Life prediction method for composite insulator core rod under electric-thermal-mechanical multi-field aging

Abstract

The present invention proposes a method for predicting the life of a composite insulator core rod under electric-thermal-mechanical multi-field aging, which comprises the following steps: conducting a multi-physical field combined aging test on the composite insulator core rod, taking aged samples with different aging intervals, and characterizing the microscopic morphology; analyzing the influence of charge energy and thermal energy on hole deformation under the combined action of electricity and heat, and obtaining the mechanical strain of the hole, the charge energy density of the hole, and the charge energy per group; adding mechanical stress to analyze the effect of the synergistic action of electricity, heat and force on the expansion of the hole; applying an electric field to obtain the charge energy of the material; calculating the volume elastic modulus of the sample through a tensile mode test; establishing a simulation model to calculate the electric field distribution on the inner wall of a single hole; using a densitometer to measure the sample density and calculate the porosity and hole radius; combining the above-mentioned use of complete fracture of the core rod as a sign of the end of life, and predicting the remaining life of the composite insulator core rod according to the relationship between the charge energy of the core rod hole and the aging time.

Description

Technical Field

[0001] The invention relates to the technical field of composite insulator life prediction, and in particular to a composite insulator core rod life prediction method under electric-thermal-mechanical multi-field aging. Background Art

[0002] Composite insulators have the advantages of light weight, excellent anti-pollution flashover performance and high mechanical strength, and are widely used in high-voltage transmission lines. However, under harsh operating conditions such as high temperature and humidity, composite insulator core rods are prone to local abnormal heating. The superposition of multiple aging stresses such as electrical, thermal, and mechanical stresses will significantly accelerate the deterioration process of the core rods, which may cause breakdown and fracture accidents under long-term operation, seriously threatening the safe and stable operation of the power system. Effectively calculating the remaining service life of composite insulators under multiple aging factors in actual operation, evaluating the operating status of composite insulators and responding to them have become the goals that researchers continue to pursue and explore. In response to the aging of composite insulators and their life prediction, domestic and foreign researchers have proposed some parameters to characterize the aging characteristics of composite insulator core rods based on the test results of the physical and chemical properties of aged composite insulator core rods, and established the relationship between some test parameters and insulator life. However, on the one hand, the composite insulator core rod aging experiments conducted at home and abroad mainly focus on the single field aging characteristics of thermal stress and multi-field aging characteristics such as electro-thermal, and there are not many reports on the combined effect of electro-thermal-mechanical stress on core rod aging; on the other hand, since the current scholars' research focus is only on the qualitative characterization of the relationship between the test parameters and the degree of aging of composite insulators, there is little research on quantitative analysis and prediction of the degree of aging and remaining service life of composite insulator core rods. Therefore, it is urgent to invent a calculation method for quantitative analysis of the remaining service life of composite insulators, quantitatively evaluate the service life of composite insulator core rods in operation, and construct a correlation mechanism between key physical parameters and service life during the aging process of composite insulator core rods.

[0003] In the past, there were insulator life assessment methods, such as a pot-type insulator life assessment method based on artificial accelerated aging test (Chinese patent document CN105203879B), which was mainly used for aging life assessment of epoxy pot-type insulators. It did not have obvious mechanical stress aging factors and only considered the impact of electrical and thermal stress on insulator life, which was not universal. Another example was a comprehensive aging status assessment system and assessment method for composite insulator materials (Chinese patent document CN116203333B), which focused on aging status assessment of composite insulators. It could only evaluate the aging status of the currently detected insulators through image recognition technology, and could not quantify the remaining service life.

[0004] In summary, studying the life prediction method of composite insulator core rod under electric-thermal-mechanical multi-field aging is of great significance for promoting the aging state and life assessment of composite insulators. Summary of the invention

[0005] The purpose of the present invention is to provide a method for predicting the life of a composite insulator core rod under electric-thermal-mechanical multi-field aging. The method of the present invention targets the accelerated degradation process caused by the superposition of multiple aging stresses such as electrical, thermal and mechanical stresses on the composite insulator core rod under actual operating conditions. An electric-thermal-mechanical multi-physical field coupled artificial accelerated aging test platform is used to carry out a multi-aging factor accelerated aging test, and characteristic parameters of the core rod samples at different aging degrees are measured. Based on the microscopic hole charge energy density, a method for predicting the life of the core rod under electric-thermal-mechanical multi-field aging is proposed. The expected service life of the core rod is calculated in combination with the measured parameters of the aging test, and the actual operating composite insulator core rod is used for comparative verification, the aging resistance characteristics and the remaining service life of the composite insulator core rod are quantitatively evaluated, and the physical correlation mechanism between the microscopic hole charge energy and the service life during the aging process of the composite insulator core rod is constructed.

[0006] The present invention is achieved by at least one of the following technical solutions.

[0007] The method for predicting the life of composite insulator core rod under electric-thermal-mechanical multi-field aging comprises the following steps:

[0008] (1) The composite insulator core rod is processed into an electro-thermal-mechanical accelerated aging sample, and the aging test temperature, applied voltage, and mechanical stress applied at both ends of the electro-thermal-mechanical accelerated aging sample are set in the aging test platform;

[0009] (2) Setting the sampling interval of the electric-thermal-mechanical combined aging test, taking aged samples with different aging intervals, and performing microscopic morphology characterization;

[0010] (3) Analyze the effects of charge energy and thermal energy on hole deformation under the combined action of electric and thermal stress, and obtain the hole mechanical strain, hole charge energy density and single group charge energy under thermal stress;

[0011] (4) adding the mechanical stress on the basis of step (3) to analyze the effect of the synergistic effect of electricity, heat and force on the hole radius and strain;

[0012] (5) Based on step (4), a dynamic thermomechanical analysis tensile mode test is performed to obtain the storage modulus at the aging test temperature as the tensile modulus, obtain the sample bulk elastic modulus, and calculate the total strain of the hole in combination with multi-physics field simulation software;

[0013] (6) Establish a finite element simulation model in the multi-physics field simulation software, and combine the total hole strain with the average field strength of a single hole to obtain the electric field distribution of the material hole;

[0014] (7) Conduct a moisture absorption test based on step (5), measure the sample density using a densitometer based on the material pore electric field distribution in step (6), and calculate the porosity;

[0015] (8) Consider the hole as a sphere and calculate the hole radius based on the porosity;

[0016] (9) On the basis of thermal-mechanical coupling, an electric field with the same direction as the mechanical stress is applied. The complete fracture of the core rod is taken as the end of life sign. The hole charge energy is used as the end of life indicator of the core rod. The relationship between the hole charge energy and the aging time is obtained, and the remaining life of the composite insulator core rod is predicted.

[0017] Furthermore, in step (1), the composite insulator core rod is processed into a dumbbell-shaped specimen as an electro-thermal-mechanical combined accelerated aging specimen; the aging test temperature of the electro-thermal-mechanical combined accelerated aging specimen is set to 178°C-182°C and the applied voltage is set to 10.45kV-10.55 kV.

[0018] Furthermore, in step (3), the mechanical strain of the hole under thermal stress , hole charge energy density and the energy of a single group charge The expressions are shown in formula (1), formula (2) and formula (3) respectively:

[0019] (1)

[0020] (2)

[0021] (3)

[0022] In the formula, N c is the number of holes per cubic meter, N m is the number of groups per hole; r 0 is the hole radius, λ is the thickness of the hole shell, K is the bulk modulus, B is the proportionality coefficient, Δ is the reactant free energy G 2 and the product free energy G 1, Δ = G 2- G 1; k is the Boltzmann constant; T is the temperature; σ em is the local charge stress, is the average field strength of a single hole, α is the electrostrictive coefficient.

[0023] Furthermore, in step (4), the electrothermal-mechanical synergistic effect has the following relationship on the hole radius and strain:

[0024] (4)

[0025] In the formula, is the hole radius under the combined thermal and mechanical action, is the mechanical strain of the hole under thermal stress, is the mechanical strain of the hole under mechanical stress, r 0 is the hole radius.

[0026] Furthermore, in step (5), the bulk elastic modulus of the sample is calculated according to the following formula: K :

[0027] (5)

[0028] In the formula, Y is the tensile modulus, μ is Poisson's ratio.

[0029] Furthermore, in step (5), the total strain of the hole is:

[0030] (6)

[0031] in is the hole radius under the combined thermal and mechanical action, is the mechanical strain of the hole under thermal stress, is the mechanical strain of the hole under mechanical stress, r 0 is the hole radius, is the total hole strain, T is the temperature, For mechanical stress.

[0032] Furthermore, in step (7), the porosity It is derived from the following formula:

[0033] (7)

[0034] In the formula, m x is the mass of the water-absorbed sample, m c is the sample mass after dehydration, ρ is the sample density.

[0035] Furthermore, in step (7), the electric-thermal-mechanical combined accelerated aging sample is placed in a heating box to be heated and dried, the sample is taken out and cooled to room temperature, the sample is taken out after being fully soaked in deionized water, wiped dry, weighed, and the mass of the water-absorbed sample is recorded.

[0036] Furthermore, in step (8), it is assumed that the number of holes per cubic meter is N c , calculate the hole radius according to the following formula :

[0037] (8)

[0038] In the formula, represents the porosity, N c is the number of holes per cubic meter.

[0039] Furthermore, in step (9), the hole charge energy for:

[0040] (9)

[0041] In the formula, is the average field strength of a single hole, α is the electrostrictive coefficient, λ is the thickness of the hole shell, r 0 is the hole radius, N m is the number of groups per hole; is the total hole strain, T is the temperature, For mechanical stress.

[0042] Compared with the existing methods, the advantages and beneficial effects of the present invention are:

[0043] (1) The present invention uses an electric, thermal and mechanical combined aging test platform to carry out a multi-stress combined aging test to explore the aging process of the composite insulator core rod under the combined action of electrical, thermal and mechanical stresses under simulated actual working conditions, which has important practical significance for promoting further research on the aging mechanism of the composite insulator core rod;

[0044] (2) Based on the charge energy density of microscopic voids, an evaluation and prediction of the electric-thermal-mechanical multi-field aging life of composite insulator core rods was proposed. The combined action of electric, thermal and mechanical stresses was transformed into the strain effect of multi-stress combined on the micro-voids of composite insulator core rods, and the physical mechanism of core rod aging under the combined action of multi-stress was clarified.

[0045] (3) The composite insulator core rod life prediction method proposed in the present invention is verified to be consistent with the actual operation composite insulator core rod hole charge energy data, providing an effective calculation method for the quantitative evaluation of the theoretical remaining life of the composite insulator in operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1a A schematic diagram of the structure of an aging sample of an embodiment;

[0047] Figure 1b It is a partial structural schematic diagram of the electric-thermal-mechanical aging test platform of the embodiment;

[0048] Figure 2 The microscopic morphology of the aged samples at different aging intervals in the embodiment;

[0049] Figure 3 This is a schematic diagram of the hole enlargement of the insulator core rod under the combined electrical, thermal and mechanical aging of the embodiment;

[0050] Figure 4 The dynamic thermomechanical analysis diagram of the aged samples at different aging intervals in the embodiment;

[0051] Figure 5 This is a graph showing the relationship between the charge energy of the insulator core rod hole and the aging time under the combined electrical, thermal and mechanical aging of the embodiment;

[0052] Figure 6 This is a comparison diagram of the hole charge energy of the aged sample in the embodiment and the actual operation sample;

[0053] Figure 7 This is the theoretical remaining life calculation diagram for the actual operation samples A, B and C. DETAILED DESCRIPTION

[0054] The present invention is further explained below in conjunction with specific embodiments and drawings.

[0055] The present embodiment provides a composite insulator core rod life prediction method under electric-thermal-mechanical multi-field aging, quantitatively evaluates the remaining service life of the composite insulator core rod, and constructs a physical correlation mechanism between microscopic hole charge energy and service life during the aging process of the composite insulator core rod, specifically including the following steps:

[0056] (1) The composite insulator core rod is processed into a dumbbell shape as an electro-thermal-mechanical combined accelerated aging sample. The core rod aging test temperature, applied voltage, and the mass of the weight corresponding to the stress are set according to the composite insulator aging test standard. The electro-thermal-mechanical multi-physics field combined aging test in the following steps is carried out respectively.

[0057] (2) Set the sampling interval of the electric-thermal-mechanical combined accelerated aging samples, set up six groups of interval test samples, take aged samples with different aging intervals, and perform microscopic morphology characterization.

[0058] (3) Combining the multi-physical field aging process and the nature of the oxidation chemical reaction, we first analyze the effect of charge energy and thermal energy on hole deformation under the combined action of electric and thermal forces, and obtain the mechanical strain of the hole under thermal stress. , hole charge energy density and the energy of a single group charge The expressions are shown in formula (1), formula (2) and formula (3) respectively:

[0059] (1)

[0060] (2)

[0061] (3)

[0062] In the formula, N c is the number of holes per cubic meter, N m is the number of groups per hole, a dimensionless variable, r 0 is the hole radius, λ is the thickness of the hole shell, K is the bulk modulus, B is the proportionality coefficient, Δ is the reactant free energy G 2 and the product free energy G 1, Δ = G 2- G 1; k is the Boltzmann constant, k =1.38×10 -23 J / K; T is the temperature in K; σ em is the local charge stress, is the average field strength of a single hole, α is the electrostrictive coefficient.

[0063] (4) Based on the electrothermal aging test, mechanical stress is added to analyze the effect of electrothermal synergy on hole expansion. The electrothermal synergy has the following relationship on hole radius and strain:

[0064] (4)

[0065] In the formula, is the hole radius under the combined thermal and mechanical action, is the mechanical strain of the hole under thermal stress, is the mechanical strain of the hole under mechanical stress, r 0 is the hole radius.

[0066] (5) Based on step (4), a dynamic thermomechanical analysis (DMA) tensile mode test is performed to obtain the storage modulus at the aging test temperature of 180°C as the tensile modulus. Y , obtain the bulk elastic modulus of the sample, and use the multi-physics simulation software COMSOL Multiphysics to simulate and calculate the total strain of the hole;

[0067] The sample bulk elastic modulus was calculated according to the following formula: K :

[0068] (5)

[0069] In the formula, μ is Poisson's ratio.

[0070] The total strain of the hole is:

[0071] (6)

[0072] in is the hole radius under the combined thermal and mechanical action, is the mechanical strain of the hole under thermal stress, is the mechanical strain of the hole under mechanical stress, r 0 is the hole radius, T is the temperature, is the total hole strain, Reflects the coupling relationship between external heating field and force field.

[0073] (6) A finite element simulation model was established in the multi-physics simulation software COMSOL Multiphysics to calculate the electric field distribution on the inner wall of a single hole by combining the total strain of the hole and the average field strength of a single hole. Specifically, electrostatic field simulation was used to obtain the electric field distribution of the material hole by combining the geometric configuration of the composite material hole and the applied electric field boundary conditions.

[0074] (7) To obtain the porosity of the sample, a moisture absorption test was conducted on the electrothermal aging sample. Before the test, the sample was placed in a heating box at 80 °C for 24 h, taken out and cooled to room temperature, and then fully soaked in deionized water. The sample was taken out, wiped dry, weighed, and the mass of the water-absorbed sample was recorded. The sample density was measured using a densitometer based on the electric field distribution of the material pores in step (6). The porosity It can be given by the following formula:

[0075] (7)

[0076] In the formula, m x is the mass of the water-absorbed sample, m c is the sample mass after dehydration, ρ is the sample density.

[0077] (8) Consider the holes as spheres and assume that the number of holes per cubic meter is N c , calculate the hole radius according to the following formula :

[0078] (8) .

[0079] (9) In combination with steps (1) to (8), on the basis of thermal-mechanical coupling, an electric field is applied in the same direction as the mechanical stress. The complete breakage of the core rod is taken as the end of life sign. The hole charge energy is used as the end of life indicator of the core rod. The relationship between the hole charge energy and the aging time is calculated and plotted to predict the remaining life of the composite insulator core rod.

[0080] Hole Charge Energy for:

[0081] (9)

[0082] In the formula, is the average field strength of a single hole, T is the temperature, α is the electrostrictive coefficient, λ is the thickness of the hole shell, r 0 is the hole radius, N m is the number of groups per hole; is the total strain of the hole and is the mechanical stress.

[0083] As a specific embodiment, a composite insulator core rod life prediction method under electric-thermal-mechanical multi-field aging in this embodiment includes the following steps:

[0084] (1) The composite insulator core rod was processed into a dumbbell-shaped specimen of conventional drawn epoxy glass fiber material with a middle diameter of 3.5 mm, a length of 50 mm, a diameter of 9 mm at both ends, and a total length of 300 mm as an electro-thermal-mechanical combined accelerated aging specimen. Figure 1a shown.

[0085] like Figure 1b As shown, a dumbbell-shaped specimen is placed in an aging test platform to carry out an electrothermal test. The aging test platform includes a heating box 2, a power supply 1, and a mechanical stress applying device; the mechanical stress applying device includes a fixed base 31 and a support rod fixed to the fixed base 31, one end of the support rod is rotatably connected to a second connecting rod 32; one end of the second connecting rod 32 extends to one side of the support rod to form an extension; one end of the dumbbell-shaped specimen is fixed to the extension, and the other end is fixed to the fixed base 31; a weight 4 is provided at one end of the second connecting rod 32 away from the extension.

[0086] The ratio of the distance between the second connecting rod 32 and the two sides of the support rod is 1:10, and an arm force of 1:10 is formed on both sides of the support rod. In this embodiment, the length of the extension portion is 2.5 cm, and the total length of the second connecting rod 32 is 27.5 cm.

[0087] A second connecting rod 33 is fixed to one side of the fixed base 31. One end of the second connecting rod 33 is fixed to the fixed base 31, and the other end is installed on the support rod. Figure 1b As shown. Electrodes 5 are provided at both ends of the middle section of the dumbbell-shaped specimen, i.e., the middle section with a small radius. The electrodes 5 are connected to a power source 1 and are used to apply voltage to the dumbbell-shaped specimen. The dumbbell-shaped specimen equipped with electrodes 5 is fixed on a mechanical stress applying device and placed in a heating box 2 to carry out a thermal test.

[0088] According to the composite insulator aging test standard, the aging test temperature of the composite insulator core rod was set to 180℃, the applied voltage was 10.5 kV, the mass of the hook weight 4 used was 5 kg, and a mechanical stress applying device was used to apply pressure to carry out the aging test.

[0089] The aging test platform has a high temperature, high pressure and mechanical stress application environment. It uses a temperature resistance of 200 ℃, a voltage resistance of 50 kV and a cross-sectional area of ​​4 mm 2 One end of the high-voltage wire is connected to the power supply 1 by a cold pressing terminal, and the other end is connected to the alligator clip by cold pressing. The alligator clip passes through the top hole of the heating box 2 and connects to the two electrodes 5 of the dumbbell-shaped sample.

[0090] In the aging test platform, copper foil tape (high temperature resistant to 250℃) is pasted on the upper and lower sides of the middle section of the dumbbell-shaped specimen, and a galvanized iron wire with a diameter of 0.75 mm is wrapped around the copper foil tape. The alligator clip can be connected to the electrode by clamping the iron wire. The exposed metal parts in the heating box 2 are covered with 250℃ heat-resistant insulating tape, such as alligator clips and screws and nuts on mechanical devices. All metal parts are covered with 250℃ heat-resistant insulating tape.

[0091] (2) Assuming that the sampling interval of the electric-thermal-mechanical accelerated aging samples is 18 h, the experiment is repeated under the same conditions in step (1) to obtain samples with electric-thermal-mechanical aging intervals of 0 h (new sample), 18 h, 36 h, 54 h, 72 h and 90 h, as well as the final fracture sample. The micromorphology of the samples with 0 h (new sample), 36 h, 72 h and the final fracture sample is characterized as follows: Figure 2 As shown in (a), (b), (c) and (d).

[0092] (3) The aging process is an oxidative chemical reaction, which includes the pre-aging state and the post-aging state. The corresponding Gibbs free energies of the two states are G 1 and G 2. Under the action of thermal stress, the pores inside the insulating material expand. When the electric and thermal forces are combined, the charge energy and thermal energy are stored in the pores at the same time, which also expands the pores. Mechanical strain of pores under thermal stress , hole charge energy density and the energy of a single group charge The expressions are shown in equations (1), (2) and (3) respectively:

[0093] (1)

[0094] (2)

[0095] (3)

[0096] In the formula, N c is the number of holes in cubic meters, N m is the number of groups per hole and is a dimensionless variable. r 0 is the hole radius, λ is the thickness of the hole shell, K is the bulk modulus, B is the proportionality coefficient, Δ is the difference in free energy between reactants and products, Δ= G 2- G 1; k is the Boltzmann constant, k =1.38×10 -23 J / K; T is the temperature in K; σ em is the local charge stress, is the average field strength of a single hole, α is the electrostrictive coefficient.

[0097] (4) Based on the electrothermal aging test, mechanical stress is added, and the synergistic effect of electrothermal force causes the hole to expand. The schematic diagram of the hole expansion is shown in Figure 3 The relationship between the hole radius under thermal stress alone and the hole mechanical strain under mechanical stress is as follows: , where is the radius of the hole under thermal stress, is the mechanical strain of the hole under thermal stress, r 0 is the hole radius. When mechanical stress acts alone, the hole is stretched into an ellipse. The relationship between the hole radius and the hole mechanical strain is: , is the radius of the hole under mechanical stress, is the mechanical strain of the hole under mechanical stress. The relationship between the hole radius and strain under the combined action of electric and thermal forces is as follows:

[0098] (4)

[0099] (5)

[0100] In the formula, is the hole radius under the combined thermal and mechanical action, is the mechanical strain of the hole under thermal stress, is the mechanical strain of the hole under mechanical stress, r 0 is the hole radius, is the total hole strain, Reflects the coupling relationship between the external heating field and the force field; it is also known that under the action of mechanical force, the stress and strain of the material have a relationship , where σ is the hole stress, Y is the tensile modulus of the material, the hole stress σ It is related to the mechanical force and cross-sectional area of ​​the sample. The tensile modulus Y It is a physical parameter related to temperature. Dynamic Mechanical Analysis (DMA) can directly measure the tensile modulus of materials at different temperatures. It is related to the applied mechanical force, cross-sectional area and temperature. On the other hand, from step (3), it can be known that the mechanical strain and bulk modulus of the hole under thermal stress K Related, it can be deduced that It reflects the coupling relationship between the external heating field and the force field. Therefore, the total strain of the hole includes the thermal strain based on the bulk modulus and the tensile strain based on the Young's modulus. That is, the total strain effect is composed of thermal strain and tensile mechanical strain.

[0101] (5) DMA tensile mode test of samples accelerated by electrical-thermal-mechanical aging, such as Figure 4 The storage modulus E' obtained at the aging test temperature of 180°C is used as the tensile modulus Y The sample bulk elastic modulus is calculated according to the following formula: K :

[0102] (6)

[0103] In the formula, μ is Poisson's ratio.

[0104] (6) A finite element simulation model was established in the multi-physics simulation software COMSOL Multiphysics, and the electric field distribution on the inner wall of a single hole was calculated by combining the total strain of the hole and the average field strength of a single hole. In the force field simulation, the material Poisson's ratio was set to 0.26 and the density was set to 1.7 g / cm 3 The calculated mechanical stress is used as the boundary condition of the force field on the material to obtain the mechanical strain of the hole under the mechanical stress ; In the electric field simulation, the dielectric constant of the material is set to 6.6. In order to simulate the unbounded electric field, the distance between the artificial boundary and the sample is much larger than the length of the sample itself. The voltage applied to the sample is used as the boundary condition to obtain the electric field intensity distribution where the sample is severely degraded; finally, the material and internal spherical hole model is established, and the hole radius is 10 nm. The electric field intensity at the point where the sample is severely degraded is the electric field boundary condition to which the material is subjected, and the electric field distribution on the inner wall of a single hole is calculated.

[0105] (7) In order to obtain the porosity of different samples, moisture absorption tests were carried out on the electric-thermal-mechanical accelerated aging samples. Before the test, the aged samples were placed in a heating box at 80 °C for 24 h, taken out and cooled to room temperature, and then fully soaked in deionized water. The samples were taken out, wiped dry, weighed, and the mass of the water-absorbed samples was recorded. The density of the samples was measured using a densitometer, and the porosity was It can be given by the following formula:

[0106] (7)

[0107] In the formula, m x is the mass of the water-absorbed sample, m c is the sample mass after dehydration, ρ is the sample density.

[0108] (8) Consider the holes as spheres and assume that the number of holes per cubic meter is N c , calculate the hole radius according to the following formula:

[0109] (8).

[0110] (9) Combine steps (1) to (8) to calculate the hole charge energy, and use the hole charge energy as an indicator of the end of the core rod life to evaluate the remaining life of the composite insulator core rod.

[0111] On the basis of thermal-mechanical coupling, an electric field is applied in the same direction as the mechanical stress. Under the action of the electric field, the mechanical strain of the hole is very small and can be ignored. The expression of the charge energy of the hole inside the material can be obtained:

[0112] (9)

[0113] In the formula, is the average field strength of a single hole, α is the electrostrictive coefficient, taken as 9.8×10 -8 N / (m·V 2 ). The hole charge energy can be obtained by taking the complete breakage of the core rod as the end of its life. Relationship with aging time.

[0114] In one embodiment, the difference in free energy between the reactants and products is taken as 3.2×10 -21 J, number of holes per cubic meter N c Take 2.39×10 21 , assuming that the number of groups in the hole N m = 1, the hole shell thickness λ Take 0.1 nm, the proportionality factor B Take 1, and the calculation results are shown in Table 1. Taking the complete breakage of the core rod as the end of life sign, the charge energy of the core rod hole is calculated and plotted. The relationship with aging time is as follows Figure 5 shown.

[0115] Table 1 Samples with different aging time Y, K, 、r 0. 、 , value

[0116]

[0117] Four groups of composite insulator samples (A, B, C, and D) of the China Southern Power Grid Company with different operating years were taken for comparative verification and analysis (detailed operating information is shown in Table 2, where the insulator No. D showed brittle fracture after 17 years of operation, and obvious electrical corrosion marks and carbonization channels were observed on the core rod surface). Based on the above-mentioned electrical-thermal-mechanical aging test, the total strain of the holes and the charge energy density of the core rod of the composite insulator in actual operation were calculated to verify the effectiveness of the present invention.

[0118] For this example, the total strain and charge energy density of the holes in the composite insulator core rod in actual operation are also calculated. Figure 6 As shown. The hole charge energy of samples A, B and C basically conforms to the variation law of the aging sample curve. The hole charge energy of sample D is much higher than that of the artificial accelerated aging sample. This is because the epoxy resin in the core rod is affected by electrocorrosion during the brittle deterioration process. If the insulator has obvious brittle fracture, the epoxy resin in the core rod is affected by electrocorrosion, and "pores" and "bubbles" appear, which increases the trap density inside the material, accumulates charges, and thus causes the hole charge energy to rise. The core rod is very likely to fail prematurely due to discharge breakdown and cannot reach the theoretical service life. When evaluating the life of composite insulators in actual operation, it is recommended to use the hole charge energy (about 0.2128 eV) when the traditional core rod breaks as the end-of-life criterion. When the hole charge energy exceeds 0.2128 eV, the core rod is very likely to fail due to discharge breakdown. The breakdown failure of sample D is a typical case to verify this situation.

[0119] Table 2 Detailed information of composite insulator core rods in actual operation

[0120]

[0121] Using piecewise linear interpolation curve, the traditional mandrel hole charge energy is established With aging time t 1's functional relationship:

[0122] .

[0123] Aging time needs to be established t 1 and actual running time t 2 equivalent relationship, determine the parameters to minimize the deviation between the running sample data and the curve. Assuming the electrical and thermal aging time t 1 and actual running time t 2 There is a linear transformation relationship to establish the aging time t 1 and actual running time t 2 Equivalence relationship , where and The traditional core rod hole charge energy is established by using piecewise linear interpolation curve With aging time t 1's functional relationship:

[0124] (10)

[0125] Substitute the sample data of sample A, sample B, and sample C into the relationship and solve for the coefficient = 5.07, =-4, the calculated electrical and thermal aging fracture time of the traditional core rod (110 h) is equivalent to 22.5 years of actual operation. This means that the theoretical service life of the 500 kV composite insulator is 22.5 years without abnormal conditions such as brittle deterioration and discharge breakdown. The core rod hole charge energy is taken as the independent variable and the aging time is taken as the dependent variable. A piecewise linear interpolation curve is drawn. The actual operation sample hole charge energy is substituted into the interpolation curve to obtain the following Figure 7The curves shown verify the commissioning time and calculate and evaluate the theoretical remaining life. The equivalent electrothermal aging times of Sample A, Sample B and Sample C are 35.82 h, 63.79 h and 100.68 h, respectively, corresponding to 7.85 years, 13.37 years and 20.65 years, respectively. At the same time, the theoretical remaining life is calculated to be 14.65 years, 9.13 years and 1.85 years. The calculation results are shown in Table 3 (relative deviation rate = | commissioning time - calculated operation time | / calculated operation time × 100%). For Sample D, since the hole charge energy is greater than 0.2128 eV during the decay and degradation process, the discharge breakdown failure occurs before the theoretical life is reached. The four groups of composite insulator core rod samples in actual operation have verified that the composite insulator core rod life prediction method proposed in the present invention is consistent with the hole charge energy data of the composite insulator core rod in actual operation, and the theoretical remaining life of the composite insulator core rod can be evaluated by calculating the hole charge energy.

[0126] Table 3 Calculated values ​​of theoretical remaining service life of composite insulator core rods in actual operation

[0127]

[0128] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well.

Claims

1. A method for predicting the life of composite insulator core rods under electric, thermal and mechanical multi-field aging, characterized in that: The following steps are involved: (1) The composite insulator core rod is processed into an electro-thermal-mechanical accelerated aging sample, and the aging test temperature, applied voltage, and mechanical stress applied at both ends of the electro-thermal-mechanical accelerated aging sample are set in the aging test platform; (2) Setting the sampling interval of the electric-thermal-mechanical combined aging test, taking aged samples with different aging intervals, and performing microscopic morphology characterization; (3) Analyze the effects of charge energy and thermal energy on hole deformation under the combined action of electric and thermal stress, and obtain the hole mechanical strain, hole charge energy density and single group charge energy under thermal stress; (4) adding the mechanical stress on the basis of step (3) to analyze the effect of the synergistic effect of electricity, heat and force on the hole radius and strain; (5) Based on step (4), a dynamic thermomechanical analysis tensile mode test is performed to obtain the storage modulus at the aging test temperature as the tensile modulus, obtain the sample bulk elastic modulus, and calculate the total strain of the hole in combination with multi-physics field simulation software; (6) Establish a finite element simulation model in the multi-physics field simulation software, and combine the total hole strain with the average field strength of a single hole to obtain the electric field distribution of the material hole; (7) Conduct a moisture absorption test based on step (5), measure the sample density using a densitometer based on the material pore electric field distribution in step (6), and calculate the porosity; (8) Consider the hole as a sphere and calculate the hole radius based on the porosity; (9) On the basis of thermal-mechanical coupling, an electric field with the same direction as the mechanical stress is applied. The complete fracture of the core rod is taken as the end of life sign. The hole charge energy is used as the end of life indicator of the core rod. The relationship between the hole charge energy and the aging time is obtained, and the remaining life of the composite insulator core rod is predicted.

2. The composite insulator core rod life prediction method under electric-thermal-mechanical multi-field aging according to claim 1 is characterized in that: In step (1), the composite insulator core rod is processed into a dumbbell-shaped specimen as an electro-thermal-mechanical combined accelerated aging specimen; the aging test temperature of the electro-thermal-mechanical combined accelerated aging specimen is set to 178°C-182°C and the applied voltage is set to 10.45kV-10.55 kV.

3. The composite insulator core rod life prediction method under electric-thermal-mechanical multi-field aging according to claim 1 is characterized in that: In step (3), the mechanical strain of the hole under thermal stress , hole charge energy density and the energy of a single group charge The expressions are shown in formula (1), formula (2) and formula (3) respectively: （1） （2） （3） In the formula, N c is the number of holes per cubic meter, N m is the number of groups per hole; r 0 is the hole radius, λ is the thickness of the hole shell, K is the bulk modulus, B is the proportionality coefficient, Δ is the reactant free energy G 2 and the product free energy G 1, Δ = G 2- G 1; k is the Boltzmann constant; T is the temperature; σ em is the local charge stress, is the average field strength of a single hole, α is the electrostrictive coefficient.

4. The composite insulator core rod life prediction method under electric-thermal-mechanical multi-field aging according to claim 1 is characterized in that: In step (4), the synergistic effect of electricity, heat and force has the following relationship on the hole radius and strain: （4） In the formula, is the hole radius under the combined thermal and mechanical action, is the mechanical strain of the hole under thermal stress, is the mechanical strain of the hole under mechanical stress, r 0 is the hole radius.

5. The composite insulator core rod life prediction method under electric-thermal-mechanical multi-field aging according to claim 1 is characterized in that: In step (5), the sample bulk elastic modulus is calculated according to the following formula: K : （5） In the formula, Y is the tensile modulus, μ is Poisson's ratio.

6. The composite insulator core rod life prediction method under electric-thermal-mechanical multi-field aging according to claim 1 is characterized in that: In step (5), the total strain of the hole is: （6） in is the hole radius under the combined thermal and mechanical action, is the mechanical strain of the hole under thermal stress, is the mechanical strain of the hole under mechanical stress, r 0 is the hole radius, is the total hole strain, T is the temperature, For mechanical stress.

7. The composite insulator core rod life prediction method under electric-thermal-mechanical multi-field aging according to claim 1 is characterized in that: In step (7), the porosity It is derived from the following formula: （7） In the formula, m x is the mass of the sample absorbing water, m c is the sample mass after dehydration, ρ is the sample density.

8. The composite insulator core rod life prediction method under electric-thermal-mechanical multi-field aging according to claim 1 is characterized in that: In step (7), the electric-thermal-mechanical combined accelerated aging sample is placed in a heating box to heat and dry, the sample is taken out and cooled to room temperature, and the sample is taken out after being fully soaked in deionized water, wiped dry, weighed, and the mass of the water-absorbed sample is recorded.

9. The composite insulator core rod life prediction method under electric-thermal-mechanical multi-field aging according to claim 1 is characterized in that: In step (8), assume that the number of holes per cubic meter is N c , calculate the hole radius according to the following formula : （8） In the formula, represents the porosity, N c is the number of holes per cubic meter.

10. The method for predicting the life of composite insulator core rods under electric, thermal and mechanical multi-field aging according to any one of claims 1 to 9, characterized in that: In step (9), the hole charge energy for: （9） In the formula, is the average field strength of a single hole, α is the electrostrictive coefficient, λ is the thickness of the hole shell, r 0 is the hole radius, N m is the number of groups per hole; is the total hole strain, T is the temperature, For mechanical stress.

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