Simulation method for contact ablation of intermediate-frequency vacuum circuit breaker

Abstract

The invention relates to a simulation method for contact ablation of an intermediate-frequency vacuum circuit breaker, and belongs to the field of vacuum circuit breakers. The method comprises the following steps: firstly, constructing a vacuum arc multi-physics field coupling model under a medium-frequency working condition, and obtaining energy flux density and current density of the surfaces of an anode and a cathode and discrete data points of arc pressure in spatial distribution; fitting data of different physical quantities by using a Gaussian function, and adding a sine function for simulating arc radial displacement; constructing an electrode switching function caused by arc reignition; introducing source items such as surface resistance joule heat, radiation heat dissipation, recoil pressure, thermal buoyancy and electromagnetic force, describing dynamic deformation of the surface of the contact based on free interface boundary conditions of a level set method, and constructing an anode ablation model under a medium-frequency working condition; and verifying the accuracy of the simulation model according to an experimental result. According to the invention, the vacuum arc behavior and the contact ablation process under the medium-frequency working condition can be accurately simulated, the dynamic displacement characteristic and the polarity conversion process of the vacuum arc can be simulated, and the experiment cost is saved.

Description

Technical Field

[0001] The present invention relates to the field of vacuum circuit breakers, and in particular to a simulation method for contact ablation of a medium-frequency vacuum circuit breaker. Background Art

[0002] Vacuum circuit breakers are used for current protection in aviation variable-frequency (360Hz-800Hz) power systems. Their interrupting performance directly impacts the reliability of power system operation. During the interruption process, vacuum circuit breakers generate arcs, which generate high arc temperatures and can cause contact erosion. Contact erosion in circuit breaker circuits can affect electrical contact performance and, in turn, interruption performance. Therefore, developing an accurate contact erosion simulation model is crucial. This contact erosion simulation model can be used to study contact erosion behavior under arcing, and can be used in engineering practice and scientific research. For example, this model can be used to predict the extent of contact erosion under specific operating conditions, improve circuit breaker design, and evaluate the erosion resistance of contact materials. Research on contact erosion simulation models can reduce experimental costs and improve equipment reliability.

[0003] Most existing contact erosion simulation models focus on power frequency operating conditions. However, the arc behavior and contact erosion under medium frequency and power frequency conditions are different: under medium frequency conditions, the vacuum arc does not form an active anode spot pattern or agglomeration pattern, and no large-scale melting area forms on the contact surface. Therefore, existing power frequency simulation models cannot be directly applied to medium frequency conditions. In addition, current contact erosion simulation methods focus on static arc characteristics, using a fixed Gaussian or exponentially distributed energy flux density to equate the arc. They only consider contact erosion when the circuit breaker successfully breaks half-wave, and are unable to accurately simulate the dynamic characteristics of the arc or consider the failure of the circuit breaker to break half-wave after polarity reversal. Therefore, existing contact erosion simulation methods have certain limitations, are not suitable for medium frequency conditions, and do not fully consider actual arc behavior and contact erosion conditions. Summary of the Invention

[0004] Based on the above, it can be seen that contact erosion is an important factor affecting the breaking performance of circuit breakers. Therefore, it is very important to establish an accurate contact erosion simulation model. The existing simulation models mainly focus on static arc characteristics and fixed polarity breaking, and cannot accurately simulate the dynamic characteristics of the arc and consider the failure of the circuit breaker to break half-wave after polarity conversion; and as the current frequency increases, the energy coupling mode between the arc and the contact under medium frequency conditions changes, so the existing power frequency simulation model is no longer fully applicable under medium frequency conditions. In response to such problems, the present invention proposes a simulation method for medium frequency vacuum circuit breaker contact erosion. According to the characteristics of medium frequency working conditions, contact erosion simulation is realized based on dynamic arc characteristics and polarity conversion mechanism.

[0005] The present invention provides a method for simulating contact ablation of a medium frequency vacuum circuit breaker, comprising the following steps:

[0006] Step 1: Construct a multi-physics coupling model of the vacuum arc under medium-frequency conditions, perform simulations under set current frequency and current peak conditions, and obtain discrete data points of the energy flux density, current density, and arc pressure distribution on the anode and cathode surfaces.

[0007] Step 2: Based on the nonlinear least squares method, curve fitting is performed on the radial distribution of the different discrete data on the anode and cathode surfaces obtained in step 1 to obtain the Gaussian function distributions of the energy flux density, current density, and arc pressure on the anode and cathode surfaces, respectively. The radial displacement of the simulated arc is modulated by a sine function and added to the fitted Gaussian function to obtain the spatiotemporal distribution functions of the energy flux density, current density, and arc pressure on the anode and cathode surfaces of the vacuum circuit breaker.

[0008] Step 3: Based on the switching mechanism of the anode and cathode of the vacuum circuit breaker after the arc reignition, an electrode switching function is constructed. During the first half-wave of the current, the energy flux density, current density, and arc pressure on the anode surface are injected into the contact surface. During the second half-wave of the current, the polarity is reversed, and the energy flux density, current density, and arc pressure on the cathode surface are injected into the contact surface.

[0009] Step 4: The spatiotemporal distribution function obtained in step 2 and the electrode switching function obtained in step 3 are used as input conditions for constructing the anode ablation model of the vacuum circuit breaker. An anode ablation model under medium-frequency conditions is established. Source terms such as surface resistance Joule heating, radiation heat dissipation, recoil pressure, thermal buoyancy, and electromagnetic force are incorporated into the model. A free interface boundary condition based on the level set method is introduced to describe the dynamic deformation of the contact surface.

[0010] Step 5: Compare the simulation results of the vacuum circuit breaker anode ablation with the existing experimental results to verify the accuracy of the established anode ablation simulation model under medium frequency conditions. If the results are consistent, it means that the accuracy of the currently established simulation model meets the requirements. Otherwise, go back to step 1 and adjust the simulation model.

[0011] The advantages and positive effects of the present invention are as follows: (1) The method of the present invention can simulate the vacuum arc behavior and contact erosion process under medium frequency conditions. (2) The method of the present invention can simulate the dynamic displacement characteristics and polarity conversion process of the vacuum arc, saving experimental costs and improving the accuracy of the simulation of vacuum circuit breaker contact erosion under medium frequency conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 1. It is a schematic diagram of a process for establishing a contact ablation simulation model for a medium frequency vacuum circuit breaker according to an embodiment of the present invention;

[0013] Figure 2 is a schematic diagram of anode surface data drawn according to an embodiment of the present invention;

[0014] Figure 3 is a schematic diagram of cathode surface data drawn according to an embodiment of the present invention;

[0015] Figure 4 This is the experimental result of anode ablation of CuCr50 vacuum circuit breaker;

[0016] Figure 5 It is the surface morphology of the molten pool area obtained by the simulation model;

[0017] Figure 6 It is a line graph of melt depth and width obtained by the simulation model;

[0018] Figure 7 This is the simulation result of anode ablation of CuCr50 vacuum circuit breaker. DETAILED DESCRIPTION

[0019] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0020] This paper provides a method for simulating contact erosion in medium-frequency vacuum circuit breakers. This method establishes a contact erosion simulation model based on dynamic arc characteristics and polarity reversal. Based on the characteristics of medium-frequency operating conditions, this method incorporates source terms such as surface resistance Joule heating, radiation heat dissipation, recoil pressure, thermal buoyancy, and electromagnetic force. Furthermore, it introduces free interface boundary conditions based on the level set method to describe the dynamic deformation of the contact surface. This method can more accurately simulate contact erosion during the actual interruption process of a medium-frequency vacuum circuit breaker, enabling research into contact material selection and structural design, as well as further optimization of vacuum circuit breaker performance.

[0021] like Figure 1 As shown, the simulation method for contact ablation of a medium frequency vacuum circuit breaker according to an embodiment of the present invention includes the following five steps.

[0022] Step 1: Construct a multi-physics field coupling model of the vacuum arc under medium frequency conditions to obtain the radial distribution curves of energy flux density, current density, and arc pressure at the peak current moment.

[0023] The medium-frequency vacuum arc model incorporates physical fields such as electricity, magnetism, heat, and fluid dynamics. An electromagnetic-fluid-heat transfer multi-physics coupling model is established using multi-physics coupling analysis software (such as COMSOL Multiphysics). For example, the simulation conditions are: a 41mm diameter plasma region between the anode and cathode of the vacuum arc, a 3mm contact spacing, a current frequency of 360Hz, and a current peak of 22.5kA.

[0024] like Figure 1As shown, the embodiment of the present invention derives the discrete data points of the energy flux density, current density and arc pressure of the vacuum arc as they vary with space from COMSOL, checks the data quality, and if it passes, then plots the radial distribution curves of different data on the anode and cathode surfaces, as shown in FIG. Figure 2 and Figure 3 If the data quality check fails, rebuild or adjust the vacuum arc simulation model under medium frequency conditions in COMSOL and then perform the simulation again.

[0025] Step 2: Based on the nonlinear least squares method, a curve fitting is performed on the radial distribution of different discrete data on the anode and cathode surfaces obtained in step 1 to obtain a Gaussian function distribution. From the existing experimental results, it can be seen that under the medium frequency working condition, the arc has overflowed to the edge of the contact at the current peak moment, and the arc reignition point is also mainly concentrated at the edge of the contact. Therefore, the fitted Gaussian function distribution is considered to be added with sinusoidal function modulation to simulate the radial displacement of the arc.

[0026] Use a high-level programming language such as Python to write a curve fitting program and define the fitting function model as follows.

[0027]

[0028] in, represents the amplitude, i.e. the peak height of the Gaussian function; represents the baseline shift, i.e. the lowest value of the Gaussian function; Indicates the center position of the Gaussian function; is the width parameter, which controls the width of the Gaussian function; is the distance from the contact center, The embodiment of the present invention performs fitting of formula (1) to obtain six sets of data on the energy flux density, current density and arc pressure of the vacuum arc on the anode and cathode surfaces. Variation of the fitting function.

[0029] The embodiment of the present invention sets the threshold of the determination coefficient to 0.9, verifies the fitting result, and when it is greater than the threshold, continues to introduce sinusoidal function modulation into the fitted Gaussian function, otherwise, continues fitting until the fitting result is verified. After the embodiment of the present invention performs fitting, the determination coefficient R in the fitting results of the energy flux density, current density, and arc pressure on the anode and cathode surfaces is 2 The minimum value is 0.98, because the coefficient of determination R 2 The value of is between 0 and 1, so the fitting effect is good and can be used as the input condition for subsequent simulations. 2 It is an indicator to evaluate the degree of data fitting.

[0030] Based on the fitted Gaussian function, sinusoidal function modulation is added to simulate the radial movement of the arc in the first half-wave and the radial movement of the arc after the arc restrike.

[0031]

[0032]

[0033] Formula (2) shows that the radial displacement distance of the arc during the first half-wave of the current when the arc moves to the edge of the contact is: Over time Function of the change; Formula (3) shows that when the arc reignites at the edge of the contact in the second half-wave of the current and moves from the edge to the center, the radial displacement distance of the arc Over time Function of change. and represents the initial radial position, and B and C represent the radial movement distances.

[0034] It is necessary to substitute Equations (2) and (3) into Equation (1) respectively to obtain the complete function model injected into the contact surface, as shown in Equations (4) and (5).

[0035]

[0036]

[0037] in, Represents the spatiotemporal distribution function of energy flux density, current density and arc pressure on the anode surface of the vacuum circuit breaker. Represents the spatiotemporal distribution function of energy flux density, current density and arc pressure on the cathode surface of the vacuum circuit breaker.

[0038] Step 3: Construct the electrode switching function based on the mechanism of switching the anode and cathode polarity of the vacuum circuit breaker after arc restrike.

[0039] Because of the problem of arc reignition and the focus on the anode erosion after the vacuum circuit breaker is interrupted by a cycle, it is set that during the first half-wave of the current, the energy flux density, current density and arc pressure of the anode are injected into the contact surface. During the second half-wave, the polarity is reversed and the energy flux density, current density and arc pressure of the cathode are injected into the contact surface. The established electrode switching function As shown in formula (8).

[0040]

[0041]

[0042]

[0043] in, and is a step function; is the medium frequency current frequency.

[0044] Step 4: Use the Gaussian + sine modulated function obtained in step 2 and the polarity switching function obtained in step 3 as input conditions for constructing the anode ablation model of the vacuum circuit breaker, and establish an electromagnetic-fluid-heat transfer-level set multi-physics field coupling model of anode ablation.

[0045] For example, the simulation conditions are: contact diameter is 41 mm, frequency is 360 Hz, current peak is 22.5 kA, contact material is CuCr50, and contact thickness is 4 mm.

[0046] In this simulation model, Joule heating from surface resistance, radiative heat dissipation, recoil pressure, thermal buoyancy, and electromagnetic forces require special consideration under medium-frequency conditions. Furthermore, for model completeness, the remaining energy, momentum, and mass source terms are fully included to better simulate actual ablation conditions and ensure simulation accuracy.

[0047] The following explains the innovation of the simulation model from the perspective of establishing a mathematical model:

[0048] Energy conservation equation:

[0049]

[0050]

[0051]

[0052]

[0053]

[0054] in, is the density, is the specific heat capacity at constant pressure, is the temperature, is the velocity vector of the fluid, is the thermal conductivity, is the gradient operator, is the evaporation flux, P is the saturated vapor pressure, is the emissivity of the material, is the Stefan-Boltzmann constant, is the ambient temperature, represents conductivity, and J represents current density.

[0055] The first term on the left side of equation (9) is the time variation term; the second term is the convection term. The first term on the right side of equation is the heat conduction term; the second term is the is the energy flux density of the equivalent arc; the third term is the energy lost by evaporation; the fourth term The energy lost by radiation. Due to the rapid arc change under medium frequency (360Hz) working conditions, heat cannot be fully diffused through heat conduction. Radiation becomes the main heat dissipation path in the arc extinction stage. If the radiation heat dissipation is ignored, the cooling time will be overestimated in the simulation, resulting in the accumulation of initial temperature of subsequent arcing and aggravated ablation. The arcing time of traditional power frequency arc is long, and the heat has sufficient time to diffuse into the deep layer of the material through heat conduction, reducing the surface temperature. Therefore, the radiation heat dissipation cannot be ignored under medium frequency working conditions. This is the heat generated by resistance when current flows through the contact surface. As the frequency increases, the skin depth decreases sharply, the current density is concentrated on the surface, and the Joule heat of the surface resistance cannot be ignored.

[0056] The momentum conservation equation is established as follows:

[0057]

[0058] in, For pressure, is the viscous stress tensor.

[0059] The first term on the left side of Equation (14) is the time derivative term; the second term is the convection term. The first term on the right side of the equation is the pressure term; the second term is the viscous force term; the rest are the recoil pressure terms. Converted into volume force , surface tension converted into volume force , Marangoni force converted into volume force , the positive pressure generated by the arc on the molten pool Converted into volume force ,gravity , electromagnetic force , Darcy resistance , thermal buoyancy .

[0060] Recoil pressure As shown in Equation (15), the evaporation of metal vapor generates recoil pressure at the gas / liquid interface, causing the free interface to sag. This force is also an important driving force for the splashing of metal droplets. Due to the skin effect under medium-frequency conditions, the surface temperature increases, which leads to an increase in recoil pressure. Therefore, recoil pressure is added to the traditional simulation model.

[0061]

[0062] in, is standard atmospheric pressure; is the vaporization temperature of the material; is the Boltzmann constant; is the latent heat of vaporization.

[0063] Using level set variables , the recoil pressure is converted into volume force as follows:

[0064]

[0065] in, represents the unit normal vector at the interface, represents the level set function.

[0066] Surface tension is the main driving force in the molten pool, and the surface tension coefficient The calculation formula is:

[0067]

[0068] in, represents the surface tension coefficient at the reference temperature, represents the reference temperature, is the temperature coefficient.

[0069] According to Laplace's formula, the pressure difference between the liquid and gas phases on both sides of the interface depends on the surface tension coefficient and the surface curvature radius, and the relationship is as follows:

[0070]

[0071] Where, and are the pressures on the liquid and gas phase sides, respectively; and are the surface curvature radii of the liquid side interface and the gas side interface, respectively.

[0072] It is still necessary to convert the surface tension into volume force as a source term in the momentum equation:

[0073]

[0074] in, Represents the surface curvature.

[0075] The temperature change of the surface tension coefficient will produce Marangoni tangential force, which is converted into volume force using level set variables as follows:

[0076]

[0077] in, Indicates the direction of surface tension change.

[0078] Arc pressure is an important factor in equivalent arc and cannot be ignored in simulation. It is calculated as follows:

[0079]

[0080] in, is the arc positive pressure, using the level set variable Convert it into volume force.

[0081] Gravity is calculated as follows:

[0082]

[0083] Buoyancy is used as a volume force to drive the molten fluid to flow in the molten pool. The magnitude and distribution of thermal buoyancy directly depend on the temperature field. The temperature field is related to the Joule heating generated by the current. Therefore, frequency indirectly affects thermal buoyancy by affecting the current distribution and the spatiotemporal characteristics of Joule heating. Due to the significant skin effect at medium frequencies, the current is concentrated in a thin layer on the surface of the conductor, and Joule heating is highly concentrated on the surface, forming a temperature gradient between a high-temperature zone and an internal low-temperature zone. Thermal buoyancy forms a strong local driving force near the surface, so this force should be considered at medium frequencies.

[0084]

[0085] in, is the linear expansion coefficient of liquid metal, is the acceleration due to gravity, is the liquidus temperature of the molten metal pool.

[0086] Similarly, due to the significant skin effect at medium frequencies, the electromagnetic force is primarily concentrated in the thin layer on the contact surface, shifting from "volume distribution" to "surface concentration," which can ultimately lead to a localized increase in the electromagnetic force. At medium frequencies, the electromagnetic force exhibits certain medium-frequency characteristics that cannot be ignored.

[0087]

[0088] Indicates the magnetic induction intensity.

[0089] Taking the Darcy drag as the source term of the momentum equation, the solidification of the material will lead to momentum loss, and the lost momentum is calculated by the Darcy drag between the solid-liquid phase transition:

[0090]

[0091]

[0092]

[0093] Where K is the permeability coefficient, is the velocity field of the fluid, and is a constant, is the liquid volume fraction, T s is the solidus temperature of the molten pool metal.

[0094] By adding a source term to the mass conservation equation, evaporation is restricted to the gas / liquid interface. The level set equations are then modified to account for the interface motion caused by evaporation. This approach is more convenient than traditional methods that use deforming meshes to simulate interface motion, and produces more accurate results.

[0095] The mass conservation equation is modified as follows:

[0096]

[0097]

[0098] Level set equation correction:

[0099]

[0100] in, is the evaporation rate; is the atomic mass of the contact material; is the condensation coefficient; is the metal vapor density, is the density of liquid metal, Indicates the interface moving speed, is the interface mobility coefficient.

[0101] During simulation, the volume force of the recoil pressure is added to the momentum conservation equation , the volume force of the positive pressure generated by the arc on the molten pool ,gravity , electromagnetic force , Darcy resistance and thermal buoyancy The energy flux density added to the energy conservation equation is the energy flux density added to the COMSOL laminar flow module, the surface tension is added to the COMSOL two-phase flow module, and the Marangoni force is added to the COMSOL Marangoni effect module. and evaporative heat dissipation energy It is necessary to set up a heat source in the fluid heat transfer module in COMSOL; radiative heat dissipation energy Added via the boundary condition for surface radiation to the environment in the Fluid Heat Transfer Module; Joule heating This is done by adding the current source boundary condition in the Electric Field Module. The correction terms for the mass conservation equation and the level set equation need to be added using the weak contribution condition in the Level Set Module in COMSOL.

[0102] Step 5: Compare the simulation results with the existing experimental results to verify the accuracy of the simulation model. After the simulation is complete, determine whether the simulation results of the vacuum circuit breaker anode ablation are consistent with the actual experimental results. If they are consistent, it means that the accuracy of the currently established anode ablation model under medium-frequency conditions meets the requirements. Otherwise, it is necessary to return to step 1 and adjust the simulation model.

[0103] Figure 4 The experimental results of anode ablation of a vacuum circuit breaker are shown in the red circle in the figure. The simulation verifies the ablation situation. Figure 5 This is the surface morphology of the molten pool area in the simulation. It can be seen that there is only a slight deformation on the molten pool surface (caused by droplet splashing). The maximum material reduction area is between the radius of 13.34mm and 20.5mm. The maximum width of material loss is 7.16mm and the maximum depth is 0.032mm. Figure 6 This is a line graph showing the changes in melting depth and melting width obtained from the anode ablation simulation model. The maximum width of the molten pool is 7.16 mm, and the maximum depth of the molten pool is 0.23 mm. Figure 7 The distribution diagram of the local area (contact edge area) of the molten pool of the 41mm diameter anode is shown in Figure 2. Figure 4 and Figure 5 、 67, it can be seen that the ablation conditions of the simulation results are basically consistent with the experimental results, which can prove the accuracy of the simulation model established by the present invention.

[0104] In general, the embodiments of the present disclosure may be implemented in hardware or dedicated circuits, software, firmware, logic, or any combination thereof. Certain aspects may be implemented in hardware, while other aspects may be implemented in firmware or software executed by a controller, microprocessor or other computing device.

[0105] Except for the technical features described in the specification, all other technical features are known to those skilled in the art. The present invention omits descriptions of well-known components and well-known technologies to avoid redundancy and unnecessary limitation of the present invention. The implementation methods described in the above embodiments do not represent all implementation methods consistent with the present application. Based on the technical solution of the present invention, various modifications or variations that can be made by those skilled in the art without creative effort are still within the scope of protection of the present invention.

Claims

1. A simulation method for contact ablation of a medium frequency vacuum circuit breaker, characterized in that: The steps include: Step 1: Construct a multi-physics coupling model of the vacuum arc under medium-frequency conditions, perform simulations under set current frequency and current peak conditions, and obtain discrete data points of the energy flux density, current density, and arc pressure distribution on the anode and cathode surfaces. Step 2: Based on the nonlinear least squares method, curve fitting is performed on the radial distribution of the different discrete data on the anode and cathode surfaces obtained in step 1 to obtain the Gaussian function distributions of the energy flux density, current density, and arc pressure on the anode and cathode surfaces, respectively. The radial displacement of the simulated arc is modulated by a sine function and added to the fitted Gaussian function to obtain the spatiotemporal distribution functions of the energy flux density, current density, and arc pressure on the anode and cathode surfaces of the vacuum circuit breaker. Step 3: Based on the switching mechanism of the anode and cathode of the vacuum circuit breaker after the arc reignition, an electrode switching function is constructed. During the first half-wave of the current, the energy flux density, current density, and arc pressure on the anode surface are injected into the contact surface. During the second half-wave of the current, the polarity is reversed, and the energy flux density, current density, and arc pressure on the cathode surface are injected into the contact surface. Step 4: The spatiotemporal distribution function obtained in step 2 and the electrode switching function obtained in step 3 are used as input conditions for constructing the anode ablation model of the vacuum circuit breaker. An anode ablation model under medium-frequency conditions is established. The model incorporates surface resistance Joule heating, radiation heat dissipation, recoil pressure, thermal buoyancy, and electromagnetic force source terms, and introduces a free interface boundary condition based on the level set method to describe the dynamic deformation of the contact surface. Step 5: Compare the simulation results of the vacuum circuit breaker anode ablation with the existing experimental results to verify the accuracy of the established anode ablation simulation model under medium frequency conditions. If the results are consistent, it means that the accuracy of the currently established simulation model meets the requirements. Otherwise, go back to step 1 and adjust the simulation model.

2. The method according to claim 1, characterized in that In the above step 2, there are six physical quantities that need to be fitted, namely, the energy flux density, current density and arc pressure on the anode and cathode surfaces. For the physical quantity to be fitted, a Gaussian function of the following form is used for fitting based on a set of discrete data points of the corresponding physical quantity: ； in, Indicates the distance from the center of the contact, represents the center position of the Gaussian function, represents the lowest value of the Gaussian function, represents the peak height of the Gaussian function, is the parameter that controls the width of the Gaussian function; The radial movement of the first half-wave arc and the radial movement of the arc after the arc is reignited are simulated by using a sine function modulation; the radial displacement distance of the first half-wave arc is Over time The modulation function of the change is ; Radial displacement distance of the arc in the second half wave of current after the arc is reignited Over time The modulation function of the change is ; and represents the initial radial position, B and C represent the radial movement distance; The modulated The function is added to the fitted Gaussian function to obtain the spatiotemporal distribution function of energy flux density, current density and arc pressure on the anode surface of the vacuum circuit breaker ,as follows: ； The modulated The function is added to the fitted Gaussian function to obtain the spatiotemporal distribution function of energy flux density, current density and arc pressure on the cathode surface of the vacuum circuit breaker. ,as follows: 。 3. The method according to claim 1 or 2, characterized in that In step 3, establish the electrode switching function Expressed as: ; in, is the medium frequency current frequency, and is a step function, which is expressed as follows: ； 。 4. The method according to claim 1, wherein In the fourth step, an anode ablation model under medium frequency working conditions is established. The mathematical model of the model is expressed as follows: (1) Establish the energy conservation equation: ; ； ； ； ； in, is the density, is the specific heat capacity at constant pressure, is the temperature, is the velocity vector of the fluid, is the gradient operator, is the thermal conductivity, is the energy flux density of the equivalent arc, The energy for evaporation heat dissipation is To radiate heat energy, It is the heat generated by resistance when current flows through the contact surface. is the evaporation flux, P is the saturated vapor pressure, is the emissivity of the material, is the Stefan-Boltzmann constant, is the ambient temperature, represents conductivity, J represents current density; (2) Establish the momentum conservation equation: ； in, For pressure, is the viscous stress tensor, Recoil pressure Converted into volume force, is the volume force converted from surface tension, is the volume force converted from Marangoni force, The positive pressure generated by the arc on the molten pool Converted into volume force, is gravity, is the electromagnetic force, For Darcy resistance, is thermal buoyancy; (3) Evaporation is limited to the gas / liquid interface, and the level set equation is modified to take into account the interface movement caused by evaporation; Establish the mass conservation equation: ; ; Correction to the level set equation: ; in, is the velocity field of the fluid, is the evaporation rate, is the level set variable, is the level set function, is the unit normal vector at the interface, is the metal vapor density, is the density of liquid metal, is the condensation coefficient, is the Boltzmann constant, is the atomic mass of the contact material, is standard atmospheric pressure, is the latent heat of vaporization, is the vaporization temperature of the material, is the interface movement speed, is the interfacial mobility coefficient, is the surface curvature.

5. The method according to claim 4, characterized in that In the fourth step, in the momentum conservation equation: Using level set variables , calculate the body forces as follows: The recoil pressure Converted into body force ; Converting surface tension into volume force , is the surface tension coefficient; Converting Marangoni force into volume force , Indicates the direction of surface tension change; The positive pressure Converted into body force ; Calculating gravity , is the acceleration due to gravity; Calculating thermal buoyancy , is the linear expansion coefficient of liquid metal, is the liquidus temperature of the molten pool metal; Calculating electromagnetic forces , Indicates the magnetic induction intensity; Calculating Darcy Drag , permeability coefficient , and is a constant, is the liquid volume fraction, calculated as: , T s is the solidus temperature of the molten pool metal.

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