Method for calculating reliability of power distribution network containing high-temperature superconducting cable based on fault tree method

Abstract

The application discloses a kind of based on fault tree method's power distribution network reliability calculation method containing high-temperature superconducting cable, comprising the following steps: (1) obtaining the reliability parameters of high-temperature superconducting cable body, terminal and cooling system, and then calculating the reliability parameters of high-temperature superconducting cable;(2) obtaining the reliability parameters of other elements in the power distribution network;(3) selecting the specific top event in the power distribution network, establishing the corresponding fault tree;(4) according to the reliability parameters of high-temperature superconducting cable and each element in the power distribution network, the reliability parameters of top event are calculated using fault tree, and then the reliability index of power distribution network is calculated.Based on actual data, the reliability index of power distribution network is calculated.The reliability level of power grid after superconducting cable is connected to power distribution network can be further evaluated by using superconducting cable reliability parameters, which guides the application of superconducting cable in power distribution network planning.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature superconducting cable technology, specifically, it relates to a method for calculating the reliability of power distribution networks containing high-temperature superconducting cables based on the fault tree method. Background Technology

[0002] With the rapid development of the global economy and the continuous advancement of industrialization, the demand for electricity continues to grow. The load density and transmission capacity requirements of power grids in large cities have increased significantly. Therefore, there is an urgent need to develop transmission channels with higher transmission capacity in the power system, which also puts forward higher requirements for the reliability and economy of power grid supply.

[0003] Superconducting power transmission technology, as one of the advanced power grid technologies, utilizes the resistance-free characteristics of superconducting materials in the superconducting state to replace conventional metal materials such as copper and aluminum as current-carrying conductors, thereby meeting the high-density and high-capacity transmission requirements of modern power grids.

[0004] Due to the unique characteristics of high-temperature superconducting cables, once they enter a quench state after being connected to the power grid, their electrical parameters will change significantly, which will also affect the safe and stable operation of the entire power supply system. Therefore, it is necessary to analyze the impact of their connection to the power grid on the reliability of the grid.

[0005] In this context, reliability analysis of distribution networks containing high-temperature superconducting cables becomes crucial. It helps power managers identify weak points affecting the reliability of the distribution network after changes occur, thereby strengthening the research and management of related technologies and ensuring that the distribution network has a high level of design and operation.

[0006] Distribution network reliability refers to the ability of the entire power distribution system and equipment from the power supply point to the user to meet the user's power and energy needs according to acceptable standards and expected quantities. Integrating superconducting cables into the system and evaluating the reliability of the power grid connected to high-temperature superconducting cables determines the impact of high-temperature superconducting cables in practical applications.

[0007] Fault tree analysis is a typical graphical analysis method. Based on the analysis of various factors that can lead to system failure, it uses logical relationships and diagrams to analyze and diagnose equipment failures and the system, drawing a logic diagram (i.e., a fault tree). It predicts possible failures, analyzes the causes of failures, calculates the probability of occurrence, and takes corresponding preventative measures to avoid such failures. This method has high reliability and is widely used in fault diagnosis and safety analysis.

[0008] This invention will use fault tree analysis to analyze the reliability of power distribution networks containing superconducting cables. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the present invention aims to provide a reliability calculation method for distribution networks containing high-temperature superconducting cables based on fault tree analysis. The method uses fault tree analysis to obtain reliability parameters of the high-temperature superconducting cable system under various states. Then, combined with the reliability parameters of other components in the distribution network, the reliability parameters of the top event in the distribution network are calculated using fault tree analysis, thereby calculating the reliability index of the distribution network.

[0010] The present invention adopts the following technical solution.

[0011] A reliability calculation method for distribution networks containing high-temperature superconducting cables based on the fault tree method, the method comprising the following steps:

[0012] (1) Obtain the reliability parameters of the high-temperature superconducting cable body, terminal and cooling system, and then calculate the reliability parameters of the high-temperature superconducting cable;

[0013] (2) Obtain the reliability parameters of other components in the power distribution network;

[0014] (3) Select a specific top event in the distribution network and establish the corresponding fault tree;

[0015] (4) Based on the reliability parameters of high-temperature superconducting cables and components in the distribution network, the reliability parameters of the top event are calculated using the fault tree, and then the reliability index of the distribution network is calculated.

[0016] Further, step (1) includes:

[0017] (1.1) Calculate the reliability parameters of the cooling system using the fault tree analysis method;

[0018] (1.2) Obtain the reliability parameters of the high-temperature superconducting cable body, the high-temperature superconducting cable terminal, and the cooling system terminal;

[0019] (1.3) Calculate the reliability parameters of the high-temperature superconducting cable using the fault tree analysis method.

[0020] Furthermore, in step (1.1),

[0021] Cooling system failures include liquid storage tank failures, liquid nitrogen pump failures, and refrigeration unit failures. Refrigeration unit failures include main refrigeration unit failures and standby refrigeration unit failures.

[0022] Based on the failure rates and mean time to repair of the liquid storage tank, liquid nitrogen pump, main refrigeration unit, and standby refrigeration unit, the failure rate and mean time to repair of the cooling system are calculated using fault tree analysis.

[0023] Among them, the failure of the liquid storage tank, the failure of the liquid nitrogen pump, and the failure of the refrigeration unit are series failures, while the failure of the main refrigeration unit and the failure of the standby refrigeration unit are parallel failures.

[0024] Furthermore, in step (1.3),

[0025] Calculating the reliability parameters of high-temperature superconducting cables includes calculating the reliability parameters under derating and outage conditions;

[0026] The derating operation mode includes cooling system failures and cooling system terminal failures. The failure rate, mean time to repair, and mean time to power outage of the derating operation mode are calculated using fault tree analysis. Among them, cooling system failures and cooling system terminal failures are series failures.

[0027] The outage state includes faults in the high-temperature superconducting cable itself and faults in the high-temperature superconducting cable terminals. The fault rate, mean repair time and mean outage time in the outage state are calculated using fault tree analysis. Among them, faults in the high-temperature superconducting cable itself and faults in the high-temperature superconducting cable terminals are series faults.

[0028] Furthermore, the reliability parameter in the outage state is selected as the failure rate λ of the high-temperature superconducting cable. HTS Mean repair time r HTS and average outage time U HTS .

[0029] Furthermore, in fault tree analysis,

[0030] For series components, the overall failure rate λ a Mean repair time r a and average outage time U a The calculation method is as follows:

[0031] λ a =λ1+λ2+…λ i …+λ n (1)

[0032]

[0033]

[0034] Where, λ i Let r be the failure rate of the i-th component. i Let i be the average repair time of the i-th element;

[0035] For parallel components, the overall failure rate λ b Mean repair time r b and average outage time U b The calculation method is as follows:

[0036]

[0037]

[0038] U b =λ b r b (6)

[0039] Where, λ i Let r be the failure rate of the i-th component. i Let be the average repair time of the i-th element.

[0040] Furthermore, step (3) includes selecting the top event and constructing a deductive tree;

[0041] List all important failure events one by one and distinguish their importance. Determine the top event for this analysis based on the purpose of the analysis and the criteria for fault judgment.

[0042] Using fault tree analysis, the direct and indirect causes of the top event are found layer by layer from top to bottom until the basic cause event is reached. The logical relationships between these events are then expressed using a logic diagram to form a fault tree.

[0043] Furthermore, in step (4),

[0044] Indicators for measuring the reliability of a power distribution network include average outage frequency, average outage duration, and average power availability.

[0045] Furthermore, the average power availability rate is the ratio of the total number of uninterrupted power hours experienced by users throughout the year to the total number of power supply hours requested by users, i.e.:

[0046]

[0047] Furthermore, step (3) is followed by a qualitative analysis of the fault tree.

[0048] Solve for the minimum cut set and minimum path set of the fault tree; where the minimum cut set represents the system's hazard and the minimum path set represents the system's reliability.

[0049] The beneficial effects of this invention are compared with those of the prior art:

[0050] This invention provides a method for calculating the reliability of power distribution networks containing high-temperature superconducting cables. It uses fault tree analysis to analyze the reliability parameters of each part and obtains the reliability parameters of the high-temperature superconducting cable system under various states. Then, it combines the reliability parameters of other components in the power distribution network and uses fault tree analysis to calculate the reliability parameters of the top event, thereby calculating the reliability index of the power distribution network. Finally, it calculates the reliability index of the power distribution network based on actual data.

[0051] Using the reliability parameters of superconducting cables can further evaluate the reliability level of the power grid after the superconducting cables are connected to the distribution network, and guide the application of superconducting cables in distribution network planning. Attached Figure Description

[0052] Figure 1 This is a flowchart of a reliability calculation method for power distribution networks containing high-temperature superconducting cables based on fault tree analysis;

[0053] Figure 2 It is a fault tree of the high-temperature superconducting cable cooling system;

[0054] Figure 3 It is a fault tree of a high-temperature superconducting cable in derating operation.

[0055] Figure 4 It is a fault tree of the high-temperature superconducting cable in the out-of-service state;

[0056] Figure 5 It is a radial power distribution network containing high-temperature superconducting cables;

[0057] Figure 6 It is the fault tree of load L1;

[0058] Figure 7 It is the fault tree of load L2. Detailed Implementation

[0059] The present application will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention, and should not be construed as limiting the scope of protection of the present application.

[0060] The reliability of a power distribution network is mainly reflected by reliability indicators. This invention uses the failure rate λ (times / year), the average fault repair time r (h / time), the average annual power outage time U (h / year), and the average service availability index (ASAI) to characterize the reliability of the power distribution network.

[0061] This invention introduces a reliability calculation method for a distribution network containing high-temperature superconducting cables, based on fault tree analysis, using a radial distribution network as an example, and obtains the reliability index of the distribution network connected to the high-temperature superconducting cables.

[0062] like Figure 1 As shown, the reliability calculation method for distribution networks containing high-temperature superconducting cables based on fault tree analysis is as follows:

[0063] Specific steps:

[0064] (1) Obtain the reliability parameters of the high-temperature superconducting cable body, terminal and cooling system, and then calculate the reliability parameters of the high-temperature superconducting cable in each state;

[0065] The high-temperature superconducting cable system mainly consists of three parts: the high-temperature superconducting cable body, the terminal, and the cooling system. The terminal is divided into two parts: the high-temperature superconducting cable terminal and the cooling system terminal.

[0066] The high-temperature superconducting cable body transmits electrical energy through the superconducting layer in a superconducting state; the cooling system keeps the superconducting layer of the high-temperature superconducting cable below the critical temperature; the terminal is the part that connects the high-temperature superconducting cable body, the cooling system, and the conventional conductor.

[0067] The various situations of the high-temperature superconducting cable system can be divided into three states: failure of the cooling system and related terminals can be classified as derating operation; failure of the high-temperature superconducting cable body and related terminals can be classified as shutdown; when all equipment is operating normally, the entire system is in normal state.

[0068] This invention calculates typical reliability parameters of superconducting cables based on actual data, and uses a general generating function to represent the reliability parameters of a high-temperature superconducting cable system under various states. To obtain the reliability parameters of the system under various states, the reliability parameters of each component must first be analyzed, and then the reliability parameters for the corresponding states must be calculated.

[0069] Since fault probability data for each part of a high-temperature superconducting cable system is not readily available, this invention calculates reliability based on the fault rate λ, mean repair time r, and average annual outage time U of each part. In other words, it uses fault tree analysis to analyze the reliability of each part of the high-temperature superconducting cable system.

[0070] In fault tree analysis, for series-connected components, the total failure rate λ is... a Mean repair time r a and average outage time U a The calculation method is as follows:

[0071] λ a =λ1+λ2+…λ i …+λ n (1)

[0072]

[0073]

[0074] Where, λ i Let r be the failure rate of the i-th component. i Let be the average repair time of the i-th element.

[0075] For parallel components, the overall failure rate λ b Mean repair time r b and average outage time U b

[0076] The calculation method is as follows:

[0077]

[0078]

[0079] U b =λ b r b (6)

[0080] Where, λ i Let r be the failure rate of the i-th component. i Let be the average repair time of the i-th element.

[0081] (1.1) Calculate the reliability parameters of the cooling system;

[0082] The cooling system consists of a liquid storage tank, a liquid nitrogen pump, a main refrigeration unit, and a backup refrigeration unit. Therefore, it is also necessary to calculate the reliability parameters of the cooling system based on these four components.

[0083] like Figure 2 As shown, the fault tree of the cooling system includes faults in the liquid storage tank, liquid nitrogen pump, and refrigeration unit; the refrigeration unit faults are further divided into main refrigeration unit faults and standby refrigeration unit faults.

[0084] When a component is in a fault state, its state is 1; when it is in a normal state, its state is 0. A refrigerator fault is only 1 when both the main refrigerator and the standby refrigerator are in a fault state; therefore, a main refrigerator fault and a standby refrigerator fault are connected using an AND gate, equivalent to a parallel connection. Conversely, if any one of the following—the liquid receiver fault, the liquid nitrogen pump fault, or the refrigerator fault—is 1, then the cooling system is in a fault state; therefore, an OR gate is used to connect them, equivalent to a series connection.

[0085] The reliability parameters of each component in the cooling system are shown in Table 1. Except for the standby chiller, the failure rate and mean time of repair of the other three components in the cooling system are all taken as the same value. Since the standby chiller has a simpler structure, it has a lower failure rate and a shorter mean time of repair.

[0086] Table 1

[0087]

[0088]

[0089] The failure rate λ and mean repair time r of the chiller are calculated using parallel formulas (4)-(6):

[0090] When n = 2, the formula is:

[0091] r b =r1+r2

[0092]

[0093] U b =λ b r b

[0094] The failure rate λ and mean time to repair (MTBT) of the cooling system are calculated using the series formulas (1)-(3):

[0095] When n = 3, the formula is:

[0096] λ a =λ1+λ2+λ3

[0097]

[0098] U a =λ1r1+λ2r2+λ3r3

[0099] The calculated failure rate λ and mean time to repair r of the cooling system are shown in Table 1.

[0100] (1.2) Obtain reliability parameters for other parts of the high-temperature superconducting cable system, provided by the relevant component manufacturers; including the high-temperature superconducting cable body, the high-temperature superconducting cable terminal, and the cooling system terminal;

[0101] Table 2 shows the reliability parameters of each part of the high-temperature superconducting cable system. Among them, the reliability parameters of the cooling system have been calculated.

[0102] Because high-temperature superconducting cables are still relatively rare in practical engineering applications and have been in operation for a short period, much of the reliability data is quite limited. Table 2 assumes that the failure rate of the high-temperature superconducting cable itself is similar to that of traditional underground cables. However, because repairs to superconducting cables require raising the temperature to room temperature and then cooling it back to the cable's operating temperature, the average repair time is longer. Furthermore, the terminals in high-temperature superconducting cable systems have a more complex structure than conventional terminals, resulting in both a higher failure rate and a longer average repair time.

[0103] Table 2

[0104]

[0105] (1.3) Calculate the reliability parameters of the corresponding states based on the state diagram;

[0106] (1.3.1) Calculate the reliability parameters of the derating operation state;

[0107] For high-temperature superconducting cable systems, when the cooling system or its terminals are in a faulty state, the entire system will operate in a derating state. Therefore, the cooling system and its terminals are connected via an OR gate, equivalent to a series connection. The fault tree for the derating state is as follows: Figure 3 As shown.

[0108] According to the series formulas (1)-(3), when n=2, the probability λ1 of the derated operation state and the average repair time r1 can be calculated to be 0.9817 times / a and 72.2h / time, respectively, and the average power outage time U1 is 70.9h.

[0109] (1.3.2) Calculate the reliability parameters in the outage state;

[0110] When the high-temperature superconducting cable body or its terminal fails, the entire system will be in a shutdown state. Therefore, the high-temperature superconducting cable body and its terminal are connected via an OR gate, essentially in series. The fault tree in the shutdown state is as follows: Figure 4 As shown.

[0111] According to the series formulas (1)-(3), when n=2, the probability λ2 of the outage state and the average repair time r2 can be calculated to be 0.105 times / a and 188.9h / time, respectively, and the average outage time U2 is 2.45h.

[0112] For high-temperature superconducting cables, they can still provide power transmission capacity under derating operation. Therefore, the derating operation is considered as the normal state. Thus, the failure rate of high-temperature superconducting cables only considers the parameters under the outage state, resulting in the failure rate λ of the high-temperature superconducting cable. HTS Mean repair time r HTS and average outage time U HTS .

[0113] (2) Collect reliability parameters of other components in the power distribution network;

[0114] Obtain the network topology of the distribution network, such as Figure 5 As shown, a radial power distribution network containing high-temperature superconducting cables includes busbars W1, W2, and W3; circuit breakers 1, 2, and 3; high-temperature superconducting cables 1, 2, and 3; and loads L1 and L2.

[0115] Collect reliability parameters for other components in the power distribution network, such as the failure rate, mean time to repair, and mean time to outage of circuit breakers, which are respectively λ. B r B U B The bus fault rate, mean repair time, and mean outage time are λ, respectively. W r W U W .

[0116] (3) Select the specific top event of the distribution network system and establish the corresponding fault tree;

[0117] Understand and master the power distribution network system. Differentiate the impact of software and human factors on the entire system, understand the different state modes the system can adopt and their correspondence with the states of other units, and clarify the mutual transformation between different modes.

[0118] Select the top event. After fully understanding the system and related information, list all important failure events one by one and distinguish their importance. Then, based on the purpose of the analysis and the criteria for fault judgment, determine the top event for this analysis.

[0119] Deductive Tree Construction. Using fault tree analysis, the direct and indirect causes of the top event are identified layer by layer from top to bottom, down to the root cause event. The logical relationships between these events are then expressed using a logic diagram, forming a fault tree. The top event is placed at the top of the fault tree, and all direct causes leading to the top event are listed in the second row, including operational malfunctions, configuration errors, platform failures, etc. Then, based on the logical relationships between faults in the system, appropriate logic gates are used to connect the top event and the aforementioned direct causes. This process is repeated, expanding downwards level by level according to the principles of tree construction, until all root causes at the bottom level are root events.

[0120] Example 1: The top event is the reliability of load L1. For load L1, if cable 1, circuit breaker 1, or bus W2 is in a faulty state, it will lose its power supply capability. Therefore, the fault tree of load L1 can be obtained as follows: Figure 6 As shown.

[0121] Example 2: The top event is the reliability of load L2. For load L2, the situation where load L1 cannot supply power also applies to L2. Furthermore, if both lines between bus W2 and bus W3 fail, or if bus W3 fails, then load L2 will also lose its power supply capability. Therefore, the fault tree for load L2 can be obtained as follows: Figure 7 As shown.

[0122] (4) Qualitative analysis is performed to obtain the minimum cut set and minimum path set of the fault tree; where the minimum cut set represents the system's risk and the minimum path set represents the system's reliability.

[0123] Every occurrence of a minimal cut set inevitably leads to the occurrence of a top event. Conversely, if a minimal path set does not occur, then the top event will also not occur. Therefore, the more minimal cut sets found, the more dangerous the system becomes; conversely, the more minimal path sets there are, the more reliable the system becomes.

[0124] The process for calculating the minimum cut set of a fault tree is as follows:

[0125] (4.1) Place the top event in the first column;

[0126] (4.2) Starting from the top event, replace the previous event with the next level input event level by level. Use logical product to replace AND gates and logical AND to replace OR gates.

[0127] (4.3) The replacement stops when all events are replaced with basic events;

[0128] (4.4) Many logical products and logical sums are obtained. Each logical product is a cut set, but it is not necessarily the smallest cut set;

[0129] (4.5) Compare all cut sets, remove those that are included or repeated, and the remaining ones are the minimum cut sets required.

[0130] Simplification of fault trees. Based on the minimum cut sets of fault trees, and under certain necessary and reasonable assumptions, the actual system diagram can be simplified into a simplified system diagram representing the main logical relationships.

[0131] (5) Based on the reliability indicators of high-temperature superconducting cables and components in the distribution network, the reliability parameters of the top event are calculated using the fault tree, and then the reliability indicators of the distribution network are calculated.

[0132] Quantitative analysis of fault trees is a key objective and main step in fault tree analysis. It is mainly used to assess and calculate the reliability characteristics of the top event and major failure events of the system, thereby determining the degree of impact of the major failure events on the top event, thus identifying the weak links of the system, and implementing rectification measures for the system design.

[0133] In the process of quantitative analysis of fault trees, it is first necessary to clarify the probability of the occurrence of the underlying events and the probability of the occurrence of the minimum cut set. Then, based on the probability of the occurrence of the underlying events, it is necessary to clarify the probability of the event itself, so as to conduct risk assessment.

[0134] For example, the reliability parameters of load L1 in Example 1 are calculated according to formulas (1)-(3):

[0135] Failure rate:

[0136] λ L1 =λ B +λ HTS +λ W

[0137] Mean time to repair:

[0138]

[0139] Average power outage duration:

[0140] U L1 =λ B r B +λHTS r HTS +λ W r W

[0141] Commonly used indicators for measuring the reliability of power distribution networks include average outage frequency, average outage duration, and average power availability.

[0142] The average outage frequency index (SAIFI) of the distribution network refers to the average number of outage incidents experienced by all power users in the target distribution network within a certain time period. This time period is usually set as one year.

[0143]

[0144] The Standard Interruption Duration Index (SAIDI) refers to the average duration of a power outage affecting all electricity users in a target distribution network.

[0145]

[0146] The average power availability rate is the ratio of the total number of hours of uninterrupted power supply experienced by users in a year to the total number of hours of power supply requested by users.

[0147]

[0148] Calculate the power grid reliability index when conventional underground cables are installed between busbars W1, W2, and W3, and the power grid reliability index when high-temperature superconducting cables are installed. Compare the differences in power grid reliability index under the two conditions and analyze the impact of high-temperature superconducting cables on power grid reliability.

[0149] The reliability parameters of each component of the power grid are shown in Table 3. The number of power supply users for loads L1 and L2 are 100 and 200, respectively. It is assumed that generator G1 and bus W1 are always in normal operation. For high-temperature superconducting cables, they can still provide power transmission capacity under derating operation conditions. Therefore, the failure rate of high-temperature superconducting cables only considers the parameters under outage conditions.

[0150] Table 3

[0151]

[0152] The reliability indices of the cable were calculated for both conventional underground cables and high-temperature superconducting cables, as shown in Tables 4 and 5. Table 4 shows the reliability parameters at load point L1, and Table 5 shows the reliability parameters at load point L2.

[0153] Table 4

[0154]

[0155] Table 5

[0156]

[0157] In this example, for a distribution network connected to a high-temperature superconducting cable, the average power supply availability index is:

[0158]

[0159] For distribution networks connected to conventional underground cables, the average power availability index is:

[0160]

[0161] Comparison reveals that the reliability of a system with high-temperature superconducting cables is slightly lower than that of a conventional underground cable. This is related to the complexity of the high-temperature superconducting cable system itself and the fact that the technology is not yet fully mature. Improving the reliability of high-temperature superconducting cables will benefit the stable operation of the power grid.

[0162] The beneficial effects of this invention are compared with those of the prior art:

[0163] This invention provides a method for calculating the reliability of power distribution networks containing high-temperature superconducting cables. It uses fault tree analysis to analyze the reliability parameters of each part and obtains the reliability parameters of the high-temperature superconducting cable system under various states. Then, it combines the reliability parameters of other components in the power distribution network and uses fault tree analysis to calculate the reliability parameters of the top event, thereby calculating the reliability index of the power distribution network. Finally, it calculates the reliability index of the power distribution network based on actual data.

[0164] Using the reliability parameters of superconducting cables can further evaluate the reliability level of the power grid after the superconducting cables are connected to the distribution network, and guide the application of superconducting cables in distribution network planning.

[0165] The applicant of this invention has provided a detailed description of the embodiments of the invention in conjunction with the accompanying drawings. However, those skilled in the art should understand that the above embodiments are merely preferred embodiments of the invention. The detailed description is only intended to help readers better understand the spirit of the invention and is not intended to limit the scope of protection of the invention. On the contrary, any improvements or modifications made based on the inventive spirit of the invention should fall within the scope of protection of the invention.

Claims

1. A reliability calculation method for distribution networks containing high-temperature superconducting cables based on fault tree method, characterized in that, The method includes the following steps: (1) Calculate the reliability parameters of the cooling system according to the fault tree analysis method, obtain the reliability parameters of the high temperature superconducting cable body, the high temperature superconducting cable terminal, and the cooling system terminal, and calculate the reliability parameters of the high temperature superconducting cable according to the fault tree analysis method; Cooling system failures include liquid storage tank failures, liquid nitrogen pump failures, and chiller failures. Chiller failures include main chiller failures and standby chiller failures. Based on the failure rates and mean time to repair of the liquid storage tank, liquid nitrogen pump, main chiller, and standby chiller, the failure rate and mean time to repair of the cooling system are calculated using fault tree analysis. (2) Obtain the reliability parameters of other components in the power distribution network; (3) Select a specific top event in the distribution network and establish the corresponding fault tree; (4) Based on the reliability parameters of high-temperature superconducting cables and components in the distribution network, the reliability parameters of the top event are calculated using the fault tree, and then the reliability index of the distribution network is calculated.

2. The method for calculating the reliability of distribution networks containing high-temperature superconducting cables based on fault tree method according to claim 1, characterized in that, In step (1), The failures of the liquid storage tank, liquid nitrogen pump, and refrigeration unit are series failures, while the failures of the main refrigeration unit and the standby refrigeration unit are parallel failures.

3. The method for calculating the reliability of distribution networks containing high-temperature superconducting cables based on fault tree method according to claim 1, characterized in that, In step (1), Calculating the reliability parameters of high-temperature superconducting cables includes calculating the reliability parameters under derating and outage conditions; The derating operation mode includes cooling system failures and cooling system terminal failures. The failure rate, mean time to repair, and mean time to power outage of the derating operation mode are calculated using fault tree analysis. Among them, cooling system failures and cooling system terminal failures are series failures. The outage state includes faults in the high-temperature superconducting cable itself and faults in the high-temperature superconducting cable terminals. The fault rate, mean repair time and mean outage time in the outage state are calculated using fault tree analysis. Among them, faults in the high-temperature superconducting cable itself and faults in the high-temperature superconducting cable terminals are series faults.

4. The method for calculating the reliability of distribution networks containing high-temperature superconducting cables based on the fault tree method according to claim 3, characterized in that, The reliability parameter in the outage state is selected as the failure rate of the high-temperature superconducting cable. Average repair time and average power outage time .

5. The method for calculating the reliability of distribution networks containing high-temperature superconducting cables based on fault tree method according to claim 1, characterized in that, In fault tree analysis, For series components, the overall failure rate is... Average repair time and average power outage time The calculation method is as follows: （1） （2） （3） in, For the first i Failure rate of individual components For the first i Average repair time for each component; For parallel components, the overall failure rate is... Average repair time and average power outage time The calculation method is as follows: （4） （5） （6） in, For the first i Failure rate of individual components For the first i Average repair time for each component.

6. The method for calculating the reliability of distribution networks containing high-temperature superconducting cables based on the fault tree method according to claim 1, characterized in that, Step (3) includes selecting the top event and constructing the tree using deductive reasoning; List all important failure events one by one and distinguish their importance. Determine the top event for this analysis based on the purpose of the analysis and the criteria for fault judgment. Using fault tree analysis, the direct and indirect causes of the top event are found layer by layer from top to bottom until the basic cause event is reached. The logical relationships between these events are then expressed using a logic diagram to form a fault tree.

7. The method for calculating the reliability of distribution networks containing high-temperature superconducting cables based on fault tree method according to claim 1, characterized in that, In step (4), Indicators for measuring the reliability of a power distribution network include average outage frequency, average outage duration, and average power availability.

8. The method for calculating the reliability of distribution networks containing high-temperature superconducting cables based on fault tree method according to claim 7, characterized in that, The average power availability rate is the ratio of the total number of hours of uninterrupted power supply experienced by users in a year to the total number of hours of power supply requested by users. 。 9. The method for calculating the reliability of distribution networks containing high-temperature superconducting cables based on fault tree method according to claim 1, characterized in that, Step (3) is followed by a qualitative analysis of the fault tree. Solve for the minimum cut set and minimum path set of the fault tree; where the minimum cut set represents the system's hazard and the minimum path set represents the system's reliability.

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