Environmentally friendly method for suppressing gaseous solid decomposition products

Abstract

The present invention discloses a method for inhibiting solid decomposition products of environmentally friendly gas, the steps comprising: step 1, combining density functional theory with reaction molecular dynamics to calculate the decomposition path and reaction rate constant of environmentally friendly gas; step 2, establishing a chemical kinetic model of continuous corona discharge of environmentally friendly gas through the decomposition path and reaction rate constant, and calculating the time evolution characteristics and formation mechanism of the decomposition products under continuous corona discharge; step 3, according to the time evolution characteristics and formation mechanism, by calculating the contribution of each relevant reaction to the generation / removal of carbon-containing solid decomposition products, by changing variables and adopting a multivariable collaborative optimization method to inhibit the components of solid decomposition products. The present invention solves the problem in the prior art that it is difficult to carry out measures to inhibit solid decomposition products due to the unclear formation mechanism of solid decomposition products.

Description

Technical Field

[0001] The invention belongs to the technical field of insulation monitoring and fault diagnosis of electric equipment, and relates to an environmentally friendly method for suppressing solid decomposition products of gas. Background Art

[0002] SF6 gas is the most commonly used medium in power equipment due to its outstanding insulation and arc extinguishing properties. However, the greenhouse effect of SF6 gas is 23,900 times that of CO2, and it has been listed as one of the six restricted greenhouse gases in the Kyoto Protocol. Therefore, it is urgent to study SF6 alternative gases to develop a green and low-carbon power industry. Existing research mainly focuses on CF3I, c-C4F8, C4F7N, C5F 10 O.C6F 12 O and other gases with good insulation properties. 420kV gas insulated transmission lines (GIL), 245kV current transformers and 145kV gas insulated switchgear (GIS) with C4F7N / CO2 mixed gas as the insulating medium have been put into trial operation. 10 A 22kV distribution switchgear prototype with C4F7N and its mixed gas, C5F 10 O and its mixed gas have the potential to replace SF6 gas.

[0003] However, various insulation defects generated by power equipment during long-term operation will cause partial discharge or even flashover, accompanied by the decomposition of environmentally friendly insulating media, resulting in a decrease in the insulation performance of power equipment. Corona discharge is a typical form of partial discharge, and is mostly caused by sharp points or protrusions on the conductor. 10 O are all carbon-fluorine gases, and their molecular structures contain carbon. When corona discharge occurs, solid decomposition products (carbon particles, etc.) are inevitably formed, posing a threat to the safe and stable operation of power equipment. Research on the inhibition method of solid decomposition products is of great significance for the reliable operation of environmentally friendly power equipment. However, the formation mechanism of solid decomposition products is still unclear, and there is a lack of relevant detection technology, which makes it difficult to carry out the inhibition method of solid decomposition products. Summary of the invention

[0004] The purpose of the present invention is to provide an environmentally friendly method for inhibiting solid decomposition products of gas, which solves the problem in the prior art that it is difficult to carry out measures to inhibit solid decomposition products due to unclear formation mechanism of solid decomposition products.

[0005] The technical solution adopted by the present invention is:

[0006] An environmentally friendly method for inhibiting gaseous solid decomposition products, comprising:

[0007] Step 1: Combine density functional theory with reaction molecular dynamics to calculate the decomposition path and reaction rate constant of environmentally friendly gases.

[0008] Step 2, establishing a chemical kinetic model of environmentally friendly gas continuous corona discharge through decomposition paths and reaction rate constants, and calculating the time evolution characteristics and formation mechanism of decomposition products under continuous corona discharge;

[0009] Step 3, according to the time evolution characteristics and formation mechanism, by calculating the contribution of each relevant reaction to the generation / removal of carbon-containing solid decomposition products, the components of solid decomposition products are suppressed by changing variables and adopting a multivariable collaborative optimization method.

[0010] The present invention is also characterized in that:

[0011] The environmentally friendly gas decomposition path and reaction rate constant in step 1 include a static decomposition path and reaction rate constant and a dynamic decomposition path and reaction rate constant;

[0012] The static decomposition path and reaction rate constant are solved by density functional theory. In the case of reactions with transition states, transition state theory is used for calculation. For reactions without transition states, variational transition state theory is used for calculation. The formula is:

[0013]

[0014] Where σ is the number of reaction channels from reactants to products, β = (k B T) -1 , k B is the Boltzmann constant, T is the temperature, h is the Planck constant, Q ≠ (T) is the partition function per unit volume of the transition state structure, Q R (T) represents the partition function of the reactant per unit volume, V ≠ represents a classical potential barrier.

[0015] The dynamic decomposition path and reaction rate constant are calculated using a reaction molecular dynamics model based on the ReaxFF force field. By establishing a periodic box in the reaction molecular dynamics model based on the ReaxFF force field and placing environmentally friendly gases and their mixtures in the periodic box, the dynamic reaction path and reaction rate constant can be obtained.

[0016] The potential energy function formula of the ReaxFF force field in the reaction molecular dynamics model of the ReaxFF force field is:

[0017] E system =E bond +E lp +E over +E under+E val +E pen +E tors +E conj +E H-bond +E vdWaals +E coulomb (2)

[0018] In the formula, E bond is the bond energy, E lp is the lone pair electron term, E over is the energy correction term for overcoordination, E under is the energy correction term for low coordination, E val is the valence angle energy term, E pen is the penalty energy term, E tors is the torsion energy term, E conj is the conjugation term of the molecule, E H-bond is the hydrogen bonding term, E vdWaals is the non-bonded van der Waals force term, E coulomb is the non-bonded Coulomb force term.

[0019] Step 2 specifically includes:

[0020] Step 2.1: Calculate the amplitude and pulse width of the electric field by coupling the migration-diffusion equations of three charged particles with the Poisson equation;

[0021] Step 2.2, the amplitude and pulse width of the electric field are used as the excitation parameters of the chemical kinetic model. The chemical kinetic model is shown in (7) to (9):

[0022]

[0023]

[0024]

[0025] In the formula, c pj is the number density of particles in the plasma region, ν ij ,ν ij ′ are the stoichiometric coefficients on the left and right sides of the chemical reaction equation, respectively, k i is the reaction rate constant, D kj is the diffusion coefficient, c gj is the number density of particles in the gas region, r p is the radius of the plasma region, r g is the radius of the gas zone, S p , V p are the area and volume of the plasma region, V g is the volume of the gas zone; E and E m are the electric field and the maximum electric field, τpls Is the pulse width.

[0026] Step 2.3, calculate the time evolution characteristics of the decomposition products under continuous corona discharge through the chemical kinetic model of environmentally friendly gas continuous corona discharge, and obtain the evolution characteristics and formation mechanism of the carbon-containing solid decomposition products.

[0027] The migration-diffusion equation and Poisson equation in step 2.1 are shown in formulas (3) to (6):

[0028]

[0029]

[0030]

[0031]

[0032] In the formula, t is time, n is e , μ e , D e are the number density, mobility and diffusion coefficient of electrons, respectively. is the electric field, α and η are the ionization coefficient and adsorption coefficient respectively, k ep is the recombination coefficient of electrons and positive ions, n p , μ p , D p are the number density, mobility and diffusion coefficient of positive ions, respectively, k np is the recombination coefficient of positive ions and negative ions, n n , μ n , D n are the number density, mobility and diffusion coefficient of negative ions, V is the applied voltage, e is the electron charge, ε r , ε0 are the relative dielectric constant and vacuum dielectric constant respectively.

[0033] Step 3 specifically includes:

[0034] Step 3.1 calculates the contribution of each relevant reaction to the generation and removal of carbon-containing solid decomposition products, as shown in formula (10), and can obtain the main generation / removal pathway of carbon-containing solid decomposition products;

[0035]

[0036] In the formula, R i is the reaction rate of the ith reaction, w i is the contribution of the ith reaction;

[0037] Step 3.2 By changing the gas pressure, voltage, needle-plate electrode distance, and micro-water and micro-oxygen content, the influence of these factors on the main generation / removal path and content of solid decomposition products can be obtained, thereby suppressing the components of solid decomposition products through multivariable collaborative optimization. The beneficial effects of the present invention are:

[0038] The invention provides an environmentally friendly method for inhibiting solid decomposition products of gas, which inhibits the solid decomposition products by revealing the main formation path of solid decomposition products under continuous corona discharge and by regulating discharge conditions and micro-water and micro-oxygen contents.

[0039] The environmentally friendly gas in the present invention can be C4F7N and its mixed gas, C5F 10 O and its mixed gas, C6F 12 O and its mixed gases, etc., can reveal the formation mechanism and main generation / removal pathways of solid decomposition products in these mixed gases, thereby guiding the inhibition measures of solid decomposition products.

[0040] The present invention adopts density functional theory combined with reaction molecular dynamics to give the formation path of solid decomposition products from both static and dynamic aspects, which can improve the database of reaction paths and reaction rate constants of decomposition products in environmentally friendly gases, and combines with chemical kinetic models to reveal the evolution characteristics of decomposition products under continuous corona discharge, obtain the evolution law of solid decomposition products and key generation / removal paths, and reduce the cost and labor and material consumption required for the experiment. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is a flow chart of an environmentally friendly method for suppressing gaseous solid decomposition products;

[0042] Figure 2 It is a schematic diagram of the chemical kinetic model. DETAILED DESCRIPTION

[0043] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0044] The environmentally friendly method for inhibiting solid decomposition products of gaseous solids of the present invention is shown in the flow chart as follows: Figure 1 As shown, the following steps are included:

[0045] Step 1: Combine density functional theory with reaction molecular dynamics to calculate the decomposition path and reaction rate constant of environmentally friendly gases.

[0046] Step 2, establishing a chemical kinetic model of environmentally friendly gas continuous corona discharge through decomposition paths and reaction rate constants, and calculating the time evolution characteristics and formation mechanism of decomposition products under continuous corona discharge;

[0047] Step 3, based on the time evolution characteristics and formation mechanism, calculate the contribution of each relevant reaction to the generation / removal of carbon-containing solid decomposition products, and suppress the components of solid decomposition products by changing variables and adopting a multivariable collaborative optimization method.

[0048] The environmentally friendly gas in step 1 can be C4F7N and its mixed gas, C5F 10 O and its mixed gas, C6F 12 O and its mixed gas, usually N2, CO2, Air are mixed with these environmentally friendly gases;

[0049] The environmentally friendly gas decomposition path and reaction rate constant in step 1 specifically include a static decomposition path and reaction rate constant and a dynamic decomposition path and reaction rate constant;

[0050] The static decomposition path and reaction rate constant are mainly solved by density functional theory. In the case of reactions with transition states, transition state theory is used for calculation, and for reactions without transition states, variational transition state theory is used for calculation. The formula is:

[0051]

[0052] Where σ is the number of reaction channels from reactants to products, β = (k B T) -1 , k B is the Boltzmann constant, T is the temperature, h is the Planck constant, Q ≠ (T) is the partition function per unit volume of the transition state structure, Q R (T) represents the partition function of the reactant per unit volume, V ≠ represents a classical potential barrier.

[0053] The dynamic decomposition path and reaction rate constant are mainly solved by molecular dynamics. The reaction molecular dynamics model based on the ReaxFF force field is used for calculation. By establishing a periodic box in the reaction molecular dynamics model based on the ReaxFF force field and placing environmentally friendly gases and their mixtures in the periodic box, the dynamic reaction path and reaction rate constant can be obtained, and the chemical reaction system of environmentally friendly gases can be improved by comparing and supplementing the results obtained by density functional theory.

[0054] The potential energy function formula of the ReaxFF force field in the reaction molecular dynamics model of the ReaxFF force field is:

[0055] E system =E bond +E lp +E over +E under +E val +E pen+E tors +E conj +E H-bond +E vdWaals +E coulomb (2)

[0056] In the formula, E bond is the bond energy, E lp is the lone pair electron term, E over is the energy correction term for overcoordination, E under is the energy correction term for low coordination, E val is the valence angle energy term, E pen is the penalty energy term, E tors is the torsion energy term, E conj is the conjugation term of the molecule, E H-bond is the hydrogen bonding term, E vdWaals is the non-bonded van der Waals force term, E coulomb is the non-bonded Coulomb force term.

[0057] The chemical reaction system in step 2 is the most critical component of the chemical kinetic model. The chemical reaction system of the chemical kinetic model in step 2 includes not only the reaction path and reaction rate constant calculated in step 1, but also the existing chemical reaction paths and rate constants related to N2, CO2, and Air. Therefore, for each environmentally friendly gas or its mixed gas, there are usually dozens of particles in the system, hundreds or thousands of chemical reactions, and it includes four major categories: electron collision reaction, ion-neutral particle reaction, ion-ion reaction, and neutral particle-neutral particle reaction.

[0058] Step 2.1: Calculate the amplitude and pulse width of the electric field.

[0059] In chemical kinetic models, electric field is often used as the excitation parameter of the model, so it is necessary to calculate the amplitude and pulse width of the electric field during the discharge process. The present invention uses the coupling of the migration-diffusion equation of three charged particles and the Poisson equation to calculate the amplitude and pulse width of the electric field; the migration-diffusion equation and the Poisson equation in step 2.2 are shown in formulas (3) to (6):

[0060]

[0061]

[0062]

[0063]

[0064] In the formula, t is time, n is e , μ e , D eare the number density, mobility and diffusion coefficient of electrons, respectively. is the electric field, α and η are the ionization coefficient and adsorption coefficient respectively, k ep is the recombination coefficient of electrons and positive ions, n p , μ p , D p are the number density, mobility and diffusion coefficient of positive ions, respectively, k np is the recombination coefficient of positive ions and negative ions, n n , μ n , D n are the number density, mobility and diffusion coefficient of negative ions, V is the applied voltage, e is the electron charge, ε r , ε0 are the relative dielectric constant and vacuum dielectric constant respectively.

[0065] Step 2.2, continuous corona discharge. Since the discharge time is usually several hours to tens of hours, the decomposition products will reach a nearly uniform distribution through diffusion. Therefore, the chemical kinetic model here uses two zero-dimensional models for coupling, representing the plasma region and the gas region respectively. The schematic diagram of the chemical kinetic model is shown in Figure 2 As shown. The plasma region and the gas region are coupled through the diffusion process. The amplitude and pulse width of the electric field are used as the excitation parameters of the chemical kinetic model. The chemical kinetic model is shown in (7) to (9):

[0066]

[0067]

[0068]

[0069] In the formula, c pj is the number density of particles in the plasma region, ν ij ,ν ij ′ are the stoichiometric coefficients on the left and right sides of the chemical reaction equation, respectively, k i is the reaction rate constant, D kj is the diffusion coefficient, c gj is the number density of particles in the gas region, r p is the radius of the plasma region, r g is the radius of the gas zone, S p , V p are the area and volume of the plasma region, V g is the volume of the gas zone; E and E m are the electric field and the maximum electric field, τ pls Is the pulse width.

[0070] Step 2.3, calculate the time evolution characteristics of the decomposition products under continuous corona discharge through the chemical kinetic model of environmentally friendly gas continuous corona discharge, and obtain the evolution characteristics and formation mechanism of the carbon-containing solid decomposition products.

[0071] Step 3.1, calculate the contribution of each relevant reaction to the generation and removal of carbon-containing solid decomposition products, as shown in formula (10), and the main generation / removal pathway of carbon-containing solid decomposition products can be obtained.

[0072]

[0073] In the formula, R i is the reaction rate of the ith reaction, w i is the contribution of the ith reaction;

[0074] Step 3.2, by changing the gas pressure, voltage, needle-plate electrode distance, and micro-water and micro-oxygen content, the influence of these factors on the main generation / removal pathways and contents of solid decomposition products can be obtained, thereby suppressing the components of solid decomposition products through multivariable collaborative optimization.

Claims

1. An environmentally friendly method for inhibiting gaseous solid decomposition products, characterized in that: include: Step 1, combining density functional theory and reaction molecular dynamics to calculate the environmentally friendly gas decomposition path and reaction rate constant; The environmentally friendly gas decomposition path and reaction rate constant described in step 1 include a static decomposition path and reaction rate constant and a dynamic decomposition path and reaction rate constant; The static decomposition path and reaction rate constant are solved by density functional theory. In the case of a reaction with a transition state, the transition state theory is used for calculation. For a reaction without a transition state, the variational transition state theory is used for calculation. The formula is: Where σ is the number of reaction channels from reactants to products, β = (k B T) -1 , k B is the Boltzmann constant, T is the temperature, h is the Planck constant, Q ≠ (T) is the partition function per unit volume of the transition state structure, Q R (T) represents the partition function per unit volume of the reactants, V ≠ represents a classical potential barrier; The dynamic decomposition path and reaction rate constant are calculated using a reaction molecular dynamics model based on the ReaxFF force field. By establishing a periodic box in the reaction molecular dynamics model based on the ReaxFF force field and placing environmentally friendly gases and their mixtures in the periodic box, the dynamic reaction path and reaction rate constant can be obtained. Step 2, establishing a chemical kinetic model of environmentally friendly gas continuous corona discharge through decomposition paths and reaction rate constants, and calculating the time evolution characteristics and formation mechanism of decomposition products under continuous corona discharge; Step 3, according to the time evolution characteristics and formation mechanism, by calculating the contribution of each relevant reaction to the generation / removal of carbon-containing solid decomposition products, the components of solid decomposition products are suppressed by changing variables and using a multivariable collaborative optimization method; Step 3 specifically includes: Step 3.1 calculates the contribution of each relevant reaction to the generation and removal of carbon-containing solid decomposition products, as shown in formula (10), and can obtain the main generation / removal pathway of carbon-containing solid decomposition products; In the formula, R i is the reaction rate of the ith reaction, w i is the contribution of the ith reaction; In step 3.2, by changing the gas pressure, voltage, needle-plate electrode distance, and micro-water and micro-oxygen content, the influence of these factors on the main generation / removal pathways and contents of solid decomposition products can be obtained, thereby suppressing the components of solid decomposition products through multivariable collaborative optimization.

2. The environmentally friendly method for suppressing gaseous solid decomposition products according to claim 1, characterized in that: The potential energy function formula of the ReaxFF force field in the reaction molecular dynamics model of the ReaxFF force field is: AND system =And bond +E lp +E over +E under +E val +E pen +E tors +E conj +E H-bond +E vdWaals +E coulomb (2) In the formula, E bond is the bond energy, E lp is the lone pair electron term, E over is the energy correction term for overcoordination, E under is the energy correction term for low coordination, E val is the valence angle energy term, E pen is the penalty energy term, E tors is the torsion energy term, E conj is the conjugation term of the molecule, E H-bond is the hydrogen bonding term, E vdWaals is the non-bonded van der Waals force term, E coulomb is the non-bonded Coulomb force term.

3. The environmentally friendly method for suppressing gaseous solid decomposition products according to claim 1, characterized in that: The step 2 specifically includes: Step 2.1: Calculate the amplitude and pulse width of the electric field by coupling the migration-diffusion equations of three charged particles with the Poisson equation; Step 2.2, the amplitude and pulse width of the electric field are used as excitation parameters of the chemical kinetic model, and the chemical kinetic model is shown in (7) to (9): In the formula, c pj is the number density of particles in the plasma region, ν ij ,ν ij ′ are the stoichiometric coefficients on the left and right sides of the chemical reaction equation, respectively, k i is the reaction rate constant, D kj is the diffusion coefficient, c gj is the number density of particles in the gas region, r p is the radius of the plasma region, r g is the radius of the gas zone, S p , V p are the area and volume of the plasma region, V g is the volume of the gas zone; E and E m are the electric field and the maximum value of the electric field, τ pls is the pulse width; Step 2.3, calculate the time evolution characteristics of the decomposition products under continuous corona discharge through the chemical kinetic model of environmentally friendly gas continuous corona discharge, and obtain the evolution characteristics and formation mechanism of the carbon-containing solid decomposition products.

4. The environmentally friendly method for suppressing gaseous solid decomposition products as claimed in claim 3, characterized in that: The migration-diffusion equation and Poisson's equation described in step 2.1 are shown in formulas (3) to (6): In the formula, t is time, n is e , μ e , D e are the number density, mobility and diffusion coefficient of electrons, respectively. is the electric field, α and η are the ionization coefficient and adsorption coefficient respectively, k ep is the recombination coefficient of electrons and positive ions, n p , μ p , D p are the number density, mobility and diffusion coefficient of positive ions, respectively, k np is the recombination coefficient of positive ions and negative ions, n n , μ n , D n are the number density, mobility and diffusion coefficient of negative ions, V is the applied voltage, e is the electron charge, ε r , ε0 are the relative dielectric constant and vacuum dielectric constant respectively.

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