Dynamic simulation method and system for opening and closing process of SF6 circuit breaker

Abstract

The invention discloses a dynamic simulation method and system for the opening and closing process of an SF6 circuit breaker, and relates to the technical field of SF6 circuit breaker performance analys.The method comprises the steps that an arc extinguish chamber simulation model is built according to actual parameters of an arc extinguish chamber of the SF6 circuit breaker, and no ablation point is arranged in a contact area in the arc extinguish chamber simulation model; and carrying out dynamic simulation calculation on the opening process of the SF6 circuit breaker by utilizing the laminar flow field calculation model, the electric field calculation model, the pre-breakdown criterion of the arc extinguish chamber, the contact moving grid calculation model of the arc extinguish chamber and the set boundary conditions and combining with the arc extinguish chamber simulation model. According to the method, the laminar flow field calculation model is combined to perform dynamic simulation calculation on the opening process of the SF6 circuit breaker, and the flow characteristics of the SF6 gas in the SF6 circuit breaker are considered in the process, so that the obtained first dynamic simulation result is more fit with the actual opening process of the SF6 circuit breaker, and more accurate data support is provided for optimizing design parameters of the SF6 circuit breaker.

Description

Technical Field

[0001] The present invention relates to the technical field of SF6 circuit breaker performance analysis, and in particular to a dynamic simulation method and system for the opening and closing process of an SF6 circuit breaker. Background Art

[0002] Sulfur hexafluoride circuit breakers (SF6 circuit breakers) are often used in high-voltage power systems, mainly for disconnecting fault currents and protecting the safe operation of equipment in high-voltage power systems. They have the advantages of high reliability and easy operation, and can effectively reduce the failure rate of equipment. At present, when optimizing the design parameters of SF6 circuit breakers, the analysis is often based on the mechanical structure of the SF6 circuit breaker. However, due to the presence of SF6 gas in the SF6 circuit breaker, the performance of the SF6 circuit breaker produced according to the optimized design parameters often fails to meet expectations, consuming a lot of manpower and material resources, and extending the R&D cycle of the SF6 circuit breaker, resulting in low R&D efficiency. Summary of the invention

[0003] The technical problem to be solved by the present invention is to address the deficiencies of the prior art and specifically provide a dynamic simulation method and system for the opening and closing process of an SF6 circuit breaker, as follows:

[0004] 1) In the first aspect, the present invention provides a dynamic simulation method for the opening and closing process of an SF6 circuit breaker, and the specific technical scheme is as follows:

[0005] According to the actual parameters of the arc extinguishing chamber of the SF6 circuit breaker, an arc extinguishing chamber simulation model is constructed, and no ablation point is set in the contact area of ​​the arc extinguishing chamber simulation model;

[0006] By using the laminar field calculation model, the electric field calculation model, the pre-breakdown criterion of the arc extinguishing chamber, the contact movement grid calculation model of the arc extinguishing chamber and the set boundary conditions, and combining the arc extinguishing chamber simulation model, the opening process of the SF6 circuit breaker is dynamically simulated and calculated to obtain the first dynamic simulation result.

[0007] The beneficial effects of the dynamic simulation method of the opening and closing process of the SF6 circuit breaker provided by the present invention are as follows:

[0008] The opening process of the SF6 circuit breaker is dynamically simulated and calculated in combination with the laminar flow field calculation model. This process takes into account the flow characteristics of the SF6 gas in the SF6 circuit breaker, so that the first dynamic simulation result is more consistent with the actual opening process of the SF6 circuit breaker, providing more accurate data support for optimizing the design parameters of the SF6 circuit breaker, so that the performance of the SF6 circuit breaker produced according to the optimized parameters meets the expectations, reduces the waste of manpower and material resources, and greatly reduces the R&D cycle of the SF6 circuit breaker, with high R&D efficiency.

[0009] 2) In the second aspect, the present invention also provides a dynamic simulation system for the opening and closing process of an SF6 circuit breaker, and the specific technical solution is as follows:

[0010] Including model building module and simulation calculation module;

[0011] The model building module is used to: build an arc extinguishing chamber simulation model according to the actual parameters of the arc extinguishing chamber of the SF6 circuit breaker, and no ablation point is set in the contact area of ​​the arc extinguishing chamber simulation model;

[0012] The simulation calculation module is used to: use the laminar field calculation model, the electric field calculation model, the pre-breakdown criterion of the arc extinguishing chamber, the contact movement grid calculation model of the arc extinguishing chamber and the set boundary conditions, and combine the arc extinguishing chamber simulation model to dynamically simulate the opening process of the SF6 circuit breaker to obtain the first dynamic simulation result.

[0013] 3) In a third aspect, the present invention further provides an electronic device, comprising a processor, the processor being coupled to a memory, the memory storing at least one computer program, the at least one computer program being loaded and executed by the processor, so that the electronic device can implement any of the above-mentioned dynamic simulation methods for the opening and closing processes of an SF6 circuit breaker.

[0014] 4) In a fourth aspect, the present invention further provides a computer-readable storage medium having a computer program stored thereon, and when the computer program is executed by a processor, the method for dynamic simulation of any of the above-mentioned SF6 circuit breaker opening and closing processes is implemented.

[0015] It should be noted that the beneficial effects achieved by the technical solutions of the second to fourth aspects of the present invention and the corresponding possible implementation methods can be found in the above-mentioned technical effects of the first aspect and its corresponding possible implementation methods, and will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments of the present invention:

[0017] Figure 1 : A schematic flow chart of a dynamic simulation method for the opening and closing process of an SF6 circuit breaker according to an embodiment of the present invention;

[0018] Figure 2 The following is a schematic diagram of the structure of the arc extinguishing chamber of the SF6 circuit breaker of model LW30-126;

[0019] Figure 3 The figure is a schematic diagram of the opening process of the SF6 circuit breaker of model LW30-126;

[0020] Figure 4: A schematic diagram of an arc extinguishing chamber simulation model obtained by modeling an arc extinguishing chamber of an SF6 circuit breaker of type LW30-126;

[0021] Figure 5 : A schematic diagram of the pressure-density function relationship of SF6 gas;

[0022] Figure 6 : A schematic diagram of the relationship between the pressure and relative dielectric constant of SF6 gas;

[0023] Figure 7 : A schematic diagram of a typical non-burned circuit breaker capacitance-time curve;

[0024] Figure 8 : A schematic diagram of a typical non-burned circuit breaker capacitance-travel curve;

[0025] Fig. 9 It is: a schematic diagram of adding 50 microns of metal fluoride model;

[0026] Fig.10 : A schematic diagram of the curve of the maximum field intensity in the arc extinguishing chamber changing with time;

[0027] Fig.11 : Schematic diagram of the model at different ablation degrees;

[0028] Fig.12 : Schematic diagram of the relationship between arc contact ablation angle and contact overtravel;

[0029] Fig.13 : Schematic diagram of the contact model under different ablation degrees;

[0030] Fig.14 : A data diagram of the duration of the pre-breakdown arc under different ablation states;

[0031] Fig.15 Schematic diagram of the contact erosion process.

[0032] Fig.16 Schematic diagram of the opening and ablation process of the contact;

[0033] Fig.17 : A schematic diagram showing the relationship between the pre-breakdown time and the internal insulation performance;

[0034] Fig.18 : A schematic diagram of the pre-breakdown time detection principle;

[0035] Fig.19 Figure 1: Schematic diagram of SF6 gas decomposition. DETAILED DESCRIPTION

[0036] The principles and features of the present invention are described below. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0037] The technical solution of the present invention and how the technical solution of the present invention solves the above-mentioned technical problems are described in detail below with specific embodiments. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments. The embodiments of the present invention will be described below in conjunction with the accompanying drawings.

[0038] like Figure 1 As shown, a dynamic simulation method for the opening and closing process of an SF6 circuit breaker according to an embodiment of the present invention comprises the following steps:

[0039] S1. According to the actual parameters of the arc extinguishing chamber of the SF6 circuit breaker, an arc extinguishing chamber simulation model is constructed, and no ablation point is set in the contact area of ​​the arc extinguishing chamber simulation model;

[0040] Take the SF6 circuit breaker model LW30-126 for example. Figure 2 As shown, the arc extinguishing chamber of the SF6 circuit breaker of model LW30-126 includes: an upper terminal board 1, an arc extinguishing porcelain sleeve 2, a static contact 3, a nozzle 4, a pressure cylinder 5, a lower terminal board 6, an insulating pull rod 7, a supporting porcelain sleeve 8, an adsorbent, a moving contact 10, a valve plate 11 and a moving contact seat 12. The static contact is divided into a static main contact 14 and a static arc contact 13, and the moving contact is divided into a moving main contact 16 and a moving arc contact 15. The main contact and the arc contact of the circuit breaker are connected in parallel. When the circuit breaker is in the closed state, the main contact and the arc contact are closed respectively, and the nozzle 4 and the static arc contact 13 are in close contact. Figure 2 (a) shows the closing state, Figure 2 (b) shows the open state, Figure 3 The figure shows the opening process of the SF6 circuit breaker of model LW30-126. Specifically, when the circuit breaker receives the opening signal, the transmission device starts to drive the moving main contact, moving arc contact, nozzle and pressure cylinder of the circuit breaker to move downward. Figure 3 As shown in (a), during the opening process, the valve plate is fixed, the nozzle is in close contact with the static arc contact, so that the nozzle is closed, and the pressure cylinder moves downward, causing the gas in the cylinder to be compressed, resulting in a rapid increase in the gas pressure in the cylinder; after moving for a distance, the main contact is designed to be shorter than the arc contact, so the contact stroke of the main contact is shorter, and the dynamic and static main contacts are separated first, as shown in Figure 2. Figure 3 (b); after moving for a distance, the moving and static arc contacts also begin to separate, and an arc is generated between the arc contacts. The arc heats the surrounding SF6 gas, causing the pressure in the cylinder to further increase. At this time, the nozzle is still closed; the transmission device continues to drive the pressure cylinder downward. When the nozzle opens, due to the high pressure in the pressure cylinder, the huge pressure difference causes the SF6 gas in the cylinder to be ejected quickly from the nozzle, acting on the arc, as shown in Figure 2. Figure 3 (c) As shown; the huge airflow causes the arc to cool down quickly, and the arc extinguishes when the current passes through zero, as shown in Figure 3 (d) as shown.

[0041] Among them, the process of constructing the arc extinguishing chamber simulation model is as follows: Use COMSOL Multiphysics simulation software or other simulation software to build a model according to the actual parameters of the arc extinguishing chamber of the SF circuit breaker. The constructed arc extinguishing chamber simulation model is a two-dimensional axisymmetric figure. This feature of the arc extinguishing chamber can be used in the simulation software to greatly simplify the difficulty of building the model. The complete arc extinguishing chamber simulation model also includes structures such as terminal blocks, insulating pull rods, porcelain sleeves, and transmission mechanisms. It mainly focuses on the change in capacitance during the opening process of the arc extinguishing chamber contacts of the circuit breaker. The size of the capacitance value mainly depends on the arc contact. Therefore, the arc extinguishing chamber simulation model is simplified, and only the main structures such as the moving contact, static contact, and nozzle in the arc extinguishing chamber are retained. The simplified calculation model is beneficial to the subsequent simulation calculation process. Therefore, the arc extinguishing chamber model of the SF6 circuit breaker with model LW30-126 is constructed. The constructed arc extinguishing chamber simulation model is as follows Figure 4 As shown, Figure 4 (a) shows the overall simulation model of the arc extinguishing chamber. Figure 4 (a) shows a part of the arc extinguishing chamber simulation model.

[0042] S2. Using the laminar flow field calculation model, the electric field calculation model, the pre-breakdown criterion of the arc extinguishing chamber, the contact movement grid calculation model of the arc extinguishing chamber and the set boundary conditions, and combining the arc extinguishing chamber simulation model, the opening process of the SF6 circuit breaker is dynamically simulated and calculated to obtain the first dynamic simulation result.

[0043] Among them, the laminar flow field calculation model includes: two-dimensional compressible Navier-Stokes equations and k-ε turbulence equations, the electric field calculation model is the Laplace equations, the two-dimensional compressible Navier-Stokes equations include mass conservation equations, momentum conservation equations and energy conservation equations, and the k-ε turbulence equations include turbulent kinetic energy equations and turbulent dissipation equations, specifically:

[0044] 1) The mass conservation equation of the Navier-Stokes equations in the two-dimensional cylindrical coordinate system is:

[0045]

[0046] In formula (1), 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.

[0047] 2) The momentum conservation equation includes equation (2) and equation (3):

[0048]

[0049] In formula (2) and formula (3), F r and F θ are the projections of the body force in the r-axis direction and the θ-axis direction respectively; μ is the gas dynamic viscosity coefficient; is the second dynamic viscosity coefficient.

[0050] Since no arc is generated during the no-load breaking process, it can be considered as isothermal flow and there is no need to consider energy changes.

[0051] 3) Turbulent kinetic energy equation:

[0052]

[0053] 4) Turbulence dissipation equation:

[0054]

[0055] Among them, μ t =C μ ρk 2 / ε, ε is the turbulent dissipation power; C1, C2, C μ , σ k , σ ε is an empirical constant in the turbulence model.

[0056] 5) During the high-voltage circuit breaker breaking process, the electric field in the arc extinguishing chamber satisfies the Laplace equations:

[0057]

[0058] in, is the potential of the static arc contact, is the potential of the moving arc contact.

[0059] The movement of the static contact in the simplified arc extinguishing chamber simulation model lacks the pre-compression stage of the SF6 gas in the compressed air chamber. Therefore, in order to simulate the gas pressure changes in the compressed air chamber during the opening and closing process of the circuit breaker arc extinguishing chamber, it is also necessary to obtain the pressure characteristics of the upper port of the compressed air chamber. There have been many studies on the compressed air characteristics of the typical 126kV SF6 circuit breaker no-load breaking process. Scholars have obtained the pressure changes at various positions in the arc extinguishing chamber during the breaking process from two perspectives: theoretical calculation and experimental measurement. The simulation uses the 126kV SF6 circuit breaker compressed air cylinder upper outlet pressure curve obtained from previous studies as the model input.

[0060] The pre-breakdown criterion of the arc extinguishing chamber is explained as follows:

[0061] In a slightly non-uniform electric field, the breakdown process of SF6 gas can be explained by streamer theory. The criterion for critical breakdown (pre-breakdown criterion) is:

[0062]

[0063] In formula (9), α is the ionization coefficient; η is the electron adsorption coefficient; K is a constant, which is 18, and the integral runs through the entire area along the electric field line. The effective ionization coefficient of the gas is defined as γ = α-η, and its value is approximately linearly related to the ratio of the electric field intensity E and the gas particle density N, which plays a key role in the breakdown of the gas gap. For SF6 gas, when the effective ionization coefficient is zero, E / N = 3.56×10-19V·m2, which is the critical value, recorded as (E / N)*. Therefore, the breakdown criterion of the gas can be expressed as:

[0064]

[0065] Considering the following relationship between gas particle density N and gas density ρ:

[0066]

[0067] In formula (11), is the molecular weight of SF6 gas; NA is Avogadro's constant, which is 6.022×10 23 .

[0068] Therefore, when breakdown occurs, we have:

[0069]

[0070] At this time, the breakdown voltage is:

[0071]

[0072] In the calculation, the NS equation can directly solve the gas pressure, and the gas density can be obtained by introducing the ideal gas state equation:

[0073]

[0074] Among them, the contact movement grid calculation model of the arc extinguishing chamber is explained as follows:

[0075] The 126kV SF6 circuit breaker arc extinguishing chamber selected in the test adopts the self-energy arc extinguishing principle, and the SF6 gas is blown out by the compressed air cylinder through the nozzle. The total stroke of the moving contact of the circuit breaker during the opening process is 150mm, the contact stroke is 27mm, and the breaking distance when fully opened is 123mm. The circuit breaker opening time is 50±10ms, and the moving contact movement speed during the breaking process is 3~3.5m / s.

[0076] Considering that the structure of the moving contact of the circuit breaker is relatively complex, while the structure of the static contact is relatively simple, when only the capacitance between the contacts is considered, the static contact can be set to move while the moving contact remains unchanged during the opening process. At this time, the relative movement process of the moving contact and the static contact is the same as the actual opening process. This can simplify the simulation calculation process, make the mesh division more refined, and obtain more accurate calculation results. Specify the static contact mesh moving speed as an expression composed of a step function step1:

[0077] v=3step1(0.045[s]≥t[s]≥0.015[s]) (15)

[0078] The actual moving speed of the grid is 3m / s, and it starts moving from 15ms. In order to simplify the calculation process, it is stipulated that the contacts stop when the contact is just opened. The first 100mm of the stroke during the opening process is selected as the calculation object, and the movement time is 30ms.

[0079] Some physical parameters of SF6 gas in the arc extinguishing chamber will change with the change of pressure, and this change is nonlinear. Therefore, it is necessary to set the functional relationship of SF6 gas density and relative dielectric constant with nonlinear change of pressure in the model. The functional relationship of each parameter is as follows:

[0080] The ideal gas state equation is:

[0081] PM=ρRT (16)

[0082] In formula (16), P is the gas pressure, Pa; M is the molar mass of the gas, kg / mol; ρ is the gas density, kg / m 3 ; R is the universal gas constant, and its value is related to the unit of the state parameter. In the International System of Units, R = 8.31 J / (mol·K); T is the temperature of the gas, K.

[0083] Since the volume, amount of substance and temperature of the gas in the arc extinguishing chamber are all constants, the density of SF6 gas is proportional to the pressure in this case. Referring to the density of SF6 gas at different pressures in the "Gas Discharge Plasma Basic Database" of Xi'an Jiaotong University, the functional relationship between the density of SF6 gas and the pressure is fitted, as shown in Figure 5 shown.

[0084] The relative dielectric constant of SF6 gas is important for the calculation of the break capacitance, and its size will directly affect the calculation results. Studies have shown that the pressure of the gas will affect the size of its relative dielectric constant. The initial pressure of the SF6 gas in the arc extinguishing chamber is 6atm. During the opening process, the pressure in the compressed gas chamber will even reach more than 10atm, which may have a certain impact on the relative dielectric constant of SF6 gas. In order to obtain a more accurate value of the break capacitance of the arc extinguishing chamber, the relative dielectric constant of SF6 gas is set as a variable that changes with pressure. In the Clausius-Mossotti equation, the macroscopic parameters and microscopic parameters of the electrolyte polarization in the electric field are linked. Its mathematical expression is as follows:

[0085]

[0086] Among them, ε r is the relative dielectric constant of the gas; ε r is the dielectric constant of vacuum air; n is the number of polarized gas particles per unit volume; α is the polarizability of air molecules.

[0087] Converting the polarizable particles per unit volume into the number of polarizable particles per molar volume yields:

[0088]

[0089] In formula (18), M is the molar mass of the gas dielectric, mol / kg; ρ is the density of the gas dielectric, kg / m3; N0 is the Avogadro constant. In the formula, [P] represents the polarization process of the dielectric particles. The right half of the formula indicates that for a given dielectric, when the polarizability is constant and is not affected by the density ρ, [P] is a constant.

[0090] This relationship is usually described by the gas state equation when humidity is not taken into account:

[0091]

[0092] ρ0, T0 and P0 are the density, temperature and pressure of the gas in a certain state respectively; T and P are the temperature and pressure of the gas in the standard state respectively.

[0093] When T0 = 273K, P0 = 101.3kPa (standard state), the density of SF6 gas is 6.0886kg / m 3 , substituting into the above formula, we can get:

[0094]

[0095] Substituting the above formula into the Clausius-Mossauddi equation, we get:

[0096]

[0097] When the temperature remains constant, Substituting into the above formula, we can get:

[0098]

[0099] Therefore, the relationship between the relative dielectric constant and pressure of the gas can be obtained as follows:

[0100]

[0101] Under standard atmospheric pressure, the relative dielectric constant of SF6 gas is 1.002049. Substituting it into Q, the above formula can be rewritten as:

[0102]

[0103] So the relationship between the relative dielectric constant of SF6 gas and gas pressure at constant temperature is obtained, such as Figure 6 shown.

[0104] The boundary conditions set include: laminar flow field boundary conditions, electrostatic field boundary conditions and dynamic grid boundary conditions. Specifically:

[0105] 1) Laminar flow field boundary conditions (also known as gas laminar flow module boundary conditions):

[0106] The boundary conditions of the laminar flow physical field include fluid properties, initial values, axisymmetry, wall, inlet, and outlet. The settings of each boundary are as follows: ① Fluid properties: The SF6 gas in the arc extinguishing chamber is set as a fluid, and the fluid properties come from the material definition; ② Initial values: The initial pressure of the SF6 gas is set to 6atm, and the initial velocity is set to 0; ③ Wall: All solid surfaces in the arc extinguishing chamber are set to walls, and the gas flow rate on the boundary is 0; ④ Symmetry axis: On the symmetry boundary, the radial velocity of the gas is zero, and the values ​​of other physical quantities are equal inside and outside the boundary; ⑤ Inlet boundary: Set the piston part as the inlet, and set the gas pressure at the inlet according to the defined pressure cylinder pressure change function; ⑥ Outlet boundary: Set the top of the arc extinguishing chamber as the outlet, and set the gas pressure at the inlet according to the initial pressure of the gas.

[0107] 2) The boundary conditions of the electrostatic field are divided into charge conservation, zero charge, axisymmetry, initial value, moving contact, and static contact. The boundary conditions are set as follows: ① Charge conservation: Except for the moving contact and static contact, other parts of the circuit breaker comply with charge conservation. ② Zero charge: Set the boundary of the air domain to zero point charge to limit the range of the electrostatic field; ③ Initial value: The circuit breaker is regarded as uncharged, and the initial value of the potential of the entire circuit breaker is 0. ④ Set the moving contact as a voltage type terminal and set its potential to 1V. ⑤ Set the static contact to a zero potential terminal.

[0108] 3) The dynamic grid boundary conditions are divided into fixed grid, free deformation, specified grid displacement and specified grid speed. The specific settings are as follows: ① Fixed grid: the nozzle and moving contact part in the arc extinguishing chamber are set as fixed grids; ② Specified grid displacement: the displacement of the fixed grid boundary, the arc extinguishing chamber wall boundary and the symmetry axis in all directions is set to zero; ③ Free deformation: the static arc contact and SF6 gas are set as free deformation areas; ④ Specified grid speed: the static arc contact is specified as the moving object, the moving speed is set to 3m / s, and the total movement time is 30ms.

[0109] The grid of the arc extinguishing chamber simulation model is divided into free triangle shapes. The grid is set to automatically re-divide the grid during the grid movement, and the specified grid quality must not be less than 0.5; in order to obtain more accurate calculation results and avoid grid distortion during grid movement, the grid around the static contact is manually set and its number of grids is fixed. The model is aimed at the dynamic value of the break capacitance during the opening process, so it is necessary to use a transient solver to solve it. Its tolerance is automatically controlled by the physical field, and the step size of the contact movement process is set to 0.1ms. The total number of free pairs solved for the model is 45682, and the total calculation time is 21 hours.

[0110] A dynamic simulation calculation is performed on the opening process of the SF6 circuit breaker to obtain a first dynamic simulation result, which includes: during the opening process, the electric field distribution in the SF6 circuit breaker, the flow velocity distribution of SF6 gas, the pressure distribution, the change in the capacitance value of the circuit breaker's break capacitance, etc.

[0111] Calculate the pressure distribution in the arc extinguishing chamber at different times. The first stage is the process from the static contact starting to move to the process of just separating from the moving contact. This process lasts about 15ms. Since the two contacts (static contact and moving contact) are in contact at this stage, this arc extinguishing chamber simulation model simulates the process after the circuit breaker contacts are separated. This process is not simulated in the model. The pressure input function in the inlet boundary of the laminar flow field boundary condition replaces the pressure change at this stage. In the arc extinguishing chamber of the actual SF6 circuit breaker, at this stage, since the moving contact has moved a distance, but the nozzle has not been opened, the SF6 gas in the compressed air chamber has been compressed, and the SF6 gas pressure gradually increases from the initial 6atm to about 10atm; the second stage is the process from the static contact and the moving contact to the nozzle is about to open. During this process, the pressure in the compressed air chamber is further compressed as the contacts move rapidly. At the same time, the high-temperature arc generated after the arc contacts are separated will heat the SF6 gas between the arc contacts. The temperature rise and expansion of the SF6 gas will further increase the pressure in the compressed air chamber. At this time, the gas pressure in the compressed air chamber can reach a maximum of 14atm, and the pressure difference inside and outside the contact port is as high as 7atm. The third stage is the process from the nozzle being fully opened to being fully opened. At 30ms, the contact port has just opened. Since the nozzle is small at this time, the SF6 gas cannot flow out quickly and in large quantities. The pressure of the SF6 gas in the compressed air chamber is still as high as 13-14atm. As the contacts move and the contact port is further opened, the SF6 gas in the compressed air chamber is quickly ejected from the nozzle, and the gas pressure also decreases.

[0112] Calculate the velocity distribution of SF6 gas in the arc extinguishing chamber at different times, specifically, calculate the velocity distribution of SF6 gas at t=10ms, calculate the velocity distribution of SF6 gas at t=20ms, calculate the velocity distribution of SF6 gas at t=30ms, and calculate the velocity distribution of SF6 gas at t=40ms. According to the velocity distribution of SF6 gas in the arc extinguishing chamber at different times, it can be seen that in the first and second stages before the contact opening, there is no obvious flow of gas in the arc extinguishing chamber, and only a small amount of gas flows out of the compressed air chamber through the gap between the contact. In the third stage, the nozzle begins to open gradually. Due to the large pressure difference between the inside and outside of the compressed air chamber, SF6 gas will be ejected quickly with the opened nozzle. At this time, the flow rate of SF6 gas can reach up to about 250m / s. It is these high-speed flowing gases that blow out the arc between the arc contacts.

[0113] Calculate the electric field distribution in the arc extinguishing chamber at different times, specifically, calculate the electric field distribution in the arc extinguishing chamber at t = 10ms, calculate the electric field distribution in the arc extinguishing chamber at t = 20ms, calculate the electric field distribution in the arc extinguishing chamber at t = 30ms, and calculate the electric field distribution in the arc extinguishing chamber at t = 40ms. Since the voltage difference between the moving contact and the static contact in the arc extinguishing chamber simulation model is constant at 1V, the electric field strength between the contacts is mainly affected by the size of the gap. As can be seen from the figure, at the moment when the contacts are just separated at t = 0ms, due to the very small distance between the contacts, the electric field strength at this time is even as high as hundreds of volts per meter; at t = 20ms, the contact moves to the nozzle position, and due to the increase in the distance between the contacts, the electric field strength decreases significantly, and only the field strength at the end of the contact is maintained at about 150v / m; at t = 32ms, the contact moves to the nozzle opening position, and the electric field strength decreases further at this time, and the maximum electric field strength is only about 20V / m.

[0114] The capacitance-time curve of a typical unburned circuit breaker contact is as follows: Figure 7 As shown in the figure, it can be found that the contacts in the model start to move at 15ms. At this time, the distance between the SF6 circuit breaker contacts is the smallest, and the corresponding capacitance value is also the largest at 21pF. As the contacts of the SF6 circuit breaker begin to move, the distance between the contacts continues to increase, and the corresponding capacitance value also shows a significant downward trend, which is consistent with the results of theoretical speculation; the capacitance value between the contacts decreases at the fastest rate within 15 to 17ms after the contacts begin to move, and the reduction in the capacitance value of the break within 3ms even exceeds half of the total reduction value. After 30ms, the rate of decrease of the capacitance value between the contacts decreases significantly.

[0115] Typical capacitance-travel curve between contacts of un-eroded circuit breaker is as follows: Figure 8 As shown. On the basis of the capacitance-time curve, the curve of the capacitance value between contacts changing with the contact stroke is obtained by measuring the distance moved by the static contact in the model. The capacitance value of the contact at different positions can be clearly shown through the capacitance-stroke curve of the contact. It can be seen from the figure that the contact starts to move from 29mm, and the capacitance between the contacts shows an obvious downward trend with the increase of stroke. Within the stroke of 29-40mm, the capacitance value between the contacts decreases very rapidly; in the second half of the stroke, the rate of decrease of the capacitance value is obviously slower than that in the first half; the overall change characteristics correspond to the capacitance-time curve.

[0116] Optionally, in the above technical solution, it also includes:

[0117] S3. Analyze the influence of the SF6 gas in the arc extinguishing chamber on the break capacitance of the SF6 circuit breaker according to the first dynamic simulation result, and analyze the closing pre-breakdown characteristics of the SF6 circuit breaker according to the first dynamic simulation result.

[0118] Among them, the analysis process of the influence of SF6 gas on the break capacitance of SF6 circuit breaker is as follows:

[0119] The change in pressure causes the relative dielectric constant of SF6 gas in the arc extinguishing chamber to have different values ​​at different times. Through simulation calculation, it is found that the relative dielectric constant of SF6 in the compressed air chamber has obvious changes during the circuit breaker breaking process. The calculation results show that the maximum relative dielectric constant of SF6 is 1.0201.

[0120] In order to explore the influence of the change of the relative dielectric constant of SF6 gas on the capacitance of the break when the circuit breaker is opened, a simulation model of the arc extinguishing chamber without considering the gas flow characteristics is set up for comparison based on the arc extinguishing chamber simulation model in the previous section. Since the flow characteristics of SF6 gas are not considered, it can be assumed that the pressure of SF6 gas remains unchanged during the opening process. At this time, there is no need to simulate the movement process of the contacts when the circuit breaker is opened. It is only necessary to calculate the capacitance of the break when the contacts are in different positions to obtain the capacitance-stroke curve of the circuit breaker.

[0121] The capacitance-stroke curve of the circuit breaker considering the gas flow characteristics and not considering them is obtained. It can be seen that there is no obvious difference in the capacitance values ​​in the two cases. The error percentage of the capacitance values ​​in the two cases is obtained by calculation. The influence of medium flow on the capacitance value is always within 1%, indicating that the influence of gas flow on the capacitance value is very small. In the subsequent simulation ablation calculation, the gas flow can no longer be considered, which can greatly simplify the calculation process of the model and shorten the calculation time of the software.

[0122] Although the pressure of SF6 gas in the compressed air chamber of the circuit breaker will increase significantly during the opening process, up to more than twice the initial gas pressure, substituting the maximum pressure P = 14*101.325kPa at this time into the formula, the relative dielectric constant = 1.01982 is obtained, which is basically consistent with the maximum relative dielectric constant obtained by simulation calculation; compared with the relative dielectric constant of SF6 gas under standard atmospheric pressure of 1.002049, the increase in relative dielectric constant brought about by the increase in pressure is very limited and cannot have a significant impact on the fracture capacitance value.

[0123] Moreover, in both cases, the error of capacitance value is the largest at the initial position of the contact. However, according to the compressed air characteristics in the arc extinguishing chamber of the circuit breaker in Chapter 2, it can be seen that the maximum pressure of SF6 gas in the compressed air chamber occurs in a small stage when the nozzle is just opened with a stroke of about 80 mm. At this time, the relative dielectric constant of SF6 gas will also reach its maximum value, and the error of capacitance value is also decreasing with the increase of stroke. This shows that the influence of the distance between contacts on the capacitance value is far greater than the influence of medium flow on the capacitance value.

[0124] The process of breaking current in SF6 circuit breakers is accompanied by complex chemical reactions. High-temperature arcs decompose SF6 gas to produce toxic gases such as SOF2, SO2F2, SOF4, SO2, and HF, and also cause metal fluoride particles to form on the contact metal and attach to the ablation site. These new components have different relative dielectric constants from SF6 gas, and theoretically may affect the break capacitance. In order to further confirm the degree of influence of these new components on the break capacitance of the circuit breaker, this chapter simulates different new components in the model based on the previous chapter to explore the change of the break capacitance, and obtains the capacitance-stroke curve under the influence of CuF and new gas.

[0125] The effects of SF6 gas decomposition components on capacitance are as follows:

[0126] SF6 is a colorless and odorless inert gas. Due to its high dielectric strength and excellent arc extinguishing performance, it is widely used as an insulating medium in the arc extinguishing chamber of circuit breakers. At high temperatures, SF6 gas will decompose to produce SF4 and SF2. As the circuit breaker ages, impurity gases such as water vapor and oxygen will be mixed into the arc extinguishing chamber. SF6, SF4, SF2 and other gases will further react with these impurity gases to produce SOF2, SO2F2, SOF4, SO2, HF and other substances.

[0127] At present, there is little information on the relative dielectric constant of the newly formed gas, and it is impossible to obtain the accurate relative dielectric constant value of each gas. However, studies have shown that the relative dielectric constant of any gas is close to 1 and greater than 1, usually in the order of 1.00x, while the relative dielectric constant of water vapor is slightly larger, 1.008. Considering that the generated component gases and the content of micro-water and micro-oxygen mixed in are extremely low, and the equivalent relative dielectric constant of the mixed medium is greater than the minimum relative dielectric constant in the mixed medium, and less than the maximum relative dielectric constant in the mixed medium. In order to explore the influence of the newly formed gas on the fracture capacitance and exaggerate the influence of the mixed medium on the relative dielectric constant, the overall relative dielectric constant of the gas medium in the arc extinguishing chamber under the influence of the newly formed gas is taken within the range of 1 to 1.05 (the relative dielectric constants of the components generated in the arc extinguishing chamber are all in this range), and the model is improved to obtain the capacitance-stroke curve when the relative dielectric constants of the gas medium are 1 and 1.05 respectively.

[0128] When the relative dielectric constants of the gas medium in the arc extinguishing chamber are 1, 1.00204 (SF6 gas) and 1.05 respectively, the capacitance-travel curves of the circuit breaker basically coincide with each other and do not change significantly; the error when the relative dielectric constant is 1.05 is significantly greater than the error when it is 1, but the maximum errors of the two are within 5%. In both cases, the error of the break capacitance decreases with the increase of the breaking distance.

[0129] The influence of metal fluoride on the contact surface on the port capacitance is as follows:

[0130] In addition to the above gas decomposition products, the SF6 gas in the arc extinguishing chamber also reacts with the contact metal to produce metal fluorides:

[0131]

[0132] These solid particles will be deposited on the contact surface, mainly concentrated in the contact surface and arc angle of the two arc contacts. The thickness of these metal particles is very small, usually around tens of microns. Based on the simulation of different ablation degree models in Chapter 3, a metal fluoride with a thickness of 50 microns is set on the surface of the static arc contact and the moving arc contact. The model settings are as follows: Fig. 9 As shown, the capacitance travel curve after adding metal fluoride at different ablation degrees was calculated.

[0133] After adding metal fluoride, the initial capacitance values ​​when ablated to 1mm, 3mm, 5mm, 8mm and 10mm were 235.72342pF, 275.85254pF, 310.8100pF, 391.23763pF and 452.77786pF, respectively, which were significantly increased compared with the fracture capacitance values ​​when no addition was made; when the stroke was 29mm, the fracture capacitance values ​​in the five cases were all around 18pF, which was very close to the capacitance values ​​when no metal fluoride was added. After that, the values ​​of the fracture capacitances tended to be the same, with no obvious difference.

[0134] The influencing factors analysis is carried out as follows:

[0135] According to the capacitance formula of a parallel plate capacitor: It can be seen that the increase of relative dielectric constant will increase the capacitance value. For the newly formed gas components in the arc extinguishing chamber, since the relative dielectric constant change it brings is small, the actual capacitance value change is also very small. As for the generated metal fluoride, its deposition on the contact surface is equivalent to changing the dielectric distribution between the contacts. Since the relative dielectric constant of metal fluoride is large, the impact on the fracture capacitance is also significantly greater than that of the newly formed gas component. However, whether it is newly formed gas or metal fluoride, their impact on the fracture capacitance decreases with the increase of stroke. This is because if the contact is equivalent to a parallel plate capacitor, d is very small when the contact is just separated. It can be seen from the formula that the change of relative dielectric constant at this time will cause a larger change in capacitance value. As d increases, the impact of the change of relative dielectric constant on capacitance value will become smaller and smaller.

[0136] In addition, some scholars have measured the decomposition products of the gas after ablation for different models of circuit breakers with different transformer levels. The results show that the content of the gas decomposition products does not exceed 0.01%, so the influence of the new gas on the relative dielectric constant of the gas medium in the arc extinguishing chamber is far from reaching the level set in the model. In practice, the influence of the new gas on the fracture capacitance is negligible.

[0137] The present invention proposes to reflect the contact state through the break capacitance of the circuit breaker, builds an arc extinguishing chamber simulation model of the typical 126KV circuit breaker arc extinguishing chamber opening process based on the break capacitance, carries out simulation experiments simulating ablation, and analyzes the change law of the relevant break capacitance; based on the new component substances generated in the arc extinguishing chamber during the actual circuit breaker ablation process, a corresponding arc extinguishing chamber simulation model is set, and the influence of these new components on the break capacitance during the opening process is calculated and analyzed.

[0138] Based on the equipment parameters and mechanical characteristics of a typical 126kV SF6 circuit breaker, this paper uses COMSOL Multiphysics to build a simulation model of the arc extinguishing chamber of the circuit breaker opening process. The model includes electrostatic field, gas flow field and dynamic mesh physical field. The gas compression characteristics and electric field distribution characteristics in the arc extinguishing chamber during the circuit breaker opening process are obtained, and the capacitance-time curve and capacitance-stroke curve of the opening are also calculated. The first dynamic simulation results show that:

[0139] 1) During the opening process of the circuit breaker, the gas in the compressed air chamber of the circuit breaker will have a significant pressure change process. The maximum pressure of 14atm will be reached 2 to 3ms after the contact port is just opened, and then the pressure will drop as the contact port opens.

[0140] 2) During the opening process of the circuit breaker, the break capacitance will decrease significantly with the increase of stroke, and tend to decrease rapidly within 5 mm after the arc contacts are separated.

[0141] 3) Based on the morphological characteristics of the arc contact of the circuit breaker after ablation, a simulation model of the arc extinguishing chamber with five degrees of ablation was built, and the influence of gas flow and ablation on the fracture capacitance was analyzed. The study found that the change in the relative dielectric constant of the arc extinguishing chamber insulation medium caused by gas flow was small, with the maximum reaching only 1.021. The error between the two results considering whether the gas flow was present was within 1%, indicating that the pressure change of the gas in the arc extinguishing chamber had little effect on the fracture capacitance and could be ignored.

[0142] 4) According to the parameters of some gas and solid impurities produced in the actual use of the circuit breaker arc extinguishing chamber, the original model was modified to study the influence of these new components on the break capacitance during the opening process. The study shows that the gas impurities SOF2, SO2F2, SOF4, SO2, HF, etc. produced in the circuit breaker arc extinguishing chamber have a very limited influence on the break capacitance, and the maximum error does not exceed 5%; while the influence of the solid impurity metal fluoride on the break capacitance is mainly reflected in a small stage after the contact separation, and the influence on the break capacitance is not obvious after the breaking distance increases.

[0143] The analysis process of the closing pre-breakdown characteristics of the SF6 circuit breaker is as follows:

[0144] The moving distance of the contact is 78mm, and the moving speed is 2.6m / s, so the time from the beginning of the contact movement to the just closing in the model is 30ms. The change of the electric field distribution in the arc extinguishing chamber during the closing process is specifically calculated as follows: at t=0ms, the electric field distribution in the arc extinguishing chamber, at t=10ms, the electric field distribution in the arc extinguishing chamber, at t=20ms, the electric field distribution in the arc extinguishing chamber, at t=29.5ms, the electric field distribution in the arc extinguishing chamber. According to the calculation results, the maximum field strength position in the arc extinguishing chamber always appears on the surface of the static arc contact, where the degree of electric field distortion is the largest, and it is also the position where streamers are most likely to be generated and breakdown occurs.

[0145] Fig.10 The maximum field strength in the arc extinguishing chamber does not change linearly with the movement of the contact. In the first 22ms, the maximum field strength value rises slowly and linearly. The field strength rises gradually from 22 to 30ms, especially around 27ms, when the maximum field strength value fluctuates, indicating that the structure of the contact has a great influence on the change of the electric field.

[0146] The calculation results show that the gas density distribution at t = 0ms, the gas density distribution at t = 10ms, the gas density distribution at t = 20ms, and the gas density distribution at t = 29.5ms. Since there is no gas blowing process during the closing process, the SF6 gas density in the entire arc extinguishing chamber does not change much, and the actual value is 36.0-36.4kg / m 3 During the closing process, the SF6 flow in the arc extinguishing chamber is small and there is no obvious pressure change.

[0147] The calculation results show that the breakdown voltage cloud diagram at t = 0ms, the breakdown voltage cloud diagram at t = 10ms, the breakdown voltage cloud diagram at t = 20ms, and the breakdown voltage cloud diagram at t = 29.5ms. It can be found that the most prone to breakdown always appears on the surface of the static arc contact, which is consistent with the above analysis. According to the result, a pre-breakdown voltage change curve is made. According to the pre-breakdown voltage change curve, it can be seen that the pre-breakdown voltage of the contact decreases as the contact approaches. The 126kV SF6 circuit breaker selected by the present invention actually works in a system with a phase voltage of 66kV. Under this voltage, the contact breaks down at 29.0946ms, and the arc is extinguished just after the contact is closed at 30ms. Therefore, the pre-breakdown arc duration of the unburned contact is 0.9054ms.

[0148] Optionally, in the above technical solution, it also includes:

[0149] S5, setting ablation points in the contact area of ​​the arc extinguishing chamber simulation model to obtain a new arc extinguishing chamber simulation model;

[0150] S6. Using the laminar flow field calculation model, the electric field calculation model, the breakdown criterion of the arc extinguishing chamber, the contact movement grid calculation model and the boundary conditions of the arc extinguishing chamber, and combining with the new arc extinguishing chamber simulation model, the opening process of the SF6 circuit breaker is dynamically simulated and calculated to obtain the second dynamic simulation result.

[0151] The process of setting the ablation point in the contact area of ​​the arc extinguishing chamber simulation model is as follows:

[0152] During the continuous opening and closing process, the contact will lose mass and deform due to the ablation of the arc. In severe cases, the contact stroke of the contact may be reduced during the emergency process. Studies have shown that this reduction can be as high as 10 to 15 mm. Usually, the static arc contact is the most severely ablated. By observing the deformation of the static arc contact with different degrees of ablation, it can be found that as the degree of ablation deepens, the end of the static arc contact becomes obviously "sharp", and the mass loss of the contact is mainly at the arc corner rather than the top.

[0153] The change of contact stroke is crucial to the simulation calculation of the break capacitance, because the break capacitance of the circuit breaker can only be obtained after the arc contacts are separated, and the change of contact stroke will directly affect the position of the initial capacitance value in the capacitance-stroke curve. Taking the above into consideration, and based on the change characteristics of the morphological characteristics during the ablation of the static arc contact in the previous article, the simulation of ablation of different degrees is set: ① Set a minimum ablation point at the arc bend of the static arc contact, assuming that there is no obvious ablation below the minimum ablation point. ② According to the degree of reduction of the contact stroke between the contacts by 1mm, 3mm, 5mm, 8mm and 10mm, respectively, Fig.11 (a) Fig.11 (b) Fig.11 (c) Fig.11 (d) and Fig.11 (e) The outer surface of the static arc contact is cut off with the lowest ablation point as the endpoint to simulate different degrees of ablation. ③ Ignore the influence of the roughness of the ablation part of the static arc contact and only consider the change of the macroscopic shape of the static arc contact. The model settings of different ablation degrees are as follows: Fig.11 As shown, specifically Fig.11 (a) to Fig.11 (e) as shown.

[0154] Optionally, in the above technical solution, it also includes:

[0155] S7. According to the second dynamic simulation result, analyze the influence of contact erosion on the break capacitance of the SF6 circuit breaker, and according to the second dynamic simulation result, analyze the influence of contact erosion on the closing pre-breakdown characteristics of the SF6 circuit breaker.

[0156] The influence of ablation degree on fracture capacitance is as follows:

[0157] Through simulation calculation, the capacitance-stroke curve of the SF6 circuit breaker under the conditions of contact ablation of 1mm, 3mm, 5mm, 8mm and 10mm was obtained. The capacitance-stroke under different ablation degrees is consistent with the capacitance-stroke curve of the typical 126kV circuit breaker in terms of change trend. With the increase of the breaking distance, the capacitance values ​​in the five cases show a significant downward trend, and the maximum value of the capacitance value decrease rate appears in the initial stroke. Due to the reduction of the contact stroke, the capacitance-stroke curve of the circuit breaker shifts to the right accordingly with the reduction of the contact stroke. The deepening of the contact ablation degree also has a certain impact on the size of the fracture capacitance. Moreover, with the deepening of the ablation degree, the initial value of the fracture capacitance increases significantly. The initial capacitance value when ablation is 10mm is as high as 210pF, which is about ten times higher than the initial capacitance value of 21pF when it is not ablated. However, the difference in capacitance values ​​under different ablation conditions is mainly before the stroke is 29mm. After 29mm, the capacitance values ​​of the circuit breakers under the five ablation conditions are very close.

[0158] Analysis of the impact of contact ablation on the fracture capacitance. Through the previous study of the contact fracture capacitance curves with different ablation degrees, it was found that the capacitance-stroke curve after ablation has obvious characteristics: ① The position of the initial capacitance value moves forward with the increase of the ablation degree. ② The initial capacitance value increases with the increase of the ablation degree. ③ The capacitance curves with different ablation degrees tend to overlap after a stroke of 30mm. In view of these characteristics, the two arc contacts of the circuit breaker can be equivalent to a pair of parallel plate capacitors. According to the capacitance calculation formula of the parallel plate capacitor After further analysis, we can find that:

[0159] As the degree of ablation increases, it can be clearly found that when the arc contact is just separated, the position of the static arc contact moves forward significantly. This is exactly the structure that we hope to achieve through the setting of the model. This also leads to a reduction in the contact stroke of the arc contact and an advance in the separation position of the arc contact. The position where the initial capacitance value appears is consistent with the separation position, so the displacement of the initial capacitance value also changes accordingly.

[0160] The reduction in contact stroke means that in the absence of contact, the static arc contact can penetrate deeper into the moving arc contact. At this time, the two are very close to each other, which means that d is extremely small. Therefore, no matter what the degree of ablation is, the initial capacitance value is significantly greater than the capacitance value in the second half of separation. The greater the degree of ablation, the deeper the static arc contact penetrates, which means that the equivalent relative area S of the two arc contacts is also larger, so the corresponding capacitance value is also larger.

[0161] When the arc contact moves to 30mm, the equivalent relative area S is very small regardless of the degree of ablation, and the relative dielectric constant does not change significantly. At this time, the capacitance value of the contact is mainly determined by the equivalent distance d, and the influence of the ablation degree on the capacitance value is negligible. Therefore, the capacitance curves under different ablation conditions tend to overlap.

[0162] The capacitance-stroke curve measured after the actual ablation experiment is calculated. The distribution characteristics of the actual capacitance-stroke curve are roughly consistent with the above analysis, which also verifies the correctness of the present invention.

[0163] The process of setting the erosion state is as follows: during the frequent switching of the capacitor bank circuit breaker, the contacts will not only be eroded by the breaking arc, but also by the pre-breakdown arc erosion and mechanical wear during the closing process. Generally, due to the plum blossom contact finger structure of the contact, after being eroded, it will not become shorter as a whole or fall off partially, but the end will become "sharp". The following figure shows the morphological characteristics of a typical arc contact after erosion.

[0164] It can be found that the appearance of the contact after ablation has two changes: on the one hand, the end of the static contact becomes sharp due to material loss, which will cause the contact stroke to become shorter during the opening and closing process. Therefore, the concept of arc contact ablation angle θ is introduced here to simulate the tip sharpening, such as Fig.12 Point A is the initial contact point of the moving and static arc contacts, and point B is the lowest contact point. It is generally believed that the moving and static arc contacts will no longer contact at a position lower than point B, and point C is the highest contact point. The ablation angle θ is defined as the acute angle between the line connecting points A and C and the vertical direction, and its value increases with the increase in the degree of contact ablation. Assuming that the contact stroke is reduced by 5mm, 10mm and 15mm respectively, the corresponding θ is 83°, 86° and 87°, and the ablation angle θ is 78° when there is no ablation.

[0165] On the other hand, the contact surface becomes uneven. This is because the contact material is generally copper-tungsten alloy. The melting and boiling points of copper and tungsten metals are 1358K, 3680K, 2840K and 5928K respectively. When the arc burns, the high temperature at the arc heel will cause the copper to melt and evaporate first, and then the tungsten skeleton will melt and vaporize, and pits will appear on the contact surface. When the arc is extinguished, the metal liquid bridge or vapor diffused in the arc path begins to solidify and may reattach to the contact surface to form convex hills. This process is difficult to quantify and characterize. In order to simplify the modeling, the new arc extinguishing chamber simulation model (arc extinguishing chamber simulation model after setting the ablation point) sets a wavy texture on the contact surface. The wave is composed of a semicircle with a radius of 0.1mm, which simulates the phenomenon that the surface of the lower end of the contact becomes uneven after ablation. According to the degradation process, considering the increase in the contact ablation angle and the unevenness of the contact surface, contact models with five degrees of ablation from light to heavy are set, such as Fig.13 In the first two models, the surface began to be uneven, but it did not lead to a reduction in stroke. In the last three models, the range of the surface unevenness and the reduction in stroke gradually increased.

[0166] The process of analyzing the influence of contact erosion on the closing pre-breakdown characteristics of the SF6 circuit breaker is as follows:

[0167] The field intensity distribution near the contact at 28ms under extremely slight ablation and non-ablation conditions is compared. It can be found that the contact ablation causes the position of the maximum field intensity to change, and the maximum field intensity appears at the slight ablation, with its value increasing from 506.8V / m to 724.6V / m, an increase of 42.9%, where streamer discharge and breakdown are more likely to occur.

[0168] The pre-breakdown characteristic curve of the circuit breaker under different ablation states is calculated. According to the pre-breakdown characteristic curve of the circuit breaker, the breakdown voltage does not decrease monotonically with the shortening of the contact distance. A slight rebound in the breakdown voltage may occur during the closing movement, which is reflected in the fluctuation decrease of the breakdown voltage curve. Overall, with the increase of the degree of ablation, the breakdown voltage curve moves downward, and the breakdown voltage curve is at the bottom when the stroke is reduced by 10mm. The breakdown voltage curve in the case of slight ablation is lower than the breakdown voltage curve in the case of a 5mm reduction in stroke before 25ms, and the relationship between the two curves is reversed after 25ms. The moment when the voltage is 66kV is extracted to calculate the duration of the pre-breakdown arc, such as Fig.14As shown in the figure, as the degree of ablation increases, the duration of the pre-breakdown arc generally shows an upward trend. The duration of the pre-breakdown arc under extremely slight ablation is not much different from that without ablation. Then, as the degree of ablation increases, the duration of the pre-breakdown arc increases, reaching 1.766ms when the stroke is reduced by 10mm. When the stroke is reduced by 15mm, the duration of the pre-breakdown arc decreases compared to when the stroke is reduced by 10mm. This shows that the degree of ablation of the contact may have a maximum value point for the distortion effect on the electric field. After exceeding this point, further increase in the degree of ablation of the contact will improve the distribution of the electric field to a certain extent.

[0169] Among them, when selecting phases for closing, it is hoped that the closing phase angle will be controlled at about 0° to minimize the inrush current and overvoltage during closing. It is necessary to consider the pre-breakdown characteristics of the closing process and the dispersion of the circuit breaker action time. In the previous phase selection closing strategy, only the influence of the closing pre-breakdown time when the contact is not ablated was considered. However, from the results in the previous section, it can be seen that contact ablation can cause the maximum increase in the duration of the pre-breakdown arc by about 0.9ms, that is, the pre-breakdown occurs 0.9ms earlier during closing, which will cause an error of nearly 1.2° in the closing phase angle. Therefore, it is necessary to consider the influence of contact ablation degradation on pre-breakdown when selecting phases for closing.

[0170] In addition, the pre-breakdown time generally increases with the increase of the degree of ablation, and the measurement of the pre-breakdown time is expected to become a new means of online monitoring of the electrical life of circuit breaker contacts. Although the occurrence of pre-breakdown is somewhat dispersed in practice, considering the frequent operation of capacitor bank circuit breakers, the measurement of pre-breakdown time can quickly accumulate a certain amount of data samples, on this basis, the statistical law of pre-breakdown time can be analyzed to reflect the electrical life state of the contact.

[0171] The present invention establishes a simulation model of the arc extinguishing chamber of a 126kV SF6 circuit breaker and a mathematical model of the closing pre-breakdown process, and calculates the electric field distribution and breakdown voltage in the arc extinguishing chamber during the closing process, i.e., the second dynamic simulation result. By changing the contact ablation angle and setting the convex hills and concave pits on the contact surface, 5 different ablation degrees of the contact are simulated, and the influence of ablation on the electric field and breakdown voltage during the closing process is simulated and studied. The conclusions are as follows:

[0172] The maximum field strength in the arc extinguishing chamber occurs on the surface of the static arc contact, where the electric field distortion is the greatest and breakdown is most likely to occur. Contact erosion will further increase the degree of electric field distortion in the arc extinguishing chamber, resulting in a decrease in breakdown voltage. As the degree of erosion increases, the pre-breakdown time of the circuit breaker closing is advanced, and the duration of the pre-breakdown arc increases, which can be increased by up to 0.9ms at the 110kV level. Therefore, the pre-breakdown caused by contact erosion should be considered when selecting the phase for closing. It also shows that it is theoretically feasible to reflect the electrical life state of the contact by measuring the pre-breakdown time.

[0173] Optionally, in the above technical solution, it also includes:

[0174] S8. Analyze the internal insulation of the arc extinguishing chamber according to the first dynamic simulation result and the second dynamic simulation result.

[0175] During the continuous opening and closing process of SF6 circuit breakers, the closing surge current and the breaking short-circuit current will continuously ablate the contacts, resulting in rough and cracked contact surfaces, condensed metal particles on the nozzle surface, and even deformation of the arc contacts, which eventually cause the contacts to be corroded and become shorter, sharper, and rougher. Contact ablation will seriously affect the electric field distribution in the arc extinguishing chamber, increase the probability of arc reignition during the breaking process, lead to breaking failure, inability to remove the fault, and even cause the arc extinguishing chamber to explode.

[0176] Contact erosion is the main factor affecting the insulation performance of circuit breakers. According to the different movement processes, erosion is mainly divided into closing erosion and breaking erosion. There are two sources of closing erosion: one is the ablation of the pre-breakdown arc before closing, and the other is mechanical wear, such as Fig.15 As shown, the contact breaking erosion is all from the arc ablation, such as Fig.16 shown.

[0177] During the closing process, the moving arc contact gradually moves from the opening position to the static arc contact. When the contact moves to a sufficiently small gap, the gap between the moving and static arc contacts will be pre-breakdown to generate an arc, which will cause a certain amount of ablation on the contact. In addition, due to the heating effect of the arc on the contact, the contact surface softens, and a certain amount of mechanical wear will occur during the subsequent contact process between the moving and static contacts. This part of mechanical wear accounts for a large proportion of closing erosion.

[0178] Unlike closing erosion, breaking arc erosion mainly occurs during the arc burning process. Before the contacts separate, the mechanical wear of this process can be basically ignored due to the high contact hardness of the contacts. The contact ablation process of breaking arc can be mainly divided into four stages: ① When the contacts are about to separate, the contact area between the moving and static arc contacts tends to be infinitesimal, and the local current density at the end of the contact is very large, which causes the temperature to rise rapidly and quickly reaches the melting point of the metal to form a molten metal pool; ② When the contacts separate, the liquid metal is pulled away from the contact surface to form a metal liquid bridge, which is rapidly elongated; ③ Because the diameter of the metal liquid bridge is very small, its temperature rises rapidly and reaches the vaporization point of the metal. At this time, the arc is maintained by metal vapor, forming an electrode voltage drop zone; ④ Subsequently, the contact gap continues to increase, and the gas ions and electrons in the surrounding environment gradually participate in the conduction, forming a plasma arc zone.

[0179] The erosion of the contacts during the opening and closing process manifests itself as a loss of contact quality, which is manifested in the following morphological aspects: the difference between the inner and outer diameters of the moving and static arc contacts continues to increase, that is, the arc contacts become thinner; the contact stroke of the moving and static arc contacts continues to decrease, that is, the arc contacts become shorter; the contact resistance of the arc contacts continues to increase and the volatility increases, that is, the surface of the arc contacts becomes uneven. The change in contact morphology caused by contact ablation will seriously affect the electric field distribution in the arc extinguishing chamber, causing the pre-breakdown time to come earlier or later, such as Fig.17 Therefore, there is a certain variation rule in the closing pre-breakdown time of the circuit breaker under different insulation states, and the internal insulation performance of the ACF circuit breaker can be evaluated by using the pre-breakdown time detection.

[0180] From the analysis of the pre-breakdown process, it can be known that the measurement of the pre-breakdown time can be analyzed by analyzing the pre-breakdown start time and the pre-breakdown arc extinction time. At the moment of pre-breakdown, the circuit is connected and current appears in the circuit. At this time, there is also a sudden change in the electromagnetic field signal. At the end of the pre-breakdown process, the contacts are in contact. The contact closing moment can be determined by the vibration signal. The principle is as follows Fig.18 shown.

[0181] As the arc ablation accumulates, the contacts are burned shorter and the contact ends become sharper and thinner, which will lead to changes in the equivalent relative area s and equivalent distance d of the two contacts; the generated gas impurities, metal particles and metal fluoride films on the contact surface will lead to the equivalent relative dielectric constant ε r Under the combined effect of multiple factors, as the degree of ablation deepens, the insulation performance in the arc extinguishing chamber deteriorates, and the fracture capacitance characteristics of the fracture will change. Therefore, by studying the fracture capacitance characteristics and obtaining the relationship between the internal insulation performance and the fracture capacitance, the insulation state of the arc extinguishing chamber can be detected and reflected through the fracture capacitance. Specifically:

[0182] 1) Contact erosion:

[0183] The wear of contacts under electrical ablation has three manifestations: evaporation and gasification, droplet splashing and solid particle injection. According to the mechanism of thermal-electric emission, in order to maintain the continuous burning of the arc, the surface temperature of the arc spot of the circuit breaker is usually higher than the boiling point of the material. The evaporation and gasification of the contact material is ongoing throughout the arc burning process, and the evaporation and gasification of the contact material will lead to reduced wear and deformation of the contact material. Splashing erosion wear refers to the phenomenon that the contact material wears in the form of metal droplets. Solid particle injection erosion wear refers to the thermal expansion and contraction force generated on the surface of the circuit breaker contact under the action of heat and force. When the force is large enough to overcome the mechanical strength of the contact material, the contact surface will expand rapidly, and solid particles will be ejected from the contact surface, causing contact wear.

[0184] Contact ablation can cause needle-shaped or pock-shaped pits or pores on the contacts, and the clamping force will decrease or the contacts will deform, causing the circuit breaker to not work properly. When the circuit breaker contacts fail seriously, the contacts may even fall off or slag off. A comparison of the CuW / CuCr arc contacts before and after failure showed that the contact surface was uneven after ablation, with high roughness and a large number of microcracks. The hardness of the CuW contact part decreased. During the contact ablation process, copper was repeatedly vaporized and deposited to form a "round bag" on the surface. During the arc ablation process of the CuW alloy, both the copper and tungsten phases melt and evaporate to varying degrees. The repeated action of thermal shock causes cracks on the contact surface, and the presence of cracks can significantly accelerate the ablation of the contact material. Under the combined effects of closing erosion and breaking erosion arc erosion, mechanical wear and collision, the contact material melts, vaporizes, and metal droplets splash, causing contact quality loss, which is reflected in the uneven contact surface, the shortened axial length and reduced radial diameter of the static arc contact end, and the thinner and larger inner diameter of the moving arc contact finger, which changes the pressure, contact resistance, and contact stroke between the contacts, reducing the breaking capacity of the circuit breaker. In addition, the metal particles generated by contact erosion are dispersed throughout the arc extinguishing chamber with the movement of the contacts, causing the distortion of the electric field distribution in the arc extinguishing chamber, increasing the possibility of heavy breakdown during the circuit breaker opening process, thereby further reducing the internal insulation performance of the circuit breaker.

[0185] 2) SF6 medium decomposition:

[0186] During the normal opening and closing process of the circuit breaker, closing arc and breaking arc will be generated. The arc current ranges from thousands of amperes to hundreds of kiloamperes. The power frequency arc will generally extinguish at the zero crossing point. The arc burning time is half a cycle to one and a half cycles. Its discharge energy is 10 5 ~10 7 J, the arc center temperature can reach 20000K. Under the action of high temperature arc, SF6 gas will decompose. After decomposition and ionization, SF6 plasma mainly includes 12 compounds: SF6, SF5, SF4, SF3, SF2, SF, F2, S2, F, S, SSFF, FSSF; 13 kinds of charged particles: SF + , SF - , S + 、F + , S - 、F - 、S2 + 、F2 + 、S3 + 、F3 + 、S2 - 、F2 - and e -During the breaking process of the filter group circuit breaker, the plasma in the arc channel is in a non-equilibrium state. At this time, the electron temperature is much higher than the gas temperature, and the energy of the electrons inside the discharge is very high. The average energy of the electrons in the SF6 partial discharge is 5 -10 eV, exceeding SF5 - F bond energy. SF4 and other sulfur low fluoride anion formation can produce various decomposition products. SF6 gas multiple decomposition may produce other low sulfur fluoride, such as SF4, SF3 and SF2. When there are no impurities in the gas or on the surface of the container, the decomposition products of SF6 gas will recombine quickly, the time is in μs level, which can be explained as SF4 + The thermal process of converting F2 to SF6. However, in the presence of oxygen and moisture, the low-sulfur fluoride reacts with impurities during the recombination process to produce sulfur fluoride oxides, HF and metal fluorides, such as Fig.19 shown.

[0187] In summary, the decline in internal insulation performance can be reflected in the change of contact morphology, the decomposition of SF6 gas medium, the generation of metal particles and the generation of metal fluoride film on the contact surface. After the moving and static contacts are separated, the moving and static contacts can be regarded as two electrodes of a capacitor, and the insulating medium between the electrodes is SF6 gas. As the opening process proceeds, the contact distance increases and the capacitance value decreases. Due to the complex shape of the contacts, it is difficult to derive the analytical formula for calculating the capacitance between the contacts in the arc extinguishing chamber, but it generally depends on the relative area between the contacts, the distance and the dielectric constant of the insulating medium in the middle. According to the calculation formula of the flat plate capacitance, the change of capacitance when the insulation performance in the arc extinguishing chamber decreases can be qualitatively analyzed.

[0188] In the above embodiments, although the steps are numbered S1, S2, etc., these are only specific embodiments given by the present invention. Those skilled in the art may adjust the execution order of S1, S2, etc. according to actual conditions, which is also within the protection scope of the present invention. It can be understood that in some embodiments, some or all of the above embodiments may be included.

[0189] A dynamic simulation system for the opening and closing process of an SF6 circuit breaker according to an embodiment of the present invention comprises a model building module and a simulation calculation module;

[0190] The model building module is used to: build an arc extinguishing chamber simulation model according to the actual parameters of the arc extinguishing chamber of the SF6 circuit breaker, and no ablation point is set in the contact area of ​​the arc extinguishing chamber simulation model;

[0191] The simulation calculation module is used to: use the laminar field calculation model, the electric field calculation model, the pre-breakdown criterion of the arc extinguishing chamber, the contact movement grid calculation model of the arc extinguishing chamber and the set boundary conditions, and combine the arc extinguishing chamber simulation model to dynamically simulate the opening process of the SF6 circuit breaker to obtain the first dynamic simulation result.

[0192] Optionally, the above technical solution also includes a data analysis module, which is used to: analyze the influence of SF6 gas in the arc extinguishing chamber on the break capacitance of the SF6 circuit breaker according to the first dynamic simulation result, and analyze the closing pre-breakdown characteristics of the SF6 circuit breaker according to the first dynamic simulation result.

[0193] Optionally, in the above technical scheme, the simulation calculation module is also used to: set ablation points in the contact area in the arc extinguishing chamber simulation model to obtain a new arc extinguishing chamber simulation model; use the laminar field calculation model, the electric field calculation model, the breakdown criterion of the arc extinguishing chamber, the contact movement grid calculation model and boundary conditions of the arc extinguishing chamber, and combine the new arc extinguishing chamber simulation model to dynamically simulate the opening process of the SF6 circuit breaker to obtain a second dynamic simulation result.

[0194] Optionally, in the above technical scheme, the data analysis module is also used to: analyze the influence of contact ablation on the break capacitance of the SF6 circuit breaker according to the second dynamic simulation results, and analyze the influence of contact ablation on the closing pre-breakdown characteristics of the SF6 circuit breaker according to the second dynamic simulation results.

[0195] Optionally, in the above technical solution, the data analysis module is also used to: analyze the internal insulation of the arc extinguishing chamber according to the first dynamic simulation result and the second dynamic simulation result.

[0196] Optionally, in the above technical solution, the data analysis module is also used for: the laminar flow field calculation model includes: two-dimensional compressible Navier-Stokes equations and k-ε turbulence equations, and the electric field calculation model is Laplace equations.

[0197] Optionally, in the above technical solution, the boundary conditions set include: laminar field boundary conditions, electrostatic field boundary conditions and moving grid boundary conditions.

[0198] It should be noted that the beneficial effects of the dynamic simulation system of the opening and closing process of an SF6 circuit breaker provided in the above embodiment are the same as the beneficial effects of the dynamic simulation method of the opening and closing process of an SF6 circuit breaker provided in the above embodiment, which will not be repeated here. In addition, when the system provided in the above embodiment realizes its functions, only the division of the above functional modules is used as an example. In actual applications, the above functions can be assigned to different functional modules as needed, that is, the system can be divided into different functional modules according to actual conditions to complete all or part of the functions described above. In addition, the system and method embodiments provided in the above embodiment belong to the same concept, and the specific implementation process is detailed in the method embodiment, which will not be repeated here.

[0199] An electronic device according to an embodiment of the present invention comprises a memory, a processor and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, any one of the above-mentioned methods for dynamic simulation of the opening and closing process of an SF6 circuit breaker is implemented. That is to say, an electronic device according to an embodiment of the present invention may include but is not limited to: a processor and a memory; a memory for storing a computer program; a processor for executing the method for dynamic simulation of the opening and closing process of an SF6 circuit breaker shown in any one of the embodiments of the present invention by calling the computer program.

[0200] In an optional embodiment, an electronic device is provided, the electronic device comprising: a processor and a memory. The processor and the memory are connected, such as through a bus. Optionally, the electronic device may also include a transceiver, which may be used for data exchange between the electronic device and other electronic devices, such as data transmission and / or data reception. It should be noted that in actual applications, the transceiver is not limited to one, and the structure of the electronic device does not constitute a limitation on the embodiments of the present invention.

[0201] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A dynamic simulation method for the opening and closing process of an SF6 circuit breaker, characterized in that: include: According to the actual parameters of the arc extinguishing chamber of the SF6 circuit breaker, an arc extinguishing chamber simulation model is constructed, wherein no ablation point is set in the contact area of ​​the arc extinguishing chamber simulation model; By using the laminar flow field calculation model, the electric field calculation model, the pre-breakdown criterion of the arc extinguishing chamber, the contact movement grid calculation model of the arc extinguishing chamber and the set boundary conditions, and in combination with the arc extinguishing chamber simulation model, a dynamic simulation calculation is performed on the opening process of the SF6 circuit breaker to obtain the first dynamic simulation result.

2. A dynamic simulation method for the opening and closing process of an SF6 circuit breaker according to claim 1, characterized in that: Also includes: According to the first dynamic simulation result, the influence of the SF6 gas in the arc extinguishing chamber on the break capacitance of the SF6 circuit breaker is analyzed, and according to the first dynamic simulation result, the closing pre-breakdown characteristics of the SF6 circuit breaker are analyzed.

3. A dynamic simulation method for the opening and closing process of an SF6 circuit breaker according to claim 2, characterized in that: Also includes: Setting ablation points in the contact region of the arc extinguishing chamber simulation model to obtain a new arc extinguishing chamber simulation model; By using the laminar flow field calculation model, the electric field calculation model, the breakdown criterion of the arc extinguishing chamber, the contact movement grid calculation model and the boundary conditions of the arc extinguishing chamber, and combining the new arc extinguishing chamber simulation model, the opening process of the SF6 circuit breaker is dynamically simulated and calculated to obtain the second dynamic simulation result.

4. A dynamic simulation method for the opening and closing process of an SF6 circuit breaker according to claim 3, characterized in that: Also includes: According to the second dynamic simulation result, the influence of contact ablation on the break capacitance of the SF6 circuit breaker is analyzed, and according to the second dynamic simulation result, the influence of contact ablation on the closing pre-breakdown characteristics of the SF6 circuit breaker is analyzed.

5. A dynamic simulation method for the opening and closing process of an SF6 circuit breaker according to claim 4, characterized in that: Also includes: The internal insulation of the arc extinguishing chamber is analyzed according to the first dynamic simulation result and the second dynamic simulation result.

6. A dynamic simulation method for the opening and closing process of an SF6 circuit breaker according to any one of claims 1 to 5, characterized in that: The laminar flow field calculation model includes: a two-dimensional compressible Navier-Stokes equation group and a k-ε turbulence equation, and the electric field calculation model is a Laplace equation group.

7. A dynamic simulation method for the opening and closing process of an SF6 circuit breaker according to any one of claims 1 to 5, characterized in that: The boundary conditions set include: laminar flow field boundary conditions, electrostatic field boundary conditions and dynamic grid boundary conditions.

8. A dynamic simulation system for the opening and closing process of an SF6 circuit breaker, characterized in that: Including model building module and simulation calculation module; The model building module is used to: build an arc extinguishing chamber simulation model according to actual parameters of the arc extinguishing chamber of the SF6 circuit breaker, and no ablation point is set in the contact area of ​​the arc extinguishing chamber simulation model; The simulation calculation module is used to: use the laminar field calculation model, the electric field calculation model, the pre-breakdown criterion of the arc extinguishing chamber, the contact movement grid calculation model of the arc extinguishing chamber and the set boundary conditions, and combine the arc extinguishing chamber simulation model to dynamically simulate the opening process of the SF6 circuit breaker to obtain a first dynamic simulation result.

9. An electronic device, characterized in that: The method comprises a memory, a processor and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, a dynamic simulation method for the opening and closing process of an SF6 circuit breaker as claimed in any one of claims 1 to 7 is implemented.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the method for dynamic simulation of the opening and closing process of an SF6 circuit breaker as claimed in any one of claims 1 to 7 is implemented.

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