Transformer fault degree evaluation method and system based on arc fault gas production content

Abstract

The invention relates to the technical field of electric power equipment detection and fault diagnosis, and discloses a transformer fault degree evaluation method and system based on arc fault gas production content. An arc channel is divided into an edge temperature zone and a core temperature zone, and according to the reaction enthalpy change relation between arc energy and oil pyrolytic reaction, the gas production content of the arc channel is calculated; the equivalent pyrolysis temperature T of the thermal decomposition reaction of hydrocarbon in the oil in the arc marginal area is solved, the marginal equilibrium constant of the thermal decomposition reaction of the marginal area is further obtained, and the fault gas content of the marginal temperature area and the fault gas content of the core temperature area when the fault occurs are accurately obtained by combining the core equilibrium constant of the core temperature area. And therefore, the fault degree of the transformer can be accurately evaluated.

Description

Technical Field

[0001] The present invention relates to the technical field of power equipment detection and fault diagnosis, and in particular to a transformer fault degree assessment method and system based on arc fault gas production content. Background Art

[0002] With the expansion of power grid scale and the growth of electricity demand, the application of large-capacity and high-voltage transformers is becoming more and more popular. However, the complexity of the equipment operating environment has led to a significant increase in the failure rate, which has posed new challenges to traditional fault diagnosis methods. Although dissolved gas analysis technology in oil has been widely used in transformer fault diagnosis, the diagnostic accuracy and prediction ability under complex working conditions still need to be improved.

[0003] In recent years, the rapid development of multi-physics simulation technology and computer science has provided new ideas for solving this problem. Especially in the context of digital design and intelligent operation and maintenance of power equipment, the demand for quantitative analysis of fault evolution is becoming more and more urgent. Transformer internal faults usually go through two key stages: high-energy arc discharge and insulating oil cracking and gas production. The volume of gas generated by the arc directly determines the intensity of the pressure wave in the oil tank.

[0004] At present, due to the complex internal structure of the transformer, when an arc fault occurs, the gas production process is affected by the interaction of multiple factors. The existing detection technology has limitations. It is difficult to accurately obtain the gas production when a fault occurs, and thus it is impossible to accurately assess the degree of transformer fault. Summary of the invention

[0005] The present invention provides a transformer fault degree assessment method and system based on arc fault gas content, which solves the technical problem of how to improve the accuracy of transformer fault degree assessment.

[0006] A first aspect of the present invention provides a transformer fault degree assessment method based on arc fault gas content, comprising:

[0007] Construct an arc channel model of the target transformer under arc fault, perform arc zoning, and determine the edge temperature zone and core temperature zone;

[0008] Based on the alkane molecule thermal decomposition reaction set of the target transformer, a thermal decomposition gas content model of the target transformer is constructed;

[0009] Acquiring electrical parameter data and oil thermal characteristic data of the edge temperature zone, and core equilibrium constant of the core temperature zone;

[0010] Determining the edge equilibrium constant of the edge temperature zone based on the electrical parameter data and the oil thermal characteristic data;

[0011] The core equilibrium constant and the edge equilibrium constant are input into the thermal decomposition gas content model for solving, and the gas content data associated with the edge temperature zone and the core temperature zone are obtained respectively;

[0012] Based on a preset gas type condition, the gas content data associated with the edge temperature zone and the core temperature zone are used to determine the fault level of the target transformer.

[0013] Optionally, constructing the thermal decomposition gas content model of the target transformer based on the alkane molecule thermal decomposition reaction set of the target transformer includes:

[0014] According to the alkane thermal decomposition theory, the alkane molecular thermal decomposition reaction set of the thermal decomposition gas content model is established;

[0015] A competitive factor for characterizing the reaction path is introduced into the alkane molecule thermal decomposition reaction set to construct a mole fraction reaction model;

[0016] Fitting the alkane molecule thermal decomposition reaction set according to the gas partial pressure definition formula to construct an equilibrium constant expression model;

[0017] Apply the laws of thermodynamics to construct an equilibrium effect expression model including the effect of temperature change;

[0018] The thermal decomposition gas content model is constructed by coupling the mole fraction reaction model, the equilibrium constant expression model and the equilibrium influence expression model.

[0019] Optionally, the electrical parameter data includes arc current, voltage drop across the arc, arc length and arc duration, and determining the edge equilibrium constant of the edge temperature zone based on the electrical parameter data and the oil thermal characteristic data includes:

[0020] Determining arc energy using the arc current, the arc duration, and the voltage drop across the arc;

[0021] Determine the total reaction enthalpy change of thermal decomposition using the arc current, arc duration, arc energy, arc length and oil thermal property data;

[0022] Determining the reaction coefficient during the thermal decomposition reaction according to the total reaction enthalpy change of the thermal decomposition;

[0023] Based on the reaction coefficient and the preset thermal reaction enthalpy change function, construct a thermal decomposition equivalent temperature equation group;

[0024] Solving the thermal decomposition equivalent temperature equations by using a numerical method to obtain the equivalent temperature;

[0025] The equilibrium influence expression model including the influence of temperature change is inputted with the equivalent temperature to solve the edge equilibrium constant of the edge temperature zone.

[0026] Optionally, the oil thermal characteristic data includes insulating oil specific heat capacity, oil hydrocarbon operating temperature, oil hydrocarbon vaporization temperature, hydrocarbon oil vapor phase latent heat, insulating oil vapor specific heat ratio, insulating oil vapor specific internal energy and atmospheric pressure, and the arc current, arc duration, arc energy, arc length and the oil thermal characteristic data are used to determine the total reaction enthalpy change of thermal decomposition, including:

[0027] Using the arc length, determining a first constant coefficient;

[0028] Determine a second constant coefficient by using a preset conversion coefficient, the insulating oil vapor specific heat ratio, and the insulating oil vapor specific internal energy;

[0029] The arc current and the arc duration determine a third constant coefficient;

[0030] Determine the increase in enthalpy of oil hydrocarbon liquid and gas by using the first constant coefficient, the second constant coefficient, the third constant coefficient, the atmospheric pressure and the arc energy;

[0031] Determine the liquid enthalpy increase of the oil hydrocarbon by using the specific heat capacity of the insulating oil, the oil hydrocarbon operating temperature and the oil hydrocarbon vaporization temperature;

[0032] The total reaction enthalpy change of thermal decomposition is determined using the hydrocarbon oil vapor phase latent heat, the hydrocarbon oil liquid enthalpy increase and the hydrocarbon oil liquid-gas enthalpy increase.

[0033] Optionally, the determining the fault level of the target transformer based on a preset gas type condition and using gas content data associated with the edge temperature zone and the core temperature zone includes:

[0034] Determining whether the gas type of the edge characteristic gas in the edge temperature zone meets a preset gas type condition;

[0035] If the gas type of the edge characteristic gas meets the set gas type condition, then based on the three-ratio method, the gas content data of each edge characteristic gas is used to perform fault judgment to generate a first fault judgment result;

[0036] If the gas type of the edge characteristic gas does not meet the set gas type condition, based on the interval judgment method, the gas content data of each edge characteristic gas is used to perform fault judgment to generate a first fault judgment result;

[0037] Determining whether the gas type of the core characteristic gas in the core temperature zone meets the preset gas type condition;

[0038] If the gas type of the core characteristic gas meets the set gas type condition, then based on the three-ratio method, the gas content data of each core characteristic gas is used to perform fault judgment to generate a second fault judgment result;

[0039] If the gas type of the core characteristic gas does not meet the set gas type condition, based on the interval judgment method, the gas content data of each core characteristic gas is used to perform fault judgment to generate a second fault judgment result;

[0040] Using a first fault value associated with the first judgment result and a second fault value associated with the second judgment result to input a preset target fault value function, and outputting a target fault value;

[0041] The target fault value is used to retrieve a preset fault level key-value pair data table to determine the fault level of the target transformer.

[0042] Optionally, the three-ratio method is based on using the gas content data of each of the edge characteristic gases to perform fault judgment to generate a first fault judgment result, including:

[0043] Randomly select two different gas content data of the edge characteristic gases to perform a ratio operation to generate a first edge judgment value, a second edge judgment value and a third edge judgment value;

[0044] When the first edge judgment value is less than a preset first edge fault threshold, the second edge judgment value is less than a preset second edge fault threshold, and the third edge judgment value is less than the preset first edge fault threshold, it is determined to be a mild fault level and used as a first fault judgment result;

[0045] When the first edge judgment value is less than the preset third edge fault threshold, and the third edge judgment value is less than the preset third edge fault threshold, it is determined as a moderate fault level and used as the first fault judgment result;

[0046] When the first edge judgment value is greater than or equal to the preset third edge fault threshold, or the second edge judgment value is greater than or equal to the preset first edge fault threshold and the third edge judgment value is greater than or equal to the preset third edge fault threshold, it is judged as a severe fault level and used as the first fault judgment result.

[0047] Optionally, the interval judgment method is based on using the gas content data of each of the edge characteristic gases to perform fault judgment to generate a first fault judgment result, including:

[0048] Respectively determine the fault interval where the gas content data of each of the edge characteristic gases is located, and generate multiple edge fault level determination results;

[0049] Wherein, the marginal fault level determination result is any one of a severe fault level, a moderate fault level and a mild fault level;

[0050] The fault levels are from high to low: severe fault level, moderate fault level and slight fault level;

[0051] The highest fault level is selected from the plurality of marginal fault level determination results as the first fault determination result.

[0052] Optionally, the three-ratio method is based on using the gas content data of each of the core characteristic gases to perform fault judgment to generate a second fault judgment result, including:

[0053] Randomly select two different gas content data of the core characteristic gases to perform a ratio operation to generate a first core judgment value, a second core judgment value and a third core judgment value;

[0054] When the first core judgment value is less than the preset first core fault threshold, the second core judgment value is less than the preset second core fault threshold, and the third core judgment value is less than the preset first core fault threshold, it is determined to be a mild fault level and used as the second fault judgment result;

[0055] When the first core determination value is less than the preset third core fault threshold, and the third core determination value is less than the preset third core fault threshold, it is determined as a moderate fault level and used as the second fault determination result;

[0056] When the first core judgment value is greater than or equal to the preset third core fault threshold, or the second core judgment value is greater than or equal to the preset first core fault threshold and the third core judgment value is greater than or equal to the preset third core fault threshold, it is judged as a severe fault level and used as the second fault judgment result.

[0057] Optionally, the interval judgment method is based on using the gas content data of each of the core characteristic gases to perform fault judgment to generate a second fault judgment result, including:

[0058] Respectively determine the fault intervals where the gas content data of each of the core characteristic gases are located, and generate multiple core fault level determination results;

[0059] The core fault level determination result is any one of a severe fault level, a moderate fault level and a mild fault level;

[0060] The fault levels are from high to low: severe fault level, moderate fault level and slight fault level;

[0061] The highest fault level is selected from the plurality of core fault level determination results as the second fault determination result.

[0062] A second aspect of the present invention provides a transformer fault degree assessment system based on arc fault gas content, comprising:

[0063] The arc partitioning module is used to construct an arc channel model of the target transformer under arc fault, and to perform arc partitioning to determine the edge temperature zone and the core temperature zone;

[0064] A model building module, used for building a thermal decomposition gas content model of the target transformer based on the alkane molecule thermal decomposition reaction set of the target transformer;

[0065] A data acquisition module, used to acquire electrical parameter data and oil thermal characteristic data of the edge temperature zone, and a core equilibrium constant of the core temperature zone;

[0066] A data processing module, for determining an edge equilibrium constant of the edge temperature zone based on the electrical parameter data and the oil thermal characteristic data;

[0067] A model solving module, used to use the core equilibrium constant and the edge equilibrium constant to input the thermal decomposition gas content model for solving, and obtain gas content data associated with the edge temperature zone and the core temperature zone respectively;

[0068] A fault level determination module is used to determine the fault level of the target transformer based on a preset gas type condition and using the gas content data associated with the edge temperature zone and the core temperature zone.

[0069] It can be seen from the above technical solutions that the present invention has the following advantages:

[0070] The present invention divides the arc channel into an edge temperature zone and a core temperature zone, and uses the relationship between the arc energy and the reaction enthalpy change of the oil pyrolysis reaction to solve the equivalent pyrolysis temperature T of the thermal decomposition reaction of hydrocarbons in the oil in the edge zone of the arc, and then obtains the edge equilibrium constant of the thermal decomposition reaction in the edge zone. Combined with the core equilibrium constant of the core temperature zone, the fault gas content in the edge temperature zone and the core temperature zone when the fault occurs is accurately obtained, thereby realizing an accurate assessment of the degree of transformer fault. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0072] Figure 1 A flowchart of a method for evaluating transformer fault degree based on arc fault gas content provided in Embodiment 1 of the present invention;

[0073] Figure 2 It is a schematic diagram of the algorithm flow for calculating the gas content of oil thermal decomposition under arc fault;

[0074] Figure 3 This is a structural block diagram of a transformer fault degree assessment system based on arc fault gas content provided in Embodiment 3 of the present invention. DETAILED DESCRIPTION

[0075] The embodiments of the present invention provide a method and system for evaluating the fault degree of a transformer based on the gas content of an arc fault, which are used to solve the technical problem of how to improve the accuracy of evaluating the fault degree of a transformer.

[0076] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0077] Since it is difficult to accurately obtain the gas production when a fault occurs, the in-depth development of related research is restricted. At present, the research on gas production by cracking of insulating oil is mainly carried out through two methods: experiments and theoretical analysis. However, due to the complex coupling relationship between gas production and arc characteristic parameters (such as current, channel volume, duration, etc.), it is difficult to fully reveal its characteristic laws by relying solely on experimental means. Therefore, from a computational perspective, combining the fault mechanism to study the quantitative relationship between energy and gas production has become an important research direction. This not only helps to clarify the corresponding relationship between latent faults and dissolved gas content, but also provides theoretical support for analyzing sudden large-energy discharge accidents and predicting transformer explosion risks. To achieve an accurate description of the gas production characteristics of insulating oil under high energy density conditions, the key lies in solving two core problems: one is to clarify the physical and chemical mechanism of thermal cracking of insulating oil, including reaction path, equilibrium characteristics and temperature effects; the other is to study the decomposition reaction characteristics under the action of arc, focusing on analyzing the influence of arc parameters on reaction equilibrium. These studies will lay an important foundation for the improvement of transformer fault diagnosis and prediction technology. The present invention conducts regional research according to the characteristics of the arc in different areas, converts the complex arc gas generation problem into a solvable mathematical model, and thus obtains the gas generation content under the arc fault.

[0078] See also Figure 1-Figure 2 , Figure 1A flowchart of the steps of a method for evaluating transformer fault degree based on arc fault gas content provided in Embodiment 1 of the present invention.

[0079] Figure 2 Schematic diagram of the algorithm flow for the gas content of oil thermal decomposition under arc fault.

[0080] The present invention provides a transformer fault degree assessment method based on arc fault gas content, comprising:

[0081] Step 101: construct an arc channel model of a target transformer under an arc fault, perform arc zoning, and determine an edge temperature zone and a core temperature zone.

[0082] In an embodiment of the present invention, the structural parameters of the target transformer, including the number of turns of the winding, the wire diameter, the size of the core, etc., are obtained, and the arc channel model of the target transformer under the arc fault is constructed using finite element analysis software. The arc channel presents a layered temperature distribution feature during the fault process: the central plasma temperature exceeds 5000K, forming the main conductive channel, and the temperature in the surrounding area is relatively low (300-2000K), and a secondary branch structure may appear. This temperature distribution characteristic is affected by many factors, including liquid molecular structure, impurity type, field intensity disturbance, space charge and mobility, etc., resulting in a dynamic non-uniform characteristic in the discharge process. Based on this, the arc channel model can be simplified into two temperature zone models: edge temperature zone (T<1500K): secondary branch flow injection area around the main arc column; core temperature zone (T>1500K): central main arc column area.

[0083] Step 102: construct a thermal decomposition gas content model of the target transformer based on the alkane molecule thermal decomposition reaction set of the target transformer.

[0084] Further, step 102 may include the following sub-steps:

[0085] S11. Based on the alkane thermal decomposition theory, a set of alkane molecular thermal decomposition reactions for the thermal decomposition gas content model is established.

[0086] The alkane thermal decomposition theory refers to the theoretical system of the principle, mechanism and related laws of the decomposition reaction of alkanes under the action of heat. In chemical equilibrium analysis, the equilibrium constant K reflects the direction and degree of the reaction. When K>105, the reaction can be considered to be completely carried out. For the convenience of calculation, the present invention adopts the equilibrium state method to solve the equilibrium constant and thermal decomposition equation. For any reaction:

[0087] (1)

[0088] Where, v1, v 11 , v 12They are the stoichiometric coefficients of reactant D and product E and F respectively. The ratio of the stoichiometric coefficients represents the ratio of the molar numbers of the substances undergoing the reaction.

[0089] In the embodiment of the present invention, according to the theory of the principle, mechanism and related laws of decomposition reaction of alkanes under heat, the thermal decomposition process of transformer oil alkane molecules D is set to n thermal decomposition reactions, and the thermal decomposition reaction formula is recorded as:

[0090]

[0091] S12. Competitive factors for characterizing the reaction pathways are introduced into the thermal decomposition reaction set of alkane molecules, and a mole fraction reaction model is constructed.

[0092] Furthermore, the mole fraction reaction model includes a reactant mole fraction reaction model, a product mole fraction reaction model and a total mole number reaction model; the reactant mole fraction reaction model is used to characterize the mole fraction of each reactant during the thermal decomposition reaction; the product mole fraction reaction model is used to characterize the mole fraction of each product during the thermal decomposition reaction, and the total mole number reaction model is used to characterize the total mole number of reactants and products. In the embodiment of the present invention, the alkane molecule D is defined as 1 part according to the concept of 1 weight part, the decomposition mole number is x parts, and the reaction progress is ξ=|x / v1| as a benchmark. By introducing competitive factors αi~αn to n thermal decomposition reactions in turn, the mole numbers of reactants and products in each thermal decomposition reaction are quantified. The mole fraction reaction model includes a reactant mole fraction reaction model and a product mole fraction reaction model, such as Formula I, and a total mole number reaction model, such as Formula II; wherein the mole fractions of each reactant and each product during the thermal decomposition reaction are calculated by Formula I;

[0093] Formula I

[0094] The sum of r(B) in formula I represents the sum of the products of the competitive factor αi of the reaction, the stoichiometric coefficient of the substance, and the reaction progress ξ in all pyrolysis reactions involving a certain product;

[0095] It should be noted that the sum of r(B) in formula I represents the competitive factor α of the reaction in all chemical reactions involving substance B. i The sum of the products of the stoichiometric coefficients of substance B (reactant vi, product vij) and the reaction progress ξ. This expression ensures the sequential accuracy of the reaction path without causing skipped reactions.

[0096] The total number of moles of reactants and products is represented by N and is calculated by formula II;

[0097] Formula II

[0098] In the formula, j refers to the product.

[0099] S13. Fit the set of thermal decomposition reactions of alkane molecules according to the definition of gas partial pressure and construct an equilibrium constant expression model.

[0100] The definition of gas partial pressure refers to K expressed as gas phase partial pressure p and K expressed as mole percent x The relationship definition between them.

[0101] Specifically:

[0102] (2)

[0103] It should be noted that this relationship can be used as the basis for establishing a set of equations for the thermal decomposition of alkane molecules, which is used to describe the relationship between the equilibrium constant and the change in the mole fraction of the substance.

[0104] In the embodiment of the present invention, according to Formula I and Formula II, the equilibrium constant expression model of each reaction under standard atmospheric pressure is obtained:

[0105] Formula III

[0106] In formula III, K p Θ is the standard equilibrium constant at standard atmospheric pressure; p Θ is the standard atmospheric pressure, 101.325 kPa; p is the total pressure of the system, kPa; x1, x2 are the mole percentages of the products of each pyrolysis reaction, unit: %; x3 is the mole percentage of the reactants of each pyrolysis reaction, unit: %; v1, v2 are the stoichiometric coefficients of the products of each pyrolysis reaction; v3 is the stoichiometric coefficients of the reactants of each pyrolysis reaction; vB is the sum of the stoichiometric coefficients of a substance in the pyrolysis reaction.

[0107] S14. Use the laws of thermodynamics to construct an equilibrium influence expression model that includes the effects of temperature changes.

[0108] Further, S14 may include the following sub-steps:

[0109] S141. Based on the formula of Van'toff's law, construct a model to express the effect of temperature on chemical equilibrium constants.

[0110] In the embodiment of the present invention, the effect of temperature on the equilibrium constant can be expressed by the Van't Hoff formula. It can be seen that the expression model of the effect of temperature on the chemical equilibrium constant is:

[0111] (3)

[0112] Where R is the molar gas constant, 8.314 J·K -1 ·mol -1 ;

[0113] T is the thermodynamic temperature, Kelvins;

[0114] Δ r H m Θ It is the reaction enthalpy change when all substances are in standard state and the progress of chemical reaction is 1 mol, kJ / mol.

[0115] Formula (3) shows that K Θ The change with temperature depends on Δ r H m Θ For the endothermic reaction of alkane thermal decomposition, Δ r H m Θ >0,K Θ It increases with the increase of temperature, promoting the reaction to proceed in the forward direction.

[0116] S142. Based on Kirchhoff's law formula, construct a model to express the relationship between reaction enthalpy change and molar heat capacity at constant pressure.

[0117] In the embodiment of the present invention, according to the integral formula of Kirchhoff's law, the reaction enthalpy change Δ r H Θ and molar heat capacity at constant pressure C p，m The relationship expression model:

[0118] (4)

[0119] Where ΔH0 is a constant; ΔCp is:

[0120] (5)

[0121] It should be noted that, in the present invention, the stoichiometric coefficient representing the product takes a positive value, and the stoichiometric coefficient representing the reactant takes a negative value.

[0122] S143. By coupling the expression model of the influence of temperature on the chemical equilibrium constant, the expression model of the relationship between reaction enthalpy change and molar heat capacity at constant pressure, and the preset expression model of the relationship between hot melt and temperature, an equilibrium influence expression model including the influence of temperature change is constructed.

[0123] From formulas (3)-(5), we can see that the effect of temperature on chemical equilibrium comes from the effect of temperature on the heat capacity of each substance involved in the reaction. Considering Cp,m as a function of temperature T in the range of 298K~1500K, it satisfies the empirical formula shown in formula (6):

[0124] (6)

[0125] Substituting formula (4)-(6) into (3), the formula for the effect of temperature on chemical equilibrium is obtained by integration:

[0126] (7)

[0127] By considering the temperature variation characteristics of heat capacity and the thermodynamic isotherm (7), the temperature T corresponding to can be obtained more accurately. .

[0128] In the embodiment of the present invention, by coupling the expression model of the influence of temperature on the chemical equilibrium constant, the expression model of the relationship between the reaction enthalpy change and the molar constant pressure heat capacity, and the preset expression model of the relationship between hot melt and temperature:

[0129] Formula IV

[0130] In formula IV, T is the transformer oil temperature, which is the thermodynamic temperature, Kelvins;

[0131] △H0 is the reaction enthalpy change when all substances are in standard state and the chemical reaction progress is 1 mol, kJ / mol;

[0132] R is the molar gas constant, 8.314 J·K -1 ·mol -1 ;

[0133] Δa, Δb, Δc are the sum of the products of the stoichiometric coefficients of each substance involved in each individual pyrolysis reaction and the coefficients of the constant term, the first-order term, and the second-order term in the specific heat capacity;

[0134] I is a constant.

[0135] It should be noted that since the empirical function of Formula IV is fitted by different experiments, it may contain higher-order terms of temperature, and the coefficients of the higher-order terms generated by it are omitted. Here, the ellipsis can be removed to obtain:

[0136] Formula IV

[0137] For ease of understanding, the following is the derivation process of Formula IV:

[0138] Take the thermal decomposition reaction formula (1) as an example:

[0139] (1)

[0140] In the thermal decomposition reaction equation (1), v1, v11, and v12 are the stoichiometric coefficients of the reactant D and the products E and F, respectively (the ratio of the stoichiometric coefficients represents the ratio of the molar numbers of the substances undergoing the reaction).

[0141] The relationship between Kp expressed as gas phase partial pressure and Kx expressed as mole percentage can be derived from the definition of gas partial pressure, as shown in formula (2):

[0142] (2)

[0143] In formula (2), Kp Θ is the standard equilibrium constant at standard atmospheric pressure (101.325 kPa);

[0144] p Θ is standard atmospheric pressure;

[0145] p is the total pressure of the system, kPa; x D , x E , x F are the mole percentages of reactant D, product E, and F, respectively, v B The value of is determined by the stoichiometric coefficient of the substance.

[0146] The effect of temperature on the chemical equilibrium constant can be seen from the Van't Hoff formula:

[0147] (3)

[0148] According to the integral formula of Kirch-Hoff's law, the reaction enthalpy change Δ r H Θ and molar heat capacity at constant pressure C p，m Relationship:

[0149] (4)

[0150] In the formula, ΔH0 is a constant; taking (1) as an example, ΔCp is:

[0151] (5)

[0152] It should be noted that, in the present invention, the stoichiometric coefficient representing the product takes a positive value, and the stoichiometric coefficient representing the reactant takes a negative value.

[0153] The preset expression of the relationship between hot melt and temperature is:

[0154] (6)

[0155] The value range of T in formula (6) is preferably 298K~1500K.

[0156] Substituting equations (4)-(6) into (3), the effect of temperature on chemical equilibrium is obtained by integration, namely equation IV.

[0157] S15. Build a thermal decomposition gas content model by coupling the mole fraction reaction model, equilibrium constant expression model and equilibrium influence expression model.

[0158] In an embodiment of the present invention, the mole fraction reaction model, the equilibrium constant expression model and the equilibrium influence expression model are coupled to construct a thermal decomposition gas content model, wherein the equilibrium constant expression model III is used as the core expression of the thermal decomposition gas content model, and the parameters in the equilibrium constant expression model III are solved by formulas I, II and IV to obtain the mole fraction of each component. In the present invention, in order to describe the phenomenon of different reaction progress between reactions, a competition factor αi∈[0,1) is established to describe the amount of reaction product generated by the strength of the competition of the reaction, and then quantify the different generation and consumption of the same characteristic gas by different thermal decomposition reactions at a certain temperature. When αi (i=1,...,n) is close to 1, it indicates that the reaction progress is high, the ability to obtain the reaction enthalpy change value in multiple reactions occurring simultaneously is strong, and the reaction competition is strong; otherwise, the reaction competition is weak.

[0159] Step 103: Obtain electrical parameter data and oil thermal characteristic data of the edge temperature zone, and core equilibrium constant of the core temperature zone.

[0160] In the embodiment of the present invention, the electrical parameter data and the oil thermal characteristic data of the edge temperature zone and the core equilibrium constant of the core temperature zone are obtained.

[0161] Step 104: Determine the edge equilibrium constant of the edge temperature zone based on the electrical parameter data and the oil thermal characteristic data.

[0162] It should be noted that the edge equilibrium constant calculation in the edge temperature zone, in the arc edge temperature zone (T < 1500K), the gas generation is mainly determined by the heat converted by the arc energy. Different temperatures correspond to different heat capacities and reaction enthalpy changes. To calculate the gas production, it is necessary to first determine the heat absorbed by the oil thermal decomposition and the reaction enthalpy change.

[0163] Arc fault energy calculation:

[0164] (13)

[0165] Where W arc is the arc energy, J; t is the arc duration, s; I arc is the arc current, A; U arc is the voltage drop across the arc, V.

[0166] The conversion of arc energy to insulating oil can be expressed as αW arc, the conversion coefficient α is generally taken as 15%~40%. The relationship between arc energy and reaction enthalpy change of oil thermal decomposition reaction is as follows:

[0167] (14)

[0168] Where ΔH oil is the enthalpy increase of hydrocarbons in oil from liquid to gas, J / (g·K); m gas is the mass of insulating oil vapor, g. In the subsequent calculations of the present invention, the value of α is set to 0.4. The enthalpy increase equation of this process is as follows:

[0169] (15)

[0170] (16)

[0171] Where ΔH1 is the liquid enthalpy increase of hydrocarbons in oil;

[0172] C oil is the specific heat capacity of the insulating oil;

[0173] T1 is the normal operating temperature of hydrocarbons in oil, 60~80 ℃;

[0174] T2 is the vaporization temperature of hydrocarbons, 400 °C;

[0175] ΔH2 is the latent heat of vaporization phase change of hydrocarbons in oil. Since the molecular weight of carbon atoms in oil is usually 15~23, taking C16H42 as an example, its latent heat of vaporization phase change is 226.15 J / g;

[0176] Δ r H is the enthalpy increase of insulating oil vapor, that is, the total reaction enthalpy change of the thermal decomposition reaction of hydrocarbons in the oil.

[0177] According to the law of mass conservation, equation (14) can be written as:

[0178] (17)

[0179] Where ρ gas is the density of insulating oil vapor, in g / m 3 , V gas is the volume of insulating oil vapor, in m 3 .

[0180] According to the ideal gas state equation, we can get:

[0181] (18)

[0182] Where P gasis the internal pressure of the insulating oil vapor bubble, Pa; μ is the specific internal energy of the insulating oil vapor, 5.68×10 6 J / kg; γ is the specific heat ratio of insulating oil vapor, 1.352.

[0183] The approximate relationship between the arc fault energy and gas production inside the transformer was obtained through experiments:

[0184] (19)

[0185] In order to obtain the relationship between the reaction enthalpy change of the oil thermal decomposition reaction and the arc energy, it is also necessary to give P gas With ΔH oil , W arc The relationship between.

[0186] (20)

[0187] In the formula, l arc , arc length, cm; P, absolute pressure, P=P gas +P0, atm.

[0188] Taking arc energy and arc current as known quantities, substituting equations (12), (19), (20) and (17) into equation (15), we can obtain the enthalpy increase ΔH of insulating oil under arc discharge: oil The calculation formula is:

[0189] (twenty one)

[0190] In the formula, k1, k2 and k3 are constant coefficients, and the expression is as follows:

[0191] (twenty two)

[0192] (twenty three)

[0193] (twenty four)

[0194] Furthermore, according to formula (15), it can be obtained that the arc energy W arc As input, the total reaction enthalpy change Δ of the thermal decomposition reaction of hydrocarbons in insulating oil r H is the solution formula as the output. The enthalpy change of a chemical reaction depends on the type and quantity of the participating substances and their molar heat capacity change. Combined with the functional relationship between heat capacity and temperature in equation (6), the reaction enthalpy change can be expressed as:

[0195] (25)

[0196] Assume that during the thermal decomposition of an alkane molecule, the coefficient of the enthalpy change obtained by the i-th reaction (i=1,···,n) in the total enthalpy change is βi, then βiΔ r H represents the enthalpy change of the reaction. Based on this, a system of equations consisting of coefficients βi and temperature T can be established:

[0197] (26)

[0198] Solving equation (26) can obtain the equivalent temperature T of the thermal decomposition reaction of hydrocarbons in the oil in the arc edge zone. Substituting it into equation IV, the edge equilibrium constant is obtained. Then the equilibrium constant is substituted into the alkane molecule thermal decomposition equation group and solved using the Levenberg–Marquardt iterative algorithm to calculate the fault gas content of the thermal decomposition reaction in the edge temperature zone.

[0199] Furthermore, the electrical parameter data includes arc current, voltage drop across the arc, arc length and arc duration. Step 104 may include the following sub-steps:

[0200] S21. Determine the arc energy using the arc current, arc duration and voltage drop across the arc.

[0201] In the embodiment of the present invention, the arc energy is calculated using formula (13).

[0202] (13)

[0203] Where W arc is the arc energy, J; t is the arc duration, s; I arc is the arc current, A; U arc is the voltage drop across the arc, V.

[0204] S22. Determine the total reaction enthalpy change of thermal decomposition using arc current, arc duration, arc energy, arc length and oil thermal property data.

[0205] Further, S22 may include the following sub-steps:

[0206] S221. Use the arc length to determine the first constant coefficient.

[0207] In the embodiment of the present invention, formula (22) is used to obtain the first constant coefficient.

[0208] (twenty two)

[0209] In the formula, represents the first constant coefficient, Indicates the arc length.

[0210] S222. Determine a second constant coefficient using a preset conversion coefficient, the insulating oil vapor specific heat ratio, and the insulating oil vapor specific internal energy.

[0211] In the embodiment of the present invention, formula (23) is used to obtain the second constant coefficient.

[0212] (twenty three)

[0213] In the formula, represents the second constant coefficient, Indicates the preset conversion factor, Indicates the specific heat ratio of insulating oil vapor, Indicates the specific internal energy of insulating oil vapor.

[0214] S223. Determine the third constant coefficient based on the arc current and arc duration.

[0215] In the embodiment of the present invention, formula (24) is used to obtain the third constant coefficient.

[0216] (twenty four)

[0217] In the formula, represents the third constant coefficient, represents the arc current, Indicates arc duration.

[0218] S224. Determine the enthalpy increase of oil hydrocarbon liquid and gas by using the first constant coefficient, the second constant coefficient, the third constant coefficient, the atmospheric pressure and the arc energy.

[0219] In the embodiment of the present invention, formula (21) is used to calculate the increase in enthalpy of oil hydrocarbon liquid and gas.

[0220] Furthermore, the expression of the increase in enthalpy of oil hydrocarbon liquid gas is specifically:

[0221]

[0222] In the formula, represents the increase in enthalpy of oil hydrocarbon liquid / gas, represents the arc energy, represents the atmospheric pressure, represents the first constant coefficient, represents the second constant coefficient, Represents the third constant coefficient.

[0223] S225. Determine the liquid enthalpy increase of the oil hydrocarbon using the specific heat capacity of the insulating oil, the oil hydrocarbon operating temperature and the oil hydrocarbon vaporization temperature.

[0224] In the embodiment of the present invention, formula (16) is used to calculate the liquid enthalpy increase of oil hydrocarbon.

[0225] (16)

[0226] In the formula, represents the increase in liquid enthalpy of oil hydrocarbon, represents the specific heat capacity of insulating oil, Indicates the oil hydrocarbon operating temperature, Indicates the vaporization temperature of oil hydrocarbons.

[0227] S226. Determine the total reaction enthalpy change of thermal decomposition by using the latent heat of hydrocarbon oil vapor phase, the enthalpy increase of hydrocarbon oil liquid phase and the enthalpy increase of hydrocarbon oil liquid gas phase.

[0228] Further, S226 may include the following sub-steps:

[0229] S2261. Perform a difference calculation using the increase in enthalpy of oil hydrocarbon liquid gas and the latent heat of hydrocarbon oil vapor phase to obtain a first difference.

[0230] S2262. Perform difference calculation using the first difference and the increase in liquid enthalpy of the oil hydrocarbon to obtain the total reaction enthalpy change of thermal decomposition.

[0231] In the embodiment of the present invention, the total enthalpy change of thermal decomposition reaction is calculated using formula (15). The above process is encapsulated into a formula form:

[0232]

[0233] In the formula, represents the total reaction enthalpy change of thermal decomposition.

[0234] S23. Determine the reaction coefficient during the thermal decomposition reaction based on the total reaction enthalpy change of the thermal decomposition.

[0235] In the embodiment of the present invention, it is assumed that during the thermal decomposition process of a certain alkane molecule, the reaction coefficient of the enthalpy change obtained by the i-th reaction (i=1,...,n) accounts for the total enthalpy change of the thermal decomposition reaction is βi.

[0236] S24. Based on the reaction coefficient and the preset thermal reaction enthalpy change function, a set of thermal decomposition equivalent temperature equations is constructed.

[0237] In the embodiment of the present invention, βiΔ r H represents the enthalpy change of the reaction. Based on this, the equation group consisting of the reaction coefficient βi and the equivalent temperature T can be established according to formula (25):

[0238] (26)

[0239] S25. Use numerical methods to solve the thermal decomposition equivalent temperature equations to obtain the equivalent temperature.

[0240] In the embodiment of the present invention, a numerical method, such as a Newton-Raphson iteration method, is used to solve the thermal decomposition equivalent temperature equations to obtain the equivalent temperature.

[0241] S26. Use equivalent temperature to input the temperature influence on the chemical equilibrium constant to express the model and obtain the edge equilibrium constant of the edge temperature zone.

[0242] In the embodiment of the present invention, the equivalent temperature input formula IV is used to solve and obtain the edge equilibrium constant of the edge temperature zone.

[0243] It is worth mentioning that when calculating the marginal equilibrium constant in the present invention, the temperature used to input the alkane molecule thermal decomposition equation group is the equivalent temperature obtained by the arc energy method, and is not directly obtained data.

[0244] Step 105: Use the core equilibrium constant and the edge equilibrium constant to input the thermal decomposition gas content model for solution, and obtain the gas content data associated with the edge temperature zone and the core temperature zone respectively.

[0245] Further, step 105 may include the following sub-steps:

[0246] S31. Use the core equilibrium constant to input the thermal decomposition gas content model to solve and obtain the gas content data of each edge characteristic gas in the edge temperature zone.

[0247] For ease of understanding, an application example is provided below:

[0248] For any alkane molecule D, assume that its thermal decomposition process consists of n thermal decomposition reactions. The thermal decomposition process is:

[0249]

[0250] According to the above thermal decomposition process, the thermal decomposition reaction of propane is taken as an example: for the alkane molecule C3H8, the CC bond breaking reaction and the dehydrogenation reaction are selected as the thermal decomposition reactions. Its thermal decomposition process can be composed of five thermal decomposition reactions (recorded as formula (8)):

[0251] (8)

[0252] The total number of moles of reactants and products is represented by N and is calculated by formula II;

[0253] Formula II

[0254] Assuming the initial molar number of C3H8 is 1 mol, ξ=x, it is converted into the total molar number of reactants and products according to formula II (9):

[0255] N=1-x+2α1x+2α2x+α3x+α4x (9);

[0256] In the specific implementation, taking i=1 in equation (8) as an example, x mol C3H8 is reacted to generate a1*x mol CH4 and C2H4;

[0257] When reaction i=2, x mol C3H8 is reacted and a2*x mol C3H6 and H2 are produced;

[0258] When reaction i=3, there are a2*x mol of C3H6, a3*x mol of C3H6 is reacted, and a2*x- a3*x mol of C3H6 is left, and a3*x mol of CH4 and C2H2 are generated at the same time;

[0259] And so on, until the molar numbers of all products are obtained. They are all produced by x mol C3H8, and there is 1-x mol left. The sum of all is the size of N.

[0260] Taking the reaction in formula (8) as an example, the molar fractions of each substance can be converted into formula (10) according to formula I:

[0261] Formula I

[0262] The mole fraction of the substance is shown in formula (10):

[0263] (10)

[0264]

[0265] The relationship between Kpθ expressed as gas phase partial pressure and Kx expressed as mole percentage is:

[0266] Formula III

[0267] Formula IV

[0268] According to formula I, formula II, formula III and formula IV, the equilibrium constant expressions of all thermal decomposition reactions are combined with the atomic conservation equations, and the thermal decomposition equations of alkane molecules with temperature T as input and the mole fraction of various gases produced during the thermal decomposition process as output can be obtained as follows:

[0269] (11)

[0270] Take the thermal decomposition reaction of propane as an example: the last reaction in formula (8) is not independent, so the reaction path consists of reactions 1-4, and the competitive factors are α1-α4. In summary, according to formula (11), it is converted into a thermal decomposition equation, as shown in formula (12):

[0271] (12)

[0272] The solution process is as follows:

[0273] For (12), according to the equilibrium constant expression model III of each reaction under standard atmospheric pressure and the equilibrium influence expression model IV including the temperature change effect, the competition factor α of each thermal decomposition reaction under the equivalent temperature T is obtained by the Levenberg–Marquardt iterative algorithm: i ~α n and the molar fraction of each component in the pyrolysis reaction. Specifically, the competition factor can be calculated by the formula (12) of the present invention. The equilibrium constant expression model III of different chemical reactions is composed of formula (12). First, the equivalent temperature T is used as input, and the equilibrium constant K is calculated by substituting it into formula IV. Then, the equilibrium constant K is substituted into the solution of formula (12) to obtain the competition factor and the reaction progress x, and then the molar fraction of each edge characteristic gas is obtained by formula (10), that is, formula I.

[0274] S32. Use the edge equilibrium constant to input the thermal decomposition gas content model to solve and obtain the gas content data of each core characteristic gas in the core temperature zone.

[0275] In the embodiment of the present invention, since the temperature of the core temperature zone of the arc channel can reach above 5000K, it is not suitable to use the arc energy method in step 104 to calculate the chemical equilibrium constant. p Θ >10 5 The reaction can be regarded as a "complete reaction". In the core temperature zone, the instantaneous high temperature causes the insulating oil alkane molecules to quickly reach a state of complete thermal decomposition. Therefore, it can be assumed that the thermal decomposition reaction equilibrium constant K in this area is p Θ =10 5 , which is consistent with the complete thermal decomposition characteristics of the molecule and avoids the technical difficulties of measuring and calculating the equilibrium constant under transient high temperature.

[0276] Solve the gas content data of each core characteristic gas in the core temperature zone, which is consistent with the application example in S31. Since the core temperature zone directly determines the core equilibrium constant K p Θ =10 5 , so the core equilibrium constant is directly substituted into the solution of equation (12), that is, , the competition factor and reaction progress x are obtained by solving, and then the molar fraction of each core characteristic gas is obtained through formula (10), that is, formula I.

[0277] Step 106: Based on the preset gas type condition, the gas content data associated with the edge temperature zone and the core temperature zone are used to determine the fault level of the target transformer.

[0278] Further, step 106 may include the following sub-steps:

[0279] S41, judging whether the gas type of the edge characteristic gas meets the preset gas type condition, and performing fault judgment on the gas content data of each edge characteristic gas in the edge temperature zone based on the judgment result to determine a first judgment result.

[0280] The preset gas type condition specifically includes methane (CH4), ethylene (C2H4), ethane (C2H6), acetylene (C2H2) and hydrogen (H2).

[0281] Further, S41 may include the following sub-steps:

[0282] S411. Determine whether the gas type of the edge characteristic gas meets a preset gas type condition.

[0283] In the embodiment of the present invention, it is determined whether the gas types of the edge characteristic gas generated in the edge temperature zone all include five gases: methane (CH4), ethylene (C2H4), ethane (C2H6), acetylene (C2H2) and hydrogen (H2).

[0284] S412: If the gas type of the edge characteristic gas meets the set gas type condition, based on the three-ratio method, the gas content data of each edge characteristic gas is used to perform fault judgment to generate a first fault judgment result.

[0285] Further, S412 may include the following sub-steps:

[0286] S4121. Randomly select gas content data of two different edge characteristic gases to perform a ratio operation to generate a first edge judgment value, a second edge judgment value, and a third edge judgment value.

[0287] In the embodiment of the present invention, when the gas type of the edge characteristic gas satisfies the set gas type condition, the first edge judgment value (C2H2 / C2H4), the second edge judgment value (CH4 / H2) and the third edge judgment value (C2H4 / C2H6) are calculated. It should be noted that the preset first edge fault threshold is preferably 1, the preset second edge fault threshold is preferably 0.1, and the preset third edge fault threshold is preferably 3.

[0288] S4122: When the first edge judgment value is less than the preset first edge fault threshold, the second edge judgment value is less than the preset second edge fault threshold, and the third edge judgment value is less than the preset first edge fault threshold, it is judged as a mild fault level and used as the first fault judgment result.

[0289] In an embodiment of the present invention, when C2H2 / C2H4<1, CH4 / H2<0.1 and C2H4 / C2H6<1, it indicates a mild arc fault, and there is a slight local discharge or an initial arc phenomenon inside the transformer, which has a relatively small impact on the overall operation of the transformer. For example, it may be due to some tiny defects in the insulating material that begin to cause local ionization, but have not yet caused serious damage to the insulating structure.

[0290] S4123: When the first edge judgment value is less than the preset third edge fault threshold, and the third edge judgment value is less than the preset third edge fault threshold, it is judged as a moderate fault level and used as the first fault judgment result.

[0291] In an embodiment of the present invention, when C2H2 / C2H4<3 and C2H4 / C2H6<3, it indicates a moderate arc fault. The arc fault has developed to a certain extent and may have caused certain damage to the insulation structure of the transformer. For example, the insulating paper begins to have local carbonization, resulting in an increase in gas generation. Further inspection and maintenance of the transformer is required, such as insulation resistance testing.

[0292] S4124. When the first edge judgment value is greater than or equal to the preset third edge fault threshold, or the second edge judgment value is greater than or equal to the preset first edge fault threshold and the third edge judgment value is greater than or equal to the preset third edge fault threshold, it is judged as a severe fault level and used as the first fault judgment result.

[0293] In an embodiment of the present invention, when C2H2 / C2H4⩾3, or CH4 / H2⩾1 and C2H4 / C2H6⩾3, it indicates a severe arc fault, severe arc discharge may exist inside the transformer, and the insulation structure may have suffered severe damage. For example, the insulation layer is broken down over a large area, which may cause serious problems such as transformer short circuit and sharp increase in oil temperature.

[0294] S413: If the gas type of the edge characteristic gas does not meet the set gas type condition, based on the interval judgment method, the gas content data of each edge characteristic gas is used to perform fault judgment to generate a first fault judgment result.

[0295] Further, S413 may include the following sub-steps:

[0296] S4131, respectively determining the fault interval where the gas content data of each edge characteristic gas is located, and generating multiple edge fault level determination results;

[0297] The marginal fault level determination result is any one of a severe fault level, a moderate fault level, and a mild fault level;

[0298] The fault levels from high to low are severe fault level, moderate fault level and slight fault level.

[0299] In an embodiment of the present invention, when the gas type of the edge characteristic gas does not meet the set gas type condition, for example, the edge characteristic gas generated under an arc fault only includes methane (CH4) and hydrogen (H2), since the mole fractions of each edge characteristic gas obtained by solving the thermal decomposition equation group are mole fractions, the following are specific examples: when the mole fraction of hydrogen (H2) is in the range of 50 - 150 μL / L (microliters per liter, converted to mole fraction), it is determined to be a mild fault level; when the mole fraction of hydrogen (H2) is in the range of 150 - 300 μL / L, it is determined to be a moderate fault level; when the mole fraction of hydrogen (H2) exceeds 300 μL / L, it is determined to be a severe fault level. When the mole fraction of methane (CH4) is in the range of 20 - 50μL / L, it is judged as a mild fault level; when the mole fraction of methane (CH4) is in the range of 50 - 100μL / L, it is judged as a moderate fault level; when the mole fraction of methane (CH4) exceeds 100μL / L, it is judged as a severe fault level.

[0300] S4132. Select the highest fault level from the multiple edge fault level determination results as the first fault determination result.

[0301] In the embodiment of the present invention, for example, when hydrogen (H2) is used for judgment, it is judged as a mild fault level, and when methane (CH4) is used for judgment, it is judged as a moderate fault level. Then, the final first fault judgment result is a moderate fault level.

[0302] S42, judging whether the gas type of the core characteristic gas meets the preset gas type condition, and performing fault judgment on the gas content data of each core characteristic gas in the core temperature zone based on the judgment result to determine a second judgment result.

[0303] Further, S42 may include the following sub-steps:

[0304] S421. Determine whether the gas type of the core characteristic gas meets a preset gas type condition.

[0305] In an embodiment of the present invention, it is determined whether the gas types of the core characteristic gas generated in the core temperature zone include five gases: methane (CH4), ethylene (C2H4), ethane (C2H6), acetylene (C2H2) and hydrogen (H2).

[0306] S422. If the gas type of the core characteristic gas meets the set gas type condition, based on the three-ratio method, the gas content data of each core characteristic gas is used to perform fault judgment to generate a second fault judgment result.

[0307] Further, S422 may include the following sub-steps:

[0308] S4221. Randomly select gas content data of two different core characteristic gases to perform ratio operation to generate a first core judgment value, a second core judgment value and a third core judgment value.

[0309] In the embodiment of the present invention, when the gas type of the core characteristic gas satisfies the set gas type condition, the first core judgment value (C2H2 / C2H4), the second core judgment value (CH4 / H2) and the third core judgment value (C2H4 / C2H6) are calculated. It should be noted that the preset first core fault threshold is preferably 1, the preset second core fault threshold is preferably 0.1, and the preset third core fault threshold is preferably 3.

[0310] S4222. When the first core judgment value is less than the preset first core fault threshold, the second core judgment value is less than the preset second core fault threshold, and the third core judgment value is less than the preset first core fault threshold, it is judged as a mild fault level and used as the second fault judgment result.

[0311] In the embodiment of the present invention, in the embodiment of the present invention, when C2H2 / C2H4<1, CH4 / H2<0.1 and C2H4 / C2H6<1, it indicates a mild arc fault, there is a slight local discharge or initial arc phenomenon inside the transformer, and the impact on the overall operation of the transformer is relatively small. For example, it may be due to some tiny defects in the insulating material that begin to cause local ionization, but have not yet caused serious damage to the insulating structure.

[0312] S4223. When the first core judgment value is less than the preset third core fault threshold, and the third core judgment value is less than the preset third core fault threshold, it is judged as a moderate fault level and used as the second fault judgment result.

[0313] In an embodiment of the present invention, when C2H2 / C2H4<3 and C2H4 / C2H6<3, it indicates a moderate arc fault. The arc fault has developed to a certain extent and may have caused certain damage to the insulation structure of the transformer. For example, the insulating paper begins to have local carbonization, resulting in an increase in gas generation. Further inspection and maintenance of the transformer is required, such as insulation resistance testing.

[0314] S4224. When the first core judgment value is greater than or equal to the preset third core fault threshold, or the second core judgment value is greater than or equal to the preset first core fault threshold and the third core judgment value is greater than or equal to the preset third core fault threshold, it is judged as a severe fault level and used as the second fault judgment result.

[0315] In an embodiment of the present invention, when C2H2 / C2H4⩾3, or CH4 / H2⩾1 and C2H4 / C2H6⩾3, it indicates a severe arc fault, severe arc discharge may exist inside the transformer, and the insulation structure may have suffered severe damage. For example, the insulation layer is broken down over a large area, which may cause serious problems such as transformer short circuit and sharp increase in oil temperature.

[0316] S423. If the gas type of the core characteristic gas does not meet the set gas type condition, based on the interval judgment method, the gas content data of each core characteristic gas is used to perform fault judgment to generate a second fault judgment result.

[0317] Further, S423 may include the following sub-steps:

[0318] S4231. Determine the fault interval of the gas content data of each core characteristic gas, and generate multiple core fault level determination results. The core fault level determination result is any one of a severe fault level, a moderate fault level, and a mild fault level; the fault levels are severe fault level, moderate fault level, and mild fault level from high to low.

[0319] In an embodiment of the present invention, when the gas type of the core characteristic gas does not meet the set gas type condition, for example, the core characteristic gas generated under an arc fault includes only methane (CH4) and hydrogen (H2), since the core characteristic gases obtained by solving the thermal decomposition equation group are mole fractions, the following are specific examples: when the mole fraction of hydrogen (H2) is in the range of 50 - 150 μL / L (microliters per liter, converted to mole fraction), it is determined to be a mild fault level; when the mole fraction of hydrogen (H2) is in the range of 150 - 300 μL / L, it is determined to be a moderate fault level; when the mole fraction of hydrogen (H2) exceeds 300 μL / L, it is determined to be a severe fault level. When the mole fraction of methane (CH4) is in the range of 20 - 50μL / L, it is judged as a mild fault level; when the mole fraction of methane (CH4) is in the range of 50 - 100μL / L, it is judged as a moderate fault level; when the mole fraction of methane (CH4) exceeds 100μL / L, it is judged as a severe fault level.

[0320] S4232. Select the highest fault level from the multiple core fault level determination results as the second fault determination result.

[0321] In the embodiment of the present invention, for example, when hydrogen (H2) is used for judgment, it is judged as a mild fault level, and when methane (CH4) is used for judgment, it is judged as a moderate fault level. Then the final second fault judgment result is a moderate fault level.

[0322] S43. Determine the fault level of the target transformer using the first judgment result and the second judgment result.

[0323] Further, S43 may include the following sub-steps:

[0324] S431. Use a first fault value associated with the first judgment result and a second fault value associated with the second judgment result to input a preset target fault value function, and output a target fault value.

[0325] In the embodiment of the present invention, the fault value is determined according to the fault level included in the judgment result. In the present invention, the fault value of the severe fault level is defined as 3, the fault value of the moderate fault level is defined as 2, and the fault value of the mild fault level is defined as 1.

[0326] The preset target fault value function is specifically:

[0327]

[0328] In the formula, represents the target fault value, represents the edge weight coefficient, represents the first fault value, represents the core weight coefficient, Indicates the second fault value.

[0329] It is worth mentioning that the core temperature zone of the transformer contains key components such as the iron core and windings. The iron core is the core part of the transformer to achieve electromagnetic conversion, and the winding is the key path for current transmission. In these areas, even a small temperature change may indicate a serious fault, so the core weight coefficient is greater than the edge weight coefficient. In the present invention, the core weight coefficient is preferably 0.6, and the edge weight coefficient is preferably 0.4.

[0330] S432. Use the target fault value to retrieve a preset fault level key-value pair data table to determine the fault level of the target transformer.

[0331] The preset fault level key-value pair data table refers to a key-value pair data table established according to the association between the target fault value and the fault level, wherein the target fault value is used as the key and the fault level is used as the value.

[0332] The preset fault level key-value pair data table is shown in the following table:

[0333] Table 1: Preset fault level key-value pair data table

[0334]

[0335] In the embodiment of the present invention, the target fault value output by the preset target fault value function can more accurately evaluate the fault level of the target transformer.

[0336] This proposal proposes a thermodynamic algorithm for oil thermal decomposition gas production under arc fault. The invention divides the arc channel into two areas: the core area of ​​the arc channel where the oil thermal decomposition reaction occurs violently, and the arc edge area where the equivalent pyrolysis temperature is lower than 1500K. The equilibrium constant of the oil thermal decomposition reaction in the core area is extremely large, which means that the reaction is completely carried out on a macroscopic level. For the edge area, the equilibrium constant of the oil thermal decomposition reaction depends on the size of the arc energy.

[0337] The oil pyrolysis thermodynamic calculation method is applied to the calculation of oil decomposition gas production in the core area. On this basis, according to the relationship between arc energy and reaction enthalpy change of oil pyrolysis reaction, the equivalent pyrolysis temperature T of the thermal decomposition reaction of hydrocarbons in the oil in the arc edge area is solved, and then the equilibrium constant of the thermal decomposition reaction in the edge area and the fault gas content are calculated.

[0338] See also Figure 3 , Figure 3 This is a structural block diagram of a transformer fault degree assessment system based on arc fault gas content provided in Embodiment 3 of the present invention.

[0339] The present invention provides a transformer fault degree assessment system based on arc fault gas content, comprising: an arc zoning module 301, used to construct an arc channel model of a target transformer under an arc fault, and to perform arc zoning to determine an edge temperature zone and a core temperature zone; a model construction module 302, used to construct a thermal decomposition gas content model of the target transformer based on the alkane molecule thermal decomposition reaction set of the target transformer; a data acquisition module 303, used to obtain electrical parameter data and oil thermal characteristic data of the edge temperature zone, and a core equilibrium constant of the core temperature zone; a data processing module 304, used to determine an edge equilibrium constant of the edge temperature zone based on the electrical parameter data and the oil thermal characteristic data; a model solving module 305, used to use the core equilibrium constant and the edge equilibrium constant to input the thermal decomposition gas content model for solving, and obtain gas content data associated with the edge temperature zone and the core temperature zone respectively; a fault level determination module 306, used to determine the fault level of the target transformer based on a preset gas type condition and using the gas content data associated with the edge temperature zone and the core temperature zone. Further, the model building module 302 includes: an alkane molecule thermal decomposition reaction set submodule, which is used to establish an alkane molecule thermal decomposition reaction set of a thermal decomposition gas content model according to the alkane thermal decomposition theory; a mole fraction reaction model submodule, which is used to introduce a competitive factor for characterizing the reaction path to the alkane molecule thermal decomposition reaction set and construct a mole fraction reaction model; an equilibrium constant expression model submodule, which is used to fit the alkane molecule thermal decomposition reaction set according to the gas partial pressure definition formula and construct an equilibrium constant expression model; an equilibrium influence expression model submodule, which is used to apply the laws of thermodynamics to construct an equilibrium influence expression model with the influence of temperature changes; a thermal decomposition gas content model submodule, which is used to build a thermal decomposition gas content model by coupling the mole fraction reaction model, the equilibrium constant expression model and the equilibrium influence expression model. Further, the mole fraction reaction model includes a reactant mole fraction reaction model, a product mole fraction reaction model and a total mole number reaction model; the reactant mole fraction reaction model is used to characterize the mole fraction of each reactant during the thermal decomposition reaction; the product mole fraction reaction model is used to characterize the mole fraction of each product during the thermal decomposition reaction; and the total mole number reaction model is used to characterize the total mole number of reactants and products. Furthermore, the equilibrium influence expression model submodule includes: an expression model unit for the influence of temperature on the chemical equilibrium constant, which is used to construct an expression model for the influence of temperature on the chemical equilibrium constant according to the formula of Van't Hoff's law; an expression model unit for the relationship between reaction enthalpy change and molar heat capacity at constant pressure, which is used to construct an expression model for the relationship between reaction enthalpy change and molar heat capacity at constant pressure according to the formula of Kirchhoff's law; a coupling unit, which is used to build an equilibrium influence expression model containing the influence of temperature changes by coupling the expression model for the influence of temperature on the chemical equilibrium constant, the expression model for the relationship between reaction enthalpy change and molar heat capacity at constant pressure, and the preset hot melt and temperature relationship expression model.Furthermore, the electrical parameter data includes arc current, voltage drop across the arc, arc length and arc duration, and the data processing module 304 includes: an arc energy submodule, which is used to determine the arc energy using the arc current, arc duration and voltage drop across the arc; a thermal decomposition total reaction enthalpy change submodule, which is used to determine the thermal decomposition total reaction enthalpy change using the arc current, arc duration, arc energy, arc length and oil thermal characteristic data; a reaction coefficient submodule, which is used to determine the reaction coefficient in the thermal decomposition reaction process according to the thermal decomposition total reaction enthalpy change; a thermal decomposition equivalent temperature equation group submodule, which is used to construct a thermal decomposition equivalent temperature equation group based on the reaction coefficient and a preset thermal reaction enthalpy change function; an equivalent temperature submodule, which is used to solve the thermal decomposition equivalent temperature equation group using a numerical method to obtain an equivalent temperature; and a marginal equilibrium constant submodule, which is used to solve the expression model of the influence of the equivalent temperature input temperature on the chemical equilibrium constant to obtain the marginal equilibrium constant of the marginal temperature zone. Furthermore, the oil thermal characteristic data include the specific heat capacity of insulating oil, the oil hydrocarbon operating temperature, the oil hydrocarbon vaporization temperature, the hydrocarbon oil vapor phase latent heat, the insulating oil vapor specific heat ratio, the insulating oil vapor specific internal energy and the atmospheric pressure, and the thermal decomposition total reaction enthalpy change submodule includes: a first constant coefficient unit, used to determine the first constant coefficient using the arc length; a second constant coefficient unit, used to determine the second constant coefficient using a preset conversion coefficient, the insulating oil vapor specific heat ratio and the insulating oil vapor specific internal energy; a third constant coefficient unit , used for arc current and arc duration to determine the third constant coefficient; oil hydrocarbon liquid gas enthalpy increase unit, used to use the first constant coefficient, the second constant coefficient, the third constant coefficient, atmospheric pressure and arc energy to determine the oil hydrocarbon liquid gas enthalpy increase; oil hydrocarbon liquid enthalpy increase unit, used to use the insulating oil specific heat capacity, oil hydrocarbon operating temperature and oil hydrocarbon vaporization temperature to determine the oil hydrocarbon liquid enthalpy increase; operation unit, used to use hydrocarbon oil vapor phase latent heat, oil hydrocarbon liquid enthalpy increase and oil hydrocarbon liquid gas enthalpy increase to determine the total reaction enthalpy change of thermal decomposition. Further, the model solution module 305 includes: a first solution submodule, used to use the core equilibrium constant to input the thermal decomposition gas content model for solution, and obtain the gas content data of each edge characteristic gas in the edge temperature zone; a second solution submodule, used to use the edge equilibrium constant to input the thermal decomposition gas content model for solution, and obtain the gas content data of each core characteristic gas in the core temperature zone. Furthermore, the fault level determination module 306 includes: a first judgment result submodule, which is used to judge whether the gas type of the edge characteristic gas meets the preset gas type condition, and based on the judgment result, performs fault judgment on the gas content data of each edge characteristic gas in the edge temperature zone to determine the first judgment result; a second judgment result submodule, which is used to judge whether the gas type of the core characteristic gas meets the preset gas type condition, and based on the judgment result, performs fault judgment on the gas content data of each core characteristic gas in the core temperature zone to determine the second judgment result; a target transformer fault level determination submodule, which is used to use the first judgment result and the second judgment result to determine the fault level of the target transformer.Furthermore, the first judgment result submodule includes: a first processing unit, used to determine whether the gas type of the edge characteristic gas meets the preset gas type condition; a second processing unit, used to perform fault judgment based on the three-ratio method and the gas content data of each edge characteristic gas to generate a first fault judgment result if the gas type of the edge characteristic gas meets the set gas type condition; a third processing unit, used to perform fault judgment based on the interval judgment method and the gas content data of each edge characteristic gas to generate a first fault judgment result if the gas type of the edge characteristic gas does not meet the set gas type condition. Further, the second processing unit includes: an edge judgment value subunit, which is used to arbitrarily select the gas content data of two different edge characteristic gases for ratio operation to generate a first edge judgment value, a second edge judgment value and a third edge judgment value; a first judgment subunit, which is used to judge as a mild fault level when the first edge judgment value is less than a preset first edge fault threshold, the second edge judgment value is less than a preset second edge fault threshold and the third edge judgment value is less than a preset first edge fault threshold, and use it as a first fault judgment result; a second judgment subunit, which is used to judge as a moderate fault level when the first edge judgment value is less than a preset third edge fault threshold and the third edge judgment value is less than a preset third edge fault threshold, and use it as a first fault judgment result; a third judgment subunit, which is used to judge as a severe fault level when the first edge judgment value is greater than or equal to the preset third edge fault threshold, or the second edge judgment value is greater than or equal to the preset first edge fault threshold and the third edge judgment value is greater than or equal to the preset third edge fault threshold, and use it as a first fault judgment result. Further, the third processing unit includes: a marginal fault level determination result subunit, which is used to respectively determine the fault interval where the gas content data of each marginal characteristic gas is located, and generate multiple marginal fault level determination results; wherein the marginal fault level determination result is any one of a severe fault level, a moderate fault level and a mild fault level; the fault levels are severe fault level, moderate fault level and mild fault level from high to low; a first selection subunit, which is used to select the highest fault level from multiple marginal fault level determination results as the first fault determination result. Further, the second judgment result submodule includes: a fourth processing unit, which is used to determine whether the gas type of the core characteristic gas meets the preset gas type condition; a fifth processing unit, which is used to perform fault determination based on the three ratio method using the gas content data of each core characteristic gas to generate a second fault determination result if the gas type of the core characteristic gas meets the set gas type condition; a sixth processing unit, which is used to perform fault determination based on the interval judgment method using the gas content data of each core characteristic gas to generate a second fault determination result if the gas type of the core characteristic gas does not meet the set gas type condition.Further, the fifth processing unit includes: a core judgment value subunit, which is used to arbitrarily select the gas content data of two different core characteristic gases for ratio operation to generate a first core judgment value, a second core judgment value and a third core judgment value; a fourth judgment subunit, which is used to judge as a light fault level when the first core judgment value is less than the preset first core fault threshold, the second core judgment value is less than the preset second core fault threshold and the third core judgment value is less than the preset first core fault threshold, and use it as the second fault judgment result; a fifth judgment subunit, which is used to judge as a moderate fault level when the first core judgment value is less than the preset third core fault threshold and the third core judgment value is less than the preset third core fault threshold, and use it as the second fault judgment result; a sixth judgment subunit, which is used to judge as a severe fault level when the first core judgment value is greater than or equal to the preset third core fault threshold, or the second core judgment value is greater than or equal to the preset first core fault threshold and the third core judgment value is greater than or equal to the preset third core fault threshold, and use it as the second fault judgment result. Further, the sixth processing unit includes: a core fault level determination result subunit, which is used to respectively determine the fault interval of the gas content data of each core characteristic gas, and generate multiple core fault level determination results; wherein the core fault level determination result is any one of a severe fault level, a moderate fault level and a mild fault level; the fault levels are severe fault level, moderate fault level and mild fault level from high to low; a second selection subunit, which is used to select the highest fault level from multiple core fault level determination results as the second fault determination result. Further, the target transformer fault level determination submodule includes: a target fault value unit, which is used to use the first fault value associated with the first judgment result and the second fault value associated with the second judgment result to input a preset target fault value function, and output a target fault value; a data output unit, which is used to use the target fault value to retrieve a preset fault level key-value pair data table to determine the fault level of the target transformer.

[0340] Those skilled in the art can clearly understand that, for the convenience and simplicity of description, the specific working process of the above-described system, device and unit can refer to the corresponding process in the aforementioned method embodiment, and will not be repeated here. In the several embodiments provided in this application, it should be understood that the disclosed system, device and method can be implemented in other ways. For example, the device embodiment described above is only schematic, for example, the division of the unit is only a logical function division, and there may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of the device or unit, which can be electrical, mechanical or other forms. The above embodiments are only used to illustrate the technical solutions of the present invention, not to limit it; although the present invention is described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that it can still modify the technical solutions recorded in the aforementioned embodiments, or replace some of the technical features therein with equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for evaluating transformer fault degree based on arc fault gas content, characterized in that: include: Construct an arc channel model of the target transformer under arc fault, perform arc zoning, and determine the edge temperature zone and core temperature zone; Based on the alkane molecule thermal decomposition reaction set of the target transformer, a thermal decomposition gas content model of the target transformer is constructed; Acquiring electrical parameter data and oil thermal characteristic data of the edge temperature zone, and core equilibrium constant of the core temperature zone; Determining an edge equilibrium constant of the edge temperature zone based on the electrical parameter data and the oil thermal characteristic data; The core equilibrium constant and the edge equilibrium constant are input into the thermal decomposition gas content model for solving, and the gas content data associated with the edge temperature zone and the core temperature zone are obtained respectively; Based on preset gas type conditions, the fault level of the target transformer is determined using gas content data associated with the edge temperature zone and the core temperature zone.

2. The transformer fault degree assessment method based on arc fault gas content according to claim 1 is characterized in that: The step of constructing a thermal decomposition gas content model of the target transformer based on the alkane molecule thermal decomposition reaction set of the target transformer includes: According to the alkane thermal decomposition theory, the alkane molecular thermal decomposition reaction set of the thermal decomposition gas content model is established; A competitive factor for characterizing the reaction path is introduced into the alkane molecule thermal decomposition reaction set to construct a mole fraction reaction model; Fitting the alkane molecule thermal decomposition reaction set according to the gas partial pressure definition formula to construct an equilibrium constant expression model; Apply the laws of thermodynamics to construct an equilibrium effect expression model including the effect of temperature change; The thermal decomposition gas content model is constructed by coupling the mole fraction reaction model, the equilibrium constant expression model and the equilibrium influence expression model.

3. The transformer fault degree assessment method based on arc fault gas content according to claim 2 is characterized in that: The electrical parameter data includes arc current, voltage drop across the arc, arc length and arc duration. The edge equilibrium constant of the edge temperature zone is determined based on the electrical parameter data and the oil thermal characteristic data, including: Determining arc energy using the arc current, the arc duration, and the voltage drop across the arc; Determine the total reaction enthalpy change of thermal decomposition using the arc current, arc duration, arc energy, arc length and oil thermal property data; Determining the reaction coefficient during the thermal decomposition reaction according to the total reaction enthalpy change of the thermal decomposition; Based on the reaction coefficient and the preset thermal reaction enthalpy change function, construct a thermal decomposition equivalent temperature equation group; Solving the thermal decomposition equivalent temperature equations by using a numerical method to obtain the equivalent temperature; The equilibrium influence expression model including the influence of temperature change is inputted with the equivalent temperature to solve the edge equilibrium constant of the edge temperature zone.

4. The transformer fault degree assessment method based on arc fault gas content according to claim 3 is characterized in that: The oil thermal characteristic data include insulating oil specific heat capacity, oil hydrocarbon operating temperature, oil hydrocarbon vaporization temperature, hydrocarbon oil vapor phase latent heat, insulating oil vapor specific heat ratio, insulating oil vapor specific internal energy and atmospheric pressure, and the arc current, arc duration, arc energy, arc length and oil thermal characteristic data are used to determine the total reaction enthalpy change of thermal decomposition, including: Using the arc length, determining a first constant coefficient; Determine a second constant coefficient by using a preset conversion coefficient, the insulating oil vapor specific heat ratio, and the insulating oil vapor specific internal energy; The arc current and the arc duration determine a third constant coefficient; Determine the increase in enthalpy of oil hydrocarbon liquid and gas by using the first constant coefficient, the second constant coefficient, the third constant coefficient, the atmospheric pressure and the arc energy; Determine the liquid enthalpy increase of the oil hydrocarbon by using the specific heat capacity of the insulating oil, the oil hydrocarbon operating temperature and the oil hydrocarbon vaporization temperature; The total reaction enthalpy change of thermal decomposition is determined using the hydrocarbon oil vapor phase latent heat, the hydrocarbon oil liquid enthalpy increase and the hydrocarbon oil liquid-gas enthalpy increase.

5. The transformer fault degree assessment method based on arc fault gas content according to claim 1 is characterized in that: The method of determining the fault level of the target transformer based on the preset gas type condition and using the gas content data associated with the edge temperature zone and the core temperature zone includes: Determining whether the gas type of the edge characteristic gas in the edge temperature zone meets a preset gas type condition; If the gas type of the edge characteristic gas meets the set gas type condition, then based on the three-ratio method, the gas content data of each edge characteristic gas is used to perform fault judgment to generate a first fault judgment result; If the gas type of the edge characteristic gas does not meet the set gas type condition, based on the interval judgment method, the gas content data of each edge characteristic gas is used to perform fault judgment to generate a first fault judgment result; Determining whether the gas type of the core characteristic gas in the core temperature zone meets the preset gas type condition; If the gas type of the core characteristic gas meets the set gas type condition, then based on the three-ratio method, the gas content data of each core characteristic gas is used to perform fault judgment to generate a second fault judgment result; If the gas type of the core characteristic gas does not meet the set gas type condition, based on the interval judgment method, the gas content data of each core characteristic gas is used to perform fault judgment to generate a second fault judgment result; Using a first fault value associated with the first judgment result and a second fault value associated with the second judgment result to input a preset target fault value function, and outputting a target fault value; The target fault value is used to retrieve a preset fault level key-value pair data table to determine the fault level of the target transformer.

6. The transformer fault degree assessment method based on arc fault gas content according to claim 5 is characterized in that: The method based on the three ratio method uses the gas content data of each of the edge characteristic gases to perform fault determination and generate a first fault determination result, including: Randomly select two different gas content data of the edge characteristic gases to perform a ratio operation to generate a first edge judgment value, a second edge judgment value and a third edge judgment value; When the first edge judgment value is less than a preset first edge fault threshold, the second edge judgment value is less than a preset second edge fault threshold, and the third edge judgment value is less than the preset first edge fault threshold, it is determined to be a mild fault level and used as a first fault judgment result; When the first edge judgment value is less than the preset third edge fault threshold, and the third edge judgment value is less than the preset third edge fault threshold, it is determined as a moderate fault level and used as the first fault judgment result; When the first edge judgment value is greater than or equal to the preset third edge fault threshold, or the second edge judgment value is greater than or equal to the preset first edge fault threshold and the third edge judgment value is greater than or equal to the preset third edge fault threshold, it is judged as a severe fault level and used as the first fault judgment result.

7. The transformer fault degree assessment method based on arc fault gas content according to claim 5 is characterized in that: The interval-based judgment method uses the gas content data of each of the edge characteristic gases to perform fault judgment and generate a first fault judgment result, including: Respectively determine the fault interval where the gas content data of each of the edge characteristic gases is located, and generate multiple edge fault level determination results; Wherein, the marginal fault level determination result is any one of a severe fault level, a moderate fault level and a mild fault level; The fault levels are from high to low: severe fault level, moderate fault level and slight fault level; The highest fault level is selected from the plurality of marginal fault level determination results as the first fault determination result.

8. The transformer fault degree assessment method based on arc fault gas content according to claim 5 is characterized in that: The method based on the three ratio method uses the gas content data of each of the core characteristic gases to perform fault determination and generate a second fault determination result, including: Randomly select two different gas content data of the core characteristic gases to perform a ratio operation to generate a first core judgment value, a second core judgment value and a third core judgment value; When the first core judgment value is less than the preset first core fault threshold, the second core judgment value is less than the preset second core fault threshold, and the third core judgment value is less than the preset first core fault threshold, it is determined to be a mild fault level and used as the second fault judgment result; When the first core determination value is less than the preset third core fault threshold, and the third core determination value is less than the preset third core fault threshold, it is determined as a moderate fault level and used as the second fault determination result; When the first core judgment value is greater than or equal to the preset third core fault threshold, or the second core judgment value is greater than or equal to the preset first core fault threshold and the third core judgment value is greater than or equal to the preset third core fault threshold, it is judged as a severe fault level and used as the second fault judgment result.

9. The transformer fault degree assessment method based on arc fault gas content according to claim 5 is characterized in that: The interval-based judgment method uses the gas content data of each of the core characteristic gases to perform fault judgment and generate a second fault judgment result, including: Respectively determine the fault intervals where the gas content data of each of the core characteristic gases are located, and generate multiple core fault level determination results; The core fault level determination result is any one of a severe fault level, a moderate fault level and a mild fault level; The fault levels are from high to low: severe fault level, moderate fault level and slight fault level; The highest fault level is selected from the plurality of core fault level determination results as the second fault determination result.

10. A transformer fault degree assessment system based on arc fault gas content, characterized in that: include: The arc partitioning module is used to construct an arc channel model of the target transformer under arc fault, and to perform arc partitioning to determine the edge temperature zone and the core temperature zone; A model building module, used for building a thermal decomposition gas content model of the target transformer based on the alkane molecule thermal decomposition reaction set of the target transformer; A data acquisition module, used to acquire electrical parameter data and oil thermal characteristic data of the edge temperature zone, and core equilibrium constant of the core temperature zone; A data processing module, for determining an edge equilibrium constant of the edge temperature zone based on the electrical parameter data and the oil thermal characteristic data; A model solving module, used to use the core equilibrium constant and the edge equilibrium constant to input the thermal decomposition gas content model for solving, and obtain gas content data associated with the edge temperature zone and the core temperature zone respectively; A fault level determination module is used to determine the fault level of the target transformer based on a preset gas type condition and using the gas content data associated with the edge temperature zone and the core temperature zone.

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