Simulation method for direct current electromagnetic switch series connection multi-fracture arc

Abstract

The invention provides a simulation method of a direct current electromagnetic switch series connection multi-fracture arc. The method comprises the following steps: S1, coupling electromagnetic system simulation and mechanical dynamics, namely obtaining a two-dimensional interpolation table of electromagnetic attraction, coil current and iron core displacement through electromagnetic system simulation, and importing a mechanical dynamics simulation model to obtain the breaking speed of a direct-current electromagnetic switch contact; s2, magnetic induction intensity of different positions is obtained through a magnetic blow-out system model, and based on the magnetohydrodynamic theory, a physical field is coupled to establish an arc simulation model of a single fracture; s3, performing series multi-fracture arc simulation by means of coupling an external circuit; according to the method, the influence of different parameters (the number of fractures, asynchronous breaking time, breaking speed, magnetic induction intensity distribution, gas physical property parameters, different loads and the like) on the evolution process of the series multi-fracture arc can be analyzed.

Description

Technical Field

[0001] The invention relates to the technical field of low-voltage switches, in particular to a simulation method for a DC electromagnetic switch with multiple series-connected arcs. Background Art

[0002] The power system is developing towards a more efficient, clean and intelligent direction. In this process, DC transmission technology has been widely used due to its advantages such as high efficiency and flexibility. As an important component of the DC system, the performance of the DC switch directly affects the safety and stability of the system. However, the switch is limited by many factors such as structure, arc extinguishing conditions, and arc extinguishing methods, and its breaking capacity is restricted. In order to increase the capacity of switching electrical appliances, multi-break switch series technology is an effective solution. The voltage borne by the series electromagnetic switch includes steady-state voltage and dynamic voltage during the breaking process. The steady-state voltage distribution is determined by the resistance of each break, and the dynamic voltage is affected by the resistance and capacitance distribution.

[0003] Magnetohydrodynamics is a branch of physics that studies the interaction between conductive fluids such as plasma and electromagnetic fields. By simulating the behavior of arc plasma in a magnetic field, we can deeply understand the arc extinction process and provide a scientific basis for the disconnection control of the switch. In recent years, series multi-break switches have gradually become a hot topic of research due to their advantages in improving rated voltage and current carrying capacity and enhancing arc extinguishing ability. However, how to accurately simulate the arc behavior of series multi-break switches during the disconnection process and evaluate their performance is still a challenging topic. In summary, the technical background of the present invention is based on the urgent need for efficient and reliable DC switches in the current new energy field, and the application value of magnetohydrodynamics in the field of switch simulation. A simulation model of a series multi-break arc is obtained by multi-physics field simulation technology, which aims to study the multi-break arc characteristics of DC electromagnetic switches and reveal the influencing factors and limits of series expansion capacity. Summary of the invention

[0004] The present invention proposes a simulation method for a DC electromagnetic switch with multiple breaks in series, which can analyze the influence of different parameters (number of breaks, asynchronous breaking time, breaking speed, magnetic induction intensity distribution, gas physical parameters, different loads, etc.) on the evolution process of the arc with multiple breaks in series.

[0005] The present invention adopts the following technical solutions.

[0006] A method for simulating arcs of a DC electromagnetic switch with multiple breaks in series, the method comprising the following steps:

[0007] Step S1, coupling electromagnetic system simulation with mechanical dynamics, that is, obtaining a two-dimensional interpolation table of electromagnetic attraction, coil current and core displacement through electromagnetic system simulation, importing the mechanical dynamics simulation model, and obtaining the breaking speed of the DC electromagnetic switch contact;

[0008] Step S2, obtaining the magnitude of magnetic induction intensity at different positions through the magnetic blowing system model, and establishing an arc simulation model of a single fracture by coupling the physical field based on the magnetohydrodynamic theory;

[0009] Step S3, performing arc simulation of multiple breaks in series by means of coupling an external circuit.

[0010] The simulation method is used to analyze the influence of different numbers of breaks, asynchronous breaking time, breaking speed, magnetic induction intensity distribution, gas physical parameters, and different loads on the arc evolution process of multiple series breaks.

[0011] Step S1: When constructing a mechanical dynamics simulation model, first establish a geometric model including a moving and static iron core, a coil and an iron yoke, then design the material properties and motion properties of the geometric model, divide the geometric model into grids, and finally add excitation and reaction force parameters to obtain the electromagnetic system simulation results.

[0012] In step S1, if the electromagnetic attraction, the core displacement and the coil current in the electromagnetic system simulation structure basically show a monotonic relationship, a parametric scan is used to obtain a two-dimensional interpolation table of the electromagnetic attraction for different coil currents and different core displacements, and a mechanical dynamics simulation model is built to calculate the motion characteristics of the components of the electromagnetic switch and the forces between the components using the obtained electromagnetic attraction interpolation table and the reaction force of the spring, and finally the breaking speed of the contact is obtained.

[0013] The coupled simulation built by Simulink is as follows Figure 2 , mainly including input module, output module, control circuit, electromagnetic-mechanical coupling module and result visualization mode.

[0014] In step S2, a magnetic blowing system model is first established, and then the installation position and size of the prototype permanent magnet are set. Then, the magnetic blowing magnetic induction intensity at different positions is obtained through a field calculator, and then a single-break contact breaking DC arc simulation model is established based on magnetohydrodynamic theory; the simulation calculation process of the single-break contact breaking DC arc simulation model requires the following conditions: the arc plasma is always in a local thermodynamic equilibrium state during the simulation calculation process, and the metal vapor generated by the arc root ablation of the contact is not considered.

[0015] The single-break contact interrupting DC arc simulation model includes:

[0016] Quality Assurance:

[0017] Where: ρ is the gas density; u is the fluid particle velocity;

[0018] Momentum conservation equation:

[0019]

[0020] Where: p is the fluid micro-element pressure; μ is the dynamic viscosity; F is the Lorentz force on the arc; J is the conduction current density; B is the magnetic induction intensity on the arc;

[0021] Energy conservation equation:

[0022]

[0023] Where: H is enthalpy; λ is thermal conductivity; S rad is the total volume radiation; is the electron enthalpy transfer; K B is the Boltzmann constant; C p is the specific heat capacity at constant pressure;

[0024] Gas Equation of State

[0025] p=ρRT Formula 6;

[0026] Where R is the ideal gas constant;

[0027] Maxwell's Equations for Electromagnetic Fields

[0028]

[0029] Where σ is the conductivity; is the electric potential; A is the vector magnetic potential; E is the electric field strength;

[0030] Cathode heat flux equation:

[0031]

[0032] The expressions of each term in the above equation are:

[0033] |J ion |=|J·n|-|J elec | Formula 9;

[0034] |J elec |=J R (T) Formula 10;

[0035]

[0036] Where: arc is the thermal conductivity of the arc; Cu is the thermal conductivity of the copper contact; V ion is the ionization potential of the arc; φ Cu is the work function of the copper contact; J ion is the ion current density; J elec is the electron current density; |J·n| is the total current density modulus of the external input; AR is the Richardson constant, is the effective work function of the electrode surface;

[0037] Anode heat flux equation:

[0038]

[0039] The physical fields in step S2 include electricity, magnetism, heat, and laminar flow.

[0040] In step S3, arc simulation is performed using an arc magnetohydrodynamics simulation model, which includes the mutual coupling of physical fields such as temperature field, laminar flow field, electric field, and magnetic field. The specific coupling relationship is shown in Figure 3 .

[0041] In the coupling relationship, the arc affects the physical properties of the gas, such as electrical conductivity, thermal conductivity, and specific heat capacity at constant pressure, through changes in its temperature, thereby affecting the electric field, current, and current density distribution; the physical properties of different gases are obtained through the "Gas Discharge Plasma Database".

[0042] In the coupling relationship, a non-uniform magnetic field is introduced through an external magnetic field to reflect the influence of the magnetic field on the arc behavior under actual working conditions. Specifically, the magnetic induction intensity of the magnetic blowing obtained from the magnetic blowing system model is introduced into the arc model in different regions, and the difference in the magnetic induction intensity of adjacent regions is guaranteed to be within 5%.

[0043] In step S3, when simulating the arc of multiple breaks in series by means of coupling an external circuit, it is assumed that the arc is already in a burning state at the initial moment of the simulation, so as to ignore the arc starting process. If there is a difference in the opening time of different breaks, the arc of the break that is broken earlier is already in the process of burning when the arc of the break that is broken later starts, and the arc starting process will affect the external circuit, then the arc starting process is equivalently processed by adjusting the external circuit coupled to the simulation model.

[0044] The advantages of the present invention are:

[0045] 1. By introducing a non-uniform magnetic field into the model, the influence of the magnetic field on the arc behavior under actual working conditions can be more realistically reflected, such as the change in arc shape, the deviation of the motion trajectory, and the acceleration of the extinction speed caused by the magnetic blowing effect. This is of great significance for optimizing the design of electromagnetic switches and reducing the damage of arcs to switches.

[0046] 2. Based on a single arc, a model of a multi-break arc in series was obtained by coupling an external circuit. The model can accurately simulate the voltage fluctuations between different breaks and the impact of asynchronous breaking on the overall arcing process.

[0047] 3. This simulation method is applicable to different electromagnetic switches. By comprehensively considering multiple factors (such as contact breaking speed, magnetic induction intensity distribution, gas physical parameters, load type, contact shape, number of breaks and asynchronous breaking time), it can achieve a comprehensive and accurate simulation of the arc behavior of different electromagnetic switches. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0049] Attached Figure 1 It is a schematic diagram of a simulation model of the present invention;

[0050] Attached Figure 2 It is a simulation diagram of Simulink;

[0051] Attached Figure 3 It is a schematic diagram of the coupling relationship of the arc simulation physical field;

[0052] Attached Figure 4 It is a schematic diagram of the external circuit coupled with the simulation model;

[0053] Attached Figure 5 It is a schematic diagram of the multi-break arc simulation frame. DETAILED DESCRIPTION

[0054] As shown in the figure, a simulation method for a DC electromagnetic switch with multiple breaks in series is provided, the method comprising the following steps:

[0055] Step S1, coupling electromagnetic system simulation with mechanical dynamics, that is, obtaining a two-dimensional interpolation table of electromagnetic attraction, coil current and core displacement through electromagnetic system simulation, importing the mechanical dynamics simulation model, and obtaining the breaking speed of the DC electromagnetic switch contact;

[0056] Step S2, obtaining the magnitude of magnetic induction intensity at different positions through the magnetic blowing system model, and establishing an arc simulation model of a single fracture by coupling the physical field based on the magnetohydrodynamic theory;

[0057] Step S3, performing arc simulation of multiple breaks in series by means of coupling an external circuit.

[0058] The simulation method is used to analyze the influence of different numbers of breaks, asynchronous breaking time, breaking speed, magnetic induction intensity distribution, gas physical parameters, and different loads on the arc evolution process of multiple series breaks.

[0059] Step S1: When constructing a mechanical dynamics simulation model, first establish a geometric model including a moving and static iron core, a coil and an iron yoke, then design the material properties and motion properties of the geometric model, divide the geometric model into grids, and finally add excitation and reaction force parameters to obtain the electromagnetic system simulation results.

[0060] In step S1, if the electromagnetic attraction, the core displacement and the coil current in the electromagnetic system simulation structure basically show a monotonic relationship, a parametric scan is used to obtain a two-dimensional interpolation table of the electromagnetic attraction for different coil currents and different core displacements, and a mechanical dynamics simulation model is built to calculate the motion characteristics of the components of the electromagnetic switch and the forces between the components using the obtained electromagnetic attraction interpolation table and the reaction force of the spring, and finally the breaking speed of the contact is obtained.

[0061] The coupled simulation built by Simulink is as follows Figure 2 , mainly including input module, output module, control circuit, electromagnetic-mechanical coupling module and result visualization mode.

[0062] In step S2, a magnetic blowing system model is first established, and then the installation position and size of the prototype permanent magnet are set. Then, the magnetic blowing magnetic induction intensity at different positions is obtained through a field calculator, and then a single-break contact breaking DC arc simulation model is established based on magnetohydrodynamic theory; the simulation calculation process of the single-break contact breaking DC arc simulation model requires the following conditions: the arc plasma is always in a local thermodynamic equilibrium state during the simulation calculation process, and the metal vapor generated by the arc root ablation of the contact is not considered.

[0063] The single-break contact interrupting DC arc simulation model includes:

[0064] Quality Assurance:

[0065] Where: ρ is the gas density; u is the fluid particle velocity;

[0066] Momentum conservation equation:

[0067]

[0068] Where: p is the fluid micro-element pressure; μ is the dynamic viscosity; F is the Lorentz force on the arc; J is the conduction current density; B is the magnetic induction intensity on the arc;

[0069] Energy conservation equation:

[0070]

[0071] Where: H is enthalpy; λ is thermal conductivity; S rad is the total volume radiation; is the electron enthalpy transfer; K B is the Boltzmann constant; C p is the specific heat capacity at constant pressure;

[0072] Gas Equation of State

[0073] p=ρRT Formula 6;

[0074] Where R is the ideal gas constant;

[0075] Maxwell's Equations for Electromagnetic Fields

[0076]

[0077] Where σ is the conductivity; is the electric potential; A is the vector magnetic potential; E is the electric field strength;

[0078] Cathode heat flux equation:

[0079]

[0080] The expressions of each term in the above equation are:

[0081] |J ion |=|J·n|-|J elec | Formula 9;

[0082] |J elec |=J R (T) Formula 10;

[0083]

[0084] Where: arc is the thermal conductivity of the arc; Cu is the thermal conductivity of the copper contact; V ion is the ionization potential of the arc; φ Cu is the work function of the copper contact; J ion is the ion current density; J elec is the electron current density; |J·n| is the total current density modulus of the external input; A R is the Richardson constant, is the effective work function of the electrode surface;

[0085] Anode heat flux equation:

[0086]

[0087] The physical fields in step S2 include electricity, magnetism, heat, and laminar flow.

[0088] In step S3, arc simulation is performed using an arc magnetohydrodynamics simulation model, which includes the mutual coupling of physical fields such as temperature field, laminar flow field, electric field, and magnetic field. The specific coupling relationship is shown in Figure 3 .

[0089] In the coupling relationship, the arc affects the physical properties of the gas, such as electrical conductivity, thermal conductivity, and specific heat capacity at constant pressure, through changes in its temperature, thereby affecting the electric field, current, and current density distribution; the physical properties of different gases are obtained through the "Gas Discharge Plasma Database".

[0090] In the coupling relationship, a non-uniform magnetic field is introduced through an external magnetic field to reflect the influence of the magnetic field on the arc behavior under actual working conditions. Specifically, the magnetic induction intensity of the magnetic blowing obtained from the magnetic blowing system model is introduced into the arc model in different regions, and the difference in the magnetic induction intensity of adjacent regions is guaranteed to be within 5%.

[0091] In step S3, when simulating the arc of multiple breaks in series by means of coupling an external circuit, it is assumed that the arc is already in a burning state at the initial moment of the simulation, so as to ignore the arc starting process. If there is a difference in the opening time of different breaks, the arc of the break that is broken earlier is already in the process of burning when the arc of the break that is broken later starts, and the arc starting process will affect the external circuit, then the arc starting process is equivalently processed by adjusting the external circuit coupled to the simulation model.

[0092] Example:

[0093] This example simulates three switch breakpoints. The same applies to more than three switches. The circuit connection relationship and circuit structure of the external circuit coupled to the simulation model are as follows: the load of the external circuit used for simulation can be a pure resistive load, or other loads such as resistive-inductive, resistive-capacitive, etc. In this external circuit, multiple electromagnetic switches K1, K2, K3, etc. are connected in series to the circuit, and a controlled current source and a variable voltage source are connected in parallel on both sides of the electromagnetic switches K2, K3, etc. The current of the controlled current source is consistent with the current I of the main circuit, ensuring that the arc currents of multiple series switches are consistent. When the voltage of other electromagnetic switches is unstable, such as during the arc starting stage, the variable voltage source is connected to the circuit to replace the voltage across the contacts of the electromagnetic switch. During the simulation process, the external circuit coupled to the simulation model is adjusted to perform equivalent processing on the arc starting process. The structure of the external circuit is shown in the attached figure. Figure 4 , including the following three stages.

[0094] In the first stage, it is assumed that switch K1 is disconnected first and an arc is generated during the simulation process, and switches K2 and K3 have not yet been disconnected. At this time, the contact resistance on switches K2 and K3 is very small, so the voltage division is very small and can be ignored. At this moment, switches S1, S3, S4, and S6 are closed, and S2 and S5 are disconnected. The voltages of the two variable voltage sources are both zero. At this time, the power supply voltage is equal to the sum of the voltage on the load and the arc voltage on switch K1, which is consistent with the actual situation. Because the arc simulation based on magnetic fluid is in the initial stage of simulation, the arc is an artificially assumed mass of high-temperature gas, and it takes a short period of time to converge to reach the actual arc voltage. Therefore, before switches K2 and K3 are opened, the switches need to be connected in series with a controlled current source. The value of the controlled current source is consistent with the main circuit current I. The arc of switches K2 and K3 is maintained by the controlled current source, which facilitates the subsequent connection of switches K2 and K3 to the main circuit.

[0095] In stage 2, switch K2 is open, switch K3 is not disconnected, and switch K3 is still connected to the controlled current source. At this time, the voltage in the main circuit should actually be the resistance voltage, the arc voltage of switch K1, and the arc voltage of switch K2. However, in the simulation, switch K2 should not be connected to the main circuit immediately at this time, because the arc voltage simulated on switch K2 is the arc voltage of stable burning at this time, ignoring the arc starting stage, while the actual switch K2 voltage is the arc starting stage voltage. The arc starting stage of switch K2 is equivalent to applying voltage to the main circuit by a variable voltage source.

[0096] In stage three, when the arc voltage of switch K2 is equal to the actual arc voltage, switch K2 can be connected to the main circuit, switches S1 and S3 are disconnected, and S2 is closed. When the arc voltage of switch K3 is equal to the actual arc voltage, switches S4 and S6 are also disconnected, and S5 is closed. The same is true for the number of other breaks, so as to realize the simulation of asynchronous breaking of arcs with multiple breaks.

[0097] The multi-break arc model takes into account multiple parameters (number of breaks, asynchronous breaking time, breaking speed, magnetic induction intensity distribution, gas physical parameters, load) and is adaptable to different electromagnetic switches.

Claims

1. A method for simulating arcs of a DC electromagnetic switch with multiple breaks in series, characterized in that: The method comprises the following steps: Step S1, coupling electromagnetic system simulation with mechanical dynamics, that is, obtaining a two-dimensional interpolation table of electromagnetic attraction, coil current and core displacement through electromagnetic system simulation, importing the mechanical dynamics simulation model, and obtaining the breaking speed of the DC electromagnetic switch contact; Step S2, obtaining the magnitude of magnetic induction intensity at different positions through the magnetic blowing system model, and establishing an arc simulation model of a single fracture by coupling the physical field based on the magnetohydrodynamic theory; Step S3, performing arc simulation of multiple breaks in series by means of coupling an external circuit.

2. The method for simulating arcs of a DC electromagnetic switch with multiple breaks in series according to claim 1, characterized in that: The simulation method is used to analyze the influence of different numbers of breaks, asynchronous breaking time, breaking speed, magnetic induction intensity distribution, gas physical parameters, and different loads on the arc evolution process of multiple series breaks.

3. The method for simulating arcs of a DC electromagnetic switch with multiple breaks in series according to claim 1, characterized in that: Step S1: When constructing a mechanical dynamics simulation model, first establish a geometric model including a moving and static iron core, a coil and an iron yoke, then design the material properties and motion properties of the geometric model, divide the geometric model into grids, and finally add excitation and reaction force parameters to obtain the electromagnetic system simulation results.

4. The method for simulating arcs of a DC electromagnetic switch with multiple breaks in series according to claim 3, characterized in that: In step S1, if the electromagnetic attraction, the core displacement and the coil current in the electromagnetic system simulation structure basically show a monotonic relationship, a parametric scan is used to obtain a two-dimensional interpolation table of the electromagnetic attraction for different coil currents and different core displacements, and a mechanical dynamics simulation model is built to calculate the motion characteristics of the components of the electromagnetic switch and the forces between the components using the obtained electromagnetic attraction interpolation table and the reaction force of the spring, and finally the breaking speed of the contact is obtained.

5. The method for simulating arcs of a DC electromagnetic switch with multiple breaks in series according to claim 1, characterized in that: In step S2, a magnetic blowing system model is first established, and then the installation position and size of the prototype permanent magnet are set. Then, the magnetic blowing magnetic induction intensity at different positions is obtained through a field calculator, and then a single-break contact breaking DC arc simulation model is established based on magnetohydrodynamic theory; the simulation calculation process of the single-break contact breaking DC arc simulation model requires the following conditions: the arc plasma is always in a local thermodynamic equilibrium state during the simulation calculation process, and the metal vapor generated by the arc root ablation of the contact is not considered.

6. The method for simulating arcs of a DC electromagnetic switch with multiple breaks in series according to claim 5, characterized in that: The single-break contact interrupting DC arc simulation model includes: Quality Assurance: Where: ρ is the gas density; u is the fluid particle velocity; Momentum conservation equation: Where: p is the fluid micro-element pressure; μ is the dynamic viscosity; F is the Lorentz force on the arc; J is the conduction current density; B is the magnetic induction intensity on the arc; Energy conservation equation: Where: H is enthalpy; λ is thermal conductivity; S rad is the total volume radiation; is the electron enthalpy transfer; K B is the Boltzmann constant; C p is the specific heat capacity at constant pressure; Gas Equation of State p=ρRT Formula 6; Where R is the ideal gas constant; Maxwell's Equations for Electromagnetic Fields Where σ is the conductivity; is the electric potential; A is the vector magnetic potential; E is the electric field strength; Cathode heat flux equation: The expressions of each term in the above equation are: |J ion |=|J·n|-|J elec | Formula 9; |J elec |=J R (T) Formula 10; Where: arc is the thermal conductivity of the arc; Cu is the thermal conductivity of the copper contact; V ion is the ionization potential of the arc; φ Cu is the work function of the copper contact; J ion is the ion current density; J elec is the electron current density; |J·n| is the total current density modulus of the external input; A R is the Richardson constant, is the effective work function of the electrode surface; Anode heat flux equation: The physical fields in step S2 include electricity, magnetism, heat, and laminar flow.

7. The method for simulating arcs of a DC electromagnetic switch with multiple breaks in series according to claim 6, characterized in that: In step S3, arc simulation is performed using an arc magnetohydrodynamics simulation model, where the model includes mutual coupling of physical fields such as temperature field, laminar flow field, electric field, and magnetic field.

8. The method for simulating arcs of a DC electromagnetic switch with multiple breaks in series according to claim 7, characterized in that: In the coupling relationship, the arc affects the physical properties of the gas, such as electrical conductivity, thermal conductivity, and specific heat capacity at constant pressure, through the change of its temperature, thereby affecting the electric field, current, and current density distribution; the physical properties of different gases are obtained through the "Gas Discharge Plasma Database".

9. The method for simulating arcs of a DC electromagnetic switch with multiple breaks in series according to claim 7, characterized in that: In the coupling relationship, a non-uniform magnetic field is introduced through an external magnetic field to reflect the influence of the magnetic field on the arc behavior under actual working conditions. Specifically, the magnetic induction intensity of the magnetic blowing obtained from the magnetic blowing system model is introduced into the arc model in different regions, and the difference in the magnetic induction intensity of adjacent regions is guaranteed to be within 5%.

10. The method for simulating arcs of a DC electromagnetic switch with multiple breaks in series according to claim 7, characterized in that: In step S3, when simulating the arc of multiple breaks in series by means of coupling an external circuit, it is assumed that the arc is already in a burning state at the initial moment of the simulation, so as to ignore the arc starting process. If there is a difference in the opening time of different breaks, the arc of the break that is broken earlier is already in the process of burning when the arc of the break that is broken later starts, and the arc starting process will affect the external circuit, then the arc starting process is equivalently processed by adjusting the external circuit coupled to the simulation model.

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