Limit power transmission distance calculation method for transient voltage stabilization

Abstract

The invention discloses a limit power transmission distance calculation method for transient voltage stability, and belongs to the field of power systems and automation thereof. The method comprises the following steps: establishing a transient energy function model based on a power system equipment mathematical model and an energy function theory; establishing a transient voltage stability evaluation index by using the model; calculating index values under different fault positions and different line parameters to obtain a sensitivity line graph of the line parameters and transient voltage stability; analyzing the line graph and scoring and positioning key lines; determining a power transmission line parameter selection range based on a key line sensitivity relation, and calculating a limit power transmission distance by combining engineering common power transmission line models and parameters. According to the method, transient voltage stability evaluation and parameter sensitivity analysis are combined, the limit power transmission distance is scientifically calculated, the defect that the transient voltage stability is neglected in a traditional method is overcome, and accurate and reliable technical reference can be provided for line erection planning and power grid operation mode optimization and adjustment in actual engineering.

Description

Technical Field

[0001] This invention belongs to the field of power systems and automation, specifically to a method for calculating the ultimate transmission distance for transient voltage stability. Background Technology

[0002] The power grid structure in the Chengdu-Chongqing region is becoming increasingly complex, with numerous transmission lines serving as core power transmission channels. The parameters of these lines influence power transmission and consequently, the system's voltage support capacity. However, the Chengdu-Chongqing region is a load center with insufficient energy resources, severely lacking the voltage support capacity provided by synchronous generators. When a serious system fault occurs, transient voltage instability is likely to occur. Assessing the transient voltage stability of the power system and calculating the maximum transmission distance can provide a reference for transmission line construction planning and grid operation adjustments. Invention patent CN108988320B describes a method for analyzing the impact of dynamic component response characteristics on transient voltage stability. The core technology of this invention is based on constructing evaluation indicators using generalized branch potential energy combined with reactive power recovery characteristics. However, it only focuses on the impact of dynamic components on transient voltage stability, without addressing transmission line parameter optimization and maximum transmission distance calculation. Therefore, it cannot provide direct reference for line construction planning and does not clearly define the positioning logic of critical lines, resulting in insufficient guidance for practical engineering applications. Invention patent CN114722333A discloses a method and system for estimating the transient voltage stability limit of a receiving-end system. The core technology of this invention calculates the stability limit using induction motor parameters and load power factor. However, it only focuses on estimating the transient voltage stability limit of the receiving-end system, failing to integrate transient voltage stability assessment with line parameter sensitivity analysis, neglecting the impact of different fault locations on line parameter selection, and failing to locate critical transmission lines. Furthermore, the calculation results do not incorporate commonly used transmission line models in engineering projects, resulting in insufficient practicality and relevance. Invention patent CN109217287B discloses a method for solving the transient voltage stability safety domain of AC / DC systems. The core technology of this invention constructs the safety domain boundary based on the energy function method and singular induced bifurcation theory. However, it only focuses on solving the transient voltage stability safety domain, without addressing the design of transmission line parameter selection ranges and the calculation of limit transmission distances. It does not incorporate actual transmission line parameters for practical application and cannot provide direct quantitative references for line construction planning and grid operation mode adjustments.

[0003] Current transmission line distance design primarily considers power quality, economic factors, and environmental factors. Two commonly used methods for calculating transmission distance exist: one uses voltage level and transmission capacity as references to calculate a broad transmission distance range, taking into account environmental factors, line and transformer power, and power transmission time; the other estimates the maximum transmission capacity using empirical formulas to guide the calculation of transmission distance. Overall, existing transmission distance calculation methods rarely consider the system's transient voltage stability, and the calculated transmission distance range is not detailed enough. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of the existing technology by providing a method for calculating the ultimate transmission distance based on transient voltage stability. This method assesses the transient voltage stability of the system, analyzes the sensitivity relationship between line parameters and the degree of transient voltage stability, designs the selection range of transmission line parameters, and calculates the ultimate transmission distance. This can provide a reference for transmission line construction planning and grid operation mode adjustments in practical engineering projects.

[0005] The technical solution for achieving the objective of this invention is as follows:

[0006] A method for calculating the ultimate transmission distance for transient voltage stability includes the following steps:

[0007] Step S1: Define the system network structure and equipment composition, and establish the system's energy function model;

[0008] Step S2: Verify whether the established energy function model satisfies the three conditions of the energy function: negative semi-definite derivative, nontriviality, and radial unboundedness;

[0009] Step S3: Set the node fault conditions, calculate the energy at the fault clearing time and the system critical energy, and construct a transient voltage stability evaluation index.

[0010] Step S4: Calculate the sensitivity relationship between line parameters and transient voltage stability index under different node fault conditions;

[0011] Step S5: Analyze and score the sensitivity relationship graphs of each line parameter to locate the key transmission lines;

[0012] Step S6: Based on the relationship between the line parameters of the critical line and the transient voltage stability sensitivity, calculate the selection range of the line parameters;

[0013] Step S7: Calculate the maximum transmission distance by combining the transmission line parameters used in the project and the range of line parameter selection.

[0014] Furthermore, a method for calculating the ultimate transmission distance for transient voltage stability is provided. Step S1 specifically involves the following process: The system network is a 4-machine, 10-node system improved from the IEEE 9 system. The doubly-fed wind turbine connected to node 10 is connected to node 9 via a transformer. Load nodes 5 and 8 are connected to static characteristic loads, load node 6 is connected to an induction motor load, and synchronous generators are located at nodes 1, 2, and 3. The system energy function is the sum of the energy functions of five types of equipment in the system: synchronous generator SG, static characteristic load SL, induction motor load M, doubly-fed wind turbine DFIG, and transmission network NET. The specific formula for the sum of the energy functions is as follows:

[0015]

[0016] In the formula, This indicates the node number where the device is located. The energy function of a synchronous generator. The energy function of the static characteristic load. The energy function of the induction motor load. The energy function of a doubly-fed wind turbine. The sum of the energy functions of the power transmission network is given by the following formulas for calculating the energy functions of the five types of equipment:

[0017]

[0018] In the formula, Let be the inertial constant of the generator. The generator's angular velocity, For generator mechanical power, The generator power angle, and They are respectively Synchronous reactance and transient reactance of shaft, for Shaft synchronous reactance, and Generator stator current in Axial components, For the magnetizing potential, To represent the transient process of the generator excitation winding shaft transient potential, The state of the system at its stable equilibrium point. Let t be the system state at time t, and the formula below contains... , Similarly;

[0019]

[0020] In the formula, , These represent the active and reactive power of the static characteristic load, respectively. , These represent the voltage magnitude and phase angle at the load node, respectively.

[0021]

[0022] In the formula, For the mechanical torque of the induction motor, The phase angle of the internal electromotive force of the induction motor. , These are equivalent synchronous reactance and transient reactance, respectively. , The dq-axis component of the stator current of the induction motor;

[0023]

[0024] In the formula, , These represent the active power and reactive power output of the doubly-fed wind turbine, respectively. , These are the voltage magnitude and phase angle at node 10, respectively.

[0025]

[0026] In the formula, , Let i and j be the voltage amplitudes at nodes i and j, respectively. , For elements in the network node admittance matrix The conductivity and susceptance components, This represents the phase angle difference of the node voltages at both ends of the line between nodes i and j.

[0027] Furthermore, in a method for calculating the ultimate transmission distance for transient voltage stability, the three conditions for verifying the energy function model in step S2 are:

[0028] Negative semi-qualitative property of the function derivative: The derivative of the system energy function with respect to time along the system trajectory is non-positive, i.e. ;

[0029] Non-triviality: if If it is not an equilibrium point, then the set In R, the measure is 0, only... At the equilibrium point ;

[0030] Radial unboundedness: If the energy function If it is bounded, then the system trajectory It also has boundaries.

[0031] Furthermore, in a method for calculating the ultimate transmission distance for transient voltage stability, step S3 specifically comprises the following steps:

[0032] A three-phase short-circuit fault occurred at a certain node of the system, and the fault time was [time missing]. , The initial time, Given the fault clearing time, transient data is obtained through simulation, and the transient energy value at the fault clearing time is calculated. Solve for the voltage-dominant unstable equilibrium point of the system. Substituting these values ​​into the system energy function expression, the critical energy of the system can be calculated. The constructed transient voltage stability evaluation index is:

[0033]

[0034] Indicates stability margin, if After a system fault, the transient voltage stabilizes; conversely, the transient voltage becomes unstable.

[0035] Furthermore, in a method for calculating the ultimate transmission distance for transient voltage stability, step S4 specifically includes the following steps:

[0036] By sequentially setting fault conditions at different nodes, the resistance of the transmission line is changed. Reactance Grounding susceptance To obtain the power transmission lines Line graph, differentiate the resulting line graph to obtain the sensitivity line graph: .

[0037] Furthermore, in a method for calculating the ultimate transmission distance for transient voltage stability, step S5 specifically includes the following steps:

[0038] Taking the absolute value of the sensitivity curve obtained in step S5 Draw a relationship curve diagram and calculate the average absolute value of the sensitivity of each line in the diagram. Assume the total number of transmission lines is... The line with the highest average score is , The remaining lines are scored in descending order of their average scores. All relationship diagrams are scored, and the total scores of each line are ranked to identify key transmission lines.

[0039] Furthermore, in a method for calculating the ultimate transmission distance for transient voltage stability, step S6 specifically includes the following steps:

[0040] Convergence point of critical path sensitivity values The minimum convergence point is taken as the boundary value of the line parameters. Combined with the positive and negative information of the sensitivity line graph to the left of the boundary value, the selection range of transmission line parameters is determined.

[0041] Furthermore, in a method for calculating the ultimate transmission distance for transient voltage stability, step S7 specifically comprises the following steps:

[0042] The range of per-unit values ​​for the critical path parameters obtained in step S7 , , Let the parameters of a certain transmission line used in the project be: number of lines. Positive sequence resistor Positive sequence reactance Positive sequence capacitor Transmission voltage level ,frequency System baseline capacity Three transmission distances were calculated based on the range of three line parameters. , , The expression is as follows:

[0043]

[0044] Actual transmission distance All three constraints must be satisfied simultaneously; the intersection of the three constraints is taken: , Limiting transmission distance , These represent the minimum and maximum values ​​of the actual transmission distance, respectively. , If the calculated transmission distances of the three types do not all overlap, then the transmission distance range obtained by selecting the line parameter with higher sensitivity should be used for calculation based on the sensitivity line diagram of the critical line.

[0045] This application presents a method for calculating the ultimate transmission distance based on transient voltage stability. Combining transient voltage stability assessment and parameter sensitivity analysis, it establishes a sensitivity relationship between line parameters and transient voltage stability indicators, thereby identifying critical transmission lines. This method enables transmission line parameter design and transmission distance calculation that considers transient voltage stability, providing a reference for adjusting line construction schemes and system operation modes in practical engineering. Compared with existing technologies, this invention has the following advantages:

[0046] 1. This invention proposes a method for calculating the ultimate transmission distance that integrates transient voltage stability assessment and line parameter sensitivity analysis. Addressing the problem that existing transmission distance calculations neglect transient voltage stability, this method establishes an energy function model incorporating multiple devices such as synchronous generators and doubly-fed wind turbines, constructs transient voltage stability assessment indices, and combines line parameter sensitivity analysis under different fault locations to accurately locate critical lines and optimize the parameter selection range. This enables the quantitative calculation of the ultimate transmission distance under transient voltage stability constraints, filling the gap in safety and stability considerations in traditional methods.

[0047] 2. This invention, through a complete process of "index construction - sensitivity analysis - critical line location - parameter optimization - distance calculation", compared with existing methods that only focus on stability analysis or limit estimation, does not rely on complex simulation software or empirical formulas. It directly combines commonly used transmission line models and parameters in engineering to output specific transmission distance ranges. The calculation results are more in line with actual engineering needs, providing direct and reliable quantitative references for line construction planning and power grid operation mode adjustment, and significantly improving practicality.

[0048] 3. This invention incorporates new energy equipment such as doubly-fed wind turbines in the energy function model construction stage and considers the impact of different fault locations on line parameters. Compared with traditional technical solutions that only target AC / DC systems or single fault scenarios, it has a wider range of applications and can adapt to modern power systems with high penetration rates of new energy and complex grid structures. At the same time, by using sensitivity scoring to locate critical lines, parameter optimization becomes more targeted, effectively improving the system's transient voltage stability and reducing the risk of voltage instability caused by faults. Attached Figure Description

[0049] Figure 1 A flowchart of a method for calculating the ultimate transmission distance for transient voltage stability;

[0050] Figure 2 This is a schematic diagram of a system grid structure and its components;

[0051] Figure 3 The system's energy function curve is shown below.

[0052] Figure 4 Sensitivity graphs of line parameters and transient voltage stability evaluation indicators;

[0053] Figure 5 A schematic diagram of the scoring results for each transmission line;

[0054] Figure 6 Sensitivity curves of line parameters and transient voltage stability indicators for critical lines at different fault locations;

[0055] Figure 7 Voltage waveforms at various nodes of the system before and after designing the parameters for key transmission lines. Detailed Implementation

[0056] To more clearly describe the ideas, technical solutions, and advantages of the present invention, specific embodiments are illustrated through examples and accompanying drawings. Obviously, the described embodiments are only a portion, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0057] A method for calculating the ultimate transmission distance for transient voltage stability includes the following steps:

[0058] Step S1: Define the system network structure and equipment composition, and establish the system's energy function model;

[0059] Step S2: Verify whether the established energy function model satisfies the three conditions of the energy function: negative semi-definite derivative, nontriviality, and radial unboundedness;

[0060] Step S3: Set the node fault conditions, calculate the energy at the fault clearing time and the system critical energy, and construct a transient voltage stability evaluation index.

[0061] Step S4: Calculate the sensitivity relationship between line parameters and transient voltage stability index under different node fault conditions;

[0062] Step S5: Analyze and score the sensitivity relationship graphs of each line parameter to locate the key transmission lines;

[0063] Step S6: Based on the relationship between the line parameters of the critical line and the transient voltage stability sensitivity, calculate the selection range of the line parameters;

[0064] Step S7: Calculate the maximum transmission distance by combining the transmission line parameters used in the project and the range of line parameter selection.

[0065] Furthermore, a method for calculating the ultimate transmission distance for transient voltage stability is provided. Step S1 specifically involves the following process: The system network is a 4-machine, 10-node system improved from the IEEE 9 system. The doubly-fed wind turbine connected to node 10 is connected to node 9 via a transformer. Load nodes 5 and 8 are connected to static characteristic loads, load node 6 is connected to an induction motor load, and synchronous generators are located at nodes 1, 2, and 3. The system energy function is the sum of the energy functions of five types of equipment in the system: synchronous generator SG, static characteristic load SL, induction motor load M, doubly-fed wind turbine DFIG, and transmission network NET. The specific formula for the sum of the energy functions is as follows:

[0066]

[0067] In the formula, This indicates the node number where the device is located. The energy function of a synchronous generator. The energy function of the static characteristic load. The energy function of the induction motor load. The energy function of a doubly-fed wind turbine. The sum of the energy functions of the power transmission network is given by the following formulas for calculating the energy functions of the five types of equipment:

[0068]

[0069] In the formula, Let be the inertial constant of the generator. The generator's angular velocity, For generator mechanical power, The generator power angle, and They are respectively Synchronous reactance and transient reactance of shaft, for Shaft synchronous reactance, and Generator stator current in Axial components, For the magnetizing potential, To represent the transient process of the generator excitation winding shaft transient potential, The state of the system at its stable equilibrium point. Let t be the system state at time t, and the formula below contains... , Similarly;

[0070]

[0071] In the formula, , These represent the active and reactive power of the static characteristic load, respectively. , These represent the voltage magnitude and phase angle at the load node, respectively.

[0072]

[0073] In the formula, For the mechanical torque of the induction motor, The phase angle of the internal electromotive force of the induction motor. , These are equivalent synchronous reactance and transient reactance, respectively. , The dq-axis component of the stator current of the induction motor;

[0074]

[0075] In the formula, , These represent the active power and reactive power output of the doubly-fed wind turbine, respectively. , These are the voltage magnitude and phase angle at node 10, respectively.

[0076]

[0077] In the formula, , Let i and j be the voltage amplitudes at nodes i and j, respectively. , For elements in the network node admittance matrix The conductivity and susceptance components, This represents the phase angle difference of the node voltages at both ends of the line between nodes i and j.

[0078] Furthermore, in a method for calculating the ultimate transmission distance for transient voltage stability, the three conditions for verifying the energy function model in step S2 are:

[0079] Negative semi-qualitative property of the function derivative: The derivative of the system energy function with respect to time along the system trajectory is non-positive, i.e. ;

[0080] Non-triviality: if If it is not an equilibrium point, then the set In R, the measure is 0, only... At the equilibrium point ;

[0081] Radial unboundedness: If the energy function If it is bounded, then the system trajectory It also has boundaries.

[0082] Furthermore, in a method for calculating the ultimate transmission distance for transient voltage stability, step S3 specifically comprises the following steps:

[0083] A three-phase short-circuit fault occurred at a certain node of the system, and the fault time was [time missing]. , The initial time, Given the fault clearing time, transient data is obtained through simulation, and the transient energy value at the fault clearing time is calculated. Solve for the voltage-dominant unstable equilibrium point of the system. Substituting these values ​​into the system energy function expression, the critical energy of the system can be calculated. The constructed transient voltage stability evaluation index is:

[0084]

[0085] Indicates stability margin, if After a system fault, the transient voltage stabilizes; conversely, the transient voltage becomes unstable.

[0086] Furthermore, in a method for calculating the ultimate transmission distance for transient voltage stability, step S4 specifically includes the following steps:

[0087] By sequentially setting fault conditions at different nodes, the resistance of the transmission line is changed. Reactance Grounding susceptance To obtain the power transmission lines Line graph, differentiate the resulting line graph to obtain the sensitivity line graph: .

[0088] Furthermore, in a method for calculating the ultimate transmission distance for transient voltage stability, step S5 specifically includes the following steps:

[0089] Taking the absolute value of the sensitivity curve obtained in step S5 Draw a relationship curve diagram and calculate the average absolute value of the sensitivity of each line in the diagram. Assume the total number of transmission lines is... The line with the highest average score is , The remaining lines are scored in descending order of their average scores. All relationship diagrams are scored, and the total scores of each line are ranked to identify key transmission lines.

[0090] Furthermore, in a method for calculating the ultimate transmission distance for transient voltage stability, step S6 specifically includes the following steps:

[0091] Convergence point of critical path sensitivity values The minimum convergence point is taken as the boundary value of the line parameters. Combined with the positive and negative information of the sensitivity line graph to the left of the boundary value, the selection range of transmission line parameters is determined.

[0092] Furthermore, in a method for calculating the ultimate transmission distance for transient voltage stability, step S7 specifically comprises the following steps:

[0093] The range of per-unit values ​​for the critical path parameters obtained in step S7 , , Let the parameters of a certain transmission line used in the project be: number of lines. Positive sequence resistor Positive sequence reactance Positive sequence capacitor Transmission voltage level ,frequency System baseline capacity Three transmission distances were calculated based on the range of three line parameters. , , The expression is as follows:

[0094]

[0095] Actual transmission distance All three constraints must be satisfied simultaneously; the intersection of the three constraints is taken: , Limiting transmission distance , These represent the minimum and maximum values ​​of the actual transmission distance, respectively. , If the calculated transmission distances of the three types do not all overlap, then the transmission distance range obtained by selecting the line parameter with higher sensitivity should be used for calculation based on the sensitivity line diagram of the critical line.

[0096] Figure 1 This is a flowchart illustrating the method for calculating the ultimate transmission distance based on transient voltage stability, as described in this invention. The specific steps are as follows:

[0097] Step S1, based on Figure 2 The embodiment describes the system's grid structure and equipment composition. Based on energy function theory, an energy function model of the system is established, and the resulting system energy function curves are obtained. like Figure 3 As shown, by Figure 3 It can be seen that the energy function curve after the system failure basically shows a downward trend, which satisfies the verification condition (1) of the energy function; observing the change characteristics of the energy function curve, there is no Furthermore, the situation of maintaining this state for a certain duration satisfies the verification condition (2) of the energy function; the energy function has upper and lower bounds, and after a certain time, the energy function tends to an equilibrium value close to 0, proving that the trajectory will be in equilibrium after the system failure, thus satisfying the verification condition (3) of the energy function;

[0098] Step S2: After verifying the rationality of the constructed system energy function, the transient isobaric stability evaluation index established under the energy function theory is as follows:

[0099]

[0100] Among them, the system energy at the fault clearing moment The critical energy of the system is calculated by substituting the transient response data during the fault into the energy function expression. The process of obtaining the equilibrium point is as follows: Using the pre-fault equilibrium point obtained from power flow calculations as the initial value, iteratively solve the post-fault system equations to obtain the post-fault stable equilibrium point; determine the dominant load node based on the electrical distance of the load bus from the fault point and the voltage drop; perform Thevenin equivalence on the system outside the dominant load node according to the post-fault stable equilibrium point, and then solve the load equations at the dominant load bus to obtain the voltage amplitude and phase angle of the static load or the slip and internal potential of the induction motor load; use the values ​​of the post-fault stable equilibrium point for the system parameters outside the dominant load node, and iteratively solve the system equations again. If the iteration converges to... If the iteration ends, then proceed; otherwise, modify the generator or load state near the dominant load bus and iterate again until convergence is reached. ;Will Substituting the system state at a point into the energy function expression, the critical energy is calculated. The larger the value, the higher the stability of the transient voltage after a system fault.

[0101] Step S3: Set the line The initial parameter value is The parameter sensitivity test ranges are respectively Sensitivity curves for the transient voltage stability index of three types of line parameters under different fault conditions were obtained: , Figure 4 The sensitivity curve is shown for a three-phase short-circuit fault at node 5.

[0102] Step S5: To demonstrate the impact of each line parameter on transient voltage stability, the average value of the absolute sensitivity curve for each line parameter is taken. This average value is used to evaluate the line parameters that have a critical impact on transient voltage stability. Each line parameter is scored according to line category, and the scoring results are as follows: Figure 5 As shown in the figure, the critical path is the path between nodes 6 and 9.

[0103] Step S6, Analysis Figure 6 The parameter sensitivity plot of the critical path shows that, for the path parameters of the critical path... Its selection range is The initial value of the line Select a set of parameters within this range. The system was tested, and the fault time was taken as the extreme clearing time of 0.68s before the line parameters were changed. The node voltage results before and after parameter design are as follows. Figure 7 As shown in the figure, the transient voltage stability of the system improved before and after the design. This demonstrates that the transmission line parameters selected according to the present invention can improve the transient voltage stability of the system.

[0104] Step S7: Based on the line parameter selection range obtained in step S6, select the model as... of For calculating the transmission distance of a single-circuit overhead transmission line, the line parameters are as follows: , , The system's baseline capacity is... The calculated transmission distance range is: .

[0105] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for calculating the ultimate transmission distance for transient voltage stability, characterized in that, Includes the following steps: Step S1: Define the system network structure and equipment composition, and establish the system's energy function model; Step S2: Verify whether the established energy function model satisfies the three conditions of the energy function: negative semi-definite derivative, nontriviality, and radial unboundedness; Step S3: Set the node fault conditions, calculate the energy at the fault clearing time and the system critical energy, and construct a transient voltage stability evaluation index. Step S4: Calculate the sensitivity relationship between line parameters and transient voltage stability index under different node fault conditions; Step S5: Analyze and score the sensitivity relationship graphs of each line parameter to locate the key transmission lines; Step S6: Based on the relationship between the line parameters of the critical line and the transient voltage stability sensitivity, calculate the selection range of the line parameters; Step S7: Calculate the maximum transmission distance by combining the transmission line parameters used in the project and the range of line parameter selection.

2. The method for calculating the ultimate transmission distance for transient voltage stability according to claim 1, characterized in that, The specific process of step S1 is as follows: The system network is a 4-machine 10-node system improved from the IEEE 9 system. The doubly-fed wind turbine connected to node 10 is connected to node 9 via a transformer. Load nodes 5 and 8 are connected to static characteristic loads, load node 6 is connected to an induction motor load, and synchronous generators are located at nodes 1, 2, and 3. The system energy function is the sum of the energy functions of the five types of equipment in the system: synchronous generator SG, static characteristic load SL, induction motor load M, doubly-fed wind turbine DFIG, and transmission network NET. The specific formula for the sum of the energy functions is as follows: In the formula, This indicates the node number where the device is located. The energy function of a synchronous generator. The energy function of the static characteristic load. The energy function of the induction motor load. The energy function of a doubly-fed wind turbine. The sum of the energy functions of the power transmission network is given by the following formulas for calculating the energy functions of the five types of equipment: In the formula, Let be the inertial constant of the generator. The generator's angular velocity, For generator mechanical power, The generator power angle, and They are respectively Synchronous reactance and transient reactance of shaft, for Shaft synchronous reactance, and Generator stator current in Axial components, For the magnetizing potential, To represent the transient process of the generator excitation winding shaft transient potential, The state of the system at its stable equilibrium point. Let t be the system state at time t, and the formula below contains... , Similarly; In the formula, , These represent the active and reactive power of the static characteristic load, respectively. , These represent the voltage magnitude and phase angle at the load node, respectively. In the formula, For the mechanical torque of the induction motor, The phase angle of the internal electromotive force of the induction motor. , These are equivalent synchronous reactance and transient reactance, respectively. , The dq-axis component of the stator current of the induction motor; In the formula, , These represent the active power and reactive power output of the doubly-fed wind turbine, respectively. , These are the voltage magnitude and phase angle at node 10, respectively. In the formula, , Let i and j be the voltage amplitudes at nodes i and j, respectively. , For elements in the network node admittance matrix The conductivity and susceptance components, This represents the phase angle difference of the node voltages at both ends of the line between nodes i and j.

3. The method for calculating the ultimate transmission distance for transient voltage stability according to claim 1, characterized in that, The three conditions for verifying the energy function model in step S2 are: Negative semi-qualitative property of the function derivative: The derivative of the system energy function with respect to time along the system trajectory is non-positive, i.e. ; Non-triviality: if If it is not an equilibrium point, then the set In R, the measure is 0, only... At the equilibrium point ; Radial unboundedness: If the energy function If it is bounded, then the system trajectory It also has boundaries.

4. The method for calculating the ultimate transmission distance for transient voltage stability according to claim 1, characterized in that, The specific steps of step S3 are as follows: A three-phase short-circuit fault occurred at a certain node of the system, and the fault time was [time missing]. , The initial time, Given the fault clearing time, transient data is obtained through simulation, and the transient energy value at the fault clearing time is calculated. Solve for the voltage-dominant unstable equilibrium point of the system. Substituting these values ​​into the system energy function expression, the critical energy of the system is calculated. The constructed transient voltage stability evaluation index is: Indicates stability margin, if After a system fault, the transient voltage stabilizes; conversely, the transient voltage becomes unstable.

5. The method for calculating the ultimate transmission distance for transient voltage stability according to claim 1, characterized in that, The specific steps of step S4 are as follows: By sequentially setting fault conditions at different nodes, the resistance of the transmission line is changed. Reactance Grounding susceptance To obtain the power transmission lines Line graph, differentiate the resulting line graph to obtain the sensitivity line graph: .

6. A method for calculating the ultimate transmission distance for transient voltage stability as described in claim 1, characterized in that, The specific steps of step S5 are as follows: Taking the absolute value of the sensitivity curve obtained in step S5 Draw a relationship curve diagram and calculate the average absolute value of the sensitivity of each line in the diagram. Assume the total number of transmission lines is... The line with the highest average score is , The remaining lines are scored in descending order of their average scores. All relationship diagrams are scored, and the total scores of each line are ranked to identify key transmission lines.

7. The method for calculating the ultimate transmission distance for transient voltage stability according to claim 1, characterized in that, The specific steps of step S6 are as follows: Convergence point of critical path sensitivity values The minimum convergence point is taken as the boundary value of the line parameters. Combined with the positive and negative information of the sensitivity line graph to the left of the boundary value, the selection range of transmission line parameters is determined.

8. The method for calculating the ultimate transmission distance for transient voltage stability according to claim 1, characterized in that, The specific steps of step S7 are as follows: The range of per-unit values ​​for the critical path parameters obtained in step S7 , , Let the parameters of a certain transmission line used in the project be: number of lines. Positive sequence resistor Positive sequence reactance Positive sequence capacitor Transmission voltage level ,frequency System baseline capacity Three transmission distances were calculated based on the range of three line parameters. , , The expression is as follows: Actual transmission distance All three constraints must be satisfied simultaneously; the intersection of the three constraints is taken: , Limiting transmission distance , These represent the minimum and maximum values ​​of the actual transmission distance, respectively. , If the calculated transmission distances of the three types do not all overlap, then the transmission distance range obtained by selecting the line parameter with higher sensitivity should be used for calculation based on the sensitivity line diagram of the critical line.

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