Characteristic parameter multi-physical field simulation method and system under early fault of power cable

Abstract

The invention provides a characteristic parameter multi-physics field simulation method and system under an early fault of a power cable. The method comprises the following steps: establishing a cable two-dimensional section model at the early fault according to the structure of the power cable; based on the frequency-dependent characteristic of a material, material parameters of each layer structure and a breakdown channel are set for the cable two-dimensional section model, and grid mapping division is carried out to obtain a cable model; based on the cable model, utilizing multiple physical fields to define distribution parameters; defining characteristic parameters according to the defined distribution parameters; and setting a reasonable simulation frequency domain range and a simulation frequency domain step length based on the defined characteristic parameters, performing simulation calculation solution and obtaining the characteristic parameters, and realizing multi-physics field simulation on the characteristic parameters. The characteristic impedance, attenuation characteristic and other information of the cable under the early fault are effectively extracted, and the early fault can be accurately early warned, identified and positioned by using a mature and reliable off-line cable fault positioning and identification means.

Description

Technical Field

[0001] The patent of this invention belongs to the field of high voltage and insulation, specifically to the field of cable insulation evaluation and fault diagnosis, and more specifically to a multi-physics field simulation method and system for characteristic parameters under early faults of power cables. Background Art

[0002] Power cables are an important part of power transmission. The cable laying environment is often harsh. During the commissioning process, partial discharge will occur due to aging, external force damage, etc.; as the insulation further deteriorates, it causes intermittent cable or accessories to break down once, and then multiple repetitive discharge faults arc faults before the system relay protection is activated, which is also called early faults; as the number of intermittent breakdowns accumulates, early faults eventually evolve into permanent faults, which pose a serious threat to the safety of personnel and equipment, social production, and social life. Domestic and foreign studies have pointed out that early faults in cable systems are an important precursor to permanent cable faults. Effective early warning, positioning, and identification of cable early faults are of great significance to ensuring the safe and stable operation of power systems.

[0003] At present, the early warning and location of early faults are mostly focused on studying the arc time-frequency signals generated under early faults, which belongs to the category of online cable detection. However, the generation of intermittent arcs under early faults is extremely random and uncertain, and the early warning is difficult, and the identification and positioning equipment are complex. It is urgent to provide early warning, identification and location methods for early faults under cable offline maintenance. Since the cable section of the cable with early faults will produce a narrow arc discharge channel, the generation of the discharge channel will inevitably affect the distribution parameters and characteristic parameters of the cable. If the characteristic impedance, attenuation characteristics and other information of the cable under early faults can be effectively extracted, the mature and reliable offline cable fault location and identification methods such as frequency domain reflection method, time domain reflection method and partial discharge method can be used to accurately warn and identify the early faults. Summary of the invention

[0004] The current research field of early-stage cable failure lacks an accurate calculation method for solving cable distribution parameters and characteristic parameters under early-stage failures. In order to solve the deficiencies in the prior art, the present invention provides a multi-physical field simulation method and system for characteristic parameters under early-stage power cable failures. The method is based on COMSOL finite element simulation software, and can more realistically perform physical modeling on narrow discharge channels under early-stage cable failures. Based on Maxwell electromagnetic field theory, magnetic field and electric field application methods and boundary conditions are set to accurately solve the specific values ​​of various distribution parameters and characteristic parameters of the cable under ultra-wide band.

[0005] The present invention adopts the following technical solutions.

[0006] The first aspect of the present invention provides a method for multi-physics field simulation of characteristic parameters under early-stage fault of a power cable, comprising:

[0007] According to the power cable structure, a two-dimensional cross-sectional model of the cable at the early fault location is established and obtained;

[0008] Based on the frequency-varying characteristics of the material, the material parameters of each layer structure and breakdown channel of the cable are set for the obtained two-dimensional cross-sectional model of the cable at the early fault, and mesh mapping is performed to obtain the cable model.

[0009] Based on the obtained cable model, the distributed parameters are defined by using multi-physics finite element to obtain the distributed parameters defined by the multi-physics finite element, where the multi-physics finite element includes the magnetic field finite element and the current and electric field finite element;

[0010] According to the obtained distribution parameters of the multi-physics field finite element definition, characteristic parameters are defined to obtain the characteristic parameters of the multi-physics field finite element definition;

[0011] A multi-physics simulation model is constructed based on the characteristic parameters defined by the multi-physics finite element, the simulation frequency domain range and the simulation frequency domain step are selected, and the characteristic parameters are solved by combining the multi-physics simulation model to obtain the characteristic parameters after multi-physics simulation.

[0012] Preferably, a two-dimensional cross-sectional model of the cable at the early fault location is established and obtained according to the power cable structure, including:

[0013] The model is modeled according to the real physical size parameters of the power cable to obtain a two-dimensional cross-sectional model. The size parameters of the instantaneous breakdown channel under early fault are set on any phase of the power cable and modeled to obtain a two-dimensional cross-sectional model of the cable. The breakdown channel penetrates the metal shielding layer and the insulating shielding layer. The main body of the breakdown channel is an air gap. The metal shielding layer, insulating shielding layer, cross-linked polyethylene and the interface between the inner and outer semi-conductive layers on both sides of the air gap are attached with a carbonized particle attachment layer.

[0014] Preferably, based on the frequency-varying characteristics of the material, the obtained two-dimensional cross-sectional model of the cable at the early fault location is used to set the material parameters of each layer structure and the breakdown channel of the cable, including:

[0015] The complex permittivity of the inner and outer semiconducting layers is defined by defining the complex permittivity analytical function with frequency as a variable in the basic settings of the material settings, and by defining the real and imaginary parts of the complex permittivity based on frequency in the dielectric loss settings.

[0016] Preferably, based on the frequency-varying characteristics of the material, the obtained two-dimensional cross-sectional model of the cable at the early fault location is used to set the material parameters of each layer structure and the breakdown channel of the cable, and perform grid mapping division, including:

[0017] During the mesh drawing process, the cable core and the cable metal shield are divided into free triangle meshes, and the cable core boundary mesh is refined;

[0018] Use mapped meshing for conductor shielding, insulation and insulation shielding of cables;

[0019] Refine the carbonization channel;

[0020] The carbonized adhesion layer is divided into extremely fine grids.

[0021] Preferably, based on the obtained cable model, the distributed parameters are defined by using multi-physics finite element method to obtain the distributed parameters defined by multi-physics finite element method, including:

[0022] When setting the magnetic field finite element for multi-physics finite element, the magnetic field of the cable model is set by setting the current flowing from the core to the metal shield. The magnetic field between the inner conductor and the outer conductor is continuous. The metal shield is set to magnetic insulation as a boundary condition. The core and the metal shield are set to coils. Other structures determine the magnetic field distribution based on Ampere's law as a constraint. The initial value of the magnetic vector potential of the entire geometric domain is set to 0.

[0023] Preferably, the distributed parameters defined by the magnetic field finite element include distributed resistance and distributed inductance, and the distributed resistance R is expressed by the following formula:

[0024]

[0025] In the formula,

[0026] E is the electric field strength,

[0027] J is the current density,

[0028] The distributed inductance L is expressed by the following formula:

[0029]

[0030] In the formula,

[0031] B is the magnetic induction intensity,

[0032] H * is the magnetic field strength,

[0033] I0 is the current flowing from the core to the metal shield, expressed as follows:

[0034] I0=∫ s J * dS (1)

[0035] In the formula,

[0036] J * is the vector current density,

[0037] S is the cross-sectional area through which the current flows.

[0038] Preferably, based on the obtained cable model, the distributed parameters are defined by using multi-physics finite element method to obtain the distributed parameters defined by multi-physics finite element method, including:

[0039] When setting the current and electric field finite element modules for multi-physics finite element, the inner and outer conductors are regarded as the positive and negative electrodes of the capacitor, the capacitor medium is cross-linked polyethylene, the inner and outer semi-conductive layers and the breakdown channel, the electric field in the cable is radially distributed, the size of the electric field on the surface of the core is set according to the charge density of the inner conductor, the size of the electric field on the inner surface of the metal shielding corresponds to the core, the metal shielding potential is set to 0, all capacitor media are set to current conservation, the core is set to the terminal as the electric field source, and the metal shielding is set to grounding as the boundary condition.

[0040] Preferably, the distributed parameters defined by the current and electric field finite element include distributed capacitance and distributed conductance, and the distributed capacitance C is expressed by the following formula:

[0041]

[0042] In the formula,

[0043] is the electric displacement vector,

[0044] S is the cross-sectional area through which the current flows,

[0045] is the vector electric field strength,

[0046] V0 is the line core voltage,

[0047] The distributed conductance G is expressed by the following formula:

[0048]

[0049] In the formula,

[0050] ω is the angular frequency,

[0051] ε is the dielectric constant.

[0052] Preferably, defining characteristic parameters according to the obtained distribution parameters of the multi-physics field finite element definition to obtain the characteristic parameters of the multi-physics field finite element definition includes:

[0053] The characteristic parameters are defined as propagation coefficient γ, attenuation coefficient β and phase coefficient α, which are expressed as follows:

[0054]

[0055] In the formula,

[0056] ω is the angular frequency,

[0057] R is the distributed resistance,

[0058] L is the distributed inductance,

[0059] C is the distributed capacitance,

[0060] G is the distributed conductance,

[0061] The characteristic impedance Z0 is expressed by the following formula:

[0062]

[0063] The wave velocity v is defined as:

[0064]

[0065] In the formula,

[0066] f is the frequency.

[0067] The second aspect of the present invention provides a multi-physics field simulation system for characteristic parameters under early-stage faults of power cables, which is used to run the multi-physics field simulation method for characteristic parameters under early-stage faults of power cables, comprising:

[0068] Cable 2D cross-section model module: used to establish and obtain the cable 2D cross-section model at the early fault location according to the power cable structure;

[0069] Cable model module: used to set the material parameters of each layer structure and breakdown channel of the cable two-dimensional cross-section model at the early fault location based on the frequency-varying characteristics of the material, and perform grid mapping to obtain the cable model;

[0070] Multi-physics field distribution parameter definition module: used to define distribution parameters based on the cable model using multi-physics field finite elements to obtain distribution parameters defined by multi-physics field finite elements. Multi-physics field finite elements include magnetic field finite elements and current and electric field finite elements.

[0071] Multi-physics field characteristic parameter definition module: used to define characteristic parameters according to the distribution parameters defined by the multi-physics field finite element, and obtain the characteristic parameters defined by the multi-physics field finite element;

[0072] Characteristic parameter multi-physics simulation module: used to build a multi-physics simulation model based on the characteristic parameters defined by the multi-physics finite element method, select the simulation frequency domain range and simulation frequency domain step, combine the multi-physics simulation model to simulate and solve the characteristic parameters, and obtain the characteristic parameters after multi-physics simulation.

[0073] An electronic device comprises: a memory, a processor and a computer program stored in the memory and executable on the processor, wherein when the computer program is loaded into the processor, the multi-physics field simulation method for characteristic parameters under early-stage fault of a power cable is implemented.

[0074] A computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the multi-physics field simulation method for characteristic parameters under early-stage faults of a power cable is implemented.

[0075] The beneficial effect of the present invention is that, compared with the prior art, the method is based on COMSOL finite element simulation software, which can more realistically perform physical modeling of narrow discharge channels under early cable faults, and based on Maxwell electromagnetic field theory, set magnetic field and electric field application methods and boundary conditions to accurately solve the specific values ​​of various distribution parameters and characteristic parameters of the cable under ultra-wide frequency band. BRIEF DESCRIPTION OF THE DRAWINGS

[0076] Figure 1 is a flow chart of the present invention;

[0077] Figure 2 The physical size model of 35kV power cable under early fault and its discharge channel in the present invention;

[0078] Figure 3 It is the grid division of 35kV power cable under early fault in the present invention;

[0079] Figure 4 It is a simulation diagram of distributed resistance in the present invention;

[0080] Figure 5 It is a simulation diagram of distributed inductance in the present invention;

[0081] Figure 6 It is a simulation diagram of distributed capacitance in the present invention;

[0082] Figure 7 It is a distributed conductivity simulation diagram in the present invention;

[0083] Figure 8 It is a characteristic impedance simulation diagram in the present invention. DETAILED DESCRIPTION

[0084] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The embodiments described in this application are only part of the embodiments of the present invention, not all of them. Based on the spirit of the present invention, other embodiments obtained by ordinary technicians in this field without creative work are all within the scope of protection of the present invention.

[0085] Example 1

[0086] Embodiment 1 of the present invention provides a method for simulating characteristic parameters of a power cable incipient fault. Figure 1 As shown, the following steps are included:

[0087] Step 1: Establish a two-dimensional cross-sectional model of the cable at the early fault location according to the power cable structure;

[0088] Power cables include medium voltage or high voltage three-core cables;

[0089] Model: YJV-26 / 35kV-3*400m 2 The 35kV power cable is taken as the simulation object. It is worth noting that this method is still fully applicable to power cables below 35kV, such as 10kV.

[0090] The model is built according to the real physical size parameters of the power cable to obtain a two-dimensional cross-sectional model. The size parameters of the instantaneous breakdown channel under early fault are set on any phase of the power cable and modeled to obtain a two-dimensional cross-sectional model of the cable. The breakdown channel penetrates the metal shielding layer and the insulating shielding layer. The main body is an air gap. The metal shielding layer, insulating shielding layer, cross-linked polyethylene and the inner and outer semi-conductive layers on both sides of the air gap are attached with an extremely narrow carbonized particle attachment layer. The model is as follows Figure 2 shown.

[0091] Step 2: Based on the frequency-dependent characteristics of the material, set the material parameters of each layer structure and the breakdown channel for the two-dimensional cable cross-section model obtained in step 1, and perform mesh mapping to obtain the cable model;

[0092] Set the material parameters of each layer of the cable structure. It is worth noting that for complex dielectric constants such as semi-conductive layers that vary greatly with frequency, it is necessary to define related functions with frequency as a variable in the corresponding material properties. Only in this way can the cable characteristic parameters and distribution parameters corresponding to each frequency point under a wide bandwidth be accurately obtained.

[0093] The complex dielectric constants of the semiconducting layer and the outer semiconducting layer are defined in the "Basic Settings" of the "Material Settings" of Comsol. The analytical function of the complex dielectric constant with respect to frequency changes is defined. In the "Dielectric Loss", the real and imaginary parts of the complex dielectric constant with respect to frequency are defined. In this way, when performing "frequency domain" solution calculations, the complex dielectric constants of the medium corresponding to different frequencies are different.

[0094] Taking into account that the calculated characteristic parameters and distribution parameters of the cable are coaxial modal parameters, and in order to maximize the calculation efficiency, the fault is selected to obtain the two-dimensional cross-sectional model of the cable corresponding to the early fault, and the mesh is refined. During the mesh drawing process, the critical edges of each structure are refined, and the core is divided into free triangle meshes. The outer layer of the core is mainly meshed by the mapping division method, and the carbonization channel under the early fault is extremely finely divided.

[0095] Grid division as Figure 3 As shown. The grid unit division accuracy used to characterize the side length of the grid unit is manually set; the grid unit is a cuboid; the 8 vertices of the cuboid correspond to the 8 corner points of the grid unit one by one; the height, bottom length and bottom width of the representative volume element are uniformly cut according to the grid unit division accuracy to obtain a representative volume element composed of the grid units in a rectangular arrangement; the representative volume element composed of the grid units is output as the grid mapping division result; the cable core part and the cable metal shield are divided into free triangle meshes, the cable core boundary is meshed, the distribution type is set to a fixed number of units, and the number of units is set to 25; the conductor shield, insulation, and insulation shield of the cable are mapped and meshed, and the carbonization channel is refined at the same time, and the fixed number of units is set to 5; the carbonization attachment layer is extremely refined, and the fixed number of units is set to 8.

[0096] Step 3: Based on the cable model obtained in step 2, the distributed parameters are defined by using the multi-physics finite element in the COMSOL simulation software to obtain the distributed parameters defined by the multi-physics finite element;

[0097] Multi-physics field finite element includes: magnetic field finite element and current and electric field finite element.

[0098] Set up the magnetic field finite element and define the solution function for the distributed resistance and distributed inductance parameters;

[0099] Considering the principle of signal transmission under coaxial transmission line, due to the skin effect between cable core and metal shield, dielectric loss of solid insulation and loss of displacement current flowing through semi-conductive shielding layer, the analytical approximate solution of cable distribution cable and distributed resistance parameters is only applicable to a certain frequency band, and the cable model with breakdown channel is not a regular coaxial conductor, so the analytical solution of distributed inductance and distributed resistance is obviously no longer applicable. The integration of electric field intensity E and current density J can realize accurate solution of distributed inductance and distributed capacitance parameters in any frequency band.

[0100] According to the magnetic field characteristics of the coaxial transmission line model, the magnetic field of the cable model is set; the magnetic field in the cable is mainly along the cable axis, and its size and direction are determined by the current in the cable. The magnetic field is continuous between the inner conductor and the outer conductor without sudden changes. According to Ampere's loop law, the size of the internal magnetic field is proportional to the total current passing through the loop.

[0101] When setting the magnetic field finite element, the magnetic field of the cable model is set by setting the current flowing from the core to the metal shield. The magnetic field between the inside and the outside is continuous. The metal shield is set as magnetic insulation as a constraint boundary condition. The core and the metal shield are set as coils. Other structures are constrained by Ampere's law to determine the magnetic field distribution. The initial value of the magnetic vector potential of the entire geometric domain is set to 0.

[0102] Then define the function in the global module, define J * is the vector current density, I0 It is the current flowing from the core to the metal shield, R is the distributed resistance, and L is the distributed inductance.

[0103] The current flowing from the core to the metal shield is expressed by the following formula:

[0104] I0=∫ s J * dS (1)

[0105] is the vector electric field strength, and is defined W0 is the conductor cross-sectional power loss, then:

[0106]

[0107] According to formula 1 and formula 2, the distributed resistance R is:

[0108]

[0109] Among them, E represents the electric field intensity, J represents the current density, and S represents the cross-sectional area through which the current flows.

[0110] The distributed inductance L is:

[0111]

[0112] Where B is the magnetic induction intensity, H * is the magnetic field strength.

[0113] Set up current and electric field finite elements, and define the solution functions for distributed capacitance and distributed conductance parameters;

[0114] The cable model with the breakdown channel is not a regular coaxial conductor, and the analytical solution of the distributed capacitance is obviously not applicable. This problem does not need to be considered when using the current and electric field finite element modules to simulate and solve the distributed capacitance and distributed conductivity. The inner and outer conductors can be regarded as the positive and negative electrodes of the capacitor, and the capacitor medium is the cross-linked polyethylene insulation, the inner and outer semi-conductive layers, and the breakdown channel.

[0115] According to the electric field characteristics of the coaxial transmission line model, the electric field and current of the cable model are set; the electric field in the cable is radially distributed. On the surface of the core, the magnitude of the electric field is determined by the charge density of the inner conductor; on the inner surface of the metal shield, the magnitude of the electric field corresponds to the core, satisfying charge continuity and Gauss's law; and the metal shield potential is set to 0.

[0116] In the current and electric field finite element module, all capacitor dielectrics are set to current conservation, the wire core is set as the terminal as the electric field source, and the metal shield grounding is set as the boundary condition.

[0117] Then define the function globally in the global module. is the electric displacement vector, We is the total energy of the electric field, V0 is the core voltage, C is the distributed capacitance, and L is the distributed inductance.

[0118] Then W e It can be defined as:

[0119]

[0120] According to formula 5, the distributed capacitance C is defined as:

[0121]

[0122] The distributed conductance G is defined as:

[0123]

[0124] Among them, ε is the dielectric constant and ω is the angular frequency.

[0125] At this point, the cable transmission line distributed parameters R, L, C, and G have all been defined.

[0126] Step 4: Define characteristic parameters according to the distribution parameters of the multi-physics field finite element definition obtained in step 3, and obtain the characteristic parameters of the multi-physics field finite element definition;

[0127] Next, the characteristic parameters of the cable under early fault conditions are globally defined.

[0128] The propagation coefficient is γ, the attenuation coefficient is β, and the phase coefficient is defined as:

[0129]

[0130] The characteristic impedance is defined as Z0:

[0131]

[0132] The wave velocity v is defined as:

[0133]

[0134] Here, f represents frequency.

[0135] Step 5: Based on the characteristic parameters of the multi-physics field finite element definition obtained in step 4, a multi-physics field simulation model is constructed, a reasonable simulation frequency domain range and simulation frequency domain step are set, and simulation calculations are performed using the multi-physics field simulation model. Finally, the characteristic parameters after multi-physics field simulation are calculated to achieve effective extraction of characteristic parameters.

[0136] Select the frequency domain module. Since the distribution parameters, propagation coefficients and other cable characteristic parameters are frequency-varying parameters, that is, parameters that change with frequency, and because it is necessary to calculate the characteristic parameters under a wide frequency band, the frequency domain module settings mainly include three parameters: initial frequency, sampling frequency step, and cutoff frequency. The frequency parameter settings depend on the frequency band of the study. The initial frequency range is generally set to about 1k-1MHz, the sampling frequency step is generally set to about 10kHz, and the cutoff frequency is set to about 10MHz-200MHz. According to the subsequent traveling wave method, the frequency domain component range is obtained, and considering the calculation efficiency, the appropriate simulation frequency domain range and simulation frequency domain step are set. Perform simulation calculations.

[0137] Example 2

[0138] Embodiment 2 of the present invention provides a multi-physics field simulation system for characteristic parameters under early-stage faults of power cables, which is used to run a multi-physics field simulation method for characteristic parameters under early-stage faults of power cables described in embodiment 1, including:

[0139] Cable 2D cross-section model module: used to establish and obtain the cable 2D cross-section model at the early fault location according to the power cable structure;

[0140] Cable model module: used to set the material parameters of each layer structure and breakdown channel of the cable two-dimensional cross-section model at the early fault location based on the frequency-varying characteristics of the material, and perform grid mapping to obtain the cable model;

[0141] Multi-physics field distribution parameter definition module: used to define distribution parameters based on the cable model using multi-physics field finite elements to obtain distribution parameters defined by multi-physics field finite elements. Multi-physics field finite elements include magnetic field finite elements and current and electric field finite elements.

[0142] Multi-physics field characteristic parameter definition module: used to define characteristic parameters according to the distribution parameters defined by the multi-physics field finite element, and obtain the characteristic parameters defined by the multi-physics field finite element;

[0143] Characteristic parameter multi-physics simulation module: used to build a multi-physics simulation model based on the characteristic parameters defined by the multi-physics finite element method, select the simulation frequency domain range and simulation frequency domain step, combine the multi-physics simulation model to simulate and solve the characteristic parameters, and obtain the characteristic parameters after multi-physics simulation.

[0144] Example 3

[0145] Embodiment 3 of the present invention uses the two-dimensional cross-sectional model of the cable in Embodiment 1 and the cable model and parameters and grid basis in Embodiment 1 to perform the multi-physics field finite element field setting and related calculation function definition in Embodiment 1, selects the frequency band lower limit of 100Hz, the frequency band upper limit of 100MHz, and the frequency step of 500KHz for calculation research, and the calculated distribution parameters and characteristic parameters of the cable part containing intermittent breakdown channels under early faults are as follows Figure 4-Figure 8 .

[0146] Analysis of the simulation results shows that compared with the healthy cable, the R, L, and G of the cable do not change much, the distributed parameter C decreases by about 3%, and the characteristic impedance increases by about 1.5%. This is the same as the C change trend of the 20cm short cable sample with 10kV early fault tested by LCR bridge, which decreases from 33.37PF to 31.13PF.

[0147] Example 4

[0148] Embodiment 4 of the present invention provides an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the computer program is loaded into the processor, a multi-physics field simulation method for characteristic parameters of an early-stage fault of a power cable is implemented according to Embodiment 1.

[0149] Example 5

[0150] Embodiment 5 of the present invention provides a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, a multi-physics field simulation method for characteristic parameters under early-stage faults of a power cable according to embodiment 1 is implemented.

[0151] The beneficial effect of the present invention is that, compared with the prior art, the method is based on COMSOL finite element simulation software, which can more realistically perform physical modeling of narrow discharge channels under early cable faults, and based on Maxwell electromagnetic field theory, set magnetic field and electric field application methods and boundary conditions to accurately solve the specific values ​​of various distribution parameters and characteristic parameters of the cable under ultra-wide frequency band.

[0152] The present disclosure may be a system, a method and / or a computer program product. The computer program product may include a computer-readable storage medium carrying computer-readable program instructions for causing a processor to implement various aspects of the present disclosure.

[0153] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for multi-physics field simulation of characteristic parameters under early fault of power cable, characterized in that: include: According to the power cable structure, a two-dimensional cross-sectional model of the cable at the early fault location is established and obtained; Based on the frequency-varying characteristics of the material, the material parameters of each layer structure and breakdown channel of the cable are set for the obtained two-dimensional cross-sectional model of the cable at the early fault, and mesh mapping is performed to obtain the cable model. Based on the obtained cable model, the distributed parameters are defined by using multi-physics finite element to obtain the distributed parameters defined by the multi-physics finite element, where the multi-physics finite element includes the magnetic field finite element and the current and electric field finite element; According to the obtained distribution parameters of the multi-physics field finite element definition, characteristic parameters are defined to obtain the characteristic parameters of the multi-physics field finite element definition; A multi-physics simulation model is constructed based on the characteristic parameters defined by the multi-physics finite element, the simulation frequency domain range and the simulation frequency domain step are selected, and the characteristic parameters are solved by combining the multi-physics simulation model to obtain the characteristic parameters after multi-physics simulation.

2. The method for multi-physics field simulation of characteristic parameters under early-stage fault of power cable according to claim 1 is characterized in that: According to the power cable structure, a two-dimensional cross-sectional model of the cable at the early fault location is established and obtained, including: The model is modeled according to the real physical size parameters of the power cable to obtain a two-dimensional cross-sectional model. The size parameters of the instantaneous breakdown channel under early fault are set on any phase of the power cable and modeled to obtain a two-dimensional cross-sectional model of the cable. The breakdown channel penetrates the metal shielding layer and the insulating shielding layer. The main body of the breakdown channel is an air gap. The metal shielding layer, insulating shielding layer, cross-linked polyethylene and the interface between the inner and outer semi-conductive layers on both sides of the air gap are attached with a carbonized particle attachment layer.

3. The method for multi-physics field simulation of characteristic parameters under early-stage fault of power cable according to claim 1 is characterized in that: Based on the frequency-dependent characteristics of the material, the material parameters of each layer structure and breakdown channel of the cable are set for the obtained two-dimensional cross-sectional model of the cable at the early fault, including: The complex permittivity of the inner and outer semiconducting layers is defined by defining the complex permittivity analytical function with frequency as a variable in the basic settings of the material settings, and by defining the real and imaginary parts of the complex permittivity based on frequency in the dielectric loss settings.

4. The method for multi-physics field simulation of characteristic parameters under early-stage fault of power cable according to claim 1 is characterized in that: Based on the frequency-varying characteristics of the material, the material parameters of each layer structure and breakdown channel of the cable are set for the obtained two-dimensional cross-section model of the cable at the early fault, and mesh mapping is performed, including: During the mesh drawing process, the cable core and the cable metal shield are divided into free triangle meshes, and the cable core boundary mesh is refined; Use mapped meshing for conductor shielding, insulation and insulation shielding of cables; Refine the carbonization channel; The carbonized adhesion layer is meshed extremely finely.

5. The method for multi-physics field simulation of characteristic parameters under early-stage fault of power cable according to claim 1, characterized in that: Based on the obtained cable model, the distributed parameters are defined by using the multi-physics finite element method, and the distributed parameters defined by the multi-physics finite element method are obtained, including: When setting the magnetic field finite element for multi-physics finite element, the magnetic field of the cable model is set by setting the current flowing from the core to the metal shield. The magnetic field between the inner conductor and the outer conductor is continuous. The metal shield is set to magnetic insulation as a boundary condition. The core and the metal shield are set to coils. Other structures determine the magnetic field distribution based on Ampere's law as a constraint. The initial value of the magnetic vector potential of the entire geometric domain is set to 0.

6. The method for multi-physics field simulation of characteristic parameters under early-stage fault of power cable according to claim 5, characterized in that: The distributed parameters defined by the magnetic field finite element include distributed resistance and distributed inductance. The distributed resistance R is expressed by the following formula: In the formula, E is the electric field strength, J is the current density, The distributed inductance L is expressed by the following formula: In the formula, B is the magnetic induction intensity, H * is the magnetic field strength, I0 is the current flowing from the core to the metal shield, expressed as follows: I0=∫ s J * dS (1) In the formula, J * is the vector current density, S is the cross-sectional area through which the current flows.

7. The method for multi-physics field simulation of characteristic parameters under early-stage fault of power cable according to claim 1, characterized in that: Based on the obtained cable model, the distributed parameters are defined by using the multi-physics finite element method, and the distributed parameters defined by the multi-physics finite element method are obtained, including: When setting the current and electric field finite element modules for multi-physics finite element, the inner and outer conductors are regarded as the positive and negative electrodes of the capacitor, the capacitor medium is cross-linked polyethylene, the inner and outer semi-conductive layers and the breakdown channel, the electric field in the cable is radially distributed, the size of the electric field on the surface of the core is set according to the charge density of the inner conductor, the size of the electric field on the inner surface of the metal shielding corresponds to the core, the metal shielding potential is set to 0, all capacitor media are set to current conservation, the core is set to the terminal as the electric field source, and the metal shielding is set to grounding as the boundary condition.

8. The method for multi-physics field simulation of characteristic parameters under early-stage fault of power cable according to claim 7, characterized in that: The distributed parameters defined by the finite element of current and electric field include distributed capacitance and distributed conductance. The distributed capacitance C is expressed by the following formula: In the formula, is the electric displacement vector, S is the cross-sectional area through which the current flows, is the vector electric field strength, V0 is the line core voltage, The distributed conductance G is expressed by the following formula: In the formula, ω is the angular frequency, ε is the dielectric constant.

9. The method for multi-physics field simulation of characteristic parameters under early-stage fault of power cable according to claim 1, characterized in that: According to the obtained distribution parameters of the multi-physics field finite element definition, characteristic parameters are defined to obtain the characteristic parameters of the multi-physics field finite element definition, including: The characteristic parameters are defined as propagation coefficient γ, attenuation coefficient β and phase coefficient α, which are expressed as follows: In the formula, ω is the angular frequency, R is the distributed resistance, L is the distributed inductance, C is the distributed capacitance, G is the distributed conductance, The characteristic impedance Z0 is expressed by the following formula: The wave velocity v is defined as: In the formula, f is the frequency.

10. A multi-physics field simulation system for characteristic parameters under early-stage faults of power cables, used for running a multi-physics field simulation method for characteristic parameters under early-stage faults of power cables according to any one of claims 1 to 9, characterized in that: include: Cable 2D cross-section model module: used to establish and obtain the cable 2D cross-section model at the early fault location according to the power cable structure; Cable model module: used to set the material parameters of each layer structure and breakdown channel of the cable two-dimensional cross-section model at the early fault location based on the frequency-varying characteristics of the material, and perform grid mapping to obtain the cable model; Multi-physics field distribution parameter definition module: used to define distribution parameters based on the cable model using multi-physics field finite elements to obtain distribution parameters defined by multi-physics field finite elements. Multi-physics field finite elements include magnetic field finite elements and current and electric field finite elements. Multi-physics field characteristic parameter definition module: used to define characteristic parameters according to the distribution parameters defined by the multi-physics field finite element, and obtain the characteristic parameters defined by the multi-physics field finite element; Characteristic parameter multi-physics simulation module: used to build a multi-physics simulation model based on the characteristic parameters defined by the multi-physics finite element method, select the simulation frequency domain range and simulation frequency domain step, combine the multi-physics simulation model to simulate and solve the characteristic parameters, and obtain the characteristic parameters after multi-physics simulation.

11. An electronic device, characterized in that: include: A memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the computer program is loaded into the processor, a multi-physics field simulation method for characteristic parameters under early-stage faults of a power cable is implemented according to any one of claims 1 to 9.

12. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, a characteristic parameter multi-physics field simulation method for early-stage faults of a power cable is implemented according to any one of claims 1 to 9.

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