Method for simulating environmental gas arc characteristics considering ablation effect

Abstract

The application provides a kind of environmental gas arc characteristic simulation method considering ablation effect, comprising: establishing the geometric model of switch device filled with C4F7N environmental mixed gas;Calculate the thermodynamic parameters and transport coefficients of C4F7N environmental mixed gas with different proportions;According to the change of the nozzle diameter of switch device obtained by calculating the solid material vapor mass generated by ablation;According to the geometric structure of the deformed switch device, repeat the geometric model establishment step and the arc burning and post-arc recovery characteristic determination step, evaluate the influence of solid component material ablation on the breaking capacity of switch device.The application uses the optimized MHD model to simulate the arc characteristics of C4F7N environmental gas switch during the whole process, and obtains the space-time distribution characteristics of the flow 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 C4F7N environmental gas circuit breaker and other switch devices.

Description

Technical Field

[0001] This invention relates to the field of gas-insulated switchgear technology, and more specifically, to an environmentally friendly gas arc characteristic simulation method that takes into account the effects of ablation. Background Technology

[0002] Sulfur hexafluoride (SF6) gas is widely used in electrical equipment as an excellent insulating and arc-quenching medium. However, SF6 has a greenhouse effect 24,300 times that of CO2 and a lifespan in the atmosphere of up to 3,200 years, resulting in extremely significant adverse environmental impacts. Domestic and international research indicates that a mixture of perfluoroisobutyronitrile (C4F7N) gas and CO2, O2, and N2 exhibits high insulating strength and a low greenhouse effect, and is considered a superior environmentally friendly alternative to SF6. During equipment interruption, the multi-component mixture of C4F7N gas and CO2, O2, and N2 generates high-temperature arc plasma. While undergoing decomposition and ionization chemical reactions, this process also erodes the electrodes and nozzle walls within the arc-quenching chamber, significantly impacting high-capacity breaking capacity. Unlike SF6 gas, the reaction mechanisms of multi-component gas mixtures and their interaction with solid components are more complex. Under supersonic flow conditions, the high-temperature and high-pressure decomposition and complex chemical reactions, controlled flow and efficient energy dissipation, and electron transport and dielectric recovery strength characteristics of multi-component gas mixtures all exhibit multi-scale, strongly coupled, and strongly nonlinear relationships, leading to significant challenges in modeling and simulation. Therefore, constructing a dynamic simulation model of the arc considering ablation effects is more urgent and necessary for the arc characteristics of C4F7N environmentally friendly mixed gas switching.

[0003] The numerical simulation model of MHD arc characteristics based on magnetohydrodynamics assumes that the plasma in the arc region is electrically neutral and satisfies local thermal equilibrium (LTE) and local chemical equilibrium (LCE). Given the changes in the properties of solid materials such as electrodes and vessel walls in the C4F7N environmentally friendly mixed gas atmosphere, as well as the interaction between gas and solid materials, there is an urgent need to establish a simulation method for arc characteristics that takes into account the effects of electrode and nozzle ablation, providing theoretical guidance for the research and development of C4F7N gas switchgear. Summary of the Invention

[0004] In view of this, the present invention proposes an environmentally friendly gas arc characteristic simulation method that takes into account the ablation effect, aiming to solve the above-mentioned technical problems existing in the prior art.

[0005] This invention proposes a simulation method for the characteristics of environmentally friendly gas arcs that takes into account the effects of ablation, including:

[0006] The geometric model establishment steps are as follows: establish a geometric model of the arc extinguishing structure of the switchgear filled with C4F7N environmentally friendly mixed gas;

[0007] The steps for determining the physical properties of electric arc plasma include determining the decomposition gases of the relevant solid components of the switching equipment under high-temperature conditions of opening or closing, and the particle composition after mixing with C4F7N environmentally friendly mixed gas, and calculating the thermodynamic parameters and transport coefficients of C4F7N environmentally friendly mixed gas with different proportions.

[0008] The steps for determining the arc combustion and post-arc recovery characteristics include: establishing a numerical simulation model of arc characteristics that takes into account the ablation effect; processing the thermodynamic parameters and transport coefficients of the C4F7N environmentally friendly mixed gas with different proportions obtained above, and using them as input data for the numerical simulation model of arc characteristics; obtaining the distribution of multiple physical fields (electric, magnetic, thermal, and fluid) in the arc extinguishing chamber during the arc formation process between the switchgear contacts; 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 steps for establishing the geometric model and determining the arc combustion and post-arc recovery characteristics are repeated based on the geometric structure of the deformed switchgear to evaluate the impact of solid component material ablation on the switching equipment's breaking capacity.

[0009] Furthermore, in the above-mentioned simulation method for environmentally friendly gas arc characteristics that takes into account the ablation effect, in the step of determining the physical property parameters of the arc plasma, 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-neutral characteristics of plasma, and the law of conservation of stoichiometry; on this basis, the thermodynamic parameters are calculated by statistical thermodynamic methods, and the transport coefficient is calculated by the Chapman-Enskog method.

[0010] Furthermore, in the above-mentioned simulation method for the arc characteristics of environmentally friendly gas that takes into account the ablation effect, the thermodynamic parameters and transport coefficient data of C4F7N environmentally friendly mixed gas with different proportions are processed according to the control equation describing the arc characteristics of C4F7N environmentally friendly mixed gas, and the temperature field distribution, pressure field distribution and gas velocity distribution are calculated.

[0011] Furthermore, in the above-mentioned simulation method for the characteristics of environmentally friendly gas arcs that takes into account the effects of ablation, the control equations describing the arc characteristics of the C4F7N environmentally friendly mixed gas switch include:

[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 inside the arc-extinguishing chamber; T is the temperature inside the arc-extinguishing chamber; h is the enthalpy of the C4F7N environmentally friendly mixed gas; J rand J z These are the radial and axial current densities, respectively; B θ ρ represents magnetic flux density; l and t represent laminar and turbulent flow, respectively; μ l The viscosity coefficient of the C4F7N environmentally friendly mixed gas under laminar flow conditions; μ t The viscosity coefficient of the C4F7N environmentally friendly gas mixture under turbulent conditions; k l The thermal conductivity of the C4F7N environmentally friendly mixed gas in laminar flow; k t ρ is the thermal conductivity of the C4F7N environmentally friendly mixed gas under turbulent conditions; q is the energy lost per unit volume through radiation; ρ is the mass density of the C4F7N environmentally friendly mixed gas; σ is the electrical conductivity of the C4F7N environmentally friendly mixed gas. Let r be the electric potential; z be the radial coordinate; E be the axial coordinate; c be the electric field strength. p is the isobaric specific heat capacity of the C4F7N environmentally friendly mixed gas, viscous dissipation is the viscous dissipation, and viscous terms are the viscous terms.

[0015] Furthermore, in the above simulation method for environmentally friendly gas arc characteristics that takes into account the ablation effect, the electric field distribution is calculated according to equation (5):

[0016]

[0017] Where ρ is the mass density of the C4F7N environmentally friendly mixed gas. It represents the electrical potential.

[0018] Furthermore, in the above simulation method for environmentally friendly gas arc characteristics that takes into account the ablation effect, the energy required for the ablation of each solid component material of the switchgear is calculated by simultaneously solving 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 These represent the mass percentages of copper vapor (electrode material) and polytetrafluoroethylene vapor (nozzle material) in the mixed medium, respectively.

[0025] Furthermore, in the above-mentioned simulation method for the characteristics of environmentally friendly gas arcs that takes into account the effects of ablation, the mass of nozzle vapor generated by ablation is determined according to the calculation formula for the radiation energy required to generate polytetrafluoroethylene vapor from the solid material ablation:

[0026]

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

[0028] Furthermore, in the above-mentioned simulation method for environmentally friendly gas arc characteristics that takes into account the effects of ablation, 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 the vaporization of a unit mass of the electrode:

[0029]

[0030]

[0031] In the formula, T a T represents the arc temperature within the first gas grid in contact with the electrode surface. c Δh 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 center of the first solid grid; j i j is the ion current density; e k is the electron current density. B K is the Boltzmann constant. B =1.38×10 -23 (J / K); U c For electrode voltage drop; U i The ionization energy of the arc plasma; φ c The working function of the electrode material; It is the electrode ablation rate; h v The energy required for vaporization per unit mass of electrode; h cu Q is the energy required for the vaporization of a unit mass of electrode material. v The energy used for electrode ablation is given by equation (12).

[0032] Furthermore, in the above-mentioned environmentally friendly gas arc characteristic simulation method that takes into account the ablation effect, the evaluation of the impact of solid component material ablation on the switching equipment breaking capacity by the arc burning and post-arc recovery characteristics includes: evaluating the impact of solid component material ablation on the switching equipment breaking capacity by comparing the arc conductance change 200ns before the current crosses zero and the maximum value of the recovery voltage rise rate (RRRV) applied by the gas insulating dielectric withstand system after the current crosses zero.

[0033] Furthermore, in the above-mentioned simulation method for environmentally friendly gas arc characteristics that takes into account the effects of ablation, the evaluation criteria for assessing the impact of solid component material ablation on the breaking capacity of switchgear include: calculating the post-arc current between the arc gaps after the short-circuit current crosses zero; if the post-arc current drops to an infinitesimal value, the breaking is successful; if the post-arc current first decreases and then increases to infinity, the breaking fails.

[0034] The simulation method for the characteristics of environmentally friendly gas arc considering the ablation effect in this invention uses the thermodynamic parameters and transport coefficients of C4F7N environmentally friendly mixed gases with different proportions as input data to establish control equations describing the arc characteristics of C4F7N environmentally friendly mixed gas switches and a calculation model for the mass of solid material vapor generated by ablation. This outputs the distribution of multiple physical fields (electric, magnetic, thermal, and fluid) in the arc-extinguishing chamber during the arc formation process between the switch contacts when the switchgear is opened or closed, the concentration distribution of solid material vapor generated by ablation, the mass of solid material vapor generated by ablation, and the volt-ampere characteristics of the arc. Based on this, the change in the nozzle diameter of the switchgear is determined to judge the breaking capacity of the switchgear, providing strong data support for the design and development of C4F7N environmentally friendly gas switchgear. Attached Figure Description

[0035] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0036] Figure 1 A flowchart illustrating the simulation method for environmentally friendly gas arc characteristics considering ablation effects provided in an embodiment of the present invention;

[0037] Figure 2 A simulation flowchart of the arc characteristics of C4F7N environmentally friendly mixed gas switch considering the ablation effect is provided for embodiments of the present invention.

[0038] Figure 3 The simulation method in this embodiment is used to simulate the pressure change in the arc-extinguishing chamber of the gas switchgear under the condition of three cumulative opening and closing cycles;

[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 of three cumulative opening and closing of the gas switch device. Detailed Implementation

[0040] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0041] See Figure 1 The simulation method for environmentally friendly gas arc characteristics considering ablation effects in embodiments of the present invention includes:

[0042] Step S1: Establish a geometric model of the arc extinguishing structure of the switchgear containing C4F7N environmentally friendly mixed gas.

[0043] Specifically, the C4F7N environmentally friendly mixed gas is a binary or ternary environmentally friendly mixed gas composed 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 switching equipment are made of metallic copper or copper-tungsten alloy, and the nozzle material 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 / arc contacts and the pressure cylinder, it is also necessary to obtain the stroke-time curve and movement speed characteristics of the moving parts (such as the opening speed) during the arc simulation process, as input data to describe the motion characteristics of the moving parts.

[0046] Step S2, which determines the physical property parameters of the arc plasma, involves determining the decomposition gas of the relevant solid components of the switching equipment under high-temperature conditions of opening or closing, and the particle composition after mixing with the C4F7N environmentally friendly mixed gas. It also involves calculating the thermodynamic parameters and transport coefficients of the C4F7N environmentally friendly mixed gas with different proportions.

[0047] Specifically, the relevant solid component can be a nozzle or an electrode.

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

[0049] In this step, the particle composition is calculated based on 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, thermodynamic parameters are calculated using statistical thermodynamic methods, and transport coefficients are calculated using the Chapman-Enskog method.

[0050] More specifically, the decomposition gases of the nozzle material (polymers such as polytetrafluoroethylene) of the switching equipment at high temperatures and their particle composition after mixing with the C4F7N environmentally friendly mixed gas are calculated separately, as well as the particle composition of the vapor of the electrode material (metal, such as copper or copper-tungsten alloy) after mixing with the C4F7N environmentally friendly mixed gas. The density and enthalpy of the multi-component mixed gas are calculated, and the isobaric specific heat of the mixed gas is obtained by numerically differentiating the enthalpy. The transport coefficients, such as electrical conductivity, thermal conductivity, and viscosity, of the multi-component mixed gas are then calculated. The calculable temperature range for the multi-component mixed gas arc plasma system is 300K to 50000K.

[0051] Step S3, determining the arc combustion and post-arc recovery characteristics, involves establishing a numerical simulation model of arc characteristics that takes into account the ablation effect. 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 for the numerical simulation model. This obtains the distribution of multiple physical fields (electric, magnetic, thermal, and fluid) during the arc formation process between the switch contacts, 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 step and the arc combustion and post-arc recovery characteristic determination step are repeated based on the geometric structure of the deformed switchgear to evaluate the impact of solid component material ablation on the switching equipment's breaking capacity.

[0052] Specifically, a numerical simulation model of arc characteristics considering ablation effects is established based on magnetohydrodynamic (MHD) theory; the numerical simulation model of arc characteristics is solved using the finite element method. The governing equations of the MHD arc simulation model include mass conservation, momentum conservation, and energy conservation equations. Since the ablation of solid components causes changes in velocity, energy, etc., in this embodiment of the invention, the influence of solid component ablation is superimposed on the momentum and energy conservation equations, making the simulation model calculation results more accurate.

[0053] Based on the governing equations describing the arc characteristics of C4F7N environmentally friendly mixed gas, the thermodynamic parameters and transport coefficient data of C4F7N environmentally friendly mixed gases with different proportions are processed to calculate the temperature field distribution, pressure field distribution, and gas velocity distribution. Preferably, the numerical simulation model of arc characteristics considering the ablation effect processes the thermodynamic parameters and transport coefficients of C4F7N environmentally friendly mixed gases with different proportions using interpolation.

[0054] In practice, the thermodynamic parameters and transport coefficients of C4F7N environmentally friendly mixed gases with different proportions are first calculated and compiled into a data table. When it is necessary to obtain the thermodynamic parameters and transport coefficients of a specific proportion of C4F7N environmentally friendly mixed gas, the interpolation algorithm in the numerical simulation model of arc characteristics that takes into account the ablation effect is invoked to calculate the corresponding values ​​based on the known data points. For example, during the simulation of 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, thereby accurately simulating arc characteristics.

[0055] Wherein: the control equations describing the switching arc characteristics of C4F7N environmentally friendly mixed gas include:

[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 inside the arc-extinguishing chamber; T is the temperature inside the arc-extinguishing chamber; h is the enthalpy of the C4F7N environmentally friendly mixed gas; J r and J z These are the radial and axial current densities, respectively; B θ ρ is the magnetic flux density; μ l μ is the viscosity coefficient under laminar flow conditions. t ρ is the viscosity coefficient under turbulent conditions; k is the thermal conductivity; q is the energy lost per unit volume through radiation; ρ is the mass density of the C4F7N environmentally friendly gas mixture; σ is the electrical conductivity of the C4F7N environmentally friendly gas mixture; l and t represent laminar and turbulent flow, respectively. It represents the electrical potential.

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

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

[0065]

[0066] Where ρ is the mass density of the C4F7N environmentally friendly mixed gas. It represents the electrical potential.

[0067] The energy required for the ablation of the solid components of the switching equipment 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 These represent the mass percentages of copper vapor (electrode material) and polytetrafluoroethylene vapor (nozzle material) in the mixed medium, respectively.

[0072] Furthermore, the mass of the nozzle vapor generated by ablation is determined based on the formula for calculating the radiation energy required to generate polytetrafluoroethylene vapor, a solid material, through ablation:

[0073]

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

[0075] In the above embodiments, the mass of electrode vapor generated by ablation is determined according to the energy conservation equation between the electric arc and the electrode and the formula for calculating the mass of copper vapor generated by ablation:

[0076]

[0077] In the formula, T a T represents the arc temperature within the first gas grid in contact with the electrode surface. cΔh 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 center of the first solid grid; j i j is the ion current density; e k is the electron current density. B K is the Boltzmann constant. B =1.38×10 -23 (J / K); U c For electrode voltage drop; U i The ionization energy of the arc plasma; φ c The working function of the electrode material; It is the electrode ablation rate; h v The energy required for vaporization per unit mass of electrode; h cu Q is the energy required for the vaporization of a unit mass of electrode material. v The energy used for electrode ablation is given by equation (12).

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

[0079] Combination Figure 2 Numerical simulation models of arc characteristics that take into account the effects 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 control equations. The radiation model describes the transmission and loss of radiative energy in the arc plasma; the turbulence model describes the turbulence phenomena in the arc plasma; and the solid component ablation model describes the heat conduction and mass transport during the ablation process of the surface material of the solid component of the gas switch.

[0081] In one embodiment of this example, the evaluation of the impact of solid component material ablation on the breaking capacity of the switchgear by the arc burning and post-arc recovery characteristics includes: evaluating the impact of solid component material ablation on the breaking capacity of the switchgear by comparing the change in arc conductivity 200 ns before the current crosses zero and the maximum value of the recovery voltage rise rate (RRRV) applied by the gas insulating dielectric withstand system after the current crosses zero.

[0082] In another embodiment of this example, the evaluation criteria for assessing the impact of solid component material ablation on the switching equipment's breaking capacity include: calculating the post-arc current between the arc gaps after the short-circuit current crosses zero; if the post-arc current decreases to an infinitesimal value, the breaking is successful; if the post-arc current first decreases and then increases to infinity, the breaking fails.

[0083] In practice, the current density can be calculated by inputting the current into the formulas above using the current waveform provided by the power grid system. As the number of interruptions increases, the ablation of solid components will lead to an increase in the nozzle diameter, affecting the interruption capability.

[0084] In this embodiment, the change in the nozzle diameter of the switchgear is calculated based on the mass of solid material vapor generated by ablation. Since the change in nozzle diameter causes a change in the geometric structure of the equipment, it is necessary to re-establish the geometric model of the arc-extinguishing structure of the switchgear. The data input in step S2 are the physical property parameters of the gas insulating medium. No matter how many ablation cycles are performed, these input data remain unchanged. Only step S3 is needed to calculate the concentration distribution of solid material vapor generated by ablation, the mass of solid material vapor generated by ablation, and the distribution of physical fields such as arc temperature, pressure, velocity, and electric field, thereby determining the breaking capacity of the switchgear.

[0085] It is evident from the above that the simulation method for the characteristics of environmentally friendly gas arcs considering ablation effects provided in this embodiment, by using the thermodynamic parameters and transport coefficients of C4F7N environmentally friendly mixed gases with different proportions as input data, establishes control equations describing the arc characteristics of C4F7N environmentally friendly mixed gas switches and a calculation model for the mass of solid material vapor generated by ablation. This outputs the distribution of multiple physical fields (electric, magnetic, thermal, and fluid) in the arc-extinguishing chamber during the arc formation process between the switch contacts when the switchgear is opened or closed, the concentration distribution of solid material vapor generated by ablation, the mass of solid material vapor generated by ablation, and the volt-ampere characteristics of the arc. Based on this, the change in the nozzle diameter of the switchgear is determined to judge the breaking capacity of the switchgear, providing strong data support for the design and development of C4F7N environmentally friendly gas switchgear.

[0086] The present invention will be 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 components such as electrodes and nozzles during the arc ignition process of the C4F7N environmentally friendly mixed gas was calculated using equations (1)-(8) provided in this invention. The results showed that the presence of solid material vapor significantly affected the temperature distribution of the arc, thereby affecting the pressure distribution and flow field distribution within the arc-extinguishing chamber of the switching equipment, such as... Figure 3The figure illustrates the pressure changes in the expansion chamber within the arc-extinguishing chamber during the breaking process of a self-energized circuit breaker. The blue curve represents the pressure curve for the first breaking operation, while the yellow and red curves represent the pressure curves for the second and third breaking operations, respectively, after considering the increased nozzle diameter caused by ablation. Although higher pressure in the expansion chamber is more beneficial for breaking the circuit breaker, ablation causes a pressure drop, thus degrading the breaking capacity to some extent. Each time the switchgear completes a breaking operation, the structural dimensions of solid components change due to ablation. Taking a self-energized circuit breaker as an example, ablation causes the nozzle throat diameter to gradually increase. As the nozzle throat diameter increases, the air blowing effect within the arc-extinguishing chamber weakens, resulting in a decrease in breaking capacity. Furthermore, during the arc combustion process, the increased throat diameter leads to a decrease in the energy required for ablation with the increase in the number of breaking operations, and the mass of steam generated by nozzle ablation also gradually decreases. Figure 4 As shown, Figure 4 The graphs, from left to right, show the energy changes for the first, second, and third ablation operations. The blue line represents ablation mass, the red line represents ablation energy, the solid line below represents the main nozzle, the dotted line represents the auxiliary nozzle, and the long dashed line represents the combined data for the main and auxiliary nozzles. This demonstrates that the ablation characteristics of solid components and their impact on arc combustion characteristics are crucial reference indicators for the optimized design of environmentally friendly switchgear, especially regarding electrode structure and nozzle throat diameter and length.

[0088] In summary, this invention uses an optimized and improved MHD model to simulate the arc characteristics of the C4F7N environmentally friendly gas switch throughout the entire process. It considers the interaction between metal vapor, polytetrafluoroethylene generated from the nozzle, and the environmentally friendly mixed gas, as well as their impact on the arc characteristics. This model realistically reflects the particle composition and key characteristic changes of the arc plasma in 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. This provides data support for the design and development of switchgear such as the C4F7N environmentally friendly gas circuit breaker.

[0089] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for simulating the characteristics of an environmental gas electric arc taking into account the ablation effect, characterized in that, include: The geometric model establishment steps are as follows: establish a geometric model of the arc extinguishing structure of the switchgear filled with C4F7N environmentally friendly mixed gas; The steps for determining the physical properties of electric arc plasma include determining the decomposition gases of the relevant solid components of the switching equipment under high-temperature conditions of opening or closing, and the particle composition after mixing with C4F7N environmentally friendly mixed gas, and calculating the thermodynamic parameters and transport coefficients of C4F7N environmentally friendly mixed gas with different proportions. The steps for determining the arc combustion and post-arc recovery characteristics include: establishing a numerical simulation model of arc characteristics that takes into account the ablation effect; processing the thermodynamic parameters and transport coefficients of the C4F7N environmentally friendly mixed gas with different proportions obtained above and using them as input data for the numerical simulation model of arc characteristics; obtaining the distribution of multiple physical fields (electric, magnetic, thermal, and fluid) in the arc extinguishing chamber during the arc formation process between the switchgear contacts; 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; and calculating the change in the nozzle diameter of the switchgear based on the mass of solid material vapor generated by ablation; and re-exercising the geometric model establishment steps to update the model based on the deformed switchgear geometry, and then re-exercising the steps for determining the arc combustion and post-arc recovery characteristics to evaluate the impact of solid component material ablation on the switching equipment's breaking capacity.

2. The simulation method for environmentally friendly gas arc characteristics considering ablation effects according to claim 1, characterized in that, In the step of determining the physical properties of the electric arc plasma, the particle composition is calculated based on the Gibbs free energy minimization theorem, the law of conservation of mass, Dalton's law of partial pressures, the quasi-neutral characteristics of plasma, and the law of conservation of stoichiometry. On this basis, the thermodynamic parameters are calculated by statistical thermodynamic methods, and the transport coefficient is calculated by the Chapman-Enskog method.

3. The simulation method for environmentally friendly gas arc characteristics considering ablation effects according to claim 1, characterized in that, Based on the control equations describing the switching arc characteristics of C4F7N environmentally friendly mixed gas, the thermodynamic parameters and transport coefficient data of C4F7N environmentally friendly mixed gas with different proportions are processed to calculate the temperature field distribution, pressure field distribution, and gas velocity distribution.

4. The simulation method for environmentally friendly gas arc characteristics considering ablation effects according to claim 3, characterized in that, The control equations describing the switching arc characteristics of C4F7N environmentally friendly mixed gas include: in, In the formula: 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 inside the arc-extinguishing chamber; J ρ is the current density; h is the enthalpy of the C4F7N environmentally friendly gas mixture; J r and J z These are the radial and axial current densities, respectively; B θ ρ represents magnetic flux density; l and t represent laminar and turbulent flow, respectively; μ l The viscosity coefficient of the C4F7N environmentally friendly mixed gas under laminar flow conditions; μ t The viscosity coefficient of the C4F7N environmentally friendly gas mixture under turbulent conditions; k l The thermal conductivity of the C4F7N environmentally friendly mixed gas in laminar flow; k t ρ is the thermal conductivity of the C4F7N environmentally friendly gas mixture under turbulent conditions; q is the energy lost per unit volume through radiation; ρ is the mass density of the C4F7N environmentally friendly gas mixture; σ is the electrical conductivity of the C4F7N environmentally friendly gas mixture; φ is the electric potential; r is the radial coordinate; z is the axial coordinate; and E is the electric field strength. c p is the isobaric specific heat capacity of the C4F7N environmentally friendly mixed gas, viscous dissipation is the viscous dissipation, and viscous terms are the viscous terms.

5. The simulation method for environmentally friendly gas arc characteristics considering ablation effects according to claim 4, characterized in that, The electric field distribution is calculated according to equation (5): Where ρ is the mass density of the C4F7N environmentally friendly mixed gas, and φ is the potential.

6. The simulation method for environmentally friendly gas arc characteristics considering ablation effects according to claim 4, characterized in that, The energy required for the ablation of the solid components of the switching equipment is calculated by combining equations (1), (2), (3), (4), (7), and (8): in, D For diffusion coefficient, c m,Cu and c m,PTFE These represent the mass percentages of copper vapor (electrode material) and polytetrafluoroethylene vapor (nozzle material) in the mixed medium, respectively.

7. The simulation method for environmentally friendly gas arc characteristics considering ablation effects according to claim 6, characterized in that, The mass of nozzle vapor generated by ablation is determined based on the formula for calculating the radiation energy required to generate polytetrafluoroethylene vapor, a solid material, during ablation. in, The mass of the nozzle steam generated by ablation. The energy used for vapor ablation of the nozzle solid material polytetrafluoroethylene is the volume integral of q in equation (4); The energy required for a unit mass of nozzle material to vaporize.

8. The simulation method for environmentally friendly gas arc characteristics considering ablation effects 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 electric arc and the electrode, and the energy required for the vaporization of a unit mass of the electrode. In the formula, T a The arc temperature within the first gas grid in contact with the electrode surface; T c Δ represents the temperature of the first solid grid on the electrode surface. h This is the distance between the centers of the first gas grid and the first solid grid. j i This represents the ion current density. j e Electron current density; k B K is the Boltzmann constant. B =1.38×10 -23 J / K; U c This refers to the electrode voltage drop; U i The ionization energy of the electric arc plasma; φ c The working function of the electrode material; It is the electrode ablation rate; h v The energy required for the vaporization of a unit mass of electrode; h cu The energy required for the vaporization of a unit mass of electrode material; The energy used for electrode ablation is given by equation (12). h v .

9. The simulation method for environmentally friendly gas arc characteristics considering ablation effects according to claim 1, characterized in that, The assessment of the impact of solid component material ablation on the breaking capacity of switchgear by the arc burning and post-arc recovery characteristics includes: assessing the impact of solid component material ablation on the breaking capacity of switchgear by comparing the change in arc conductivity 200 ns before the current crosses zero and the maximum value of the recovery voltage rise rate applied by the gas insulating dielectric withstand system after the current crosses zero.

10. The simulation method for environmentally friendly gas arc characteristics considering ablation effects according to claim 1, characterized in that, The evaluation criteria for assessing the impact of solid component material ablation on the breaking capacity of switchgear include: calculating the post-arc current between the arc gaps after the short-circuit current crosses zero; if the post-arc current drops to an infinitesimal value, the breaking is successful; if the post-arc current first decreases and then increases to infinity, the breaking fails.

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