Method and device for measuring parameters of cable joint

Abstract

The invention is suitable for the technical field of cable joint monitoring, and provides a cable joint parameter measurement method and device, and the method comprises the steps: obtaining the magnetic field data of a cable joint; the magnetic field data is obtained by additionally arranging a preset number of magnetic sensors in the circumferential direction of the cable joint; the current of the cable phase core is inverted based on the magnetic field data, and the corresponding relation between the magnetic field data and the current is obtained; based on the current of the cable phase core, obtaining the temperature of the cable joint under different load current conditions and the stress of the cable joint under different temperature conditions by adopting finite element simulation; determining electro-thermal coupling data of the magnetic field, the current, the temperature and the stress based on the corresponding relation between the magnetic field data and the current, the temperature of the cable joint under different load current conditions and the stress of the cable joint under different temperature conditions; the electro-thermal coupling data is used for measuring real-time parameters of the cable joint. The current, temperature and stress of the cable joint can be obtained by measuring the magnetic field of the cable joint.

Description

Technical Field

[0001] The present application belongs to the technical field of cable joint monitoring, and in particular, relates to a method and device for measuring cable joint parameters. Background Art

[0002] With the rapid development of the economy and society and the continuous improvement of urbanization, my country's electricity demand continues to increase. The construction of urban transmission lines is of great significance to meet the needs of urban economic development. In the construction of urban transmission lines, due to the scarcity of urban land resources, the overhead line transmission corridor is often relatively tight, and the construction of overhead lines will have an impact on the urban landscape. Therefore, when constructing urban transmission lines, cables with high transmission corridor utilization and environmental friendliness are often used. In order to ensure the safe operation of the cable system, it is necessary to realize the operation status monitoring of the cable system.

[0003] In the cable system, faults mainly occur in the accessories, especially cable joint faults. Therefore, it is very necessary to monitor the status of cable joints. The current, temperature and stress of cable joints are the key parameters that reflect their operating status. For the current of cable joints, current transformers and Rogowski coils are mainly used for measurement. Among them, current transformers are large in size and need to be installed at the end of the cable when the cable is laid. After installation, they are difficult to move and have poor convenience. A single-core cable requires one current transformer, and a three-core cable requires three current transformers, which significantly increases the cost and space. In addition to current transformers, there are also current measurement methods based on magnetic fields, such as Rogowski coils, but Rogowski coils can only measure single-core cables. The magnetic field of three-core cables has a canceling effect, so Rogowski coils are no longer applicable. For the temperature of cable joints, there are mainly thermocouples, infrared temperature measurement and optical fiber temperature measurement methods. Among them, thermocouples and infrared temperature measurement can only achieve temperature measurement at individual points, while optical fiber temperature measurement can achieve distributed temperature monitoring, but these methods require independent installation of temperature sensors, which increases the cost of the cable monitoring system. With regard to cable joint stress, currently only pressure sensors are theoretically feasible. However, implanting sensors into cable joints will affect the internal structure and electromagnetic field distribution of the joints, which may cause damage to the cable joints.

[0004] Currently, independent sensors are required to measure the current, temperature and stress of cable joints, and there is no method to achieve synchronous measurement of the current, temperature and stress of cable joints. Summary of the invention

[0005] The embodiments of the present application provide a method and device for measuring cable joint parameters, which can obtain the cable joint current, temperature and stress by measuring the cable joint magnetic field.

[0006] This application is implemented through the following technical solutions:

[0007] In a first aspect, an embodiment of the present application provides a method for measuring cable joint parameters, comprising:

[0008] Acquire magnetic field data of the cable joint; the magnetic field data is obtained by installing a preset number of magnetic sensors in the circumference of the cable joint;

[0009] Based on the magnetic field data, the current of the cable phase core is inverted, and the corresponding relationship between the magnetic field data and the current is obtained;

[0010] Based on the current of the cable core, the finite element simulation is used to obtain the temperature of the cable joint under different load current conditions and the stress of the cable joint under different temperature conditions;

[0011] Based on the correspondence between magnetic field data and current, the temperature of cable joints under different load current conditions and the stress of cable joints under different temperature conditions, the electro-thermal-mechanical coupling data of magnetic field and current, temperature and stress are determined; the electro-thermal-mechanical coupling data are used to measure the real-time parameters of cable joints.

[0012] In a possible implementation manner of the first aspect, inverting the current of the cable phase core based on the magnetic field data includes:

[0013] If the cable connector is a three-core cable connector, the current of the cable phase core is inverted based on the magnetic field data using the particle swarm optimization algorithm.

[0014] In a possible implementation of the first aspect, based on magnetic field data, using a particle swarm optimization algorithm to invert the current of the cable phase core includes:

[0015] Using magnetic field data, solve the tangential magnetic induction intensity equation at the location of the magnetic sensor to determine the initial three-phase current of the cable phase core;

[0016] The preset rotation angle of the target sensor and the corresponding initial three-phase current of the cable phase core are set as particle variables, and the particle swarm optimization algorithm is used for back fitting to inversely perform the optimized three-phase current of the cable phase core; the number of target sensors is 2; and the position angle between the two target sensors is 120°.

[0017] In a possible implementation of the first aspect, based on the current of the cable phase core, finite element simulation is used to obtain the temperature of the cable joint under different load current conditions, including:

[0018] Use finite element simulation software to establish a three-dimensional geometric model of the cable connector;

[0019] Based on the current of the cable core, the heat conduction control equation and boundary conditions of the steady-state temperature field of the three-dimensional geometric model of the cable joint are set;

[0020] The thermal conductivity control equation and boundary conditions of the steady-state temperature field of the three-dimensional geometric model of the cable joint are simulated and analyzed to obtain the temperature of the cable joint under different load current conditions.

[0021] In a possible implementation manner of the first aspect, the heat conduction control equation of the steady-state temperature field of the three-dimensional geometric model of the cable connector is expressed as:

[0022]

[0023] Where T is temperature; x, y, z are the spatial coordinates of the three-dimensional geometric model; λ is the thermal conductivity; Q v is the volume heat generation rate;

[0024] The boundary conditions are expressed as:

[0025]

[0026] Among them, q is the normal heat flux density; n is the boundary normal direction; r is the normal direction.

[0027] In a possible implementation of the first aspect, using finite element simulation to obtain cable joint stress under different temperature conditions includes:

[0028] Based on the temperature of the cable joint under different load current conditions, the finite element simulation is used to obtain the stress of the cable joint under different temperature conditions.

[0029] In a possible implementation of the first aspect, based on the temperature of the cable joint under different load current conditions, finite element simulation is used to obtain the cable joint stress under different temperature conditions, including:

[0030] Use finite element simulation software to establish a three-dimensional geometric model of the cable connector;

[0031] Based on the temperature of the cable joint under different load current conditions, the node equilibrium equation of the three-dimensional geometric model of the cable joint is set;

[0032] The simulation analysis is carried out based on the node equilibrium equation of the three-dimensional geometric model of the cable joint to obtain the cable joint stress under different temperature conditions.

[0033] In a possible implementation manner of the first aspect, the node equilibrium equation of the three-dimensional geometric model of the cable connector is expressed as:

[0034] dσ h =Kdδ

[0035] Among them, dσ h is the node temperature load increment; K is the node stiffness matrix; dδ is the node deformation increment.

[0036] In a possible implementation manner of the first aspect, when the cable connector is a single-core cable connector, a magnetic sensor is embedded in the cable connector, and the magnetic field data includes a magnetic induction intensity at an embedded position measured by the magnetic sensor;

[0037] When the cable connector is a three-core cable connector, a magnetic sensor array formed by four magnetic sensors is embedded in the cable connector, and the magnetic field data includes the tangential magnetic induction intensity at the locations of the four magnetic sensors.

[0038] In a second aspect, an embodiment of the present application provides a device for measuring cable joint parameters, which implements the method for measuring cable joint parameters in the first aspect. The device for measuring cable joint parameters includes:

[0039] A magnetic field data acquisition module is used to acquire magnetic field data of the cable joint; the magnetic field data is acquired by installing a preset number of magnetic sensors in the circumference of the cable joint;

[0040] A current determination module is used to invert the current of the cable phase core based on the magnetic field data and obtain the corresponding relationship between the magnetic field data and the current;

[0041] The temperature and stress determination module is used to obtain the temperature of the cable joint under different load current conditions and the stress of the cable joint under different temperature conditions based on the current of the cable phase core by finite element simulation;

[0042] The current-temperature-stress coupling module is used to determine the electro-thermal-mechanical coupling data of the magnetic field and current, temperature, and stress based on the corresponding relationship between the magnetic field data and the current, the temperature of the cable joint under different load current conditions, and the stress of the cable joint under different temperature conditions; the electro-thermal-mechanical coupling data is used to analyze the operating status of the cable joint.

[0043] Compared with the related art, the embodiments of the present application have the following beneficial effects:

[0044] The cable joint parameter measurement method and device of the embodiment of the present application measures the magnetic field of the cable joint through a magnetic sensor, establishes the relationship between the magnetic field and the current to invert and obtain the current of the cable joint, obtains the corresponding temperature and stress according to the current of the cable joint in the current state, and simultaneously realizes the measurement of the current, temperature and stress of the cable joint. Compared with the independent measurement system of the traditional method, this method uses sensor detection and simulation reasoning to realize a set of magnetic sensors to measure multiple cable state quantities, which is simpler and convenient for judging the operating status of the cable.

[0045] The beneficial effects of the above-mentioned second aspect embodiment refer to the beneficial effects of the first aspect embodiment, which will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or related technical descriptions will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0047] Figure 1 This is an application scenario diagram of a cable joint parameter measurement method and device provided in an embodiment of the present application;

[0048] Figure 2 It is a flow chart of a method for measuring cable joint parameters provided in one embodiment of the present application;

[0049] Figure 3 It is a schematic diagram of single-core cable joint detection provided by an embodiment of the present application;

[0050] Figure 4 It is a schematic diagram of three-core cable connector detection provided by an embodiment of the present application;

[0051] Figure 5 This is a simulation schematic diagram of a three-core cable connector provided in an embodiment of the present application;

[0052] Figure 6 It is a schematic diagram of various angles of a three-core cable connector provided in an embodiment of the present application;

[0053] Figure 7 It is a preliminary three-dimensional geometric model of the integral prefabricated joint provided in one embodiment of the present application;

[0054] Figure 8 is a schematic diagram of a typical temperature distribution result provided by an embodiment of the present application;

[0055] Fig. 9 is a schematic diagram of a typical stress distribution result provided by an embodiment of the present application;

[0056] Fig.10 It is a structural schematic diagram of a device for measuring cable joint parameters provided in one embodiment of the present application. DETAILED DESCRIPTION

[0057] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present application. However, it should be clear to those skilled in the art that the present application may also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present application.

[0058] It should be understood that when used in the present specification and the appended claims, the term "comprising" indicates the presence of described features, wholes, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or combinations thereof.

[0059] It should also be understood that the term “and / or” used in the specification and appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0060] In addition, in the description of the present application specification and the appended claims, the terms "first", "second", "third", etc. are only used to distinguish the descriptions and cannot be understood as indicating or implying relative importance.

[0061] References to "an embodiment", "one embodiment" or "some embodiments" described in the specification of this application mean that one or more embodiments of the present application include specific features, structures or characteristics described in conjunction with the embodiment. Therefore, the statements "in one embodiment", "in some embodiments", "in some other embodiments", "in some other embodiments", etc. that appear in different places in this specification do not necessarily refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. The terms "including", "comprising", "having" and their variations all mean "including but not limited to", unless otherwise specifically emphasized in other ways.

[0062] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings and specific implementation methods. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0063] Figure 1 The present application provides an application scenario diagram of a cable joint parameter measurement method. The cable joint parameter measurement method can be applied to a cable joint detection device 102, which is used to detect parameters, status, etc. of the cable joint 101. The cable joint detection device can have offline detection or online monitoring functions, that is, achieved through wired or wireless transmission of a magnetic sensor.

[0064] The cable joint detection device 102 can be applied to technologies such as cable completion acceptance test, cable temperature monitoring and simulation of cable status influence.

[0065] Figure 2 The present invention provides a method for measuring cable connector parameters. Figure 2 , the measurement method of the cable joint parameters includes:

[0066] Step 201, obtaining magnetic field data of a cable connector.

[0067] The magnetic field data is obtained by installing a preset number of magnetic sensors in the circumferential direction of the cable connector.

[0068] Exemplarily, when the cable connector is a single-core cable connector, one magnetic sensor is embedded in the cable connector, and the magnetic field data includes the magnetic induction intensity of the embedded position measured by the one magnetic sensor.

[0069] For single-core cable connectors, just add a magnetic sensor, such as Figure 3 As shown, the magnetic sensor may be directly opposite to the inner conductor connecting portion in the circumferential direction of the cable connector.

[0070] When the cable connector is a three-core cable connector, a plurality of magnetic sensors are embedded in the cable connector. For example, a magnetic sensor array formed by four magnetic sensors may be embedded in the cable connector, and the magnetic field data includes the tangential magnetic induction intensity at the locations of the four magnetic sensors.

[0071] For three-core cable connectors, multiple magnetic sensors are installed to form a magnetic sensor array, such as Figure 4 As shown, the magnetic sensors can also be distributed around the cable connector and face the inner conductor connection portion.

[0072] Step 202: Invert the current of the cable phase core based on the magnetic field data, and obtain the corresponding relationship between the magnetic field data and the current.

[0073] According to Ampere's law, the current in the cable phase core can be inverted using the magnetic field data, and the corresponding relationship between the magnetic induction intensity and the current in the magnetic field data can be obtained.

[0074] Step 203: Based on the current of the cable phase core, finite element simulation is used to obtain the temperature of the cable joint under different load current conditions and the stress of the cable joint under different temperature conditions.

[0075] Step 204, based on the correspondence between the magnetic field data and the current, the temperature of the cable joint under different load current conditions and the stress of the cable joint under different temperature conditions, the electro-thermal-mechanical coupling data of the magnetic field and the current, temperature and stress are determined.

[0076] Among them, the electro-thermal-mechanical coupling data is used to measure the real-time parameters of the cable joint.

[0077] Exemplarily, after step 204, the method further includes:

[0078] The real-time magnetic field data of the cable joint is obtained; based on the electrothermal-mechanical coupling data, the current, temperature and stress corresponding to the real-time magnetic field data are determined as the real-time current, real-time temperature and real-time stress of the cable joint.

[0079] The magnetic field data involved in step 201 and step 202 is a collection of magnetic field data obtained through experiments or historical measurement data, and the real-time magnetic field data is the magnetic field data obtained in real time when the method is applied for actual detection. Of course, after the real-time magnetic field data is used, it will be updated to the magnetic field data to further improve and enrich the magnetic field data.

[0080] In this embodiment, the magnetic field of the cable joint is measured by a magnetic sensor, the relationship between the magnetic field and the current is established to invert the current of the cable joint, the corresponding temperature and stress are obtained according to the current of the cable joint in the current state, and the measurement of the current, temperature and stress of the cable joint is realized simultaneously. Compared with the independent measurement system of the traditional method, this method uses sensor detection and simulation reasoning to realize a set of magnetic sensors to measure multiple cable state quantities, which is simpler and convenient for judging the operating status of the cable.

[0081] In one embodiment, a specific implementation of step 202 is introduced, wherein, for a single-core cable joint, the magnetic field distribution of a single-phase cable can be regarded as the magnetic field distribution of a single conductor. For a single-phase conductor, its current and magnetic field conform to the Ampere loop theorem, and its magnetic field is different from that of a three-phase cable and will not be interfered by the other two phases. The cable can be regarded as an infinitely long straight conductor. Therefore, the current of the cable phase core is inverted based on the magnetic field data, including: based on the relationship between the magnetic induction intensity and the current, the current of the cable phase core is inverted from the magnetic field data.

[0082] The relationship between magnetic induction intensity and current can be expressed as:

[0083]

[0084] Among them, u is the vacuum magnetic permeability, I is the current through the cable, and x is the distance between the measuring point and the cable conductor. By embedding the magnetic sensor into the cable joint, the magnetic induction intensity of the corresponding measuring point can be measured, thereby calculating the current of the cable phase core.

[0085] Exemplarily, for a three-core cable joint, the current of the cable phase core is inverted based on the magnetic field data, and further includes:

[0086] If the cable connector is a three-core cable connector, the current of the cable phase core is inverted based on the magnetic field data using the particle swarm optimization algorithm.

[0087] Exemplarily, based on magnetic field data, the current of the cable phase core is inverted using a particle swarm optimization algorithm, including:

[0088] Firstly, the magnetic field data is used to solve the tangential magnetic induction intensity equation at the location of the magnetic sensor to determine the initial three-phase current of the cable phase core.

[0089] For three-phase cables, the magnetic field in the cable space is the superposition of the magnetic fields generated by the currents in each core line. It is impossible to measure the currents in each core line in the three-phase cable by relying only on the magnetic field information measured by a single magnetic sensor. Therefore, it is necessary to install multiple magnetic sensors around the cable to form a magnetic sensor array to obtain sufficient magnetic field data to invert the phase core current of the three-phase cable.

[0090] For example, the actual device is equipped with four magnetic sensors. Figure 4 The cross section is shown, so only two are shown. Four magnetic sensors are embedded in the cable connector and are numbered S1-S4. Figure 5 The three-core cable connector simulation diagram shown can be placed anywhere on the surface of the three-core cable as long as the relative position is in accordance with Figure 5 The four magnetic sensors can be placed at the corresponding positions of the three-core cable connector at the angle intervals shown in the figure. There is no need to install them on the extension line of the line connecting the center of the cable connector and the center of the phase core. Point O is the center of the three-core cable connector, and points A, B, and C are the centers of the A, B, and C phase cores respectively. The distances from point O to the center of each phase core are r A 、r B 、r C , the radius of the cable is R. O is also the centroid of triangle ABC. The angles between OA, OB, OC and the positive direction of the x-axis are α, β, and γ, which differ by 120°. Figure 6 shown.

[0091] According to Ampere's law and cosine law, the magnetic induction intensity B1-B4 generated along the tangential direction at S1-S4 can be obtained as shown in equations (2) to (5). A ,I B ,I C The rotation angle α is an unknown quantity, the cable radius R, and the distance r from the cable center to the three-phase core center A 、r B 、r C The magnetic induction intensity B measured by the magnetic sensor is a known quantity. Solving this set of equations will yield the phase current of the cable.

[0092]

[0093]

[0094] Since there is a sinusoidal term about the rotation angle α in the formula, the equation group is nonlinear, and it is not easy to obtain the explicit relationship between the current and the magnetic induction intensity. The analytical solution of the nonlinear equation group is difficult to obtain. Therefore, the nonlinear least squares method can be used to solve the relevant equations. This embodiment uses the Newton-Raphson method for specific calculations to obtain the three-phase current.

[0095] Secondly, in order to further simplify the measurement device, the optimization algorithm is used to reduce the above four sensors to two. Assuming that B1 and B4 corresponding to S1 and S4 sensors are measured values, because the angle difference between the two is 120°, the measured magnetic induction intensity should be equal. The optimization algorithm is used for corresponding inverse fitting, and then the correct three-phase current can be obtained.

[0096] The preset rotation angle of the target sensor and the corresponding initial three-phase current of the cable phase core are set as particle variables, and the particle swarm optimization algorithm is used for back fitting to inversely perform the optimized three-phase current of the cable phase core.

[0097] The number of target sensors is 2, and the position angle between the two target sensors is 120°.

[0098] The optimization goal of the particle swarm optimization algorithm is to calculate the minimum value of h(x).

[0099] h(x)=|B1-B4| (6)

[0100] The main steps of the particle swarm algorithm include:

[0101] 1) Initializing particles: Initializing particles includes initializing random positions and velocities of particles. The particle variables involved in this embodiment are the rotation angle α and the current I (assuming that the three-phase currents are balanced, i.e., equal in magnitude and 120° apart in angle).

[0102] 2) Determine the fitness of each particle.

[0103] 3) For each particle, compare the fitness value of the particle with the best position pbest it has experienced. If the fitness value is better, take the position corresponding to the fitness value of the particle as the current best position pbest.

[0104] 4) For each particle, compare the particle's fitness value with the best position experienced by gbest globally, and if it is better, reset the position of gbest.

[0105] 5) The velocity and position of the particle change according to the following equations (7) and (8).

[0106]

[0107] xid(t+1)=xid(t)+vid(t+1) (8)

[0108] Among them, ω is the inertia weight; vid(t) is the velocity of a particle at the tth iteration; pbest is the best position of a particle; xid(t) is the position of a particle at the tth iteration; gbest is the best position of the entire group; c1 and c2 are acceleration constants; rand() is a random value that varies in the range [0,1].

[0109] 6) If the end condition is not met, return to step 2). The end condition is usually to achieve a good enough fit or to reach the default maximum number of iterations G. max .

[0110] This embodiment can use the above method to measure the current of the three-core cable connector based on two magnetic sensors, reducing the above four magnetic sensors to two, thereby reducing the number of magnetic sensors, further simplifying the measuring device, and reducing equipment costs.

[0111] Exemplarily, in step 203, a specific implementation method of obtaining the temperature of the cable joint under different load current conditions and the stress of the cable joint under different temperature conditions is introduced.

[0112] Based on the current of the cable core, the temperature of the cable joint under different load current conditions is obtained by finite element simulation, including:

[0113] Firstly, the finite element simulation software is used to establish the three-dimensional geometric model of the cable connector.

[0114] At present, the intermediate joints of XLPE (cross-linked polyethylene) power cables are mainly prefabricated. According to different structural forms, prefabricated cable connectors are divided into assembled prefabricated and integral prefabricated types. The integral prefabricated cable connector has fewer insulation interfaces and is easy to install on site, so it is widely used in the power industry. In this embodiment, taking the integral prefabricated connector as an example, finite element simulation software is used to perform three-dimensional geometric modeling of the integral prefabricated connector, and its temperature field is simulated and analyzed. Among them, the geometric parameters of the conductor radius, inner semi-conductive layer thickness, insulation layer, outer semi-conductive layer thickness, metal sheath thickness and outer sheath thickness of the cable connector are mainly set to obtain a preliminary three-dimensional geometric model of the integral prefabricated connector, such as Figure 7 shown.

[0115] After the geometric parameters are set, the material properties need to be defined. Because the material library in the finite element simulation software allows users to add it directly for use. If the required material is not available in the material library, users can also add it by customizing the empty material in the module. After adding the material, the basic parameters of the material can be set. Mainly set the parameters for the copper core, inner semi-conductive layer, XLPE, outer semi-conductive layer, metal sheath, and outer sheath.

[0116] Secondly, based on the current of the cable phase core, the thermal conduction control equations and boundary conditions of the steady-state temperature field of the three-dimensional geometric model of the cable joint are set.

[0117] For example, after the three-dimensional geometric model of the cable intermediate joint is established by finite element simulation software, the boundary conditions of the model need to be set. The heat generated by the cable joint mainly comes from the conductor loss and the dielectric loss of the insulation structure. This heat is continuously transferred through the heat exchange process, and finally reaches a thermal equilibrium state to form the temperature field of the cable joint. Therefore, in the analysis and solution process, it is necessary to set the heat transfer boundary conditions.

[0118] The conductor loss of the cable joint is the main heat source of the joint temperature rise. According to Joule's law, the heat loss generated when the current passes through the conductor can be expressed as:

[0119] Q=I 2 R (9)

[0120] Among them, Q represents the heat generated when current passes through the conductor; I is the current passing through the conductor; and R is the AC resistance value of the conductor per unit length.

[0121] When the cable conductor passes through the alternating current, the energy loss of the cable insulation layer under the action of the AC voltage is called the insulation dielectric loss. The specific calculation formula is:

[0122]

[0123] Among them, c represents the cable capacitance per unit length; ω is the angular frequency; U0 is the phase voltage applied to the cable; and tanδ is the dielectric loss factor of the specific material.

[0124] Heat conduction is a heat transfer process that occurs inside the same object or between two different objects in contact with each other. It generates energy transfer through the microscopic movement of particles. The specific expression is:

[0125]

[0126] Among them, q is the heat flux density; φ represents the heat flow on area A; λ is the thermal conductivity of the object; T is the temperature; and x is the spatial coordinate. In the temperature field simulation of the cable joint, heat conduction exists between the various structures inside the joint and the objects in contact with the outer surface of the joint.

[0127] According to the heat transfer theory, the temperature field of the cable joint belongs to the heat dissipation balance process in a certain area. Its internal heat source is the heat generated by the core loss and the insulation medium loss, and the heat is transferred by heat conduction. The heat conduction control equation of the steady-state temperature field of the three-dimensional geometric model of the cable joint is expressed as:

[0128]

[0129] Where T is temperature; x, y, z are the spatial coordinates of the three-dimensional geometric model; λ is the thermal conductivity; Q v is the volume heat generation rate;

[0130] When solving the thermal conductivity control equation of the cable joint temperature field, it is necessary to set the boundary conditions for the solution. The boundary conditions are expressed as:

[0131]

[0132] Among them, q is the normal heat flux density; n is the boundary normal direction; r is the normal direction; is the temperature gradient along the normal direction to the boundary.

[0133] Finally, simulation analysis is performed based on the thermal conduction control equation and boundary conditions of the steady-state temperature field of the three-dimensional geometric model of the cable joint to obtain the temperature of the cable joint under different load current conditions.

[0134] Through simulation analysis, the temperature field distribution inside the cable connector can be obtained when the cable connector is running under specific current. Typical temperature distribution results are as follows: Figure 8 As shown. Among them, the copper core and the conductive layer are red, which are areas with higher temperatures. Through the above settings, the cable joint temperature under different load current conditions can be obtained, thereby establishing the relationship between the current and the temperature of the cable joint.

[0135] The temperature field simulation of a single-core cable joint is similar to that of a three-core cable joint. Both of them build a geometric model according to the above process, define the properties of related materials, and then set boundary conditions. After that, the internal temperature field distribution can be obtained.

[0136] Exemplarily, in step 203, finite element simulation is used to obtain cable joint stress under different temperature conditions, including:

[0137] Based on the temperature of the cable joint under different load current conditions, the finite element simulation is used to obtain the stress of the cable joint under different temperature conditions.

[0138] Based on the temperature of the cable joint under different load current conditions, finite element simulation is used to obtain the stress of the cable joint under different temperature conditions, including:

[0139] Firstly, the finite element simulation software is used to establish the three-dimensional geometric model of the cable connector.

[0140] Exemplarily, similar to the above-mentioned current and temperature simulation, the three-dimensional geometric model including the cable joint stress also needs to establish a geometric model, define material properties and set boundary conditions. The current-temperature-stress simulation part as well as the geometric model and define material properties are similar to the above process.

[0141] Secondly, based on the temperature of the cable joint under different load current conditions, the node equilibrium equations of the three-dimensional geometric model of the cable joint are set.

[0142] The cable joint will generate thermal strain when the temperature changes due to thermal expansion and contraction. The layers of the structure are mutually constrained and the temperature distribution is uneven. The strain cannot develop freely, which leads to thermal stress. At this time, the strain of each unit is the superposition of the thermal strain caused by temperature change and the elastic strain caused by stress. For a certain node in the cable joint structure, the equilibrium equation can be constructed as shown in formula (14).

[0143] The node equilibrium equation of the three-dimensional geometric model of the cable joint is expressed as:

[0144] dσ h =Kdδ (14)

[0145] Among them, dσ h is the node temperature load increment; K is the node stiffness matrix; dδ is the node deformation increment.

[0146] dσ h =∫B T CdTdV (15)

[0147] K = ∫B T DBdV (16)

[0148] Where B is the transformation matrix of strain ε and deformation δ; V represents volume; C is the matrix related to temperature, which can be obtained by formula (17).

[0149]

[0150] Among them, α is the thermal expansion coefficient vector; D is the elastic matrix, which is determined by the elastic modulus and Poisson's ratio; σ is the stress tensor.

[0151] Finally, simulation analysis is carried out based on the node equilibrium equation of the three-dimensional geometric model of the cable joint to obtain the cable joint stress under different temperature conditions.

[0152] Through simulation analysis, the stress field distribution inside the cable connector can be obtained when it is running under specific conditions. Typical stress distribution results are as follows: Fig. 9 shown.

[0153] Through the above settings, the stress distribution of the cable joint under different temperature conditions can be obtained, so as to establish the relationship between temperature and joint stress, and the electrical-thermal-mechanical relationship of the cable joint can be established, so as to obtain the relationship between the magnetic field and stress, and thus obtain the stress distribution through the magnetic field.

[0154] The electrical-thermal-force field simulation method for single-core cable joints and three-core cable joints is similar to that for single-core cables. It also begins with establishing a geometric model, defining the properties of related materials, and then setting boundary conditions. After that, the internal stress field distribution can be obtained.

[0155] This embodiment further uses finite element simulation to establish the relationship between the stress and current of the cable joint, and obtains the stress distribution and temperature distribution of the cable joint, that is, the current, temperature and stress distribution can be measured through the magnetic field of the cable joint.

[0156] The embodiments of the present application simultaneously measure the current, temperature and stress of the cable joint, and are applicable to single-core cable joints and three-core cable joints. Compared with the independent measurement system of the traditional method, this method uses a simulation model to realize a set of magnetic sensors to measure multiple cable state quantities, which is simpler.

[0157] See also Fig.10 An embodiment of the present application provides a device for measuring cable joint parameters, which implements the method for measuring cable joint parameters as in the above embodiment. The device for measuring cable joint parameters includes a magnetic field data acquisition module 301, a current determination module 302, a temperature and stress determination module 303 and a current-temperature-stress coupling module 304.

[0158] The magnetic field data acquisition module 301 is used to acquire the magnetic field data of the cable joint; the magnetic field data is acquired by installing a preset number of magnetic sensors in the circumference of the cable joint.

[0159] The current determination module 302 is used to invert the current of the cable phase core based on the magnetic field data and obtain the corresponding relationship between the magnetic field data and the current.

[0160] The temperature and stress determination module 303 is used to obtain the temperature of the cable joint under different load current conditions and the stress of the cable joint under different temperature conditions by using finite element simulation based on the current of the cable phase core.

[0161] The current-temperature-stress coupling module 304 is used to determine the electro-thermal-mechanical coupling data of the magnetic field and the current, temperature, and stress based on the corresponding relationship between the magnetic field data and the current, the temperature of the cable joint under different load current conditions, and the stress of the cable joint under different temperature conditions; the electro-thermal-mechanical coupling data is used to analyze the operating status of the cable joint.

[0162] Exemplarily, in the current determination module 302, the current of the cable phase core is inverted based on the magnetic field data, including: if the cable joint is a three-core cable joint, the current of the cable phase core is inverted based on the magnetic field data using a particle swarm optimization algorithm.

[0163] Exemplarily, based on magnetic field data, the current of the cable phase core is inverted using a particle swarm optimization algorithm, including:

[0164] Using magnetic field data, solve the tangential magnetic induction intensity equation at the location of the magnetic sensor to determine the initial three-phase current of the cable phase core;

[0165] The preset rotation angle of the target sensor and the corresponding initial three-phase current of the cable phase core are set as particle variables, and the particle swarm optimization algorithm is used for back fitting to inversely perform the optimized three-phase current of the cable phase core; the number of target sensors is 2; and the position angle between the two target sensors is 120°.

[0166] Exemplarily, in the temperature and stress determination module 303, based on the current of the cable phase core, the temperature of the cable joint under different load current conditions is obtained by finite element simulation, including:

[0167] Use finite element simulation software to establish a three-dimensional geometric model of the cable connector;

[0168] Based on the current of the cable core, the heat conduction control equation and boundary conditions of the steady-state temperature field of the three-dimensional geometric model of the cable joint are set;

[0169] The thermal conductivity control equation and boundary conditions of the steady-state temperature field of the three-dimensional geometric model of the cable joint are simulated and analyzed to obtain the temperature of the cable joint under different load current conditions.

[0170] Exemplarily, the heat conduction control equation of the steady-state temperature field of the three-dimensional geometric model of the cable joint is expressed as:

[0171]

[0172] Where T is temperature; x, y, z are the spatial coordinates of the three-dimensional geometric model; λ is the thermal conductivity; Q v is the volume heat generation rate;

[0173] The boundary conditions are expressed as:

[0174]

[0175] Where q is the normal heat flux; n is the boundary normal direction; r is the normal direction, is the temperature gradient along the normal direction to the boundary.

[0176] Exemplarily, in the temperature and stress determination module 303, finite element simulation is used to obtain the cable joint stress under different temperature conditions, including:

[0177] Based on the temperature of the cable joint under different load current conditions, the finite element simulation is used to obtain the stress of the cable joint under different temperature conditions.

[0178] Exemplarily, based on the temperature of the cable joint under different load current conditions, finite element simulation is used to obtain the stress of the cable joint under different temperature conditions, including:

[0179] Use finite element simulation software to establish a three-dimensional geometric model of the cable connector;

[0180] Based on the temperature of the cable joint under different load current conditions, the node equilibrium equation of the three-dimensional geometric model of the cable joint is set;

[0181] The simulation analysis is carried out based on the node equilibrium equation of the three-dimensional geometric model of the cable joint to obtain the cable joint stress under different temperature conditions.

[0182] Exemplarily, the node equilibrium equation of the three-dimensional geometric model of the cable connector is expressed as:

[0183] dσ h =Kdδ (14)

[0184] Among them, dσ h is the node temperature load increment; K is the node stiffness matrix; dδ is the node deformation increment.

[0185] Exemplarily, in the magnetic field data acquisition module 301, when the cable connector is a single-core cable connector, a magnetic sensor is embedded in the cable connector, and the magnetic field data includes the magnetic induction intensity of the embedded position measured by the magnetic sensor;

[0186] When the cable connector is a three-core cable connector, a magnetic sensor array formed by four magnetic sensors is embedded in the cable connector, and the magnetic field data includes the tangential magnetic induction intensity at the locations of the four magnetic sensors.

[0187] It should be noted that, although several units / modules or sub-units / modules of the measuring device for cable joint parameters are mentioned in the above detailed description, such division is merely exemplary and not mandatory. In fact, according to the embodiments of the present application, the features and functions of two or more units / modules described above may be embodied in one unit / module. Conversely, the features and functions of one unit / module described above may be further divided into multiple units / modules for embodiment.

[0188] In addition, although the operations of the method of the present application are described in a specific order in the drawings, this does not require or imply that the operations must be performed in this specific order, or that all the operations shown must be performed to achieve the desired results. Additionally or alternatively, some steps may be omitted, multiple steps may be combined into one step, and / or one step may be decomposed into multiple steps.

[0189] The present application also provides a computer-readable storage medium, in which computer-executable instructions are stored. When a processor executes the computer-executable instructions, the cable joint parameter measurement method provided in the above embodiment of the present application is implemented.

[0190] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0191] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A method for measuring cable joint parameters, characterized in that: include: Get the magnetic field data of the cable joint; The magnetic field data is obtained by installing a preset number of magnetic sensors in the circumference of the cable connector; Inverting the current of the cable phase core based on the magnetic field data, and obtaining the corresponding relationship between the magnetic field data and the current; Based on the current of the cable phase core, the temperature of the cable joint under different load current conditions and the stress of the cable joint under different temperature conditions are obtained by finite element simulation; Based on the corresponding relationship between the magnetic field data and the current, the temperature of the cable joint under the different load current conditions and the stress of the cable joint under different temperature conditions, the electro-thermal-mechanical coupling data of the magnetic field and the current, temperature and stress are determined; The electrical, thermal and mechanical coupling data is used to measure the real-time parameters of the cable joint.

2. The method for measuring cable joint parameters according to claim 1, characterized in that: The inverting the current of the cable phase core based on the magnetic field data comprises: If the cable connector is a three-core cable connector, the current of the cable phase core is inverted using a particle swarm optimization algorithm based on the magnetic field data.

3. The method for measuring cable joint parameters according to claim 2, characterized in that: The method of inverting the current of the cable phase core based on the magnetic field data by using a particle swarm optimization algorithm includes: Using the magnetic field data, solving the tangential magnetic induction intensity equation at the location of the magnetic sensor, and determining the initial three-phase current of the cable phase core; The preset rotation angle of the target sensor and the corresponding initial three-phase current of the cable phase core are set as particle variables, and the particle swarm optimization algorithm is used for back fitting to inversely perform the optimized three-phase current of the cable phase core; the number of the target sensors is 2; and the position angle between the two target sensors is 120°.

4. The method for measuring cable joint parameters according to claim 1, characterized in that: The method of using finite element simulation to obtain the temperature of the cable joint under different load current conditions based on the current of the cable phase core includes: Using finite element simulation software to establish a three-dimensional geometric model of the cable connector; Based on the current of the cable phase core, setting the heat conduction control equation and boundary conditions of the steady-state temperature field of the three-dimensional geometric model of the cable joint; A simulation analysis is performed based on the heat conduction control equation and boundary conditions of the steady-state temperature field of the three-dimensional geometric model of the cable joint to obtain the temperature of the cable joint under different load current conditions.

5. The method for measuring cable joint parameters according to claim 4, characterized in that: The heat conduction control equation of the steady-state temperature field of the three-dimensional geometric model of the cable joint is expressed as: Where T is temperature; x, y, z are the spatial coordinates of the three-dimensional geometric model; λ is the thermal conductivity; Q v is the volume heat generation rate; The boundary condition is expressed as: Among them, q is the normal heat flux density; n is the boundary normal direction; r is the normal direction.

6. The method for measuring cable joint parameters according to claim 1, characterized in that: Finite element simulation is used to obtain the cable joint stress under different temperature conditions, including: Based on the temperature of the cable joint under the different load current conditions, the cable joint stress under the different temperature conditions is obtained by finite element simulation.

7. The method for measuring cable joint parameters according to claim 6, characterized in that: The method of obtaining the cable joint stress under the different temperature conditions by finite element simulation based on the temperature of the cable joint under the different load current conditions includes: Using finite element simulation software to establish a three-dimensional geometric model of the cable connector; Based on the temperature of the cable joint under the different load current conditions, setting a node balance equation of the three-dimensional geometric model of the cable joint; A simulation analysis is performed based on the node equilibrium equations of the three-dimensional geometric model of the cable joint to obtain the cable joint stress under different temperature conditions.

8. The method for measuring cable joint parameters according to claim 7, characterized in that: The node equilibrium equation of the three-dimensional geometric model of the cable connector is expressed as: dσ h =Kdδ Among them, dσ h is the node temperature load increment; K is the node stiffness matrix; dδ is the node deformation increment.

9. The method for measuring cable joint parameters according to claim 1, characterized in that: When the cable connector is a single-core cable connector, a magnetic sensor is embedded in the cable connector, and the magnetic field data includes the magnetic induction intensity of the embedded position measured by the magnetic sensor; When the cable connector is a three-core cable connector, a magnetic sensor array formed by four magnetic sensors is embedded in the cable connector, and the magnetic field data includes the tangential magnetic induction intensity at the locations of the four magnetic sensors.

10. A device for measuring cable joint parameters, characterized in that: The method for measuring the cable joint parameters according to any one of claims 1 to 9 is implemented, and the device for measuring the cable joint parameters comprises: A magnetic field data acquisition module, used to acquire magnetic field data of the cable joint; the magnetic field data is obtained by installing a preset number of magnetic sensors in the circumference of the cable joint; A current determination module, used to invert the current of the cable phase core based on the magnetic field data, and obtain the corresponding relationship between the magnetic field data and the current; A temperature and stress determination module, used to obtain the temperature of the cable joint under different load current conditions and the stress of the cable joint under different temperature conditions by finite element simulation based on the current of the cable phase core; The current-temperature-stress coupling module is used to determine the electro-thermal-mechanical coupling data of the magnetic field and the current, temperature, and stress based on the corresponding relationship between the magnetic field data and the current, the temperature of the cable joint under the different load current conditions, and the stress of the cable joint under different temperature conditions; the electro-thermal-mechanical coupling data is used to analyze the operating status of the cable joint.

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