Simulation method for detecting partial discharge of insulation defects in air switchgear by gas method

Abstract

The present invention discloses a simulation method for detecting partial discharge of insulation defects in air switchgear by the gas method. A hydrodynamic model is established by coupling the particle continuity equation and Poisson equation for describing discharge with the electron energy density equation. According to the collision theory, the actual chemical reactions are screened, a metal protrusion defect model is established in the multi-physics field simulation software COMSOL, and the calculation region is set. An experimental model is built. It is verified whether the set control equations and chemical model can describe the discharge process of the metal protrusion model. The relationship between the partial discharge amount and various gas products is established. From the perspective of numerical analysis, the present invention analyzes the volume fraction of the gas generated when the switchgear has an insulation defect partial discharge fault, and judges the severity of the insulation defect of the switchgear by detecting the change of the gas volume fraction in the air switchgear, thereby improving the safety of the system.

Description

Technical Field

[0001] The present invention belongs to the technical field of analyzing the severity of partial discharge of insulation defects in switchgear, and particularly relates to a simulation method for detecting partial discharge of insulation defects in air switchgear by the gas method. Background Art

[0002] Electric energy is playing an increasingly important role in the national production and life of our country. However, with the increase of the operation years, the aging problem of insulation defects in switchgear has gradually become prominent. Once this potential safety hazard breaks out further, it will cause huge economic losses and casualties. Therefore, it is very necessary to conduct research on the internal insulation defects of switchgear and design a set of devices that can effectively monitor the severity of its discharge. In order to cope with the influence of the surrounding environment factors of switchgear on the monitoring means, it is very promising to design an on-line monitoring device based on the gas method. However, due to the limitations of experimental sites, funds, etc., it is very difficult to study the micro-process of gas generation during partial discharge through experiments. In recent years, with the continuous development of computer hardware and computing performance, and the continuous development of technologies such as fluid mechanics, plasma, and numerical analysis of gas reactions, numerical simulation has become a powerful means to study the influence of partial discharge on air gas components. Summary of the Invention

[0003] The purpose of the present invention is to provide a simulation method for detecting partial discharge of insulation defects in air switchgear by the gas method, analyze the volume fraction of gas generated when the switchgear has an insulation defect partial discharge fault from the perspective of numerical analysis, and judge the severity of the insulation defect of the switchgear by detecting the change of the gas volume fraction in the air switchgear, so as to improve the safety of the system.

[0004] The technical solution adopted by the present invention is a simulation method for detecting partial discharge of insulation defects in air switchgear by the gas method, which realizes the simulation of the gas method detection of insulation defects in air switchgear by establishing a numerical analysis model.

[0005] The present invention is also characterized in that

[0006] Specifically, it is implemented according to the following steps:

[0007] Step 1: Couple the particle continuity equation and Poisson equation for describing discharge with the electron energy density equation to establish a hydrodynamic model;

[0008] Step 2: Screen the actual chemical reactions according to the collision theory, ignore the secondary reactions, and retain the reactions that have a greater impact on the results;

[0009] Step 3: Establish a metal protrusion defect model in the multi-physics field simulation software COMSOL and set the calculation area;

[0010] Step 4: Build a test model with the same parameters as in Step 3 according to the common insulation defect types of air switchgear;

[0011] Step 5: Verify whether the set control equations and chemical models can describe the discharge process of the metal protrusion model based on the volt-ampere characteristic curve;

[0012] Step 6: Establish the relationship between the partial discharge amount and various gas products.

[0013] Step 1 is specifically implemented according to the following steps:

[0014] Step 1.1: The control equations include:

[0015] Electron continuity equation:

[0016] Heavy particle continuity equation:

[0017] Electron energy equation:

[0018] Electric field potential Poisson equation: -▽*ε0ε r ▽V = ρ q

[0019]

[0020] Where: n e is the free electron density number; n ε is the electron energy density number; n k is the heavy particle density number; μ e is the free electron mobility; μ ε is the electron energy mobility; D e is the electron diffusion rate; D ε Electron energy diffusion rate; R e is the electron chemical source term; R ε Electron energy source term; ρ is the mixed gas density; R k is the heavy particle mass fraction; u is the mass average fluid velocity vector; j k is the diffusion flux vector; k R is the generation rate of heavy particle k; ε0 and ε r are the vacuum permittivity and relative permittivity respectively; ρ q is the space charge density; e is the elementary charge; Z k is the electric charge carried by particle k; E is the electric field vector; V is the applied potential;

[0021] Step 1.2: Convert the several differential equations in Step 1.1 into weak forms before solving.

[0022] Step 1.3. The ion diffusion rate is calculated by the following formula:

[0023]

[0024] In the formula: k B is the Boltzmann constant; T is the thermodynamic temperature of the gas; Q ion is the corresponding ion charge number.

[0025] Step 2 is specifically implemented according to the following steps:

[0026] Step 2.1. Select 65 chemical reactions that have a greater impact on the results;

[0027] Step 2.2. Convert the chemical reaction formula into a reaction rate equation. For the elementary reaction aA + bB → gC + dD, the reaction rate equation is

[0028] At the same time:

[0029] Then

[0030]

[0031]

[0032] Among them, k is the reaction rate constant, which is divided into the collision reaction rate constant k e and the chemical group reaction rate constant k r , and the calculation formulas are as follows:

[0033] Collision reaction:

[0034] Chemical group reaction:

[0035] In the formula: γ is the viscosity coefficient, σ j (ε) is the electron collision cross-section data; ε is the electron energy; f(ε) is the electron energy distribution function, and f(ε) is obtained by solving the two-term estimated Boltzmann equation by combining the electron collision cross-section data σ j (ε) with the BOLSIG+ software; A f is the frequency factor; E a is the apparent activation energy; T is the thermodynamic temperature of the gas; R g is the molar gas constant.

[0036] Step 3 is specifically implemented according to the following steps:

[0037] Step 3.1: Common insulation defects in switchgear include: metal protrusion defects, free metal particle defects, and floating potential defects. Metal protrusion defects include two parts: a needle electrode and a plate electrode.

[0038] Step 3.2: Establish a metal protrusion defect model, that is, connect the needle electrode to high voltage and the plate electrode to ground. The tip of the needle electrode is 1 mm high; the discharge gap is 1 mm; the gas composition in the gap is 21% oxygen and 79% nitrogen; the thickness of the plate electrode is 1 mm. Set the above parameters in the multi-physics field simulation software COMSOL to obtain a simulation model, and divide the finite element triangular mesh for the calculation area.

[0039] Step 4 is specifically implemented according to the following steps:

[0040] Step 4.1: Fabricate a metal protrusion insulation defect model with the same parameters as the simulation model in Step 3.

[0041] Step 4.2: Connect the needle electrode to the high-voltage end of a non-discharge high-voltage test transformer, and ground the plate electrode.

[0042] Step 4.3: According to the principle of the pulse current method, connect the high-voltage side of the metal protrusion defect model described in Step 4.2 to a coupling capacitor, and connect the other end of the coupling capacitor to a partial discharge detector.

[0043] Step 5 is specifically implemented according to the following steps:

[0044] Step 5.1: Collect the time-domain data of voltage and current during partial discharge of metal protrusion insulation defects on the test platform built in Step 4, and input the voltage time-domain data into the built simulation model as the excitation voltage of the simulation model.

[0045] Step 5.2: When the discharge current of the simulation model in Step 3 has the same change trend, similar peak points and zero-crossing points as the discharge current of the test platform in Step 4, it is considered that the numerical analysis model can describe the physical process of the test platform.

[0046] Step 5.3: Use the partial discharge detector described in Step 4 to measure the partial discharge quantity during one partial discharge process.

[0047] Step 5.4: Substitute the partial discharge quantity in Step 5.1 into the numerical analysis model in Step 1.

[0048] Step 5.5: Derive the volume fractions of various gas products from the numerical analysis model in Step 5.4, and draw a time-domain graph with the time axis as the abscissa and the gas volume fraction as the ordinate.

[0049] Step 6 is specifically implemented according to the following steps:

[0050] Step 6.1: Keep the temperature constant and establish a time-domain graph between the partial discharge amount and various gas products under different humidities. The abscissa is the time axis, and the ordinate is the volume fraction of the gas.

[0051] Step 6.2: Keep the humidity constant and establish a curve graph between the partial discharge amount and various gas products under different temperatures. The abscissa is the partial discharge amount, and the ordinate is the volume fraction of the gas.

[0052] Step 6.3: The above Steps 6.1 and 6.2 achieve the simulation of the partial discharge of the insulation defect of the air switch cabinet.

[0053] The beneficial effect of the present invention is that for the simulation method of the partial discharge of the insulation defect of the air switch cabinet by the gas method, first, according to the basic principles of fluid mechanics, the control equation of the plasma during partial discharge is constructed; second, the collision theory of gas reactions is used to screen out effective reaction equations that have a greater impact on the results, and the reaction rate equation is established; third, a suitable test model and simulation model are built according to the insulation defects that occur on-site, and the calculation area of the simulation model is appropriately simplified; fourth, the volt-ampere characteristic curve is used to verify the equivalence of the test platform and the numerical analysis model in the chemical reaction process; fifth, the partial discharge amount during partial discharge of the test platform is measured; finally, the partial discharge amount is used as the independent variable and input into the numerical analysis model to analyze the volume fraction of the characteristic gas. The present invention can calculate the changes of various characteristic gases in the air when the switch cabinet has insulation defects through mathematical analysis methods, which expands new ideas for the research of monitoring insulation defects by the gas method and gets rid of the limitations of experimental sites, scientific research funds, etc. Description of the Drawings

[0054] Figure 1 It is the working flow chart of the numerical analysis model of the simulation method for the partial discharge of the insulation defect of the air switch cabinet by the gas method of the present invention;

[0055] Figure 2 It is the working flow chart of the test platform of the simulation method for the partial discharge of the insulation defect of the air switch cabinet by the gas method of the present invention;

[0056] Figure 3 It is the schematic diagram of the test platform for the partial discharge of the insulation defect of the air switch cabinet by the gas method of the present invention. Detailed Embodiments

[0057] The present invention will be described in detail below with reference to the drawings and specific embodiments.

[0058] The present invention realizes the simulation of the gas method for detecting insulation defects in air switchgear by establishing a numerical analysis model. The numerical analysis model mainly consists of the hydrodynamic control equations and the chemical reaction rate equations. Among them, the control equations include the electron continuity equation, the heavy particle continuity equation, the electron energy equation, and the electric field potential Poisson equation, which describe the movement and transfer of plasma from the perspective of fluid mechanics. The chemical reaction rate equation calculates the increase and decrease of substances from the perspective of chemical reactions. At the same time, the present invention designs a verification idea for verifying the consistency between the numerical analysis model and the test platform by using the volt-ampere characteristic curve. Finally, the present invention aims to output the relationship curve between the partial discharge amount and various characteristic gases, opening up another research idea for monitoring the partial discharge of insulation defects in switchgear by the gas method.

[0059] The simulation method for the gas method to detect partial discharge of insulation defects in air switchgear according to the present invention has a flow chart as Figure 1 shown, and is specifically implemented according to the following steps:

[0060] Step 1: Couple the particle continuity equation and the Poisson equation for describing discharge with the electron energy density equation to establish a hydrodynamic model;

[0061] Step 1 is specifically implemented according to the following steps:

[0062] Step 1.1: The control equations include:

[0063] Electron continuity equation:

[0064] Heavy particle continuity equation:

[0065] Electron energy equation:

[0066] Electric field potential Poisson equation: -▽*ε0ε r ▽V=ρ q

[0067]

[0068] In the formula: n e is the free electron density number; n ε is the electron energy density number; n k is the heavy particle density number; μ e is the free electron mobility; μ ε is the electron energy mobility; D e is the electron diffusion rate; D ε electron energy diffusion rate; R e is the electron chemical source term; R ε electron energy source term; ρ is the mixed gas density; R kis the heavy particle mass fraction; u is the mass-average fluid velocity vector; j k is the diffusion flux vector; k R is the production rate of heavy particle k; ε0 and ε r are the vacuum permittivity and relative permittivity respectively; ρ q is the space charge density; e is the elementary charge; Z k is the electric charge carried by particle k; E is the electric field vector; V is the applied electric potential;

[0069] Step 1.2: Before solving the several differential equations in Step 1.1, convert them into the weak form;

[0070] In Step 1.1, the electron energy mobility μ ε and the electron energy diffusivity D e are calculated using the BOLSIG+ software;

[0071] Step 1.3: The ion diffusivity is calculated by the following formula:

[0072]

[0073] where: k B is the Boltzmann constant; T is the thermodynamic temperature of the gas; Q ion is the corresponding ion charge number.

[0074] Step 2: Screen the actually occurring chemical reactions based on the collision theory, ignore the minor reactions, and retain the reactions that have a greater impact on the results;

[0075] Step 2 is specifically implemented according to the following steps:

[0076] Step 2.1: Select some chemical reaction equations that have a greater impact on the results, and at the same time ignore other minor reactions. In this example, 65 chemical reactions that have a greater impact on the results are selected;

[0077] Step 2.2: Convert the chemical reaction equation into a reaction rate equation. According to the elementary reaction aA + bB → gC + dD, the reaction rate equation is

[0078] At the same time:

[0079] Then

[0080]

[0081]

[0082] where k is the reaction rate constant, which is divided into the collision reaction rate constant k e and the chemical group reaction rate constant kr , the calculation formula is as follows:

[0083] Collision reaction:

[0084] Chemical group reaction:

[0085] In the formula: γ is the viscosity coefficient, and its value in this example is 1; σ j (ε) is the electron collision cross-section data; ε is the electron energy; f(ε) is the electron energy distribution function, and f(ε) is obtained by solving the Boltzmann equation estimated by two terms in combination with the electron collision cross-section data σ j (ε); A f is the frequency factor; E a is the apparent activation energy; T is the thermodynamic temperature of the gas; R g is the molar gas constant.

[0086] Step 3: Establish a metal protrusion defect model in the multi-physics simulation software COMSOL and set the calculation area;

[0087] Step 3 is specifically implemented according to the following steps:

[0088] Step 3.1: Common defects in the insulation defects of switchgear include: metal protrusion defects, free metal particle defects, and floating potential defects. The metal protrusion defect includes two parts: a needle electrode and a plate electrode;

[0089] Step 3.2: Establish a metal protrusion defect model, that is, the needle electrode is connected to high voltage, the plate electrode is grounded, the tip of the needle electrode is 1 mm high; the discharge gap is 1 mm; the gas composition in the gap is 21% oxygen and 79% nitrogen; the thickness of the plate electrode is 1 mm. Set the above parameters in the multi-physics simulation software COMSOL to obtain a simulation model, and divide the finite element triangular mesh for the calculation area;

[0090] Combined with Figure 2 , Figure 3 , Step 4: According to the common insulation defect types of air switchgear, build a test model with the same parameters as in Step 3;

[0091] Step 4 is specifically implemented according to the following steps:

[0092] Step 4.1: Fabricate a metal protrusion insulation defect model with the same parameters as the simulation model in Step 3;

[0093] Step 4.2: Connect the needle electrode to the high-voltage terminal of a non-discharge high-voltage test transformer, and ground the plate electrode;

[0094] Step 4.3: According to the principle of the pulse current method, connect the high-voltage side of the metal protrusion defect model described in Step 4.2 to the coupling capacitor, and connect the other end of the coupling capacitor to the partial discharge detector. The schematic diagram is as Figure 2 shown.

[0095] Step 5: Based on the volt-ampere characteristic curve, verify whether the set control equation and chemical model can describe the discharge process of the metal protrusion model;

[0096] Step 5 is specifically implemented according to the following steps:

[0097] Step 5.1: Collect the time-domain data of voltage and current during partial discharge of the metal protrusion insulation defect on the test platform built in Step 4, and input the voltage time-domain data into the built simulation model as the excitation voltage of the simulation model;

[0098] Step 5.2: When the discharge current of the simulation model in Step 3 has the same change trend, similar peak points and zero-crossing points as the discharge current of the test platform in Step 4, it is considered that the numerical analysis model can describe the physical process of the test platform;

[0099] Step 5.3: Use the partial discharge detector described in Step 4 to measure the partial discharge quantity during one partial discharge process;

[0100] Step 5.4: Substitute the partial discharge quantity in Step 5.1 into the numerical analysis model in Step 1;

[0101] Step 5.5: Derive the volume fractions of various gas products from the numerical analysis model in Step 5.4, and draw a time-domain diagram with the time axis as the abscissa and the volume fraction of the gas as the ordinate.

[0102] Step 6: Establish the relationship between the partial discharge quantity and various gas products.

[0103] Step 6 is specifically implemented according to the following steps:

[0104] Step 6.1: Keep the temperature constant and establish a time-domain diagram of the partial discharge quantity and various gas products under different humidities, with the time axis as the abscissa and the volume fraction of the gas as the ordinate;

[0105] Step 6.2: Keep the humidity constant and establish a curve diagram of the partial discharge quantity and various gas products under different temperatures, with the partial discharge quantity as the abscissa and the volume fraction of the gas as the ordinate;

[0106] Step 6.3: Steps 6.1 and 6.2 realize the simulation of partial discharge of the insulation defect of the air switch cabinet.

[0107] Example 1

[0108] The simulation method of the present invention for detecting partial discharge of insulation defects in air switchgear by gas method, the flow chart is as Figure 1 shown, and is specifically implemented according to the following steps:

[0109] Step 1: Couple the particle continuity equation and Poisson equation for describing discharge with the electron energy density equation to establish a hydrodynamic model;

[0110] Step 2: Screen the actual chemical reactions according to the collision theory, ignore the minor reactions, and retain the reactions that have a greater impact on the results;

[0111] Step 3: Establish a metal protrusion defect model in the multi-physics simulation software COMSOL and set the calculation area;

[0112] Step 4: Build a test model with the same parameters as in Step 3 according to the common insulation defect types of air switchgear;

[0113] Step 5: Verify whether the set control equations and chemical models can describe the discharge process of the metal protrusion model according to the volt-ampere characteristic curve;

[0114] Step 6: Establish the relationship between the partial discharge amount and various gas products.

[0115] Example 2

[0116] The simulation method of the present invention for detecting partial discharge of insulation defects in air switchgear by gas method, the flow chart is as Figure 1 shown, and is specifically implemented according to the following steps:

[0117] Step 1: Couple the particle continuity equation and Poisson equation for describing discharge with the electron energy density equation to establish a hydrodynamic model;

[0118] Step 1 is specifically implemented according to the following steps:

[0119] Step 1.1: The control equations include:

[0120] Electron continuity equation:

[0121] Heavy particle continuity equation:

[0122] Electron energy equation:

[0123] Electric field potential Poisson equation: -▽*ε0ε r ▽V = ρ q

[0124]

[0125] In the formula: ne is the free electron density number; n ε is the electron energy density number; n k is the heavy particle density number; μ e is the free electron mobility; μ ε is the electron energy mobility; D e is the electron diffusivity; D ε Electron energy diffusivity; R e is the electron chemical source term; R ε Electron energy source term; ρ is the density of the mixed gas; R k is the heavy particle mass fraction; u is the mass-averaged fluid velocity vector; j k is the diffusion flux vector; k R is the production rate of heavy particle k; ε0 and ε r are the vacuum permittivity and relative permittivity respectively; ρ q is the space charge density; e is the elementary charge; Z k is the electric charge carried by particle k; E is the electric field vector; V is the applied electric potential;

[0126] Step 1.2: Before solving the several differential equations in Step 1.1, convert them into the weak form;

[0127] In Step 1.1, the electron energy mobility μ ε and the electron energy diffusivity D e are calculated using BOLSIG+ software;

[0128] Step 1.3: The ion diffusivity is calculated by the following formula:

[0129]

[0130] where: k B is the Boltzmann constant; T is the thermodynamic temperature of the gas; Q ion is the corresponding ion charge number.

[0131] Step 2: Screen the actual chemical reactions according to the collision theory, ignore the minor reactions, and retain the reactions that have a greater impact on the results;

[0132] Step 2 is specifically implemented according to the following steps:

[0133] Step 3: Establish a metal protrusion defect model in the multi-physics simulation software COMSOL and set the calculation region;

[0134] Step 3 is specifically implemented according to the following steps:

[0135] Step 3.1: The common insulation defects in switchgear include: metal protrusion defects, free metal particle defects, and floating potential defects. Metal protrusion defects include two parts: a needle electrode and a plate electrode.

[0136] Step 3.2: Establish a metal protrusion defect model, that is, connect the needle electrode to high voltage and the plate electrode to ground. The tip of the needle electrode is 1 mm high; the discharge gap is 1 mm; the gas composition in the gap is 21% oxygen and 79% nitrogen; the thickness of the plate electrode is 1 mm. Set the above parameters in the multi-physics field simulation software COMSOL to obtain a simulation model, and divide the finite element triangular mesh for the calculation area.

[0137] Step 4: According to the common insulation defect types of air switchgear, build a test model with the same parameters as in Step 3.

[0138] Step 4 is specifically implemented according to the following steps:

[0139] Step 4.1: Make a metal protrusion insulation defect model with the same parameters as the simulation model in Step 3.

[0140] Step 4.2: Connect the needle electrode to the high-voltage end of a non-discharge high-voltage test transformer, and ground the plate electrode.

[0141] Step 4.3: According to the principle of the pulse current method, connect the high-voltage side of the metal protrusion defect model described in Step 4.2 to a coupling capacitor, and connect the other end of the coupling capacitor to a partial discharge detector. The schematic diagram is as Figure 2 shown.

[0142] Step 5: Based on the volt-ampere characteristic curve, verify whether the set control equation and chemical model can describe the discharge process of the metal protrusion model.

[0143] Step 5 is specifically implemented according to the following steps:

[0144] Step 5.1: Collect the time-domain data of voltage and current during partial discharge of the metal protrusion insulation defect on the test platform built in Step 4, and input the voltage time-domain data into the built simulation model as the excitation voltage of the simulation model.

[0145] Step 5.2: When the discharge current of the simulation model in Step 3 has the same change trend, similar peak points and zero-crossing points as the discharge current of the test platform described in Step 4, it is considered that the numerical analysis model can describe the physical process of the test platform.

[0146] Step 5.3: Use the partial discharge detector described in Step 4 to measure the partial discharge quantity during one partial discharge process.

[0147] Step 5.4: Substitute the partial discharge quantity in Step 5.1 into the numerical analysis model in Step 1.

[0148] Step 5.5: Derive the volume fractions of various gas products from the numerical analysis model in Step 5.4, and plot a time-domain graph with the time axis as the abscissa and the gas volume fraction as the ordinate.

[0149] Step 6: Establish the relationship between the partial discharge amount and various gas products.

[0150] Step 6 is specifically implemented according to the following steps:

[0151] Step 6.1: Keep the temperature constant, and establish a time-domain graph of the relationship between the partial discharge amount and various gas products under different humidities, with the time axis as the abscissa and the gas volume fraction as the ordinate;

[0152] Step 6.2: Keep the humidity constant, and establish a curve graph of the relationship between the partial discharge amount and various gas products under different temperatures, with the partial discharge amount as the abscissa and the gas volume fraction as the ordinate;

[0153] Step 6.3: The above Steps 6.1 and 6.2 realize the simulation of the partial discharge of the insulation defect of the air switchgear.

[0154] Embodiment 3

[0155] The simulation method for detecting the partial discharge of the insulation defect of the air switchgear by the gas method of the present invention has a flow chart as Figure 1 shown, and is specifically implemented according to the following steps:

[0156] Step 1: Couple the particle continuity equation and Poisson equation for describing discharge with the electron energy density equation to establish a hydrodynamic model;

[0157] Step 1 is specifically implemented according to the following steps:

[0158] Step 1.1: The control equations include:

[0159] Electron continuity equation:

[0160] Heavy particle continuity equation:

[0161] Electron energy equation:

[0162] Electric field potential Poisson equation: -▽*ε0ε r ▽V = ρ q

[0163]

[0164] Where: n e is the free electron density number; n ε is the electron energy density number; nk is the heavy particle density number; μ e is the free electron mobility; μ ε is the electron energy mobility; D e is the electron diffusion rate; D ε Electron energy diffusion rate; R e is the electron chemical source term; R ε Electron energy source term; ρ is the density of the mixed gas; R k is the heavy particle mass fraction; u is the mass-averaged fluid velocity vector; j k is the diffusion flux vector; k R is the production rate of heavy particle k; ε0 and ε r are the vacuum permittivity and relative permittivity respectively; ρ q is the space charge density; e is the elementary charge; Z k is the electric charge carried by particle k; E is the electric field vector; V is the applied electric potential;

[0165] Step 1.2: Before solving the several differential equations in Step 1.1, convert them into the weak form;

[0166] In Step 1.1, the electron energy mobility μ ε and the electron energy diffusion rate D e are calculated using BOLSIG+ software;

[0167] Step 1.3: The ion diffusion rate is calculated by the following formula:

[0168]

[0169] where: k B is the Boltzmann constant; T is the thermodynamic temperature of the gas; Q ion is the corresponding ion charge number.

[0170] Step 2: Screen the actual chemical reactions according to the collision theory, ignore the minor reactions, and retain the reactions that have a greater impact on the results;

[0171] Step 2 is specifically implemented according to the following steps:

[0172] Step 2.1: Select some chemical reaction equations that have a greater impact on the results, and at the same time ignore other minor reactions. In this example, 65 chemical reactions that have a greater impact on the results are selected;

[0173] Step 2.2: Convert the chemical reaction equations into reaction rate equations. According to the elementary reaction aA + bB → gC + dD, the reaction rate equation is

[0174] Meanwhile:

[0175] Then

[0176]

[0177]

[0178] where k is the reaction rate constant, which is divided into the collision reaction rate constant k e and the chemical group reaction rate constant k r , and the calculation formulas are as follows:

[0179] Collision reaction:

[0180] Chemical group reaction:

[0181] In the formula: γ is the viscosity coefficient, and its value in this example is 1; σ j (ε) is the electron collision cross-section data; ε is the electron energy; f(ε) is the electron energy distribution function, and f(ε) is obtained by solving the two-term estimated Boltzmann equation by combining the electron collision cross-section data σ j (ε); A f is the frequency factor; E a is the apparent activation energy; T is the thermodynamic temperature of the gas; R g is the molar gas constant.

[0182] Step 3: Establish a metal protrusion defect model in the multi-physics simulation software COMSOL and set the calculation region;

[0183] Step 4: Build a test model with the same parameters as in Step 3 according to the common insulation defect types of air switchgear;

[0184] Step 4 is specifically implemented according to the following steps:

[0185] Step 4.1: Fabricate a metal protrusion insulation defect model with the same parameters as the simulation model in Step 3;

[0186] Step 4.2: Connect the needle electrode to the high-voltage terminal of the non-discharge high-voltage test transformer, and ground the plate electrode;

[0187] Step 4.3: According to the principle of the pulse current method, connect the high-voltage side of the metal protrusion defect model described in Step 4.2 to the coupling capacitor, and connect the other end of the coupling capacitor to the partial discharge detector. The schematic diagram is as Figure 2 shown.

[0188] Step 5: Verify whether the set control equation and chemical model can describe the discharge process of the metal protrusion model based on the volt-ampere characteristic curve;

[0189] Step 5 is specifically implemented according to the following steps:

[0190] Step 5.1: Collect the time-domain data of voltage and current during partial discharge of the insulation defect with metal protrusions on the test platform built in Step 4, and input the voltage time-domain data into the built simulation model as the excitation voltage of the simulation model;

[0191] Step 5.2: When the discharge current of the simulation model in Step 3 has the same change trend, similar peak points and zero-crossing points as the discharge current of the test platform in Step 4, it is considered that the numerical analysis model can describe the physical process of the test platform;

[0192] Step 5.3: Use the partial discharge detector in Step 4 to measure the partial discharge quantity during one partial discharge process;

[0193] Step 5.4: Substitute the partial discharge quantity in Step 5.1 into the numerical analysis model in Step 1;

[0194] Step 5.5: Derive the volume fractions of various gas products from the numerical analysis model in Step 5.4, and draw a time-domain graph with the abscissa as the time axis and the ordinate as the volume fraction of the gas.

[0195] Step 6: Establish the relationship between the partial discharge quantity and various gas products.

[0196] Step 6 is specifically implemented according to the following steps:

[0197] Step 6.1: Keep the temperature constant, and establish a time-domain graph of the relationship between the partial discharge quantity and various gas products under different humidities, with the abscissa as the time axis and the ordinate as the volume fraction of the gas;

[0198] Step 6.2: Keep the humidity constant, and establish a curve graph of the relationship between the partial discharge quantity and various gas products under different temperatures, with the abscissa as the partial discharge quantity and the ordinate as the volume fraction of the gas;

[0199] Step 6.3: Steps 6.1 and 6.2 realize the simulation of partial discharge of the insulation defect of the air switchgear.

Claims

1. A simulation method for detecting partial discharge of insulation defects in air switchgear by gas method, characterized in that, The simulation of the gas method for detecting insulation defects in air switchgear is realized by establishing a numerical analysis model, which is specifically implemented according to the following steps: Step 1: Couple the particle continuity equation and Poisson equation for describing discharge with the electron energy density equation to establish a hydrodynamic model; Step 2: Screen the actual chemical reactions according to the collision theory, ignore the minor reactions, and retain the reactions that have a greater impact on the results; Step 3: Establish a metal protrusion defect model in the multi-physics field simulation software COMSOL and set the calculation area; The specific implementation of Step 3 is as follows: Step 3.1: Common defects in the insulation defects of switchgear include: metal protrusion defects, free metal particle defects, and floating potential defects. The metal protrusion defect includes two parts: a needle electrode and a plate electrode; Step 3.2: Establish a metal protrusion defect model, that is, the needle electrode is connected to high voltage, the plate electrode is grounded, the tip of the needle electrode is 1 mm high; the discharge gap is 1 mm; the gas composition in the gap is 21% oxygen and 79% nitrogen; the thickness of the plate electrode is 1 mm. Set the above parameters in the multi-physics field simulation software COMSOL to obtain a simulation model, and divide the finite element triangular grid for the calculation area; Step 4: According to the common insulation defect types of air switchgear, build a test model with the same parameters as in Step 3; The specific implementation of Step 4 is as follows: Step 4.1: Make a metal protrusion insulation defect model with the same parameters as the simulation model in Step 3; Step 4.2: Connect the needle electrode to the high-voltage end of a non-discharge high-voltage test transformer, and the plate electrode is grounded; Step 4.3: According to the principle of the pulse current method, connect the high-voltage side of the metal protrusion defect model described in Step 4.2 to a coupling capacitor, and the other end of the coupling capacitor is connected to a partial discharge detector; Step 5: Verify whether the set control equation and chemical model can describe the discharge process of the metal protrusion model according to the volt-ampere characteristic curve; The specific implementation of Step 5 is as follows: Step 5.1: Collect the time-domain data of voltage and current during partial discharge of the metal protrusion insulation defect on the test platform built in Step 4, and input the voltage time-domain data into the built simulation model as the excitation voltage of the simulation model; Step 5.2: When the discharge current of the simulation model in Step 3 has the same change trend, similar peak points and zero-crossing points as the discharge current of the test platform in Step 4, it is considered that the numerical analysis model can describe the physical process of the test platform; Step 5.3: Use the partial discharge detector described in Step 4 to measure the partial discharge quantity during one partial discharge process; Step 5.4: Substitute the partial discharge quantity in Step 5.1 into the numerical analysis model in Step 1; Step 5.5: Derive the volume fractions of various gas products from the numerical analysis model in Step 5.4 and draw a time-domain diagram, with the time axis as the abscissa and the volume fraction of the gas as the ordinate; Step 6: Establish the relationship between the partial discharge quantity and various gas products; The specific implementation of Step 6 is as follows: Step 6.1: Keep the temperature constant and establish a time-domain graph between the partial discharge amount and various gas products at different humidities. The abscissa is the time axis, and the ordinate is the volume fraction of the gas; Step 6.2: Keep the humidity constant and establish a curve graph between the partial discharge amount and various gas products at different temperatures. The abscissa is the partial discharge amount, and the ordinate is the volume fraction of the gas; Step 6.3: The simulations in Steps 6.1 and 6.2 achieve the partial discharge of the insulation defect in the air switch cabinet.

2. The simulation method for detecting partial discharge of insulation defects in air switchgear by gas method according to claim 1, wherein, The specific implementation of Step 1 is as follows: Step 1.1: The governing equations include: Electronic continuity equation: Heavy particle continuity equation: Electronic energy equation: Electric field electric potential Poisson equation: where: n e is the free electron density number; n ε is the electron energy density number; n k is the heavy particle density number; μ e is the free electron mobility; μ ε is the electron energy mobility; D e is the electron diffusivity; D ε electron energy diffusivity; R e is the electron chemical source term; R ε electron energy source term; ρ is the density of the mixed gas; R k is the mass fraction of heavy particles; u is the mass-averaged fluid velocity vector; j k is the diffusion flux vector; k R is the production rate of heavy particle k; ε0 and ε r are the vacuum permittivity and relative permittivity respectively; ρ q is the space charge density; e is the elementary charge; Z k is the electric charge carried by particle k; E is the electric field vector; V is the applied electric potential; Step 1.2: Convert several differential equations in Step 1.1 into weak forms before solving; Step 1.3: The ion diffusivity is calculated by the following formula: where: k B is the Boltzmann constant; T is the thermodynamic temperature of the gas; Q ion is the corresponding ionic charge number.

3. The simulation method for detecting partial discharge of insulation defects in air switchgear by gas method according to claim 2, wherein The specific implementation of Step 2 is as follows: Step 2.1: Select 65 chemical reactions that have a greater impact on the results; Step 2.

2. Convert the chemical reaction equation into a reaction rate equation. For the elementary reaction aA + bB → gC + dD, the reaction rate equation is Meanwhile: Then where k is the reaction rate constant, which is divided into the collision reaction rate constant k e and the chemical group reaction rate constant k r , and the calculation formula is as follows: Collision reaction: Chemical group reaction: Where: γ is the viscosity coefficient, σ j (ε) is the electron impact cross-section data; ε is the electron energy; f(ε) is the electron energy distribution function, and f(ε) is obtained by solving the Boltzmann equation estimated by two terms using the BOLSIG+ software in combination with the electron impact cross-section data σ j (ε); A f is the frequency factor; E a is the apparent activation energy; T is the thermodynamic temperature of the gas; R g is the molar gas constant.

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