A Site Selection Method for Upgrading and Retrofitting Circuit Breakers in High-Voltage Power Stations at the Receiving End of the Power Grid

Abstract

This invention discloses a site selection method for upgrading and retrofitting circuit breakers at high-voltage substations in a receiving-end power grid, comprising: S1: calculating the first short-circuit current of each high-voltage substation considering aperiodic components, calculating the decay time from the first short-circuit current to the circuit breaker breaking current, and determining the circuit breaker opening time of each high-voltage substation based on the decay time; S2: verifying the stability of each high-voltage substation under AC fault conditions based on the opening time; S3: optimizing the high-voltage substations in an unstable state, repeating S1 and S2 until the unstable high-voltage substations reach a stable state; S4: calculating the second short-circuit current of each high-voltage substation without considering aperiodic components, and determining the substations requiring circuit breaker upgrades based on the second short-circuit current and the circuit breaker breaking current. This invention selects substations with a significant impact on power system stability for circuit breaker upgrades while ensuring the safe and stable operation of the power system, and has good application prospects.

Description

Technical Field

[0001] This invention relates to the field of power technology, and in particular to a method for selecting sites for upgrading and retrofitting high-voltage substation circuit breakers in receiving-end power grids. Background Technology

[0002] With the continuous increase in electricity load density, in order to improve system stability and power supply reliability, my country's power grid has formed a main grid structure at the 500kV voltage level, and the grid structure is still being strengthened. This has caused the short-circuit current at load centers to gradually approach or even exceed the breaking capacity of circuit breakers. This is generally addressed by optimizing the grid structure and restarting equipment, but this weakens the integrity of the grid structure. Therefore, a contradiction exists between grid stability and excessive short-circuit current, making it urgent to upgrade the circuit breakers of 500kV substations at load centers where short-circuit currents exceed limits.

[0003] Short-circuit currents during AC faults contain both periodic and aperiodic components. Traditional calculations typically only consider the periodic component. However, because short-circuit currents cannot change abruptly, the current after adding the aperiodic component exceeds the circuit breaker's breaking current. The circuit breaker can only disconnect the line when the aperiodic component decays to below the breaking current over time. If a method incorporating the aperiodic component is used to evaluate circuit breaker upgrade sites, upgrading circuit breakers in numerous high-voltage substations (e.g., 500kV substations) would be necessary to ensure the safe and stable operation of the power system. A single 500kV substation typically has at least 10 circuit breakers, and the large capacity of these breakers could present challenges such as insufficient land. Circuit breaker upgrade projects are large-scale, time-consuming, and costly. Therefore, it is necessary to selectively upgrade only a subset of circuit breakers while ensuring the stability of the power system. Summary of the Invention

[0004] The purpose of this invention is to provide a site selection method for upgrading and retrofitting circuit breakers in high-voltage substations of receiving-end power grids, so as to solve the technical problems of existing technologies that lack specificity, large project scale, and long time consumption in upgrading circuit breakers in high-voltage substations of receiving-end power grids.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A method for selecting sites for upgrading and retrofitting circuit breakers at high-voltage substations in a receiving-end power grid, wherein the receiving-end power grid includes multiple high-voltage substations, the method comprising:

[0007] S1: Calculate the first short-circuit current of each of the high-voltage substations, calculate the decay time of each of the high-voltage substations based on the first short-circuit current, and determine the circuit breaker breaking time of each of the high-voltage substations based on the decay time; wherein, the first short-circuit current is a three-phase short-circuit current considering non-periodic components, the decay time is the time it takes for the first short-circuit current to decay to the circuit breaker breaking current, and the circuit breaker breaking current is the maximum value of the current that the circuit breaker breaks.

[0008] S2: Based on the interruption time, verify the stability of each of the high-voltage substations when an AC fault occurs, the stability including a stable state and an unstable state;

[0009] S3: Optimize the high-voltage power station that is in an unstable state, and repeat steps S1 and S2 until the high-voltage power station in an unstable state reaches a stable state.

[0010] S4: Calculate the second short-circuit current of each of the high-voltage substations, and determine the high-voltage substations that need to be upgraded based on the second short-circuit current and the circuit breaker breaking current. The second short-circuit current is the three-phase short-circuit current without considering non-periodic components.

[0011] Optionally, the high-voltage substations requiring circuit breaker upgrades are determined based on the second short-circuit current and the circuit breaker breaking current, including:

[0012] The system sequentially determines whether the second short-circuit current of each high-voltage substation is greater than the circuit breaker breaking current. If so, the circuit breaker of the high-voltage substation needs to be upgraded.

[0013] Optionally, determining the breaking time of each high-voltage substation circuit breaker based on the attenuation time includes:

[0014] The attenuation time corresponding to the high-voltage substation multiplied by a preset coefficient is used as the breaking time of the circuit breaker of the high-voltage substation.

[0015] Optionally, the preset coefficient is 1.1.

[0016] Optionally, optimizing the high-voltage power station in an unstable state includes at least:

[0017] A dynamic reactive power compensation device is installed at the high-voltage power station that is in an unstable state.

[0018] Optionally, optimizing the high-voltage power station in an unstable state further includes:

[0019] Add outgoing lines to the high-voltage substation that is in an unstable state.

[0020] Optionally, the AC fault is:

[0021] Three-phase short circuit N-1 fault and / or three-phase short circuit N-2 fault.

[0022] Optionally, the stability of each of the high-voltage substations under AC fault conditions is checked, including:

[0023] An electromechanical transient simulation program was used to simulate and calculate the AC faults that occurred in each of the high-voltage power plants, and the stability of the high-voltage power plants when AC faults occurred was judged based on the simulation results.

[0024] When the simulation results meet the preset stability conditions, the high-voltage power station is in a stable state; otherwise, the high-voltage power station is in an unstable state.

[0025] Optionally, the preset stability condition is:

[0026] Guidelines for the safety and stability of power systems.

[0027] Optionally, the high-voltage substation is a 500kV substation.

[0028] This invention provides a method for selecting sites for upgrading and retrofitting circuit breakers at high-voltage substations in a receiving-end power grid. The receiving-end power grid includes multiple high-voltage substations. The method includes: S1: calculating the first short-circuit current of each high-voltage substation, calculating the decay time corresponding to each high-voltage substation based on the first short-circuit current, and determining the breaking time of the circuit breaker at each high-voltage substation based on the decay time; wherein, the first short-circuit current is a three-phase short-circuit current considering aperiodic components, the decay time is the time it takes for the first short-circuit current to decay to the breaking current of the circuit breaker, and the breaking current of the circuit breaker is the time it takes for the circuit breaker to break. S1: The maximum current value; S2: According to the interruption time, check the stability of each high-voltage substation when an AC fault occurs, the stability includes a stable state and an unstable state; S3: Optimize the high-voltage substation in the unstable state, repeat steps S1 and S2 until the high-voltage substation in the unstable state reaches a stable state; S4: Calculate the second short-circuit current of each high-voltage substation, and determine the high-voltage substations that need to be upgraded based on the second short-circuit current and the circuit breaker interruption current, the second short-circuit current is the three-phase short-circuit current without considering non-periodic components.

[0029] In view of this, the beneficial effects of this invention are:

[0030] This invention calculates the first short-circuit current of each high-voltage substation, considering the aperiodic component, and further obtains the decay time and circuit breaker breaking time. Based on the breaking time, it verifies the stability of each high-voltage substation during AC faults, optimizes substations in unstable states until they reach a stable state, and selects substations where the second short-circuit current (excluding the aperiodic component) is greater than the circuit breaker breaking current for circuit breaker upgrades. This invention selectively upgrades circuit breakers in substations that significantly impact power system stability, while ensuring the safe and stable operation of the power system. It reduces the scale of circuit breaker upgrades, saves time and costs, and has high practical value and application prospects. Attached Figure Description

[0031] Figure 1 This is a schematic flowchart of the method of the present invention;

[0032] Figure 2 This is a flowchart illustrating an embodiment of the present invention. Detailed Implementation

[0033] This invention provides a site selection method for upgrading and retrofitting circuit breakers in high-voltage substations of receiving-end power grids, in order to solve the technical problems of existing technologies that lack specificity, involve large-scale projects, and are time-consuming when retrofitting circuit breakers in high-voltage substations of receiving-end power grids.

[0034] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0036] Short-circuit currents during AC faults contain both periodic and aperiodic components. Traditional calculations typically only consider the periodic component. However, because short-circuit currents cannot change abruptly, the current after adding the aperiodic component often exceeds the circuit breaker's breaking current. The circuit breaker can only disconnect the line when the aperiodic component decays to below the breaking current over time. If a method incorporating the aperiodic component is used to evaluate circuit breaker upgrade locations, a large number of circuit breakers would need to be upgraded. Circuit breaker upgrade projects are large-scale, time-consuming, and costly, resulting in poor economic efficiency. Therefore, a comprehensive approach considering stability is needed to optimize circuit breaker upgrade locations.

[0037] The inventors discovered that, based on short-circuit current calculations that take into account aperiodic components, nearly 70% of high-voltage substations in the Guangdong power grid, such as 500kV substations, have short-circuit currents exceeding the breaking capacity of their circuit breakers. If a method considering aperiodic components of short-circuit current is used to evaluate the selection of circuit breaker upgrade sites, then the circuit breakers of these nearly 70% of substations would need to be upgraded. This upgrade project would be large-scale, time-consuming, and costly. However, the actual stability margin of the large power grid is relatively high. By evaluating the impact of circuit breaker breaking time on system stability, the inventors can selectively upgrade the circuit breakers at sites with a greater impact on stability, thereby ensuring the safe and stable operation of the power system.

[0038] It should be noted that the periodic component is the stable short-circuit current after the short-circuit transition process ends; the non-periodic component is the component that decays exponentially during the transition process, generally decaying to zero in ten cycles.

[0039] Please see Figure 1 The following are embodiments of the site selection method for upgrading and retrofitting high-voltage substation circuit breakers in the receiving-end power grid according to the present invention, including:

[0040] S100: Calculate the first short-circuit current of each of the high-voltage substations, calculate the decay time corresponding to each of the high-voltage substations based on the first short-circuit current, and determine the circuit breaker breaking time of each of the high-voltage substations based on the decay time; wherein, the first short-circuit current is a three-phase short-circuit current considering non-periodic components, the decay time is the time it takes for the first short-circuit current to decay to the circuit breaker breaking current, and the circuit breaker breaking current is the maximum value of the current broken by the circuit breaker.

[0041] S200: Based on the interruption time, verify the stability of each of the high-voltage substations when an AC fault occurs, the stability including a stable state and an unstable state;

[0042] S300: Optimize the high-voltage power station that is in an unstable state, and repeat steps S1 and S2 until the high-voltage power station in an unstable state reaches a stable state.

[0043] S400: Calculate the second short-circuit current of each of the high-voltage substations, and determine the high-voltage substations that need to be upgraded based on the second short-circuit current and the circuit breaker breaking current. The second short-circuit current is a three-phase short-circuit current that does not consider non-periodic components.

[0044] In this embodiment, the high-voltage substation of the receiving-end power grid can be a 500KV substation, and the circuit breaker breaking current is the maximum value of the current that the circuit breaker disconnects, which depends on the equipment manufacturing.

[0045] In step S100, the first short-circuit current of each high-voltage substation in the receiving-end power grid is calculated. The first short-circuit current is a three-phase short-circuit current considering non-periodic components. The decay time corresponding to each high-voltage substation is calculated based on the first short-circuit current, and the opening time of the circuit breaker of each high-voltage substation is determined based on the decay time.

[0046] The decay time for high-voltage substations refers to the time it takes for the initial short-circuit current to decay to the breaking current of the circuit breaker, where the breaking current is the maximum value of the current interrupted by the circuit breaker. It is understandable that each high-voltage substation has its own decay time, and the decay times of different substations may be the same or different.

[0047] Specifically, determining the opening time of each high-voltage substation circuit breaker based on the attenuation time includes: using the attenuation time corresponding to the high-voltage substation multiplied by a preset coefficient as the opening time of the circuit breaker for that high-voltage substation; in a preferred embodiment, the preset coefficient is 1.1, that is, the opening time of the high-voltage substation circuit breaker is equal to the attenuation time corresponding to that high-voltage substation multiplied by 1.1.

[0048] In step S200, the stability of each high-voltage substation under AC fault conditions is checked based on the interruption time. For example, the simulated AC fault is a three-phase short-circuit N-1 fault and / or a three-phase short-circuit N-2 fault. Stability includes a stable state and an unstable state. Specifically, an electromechanical transient simulation program is used to simulate and calculate the AC faults occurring in each high-voltage substation. The stability of the high-voltage substation under AC fault conditions is determined based on the simulation results. When the simulation results meet the preset stability conditions, the high-voltage substation is in a stable state; otherwise, the high-voltage substation is in an unstable state.

[0049] In this embodiment, the preset stability condition is: the power system safety and stability guidelines or the preset stability level target.

[0050] In this embodiment, an electromechanical transient simulation program is used to simulate AC system faults in the vicinity of power plants. Based on the power system safety and stability guidelines, it is determined whether the high-voltage power plants are stable when AC faults occur. The simulation of AC system faults includes simulating single component faults or simulating combined component faults.

[0051] It should be noted that, in addition to simulating three-phase short-circuit N-1 faults and / or three-phase short-circuit N-2 faults, this embodiment can also simulate more complex AC faults, depending on the desired range of AC fault resistance; generally, it is based on the first two levels of safety and stability standards regarding the power system's ability to withstand large disturbances in the power system safety and stability guidelines.

[0052] In step S300, optimizing the high-voltage substation in an unstable state includes at least: installing a dynamic reactive power compensation device on the high-voltage substation in an unstable state; in a preferred embodiment, installing a dynamic reactive power compensation device 300MVar on the high-voltage substation in an unstable state; it may also include: adding outgoing lines to the high-voltage substation in an unstable state.

[0053] In step S400, determining the high-voltage substations requiring circuit breaker upgrades based on the second short-circuit current and the circuit breaker breaking current includes: sequentially determining whether the second short-circuit current of each high-voltage substation is greater than the circuit breaker breaking current; if so, the high-voltage substation needs to undergo circuit breaker upgrades. The theoretical basis is the short-circuit current safety verification criterion in the power system safety and stability guidelines: the bus short-circuit current level does not exceed the breaking capacity of its circuit breaker (switch).

[0054] The method for selecting sites for upgrading and retrofitting circuit breakers at high-voltage substations in the receiving-end power grid provided in this embodiment calculates the first short-circuit current of each high-voltage substation considering the non-periodic component, and further obtains the decay time and the circuit breaker's breaking time. Based on the breaking time, the stability of each high-voltage substation during AC faults is checked, and substations in an unstable state are optimized until a stable state is achieved. Substations with a second short-circuit current (excluding the non-periodic component) greater than the circuit breaker's breaking current are selected for circuit breaker upgrades. This method selectively targets substations with a significant impact on power system stability for circuit breaker upgrades, while ensuring the safe and stable operation of the power system. It reduces the scale of circuit breaker upgrades, saves time and costs, and has high practical value and application prospects.

[0055] Please see Figure 2 Another embodiment of the site selection method for upgrading and retrofitting high-voltage substation circuit breakers in the receiving-end power grid provided by the present invention is described in detail below:

[0056] Step 1: Based on the full-operation mode of the power grid, calculate the three-phase short-circuit current of the 500kV substations that take into account the non-periodic component. Calculate the time it takes for the effective value of the short-circuit current of each substation to decay to the maximum value of the circuit breaker breaking current, i.e., the decay time. Multiply the time by 1.1 to obtain the breaking time of the circuit breaker.

[0057] Step 2: Select the stringent operating mode and the above-mentioned interruption time, and verify the stability level of each plant and station in the event of an AC fault;

[0058] Step 3: For the unstable fault point, by optimizing the near-zone wiring method and adding dynamic reactive power compensation, recalculate the short-circuit current and breaking time under the non-periodic component according to Step 1, and calculate the stability level according to Step 2, until the power system safety and stability guidelines or the established stability level target are met.

[0059] Step 4: Based on the above optimization measures, calculate the short-circuit current without considering the non-periodic component. Substations that exceed the circuit breaker breaking current are the substations where the circuit breaker needs to be upgraded.

[0060] Referring to Tables 1 to 4, the process of this invention will be described below with a specific example:

[0061] Step 1: Based on the full-load, full-connection operation mode of a provincial power grid, calculate the three-phase short-circuit current of each 500kV substation, taking into account the non-periodic component. Based on the maximum interrupted current of each 500kV substation's circuit breaker, obtain the time it takes for the effective value of the short-circuit current to decay to that value, and the time it takes to multiply that value by 1.1. Substations requiring close monitoring of stability are shown in Table 1.

[0062] Table 1

[0063] Factory Station voltage level Maximum breaking current decay time 1.1 × decay time Plant A 500kV 67kA 0.23 seconds 0.253 seconds Plant B 500kV 63kA 0.35 seconds 0.385 seconds Plant C 500kV 64kA 0.40 seconds 0.44 seconds

[0064] Step 2: Since the provincial power grid is a multi-DC-feed receiving-end grid, the summer high-load mode is selected as the stringent mode. Based on the above 1.1 × decay time as the circuit breaker breaking time, electromechanical transient simulation calculations are performed on the three-phase short-circuit N-1 fault and three-phase short-circuit N-2 fault of the substation outgoing lines. The simulation results show that the system operates stably under the three-phase short-circuit N-1 fault of the above three substation outgoing lines. Under the three-phase short-circuit N-2 fault, voltage instability occurs in substations A and B.

[0065] Step 3: Consider installing dynamic reactive power compensation equipment (STATCOM or synchronous condenser) of 300MVar each at plant A and plant B. Recalculate the short-circuit current and breaking time considering the non-periodic component as shown in Table 2, following Step 1:

[0066] Table 2

[0067] Factory Station voltage level Maximum breaking current decay time 1.1 × decay time Plant A 500kV 67kA 0.29 seconds 0.319 seconds Plant B 500kV 63kA 0.41 seconds 0.451 seconds

[0068] Selecting three-phase short-circuit N-1 fault and three-phase short-circuit N-2 fault on the outgoing lines of the substation, and using 1.1 × decay time as the circuit breaker breaking time, electromechanical transient simulation calculations were performed again. The simulation results show that the systems of the two substations with three-phase short-circuit N-1 faults operate stably, while the substation B system exhibits voltage instability under the three-phase short-circuit N-2 fault, and the substation A system remains stable.

[0069] Similarly, a 300MVar dynamic reactive power compensation device is installed at plant B, and an additional outgoing line is added to plant B. The short-circuit current and breaking time, taking into account the non-periodic components, are recalculated according to step 1, as shown in Table 3.

[0070] Table 3

[0071] Factory Station voltage level Maximum breaking current decay time 1.1 × decay time Plant B 500kV 63kA 0.44 seconds 0.484 seconds

[0072] Selecting three-phase short-circuit N-1 fault and three-phase short-circuit N-2 fault on the outgoing line of the substation, and using 1.1 × decay time as the circuit breaker breaking time, electromechanical transient simulation calculations were performed again. The simulation results show that the system operates stably under both three-phase short-circuit N-1 fault and three-phase short-circuit N-2 fault on the outgoing line of substation B.

[0073] Step 4: Based on the above optimization measures, calculate the short-circuit current without considering the aperiodic component, as shown in Table 4:

[0074] Table 4

[0075]

[0076]

[0077] The calculation results show that the short circuit in plant B exceeds the breaking current of the circuit breaker. Therefore, the circuit breaker in plant B should be selected for upgrading and renovation first.

[0078] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0079] In the embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection between devices or units through some interfaces, and may be electrical, mechanical, or other forms.

[0080] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0081] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0082] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0083] 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 in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for selecting sites for upgrading and retrofitting high-voltage substation circuit breakers in a receiving-end power grid, characterized in that, The receiving-end power grid includes multiple high-voltage substations, and the method includes: S1: Calculate the first short-circuit current of each of the high-voltage substations, calculate the decay time corresponding to each of the high-voltage substations based on the first short-circuit current, and determine the circuit breaker breaking time of each of the high-voltage substations based on the decay time; wherein, the first short-circuit current is a three-phase short-circuit current considering non-periodic components, the decay time is the time it takes for the first short-circuit current to decay to the circuit breaker breaking current, and the circuit breaker breaking current is the maximum value of the current broken by the circuit breaker. S2: Based on the interruption time, verify the stability of each of the high-voltage substations when an AC fault occurs, the stability including a stable state and an unstable state; S3: Optimize the high-voltage power station that is in an unstable state, and repeat steps S1 and S2 until the high-voltage power station in an unstable state reaches a stable state. S4: Calculate the second short-circuit current of each of the high-voltage substations, and determine the high-voltage substations that need to be upgraded based on the second short-circuit current and the circuit breaker breaking current. The second short-circuit current is the three-phase short-circuit current without considering non-periodic components.

2. The site selection method for upgrading and retrofitting high-voltage substation circuit breakers in the receiving-end power grid according to claim 1, characterized in that, Based on the second short-circuit current and the circuit breaker breaking current, the high-voltage substations requiring circuit breaker upgrades include: The system sequentially determines whether the second short-circuit current of each high-voltage substation is greater than the circuit breaker breaking current. If so, the circuit breaker of the high-voltage substation needs to be upgraded.

3. The site selection method for upgrading and retrofitting high-voltage substation circuit breakers in the receiving-end power grid according to claim 1, characterized in that, Determining the breaking time of each high-voltage substation circuit breaker based on the attenuation time includes: The attenuation time corresponding to the high-voltage substation multiplied by a preset coefficient is used as the breaking time of the circuit breaker of the high-voltage substation.

4. The site selection method for upgrading and retrofitting high-voltage substation circuit breakers in the receiving-end power grid according to claim 3, characterized in that, The preset coefficient is 1.

1.

5. The site selection method for upgrading and retrofitting high-voltage substation circuit breakers in the receiving-end power grid according to claim 1, characterized in that, Optimization of the high-voltage power plant in an unstable state includes at least the following: A dynamic reactive power compensation device is installed at the high-voltage power station that is in an unstable state.

6. The site selection method for upgrading and retrofitting high-voltage substation circuit breakers in the receiving-end power grid according to claim 1, characterized in that, Optimization of the high-voltage power plant in an unstable state also includes: Add outgoing lines to the high-voltage substation that is in an unstable state.

7. The site selection method for upgrading and retrofitting high-voltage substation circuit breakers in the receiving-end power grid according to claim 1, characterized in that, The AC fault is: Three-phase short circuit N-1 fault and / or three-phase short circuit N-2 fault.

8. The site selection method for upgrading and retrofitting high-voltage substation circuit breakers in the receiving-end power grid according to claim 1, characterized in that, The stability of each of the aforementioned high-voltage substations under AC fault conditions includes: An electromechanical transient simulation program was used to simulate and calculate the AC faults that occurred in each of the high-voltage power plants, and the stability of the high-voltage power plants when AC faults occurred was judged based on the simulation results. When the simulation results meet the preset stability conditions, the high-voltage power station is in a stable state; otherwise, the high-voltage power station is in an unstable state.

9. The site selection method for upgrading and retrofitting high-voltage substation circuit breakers in the receiving-end power grid according to claim 8, characterized in that, The preset stability condition is: Guidelines for the safety and stability of power systems.

10. The site selection method for upgrading and retrofitting high-voltage substation circuit breakers in the receiving-end power grid according to any one of claims 1-9, characterized in that, The high-voltage substation is a 500kV substation.

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