Power system risk assessment method based on a quadratic coupling multiple fault model

Abstract

The application particularly relates to a power system risk assessment method based on a primary-secondary coupling multiple fault model, which comprises the following steps: calculating a power transmission line fault probability of a power system; performing multiple fault sampling based on a Latin hypercube sampling method; establishing a corresponding primary-secondary coupling multiple fault model for each scene; determining a power transmission line fault state and a protection action state, and then assessing a risk index of the corresponding scene; calculating a corresponding comprehensive severity index based on the risk index of a single scene, and then obtaining one or more scenes with the highest comprehensive severity index through screening and sorting to analyze weak links of the power system; and calculating a system risk value by comprehensively considering the risk index of all scenes and a protection refusal probability, so as to assess the overall operation risk of the power system. The application can reflect the influence of the expansion of the fault range caused by incorrect protection action on the operation safety of the power grid, and can normalize and scientifically sort different dimension risk indexes.

Description

Technical Field

[0001] This invention relates to the field of power system operation risk assessment technology, specifically to a power system risk assessment method based on a primary-secondary coupled multiple fault model. Background Technology

[0002] With the increasing scale of inter-regional and inter-provincial power grid interconnection, such as the West-to-East Power Transmission Project, the number of transmission lines with multiple circuits on the same tower, crossings, and dense corridors is increasing. These lines are increasingly susceptible to multiple faults due to external factors such as extreme weather, natural disasters, and cyberattacks, as well as internal secondary systems such as protection and stability control failures. A review of several major power outages in recent years reveals that simultaneous and successive multiple faults are the main causes of many such incidents. Power grid faults are often triggered by meteorological disasters. When an initial system fault occurs, if secondary equipment operates incorrectly, it can cause multiple adjacent devices to trip, expanding the scope of the fault and driving the occurrence and development of cascading failures.

[0003] Regarding system risk assessment technology for primary equipment (transmission lines) failures caused by meteorological disasters, Chinese patent CN107633320A discloses "A Method for Assessing the Importance of Power Grid Lines Based on Meteorological Forecasting and Risk Assessment." This method first identifies the fault set of lines under typhoon weather; then, it establishes an effective typhoon wind speed model and constructs a mathematical model describing the impact of effective typhoon wind speed on the probability of line failures, thereby determining the probability of occurrence of each fault in the fault set. This allows for real-time and effective identification of critical transmission lines in the regional power grid based on power grid parameters and typhoon weather forecast data. However, this existing technology is limited to considering typhoon weather and does not comprehensively consider the impact of natural disasters such as lightning strikes, heavy rain, and icing on power grid operation risks, thus limiting its application scope.

[0004] In the field of power grid risk assessment and fault ranking technology, Chinese patent CN111275312A discloses "A method and system for comprehensively evaluating and ranking the severity of multiple power grid faults." This method identifies and calculates multiple evaluation indicators for the severity of multiple power grid faults, then normalizes the values ​​of these indicators, sets evaluation weights for each indicator, and calculates a comprehensive evaluation index based on these weights and the normalized values. However, this existing solution does not consider voltage and power flow limits, as well as load shedding risk indicators, and the indicator system needs improvement. Chinese patent CN111768026A discloses "A power grid risk assessment method considering low-probability events in dispatching operations." This method uses a non-sequential Monte Carlo simulation method, based on a multiple fault search model considering low-probability events including dead-zone faults, relay protection failures, and circuit breaker failures, and an optimal DC power flow load shedding algorithm to assess system risk. However, the existing scheme uses a single risk assessment indicator, which cannot fully reflect the impact of multiple faults of low probability events on the risk of power grid operation. At the same time, the method has not overcome the problem of generating a large number of repetitive scenarios in terms of fault set generation, and the calculation speed and efficiency need to be improved.

[0005] The aforementioned existing technologies either focus on multiple failures of primary equipment under severe weather conditions or on the cascading trip risks caused by latent secondary system failures (low-probability events), neglecting the development pattern of primary equipment failures leading to the exposure of latent protection faults, which in turn triggers multiple failures. Therefore, they cannot comprehensively reflect the multiple failure risks of the system, resulting in poor comprehensiveness of power system risk assessment. Furthermore, existing risk assessment indicators mainly focus on adequacy indicators such as the probability of system load shedding (LOLP) and expected system power shortage (EDNS), or operational risk indicators such as node voltage exceeding limits and branch power flow exceeding limits. They rarely comprehensively consider the overall system risk reflected by these indicators, and the ranking of risk indicators across different dimensions lacks scientific and reasonable normalization, resulting in weak correlation between the ranking results and the management of high-risk events and weak links in the power system, thus leading to insufficient effectiveness of power system risk assessment. Therefore, designing a method to improve the comprehensiveness and effectiveness of power system risk assessment is an urgent technical problem to be solved. Summary of the Invention

[0006] To address the shortcomings of the existing technologies, the technical problem to be solved by this invention is: how to provide a power system risk assessment method based on a primary and secondary coupled multiple fault model, which can reflect the impact of fault range expansion on power grid operation safety when protection fails to operate correctly, and can normalize and scientifically rank risk indicators of different dimensions, thereby improving the comprehensiveness and effectiveness of power system risk assessment.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] Power system risk assessment methods based on primary and secondary coupled multiple fault models include:

[0009] S1: Calculate the probability of power transmission line faults in the power system based on meteorological data;

[0010] S2: Multiple fault sampling is performed based on the Latin hypercube sampling method to obtain several sets of data; each set of data corresponds to a scenario, and the system operation status of each scenario is determined by the transmission line fault probability.

[0011] S3: Establish corresponding primary and secondary coupled multiple fault models for each scenario; then, based on the system operation status of each scenario, determine the transmission line status and protection action status in the system corresponding to the primary and secondary coupled multiple fault models, and evaluate the risk indicators of the corresponding scenarios.

[0012] S4: Calculate the corresponding comprehensive severity index based on the risk index of a single scenario, and then obtain one or more scenarios with the highest comprehensive severity index through screening and sorting. Analyze the weak links of the power system and identify the key transmission lines and busbars that affect the system risk in the disaster weather area.

[0013] S5: Calculate the system risk value of the power system by integrating risk indicators from all scenarios and their protection failure probabilities, and then assess the overall operational risk of the power system based on the system risk value.

[0014] Preferably, in step S1, the transmission line fault probability is calculated using the following formula:

[0015]

[0016] In the formula: P Lf -λ represents the probability of a transmission line fault; ave Δt represents the average failure rate of the transmission line under weather conditions w; Δt represents the assessment time.

[0017] Preferably, in step S2, for a power system containing m transmission lines: firstly, n sets of data are obtained through Latin hypercube sampling, each set of data corresponds to a scenario, and each scenario contains m random numbers between 0 and 1 corresponding to the m transmission lines; then, the random numbers are compared with the transmission line fault probability: if the random number is greater than the transmission line fault probability, it indicates that the transmission line is in normal operation; otherwise, it indicates that the transmission line is in a fault outage state; finally, the system operation status of the n scenarios is determined by comparing the m random numbers in each scenario with the transmission line fault probability.

[0018] Preferably, in step S3, the constructed primary and secondary coupled multiple fault model includes a transmission line module, two sets of transmission line main protection device modules, a transmission line backup protection device module, and a circuit breaker module; wherein, the two sets of main protection device modules are connected in parallel with the backup protection device module, and connected in series with the transmission line module and the circuit breaker module.

[0019] Preferably, the protection action status of the primary and secondary coupled multiple fault model includes correct protection action and protection failure to operate; protection failure to operate includes a first type of failure to operate, namely the failure to operate mode in which the trip signal cannot be correctly generated and transmitted due to the circuit disconnection or hardware failure of the secondary system, and a second type of failure to operate, namely the failure to operate mode caused by the influence of the operating environment parameters of the protection device.

[0020] The protection failure probability of the primary and secondary coupled multiple fault model is calculated using the following formula:

[0021]

[0022]

[0023] In the formula: P R P represents the probability of protection against activation; Lf P represents the probability of a transmission line fault. R1 λ represents the probability of a class of refusal to move; Δt represents the evaluation time; λ represents the probability of a class of refusal to move. R1 N represents the failure rate of a class of refusal to move; rp Indicates the number of protective sleeves installed on a single line; P R2 (i) represents a single transmission line N in the power system. rp The probability of type II failure to operate of the i-th set of protection devices in the set of protection.

[0024] Preferably, the risk indicators for the scenario include voltage over-limit risk, power flow over-limit risk, and system underload risk;

[0025] 1) Risk of voltage exceeding limits

[0026] Define the node voltage exceedance risk of the i-th node in a power system and the overall system voltage exceedance risk as follows:

[0027] R i (u)=P r (u i )·S ev (w i );

[0028]

[0029] In the formula: R i (u) represents the node voltage over-limit risk value of the i-th node; P r (u iS represents the probability of the node voltage exceeding the limit at the i-th node; ev (w i R(u) represents the severity of the voltage exceedance at the i-th node; I represents the total number of nodes in the power system; R(u) represents the overall voltage exceedance risk of the system.

[0030] Define the node voltage over-limit value for the i-th node as:

[0031]

[0032] The severity of node voltage exceedance is expressed by the following formula:

[0033]

[0034] In the formula: U i w represents the per-unit voltage value of the i-th node; i This represents the voltage limit exceeding the specified value at the i-th node;

[0035] 2) Risk of exceeding the limits of trends

[0036] Define the branch power flow limit exceedance risk of the b-th branch in the power system and the overall system power flow limit exceedance risk as follows:

[0037] R b (s)=P r (s b )·S ev (w sb );

[0038]

[0039] In the formula: R b (s) represents the branch power flow exceeding the limit risk value of the b-th branch; P r (s b S represents the probability of the power flow exceeding the limit in the b-th branch; ev (w sb R(s) represents the severity of the power flow exceeding the limit in the b-th branch; B represents the total number of branches in the power system; R(s) represents the overall power flow exceeding the limit risk of the system.

[0040] The power flow limit exceeding the limit of the b-th branch is expressed as:

[0041]

[0042] The severity of branch power flow exceeding the limit is expressed by the following formula:

[0043]

[0044] In the formula: w sb This represents the power flow limit exceedance value of the b-th branch; sb This represents the actual transmission power of the b-th branch; s0 is 0.9 times the branch power limit.

[0045] 3) System load failure risk

[0046] The system failure risk is defined as:

[0047] R(l)=P r (l)·S ev (w l );

[0048] In the formula: R(l) represents the system's risk of load failure; P r (l) represents the system failure probability; S ev (w l The sign indicates the severity of system load failure.

[0049] The severity of system load failure is expressed by the following formula:

[0050]

[0051] In the formula: w l S(l) represents the system load loss in the current scenario; S(l) represents the total system load.

[0052] Preferably, in step S4, the comprehensive severity index is calculated using the following formula:

[0053]

[0054] In the formula: Sev represents the overall severity index of the system; N node N represents the total number of nodes in the power system. branch This represents the total number of branches in the power system; α and β represent the weights of the severity of node voltage exceedance and the severity of branch power flow exceedance, respectively.

[0055] Preferably, the comprehensive severity index of each scenario is first calculated and sorted in descending order; then, one or more scenarios with the highest ranking are selected, and the out-of-line power transmission, fault propagation path, system load loss and limit exceedance index of the corresponding scenario are obtained; finally, the weak links of the power system are determined based on the corresponding out-of-line power transmission and fault propagation path.

[0056] Preferably, in step S5, the protection failure probability of the primary and secondary coupled multiple fault model is first determined; then, the system severity of the correct protection action and the system severity of the protection failure are weighted and calculated based on the protection failure probability to obtain the system severity in a single scenario; finally, the system severity of each scenario is summed and averaged to obtain the corresponding system risk value.

[0057] Preferably, the system risk value of the power system is calculated using the following formula:

[0058]

[0059]

[0060] In the formula: R cp (x) represents the system risk value; n represents the total number of scenarios sampled; J is the number of states caused by the failure to operate on the M side of the system fault line in a single scenario, and K is the number of states caused by the failure to operate on the N side; S wq (x) represents the system severity of protection refusal to activate in the q-th scenario; S rq (x) represents the system severity for protecting the correct action in the q-th scenario; S evi (x) represents the system severity under the i-th failure-to-operate state; x represents the node voltage over-limit value, branch power flow over-limit value, and system load loss value.

[0061] The power system risk assessment method based on a primary-secondary coupled multiple fault model in this invention has the following beneficial effects:

[0062] This invention establishes a primary and secondary coupled multiple fault model based on various scenarios, and determines the transmission line fault state and protection action state of the primary and secondary coupled multiple fault model. This fully considers the grid operation risk of multiple faults under primary and secondary equipment coupling. Compared with existing solutions that only consider the risk of primary equipment faults or latent faults in the secondary system, it can effectively reflect the development mode of primary equipment faults leading to the exposure of latent protection faults (protection device failure to operate), which in turn triggers multiple faults or the expansion of the fault range. In other words, it can reflect the impact of the expansion of the fault range on the safety of grid operation when the protection does not operate correctly, thereby improving the comprehensiveness of power system risk assessment.

[0063] This invention calculates a comprehensive severity index based on scenario-based risk indicators, enabling the normalization and scientific ranking of risk indicators across different dimensions. This enhances the relevance of the ranking results and facilitates the accurate screening of key transmission lines and busbars within meteorological disaster zones that impact system risks. Consequently, it provides a basis for decision-making regarding power system risk prevention and control and the management of weak links in the power grid, thereby improving the effectiveness of power system risk assessment.

[0064] This invention integrates risk indicators from all scenarios and their protection failure probabilities to calculate the system risk value of the power system, thereby achieving an assessment of the overall operational risk of the power system considering primary and secondary coupling. This improves the effectiveness of power system risk assessment and facilitates the screening of high-risk events and the mitigation of weak links in the power system. Furthermore, the multi-dimensional indicators used in this invention, such as voltage over-limit risk, power flow over-limit risk, and system load shedding risk, can more effectively reflect the overall system risk, making the indicator system more comprehensive.

[0065] This invention calculates the probability of transmission line faults in a power system based on meteorological data, and then uses Latin hypercube sampling to perform multiple fault sampling to generate fault scenarios. Latin hypercube sampling has the characteristics of stratified sampling, which can take into account the differences in the probability distribution of transmission line faults in different meteorological zones. Compared with traditional Monte Carlo sampling, it can improve sampling efficiency while reducing the sample size, thereby better ensuring the comprehensiveness of multiple fault samples. Attached Figure Description

[0066] To make the objectives, technical solutions, and advantages of the invention clearer, the invention will now be described in further detail with reference to the accompanying drawings, wherein:

[0067] Figure 1 The diagram shows the logic block diagram of the power system risk assessment method based on a primary and secondary coupled multiple fault model.

[0068] Figure 2 Wiring diagram for the IEEE-39 node system;

[0069] Figure 3 This is a primary and secondary coupled multiple fault model;

[0070] Figure 4 This is a schematic diagram of the operation of the primary and secondary equipment coupling fault protection.

[0071] Figure 5 To take into account the multiple failure risk assessment process involving primary and secondary coupling;

[0072] Figure 6 The system load loss risk values ​​under different meteorological conditions;

[0073] Figure 7 This represents the percentage of power flow exceeding limits on transmission lines during severe weather events.

[0074] Figure 8 To mitigate the risk of system voltage exceeding limits under different simulation scenarios;

[0075] Figure 9 To mitigate the risk of system power flow exceeding limits under different simulation scenarios. Detailed Implementation

[0076] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but only to illustrate selected embodiments of the 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.

[0077] It should be noted that similar reference numerals and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the figures, or the orientation or positional relationship commonly used when the product is in use. They are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance. In addition, the terms "horizontal," "vertical," etc., do not indicate that the component is required to be absolutely horizontal or suspended, but can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted. In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0078] The following detailed explanation illustrates the specific implementation methods:

[0079] Example:

[0080] This embodiment discloses a power system risk assessment method based on a primary and secondary coupled multiple fault model.

[0081] like Figure 1 As shown, the power system risk assessment method based on a primary-secondary coupled multiple fault model includes:

[0082] S1: Calculate the probability of power transmission line faults in the power system based on meteorological data;

[0083] S2: Multiple fault sampling is performed based on the Latin hypercube sampling method to obtain several sets of data; each set of data corresponds to a scenario, and the system operation status of each scenario is determined by the transmission line fault probability.

[0084] S3: Establish corresponding primary and secondary coupled multiple fault models for each scenario; then, based on the system operation status of each scenario, determine the transmission line status and protection action status in the system corresponding to the primary and secondary coupled multiple fault models, and evaluate the risk indicators of the corresponding scenarios.

[0085] In this embodiment, the risk indicators include voltage over-limit risk, power flow over-limit risk, and system underload risk.

[0086] S4: Calculate the corresponding comprehensive severity index based on the risk index of a single scenario, and then obtain one or more scenarios with the highest comprehensive severity index through screening and sorting. Analyze the weak links of the power system and identify the key transmission lines and busbars that affect the system risk in the disaster weather area.

[0087] In this embodiment, the comprehensive severity index of each scenario is first calculated and sorted in descending order; then, one or more scenarios with the highest ranking are selected, and the outage transmission lines, fault propagation paths, system load loss and limit exceedance indicators for the corresponding scenarios are obtained; finally, the weak links of the power system are determined based on the corresponding outage transmission lines and fault propagation paths.

[0088] S5: Calculate the system risk value of the power system by integrating risk indicators from all scenarios and their protection failure probabilities, and then assess the overall operational risk of the power system based on the system risk value.

[0089] In this embodiment, assessing the overall operational risk of a power system based on the system risk value means judging the severity of the overall operational risk of the power system based on the magnitude of the system risk value, and the relationship between the magnitude of the system risk value and the severity can be determined by human intervention.

[0090] Specifically, firstly, the protection failure probability of the primary and secondary coupled multiple fault model is determined; then, based on the protection failure probability, the system severity of the correct protection action and the system severity of the protection failure are weighted and calculated to obtain the system severity in a single scenario; finally, the system severity of each scenario is summed and averaged to obtain the corresponding system risk value.

[0091] Among them, latent faults refer to problems that cannot be detected when the relay protection device is in a normal power grid state. The latent fault, "protection failure to operate," is only exposed when the primary equipment (transmission line) fails. Protection failure to operate is a latent fault of secondary equipment. Considering the situation where the failure of protection to operate after the primary equipment (transmission line) fails, the upstream line is disconnected, expanding the fault range, this invention considers the scenario of multiple primary and secondary coupled faults.

[0092] This invention establishes a primary and secondary coupled multiple fault model based on various scenarios, and determines the transmission line fault state and protection action state of the primary and secondary coupled multiple fault model. This fully considers the grid operation risk of multiple faults under primary and secondary equipment coupling. Compared with existing solutions that only consider the risk of primary equipment faults or latent faults in the secondary system, it can effectively reflect the development mode of primary equipment faults leading to the exposure of latent protection faults (protection device failure to operate), which in turn triggers multiple faults or the expansion of the fault range. In other words, it can reflect the impact of the expansion of the fault range on the safety of grid operation when the protection does not operate correctly, thereby improving the comprehensiveness of power system risk assessment.

[0093] This invention calculates a comprehensive severity index based on scenario-based risk indicators, enabling the normalization and scientific ranking of risk indicators across different dimensions. This enhances the relevance of the ranking results and facilitates the accurate screening of key transmission lines and busbars within meteorological disaster zones that impact system risks. Consequently, it provides a basis for decision-making regarding power system risk prevention and control and the management of weak links in the power grid, thereby improving the effectiveness of power system risk assessment.

[0094] This invention integrates risk indicators from all scenarios and their protection failure probabilities to calculate the system risk value of the power system, thereby achieving an assessment of the overall operational risk of the power system considering primary and secondary coupling. This improves the effectiveness of power system risk assessment and facilitates the screening of high-risk events and the mitigation of weak links in the power system. Furthermore, the multi-dimensional indicators used in this invention, such as voltage over-limit risk, power flow over-limit risk, and system load shedding risk, can more effectively reflect the overall system risk, making the indicator system more comprehensive.

[0095] This invention calculates the probability of transmission line faults in a power system based on meteorological data, and then uses Latin hypercube sampling to perform multiple fault sampling to generate fault scenarios. Latin hypercube sampling has the characteristics of stratified sampling, which can take into account the differences in the probability distribution of transmission line faults in different meteorological zones. Compared with traditional Monte Carlo sampling, it can improve sampling efficiency while reducing the sample size, thereby better ensuring the comprehensiveness of multiple fault samples.

[0096] In specific implementation, the method of this invention is implemented using the IEEE-39 node system as an example. Figure 2For the IEEE-39 node system topology, meteorological conditions are divided into four categories: normal weather, severe weather, hazardous weather, and extreme weather. Three transmission lines, "5-8", "8-9", and "9-39", are identified as having concentrated coverage areas for different weather conditions. The failure probability of the transmission lines is calculated using failure rates statistically based on weather conditions. Considering that weather conditions remain relatively constant over a short period Δt (several hours to one day), the failure rate of the transmission lines is simplified to remain constant. Furthermore, it is assumed that failures on transmission lines during prolonged periods of severe weather are irreparable.

[0097] Specifically, the probability of transmission line faults is calculated using the following formula:

[0098]

[0099] In the formula: P Lf -λ represents the probability of a transmission line fault; ave Δt represents the average failure rate of the transmission line under weather conditions w; Δt represents the assessment time.

[0100] In this embodiment, the probability of transmission line failure within the disaster area is calculated based on the meteorological disaster coverage area. The failure probability of transmission lines within the disaster area is calculated using a reference index model. The failure probability of transmission lines within the disaster area is set to decrease progressively from the center to the edge. The initial outage probability of transmission lines outside the disaster area and under normal weather conditions is selected as the historical outage probability of each transmission line. The failure probabilities of transmission lines in the IEEE-39 node system are shown in the table below:

[0101] Table 1. Transmission line fault probabilities in the IEEE-39 Node system

[0102]

[0103] In the specific implementation process, for a power system containing m transmission lines: First, an initial fault set containing n sets of data is obtained through Latin hypercube sampling. Each set of data in the initial fault set corresponds to a scenario, and each scenario contains m random numbers between 0 and 1 corresponding to the m transmission lines. Then, the random numbers are compared with the transmission line fault probability: if the random number is greater than the transmission line fault probability, it indicates that the transmission line is in normal operation; otherwise, it indicates that the transmission line is in a fault outage state. Finally, by comparing the m random numbers in each scenario with the transmission line fault probability, the system operating status of the n scenarios is determined.

[0104]

[0105] In the formula: r n F represents a random number; n This indicates the probability of a power transmission line failure.

[0106] In the specific implementation process, such as Figure 3 As shown, the constructed primary and secondary coupled multiple fault model includes a transmission line module, two sets of transmission line main protection device modules, a transmission line backup protection device module, and a circuit breaker module. The two sets of main protection device modules are connected in parallel with the backup protection device module and in series with the transmission line module and the circuit breaker module. Wherein, PE represents the transmission line module; P... l P2 represents the main protection device module for the first and second sets of transmission lines, respectively; B represents the backup protection device module; CB represents the circuit breaker module; and K1 and K2 represent pressure plate switches.

[0107] The protection action status of the primary and secondary coupled multiple fault model includes correct protection action and protection failure to operate; protection failure to operate includes a first type of failure to operate, which is a failure to operate mode in which the trip signal cannot be correctly generated and transmitted due to the circuit disconnection or hardware failure of the secondary system, and a second type of failure to operate, which is a failure to operate mode caused by the influence of the operating environment parameters of the protection device.

[0108] The protection failure probability of the primary and secondary coupled multiple fault model is calculated using the following formula:

[0109]

[0110]

[0111] In the formula: P R P represents the probability of protection against activation; Lf P represents the probability of a transmission line fault. R1 λ represents the probability of a class of refusal to move; Δt represents the evaluation time; λ represents the probability of a class of refusal to move. R1 N represents the failure rate of a class of refusal to move; rp Indicates the number of protective sleeves installed on a single line; P R2 (i) represents a single transmission line N in the power system. rp The probability of type II failure to operate of the i-th set of protection devices in the set of protection.

[0112] In a primary-secondary coupled multiple fault model, let the failure probability of the primary equipment be P. PE The probabilities of failure of the first and second main protection and backup protection devices are P1, P2 and P3 respectively, and the probability of normal operation of the circuit breaker is P. CB Analyzing the series-parallel model yields the probability P that the system will experience only one equipment outage. Normal for:

[0113] P Normal =P PE (1-P1P2)P CB ;

[0114] The probability P of coupled outage where the main protection fails to operate and the backup protection operates correctly is... Failure for:

[0115] P Failure =P PE (P1P2-P1P2P3)P CB .

[0116] Figure 4 This is a schematic diagram of the protection operation of a primary and secondary coupled multiple fault model, where L is the transmission line; MP is the main protection device; BP is the remote backup protection device; M is the first segment of the line; and N is the end of the line.

[0117] Extending the protection equipment to both sides of the line, when a line fault occurs, if the protection fails to operate, the system will automatically activate the failure protection to trip all adjacent components. Based on the location of the protection failure, the scope of the fault expansion is divided into the following two situations:

[0118] 1) The protection at the beginning of the line fails to operate, causing the faulty line and all adjacent lines at its beginning to trip and stop operating;

[0119] 2) If the protection at the end of the line fails to operate, the faulty line and all adjacent lines at its end will trip and stop operating;

[0120] Since the failure to operate on both sides simultaneously is an extremely low probability event, only the failure to operate on one side of the line protection is considered, and the failure to operate on both sides simultaneously is not taken into account.

[0121] In the specific implementation process, combined with Figure 5 As shown, risk indicators are determined through power flow calculations; these risk indicators include voltage over-limit risk, power flow over-limit risk, and system underload risk.

[0122] 1) Risk of voltage exceeding limits

[0123] Define the node voltage exceedance risk of the i-th node in a power system and the overall system voltage exceedance risk as follows:

[0124] R i (u)=P r (u i )·S ev (w i );

[0125]

[0126] In the formula: R i (u) represents the node voltage over-limit risk value of the i-th node; P r (u i (represents the probability of the node voltage exceeding the limit for the i-th node; S) ev (w iR(u) represents the severity of the voltage exceedance at the i-th node; I represents the total number of nodes in the power system; R(u) represents the overall voltage exceedance risk of the system.

[0127] Define the node voltage over-limit value for the i-th node as:

[0128]

[0129] The severity of node voltage exceedance is expressed by the following formula:

[0130]

[0131] In the formula: U i w represents the per-unit voltage value of the i-th node; i This represents the voltage limit exceeding the specified value at the i-th node;

[0132] 2) Risk of exceeding the limits of trends

[0133] Define the branch power flow limit exceedance risk of the b-th branch in the power system and the overall system power flow limit exceedance risk as follows:

[0134] R b (s)=P r (s b )·S ev (w sb );

[0135]

[0136] In the formula: R b (s) represents the branch power flow exceeding the limit risk value of the b-th branch; P r (s b S represents the probability of the power flow exceeding the limit in the b-th branch; ev (w sb R(s) represents the severity of the power flow exceeding the limit in the b-th branch; B represents the total number of branches in the power system; R(s) represents the overall power flow exceeding the limit risk of the system.

[0137] The power flow limit exceeding the limit of the b-th branch is expressed as:

[0138]

[0139] The severity of branch power flow exceeding the limit is expressed by the following formula:

[0140]

[0141] In the formula: w sb This represents the power flow limit exceedance value of the b-th branch; s b This represents the actual transmission power of the b-th branch; s0 is 0.9 times the branch power limit.

[0142] 3) System load failure risk

[0143] The system failure risk is defined as:

[0144] R(l)=P r (l)·S ev (w l );

[0145] In the formula: R(l) represents the system's risk of load failure; P r (l) represents the system failure probability; S ev (w l The sign indicates the severity of system load failure.

[0146] The severity of system load failure is expressed by the following formula:

[0147]

[0148] In the formula: w l S(l) represents the system load loss in the current scenario; S(l) represents the total system load.

[0149] In practice, the comprehensive severity index is calculated using the following formula:

[0150]

[0151] In the formula: Sev represents the overall severity index of the system; N node N represents the total number of nodes in the power system. branch This represents the total number of branches in the power system; α and β represent the weights of the severity of node voltage exceedance and the severity of branch power flow exceedance, respectively.

[0152] In practice, the system risk value of the power system is calculated using the following formula:

[0153]

[0154]

[0155] In the formula: R cp (x) represents the system risk value; n represents the total number of scenarios sampled; J is the number of states caused by the failure to operate on the M side of the system fault line in a single scenario, and K is the number of states caused by the failure to operate on the N side; S wq (x) represents the system severity of protection refusal to activate in the q-th scenario; S rq (x) represents the system severity for protecting the correct action in the q-th scenario; S evi (x) represents the system severity under the i-th failure-to-operate state; x represents the node voltage over-limit value, branch power flow over-limit value, and system load loss value.

[0156] To better illustrate the advantages of the technical solution of the present invention, the following experiments are disclosed in this embodiment.

[0157] This experiment sets up the following 3 simulation scenarios:

[0158] Scenario 1: Under multiple fault scenarios, the protection operates normally, and only the selected faulty line is out of service;

[0159] Scenario 2: The protection fails to operate at the beginning of the faulty line, and the selected faulty line and all adjacent upstream lines connected to the beginning of the faulty line are shut down.

[0160] Scenario 3: The protection fails to operate at the end of the faulty line, and the extracted faulty line and all adjacent upstream lines connected to the end of the faulty line are shut down.

[0161] The simultaneous failure of protection devices on both sides of a line to operate is an extremely low probability event. Therefore, scenarios 2 and 3 are set to consider only the failure of protection devices on one side of the faulty line each time, and the initial fault set is generated using Nk (k = 1, 2, ...) events.

[0162] Latin hypercube sampling was used to generate the initial fault set, with a sampling count of 10,000. The probability of failure for both the first and last segments of the line to operate incorrectly was set to 1%. Scenario 1 corresponds to the risk analysis considering only primary equipment failures. By comprehensively analyzing scenarios 2 and 3, the system's multiple fault risks considering primary and secondary coupling can be obtained.

[0163] In the experiment, the risk assessment results of the IEEE-39 power-saving system based on multiple faults of primary and secondary coupling are as follows. Tables 2 and 3 show the line power flow and bus voltage over-limit risks under different simulation scenarios.

[0164] Table 2. Risk of Line Power Flow Exceeding Limits under Different Simulation Scenarios

[0165]

[0166]

[0167] Table 3. Risk of Bus Voltage Exceeding Limits under Different Simulation Scenarios

[0168]

[0169] In the experiment, after obtaining various indicators through system risk assessment, the percentage of power flow exceeding the limit for each transmission line under different meteorological scenarios was statistically analyzed and sorted to identify the weak links of the grid lines under different meteorological scenarios. Figure 6 , Figure 7 , Figure 8 and Figure 9The calculated values ​​of various risk indicators for the system under different meteorological conditions and simulation scenarios show that this invention can effectively highlight the weak links of the power grid under weather conditions. When analyzing the risk of multiple faults in a system with primary and secondary coupling, the risk of system load loss, system voltage and power flow exceeding limits all increase to varying degrees depending on the meteorological conditions. Simultaneously, affected by the weather conditions, the risk value also spreads from the center of the weather zone to the surrounding areas, making the power grid within the disaster zone more vulnerable. By referring to this invention to assess system risk and making advance power grid dispatching arrangements based on meteorological forecasts and meteorological disaster warnings, the possibility of high-risk events caused by multiple faults can be effectively reduced.

[0170] In the experiment, in order to screen out the most severe fault scenarios among all the sampled samples, the comprehensive severity index was used as the standard for sorting and screening. The weights of α and β in the comprehensive severity index were each set to 0.5. The sorting and screening results under extreme weather conditions are shown in Table 4. The fault lines marked in bold are the lines where the protection failed to operate, and the lines marked in underline are the upstream lines that were disconnected after the protection failed to operate.

[0171] Table 4. Ranking and screening results of comprehensive severity index under different simulation scenarios.

[0172]

[0173] When considering multiple failures coupled with primary and secondary faults, the risk severity of considering the comprehensive severity index is higher than that of multiple failures of primary equipment only. The ranking results effectively verify the necessity of considering multiple failures coupled with primary and secondary faults in system risk assessment and the effectiveness of the method of this invention.

[0174] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A method for power system risk assessment based on a quadratic coupled multiple contingency model, characterized in that, The method comprises the following steps: S1: calculating the transmission line fault probability of the power system based on meteorological data; S2: performing multiple fault sampling based on the Latin hypercube sampling method to obtain a plurality of groups of data; each group of data corresponds to a scenario, and the system operating state of each scenario is determined through the transmission line fault probability; In step S2, for those containing The power system of the transmission lines: firstly, it is obtained through Latin hypercube sampling. Groups of data, each group corresponding to a scenario, and each scenario containing corresponding data. The transmission line A random number between 0 and 1; Then the random number is compared with the transmission line failure probability: if the random number is greater than the transmission line failure probability, it indicates that the transmission line is in normal operation state, otherwise it indicates that the transmission line is in failure outage state; finally, by comparing the random number in each scenario with the transmission line failure probability, the system operation state of the scenarios is determined . S3: establishing a primary-secondary coupling multiple fault model corresponding to each scenario; then, the transmission line state and protection action state in the system corresponding to the primary-secondary coupling multiple fault model are determined based on the system operating state of each scenario, and the risk index of the corresponding scenario is evaluated; The protection action state of the primary-secondary coupling multiple fault model includes correct protection action and protection refusal; the protection refusal includes a first type of refusal, i.e., a refusal mode caused by the fact that the trip signal cannot be correctly generated and transmitted due to the loop disconnection or hardware failure of the secondary system, and a second type of refusal, i.e., a refusal mode caused by the influence of the operating environment parameters of the protection device; The protection refusal probability of the primary-secondary coupling multiple fault model is calculated by the following formula: ； ； In the formula: denotes the protection rejection probability; denotes the transmission line fault probability; denotes a type of rejection probability; denotes the evaluation time; denotes the failure rate of a type of rejection; denotes the number of protection sets installed for a single line; denotes a single transmission line of a power system the second type of rejection probability of the protection device S4: calculating the corresponding comprehensive severity index based on the risk index of a single scenario, and then obtaining one or more scenarios with the highest comprehensive severity index through screening and sorting to analyze the weak link of the power system; S5: calculating the system risk value of the power system by comprehensively considering the risk index and the protection refusal probability of all scenarios, and then evaluating the overall operation risk of the power system based on the system risk value; In step S5, the protection refusal probability of the primary-secondary coupling multiple fault model is first determined; Then, the system severity of correct protection action and the system severity of protection refusal are weighted and calculated based on the protection refusal probability, to obtain the system severity under a single scenario; finally, the system severity of each scenario is accumulated and summed, and the corresponding system risk value is calculated by averaging.

2. The method for power system risk assessment based on a quadratic coupling multiple failure model according to claim 1, wherein: In step S1, the transmission line fault probability is calculated by the following formula: ； wherein: represents the probability of failure of the transmission line; represents the average failure rate of the transmission line under meteorological conditions ; represents the evaluation time.

3. The method for power system risk assessment based on a quadratic coupling multiple failure model according to claim 1, wherein: In step S3, the primary-secondary coupling multiple fault model constructed comprises a transmission line module, two sets of transmission line main protection device modules, a transmission line backup protection device module, and a circuit breaker module; wherein the two sets of main protection device modules are connected in parallel with the backup protection device module, and are connected in series with the transmission line module and the circuit breaker module.

4. The method for power system risk assessment based on a quadratic coupling multiple failure model according to claim 1, wherein: The risk index of a scenario includes voltage out-of-limit risk, power flow out-of-limit risk, and system load loss risk; 1) Voltage out-of-limit risk Defining the node voltage out-of-limit risk of the i-th node and the system comprehensive voltage out-of-limit risk as: ​ ； ； In the formula: represents the node voltage out-of-limit risk value of the i-th node; represents the node voltage out-of-limit probability of the i-th node; represents the node voltage out-of-limit severity of the i-th node; represents the total number of nodes of the power system; represents the system comprehensive voltage out-of-limit risk;​​​ Definition of the first The node voltage over-limit value for each node is: ； The node voltage out-of-limit severity is represented by the following formula: ； wherein: Vn represents the voltage norm of the nth node; Vn represents the voltage norm of the nth node; Vn represents the voltage norm of the nth node; Vn represents the voltage norm of the nth node; 2) Power flow out-of-limit risk Defining branch power flow over-limit risk and system comprehensive power flow over-limit risk of a power system branch is: ； ； In the formula: represents the branch flow out-of-limit risk value of the mth branch; represents the branch flow out-of-limit probability of the mth branch; represents the branch flow out-of-limit severity of the mth branch; represents the total number of branches of the power system; represents the system comprehensive flow out-of-limit risk;​​​ No. The branch power flow limit exceeding the limit value of each branch is expressed as: ； The branch power flow out-of-limit severity is represented by the following formula: ； In the formula: represents the flow limit value of the first branch; represents the actual transmission power of the first branch; is 0.9 times the branch power limit. 3) System load loss risk The system load loss risk is defined as: ； In the formulae: represents the system loss of load risk; represents the system loss of load probability; represents the system loss of load severity; The system load loss severity is represented by the following formula: ； In the formulae: represents the system load at the current scenario; represents the total system load.

5. The method for power system risk assessment based on a quadratic coupling multiple failure model according to claim 4, wherein: In step S4, the comprehensive severity index is calculated by the following formula: ； In the formula: represents the system comprehensive severity index; represents the total number of nodes of the power system; represents the total number of branches of the power system; and respectively represent the weight of the node voltage out-of-limit severity and the weight of the branch power flow out-of-limit severity.

6. The method for power system risk assessment based on a quadratic coupling multiple failure model according to claim 5, wherein: First, the comprehensive severity index of each scenario is calculated and sorted in descending order; then, one or more scenarios with high ranking are selected, and the outage transmission line and fault propagation path corresponding to the scenario are obtained; finally, the weak link of the power system is determined based on the corresponding outage transmission line and fault propagation path.

7. The method for power system risk assessment based on a quadratic coupling multiple failure model according to claim 1, wherein: The system risk value of the power system is calculated by the following formula: ； ； In the formula: Indicates the system risk value; This represents the total number of scenarios sampled; system fault lines in a single scenario. The number of states generated by lateral resistance is , The number of states generated by lateral resistance is ; Indicates the first The severity of system protection against non-activation in each scenario; Indicates the first The severity of the system's ability to protect correct actions in a given scenario; Indicates the first The severity of a system in a state of refusal to move; This represents the node voltage exceeding the limit, the branch power flow exceeding the limit, and the system load shedding value; Indicates the first The power flow of each branch exceeds the limit; Indicates the first The voltage of each node exceeds the limit; This indicates the system load loss in the current scenario.

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