Elastic evaluation method for power transmission system under debris flow disaster

Abstract

The present application discloses a method for evaluating the flexibility of a power transmission system under the disaster of debris flow, and belongs to the technical field of the flexibility evaluation method of a power transmission system. The method comprises the following steps: S1, constructing a debris flow model; S11, calculating the length L of the debris flow by using the Rickenmann model; S12, calculating the width w of the debris flow by using an empirical formula of the width of the debris flow; S13, calculating the depth h of the debris flow based on the constant flow of the debris flow; S2, constructing a model for evaluating the failure rate of a tower; S21, calculating the impact force F of the debris flow; S211, using the average flow velocity of the debris flow to represent the overall flow velocity v of the debris flow; S212, calculating the impact force F0 of the flow head and the impact force F(t) of the flow tail; S22, calculating the maximum impact force Fmax that can be borne by the tower; S23, defining the difference between the impact force of the debris flow and the maximum impact force that can be borne by the tower as the tension; S3, constructing a model for the failure rate of the tower under the action of external force, and evaluating the failure probability.

Description

Technical Field

[0001] This invention belongs to the technical field of resilient assessment methods for power transmission systems, and particularly relates to a resilient assessment method for power transmission systems under debris flow disasters. Background Technology

[0002] Debris flows are a common natural disaster with powerful impact and destructive force, posing a serious threat to power transmission systems. The impact force, duration, and affected area of ​​debris flows are the main factors leading to transmission tower failures. Traditional power transmission systems often lack sufficient resilience in the face of natural disasters, easily leading to large-scale power outages and prolonged recovery difficulties. Therefore, research on the resilience assessment of power transmission systems under debris flow disasters is of great significance. By analyzing parameters such as the length, width, and depth of debris flows, the affected area of ​​debris flows on transmission towers can be determined. Empirical formulas such as the Rickenmann model are widely used to calculate the length and width of debris flows, taking into account factors such as flow rate, slope, and geological conditions. The impact force of debris flows on transmission towers is studied, including the impact forces at the head and tail of the flow. The impact force at the head is larger, while the impact force at the tail, although smaller, lasts longer and can also lead to tower failure. The calculation of impact force needs to consider factors such as the flow velocity, density, slope, and terrain roughness of the debris flow.

[0003] Resilience assessment is a crucial means of measuring the resilience and disaster resistance of power transmission systems under natural disasters. Traditional assessment methods primarily focus on component failure rates, neglecting changes in failure rates under external forces. Therefore, it is necessary to construct failure rate models that consider external forces to more accurately assess the resilience of power transmission systems. Resilience indices quantitatively describe the resilience of power transmission networks by measuring the stability of critical load supply and the damage resistance of the grid structure. The resilience triangle is an effective method for quantifying system resilience, obtaining the resilience index by calculating the degradation region of the system performance curve during a disaster. The non-sequential Monte Carlo method is a commonly used system state sampling method. By assuming a defined state probability distribution for each component, it combines each component to generate the system state. This method does not calculate the time series of components, significantly reducing computation time and offering a high solution rate.

[0004] Existing assessment methods have the following shortcomings:

[0005] I. Due to the widespread distribution of power towers, not all towers are affected during a debris flow; therefore, it is necessary to analyze the impact range of the debris flow. The impact range of a debris flow is described using three parameters: its length, width, and depth.

[0006] II. Mud and sand will continuously impact the base of the transmission tower and even the tower body. In most cases, mudslides mainly destroy the tower base, causing tower failure.

[0007] III. The failure rate described by the bathtub curve only considers the aging factor of the components themselves. Since the aging process of components is very slow during stable operation, the failure rate is assumed to be constant. However, under external forces such as mudslides, the failure rate can increase significantly. Therefore, a constant failure rate cannot be directly used to assess the failure probability of transmission components. Thus, for towers and transmission lines, it is necessary to construct a failure rate model under external forces and assess the failure probability. Summary of the Invention

[0008] The purpose of this invention is to provide a method for assessing the resilience of power transmission systems under debris flow disasters, in order to solve the technical problem of existing failure rate consideration factors being too singular.

[0009] This invention is achieved using the following technical solution:

[0010] A method for assessing the resilience of power transmission systems under debris flow disasters includes the following steps:

[0011] S1. Construct a debris flow model;

[0012] S11. Calculate the debris flow length L using the Rickenmann model;

[0013] S12. Calculate the debris flow width w using the empirical formula for debris flow width;

[0014] S13. Calculate the debris flow depth h based on a constant flow rate frame design;

[0015] S2. Construct a tower failure rate assessment model;

[0016] S21. Calculate the impact force F of the debris flow;

[0017] S211. The average velocity of debris flow is used to represent the overall velocity v of debris flow.

[0018] S212. Calculate the head impact force F0 and tail impact force F(t);

[0019] S22. Calculate the maximum impact force Fmax that the tower can withstand;

[0020] S23. The difference between the impact force of a debris flow and the maximum impact force that a tower can withstand is defined as tension.

[0021] S3. Construct a tower failure rate model under external force and assess the failure probability.

[0022] In a further optimized version, the model in step S1 considers the total mass of debris flow deposits, M, and the height difference H between the debris flow location and the tower base; since the debris flow density is relatively constant, M reflects the total mass of the debris flow. Clearly, L is proportional to these two parameters, as shown in the following formula:

[0023] L = b(MH) c

[0024] In the formula, the total amount of debris flow deposits is represented by M, and the height difference between the debris flow location and the tower base is represented by H.

[0025] A further preferred empirical formula for the debris flow width in step S11 is: w = rQ m S -n .

[0026] In the formula, the debris flow rate is represented by Q, and the slope of the mountain is represented by S.

[0027] In a further preferred embodiment, the debris flow depth in S12 refers to the average depth of the entire debris flow, rather than the depth at a specific location.

[0028] A further preferred formula for calculating the debris flow depth h is:

[0029]

[0030] In the formula, the debris flow rate is represented by Q, and the slope of the mountain is represented by S.

[0031] Further preferred, in S13, the calculation formula is as follows:

[0032]

[0033] A further optimized formula for calculating the impact force of the flow head;

[0034] F0=κF sinβ=κma sinβ=κρLhwa sinβ;

[0035] The impact force of a tower at time t after being hit by a debris flow can be expressed by a formula;

[0036] F(t) = F0e -2γt (1+δt).

[0037] Furthermore, the Fmax at different positions of the tower in S15 is expressed as:

[0038]

[0039] Traditional power transmission networks often experience outages when damaged by natural disasters, relying solely on relay protection devices to restore power to the widest possible area. This can lead to prolonged blackouts or even expand the affected area. Research on power transmission network resilience primarily considers the network's ability to withstand natural disasters. Therefore, the resilience index quantitatively describes the resilience of the power transmission network by measuring the stability of power supply to critical loads and the damage resistance of the network structure. During natural disasters, the performance of the power transmission network changes with the severity of the disaster. Attached Figure Description

[0040] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 This is a geospatial diagram showing the relationship between the debris flow path and the power transmission system according to the present invention.

[0043] Figure 2 This diagram illustrates the flow of debris along a mountainside according to the present invention.

[0044] Figure 3 This invention represents 3Hx 2 -x 3 Graph of the function.

[0045] Figure 4 This diagram illustrates the debris flow impact tower of the present invention.

[0046] Figure 5 This represents the IEEE-30 node topology diagram of the present invention.

[0047] Figure 6 This refers to the tower that was impacted by a debris flow according to the present invention.

[0048] Figure 7 This diagram illustrates the impact force of debris flow on each tower of the present invention.

[0049] Figure 8 This diagram illustrates the failure probability of the transmission towers according to the present invention.

[0050] Figure 9 This diagram shows the load curve of the power transmission system of the present invention.

[0051] In the diagram: 1-mountain, 2-mudslide, 3-tower, Ⅰ-impacted area. Detailed Implementation

[0052] To better understand the above-mentioned objectives, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0053] In this description, it should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. It should also be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joint" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0054] Many specific details are set forth in the following description in order to provide a full understanding of the invention, but the invention may also be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of the invention, and not all embodiments.

[0055] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0056] Example 1: A method for assessing the resilience of power transmission systems under debris flow disasters, comprising the following steps:

[0057] S1. Construct a debris flow model;

[0058] S11. Calculate the debris flow length L using the Rickenmann model;

[0059] This model considers the total mass of debris flow deposits, M, and the height difference, H, between the debris flow location and the tower base. Since the debris flow density is relatively constant, M reflects the total mass of the debris flow. Clearly, L is proportional to both of these parameters.

[0060] The specific formula used in this embodiment is: L=b(MH) c .

[0061] S12. Calculate the debris flow width w using the empirical formula for debris flow width;

[0062] The width w of a debris flow is mainly determined by the flow rate Q and the slope of the mountain. A larger flow rate Q results in a wider debris flow. The slope S affects the flow velocity and its spread; a shallower slope allows debris to accumulate more easily, thus resulting in a wider flow.

[0063] Empirical formula for debris flow width: w = rQ m S -n .

[0064] S13. Calculate the debris flow depth h based on a constant flow rate frame design;

[0065] The calculation of the debris flow depth h is based on the assumption of constant flow rate, meaning that the total volume of sediment flowing through the debris flow cross-section per unit time remains constant. The depth at the head of the debris flow is directly proportional to the slope, while the depth at the tail is inversely proportional to the slope. The depth mentioned in this paper refers to the average depth of the entire debris flow, not the depth at a specific location.

[0066] Calculation formula:

[0067] S2. Construct a tower failure rate assessment model;

[0068] S21. Calculate the impact force F of the debris flow;

[0069] The impact force of a debris flow is strongly correlated with its velocity. When a debris flow moves across a mountainside, the velocity is uneven due to the mountain's unevenness. For example... Figure 2 As shown, the stepped area represents the mountain, and the shaded area represents the debris flow. Clearly, the downstream velocity of the debris flow is higher than the upstream velocity; even at the same location, the velocity near the ground is lower than the velocity further away.

[0070] S211. The average velocity of debris flow is used to represent the overall velocity v of debris flow.

[0071] The following formula can be used for calculation:

[0072] S212. Calculate the head impact force F0 and tail impact force F(t);

[0073] Impact force of a debris flow: According to Newton's second law, force equals mass multiplied by acceleration. Therefore, along the direction of the mountain, the impact force of a debris flow is the mass of the debris flow multiplied by its acceleration. For example... Figure 2 As shown, the force along the mountain direction is decomposed into horizontal and vertical directions. The horizontal force is the impact force that causes tower failure.

[0074] The formula for calculating the impact force of the flow head is: F0=κFsinβ=κmasinβ=κρLhwasinβ.

[0075] Impact force at the tail of a debris flow: During the flow process, the impact force of a debris flow decreases over time or distance due to factors such as friction and resistance. Obviously, the rougher the terrain, the faster the impact force decreases; the lower the density of the debris flow, the greater the decrease in impact force.

[0076] The impact force on the pole tower at time t after being impacted by debris flow can be expressed by the formula: F(t)=F0e -2γt (1+δt).

[0077] S22. Calculate the maximum impact force Fmax that the pole tower can withstand;

[0078] S23. Define the difference between the debris flow impact force and the maximum impact force that the pole tower can withstand as tension;

[0079] The failure rate of the pole tower depends on the debris flow impact force F and the maximum impact force Fmax that the pole tower can withstand, and the difference between the two is defined as tension. Obviously, the failure rate is related to the tension: the greater the tension, the higher the failure rate of the pole tower. According to DL / T5154—2012 "Technical Code for Design of Tower Structures of Overhead Transmission Lines", Fmax at different positions of the pole tower can be expressed as:

[0080]

[0081] S3. Construct a failure rate model of the pole tower under external force to evaluate the failure probability.

[0082] Debris flow will impact different positions of the pole tower, and the failure rate of the pole tower depends on the most vulnerable point in the impacted area, that is, the point with the minimum Fmax. The point with the minimum Fmax appears when the denominator (3Hx 2 -x 3 ) is the maximum, and the function graph of the denominator is as shown Figure 3 shown. It can be seen from the function graph that the denominator reaches the maximum when x=2H.

[0083] The process of debris flow impacting the pole tower is as shown Figure 4 shown, and obviously h<H. Therefore, 0<x≤h<2H, and the point where the denominator is maximum is x=h.

[0084] In the second embodiment, taking the Figure 5 shown IEEE-30 bus system as an example, the resilience of the transmission system under the debris flow disaster as shown Figure 6 shown is studied.

[0085] The structural performance of the power transmission element itself determines its ability to resist debris flow, and the specific parameters of the transmission pole tower and the transmission line are shown in Table 1 and Table 2.

[0086] Table 1 Structural parameters of the transmission pole tower

[0087]

[0088] Table 2 Structural parameters of the transmission line

[0089]

[0090] Debris flows can impact transmission towers to varying degrees during their descent. Clearly, towers on mountaintops are not affected by debris flows. Therefore, this embodiment provides debris flow information for towers other than No. 3 and No. 8, as shown in Table 3.

[0091] Table 3 Information on debris flows suffered by each tower

[0092]

[0093] Based on the data in Table 3, the impact force borne by each tower was calculated according to the tower failure rate assessment model proposed in the embodiment. The calculated impact forces borne by towers 1-10 are as follows: Figure 7 As shown.

[0094] Depend on Figure 6 It can be seen that towers No. 3 and No. 8 are located on the mountaintop and therefore will not be affected by debris flows. Towers No. 2, 4, 7, and 9 are located close to the mountaintop, and debris flows will impact these towers earlier; therefore, the initial change in their impact force curves occurs earlier than that of towers No. 1, 5, 6, and 10. Tower No. 6 is located in the valley and will be impacted by debris flows from both sides, resulting in two peaks in the impact force. In conclusion, the impact force experienced by each tower is highly dependent on its geographical location and the debris flow path.

[0095] After obtaining the disaster resistance capability and debris flow impact force of the components, the failure probability of each component can be calculated. Figure 8 The figure shows the failure probability of towers 1-10 during a debris flow.

[0096] Referring to Table 3, under the same conditions, the debris flow depths corresponding to towers 4 and 5 differ by 0.51m, with failure probabilities of 0.0212 and 0.0052, respectively. Similarly, the cross-sectional areas of the debris flows corresponding to towers 2 and 10 differ by approximately double, with failure probabilities of 0.3545 and 0.7210, respectively; and the slope angles corresponding to towers 1 and 6 are different, with failure probabilities of 0.2721 and 0.0290, respectively. The comparison shows that the impact of each factor on the tower failure probability is not negligible. Therefore, the magnitude of the debris flow impact force should be determined by comprehensively considering all factors.

[0097] If the location of the tower is on a steep mountainside, with deep and large-section mudslides, such as towers No. 1 and No. 9, the impact force it receives will undoubtedly be greater, and the probability of failure will be relatively higher. Towers in such locations should receive extra attention. In addition, the disaster resistance performance of the tower itself should not be ignored.

[0098] Based on the obtained failure probabilities of transmission components, the system state is sampled using a non-sequential Monte Carlo method to obtain the system load curve, as shown below. Figure 9 As shown.

[0099] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the present invention. Although detailed descriptions have been provided 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 or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments, and they should all be covered within the protection scope of the claims.

Claims

1. A method for assessing the resilience of power transmission systems under debris flow disasters, characterized in that: Includes the following steps: S1. Construct a debris flow model; S11. Calculate the debris flow length L using the Rickenmann model; S12. Calculate the debris flow width w using the empirical formula for debris flow width; S13. Calculate the debris flow depth h based on a constant flow rate frame design; S2. Construct a tower failure rate assessment model; S21. Calculate the impact force F of the debris flow; S211. The average velocity of debris flow is used to represent the overall velocity v of debris flow. S212. Calculate the head impact force F0 and tail impact force F(t); S22. Calculate the maximum impact force Fmax that the tower can withstand; S23. The difference between the impact force of a debris flow and the maximum impact force that a tower can withstand is defined as tension. S3. Construct a tower failure rate model under external force and assess the failure probability.

2. The method for assessing the resilience of power transmission systems under debris flow disasters according to claim 1, characterized in that: The model in step S1 considers the total mass of debris flow deposits, M, and the height difference H between the debris flow location and the tower base. Since the density of debris flow is relatively constant, M reflects the total mass of the debris flow. Obviously, L is proportional to these two parameters, as shown in the specific formula: L=b(MH) c In the formula, the total amount of debris flow deposits is represented by M, and the height difference between the debris flow location and the tower base is represented by H.

3. The method for assessing the resilience of power transmission systems under debris flow disasters according to claim 1, characterized in that: The empirical formula for the width of the debris flow in step S11 is: w = rQ m S -n In the formula, the debris flow rate is represented by Q, and the slope of the mountain is represented by S.

4. The method for assessing the resilience of power transmission systems under debris flow disasters according to claim 1, characterized in that: In S12, the depth of a debris flow refers to the average depth of the entire debris flow, not the depth at a specific location.

5. The method for assessing the resilience of power transmission systems under debris flow disasters according to claim 4, characterized in that: The formula for calculating the depth h of a debris flow is: In the formula, the debris flow rate is represented by Q, and the slope of the mountain is represented by S.

6. The method for assessing the resilience of power transmission systems under debris flow disasters according to claim 4, characterized in that: The calculation formula in S13 is as follows:

7. The method for assessing the resilience of power transmission systems under debris flow disasters according to claim 4, characterized in that: Formula for calculating the impact force of a flow head; F0=κFsinβ=κmasinβ=κρLhwasinβ; The impact force of a tower at time t after being hit by a debris flow can be expressed by a formula; F(t)=F0e -2γt (1+δt)。 8. The method for assessing the resilience of power transmission systems under debris flow disasters according to claim 4, characterized in that: The Fmax at different positions of the tower in S15 is represented as follows:

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