Multi-physics field coupling simulation method for breaking process in arc extinguishing chamber of SF6 circuit breaker

Abstract

This invention relates to the field of theoretical analysis of the breaking process of SF6 circuit breakers, and discloses a multi-physics coupling simulation method for the breaking process in the arc-extinguishing chamber of an SF6 circuit breaker. This method includes using a two-dimensional axisymmetric model to reduce computational load; using a simplified model to reduce model complexity; and using measured contact velocity and cylinder upper pressure change curves as physical boundary conditions. The multi-physics coupling relationship is established based on Joule's law, Laplace's equation, and Navier-Stokes' equation. The thermophysical parameters of SF6 gas are calculated based on element stoichiometry, Dalton's law of partial pressures, the law of mass action, and the quasi-neutral charge condition of plasma. This invention features appropriate simplification, a reasonable mathematical model, and boundary condition data that closely approximate reality. The calculated results of the changes in various physical fields during the breaking process in the arc-extinguishing chamber of an SF6 circuit breaker are accurate, which is beneficial for revealing the breaking process and principle of SF6 circuit breakers and provides theoretical support for circuit breaker design and condition assessment.

Description

Technical Field

[0001] The present invention relates to the technical field of theoretical analysis of the breaking process of an SF6 circuit breaker, and in particular to a multi-physical field coupling simulation method for the breaking process in an arc extinguishing chamber of an SF6 circuit breaker. Background Art

[0002] As the most important control and protection equipment in the power system, the circuit breaker plays a vital role in ensuring the safety of the power system. With the vigorous construction and development of my country's power system and the increase in voltage levels, the number of power grid equipment is increasing, and the network complexity is increasing. Once a fault occurs and cannot be removed in time, the goal of improving power supply reliability and reducing economic losses will not be achieved. As the most important control and protection equipment in the power system, the circuit breaker plays a vital role in the safety of the power system. Although the proportion of DC lines in the existing power grid has increased significantly, the reliability and economy of DC circuit breakers need to be further improved. At present, AC circuit breakers play a leading role in power grid equipment. Among them, SF6 circuit breakers have become the absolute main force of existing circuit breaker products due to their high electronegativity, high electrical strength and excellent thermochemical properties of arc extinguishing medium, especially in the field of high and ultra-high voltage, playing an irreplaceable role. Therefore, it is of great significance to detect and eliminate faults in the operation of SF6 circuit breakers as soon as possible to improve the reliability of power supply in the power system and ensure the production of the national economy.

[0003] Generally, the mechanical life of SF6 circuit breakers can reach thousands or even tens of thousands of times, while its electrical life is only tens to less than one hundred times when breaking the rated short-circuit current. Considering the safety, reliability and operational stability of the power system, it is necessary to conduct in-depth research on the breaking capacity of SF6 circuit breakers and explore the breaking process and mechanism of SF6 circuit breakers. There is a complex electrical-thermal-mechanical physical process in the arc extinguishing chamber during the current breaking process, which causes the arc contact quality loss and state deterioration, and finally manifests as life degradation. However, since the arc extinguishing chamber is in a closed state, it is impossible to directly observe the arc breaking process in the arc extinguishing chamber. At present, finite element simulation is very mature. By coupling electromagnetic field, temperature field, flow field and dynamic grid technology, the changing state of each physical quantity in the arc extinguishing chamber breaking process can be obtained, which helps to reveal the process and mechanism of the circuit breaker arc extinguishing chamber breaking the short-circuit arc, and can reveal the failure mechanism of the circuit breaker electrical life.

[0004] At present, researchers have calculated the thermodynamic parameters and transport coefficients of SF6 plasma based on the conservation of element stoichiometry, Dalton's law of partial pressure, the law of mass action, and the quasi-neutral conditions of plasma charge, and established a mathematical model of arc magnetohydrodynamics, and studied the arc extinguishing process of non-equilibrium plasma. However, when the short-circuit current is interrupted, the SF6 arc is fully ionized into an equilibrium plasma. At this time, the changes in the electric field, temperature, flow field and other physical parameters in the arc extinguishing chamber affect each other, and the degree of coupling is high. The existing calculation method is not accurate enough for the changes in the physical fields in the arc extinguishing chamber of the SF6 circuit breaker during the interruption process. The coupling process of multiple physical fields needs to be considered in the simulation calculation. Summary of the invention

[0005] The purpose of the present invention is to propose a multi-physical field coupling simulation model of the breaking process in the arc extinguishing chamber of an SF6 circuit breaker, to obtain the changing laws of various physical fields in the breaking process of the arc extinguishing chamber of the SF6 circuit breaker, so as to obtain the breaking process and arc extinguishing mechanism.

[0006] To achieve the above object, the present invention provides a multi-physical field coupling simulation method for the breaking process in the arc extinguishing chamber of an SF6 circuit breaker, comprising the following steps:

[0007] S1. Establishing a simulation model: Establishing a simulation model based on the structural parameters of the actual circuit breaker arc extinguishing chamber, taking into account the amount of calculation and the degree of nonlinearity, adopting a two-dimensional axisymmetric model;

[0008] S2. Setting physical conditions for breaking: The physical conditions for breaking include the moving speed of the contact and the pressure change of the cylinder. These data are obtained by actual measurement of the real circuit breaker. Considering relative motion, the moving speed of the arc contact, nozzle and cylinder is assigned to the main contact to reduce the complexity of the calculation. The compression process of the cylinder is not considered, and the measured value of the upper wall pressure of the cylinder is directly set as the boundary condition to reduce the complexity of the model.

[0009] S3, obtaining a mathematical model of short-circuit arc interruption, including the following steps:

[0010] S3-1. Obtaining the equilibrium plasma thermal balance model: The arc unit energy balance formula obtained by Joule's law, the arc energy term Q per unit volume consists of three terms, namely Joule energy (resistance consumption), enthalpy heat transfer (short-circuit current energy) and thermal radiation energy;

[0011] S3-2, electric field calculation model: During the high-voltage circuit breaker breaking process, the electric field solution of the arc extinguishing chamber satisfies the Laplace equations. The moving contact is connected to the high-voltage end and the static contact is grounded. Both are first-class boundary conditions.

[0012] S3-3. Mathematical model of arc and airflow field energy coupling: The airflow field model in high-voltage circuit breakers adopts a two-dimensional compressible Navier-Stokes equation group, and the energy conservation equation includes the arc energy per unit volume; it is assumed that the gas satisfies the ideal gas state equation during the flow process; the standard k-ε two equations are used to describe the turbulence model;

[0013] S4. Calculate the thermophysical properties of SF6 gas based on the conservation of element stoichiometry, Dalton's law of partial pressures, the law of mass action, and the quasi-neutral condition of plasma charge.

[0014] As a further technical improvement, the arc unit energy balance formula in step S3-1 is:

[0015]

[0016] Where: ρ is the gas density, unit is kg / m 3 ; C p is the constant pressure heat capacity of the gas, in J / kg·K; μ is the gas dynamic viscosity, in Pa·s; k is the thermal conductivity, in W / m·K; T is the temperature, in K; Q is the arc energy per unit volume, in W / m 3 The arc energy per unit volume Q consists of three items, namely Joule energy (resistance consumption), enthalpy heat transfer (short-circuit current energy) and thermal radiation energy. Its expression is:

[0017]

[0018] Where: J is the arc column current density, unit is A / m 2 ; E is the electric field strength, unit is V / m; q is the heat flux, unit is W / m 2 ;Q rad is the net radiated power density, in W / m 2 .

[0019] As a further technical improvement, the electric field calculation model in step S3-2 is specifically:

[0020] During the interruption process of the high-voltage circuit breaker, the electric field in the arc extinguishing chamber satisfies the Laplace equations:

[0021]

[0022] In the formula, is the potential; the moving contact is connected to the high voltage end, and the static contact is grounded. Both are first-class boundary conditions:

[0023]

[0024] In the formula, is the potential of the contacts.

[0025] As a further technical improvement, step S3-3 is specifically as follows: the airflow field model in the high-voltage circuit breaker adopts a two-dimensional compressible Navier-Stokes equation group, and the airflow field in the high-voltage circuit breaker has the characteristics of transonic, compressible, viscous, and complex flow path boundary conditions; the NS equation group is the most basic equation for calculating the gas fluid field, including the mass conservation equation, the momentum conservation equation, and the energy conservation equation. Since the arc extinguishing chamber of the circuit breaker is symmetrical about the central axis, the NS equation group expressed in cylindrical coordinates (r, θ, z) is given below;

[0026] The mass conservation equation is:

[0027]

[0028] Where: is the material derivative, which physically tracks the rate of change of a SF6 fluid micro-group over time; ρ is the SF6 gas density; v r 、v θ 、v z are the flow velocities of the fluid particles in the r, θ, and z directions respectively;

[0029] The momentum conservation equation is:

[0030]

[0031]

[0032]

[0033] Where: F r 、F θ 、F z are the projections of the body force in the r, θ, and z directions respectively; μ is the gas dynamic viscosity coefficient; is the second dynamic viscosity coefficient, which is similar in the θ and z directions; the velocity divergence in the cylindrical coordinates The expression is:

[0034]

[0035] The energy conservation equation is:

[0036]

[0037] Where: h is the gas enthalpy; k is the gas thermal conductivity; C p is the constant pressure heat capacity of gas; Q is the arc energy per unit volume;

[0038] At the same time, it is assumed that the gas satisfies the ideal gas state equation during the flow process:

[0039] P=ρRT (11)

[0040] Where: P is the gas pressure; ρ is the gas density; R is the gas constant; T is the gas temperature;

[0041] The standard k-ε two-equation turbulence model includes the turbulent kinetic energy equation and the turbulent dissipation equation:

[0042] Turbulent kinetic energy equation:

[0043]

[0044] Turbulence dissipation equation:

[0045]

[0046] μ t =C μ ρk 2 / ε (14)

[0047] Where: k is the turbulent kinetic energy; ε is the turbulent dissipated power; C1, C2, C μ , σ k , σ ε are empirical constants in the turbulence model, which are 1.44, 1.92, 0.09, 1.0, and 1.3 respectively.

[0048] As a further technical improvement, the calculation of the thermal physical property parameters of SF6 gas in step S4 includes the following steps:

[0049] S4-1. Calculate gas density:

[0050]

[0051] Where: ρ is the density of arc plasma, in kg / m 3 ; is the number of gas phase particles in the reaction system; n i is the number density of particle i, in m -3 ;

[0052] S4-2. Calculate specific heat at constant pressure:

[0053]

[0054] Where: h is the specific enthalpy of arc plasma, in J / kg; is the standard state enthalpy of particle i, in J / mol; is the standard constant-pressure specific heat of particle i, in J / K·mol;

[0055] S4-3. Calculate the dynamic viscosity coefficient:

[0056]

[0057] Where: η is the dynamic viscosity coefficient of arc plasma, unit is Pa·s; b j0 is the expansion coefficient, which is obtained by the following linear equation;

[0058]

[0059] S4-4. Calculate thermal conductivity:

[0060] Thermal conductivity characterizes the ability of a material to conduct heat directly; the thermal conductivity of arc plasma is determined by the internal thermal conductivity λ int , reaction thermal conductivity λ reac and translational thermal conductivity λ trans It consists of three parts;

[0061] λ Total =λ int +λ reac +λ trans (19)

[0062] The presence of internal degrees of freedom of the ion due to vibration, rotation and electronic excitation can affect the heat flux vector, and the resulting internal thermal conductivity is calculated using the Hirschfelder-Eucken approximation:

[0063]

[0064] Where: int is the internal thermal conductivity of arc plasma, in W / m·K; D ii is the self-diffusion coefficient of particle i, in kg / m·K; C P,i is the constant-pressure specific heat of particle i, in J / K·mol; x i is the volume fraction of particle i;

[0065] The chemical reactions (ionization, decomposition, recombination, etc.) inside the arc plasma also contribute to heat transfer and produce reaction thermal conductivity. The expression of reaction thermal conductivity was first derived by Butler and Brokaw when studying the heat transfer phenomenon of neutral particles, and was extended to ionized gas and arc plasma by Meador and Stanton. The reaction thermal conductivity of the local thermodynamic equilibrium state is calculated by the following formula:

[0066]

[0067] Where: reac is the thermal conductivity of arc plasma, in W / m·K; ΔH iis the reaction enthalpy of reaction i, in J / mol; μ is the number of independent chemical reactions;

[0068]

[0069] Where: H k is the enthalpy value of the kth particle, in J / mol; υ is the number of chemical particles; a ik For particle A k Stoichiometric coefficient;

[0070]

[0071] Parameter λ r,i Solving the following linear equations yields:

[0072]

[0073]

[0074] Where: D kl is the binary diffusion coefficient of particles k and l, kg / m·K;

[0075] The translational thermal conductivity of the arc plasma is calculated by the following expression:

[0076]

[0077]

[0078] Where: E i,j D ij m j The inverse matrix elements of the matrix;

[0079] The translational thermal conductivity of electrons and heavy particles can be obtained by treating electrons and heavy particles differently according to the simplified treatment method obtained by Devoto, which ignores the interaction between electrons and heavy particles.

[0080] S4-5. Calculate the conductivity:

[0081] The conductivity is related to the charge transfer inside the arc plasma and is calculated by the following expression:

[0082]

[0083] Where: m i is the mass of particle i, in kg; Z i is the charge number of particle i;

[0084] Ignoring the contribution of heavy particles to conductivity and only considering the influence of electrons, the simplified expression of conductivity is:

[0085]

[0086] When the electron density is large, the accuracy of the conductivity is determined by the accuracy of the electron and neutral particle collision integral and the relatively slow convergence rate of the Chapman-Enskog approximation method.

[0087] Compared with the prior art, the present invention has the following beneficial technical effects:

[0088] The present invention proposes a simulation calculation of the arc breaking process in the arc extinguishing chamber of an SF6 circuit breaker that couples the temperature field, flow field and electric field. The model takes into account the mutual coupling relationship of the three physical fields. At the same time, the model is appropriately simplified, the physical boundary conditions use actual measurement data, and the simulation model uses a theoretical derivation model. The calculation results of each physical field are accurate, and the change law of each physical field in the breaking process of the arc extinguishing chamber of the SF6 circuit breaker is effectively obtained, and the breaking process and arc extinguishing mechanism are obtained, which is of great significance for revealing the breaking process and principle of the SF6 circuit breaker. BRIEF DESCRIPTION OF THE DRAWINGS

[0089] In order to more clearly illustrate the embodiments of the present invention, the drawings required for the embodiments will be briefly introduced below. It is obvious that the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0090] Figure 1 It is a flow chart of the simulation method of the present invention.

[0091] Figure 2 It is a schematic diagram of the simulation model of the present invention.

[0092] Figure 3 This is a typical breaking process contact speed curve of the present invention

[0093] Figure symbols: 1- calculation boundary, 2- symmetry axis, 3- static arc contact, 4- pressure outlet, 5- pressure inlet, 6- large nozzle, 7- small nozzle, 8- moving arc contact, 9- SF6 insulating medium. DETAILED DESCRIPTION

[0094] The embodiments of the present disclosure are described in detail below with reference to the accompanying drawings.

[0095] The following describes the embodiments of the present disclosure through specific examples, and those skilled in the art can easily understand other advantages and effects of the present disclosure from the contents disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, rather than all of the embodiments. The present disclosure can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present disclosure. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict. Based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present disclosure.

[0096] Example:

[0097] As attached Figure 1-3 As shown, this embodiment provides a multi-physics field coupling simulation method for the breaking process in the arc extinguishing chamber of an SF6 circuit breaker, comprising the following steps:

[0098] S1. Establishing a simulation model: Establishing a simulation model based on the structural parameters of the actual circuit breaker arc extinguishing chamber, taking into account the amount of calculation and the degree of nonlinearity, adopting a two-dimensional axisymmetric model;

[0099] S2. Setting physical conditions for breaking: The physical conditions for breaking include the moving speed of the contact and the pressure change of the cylinder. These data are obtained by actual measurement of the real circuit breaker. Considering relative motion, the moving speed of the arc contact, nozzle and cylinder is assigned to the main contact to reduce the complexity of the calculation. The compression process of the cylinder is not considered, and the measured value of the upper wall pressure of the cylinder is directly set as the boundary condition to reduce the complexity of the model.

[0100] S3, obtaining a mathematical model of short-circuit arc interruption, including the following steps:

[0101] S3-1. Obtaining the equilibrium plasma thermal balance model: The arc unit energy balance formula is obtained by Joule's law. The arc energy term Q per unit volume consists of three terms, namely Joule energy (resistance consumption), enthalpy heat transfer (short-circuit current energy) and thermal radiation energy; the arc unit energy balance formula is:

[0102]

[0103] Where: ρ is the gas density, unit is kg / m 3 ; C p is the constant pressure heat capacity of the gas, in J / kg·K; μ is the gas dynamic viscosity, in Pa·s; k is the thermal conductivity, in W / m·K; T is the temperature, in K; Q is the arc energy per unit volume, in W / m 3The arc energy per unit volume Q consists of three items, namely Joule energy (resistance consumption), enthalpy heat transfer (short-circuit current energy) and thermal radiation energy. Its expression is:

[0104]

[0105] Where: J is the arc column current density, unit is A / m 2 ; E is the electric field strength, unit is V / m; q is the heat flux, unit is W / m 2 ;Q rad is the net radiated power density in W / m 2 .

[0106] S3-2. Electric field calculation model: During the high-voltage circuit breaker opening process, the electric field in the arc extinguishing chamber satisfies the Laplace equations:

[0107]

[0108] In the formula, is the potential; the moving contact is connected to the high voltage end, and the static contact is grounded. Both are first-class boundary conditions:

[0109]

[0110] In the formula, is the potential of the contacts.

[0111] S3-3. Mathematical model of energy coupling between arc and airflow field: The airflow field model in high-voltage circuit breaker adopts two-dimensional compressible Navier-Stokes equations, and the energy conservation equation includes the arc energy per unit volume; it is assumed that the gas satisfies the ideal gas state equation during the flow process; the standard k-ε two equations are used to describe the turbulence model; the airflow field in the high-voltage circuit breaker has the characteristics of transonic, compressible, viscous, and complex flow path boundary conditions; the NS equations are the most basic equations for calculating the gas fluid field, including the mass conservation equation, momentum conservation equation and energy conservation equation. Since the circuit breaker arc extinguishing chamber is symmetrical about the central axis, the NS equations expressed in cylindrical coordinates (r, θ, z) are given below;

[0112] The mass conservation equation is:

[0113]

[0114] Where: is the material derivative, which physically tracks the rate of change of a SF6 fluid micro-group over time; ρ is the SF6 gas density; v r 、v θ 、v z are the flow velocities of the fluid particles in the r, θ, and z directions respectively;

[0115] The momentum conservation equation is:

[0116]

[0117]

[0118]

[0119] Where: F r 、F θ 、F z are the projections of the body force in the r, θ, and z directions respectively; μ is the gas dynamic viscosity coefficient; is the second dynamic viscosity coefficient, which is similar in the θ and z directions; the velocity divergence in the cylindrical coordinates The expression is:

[0120]

[0121] The energy conservation equation is:

[0122]

[0123] Where: h is the gas enthalpy; k is the gas thermal conductivity; C p is the constant pressure heat capacity of gas; Q is the arc energy per unit volume;

[0124] At the same time, it is assumed that the gas satisfies the ideal gas state equation during the flow process:

[0125] P=ρRT (11)

[0126] Where: P is the gas pressure; ρ is the gas density; R is the gas constant; T is the gas temperature;

[0127] The standard k-ε two-equation turbulence model includes the turbulent kinetic energy equation and the turbulent dissipation equation:

[0128] Turbulent kinetic energy equation:

[0129]

[0130] Turbulence dissipation equation:

[0131]

[0132] μ t =C μ ρk 2 / ε (14)

[0133] Where: k is the turbulent kinetic energy; ε is the turbulent dissipated power; C1, C2, C μ , σ k , σ εare empirical constants in the turbulence model, which are 1.44, 1.92, 0.09, 1.0, and 1.3 respectively.

[0134] S4. Calculate the thermophysical properties of SF6 gas based on the conservation of element stoichiometry, Dalton's law of partial pressure, the law of mass action, and the quasi-neutral condition of plasma charge, specifically including the following steps:

[0135] S4-1. Calculate gas density:

[0136]

[0137] Where: ρ is the density of arc plasma, in kg / m 3 ; is the number of gas phase particles in the reaction system; n i is the number density of particle i, in m -3 ;

[0138] S4-2. Calculate specific heat at constant pressure:

[0139]

[0140] Where: h is the specific enthalpy of arc plasma, in J / kg; is the standard state enthalpy of particle i, in J / mol; is the standard constant-pressure specific heat of particle i, in J / K·mol;

[0141] S4-3. Calculate the dynamic viscosity coefficient:

[0142]

[0143] Where: η is the dynamic viscosity coefficient of arc plasma, unit is Pa·s; b j0 is the expansion coefficient, which is obtained by the following linear equation;

[0144]

[0145] S4-4. Calculate thermal conductivity:

[0146] Thermal conductivity characterizes the ability of a material to conduct heat directly; the thermal conductivity of arc plasma is determined by the internal thermal conductivity λ int , reaction thermal conductivity λ reac and translational thermal conductivity λ trans It consists of three parts;

[0147] λ Total =λ int +λ reac +λ trans (19)

[0148] The presence of internal degrees of freedom of the ion due to vibration, rotation and electronic excitation can affect the heat flux vector, and the resulting internal thermal conductivity is calculated using the Hirschfelder-Eucken approximation:

[0149]

[0150] Where: int is the internal thermal conductivity of arc plasma, in W / m·K; D ii is the self-diffusion coefficient of particle i, in kg / m·K; C P,i is the constant-pressure specific heat of particle i, in J / K·mol; x i is the volume fraction of particle i;

[0151] The chemical reactions (ionization, decomposition, recombination, etc.) inside the arc plasma also contribute to heat transfer and produce reaction thermal conductivity. The expression of reaction thermal conductivity was first derived by Butler and Brokaw when studying the heat transfer phenomenon of neutral particles, and was extended to ionized gas and arc plasma by Meador and Stanton. The reaction thermal conductivity of the local thermodynamic equilibrium state is calculated by the following formula:

[0152]

[0153] Where: reac is the thermal conductivity of arc plasma, in W / m·K; ΔH i is the reaction enthalpy of reaction i, in J / mol; μ is the number of independent chemical reactions;

[0154]

[0155] Where: H k is the enthalpy value of the kth particle, in J / mol; υ is the number of chemical particles; a ik For particle A k Stoichiometric coefficient;

[0156]

[0157] Parameter λ r,i Solving the following linear equations yields:

[0158]

[0159]

[0160] Where: D kl is the binary diffusion coefficient of particles k and l, kg / m·K;

[0161] The translational thermal conductivity of the arc plasma is calculated by the following expression:

[0162]

[0163]

[0164] Where: E i,j D ij m j The inverse matrix elements of the matrix;

[0165] The translational thermal conductivity of electrons and heavy particles can be obtained by treating electrons and heavy particles differently according to the simplified treatment method obtained by Devoto, which ignores the interaction between electrons and heavy particles.

[0166] S4-5. Calculate the conductivity:

[0167] The conductivity is related to the charge transfer inside the arc plasma and is calculated by the following expression:

[0168]

[0169] Where: m i is the mass of particle i, in kg; Z i is the charge number of particle i;

[0170] Ignoring the contribution of heavy particles to conductivity and only considering the influence of electrons, the simplified expression of conductivity is:

[0171]

[0172] When the electron density is large, the accuracy of the conductivity is determined by the accuracy of the electron and neutral particle collision integral and the relatively slow convergence rate of the Chapman-Enskog approximation method.

[0173] The above description is only a preferred feasible embodiment of the present invention, and does not limit the scope of rights of the present invention. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. All equivalent changes made using the contents of the present invention specification and its drawings are included in the scope of rights of the present invention.

Claims

1. A multi-physical field coupling simulation method for the breaking process in the arc extinguishing chamber of an SF6 circuit breaker, characterized in that: The following steps are involved: S1. Establishing a simulation model: Establishing a simulation model based on the structural parameters of the actual circuit breaker arc extinguishing chamber, taking into account the amount of calculation and the degree of nonlinearity, adopting a two-dimensional axisymmetric model; S2. Setting physical conditions for breaking: The physical conditions for breaking include the moving speed of the contact and the pressure change of the cylinder. These data are obtained by actual measurement of the real circuit breaker. Considering relative motion, the moving speed of the arc contact, nozzle and cylinder is assigned to the main contact to reduce the complexity of the calculation. The compression process of the cylinder is not considered, and the measured value of the upper wall pressure of the cylinder is directly set as the boundary condition to reduce the complexity of the model. S3, obtaining a mathematical model of short-circuit arc interruption, including the following steps: S3-1. Obtaining the equilibrium plasma thermal balance model: The arc unit energy balance formula obtained by Joule's law, the unit volume arc energy term Q is composed of three terms, namely Joule energy, enthalpy heat transfer and thermal radiation energy; S3-2, electric field calculation model: During the high-voltage circuit breaker breaking process, the electric field solution of the arc extinguishing chamber satisfies the Laplace equations. The moving contact is connected to the high-voltage end and the static contact is grounded. Both are first-class boundary conditions. S3-3. Mathematical model of arc and airflow field energy coupling: The airflow field model in high-voltage circuit breakers adopts a two-dimensional compressible Navier-Stokes equation group, and the energy conservation equation includes the arc energy per unit volume; it is assumed that the gas satisfies the ideal gas state equation during the flow process; the standard k-ε two equations are used to describe the turbulence model; S4. Calculate the thermophysical properties of SF6 gas based on the conservation of element stoichiometry, Dalton's law of partial pressures, the law of mass action, and the quasi-neutral condition of plasma charge.

2. The multi-physical field coupling simulation method for the breaking process in the arc extinguishing chamber of the SF6 circuit breaker according to claim 1 is characterized in that: The arc unit energy balance formula in step S3-1 is: ； Where: ρ is the gas density, unit is kg / m 3 ; C p is the constant pressure heat capacity of gas, in J / kg∙K; μ is the gas dynamic viscosity, in Pa∙s; k is the thermal conductivity, in W / m∙K; T is temperature, in K; Q is the arc energy per unit volume, in W / m 3 ; The arc energy per unit volume Q consists of three terms, namely Joule energy, enthalpy heat transfer and thermal radiation energy, and its expression is: ； Where: J is the arc column current density, unit is A / m 2 ; E is the electric field strength, unit is V / m; q is the heat flux, unit is W / m 2 ;Q rad is the net radiated power density in W / m 2 .

3. The multi-physical field coupling simulation method for the breaking process in the arc extinguishing chamber of the SF6 circuit breaker according to claim 1 is characterized in that: The electric field calculation model in step S3-2 is specifically: During the interruption process of the high-voltage circuit breaker, the electric field in the arc extinguishing chamber satisfies the Laplace equations: ； In the formula, φ is the potential; the moving contact is connected to the high voltage end, and the static contact is grounded. Both are first-class boundary conditions: ； In the formula, is the potential of the contacts.

4. The multi-physical field coupling simulation method for the breaking process in the arc extinguishing chamber of the SF6 circuit breaker according to claim 1 is characterized in that: Specifically, step S3-3 includes: the airflow field model in the high-voltage circuit breaker adopts a two-dimensional compressible Navier-Stokes equation group, and the airflow field in the high-voltage circuit breaker has the characteristics of transonic, compressible, viscous, and complex flow path boundary conditions; the NS equation group is the most basic equation for calculating the gas fluid field, including the mass conservation equation, the momentum conservation equation, and the energy conservation equation. Since the arc extinguishing chamber of the circuit breaker is symmetrical about the central axis, the NS equation group expressed in cylindrical coordinates (r, θ, z) is given below; The mass conservation equation is: ； Where: is the material derivative, which physically tracks the rate of change of a SF6 fluid micro-group over time; ρ is the SF6 gas density; v r 、v θ 、v z are the flow velocities of the fluid particles in the r, θ, and z directions respectively; The momentum conservation equation is: Where: F r 、 F θ 、 F z The volume force is 、 θ 、 The projection in the z-axis direction; μ is the gas dynamic viscosity coefficient; , is the second dynamic viscosity coefficient, θ 、 Similar in the z-axis direction; velocity divergence in cylindrical coordinates The expression is: ； The energy conservation equation is: Where: h is the gas enthalpy; k is the gas thermal conductivity; C p is the constant pressure heat capacity of the gas; Q is the arc energy per unit volume; at the same time, it is assumed that the gas satisfies the ideal gas state equation during the flow process: ； Where: P is the gas pressure; ρ is the gas density; R is the gas constant; T is the gas temperature; The standard k-ε two-equation turbulence model includes the turbulence kinetic energy equation and the turbulence dissipation equation: Turbulent kinetic energy equation: ； Turbulence dissipation equation: ； ； Where: k is the turbulent kinetic energy; ε is the turbulent dissipated power; C1, C2, C μ , σ k , σ ε are empirical constants in the turbulence model, which are 1.44, 1.92, 0.09, 1.0, and 1.3 respectively.

5. The multi-physical field coupling simulation method for the breaking process in the arc extinguishing chamber of the SF6 circuit breaker according to claim 1 is characterized in that: The calculation of the thermal physical property parameters of SF6 gas in step S4 includes the following steps: S4-1. Calculate gas density: ； Where: ρ is the density of arc plasma, in kg / m 3 ; is the number of gas phase particles in the reaction system; n i is the number density of particle i, in m -3 ; S4-2. Calculate specific heat at constant pressure: ； Where: h is the specific enthalpy of arc plasma, in J / kg; is the standard state enthalpy of particle i, in J / mol; is the standard constant-pressure specific heat of particle i, in J / K∙mol; S4-3. Calculate the dynamic viscosity coefficient: ； Where: η is the dynamic viscosity coefficient of arc plasma, unit is Pa∙s; is the expansion coefficient, which is obtained by the following linear equation; ； S4-4. Calculate thermal conductivity: Thermal conductivity characterizes the ability of a material to conduct heat directly; the thermal conductivity of arc plasma is determined by the internal thermal conductivity λ int , reaction thermal conductivity λ reac and translational thermal conductivity λ trans It consists of three parts; ； The presence of internal degrees of freedom of the ion due to vibration, rotation and electronic excitation can affect the heat flux vector, and the resulting internal thermal conductivity is calculated using the Hirschfelder-Eucken approximation: ； Where: int is the internal thermal conductivity of arc plasma, in W / m∙K; D ii is the self-diffusion coefficient of particle i, in kg / m∙K; C P,i is the constant-pressure specific heat of particle i, in J / K∙mol; x i is the volume fraction of particle i; The chemical reactions inside the arc plasma also contribute to heat transfer, generating reaction thermal conductivity. The expression of reaction thermal conductivity was first derived by Butler and Brokaw when studying the heat transfer phenomenon of neutral particles, and was extended to ionized gases and arc plasmas by Meador and Stanton. The reaction thermal conductivity of the local thermodynamic equilibrium state is calculated by the following formula: ； Where: reac is the reaction thermal conductivity of arc plasma, in W / m∙K; is the reaction enthalpy of reaction i, in J / mol; μ is the number of independent chemical reactions; ； Where: is the enthalpy of the kth particle, in J / mol; υ is the number of chemical particles; For particle A k Stoichiometric coefficient; ； parameter Solving the following linear equations yields: ； ； Where: is the binary diffusion coefficient of particles k and l, kg / m∙K; the translational thermal conductivity of arc plasma is calculated by the following expression: ； ； Where: D ij m j The inverse matrix element of the matrix; the translational thermal conductivity of electrons and the translational thermal conductivity of heavy particles can be obtained by treating electrons and heavy particles differently according to the simplified treatment method obtained by Devoto by ignoring the interaction between electrons and heavy particles; S4-5. Calculate the conductivity: The conductivity is related to the charge transfer inside the arc plasma and is calculated by the following expression: ； Where: is the mass of particle i, in kg; is the charge number of particle i; Ignoring the contribution of heavy particles to conductivity and only considering the influence of electrons, the simplified expression of conductivity is: ； When the electron density is large, the accuracy of the conductivity is determined by the accuracy of the electron and neutral particle collision integral and the relatively slow convergence rate of the Chapman-Enskog approximation method.

Images