Method for predicting corona initial voltage of twisted wire based on finite element method

Abstract

The invention discloses a twisted wire corona initial voltage prediction method based on a finite element method, and the method comprises the steps: selecting a parallel smooth wire with the same outer radius as a target twisted wire as a reference structure, calculating the corona initial field intensity of the reference structure through employing a Pickup formula, and calculating the electric field distribution of the reference structure based on the corona initial field intensity, a dynamic criterion constant suitable for the target twisted wire is obtained through classical corona initial criterion back calculation in combination with the integral relation between the electron ionization coefficient and the electron adhesion coefficient; establishing a finite element model based on the actual structure parameters of the target twisted wire, and calculating the electric field distribution of the surface of the twisted wire and the adjacent area of the model under the applied voltage through a finite element method; and combining the dynamic criterion constant with the electric field distribution of the target twisted wire, and solving a voltage value meeting a corona initial condition and a corona initial voltage corresponding to the target twisted wire through iterative calculation.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power system and its automation technology, in particular to the corona discharge characteristic analysis technology in high-voltage transmission line design, and more particularly to a twisted wire corona inception voltage prediction method based on finite element method. BACKGROUND

[0002] Twisted wire is widely used in overhead high-voltage transmission lines due to its excellent mechanical and electrical properties. However, with the increase of transmission voltage level and the adoption of compact line design to save corridor resources, the electric field intensity on the surface of the conductor is significantly increased, making the problems of radio interference and audible noise caused by corona effect become the key factors restricting the design and performance of the line. Therefore, accurately predicting the corona inception voltage of the twisted wire is an important issue that needs to be broken through in the power system.

[0003] The core of the corona inception problem lies in the electric field distribution on the surface of the conductor and its adjacent area. The irregular structure on the surface of the twisted wire distorts the electric field, which is the main factor to reduce the corona inception voltage of the twisted wire. To quantify this influence, early research introduced a surface irregularity factor to correct the smooth conductor formula, but did not reveal the specific relationship between the factor and the twisted wire. Subsequent research further explored the relationship between the two by defining the twist ratio and conducting related experiments. In addition, considering the electric field distribution on the surface of the twisted wire and its adjacent area, and based on the numerical simulation of the classic corona inception criterion, the surface irregularity factor of the twisted wire in the coaxial cylinder was studied, but its accuracy is seriously dependent on the electrode structure type and gas conditions, which is the limitation of the existing method.

[0004] The existing prediction of the corona inception voltage of the twisted wire is generally based on the streamer inception criterion, but the use of a fixed threshold value in the streamer inception criterion leads to poor universality. SUMMARY

[0005] In view of the defects and deficiencies of the prior art, the present application provides a twisted wire corona inception voltage prediction method, system and computer equipment based on finite element method, aiming to solve the technical problems that the existing prediction of the corona inception voltage of the twisted wire relies on a fixed threshold value, resulting in poor universality and accuracy limited by electrode structure and gas conditions.

[0006] The method first selects a parallel smooth conductor with the same outer radius as the target twisted wire as a reference structure, calculates the corona inception field strength of the reference structure using the Peek formula, calculates the electric field distribution of the reference structure based on the field strength, combines the integral relationship between the electron ionization coefficient and the electron attachment coefficient, and solves the dynamic criterion constant applicable to the target twisted wire through the classical corona inception criterion to replace the traditional fixed threshold value; subsequently, a finite element model based on the actual structural parameters of the target twisted wire is established, and the electric field distribution on the surface and adjacent area of the target twisted wire is accurately calculated by the finite element method; finally, the dynamic criterion constant and the electric field distribution of the target twisted wire are combined, and the voltage value satisfying the corona inception condition is solved through iterative calculation, which is the corona inception voltage of the target twisted wire.

[0007] Correspondingly, the application also provides a prediction system for realizing the above method, which comprises a criterion constant calculation module, an electric field distribution calculation module and a voltage solving module, each module corresponds to the steps of the above method; and a computer device is also provided, which realizes the above prediction method by executing the computer program stored in the memory through the processor.

[0008] The application replaces the fixed threshold value with the dynamic criterion constant, effectively improves the universality and adaptability of the prediction method, and can be applied to the corona inception voltage prediction of twisted wires with different numbers of strands, outer radii and heights above the ground; combined with the accurate calculation of the electric field distribution by the finite element method, the accuracy of the prediction result is significantly improved, without relying on specific electrode structures and gas conditions, which provides reliable support for the optimization design of high-voltage transmission lines, helps to save transmission corridor resources under the premise of ensuring power transmission safety and controlling electromagnetic interference, and has good engineering application value.

[0009] The application specifically adopts the following technical solutions:

[0010] A twisted wire corona inception voltage prediction method based on the finite element method, comprising:

[0011] A parallel smooth conductor with the same outer radius as the target twisted wire is selected as a reference structure, the corona inception field strength of the reference structure is calculated using the Peek formula, the electric field distribution of the reference structure is calculated based on the corona inception field strength, and the dynamic criterion constant applicable to the target twisted wire is inversely calculated through the classical corona inception criterion combined with the integral relationship between the electron ionization coefficient and the electron attachment coefficient;

[0012] A finite element model based on the actual structural parameters of the target twisted wire is established, and the electric field distribution on the surface and adjacent area of the twisted wire under the applied voltage is calculated by the finite element method;

[0013] The dynamic criterion constant is combined with the electric field distribution of the target twisted wire, and the voltage value satisfying the corona inception condition is solved through iterative calculation, which corresponds to the corona inception voltage of the target twisted wire.

[0014] Further, the finite element model is a two-dimensional equivalent geometric model, and a center height of the target twisted wire is located above a ground plane in the two-dimensional equivalent geometric model.

[0015] Further, the integral relationship between the electron ionization coefficient and the electron attachment coefficient is specifically an integral along an electron avalanche development path, and a starting point of the electron avalanche development path is at an outer radius of the reference structure, and an end point of the electron avalanche development path is at a position where the electron ionization coefficient is equal to the electron attachment coefficient.

[0016] Further, when the electric field distribution is calculated by the finite element method, fine mesh division is performed on a surface of the twisted wire and a nearby electric field concentration area, and a mesh division size is adapted to a calculation precision requirement of the electric field distribution.

[0017] Further, when the corona inception field strength of the reference structure is calculated by using the Peek formula, a relative air density is introduced for correction, and the relative air density is determined according to an actual atmospheric pressure, an air temperature, and a standard atmospheric parameter.

[0018] Further, a specific process of the iterative calculation is as follows: an initial value of the corona inception voltage is set, the dynamic criterion constant and the electric field distribution of the target twisted wire are substituted into a classical corona inception criterion for calculation, if a calculation result does not satisfy a corona inception condition, the voltage value is adjusted by a preset adjustment amount and recalculation is performed until the result satisfies the corona inception condition, and a current voltage value is output.

[0019] Further, the actual structure parameters of the target twisted wire include a strand number, an outer radius, and a ground height of the twisted wire.

[0020] Further, when the finite element model is established, material properties of the model are defined, a static electric field is set, an engineering problem of the twisted wire corona inception voltage prediction is converted into a calculable static electric field problem, and then boundary conditions are applied to the static electric field, and finite element calculation is performed.

[0021] And a twisted wire corona inception voltage prediction system based on a finite element method, comprising:

[0022] The criterion constant calculation module is configured to select a parallel smooth wire with the same outer radius as the target twisted wire as a reference structure, calculate a corona inception field strength of the reference structure by using the Peek formula, calculate an electric field distribution of the reference structure based on the corona inception field strength, and inversely calculate a dynamic criterion constant applicable to the target twisted wire by using a classical corona inception criterion in combination with an integral relationship between an electron ionization coefficient and an electron attachment coefficient.

[0023] The electric field distribution calculation module is configured to establish a finite element model based on actual structure parameters of the target twisted wire, and calculate an electric field distribution of a surface of the twisted wire and a nearby area of the model under an applied voltage by using the finite element method.

[0024] a voltage solving module, configured to combine the dynamic criterion constant with an electric field distribution of the target twisted wire, and to solve a voltage value satisfying a corona inception condition through iterative calculation, the voltage value being the corona inception voltage of the target twisted wire.

[0025] Also, an electronic device comprises a memory, a processor, and a computer program stored in the memory and executable on the processor, the processor implementing the steps of the method as described above when executing the program.

[0026] A non-transitory computer-readable storage medium having stored thereon a computer program, the computer program being executable by a processor to implement the steps of the method as described above.

[0027] Compared with the prior art, the present application and the preferred solutions thereof at least have the following beneficial effects:

[0028] Firstly, by introducing the innovative design of the dynamic criterion constant, the limitations of the traditional method relying on fixed threshold are fundamentally overcome. The problem of poor universality caused by the use of an unchanged threshold in the traditional streamer inception criterion is effectively solved, enabling the prediction method to adapt to different twisted wire structure parameters and working conditions, significantly improving the applicability and accuracy of the method.

[0029] Secondly, the finite element method is used to establish an equivalent geometric model of the twisted wire, realizing accurate quantification of the complex electric field distribution caused by the irregular structure of the wire surface. Through adaptive meshing and boundary condition optimization, the details of the electric field concentration area can be effectively captured, providing a more reliable physical basis for the prediction of the corona inception voltage.

[0030] Thirdly, the Pick formula calculation is organically combined with the classic corona inception criterion, and the prediction results are self-verified and optimized through an iterative calculation process. This method not only ensures the stability of the calculation process, but also makes the prediction results consistent with the experimental measurement values, providing a reliable basis for engineering applications.

[0031] In addition, the present solution enhances the adaptability of the prediction model under actual atmospheric conditions through the integration mechanism of relative air density correction and other environmental parameters. The two-dimensional model simplification and meshing strategy involved in the preferred solution further improve the calculation efficiency, making the method have good engineering practicability while ensuring accuracy.

[0032] Finally, the method provided by the present application provides an effective analysis tool for the design of high-voltage transmission lines, especially the optimization of compact lines, which can play an important role in controlling corona effects and reducing electromagnetic interference, and has significant technical value and application prospects. BRIEF DESCRIPTION OF DRAWINGS

[0033] The application will be described in further detail below with reference to the drawings and specific embodiments.

[0034] Figure 1 A two-dimensional equivalent model diagram of a twisted wire according to an embodiment of the application;

[0035] Figure 2 A flowchart of calculating the corona inception voltage according to an embodiment of the application;

[0036] Figure 3 A comparison diagram of calculated and measured corona inception voltages of parallel wires with different center distances according to an embodiment of the application;

[0037] Figure 4 A comparison diagram of calculated and measured corona inception voltages of twisted wires with different outer radii and center heights according to an embodiment of the application. DETAILED DESCRIPTION

[0038] In the following, specific embodiments of the present application will be described in detail with reference to the accompanying drawings, and those skilled in the art can clearly understand the present application and implement the present application according to these detailed descriptions. The features in each different embodiment can be combined to obtain new embodiments or replace some features in some embodiments to obtain other preferred embodiments without departing from the principles of the present application.

[0039] In order to make the features and advantages of the present application more obvious and easy to understand, the following specific embodiments are described in detail below, and the accompanying drawings are used for illustration as follows:

[0040] The present application proposes a numerical prediction method of the corona inception voltage of a twisted wire based on the finite element method. First, the classical corona inception criterion is modified, and the number of electrons in the head of the electron avalanche is calculated by using the Pick formula. Then, the two-dimensional finite element method is used to calculate the electric field distribution near the twisted wire, and finally the corona inception voltage of the twisted wire is calculated by using the improved corona inception criterion. Compared with the published experimental data, the present application can effectively predict the corona inception voltage of the twisted wire, and provides a reliable analysis tool for the optimal design of high-voltage transmission lines.

[0041] The specific implementation of the present application scheme will be further demonstrated and introduced below by means of a specific embodiment in combination with the accompanying drawings:

[0042] 1. Finite element model establishment

[0043] This embodiment first establishes a two-dimensional equivalent geometric model based on the actual structure of the conductor to provide an accurate physical basis for the calculation; then, it defines material properties and sets the electrostatic physical field to transform the engineering problem into a computable electrostatic field problem; then, it ensures the accuracy of the numerical calculation by applying boundary conditions and performing fine meshing in the electric field concentration region; subsequently, it performs finite element calculation to extract the electric field distribution on the surface of the conductor; finally, it uses the obtained electric field data to calculate the corona initiation voltage.

[0044] 2. Calculation Principle

[0045] The model principle is illustrated using a seven-strand twisted wire as an example. The two-dimensional equivalent model of the twisted wire is as follows: Figure 1 As shown, its outer radius is R, and its center height H is located above the grounding plane. The development path of both negative and positive corona extends from the conductor surface R to position R. i At this point, the electron ionization coefficient α is equal to the electron adhesion coefficient η. The classical corona initiation criterion is as follows:

[0046]

[0047] In the formula, l is the distance from the center of the conductor along the electron avalanche propagation path, and Q is a constant (corresponding to the dynamic criterion constant mentioned above). For a smooth conductor, R is equal to the conductor radius.

[0048] The formulas for calculating the electron ionization coefficient and adhesion coefficient are as follows:

[0049]

[0050]

[0051] Where E is in kV / cm, and α and η are in cm⁻¹. The formulas for calculating the relative air density δ in equations (2) and (3) are as follows:

[0052]

[0053] In the formula, P is atmospheric pressure, T is air temperature, P0 is 101.325 kPa, and T0 is 293 K.

[0054] The electric field distribution varies depending on the electrode structure. The formula for calculating the electric field distribution near the conductor is as follows:

[0055]

[0056] In the formula, r is the radial position from the center of the conductor, and E0 is the initial electric field on the surface.

[0057] The Q value of the corona inception criterion of the parallel conductor or the conductor-ground plane is significantly different from that of the coaxial conductor. The present application calculates the surface inception electric field of the parallel conductor by applying the Peek formula, and the calculation formula is as follows:

[0058]

[0059] wherein E0 is in kV / cm, R is in cm, and δ0 / δ=298 / 293. This is because the reference temperature of the Peek experiment is 298 K. Then the electric field distribution is calculated by formula (5), and the Q value can be obtained by using formula (1). The Q value obtained by applying the formula of the parallel conductor by Peek to the smooth conductor is also applicable to the twisted wire with the same outer radius.

[0060] After completing the geometric modeling, the material of the finite element simulation model, the size of the calculation domain, the size of the mesh division, and the solver are set according to the actual power transmission line conditions to construct the real operating condition. Then the calculated electric field distribution is substituted into formula (1) to obtain the Q value of the twisted wire under different radii, and finally the corona inception voltage of the twisted wire is calculated through continuous iteration, and the specific process is as shown in Figure 2

[0061] 1. Start the calculation process and set the initial value of the corona inception voltage U0.

[0062] 2. Extract the electric field distribution data of the twisted wire through the post-processing of the finite element simulation.

[0063] 3. Calculate the electron ionization coefficient α and the electron attachment coefficient η based on the electric field distribution.

[0064] 4. Solve the Q value in the interval where α>η, and determine whether it reaches the threshold Q0.

[0065] 5. If Q0≥Q, directly output the current corona inception voltage U; if it does not meet the condition, update the voltage value U0=U0+ΔU, return to step 2 for repeated iteration until the condition is met.

[0066] wherein the voltage adjustment amount ΔU can be set according to the calculation accuracy requirement of the electric field distribution of the twisted wire.

[0067] 3 Example analysis

[0068] In order to verify the accuracy of the prediction result, the predicted and experimentally measured corona inception voltages of the parallel smooth conductor with the same radius (0.1715 mm) under different center distances s (s=2H) are compared by using the scheme provided in the above embodiment, and the Q value under this condition is about 2.266×103 calculated by the method of the present application. The inception voltage linearly increases with the logarithmic value of s, and the calculation data are in good agreement with the experimental data of the parallel conductor, and the results are as shown in Figure 3 .​

[0069] In addition, the embodiment compares the predicted and experimentally measured corona inception voltage of the 7-strand twisted wire under different outer radii and center heights. The Q value is about 700. The predicted corona inception voltage increases with the increase of the center height or the outer radius, and the calculation result is consistent with the experiment data of the negative corona discharge of the twisted wire, and the result is shown in Figure 4 .

[0070] As can be seen, the core of the embodiment of the present application is to construct an efficient and practical twisted wire corona inception voltage prediction model by using the finite element method. The traditional method uses a fixed threshold value, and the present method first obtains a variable threshold value through the Pick formula, and then combines the classic corona inception criterion to accurately predict the inception voltage of the twisted wire. This provides direct data support and theoretical basis for the optimization design of the wire structure, and has great engineering application value.

[0071] The present application can be used to predict the twisted wire corona inception voltage under different twisted wire radii, twisted wire strand numbers, wire heights, etc. It is suitable for the optimization design of high-voltage transmission lines. It can compress the line width as much as possible under the premise of ensuring power transmission safety and controlling electromagnetic interference, thereby significantly saving valuable power transmission corridor resources and bringing direct economic and social benefits.

[0072] Based on the same inventive concept, the present application also provides a computer device, which comprises one or more processors and a memory for storing one or more computer programs; the program comprises program instructions, and the processor is used to execute the program instructions stored in the memory. The processor can be a central processing unit (CPU), and can also be other general-purpose processors, digital signal processors (DSP), application specific integrated circuits (ASIC), field programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, and is used to implement one or more instructions, and is specifically used to load and execute one or more instructions in the computer storage medium to realize the above-mentioned method.

[0073] It should be further explained that based on the same inventive concept, the present application also provides a computer storage medium, which stores a computer program, and the computer program is executed by a processor to perform the above method. The storage medium can adopt any combination of one or more computer readable media. The computer readable medium can be a computer readable signal medium or a computer readable storage medium. The computer readable storage medium may, for example, but is not limited to, an electrical, magnetic, optical, infrared, or semiconductor system, device or apparatus, or any combination of the above. More specific examples (non-exhaustive list) of the computer readable storage medium include: electrical connections having one or more wires, portable computer disks, hard drives, random access memories (RAM), read-only memories (ROM), erasable programmable read-only memories (EPROM or flash memory), optical fibers, portable compact disk read-only memories (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination of the above. In the present application, the computer readable storage medium can be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, device or apparatus.

[0074] In the description of the present application, the description of the terms "one embodiment", "an example", "a specific example" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present disclosure. In the present specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0075] The above shows and describes the basic principles, main features and advantages of the present disclosure. It should be understood by those skilled in the art that the present disclosure is not limited by the above embodiments, and the above embodiments and descriptions in the specification are only to illustrate the principles of the present disclosure. Without departing from the spirit and scope of the present disclosure, various changes and improvements can be made to the present disclosure, and these changes and improvements all fall within the scope of the claimed present disclosure.

[0076] The present application is not limited to the above best mode, and anyone can derive other various forms of a twisted wire corona starting voltage prediction method based on the finite element method under the inspiration of the present application. Any equivalent changes and modifications made within the scope of the present application application patent range shall fall within the scope of the present application.

Claims

1. A method for predicting the corona initiation voltage of a twisted wire based on the finite element method, characterized in that, include: A parallel smooth wire with the same outer radius as the target twisted wire is selected as the reference structure. The corona initiation field strength of the reference structure is calculated using the Pick formula, and the electric field distribution of the reference structure is calculated based on the corona initiation field strength. Then, combined with the integral relationship between the electron ionization coefficient and the electron adhesion coefficient, the dynamic criterion constant applicable to the target twisted wire is obtained by back-calculation using the classical corona initiation criterion. A finite element model based on the actual structural parameters of the target twisted wire was established, and the electric field distribution of the model on the surface of the twisted wire and the adjacent area under the applied voltage was calculated by the finite element method. By combining the dynamic criterion constant with the electric field distribution of the target twisted wire, the voltage value that satisfies the corona initiation condition is solved through iterative calculation, which corresponds to the corona initiation voltage of the target twisted wire.

2. The method for predicting the corona initiation voltage of a twisted wire based on the finite element method according to claim 1, characterized in that: The finite element model is a two-dimensional equivalent geometric model, in which the center height of the target twisted wire is located above the ground plane.

3. The method for predicting the corona initiation voltage of a twisted wire based on the finite element method according to claim 1, characterized in that: The integral relationship between the electron ionization coefficient and the electron adhesion coefficient is specifically the integral along the electron avalanche propagation path, where the starting point of the electron avalanche propagation path is at the outer radius of the reference structure, and the ending point is at the position where the electron ionization coefficient equals the electron adhesion coefficient.

4. The method for predicting the corona initiation voltage of a twisted wire based on the finite element method according to claim 1, characterized in that: When calculating the electric field distribution using the finite element method, a fine mesh is generated on the surface of the twisted wire and in the adjacent area where the electric field is concentrated. The mesh size is adapted to the accuracy requirements of the electric field distribution calculation.

5. The method for predicting the corona initiation voltage of a twisted wire based on the finite element method according to claim 1, characterized in that: When calculating the corona initiation field strength of the reference structure using the Pick formula, a relative air density is introduced for correction. The relative air density is determined based on the actual atmospheric pressure, air temperature, and standard atmospheric parameters.

6. The method for predicting the corona initiation voltage of a twisted wire based on the finite element method according to claim 1, characterized in that: The specific process of the iterative calculation is as follows: set the initial value of the corona initiation voltage, substitute the dynamic criterion constant and the electric field distribution of the target twisted wire into the classical corona initiation criterion for calculation, if the calculation result does not meet the corona initiation condition, adjust the voltage value according to the preset adjustment amount and recalculate until the result meets the corona initiation condition, and output the current voltage value.

7. The method for predicting the corona initiation voltage of a twisted wire based on the finite element method according to claim 1, characterized in that: The actual structural parameters of the target twisted wire include the number of strands, outer radius, and height above the ground.

8. The method for predicting the corona initiation voltage of a twisted wire based on the finite element method according to claim 1, characterized in that: When establishing the finite element model, the material properties of the model are defined and the electrostatic physical field is set. The engineering problem of predicting the corona initiation voltage of the twisted wire is transformed into a computable electrostatic field problem. Then, boundary conditions are applied to the electrostatic physical field and the finite element calculation is performed.

9. A system for predicting the corona initiation voltage of a twisted wire based on the finite element method, characterized in that, include: The criterion constant calculation module is used to select a parallel smooth wire with the same outer radius as the target twisted wire as a reference structure, calculate the corona initiation field strength of the reference structure using the Pick formula, calculate the electric field distribution of the reference structure based on the corona initiation field strength, and then combine the integral relationship between the electron ionization coefficient and the electron adhesion coefficient to obtain the dynamic criterion constant applicable to the target twisted wire through the classical corona initiation criterion. The electric field distribution calculation module is used to establish a finite element model based on the actual structural parameters of the target twisted wire, and to calculate the electric field distribution of the model on the surface of the twisted wire and the adjacent area under the applied voltage using the finite element method. The voltage calculation module is used to combine the dynamic criterion constant with the electric field distribution of the target twisted wire, and to calculate the voltage value that satisfies the corona initiation condition through iterative calculation. The voltage value is the corona initiation voltage of the target twisted wire.

10. A computer device, characterized in that, It includes a processor and a memory storing a computer program, wherein when the processor executes the computer program, it implements the method of any one of claims 1-8.

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