A power grid operation risk assessment method for 110-kilovolt voltage level loop closing battery replacement

Abstract

This invention discloses a method for assessing the operational risks of 110 kV voltage-level closed-loop power swapping, belonging to the field of power grid safety and stability analysis technology. The invention includes three steps: Step 1: analyzing the influencing factors of closed-loop power swapping based on existing problems and conditions; Step 2: quantitatively analyzing the closed-loop power swapping process based on the status of primary and secondary power grid equipment and the overall power grid operation; Step 3: deriving closed-loop risk assessment indicators based on Steps 1 and 2, forming a risk assessment mechanism, and conducting risk assessments for 110 kV voltage-level closed-loop power swapping operations. This invention can comprehensively analyze the impact and feasibility of closed-loop operations on the power grid, and conduct a comprehensive risk assessment of the safety of the 500 kV cross-regional electromagnetic loop network formed by short-term 110 kV closed-loop power swapping, facilitating scientific guidance for closed-loop power swapping operations. This invention has strong applicability and high reliability.

Description

Technical Field

[0001] This invention relates to the field of power grid safety and stability analysis technology, and in particular to a method for assessing the operational risks of a 110 kV voltage level closed-loop power swapping system. Background Technology

[0002] The construction of a robust power grid has led to increasingly higher reliability of power supply from large power grids. However, in some areas, due to constraints on the grid structure and a lack of economic viability for upgrades, a significant mismatch exists between power supply capacity and load growth during the development phase. To appropriately improve the power supply reliability of local power grids, avoid power outages for users, and reduce the total duration of power outages throughout the year, short-term loop closures can be used for load transfer.

[0003] According to the power system dispatching regulations, when a power grid operating in zones is closed in a loop, it should meet three conditions: "same system, correct phase, and reasonable voltage difference". In a 110 kV loop, the voltage amplitude difference on both sides of the loop closing point should not exceed 30%, and the phase angle difference should not exceed 30 degrees. In a 500 kV loop, the voltage amplitude difference on both sides of the loop closing switch should not exceed 20%, and the phase angle difference should not exceed 20 degrees.

[0004] In the event of a disconnection of the 220 kV interconnection line in a given area, the 110 kV voltage level loop connection would create a large electromagnetic loop network between two 500 kV power supply areas. In this case, loop connection and power swapping can provide a feasible solution for uninterrupted power supply in the weak areas of the 110 kV grid. However, the operation of the electromagnetic loop network formed by the short-term loop connection may bring grid safety issues. Therefore, a risk assessment is required for the 110 kV voltage level cross-area loop connection. Summary of the Invention

[0005] The purpose of this invention is to propose a risk assessment method for 110 kV voltage level closed-loop power swapping, to conduct risk assessment on 110 kV voltage level closed-loop power swapping, and to solve the problem of the impact of closed-loop power swapping on the safety of the power grid and equipment.

[0006] The technical solution adopted in this invention is as follows:

[0007] This invention is a method for assessing the operational risks of a 110 kV voltage level closed-loop power swapping system, comprising the following steps:

[0008] Step 1: Analyze the influencing factors of closed-loop battery swapping based on the existing problems and conditions;

[0009] Specifically, the electrical quantity change curves of the loop closure process are decomposed and analyzed using the empirical mode decomposition method to gain a comprehensive and intuitive understanding of the electrical quantity composition. The decomposition diagrams at different frequencies are compared with the actual phenomena before and after the loop closure to intuitively determine the magnitude of the impact of the loop closure on the power grid at different frequencies. The objective and subjective influencing factors that cause this phenomenon are qualitatively analyzed.

[0010] Step 2: Quantitatively analyze the changes in the power grid state after the loop closure operation, taking into account the status of the primary and secondary equipment and the power grid operation status.

[0011] Specifically, this includes transient and steady-state calculation analysis of the power grid during the loop closure process. The transient calculation mainly analyzes the impact of the loop closure and power angle operation on the voltage and power angle stability of the power grid, and determines whether the power grid will generate high-frequency oscillations. The steady-state calculation mainly analyzes the power flow transfer of the power grid before and after the loop closure and the short-circuit current exceeding the limit of the power grid.

[0012] Step 3: Based on Step 1 and Step 2, obtain the risk assessment indicators for loop closure and form a risk assessment mechanism to conduct a risk assessment on the loop closure operation at the 110 kV voltage level.

[0013] Furthermore, in step 1, the empirical mode decomposition method decomposes the input signal into M intrinsic mode functions (IMFs). m (n) and a residual res M (n) is composed of the following formula:

[0014]

[0015]

[0016] Where I(n) represents the input signal, IMF m (n) represents M th The intrinsic modulus function, res M (n) represents the residual.

[0017] Furthermore, in step 1, the impact of the loop closing operation on the power grid at different frequencies is analyzed in a direct and qualitative manner, and the sources of influencing factors of the loop closing operation are summarized and categorized into two parts: objective influencing factors and subjective influencing factors.

[0018] Objective influencing factors: First, the influence of different power grid zones to which the loop line belongs; second, the influence of different loads and load types on both sides of the loop, i.e., impedance angle differences; third, the influence of the impedance of relevant transformers along the power supply path from the power source point to the loop point; and fourth, the influence of the loads carried by relevant transformers along the power supply path from the power source point to the loop point.

[0019] Subjective influencing factors: The data packets used in the offline calculations performed before the loop closure operation are not consistent with the actual operating state of the power grid at the time of loop closure. In addition, different equivalent methods for load and power system in the loop closure calculation can also lead to certain deviations in the loop closure calculation results, affecting the accuracy of the risk assessment of the loop closure operation.

[0020] Furthermore, in step 3, the closed-loop risk assessment indicators include power flow distribution change indicators, safety risk indicators, power grid impact risk indicators, and short-circuit current risk indicators.

[0021] Furthermore, in step 3, the power flow distribution change index specifically refers to:

[0022] The power flow transfer ratio η1 after loop closure is used to evaluate the change in power flow distribution on key lines near the loop closure point before and after loop closure. The specific formula for the power flow transfer ratio η1 is as follows:

[0023]

[0024] In the formula, P L′ P L The values ​​are the power flow of line L before and after loop closure. The larger the value of |η1|, the greater the impact of loop closure on line L. If η1 is positive, line L is at risk of overload; if η1 is negative, line L is under light load.

[0025] Furthermore, in step 3, the safety risk indicator is:

[0026] The power flow transfer ratio η2 under fault conditions after loop closure is used to evaluate the degree of change in power flow distribution near the loop closure point when an N-1 fault occurs on an important line after loop closure. The specific formula for the power flow transfer ratio η2 under fault conditions is as follows:

[0027]

[0028] In the formula, P L″ For the power flow and P of line L when a fault occurs on an important line after the loop is closed L The values ​​represent the power flow of line L before loop closure. If η2 is positive, line L is at risk of overload. If η1 is negative, line L is lightly loaded. The larger η2 is, the more significant the support effect of line L on the power supply area.

[0029] Furthermore, in step 3, the power grid impact risk indicator is:

[0030] The duration and peak value of the inrush current are used as risk indicators for inrush current. During the loop closing process, it should be ensured that the relay protection device does not malfunction.

[0031] Inrush current duration: t cx <t bh (5)

[0032] Peak inrush current: I max bh (6)

[0033] In the formula, t cx To simulate the duration of the inrush current, t bh To protect the action delay; I​max For the peak value of the inrush current, I bh To protect the set value.

[0034] Furthermore, in step 3, the short-circuit current risk index is:

[0035] When the system is in closed-loop operation, a short circuit occurs, reducing impedance and leading to an increase in short-circuit current during a fault. Whether the short-circuit current exceeds the switch's breaking capacity is used as the short-circuit current evaluation criterion, as shown in the formula:

[0036] I dl zd (7)

[0037] In the formula, I dl I represents the maximum short-circuit current value of the power grid transformer or line. zd For switch blocking capacity.

[0038] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0039] This invention provides a risk assessment method for 110 kV voltage level closed-loop power swapping. It provides a direct understanding of the impact of closed-loop power swapping on the power grid, quantitatively analyzes the impact of closed-loop power swapping on the status of primary and secondary equipment and the overall operation of the power grid, and can comprehensively analyze the impact and feasibility of closed-loop operation on the power grid. It also conducts a comprehensive risk assessment of the safety of the 500 kV cross-regional electromagnetic ring network formed by 110 kV short-term closed-loop power swapping, establishes a sound risk assessment mechanism, provides theoretical support, and facilitates scientific guidance for closed-loop power swapping operations. This invention has strong applicability and high reliability. Attached Figure Description

[0040] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort, wherein:

[0041] Figure 1 This is a diagram of the risk assessment method in this invention;

[0042] Figure 2 This is a diagram of the loop-closing point voltage curve in an embodiment of the present invention;

[0043] Figure 3 This is a diagram of the loop-closing point current curve in an embodiment of the present invention;

[0044] Figure 4 This is a power grid power angle curve diagram in an embodiment of the present invention; ​

[0045] Figure 5 yes Figure 2 Exploded view;

[0046] Figure 6 yes Figure 3 Exploded view;

[0047] Figure 7 yes Figure 4 Exploded view;

[0048] Figure 8 This is a regional power grid structure in an embodiment of the present invention. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described embodiments are merely some embodiments of the invention, and not all embodiments. The components of the embodiments of the invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0050] It should be noted that the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0051] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0052] Example 1

[0053] This invention is a method for assessing the operational risks of a 110 kV voltage level closed-loop power swapping system, such as... Figure 1 As shown, the specific steps are as follows:

[0054] Step 1: Analyze the influencing factors of closed-loop battery swapping based on the existing problems and conditions;

[0055] Specifically, the electrical quantity change curves of the loop closure process are decomposed and analyzed using the empirical mode decomposition method to gain a comprehensive and intuitive understanding of the electrical quantity composition. The decomposition diagrams at different frequencies are compared with the actual phenomena before and after the loop closure to intuitively determine the magnitude of the impact of the loop closure on the power grid at different frequencies. The objective and subjective influencing factors that cause this phenomenon are qualitatively analyzed.

[0056] The main problems with loop-based power swapping described in Step 1 are the transient and steady-state impacts of loop closure on the power grid, which affect grid security and the normal and stable operation of grid equipment. By monitoring electrical quantities during the loop closure process and using empirical mode decomposition analysis to analyze them, we can gain a comprehensive and intuitive understanding of the composition of electrical quantities, and a deeper understanding of the objective and subjective factors affecting the loop closure operation. This allows us to predict the risks associated with loop closure conditions and reduce the impact of loop closure on the power grid.

[0057] In step 1, the empirical mode decomposition method decomposes the input signal into M intrinsic mode functions (IMFs). m (n) and a residual res M (n) is composed of the following formula:

[0058]

[0059]

[0060] Where I(n) represents the input signal, IMF m (n) represents M th The intrinsic modulus function, res M (n) represents the residual.

[0061] The impact of loop closing operations on the power grid at different frequencies is analyzed intuitively and qualitatively. The sources of influencing factors of loop closing operations are summarized and categorized into two parts: objective influencing factors and subjective influencing factors.

[0062] Objective influencing factors: First, the influence of different power grid zones to which the loop line belongs; second, the influence of different loads and load types on both sides of the loop, i.e., impedance angle differences; third, the influence of the impedance of relevant transformers along the power supply path from the power source point to the loop point; and fourth, the influence of the loads carried by relevant transformers along the power supply path from the power source point to the loop point.

[0063] Subjective influencing factors: The data packets used in the offline calculations performed before the loop closure operation are not consistent with the actual operating state of the power grid at the time of loop closure. In addition, different equivalent methods for load and power system in the loop closure calculation can also lead to certain deviations in the loop closure calculation results, affecting the accuracy of the risk assessment of the loop closure operation.

[0064] Step 2: Quantitatively analyze the changes in the power grid state after the loop closure operation, taking into account the status of the primary and secondary equipment and the power grid operation status.

[0065] Specifically, this includes transient and steady-state calculation analysis of the power grid during the loop closure process. The transient calculation mainly analyzes the impact of the loop closure and power angle operation on the voltage and power angle stability of the power grid, and determines whether the power grid will generate high-frequency oscillations. The steady-state calculation mainly analyzes the power flow transfer of the power grid before and after the loop closure and the short-circuit current exceeding the limit of the power grid.

[0066] Electromagnetic loop closing is a disturbance to the power system, causing short-term oscillations and threatening the stable operation of the power grid. Firstly, in terms of transients, the power grid is affected by inrush current and voltage at the moment of loop closing, requiring analysis of grid voltage stability and power angle stability to determine whether high-frequency oscillations occur. Secondly, in terms of steady-state conditions, it is necessary to analyze the power flow transfer and short-circuit current exceeding limits before and after loop closing.

[0067] Transient and steady-state calculations and analyses are performed on any AC line, transformer, busbar, or double-circuit or higher line on the same tower within the two 500 kV zones of the power grid after the loop is closed, to ensure that the 110 kV voltage level loop operation does not add any new risks of general or higher power safety accidents, nor does it add any new risks of power outages that would have a major adverse impact on society.

[0068] Step 3: Based on Step 1 and Step 2, obtain the risk assessment indicators for loop closure and form a risk assessment mechanism to conduct a risk assessment on the loop closure operation at the 110 kV voltage level.

[0069] Preferably, in step 3, the closed-loop risk assessment indicators include power flow distribution change indicators, safety risk indicators, power grid impact risk indicators, and short-circuit current risk indicators.

[0070] Preferably, in step 3, to describe whether the loop closure operation affects the safe operation conditions of the power grid, the power flow transfer ratio before and after loop closure is selected as the steady-state evaluation condition for loop closure. The power flow distribution change index is specifically: the power flow transfer ratio η1 after loop closure is used to evaluate the degree of change in power flow distribution of key lines near the loop closure point before and after loop closure. The specific formula for the power flow transfer ratio η1 is:

[0071]

[0072] In the formula, P L′ P L The values ​​are the power flow of line L before and after loop closure. The larger the value of |η1|, the greater the impact of loop closure on line L. If η1 is positive, line L is at risk of overload; if η1 is negative, line L is under light load.

[0073] Preferably, in step 3, the safety risk indicator is:

[0074] The power flow transfer ratio η2 under fault conditions after loop closure is used to evaluate the degree of change in power flow distribution near the loop closure point when an N-1 fault occurs on an important line after loop closure. The specific formula for the power flow transfer ratio η2 under fault conditions is as follows:

[0075]

[0076] In the formula, P L″ For the power flow and P of line L when a fault occurs on an important line after the loop is closed LThe values ​​represent the power flow of line L before loop closure. If η2 is positive, line L is at risk of overload. If η1 is negative, line L is lightly loaded. The larger η2 is, the more significant the support effect of line L on the power supply area.

[0077] Preferably, in step 3, the power grid impact risk index is:

[0078] The duration and peak value of the inrush current are used as inrush current risk indicators. During the loop closing process, it should be ensured that the relay protection device does not malfunction.

[0079] Inrush current duration: t cx <t bh (5)

[0080] Peak inrush current: I max bh (6)

[0081] In the formula, t cx To simulate the duration of the inrush current, t bh To protect the action delay; I max For the peak value of the inrush current, I bh To protect the set value.

[0082] Preferably, in step 3, the short-circuit current risk index is:

[0083] When the system is in closed-loop operation, a short circuit occurs, reducing impedance and leading to an increase in short-circuit current during a fault. Whether the short-circuit current exceeds the switch's breaking capacity is used as the short-circuit current evaluation criterion, as shown in the formula:

[0084] I dl zd (7)

[0085] In the formula, I dl I represents the maximum short-circuit current value of the power grid transformer or line. zd For switch blocking capacity.

[0086] This embodiment uses empirical mode decomposition to analyze the electrical quantities monitored during the loop closing process. Taking the 110kV loop closing of a certain regional power grid as an example, the loop closing process is simulated through a simulation program, and the obtained loop closing point voltage curve is shown below. Figure 2 The current curve at the loop closure point is as follows: Figure 3 And the power angle curve of the power grid, such as Figure 4 The closed-loop voltage curve was obtained by decomposition using the empirical mode method. Figure 5 The current curve at the loop point was obtained by decomposition using the empirical mode method. Figure 6 The power angle curve of the power grid is obtained by decomposition using the empirical mode method. Figure 7 ​​In the curve decomposition diagram, the res portion represents the trend, while the other parts of the decomposition diagram represent the fluctuations of various electrical quantities at different frequencies after the loop closure operation. The res decomposition values ​​in the current curve and the power angle curve decomposition diagram return to 0, and the res decomposition value in the voltage curve returns to a stable value. This res decomposition value is close to the oscillation time of the actual curve and can be represented as the steady-state impact of the loop closure operation on the power grid, which eventually forms a new stable state. At the same time, in the voltage curve, current curve, and power angle curve decomposition diagram, there is a decomposition value that fluctuates greatly initially and then stabilizes. This decomposition value is consistent with the phenomenon of oscillation of the impulsive voltage and current and the generator power angle after the actual loop closure operation and can be represented as the transient impact of the loop closure operation on the power grid.

[0087] Transient and steady-state calculations are performed on the loop-closing operation of a power grid in a certain region. The loop-closing point is at the 110kV section bus tie circuit breaker of station n. The power grid structure of the region is as follows: Figure 8 As shown. On the one hand, the voltage and power angle stability characteristics of the power grid are calculated to analyze whether the power grid experiences high-frequency oscillations; on the other hand, the power flow transfer and short-circuit current exceeding limits of the power grid before and after loop closure are calculated and analyzed. The calculation process will not be described in detail here.

[0088] Finally, four indicators were used to conduct a risk assessment of the loop-loop battery swapping operation, verify the impact of the loop-loop operation on the power grid, and quickly judge and scientifically guide the loop-loop operation.

[0089] (1) Indicators of tidal current distribution change

[0090] The maximum power flow transfer ratios of the lines near the loop closure point before and after loop closure are 127.8% for line hn and 12.9% for line Aa. After loop closure, the power flow of the near-loop lines is within the thermal stability limit, meeting the thermal stability requirements of the lines. The power flow conditions of each line before and after loop closure are shown in Table 1.

[0091] Table 1. Distribution of Flow Current and Flow Transfer Ratio in the Closed Loop (Unit: MW)

[0092]

[0093]

[0094] (2) Safety risk indicators

[0095] An N-1 safety analysis was performed on important lines near the loop closure point. The results are shown in Table 2. When an N-1 fault occurs on the line, there is no power flow exceeding the limit, and the N-1 safety risk requirement is met.

[0096] Table 2N-1 Risk Assessment (Unit: MW)

[0097] Line Name Before closing the loop Line N-1 Line thermal stability limit AB Line 1 / 2 778 / 768 1375 2890 Aa First / Second Tier 154 / 155 178.5 670 Be First / Second Tier 219 / 215 311.9 960 Bg First / Second Line 204 / 204 285.8 1010

[0098] (3) Power grid impact risk indicators

[0099] t cx <t bh

[0100] I max bh

[0101] No relay protection device operates during the loop closing process. The peak value of the inrush current at the loop closing point is less than the protection starting current, and the duration of the inrush current does not reach the current protection starting delay, so it will not cause the relay protection to malfunction. Therefore, it meets the requirements for loop closing inrush current risk.

[0102] (4) Short-circuit current risk indicators

[0103] This example only considers the most severe fault scenario, i.e., a three-phase short circuit on the line, and the short-circuit current of the busbars of important substations near the loop closure point. The results are shown in Table 3. Due to the change in the grid structure before and after loop closure, the short-circuit current of the busbars increases. Among them, the short-circuit current on the 220kV side of Substation B is 54.157kA after loop closure, which does not meet the breaking capacity limit, and corresponding contingency plans need to be developed.

[0104] Table 3 Busbar Short-Circuit Current (Unit: kV)

[0105] Plant / Station Name Before closing the loop After loop closure Station A 500kV 33.9998 34.487 Bilibili 500kV 37.734 39.032 Station A 220kV 42.109 42.57 Bilibili 220kV 43.35 54.157 Station A 220kV 33.779 34.526 G station 220kV 29.258 34.379 H station 220kV 28.252 29.213 r station 220kV 26.324 30.766

[0106] This invention provides a direct understanding of the impact of loop-loop power swapping on the power grid, quantitatively analyzes the impact of loop-loop power swapping on the status of primary and secondary equipment and the operating status of the power grid, and can comprehensively analyze the impact and feasibility of loop-loop operation on the power grid. It also conducts a comprehensive risk assessment of the safety of the 500 kV cross-regional electromagnetic loop network formed by 110 kV short-term loop-loop power swapping, establishes a sound risk assessment mechanism, provides theoretical support, and facilitates scientific guidance for loop-loop power swapping operation. This invention has strong applicability and high reliability.

[0107] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be conceived by those skilled in the art within the technical scope disclosed in the present invention without creative effort should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.​

Claims

1. A method for assessing the operational risks of a 110 kV voltage level closed-loop power swapping system, characterized in that, Includes the following steps: Step 1: Analyze the influencing factors of closed-loop battery swapping based on the existing problems and conditions; Specifically, the electrical quantity change curves of the loop closure process are decomposed and analyzed using the empirical mode decomposition method to gain a comprehensive and intuitive understanding of the electrical quantity composition. The decomposition diagrams at different frequencies are compared with the actual phenomena before and after the loop closure to intuitively determine the magnitude of the impact of the loop closure on the power grid at different frequencies. The objective and subjective influencing factors that cause this phenomenon are qualitatively analyzed. Step 2: Quantitatively analyze the changes in the power grid state after the loop closure operation, taking into account the status of the primary and secondary equipment and the power grid operation status. Specifically, this includes transient and steady-state calculation analysis of the power grid during the loop closure process. The transient calculation analysis examines the impact of the loop closure and battery swapping operation on the voltage and power angle stability of the power grid, and determines whether the power grid generates high-frequency oscillations. The steady-state calculation analysis examines the power flow transfer and short-circuit current exceeding the limit of the power grid before and after the loop closure. Step 3: Based on Step 1 and Step 2, obtain the risk assessment indicators for loop closure and form a risk assessment mechanism to conduct a risk assessment on the loop closure operation at the 110 kV voltage level. In step 3, the closed-loop risk assessment indicators include power flow distribution change indicators, safety risk indicators, power grid impact risk indicators, and short-circuit current risk indicators. In step 3, the specific indicators of tidal current distribution change are: Based on the power flow transfer ratio after loop closure Assess the degree of change in power flow distribution along key routes near the loop closure point before and after loop closure, and the power flow transfer ratio. The specific formula is: （3） In the formula, , The lines before and after the loop are respectively trend, The larger the value, the better the loop connection is for the line. The greater the impact, if If positive, then the line There is an overload risk, if If it is negative, then the line Light load; In step 3, the safety risk indicator is: Power flow transfer ratio under fault conditions after loop closure After assessing the loop closure, when an N-1 fault occurs on a critical line, the degree of change in power flow distribution near the loop closure point and the power flow transfer ratio under fault conditions are evaluated. The specific formula is: （4） In the formula, For the line when a fault occurs on an important line after the loop is closed trends The lines before the loop closure Trends, if If positive, then the line There is an overload risk, if If it is negative, then the line Light load, The larger the value, the better the circuit. The support effect on the power supply area is obvious; In step 3, the power grid impact risk indicator is: The duration and peak value of the inrush current are used as risk indicators for inrush current. During the loop closing process, it should be ensured that the relay protection device does not malfunction. Inrush current duration: (5) Peak inrush current: (6) In the formula, To simulate the duration of the inrush current, Delay the protective action; This is the peak value of the inrush current. To protect the set value; In step 3, the short-circuit current risk indicator is: When the system is in closed-loop operation, a short circuit occurs, reducing impedance and leading to an increase in short-circuit current during a fault. Whether the short-circuit current exceeds the switch's breaking capacity is used as the short-circuit current evaluation criterion, as shown in the formula: （7） In the formula, This refers to the maximum short-circuit current value of the power grid transformer or line. For switch blocking capacity.

2. The method for assessing the operational risk of a 110 kV voltage level closed-loop power swapping system according to claim 1, characterized in that, In step 1, the empirical mode decomposition method decomposes the input signal into M eigenmode functions. and a residual The composition is specifically represented by the following formula: （1） （2） in Indicates the input signal. express The intrinsic modulus function, Represents the residual.

3. The method for assessing the operational risk of a 110 kV voltage level closed-loop power swapping system according to claim 2, characterized in that, In step 1, the impact of loop closing operation on the power grid at different frequencies is analyzed in a direct and qualitative manner, and the sources of influencing factors of loop closing operation are summarized and classified into two parts: objective influencing factors and subjective influencing factors. Objective influencing factors: First, the influence of different power grid zones to which the loop line belongs; second, the influence of different loads and load types on both sides of the loop, i.e., impedance angle differences; third, the influence of the impedance of relevant transformers along the power supply path from the power source point to the loop point; and fourth, the influence of the loads carried by relevant transformers along the power supply path from the power source point to the loop point. Subjective influencing factors: The data packets used in the offline calculations performed before the loop closure operation do not match the actual operating state of the power grid at the time of loop closure; In addition, different equivalent methods for load and power system in loop closing calculations can also lead to certain deviations in the loop closing calculation results, affecting the accuracy of the risk assessment of loop closing operations.

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