Calculation method for vacuum circuit breaker closing electric breakdown multi-physics coupling simulation

Abstract

The invention discloses a vacuum circuit breaker closing electric breakdown multi-physical field coupling simulation calculation method, which comprises the following steps of: performing simulation analysis on an electric field on the surface of a single micro-bulge by constructing a geometric model of a micro-bulge on the surface of a contact of a vacuum circuit breaker to obtain the electric field intensity of the micro-bulge surface and the current density of field emission in the closing process of the vacuum circuit breaker; the critical opening range of field emission is determined; obtaining metal vapor pressure distribution characteristics of the contact material at different moments by taking a critical opening range of field emission as an initial condition; and according to the metal vapor pressure distribution characteristics, obtaining the electron density in the breakdown process of the vacuum circuit breaker so as to determine the evolution rule of the microcosmic plasma parameters and obtain the closing breakdown characteristics. According to the method, the electric breakdown characteristics under different contact surface structures can be accurately analyzed, and an initial plasma condition can be provided for pre-breakdown equilibrium arc modeling, so that the modeling precision is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of vacuum circuit breaker simulation calculation technology, and in particular to a calculation method for multi-physics coupling simulation of vacuum circuit breaker closing electrical breakdown. Background Technology

[0002] In recent years, with the development of power grids, the number and frequency of vacuum circuit breakers used for switching capacitor banks have increased, leading to an increasing trend in the re-breakdown rate during actual operation. Research shows that the contact surface of vacuum circuit breakers, after being subjected to a high-frequency pre-breakdown arc during closing, can effectively reduce the probability of re-breakdown. The electrical breakdown process during the closing of a vacuum circuit breaker is a prerequisite for the occurrence and development of the pre-breakdown arc, determining the cathode surface temperature, electric field strength, and plasma density of the pre-breakdown arc.

[0003] Currently, research on vacuum arc characteristics mainly focuses on the analysis of arc-breaking characteristics. For simulation modeling of vacuum pre-breakdown arcs, the scarcity of initial plasma parameter data has become a key bottleneck restricting modeling accuracy, making it difficult for existing modeling methods to achieve ideal precision. Simultaneously, the influence mechanism of contact surface microstructure on plasma generation and evolution is difficult to quantify. However, electrical breakdown during the closing process directly affects the formation and development of the pre-breakdown arc and can provide accurate initial plasma conditions for modeling the pre-breakdown equilibrium arc; therefore, in-depth research into its physical mechanisms is urgently needed. Summary of the Invention

[0004] This invention discloses a calculation method for multi-physics coupling simulation of the closing electrical breakdown of a vacuum circuit breaker, in order to overcome the above-mentioned technical problems.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A calculation method for multi-physics coupling simulation of electrical breakdown during vacuum circuit breaker closing includes the following steps:

[0007] S1: Obtain the height and radius of curvature of the micro-protrusions on the surface of the vacuum circuit breaker contacts in order to establish a geometric model of the micro-protrusions on the surface of the vacuum circuit breaker contacts.

[0008] S2: Based on the geometric model of the micro-protrusions on the contact surface of the vacuum circuit breaker, the electric field on the surface of a single micro-protrusion on the contact surface during the closing process of the vacuum circuit breaker is simulated to obtain the electric field strength and field emission current density of the micro-protrusion surface during the closing process of the vacuum circuit breaker, so as to determine the critical opening distance of field emission.

[0009] S3: Using the critical opening distance of field emission as the initial condition, obtain the metal vapor pressure distribution characteristics of the contact material at different times;

[0010] S4: Based on the characteristics of metal vapor pressure distribution, obtain the electron density and ion density during the breakdown process of the vacuum circuit breaker, so as to determine the evolution law of microscopic plasma parameters including electron density and ion density, obtain the closing breakdown characteristics, and realize the multi-physics field coupling simulation of the closing electrical breakdown of the vacuum circuit breaker.

[0011] Furthermore, the method for obtaining the metal vapor pressure distribution characteristics of the contact material at different times is as follows:

[0012] S31: Obtain the surface temperature of the micro-protrusion based on the current density of field emission;

[0013] S32: Obtain the saturated vapor pressure of the contact material based on the surface temperature of the micro-protrusions;

[0014] S33: Obtain the evaporation rate of the micro-protrusion surface based on the saturated vapor pressure of the contact material;

[0015] S34: Obtain the metal vapor concentration of the contact material based on the evaporation rate of the micro-protrusion surface; and obtain the metal vapor pressure distribution characteristics.

[0016] Furthermore, the formula used to obtain the surface temperature of the micro-protrusions is as follows:

[0017]

[0018] In the formula: ρ con Contact density; C con The contact heat capacity is T; the surface temperature of the micro-protrusion is T; and time is t. For the Nabla operator; k con σ is the thermal conductivity of the contact material; con The electrical conductivity of the contact material; For temperature gradient; J e The field emission current density is the field-induced emission current density of the micro-protrusion surface during the closing process.

[0019] Furthermore, the formula used to obtain the saturated vapor pressure of the contact material is as follows:

[0020]

[0021] In the formula: C1 and C2 are constants related to the contact material; P v ρ is the saturated vapor pressure of the contact material; e is the natural base.

[0022] Furthermore, the formula used to obtain the evaporation rate of the micro-protrusion surface is as follows:

[0023]

[0024] In the formula: P represents the evaporation rate of the micro-protruding surface.v (T(t)) is the saturated vapor pressure of the contact material when the surface temperature of the micro-protrusion is T at time t; M is the molar mass of the contact material; R is the gas constant; T(t) is the surface temperature of the micro-protrusion at time t.

[0025] Furthermore, the formula used to obtain the metal vapor concentration of the contact material is as follows:

[0026]

[0027] In the formula: n(r,t) is the concentration of metal vapor at position r and time t; D is the diffusion coefficient; The evaporation concentration gradient is represented by S(r,t), which is related to the evaporation rate. The evaporation source of the micro-protrusion surface is related; r is the spatial coordinate; δ(r) is the delta function; r0 represents the evaporation position coordinate of the micro-protrusion surface.

[0028] Furthermore, the formula used to obtain the electron density during the breakdown process of the vacuum circuit breaker is as follows:

[0029]

[0030] Where: n e t represents electron density; t represents time. For the Nabla operator; μ e E is the electron mobility; E is the electric field strength between the contacts; D is the electric field strength between the contacts. e The electron diffusion coefficient; R represents the electron density gradient. e For electron source; v e n represents the electron velocity. ε Electron energy density; μ ε D represents electron mobility. ε The electron energy diffusion coefficient; R represents the electron energy gradient. ε For electron energy loss; M n R is the average molar mass of the mixture of heavy substances; R is the gas constant; T mix Temperature of the mixture of heavy substances; w k The mass fraction of heavy matter particles k; u mix The velocity of a mixture of heavy substances; v k R is the diffusion velocity of heavy matter particle k; k Let εk be the collision reaction rate of the heavy matter particle k; ε0 be the vacuum permittivity; εk be the velocity of the collision reaction of the heavy matter particle k. r ρ is the relative permittivity, ρ is the surface charge density of the micro-bumps, and k is the index of the type of heavy matter particle.

[0031] in,

[0032]

[0033] In the formula: R e is the electron source; j is the index number of the equation concerning the change in electron number density; J represents the total number of equations concerning the change in electron number density; x j k represents the mole fraction of the selected substance in the j-th equation relating to the change in electron number density; j The ratio coefficient of the j-th equation relating to the change in electron number density; N n n represents the number density of all neutral particles; e is the electron density; p is the index number of the non-collision reaction equation between electrons and neutral particles; P represents the total number of non-collision reaction equations between electrons and neutral particles; x p k represents the mole fraction of the selected substance in the non-collision reaction equation between the p-th electron and the neutral particle; p The ratio coefficient of the non-collision reaction equation between the p-th electron and the neutral particle; Δε p This represents the energy loss from the non-collision reaction between the p-th electron and the neutral particle.

[0034]

[0035] In the formula: w k Let k be the mass fraction of heavy matter particles, which includes metal atoms, excited-state metal atoms, and metal ions; n represents the total number of heavy matter particles; M k v is the molar mass of the heavy particle k; ki This is the stoichiometry matrix; N is the total number of chemical reactions; i is the index of the chemical reaction; r i Let be the reaction rate of the i-th chemical reaction.

[0036] Furthermore, the formulas used to obtain the electric field strength on the surface of the micro-protrusions and the current density of field emission during the closing process of the vacuum circuit breaker are as follows:

[0037]

[0038] In the formula: E0 is the electric field intensity of the micro-protrusion surface; β is the field enhancement factor used to describe the degree of electric field non-uniformity; U is the closing voltage; K is the contact gap; J e Let A be the field emission current density on the micro-protrusion surface during the closing process; A and B are both constants. t is the surface work function of the contact material; 2 (y) is a quadratic function of y; y is the rate at which the Schottky effect reduces the potential barrier; V(y) is a linear function of y.

[0039] Beneficial Effects: This invention provides a calculation method for multi-physics field coupling simulation of vacuum circuit breaker closing electrical breakdown. It establishes a geometric model of the micro-protrusions on the surface of the vacuum circuit breaker contacts by analyzing the height and radius of curvature of the micro-protrusions. The electric field of a single micro-protrusion on the geometric model is then simulated and analyzed to obtain the electric field strength and field emission current density on the surface of the micro-protrusions during the closing process, thus determining the critical opening distance for field emission. Furthermore, using the critical opening distance for field emission as the initial condition, the metal vapor pressure distribution characteristics of the contact material at different times are obtained. Based on the metal vapor pressure distribution characteristics, the electron density during the breakdown process of the vacuum circuit breaker is obtained to determine the evolution law of microscopic plasma parameters, acquire the closing breakdown characteristics, and achieve multi-physics field coupling simulation of vacuum circuit breaker closing electrical breakdown. This invention solves the problem of scarce initial plasma parameter data, enabling accurate analysis of electrical breakdown characteristics under different contact surface structures, and providing accurate initial plasma conditions for pre-breakdown equilibrium arc modeling. It quantifies the evolution law of microscopic plasma parameters, greatly improving modeling accuracy. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1 This is a flowchart of the calculation method for multi-physics coupling simulation of vacuum circuit breaker closing electrical breakdown according to the present invention;

[0042] Figure 2 This is a schematic diagram of the three-dimensional structure of the micro-protrusion surface provided in an embodiment of the present invention;

[0043] Figure 3 This is a diagram showing the change in electric field intensity on the surface of the micro-protrusion during the closing process, provided in an embodiment of the present invention.

[0044] Figure 4 The diagram showing the change in current density of field emission during the closing process provided in this embodiment of the invention;

[0045] Figure 5 This is a graph showing the variation of surface temperature of the micro-protrusions with the saturated vapor pressure of the contact material, provided in an embodiment of the present invention.

[0046] Figure 6 The electron density variation diagram at different times during the plasma discharge process is provided for an embodiment of the present invention;

[0047] Figure 7This is a schematic diagram illustrating the transfer of simulation calculation parameters for each physical process provided in the embodiments of the present invention. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0049] This embodiment introduces a calculation method for multi-physics coupling simulation of the closing electrical breakdown of a vacuum circuit breaker, including the following steps: Figure 1 As shown:

[0050] S1: Obtain the height and radius of curvature of the micro-protrusion to establish a geometric model of the micro-protrusion on the surface of the vacuum circuit breaker contact;

[0051] Specifically, this embodiment uses a laser confocal microscope to scan a typical local area on the contact surface to obtain structural parameters such as the height and radius of curvature of individual sharp micro-protrusions, thereby completing the modeling of the contact surface geometry. Figure 2 As shown. These structural parameters serve as initial conditions for calculating the surface electric field intensity of the micro-bumps and determining the critical breakdown distance. The micro-bump geometry is not limited to the geometry exemplified in this embodiment. The micro-bump height is obtained by scanning along the axial direction, yielding the height difference between the micro-bump apex and the substrate.

[0052] h = h max -h min (1)

[0053] In the formula: h is the height of the micro-protrusion; h max h is the maximum height of the micro-protrusion. min This is the height of the base reference surface.

[0054] Specifically, based on the scanned 3D topographic data points, the xz cross-sectional data of the micro-protrusion is extracted, and the radius of curvature of the micro-protrusion vertex is calculated using a three-point fitting method:

[0055]

[0056] In the formula: r M Let be the radius of curvature of the micro-protrusion; z and x are the position coordinates on the cross section of the micro-protrusion.

[0057] S2: Based on the geometric model of the micro-protrusions on the contact surface of the vacuum circuit breaker, the electric field on the surface of a single micro-protrusion on the contact surface is simulated and analyzed during the closing process of the vacuum circuit breaker. The electric field strength and current density of field emission on the surface of the micro-protrusion during the closing process of the vacuum circuit breaker are obtained to determine the critical opening distance of field emission.

[0058] Specifically, this embodiment uses mature and widely used finite element multiphysics simulation software to calculate the electrical breakdown process of vacuum circuit breaker closing. Figure 7 This is a schematic diagram illustrating the parameter transfer for the simulation calculations of each physical process provided in this embodiment. By performing electrostatic field calculations on the geometric model of a single micro-protrusion on the contact surface, and inputting initial conditions such as closing voltage and closing speed, the electric field strength and field-induced emission current density of the micro-protrusion surface during the closing process are calculated. The electric field strength E0 on the micro-protrusion surface and the emitted electron current density J are also calculated. e (Fowler-Nordheim formula), calculated from the following equation:

[0059]

[0060] In the formula: E0 is the electric field intensity of the micro-protrusion surface; β is the field enhancement factor used to describe the degree of electric field non-uniformity; K is the contact gap; J e Let A be the field emission current density on the micro-protrusion surface during the closing process; A and B are both constants. t is the surface work function of the contact material; 2 (y) is a quadratic function of y; y is the rate at which the Schottky effect reduces the potential barrier; V(y) is a linear function of y; U is the closing voltage.

[0061] Specifically, based on the breakdown theory of vacuum gaps, during the closing process of a vacuum circuit breaker, as the contact spacing decreases, the electric field strength on the micro-protrusions on the cathode surface continuously increases. When the electric field strength exceeds the critical field strength for field emission, electrons begin to be emitted. Therefore, using the above formula (3), the electric field strength at different opening distances can be calculated, thereby determining whether field emission has occurred and thus identifying the critical opening distance for field emission. Simulation results are available in [reference]. Figures 3 to 4 As shown.

[0062] S3: Using the critical opening distance of field emission as the initial condition, the heat transfer process of the micro-protrusion is simulated and calculated. The heat transfer characteristics of the micro-protrusion surface are analyzed. The temperature change of the micro-protrusion with time and the transient process of vapor diffusion are considered to obtain the metal vapor pressure distribution characteristics of the contact material at different times.

[0063] Specifically, using the critical opening distance of field emission as the initial condition, the heat transfer process of the micro-protrusion was calculated, obtaining the temperature-time variation curve of the micro-protrusion surface. Based on the surface temperature of the micro-protrusion, the saturated vapor pressure of the contact material was calculated. The evaporation rate of the micro-protrusion surface was further calculated using the saturated vapor pressure. Then, the transient diffusion equation was used to obtain the vapor concentration distribution of the contact material at different times and locations. Finally, the vapor pressure distribution characteristics of the contact material at different times and locations were calculated based on the ideal gas law. The simulation results are shown in [reference needed]. Figure 5 As shown.

[0064] S31: Obtain the surface temperature of the micro-protrusion based on the current density of field emission;

[0065] Specifically, the method for determining the heat transfer process of the micro-protrusion is as follows: Under the Joule heating effect of the field emission electron current, the surface of the micro-protrusion undergoes melting and evaporation. Therefore, the field emission current density and the physical properties of the contact material need to be input, and the surface temperature of the micro-protrusion is calculated by the heat transfer equation. The heat source term mainly consists of the Joule heating term caused by the field emission electron current and the heat conduction term of the contact material, as shown in the following equation:

[0066]

[0067] In the formula: ρ con Contact density; C con The contact heat capacity is T; the surface temperature of the micro-protrusion is T; and time is t. For the Nabla operator; k con σ is the thermal conductivity of the contact material; con The electrical conductivity of the contact material; For temperature gradient; J e The field emission current density is the field-induced emission current density of the micro-protrusion surface during the closing process.

[0068] S32: Obtain the saturated vapor pressure of the contact material based on the surface temperature of the micro-protrusions;

[0069] Specifically, the saturated vapor pressure P of the contact material v P is related to the surface temperature T of the micro-protrusions. v Calculated using the Clausius-Clapeyron equation, see the equation below:

[0070]

[0071] In the formula: C1 and C2 are constants related to the contact material; P v ρ is the saturated vapor pressure of the contact material; e is the natural base.

[0072] S33: Obtain the evaporation rate of the micro-protrusion surface based on the saturated vapor pressure of the contact material;

[0073] Specifically, the evaporation of metal vapor from a micro-protruding surface under Joule heating in a vacuum involves complex non-equilibrium physical phenomena. Therefore, the saturated vapor pressure of the metal cannot be directly used; further calculations of the evaporation flux on the micro-protruding surface are required. The evaporation rate of the micro-protruding surface is calculated using the Langmuir formula:

[0074]

[0075] In the formula: P represents the evaporation rate of the micro-protruding surface. v (T(t)) is the saturated vapor pressure of the contact material when the surface temperature of the micro-protrusion is T at time t; M is the molar mass of the contact material; R is the gas constant; T(t) is the surface temperature of the micro-protrusion at time t.

[0076] S34: Based on the evaporation rate of the micro-protrusion surface, obtain the metal vapor concentration n(r,t) of the contact material to obtain the metal vapor pressure distribution characteristics;

[0077] Specifically, the metal atoms evaporated from the micro-protrusion surface rapidly diffuse in the vacuum within a short time, failing to reach a stable equilibrium state. Since convection effects are negligible in the vacuum environment, the transport mechanism of the metal vapor is primarily diffusion. The diffusion process is described by a transient diffusion equation, as shown below:

[0078]

[0079] In the formula: n(r,t) is the concentration of metal vapor at position r and time t; D is the diffusion coefficient; The evaporation concentration gradient is represented by S(r,t), which is related to the evaporation rate. The evaporation source of the micro-protrusion surface is related; r is the spatial coordinate of the metal atom; δ(r) is the delta function; r0 represents the evaporation position coordinate of the micro-protrusion surface.

[0080] Specifically, the metal vapor concentration of the contact material can be used to obtain the characteristics of the metal vapor pressure distribution.

[0081] Specifically, by solving the transient diffusion equation, n(r,t) is obtained. Substituting the metal atom concentration n(r,t) into the ideal gas law, the vapor pressure p of the contact material at different positions and times is obtained. con See the following equation:

[0082] p con =n(r,t)k B T(t) (10)

[0083] In the formula: p con k is the vapor pressure of the metal.B is the Boltzmann constant; T(t) is the surface temperature of the micro-protrusion at time t.

[0084] By solving the above equations together, the transient metal vapor pressure distribution characteristics at different locations and times can be calculated, providing initial conditions for the formation of subsequent electrical breakdown discharge channels. The breakdown conditions include field emission electron density, metal vapor pressure of the contact material, and critical breakdown distance.

[0085] This embodiment calculates the temperature change of the micro-protrusion under the Joule heating effect of the field emission electron current through the heat transfer process of the micro-protrusion, so as to solve the metal vapor pressure distribution characteristics of the contact material under the action of electron current and provide background gas for plasma discharge in the vacuum gap.

[0086] S4: Based on the micro-protrusion geometry, field emission characteristics, and metal vapor pressure distribution characteristics, the breakdown process in the arc-extinguishing chamber of the vacuum circuit breaker is simulated and analyzed. The evolution of microscopic plasma parameters such as electron density and ion density during the breakdown process of the vacuum circuit breaker is calculated, and the closing breakdown characteristics are obtained.

[0087] Specifically, using the micro-protrusion structure determined by S1, the field emission critical opening distance calculated by S2, the field emission current density, and the metal vapor pressure distribution characteristics determined by S3 as initial input conditions, the breakdown process in the arc-extinguishing chamber of the vacuum circuit breaker is simulated and analyzed. Microscopic plasma parameters such as electron density and ion density are calculated during plasma discharge to obtain the closing electrical breakdown characteristics of the vacuum circuit breaker. The simulation results are shown in [reference needed]. Figure 6 As shown, the theoretical model used mainly includes the electron density diffusion equation, electron energy diffusion equation, heavy matter transport equation, and electrostatic field equation. This embodiment, by substituting the calculation parameters into the breakdown model, can simulate the dynamic evolution of plasma under specific contact structures. This model can quantitatively obtain the distribution characteristics of key microscopic parameters at the moment of breakdown, including electron density, electron energy, ion density, and ion energy, which can serve as initial conditions for steady-state plasma modeling. Furthermore, this model can clearly characterize the differences in breakdown characteristics under different breakdown voltage levels and different contact microstructures.

[0088] Specifically, during the vacuum gap plasma discharge process, although the particle velocities vary, the number of particles within a certain velocity range follows statistical laws for most particles. Therefore, the drift-diffusion equation is used as the mathematical model for solving the collisional ionization process in the gap. The electron drift-diffusion equation includes the electron density diffusion equation (11) and the electron energy density diffusion equation (12), which are used to describe the dynamic evolution characteristics of electron density and electron energy during collisional ionization. The heavy matter transport equation (13) uses mass conservation to solve for the mass fraction of each substance in the contact material metal atoms, excited-state metal atoms, and metal ions during collisional ionization. Coupled solving of the electron drift-diffusion equation, the heavy matter transport equation, and the electrostatic field equation can accurately describe the occurrence and development process of collisional ionization of charged particles under the action of an electric field, as shown in the following set of equations:

[0089]

[0090] Where: n e t represents electron density; t represents time. For the Nabla operator; μ e E is the electron mobility; E is the electric field strength between the contacts; D is the electric field strength between the contacts. e The electron diffusion coefficient; R represents the electron density gradient. e For electron source; v e n represents the electron velocity. ε Electron energy density; μ ε D represents electron mobility. ε The electron energy diffusion coefficient; R represents the electron energy gradient. ε For electron energy loss; M n R is the average molar mass of the mixture of heavy substances; R is the gas constant; T mix Temperature of the mixture of heavy substances; w k The mass fraction of heavy matter particles k; u mix The velocity of a mixture of heavy substances; v k R is the diffusion velocity of heavy matter particle k; k Let εk be the collision reaction rate of the heavy matter particle k; ε0 be the vacuum permittivity; εk be the velocity of the collision reaction of the heavy matter particle k. r ρ is the relative permittivity, ρ is the surface charge density of the micro-bumps, and k is the index of the heavy matter particles.

[0091] Assume there are J equations relating the change in electron number density during collisional ionization within the main gap, and P equations relating the non-collision reactions between electrons and neutral particles. Electron source R e The sum of changes in electron number density, and electron energy loss R ε The sum of energy losses from reaction collisions is given by the following equation:

[0092]

[0093] In the formula: R e is the electron source; j is the index number of the equation concerning the change in electron number density; J represents the total number of equations concerning the change in electron number density; x j k represents the mole fraction of the selected substance in the j-th equation relating to the change in electron number density; j The ratio coefficient of the j-th equation relating to the change in electron number density; N n n represents the number density of all neutral particles; e is the electron density; p is the index number of the non-collision reaction equation between electrons and neutral particles; P represents the total number of non-collision reaction equations between electrons and neutral particles; x p k represents the mole fraction of the selected substance in the non-collision reaction equation between the p-th electron and the neutral particle; p The ratio coefficient of the non-collision reaction equation between the p-th electron and the neutral particle; Δε p This represents the energy loss from the non-collision reaction between the p-th electron and the neutral particle.

[0094] Specifically, for the heavy matter transport equation, the mass fraction w k Collision reaction rate R k From the following equation, we get:

[0095]

[0096]

[0097] In the formula: w k Let k be the mass fraction of heavy matter particles, which includes metal atoms, excited-state metal atoms, and metal ions; n represents the total number of heavy matter particles; M k v is the molar mass of the heavy particle k; ki This is the stoichiometry matrix; N is the total number of chemical reactions; i is the index of the chemical reaction; r i Let be the reaction rate of the i-th chemical reaction.

[0098] Specifically, the collisional ionization process of vacuum gap plasma is simulated using drift-diffusion equations and other related theories, based on the initial breakdown conditions. This describes the occurrence and development of collisional ionization of charged particles under the influence of an electric field, thus achieving a simulation of vacuum circuit breaker closing breakdown. The charged particle collision process includes elastic collision reactions between electrons and metal atoms, excited collision reactions, ionization collision reactions, and the secondary electron process generated by collisions between metal ions and the cathode.

[0099] In summary, this embodiment uses multiphysics system simulation analysis to comprehensively reflect the plasma generation and evolution characteristics during the closing breakdown process by analyzing the field emission characteristics, heat transfer characteristics, and plasma discharge characteristics of the micro-protrusions on the contact surface during the closing process of the vacuum circuit breaker.

[0100] Specifically, this embodiment includes the following calculations: the field emission process of the micro-protrusion, the heat transfer process of the micro-protrusion, and the plasma collision ionization process in the vacuum gap. The specific calculation process includes: completing the geometric modeling of the micro-protrusion and clarifying the structural parameters such as the height and radius of curvature of the micro-protrusion; calculating the critical breakdown distance of the field emission of the micro-protrusion and using it as the input condition for the breakdown model; calculating the heat transfer model of the micro-protrusion, calculating the metal vapor distribution characteristics of the contact material at different times based on its heat transfer characteristics, and transferring it to the breakdown model; calculating the closing breakdown model, analyzing the evolution law of microscopic plasma parameters, and obtaining the closing breakdown characteristics. By studying the formation mechanism of the plasma discharge channel during the closing process, this study provides an effective numerical analysis method to solve the problems of clarifying the initial plasma characteristics of the pre-breakdown arc formation and development during the closing process of the vacuum circuit breaker, and the breakdown characteristics under different contact surface defect types.

[0101] Specifically, based on the coupling relationship between the field emission process of the micro-protrusion, the heat transfer process of the micro-protrusion surface, and the plasma collision ionization process in the vacuum gap, when the closing distance reaches a certain distance, the electric field strength of the micro-protrusion surface reaches the critical field strength for field emission, thus starting to emit electrons into the vacuum gap; under the action of the electron current, the temperature of the micro-protrusion surface rises rapidly due to the relatively concentrated current, and the micro-protrusion surface begins to evaporate; then, electrons and metal atoms in the main gap begin to undergo collision ionization reactions under the action of the external electric field, leading to gap breakdown. Thus, the multi-physics field coupling simulation calculation of the electrical breakdown characteristics of the vacuum circuit breaker closing process is completed.

[0102] This embodiment presents a calculation method for multi-physics field coupling simulation of vacuum circuit breaker closing electrical breakdown. It establishes a geometric model of the micro-protrusions on the surface of the vacuum circuit breaker contacts by analyzing the height and radius of curvature of the micro-protrusions. The electric field of a single micro-protrusion surface within the geometric model is then simulated to obtain the electric field strength and field emission current density on the micro-protrusion surface during the vacuum circuit breaker closing process, thus determining the critical opening distance for field emission. Furthermore, using the critical opening distance for field emission as the initial condition, the metal vapor pressure distribution characteristics of the contact material at different times are obtained. Based on the metal vapor pressure distribution characteristics, the electron density during the vacuum circuit breaker breakdown process is obtained to determine the evolution law of microscopic plasma parameters, acquire the closing breakdown characteristics, and achieve multi-physics field coupling simulation of vacuum circuit breaker closing electrical breakdown. This embodiment systematically models the closing process of a vacuum circuit breaker, simulating and analyzing the field emission characteristics, heat transfer characteristics, and plasma evolution characteristics within the gap of the micro-protrusions on the contact surface. It can accurately analyze the electrical breakdown characteristics under different contact surface structures and provide accurate initial plasma conditions for modeling the pre-breakdown steady-state arc, quantifying the evolution law of microscopic plasma parameters and greatly improving modeling accuracy. This embodiment helps to reveal the formation mechanism of the pre-breakdown arc and its interaction with the contact surface, comprehensively reflecting the closing breakdown performance of the circuit breaker, and providing technical support for the design of high-performance vacuum circuit breakers with capacitive breaking parameters and phase selection strategies.

[0103] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A calculation method for multi-physics coupling simulation of electrical breakdown during vacuum circuit breaker closing, characterized in that, Includes the following steps: S1: Obtain the height and radius of curvature of the micro-protrusions on the surface of the vacuum circuit breaker contacts in order to establish a geometric model of the micro-protrusions on the surface of the vacuum circuit breaker contacts. S2: Based on the geometric model of the micro-protrusions on the contact surface of the vacuum circuit breaker, the electric field on the surface of a single micro-protrusion on the contact surface during the closing process of the vacuum circuit breaker is simulated to obtain the electric field strength and field emission current density of the micro-protrusion surface during the closing process of the vacuum circuit breaker, so as to determine the critical opening distance of field emission. S3: Using the critical opening distance of field emission as the initial condition, obtain the metal vapor pressure distribution characteristics of the contact material at different times; S4: Based on the characteristics of metal vapor pressure distribution, obtain the electron density and ion density during the breakdown process of the vacuum circuit breaker, so as to determine the evolution law of microscopic plasma parameters including electron density and ion density, obtain the closing breakdown characteristics, and realize the multi-physics field coupling simulation of the closing electrical breakdown of the vacuum circuit breaker.

2. The calculation method for multi-physics coupling simulation of closing electrical breakdown of a vacuum circuit breaker according to claim 1, characterized in that, The method for obtaining the metal vapor pressure distribution characteristics of the contact material at different times is as follows: S31: Obtain the surface temperature of the micro-protrusion based on the current density of field emission; S32: Obtain the saturated vapor pressure of the contact material based on the surface temperature of the micro-protrusions; S33: Obtain the evaporation rate of the micro-protrusion surface based on the saturated vapor pressure of the contact material; S34: Based on the evaporation rate of the micro-protrusion surface, obtain the metal vapor concentration of the contact material to obtain the metal vapor pressure distribution characteristics.

3. The calculation method for multi-physics coupling simulation of closing electrical breakdown of a vacuum circuit breaker according to claim 2, characterized in that, The formula used to obtain the surface temperature of the micro-protrusion is as follows: In the formula: ρ con Contact density; C con The contact heat capacity is T; the surface temperature of the micro-protrusion is T; and time is t. For the Nabla operator; k con σ is the thermal conductivity of the contact material; con The electrical conductivity of the contact material; For temperature gradient; J e The field emission current density is the field-induced emission current density of the micro-protrusion surface during the closing process.

4. The calculation method for multi-physics coupling simulation of closing electrical breakdown of a vacuum circuit breaker according to claim 3, characterized in that, The formula used to obtain the saturated vapor pressure of the contact material is as follows: In the formula: C1 and C2 are constants related to the contact material; P v ρ is the saturated vapor pressure of the contact material; e is the natural base.

5. The calculation method for multi-physics coupling simulation of closing electrical breakdown of a vacuum circuit breaker according to claim 4, characterized in that, The formula used to obtain the evaporation rate of the micro-protrusion surface is as follows: In the formula: P represents the evaporation rate of the micro-protruding surface. v (T(t)) is the saturated vapor pressure of the contact material when the surface temperature of the micro-protrusion is T at time t; M is the molar mass of the contact material; R is the gas constant; T(t) is the surface temperature of the micro-protrusion at time t.

6. The calculation method for multi-physics coupling simulation of closing electrical breakdown of a vacuum circuit breaker according to claim 5, characterized in that, The formula used to obtain the metal vapor concentration of the contact material is as follows: In the formula: n(r,t) is the concentration of metal vapor at position r and time t; D is the diffusion coefficient; The evaporation concentration gradient is represented by S(r,t), which is related to the evaporation rate. The evaporation source of the micro-protrusion surface is related; r is the spatial coordinate; δ(r) is the delta function; r0 represents the evaporation position coordinate of the micro-protrusion surface.

7. The calculation method for multi-physics coupling simulation of closing electrical breakdown of a vacuum circuit breaker according to claim 6, characterized in that, The formula used to obtain the electron density during the breakdown process of a vacuum circuit breaker is as follows: Where: n e t represents electron density; t represents time. For the Nabla operator; μ e E is the electron mobility; E is the electric field strength between the contacts; D is the electric field strength between the contacts. e The electron diffusion coefficient; R represents the electron density gradient. e For electron source; v e n represents the electron velocity. ε Electron energy density; μ ε D represents electron mobility. ε The electron energy diffusion coefficient; R represents the electron energy gradient. ε For electron energy loss; M n R is the average molar mass of the mixture of heavy substances; R is the gas constant; T mix Temperature of the mixture of heavy substances; w k The mass fraction of heavy matter particles k; u mix The velocity of a mixture of heavy substances; v k R is the diffusion velocity of heavy matter particle k; k Let εk be the collision reaction rate of the heavy matter particle k; ε0 be the vacuum permittivity; εk be the velocity of the collision reaction of the heavy matter particle k. r ρ is the relative permittivity, ρ is the surface charge density of the micro-bumps, and k is the index of the heavy matter particle type. in, In the formula: R e is the electron source; j is the index number of the equation concerning the change in electron number density; J represents the total number of equations concerning the change in electron number density; x j k represents the mole fraction of the selected substance in the j-th equation relating to the change in electron number density; j The ratio coefficient of the j-th equation relating to the change in electron number density; N n n represents the number density of all neutral particles; e is the electron density; p is the index number of the non-collision reaction equation between electrons and neutral particles; P represents the total number of non-collision reaction equations between electrons and neutral particles; x p k represents the mole fraction of the selected substance in the non-collision reaction equation between the p-th electron and the neutral particle; p The ratio coefficient of the non-collision reaction equation between the p-th electron and the neutral particle; Δε p This represents the energy loss from the non-collision reaction between the p-th electron and the neutral particle; In the formula: w k Let k be the mass fraction of heavy matter particles, which includes metal atoms, excited-state metal atoms, and metal ions; n represents the total number of heavy matter particles; M k v is the molar mass of the heavy particle k; ki This is the stoichiometry matrix; N is the total number of chemical reactions; i is the index of the chemical reaction; r i Let be the reaction rate of the i-th chemical reaction.

8. The calculation method for multi-physics coupling simulation of closing electrical breakdown of a vacuum circuit breaker according to claim 1, characterized in that, The formulas used to obtain the electric field strength and field emission current density on the surface of the micro-protrusions during the closing process of the vacuum circuit breaker are as follows: In the formula: E0 is the electric field intensity of the micro-protrusion surface; β is the field enhancement factor used to describe the degree of electric field non-uniformity; U is the closing voltage; K is the contact gap; J e Let A be the field emission current density on the micro-protrusion surface during the closing process; A and B are both constants. t is the surface work function of the contact material; 2 (y) is a quadratic function of y; y is the rate at which the Schottky effect reduces the potential barrier; V(y) is a linear function of y.

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