CN110728018A - Method for analyzing dirt accumulation characteristics of large umbrella skirt composite insulator under different air humidity - Google Patents
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Abstract
A method for analyzing the pollution accumulation characteristic of a large umbrella skirt composite insulator under different air humidity based on Fluent finite element simulation analysis and calculation is characterized by comprising the following steps: 1) determining the wind speed of an air flow field, the concentration of pollutant particles, the variation range of particle size and the variation range of air humidity according to the meteorological characteristics of the area where the power transmission line is located; 2) establishing a flow field and insulator simulation model; 3) solving the simulation model to calculate the distribution of the airflow field around the insulator; 4) adding pollutant particles into the air flow field obtained in the step 3), changing the pollutant particles into a gas-solid coupled two-phase flow model, and continuously solving to analyze the change rule of the collision rate of the pollutant particles and the insulator so as to obtain the pollution accumulation characteristic of the composite insulator. The method analyzes and summarizes the characterization method of the air humidity, converts the relative humidity and the absolute humidity according to the representation mode of the humidity in the simulation software Fluent, and provides a theoretical basis for selecting the variation range of the air humidity of the control variable.
Description
Technical Field
The invention relates to an analysis method for the pollution accumulation characteristic of a large umbrella skirt composite insulator under different air humidity, in particular to a method for calculating the pollution accumulation characteristic of the insulator based on Fluent finite element simulation analysis.
Background
The pollution flashover, ice flashover, rain flashover, lightning stroke and operation impact flashover of the insulator cause great damage to the safe operation of a power system, the lightning stroke accident occurs in the largest number in the accident of the outer insulator, but the pollution flashover accident causes the largest economic loss. The main processes of occurrence of the pollution flashover include four processes: the pollution accumulation, the damp, the partial discharge arc and the electric arc are generated and developed until the partial discharge arc and the electric arc penetrate through the surface of the insulator, so the pollution flashover is deposited on the premise of the pollution flashover, the process of the pollution flashover deposition of different insulators is researched, and the pollution flashover accident is necessarily restrained from the source.
In order to reduce the occurrence of pollution flashover accidents of the power transmission line, the line region where ice flashover, snow flashover and pollution flashover accidents easily occur is partially subjected to line transformation, and an anti-ice and snow composite insulator with an enlarged umbrella skirt is adopted. Along with the increase of the diameter of the umbrella skirt, the distance of the insulator along the surface discharge is increased, so that the flashover voltage of the insulator is increased, and the occurrence of pollution flashover accidents can be effectively reduced. Compared with a porcelain insulator, a glass insulator and a traditional composite insulator, the shed structure of the large shed ice and snow prevention composite insulator has larger change, so that the flow field distribution and the particle motion trail around the insulator have larger change under different air humidity.
At present, the research on the pollution accumulation characteristics of insulators mainly comprises the following steps: natural pollution accumulation test, artificial wind tunnel test and numerical simulation calculation.
(1) The natural pollution accumulation test refers to that a test section is specially established in a specific area, and the pollution accumulation characteristic of the insulator under natural conditions is researched by utilizing an operating power transmission line. But the method has the advantages of long test period, high test result dispersity and no universality due to the limitation of seasons and geographical environments.
(2) The artificial wind tunnel test is to adopt an artificial wind tunnel device, artificially control a certain influencing factor as a variable and artificially simulate the pollution accumulation process of pollutant particles on the surface of an insulator. The influence of natural environment factors is small, the period of a natural pollutant accumulation test is short, but the factors such as the nonuniformity of pollutant particle distribution, the transient change of wind speed and the like in a wind tunnel pollutant accumulation test are easy to ignore.
(3) The simulation analysis calculation is mainly based on simulation software coupled by multiple physical fields such as fluid mechanics, electromagnetic field and the like, and carries out simulation on the motion trail of the pollutant particles. The motion trail and the pollutant accumulation state of pollutant particles are theoretically analyzed, and the research results of a natural pollutant accumulation test and a manual simulation test can be supplemented to a certain extent through numerical simulation.
In the past, the factors such as wind speed, particle concentration in air, particle size and the like are mainly considered for the research on the pollution accumulation characteristics of the insulator, but with the increase of haze weather, the humidity content in the air is greatly changed, the water vapor or suspended small liquid drops under different air humidity also have influence on the existence of particulate matters in the atmosphere, and the research on the influence of the air humidity on the pollution accumulation characteristics of the insulator is relatively less, so that a method for analyzing the pollution accumulation characteristics of the insulator under different air humidity is needed.
Disclosure of Invention
The invention aims to provide a method for researching the dirt accumulation characteristic of a large umbrella skirt composite insulator under different air humidity on the basis of the traditional research on the dirt accumulation characteristic of the composite insulator. The method analyzes and determines a characterization method of the air humidity according to the climate and meteorological characteristics of the specific power transmission line, provides a conversion method of the air humidity in Fluent, establishes an insulator and flow field model, analyzes the change rule of the collision rate of the insulator surface and pollutant particles under different air humidity, is beneficial to predicting the occurrence of flashover accidents of the power transmission line under haze and rainy weather, and provides a theoretical basis for adopting reasonable measures to reduce the flashover accidents.
Based on the purpose, the invention adopts the following technical scheme: a method for analyzing the pollution accumulation characteristic of a large umbrella skirt composite insulator under different air humidity based on Fluent finite element simulation analysis and calculation is characterized by comprising the following steps:
1) determining the wind speed of an air flow field, the concentration of pollutant particles, the variation range of particle size and the variation range of air humidity according to the meteorological characteristics of the area where the power transmission line is located;
2) establishing a flow field and insulator simulation model;
3) solving the simulation model to calculate the distribution of the airflow field around the insulator;
4) adding pollutant particles into the air flow field obtained in the step 3), changing the pollutant particles into a gas-solid coupled two-phase flow model, and continuously solving to analyze the change rule of the collision rate of the pollutant particles and the insulator so as to obtain the pollution accumulation characteristic of the composite insulator.
Preferably, before the step 1), when the pollutant particles around the insulator are subjected to stress analysis, the pollutant particles are equivalent to spherical particles, and the influence of fluid drag force and gravity is mainly analyzed.
Preferably, in step 1), the pollutant particle concentration and the wind speed of the area under different meteorological environments are collected, an intermediate value of the pollutant particle concentration and the wind speed is taken as a constant value of the pollutant particle concentration and the wind speed to be used in simulation calculation, and the pollutant particle concentration is converted into the number of particles per unit area of the inlet of the flow field in the process of the simulation calculation.
Preferably, in step 1), the collected air humidity is relative humidity, and the relative humidity is converted into absolute humidity in the process of simulation calculation.
Preferably, the simulation calculation model in the step 2) selects a ratio of 1: 1 of the anti-ice and snow composite insulator of the large shed, 1.5 shed units are intercepted, a rectangular flow field is arranged, the symmetrical axis of the double-string insulator is preferably located at 1/3 of a connecting line of an air inlet and an air outlet of the rectangular flow field, one side of the rectangular flow field is the air inlet, and the other side of the rectangular flow field is the air outlet.
Preferably, in the step 3), the fluid area of the simulation model is divided into 9 parts, tetrahedral meshes are adopted for subdivision in the area around the insulator, and finer meshes are adopted in the area in contact with the surface of the insulator; and for other 8 areas of the flow field model, carrying out meshing on the flow field area by adopting a hexahedral mesh.
Preferably, in the step 4), the particle size of the pollutant particles and the air humidity are used as variables to simulate and calculate the change rule of the collision rate of the pollutant particles and the insulator.
The invention has the following specific beneficial effects:
1. the method analyzes and summarizes a characterization method of the air humidity, converts the relative humidity and the absolute humidity according to a humidity representation mode in simulation software Fluent, and provides a theoretical basis for selection of a control variable air humidity change range.
2. The movement tracks of the particles are analyzed by finite element simulation, the flow field distribution and the particle movement tracks of the composite insulator under the large shed under the influence of air humidity are obtained, the change rule of the collision rate of the particles and the surface of the insulator is obtained, a theoretical basis is laid for the analysis of the dirt accumulation characteristic of the large shed insulator, and the dirt accumulation characteristic of the large shed insulator is researched in principle.
3. The method has the advantages that the Fluent is used for establishing a model based on the large shed composite insulator and the air flow field, 1.5 shed units are selected, the calculation model is simplified, the calculation period of simulation calculation is saved, the air humidity is changed by changing the absolute humidity in the simulation calculation, and the accurate control of the humidity is realized.
Drawings
Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. Also, like reference numerals are used to refer to like parts throughout the drawings. In the drawings:
FIG. 1 is a schematic diagram of a 500kV ice and snow prevention large shed composite insulator structure and size;
FIG. 2 is a simplified simulation calculation model of a composite insulator;
FIG. 3 is a schematic diagram of a fluid flow field simulation meshing;
FIG. 4 is a scanning electron microscope photograph of the distribution of particles on the surface of the insulator;
FIG. 5 is a vector diagram of the velocity of the flow field around the insulator at a wind speed of 10 m/s;
FIG. 6 is a graph of the movement traces of particles of different particle sizes at a wind speed of 10 m/s;
FIG. 7 is a graph showing the variation of the collision rate of small particles with relative humidity;
FIG. 8 is a graph of the relative humidity as a function of the collision rate for larger particles.
Detailed Description
Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.
In a specific embodiment of the invention, a method for analyzing the pollution accumulation characteristic of a large umbrella skirt composite insulator under different air humidity based on Fluent finite element simulation analysis calculation comprises the following specific steps:
1. and (3) carrying out stress analysis on pollutant particles around the insulator:
(1) force generated by electric field
An electric field exists around the insulator in an actual operating line, and a polarizing force and an electric field force are generated on pollutant particles. The two ends of the pollutant particles in the electric field are polarized into charges with different polarities, the particles with the polarized charges are acted by the polarized force under the action of the electric field, and the formula of the polarized force is
a is the radius of the contaminant particle, m; epsilon0Is a vacuum dielectric constant; epsilonrIs the relative dielectric constant of the particles,
electric field strength, V/m. The formula shows that no matter how the electric field intensity changes, the direction of the polarization force always points to the direction of the electric field strengthening, and the particles can not be subjected to the polarization force in the uniform electric field.
The polarization force experienced.
There are three main ways in which contaminant particles are charged in air: electrostatic charging, diffusion charging, and field charging. The charged particles are under the action of an electric field force:
wherein
Represents the electric field force to which the particles are subjected, q is the charge amount of the particles, C;
electric field strength, V/m.
(2) Acting force generated by air field
Pollutant particles are mainly subjected to fluid drag force, thermophoretic force, Basset force, virtual mass force, Brownian motion force, pressure gradient force, Saffman lifting force and the like in an air field. The influence of fluid drag force on particle motion is the largest, other acting forces are smaller and can be basically ignored under the natural state, the motion model of fluid in air is mainly a turbulence model at present, and the viscosity of air can not be ignored.
(3) Acting force generated by gravitational field
Assuming that the radius of a spherical particle is a, the gravity expression of the particle is:
in the formulaRho ofpDensity of pollutant particles, kg/m3；
Acceleration of gravity, m/s2。
Although the stress analysis mainly considers the fluid drag force, the electric field force and the gravity, the polarization force and the electric field force are relatively small, the electric field around the insulator hardly changes the motion track of particles, and only the particles can be firmly attached to the surface of the insulator.
2. Determining the variation range of the wind speed, the particle concentration, the particle diameter and the air humidity of the air flow field
In order to research the influence of different humidity on the pollution accumulation characteristic of the insulator, the invention takes the air humidity and the particle size as independent variables and controls the concentration of atmospheric particles and the wind speed to be constant values.
Research shows that the concentration of the particulate matters in a certain city under different meteorological environments is 30 mu g/m3～260μg/m3The median particle concentration of 150. mu.g/m3As the particle concentration, in the process of simulation calculation, the concentration of pollutant particles is converted into the number of particles per unit area of the flow field inlet, and the size of the particles is 44784 particles/m2. According to the analysis, the wind speed is set to 10 m/s.
(1) Determining air humidity distribution range
There are two main concepts of air humidity, namely absolute humidity and relative humidity. Absolute humidity refers to the mass of water vapor contained in a volume of air, in g/m3. Relative humidity refers to the proportion of water vapor in the air that is saturated at that temperature.
In engineering practice, the relative humidity is mostly adopted to represent the humidity in the air, the meteorological characteristics of the area in different seasons are obtained, the change rule of the air humidity in different weather is obtained, and the change range of the relative humidity of the air in the area in different seasons in one year is determined.
The absolute humidity in the simulation software Fluent characterizes the water vapor content in the air, so the present invention converts the relative humidity to absolute humidity. The conversion formula of relative humidity and absolute humidity is:
where ρ iswIn terms of absolute humidity, in kg/m3E is the actual pressure of water vapor in the air and has the unit of Pa, RwThe gas constant of water vapor is 462 (N.m)/(kg.K), and T is absolute temperature and K. Phi is the relative humidity of air, E is the saturated vapor pressure, Pa, rhomaxIs a unit of saturated humidity of kg/m3。
Through making statistics of meteorological conditions of a large umbrella skirt composite insulator using area, the distribution range of relative humidity in air is mainly between 30% and 80%, in order to research the influence of different air humidity on particle collision rate, the insulator suspension angle is vertical suspension, and the change gradient of the relative humidity of air is 35%, 50%, 65% and 80%.
(2) Determining the particle size distribution range of the surface deposition particles of the insulator
The pollutants in the atmosphere can be mainly divided into three types: natural pollutants, industrial pollutants, and domestic pollutants. Mainly comprises pollutant particles such as farmland flying dust, air spray, industrial exhaust gas, automobile exhaust and the like. And determining the particle size distribution range of the particles in the atmosphere according to the environment of the area where the power transmission line is located and the season of the area.
The particle size of the contaminants on the surface of the insulator is analyzed by a scanning electron microscope, and a Scanning Electron Microscope (SEM) image of the surface of the insulator is shown in fig. 4. As shown, the particle size distribution of the insulator surface particles is mainly between 1 μm and 50 μm, and the surface particles are composed of dust and construction dust generated by mechanical processes. Therefore, the particle size range of the particles is selected to be 1-50 μm, the appearance characteristics of the particles are ignored, and the particles are set to be spherical.
3. Establishing insulator simulation models at different angles:
in order to simplify a simulation calculation model, a proportion of 1: 1 of an anti-ice and snow composite insulator of a 500kV large shed is taken as an example (a specific structure and a size are shown in figure 1) for analysis, 1.5 shed units are intercepted, specifically, a cuboid flow field is arranged, the size of a flow field area is 2500 multiplied by 3000 multiplied by 3500mm, the flow field area meets the conditions and can effectively avoid a boundary effect, one side of the cuboid flow field is an air inlet, the other side of the cuboid flow field is an air outlet, a symmetrical axis of the double-string insulator is preferably located at 1/3 of a connecting line of the air inlet and the air outlet of the cuboid flow field, and at least the distance from the air inlet is ensured to avoid inaccurate simulation calculation caused by excessively approaching the air inlet, one side of the cuboid flow field is. In order to study the influence of different air humidity on the particle collision rate, the insulator suspension angle is vertical suspension, and an insulator simulation model is shown in fig. 2.
4. Calculating the distribution of the flow field around the insulator:
because the surface of the insulator is complex in shape and has a small curvature radius, the requirement on the accuracy of grid division of a simulation model is high, a fluid region is divided into 9 parts, a tetrahedral grid is adopted to divide the region around the insulator, and a finer grid is adopted in a region in contact with the surface of the insulator; for the other 8 regions of the flow field model, hexahedral mesh is adopted to perform mesh division on the flow field region, and a mesh division schematic diagram of the simulation model is shown in fig. 3.
When the airflow passes through a flow field around the insulator, large turbulence exists, a model simulation can solve a flowing momentum equation during calculation, then a pressure correction equation is solved, finally a turbulence control equation is solved, and when the model is solved, the equation is calculated by means of an RNG k-epsilon turbulence model.
An N-S equation is often adopted for calculating a turbulent motion model of a continuous phase, and a specific Navier-Stokes control equation is as follows:
wherein u is the velocity of the air fluid in m/s; ρ is the fluid density in kg · m-3(ii) a p is the fluid pressure; μ is the gas flow viscosity; f is the mass force per unit mass of fluid; x is the number ofi，xjRespectively represent three rectangular coordinate components (i, j ≠ 1, 2, 3, i ≠ j);
is the reynolds stress component.
Solving the turbulence model by increasing the number of equations using an RNG k-epsilon turbulence model, where k refers to the kinetic energy of the turbulence and m is2·s-2ε means the dissipation ratio, m2·s-3The specific equation is as follows:
wherein G iskRefers to the turbulent kinetic energy produced by the mean velocity gradient, CμRefers to an empirical constant with a magnitude of 0.0845, C1εContaining time-averaged strain rate of main fluid flow, C2εIs constant and has a magnitude of 1.68.
When the airflow passes through the flow field around the insulator, a large turbulent flow exists, and when the model is simulated and calculated, a flowing momentum equation is solved first, and then a pressure correction equation is solved. Fig. 5 is a velocity vector diagram of a flow field around the insulator at a wind speed of 10m/s, and fig. 5c is an enlarged image of the flow field around the insulator, as shown in the figure, at the wind speed of 10m/s, the difference between the velocities of the windward side and the leeward side becomes larger and larger with the increase of the wind speed, the velocity of the flow field at the windward side is obviously increased, the vector distribution is denser, and the wind speed of the flow field is the largest at a position 300mm away from the windward side of the insulator.
5. Analyzing the change rule of the collision rate of pollutant particles and insulators with different suspension angles:
and after the calculation of the insulator flow field is finished, adding pollutant particles with the initial velocity same as the flow field velocity into the air flow field, and analyzing the collision condition of the particles and the surface of the insulator under different air humidity.
Solid particles are added into an air medium, a single air fluid becomes a gas-solid coupled two-phase flow model, the distribution characteristics and the motion trail of a flow field, the particles and air humidity are analyzed by a gas-solid two-phase flow calculation method, and a single-phase coupling mode is adopted in the fluid-solid coupling process. The movement locus of the particles of different sizes at a wind speed of 10m/s is shown in FIG. 6 (5 μm in FIG. 6a and 30 μm in FIG. 6 b).
When the pollutant particles in the flow field collide with the surface of the insulator, the pollutant particles are absorbed by the surface of the insulator, the rest pollutant particles are absorbed by the outer wall of the flow field, and the collision rate of the pollutant particles is judged according to the proportion of the particles absorbed by the surface of the insulator.
The particle size of the pollutant particles and the air humidity are used as variables to simulate and calculate the change rule of the collision rate of the pollutant particles and the insulator.
When the particle size of the particles is small and the wind power is large, the movement of the particles is mainly influenced by the drag force of the fluid, the action of gravity on the particles is small, the movement track of the particles is estimated to be almost parallel to the horizontal plane, and few pollutant particles collide with the umbrella skirt of the insulator. Along with the increase of the particle size, the action of gravity is gradually increased, the particles are horizontally thrown and moved under the action of gravity and fluid drag force, and the collision rate of the particles is gradually increased along with the increase of the particle size through analysis from the movement angle of the particles.
Specifically, when the particle size is small, the change rule of the particle collision rate with the increase of the relative humidity is as shown in fig. 7, the small particle size particles are greatly influenced by the air humidity, the collision rate is remarkably reduced with the increase of the relative humidity, and when the air humidity is high, the particle size is small, aggregation or collision between particles may occur before the particles collide with the surface of the insulator, so that the particle collision rate is remarkably reduced.
When the particle size is larger and is in the range of 10 μm to 50 μm, the collision rate of the particles gradually decreases with the increase of the relative humidity of the air, but the decrease is weaker than that when the particle size is smaller, and the change rule is as shown in fig. 8.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.
Claims (7)
1. A method for analyzing the pollution accumulation characteristic of a large umbrella skirt composite insulator under different air humidity based on Fluent finite element simulation analysis and calculation is characterized by comprising the following steps:
1) determining the wind speed of an air flow field, the concentration of pollutant particles, the variation range of particle size and the variation range of air humidity according to the meteorological characteristics of the area where the power transmission line is located;
2) establishing a flow field and insulator simulation model;
3) solving the simulation model to calculate the distribution of the airflow field around the insulator;
4) adding pollutant particles into the air flow field obtained in the step 3), changing the pollutant particles into a gas-solid coupled two-phase flow model, and continuously solving to analyze the change rule of the collision rate of the pollutant particles and the insulator so as to obtain the pollution accumulation characteristic of the composite insulator.
2. The method of claim 1, wherein: before the step 1), when the stress analysis is carried out on the pollutant particles around the insulator, the pollutant particles are equivalent to spherical particles, and the influence of fluid drag force and gravity is mainly analyzed.
3. The method of claim 1, wherein: in the step 1), the pollutant particle concentration and the wind speed of the area under different meteorological environments are collected, the intermediate value of the pollutant particle concentration and the wind speed is used as a constant value of the pollutant particle concentration and the wind speed for simulation calculation, and in the process of simulation calculation, the pollutant particle concentration is converted into the particle number of the unit area of the flow field inlet.
4. The method of claim 1, wherein: in the step 1), the collected air humidity is relative humidity, and the relative humidity is converted into absolute humidity in the process of simulation calculation.
5. The method of claim 1, wherein: in the simulation calculation model in the step 2), the proportion of the anti-ice and snow composite insulator of the large shed is selected to be 1: 1, 1.5 shed units are intercepted, a cuboid flow field is arranged, the symmetrical axis of the double-string insulator is preferably located at 1/3 of a connecting line of an air inlet and an air outlet of the cuboid flow field, one side of the cuboid flow field is the air inlet, and the other side of the cuboid flow field is the air outlet.
6. The method of claim 1, wherein: in the step 3), the fluid area of the simulation model is divided into 9 parts, tetrahedral meshes are adopted to divide the area around the insulator, and more refined meshes are adopted in the area in contact with the surface of the insulator; and for other 8 areas of the flow field model, carrying out meshing on the flow field area by adopting a hexahedral mesh.
7. The method of claim 1, wherein: and 4) in the step 4), the particle size of the pollutant particles and the air humidity are used as variables to simulate and calculate the change rule of the collision rate of the pollutant particles and the insulator.
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| CN111709646A (en) * | 2020-06-17 | 2020-09-25 | 九江学院 | Air pollution exposure risk evaluation method and system |
| CN113111431A (en) * | 2021-03-08 | 2021-07-13 | 东风柳州汽车有限公司 | Simulation evaluation method and device for dust pollution of heavy-duty truck |
| CN114166705A (en) * | 2021-12-06 | 2022-03-11 | 南方电网科学研究院有限责任公司 | Evaluation method for silicon rubber microstructure |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN111709646A (en) * | 2020-06-17 | 2020-09-25 | 九江学院 | Air pollution exposure risk evaluation method and system |
| CN111709646B (en) * | 2020-06-17 | 2024-02-09 | 九江学院 | Air pollution exposure risk evaluation method and system |
| CN111665189A (en) * | 2020-07-09 | 2020-09-15 | 中车青岛四方机车车辆股份有限公司 | Abrasion test method for surface coating of car roof insulator |
| CN111665189B (en) * | 2020-07-09 | 2023-11-21 | 中车青岛四方机车车辆股份有限公司 | Abrasion test method for surface coating of roof insulator |
| CN113111431A (en) * | 2021-03-08 | 2021-07-13 | 东风柳州汽车有限公司 | Simulation evaluation method and device for dust pollution of heavy-duty truck |
| CN114166705A (en) * | 2021-12-06 | 2022-03-11 | 南方电网科学研究院有限责任公司 | Evaluation method for silicon rubber microstructure |
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