Method for analyzing internal overvoltage of power transmission project

Abstract

The invention discloses a power transmission project internal overvoltage analysis method, and belongs to the technical field of power system overvoltage control. In order to solve the problem of poor overvoltage evaluation accuracy in operation of a supporting project after centralized development of new energy, the method comprises the following steps: determining a new energy consumption level through load flow calculation, and performing load flow adjustment to obtain a load flow mode; performing multi-point network equivalence calculation on the target power transmission project to obtain an equivalence parameter; constructing a power transmission system equivalent simulation model, performing power flow verification, and adjusting equivalent parameters to enable a power flow result to be consistent with a power flow mode result obtained through power flow calculation; based on the verified equivalent simulation model, simulation calculation of power frequency overvoltage and operation overvoltage is carried out, and simulation calculation of secondary arc current and recovery voltage is carried out; and according to a simulation calculation result, a debugging and starting scheme of the power transmission system is obtained, and a basis is provided for secondary equipment constant value setting, overvoltage protection device model selection and engineering implementation. The method is used for an electric power system.

Description

Technical Field

[0001] This invention relates to a method for analyzing overvoltages inside power transmission projects, belonging to the field of power system overvoltage control technology. Background Technology

[0002] The scale of new energy power generation, represented by wind and solar power, continues to expand. Taking Heilongjiang Province as an example, its new energy development is progressing well, adhering to a development path of large-scale centralized development, high-voltage access, and high-level consumption. It has already established several large-scale new energy bases in Harbin, Daqing, Qiqihar, Suihua, and the eastern region. To meet the demand for large-scale grid-connected power generation from new energy sources, Heilongjiang Province is actively promoting the construction of a "four horizontal and five vertical" 500kV backbone grid, aiming to comprehensively improve the capacity for transmitting new energy to other regions, optimize the allocation of power resources within the province, and strengthen interconnection with external power grids, thus laying a solid foundation for regional economic development and energy transformation.

[0003] Against this backdrop, the safe and stable operation of 500kV transmission projects, as a crucial component of the power grid backbone, is of paramount importance. Internal overvoltages are one of the main threats to the safety of ultra-high voltage power grids, primarily including power frequency overvoltages, switching overvoltages, and transient overvoltages. If these overvoltages are not effectively controlled, they may lead to serious accidents such as insulation flashover, equipment damage, or even system collapse. For newly constructed 500kV transmission projects, system commissioning and startup scheme verification must be conducted before commissioning, providing accurate basis for the setting of secondary equipment protection settings.

[0004] Currently, traditional internal overvoltage analysis methods mostly rely on simplified calculations or simulations based on specific operating modes, making it difficult to comprehensively reflect the overvoltage characteristics under complex power grid environments, especially after a high proportion of renewable energy integration. The randomness and volatility of renewable energy generation, along with the widespread application of power electronic equipment, make system operating characteristics more complex, and the generation mechanism and propagation characteristics of internal overvoltages have also changed significantly. Existing analysis methods have the following shortcomings: first, they do not adequately consider the spatiotemporal distribution characteristics of overvoltages under scenarios of concentrated renewable energy integration; second, they lack quantitative analysis of the mutual influence of overvoltages under complex grid structures; and third, their adaptability to actual engineering parameters needs to be improved in simulation modeling.

[0005] Therefore, there is an urgent need for a method for studying and analyzing internal overvoltages in newly built 500kV transmission projects. This method should be able to accurately simulate actual system operating conditions, comprehensively assess overvoltage levels under various operating conditions, provide a reliable theoretical basis for project implementation, and provide a reference for system commissioning and operation, thereby ensuring the safe and stable operation of the power system in the future. Summary of the Invention

[0006] The purpose of this invention is to address the problem of poor accuracy in overvoltage assessment during the commissioning of supporting projects after the centralized development of new energy sources, and to provide a method for analyzing overvoltage within power transmission projects.

[0007] The present invention discloses a method for analyzing internal overvoltages in power transmission projects, comprising:

[0008] Based on the impact of newly built power transmission projects and the commissioning of new energy collection stations on the power grid, the level of new energy absorption is determined through power flow calculation, and power flow adjustment is carried out to obtain the power flow mode.

[0009] A simulation software platform was used to perform multi-point network equivalent calculations on the target power transmission project to obtain equivalent parameters.

[0010] Based on the obtained equivalent parameters, an equivalent simulation model of the power transmission system is constructed.

[0011] The equivalent simulation model is verified by power flow. By adjusting the equivalent parameters, the power flow results of the equivalent simulation model are made consistent with the power flow results obtained by power flow calculation.

[0012] Based on the verified equivalent simulation model, simulation calculations were performed on power frequency overvoltage and switching overvoltage, as well as simulation calculations on inrush current and recovery voltage.

[0013] Based on the simulation results, a commissioning and startup scheme for the power transmission system is obtained, providing a basis for setting secondary equipment settings, selecting overvoltage protection devices, and implementing the project.

[0014] Preferably, the goal of the power flow adjustment is to control the line power flow and node voltage within a threshold range.

[0015] Preferably, the equivalent parameters include equivalent impedance parameters and equivalent power supply parameters;

[0016] The equivalent impedance parameters include the equivalent positive sequence impedance and the equivalent zero sequence impedance;

[0017] The equivalent power source parameters include the voltage, phase angle, and frequency of the equivalent power source.

[0018] Preferably, an equivalent simulation model of the power transmission system is constructed on an electromagnetic transient simulation platform; the electromagnetic transient simulation platform is the PSCAD software platform.

[0019] Preferably, the equivalent simulation model includes selecting the corresponding transmission line model according to the line type, and connecting the equivalent impedance parameters and equivalent power supply parameters at the nodes.

[0020] Preferably, the step of selecting the corresponding transmission line model according to the line type specifically includes: using the Bergeron model for single-circuit lines and using the tower model for double-circuit lines;

[0021] The parameters modeled using the Bergeron model for the single-circuit line include: line length, positive sequence impedance, positive sequence reactance, positive sequence capacitive reactance, zero sequence impedance, zero sequence reactance, and zero sequence capacitive reactance.

[0022] The parameters for modeling the double-circuit line using a tower model include: line length, tower data, ground wire radius, DC resistance of the wire, sag, and earth resistivity.

[0023] Preferably, the specific method for performing power frequency overvoltage simulation calculation based on the verified equivalent simulation model includes: simulating the actual circuit breaker operation sequence on the verified equivalent simulation model, performing power frequency overvoltage simulation under the operating mode, and obtaining the value and waveform of the power frequency overvoltage;

[0024] The operating modes include no-line operation and single-phase reclosing operation;

[0025] Under the commissioning mode, calculate the power frequency overvoltage under two conditions: the no-load long-line capacitive rise effect caused by the closing of a circuit breaker in a section of the out-of-operation line when the new substation is not connected to the power system, and the single-phase short circuit at the end of the line in operation.

[0026] Under normal conditions, calculate the power frequency overvoltages of the line after a faultless trip at both ends of the line when the new substation is connected to the power system, including the rise of the no-load long line voltage and the power frequency overvoltages of the phase-to-ground and phase-to-phase after a single-phase short circuit and load shedding at the end of the line.

[0027] Under maintenance conditions, calculate the voltage rise of the no-load long line after a faultless trip at one end of the operating line when the new substation is connected to the power system, and the phase-to-ground and phase-to-phase power frequency overvoltages after a single-phase short circuit and load shedding at the end of the operating line.

[0028] Preferably, the specific method for simulating and calculating the operational overvoltage based on the verified equivalent simulation model includes: simulating the circuit breaker operation sequence that conforms to statistical laws on the verified equivalent simulation model, performing multiple no-load charging and single-phase reclosing operational overvoltage simulations, and obtaining the value and waveform of the operational overvoltage through statistical methods.

[0029] Preferably, the circuit breaker operating sequence conforming to statistical laws specifically includes: performing multiple simulations using the Multiple Run module; using 2% statistical overvoltage in conjunction with insulation for operational overvoltage; the three-phase operating time of the switch following a random uniform distribution within one cycle; and the asynchronicity time of the three-phase switch following a normal distribution within the interval [-0.0025s, 0.0025s].

[0030] The number of times the overvoltage simulation of multiple empty-charge closing and single-phase reclosing operations is performed is 120.

[0031] The statistical method used is the Monte Carlo method, which is used to calculate the average value of the operating overvoltage.

[0032] Preferably, the specific method for simulating the leakage current and recovery voltage based on the verified equivalent simulation model includes: simulating a single-phase grounding arc using a variable arc resistor on the verified equivalent simulation model, and simulating the leakage current and recovery voltage to obtain their values ​​and waveforms.

[0033] Advantages of this invention: This invention proposes an analysis method for internal overvoltage in power transmission projects. It discusses the impact of new energy substation-supporting power transmission projects on regional power flow distribution after grid connection from three aspects: power flow scheme analysis, accurate simulation modeling, and accurate calculation of internal overvoltage. Through internal overvoltage calculation, it obtains the theoretical basis for the setting values ​​of secondary equipment in supporting power transmission projects and the selection of overvoltage protection. It has the following advantages:

[0034] 1. Improved accuracy and engineering applicability of overvoltage calculations: In the calculation of operational overvoltages, by introducing Monte Carlo statistical methods, Multiple Run batch simulations, and considering the mechanical dispersion of circuit breakers (random uniform distribution and normal distribution), the calculation results are transformed from a single "maximum value" into a more scientific "statistical value," which can more realistically reflect the probability distribution characteristics of overvoltages and provide a more reliable and economical theoretical basis for insulation coordination and equipment selection.

[0035] 2. Improved comprehensive assessment of key electrical characteristics of new energy transmission projects: This invention not only covers conventional power frequency overvoltage and switching overvoltage, but also specifically targets single-phase reclosing technology to ensure stable grid operation. It conducts accurate simulation of inrush current and recovery voltage, and dynamically simulates the electric arc using a variable arc resistance model. The assessment results are more accurate and directly guide the setting of secondary system settings and the formulation of reclosing strategies.

[0036] 3. Provides direct and comprehensive decision support for project commissioning: This method ultimately outputs a comprehensive solution integrating commissioning and startup plans, secondary equipment setting recommendations, and overvoltage protection device selection. It fundamentally reduces the technical risks of new construction projects, especially new energy supporting projects, during commissioning, providing an indispensable technical prerequisite and guarantee for the safe and stable power transmission from large-scale new energy bases like Heilongjiang Province. Attached Figure Description

[0037] Figure 1 This is a flowchart of an analysis method for internal overvoltage in power transmission projects according to the present invention. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0040] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of the invention.

[0041] Example 1:

[0042] The following is combined with Figure 1 This embodiment describes a method for analyzing overvoltages inside a power transmission project, which includes:

[0043] Based on the impact of newly built power transmission projects and the commissioning of new energy collection stations on the power grid, the level of new energy absorption is determined through power flow calculation, and power flow adjustment is carried out to obtain the power flow mode.

[0044] A simulation software platform was used to perform multi-point network equivalent calculations on the target power transmission project to obtain equivalent parameters.

[0045] Based on the obtained equivalent parameters, an equivalent simulation model of the power transmission system is constructed.

[0046] The equivalent simulation model is verified by power flow. By adjusting the equivalent parameters, the power flow results of the equivalent simulation model are made consistent with the power flow results obtained by power flow calculation.

[0047] Based on the verified equivalent simulation model, simulation calculations were performed on power frequency overvoltage and switching overvoltage, as well as simulation calculations on inrush current and recovery voltage.

[0048] Based on the simulation results, a commissioning and startup scheme for the power transmission system is obtained, providing a basis for setting secondary equipment settings, selecting overvoltage protection devices, and implementing the project.

[0049] Furthermore, the goal of the power flow adjustment is to control the line power flow and node voltage within a threshold range.

[0050] Furthermore, the equivalent parameters include equivalent impedance parameters and equivalent power supply parameters;

[0051] The equivalent impedance parameters include the equivalent positive sequence impedance and the equivalent zero sequence impedance;

[0052] The equivalent power source parameters include the voltage, phase angle, and frequency of the equivalent power source.

[0053] Furthermore, an equivalent simulation model of the power transmission system is constructed on an electromagnetic transient simulation platform; the electromagnetic transient simulation platform is the PSCAD software platform.

[0054] Furthermore, the equivalent simulation model includes selecting the corresponding transmission line model according to the line type, and connecting the equivalent impedance parameters and equivalent power supply parameters at the nodes.

[0055] Furthermore, the selection of the corresponding transmission line model according to the line type specifically includes: single-circuit lines are modeled using the Bergeron model, and double-circuit lines are modeled using the tower model.

[0056] The parameters modeled using the Bergeron model for the single-circuit line include: line length, positive sequence impedance, positive sequence reactance, positive sequence capacitive reactance, zero sequence impedance, zero sequence reactance, and zero sequence capacitive reactance.

[0057] The parameters for modeling the double-circuit line using a tower model include: line length, tower data, ground wire radius, DC resistance of the wire, sag, and earth resistivity.

[0058] Furthermore, the specific method for simulating and calculating power frequency overvoltage based on the verified equivalent simulation model includes: simulating the actual circuit breaker operating sequence on the verified equivalent simulation model, performing power frequency overvoltage simulation under the operating mode, and obtaining the value and waveform of the power frequency overvoltage.

[0059] The operating modes include no-line operation and single-phase reclosing operation;

[0060] Under the commissioning mode, calculate the power frequency overvoltage under two conditions: the no-load long-line capacitive rise effect caused by the closing of a circuit breaker in a section of the out-of-operation line when the new substation is not connected to the power system, and the single-phase short circuit at the end of the line in operation.

[0061] Under normal conditions, calculate the power frequency overvoltages of the line after a faultless trip at both ends of the line when the new substation is connected to the power system, including the rise of the no-load long line voltage and the power frequency overvoltages of the phase-to-ground and phase-to-phase after a single-phase short circuit and load shedding at the end of the line.

[0062] Under the maintenance mode, calculate the overvoltage of the no-load long line after a fault-free tripping occurs at one end of the operating line and the power frequency overvoltage between phases and relative to ground after a single-phase short circuit and load shedding at the end of the operating line when the new substation is connected to the power system. Further, the specific method for simulating the switching overvoltage based on the verified equivalent simulation model includes: on the verified equivalent simulation model, simulate the breaker operation sequence that conforms to the statistical law, conduct multiple no-load closing and single-phase reclosing switching overvoltage simulations, and obtain the values and waveforms of the switching overvoltage through statistical methods.

[0063] Further, the breaker operation sequence that conforms to the statistical law specifically includes: using the Multiple Run module to conduct multiple simulations; using 2% statistical overvoltage for the insulation coordination of switching overvoltage; the three-phase operation time of the switch follows a random uniform distribution within one cycle; the three-phase non-synchronization time of the switch follows a normal distribution within the interval [-0.0025 s, 0.0025 s];

[0064] The number of times of conducting multiple no-load closing and single-phase reclosing switching overvoltage simulations is 120 times;

[0065] The statistical method is the Monte Carlo method, which is used to obtain the average value of the switching overvoltage.

[0066] Further, the specific method for simulating the induced current and recovery voltage based on the verified equivalent simulation model includes: on the verified equivalent simulation model, simulate the single-phase grounding arc through a variable arc resistance, conduct the simulation of the induced current and recovery voltage, and obtain their values and waveforms.

[0067] In this invention, it aims to solve the internal overvoltage problem faced by the supporting 500 kV transmission project during the commissioning process after the centralized development of new energy. This invention provides a complete research method from macroscopic power flow analysis to microscopic electromagnetic transient simulation and then to engineering decision-making.

[0068] Taking a 500 kV new energy collection and transmission project in a certain provincial power grid as an example, the specific steps are as follows:

[0069] Step 1: Determine the power flow mode. Considering the impact of the commissioning of the newly built transmission line and the large power generation of the new energy collection station on the power flow and voltage of the nearby lines, adjust the power flow to a reasonable range and determine the new energy consumption situation in the region.

[0070] This step, fundamental to the entire study, aims to determine the most stringent yet reasonable computational conditions. Based on the region's power grid planning data, we established a full power grid model in the BPA power flow calculation software. We specifically considered the extreme operating conditions after the commissioning of newly built 500kV lines and the large-scale generation of wind and solar power at renewable energy collection stations (e.g., output exceeding 90% of installed capacity). Calculations revealed that under these conditions, the voltage at a nearby 500kV hub station was too high, reaching 545kV. Subsequently, by adjusting transformer tap changes and switching reactive power compensation devices, we stabilized the voltage within a reasonable range of 525kV-540kV, confirming that the renewable energy absorption capacity under this method was 3500MW. This specific and validated power flow mode will serve as the sole benchmark operating state for all subsequent electromagnetic transient simulations.

[0071] Step 2: Select the newly constructed power transmission project to be studied, and use the multi-point network equivalent function of the BAP software platform to calculate the equivalent impedance and equivalent power source point of the target power transmission project, and obtain the equivalent positive sequence and zero sequence impedance, the phase angle, frequency and voltage of the equivalent power source.

[0072] In this step, to perform detailed overvoltage simulation in PSCAD, it is neither necessary nor possible to build a model of the entire regional power grid. Therefore, this step builds upon the baseline operating conditions determined in the first step, utilizing the multi-point network equivalence function of BPA software to simplify the complex external power grid using the newly built 500kV transmission project as the boundary. After calculation, we obtain the equivalent positive-sequence impedance, equivalent zero-sequence impedance, and the voltage and phase angle of the equivalent power source at the boundary points. These equivalent parameters accurately represent the impact of the external power grid on the target project under the operating conditions described in the first step.

[0073] Step 3: Select the PSCAD simulation software platform to perform equivalent modeling of the power transmission and transformation system; according to the specific situation of the power transmission project, the Bergeron model is used for single-circuit lines (required parameters: line length, positive sequence impedance, positive sequence reactance, positive sequence capacitive reactance, zero sequence impedance, zero sequence reactance, zero sequence capacitive reactance), and the tower model is used for double-circuit lines (required parameters: line length, tower data, ground wire radius, DC resistance and sag of the wire, and earth resistivity). Equivalent impedance and equivalent power supply are added at the nodes.

[0074] In this step, we build a detailed model of the 500kV transmission project in the PSCAD / EMTDC simulation platform. Finally, at the boundary nodes of the model, we connect the equivalent impedance and equivalent power source calculated in the second step, thus forming a complete simulation model that includes both engineering details and considers the influence of external systems.

[0075] Step 4: Power flow adjustment to verify the correctness and rationality of the established model; by adjusting the power supply voltage and phase angle of the equivalent power source, the power flow direction and values ​​of the transmission project are made consistent with the power flow results in BPA.

[0076] In this step, to ensure the accuracy and reliability of the model, we performed power flow verification. Steady-state calculations were initiated in PSCAD. By fine-tuning the voltage magnitude and phase angle of the equivalent power source obtained in the second step, we ensured that the magnitude and direction of the power flow through the newly built line in the model (e.g., active power of 1250MW flowing from the collecting station to the main grid) were highly consistent with the results of the BPA power flow calculation in the first step. This process demonstrates that our electromagnetic transient model can accurately reflect the steady-state operating conditions of the power grid, laying a solid foundation for the reliability of subsequent transient calculations.

[0077] Step 5: Use the PSCAD platform to calculate power frequency overvoltage. The control of circuit breaker timing must conform to the actual situation. Simulate and analyze the power frequency overvoltage values ​​and waveform changes under different operating modes, such as closing the open line, single-phase reclosing, and simulation analysis.

[0078] In this step, based on the validated model, we simulate the circuit breaker operating sequence during actual dispatch operations to calculate power frequency overvoltage. Simulation results show that the power frequency overvoltage level is within the safe range.

[0079] Step Six: Use the PSCAD platform to calculate the overvoltage during operation. The timing control of the circuit breaker must conform to the actual situation. The overvoltage during operation should follow statistical laws. Select the Multiple Run module. Use 2% statistical voltage for insulation coordination. The three-phase switch operation time should follow a random uniform distribution within one cycle. The asynchrony of the three phases of the switch should follow a normal distribution in the interval [-0.0025-0.0025]. Perform 120 calculations of no-load charging and single-phase reclosing for the newly built power transmission project model. Introduce the Monte Carlo method to obtain the average value of the 120 operating overvoltages and obtain the value and waveform changes of the operating overvoltage.

[0080] In this step, we perform 120 random no-load charging and single-phase reclosing simulations on the newly built engineering model. After the calculations are completed, the system automatically processes all the data to obtain the 2% statistical value of the operating overvoltage of the project, providing accurate data support for surge arrester configuration and insulation coordination.

[0081] Step 7: Use the PSCAD platform to perform simulation calculations and analysis of the inrush current and recovery voltage of the power transmission system; use the FAULTG module to set the arc resistance, and use a variable arc resistance to simulate the arc length of a single-phase grounding arc, and simulate the numerical and waveform changes of the inrush current and recovery voltage.

[0082] In this step, based on this data, it can be determined whether suppression measures such as installing high-speed grounding switches are needed.

[0083] Step 8: Taking into account steps 5, 6, and 7, the optimal commissioning and startup scheme can be determined, providing a theoretical basis for the setting of secondary equipment values, the selection of overvoltage protection devices, and the implementation of the project, ultimately achieving the safe and stable operation of the newly built line and the effective transmission and consumption of power from the new energy collection station.

[0084] Based on the above analysis, we finalized the commissioning and startup plan for the project in this step, including the circuit breaker operation sequence, relay protection setting recommendations, and overvoltage protection device selection, ensuring the successful commissioning of the new line on the first attempt and guaranteeing the effective transmission of new energy power.

[0085] While the invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that different dependent claims and features described herein can be combined in ways different from those described in the original claims. It is also understood that features described in conjunction with individual embodiments can be used in other described embodiments.

Claims

1. A method for analyzing overvoltages inside power transmission projects, characterized in that, It includes: Based on the impact of newly built power transmission projects and the commissioning of new energy collection stations on the power grid, the level of new energy absorption is determined through power flow calculation, and power flow adjustment is carried out to obtain the power flow mode. A simulation software platform was used to perform multi-point network equivalent calculations on the target power transmission project to obtain equivalent parameters. Based on the obtained equivalent parameters, an equivalent simulation model of the power transmission system is constructed. The equivalent simulation model is verified by power flow. By adjusting the equivalent parameters, the power flow results of the equivalent simulation model are made consistent with the power flow results obtained by power flow calculation. Based on the verified equivalent simulation model, simulation calculations were performed on power frequency overvoltage and switching overvoltage, as well as simulation calculations on inrush current and recovery voltage. Based on the simulation results, a commissioning and startup scheme for the power transmission system is obtained, providing a basis for setting secondary equipment settings, selecting overvoltage protection devices, and implementing the project.

2. The method for analyzing overvoltages inside a power transmission project according to claim 1, characterized in that, The goal of the power flow adjustment is to control the line power flow and node voltage within a threshold range.

3. The method for analyzing overvoltages inside a power transmission project according to claim 1, characterized in that, The equivalent parameters include equivalent impedance parameters and equivalent power supply parameters; The equivalent impedance parameters include the equivalent positive sequence impedance and the equivalent zero sequence impedance; The equivalent power source parameters include the voltage, phase angle, and frequency of the equivalent power source.

4. The method for analyzing overvoltages inside a power transmission project according to claim 1, characterized in that, An equivalent simulation model of the power transmission system is constructed on an electromagnetic transient simulation platform, which is the PSCAD software platform.

5. A method for analyzing internal overvoltages in a power transmission project according to claim 1 or 4, characterized in that, The equivalent simulation model includes selecting the corresponding transmission line model according to the line type, and connecting the equivalent impedance parameters and equivalent power supply parameters at the nodes.

6. The method for analyzing overvoltages inside a power transmission project according to claim 4, characterized in that, The specific steps for selecting the appropriate transmission line model based on the line type include: using the Bergeron model for single-circuit lines and using the tower model for double-circuit lines. The parameters modeled using the Bergeron model for the single-circuit line include: line length, positive sequence impedance, positive sequence reactance, positive sequence capacitive reactance, zero sequence impedance, zero sequence reactance, and zero sequence capacitive reactance. The parameters for modeling the double-circuit line using a tower model include: line length, tower data, ground wire radius, DC resistance of the wire, sag, and earth resistivity.

7. The method for analyzing overvoltages inside a power transmission project according to claim 1, characterized in that, The specific method for simulating power frequency overvoltage based on the verified equivalent simulation model includes: simulating the actual circuit breaker operating sequence on the verified equivalent simulation model, performing power frequency overvoltage simulation under the operating mode, and obtaining the value and waveform of the power frequency overvoltage. The operating modes include no-line operation and single-phase reclosing operation; Under the commissioning mode, calculate the power frequency overvoltage under two conditions: the no-load long-line capacitive rise effect caused by the closing of a circuit breaker in a section of the out-of-operation line when the new substation is not connected to the power system, and the single-phase short circuit at the end of the line in operation. Under normal conditions, calculate the power frequency overvoltages of the line after a faultless trip at both ends of the line when the new substation is connected to the power system, including the rise of the no-load long line voltage and the power frequency overvoltages of the phase-to-ground and phase-to-phase after a single-phase short circuit and load shedding at the end of the line. Under maintenance conditions, calculate the voltage rise of the no-load long line after a faultless trip at one end of the operating line when the new substation is connected to the power system, and the phase-to-ground and phase-to-phase power frequency overvoltages after a single-phase short circuit and load shedding at the end of the operating line.

8. The method for analyzing overvoltages inside a power transmission project according to claim 1, characterized in that, The specific method for simulating and calculating the operational overvoltage based on the verified equivalent simulation model includes: simulating the circuit breaker operation sequence that conforms to statistical laws on the verified equivalent simulation model, performing multiple no-load charging and single-phase reclosing operational overvoltage simulations, and obtaining the numerical value and waveform of the operational overvoltage through statistical methods.

9. The method for analyzing overvoltages inside a power transmission project according to claim 8, characterized in that, The circuit breaker operating sequence that conforms to statistical laws specifically includes: performing multiple simulations using the Multiple Run module; using 2% statistical overvoltage in conjunction with insulation for operational overvoltage; ensuring that the three-phase operating time of the switch follows a random uniform distribution within one cycle; and ensuring that the asynchronicity time of the three-phase switch follows a normal distribution within the interval [-0.0025s, 0.0025s]. The number of times the overvoltage simulation of multiple empty-charge closing and single-phase reclosing operations is performed is 120. The statistical method used is the Monte Carlo method, which is used to calculate the average value of the operating overvoltage.

10. The method for analyzing overvoltages inside a power transmission project according to claim 1, characterized in that, The specific method for simulating and calculating the inrush current and recovery voltage based on the verified equivalent simulation model includes: simulating a single-phase grounding arc using a variable arc resistor on the verified equivalent simulation model, and simulating the inrush current and recovery voltage to obtain their values ​​and waveforms.

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