overcome the difficulties of load current fluctuations, environmental interference, and large dispersion of joint materials and structures, and accurately calculate the temperature of the cable's internal conductor. Among them, the temperature inversion coefficient links the cable skin temperature and current parameters with the temperature of the cable's internal conductor. This connection is achieved by establishing a mathematical model. The schematic diagram of the inversion principle is shown in the figure. Figure 2 shown.

[0026] The specific acquisition of the temperature inversion coefficient can be achieved based on existing technologies, or can be calculated based on the following mathematical model: Define the temperature inversion coefficient in steady state ; Where R i It is the sum of the thermal resistance of each layer structure between the cable conductor (mainly the insulation layer) and the temperature monitoring point; R e It is the sum of the thermal resistances between the temperature monitoring points mainly based on the sheath layer and the external environment.

[0027] In S2, material parameters include thickness, thermal conductivity, density and specific heat capacity.

[0028] In S3, when establishing the electromagnetic field simulation model of the cable intermediate connection, the following assumptions are made: the cable core current is an AC current with an industrial frequency of 50Hz. Since the displacement current density is extremely small, the influence of the displacement current is not considered; except for the cable core material, the materials of other cable components are isotropic, and the material parameters are all considered constants; there is no free charge in the field; According to the above assumptions, based on Maxwell's equations, the vector magnetic potential is introduced. In the presence of an external excitation source, its control equation is: ; For the non-current region without external excitation source, the control equation is: ; In the formula, is the gradient operator; is the magnetic permeability; A is the vector magnetic potential; is the external source current density; j is the imaginary unit; is the angular frequency; is the conductivity.

[0029] In S4, when establishing the solid temperature field simulation model, the following assumptions are made: in order to simplify the calculation, the radiation of the internal parts of the cable intermediate connection is not considered, and it is assumed that the cable intermediate connection only radiates energy to the surrounding environment through the outer surface, and the radiation heat transfer coefficient is used to equivalently express the heat transfer process; in order to reduce the calculation error during the heat transfer calculation, the temperature change characteristics of the multi-layer structure of the power cable intermediate connection are considered; Due to the uneven distribution of the thermal field in the cable intermediate connection, it is assumed that the relative velocity between the outer surface of the cable intermediate connection and the cable core is 0, and the outer surface temperature is consistent with the ambient fluid temperature; the heat conduction and heat convection of each part inside the cable are fully considered, and the outer surface of the cable intermediate connection is simplified to a smooth plane, that is, the heat dissipation process of the outer surface of the cable intermediate connection is considered to be longitudinal flat plate convection heat transfer, and the convection heat transfer coefficient is used to equivalently express the heat transfer process between the power cable intermediate connection and the outside world.

[0030] In the solid temperature field simulation model, the influence of temperature gradient is considered, and the direction is radial. The heat balance equation is followed in solid heat transfer, indicating that the sum of the heat energy transferred from the outside to the inside of the object and the energy generated by the object itself is equal to the heat energy consumed by the temperature change of the object; the temperature field problem of the cable middle connection satisfies the three-dimensional control equation, and its expression is as follows: ; In the formula, is the material density; c is the material specific heat capacity; T is the temperature to be determined; t is the time; , , are the thermal conductivities of the object in the X, Y, and Z directions respectively; is the internal heat energy of the object; x, y, z are the components of the object in the X, Y, and Z directions, respectively, indicating spatial coordinates; the object is the component in the geometric model; When calculating heat transfer, boundary conditions include the following three categories: The first type: Boundary conditions with known temperature distribution on the boundary. When the temperature on the boundary is a fixed value, the control equation is: ; In the formula, To solve the domain boundary; is the boundary temperature; The second category: The boundary conditions of the convective heat transfer and the fluid temperature on the known boundary are applicable to the boundary heat transfer process where the solid and the gas intersect. The control equation is: ; In the formula, is the thermal conductivity; h is the convective heat transfer coefficient; is the fluid temperature; n is the normal vector on the boundary; is the mark of the boundary, indicating a point on the boundary; The third category: The boundary conditions of the ambient temperature and the convection heat transfer coefficient are known, and the heat dissipation has reached a balanced thermal insulation boundary condition. The control equation is: ; In the formula, is the ambient temperature.

[0031] In the solid temperature field simulation model, for the middle connection of the cable whose outer surface is exposed to the air, its outer surface also transfers heat with the external environment through thermal radiation, and its control equation is: ; In the formula, is the Stefan-Boltzmann constant; is the external surface emissivity.

[0032] In S5, the electromagnetic-thermal coupling model of the power cable intermediate connection under the rated operating condition is numerically solved to obtain the electromagnetic loss of the power cable intermediate connection, and the electromagnetic loss is coupled to the fluid temperature field as the initial heat source; Taking resistance loss and load loss as heat sources, the weighted interpolation method is used to map heterogeneous grids, and the loss value in the grid of the electromagnetic field calculation result is applied to the corresponding grid node of the cable fluid temperature field; comprehensively considering the heat dissipation intensity of the outer surface of the cable intermediate connection and the internal heat transfer characteristics, the mass, momentum, and energy conservation equations of the cable intermediate connection are numerically solved and calculated to obtain the temperature values ​​of each part of the cable intermediate connection under rated operating conditions; The short-circuit method is used to conduct a temperature rise test on the cable intermediate connection. The electromagnetic-thermal coupling model of the cable intermediate connection under different operating conditions is calibrated based on the test data of the temperature rise of the cable intermediate connection and the temperature rise of the surrounding environment to ensure that the calculation error is within a reasonable range. After the electromagnetic-thermal coupling model is calibrated, a short-circuit fault is set in the intermediate cable connection. The electromagnetic losses of the faulty cable and the normal cable are obtained by solving the equivalent circuit equation of the short-circuit fault and the electromagnetic field mathematical model. The losses of each part are coupled to the corresponding part of the intermediate cable connection by using the heterogeneous grid mapping of the weighted interpolation method. According to the calculation conditions under the rated operating conditions of the intermediate cable connection, the temperature distribution characteristics of the short-circuit fault of the intermediate cable connection are calculated, including the temperature of the intermediate high-voltage cable connection, the temperature at the short-circuit position, and the temperature distribution of the outer surface of the intermediate cable connection.

[0033] In heterogeneous grid mapping, weighted interpolation is used to transfer data between grids of different resolutions or different structures. Heterogeneous grids refer to grids with inconsistent grid cell sizes or shapes. Such grids are very useful in simulations of complex geometries because they can adapt to geometric boundaries and features more effectively. In multi-physics coupled simulations, different physical fields (such as fluid flow, heat transfer, electromagnetic fields, etc.) may be solved on different grids. Weighted interpolation can be used to transfer coupling information between these grids to achieve interaction between physical fields.

[0034] At the same time, in order to enhance the adaptability of the electromagnetic-thermal coupling model, machine learning algorithms can be used to adaptively adjust model parameters to adapt to the interaction between electromagnetic and thermal fields, changes in material properties, dynamic operating conditions, and boundary conditions. By integrating real-time monitoring data and using machine learning technology, the electromagnetic-thermal coupling model can more accurately simulate and predict the behavior of cables under variable conditions, thereby significantly improving the reliability and safety of cable systems. Using machine learning algorithms to enhance the adaptability of the electromagnetic-thermal coupling model can more accurately simulate and predict the behavior of cables under various operating and fault conditions, which helps to improve the reliability and safety of cable systems.

[0035] In S6, based on the results obtained from the solution, the temperature curves under different insulation conditions are plotted, the cable intermediate connection status corresponding to the temperature distribution characteristics is analyzed, and a cable intermediate connection temperature test platform is built using distributed optical fiber temperature measurement to verify the accuracy between the simulation calculation and the actual measured temperature.

[0036] The cable intermediate connection temperature test platform can be built by known technology. In a specific cable intermediate connection temperature test platform, it includes a current generator, a transformer, an optical fiber test system, and a data acquisition device. The temperature sensors are distributed at 5 temperature measurement points on the cable conductor and the skin, different load currents are applied, and the temperature of the temperature measurement points is collected to verify the reliability of the simulation calculation.

[0037] In the schematic structure of a specific high-voltage power cable intermediate connection thermal fault circuit model, a current generator, a transformer, an optical fiber test system, and a data acquisition device are included. Artificial scratches are made on the cable surface as a defect fault, and temperature sensors are placed at the fault location and non-fault location. Different load currents are applied, and the temperature of the temperature measurement point is collected. The temperature at different locations is analyzed to dialectically identify the fault type.

[0038] Embodiment 2: A modeling and analysis device for a high-voltage power cable intermediate connection thermal path fault, 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 modeling and analysis method of the high-voltage power cable intermediate connection thermal path fault described in Example 1.

Claims

1. Modeling and analysis method for high-voltage power cable intermediate connection thermal circuit fault, characterized by The following steps are involved: S1. By analyzing the temperature inversion principle of the cable intermediate connection, setting the cable intermediate connection equivalent circuit, establishing the high-voltage power cable intermediate connection thermal path fault circuit model including the cable core current, convection heat transfer coefficient and main insulation thermal conductivity, completing the setting of the high-voltage power cable intermediate connection insulation degradation fault; S2. Use Comsol finite element simulation software to establish a geometric model for multi-physical field analysis of the intermediate connection of high-voltage power cables. The components in the geometric model include cable core, inner shielding layer, cross-linked polyethylene, outer shielding layer, aluminum sheath and outer sheath. Set the material parameters of each component and set the field parameters. The cable core is a single core and cross-linked polyethylene is the insulation material of the intermediate connection part of the cable. S3, add the electromagnetic field module, set the field component to be solved as the out-of-plane vector potential, set the background field to solve the whole field, set the boundary conditions of the electromagnetic field analysis, construct the electromagnetic field solution area, divide the electromagnetic field grid, and obtain the electromagnetic field simulation model of the cable middle connection; S4. Add a solid heat transfer module, add a temperature monitoring position, perform steady-state field calculation, obtain the steady-state temperature of the cable under normal working conditions, use it as the initial temperature for the solid temperature field calculation of the cable intermediate connection insulation degradation, apply the resistance loss of the cable intermediate connection as a heat source to the solid temperature field, set the boundary conditions for the solid temperature field calculation, divide the calculation grids for each component of the cable intermediate connection, and obtain a solid temperature field simulation model; S5. Couple the electromagnetic field simulation model of the cable intermediate connection to the solid temperature field simulation model to obtain an electromagnetic-thermal coupling model, add transient research to the physical field interface, numerically solve the electromagnetic-thermal coupling model of the cable intermediate connection under rated operating conditions, and obtain the temperature, current, and loss of the cable intermediate connection core and outer surface in different insulation states; S6. Perform post-processing of the solution results.

2. The modeling and analysis method for high-voltage power cable intermediate connection thermal path fault according to claim 1 is characterized in that: In the above S1, the principle of analyzing the temperature inversion of the middle connection of the cable is to obtain the temperature of the middle connection wire core of the cable by inverting the temperature measuring point. , expressed as: ； In the formula, is the temperature of the measuring point, and β is the inversion coefficient.

3. The modeling and analysis method for the thermal path fault of the intermediate connection of the high-voltage power cable according to claim 1 is characterized by: In the above-mentioned S2, the material parameters include thickness, thermal conductivity, density and specific heat capacity.

4. The modeling and analysis method for high-voltage power cable intermediate connection thermal path fault according to claim 1 is characterized in that: In the above S3, when establishing the electromagnetic field simulation model of the cable intermediate connection, the following assumptions are made: the cable core current is an AC current with an industrial frequency of 50 Hz, and the influence of displacement current is not considered; except for the cable core material, the materials of other cable components are isotropic, and the material parameters are all regarded as constants; there is no free charge in the field; According to the above assumptions, based on Maxwell's equations, the vector magnetic potential is introduced. In the presence of an external excitation source, its control equation is: ； For the non-current region without external excitation source, the control equation is: ； In the formula, is the gradient operator; is the magnetic permeability; A is the vector magnetic potential; is the external source current density; j is the imaginary unit; is the angular frequency; is the conductivity.

5. The modeling and analysis method for high-voltage power cable intermediate connection thermal path fault according to claim 1 is characterized in that: In the above S4, when establishing the solid temperature field simulation model, the following assumptions are made: the radiation of the internal parts of the cable intermediate connection is not considered, and it is assumed that the cable intermediate connection radiates energy to the surrounding environment only through the outer surface, and the heat transfer process is equivalently expressed by the radiation heat transfer coefficient; when calculating the heat transfer, the temperature change characteristics of the multilayer structure of the power cable intermediate connection are considered; Due to the uneven distribution of the thermal field in the cable intermediate connection, it is assumed that the relative velocity between the outer surface of the cable intermediate connection and the cable core is 0, and the outer surface temperature is consistent with the ambient fluid temperature; the heat conduction and heat convection of each part inside the cable are fully considered, and the outer surface of the cable intermediate connection is simplified to a smooth plane, that is, the heat dissipation process of the outer surface of the cable intermediate connection is considered to be longitudinal flat plate convection heat transfer, and the convection heat transfer coefficient is used to equivalently express the heat transfer process between the power cable intermediate connection and the outside world.

6. The modeling and analysis method for high-voltage power cable intermediate connection thermal path fault according to claim 5 is characterized by: In the solid temperature field simulation model, the influence of temperature gradient is considered, and the direction is radial. The heat balance equation is followed in solid heat transfer, indicating that the sum of the heat energy transferred from the outside to the inside of the object and the energy generated by the object itself is equal to the heat energy consumed by the temperature change of the object; the temperature field problem of the middle connection of the cable satisfies the three-dimensional control equation, and its expression is as follows: ； In the formula, is the material density; c is the material specific heat capacity; T is the temperature to be determined; t is the time; , , are the thermal conductivities of the object in the X, Y, and Z directions respectively; is the internal heat energy of the object; x, y, z are the components of the object in the X, Y, and Z directions, respectively, indicating the spatial coordinates; the object is the component in the geometric model; When calculating heat transfer, boundary conditions include the following three categories: The first type: Boundary conditions with known temperature distribution on the boundary. When the temperature on the boundary is a fixed value, the control equation is: ； In the formula, To solve the domain boundary; is the boundary temperature; The second category: The boundary conditions of the convective heat transfer and the fluid temperature on the known boundary are applicable to the boundary heat transfer process where the solid and the gas intersect. The control equation is: ； In the formula, is the thermal conductivity; h is the convective heat transfer coefficient; is the fluid temperature; n is the normal vector on the boundary; is the mark of the boundary, indicating a point on the boundary; The third category: The boundary conditions of the ambient temperature and the convection heat transfer coefficient are known, and the heat dissipation has reached a balanced thermal insulation boundary condition. The control equation is: ； In the formula, is the ambient temperature.

7. The modeling and analysis method for high-voltage power cable intermediate connection thermal path fault according to claim 6 is characterized in that: In the solid temperature field simulation model, the outer surface of the cable is exposed to the air in the middle of the cable connection, and its outer surface also transfers heat with the external environment through thermal radiation. The control equation is: ； In the formula, is the Stefan-Boltzmann constant; is the external surface emissivity.

8. The modeling and analysis method for high-voltage power cable intermediate connection thermal path fault according to claim 1 is characterized by: In the above S5, the electromagnetic loss of the intermediate connection of the power cable is obtained by numerically solving the electromagnetic-thermal coupling model under the rated operating conditions of the intermediate connection of the power cable, and the electromagnetic loss is coupled into the fluid temperature field as an initial heat source; Taking resistance loss and load loss as heat sources, the weighted interpolation method is used to map heterogeneous grids, and the loss value in the grid of the electromagnetic field calculation result is applied to the corresponding grid node of the cable fluid temperature field; comprehensively considering the heat dissipation intensity of the outer surface of the cable intermediate connection and the internal heat transfer characteristics, the mass, momentum, and energy conservation equations of the cable intermediate connection are numerically solved and calculated to obtain the temperature values ​​of each part of the cable intermediate connection under rated operating conditions; The short-circuit method is used to conduct a temperature rise test on the cable intermediate connection. The electromagnetic-thermal coupling model of the cable intermediate connection under different operating conditions is calibrated based on the test data of the temperature rise of the cable intermediate connection and the temperature rise of the surrounding environment to ensure that the calculation error is within a reasonable range. After the electromagnetic-thermal coupling model is calibrated, a short-circuit fault is set in the intermediate cable connection. The electromagnetic losses of the faulty cable and the normal cable are obtained by solving the equivalent circuit equation of the short-circuit fault and the electromagnetic field mathematical model. The losses of each part are coupled to the corresponding part of the intermediate cable connection by using the heterogeneous grid mapping of the weighted interpolation method. According to the calculation conditions under the rated operating conditions of the intermediate cable connection, the temperature distribution characteristics of the short-circuit fault of the intermediate cable connection are calculated, including the temperature of the intermediate high-voltage cable connection, the temperature at the short-circuit position, and the temperature distribution of the outer surface of the intermediate cable connection.

9. The modeling and analysis method for high-voltage power cable intermediate connection thermal path fault according to claim 1 is characterized by: In the S6, based on the results obtained from the solution, temperature curves under different insulation states are drawn, the cable intermediate connection state corresponding to the temperature distribution characteristics is analyzed, and a cable intermediate connection temperature test platform is built using distributed optical fiber temperature measurement to verify the accuracy between the simulation calculation and the actual measured temperature.

10. A modeling and analysis device for a high-voltage power cable intermediate connection thermal circuit fault, 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 the modeling and analysis method for a thermal path fault in an intermediate connection of a high-voltage power cable as described in any one of claims 1 to 9.

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