Environment-friendly gas arc characteristic simulation method considering ablation influence

Abstract

The invention provides an environment-friendly gas arc characteristic simulation method considering ablation influence. The method comprises the following steps: establishing a geometric model of switch equipment filled with C4F7N environment-friendly mixed gas; calculating thermodynamic parameters and transport coefficients of the C4F7N environment-friendly mixed gas in different proportions; calculating the change of the diameter of the nozzle of the switch equipment according to the steam mass of the solid material generated by ablation; and according to the deformed geometric structure of the switchgear, repeating the geometric model establishment step and the arc arcing and post-arc recovery characteristic determination step, and evaluating the influence of solid component material ablation on the breaking capacity of the switchgear. According to the method, the optimized and improved MHD model is adopted to simulate the whole-process arc characteristics of the C4F7N environment-friendly gas switch, the spatial and temporal distribution characteristics of a gas flow field, a pressure field, a temperature field, an electric field and the like in the arc extinguish chamber in the on-off process are obtained, and data support is provided for designing, researching and developing switch equipment such as a C4F7N environment-friendly gas circuit breaker and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of gas insulated switchgear, and in particular to a method for simulating arc characteristics of environmentally friendly gas taking into account the influence of ablation. Background Art

[0002] Sulfur hexafluoride (SF6) gas is widely used in electrical equipment as an excellent insulating and arc-extinguishing medium. However, the greenhouse effect of SF6 is 24,300 times that of CO2, and its lifespan in the atmosphere is as long as 3,200 years, which has a significant adverse impact on the environment. Domestic and foreign studies have shown that the mixed gas composed of perfluoroisobutyronitrile (C4F7N) environmentally friendly gas and CO2, O2, and N2 has high insulation strength and low greenhouse effect, and is considered to be the best environmentally friendly alternative to SF6. Under the condition of equipment interruption, the multi-component mixed gas composed of C4F7N gas and CO2, O2, N2 and other gases produces high-temperature arc plasma, which will produce chemical reactions such as decomposition and ionization, and will burn the electrodes and nozzle walls in the arc-extinguishing chamber, which has a great impact on the large-capacity interruption capacity. Unlike SF6 gas, the reaction of multi-component mixed gas and its interaction mechanism with solid components are more complicated. The high-temperature and high-pressure decomposition and complex chemical reaction, controlled flow and efficient energy dissipation, electron transport and dielectric recovery strength characteristics of multi-component gas mixed system under supersonic flow conditions all show multi-scale, strong coupling and strong nonlinear relationships, which makes modeling and simulation difficult. In view of the arc characteristics of C4F7N environmentally friendly mixed gas switches, it is more urgent and necessary to build an arc dynamic simulation model that takes into account the influence of ablation.

[0003] The calculation premise of the numerical simulation model of MHD arc characteristics based on magnetohydrodynamics is that the plasma in the arc area is electrically neutral and satisfies the local thermodynamic equilibrium (LTE) and local chemical equilibrium (LCE). The changes in the properties of solid materials such as electrodes and walls and the interaction between gas and solid materials in the C4F7N environmentally friendly mixed gas atmosphere require the establishment of an arc characteristic simulation method that takes into account the influence of electrode and nozzle ablation, so as to provide theoretical guidance for the research and development of C4F7N gas switch equipment. Summary of the invention

[0004] In view of this, the present invention proposes a method for simulating arc characteristics of environmentally friendly gas taking into account the influence of ablation, aiming to solve the above-mentioned technical problems existing in the prior art.

[0005] The present invention proposes a method for simulating arc characteristics of environmentally friendly gas taking into account the influence of ablation, comprising:

[0006] The geometric model establishment step is to establish a geometric model of the arc extinguishing structure of the switchgear filled with C4F7N environmentally friendly mixed gas;

[0007] The arc plasma physical property parameter determination step is to determine the decomposition gas of the material of the relevant solid parts of the switchgear under the high temperature conditions of opening or closing and the particle components after mixing with the C4F7N environmentally friendly mixed gas, and calculate the thermodynamic parameters and transport coefficients of the C4F7N environmentally friendly mixed gas with different proportions;

[0008] The arc burning and post-arc recovery characteristics are determined in steps, and a numerical simulation model of arc characteristics taking into account the influence of ablation is established. The thermodynamic parameters and transport coefficients of the C4F7N environmentally friendly mixed gas with different proportions obtained above are processed and used as input data of the arc characteristics numerical simulation model, so as to obtain the electric, magnetic, thermal and flow multi-physical field distributions in the arc extinguishing chamber during the arc formation between the contacts of the switchgear, the solid material vapor concentration distribution generated by ablation, the solid material vapor mass generated by ablation and the physical field distribution of the arc, and the change in the nozzle diameter of the switchgear is calculated based on the mass of the solid material vapor generated by ablation; the geometric model establishment steps and the arc burning and post-arc recovery characteristics determination steps are repeated according to the geometric structure of the deformed switchgear, and the influence of the ablation of the solid component material on the breaking capacity of the switchgear is evaluated.

[0009] Furthermore, in the above-mentioned environmentally friendly gas arc characteristic simulation method taking into account the influence of ablation, in the arc plasma physical property parameter determination step, the particle components are calculated according to the Gibbs free energy minimization theorem, the law of conservation of mass, Dalton's partial pressure law, the plasma quasi-neutrality characteristics and the law of conservation of stoichiometry; on this basis, the thermodynamic parameters are calculated by statistical thermodynamics methods, and the transport coefficient is calculated by the Chapman-Enskog method.

[0010] Furthermore, in the above-mentioned simulation method of environmentally friendly gas arc characteristics taking into account the influence of ablation, the thermodynamic parameters and transport coefficient data of C4F7N environmentally friendly mixed gases with different composition ratios are processed according to the control equation describing the switch arc characteristics of C4F7N environmentally friendly mixed gas, and the temperature field distribution, pressure field distribution and gas flow rate distribution are calculated.

[0011] Furthermore, in the above-mentioned simulation method of arc characteristics of environmentally friendly gas taking into account the influence of ablation, the control equation describing the arc characteristics of the C4F7N environmentally friendly mixed gas switch includes:

[0012]

[0013] in,

[0014] Where: t is time; w and v are the axial and radial velocity components of the C4F7N environmentally friendly mixed gas, respectively; p is the pressure in the arc extinguishing chamber; T is the temperature in the arc extinguishing chamber; h is the thermal enthalpy of the C4F7N environmentally friendly mixed gas; J rand J z are the radial and axial current densities respectively; B θ is the magnetic induction intensity; l and t represent laminar flow and turbulent flow respectively; μ l is the viscosity coefficient of C4F7N environmentally friendly mixed gas in laminar flow state; μ t is the viscosity coefficient of C4F7N environmentally friendly mixed gas in turbulent state; k l k is the thermal conductivity of C4F7N environmentally friendly mixed gas under laminar flow; t is the thermal conductivity of the C4F7N environmentally friendly mixed gas under turbulent state; q is the energy lost by radiation per unit volume; ρ is the mass density of the C4F7N environmentally friendly mixed gas; σ is the electrical conductivity of the C4F7N environmentally friendly mixed gas; is the potential; r is the radial coordinate, z is the axial coordinate, E is the electric field intensity, c p is the constant pressure specific heat capacity of C4F7N environmentally friendly mixed gas, viscous dissipation is viscous dissipation, and viscous terms are viscous terms.

[0015] Furthermore, in the above-mentioned simulation method of environmental gas arc characteristics taking into account the influence of ablation, the electric field distribution is calculated according to formula (5):

[0016]

[0017] Where ρ is the mass density of C4F7N environmentally friendly mixed gas, For electric potential.

[0018] Furthermore, in the above-mentioned simulation method of environmental gas arc characteristics taking into account the influence of ablation, the energy items required for ablation of each solid component material of the switchgear are calculated by the combined equations (1), (2), (3), (4), (7) and (8):

[0019]

[0020]

[0021] in:

[0022]

[0023]

[0024] Where D is the diffusion coefficient, C m，Cu and C m，PTFE They are respectively the mass proportion of the vapor of the electrode material copper and the mass proportion of the vapor of the nozzle material polytetrafluoroethylene in the mixed medium.

[0025] Furthermore, in the above-mentioned simulation method of environmental gas arc characteristics taking into account the influence of ablation, the mass of the nozzle steam generated by ablation is determined according to the calculation formula of the radiation energy required to generate the solid material polytetrafluoroethylene vapor by ablation:

[0026]

[0027] Among them, m PTFE is the nozzle vapor mass generated by ablation, Q ablation is the energy used for ablation of the solid material polytetrafluoroethylene vapor at the nozzle, which is the volume integral of q in equation (4); h PTFE The energy required to vaporize unit mass of nozzle material.

[0028] Furthermore, in the above-mentioned simulation method of environmental gas arc characteristics taking into account the influence of ablation, the mass of electrode vapor generated by ablation is determined according to the energy conservation equation between the arc and the electrode and the energy required for gasification of the electrode unit mass:

[0029]

[0030]

[0031] Where, T a is the arc temperature in the first gas grid in contact with the electrode surface; T c is the temperature of the first solid grid on the electrode surface; Δh is the distance between the center of the first gas grid and the first solid grid; j i is the ion current density; j e is the electron current density; k B is the Boltzmann constant, k B =1.38×10 -23 (J / K); U c is the electrode voltage drop; U i is the ionization energy of arc plasma; φ c is the work function of the electrode material; is the electrode ablation rate; h v The energy required for gasification of unit mass of electrode; h cu The energy required to gasify the electrode material per unit mass; Q v is the energy used for electrode ablation, which is

[0032] Furthermore, in the above-mentioned environmentally friendly gas arc characteristic simulation method taking into account the influence of ablation, the influence of ablation of solid component materials on the breaking capacity of the switching device is evaluated through arc burning and post-arc recovery characteristics, including: by comparing the arc conductivity change 200ns before the current passes through zero and the maximum value of the recovery voltage rise rate (RRRV) applied by the gas insulation medium withstand system after the current passes through zero, the influence of ablation of solid component materials on the breaking capacity of the switching device is evaluated.

[0033] Furthermore, in the above-mentioned environmental gas arc characteristic simulation method taking into account the influence of ablation, the evaluation criteria for evaluating the influence of ablation of solid component materials on the breaking capacity of the switching device include: calculating the post-arc current between the arc gap after the short-circuit current passes through zero. If the post-arc current drops to an infinitesimal value, it indicates that the breaking is successful; if the post-arc current first decreases and then increases to infinity, the breaking fails.

[0034] The environmental gas arc characteristic simulation method taking into account the ablation effect in the present invention uses the thermodynamic parameters and transport coefficients of C4F7N environmental mixed gas with different proportions as input data, establishes the control equation describing the arc characteristics of the C4F7N environmental mixed gas switch and the solid material vapor mass calculation model generated by ablation, so as to output the electric, magnetic, thermal and flow multi-physical field distribution in the arc extinguishing chamber during the process of arc formation between the switch contacts when the switch device is opened or closed, the solid material vapor concentration distribution generated by ablation, the solid material vapor mass generated by ablation and the volt-ampere characteristics of the arc, and determines the change in the nozzle diameter of the switch device based on this to judge the breaking capacity of the switch device, providing strong data support for the design and development of C4F7N environmental gas switch device. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Moreover, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0036] Figure 1 A schematic flow chart of a method for simulating arc characteristics of an environmentally friendly gas taking into account the influence of ablation provided in an embodiment of the present invention;

[0037] Figure 2 A flow chart of the simulation of arc characteristics of a C4F7N environmentally friendly mixed gas switch taking into account the influence of ablation provided by an embodiment of the present invention;

[0038] Figure 3 To use the simulation method in this embodiment to simulate the change of pressure in the arc extinguishing chamber under the condition of three cumulative interruptions of the gas switchgear;

[0039] Figure 4The simulation method in this embodiment is used to simulate the energy change required for nozzle ablation and the mass change of solid material vapor generated by ablation under the condition that the gas switch device is interrupted three times cumulatively. DETAILED DESCRIPTION

[0040] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present disclosure and to be able to fully convey the scope of the present disclosure to those skilled in the art. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features described in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0041] See also Figure 1 The environmental gas arc characteristic simulation method taking into account the ablation effect of the embodiment of the present invention includes:

[0042] The geometric model building step S1 is to build a geometric model of the arc extinguishing structure of the switchgear with C4F7N environmentally friendly mixed gas.

[0043] Specifically, the C4F7N environmentally friendly mixed gas is a binary or ternary environmentally friendly mixed gas consisting of the environmentally friendly insulating gas C4F7N and a buffer gas; the buffer gas is selected from at least one of carbon dioxide and nitrogen.

[0044] The electrodes of the switch device are made of metal copper or copper-tungsten alloy, and the material of the nozzle can be polytetrafluoroethylene.

[0045] In this step, since the switchgear has an operating mechanism, which is used to control the moving parts in the arc extinguishing chamber, such as the main / arcing contacts, pressure cylinders, etc., during the arc simulation process, it is also necessary to obtain the travel-time curve and movement speed and other characteristics of the moving parts (such as the opening speed) as input data to describe the movement characteristics of the moving parts.

[0046] The arc plasma physical property parameter determination step S2 determines the decomposition gas of the materials of the relevant solid components of the switchgear under high temperature conditions of opening or closing and the particle components after mixing with the C4F7N environmentally friendly mixed gas, and calculates the thermodynamic parameters and transport coefficients of the C4F7N environmentally friendly mixed gas with different proportions.

[0047] Specifically, the relevant solid component may be a showerhead or an electrode.

[0048] Thermodynamic parameters include density, enthalpy, and specific heat at constant pressure. Transport coefficients include electrical conductivity, thermal conductivity, and viscosity. Thermodynamic parameters are calculated using statistical thermodynamics methods, and transport coefficients are calculated using the Chapman-Enskog method.

[0049] In this step, the particle composition is calculated according to the Gibbs free energy minimization theorem, the law of conservation of mass, Dalton's law of partial pressures, the quasi-neutrality of plasma and the law of conservation of stoichiometry; on this basis, the thermodynamic parameters are calculated by statistical thermodynamics methods, and the transport coefficients are calculated by the Chapman-Enskog method.

[0050] More specifically, the decomposition gas of the nozzle material (polymers such as polytetrafluoroethylene) of the switchgear at high temperature and its particle components after mixing with the C4F7N environmentally friendly mixed gas, as well as the particle components after mixing the vapor of the electrode material (metal, such as copper or copper-tungsten alloy) with the C4F7N environmentally friendly mixed gas are calculated respectively, and the density and enthalpy of the multi-component mixed gas are calculated, and the constant pressure specific heat of the mixed gas is obtained by numerically derivation of the enthalpy value, and the transport coefficients such as the conductivity, thermal conductivity and viscosity coefficient of the multi-component mixed gas are solved. Among them, the temperature range that can be calculated by the multi-component mixed gas arc plasma system is 300K~50000K.

[0051] In step S3, the arc burning and post-arc recovery characteristics are determined, and a numerical simulation model of arc characteristics taking into account the influence of ablation is established. The thermodynamic parameters and transport coefficients of the C4F7N environmentally friendly mixed gas with different proportions obtained above are processed as input data of the arc characteristics numerical simulation model, and the electric, magnetic, thermal and flow multi-physical field distributions in the process of arc formation between the switch contacts are obtained, and the solid material vapor concentration distribution generated by ablation, the solid material vapor mass generated by ablation and the physical field distribution of the arc are obtained. The change in the nozzle diameter of the switch device is calculated based on the mass of the solid material vapor generated by ablation; the geometric model establishment steps and the arc burning and post-arc recovery characteristics determination steps are repeated according to the geometric structure of the deformed switch device to evaluate the influence of the ablation of the solid component material on the breaking capacity of the switch device.

[0052] Specifically, a numerical simulation model of arc characteristics taking into account the influence of ablation is established based on the magnetohydrodynamic theory (MHD); the numerical simulation model of arc characteristics is solved by the finite element analysis method. The control equations of the MHD arc simulation model include the conservation of mass, conservation of momentum, and conservation of energy equations. Since the ablation of solid components brings about changes in speed, energy, etc., the influence of ablation of solid components is superimposed on the momentum and energy conservation equations in the embodiment of the present invention, so that the results calculated by the simulation model are more accurate.

[0053] According to the control equation describing the arc characteristics of the C4F7N environmentally friendly mixed gas switch, the thermodynamic parameters and transport coefficient data of the C4F7N environmentally friendly mixed gas with different proportions are processed to calculate the temperature field distribution, pressure field distribution and gas flow rate distribution. Preferably, the arc characteristic numerical simulation model taking into account the influence of ablation processes the thermodynamic parameters and transport coefficients of the C4F7N environmentally friendly mixed gas with different proportions by interpolation method.

[0054] In the specific implementation, the thermodynamic parameters and transport coefficients of C4F7N environmentally friendly mixed gases with different proportions are first calculated and sorted into a data table. When it is necessary to obtain the thermodynamic parameters and transport coefficients of a certain proportion of C4F7N environmentally friendly mixed gas, the interpolation algorithm in the arc characteristic numerical simulation model taking into account the ablation effect is called to calculate the corresponding values ​​based on the known data points. For example, in the process of simulating arc combustion, as the composition of the C4F7N environmentally friendly mixed gas changes dynamically, the model can continuously use the interpolation method to obtain real-time thermodynamic parameters and transport coefficients, so as to accurately simulate the arc characteristics.

[0055] Wherein: the control equation describing the arc characteristics of the C4F7N environmentally friendly mixed gas switch includes:

[0056]

[0057]

[0058]

[0059]

[0060]

[0061] in,

[0062] Where: t is time; w and v are the axial and radial velocity components of the C4F7N environmentally friendly mixed gas, respectively; p is the pressure in the arc extinguishing chamber; T is the temperature in the arc extinguishing chamber; h is the thermal enthalpy of the C4F7N environmentally friendly mixed gas; J r and J z are the radial and axial current densities respectively; B θ is the magnetic induction intensity; μ l is the viscosity coefficient under laminar flow; μ t is the viscosity coefficient under turbulent state; k is the thermal conductivity; q is the energy lost by radiation per unit volume; ρ is the mass density of C4F7N environmentally friendly mixed gas; σ is the conductivity of C4F7N environmentally friendly mixed gas; l and t represent laminar flow and turbulent flow respectively, For electric potential.

[0063] Formula (6) shows that the current density J is related to the potential gradient It is directly proportional, the direction of the current density is opposite to the direction of the potential gradient, and the proportionality coefficient is the conductivity σ of the C4F7N environmentally friendly mixed gas.

[0064] The electric field distribution is calculated according to formula (5):

[0065]

[0066] Where ρ is the mass density of C4F7N environmentally friendly mixed gas, For electric potential.

[0067] The energy required for the ablation of the solid components of the switchgear is calculated by combining equations (1), (2), (3), (4), (7) and (8):

[0068]

[0069] in:

[0070]

[0071] Where D is the diffusion coefficient, c m，Cu and c m，PTFE They are respectively the mass proportion of the vapor of the electrode material copper and the mass proportion of the vapor of the nozzle material polytetrafluoroethylene in the mixed medium.

[0072] Furthermore, the mass of the nozzle vapor generated by ablation is determined according to the calculation formula of the radiation energy required to generate the vapor of solid material polytetrafluoroethylene by ablation:

[0073]

[0074] Among them, m PTFE is the nozzle vapor mass generated by ablation, Q ablation is the energy used for the vapor ablation of the solid material polytetrafluoroethylene at the nozzle, which is the volume integral of q in equation (4); h PTFE The energy required to vaporize unit mass of nozzle material.

[0075] In the above embodiment, the mass of electrode vapor generated by ablation is determined according to the energy conservation equation between the arc and the electrode and the calculation formula of the vapor mass of the solid material copper generated by ablation:

[0076]

[0077] Where, T a is the arc temperature in the first gas grid in contact with the electrode surface; T cis the temperature of the first solid grid on the electrode surface; Δh is the distance between the center of the first gas grid and the first solid grid; j i is the ion current density; j e is the electron current density; k B is the Boltzmann constant, k B =1.38×10 -23 (J / K); U c is the electrode voltage drop; U i is the ionization energy of arc plasma; φ c is the work function of the electrode material; is the electrode ablation rate; h v The energy required for gasification of unit mass of electrode; h cu The energy required to gasify the electrode material per unit mass; Q v is the energy used for electrode ablation, which is

[0078] It should be noted that after the switchgear geometry is established, the geometry needs to be meshed. The gas mesh is the mesh of the gas area, and the solid mesh is the mesh of the solid area.

[0079] Combination Figure 2 The numerical simulation models of arc characteristics taking into account the influence of ablation include: Navier-Stokes fluid control equations, radiation model, turbulence model and solid component ablation model.

[0080] More specifically, equations (1), (2), (3), (4), (7) and (8) together form the Navier-Stokes fluid governing equations. The radiation model describes the transmission and loss process of radiation energy in arc plasma; the turbulence model describes the turbulence phenomenon in arc plasma; and the solid component ablation model gas describes the heat conduction and material transport during the ablation process of the surface material of the gas switch solid component.

[0081] In one implementation of the present embodiment, the evaluation of the influence of ablation of solid component materials on the breaking capacity of the switching device through arcing and post-arc recovery characteristics includes: evaluating the influence of ablation of solid component materials on the breaking capacity of the switching device by comparing the change in arc conductivity 200ns before the current passes through zero and the maximum value of the recovery voltage rise rate (RRRV) applied by the gas insulation dielectric withstand system after the current passes through zero.

[0082] In another implementation of this embodiment, the evaluation criteria for assessing the impact of solid component material ablation on the breaking capacity of the switching device include: calculating the post-arc current between the arc gap after the short-circuit current passes through zero. If the post-arc current drops to an infinitesimal value, it indicates that the breaking is successful; if the post-arc current first decreases and then increases to infinity, the breaking fails.

[0083] In specific implementation, the current density can be calculated by inputting the current into the above formulas using the current waveform provided by the power grid system. As the number of interruptions increases, the ablation of solid components will cause the nozzle diameter to grow, affecting the interruption capacity.

[0084] In this embodiment, the change in the nozzle diameter of the switch device is obtained by calculating the mass of the solid material vapor generated by ablation. Since the change in the nozzle diameter causes the geometric structure of the device to change, it is necessary to re-establish the geometric model of the arc extinguishing structure of the switch device. The data input in step S2 are the physical parameters of the gas insulating medium. No matter how many times the ablation is performed, these input data remain unchanged. Only step S3 is required to calculate the concentration distribution of the solid material vapor generated by ablation, the mass of the solid material vapor generated by ablation, and the distribution of physical fields such as arc temperature, pressure, velocity, and electric field, so as to determine the breaking capacity of the switch device.

[0085] It can be obviously concluded from the above that the environmentally friendly gas arc characteristic simulation method taking into account the influence of ablation provided in this embodiment, by taking the thermodynamic parameters and transport coefficients of the C4F7N environmentally friendly mixed gas composed of different proportions as input data, establishes the control equation describing the arc characteristics of the C4F7N environmentally friendly mixed gas switch and the solid material vapor mass calculation model generated by ablation, so as to output the electric, magnetic, thermal and flow multi-physical field distribution in the arc extinguishing chamber during the process of forming an arc between the switch contacts when the switch device is opened or closed, the solid material vapor concentration distribution generated by ablation, the solid material vapor mass generated by ablation and the volt-ampere characteristics of the arc, and determines the change in the nozzle diameter of the switch device based on this to judge the breaking capacity of the switch device, which provides strong data support for the design and development of C4F7N environmentally friendly gas switch device.

[0086] The present invention is described in detail below by exploring the arc characteristics of C4F7N environmentally friendly mixed gas under the influence of solid material ablation:

[0087] First, the vapor concentration distribution generated by the ablation of solid parts such as electrodes and nozzles during the arc burning process of the C4F7N environmentally friendly mixed gas is calculated using equations (1)-(8) provided by the present invention. It is found that the presence of solid material vapor significantly affects the temperature distribution of the arc, thereby affecting the pressure distribution and flow field distribution in the arc extinguishing chamber of the switchgear, such as Figure 3As shown: The figure describes the pressure change in the expansion chamber of the arc extinguishing chamber during the opening process of the self-energized circuit breaker. The blue curve is the pressure curve for the first opening, and the yellow curve and the red curve are the pressure curves for the second and third times respectively after considering the increase in nozzle diameter caused by ablation. Although the higher the pressure in the expansion chamber is during the circuit breaker opening process, the more conducive it is to breaking, but ablation causes the pressure to drop, which leads to a degradation of the breaking capacity to a certain extent. Every time the switchgear completes a breaking, the structural dimensions of the solid components will also change due to the influence of ablation. Taking the self-energized circuit breaker as an example, ablation causes the throat diameter of the nozzle to gradually increase, and as the throat diameter of the nozzle increases, the air blowing effect in the arc extinguishing chamber is weakened, resulting in a decrease in breaking capacity. In addition, during the arc burning process, the increase in the throat diameter causes the energy required for ablation to decrease with the increase in the number of breaking times, and the mass of steam generated by nozzle ablation also gradually decreases, such as Figure 4 As shown, Figure 4 From left to right in the figure are the energy change curves of the first, second and third interruptions, where: the blue line represents the ablation quality, the red line represents the ablation energy, the solid line below is the main nozzle, the dotted line is the auxiliary nozzle, and the long dashed line is the total data of the main nozzle and the auxiliary nozzle. It can be seen that the ablation characteristics of solid components and their influence on the arc burning characteristics are important reference indicators for the optimal design of environmental protection switchgear, especially the electrode structure and the nozzle throat diameter and length.

[0088] In summary, the present invention adopts the optimized and improved MHD model to simulate the arc characteristics of the whole process of C4F7N environmentally friendly gas switch, takes into account the interaction between metal vapor, polytetrafluoroethylene produced by the nozzle and the environmentally friendly mixed gas and its influence on the arc characteristics, truly reflects the particle composition and key characteristic changes of the arc plasma of the environmentally friendly gas switch, and obtains the spatiotemporal distribution characteristics of the airflow field, pressure field, temperature field and electric field in the arc extinguishing chamber during the breaking process, which provides data support for the design and development of switching equipment such as C4F7N environmentally friendly gas circuit breakers.

[0089] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for simulating arc characteristics of environmentally friendly gas taking into account the influence of ablation, characterized in that: include: The geometric model establishment step is to establish a geometric model of the arc extinguishing structure of the switchgear filled with C4F7N environmentally friendly mixed gas; The arc plasma physical property parameter determination step is to determine the decomposition gas of the material of the relevant solid parts of the switchgear under the high temperature conditions of opening or closing and the particle components after mixing with the C4F7N environmentally friendly mixed gas, and calculate the thermodynamic parameters and transport coefficients of the C4F7N environmentally friendly mixed gas with different proportions; The arc burning and post-arc recovery characteristics are determined in steps, and a numerical simulation model of arc characteristics taking into account the influence of ablation is established. The thermodynamic parameters and transport coefficients of the C4F7N environmentally friendly mixed gas with different proportions obtained above are processed as input data of the arc characteristics numerical simulation model, and the electric, magnetic, thermal and flow multi-physical field distributions in the arc extinguishing chamber during the arc formation between the contacts of the switchgear are obtained, as well as the concentration distribution of solid material vapor generated by ablation, the mass of solid material vapor generated by ablation and the physical field distribution of the arc. The change in the nozzle diameter of the switchgear is calculated based on the mass of solid material vapor generated by ablation; the geometric model establishment steps and the arc burning and post-arc recovery characteristics determination steps are repeated according to the geometric structure of the deformed switchgear, and the influence of ablation of solid component materials on the breaking capacity of the switchgear is evaluated.

2. The method for simulating arc characteristics of environmentally friendly gas taking into account the influence of ablation according to claim 1, characterized in that: In the arc plasma physical property parameter determination step, the particle components are calculated according to the Gibbs free energy minimization theorem, the mass conservation law, the Dalton partial pressure law, the plasma quasi-neutrality characteristics and the stoichiometric conservation law; on this basis, the thermodynamic parameters are calculated by the statistical thermodynamic method, and the transport coefficient is calculated by the Chapman-Enskog method.

3. The method for simulating arc characteristics of environmentally friendly gas taking into account the influence of ablation according to claim 1, characterized in that: According to the control equation describing the arc characteristics of C4F7N environmentally friendly mixed gas switches, the thermodynamic parameters and transport coefficient data of C4F7N environmentally friendly mixed gases with different composition ratios are processed, and the temperature field distribution, pressure field distribution and gas flow rate distribution are calculated.

4. The method for simulating arc characteristics of environmentally friendly gas taking into account the influence of ablation according to claim 3, characterized in that: The control equations describing the arc characteristics of the C4F7N environmentally friendly mixed gas switch include: in, Where: t is time; w and v are the axial and radial velocity components of the C4F7N environmentally friendly mixed gas, respectively; p is the pressure in the arc extinguishing chamber; T is the temperature in the arc extinguishing chamber; h is the thermal enthalpy of the C4F7N environmentally friendly mixed gas; J r and J z are the radial and axial current densities respectively; B θ is the magnetic induction intensity; l and t represent laminar flow and turbulent flow respectively; μ l is the viscosity coefficient of C4F7N environmentally friendly mixed gas in laminar flow state; μ t is the viscosity coefficient of C4F7N environmentally friendly mixed gas in turbulent state; k l k is the thermal conductivity of C4F7N environmentally friendly mixed gas under laminar flow; t is the thermal conductivity of the C4F7N environmentally friendly mixed gas under turbulent state; q is the energy lost by radiation per unit volume; ρ is the mass density of the C4F7N environmentally friendly mixed gas; σ is the electrical conductivity of the C4F7N environmentally friendly mixed gas; is the potential; r is the radial coordinate, z is the axial coordinate, E is the electric field intensity, c p is the constant pressure specific heat capacity of C4F7N environmentally friendly mixed gas, viscous dissipation is viscous dissipation, and viscous terms are viscous terms.

5. The method for simulating arc characteristics of environmentally friendly gas taking into account the influence of ablation according to claim 4, characterized in that: The electric field distribution is calculated according to formula (5): Where ρ is the mass density of C4F7N environmentally friendly mixed gas, For electric potential.

6. The method for simulating arc characteristics of environmentally friendly gas taking into account the influence of ablation according to claim 4, characterized in that: The energy required for the ablation of the solid components of the switchgear is calculated by combining equations (1), (2), (3), (4), (7) and (8): in: Where D is the diffusion coefficient, c m，Cu and c m，PTFE They are respectively the mass proportion of the vapor of the electrode material copper and the mass proportion of the vapor of the nozzle material polytetrafluoroethylene in the mixed medium.

7. The method for simulating arc characteristics of environmentally friendly gas taking into account the influence of ablation according to claim 4, characterized in that: The mass of the nozzle steam produced by ablation is determined according to the calculation formula of the radiation energy required to produce solid material polytetrafluoroethylene vapor: Among them, m PTFE is the nozzle vapor mass generated by ablation, Q ablation is the energy used for ablation of the solid material polytetrafluoroethylene vapor at the nozzle, which is the volume integral of q in equation (4); h PTFE The energy required to vaporize unit mass of nozzle material.

8. The method for simulating arc characteristics of environmentally friendly gas taking into account the influence of ablation according to claim 1, characterized in that: The mass of electrode vapor generated by ablation is determined based on the energy conservation equation between the arc and the electrode and the energy required for gasification of the electrode unit mass: Where, T a is the arc temperature in the first gas grid in contact with the electrode surface; T c is the temperature of the first solid grid on the electrode surface; Δh is the distance between the center of the first gas grid and the first solid grid; j i is the ion current density; j e is the electron current density; k B is the Boltzmann constant, k B =1.38×10 -23 (J / K); U c is the electrode voltage drop; U i is the ionization energy of arc plasma; φ c is the work function of the electrode material; is the electrode ablation rate; h v The energy required for gasification of unit mass of electrode; h cu The energy required to gasify the electrode material per unit mass; Q v is the energy used for electrode ablation, which is 9. The method for simulating arc characteristics of environmentally friendly gas taking into account the influence of ablation according to claim 1, characterized in that: The method of evaluating the influence of ablation of solid component materials on the breaking capacity of the switch device through arcing and post-arc recovery characteristics includes: evaluating the influence of ablation of solid component materials on the breaking capacity of the switch device by comparing the change of arc conductivity 200ns before the current passes through zero and the maximum value of the recovery voltage rise rate applied by the gas insulation medium withstand system after the current passes through zero.

10. The method for simulating arc characteristics of environmentally friendly gas taking into account the influence of ablation according to claim 1, characterized in that: The evaluation criteria for assessing the impact of ablation of solid component materials on the breaking capacity of the switchgear include: calculating the post-arc current between the arc gaps after the short-circuit current passes through zero, and if the post-arc current drops to an infinitesimal value, it indicates that the breaking is successful; if the post-arc current first decreases and then increases to infinity, the breaking fails.

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