Simulation method for electric arc in contact closing process of switching device under impact current

Abstract

The invention provides a simulation method for an electric arc in the contact closing process of a switching device under impact current, and belongs to the technical field of electric arc simulation modeling. The simulation modeling method for the electric arc in the contact closing process of the switching device under the impact current comprises the following steps: selecting a spatial dimension according to the geometric characteristics of the electric arc to be researched, and establishing a geometric model by using COMSOL software; sequentially adding size parameters, substituting the size parameters into the geometric model, and setting materials required by the geometric model; adding a physical field interface of the simulation model; setting specific parameters and boundary conditions of each physical field interface, and adding multi-physical field coupling; transient research is added to the geometric model after grid division, a transient solver is configured, a result is calculated, and the change rule of the arc temperature, the arc voltage and current curve and the erosion area of the arc to the contact is analyzed. The method can effectively reduce the experiment cost, reduce the resource loss, optimize the product design of the switching device, and prolong the service life.

Description

Technical Field

[0001] The present invention relates to a simulation method for simulating an arc in a contact closing process of a switch under an impact current condition, and more particularly to simulating the behavior of arc plasma by simulating the impact current by applying a current source waveform and simulating the contact closing process by introducing a motion function. Background Art

[0002] At present, switching electrical appliances are widely used in industrial automation, energy systems, transportation, household appliances, and communication equipment. Their main functions are to control the on and off of circuits, protect equipment from overload, short circuit and other faults, and provide power isolation and fault protection in emergency situations. As a key component of switching electrical appliances, contacts play the role of isolating, connecting and disconnecting circuits. During the process of contact breaking or closing, the voltage may break through the air to form an arc, causing the surface material of the contact to melt, and then cause contact failure. Especially in new energy vehicles, due to the presence of capacitive loads in the circuit, a large impact current will be generated when the contact is closed. The closing arc caused by it will cause contact welding and adhesion failure, which has become a major failure type. Therefore, it is of great significance to study the contact closing arc under impact current.

[0003] CN202310454688.X discloses a magnetohydrodynamic simulation modeling method suitable for the arc starting process of a switch arc, including establishing a circuit structure and a geometric model in the simulation software, defining the solution domain of electrodes and arc plasma, adding material properties and physical parameter constraints, and completing multi-frame simulation through meshing and transient research steps to obtain the initial value of the arc temperature, thereby improving the simulation accuracy and solving the problem that the circuit cannot be turned on at low temperatures.

[0004] CN202110421377.4 discloses an arc plasma simulation and analysis method involving the metallurgical industry, which specifically includes establishing a two-dimensional axisymmetric space and arc geometric model, setting material properties and multi-physical field parameters, meshing and solving the geometric model, generating arc temperature and current density distribution diagrams, and simulating the influence of current on arc characteristics.

[0005] CN202210577197.X proposed a method for obtaining the magnetohydrodynamic and circuit models of switchgear and performed field-circuit coupling simulation. The method takes into account the changes in the motion state of the fluid inside the arc to determine the impact of the DC current on the internal gas pressure and temperature of the equipment during the breaking process.

[0006] CN202410359696.0 discloses a circuit breaker arc simulation method, which establishes an arc magnetohydrodynamic model to describe the behavior of plasma in a magnetic field, and couples multiple physical fields such as electricity, magnetism, and heat with the model to accurately describe the circuit breaker breaking process, and obtains the dynamic characteristics of the arc by solving the model to optimize the circuit breaker design.

[0007] Inrush current is usually caused by instantaneous changes in energy in the circuit, such as capacitor charging, short circuit faults, etc. This current peak may cause burning and welding of the switch contacts, increase the arc burning energy, and thus increase the failure rate of the switch.

[0008] Current research focuses on the arc generated during the contact breaking process of switching electrical appliances under DC or AC conditions. However, due to the characteristics of high amplitude and short duration of impulse current, the arc phenomenon during the contact closing process is more serious, so in-depth research and analysis is needed.

[0009] In view of the specific situation of switching electrical appliances in actual applications, the causes of impulse current in the circuit are complex and diverse, which may involve factors such as transient changes in energy, changes in load characteristics, and short-circuit faults, making it difficult to determine its specific waveform characteristics. In addition, the impulse current usually has a high peak value and a very short duration, usually only a few milliseconds to tens of milliseconds, and then decays rapidly. This characteristic causes the arc phenomenon in the contact closing process to be more serious than the opening process. Summary of the invention

[0010] In order to make up for the above shortcomings, the present application establishes a simulation model for simulating the arc in the contact closing process of a switching electrical appliance under an impulse current, aiming to simulate the arc behavior in the contact closing process under impulse current conditions.

[0011] Among them, the electrical contact experiment is designed according to the common failure types of switch contacts in practical applications; the contacts can be reliably disconnected and closed under normal working conditions, but when there is a capacitive load in the circuit or a short circuit occurs, a huge impact current will pass through the contacts at the moment of connection. The arc generated will cause serious welding of the contacts, or even adhesion failure, making it impossible to disconnect reliably. The electrical contact experiment verifies that switching devices often fail due to adhesion after passing through a single impact current. In addition, during the contact connection process, the spacing between the moving and static contacts decreases from the maximum opening distance to zero, and the peak moment of the impact current will be experienced. At this time, the arc generated is the most violent, and the contact erosion caused is also the most serious. Therefore, it is of great significance to study the single arc generated during the movement of the moving contact from the maximum opening distance to the static contact.

[0012] The embodiment of the present application provides a simulation modeling method for arc in the contact closing process of a switching device under an inrush current, which is characterized by comprising the following steps: Step 1: Select a spatial dimension according to the arc geometric characteristics to be studied, wherein the spatial dimension includes two-dimensional, two-dimensional axisymmetric and three-dimensional dimensions; establish a geometric model using COMSOL software, and model the model according to the actual contact shape, wherein the model includes a moving contact, a stationary contact and an air domain; Step 2: Add dimension parameters in sequence and substitute them into the geometric model. The dimension parameters include the width and height of the moving contact and the static contact, and set the range of the air domain according to actual needs to achieve accurate modeling of different contact structures. Step 3: Set the materials required for the model, add materials from the material library and manually define the material application domain to adapt to the flexible simulation application of different contact materials. The specific material type can be selected according to the actual contact material; Step 4: Add the physical field interfaces of the simulation model, including the current interface, laminar flow interface, circuit interface, fluid heat transfer interface, magnetic field interface, and dynamic mesh interface. You can also add other physical field interfaces for simulation research and analysis. Step 5: Set the specific parameters and boundary conditions of each physical field interface and add multi-physics field coupling; simulate the discharge process of arc plasma under impulse current by setting the coupling relationship between multi-physics field interfaces; The circuit interface simulates the impact current by adding a current source. The current source waveform function is based on the actual impact current electrical contact experimental data. First, the capacitor is charged to the specified initial voltage, and then the switch is placed in the capacitor discharge loop. The peak value of the impact current is controlled by adjusting the size of the external resistance. In the experiment, an oscilloscope is used to collect current values ​​in real time, and these measured data are imported into the circuit interface of the COMSOL software through the interpolation function. The specific parameters of the experiment can be set by yourself.

[0013] Among them, the dynamic mesh interface realizes the contact closing process by defining the velocity function of the moving contact. The velocity change can be defined by a piecewise function, so that the moving contact and its connected area move toward the static contact. The static contact area is set as a fixed mesh, and all other areas are set as free deformation domains to ensure that the mesh can deform smoothly with the displacement of the moving contact. Finally, the contact closing process is realized by changing the moving contact velocity function. The specific velocity function can be set by yourself.

[0014] Step 6: Add transient research to the geometric model after mesh analysis, configure the transient solver, calculate the results and analyze the arc temperature, arc voltage-current curve, and change law of arc erosion area on the contact under different impulse currents, etc., and perform corresponding simulation calculation and analysis according to actual needs.

[0015] In a preferred embodiment of the present invention, step 2 comprises: Based on the size range of the switch bridge contact, the width of the static contact is set to 2mm-10mm; the height is 2mm-5mm; the width of the moving contact is 2mm-10mm; the height is 1mm-5mm; the remaining area is the gas domain, the width of the gas domain is greater than the contact width, and the height of the gas domain is equal to the sum of the heights of the moving and static contacts; Applicable contact types include but are not limited to wedge contacts, sliding contacts, knife contacts, etc., all of which can be simulated and modeled.

[0016] In a preferred embodiment of the present invention, step three comprises: The phase change parameters of the contact material from solid to liquid, including melting point and latent heat coefficient, need to define the necessary physical property parameters according to the type of physical field interface added by the user, and the corresponding material can be selected according to the actual situation; When adding model materials, both the solid and liquid physical property parameters of the contact material need to be added accordingly.

[0017] In a preferred embodiment of the present invention, step five comprises: In COMSOL software, the initial temperature of the moving and static contacts is set to room temperature 293.15K. To ensure arc starting, the initial arc temperature in the central area of ​​the air domain is assumed to be (6000-10000)K. In the circuit interface, first set the global current conservation, connect the anode to the current source, and the cathode to the ground to form a complete loop. Simulate the impact current by manually adding different current source waveform functions to meet various experimental needs. Based on the actual measurement data of the switching device in the impact current electrical contact experiment, first measure the current value at each moment in the experiment through an oscilloscope, record the corresponding data of time and current, and then import these data into the definition function part of the COMSOL software to add an interpolation function. In addition, the current function can be customized according to actual needs, including but not limited to any waveform such as sine wave, triangle wave, rectangular wave, step wave, etc. Each waveform form can simulate different types of impact current. For example, sine waves are used in periodic change scenarios, rectangular waves are suitable for instantaneous impacts, and step waves are used in segmented change scenarios to meet the simulation needs of impact current in different experimental scenarios.

[0018] Laminar interface gas pressure setting, set the pressure range of the arc extinguishing medium, i.e. the air domain, to 1.5-5 standard atmospheres. Manually define fluid properties, such as fluid discretization settings, constitutive relations and other important parameters, and set the magnitude and direction of the Lorentz force, define the expression of the Lorentz force, and simulate the effect of electromagnetic force on the fluid; By setting the dynamic mesh interface, manually add the velocity function to simulate the characteristics of the arc plasma during the closing (i.e., connection) process of the switch contacts after being subjected to the impact current. The dynamic mesh interface sets the static contact area as a fixed mesh, and the moving contact and its related areas as a free deformation domain to ensure that the mesh can deform smoothly with the displacement of the moving contact, avoiding mesh distortion and solver convergence problems. The speed change of the moving contact can be defined by a piecewise function to ensure that it maintains a smooth movement during the closing process. The velocity function can be flexibly adjusted according to the actual motion trajectory to accurately reflect the movement behavior of the contact under different conditions.

[0019] In a preferred embodiment of the present invention, step five comprises: In the magnetic field part, set the initial value of magnetic potential loss to 0, that is, the model boundary is magnetically insulated, then set the out-of-plane vector potential and apply the transverse magnetic field, and manually define the value of the magnetic field strength. The magnetic field strength is defined as 1mT-10mT, which is used in the expression of the Lorentz force in the laminar flow module; Through multi-physics field coupling, including Lorentz force, balanced discharge heat source, Lorentz force, non-isothermal flow and other multi-physics field coupling, initial values ​​and boundary conditions are manually added to improve simulation accuracy.

[0020] In a preferred embodiment of the present invention, step six comprises: Mesh division, including triangular and quadrilateral meshes, needs to be adjusted manually. The convergence of the calculation results can be improved by changing the fineness of the mesh. The finer the mesh distribution, the better the convergence, but at the same time the amount of calculation will also be greater. The calculation situation should be considered comprehensively. The amount of calculation should be reduced as much as possible while ensuring convergence, so as to optimize the simulation efficiency.

[0021] The advantages of the present invention are: 1. The present invention adopts a method of setting the current source waveform to simulate the impact current, which can be set based on the actual current waveform obtained in the experiment, so that the simulation result is more in line with the actual working condition and the simulation accuracy is significantly improved.

[0022] 2. The present invention is to perform arc simulation modeling during the contact closing process. By setting the moving contact speed function to control the movement speed and direction of the moving contact, the generation, development and extinction of the arc during the contact closing process can be accurately simulated, and then the influence of the impact current on the contact can be reflected, which is helpful to optimize the design of the switching electrical appliance.

[0023] 3. The present invention has been verified many times, and the current source waveform that can be used includes but is not limited to any waveform such as sine wave, triangle wave, rectangular wave, step wave, etc., which successfully solves the problem that the impulse current is difficult to apply in the simulation model. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the implementation methods of the present application, the drawings required for use in the implementation methods will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 is the two-dimensional contact geometric model of Example 1; Figure 2 is the current source waveform function of Example 1; Figure 3 is the moving contact speed function of Example 1; Figure 4 The arc temperature and contact temperature variation curve of Example 1; Figure 5 Arc erosion area curve of Example 1 Figure 6 is the two-dimensional contact geometric model of Example 2; Figure 7 is the current source waveform function of Example 2; Figure 8 is the moving contact speed function of Example 2; Fig. 9 The arc temperature and contact temperature variation curve of Example 2; Fig.10 This is the arc erosion area curve of Example 2. DETAILED DESCRIPTION

[0026] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0027] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0028] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application.

[0029] Example 1: peak value of impulse current 1000A; See also Figure 1-Figure 5 The present invention provides a simulation method for the arc in the closing process of the contact of a switch electrical appliance under an impact current. According to the geometric characteristics of the arc to be studied, the corresponding spatial dimension is selected to construct a geometric model identical to the actual switch electrical appliance contact; the spatial dimension can be selected as two-dimensional, two-dimensional axisymmetric or three-dimensional; firstly, the two-dimensional spatial dimension is selected to improve the calculation efficiency. Establish a geometric model and set the model size. The geometric model includes a moving contact, a static contact and a gas domain. The actual measured values ​​of the switch electrical appliance contact are substituted: the static contact size is set to 2mm in width and 2mm in height, the moving contact size is set to 2mm in width and 1mm in height, and the remaining area is the gas domain. The range of the gas domain is set according to actual needs to achieve accurate modeling of different contact structures. Applicable contact types include but are not limited to wedge contacts, sliding contacts, knife contacts, etc., which can all be simulated and modeled; the initial opening distance is set to 2mm, the geometric model is imported into the COMSOL software, the relevant parameters such as the contact size are set, and the anode and cathode domains in the geometric model are defined to ensure the integrity and accuracy of the model.

[0030] The moving contact and the stationary contact are initially in a separated position, the moving contact moves from the maximum opening distance position toward the stationary contact, and the initial distance between the two contacts is set to the maximum opening distance between the moving and stationary contacts; Manually add the materials and physical parameters required in the geometric model. Select and add the solid and liquid physical parameters of copper-based materials and silver-based materials according to the actual contact materials of the switch electrical appliance, including density, electrical conductivity, constant-pressure heat capacity, etc., as well as arc-extinguishing media with hydrogen as the main component, including density, thermal conductivity, dynamic viscosity and other physical properties; when adding model materials, both the solid and liquid properties of the contact materials need to be added accordingly.

[0031] Add various physical field modules, including AC / DC, heat transfer, fluid flow, etc.; Add physical field interfaces to the model, including electric current interface (ec), laminar flow interface (spf), circuit interface (cir), fluid heat transfer interface (ht), magnetic field interface (mf) and dynamic mesh interface (ale), etc. You can also add other physical field interfaces for simulation research and analysis; Set the specific parameters and boundary conditions of each physical field interface, and set the coupling relationship between multiple physical field interfaces to simulate the discharge process of arc plasma under impulse current; Among them, the circuit interface (cir) simulates the impact current by adding a current source. The source type is set to a generalized source. The current source is connected to the anode in the geometric model, and the cathode is grounded. The waveform of the current source is based on the actual measurement data in the switching electrical appliance impact current experiment. First, the current value at each moment in the experiment is measured by an oscilloscope, and the corresponding data of time and current are recorded. Then these data are imported into the definition function part of the COMSOL software, and the interpolation function is added, and it is ensured that the interpolation function has a valid value within the total calculation time. Define the name and variable of the interpolation function, and finally set the current of the generalized source to the interpolation function through the circuit interface (cir), that is, the waveform of the current source in the simulation model is input according to the current data measured in the experiment, and the setting of the current source is completed. The specific parameters of the experiment can be set by yourself.

[0032] Among them, the dynamic mesh interface (ale) first selects the mesh smoothing type to ensure the smoothness of the mesh during deformation. Set the static contact to a fixed mesh, specify the mesh displacements of the static contact and its connected areas in the x and y directions to be 0, and ensure that the static contact position remains unchanged. All other areas except the static contact are set as free deformation domains, allowing the meshes in these areas to deform freely according to the movement of the dynamic contact. Specify the velocity function of the mesh of the dynamic contact and its connected areas in the x and y directions as a piecewise function to ensure that the movement of the dynamic contact is smooth and without mutations. By setting the velocity function to control the movement direction and velocity of the dynamic contact, the opening distance between the dynamic and static contacts becomes smaller, simulating the contact closing process. The specific velocity function can be set by yourself.

[0033] In the circuit interface (cir), first set the global current conservation, connect the anode to the current source, and the cathode to the ground to form a complete loop. Simulate the impact current by manually adding different current source waveform functions to meet various experimental needs. Based on the actual measurement data of the switching device in the impact current electrical contact experiment, first measure the current value at each moment in the experiment through an oscilloscope, record the corresponding data of time and current, and then import these data into the definition function part of the COMSOL software to add an interpolation function. In addition, the current function can be customized according to actual needs, including but not limited to any waveform such as sine wave, triangle wave, rectangular wave, step wave, etc. Each waveform form can simulate different types of impact current. For example, sine waves are used in periodic change scenarios, rectangular waves are suitable for instantaneous impacts, and step waves are used in segmented change scenarios to meet the simulation needs of impact current in different experimental scenarios.

[0034] By setting the dynamic mesh interface (ale), manually add the velocity function to simulate the characteristics of the arc plasma during the closing (connection) process of the switch contacts after the impact current. The dynamic mesh interface (ale) sets the static contact area as a fixed mesh, and the moving contact and its related areas as a free deformation domain to ensure that the mesh can deform smoothly with the displacement of the moving contact, avoiding mesh distortion and solver convergence problems. The speed change of the moving contact can be defined by a piecewise function to ensure that it maintains a smooth movement during the closing process. The velocity function can be flexibly adjusted according to the actual motion trajectory to accurately reflect the movement behavior of the contact under different conditions.

[0035] Add transient research to the meshed geometric model, configure the transient solver, calculate the results and analyze the arc temperature, arc voltage-current curve, and change law of arc erosion area on the contact under different impulse currents, etc., and perform corresponding simulation calculation and analysis according to actual needs.

[0036] Among them, by configuring the transient solver, the arc phenomenon during the contact closing process is deeply studied. Since the arc is compressed during the closing process and the computational grid undergoes free deformation, the calculation process is more complicated, and the linear solver and its error need to be properly adjusted. By reasonably setting the movement speed and path of the moving contact, it is ensured that the solver convergence problem will not be caused during the contact closing process. In addition, for the transient simulation of the arc during the closing process, it is necessary to optimize the mesh division and time step configuration to ensure the stability of the transient solver under the complex multi-physical field coupling and avoid calculation errors during the simulation process.

[0037] In the solid and fluid heat transfer module, first select the temperature discretization as linear units, with the dependent variable being temperature T. Then set the initial values ​​of the moving and static contacts to 293.15K (i.e., room temperature 20°C), and set the initial value of 8000K at the center of the gas domain to ensure that the arc can be successfully started. Finally, set the phase change parameters of the contact material according to the material properties, such as the melting point from solid to liquid and the latent heat coefficient.

[0038] Gas pressure setting of laminar flow module, definition of fluid properties, selection of arc extinguishing medium (mainly hydrogen) as laminar gas domain, setting to incompressible flow, fluid discretization set to P1+P1 (velocity and pressure are both linear elements), constitutive relationship set to Newtonian fluid, static pressure selected as pressure, enable the option of suppressing backflow, use unit constraints on boundaries, set pressure value to 2.5atm (i.e. 2.5 standard atmospheric pressures), set the boundary conditions of moving and static contacts to slip, and at the same time, add volume force, i.e. the formula of Lorentz force, to simulate the effect of electromagnetic force on fluid.

[0039] Magnetic field settings, the initial magnetic vector potential is set to 0, the magnetic field is an out-of-plane vector potential (perpendicular to the two-dimensional plane), the background field selects full-field solution, the magnetic vector potential is discretized into linear units, satisfies Ampere's law, and the transverse magnetic field strength is set to 6mT.

[0040] Current and external circuit settings: First, set the potential discretization to linear units, the entire domain satisfies the law of current conservation, the static contact (anode) is connected to the current source, and the moving contact (cathode) is grounded. Manually add the current source waveform function so that the peak value of the external circuit impact current of the model reaches 1000A.

[0041] The specific process of obtaining the current source waveform function is as follows: through the impulse current electrical contact experiment, the capacitor is first charged to the specified initial voltage, and then the switch is placed in the capacitor discharge loop. The peak value of the impulse current is adjusted by adjusting the size of the external resistor, and the current value is collected in real time using an oscilloscope to obtain the waveform of the current changing with time. Finally, it is imported into the circuit interface (cir) in the COMSOL software through the interpolation function.

[0042] Dynamic mesh settings, first set the geometric shape function to 1, select the Laplace method for mesh smoothing type, and define the connection speed function of the moving contact. Set its action speed to 0.3m / s, the action time to 2.5ms, the moving contact and its connected area move along the y-axis toward the static contact, and define the speed change of the moving contact through a piecewise function. In this embodiment, the moving contact moves at a constant speed of 0.3m / s to achieve the closing process of the moving and static contacts. In the dynamic mesh interface (ale), set the static contact area to a fixed mesh, and all other areas to free deformation to ensure that the mesh deforms smoothly with the displacement of the moving contact to avoid mesh distortion.

[0043] Multi-physics coupling, simulation involves the interaction of multiple physical fields, including Lorentz force, balanced discharge heat source, non-isothermal flow, etc. The mutual coupling between each physical field is manually added and set, so that these coupling phenomena can be fully simulated during the arc compression process; through multi-physics coupling, including Lorentz force, balanced discharge heat source, Lorentz force, non-isothermal flow and other multi-physics field coupling, manually add initial values ​​and boundary conditions to improve simulation accuracy.

[0044] For meshing, first select the user-controlled network and the calibration type is fluid dynamics, which is suitable for fluid and thermodynamic calculations. The finer the mesh distribution, the better the convergence, but at the same time the amount of calculation is also greater. Therefore, the calculation situation should be considered comprehensively to reduce the amount of calculation as much as possible under the premise of ensuring convergence. Therefore, a combination of triangular and quadrilateral meshes is used to divide the model. Manually adjust the fineness of the mesh, and locally encrypt the mesh in key areas such as the arc area and the edge of the contact to improve the calculation accuracy. In other areas, appropriately reduce the mesh density to reduce the amount of calculation. Ensure that the mesh is not distorted, meet the convergence requirements of the calculation results, and optimize computing resources and time; Configure the solver and select transient study, which is suitable for time-dependent transient analysis. Set the total simulation calculation time to 15ms and the time step to 0.01ms to capture the rapidly changing physical process during arc discharge. In order to ensure the accuracy and stability of the calculation results, set reasonable convergence criteria, including relative tolerance and absolute tolerance. The time stepping method selects the backward difference formula and limits the maximum and minimum time steps to prevent the calculation from being unstable due to too large a time step, or too long a calculation time due to too small a time step. For algebraic variables, set consistent initialization and use the backward Euler method for initialization. According to the model complexity and computing resources, appropriately adjust the memory allocation and parallel computing options to improve computing efficiency.

[0045] Example 2: peak value of impulse current 3000A; See also Figure 6-Figure 10The present invention provides a method for simulating arcs during the closing process of contacts of a switching device under an impact current. According to the geometric characteristics of the arc to be studied, the corresponding spatial dimension is selected to construct a geometric model identical to the actual contact of the switching device. First, a two-dimensional spatial dimension is selected to improve the calculation efficiency. A geometric model is established and the model size is set. The geometric model includes a moving contact, a static contact, and a gas domain. The actual measured values ​​of the contacts of the switching device are substituted: the static contact size is set to 2mm in width and 2mm in height, the moving contact size is set to 2mm in width and 1mm in height, and the remaining area is the gas domain. The range of the gas domain is set according to actual needs to achieve accurate modeling of different contact structures. The initial opening distance is set to 2mm. The geometric model is imported into the COMSOL software, the contact size and other related parameters are set, and the anode and cathode domains in the geometric model are defined to ensure the integrity and accuracy of the model.

[0046] The moving contact and the stationary contact are initially in a separated position, the moving contact moves from the open distance position toward the stationary contact, and the initial distance between the two contacts is set to the maximum open distance between the moving and stationary contacts; Manually add the materials and physical parameters required in the geometric model. Select and add the solid and liquid physical parameters of copper-based materials and silver-based materials according to the actual contact materials of the switch electrical appliance, including density, electrical conductivity, constant-pressure heat capacity, etc., as well as arc-extinguishing media with hydrogen as the main component, including density, thermal conductivity, dynamic viscosity and other physical properties; when adding model materials, both the solid and liquid properties of the contact materials need to be added accordingly.

[0047] Add various physical field modules, including AC / DC, heat transfer, fluid flow, etc.; Add physical field interfaces to the model, including electric current interface (ec), laminar flow interface (spf), circuit interface (cir), fluid heat transfer interface (ht), magnetic field interface (mf) and dynamic mesh interface (ale), etc. You can also add other physical field interfaces for simulation research and analysis; Set the specific parameters and boundary conditions of each physical field interface, and set the coupling relationship between multiple physical field interfaces to simulate the discharge process of arc plasma under impulse current; Among them, the circuit interface (cir) simulates the impact current by adding a current source. The source type is set to a generalized source. The current source is connected to the anode in the geometric model, and the cathode is grounded. The waveform of the current source is based on the actual measurement data in the switching electrical appliance impact current experiment. First, the current value at each moment in the experiment is measured by an oscilloscope, and the corresponding data of time and current are recorded. Then these data are imported into the definition function part of the COMSOL software, and the interpolation function is added, and it is ensured that the interpolation function has a valid value within the total calculation time. Define the name and variable of the interpolation function, and finally set the current of the generalized source to the interpolation function through the circuit interface (cir), that is, the waveform of the current source in the geometric model is input according to the current data measured in the experiment, and the setting of the current source is completed. The specific parameters of the experiment can be set by yourself.

[0048] Among them, the dynamic mesh interface (ale) first selects the mesh smoothing type to ensure the smoothness of the mesh during deformation. Set the static contact to a fixed mesh, specify the mesh displacements of the static contact and its connected areas in the x and y directions to be 0, and ensure that the static contact position remains unchanged. All other areas except the static contact are set as free deformation domains, allowing the meshes in these areas to deform freely according to the movement of the dynamic contact. Specify the velocity function of the mesh of the dynamic contact and its connected areas in the x and y directions as a piecewise function to ensure that the movement of the dynamic contact is smooth and without mutations. By setting the velocity function to control the movement direction and velocity of the dynamic contact, the opening distance between the dynamic and static contacts becomes smaller, simulating the contact closing process. The specific velocity function can be set by yourself.

[0049] In the circuit interface (cir), first set the global current conservation, connect the anode to the current source, and the cathode to the ground to form a complete loop. Manually add different current source waveform functions to simulate the impact current to meet various experimental needs. Based on the actual measurement data of the switching device in the impact current electrical contact experiment, first use an oscilloscope to measure the current value at each moment in the experiment, record the corresponding data of time and current, and then import these data into the definition function part of the COMSOL software to add an interpolation function.

[0050] By setting the dynamic mesh interface (ale), manually add the velocity function to simulate the characteristics of the arc plasma during the closing (connection) process of the switch contacts after the impact current. The dynamic mesh interface (ale) sets the static contact area as a fixed mesh, and the moving contact and its related areas as a free deformation domain to ensure that the mesh can deform smoothly with the displacement of the moving contact, avoiding mesh distortion and solver convergence problems. The speed change of the moving contact can be defined by a piecewise function to ensure that it maintains a smooth movement during the closing process. The velocity function can be flexibly adjusted according to the actual motion trajectory to accurately reflect the movement behavior of the contact under different conditions.

[0051] Add transient research to the meshed geometric model, configure the transient solver, calculate the results and analyze the arc temperature, arc voltage-current curve, and change law of arc erosion area on the contact under different impulse currents, etc., and perform corresponding simulation calculation and analysis according to actual needs.

[0052] Among them, by configuring the transient solver, the arc phenomenon during the contact closing process is deeply studied. Since the arc is compressed during the closing process and the computational grid undergoes free deformation, the calculation process is more complicated, and the linear solver and its error need to be properly adjusted. By reasonably setting the movement speed and path of the moving contact, it is ensured that the solver convergence problem will not be caused during the contact closing process. In addition, for the transient simulation of the arc during the closing process, it is necessary to optimize the mesh division and time step configuration to ensure the stability of the transient solver under the complex multi-physical field coupling and avoid calculation errors during the simulation process.

[0053] In the solid and fluid heat transfer module, first select the temperature discretization as linear units, with the dependent variable being temperature T. Then set the initial values ​​of the moving and static contacts to 293.15K (i.e., room temperature 20°C), and set the initial value of 8000K at the center of the gas domain to ensure that the arc can be successfully started. Finally, set the phase change parameters of the contact material according to the material properties, such as the melting point from solid to liquid and the latent heat coefficient.

[0054] Gas pressure setting of laminar flow module, definition of fluid properties, selection of arc extinguishing medium (mainly hydrogen) as laminar gas domain, setting to incompressible flow, fluid discretization set to P1+P1 (velocity and pressure are both linear elements), constitutive relationship set to Newtonian fluid, static pressure selected as pressure, enable the option of suppressing backflow, use unit constraints on boundaries, set pressure value to 2.5atm (i.e. 2.5 standard atmospheric pressures), set the boundary conditions of moving and static contacts to slip, and at the same time, add volume force, i.e. the formula of Lorentz force, to simulate the effect of electromagnetic force on fluid.

[0055] Magnetic field settings, the initial magnetic vector potential is set to 0, the magnetic field is an out-of-plane vector potential (perpendicular to the two-dimensional plane), the background field selects full-field solution, the magnetic vector potential is discretized into linear units, satisfies Ampere's law, and the transverse magnetic field strength is set to 6mT.

[0056] Current and external circuit settings: First, set the potential discretization to linear units, the entire domain satisfies the law of conservation of current, the static contact (anode) is connected to the current source, and the moving contact (cathode) is grounded. Manually add the current source waveform function so that the peak value of the external circuit impact current of the model reaches 3000A.

[0057] The specific process of obtaining the current source waveform function is as follows: through the impulse current electrical contact experiment, the capacitor is first charged to the specified initial voltage, and then the switch is placed in the capacitor discharge loop. The peak value of the impulse current is adjusted by adjusting the size of the external resistor, and the current value is collected in real time using an oscilloscope to obtain the waveform of the current changing with time. Finally, it is imported into the circuit interface (cir) in the COMSOL software through the interpolation function.

[0058] Dynamic mesh settings, first set the geometric shape function to 1, select the Laplace method for mesh smoothing type, and define the connection speed function of the moving contact. Set its action speed to 0.6m / s, the action time to 3ms, the moving contact and its connected area move along the y-axis toward the static contact, and define the speed change of the moving contact through a piecewise function. In this embodiment, the moving contact moves at a constant speed of 0.6m / s to achieve the closing process of the moving and static contacts. In the dynamic mesh interface (ale), set the static contact area to a fixed mesh, and all other areas to free deformation to ensure that the mesh deforms smoothly with the displacement of the moving contact to avoid mesh distortion.

[0059] Multi-physics coupling, simulation involves the interaction of multiple physical fields, including Lorentz force, balanced discharge heat source, non-isothermal flow, etc. The mutual coupling between each physical field is manually added and set, so that these coupling phenomena can be fully simulated during the arc compression process; through multi-physics coupling, including Lorentz force, balanced discharge heat source, Lorentz force, non-isothermal flow and other multi-physics field coupling, manually add initial values ​​and boundary conditions to improve simulation accuracy.

[0060] For meshing, first select the user-controlled network and the calibration type is fluid dynamics, which is suitable for fluid and thermodynamic calculations. The finer the mesh distribution, the better the convergence, but at the same time the amount of calculation is also greater. Therefore, the calculation situation should be considered comprehensively to reduce the amount of calculation as much as possible under the premise of ensuring convergence. Therefore, a combination of triangular and quadrilateral meshes is used to divide the model. Manually adjust the fineness of the mesh, and locally encrypt the mesh in key areas such as the arc area and the edge of the contact to improve the calculation accuracy. In other areas, appropriately reduce the mesh density to reduce the amount of calculation. Ensure that the mesh is not distorted, meet the convergence requirements of the calculation results, optimize computing resources and time, and optimize simulation efficiency.

[0061] Configure the solver and select transient study, which is suitable for time-dependent transient analysis. Set the total simulation calculation time to 15ms and the time step to 0.01ms to capture the rapidly changing physical process during arc discharge. In order to ensure the accuracy and stability of the calculation results, set reasonable convergence criteria, including relative tolerance and absolute tolerance. The time stepping method selects the backward difference formula and limits the maximum and minimum time steps to prevent the calculation from being unstable due to too large a time step, or too long a calculation time due to too small a time step. For algebraic variables, set consistent initialization and use the backward Euler method for initialization. According to the model complexity and computing resources, appropriately adjust the memory allocation and parallel computing options to improve computing efficiency.

[0062] Based on the electrical contact experiment of actual switching electrical products under impulse current conditions, a simulation model was established to simulate the arc in the contact closing process of switching electrical appliances under impulse current. It can effectively reduce experimental costs, reduce resource loss, optimize the design of switching electrical products, and improve service life.

[0063] The above are only preferred embodiments of the present invention. The protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A simulation modeling method for arc in the contact closing process of a switching device under an impulse current, characterized in that: The steps are as follows: Step 1: Select a spatial dimension according to the arc geometric characteristics to be studied, the spatial dimension includes two-dimensional, two-dimensional axisymmetric and three-dimensional dimensions; use COMSOL software to establish a geometric model, the geometric model includes a moving contact, a stationary contact, and a gas domain, and the model is modeled according to the actual contact shape; Step 2: Add dimension parameters in sequence and substitute them into the geometric model, wherein the dimension parameters include the width and height of the moving contact and the stationary contact; Step 3: Set the materials required for the geometric model, add materials from the material library and manually define the material application domain to adapt to the flexible simulation application of different contact materials; Step 4: Add the physical field interface of the simulation model, which includes the current interface, laminar flow interface, circuit interface, fluid heat transfer interface, magnetic field interface and dynamic mesh interface; Step 5: Set specific parameters and boundary conditions of each physical field interface, and add multi-physical field coupling; the circuit interface simulates the impact current by adding a current source, and the current source waveform function is based on the actual impact current electrical contact experimental data; the moving grid interface realizes the closing process of the contact by defining the velocity function of the moving contact; Step 6: Add a transient study to the meshed geometric model, configure the transient solver, calculate the results, and analyze the changes in the arc temperature, arc voltage-current curve, and arc-induced contact erosion area.

2. The arc simulation modeling method of the contact closing process of a switching device under an impact current as claimed in claim 1 is characterized in that: Step 2 includes: Based on the size range setting of the bridge contact of the switching electrical appliance, the width is 2mm-10mm, and the height is 2mm-5mm; the size range setting of the moving contact is 2mm-10mm, and the height is 1mm-5mm; the remaining area is the gas domain, the width of the gas domain is greater than the contact width, and the height of the gas domain is equal to the sum of the heights of the moving and static contacts.

3. The arc simulation modeling method of the contact closing process of a switching device under an impact current as claimed in claim 1 is characterized in that: Step three includes: The contact material phase change parameters from solid to liquid, including melting point and latent heat coefficient, need to define the necessary physical property parameters according to the type of physics field interface added.

4. The arc simulation modeling method of the contact closing process of a switching device under an impact current as claimed in claim 1 is characterized in that: Step five includes: Laminar flow interface gas pressure setting, set the pressure of the arc extinguishing medium, i.e. the gas domain, to 1.5-5 standard atmospheres; manually define the fluid properties, set the magnitude and direction of the Lorentz force, define the expression of the Lorentz force, and simulate the effect of electromagnetic force on the fluid.

5. The arc simulation modeling method of the contact closing process of a switching device under an impact current as claimed in claim 1 is characterized in that: The step five comprises: In the magnetic field part, set the initial value of the magnetic potential loss to 0, that is, the model boundary is magnetically insulated, then set the out-of-plane vector potential and apply the transverse magnetic field, and manually define the value of the magnetic field strength, which is 1mT-10mT, for use in the expression of the Lorentz force in the laminar flow module.

6. The arc simulation modeling method of the contact closing process of a switching device under an impact current as claimed in claim 1 is characterized in that: In step six, the grid division includes triangular and quadrilateral grids, which need to be adjusted manually. The convergence of the calculation results is improved by changing the fineness of the grid. The finer the grid distribution, the better the convergence, and the greater the amount of calculation.

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