A method for calculating flashover voltage of composite insulators under heavy pollution conditions

Abstract

The present invention relates to the technical field of power equipment monitoring and diagnosis, and specifically to a method for calculating the flashover voltage of a composite insulator under heavy pollution conditions. The method comprises inputting initial parameters into a target pollution flash circuit model to calculate the arc root radius; calculating the target residual pollution layer resistance based on the arc root radius, and calculating the initial arc current based on the Newton secant method; calculating the pollution layer voltage gradient and arc voltage gradient based on the initial arc current; determining whether flashover has occurred based on the initial local arc length and the insulator creepage length; and, if flashover has not occurred, correspondingly increasing the initial local arc length or the initial applied voltage based on the magnitude of the pollution layer voltage gradient and the arc voltage gradient until the pollution flashover voltage is calculated when flashover occurs. The present invention implements the calculation of the flashover voltage of a composite insulator under heavy pollution conditions and has excellent application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of power equipment monitoring and diagnosis, and in particular to a method for calculating the flashover voltage of a composite insulator under heavy pollution conditions. Background Art

[0002] The rapid economic development has brought about the continuous expansion of the power grid. Overhead transmission lines are an important part of the power grid. They span a vast area and have a complex and changeable operating environment. Therefore, they inevitably pass through some special environmental areas, including high-pollution environmental areas. High-pollution environmental areas are prone to repeated pollution flashover and tripping of transmission lines, which seriously affects the safe and stable operation of the power grid; the shortage of transmission line corridors makes the relocation cost of transmission lines operating in high-pollution areas high. How to effectively prevent and control pollution flashover and tripping of transmission lines in high-pollution areas, and how to safely and reliably operate and maintain transmission lines in high-pollution areas, have always been the focus of relevant technical researchers.

[0003] Among them, the saturated equivalent salt density in highly polluted environmental areas is generally greater than 0.35 mg / cm 2 The line design and operation and maintenance units use the "unified creepage distance method" to configure the insulation string length, which cannot meet the requirements of the operating environment and is generally prone to inaccurate insulation configuration. The State Grid Corporation's 18 countermeasures point out that the saturated equivalent salt density is greater than 0.35mg / cm 2 Insulation configuration should be individually verified, but there are no standard specifications to guide this verification. This problem is common on transmission lines operating in areas such as Pinglu, Shuozhou, Shanxi, Wuhai, Inner Mongolia, the Qinghai Salt Lake area, and some coastal areas. Accurate insulation configuration in highly polluted areas is an urgent issue that needs to be addressed.

[0004] Composite insulators are widely used due to their light weight, compact size, and ease of installation, replacement, and transportation. They also offer excellent flashover resistance due to their low surface energy and strong hydrophobicity, making them less likely to form a continuous water film. Consequently, leakage current is low, local arcing is less likely, and surface flashover is less likely. However, operational experience shows that flashover accidents involving composite insulators remain a significant problem under heavy pollution conditions.

[0005] Therefore, accurate calculation of the pollution flashover voltage of composite insulators is a key method for insulation configuration and pollution flashover warning under high-pollution conditions. Relevant research institutions at home and abroad have conducted extensive research on the pollution flashover mechanisms and models of insulators, but this research mainly focuses on the conventional pollution levels specified in the standards. Therefore, despite some research on the pollution flashover mechanisms and warning technologies for insulators, existing methods still have the following significant shortcomings: 1) There is a lack of research on the flashover characteristics of composite insulators under "high" pollution levels. Therefore, relying on the results of "medium" and "low" pollution flashover tests to configure composite insulators for high-pollution transmission lines is not rational. 2) Current AC arc reignition mathematical models and pollution layer resistance derivation methods are based on research results under medium and low pollution levels. If traditional methods are directly applied to these key calculation steps and parameters in the flashover model under high pollution levels, the calculation model will lack scientific rationality and lead to large model calculation errors. Summary of the Invention

[0006] Therefore, the technical problem to be solved by the present invention is to overcome the problem in the prior art that the flashover voltage calculation of the composite insulator under heavy pollution conditions cannot be realized.

[0007] To solve the above technical problems, the present invention provides a method for calculating the flashover voltage of a composite insulator under heavy pollution conditions, comprising:

[0008] Inputting initial parameters into the target pollution lightning circuit model to calculate the arc root radius; the initial parameters include initial applied voltage, initial local arc length, rod radius, insulator creepage length, initial arc current, local arc length increase, and applied voltage increase;

[0009] Calculating the target residual contamination layer resistance according to the arc root radius, and calculating the initial arc current based on the Newton secant method;

[0010] Calculating the contamination layer voltage gradient and the arc voltage gradient according to the initial arc current;

[0011] Whether flashover has occurred is determined by the initial local arc length and the insulator creepage length. If flashover has not occurred, the initial local arc length or the initial applied voltage is correspondingly increased based on the magnitude of the pollution layer voltage gradient and the arc voltage gradient until the pollution flashover voltage is calculated when flashover has occurred.

[0012] In one embodiment of the present invention, the target polluted lightning circuit model is obtained by introducing random small arcs into the initial polluted lightning circuit model; the target polluted lightning circuit model is a polluted lightning circuit model under heavy pollution conditions of composite insulators.

[0013] In one embodiment of the present invention, the initial parameters are input into the target contaminated lightning circuit model to calculate the arc root radius. The specific formula is:

[0014]

[0015] Where r0 is the arc root radius and I is the initial arc current.

[0016] In one embodiment of the present invention, the target residual contamination layer resistance is calculated based on the arc root radius. The specific formula is:

[0017]

[0018] Among them, R(x,I) is the target residual pollution layer resistance, σ s is the conductivity of the surface pollution layer, L is the creepage length of the insulator, x is the initial local arc length, r1 is the rod radius, and r0 is the arc root radius.

[0019] In one embodiment of the present invention, the pollution layer voltage gradient and the arc voltage gradient are calculated based on the initial arc current. The specific formula is:

[0020]

[0021] Among them, E p is the voltage gradient of the pollution layer, U p is the pollution layer voltage, R(x,I) is the target residual pollution layer resistance, x is the initial local arc length, L is the insulator creepage length, and I is the initial arc current;

[0022]

[0023] Among them, E arc is the arc voltage gradient, U arc is the arc voltage, A and n are constants reflecting the arc characteristics.

[0024] In one embodiment of the present invention, judging whether flashover has occurred based on the initial local arc length and the insulator creepage length includes:

[0025] When the initial local arc length is greater than or equal to the insulator creepage length, the flashover is reached;

[0026] When the initial local arc length is less than the insulator creepage length, flashover has not yet occurred, and the pollution layer voltage gradient and the arc voltage gradient are compared.

[0027] In one embodiment of the present invention, when flashover has not yet occurred, increasing the initial local arc length or the initial applied voltage accordingly based on the magnitudes of the pollution layer voltage gradient and the arc voltage gradient includes:

[0028] When the pollution layer voltage gradient is greater than the arc voltage gradient, increasing the initial local arc length to a target local arc length;

[0029] When the contamination layer voltage gradient is less than or equal to the arc voltage gradient, the initial applied voltage is increased to a target applied voltage.

[0030] In one embodiment of the present invention, the specific formula for obtaining the target local arc length and the target applied voltage is:

[0031] x 目标 =x+vdt;

[0032] Among them, x 目标 is the target local arc length, x is the initial local arc length, v is the arc development speed, and dt is the increase in local arc length;

[0033] U 目标 =U+dU;

[0034] Among them, U 目标 is the target applied voltage, U is the initial applied voltage, and dU is the increase in applied voltage.

[0035] In one embodiment of the present invention, under DC conditions, the pollution flashover voltage is calculated using the following formula:

[0036] U c1 =AxI -n +R(x,I)I;

[0037] Among them, U c1 is the pollution flashover voltage under DC conditions, R(x,I) is the target residual pollution layer resistance, A and n are constants reflecting the arc characteristics, x is the initial local arc length, and I is the initial arc current.

[0038] In one embodiment of the present invention, under AC conditions, the pollution flashover voltage is calculated using the following formula:

[0039]

[0040] Among them, U c2 is the pollution flashover voltage under AC conditions, x is the initial local arc length, and I is the initial arc current.

[0041] The above technical solution of the present invention has the following beneficial effects compared with the prior art:

[0042] The present invention provides a method for calculating the flashover voltage of a composite insulator under heavy pollution conditions. The method introduces the concept of random arcs, which is more consistent with the arc development state under heavy pollution conditions. The residual pollution layer is derived based on the electric axis method in electromagnetic field theory, which is more suitable for the state of multiple arcs. The key model parameters under heavy pollution conditions are tested and corrected. The flashover voltage calculation of a composite insulator under heavy pollution conditions is realized, and the method has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0044] Figure 1 A flow chart of a method for calculating flashover voltage of a composite insulator under heavy pollution conditions provided by an embodiment of the present invention;

[0045] Figure 2 A schematic diagram of a traditional dirty lightning circuit model provided by an embodiment of the present invention;

[0046] Figure 3 A schematic diagram of a polluted lightning circuit model with random arcs provided by an embodiment of the present invention;

[0047] Figure 4 A schematic diagram of the residual contamination layer resistance between two circular electrodes provided in an embodiment of the present invention;

[0048] Figure 5 A schematic diagram of the residual contamination layer resistance provided by an embodiment of the present invention;

[0049] Figure 6 This is a general flow chart for calculating the flashover voltage of composite insulators under high pollution conditions provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0050] The present invention will be further described below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0051] In order to overcome the problems existing in the prior art, the present invention proposes a method for calculating the flashover voltage under heavy pollution conditions of composite insulators. Figure 1 As shown, Figure 1 A flowchart of a method for calculating the flashover voltage of a composite insulator under heavy pollution conditions provided by an embodiment of the present invention, the method comprising:

[0052] S101: Inputting initial parameters into the target contaminated lightning circuit model to calculate the arc root radius; the initial parameters include initial applied voltage, initial local arc length, rod radius, insulator creepage length, initial arc current, local arc length increase and applied voltage increase.

[0053] Exemplarily, the input initial parameters include initial applied voltage U, initial local arc length x, rod radius r1, insulator creepage length L, initial arc current I, initial Ii=0 and Ii=1, local arc length increase dt and applied voltage increase dU.

[0054] In some possible implementations, in step S101, the target polluted lightning circuit model is obtained by introducing a random small arc into the initial polluted lightning circuit model; the target polluted lightning circuit model is a polluted lightning circuit model under heavy pollution conditions of composite insulators.

[0055] For example, Figure 2 As shown in Figure 2, Obenos proposed the classic local arc-residual pollution layer resistance series circuit model, and obtained the voltage-current relationship in the pollution flashover equivalent circuit as: U = AxI -n +RI. Where U is the applied voltage in kV; x is the local arc length in cm; I is the leakage current in A; R is the residual resistance of the contamination layer in Ω; A and n are constants reflecting the arc characteristics. The values ​​of A and n obtained by different researchers vary greatly, ranging from 3 ≤ A ≤ 200 and 0.45 ≤ n ≤ 1, respectively.

[0056] like Figure 3 As shown, this application introduces random small arcs into the traditional pollution lightning circuit model, because under heavy pollution conditions, the early arc usually develops violently, not just from the high-voltage end, but there are multiple small arcs on the residual pollution layer. Figure 3 The pollution lightning circuit model with random arc introduced is shown. The pollution layer resistance derivation of this application does not use the conventional "simple expansion into a rectangle or equivalently into a cylinder to calculate its pollution layer resistance".

[0057] At the same time, considering that after the local arc appears, the current density distribution of the pollution layer is uneven due to the contraction of the arc root current line, and the rectangular resistance model cannot reflect this unevenness, it is assumed that multiple arcs are in series contact with the residual pollution layer through the arc root, and the thermal characteristics of the arc and the pollution layer are ignored. The resistance of the residual pollution layer is regarded as the resistance between multiple circular electrodes, such as Figure 4 shown. Figure 4In the diagram, the circular electrodes represent the arc root and arc root, arc root and composite insulator pole respectively, where r0 is the arc root radius, r1 is the pole radius, and the conductivity of the medium between the two electrodes is the pollution layer conductivity. Taking the arc root and composite insulator pole as an example when there is only one arc, the pollution layer resistance diagram is as follows: Figure 5 shown.

[0058] According to the electric axis method in electromagnetic field theory, the resistance between two circular electrodes on an infinite conductive plane can be derived and expressed as:

[0059]

[0060] In the above formula (1), σ e The corresponding value is the effective conductivity of the pollution layer on the surface of the insulator, with the unit being S. D=L-x+r1, where L is the leakage distance of the insulator, with the unit being cm.

[0061] Usually the effective conductivity of the pollution layer is σ e and the surface dirt layer conductivity σ s The relationship is as follows (2):

[0062] σ e ≈1.25σ s (2);

[0063] The relationship between arc root radius and arc current is determined by the following formula (3).

[0064] In some possible implementations, in step S101, the initial parameters are input into the target contaminated lightning circuit model to calculate the arc root radius. The specific formula is:

[0065]

[0066] Where r0 is the arc root radius and I is the initial arc current.

[0067] At the same time, if during the actual arc development process, the arc root radius is much smaller than the composite insulator pole radius (related to the composite insulator sample), that is, r0<<r1, then D 2 -r1 2 -r0 2 ≈D 2 -r1 2 , and D 2 -r1 2 =(L-x+r1) 2 -r1 2 >0

[0068] It can be simplified into the following formula (4):

[0069]

[0070] Apply the identity transformation The analytical expression of the residual contamination layer resistance R(x,I) can be obtained as the following equation (5).

[0071] S102: Calculate the target residual contamination layer resistance according to the arc root radius, and calculate the initial arc current based on the Newton secant method.

[0072] In some possible implementations, in step S102, the target residual contamination layer resistance is calculated based on the arc root radius, and the specific formula is:

[0073]

[0074] Among them, R(x,I) is the target residual pollution layer resistance, σ s is the conductivity of the surface pollution layer, L is the creepage length of the insulator, x is the initial local arc length, r1 is the rod radius, and r0 is the arc root radius.

[0075] It should be noted that R(x,I) is a function of two parameters, arc length x and arc current I, and x and I affect each other, so the accurate calculation of flashover voltage U c The arc current needs to be recalculated at each new position of the arc root.

[0076] At this point, rewrite the circuit equation as:

[0077]

[0078] Since the above equation (6) is a nonlinear equation about the arc current I, it is difficult to obtain an analytical solution. Therefore, the Newton-secant method can be used to numerically solve it and rewrite the equation as a function of I:

[0079]

[0080] The iteration format is:

[0081]

[0082] In the above formula (8), I i+1 and I i It is the current between two adjacent currents in the iterative calculation process. By setting two initial values ​​I0 and I1 close to the analytical solution and the error limit ε, and starting the iteration, a numerical solution of I with an accuracy that meets the calculation requirements can be obtained.

[0083] The development of local arc needs to meet certain conditions, namely the residual pollution layer voltage gradient E p Greater than the arc voltage gradient E arc , so calculate E under certain x and I values arc and E p , the specific formulas are the following formula (9) and the following formula (10).

[0084] S103: Calculating the pollution layer voltage gradient and the arc voltage gradient according to the initial arc current.

[0085] In some possible implementations, in step S103, the contamination layer voltage gradient and the arc voltage gradient are calculated based on the initial arc current. The specific formula is:

[0086]

[0087] Among them, E p is the voltage gradient of the pollution layer, U p is the pollution layer voltage, R(x,I) is the target residual pollution layer resistance, x is the initial local arc length, L is the insulator creepage length, and I is the initial arc current;

[0088]

[0089] Among them, E arc is the arc voltage gradient, U arc is the arc voltage, A and n are constants reflecting the arc characteristics.

[0090] S104: Determine whether flashover has occurred based on the initial local arc length and the insulator creepage length, and if flashover has not occurred, increase the initial local arc length or the initial applied voltage accordingly based on the magnitude of the pollution layer voltage gradient and the arc voltage gradient, until the pollution flashover voltage is calculated when flashover has occurred.

[0091] In some possible implementations, in step S104, determining whether flashover has occurred based on the initial local arc length and the insulator creepage length includes:

[0092] When the initial local arc length is greater than or equal to the insulator creepage length, the flashover is reached;

[0093] When the initial local arc length is less than the insulator creepage length, flashover has not yet occurred, and the pollution layer voltage gradient and the arc voltage gradient are compared.

[0094] In some possible implementations, when flashover has not yet occurred, increasing the initial local arc length or the initial applied voltage accordingly based on the magnitudes of the pollution layer voltage gradient and the arc voltage gradient includes:

[0095] When the pollution layer voltage gradient is greater than the arc voltage gradient, increasing the initial local arc length to a target local arc length;

[0096] When the contamination layer voltage gradient is less than or equal to the arc voltage gradient, the initial applied voltage is increased to a target applied voltage.

[0097] In some possible implementations, the specific formula for obtaining the target local arc length and the target applied voltage is:

[0098] x 目标 =x+vdt (11);

[0099] Among them, x 目标 is the target local arc length, x is the initial local arc length, v is the arc development speed, and dt is the increase in local arc length;

[0100] U 目标 =U+dU (12);

[0101] Among them, U 目标 is the target applied voltage, U is the initial applied voltage, and dU is the increase in applied voltage.

[0102] For example, at a given voltage, the arc propagation criterion (E p >E arc ) is used as the criterion for arc development. If the criterion is met, the arc length will develop along the leakage distance. Otherwise, the arc will be extinguished or the external applied voltage will need to be increased to make the arc continue to develop. The external applied voltage and arc current are updated, and recalculated to determine whether the arc development conditions are met.

[0103] In some possible implementations, under DC conditions, the pollution flashover voltage is calculated using the following formula:

[0104] U c1 =AxI -n +R(x,I)I (13);

[0105] Among them, U c1 is the pollution flashover voltage under DC conditions, R(x,I) is the target residual pollution layer resistance, A and n are constants reflecting the arc characteristics, x is the initial local arc length, and I is the initial arc current.

[0106] For example, for the dirty flashover situation under AC conditions, which is different from DC conditions, the arc development to flashover must also meet the reignition condition of the following formula (14).

[0107] In some possible implementations, under AC conditions, the pollution flashover voltage is calculated using the following formula:

[0108]

[0109] Among them, U c2is the pollution flashover voltage under AC conditions, x is the initial local arc length, and I is the initial arc current.

[0110] Furthermore, in the implementation case of this application, the surface dirt layer conductivity σ applicable to high pollution conditions was tested. s The relationship with salt density SDD is σ s =1.32×(372.35×SDD+0.47)×10 -6 .

[0111] The constant A, which reflects the arc characteristics, takes a value of 152.8, and n takes a value of 0.63. The arc development speed is determined by the mobility and the electric field strength, and the relationship is v = μE arc , where the mobility μ = 25 cm 2 / (V·s).

[0112] Random small arcs are generated by random functions, and the generation parameters are mainly length parameters, where the length parameter is less than 1 / 10 of the insulator length.

[0113] In a specific embodiment, experimental verification shows that there is a random small arc phenomenon under heavy pollution conditions, which is very consistent with the target pollution lightning circuit model proposed in this application. The specific calculation results are shown in Table 1 below. The maximum error percentage is less than 10%. It can be seen that the flashover voltage calculation method of the composite insulator under heavy pollution conditions provided by this application has high accuracy.

[0114] <![CDATA[ESDD(mg / cm 2 )]]> Flashover voltage (kV / m) Calculation results (kV / m) Error (kV / m) Percent error 0.4 31.6 30 1.6 5.06％ 0.6 26.5 25.1 1.4 5.28％ 0.8 24.6 22.3 2.3 9.35％ 1.2 23.3 21.1 2.2 9.44％

[0115] Table 1

[0116] In summary, see Figure 6 ,The overall process of this application is as follows: input the initial parameters L, r1, initial x and U, dU, dt, initial Ii = 0 and Ii = 1;

[0117] Calculate r0 and the contamination layer resistance R(x,I) based on the initial parameters, and solve for I using the Newton-secant method;

[0118] Calculate the pollution layer voltage gradient E according to I p and arc voltage gradient E arc ;

[0119] Determine whether the arc length reaches the insulator creepage distance. If it reaches, it means flashover has occurred. If not, further calculation is required.

[0120] The further calculation process mainly determines the voltage gradient E of the pollution layer p and arc voltage gradient E arc The size of E pIf the voltage is large, the arc develops and the length x increases to x + vdt; otherwise, it indicates that the voltage is not enough to maintain the arc development, and the increased voltage is U = U + dU.

[0121] The calculation is repeated in this way until a flashover occurs, at which point U is the flashover voltage Uc.

[0122] Based on the same application concept, the present application also provides an electronic device, comprising: a processor, a memory, and a bus. The memory is used to store execution instructions, including internal memory and external memory. The internal memory, also referred to as internal memory, is used to temporarily store calculation data in the processor, as well as data exchanged with external memory such as a hard disk. The processor exchanges data with the external memory through the internal memory. When the electronic device is in operation, the processor and the memory communicate via the bus, allowing the processor to execute the steps of the method for calculating the flashover voltage of a composite insulator under heavy pollution conditions as shown in the above method embodiments. The memory stores machine-readable instructions executable by the processor. When the electronic device is in operation, the processor and the memory communicate via the bus, and the machine-readable instructions are executed by the processor to execute the steps of the method for calculating the flashover voltage of a composite insulator under heavy pollution conditions as described in any of the above embodiments.

[0123] Based on the same application concept, an embodiment of the present application further provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of the method for calculating the flashover voltage of a composite insulator under heavy pollution conditions provided in the above embodiment are executed.

[0124] Specifically, the storage medium can be a general storage medium, such as a mobile disk, a hard disk, etc. When the computer program on the storage medium is run, the above-mentioned method for calculating the flashover voltage of the composite insulator under heavy pollution conditions can be executed.

[0125] In the embodiment of the present application, the computer program can also execute other machine-readable instructions when run by the processor to execute other methods described in the embodiment. For the specific execution method steps and principles, please refer to the description of the embodiment and will not be repeated here.

[0126] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0127] The present application is described with reference to flowcharts and / or block diagrams of methods according to embodiments of the present application.

[0128] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for calculating the flashover voltage of a composite insulator under heavy pollution conditions, characterized in that: include: Initial parameters are input into a target polluted lightning circuit model to calculate the arc root radius; the initial parameters include initial applied voltage, initial local arc length, rod radius, insulator creepage length, initial arc current, local arc length increase, and applied voltage increase; the target polluted lightning circuit model is obtained by introducing a random small arc into the initial polluted lightning circuit model; the target polluted lightning circuit model is a polluted lightning circuit model under heavy pollution conditions on composite insulators; Calculating the target residual contamination layer resistance according to the arc root radius, and calculating the initial arc current based on the Newton secant method; Calculating the contamination layer voltage gradient and the arc voltage gradient according to the initial arc current; Determining whether flashover has occurred based on the initial local arc length and the insulator creepage length, and if flashover has not occurred, correspondingly increasing the initial local arc length or the initial applied voltage based on the magnitudes of the pollution layer voltage gradient and the arc voltage gradient until a pollution flashover voltage is calculated when flashover has occurred; The target residual contamination layer resistance is calculated according to the arc root radius, and the specific formula is: Among them, R(x,I) is the target residual pollution layer resistance, σ s is the conductivity of the surface pollution layer, L is the creepage length of the insulator, x is the initial local arc length, r1 is the rod radius, and r0 is the arc root radius.

2. The method for calculating the flashover voltage of a composite insulator under heavy pollution conditions according to claim 1 is characterized in that: Input the initial parameters into the target contaminated lightning circuit model and calculate the arc root radius. The specific formula is: Where r0 is the arc root radius and I is the initial arc current.

3. The method for calculating the flashover voltage of a composite insulator under heavy pollution conditions according to claim 1 is characterized in that: The pollution layer voltage gradient and arc voltage gradient are calculated based on the initial arc current. The specific formula is: Among them, E p is the voltage gradient of the pollution layer, U p is the pollution layer voltage, R(x,I) is the target residual pollution layer resistance, x is the initial local arc length, L is the insulator creepage length, and I is the initial arc current; Among them, E arc is the arc voltage gradient, U arc is the arc voltage, A and n are constants reflecting the arc characteristics.

4. The method for calculating the flashover voltage of a composite insulator under heavy pollution conditions according to claim 1 is characterized in that: Determining whether flashover has occurred based on the initial local arc length and the insulator creepage length includes: When the initial local arc length is greater than or equal to the insulator creepage length, the flashover is reached; When the initial local arc length is less than the insulator creepage length, flashover has not yet occurred, and the pollution layer voltage gradient and the arc voltage gradient are compared.

5. The method for calculating the flashover voltage of a composite insulator under heavy pollution conditions according to claim 4 is characterized in that: When flashover has not yet occurred, the initial local arc length or the initial applied voltage is correspondingly increased based on the magnitudes of the pollution layer voltage gradient and the arc voltage gradient, including: When the pollution layer voltage gradient is greater than the arc voltage gradient, increasing the initial local arc length to a target local arc length; When the contamination layer voltage gradient is less than or equal to the arc voltage gradient, the initial applied voltage is increased to a target applied voltage.

6. The method for calculating the flashover voltage of a composite insulator under heavy pollution conditions according to claim 5 is characterized in that: The specific formula for obtaining the target local arc length and the target applied voltage is: x 目标 =x+vdt; Among them, x 目标 is the target local arc length, x is the initial local arc length, v is the arc development speed, and dt is the increase in local arc length; U 目标 =U+dU; Among them, U 目标 is the target applied voltage, U is the initial applied voltage, and dU is the increase in applied voltage.

7. The method for calculating the flashover voltage of a composite insulator under heavy pollution conditions according to claim 1 is characterized in that: Under DC conditions, the pollution flashover voltage is calculated as follows: U c1 =AxI -n +R(x,I)I; Among them, U c1 is the pollution flashover voltage under DC conditions, R(x,I) is the target residual pollution layer resistance, A and n are constants reflecting the arc characteristics, x is the initial local arc length, and I is the initial arc current.

8. The method for calculating the flashover voltage of a composite insulator under heavy pollution conditions according to claim 1 is characterized in that: Under AC conditions, the pollution flashover voltage is calculated as follows: Among them, U c2 is the pollution flashover voltage under AC conditions, x is the initial local arc length, and I is the initial arc current.

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