Method for improving transient temperature distribution of distribution network lightning arrester based on inserted aluminum gasket

Abstract

The invention provides a distribution network lightning arrester transient temperature distribution improvement method based on insertion of an aluminum gasket, and belongs to the technical field of electrical equipment, and the method comprises the steps: constructing a lightning arrester three-dimensional model in simulation software; constructing the lightning arrester conductivity of the coupling temperature; constructing a lightning stroke simulation model of the lightning arrester; lightning stroke transient temperature distribution of the lightning arrester is obtained, and a lightning stroke comparison result before and after addition of the aluminum gasket is obtained; constructing an aluminum gasket thickness-position set; and obtaining the position-thickness optimization relation of the aluminum gasket, constructing a genetic algorithm model according to the aluminum gasket thickness-position set, and obtaining the optimal aluminum gasket thickness based on the position. The method has the advantages that the temperature change of the ZnO valve plate of the lightning arrester under the lightning impulse is obtained, and the transient temperature distribution of the lightning arrester during the lightning impulse is obtained by using the temperature distribution coefficient; comparing the transient temperature distribution of the lightning arrester before and after adding the aluminum gasket to confirm that the temperature distribution of the lightning arrester can be optimized by adding the aluminum gasket; therefore, the method for introducing the aluminum gasket between the lightning arrester valve plates is provided.

Description

Technical Field

[0001] The invention belongs to the technical field of electrical equipment, and in particular relates to a method for improving transient temperature distribution of a distribution network arrester based on inserting an aluminum gasket. Background Art

[0002] Zinc oxide arresters are widely used in power systems to limit operating or lightning overvoltages and protect the safe operation of power equipment due to their excellent nonlinear volt-ampere characteristics and good current-carrying capacity. Arrester consists of zinc oxide resistors, insulating elements, porcelain jackets or composite jackets, among which zinc oxide resistors are the core components. They are made of zinc oxide and a variety of metal oxides and have good nonlinear volt-ampere characteristics. At normal operating voltage, the current flowing through the arrester is extremely small; when overvoltage acts, the arrester resistance drops sharply, discharging the overvoltage energy to achieve a protective effect.

[0003] In recent years, the climate dividing line has shown a trend of moving northward, lightning activities have become more frequent, and the failure rate of distribution network arresters has shown an upward trend. According to statistics, the main cause of distribution network arrester failure is the aging of valve plates or even thermal collapse due to excessive heat accumulation during lightning intrusion.

[0004] In practical applications, due to the insufficient actual current-carrying capacity (ability to absorb lightning energy) of the lightning arrester, explosions and protection failures often occur. On the one hand, this is because lightning currents often have multiple impacts, and the safety margin of the lightning arrester used is not high enough; on the other hand, it is because the lightning arrester ages and its performance deteriorates. Therefore, it is necessary to obtain the transient temperature distribution of the lightning arrester during lightning impact and optimize the lightning arrester according to the transient temperature distribution. Summary of the invention

[0005] The technical problem to be solved by the present invention is to solve the problem of local overheating of a lightning arrester when it is struck by lightning, and to address the shortcomings of the prior art, a method for improving the transient temperature distribution of a distribution network lightning arrester based on inserting an aluminum gasket that can alleviate local overheating is provided. To solve the above technical problems, the technical solution adopted by the present invention is: constructing a three-dimensional model of the lightning arrester in simulation software, and setting the parameters of the three-dimensional model of the lightning arrester; constructing the conductivity of the lightning arrester coupled with temperature; constructing a lightning strike simulation model of the lightning arrester; obtaining the transient temperature distribution of the lightning arrester, and obtaining the comparison results of the lightning strike before and after adding the aluminum gasket; adjusting the thickness and position of the aluminum gasket to simulate and construct an aluminum gasket thickness-position set; obtaining the optimal relationship between the position and thickness of the aluminum gasket through the transient temperature distribution of the lightning arrester, and constructing a genetic algorithm model according to the aluminum gasket thickness-position set to obtain the optimal aluminum gasket thickness based on the position;

[0006] Furthermore, the method of constructing a three-dimensional model of a lightning arrester in a simulation software includes:

[0007] Constructing a two-dimensional structural model in the simulation software, and constructing a three-dimensional structural model based on the two-dimensional structural model;

[0008] The simplified three-dimensional structural model of the arrester zinc oxide valve plate group and silicone rubber sheath is retained.

[0009] Furthermore, the parameters of the arrester 3D model include:

[0010] Resistor parameters: thermal conductivity k is 26W / m·K; normal pressure heat capacity C is 520J / kg·K; relative dielectric constant ε is 700; density ρ is 5500kg / m 3 ;

[0011] Aluminum gasket parameters: conductivity d is 4×10 7 S / m; thermal conductivity k() is 217.7W / m·K; heat capacity C at normal pressure is 883J / kg·K; relative dielectric constant ε is 100000; density ρ is 2787kg / m 3 ;

[0012] Silicone rubber parameters: conductivity d is 10 -16 S / m; thermal conductivity k is 0.25W / m·K; heat capacity C at normal pressure is 880J / kg·K; relative dielectric constant ε is 4; density is 1500kg / m 3 ;

[0013] Hardware parameters: conductivity d is 5.998×10 7 S / m; thermal conductivity k is 237W / m·K; heat capacity C at normal pressure is 885J / kg·K; relative dielectric constant ε is 10 18 ; Density ρ is 2800kg / m 3 .

[0014] Furthermore, the Arrhenius equation is constructed:

[0015]

[0016] Where: k is the reaction rate constant; A is the pre-factor or frequency factor, which represents the maximum reaction rate constant at infinitely high temperature; E a is the activation energy, in J / mol, i.e., the minimum energy required for the reaction to occur; R is the ideal gas constant; T is the absolute temperature, in Kelvin, K;

[0017] Construct the Arrhenius equation for the variation of conductivity with temperature:

[0018]

[0019] Where: σ is the conductivity of the material at temperature T; σ0 is the conductivity of the material at infinitely high temperature; Ea It is the activation energy required for a carrier to cross an energy level or transition;

[0020] The parameter settings of the conductivity of the zinc oxide valve sheet changing with temperature are obtained through the Arrhenius equation of the conductivity changing with temperature.

[0021] Furthermore, the method for constructing a lightning arrester lightning strike simulation model includes:

[0022] Constructing the electrothermal coupling multiphysics of the arrester:

[0023] Integrate electrostatic field analysis, solid heat conduction and coupled multi-physics field calculation modules to simulate and analyze the heating of arrester resistors; in the electrostatic field module, set the application position of the impulse current, the grounding position and the waveform characteristics of the impulse current; in the solid heat transfer module, define the resistor as a heat source and adjust the heat exchange rate between the arrester and the outside world to the preset value;

[0024] The Joule heat generated by the current is as follows:

[0025]

[0026] Q e =J.E

[0027] The heat transfer equation is as follows:

[0028]

[0029] is the divergence of the current density, σ is the conductivity, Je, Qj and v are the partial derivatives of the negative space charge density with time, Je is the additional current determined by the thermoelectric effect and the photoelectric effect, is the gradient of the potential V, J is the current density; E is the electric field intensity; D is the electric displacement;

[0030] ρ represents the material density; C p represents constant pressure heat capacity; T represents material temperature; q represents heat flux; Q e represents the heat source, t is the time, is the temperature gradient, is the divergence of heat flux, K is the thermal conductivity of the material;

[0031] Construct a simulated lightning excitation source:

[0032] Set the applied current in the electric field module of the simulation software and use the impulse function to simulate the lightning current waveform:

[0033]

[0034] I mis the peak value of lightning current; η is the current correction factor; n is the current steepness factor; τ1 is the wave head time constant; τ2 is the wave tail time constant

[0035] In the simulation software, adjust the lightning current waveform to the preset value to simulate the transient process of the arrester when it is struck by lightning; the relationship between the lightning strike probability and the lightning current amplitude is expressed as:

[0036]

[0037] Where: I is the lightning current amplitude, kA; P is the probability that the lightning current amplitude is greater than or equal to I;

[0038] The simulation setting value of the lightning current amplitude is obtained from the relationship between the lightning strike probability and the lightning current amplitude.

[0039] Furthermore, the method for obtaining the transient temperature distribution of the lightning arrester includes:

[0040] The transient heat energy E caused by the lightning current impulse absorbed by MOA is expressed as;

[0041]

[0042] u is the residual voltage, the unit is V; i is the impulse current, the unit is A; t0 is the current duration, the unit is s;

[0043] The relationship between the temperature rise ΔT of the arrester valve and the injected energy E is:

[0044] Define u(t) as the terminal voltage of the arrester at the moment of lightning current impact, i(t) represents the current flowing through the arrester body at that moment; parameter t0 represents the duration of the arrester to withstand the lightning current impact; assume that the ZnO valve plate completely absorbs the lightning current energy; according to the principle of conservation of energy, the temperature change of the ZnO valve plate is directly related to the energy it absorbs, and so on:

[0045]

[0046] C is the specific heat capacity of ZnO valve plate; m i is the mass of its ith piece; ΔT i is the temperature rise change on the resistor valve plate, in K;

[0047] The temperature distribution coefficient is used to characterize the uniformity of temperature distribution, which is expressed as:

[0048]

[0049] α Temperature distribution coefficient; σ T Standard deviation of temperature; T av The average value of temperature;

[0050] Methods for obtaining lightning strike comparison results before and after adding aluminum spacers include:

[0051] Compare the temperature distribution before and after adding the aluminum gasket to obtain the result of whether adding the aluminum gasket can optimize the temperature distribution of the lightning arrester.

[0052] Furthermore, the optimal relationship between the position and thickness of the aluminum gasket is obtained through the transient temperature distribution of the lightning arrester:

[0053] The transient temperature distribution law is obtained by the transient temperature distribution of the lightning arrester. Assume that the middle position of the arrester valve W (N-1) / 2 The temperature is the maximum temperature, denoted as T max , as the sample reference variable; β is obtained from the temperature distribution uniformity characterization formula and the temperature change of the ZnO valve plate and the energy absorbed by it. The relationship between thickness and position is expressed as:

[0054]

[0055] H i is the thickness of the aluminum gasket at position i; β is the correction coefficient; W i is the location of the aluminum gasket; Tmax is the maximum temperature of the arrester, T i is the valve center temperature at position i; T av is the overall average temperature of the arrester; h is the thickness of the aluminum gasket, in mm.

[0056] Furthermore, a genetic algorithm model is constructed according to the aluminum gasket thickness-position set, and a method for obtaining an optimal aluminum gasket thickness based on position includes:

[0057] Taking the optimization relationship between position and aluminum gasket thickness as the objective function, the temperature obtained by the aluminum gasket thickness-position set simulation is processed as follows:

[0058] 1) Encoding weights and thresholds:

[0059] The population is initialized, the aluminum gasket thickness weight and threshold in the aluminum gasket thickness-position set fluctuate in the interval [H1, H2], and the i-th network weight s i And the corresponding unsigned number H i The mapping relationship is:

[0060]

[0061] Where n is the length of the individual;

[0062] 2) Evaluate the fitness value of the individual:

[0063] The individual fitness f(i) in the population is:

[0064]

[0065] In the formula, It represents the value of the jth output position of the kth sample data under the action of the i-th individual. is the desired output value, l is the number of training samples, i=1,2…M, M is the population size;

[0066] 3) Crossover and mutation:

[0067] A Crossover: After fitness evaluation, select two individuals for partial gene exchange to obtain the crossover probability:

[0068]

[0069] Where k1 and k2 are constants in [0,1], f c is the fitness value of the two crossed individuals with the larger value, f max is the maximum fitness value in the population, f avg is the average fitness value of the population;

[0070] B mutation: Use alleles to replace specific gene values ​​in the individual coding string to develop new individuals. The probability of individual mutation is:

[0071]

[0072] Where k3 and k4 are constants in [0,0.5], f m is the fitness value of the mutant individual string;

[0073] The aluminum gasket thickness value of the aluminum gasket thickness-position set is substituted into the genetic algorithm model to obtain the optimal solution of the aluminum gasket thickness in the aluminum gasket thickness-position set.

[0074] Compared with the prior art, the present invention has the following beneficial effects:

[0075] 1. By constructing the transient heat energy expression caused by MOA absorbing lightning current impulse and the temperature change expression of ZnO valve plate, the temperature change of ZnO valve plate of lightning impulse arrester is obtained, and the transient temperature distribution of lightning arrester during lightning impulse is obtained by using the temperature distribution coefficient;

[0076] The transient temperature distribution of the arrester before and after adding the aluminum gasket was compared to confirm that adding the aluminum gasket can optimize the temperature distribution of the arrester;

[0077] Based on this, a method of introducing aluminum gaskets between valve plates of lightning arresters is proposed to improve the transient temperature distribution characteristics of lightning arresters. At the same time, the key influencing factors of aluminum gaskets are analyzed and optimized, and the optimal aluminum gasket thickness based on position is calculated to ensure the thermal stability of lightning arresters under lightning impact and the reliability of long-term operation.

[0078] 2. Through the calculation of the model example, when the aluminum gasket is applied between the two valve plates, the temperature distribution reaches the best when the thickness from top to bottom is 3.22mm, 4.33mm, and 2.82mm. The maximum temperature of the valve plate is 123℃, which is 6.5% lower than that of the traditional arrester without aluminum gasket. The uniformity of temperature distribution is improved by 36.36%. The results provide a new method for improving the operational reliability of distribution network arresters. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0080] Figure 1 : Schematic diagram of the geometric model structure of the ZnO arrester in the present invention;

[0081] Figure 2 : Schematic diagram of aluminum gasket thickness after genetic algorithm optimization in the present invention;

[0082] Figure 3 : Schematic diagram of temperature distribution of aluminum gasket thickness at different positions in the present invention;

[0083] Figure 4 : Schematic diagram of the process of optimizing transient temperature distribution of the arrester and inserting the aluminum gasket in the present invention; DETAILED DESCRIPTION

[0084] In order to better understand the present invention, the content of the present invention is further clearly described below in conjunction with the embodiments and the accompanying drawings, but the protection content of the present invention is not limited to the following embodiments. In the following description, a large number of specific details are provided to provide a more thorough understanding of the present invention. However, it is obvious to those skilled in the art that the present invention can be implemented without one or more of these details.

[0085] Embodiment 1: A method for improving transient temperature distribution of a distribution network arrester based on inserting an aluminum gasket in this embodiment;

[0086] MOA transient temperature field calculation model based on electrical-thermal coupling

[0087] 1.1 MOA finite element simulation model

[0088] In view of the axisymmetric characteristics of the arrester, this embodiment uses the finite element analysis method. On the basis of ensuring the accuracy of the calculation results, the two-dimensional structural model is rotated to form a three-dimensional model to improve the efficiency and convergence of the multi-physics field coupling solution. Table 1 lists the size parameters of the key structures of the arrester in detail.

[0089] Table 1 Main parameters of the three-dimensional geometric model of zinc oxide arrester

[0090]

[0091]

[0092] The internal structure of the ZnO arrester is relatively complex, but the main factors affecting the transient temperature distribution of the arrester are the internal zinc oxide valve plate group and the coated silicone rubber sheath. Therefore, when simulating and modeling, the irrelevant parts are ignored. The geometric model of the zinc oxide arrester is simplified accordingly, as follows:

[0093] (1) The surfaces of all components are considered to be smooth and flawless, and there are no unevenness or gaps in the contact surfaces between components;

[0094] (2) The ZnO resistor is wrapped in a layer of epoxy resin tube, and the heat dissipation characteristics of this structure are similar to those of silicone rubber. In the simulation calculation, it is regarded as a simplified single entity;

[0095] (3) The force on the insulating tube mainly comes from the lateral deformation of the ZnO resistor, while the metal components at the top and bottom (such as the top cover, fixing screws, etc.) have little effect on it. Therefore, in the simulation calculation, it is treated as a whole.

[0096] like Figure 1 As shown, a simplified axial cross-section diagram and three-dimensional structural model of a gapless zinc oxide arrester are shown.

[0097] The arrester model is mainly composed of three components: ZnO resistor, hardware and silicone rubber shed. The material inside the component is evenly distributed, the physical properties in all directions are the same, and the material parameters are set to standard conditions (temperature is 20℃, pressure is 1.03kPa).

[0098] 1.2 Physical field control equations, boundary conditions and excitation sources

[0099] When conducting a large current impact test, the thermal effect of the ZnO arrester is mainly caused by Joule heat, especially the heating phenomenon of the resistor part is more significant. In the simulation model, the present invention integrates two calculation modules: electrostatic field analysis, solid heat conduction, and multi-physics field coupling to simulate and analyze this phenomenon.

[0100] In the electrostatic field module, the application position of the impulse current, the grounding position, and the waveform characteristics of the impulse current are set. In the solid heat transfer module, the resistor is defined as a heat source and the heat exchange rate between the arrester and the outside world is set. The heat exchange rate is usually in the range of 5 to 10 W / m 2 K, in the simulation of this arrester, is taken as 5W / m 2 ·K.

[0101] The simulation calculation formula is as follows:

[0102]

[0103]

[0104] is the divergence of the current density, σ is the conductivity, Je, Qj and v are the partial derivatives of the negative space charge density with time, Je is the additional current determined by the thermoelectric effect and the photoelectric effect, is the gradient of the potential V, J is the current density; E is the electric field intensity; D is the electric displacement;

[0105] ρ represents the material density; C p represents constant pressure heat capacity; T represents material temperature; q represents heat flux; Q e represents the heat source, t is the time, is the temperature gradient, is the divergence of heat flux, K is the thermal conductivity of the material;

[0106] Formula (1) is the Joule heat generated by the current, and formula (2) is the heat transfer equation.

[0107] The applied current is set in the electric field module. Usually, the impulse function is used to simulate the lightning current waveform in simulation, as shown in formula (3):

[0108]

[0109] I m is the peak value of lightning current; η is the current correction factor; n is the current steepness factor; τ1 is the wave head time constant; τ2 is the wave tail time constant

[0110] In order to simulate the transient process of the arrester when it is struck by lightning, the standard lightning current waveform, 2.6 / 50μs, is selected. According to the observation results in my country, the relationship between the lightning strike probability and the lightning current amplitude can be obtained by formula (4).

[0111]

[0112] Where: I is the lightning current amplitude, kA; P is the probability that the lightning current amplitude is greater than or equal to I.

[0113] From formula (4), we can know that when lightning strikes, the probability of a lightning current with an amplitude not less than 50kA is 27%; the probability of a lightning current with an amplitude not less than 88kA is 10%. In order to conduct a stricter verification, the lightning current amplitude set in the simulation is 88kA.

[0114] 1.3 Key parameter settings

[0115] The parameter settings of the zinc oxide valve sheet are mainly shown in Table 2.

[0116] Table 2 Parameters of existing ZnO resistors

[0117]

[0118]

[0119] The parameters of the jacket and accessories are shown in Table 3.

[0120] Table 3 Parameters of jacket and accessories

[0121]

[0122] When the arrester is subjected to a large current shock, in the steady-state analysis, the degradation of the valve plate is mainly reflected in the change of leakage current. In the transient process of the action, due to the large current shock, the volt-ampere relationship of the arrester is regarded as a conducting state. The temperature rises suddenly, and the conductivity of the valve plate increases exponentially with the change of temperature. This is a process that cannot be ignored in the analysis of transient temperature distribution. Therefore, in order to more accurately simulate the transient temperature rise process of the arrester under lightning strike, it is necessary to use the conductivity parameter setting coupled with temperature.

[0123] The Arrhenius equation is an empirical equation that describes the exponential relationship between the conductivity of a substance and the temperature. It is often used to react as shown in formula (5):

[0124]

[0125] Where: k is the reaction rate constant; A is the pre-factor or frequency factor, which represents the maximum reaction rate constant at infinitely high temperature and is also related to the frequency and collision probability of the reactants; E a is the activation energy (in J / mol), which is the minimum energy required for the reaction to occur; R is the ideal gas constant; T is the absolute temperature (in Kelvin, K)

[0126] In the context of the variation of conductivity with temperature, the Arrhenius equation is optimized to:

[0127]

[0128] Where: σ is the conductivity of the material at temperature T; σ0 is the conductivity of the material at infinitely high temperature; E a It is the activation energy required for a charge carrier (such as an electron or a hole) to cross an energy level or transition.

[0129] The parameter setting of the conductivity of the zinc oxide valve sheet changing with temperature can be obtained by formula (6), as shown in formula (7).

[0130] (1.785×10 -7 )×e (0.027×(T+273.15)) (7)

[0131] By setting the conductivity for temperature changes, the transient temperature field simulation when the arrester is in action can be made more accurate.

[0132] 1.4 Calculation method

[0133] The transient heat energy caused by the lightning current impulse absorbed by MOA is expressed as;

[0134]

[0135] u is the residual pressure, V; i is the impact current, A; t0 is the current duration, s; the relationship between the temperature rise ΔT (in K) of the valve plate and the injected energy E is:

[0136] In formula 8, u(t) is defined as the terminal voltage of the arrester at the moment of lightning current impact, and i(t) represents the current flowing through the arrester body at that moment. Parameter t0 represents the duration of the arrester withstanding the lightning current impact. Given that the resistivity of the ZnO valve plate is much higher than other components in the arrester, such as hardware, the absorption of lightning current energy by other components can be ignored. Therefore, it is assumed that the ZnO valve plate completely absorbs the energy of the lightning current. According to the principle of conservation of energy, the temperature change of the ZnO valve plate is directly related to the energy it absorbs, as follows:

[0137]

[0138] C is the specific heat capacity of ZnO valve plate; m i is the mass of its ith piece; ΔT i is the temperature rise change on the resistor valve plate.

[0139] This paper uses the temperature distribution coefficient to characterize the uniformity of temperature distribution. It is obtained by calculating the ratio of the temperature variation in a specific spatial region to the average temperature in the region. The smaller the temperature distribution coefficient, the more uniform the temperature distribution; the larger the temperature distribution coefficient, the more uneven the temperature distribution. As shown in formula (10):

[0140]

[0141] α Temperature distribution coefficient; σ T Standard deviation of temperature; T av The average value of the temperature.

[0142] 2 Aluminum gasket application strategy based on genetic optimization algorithm

[0143] In the multi-physics finite element analysis of transient temperature distribution of zinc oxide arrester under lightning impulse current, the previous article simulated and theoretically analyzed aluminum gaskets with different thicknesses. In this section, it is necessary to apply aluminum gaskets of different thicknesses at different positions, and optimize the thickness through genetic optimization algorithm to achieve the best temperature rise limitation effect.

[0144] 2.1 Calculation method

[0145] The main factor affecting the transient temperature rise process of the arrester is the thickness of the aluminum gasket at different positions, that is, it is mainly affected by the following two dependent variables:

[0146] 1. Aluminum gasket thickness (H): The range of aluminum gasket thickness needs to be limited. In order to make the specifications of the arrester not exceed twice of itself, the thickness of the aluminum gasket should be less than or equal to the thickness of the valve plate. Therefore, the thickness of the aluminum gasket should be controlled within [1mm, 15mm].

[0147] 2. Aluminum gasket application position (W): The position where the aluminum gasket is applied will change its temperature distribution, so the application position can reduce the heat concentration area.

[0148] Aluminum gaskets are added between two valve plates. The number of valve plates is 1, 2, 3, ..., N from top to bottom; the number of aluminum gaskets is 1, 2, 3, ..., N-1; the thickness of the aluminum gasket is recorded as: H1, H2, H3, ..., H N-1 ; The positions of the aluminum gaskets are recorded as: W1, W2, W3, ..., W N-1 By training samples of the maximum temperature values ​​under aluminum gaskets of different thicknesses, the optimal aluminum gasket thickness at different positions is finally obtained.

[0149] The genetic optimization algorithm in MATLAB was used to establish the objective function for the maximum temperature, the thickness of the aluminum gasket, and different application positions; the following is the calculation method for the thickness of the aluminum gasket at different positions.

[0150] The transient temperature distribution obtained by simulation analysis shows that the temperature in the middle of the valve plate is the highest and the temperature at both ends is lower. It can be seen that the maximum temperature appears in the middle of the valve plate. Therefore, when 1000ms is selected, the middle position W (N-1) / 2 The temperature is the maximum temperature, denoted as T max , as the sample reference variable. β is obtained from formulas (9) and (10), and the relationship between thickness and position is shown in formula (11):

[0151]

[0152] H i is the thickness of the aluminum gasket at position i; β is the correction coefficient; W i is the location of the aluminum gasket; T i is the valve center temperature at position i; T av is the overall average temperature of the arrester; Tmax is the maximum temperature of the arrester; h is the thickness of the aluminum gasket, in mm.

[0153] Therefore, the optimal relationship between the position and the thickness of the aluminum gasket is derived, which is used as the main objective function of this program. The temperature of the aluminum gaskets with different thicknesses simulated in Chapter 2 is then processed as follows.

[0154] 1) Encoding weights and thresholds.

[0155] Initialize the population, the weights and thresholds of the aluminum gasket thickness at different positions fluctuate in the interval [H1, H2], and the i-th network weight s i (or threshold) and the corresponding unsigned number H i The mapping relationship between

[0156]

[0157] Where n is the length of the individual.

[0158] 2) Evaluate the fitness value of the individual.

[0159] In the process of optimizing the network model, the fitness value of individuals in the population is an important factor affecting the inheritance of the next generation. The individual fitness f(i) is

[0160]

[0161] In the formula, i

[0162] z kj represents the value of the jth output position of the kth sample data under the action of the ith individual, t i kj is the desired output value, l is the number of training samples, i=1,2…M (M is the population size).

[0163] 3) Crossover and mutation.

[0164] A Crossover: After fitness evaluation, two individuals are selected from the population for partial gene exchange, and the crossover probability is

[0165]

[0166] Where k1 and k2 are constants in [0,1], f c is the fitness value of the two crossed individuals with the larger value, f max is the maximum fitness value in the population, f avg is the average fitness value of the population.

[0167] B mutation: Use alleles at other points to replace certain specific gene values ​​in the individual coding string, thereby developing into a new individual. The probability of individual mutation is

[0168]

[0169] Where k3 and k4 are constants in [0,0.5], f m is the fitness value of the mutant individual string.

[0170] Finally, the thickness values ​​of the aluminum gaskets at different positions are substituted into the genetic algorithm model to obtain the optimal solution for the thickness of the aluminum gaskets at different positions.

[0171] 2.2 Example Calculation

[0172] This optimization object takes the model shown in Section 1 as an example, and optimizes the aluminum gasket.

[0173] The model has three zinc oxide valve plates, so there are three locations for applying aluminum gaskets, namely W1, W2, and W3 from top to bottom. The data is sorted according to the calculation method shown in Section 2.1, as shown in Table 4.

[0174] Table 4 Simulation parameters of aluminum gaskets with different thicknesses

[0175]

[0176] The above sample data is brought into the main program of the genetic algorithm. Through data iteration, the optimized aluminum gasket thickness at different positions is obtained, such as Figure 2 shown.

[0177] Based on the genetic optimization algorithm, after multiple data iterations, the optimal thickness is finally obtained as shown in Table 5.

[0178] Table 5 Optimal thickness of aluminum gasket at different positions

[0179]

[0180] The optimal aluminum gasket thicknesses at position 1, position 2, and position 3 are 3.22 mm, 4.33 mm, and 2.82 mm, respectively; and they are applied between each pair of aluminum gaskets.

[0181] Beneficial effects:

[0182] 1. By constructing the transient heat energy expression caused by MOA absorbing lightning current impulse and the temperature change expression of ZnO valve plate, the temperature change of ZnO valve plate of lightning impulse arrester is obtained, and the transient temperature distribution of lightning arrester during lightning impulse is obtained by using the temperature distribution coefficient;

[0183] The transient temperature distribution of the arrester before and after adding the aluminum gasket was compared to confirm that adding the aluminum gasket can optimize the temperature distribution of the arrester;

[0184] Based on this, a method of introducing aluminum gaskets between valve plates of lightning arresters is proposed to improve the transient temperature distribution characteristics of lightning arresters. At the same time, the key influencing factors of aluminum gaskets are analyzed and optimized, and the optimal aluminum gasket thickness based on position is calculated to ensure the thermal stability of lightning arresters under lightning impact and the reliability of long-term operation.

[0185] 2. Through transient simulation calculation, it is found that the uneven temperature distribution may lead to accelerated aging of the valve plate. Through model example calculation, when the aluminum gasket is applied between the two valve plates, the temperature distribution reaches the best when the thickness from top to bottom is 3.22mm, 4.33mm, and 2.82mm. The maximum temperature of the valve plate is 123℃, which is 6.5% lower than that of the traditional arrester without aluminum gasket. The uniformity of temperature distribution is improved by 36.36%. The results provide a new method for improving the operational reliability of distribution network arresters.

[0186] 2. The thickness of aluminum gaskets at different positions obtained through algorithm optimization. In a typical 10kV arrester, aluminum gaskets of different thicknesses are added to the zinc oxide valve column according to the data shown in Table 5. When a 10kV arrester is subjected to a 2.6 / 50μs, 88kA lightning strike, the temperature distribution at 1000ms is as follows: Figure 3 As shown in the figure, after being struck by lightning for 1000ms, the maximum temperature of the 10kV arrester is 123℃, and the temperature distribution coefficient is 0.0293. By comparing the temperature distribution of equal thickness at different positions, the overall temperature distribution of the zinc oxide valve column optimized by the genetic algorithm is more uniform, the maximum temperature is reduced by 3℃, a decrease of 2.38%, and the temperature distribution coefficient is increased by 36.1%. It can be seen that the transient temperature rise process of the 10kV arrester under lightning strike is more uniform after algorithm optimization.

[0187] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Other modifications or equivalent substitutions made to the technical solution of the present invention by ordinary technicians in the field should be included in the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for improving transient temperature distribution of distribution network arrester based on inserting aluminum gasket, characterized in that: include: Constructing a three-dimensional model of the arrester in the simulation software and setting parameters of the three-dimensional model of the arrester; Construct arrester conductivity coupled with temperature; Construct a lightning arrester lightning strike simulation model; Obtain the transient temperature distribution of the arrester after a lightning strike, and obtain the comparison results of the lightning strike before and after adding the aluminum gasket; Adjust the thickness and position of the aluminum gasket to simulate and construct the aluminum gasket thickness-position set; The optimal relationship between the position and thickness of the aluminum gasket is obtained through the transient temperature distribution of the lightning arrester. A genetic algorithm model is constructed according to the aluminum gasket thickness-position set to obtain the optimal aluminum gasket thickness based on position.

2. The method for improving transient temperature distribution of a distribution network arrester based on inserting an aluminum gasket as claimed in claim 1, characterized in that: Methods for constructing a 3D model of a lightning arrester in simulation software include: Constructing a two-dimensional structural model in the simulation software, and constructing a three-dimensional structural model based on the two-dimensional structural model; The simplified three-dimensional structural model of the arrester zinc oxide valve plate group and silicone rubber sheath is retained.

3. The method for improving transient temperature distribution of a distribution network arrester based on inserting an aluminum gasket as claimed in claim 1, characterized in that: The parameters of the arrester 3D model include: Resistor parameters: thermal conductivity k is 26W / m·K; normal pressure heat capacity C is 520J / kg·K; relative dielectric constant ε is 700; density ρ is 5500kg / m 3 ; Aluminum gasket parameters: conductivity d is 4×10 7 S / m; thermal conductivity k() is 217.7W / m·K; heat capacity C at normal pressure is 883J / kg·K; relative dielectric constant ε is 100000; density ρ is 2787kg / m 3 ; Silicone rubber parameters: conductivity d is 10 -16 S / m; thermal conductivity k is 0.25W / m·K; heat capacity C at normal pressure is 880J / kg·K; relative dielectric constant ε is 4; density is 1500kg / m 3 ; Hardware parameters: conductivity d is 5.998×10 7 S / m; thermal conductivity k is 237W / m·K; heat capacity C at normal pressure is 885J / kg·K; relative dielectric constant ε is 10 18 ; Density ρ is 2800kg / m 3 .

4. The method for improving transient temperature distribution of a distribution network arrester based on inserting an aluminum gasket as claimed in claim 1, characterized in that: Methods for constructing temperature-coupled arrester conductivity include: Construct the Arrhenius equation: Where: k is the reaction rate constant; A is the pre-factor or frequency factor, which represents the maximum reaction rate constant at infinitely high temperature; E a is the activation energy, in J / mol, i.e., the minimum energy required for the reaction to occur; R is the ideal gas constant; T is the absolute temperature, in Kelvin, K; Construct the Arrhenius equation for the variation of conductivity with temperature: Where: σ is the conductivity of the material at temperature T; σ0 is the conductivity of the material at infinitely high temperature; E a It is the activation energy required for a carrier to cross an energy level or transition; The parameter settings of the conductivity of the zinc oxide valve sheet changing with temperature are obtained through the Arrhenius equation of the conductivity changing with temperature.

5. The method for improving transient temperature distribution of a distribution network arrester based on inserting an aluminum gasket as claimed in claim 1, characterized in that: Methods for constructing a lightning arrester lightning strike simulation model include: Constructing the electrothermal coupling multiphysics of the arrester: Integrate electrostatic field analysis, solid heat conduction and coupled multi-physics field calculation modules to simulate and analyze the heating of arrester resistors; in the electrostatic field module, set the application position of the impulse current, the grounding position and the waveform characteristics of the impulse current; in the solid heat transfer module, define the resistor as a heat source and adjust the heat exchange rate between the arrester and the outside world to the preset value; The Joule heat generated by the current is as follows: Q e =J·E The heat transfer equation is as follows: ▽J is the divergence of current density, σ is the conductivity, Je, Qj and v are the partial derivatives of negative space charge density with time, Je is the additional current determined by the thermoelectric effect and the photoelectric effect, ▽V is the gradient of the potential V, J represents the current density; E represents the electric field intensity; D represents the electric displacement; ρ represents the material density; C p represents constant pressure heat capacity; T represents material temperature; q represents heat flux; Q e represents the heat source, t is the time, ▽T is the temperature gradient, ▽q is the divergence of the heat flux, and K is the thermal conductivity of the material; Construct a simulated lightning excitation source: Set the applied current in the electric field module of the simulation software and use the impulse function to simulate the lightning current waveform: I m is the peak value of lightning current; η is the current correction factor; n is the current steepness factor; τ1 is the wave head time constant; τ2 is the wave tail time constant In the simulation software, adjust the lightning current waveform to the preset value to simulate the transient process of the arrester when it is struck by lightning; the relationship between the lightning strike probability and the lightning current amplitude is expressed as: Where: I is the lightning current amplitude, kA; P is the probability that the lightning current amplitude is greater than or equal to I; The simulation setting value of the lightning current amplitude is obtained from the relationship between the lightning strike probability and the lightning current amplitude.

6. The method for improving transient temperature distribution of distribution network arrester based on inserting aluminum gaskets according to claim 1, characterized in that: Methods for obtaining lightning arrester transient temperature distribution include: The transient heat energy E caused by the lightning current impulse absorbed by MOA is expressed as; u is the residual voltage, the unit is V; i is the impulse current, the unit is A; t0 is the current duration, the unit is s; The relationship between the temperature rise ΔT of the arrester valve and the injected energy E is: Define u(t) as the terminal voltage of the arrester at the moment of lightning current impact, i(t) represents the current flowing through the arrester body at that moment; parameter t0 represents the duration of the arrester to withstand the lightning current impact; assume that the ZnO valve plate completely absorbs the lightning current energy; according to the principle of conservation of energy, the temperature change of the ZnO valve plate is directly related to the energy it absorbs, and so on: C is the specific heat capacity of ZnO valve plate; m i is the mass of its ith piece; ΔT i is the temperature rise change on the resistor valve plate, in K; The temperature distribution coefficient is used to characterize the uniformity of temperature distribution, which is expressed as: α Temperature distribution coefficient; σ T Standard deviation of temperature; T av The average value of temperature; Methods for obtaining lightning strike comparison results before and after adding aluminum spacers include: Compare the temperature distribution before and after adding the aluminum gasket to obtain the result of whether adding the aluminum gasket can optimize the temperature distribution of the arrester.

7. The method for improving transient temperature distribution of a distribution network arrester based on inserting an aluminum gasket as claimed in claim 6, characterized in that: The optimal relationship between the position and thickness of the aluminum gasket is obtained through the transient temperature distribution of the lightning arrester: The transient temperature distribution law is obtained by the transient temperature distribution of the lightning arrester. Assume that the middle position of the arrester valve W (N-1) / 2 The temperature is the maximum temperature, denoted as T max , as the sample reference variable; β is obtained from the temperature distribution uniformity characterization formula and the temperature change of the ZnO valve plate and the energy absorbed by it. The relationship between thickness and position is expressed as: H i is the thickness of the aluminum gasket at position i; β is the correction coefficient; W i is the location of the aluminum gasket; Tmax is the maximum temperature of the arrester, T i is the valve center temperature at position i; T av is the overall average temperature of the arrester; h is the thickness of the aluminum gasket, in mm.

8. The method for improving transient temperature distribution of a distribution network arrester based on inserting an aluminum gasket as claimed in claim 1, characterized in that: A genetic algorithm model is constructed according to the aluminum gasket thickness-position set, and a method for obtaining an optimal aluminum gasket thickness based on a position includes: Taking the optimization relationship between position and aluminum gasket thickness as the objective function, the temperature obtained by the aluminum gasket thickness-position set simulation is processed as follows: 1) Encoding weights and thresholds: The population is initialized, the aluminum gasket thickness weight and threshold in the aluminum gasket thickness-position set fluctuate in the interval [H1, H2], and the i-th network weight s i And the corresponding unsigned number H i The mapping relationship is: Where n is the length of the individual; 2) Evaluate the fitness value of the individual: The individual fitness f(i) in the population is: In the formula, z i kj It represents the value of the jth output position of the kth sample data under the action of the i-th individual, t i kj is the desired output value, l is the number of training samples, i=1,2…M, M is the population size; 3) Crossover and mutation: A Crossover: After fitness evaluation, select two individuals for partial gene exchange to obtain the crossover probability: Where k1 and k2 are constants in [0,1], f c is the fitness value of the two crossed individuals with the larger value, f max is the maximum fitness value in the population, f avg is the average fitness value of the population; B mutation: Use alleles to replace specific gene values ​​in the individual coding string to develop new individuals. The probability of individual mutation is: Where k3 and k4 are constants in [0,0.5], f m is the fitness value of the mutant individual string; The aluminum gasket thickness value of the aluminum gasket thickness-position set is substituted into the genetic algorithm model to obtain the optimal solution of the aluminum gasket thickness in the aluminum gasket thickness-position set.

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