Environment-friendly insulating gas characteristic product screening method based on leading reaction path

Abstract

The invention discloses an environment-friendly insulating gas characteristic product screening method based on a dominant reaction path, which comprises the following steps: step 1, revealing evolution characteristics of decomposition products by combining decomposition product experimental detection and chemical kinetic model simulation calculation; step 2, calculating a dominant reaction path of the decomposition product according to evolution characteristics of the decomposition product; and step 3, screening characteristic decomposition products according to the dominant reaction path. The problems that in the prior art, feature products are difficult to extract, and the decomposition products are difficult to carry out fault diagnosis on the environment-friendly gas insulation electric power equipment are solved, the generation mechanism of the decomposition products can be deeply revealed in the chemical reaction level, and the types of the feature products are screened out according to the dominant reaction path of the decomposition products.

Description

Technical Field

[0001] The present invention belongs to the technical field of insulation monitoring and fault diagnosis of electric power equipment, and in particular relates to a method for screening characteristic products of environmentally friendly insulating gas based on a dominant reaction path. Background Art

[0002] SF6 gas, which is widely used in gas-insulated power equipment, has a strong greenhouse effect and has a serious impact on the environment. Finding alternative gases to SF6 is an important measure to adapt to the global energy low-carbon transformation and respond to my country's "dual carbon" goals. It is also a key technology to promote the industrialization and upgrading of power equipment. Existing research mainly focuses on SF6 mixed gas, CF3I mixed gas, C4F7N mixed gas, C5F 10 O mixed gas, C6F 12 O mixed gas, K6 gas, clean air, etc. At present, C4F7N mixed gas and C5F 10 Some power equipment using O mixed gas as insulating gas has been put into operation.

[0003] However, it is inevitable that power equipment will have insulation defects during long-term operation, causing local overheating or discharge failures, leading to decomposition of gas insulation media. Power equipment fault diagnosis based on decomposition product analysis has the advantage of not being subject to electromagnetic interference, and has been widely used in fault diagnosis of SF6 gas-insulated power equipment. The decomposition products of environmentally friendly gas insulation media are very diverse and have complex structures. Commonly used detection methods such as gas chromatography-mass spectrometry and Fourier transform infrared spectrometer can only detect part of the decomposition products, resulting in the evolution mechanism of the decomposition products being difficult to obtain directly through experiments. Existing simulation calculations mainly focus on calculating the decomposition path and related energy barriers of environmentally friendly gas insulation media, and it is difficult to reveal the key generation mechanism of decomposition products. Therefore, it is difficult to obtain the characteristic decomposition products of environmentally friendly gas insulation media, which hinders the application of decomposition product analysis to power equipment fault diagnosis. Summary of the invention

[0004] The purpose of the present invention is to provide a method for screening characteristic products of environmentally friendly insulating gas based on the dominant reaction path, which solves the problem in the prior art that characteristic products are difficult to extract and decomposition products are difficult to use for fault diagnosis of environmentally friendly gas-insulated power equipment.

[0005] The technical solution adopted by the present invention is: a method for screening characteristic products of environmentally friendly insulating gas based on a dominant reaction path, which specifically includes the following steps: Step 1: Combining experimental detection of decomposition products with simulation calculation of chemical kinetic model to reveal the evolution characteristics of decomposition products; Step 2: Calculate the dominant reaction path of the decomposition products according to the evolution characteristics of the decomposition products; Step 3: Screen the characteristic decomposition products according to the dominant reaction pathway.

[0006] The technical solution adopted by the present invention is also characterized in that: Furthermore, step 1 is specifically as follows: detecting the decomposition products of the environmental gas, establishing a chemical kinetic model through the chemical reactions involved in the decomposition products and related reaction rate constants, and obtaining the evolution characteristics of the decomposition products through simulation and experiments.

[0007] Furthermore, step 1 is specifically implemented according to the following steps: Step 1.1, using gas chromatography-mass spectrometry and electron attachment mass spectrometry to detect the decomposition products of environmental protection gases; Step 1.2, based on the test results of the types and contents of the decomposition products of the environmentally friendly gas in step 1.1, summarize the chemical reactions and related reaction rate constants involved in the possible decomposition products of the environmentally friendly gas, and establish a chemical kinetic model; Step 1.3: The calculation results of the chemical kinetic model in step 1.2 are verified by the decomposition product detection results and the chemical kinetic model is corrected. The evolution characteristics of the decomposition products of the environmentally friendly gas are revealed by combining simulation and experiment.

[0008] Furthermore, the establishment of the chemical kinetic model in step 1.2 includes modeling of local overheating, spark discharge and corona discharge.

[0009] Furthermore, the local overheating modeling is as follows: The local overheating model is a 0-dimensional global model. All chemical reactions are reversible. The equation for the change of particle concentration in the discharge area with time is shown in equation (1):

[0010] in, n i and n j For particles i and j The concentration of r fk and r rk Respectively k The forward reaction rate constant and the reverse reaction rate constant of a reaction are v jkf and v jkr For the j The particle in k The stoichiometric coefficients on the left and right sides of a chemical reaction equation; The forward reaction rate constant is known, and the reverse reaction rate constant is obtained by the ratio of the forward reaction rate constant to the equilibrium constant. The equilibrium constant expression is shown in formula (2):

[0011] in, K k ( T ) is the equilibrium constant, m i 0 (T) represents the standard Gibbs free energy, p 0 is the standard atmospheric pressure; Since the chemical reaction system deviates from the local thermodynamic equilibrium state, the ratio of the electron temperature to the temperature of other heavy particles is defined as a value that varies with the electron number density, as shown in formula (3):

[0012] in, T e and T h are the electron temperature and heavy particle temperature, i e for T e and T h The ratio of n e is the electron concentration, n e max is the critical number density of electrons. When the electron concentration exceeds n e max When , the chemical system approximately satisfies the local thermodynamic equilibrium; By solving equations (1) to (3) simultaneously, the evolution characteristics of the decomposition products at each temperature over time can be calculated, and the evolution law of the decomposition products with temperature can also be obtained.

[0013] Furthermore, the spark discharge and corona discharge are modeled as follows: The decomposition products of spark discharge and corona discharge are an accumulation process. After the discharge generates decomposition products, the decomposition products continue to diffuse. Therefore, the plasma zone and gas zone are used to simulate the generation and diffusion process of decomposition products under spark discharge and corona discharge. The control equations of the plasma zone and gas zone are shown in equations (4) and (5):

[0014] in, t For time, c pjand c gj are the number densities of particles in the plasma and gas regions, respectively, v ij and v ij ’ are the stoichiometric coefficients on the left and right sides of the chemical reaction equation, respectively. k i is the reaction rate constant, c pl For the plasma region l The number density of particles, v il The left side of the reaction equation l The stoichiometric number of particles, D kj is the diffusion coefficient, r p and r g are the radii of the plasma region and the gas region, respectively, S p and V p are the area and volume of the plasma region, V g is the volume of the gas zone; When the gas pressure is high, spark discharge and corona discharge occur in the form of pulses or pulse clusters. In order to avoid the computational workload of solving the Poisson equation, an external electric field is used as the discharge excitation. All pulses are combined into one discharge pulse in each discharge cycle, and the periodic combined discharge pulse is used to calculate the interaction between charged particles and neutral particles under many repeated single pulses, as shown in Equation (6):

[0015] in, E m is the peak value of the electric field intensity, t pls is the duration of the combined discharge pulse; The peak value and duration of the pulse electric field of spark discharge and corona discharge are different; although the electric fields of spark discharge and corona discharge are both in the form of pulses, there are obvious differences in the pulse amplitude and duration between the two. Spark discharge is usually a small gap spark discharge with a short duration, while corona discharge is usually a stable discharge pulse form; Spark discharge and corona discharge span very large time and space scales, and multiple time scales are used to simultaneously calculate the fast discharge process in the plasma region and the slow gas phase reaction process in the gas region. Since the discharge process contains many steady-state decomposition products and transient decomposition products, the particles are divided into long-lived particles and short-lived particles according to their life cycle. Short-lived particles are only in the plasma region, while long-lived particles can diffuse from the plasma region into the gas region, thereby forming steady-state decomposition products through a series of reactions. In order to decouple long-lived particles and short-lived particles in the model, the average reaction rate constant of short-lived particles is introduced, as shown in Equation (7):

[0016] in, W i is the periodic average reaction rate constant, t rep is the discharge time of one cycle, c sl is the number density of short-lived particles; The model uses multiple time scales to simultaneously solve the rapid discharge process in the plasma region and the slow gas phase reaction process in the gas region. First, several discharge cycles are calculated for short-lived particles and long-lived particles according to equations (4) to (6), so that the number density of short-lived particles approaches a periodic stable state. Second, the average reaction rate constant of short-lived particles in one cycle is calculated according to equation (7). Finally, the periodic average reaction rate constant of short-lived particles is used to replace the original rate constant that varies with time, and the long-lived particles are solved to obtain the content of stable decomposition products.

[0017] Furthermore, step 2 is specifically as follows: according to the chemical kinetic model of step 1, the dominant reaction paths of the decomposition products under local overheating, spark discharge and corona discharge are calculated respectively.

[0018] Furthermore, step 2 calculates the reaction rate percentage of the chemical reaction pathway related to each decomposition product to quantitatively obtain the contribution of the related reaction pathway to the generation and removal of the decomposition product, thereby determining the dominant chemical reaction pathway according to the contribution rate.

[0019] Furthermore, step 3 draws a relationship diagram between the decomposition products according to the dominant reaction path of the decomposition products calculated in step 2, quantitatively characterizes the spectrum generated by the decomposition products, and selects independent decomposition products as characteristic products according to the quantitative spectrum relationship between the decomposition products. The fault type is characterized according to the characteristic products, thereby diagnosing local overheating, spark discharge and corona discharge.

[0020] The beneficial effects of the present invention are: (1) The present invention provides a method for screening characteristic products of environmentally friendly insulating gas based on the dominant reaction path, which can reveal the generation mechanism of decomposition products at the chemical reaction level and screen out the types of characteristic products according to the dominant reaction path of the decomposition products.

[0021] (2) The environmentally friendly gas insulating medium in the screening method of the present invention can be C4F7N and its mixed gas, C5F 10 O and its mixed gas, C6F 12 O and its mixed gas, K6 gas, etc. can extract their characteristic decomposition products according to the dominant reaction paths of the decomposition products of these environmentally friendly insulating media, which can be used to guide the insulation fault diagnosis of these environmentally friendly gases.

[0022] (3) The screening method of the present invention combines the detection of decomposition products with the chemical kinetic model to quantitatively calculate the dominant reaction pathway of the decomposition products, thereby screening characteristic decomposition products based on the dominant reaction pathway, which can reduce the manpower, material and financial resources required for actual experimental exploration and save costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the decomposition product detection and decomposition product simulation calculation of the screening method of the present invention; Figure 2 It is a schematic diagram of the principle of screening characteristic decomposition products based on the dominant reaction pathway of the present invention. DETAILED DESCRIPTION

[0024] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] The present invention provides a method for screening characteristic products of environmentally friendly insulating gas based on a dominant reaction path, comprising the following steps: Step 1: Combine the experimental detection of decomposition products with the simulation calculation of chemical kinetics model to reveal the evolution characteristics of decomposition products.

[0026] In step 1, the decomposition products of environmentally friendly gases are first detected by gas chromatography-mass spectrometry and electron attachment mass spectrometry. Gas chromatography-mass spectrometry combines the advantages of chromatograph and mass spectrometer, and can qualitatively and quantitatively detect decomposition products, and the types of decomposition products are mainly carbon-fluorine decomposition products. Electron attachment mass spectrometry diagnoses decomposition products by detecting negative ions and tracing their negative ionization paths, and has great advantages in detecting carbon-oxygen-fluorine decomposition products. Combining these two methods, the types and contents of environmentally friendly gas decomposition products are diagnosed.

[0027] In step 1, the chemical reactions and related reaction rate constants involved in the possible decomposition products of environmentally friendly gases are summarized and a chemical kinetic model is established to reveal the evolution characteristics of the decomposition products.

[0028] The chemical kinetic model established in step 1 includes modeling of local overheating, spark discharge and corona discharge.

[0029] In a local overheating fault, the decomposition products are greatly affected by temperature. When the temperature is high, the energy exchange between electrons and other particles is sufficient, and the entire system is approximately in a state of local thermodynamic equilibrium. When the temperature is low, the electron number density is small, and the energy exchange between electrons and other particles is not sufficient, causing the entire system to deviate from the local thermodynamic equilibrium. Therefore, by establishing a chemical kinetic model that considers thermodynamic nonequilibrium, the electron temperature and other particle temperatures are distinguished in the model, so as to obtain the evolution characteristics of the decomposition products at each temperature and the evolution characteristics of the decomposition products with temperature.

[0030] The decomposition products in spark discharge and corona discharge are a long-term accumulation process. A chemical kinetic model is established in which the plasma zone is coupled with the gas zone, and the two zones are coupled through a diffusion process. The plasma zone contains complex reaction processes such as electron impact reaction, ion-neutral particle reaction, ion-ion reaction and neutral particle-neutral particle reaction. The gas zone is mainly a slow gas phase reaction process. The entire discharge process spans a very wide time scale, from a single discharge pulse (1~10ns) to a particularly slow neutral particle reaction (1h). The complex chemical reaction system is decoupled by dividing the particles into long-lived particles and short-lived particles according to their life cycle. Short-lived particles are only contained in the plasma zone, while long-lived particles can enter the gas zone from the plasma zone through diffusion. When the concentration of short-lived particles tends to a periodic stable state, the periodic average reaction rate constant is solved for the chemical reaction containing short-lived particles, and the change of the reaction rate constant within a period is ignored. Therefore, the long-lived particles are calculated based on the periodic average reaction rate constant. The rapid discharge process in the plasma region and the slow gas phase reaction process in the gas region are calculated simultaneously using multiple time scales to obtain the evolution characteristics of the decomposition products.

[0031] The calculation results of the chemical kinetic model in step 1 are verified by the decomposition product detection results and the chemical kinetic model is corrected, thereby combining simulation and experiment to reveal the evolution characteristics of environmentally friendly gas decomposition products, such as Figure 1 shown.

[0032] Step 2: Calculate the dominant reaction path of the decomposition products based on the evolution characteristics of the decomposition products.

[0033] The principle of calculating the dominant reaction path in step 2 is as follows Figure 2 shown.

[0034] In step 2, the dominant reaction paths of the decomposition products under local overheating, spark discharge and corona discharge are calculated according to the chemical kinetic model of step 1.

[0035] Step 2 uses reaction rate to quantitatively characterize the contribution of chemical reaction pathways to the generation and removal of relevant decomposition products. Therefore, by calculating the reaction rate percentage of the chemical reaction pathway related to each decomposition product, the contribution of the relevant reaction pathway to the generation and removal of the decomposition product is quantitatively obtained, thereby determining the dominant chemical reaction pathway based on the contribution rate.

[0036] The dominant reaction path calculated in step 2 varies with temperature under local overheating and with time under spark discharge and corona discharge. Since the types of decomposition products under local overheating vary significantly with temperature, local overheating can be divided into mild overheating, moderate overheating and severe overheating according to the temperature range, so as to determine the dominant reaction path in each temperature range. Under spark discharge and corona discharge, although the dominant reaction path varies with time, the types of decomposition products tend to be stable due to the long discharge time studied. Therefore, by calculating the evolution law of the dominant reaction path of the decomposition products over time, the dominant reaction path of the generation and removal of the decomposition products can be characterized.

[0037] Step 3: Screen the characteristic decomposition products according to the dominant reaction pathway.

[0038] In step 3, according to the dominant reaction path of the decomposition products calculated in step 2, a relationship diagram between the decomposition products is drawn, the spectrum generated by the decomposition products is quantitatively characterized, and the generation mechanism of the decomposition products is revealed. Then, according to the quantitative spectrum relationship between the decomposition products, several independent decomposition products are screened as characteristic products, and the fault type can be characterized according to the characteristic products, thereby diagnosing local overheating, spark discharge and corona discharge.

[0039] The technical solution of the present invention is further described below through the drawings and embodiments.

[0040] Example 1 The method for screening characteristic products of environmentally friendly insulating gas based on the dominant reaction path specifically includes the following steps: Step 1: Combining experimental detection of decomposition products with simulation calculation of chemical kinetic model to reveal the evolution characteristics of decomposition products; Step 2: Calculate the dominant reaction path of the decomposition products based on the evolution characteristics of the decomposition products; the decomposition products involve complex chemical reaction processes, so the generation and removal of decomposition products are related to multiple reaction paths. Taking CF3 in C4F7N and its mixed gas as an example, the generation of CF3 may come from the decomposition reaction of C4F7N and C3F7, and the removal of CF3 may include multiple paths, such as two CF3 molecules generating C2F6 through recombination reaction, and CF3 and C3F7 generating C4F 10 , CF3 and CN generate C2F3N etc. through recombination reaction.

[0041] Step 3: Screen the characteristic decomposition products according to the dominant reaction pathway.

[0042] Example 2 The method for screening characteristic products of environmentally friendly insulating gas based on the dominant reaction path specifically includes the following steps: Step 1: Combining experimental detection of decomposition products with simulation calculation of chemical kinetic model to reveal the evolution characteristics of decomposition products; Detect the decomposition products of environmentally friendly gases, establish a chemical kinetic model through the chemical reactions involved in the decomposition products and the related reaction rate constants, and obtain the evolution characteristics of the decomposition products through simulation and experiments; Please follow the steps below to implement: Step 1.1, using gas chromatography-mass spectrometry and electron attachment mass spectrometry to detect the decomposition products of environmental protection gases; Step 1.2, based on the test results of the types and contents of the decomposition products of the environmentally friendly gas in step 1.1, summarize the chemical reactions and related reaction rate constants involved in the possible decomposition products of the environmentally friendly gas, and establish a chemical kinetic model; The chemical kinetics modeling includes modeling of local overheating, spark discharge, and corona discharge; The local overheating is modeled as follows: The local overheating model is a 0-dimensional global model. All chemical reactions are reversible. The equation for the change of particle concentration in the discharge area with time is shown in equation (1):

[0043] in, n i and n j For particles i and j The concentration of r fk and r rk Respectively k The forward reaction rate constant and the reverse reaction rate constant of a reaction are v jkf and v jkr For the j The particle in k The stoichiometric coefficients on the left and right sides of a chemical reaction equation; The forward reaction rate constant is known, and the reverse reaction rate constant is obtained by the ratio of the forward reaction rate constant to the equilibrium constant. The equilibrium constant expression is shown in formula (2):

[0044] in,K k ( T ) is the equilibrium constant, m i 0 (T) represents the standard Gibbs free energy, p 0 is the standard atmospheric pressure; Since the chemical reaction system deviates from the local thermodynamic equilibrium state, the ratio of the electron temperature to the temperature of other heavy particles is defined as a value that varies with the electron number density, as shown in formula (3):

[0045] in, T e and T h are the electron temperature and heavy particle temperature, i e for T e and T h The ratio of n e is the electron concentration, n e max is the critical number density of electrons. When the electron concentration exceeds n e max When , the chemical system approximately satisfies the local thermodynamic equilibrium; By solving equations (1) to (3) simultaneously, the evolution characteristics of the decomposition products at each temperature over time can be calculated, and the evolution law of the decomposition products with temperature can also be obtained; The spark discharge and corona discharge are modeled as follows: The decomposition products of spark discharge and corona discharge are an accumulation process. After the discharge generates decomposition products, the decomposition products continue to diffuse. Therefore, the plasma zone and gas zone are used to simulate the generation and diffusion process of decomposition products under spark discharge and corona discharge. The control equations of the plasma zone and gas zone are shown in equations (4) and (5):

[0046] in, t For time, c pj and c gj are the number densities of particles in the plasma and gas regions, respectively, v ij and v ij ’are the stoichiometric coefficients on the left and right sides of the chemical reaction equation, respectively. k i is the reaction rate constant, c pl For the plasma region l The number density of particles, v il The left side of the reaction equation l The stoichiometric number of particles, D kj is the diffusion coefficient, r p and r g are the radii of the plasma region and the gas region, respectively, S p and V p are the area and volume of the plasma region, V g is the volume of the gas zone; When the gas pressure is high, spark discharge and corona discharge occur in the form of pulses or pulse clusters. In order to avoid the computational workload of solving the Poisson equation, an external electric field is used as the discharge excitation. All pulses are combined into one discharge pulse in each discharge cycle, and the periodic combined discharge pulse is used to calculate the interaction between charged particles and neutral particles under many repeated single pulses, as shown in Equation (6):

[0047] in, E m is the peak value of the electric field intensity, t pls is the duration of the combined discharge pulse; The peak value and duration of the pulse electric field of spark discharge and corona discharge are different; although the electric fields of spark discharge and corona discharge are both in the form of pulses, there are obvious differences in the pulse amplitude and duration between the two. Spark discharge is usually a small gap spark discharge with a short duration, while corona discharge is usually a stable discharge pulse form; Spark discharge and corona discharge span very large time and space scales, and multiple time scales are used to simultaneously calculate the fast discharge process in the plasma region and the slow gas phase reaction process in the gas region. Since the discharge process contains many steady-state decomposition products and transient decomposition products, the particles are divided into long-lived particles and short-lived particles according to their life cycle. Short-lived particles are only in the plasma region, while long-lived particles can diffuse from the plasma region into the gas region, thereby forming steady-state decomposition products through a series of reactions. In order to decouple long-lived particles and short-lived particles in the model, the average reaction rate constant of short-lived particles is introduced, as shown in Equation (7):

[0048] in, W i is the periodic average reaction rate constant, t rep is the discharge time of one cycle, c sl is the number density of short-lived particles; The model uses multiple time scales to simultaneously solve the rapid discharge process in the plasma region and the slow gas phase reaction process in the gas region. First, according to equations (4) to (6), several discharge cycles are calculated for short-lived particles and long-lived particles at the same time, so that the number density of short-lived particles approaches a periodic stable state. Secondly, the average reaction rate constant of short-lived particles in one cycle is calculated according to equation (7). Finally, the periodic average reaction rate constant of short-lived particles is used to replace the original rate constant that varies with time, and the long-lived particles are solved to obtain the content of stable decomposition products. Step 1.3, verifying the calculation results of the chemical kinetic model in step 1.2 with the decomposition product detection results and correcting the chemical kinetic model, combining simulation and experiment to reveal the evolution characteristics of the decomposition products of the environmentally friendly gas; Step 2: Calculate the dominant reaction path of the decomposition products according to the evolution characteristics of the decomposition products; According to the above chemical kinetic model, the dominant reaction paths of the decomposition products under local overheating, spark discharge and corona discharge are calculated respectively; By calculating the reaction rate percentage of the chemical reaction pathway related to each decomposition product, the contribution of the related reaction pathway to the generation and removal of the decomposition product is quantitatively obtained, so as to determine the dominant chemical reaction pathway according to the contribution rate; Step 3: Screening characteristic decomposition products according to the dominant reaction path; According to the dominant reaction path of the decomposition products calculated in step 2, a relationship diagram between the decomposition products is drawn to quantitatively characterize the spectrum generated by the decomposition products. According to the quantitative spectrum relationship between the decomposition products, independent decomposition products are screened out as characteristic products. The fault type is characterized according to the characteristic products, thereby diagnosing local overheating, spark discharge and corona discharge.

[0049] Example 3 C5F 10Taking the O / CO2 mixed gas as an example, the dominant reaction paths in different temperature ranges under local overheating are obtained. By analyzing the evolution law of local overheating decomposition products, it can be seen that the main products in the temperature range of 2500K~3500K are CO, C2F3O, C3F4O, CF and C2FO, the main products in the temperature range of 1500K~2500K are CO, C3F7, CF3, C2F3O, C4F7O and C2F4, and the products below 1500K are mainly C3F7, CF3 and CO. By calculating the dominant reaction paths of the decomposition products in each temperature range, it can be obtained that in the temperature range of 2500K~3000K, the generation of CO mainly comes from the reaction of CO2 and O, that is, CO2+O→CO+O, the generation of C2F3O comes from the decomposition reaction of C3F4O, the generation of C3F4O mainly comes from the decomposition reaction of C4F7O, the generation of CF mainly comes from the decomposition reaction of C3F4O, and the generation of C2FO comes from the recombination reaction of CF and CO. In the temperature range of 1500K~2500K, the generation of CO mainly comes from the decomposition reaction of C4F7O, the generation of C3F7 mainly comes from the decomposition reaction of C4F7O, and the generation of CF3 mainly comes from the decomposition reaction of C5F 10 O decomposition reaction, the formation of C2F3O mainly comes from the decomposition reaction of C4F7O, and the formation of C4F7O mainly comes from the decomposition reaction of C5F 10 O decomposition reaction, the formation of C2F4 mainly comes from the decomposition reaction of C3F7. In the temperature range below 1500K, the formation of C3F7 mainly comes from C5F 10 O decomposition reaction, the generation of CF3 mainly comes from C5F 10 O decomposition reaction, the generation of CO mainly comes from the decomposition of C4F7O. Therefore, according to the dominant reaction paths in the three temperature ranges, the characteristic products of 2500K~3500K are screened as CO, C2F3O and C2FO, the characteristic products of 1500K~2500K are CO, C2F4, CF3 and C2F3O, and the characteristic products in the temperature range below 1500K are C3F7, CF3 and CO.

Claims

1. A method for screening characteristic products of environmentally friendly insulating gas based on dominant reaction pathways, characterized in that: The specific steps include: Step 1: Combining experimental detection of decomposition products with simulation calculation of chemical kinetic model to reveal the evolution characteristics of decomposition products; Step 2: Calculate the dominant reaction path of the decomposition products according to the evolution characteristics of the decomposition products; Step 3: Screen the characteristic decomposition products according to the dominant reaction pathway.

2. The method for screening characteristic products of environmentally friendly insulating gas based on dominant reaction paths according to claim 1, characterized in that: The step 1 specifically includes: detecting the decomposition products of the environmental gas, establishing a chemical kinetic model through the chemical reactions involved in the decomposition products and the related reaction rate constants, and obtaining the evolution characteristics of the decomposition products through simulation and experiments.

3. The method for screening characteristic products of environmentally friendly insulating gas based on dominant reaction paths according to claim 2, characterized in that: The step 1 is specifically implemented according to the following steps: Step 1.1, using gas chromatography-mass spectrometry and electron attachment mass spectrometry to detect the decomposition products of environmental protection gases; Step 1.2, based on the test results of the types and contents of the decomposition products of the environmentally friendly gas in step 1.1, summarize the chemical reactions and related reaction rate constants involved in the possible decomposition products of the environmentally friendly gas, and establish a chemical kinetic model; Step 1.3: The calculation results of the chemical kinetic model in step 1.2 are verified by the decomposition product detection results and the chemical kinetic model is corrected. The evolution characteristics of the decomposition products of the environmentally friendly gas are revealed by combining simulation and experiment.

4. The method for screening characteristic products of environmentally friendly insulating gas based on dominant reaction paths according to claim 3 is characterized in that: The establishment of the chemical kinetic model in step 1.2 includes modeling local overheating, spark discharge and corona discharge.

5. The method for screening characteristic products of environmentally friendly insulating gas based on dominant reaction paths according to claim 4, characterized in that: The local overheating modeling is specifically as follows: The local overheating model is a 0-dimensional global model. All chemical reactions are reversible. The equation for the change of particle concentration in the discharge area with time is shown in equation (1): in, n i and n j For particles i and j The concentration of r fk and r rk Respectively k The forward reaction rate constant and the reverse reaction rate constant of a reaction are v jkf and v jkr For the j The particle in k The stoichiometric coefficients on the left and right sides of a chemical reaction equation; The forward reaction rate constant is known, and the reverse reaction rate constant is obtained by the ratio of the forward reaction rate constant to the equilibrium constant. The equilibrium constant expression is shown in formula (2): in, K k ( T ) is the equilibrium constant, μ i 0 (T) represents the standard Gibbs free energy, p 0 is the standard atmospheric pressure; Since the chemical reaction system deviates from the local thermodynamic equilibrium state, the ratio of the electron temperature to the temperature of other heavy particles is defined as a value that varies with the electron number density, as shown in formula (3): in, T e and T h are the electron temperature and heavy particle temperature, θ e for T e and T h The ratio of n e is the electron concentration, n e max is the critical number density of electrons. When the electron concentration exceeds n e max When , the chemical system approximately satisfies the local thermodynamic equilibrium; By solving equations (1) to (3) simultaneously, the evolution characteristics of the decomposition products at each temperature over time can be calculated, and the evolution law of the decomposition products with temperature can also be obtained.

6. The method for screening characteristic products of environmentally friendly insulating gas based on dominant reaction paths according to claim 4, characterized in that: The spark discharge and corona discharge modeling are specifically as follows: The decomposition products of spark discharge and corona discharge are an accumulation process. After the discharge generates decomposition products, the decomposition products continue to diffuse. Therefore, the plasma zone and gas zone are used to simulate the generation and diffusion process of decomposition products under spark discharge and corona discharge. The control equations of the plasma zone and gas zone are shown in equations (4) and (5): in, t For time, c pj and c gj are the number densities of particles in the plasma and gas regions, respectively, v ij and v ij ’ are the stoichiometric coefficients on the left and right sides of the chemical reaction equation, respectively. k i is the reaction rate constant, c pl For the plasma region l The number density of particles, v il The left side of the reaction equation l The stoichiometric number of particles, D kj is the diffusion coefficient, r p and r g are the radii of the plasma region and the gas region, respectively, S p and V p are the area and volume of the plasma region, V g is the volume of the gas zone; When the gas pressure is high, spark discharge and corona discharge occur in the form of pulses or pulse clusters. In order to avoid the computational workload of solving the Poisson equation, an external electric field is used as the discharge excitation. All pulses are combined into one discharge pulse in each discharge cycle, and the periodic combined discharge pulse is used to calculate the interaction between charged particles and neutral particles under many repeated single pulses, as shown in Equation (6): in, E m is the peak value of the electric field intensity, τ pls is the duration of the combined discharge pulse; It should be noted that the peak value and duration of the pulse electric field of spark discharge and corona discharge are different; although the electric fields of spark discharge and corona discharge are both in the form of pulses, there are obvious differences in the pulse amplitude and duration between the two. Spark discharge is usually a small gap spark discharge with a short duration, while corona discharge is usually a stable discharge pulse form. Spark discharge and corona discharge span very large time and space scales, and multiple time scales are used to simultaneously calculate the fast discharge process in the plasma region and the slow gas phase reaction process in the gas region. Since the discharge process contains many steady-state decomposition products and transient decomposition products, the particles are divided into long-lived particles and short-lived particles according to their life cycle. Short-lived particles are only in the plasma region, while long-lived particles can diffuse from the plasma region into the gas region, thereby forming steady-state decomposition products through a series of reactions. In order to decouple long-lived particles and short-lived particles in the model, the average reaction rate constant of short-lived particles is introduced, as shown in Equation (7): in, W i is the periodic average reaction rate constant, τ rep is the discharge time of one cycle, c sl is the number density of short-lived particles; The model uses multiple time scales to simultaneously solve the rapid discharge process in the plasma region and the slow gas phase reaction process in the gas region. First, several discharge cycles are calculated for short-lived particles and long-lived particles according to equations (4) to (6), so that the number density of short-lived particles approaches a periodic stable state. Second, the average reaction rate constant of short-lived particles in one cycle is calculated according to equation (7). Finally, the periodic average reaction rate constant of short-lived particles is used to replace the original rate constant that varies with time, and the long-lived particles are solved to obtain the content of stable decomposition products.

7. The method for screening characteristic products of environmentally friendly insulating gas based on dominant reaction paths according to claim 4, characterized in that: The step 2 is specifically as follows: according to the chemical kinetic model described in step 1, the dominant reaction paths of the decomposition products under local overheating, spark discharge and corona discharge are calculated respectively.

8. The method for screening characteristic products of environmentally friendly insulating gas based on dominant reaction paths according to claim 7, characterized in that: The step 2 calculates the reaction rate percentage of the chemical reaction path related to each decomposition product, quantitatively obtains the contribution of the related reaction path to the generation and removal of the decomposition product, and thus determines the dominant chemical reaction path according to the contribution rate.

9. The method for screening characteristic products of environmentally friendly insulating gas based on dominant reaction paths according to claim 1, characterized in that: The step 3 draws a relationship diagram between the decomposition products according to the dominant reaction path of the decomposition products calculated in step 2, quantitatively characterizes the spectrum generated by the decomposition products, and selects independent decomposition products as characteristic products according to the quantitative spectrum relationship between the decomposition products. Characterize the fault type based on characteristic products to diagnose local overheating, spark discharge and corona discharge.

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