Air gap development model in dry-type sleeve core body and carbonization ablation judgment method and system

Abstract

The invention belongs to the technical field of electrical equipment, discloses a dry-type sleeve epoxy core air gap defect development model and a carbonization ablation judgment method, and researches the ablation behavior of epoxy resin under external heat application through numerical simulation. An MATLAB simulation environment is used, a program uses a finite difference method to simulate heat conduction and mass loss processes, continuous heat flow can be applied to the surface through material ablation, the heat flow is conducted to the interior of the material to cause temperature rise of the surface and the interior of the material, once epoxy resin reaches a stationary point temperature under the influence of an externally applied heat source, the material is ablated, and the heat loss is reduced. And the temperature rise causes a chemical reaction of the material to generate a gas-phase product to remove the surface of the material, and the internal material is exposed, namely, the material continuously generates a new surface. The study on the ablation behavior of the epoxy resin material is helpful for deeply revealing the defect evolution rule and the insulating property damage mechanism of the dry-type bushing epoxy core body under the complex working condition.

Description

Technical Field

[0001] The invention belongs to the technical field of electrical equipment, and in particular relates to a dry-type bushing epoxy core air gap defect development model and a carbonization ablation determination method and system. Background Art

[0002] During long-term operation, dry bushings always carry voltage, current and strong mechanical loads. These loads can cause small internal defects to gradually develop into insulation failures under the combined action of high electrical, thermal and mechanical stresses, posing a huge safety hazard. Therefore, the study of internal defects of dry bushings is particularly important.

[0003] At present, the research of domestic and foreign scholars on dry bushing defects mainly focuses on establishing typical defect models, studying the insulation characteristic parameters corresponding to the defects, simulating them in actual bushings, and analyzing the fault phenomena caused by the defects. However, most of the research focuses on the temperature field distribution of overheating defects, while there is little research on the changes in electrical characteristics caused by typical defects inside the capacitor core. The operating environment of dry bushings is complex, and the internal micro defects can easily expand into serious insulation faults under the combined effect of electrical, thermal and mechanical stresses. The evolution process of these defects will have a serious impact on the insulation performance of the bushing and even lead to catastrophic failure of the system. In dry bushings, epoxy resin is the main insulating material, and its internal air gap defects are particularly common. Local discharge will occur in the air gap during operation, resulting in multiple discharges accumulating and generating discharge power. As the discharge power increases, the temperature inside the air gap gradually increases. In a high temperature environment, the epoxy resin material will undergo ablation, which will further damage the insulation performance of the bushing.

[0004] Through the above analysis, the problems and defects of the prior art are as follows:

[0005] Most studies focus on the temperature field distribution of overheating defects, but less research is done on the changes in electrical characteristics caused by typical defects inside the capacitor core. The operating environment of dry bushings is complex, and small internal defects can easily expand into serious insulation failures under the combined effects of electrical, thermal, and mechanical stresses. The evolution of these defects can have a serious impact on the insulation performance of the bushing and even lead to catastrophic failure of the system. Summary of the invention

[0006] In view of the problems existing in the prior art, the present invention provides a dry-type sleeve epoxy core air gap defect development model and a carbonization and ablation determination method.

[0007] The present invention is implemented in this way: a dry sleeve epoxy core air gap defect development model and a carbonization ablation determination method include:

[0008] Step 1: Through numerical simulation, study the ablation behavior of epoxy resin under external heat application; use the finite difference method to simulate the heat conduction and mass loss process to reveal the behavioral characteristics of the material under high temperature environment;

[0009] Step 2, constructing an air gap discharge simulation model;

[0010] Step 3: construct an air gap ablation calculation model.

[0011] Further, the air gap discharge simulation model is constructed:

[0012] For the branch where the air gap is located, the calculation formulas for the air gap capacitance Ca and the solid insulation capacitance Ca and Cb are:

[0013]

[0014] Apparent discharge charge of insulator

[0015]

[0016] The starting discharge voltage is:

[0017]

[0018] U CB =E i ·h (4)

[0019] Where B is a constant related to the gas in the air gap. When the air gap is air, B = 8.6 (Pa·m)1 / 2.

[0020] The relative dielectric constant ε of the solid insulating medium r =4.65, vacuum dielectric constant ε0 = 8.85 × 10-12 F / m, air gap radii are 0.1 mm, 0.25 mm, 0.5 mm, respectively, air pressure in the air gap p = 1 × 105 Pa, since the sampling position is located close to the outer surface of the core, the potential here is low, so the external voltage is set to Um = 10 kV, f = 50 Hz; the electric field intensity Ei corresponding to the start of discharge and the starting discharge voltage Ui can be obtained;

[0021] The calculation formula of discharge repetition rate is as follows:

[0022]

[0023] Where, f is the frequency of the externally applied voltage.

[0024] Um--peak value of applied voltage

[0025] UCB--breakdown voltage of air gap

[0026] Assume that there are m discharges in the measurement time T, and the product of the apparent discharge charge and the instantaneous value of the applied voltage corresponding to each discharge is q1ut1, q2ut2, ..., qmutm respectively, then

[0027]

[0028] Further, the air gap ablation calculation model is constructed:

[0029] The heat conduction equation can be expressed as:

[0030]

[0031] Pyrolysis and oxidation reactions occur at high temperatures, resulting in mass loss of the material. The rate of the ablation reaction can be described by the Arrhenius equation:

[0032]

[0033] The mass balance equation of the surface chemical element k without considering the mechanical erosion of the material is as follows:

[0034]

[0035] Wherein, mc: ablation mass flow rate; mf: liquid phase mass loss flow rate; jkw: element k diffusion mass flow rate on the wall; (ρv): ejection gas mass flow rate; Ykc, Ykw, Ykf: represent the mass concentration of element k in ablation, diffusion and liquid layer loss, respectively;

[0036] Thermochemical equilibrium reaction equation

[0037]

[0038] The chemical equilibrium constant expression of the equation is:

[0039]

[0040] Among them, Kp: represents the equilibrium constant of the chemical reaction, Pj represents the partial pressure of the gas product, and Pk represents the partial pressure of the gas reactant; the coefficient Ai represents the fact that each condensed phase component shares the material ablation surface, that is, the contact area between each condensed phase component and the gas phase component is limited and the size of the contact area is related to its molar fraction on the material ablation surface; therefore:

[0041]

[0042] The sum of the partial pressures Pi of the gas components is equal to the total pressure P0, that is:

[0043]

[0044] The reaction equation involves four elements, C, H, O, and N; therefore, a nonlinear closed equation system with 17 unknowns, A (i = 1, 2, 3), M, Bc, and P (i = 1, 2, ..., 12) can be formed;

[0045] The material line ablation rate is calculated as follows:

[0046] v=Bq or / ρh r (13)

[0047] Where ρ is the material density, kg / m 3 ; v is the linear ablation rate, m / s; hr is the total enthalpy of the incoming flow, kg / kJ; qor is the heat flux, kW / m 2 .

[0048] Another object of the present invention is to provide a dry sleeve epoxy core air gap defect development model and carbonization ablation calculation system including:

[0049] The simulation module is used to study the ablation behavior of epoxy resin under external heat through numerical simulation; the finite difference method is used to simulate the heat conduction and mass loss process to reveal the behavior characteristics of the material under high temperature environment;

[0050] A simulation model building module, used to build an air gap discharge simulation model;

[0051] The computational model building module is used to build an air gap ablation computational model.

[0052] Another object of the present invention is to provide a computer device, comprising a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of the dry sleeve epoxy core air gap defect development model and the carbonization and ablation determination method.

[0053] Another object of the present invention is to provide a computer-readable storage medium storing a computer program, which, when executed by a processor, enables the processor to execute the steps of the dry sleeve epoxy core air gap defect development model and carbonization ablation determination method.

[0054] Another object of the present invention is to provide an information data processing terminal, which is used to implement the dry sleeve epoxy core air gap defect development model and carbonization ablation calculation system.

[0055] Another object of the present invention is to provide a system for calculating the air gap defect development and carbonization ablation of the epoxy core of a dry sleeve, the system comprising:

[0056] Numerical simulation module, used to study the ablation behavior of epoxy resin under externally applied heat, simulating the heat conduction and mass loss process based on the finite difference method (FDM) to reveal the behavioral characteristics of the material under high temperature environment;

[0057] Air gap discharge simulation module, used to build an air gap discharge model and simulate the electric field distribution and discharge behavior in the air gap;

[0058] The air gap ablation calculation module is used to combine air gap discharge simulation and heat conduction simulation to calculate the ablation of epoxy resin and material loss.

[0059] Furthermore, the numerical simulation module is further used to simulate the thermal decomposition, ablation depth, degradation rate and mass loss of epoxy resin materials in a high temperature environment by using a finite difference method.

[0060] Furthermore, the air gap discharge simulation module includes:

[0061] A capacitance calculation unit for calculating air gap capacitance;

[0062] Electric field simulation unit used to simulate and analyze the electric field strength and starting discharge voltage in the air gap.

[0063] Furthermore, the air gap ablation calculation module further includes:

[0064] Heat conduction calculation unit, used to calculate the temperature distribution of materials based on the heat conduction equation;

[0065] The ablation rate calculation unit is used to calculate the ablation rate and mass loss of materials based on the Arrhenius equation and the mass conservation equation.

[0066] In combination with the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solutions to be protected by the present invention are as follows:

[0067] First, the ablation process of epoxy resin involves complex heat conduction and chemical reactions. Through numerical simulation, the ablation behavior of epoxy resin under external heat can be studied. The finite difference method is used to simulate the heat conduction and mass loss process, which can reveal the behavioral characteristics of the material under high temperature environment. When the epoxy resin reaches the stagnation temperature, the material will ablate, resulting in an increase in surface and internal temperature, and chemical reactions will generate gas phase products, which will gradually remove the surface of the material and expose a new surface. The study of the ablation behavior of epoxy resin materials is helpful to predict the performance changes of dry bushings under high temperature environments. By establishing a development model of air gap defects in the epoxy core of dry bushings and a calculation method for carbonization ablation, the defect evolution law and insulation performance damage mechanism of dry bushings under complex working conditions can be deeply revealed. The research of the present invention not only provides a scientific basis for the reliable operation of power equipment, but also provides new ideas and methods for future research.

[0068] After local discharge occurs in the air gap inside the epoxy resin, multiple discharges accumulate to generate discharge power. As the discharge power increases, the temperature inside the air gap increases. In a high temperature environment, the epoxy resin material will undergo an ablation process. The present invention studies the ablation behavior of epoxy resin under external heat application through numerical simulation. Using the MATLAB simulation environment, the program uses the finite difference method to simulate the heat conduction and mass loss process. Material ablation will apply a continuous heat flow on the surface, and the heat flow will be conducted to the inside of the material, causing the surface and internal temperature of the material to increase. Once the epoxy resin reaches the stagnation temperature under the influence of the external heat source, the material will ablate, and the temperature increase causes the material to undergo a chemical reaction to generate gas phase products, resulting in the removal of the material surface, and exposing the internal material, that is, the material continuously generates a new surface. The study of the ablation behavior of epoxy resin materials is helpful to deeply reveal the defect evolution law and insulation performance damage mechanism of the dry sleeve epoxy core under complex working conditions.

[0069] Second, the technical solution of the present invention fills the technical gap in the industry at home and abroad:

[0070] At present, most of the research focuses on the temperature field distribution of overheating defects, while there is less research on the changes in electrical characteristics caused by typical defects inside the capacitor core. In dry bushings, epoxy resin is the main insulating material. Due to process defects or its internal air gap defects, local discharge will occur during long-term electrothermal operation, resulting in multiple discharge accumulation and discharge power. As the discharge power increases, the temperature inside the air gap gradually increases. In a high temperature environment, the epoxy resin material will undergo ablation, which will further damage the insulation performance of the bushing.

[0071] The ablation process of epoxy resin involves complex heat conduction and chemical reactions. The present invention can study the ablation behavior of epoxy resin under external heat through numerical simulation. It reveals the behavioral characteristics of the material under high temperature environment. It helps to predict the performance changes of the core inside the dry bushing under high temperature environment, and deeply reveals the defect evolution law and insulation performance damage mechanism of the dry bushing under complex working conditions. It provides a scientific basis for the reliable operation of power equipment and provides new ideas and methods for future research.

[0072] Third, existing technical problems:

[0073] 1. Electrical failure caused by air gap defects: The existing dry bushing design is prone to discharge failures due to air gap defects during long-term operation. Air gap discharge is one of the important reasons for insulation failure. Traditional monitoring methods are not sensitive enough to air gap discharge detection and cannot predict the ablation behavior during the development of air gaps. This situation may cause major equipment damage or even safety accidents.

[0074] 2. The air gap defect ablation model lacks accurate description: Most of the existing ablation models are aimed at large-scale defects or macroscopic material damage. In the epoxy resin core of the dry bushing, the air gap is a microstructure. The existing model cannot accurately capture its ablation evolution process under high temperature and electric field, and lacks an accurate description of the air gap ablation behavior.

[0075] 3. Lack of accurate fault prediction and prevention measures: Current fault diagnosis methods are limited to simple thermal monitoring or electric field monitoring, and lack comprehensive consideration of material ablation, mass loss and pyrolysis reactions. Traditional fault monitoring methods are often lagging and cannot provide early warning and timely processing.

[0076] The technical solution and significant technical progress of the present invention:

[0077] 1. Air gap defect development model with multi-physics coupling:

[0078] The air gap defect development model proposed in the present invention combines numerical simulation with physical experiments to establish a multi-physical field coupling model of air gap discharge and air gap ablation. The model integrates multiple factors such as heat conduction, discharge, and mass loss, and simulates the behavior of the air gap under high temperature and electric field environment through the finite difference method. Compared with the prior art, the present invention can more accurately capture the development process of epoxy resin air gap defects and predict the ablation rate under different air gap conditions, filling the current research gap in the industry on air gap ablation behavior. 2. Simulation prediction of dynamic air gap discharge and ablation behavior:

[0079] The present invention effectively simulates the air gap discharge phenomenon under different voltages and frequencies by constructing an air gap discharge simulation model and an air gap ablation calculation model. Using the discharge voltage formula and the discharge repetition rate formula, the present invention can dynamically predict the frequency and intensity of the air gap discharge, and calculate the ablation mass loss and pyrolysis reaction rate of the material by combining the heat conduction equation with the Arrhenius equation. This technology breaks through the limitation of traditional methods that only rely on experimental data, realizes accurate simulation based on physical models, and significantly improves the prediction accuracy of material ablation behavior.

[0080] 3. Advanced air gap carbonization ablation determination method:

[0081] Chemical reactions on the surface of materials at high temperatures lead to mass loss, which in turn causes carbonization and ablation. The present invention proposes an accurate carbonization and ablation determination method by establishing a chemical reaction equilibrium equation and combining the linear equation of the reaction equilibrium constant and the material ablation rate. This method can evaluate the carbonization and ablation process of materials in the air gap in real time, thereby providing a scientific basis for early warning and maintenance of equipment failures. Compared with traditional monitoring methods, the ablation determination method of the present invention has the advantages of real-time and accuracy, which greatly improves the safety and stability of equipment operation.

[0082] 4. Significant industrial application value:

[0083] Improve equipment operation safety: Through this technical solution, the development of air gap defects and ablation behavior can be monitored in real time during the operation of electrical equipment, and possible faults can be warned in advance, thereby improving the safe operation level of the equipment and reducing the incidence of sudden accidents.

[0084] Extend equipment life and reduce maintenance costs: The defect diagnosis and ablation prediction technology of the present invention can help power companies to promptly identify potential problems, optimize maintenance strategies, extend the service life of equipment such as dry bushings, reduce sudden failures caused by air gap defects, and thus reduce equipment maintenance and replacement costs.

[0085] Improve the technical level of the industry: The technology of the present invention fills the gap in the research of air gap defect development and ablation behavior at home and abroad, provides new ideas in the field of insulation fault monitoring and material ablation, and promotes the progress of power equipment fault diagnosis technology.

[0086] In summary, the dry-type sleeve epoxy core air gap defect development model and carbonization ablation judgment method proposed in the present invention have broken through the limitations of traditional technology, significantly improved the accuracy and real-time performance of equipment fault diagnosis, and have significant technological progress and industrial application prospects in terms of safety, cost-effectiveness, and wide application. BRIEF DESCRIPTION OF THE DRAWINGS

[0087] Figure 1 It is a flow chart of the dry-type sleeve epoxy core air gap defect development model and carbonization ablation determination method provided by the embodiment of the present invention.

[0088] Figure 2 It is a structural block diagram of a dry-type sleeve epoxy core air gap defect development model and a carbonization ablation calculation system provided by an embodiment of the present invention.

[0089] Figure 3 1 is an equivalent circuit diagram of air gap discharge provided by an embodiment of the present invention.

[0090] Figure 4 It is a heat flow schematic diagram provided by an embodiment of the present invention.

[0091] Figure 5 It is a calculation flow chart provided by an embodiment of the present invention.

[0092] Figure 6 This is a graph showing the change in epoxy resin ablation amount over time at an ablation time of 3600s (1h) provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0093] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0094] Industrial Application Example 1: Air Gap Defect Monitoring and Ablation Warning System in High Voltage Dry-Type Transformer

[0095] High-voltage dry-type transformers are commonly used in power systems, and epoxy resin is used as the insulation material inside. However, with long-term operation, the air gap defects in the epoxy resin will gradually evolve into discharge faults, leading to local ablation, and ultimately affecting the insulation performance and operating life of the transformer. Therefore, real-time monitoring of the evolution of air gap defects, especially the ablation process, is crucial to improving equipment safety.

[0096] Application solutions:

[0097] The "air gap defect development model and carbonization ablation judgment method" of the present invention is applied in high-voltage dry-type transformers to monitor the air gap defects of epoxy resin inside the transformer in real time. By installing high-precision temperature sensors and electric field sensors inside the transformer, air gap discharge data under high temperature and voltage conditions are collected, and the heat conduction and mass loss process in the air gap are calculated using the finite difference method. The discharge frequency and ablation rate of air gap defects are analyzed using the air gap discharge simulation model and the ablation calculation model.

[0098] The system generates a health status report for the equipment based on the real-time calculation of the ablation reaction rate and mass loss. If it is found that the air gap ablation is intensifying or the local temperature is abnormally high, an early warning prompt will be triggered to remind the equipment maintenance personnel to carry out maintenance to avoid sudden failures.

[0099] Effects and benefits:

[0100] Improve safety: By real-time monitoring of the evolution of transformer air gap defects, early warning of discharge and ablation faults can be provided to avoid equipment damage caused by sudden shutdown or insulation breakdown.

[0101] Reduced maintenance costs: By accurately determining the development of air gap defects, power companies can optimize maintenance cycles, avoid unnecessary frequent shutdowns for maintenance, reduce maintenance costs and extend equipment life.

[0102] Industrial Application Example 2: Monitoring of epoxy resin air gap ablation in power cable terminal heads

[0103] In the power transmission and distribution system, the cable terminal head is a component prone to insulation failure. There are often tiny air gaps in the epoxy resin in the terminal head. These air gaps may cause local discharge under the action of high electric fields, resulting in local ablation and carbonization of the material, and gradually developing into insulation failure. Therefore, fault monitoring of cable terminal heads is particularly important for the safe operation of the power grid.

[0104] Application solutions:

[0105] The "air gap defect development model and carbonization ablation determination method" of the present invention is applied to the fault monitoring system of the cable terminal head. The air gap discharge and temperature changes inside the cable are monitored by embedding micro sensors inside the epoxy resin of the cable terminal head. By using numerical simulation technology, combined with the electric field, temperature and material ablation characteristics, an air gap discharge simulation model and an ablation calculation model are established to calculate the discharge frequency, heat conduction and mass loss in the air gap in real time.

[0106] During the operation of the cable terminal, the system will regularly analyze the carbonization and ablation caused by air gap discharge and give a fault assessment report based on real-time data. When the air gap discharge reaches a certain intensity or the ablation rate exceeds the safety threshold, the system will issue an early warning signal to remind the operation and maintenance personnel to take preventive measures in advance.

[0107] Effects and benefits:

[0108] Prevent major failures: Through early monitoring and evaluation of air gap defects and ablation behavior in the cable terminal head, hidden dangers can be discovered and countermeasures can be taken in time to prevent serious power failures caused by insulation failure of the cable terminal.

[0109] Extending cable life: By predicting the ablation evolution of air gap defects, the operation and maintenance team can carry out targeted local repairs and maintenance to avoid premature retirement of the terminal head, thereby extending the service life of the cable.

[0110] These two embodiments demonstrate the application of the present invention in different power equipment. Through accurate air gap defect monitoring and ablation judgment, the safety and reliability of power equipment are effectively improved, and the failure risk and maintenance cost are reduced.

[0111] like Figure 1 As shown, a dry-type sleeve epoxy core air gap defect development model and a carbonization ablation determination method provided by an embodiment of the present invention include the following steps:

[0112] S101, through numerical simulation, the ablation behavior of epoxy resin under external heat is studied; the finite difference method is used to simulate the heat conduction and mass loss process to reveal the behavioral characteristics of the material under high temperature environment;

[0113] S102, constructing an air gap discharge simulation model;

[0114] S103, constructing an air gap ablation calculation model.

[0115] The embodiment of the present invention provides a simulation model for constructing an air gap discharge:

[0116] For the branch where the air gap is located, the calculation formulas for the air gap capacitance Ca and the solid insulation capacitance Ca and Cb are:

[0117]

[0118] Apparent discharge charge of insulator

[0119]

[0120] The starting discharge voltage is:

[0121]

[0122] U CB =E i ·h (4)

[0123] Where S is the equivalent area, d is the equivalent thickness, r is the air gap radius, and B is a constant related to the gas in the air gap. When the air gap is air, B = 8.6 (Pa·m) 1 / 2 , δ is the air gap thickness parallel to the electric field direction.

[0124] The relative dielectric constant ε of the solid insulating medium r =4.65, vacuum dielectric constant ε0 = 8.85×10 -12 F / m, the air gap radii are 0.1mm, 0.25mm, and 0.5mm respectively, and the air pressure in the air gap is p=1×10 5 Pa, since the sampling position is located near the outer surface of the core, where the potential is low, the external voltage is set to Um = 10kV, f = 50Hz; the electric field intensity Ei and the initial discharge voltage Ui corresponding to the start of discharge can be obtained;

[0125] The calculation formula of discharge repetition rate is as follows:

[0126]

[0127] Where, f is the frequency of the externally applied voltage.

[0128] U m --Peak value of applied voltage

[0129] U CB -- Breakdown voltage of air gap

[0130] Assume that there are m discharges in the measurement time T, and the product of the apparent discharge charge and the instantaneous value of the applied voltage corresponding to each discharge is q1ut1, q2ut2, ..., qmutm respectively, then

[0131]

[0132] The air gap ablation calculation model provided by the embodiment of the present invention is as follows:

[0133] The heat conduction equation can be expressed as:

[0134]

[0135] Among them, T is temperature, k is heat transfer coefficient, q is heat, ρ is density, and Cp is specific heat capacity.

[0136] Pyrolysis and oxidation reactions occur at high temperatures, resulting in mass loss of the material. The rate of the ablation reaction can be described by the Arrhenius equation:

[0137]

[0138] The mass balance equation of the surface chemical element k without considering the mechanical erosion of the material is as follows:

[0139]

[0140] Wherein, mc: ablation mass flow rate; mf: liquid phase mass loss flow rate; jkw: element k diffusion mass flow rate on the wall; (ρv): ejection gas mass flow rate; Ykc, Ykw, Ykf: represent the mass concentration of element k in ablation, diffusion and liquid layer loss, respectively;

[0141] Thermochemical equilibrium reaction equation

[0142]

[0143] The chemical equilibrium constant expression of the equation is:

[0144]

[0145] Among them, Kp: represents the equilibrium constant of the chemical reaction, Pj represents the partial pressure of the gas product, and Pk represents the partial pressure of the gas reactant; the coefficient Ai represents the fact that each condensed phase component shares the material ablation surface, that is, the contact area between each condensed phase component and the gas phase component is limited and the size of the contact area is related to its molar fraction on the material ablation surface; therefore:

[0146]

[0147] The sum of the partial pressures Pi of the gas components is equal to the total pressure P0, that is:

[0148]

[0149] The reaction equation involves four elements, C, H, O, and N; therefore, a nonlinear closed equation system with 17 unknowns, A (i = 1, 2, 3), M, Bc, and P (i = 1, 2, ..., 12) can be formed;

[0150] The material line ablation rate is calculated as follows:

[0151] v=Bq or / ρh r (13)

[0152] Where ρ is the material density, kg / m 3 ; v is the linear ablation rate, m / s; hr is the total enthalpy of the incoming flow, kg / kJ; qor is the heat flux, kW / m 2 .

[0153] like Figure 2 As shown, a dry sleeve epoxy core air gap defect development model and carbonization ablation calculation system provided by an embodiment of the present invention includes:

[0154] The simulation module is used to study the ablation behavior of epoxy resin under external heat through numerical simulation; the finite difference method is used to simulate the heat conduction and mass loss process to reveal the behavior characteristics of the material under high temperature environment;

[0155] A simulation model building module, used to build an air gap discharge simulation model;

[0156] The computational model building module is used to build an air gap ablation computational model.

[0157] Another object of the present invention is to provide a computer device, comprising a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of the dry sleeve epoxy core air gap defect development model and the carbonization and ablation determination method.

[0158] Another object of the present invention is to provide a computer-readable storage medium storing a computer program, which, when executed by a processor, enables the processor to execute the steps of the dry sleeve epoxy core air gap defect development model and carbonization ablation determination method.

[0159] Another object of the present invention is to provide an information data processing terminal, which is used to implement the dry sleeve epoxy core air gap defect development model and carbonization ablation calculation system.

[0160] The present invention is specifically implemented:

[0161] 1 The research of this invention not only provides a scientific basis for the reliable operation of power equipment, but also provides new ideas and methods for future research.

[0162] 2 Air Gap Discharge Simulation Model

[0163] like Figure 3 The figure shows a schematic diagram of the air gap discharge model in epoxy resin solid insulation. In the actual epoxy core casting and the core curing process, air gaps are generated on the core surface. As shown in the figure, many bubbles visible to the naked eye exist on the core surface due to improper process control after the epoxy core is cured and demolded. Therefore, this paper selects the air gaps existing in the epoxy resin material near the core surface to establish an air gap development model. The overall length of the model is 10mm, the width is 2mm, and the spherical air gap is located inside the epoxy resin material.

[0164] In order to study the amount and number of partial discharges in the air gap, a three-capacitor equivalent model of classic air gap discharge is proposed as shown in the figure. For the branch where the air gap is located, the calculation formulas for the air gap capacitance Ca and the solid insulation capacitance Ca and Cb are:

[0165]

[0166] When a voltage difference is generated on the insulator, the charge at both ends is generated due to this voltage difference, which is called apparent charge. The existing transient charge can be injected into the two ends of the insulator to simulate partial discharge. If the apparent voltage value is the same as the actual pulse voltage value, the charge at both ends of the insulator can be regarded as the apparent charge, and its unit is "pc". In the discharge experiment of some test products, the time of occurrence is basically the same. At this time, the maximum and most stable charge should be given priority. For example, the change between the actual discharge charge q and the corresponding voltage capacitance can be obtained from the equivalent circuit diagram. When the bubble produces partial discharge, the voltage change is UCB, and the actual discharge can be represented by the charge change at both ends of the bubble:

[0167] Apparent discharge charge of insulator

[0168]

[0169] The starting discharge voltage is the minimum voltage that can produce partial discharge. In electrical experiments, the applied voltage when the initial discharge amount is greater than or equal to a certain set value is called the starting discharge voltage. The discharge voltages of several typical insulation structures can be calculated by formula. The starting discharge voltage of small bubbles in the solid medium of a flat capacitor is:

[0170]

[0171] U CB =E i ·h (4)

[0172] Where B is a constant related to the gas in the air gap. When the air gap is air, B = 8.6 (Pa·m)1 / 2.

[0173] The relative dielectric constant ε of the solid insulating medium r =4.65, vacuum dielectric constant ε0 = 8.85×10-12F / m, air gap radii are 0.1mm, 0.25mm, 0.5mm, respectively, air pressure in the air gap p = 1×105Pa, since the sampling position is located near the outer surface of the core, the potential here is low, so the external voltage is set to Um = 10kV, f = 50Hz. The corresponding electric field strength Ei at the beginning of discharge and the starting discharge voltage Ui can be obtained.

[0174] The calculation formula of discharge repetition rate is as follows:

[0175]

[0176] Where, f is the frequency of the externally applied voltage.

[0177] Um--peak value of applied voltage

[0178] UCB--breakdown voltage of air gap

[0179] At the initial discharge voltage, the energy consumed in each discharge can be expressed by the product of the maximum or effective value of the applied voltage and the apparent discharge charge. When the external voltage is higher than the initial voltage, multiple discharges may occur at the time points in the aforementioned cycle. The energy value is equal to the product of the apparent discharge charge and the instantaneous value of the external voltage.

[0180] Assume that there are m discharges in the measurement time T, and the product of the apparent discharge charge and the instantaneous value of the applied voltage corresponding to each discharge is q1ut1, q2ut2, ..., qmutm respectively, then

[0181]

[0182] The above numerical values ​​can express the relationship between the specific discharge amount, the discharge base and the instantaneous value of the external applied discharge voltage. Compared with other forms of expression, this form of expression is more intuitive and takes into account more comprehensive influencing factors.

[0183] The discharge times and apparent discharge amount of the air gap in one cycle of AC voltage calculated according to the above formula are shown in the following table. The larger the air gap, the fewer the discharge times, the larger the discharge amount, and the larger the discharge power.

[0184] Table 1 Calculation of air gap parameters

[0185]

[0186]

[0187] 3 Air gap ablation calculation model

[0188] A basic characteristic of material ablation is the rapid increase in the temperature of the material surface and inside under the action of continuous heat flow. Therefore, the primary task of material ablation modeling is to calculate the temperature change process of the material under the action of heat flow. In order to simulate this process, an ablation model diagram as shown in the figure is established. Within a given pressure and temperature range, the control body is always in a state of chemical equilibrium. The mass diffusion of gaseous components on the surface of the material adopts the assumption of two-component equal diffusion coefficients, and the mass loss caused by thermochemical ablation is controlled by the diffusion characteristics of the surface components. Figure 4 As shown in the figure, in the initial stage of applying the external heat source, when the energy is applied to the surface of the material, part of the heat enters the interior of the material, and due to the local heat concentration, the surface temperature of the material will rise rapidly. When the temperature reaches the pyrolysis temperature of the epoxy resin, pyrolysis gas and residual carbon are generated, and the combustible gas (CO and H2) reacts with O2 to release heat on the surface.

[0189] The temperature distribution of epoxy resin in a high temperature environment is a key factor affecting its ablation behavior. The heat conduction equation describes the temperature change inside the material. For a one-dimensional heat conduction process, the heat conduction equation can be expressed as:

[0190]

[0191] Pyrolysis and oxidation reactions occur at high temperatures, resulting in mass loss of the material. The rate of the ablation reaction can be described by the Arrhenius equation:

[0192]

[0193] The Arrhenius equation describes the relationship between chemical reaction rate and temperature. Through this equation, the reaction rate of the material at different temperatures can be calculated, thereby predicting the mass loss of the material. The ablation reaction rate increases significantly at high temperatures because high temperatures accelerate the chemical reaction, causing the material to decompose rapidly. In this study, externally applied heat is the main driving force that triggers the ablation process. The externally applied heat is transferred to the interior of the material through heat conduction, causing the material temperature to rise, and when it reaches the ablation temperature, it triggers thermal decomposition and oxidation reactions.

[0194] The simulation uses the MATLAB program. First, the thermophysical parameters of the material, external heat, initial temperature, ablation temperature, activation energy, gas constant, pre-exponential factor and other constants are defined, and the time step and space step are set. The explicit finite difference method is used for numerical calculation. This method discretizes the continuous problem in time and space, and converts the partial differential equation into an algebraic equation for solution. The sample is divided into several spatial steps, and the temperature and mass loss are calculated at each time step. The ablation behavior of the material in a high temperature environment is simulated by the heat conduction equation, Arrhenius equation and mass loss calculation formula.

[0195] The mass balance equation of the surface chemical element k without considering the mechanical erosion of the material is as follows:

[0196]

[0197] Wherein, mc: ablation mass flow rate; mf: liquid phase mass loss flow rate; jkw: wall diffusion mass flow rate of element k; (ρv): ejected gas mass flow rate; Ykc, Ykw, Ykf: represent the mass concentration of element k in ablation, diffusion and liquid layer loss, respectively.

[0198] Thermochemical equilibrium reaction equation

[0199]

[0200] The chemical equilibrium constant expression of the equation is:

[0201]

[0202] Among them, Kp: represents the equilibrium constant of the chemical reaction, Pj represents the partial pressure of the gas product, and Pk represents the partial pressure of the gas reactant. The coefficient Ai represents the fact that each condensed phase component shares the material ablation surface, that is, the contact area between each condensed phase component and the gas phase component is limited and the size of the contact area is related to its molar fraction on the material ablation surface. Therefore:

[0203]

[0204] The sum of the partial pressures Pi of the gas components is equal to the total pressure P0, that is:

[0205]

[0206] The reaction equation involves four elements: C, H, O, and N. Therefore, a nonlinear closed equation system with 17 unknowns, A (i = 1, 2, 3), M, Bc, and P (i = 1, 2, ..., 12), can be formed.

[0207] The Newton-Raphson algorithm with parameters is used to solve the nonlinear equation. By solving the thermochemical ablation equation, the Newton-Raphson algorithm with parameters is established in Matlab to solve the above nonlinear equation. Given the initial value of the unknown quantity, the dimensionless ablation rate at each temperature under a constant total pressure is solved after multiple iterations. The algorithm flow chart is shown below: Figure 5 As shown:

[0208] The material line ablation rate is calculated as follows:

[0209] v=Bq or / ρh r (13)

[0210] Among them, ρ is the material density, kg / m3; v is the linear ablation rate, m / s; hr is the total enthalpy of the incoming flow, kg / kJ; qor is the heat flux, kW / m2.

[0211] like Figure 6 The graph shows the change of epoxy resin ablation amount over time under the ablation time of 3600s (1h). When the external applied heat is 2.1462mW / mm2, the ablation amount reaches 1.896mm at 3600s, and the ablation rate is 0.5266μm / s under this heat. As the external applied heat gradually increases, the ablation rate gradually increases. As the air gap radius increases, the discharge amount gradually increases, resulting in a gradual increase in ablation heat, and the ablation amount, mass loss and ablation rate gradually increase.

[0212] After local discharge occurs in the air gap inside the epoxy resin, multiple discharges accumulate to generate discharge power. As the discharge power increases, the temperature inside the air gap rises. In a high temperature environment, the epoxy resin material will undergo ablation. This paper studies the ablation behavior of epoxy resin under external heat application through numerical simulation. Using the MATLAB simulation environment, the program uses the finite difference method to simulate the heat conduction and mass loss process. Material ablation will apply a continuous heat flow on the surface, and the heat flow will be conducted to the inside of the material, causing the surface and internal temperature of the material to rise. Once the epoxy resin reaches the stagnation temperature under the influence of the external heat source, the material will ablate, and the temperature increase causes the material to undergo a chemical reaction to generate gas phase products, resulting in the removal of the material surface and exposing the internal material, that is, the material continuously generates a new surface. The study of the ablation behavior of epoxy resin materials is helpful to deeply reveal the defect evolution law and insulation performance damage mechanism of the epoxy core of the dry bushing under complex working conditions.

[0213] Figure 3 , 4 is a schematic diagram of the model. Figure 5 Calculate the program flow. Figure 6 This is a data graph of ablation calculation results.

[0214] It should be noted that the embodiments of the present invention can be implemented by hardware, software, or a combination of software and hardware. The hardware part can be implemented using dedicated logic; the software part can be stored in a memory and executed by an appropriate instruction execution system, such as a microprocessor or dedicated design hardware. It can be understood by a person of ordinary skill in the art that the above-mentioned devices and methods can be implemented using computer executable instructions and / or contained in a processor control code, such as a carrier medium such as a disk, CD or DVD-ROM, a programmable memory such as a read-only memory (firmware), or a data carrier such as an optical or electronic signal carrier. Such code is provided on the carrier medium. The device and its modules of the present invention can be implemented by hardware circuits such as very large-scale integrated circuits or gate arrays, semiconductors such as logic chips, transistors, etc., or programmable hardware devices such as field programmable gate arrays, programmable logic devices, etc., can also be implemented by software executed by various types of processors, and can also be implemented by a combination of the above-mentioned hardware circuits and software, such as firmware.

[0215] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principle of the present invention should be covered by the protection scope of the present invention.

Claims

1. A dry-type sleeve epoxy core air gap defect development model and carbonization ablation determination method, characterized in that: The following steps are involved: S101: The ablation behavior of epoxy resin when external heat is applied is studied through numerical simulation. The finite difference method is used to simulate the heat conduction and mass loss process to reveal the behavioral characteristics of the material under high temperature environment. S102: Construct an air gap discharge simulation model to analyze the electric field distribution and discharge behavior in the air gap; S103: Construct an air gap ablation calculation model, and calculate the ablation of epoxy resin and material loss by combining air gap discharge and heat conduction characteristics.

2. The method according to claim 1, characterized in that: In step S101, the thermal degradation process of the epoxy resin material in a high temperature environment is simulated by the finite difference method to calculate the ablation depth, degradation rate and mass loss.

3. The method according to claim 1, characterized in that: The construction of the air gap discharge simulation model in step S102 includes the following contents: Use the air gap capacitance formula to calculate the air gap capacitance and solid insulation capacitance; The discharge electric field strength and discharge starting voltage are analyzed through simulation.

4. The method according to claim 1, characterized in that: In step S102, the discharge repetition rate is calculated based on the externally applied voltage frequency, the externally applied voltage peak value and the air gap breakdown voltage.

5. The method according to claim 1, characterized in that The air gap ablation calculation model in step S103 is calculated by the following steps: Use the heat conduction equation to calculate the temperature distribution of the material; The ablation rate is evaluated based on the pyrolysis and oxidation reaction rates, as well as the material mass conservation equation.

6. The method according to claim 1, characterized in that In step S103, the linear ablation rate of the material is calculated based on the material density, the total enthalpy of the incoming flow and the heat flux density.

7. The dry-type sleeve epoxy core air gap defect development model and carbonization ablation determination method as claimed in claim 1, characterized in that: The air gap discharge simulation model is constructed as follows: For the branch where the air gap is located, the calculation formulas for the air gap capacitance Ca and the solid insulation capacitance Ca and Cb are: Apparent discharge charge of insulator The starting discharge voltage is: U CB =E i h (4) Where B is a constant related to the gas in the air gap. When the air gap is air, B = 8.6 (Pa·m)1 / 2. The relative dielectric constant ε of the solid insulating medium r =4.65, vacuum dielectric constant ε0 = 8.85 × 10-12 F / m, air gap radii are 0.1 mm, 0.25 mm, 0.5 mm, respectively, air pressure in the air gap p = 1 × 105 Pa, since the sampling position is located close to the outer surface of the core, the potential here is low, so the external voltage is set to Um = 10 kV, f = 50 Hz; the electric field intensity Ei corresponding to the start of discharge and the starting discharge voltage Ui can be obtained; The calculation formula of discharge repetition rate is as follows: Where, f is the frequency of the externally applied voltage. Um--peak value of applied voltage UCB--breakdown voltage of air gap Assume that there are m discharges in the measurement time T, and the product of the apparent discharge charge and the instantaneous value of the applied voltage corresponding to each discharge is q1ut1, q2ut2, ..., qmutm respectively, then 8. The dry-type sleeve epoxy core air gap defect development model and carbonization ablation determination method as claimed in claim 1, characterized in that: The air gap ablation calculation model is constructed as follows: The heat conduction equation can be expressed as: Pyrolysis and oxidation reactions occur at high temperatures, resulting in mass loss of the material. The rate of the ablation reaction can be described by the Arrhenius equation: The mass balance equation of the surface chemical element k without considering the mechanical erosion of the material is as follows: Wherein, mc: ablation mass flow rate; mf: liquid phase mass loss flow rate; jkw: element k diffusion mass flow rate on the wall; (ρv): ejection gas mass flow rate; Ykc, Ykw, Ykf: represent the mass concentration of element k in ablation, diffusion and liquid layer loss, respectively; Thermochemical equilibrium reaction equation The chemical equilibrium constant expression of the equation is: Among them, Kp: represents the equilibrium constant of the chemical reaction, Pj represents the partial pressure of the gas product, and Pk represents the partial pressure of the gas reactant; the coefficient Ai represents the fact that each condensed phase component shares the material ablation surface, that is, the contact area between each condensed phase component and the gas phase component is limited and the size of the contact area is related to its molar fraction on the material ablation surface; therefore: The sum of the partial pressures Pi of the gas components is equal to the total pressure P0, that is: The reaction equation involves four elements, C, H, O, and N; therefore, a nonlinear closed equation system with 17 unknowns, A (i = 1, 2, 3), M, Bc, and P (i = 1, 2, ..., 12) can be formed; The material line ablation rate is calculated as follows: v=Bq or / ρh r (13) Where ρ is the material density, kg / m 3 ; v is the linear ablation rate, m / s; hr is the total enthalpy of the incoming flow, kg / kJ; qor is the heat flux, kW / m 2 .

9. A system for calculating the air gap defect development and carbonization ablation of dry sleeve epoxy core, characterized in that: The system comprises: Numerical simulation module, used to study the ablation behavior of epoxy resin under externally applied heat, simulating the heat conduction and mass loss process based on the finite difference method (FDM) to reveal the behavioral characteristics of the material under high temperature environment; Air gap discharge simulation module, used to build an air gap discharge model and simulate the electric field distribution and discharge behavior in the air gap; The air gap ablation calculation module is used to combine air gap discharge simulation and heat conduction simulation to calculate the ablation of epoxy resin and material loss.

10. The system according to claim 9, characterized in that The numerical simulation module is further used to simulate the thermal decomposition, ablation depth, degradation rate and mass loss of epoxy resin materials in a high temperature environment by finite difference method.

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