A reliability assessment method and system for a wide area backup protection system

Abstract

The present application discloses a reliability evaluation method and system for a wide-area backup protection system. The method includes: dividing the wide-area backup protection system into multiple subsystems, comprehensively utilizing the fault tree analysis method and the Markov state space to establish the reliability model of each subsystem and the entire system, and finally utilizing the fault tree structure function and the Monte Carlo simulation model to evaluate the reliability of the wide-area backup protection system. Compared with the prior art, the reliability evaluation complexity is reduced; various random factors affecting reliability are considered, and the correctness of the reliability evaluation is improved. Thus, the technical problem that the prior art has the computational complexity and cannot guarantee the correctness of the reliability evaluation is solved.

Description

Technical Field

[0001] The present application relates to the field of electric power technology, and in particular to a reliability assessment method and system for a wide-area backup protection system. Background Art

[0002] The wide-area backup protection system is a distributed system that uses a number of intelligent electronic devices in multiple substations to communicate, interact, collaborate, and coordinate to jointly complete the backup protection function of primary equipment. Regional centralized wide-area backup protection has the operating characteristics of centralized tripping decisions. Once the wide-area backup protection malfunctions, it may cause a large range of primary equipment to be mis-tripped; at the same time, if some reason occurs, such as a failure in the decision-making center, the wide-area backup protection of the entire area will fail. Therefore, the research on the reliability of wide-area backup protection is of great significance.

[0003] Compared with traditional protection, as a distributed system, wide-area backup protection has undergone major changes in protection principles, implementation methods, information domains, and scopes. The factors and links that affect its reliability have increased, and these factors may not be independent of each other. This feature restricts the original models or methods used to study traditional protection in the process of studying wide-area backup protection. When evaluating the reliability of a system, we are concerned about the possibility of the system completing the predetermined function. The completion of the function requires both hardware and software to work reliably at the same time. The wide-area backup protection system is a distributed complex system, and its function belongs to distributed real-time function, that is, the function requires multiple IEDs to work together by exchanging information and complete it within a specified time. The wide-area backup protection algorithm has a certain fault-tolerant performance. In the case of partial information errors, IED failures or communication failures leading to partial information loss, the wide-area backup protection can still make correct decisions and remove the faulty components. This greatly increases the difficulty of evaluating the reliability of wide-area backup protection. How to effectively evaluate the reliability of the wide-area backup protection system has become an important issue that is expected to be solved in engineering applications.

[0004] At present, the commonly used methods for studying reliability are mainly divided into analytical methods and simulation methods. The analytical methods include: network method, minimum path set method, minimum cut set method, Markov state space method, fault tree analysis method, GO method; the simulation methods mainly include Monte Carlo simulation method. However, when the conventional fault tree analysis method, minimum path set method, minimum cut set method and GO method involve the repair process, they also need to be combined with the modular algorithm of the Markov model, which increases the computational complexity and cannot guarantee the correctness of the reliability assessment. Summary of the invention

[0005] The present application provides a wide-area backup protection system reliability assessment method and system, which are used to solve the technical problem that the prior art has computational complexity and cannot guarantee the correctness of reliability assessment.

[0006] In view of this, the first aspect of the present application provides a method for evaluating the reliability of a wide-area backup protection system, the method comprising:

[0007] Divide the wide-area backup protection system into a wide-area backup protection sampling system, a wide-area power communication network, a relay protection device, and a wide-area backup protection tripping system;

[0008] Based on the substation IED and the double-star network topology, the refusal to operate failure and malfunction failure of the wide-area backup protection sampling system and the wide-area backup protection tripping system are analyzed, and a fault tree model is constructed according to the refusal to operate failure and a fault tree model is constructed according to the malfunction failure;

[0009] Establishing a wide area power communication network reliability model of the wide area power communication network with a ring network and a linear network respectively, analyzing the failure conditions of the wide area power communication network reliability model, and establishing a fault tree model of the wide area power communication network according to the failure conditions;

[0010] According to the relationship between the failure of the hardware module of the relay protection device and the failure of refusal or malfunction, a fault tree model of the failure of refusal or malfunction of the hardware module is constructed; a Markov state space diagram of the software of the relay protection device is established, and a fault tree model of the failure of refusal or malfunction of the software is constructed according to the Markov state space diagram;

[0011] Constructing an overall reliability fault tree model of the wide-area backup protection system according to the fault tree model of the wide-area backup protection sampling system, the fault tree model of the wide-area power communication network, the fault tree model of the relay protection device, and the fault tree model of the wide-area backup protection tripping system;

[0012] The reliability simulation analysis of the overall reliability fault tree model is carried out by using a sequential Monte Carlo simulation method of a fault tree structure function to obtain a reliability evaluation result of the wide area backup protection system.

[0013] Optionally, the method of constructing a fault tree model of failure of hardware module failure or malfunction failure according to the relationship between failure of the hardware module of the relay protection device and failure of refusal or malfunction; establishing a Markov state space diagram of the software of the relay protection device, and constructing a fault tree model of failure of software failure or malfunction failure according to the Markov state space diagram, specifically includes:

[0014] Analyze the relationship between the failure of the hardware module of the relay protection device and the failure of refusal to operate or malfunction to obtain the failure rate of refusal to operate and the failure rate of malfunction to operate of the relay protection device, and establish a fault tree model of the failure of refusal to operate or malfunction to operate of the hardware module of the relay protection device;

[0015] The software failure modes of the relay protection device are divided into failure due to refusal to operate and failure due to malfunction, a Markov state space diagram of the relay protection device is established, a Markov state equation is established based on the Markov state space diagram, the steady-state probability of each state is solved based on the Markov state equation, the failure rate due to refusal to operate and the failure rate due to malfunction are obtained, and a fault tree model of failure due to refusal to operate or malfunction of the software of the relay protection device is established.

[0016] Optionally, the Markov state space diagram specifically includes:

[0017] Normal working state, hardware refusal state that cannot be self-checked, hardware refusal state that can be self-checked, hardware malfunction state that cannot be self-checked, hardware malfunction state that can be self-checked, software malfunction state, software refusal state, refusal state due to human error, malfunction state due to human error.

[0018] Optionally, the refusal to operate failure condition of the wide-area backup protection sampling system specifically includes:

[0019] The LTU cannot obtain the merging unit sampling value information, which is divided into the merging unit hardware failure and the communication network failure from the merging unit to the LTU;

[0020] LTU cannot obtain the logical quantity information of the protection device, which is divided into protection device failure and protection device to LTU communication network failure; protection device failure includes: failure to obtain the sampling value information of the merging unit, resulting in protection device principle failure, which is divided into merging unit hardware failure and merging unit to protection device communication network failure; protection device refusal to operate failure;

[0021] The LTU device refuses to operate and fails.

[0022] Optionally, the malfunction failure of the wide-area backup protection tripping system specifically includes:

[0023] All protection information errors of one or more traditional protection devices lead to false operation and failure of wide-area backup protection;

[0024] The communication network within the station is normal;

[0025] The LTU device is normal, among which all protection information errors of the traditional protection device are divided into two situations: failure of the traditional protection device, including false operation and refusal to operate failure; failure of the merging unit, the output sampling value is wrong, resulting in all protection information errors of the protection device.

[0026] Optionally, the refusal to operate failure condition of the wide-area backup protection tripping system specifically includes:

[0027] The LTU device fails to operate; the communication network from the LTU to the intelligent terminal fails; the intelligent terminal fails.

[0028] Optionally, the refusal to operate failure condition of the wide area backup protection sampling system specifically includes: LTU device malfunction failure; the in-station communication network is normal; the intelligent terminal is normal.

[0029] A second aspect of the present application provides a wide-area backup protection system reliability assessment system, the system comprising:

[0030] A division unit, used for dividing the wide-area backup protection system into a wide-area backup protection sampling system, a wide-area power communication network, a relay protection device, and a wide-area backup protection tripping system;

[0031] The first construction unit is used to analyze the refusal to operate failure situation and the malfunction failure situation of the wide-area backup protection sampling system and the wide-area backup protection tripping system based on the substation IED and the double-star network topology structure, and to construct a fault tree model according to the refusal to operate failure situation and to construct a fault tree model according to the malfunction failure situation;

[0032] A second construction unit is used to establish a wide area power communication network reliability model of the wide area power communication network with a ring network and a linear network respectively, analyze the failure situation of the wide area power communication network reliability model, and establish a fault tree model of the wide area power communication network according to the failure situation;

[0033] The third construction unit is used to construct a fault tree model of failure of refusal or malfunction of the hardware module according to the relationship between failure of the hardware module of the relay protection device and failure of refusal or malfunction; establish a Markov state space diagram of the software of the relay protection device, and construct a fault tree model of failure of refusal or malfunction of the software according to the Markov state space diagram;

[0034] A fourth construction unit is used to construct an overall reliability fault tree model of the wide-area backup protection system according to the fault tree model of the wide-area backup protection sampling system, the fault tree model of the wide-area power communication network, the fault tree model of the relay protection device, and the fault tree model of the wide-area backup protection tripping system;

[0035] The simulation unit is used to perform reliability simulation analysis on the overall reliability fault tree model by using a sequential Monte Carlo simulation method of a fault tree structure function to obtain a reliability evaluation result of the wide area backup protection system.

[0036] Optionally, the third building unit is specifically used to:

[0037] Analyze the relationship between the failure of the hardware module of the relay protection device and the failure of refusal to operate or malfunction to obtain the failure rate of refusal to operate and the failure rate of malfunction to operate of the relay protection device, and establish a fault tree model of the failure of refusal to operate or malfunction to operate of the hardware module of the relay protection device;

[0038] The software failure modes of the relay protection device are divided into failure due to refusal to operate and failure due to malfunction, a Markov state space diagram of the relay protection device is established, a Markov state equation is established based on the Markov state space diagram, the steady-state probability of each state is solved based on the Markov state equation, the failure rate due to refusal to operate and the failure rate due to malfunction are obtained, and a fault tree model of failure due to refusal to operate or malfunction of the software of the relay protection device is established.

[0039] Optionally, the Markov state space diagram specifically includes:

[0040] Normal working state, hardware refusal state that cannot be self-checked, hardware refusal state that can be self-checked, hardware malfunction state that cannot be self-checked, hardware malfunction state that can be self-checked, software malfunction state, software refusal state, refusal state due to human error, malfunction state due to human error.

[0041] It can be seen from the above technical solutions that this application has the following advantages:

[0042] The present application provides a reliability assessment method for a wide-area backup protection system, including: dividing the wide-area backup protection system into a wide-area backup protection sampling system, a wide-area power communication network, a relay protection device, and a wide-area backup protection tripping system; based on a substation IED and a double-star network topology, analyzing the refusal to operate failure and malfunction failure of the wide-area backup protection sampling system and the wide-area backup protection tripping system, constructing a fault tree model according to the refusal to operate failure, and constructing a fault tree model according to the malfunction failure; establishing a wide-area power communication network reliability model of the wide-area power communication network with a ring network and a linear network respectively, analyzing the failure of the wide-area power communication network reliability model, and constructing a fault tree model according to the failure failure. A fault tree model of the wide-area power communication network is established based on the situation; a fault tree model of the hardware module failure or malfunction failure is constructed based on the relationship between the hardware module failure and the failure of refusal or malfunction of the relay protection device; a Markov state space diagram of the software of the relay protection device is established, and a fault tree model of the software failure or malfunction failure is constructed based on the Markov state space diagram; an overall reliability fault tree model of the wide-area backup protection system is constructed based on the fault tree model of the wide-area backup protection sampling system, the fault tree model of the wide-area power communication network, the fault tree model of the relay protection device, and the fault tree model of the wide-area backup protection tripping system; a reliability simulation analysis of the overall reliability fault tree model is carried out through the sequential Monte Carlo simulation method of the fault tree structure function, and the reliability evaluation result of the wide-area backup protection system is obtained.

[0043] This application divides the wide-area backup protection system into multiple subsystems, comprehensively utilizes the fault tree analysis method and Markov state space to establish the reliability model of each subsystem and the entire system, and finally uses the fault tree structure function and Monte Carlo simulation model to evaluate the reliability of the wide-area backup protection system. Compared with the prior art, it reduces the complexity of reliability evaluation, considers various random factors that affect reliability, and improves the correctness of reliability evaluation. This solves the technical problem that the prior art has computational complexity and cannot guarantee the correctness of reliability evaluation. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 A flowchart of an embodiment of a wide-area backup protection system reliability assessment method provided in an embodiment of the present application;

[0045] Figure 2 A schematic diagram of a wide area backup protection system with a regional centralized WAPS structure provided in an embodiment of the present application;

[0046] Figure 3 A schematic diagram of a substation IED and network topology provided in an embodiment of the present application;

[0047] Figure 4 A schematic diagram of a fault tree model of a wide-area backup protection sampling system failure to operate provided in an embodiment of the present application;

[0048] Figure 5 A schematic diagram of a fault tree model of a communication network from a merging unit or a protection device to an LTU provided in an embodiment of the present application;

[0049] Figure 6 A schematic diagram of a fault tree model for malfunction failure of a wide-area backup protection sampling system provided in an embodiment of the present application;

[0050] Figure 7 A schematic diagram of a fault tree model of a wide-area backup protection tripping system failure to operate provided in an embodiment of the present application;

[0051] Figure 8 A schematic diagram of a fault tree model for malfunction failure of a wide-area backup protection tripping system provided in an embodiment of the present application;

[0052] Fig. 9 A schematic diagram of a 4-node 2-fiber unidirectional channel protection ring network provided in an embodiment of the present application;

[0053] Fig.10 A schematic diagram of LTU2 to the master station RDU and RDU to the master station LTU2 provided in an embodiment of the present application;

[0054] Fig.11Schematic diagram of LTU to master station RDU and RDU to master station LTU provided in the embodiment of the present application;

[0055] Fig.12 This is a functional module structure diagram of a digital relay protection device provided in an embodiment of the present application;

[0056] Fig.13 A schematic diagram of a fault tree model of a protection device failure to operate or malfunction provided in an embodiment of the present application;

[0057] Fig.14 It is a Markov state space diagram of the state of the protection device 8 provided in the embodiment of the present application;

[0058] Fig.15a A schematic diagram of the overall malfunction reliability of the wide-area backup protection system provided in an embodiment of the present application;

[0059] Fig.15b A schematic diagram of the overall refusal reliability of the wide-area backup protection system provided in an embodiment of the present application;

[0060] Fig.15c A schematic diagram of the overall reliability of the wide-area backup protection system provided in an embodiment of the present application;

[0061] Fig.16 A schematic diagram of a sequential Monte Carlo simulation of a system provided in an embodiment of the present application;

[0062] Fig.17 It is a structural schematic diagram of an embodiment of a wide-area backup protection system reliability assessment system provided in an embodiment of the present application. DETAILED DESCRIPTION

[0063] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0064] See also Figure 1 A wide-area backup protection system reliability assessment method provided in an embodiment of the present application includes:

[0065] Step 101, dividing the wide area backup protection system into a wide area backup protection sampling system, a wide area power communication network, a relay protection device, and a wide area backup protection tripping system;

[0066] It should be noted that the wide area backup protection system model based on the regional centralized WAPS structure is as follows Figure 2 This application divides the overall reliability of the wide-area backup protection system into the following categories: Figure 2 The four subsystems shown are: wide-area backup protection sampling system reliability, wide-area power communication network reliability, master station decision center RDU reliability (relay protection device) and wide-area backup protection tripping system reliability.

[0067] Step 102: Based on the substation IED and the dual-star network topology, analyze the refusal to operate failure and malfunction failure of the wide-area backup protection sampling system and the wide-area backup protection tripping system, build a fault tree model according to the refusal to operate failure, and build a fault tree model according to the malfunction failure;

[0068] It can be understood that the fault tree model constructed in this embodiment includes: a fault tree model for the failure of the wide-area backup protection sampling system to refuse to operate and a fault tree model for the failure of the malfunction; a fault tree model for the failure of the wide-area backup protection tripping system to refuse to operate and a fault tree model for the failure of the malfunction.

[0069] It should be noted that if Figure 3 As shown, Figure 3 It is a substation IED and dual-star network topology based on the IEC 61850 standard, including merging units (MU), smart terminals (ST), protection devices (protective relay, PR), measurement and control devices (measure & control, M&C), LTU devices, switches (switch, SW), optical fibers (optical fiber, FI) and other components. The process layer network structure uses SMV network and GOOSE network to form independent networks, and two intervals share one SMV network or GOOSE network.

[0070] Fault tree model of the wide area backup protection sampling system refusal to operate failure:

[0071] For wide-area backup protection, the failure of the wide-area backup protection sampling system is divided into the following three situations: 1) LTU is unable to obtain the sampling value information of the merging unit, which is divided into the failure of the merging unit hardware failure and the failure of the communication network from the merging unit to the LTU. 2) LTU is unable to obtain the logical quantity information of the protection device, which is divided into the failure of the protection device and the failure of the communication network from the protection device to the LTU; wherein, the failure of the protection device includes: ① The failure of the protection device principle due to the inability to obtain the sampling value information of the merging unit is divided into the failure of the merging unit hardware failure and the failure of the communication network from the merging unit to the protection device; ② The failure of the protection device to refuse to operate. 3) LTU device failure to refuse to operate. Assuming that there are m substations in a certain wide-area backup protection area, a fault tree model is established based on the above failure of the wide-area backup protection sampling system to refuse to operate, such as Figure 4 As shown. In the figure, x means that when x substation sampling systems fail to operate, the wide-area backup protection system fails to operate. The substation communication network from the merging unit or protection device to the LTU adopts the minimum cut set method. This method uses topological graph processing technology to quickly obtain the minimum cut set between node pairs. Once the minimum cut set of the substation communication network from the merging unit or protection device to the LTU is determined, the fault tree model can be established, as shown in Figure 5 As shown. Similarly, the fault tree model of the communication network failure from the protection device to the LTU can be obtained. The reliability of the protection device has the same model as the reliability of the LTU and RDU, which will be analyzed in the reliability of the relay protection device later.

[0072] Fault tree model of malfunction failure of wide area backup protection sampling system:

[0073] The false operation failure of the wide-area backup protection sampling system meets the following conditions: 1) All protection information errors of one or more traditional protection devices lead to false operation failure of the wide-area backup protection; 2) The communication network within the station is normal; 3) The LTU device is normal. Among them, all protection information errors of traditional protection devices are divided into two situations: ① Failure of traditional protection devices, including false operation and refusal to operate failure; ② Merging unit failure, output sampling value error, resulting in all protection information errors of the protection device. According to the above false operation failure of the wide-area backup protection sampling system, a fault tree model is established, such as Figure 6 shown.

[0074] Fault tree model for the failure of wide-area backup protection tripping system:

[0075] The wide area backup protection tripping system malfunction failure meets the following conditions: 1) LTU device malfunction failure; 2) The station communication network is normal; 3) The intelligent terminal is normal. According to the above wide area backup protection tripping system malfunction failure situation, a fault tree model is established, such as Figure 7 shown.

[0076] Fault tree model for malfunction of wide-area backup protection tripping system:

[0077] The wide area backup protection tripping system malfunction failure meets the following conditions: 1) LTU device malfunction failure; 2) The station communication network is normal; 3) The intelligent terminal is normal. According to the above wide area backup protection tripping system malfunction failure situation, a fault tree model is established, such as Figure 8 shown.

[0078] Step 103: Establish a wide area power communication network reliability model of the wide area power communication network using a ring network and a linear network respectively, analyze the failure conditions of the wide area power communication network reliability model, and establish a fault tree model of the wide area power communication network according to the failure conditions;

[0079] It should be noted that the current wide-area power communication network mainly adopts SDH ring network, and some are linear networks. Fig. 9 Taking the 4-node 2-fiber unidirectional channel protection ring network as an example, a wide-area power communication network reliability model is established. The wide-area power communication network reliability model of the linear network is similar.

[0080] Wide area backup protection adopts network protection. Since network protection predetermines the main path and backup path, when the optical fiber link or network equipment on the main path fails, it can immediately switch to the backup path to restore information transmission. Taking the wide area communication network reliability between LTU2 of substation 2 and RDU of the main station as an example, its fault tree model is as follows: Figure 7-11 As shown. The 2-fiber unidirectional channel protection ring adopts the "double-send selective reception" method. The main path for LTU2 to send data to RDU is: MSTP2→FI'23→MSTP3→FI'34→MSTP4; the backup path is: MSTP2→FI 12→MSTP1→FI 14→MSTP4; therefore, the fault tree model of LTU2 to RDU wide area communication is as follows: Fig.10 (The left area in the figure). Similarly, the fault tree model of wide area communication from RDU to LTU2 is as follows: Fig.10 (right area in the figure).

[0081] Therefore, the wide area communication network system failure fault tree model is as follows: Fig.11 As shown. Fig.11 As shown in the left area of ​​the figure, since the wide-area backup protection has a certain fault tolerance, when the wide-area backup protection communication from x-1 substation LTUs to the main station RDU fails, the wide-area backup protection can still make correct decisions; when the wide-area backup protection communication from x substation LTUs to the main station RDU fails, the wide-area backup protection system fails. Fig.11 As shown in the right area of ​​the figure, the RDU sends wide-area backup protection action instructions to the LTUs of the substations on both sides of the faulty line. When the wide-area communication from the RDU to the LTU on either side fails, the wide-area backup protection system fails.

[0082] Step 104: construct a fault tree model of hardware module failure or malfunction failure according to the relationship between hardware module failure and failure of refusal or malfunction of the relay protection device; establish a Markov state space diagram of the software of the relay protection device, and construct a fault tree model of software failure or malfunction failure according to the Markov state space diagram;

[0083] It should be noted that digital relay protection devices such as traditional protection devices, LTU devices, and RDU devices are actually a special type of industrial control computer system, which can generally be divided into the following categories: Fig.12There are five functional modules shown in the figure, among which the power supply module (PSU) provides working power for each module; the central processing module (CPU) is the core of the protection device, completing the analysis, calculation and judgment functions of the protection; the communication module (CU) completes data communication with the outside world; various RAM, ROM and interfaces are classified as memory (MEM), which is used to complete data storage and caching; the human-machine interface module (MMI) includes keyboard, display, etc.

[0084] The following is an explanation of building a fault tree model for hardware module failures due to refusal or malfunction:

[0085] By analyzing the working process of the protection device, the corresponding relationship between the four functional modules of the protection and the functional failure of the relay protection system can be obtained, as shown in Table 1. Among them, "*" indicates that the functional module is related to the refusal / malfunction of the protection device.

[0086] Table 1 Module failure analysis table

[0087]

[0088] Therefore, the relationship between the failure of the hardware module of the protection device and the failure of the protection device to refuse to operate or to malfunction can be obtained as follows: Fig.13 In the analysis, it is assumed that these two failure modes each account for 50% of the module failure rate, so the device failure rate λ hj and the false failure rate λ hw They are:

[0089] λ hj =(λ CPU +λ CU +λ MEM ) / 2+λ PSU

[0090] λ hw =(λ CPU +λ MEM ) / 2

[0091] In the above formula, λ CPU , CU , MEM , PSU are the failure rates of each module respectively.

[0092] The following are instructions for constructing a fault tree model for software failure to operate or malfunction:

[0093] Hardware is the platform for realizing protection functions, and software algorithms are the core of realizing protection functions.

[0094] The main factors affecting the reliability of software design and operation that are not related to the protection principle (except the protection principle) include: 1) Inaccurate definition of demand analysis, such as incomplete requirements proposed by users, failure to digest changes in user requirements in a timely manner, and different understandings of requirements between software developers and users; 2) Software structure design errors, lack of consideration of special situations and error handling when designing the overall software structure; 3) Coding errors; 4) Irregular testing; 5) Errors introduced by program testing and editing environments or errors caused by the operating environment. Since the reliability of protection software is currently mainly affected by the hardware system environment, faults will be considered in the hardware system.

[0095] At the same time, this paper also selects the software failure model based on the following understandings: 1) Software failure of digital protection devices is mainly caused by design defects. During the software testing and operation process, software vulnerabilities and errors are constantly discovered and corrected and improved. Assuming that no new errors are introduced, it can be considered that the software failure rate decreases with the number of times its vulnerabilities are discovered; 2) There is no variation, that is, all copies of the same program are exactly the same, and reliability is independent of time; 3) If the parallel paths are the same, redundancy cannot improve reliability; 4) There are very few cases of protection misoperation and refusal to operate due to software vulnerabilities themselves, and zero failure data may be generated in a limited statistical period and statistical sample.

[0096] Therefore, this paper uses the Logarithmic exponential model to study the reliability of protection software. From this model, the failure rate of protection algorithm software can be obtained as:

[0097] λ(u)=λ0e -θu

[0098] Among them, λ0 is the initial failure rate, θ is the vulnerability reduction rate coefficient, and m is the cumulative number of vulnerabilities found during system operation. In order to correspond to the hardware failure and system failure analysis, the software failure mode is also divided into refusal failure and false operation failure.

[0099] The working process of the digital relay protection device is a Markov random process, so the Markov state space method will be used to solve its reliability index. The following assumptions are made when establishing the system state space diagram: 1) The software failure and hardware failure of the digital relay protection device are independent of each other; 2) The software is very mature, and its false operation failure rate is regarded as a constant; 3) The system has self-diagnosis capability, and the hardware refusal failure is divided into two types: refusal failure mode that cannot be self-detected and refusal failure mode that can be self-detected. The hardware false operation failure is also divided into self-detectable and non-self-detectable; 4) The hardware refusal failure that cannot be self-detected can be discovered and repaired during regular maintenance, and the software refusal failure is repaired during the software upgrade process. In the analysis, it is considered that the repair rate of these two refusal failures is u1, the software failure repair rate is u3, and the repair rate of other failure states is u2. The probability that the hardware failure can be self-detected is set as a constant, represented by c; 5) The failure of the protection device is caused by human error, and the failure rate λ p It is also divided into refusal failure λ pj and malfunction failure λ pw , and each accounts for the failure rate λ p The failure repair rate of the protection device caused by personnel is half of that of human personnel.

[0100] Personnel reliability analysis is an important part of safety analysis. It has great uncertainty, mainly due to the lack of operator error data. At present, most personnel reliability directly uses general data. After in-depth research, personnel reliability analysis methods have been developed to nearly 20 types. This paper uses the two-parameter Weibull analysis fitting method in the human cognitive reliability model technology for quantitative calculation, and its failure formula is:

[0101]

[0102] Where t is the response time; T0.5 is the median time taken by the executor to complete a task; η and β are the scale and shape factor of the cognitive behavior model, respectively, obtained by relevant mathematical methods, and the relationship satisfies:

[0103] According to the above assumptions, the Markov state space of the digital relay protection device can be obtained as follows: Fig.14 As shown. Among them, state 0 is the normal working state, state 1 is the non-self-checking hardware refusal state, state 2 is the self-checking hardware refusal state, state 3 is the non-self-checking hardware malfunction state, and state 4 is the self-checking hardware malfunction state. State 5 is the software malfunction state, and state 6 is the software refusal state. State 7 is the refusal state caused by human error, and state 8 is the malfunction state caused by human error. The combination state J is the refusal state, and W is the malfunction state.

[0104] Follow these steps to Fig.14The state space diagram establishes the Markov state equation and solves the steady-state probability of each state:

[0105] 1) According to Fig.14 Establish the state transfer matrix A, where Z = λ hw +λ hj +λ sj +λ sw +λ pj +λ pw .

[0106]

[0107] 2) Establish and solve the mathematical expectation of the fault working time Calculate the steady-state probability P = [p1 p2 p3 p4 p5 p6 p7 p8] of each state of the system.

[0108]

[0109] Solved Fig.14 The steady-state probabilities of each state in are as follows:

[0110] p1=(u1u2u3u4) / [u1u2u3u4+λ hj u2u3u4+λ hw u1u3u4+λ sj u2u3u4+λ sw u1u2u4+c(λ hj u1u3u4-λ hj u2u3u4)+λ pj u1u2u3+λ pw u1u2u3]

[0111] p2=[(1-c)λ hj / u1]p1 p3=(cλ hj / u2)p1

[0112] p4=[(1-c)λ hw / u2]p1 p5=(cλ hw / u2)p1

[0113] p6=(λ sw / u3)p1 p7=(λ sj / u1)p1

[0114] p8=(λ m / u4)p1 p9=(λ m / u4)p1

[0115] Therefore, the availability of the protection device is A = p1. The failure rate of the protection device's refusal to operate is the rate of transition from state 0 to combination state J, and the failure rate of the malfunction is the rate of transition from state 0 to combination state W, which are respectively expressed as:

[0116] λ w =(1-c)λ hw +λ sw +λ pw

[0117] λ j =(1-c)λ hj +λ sj +λ pj

[0118] Therefore, a fault tree model of software failure due to refusal to operate or malfunction is constructed based on the Markov state space diagram.

[0119] Step 105: construct an overall reliability fault tree model of the wide-area backup protection system according to the fault tree model of the wide-area backup protection sampling system, the fault tree model of the wide-area power communication network, the fault tree model of the relay protection device, and the fault tree model of the wide-area backup protection tripping system;

[0120] It should be noted that according to the analysis and Figure 2 , the overall reliability fault tree model of the wide-area backup protection system can be obtained, as Fig.15a , Fig.15b , Fig.15c shown.

[0121] like Fig.15a As shown, the wide-area backup protection system false operation failure takes into account three aspects: 1) The RDU of the master station has a false operation failure; at this time, when the wide-area backup protection sampling system, tripping system and wide-area communication network are all normal, the RDU protection device false operation leads to the wide-area backup protection system false operation failure. 2) The LTU of the substation where the faulty line is located has a false operation failure; at this time, when the wide-area backup protection sampling system, RDU protection device and wide-area communication network are all normal, the tripping system false operation failure leads to the wide-area backup protection system false operation failure. 3) All protection information errors of the traditional protection devices of one or more substations lead to the wide-area backup protection false operation failure; at this time, when the wide-area backup protection tripping system, RDU protection device and wide-area communication network are all normal, the wide-area backup protection sampling system false operation failure leads to the wide-area backup protection system false operation failure.

[0122] like Fig.15bAs shown in the figure, the failure of the wide-area backup protection system to operate is considered in five aspects: 1) the failure of the wide-area backup protection sampling system to operate; 2) the failure of the wide-area communication system from the substation to the RDU; 3) the failure of the wide-area communication from the RDU to the substations on both sides of the fault line; 4) the failure of the wide-area backup protection tripping system to operate;

[0123] 5) RDU protection device fails to operate. If any of the above five aspects fails, the wide area backup protection system fails to operate.

[0124] The dynamic process of system-level failure repair is reflected in the model solution based on the fault tree structure function and Monte Carlo simulation in step 106.

[0125] Step 106: Perform reliability simulation analysis on the overall reliability fault tree model by using a sequential Monte Carlo simulation method of a fault tree structure function to obtain a reliability evaluation result of the wide area backup protection system.

[0126] It should be noted that Monte Carlo simulation technology is based on the law of large numbers, reflects the reliability behavior of the system by simulating sampling, obtains the reliability parameters of the system by calculating the statistical characteristics of the sampled samples, is insensitive to the dimension of the problem, has strong adaptability and problem-solving ability, and compared with the Markov method, Monte Carlo simulation analysis has no restrictions on the failure distribution of the bottom event of the fault tree. Based on this, this paper adopts the sequential Monte Carlo simulation method based on the fault tree structure function to perform system reliability analysis.

[0127] The structure function of the fault tree expresses the static logical relationship of the system and is a single-valued function. To apply the structure function in dynamic simulation, we must first find a method that can staticize the dynamic simulation process. According to this method, the simulation time is divided into many small time periods, and in each small time period, it can be assumed that the status of all bottom events does not change. Then, simulation analysis is performed on these time periods separately, which can effectively reduce the complexity of solving the problem.

[0128] The sequential simulation algorithm based on the fault tree can obtain the timing information of the system's operating state and accurately simulate the duration of the system in each state and the frequency of transitions between states. Fig.16 shown.

[0129] The simulation state of the component is: failure-repair-failure-repair... According to the sampling principle shown in the above formula, the operating state of each component within a certain simulation time can be obtained. Then, the operating state sequence of the system can be obtained by combining the information of each component. 1 means normal and 0 means shutdown. Fig.16In the figure, "00", "01", "10", and "11" represent the combined state of the system composed of two components. The short-term simulation of the system has a greater degree of randomness, but the reliability index obtained by simulating the long-term operation process of the system is close to the actual situation of the system. The steps of sequential Monte Carlo simulation based on the fault tree structure function are as follows:

[0130] 1) The maximum working time specified by the system is Tmax, which is divided into M time intervals, each of which is Δt, then Δt=T max / M, where t r is the time of the end point of the rth interval, that is:

[0131] 2) The fault tree of the system has n bottom events, which are the failure events of n basic components in the system S. For the jth basic component, its failure distribution function is a known exponential function distribution.

[0132] 3) Introducing the time variable t, the structural function Φ[X(t)] can be obtained from the fault tree, where:

[0133] X(t)=[x1(t),x2(t),...,x n (t)]

[0134] is the system state variable, x i (t) represents the state of the i-th unit, which is defined as follows:

[0135]

[0136] It can be seen that the system has n bottom events, each of which has two states: 0 and 1, so the system state variables are 2 n , use φ(t) to represent the state of the top event at time t, then:

[0137]

[0138] And we have: φ(t)=φ[x(t)].

[0139] 4) The failure time tij of the jth component in the i-th simulation is:

[0140]

[0141] In the sequential Monte Carlo simulation, assuming that the fault-free working time and maintenance time of the component are t and t', and both are random variables subject to exponential distribution, the values ​​of t and t' are sampled according to the following formula:

[0142]

[0143] Among them, ε1, ε2 are random numbers uniformly distributed on [0,1].

[0144] 5) During the simulation, sort tij in ascending order of sampling time:

[0145] 0=t0<t 1j <t 2j <...<t mj =T max

[0146] 6) Let the simulation time t=0, record the time and number of normal operation of the system as ts=0, As=0 respectively, record the time and number of failure of the system as tk=0, Nsr=0 respectively, and set each bottom event to be normal.

[0147] 7) Start the simulation according to the formula in steps 4)-6) above, setting s=1, t∈(t r-1 , t r ), determine the state of each bottom event in this interval. Determine the system state according to the system structure function Φ[X(t)]. If Φ[X(t)]=1, the system fails and records Nsr=1; if Φ[X(t)]=0, the system is normal and records As=1.

[0148] 8) t=t+t r -t r-1 If t>Tmax, the simulation ends. Otherwise, go to step 7).

[0149] 9) Obtaining reliability index: cumulatively calculate the number of values ​​in the system failure time series that fall into each time interval. For example, if tsj falls into the rth time interval, then let ΔN sr =ΔN sr +1, the statistical sequence of system failure times in each time interval is as follows: ΔN S =(ΔN S1 , ..., ΔN Sr ,...,N SM ).

[0150] When t≤t r The system failure rate at : Where N is t≤t r After multiple simulations, the final statistical analysis is performed.

[0151] The above is a wide-area backup protection system reliability assessment method provided in an embodiment of the present application, and the following is a wide-area backup protection system reliability assessment system provided in an embodiment of the present application.

[0152] See also Fig.17, a wide area backup protection system reliability assessment system provided in an embodiment of the present application includes:

[0153] A division unit 201 is used to divide the wide-area backup protection system into a wide-area backup protection sampling system, a wide-area power communication network, a relay protection device, and a wide-area backup protection tripping system;

[0154] The first construction unit 202 is used to analyze the refusal to operate failure and malfunction failure of the wide-area backup protection sampling system and the wide-area backup protection tripping system based on the substation IED and the double-star network topology, and to construct a fault tree model according to the refusal to operate failure and to construct a fault tree model according to the malfunction failure;

[0155] The second construction unit 203 is used to establish a wide area power communication network reliability model of the wide area power communication network with a ring network and a linear network respectively, analyze the failure situation of the wide area power communication network reliability model, and establish a fault tree model of the wide area power communication network according to the failure situation;

[0156] The third construction unit 204 is used to construct a fault tree model of failure of refusal or malfunction of the hardware module according to the relationship between failure of the hardware module of the relay protection device and failure of refusal or malfunction; establish a Markov state space diagram of the software of the relay protection device, and construct a fault tree model of failure of refusal or malfunction of the software according to the Markov state space diagram;

[0157] The fourth construction unit 205 is used to construct an overall reliability fault tree model of the wide-area backup protection system according to the fault tree model of the wide-area backup protection sampling system, the fault tree model of the wide-area power communication network, the fault tree model of the relay protection device, and the fault tree model of the wide-area backup protection tripping system;

[0158] The simulation unit 206 is used to perform reliability simulation analysis on the overall reliability fault tree model by using a sequential Monte Carlo simulation method of a fault tree structure function to obtain a reliability evaluation result of the wide area backup protection system.

[0159] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the systems and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0160] The terms "first", "second", "third", "fourth", etc. in the specification of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein, for example. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0161] It should be understood that in the present application, "at least one (item)" means one or more, and "plurality" means two or more. "And / or" is used to describe the association relationship of associated objects, indicating that three relationships may exist. For example, "A and / or B" can mean: only A exists, only B exists, and A and B exist at the same time, where A and B can be singular or plural. The character " / " generally indicates that the objects associated before and after are in an "or" relationship. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items. For example, at least one of a, b or c can mean: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, c can be single or multiple.

[0162] In the several embodiments provided in the present application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or units, which can be electrical, mechanical or other forms.

[0163] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0164] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0165] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present application is essentially or the part that contributes to the prior art or all or part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including a number of instructions to enable a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present application. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (full name in English: Read-Only Memory, English abbreviation: ROM), random access memory (full name in English: Random Access Memory, English abbreviation: RAM), disk or optical disk and other media that can store program codes.

[0166] As described above, the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A reliability assessment method for a wide area backup protection system, characterized in that: include: Divide the wide-area backup protection system into a wide-area backup protection sampling system, a wide-area power communication network, a relay protection device, and a wide-area backup protection tripping system; Based on the substation IED and the double-star network topology, the refusal to operate failure and malfunction failure of the wide-area backup protection sampling system and the wide-area backup protection tripping system are analyzed, and a fault tree model is constructed according to the refusal to operate failure and a fault tree model is constructed according to the malfunction failure; Establishing a wide area power communication network reliability model of the wide area power communication network with a ring network and a linear network respectively, analyzing the failure conditions of the wide area power communication network reliability model, and establishing a fault tree model of the wide area power communication network according to the failure conditions; According to the relationship between the failure of the hardware module of the relay protection device and the failure of refusal or malfunction, a fault tree model of the failure of refusal or malfunction of the hardware module is constructed; a Markov state space diagram of the software of the relay protection device is established, and a fault tree model of the failure of refusal or malfunction of the software is constructed according to the Markov state space diagram; Constructing an overall reliability fault tree model of the wide-area backup protection system according to the fault tree model of the wide-area backup protection sampling system, the fault tree model of the wide-area power communication network, the fault tree model of the relay protection device, and the fault tree model of the wide-area backup protection tripping system; The reliability simulation analysis of the overall reliability fault tree model is carried out by using a sequential Monte Carlo simulation method of a fault tree structure function to obtain a reliability evaluation result of the wide area backup protection system.

2. The wide area backup protection system reliability assessment method according to claim 1, characterized in that: According to the relationship between the failure of the hardware module of the relay protection device and the failure of refusal or malfunction, a fault tree model of the failure of refusal or malfunction of the hardware module is constructed; a Markov state space diagram of the software of the relay protection device is established, and a fault tree model of the failure of refusal or malfunction of the software is constructed according to the Markov state space diagram, which specifically includes: Analyze the relationship between the failure of the hardware module of the relay protection device and the failure of refusal to operate or malfunction to obtain the failure rate of refusal to operate and the failure rate of malfunction to operate of the relay protection device, and establish a fault tree model of the failure of refusal to operate or malfunction to operate of the hardware module of the relay protection device; The software failure modes of the relay protection device are divided into failure due to refusal to operate and failure due to malfunction, a Markov state space diagram of the relay protection device is established, a Markov state equation is established based on the Markov state space diagram, the steady-state probability of each state is solved based on the Markov state equation, the failure rate due to refusal to operate and the failure rate due to malfunction are obtained, and a fault tree model of failure due to refusal to operate or malfunction of the software of the relay protection device is established.

3. The wide area backup protection system reliability assessment method according to claim 2, characterized in that: The Markov state space diagram specifically includes: Normal working state, hardware refusal state that cannot be self-checked, hardware refusal state that can be self-checked, hardware malfunction state that cannot be self-checked, hardware malfunction state that can be self-checked, software malfunction state, software refusal state, refusal state due to human error, malfunction state due to human error.

4. The wide area backup protection system reliability assessment method according to claim 1, characterized in that: The refusal to operate failure conditions of the wide-area backup protection sampling system specifically include: The LTU cannot obtain the merging unit sampling value information, which is divided into the merging unit hardware failure and the communication network failure from the merging unit to the LTU; LTU cannot obtain the logical quantity information of the protection device, which is divided into protection device failure and protection device to LTU communication network failure; protection device failure includes: failure to obtain the sampling value information of the merging unit, resulting in protection device principle failure, which is divided into merging unit hardware failure and merging unit to protection device communication network failure; protection device refusal to operate failure; The LTU device refuses to operate and fails.

5. The wide area backup protection system reliability assessment method according to claim 1, characterized in that: The malfunction failure of the wide-area backup protection tripping system specifically includes: All protection information errors of one or more traditional protection devices lead to false operation and failure of wide-area backup protection; The communication network within the station is normal; The LTU device is normal, among which all protection information errors of the traditional protection device are divided into two situations: failure of the traditional protection device, including false operation and refusal to operate failure; failure of the merging unit, the output sampling value is wrong, resulting in all protection information errors of the protection device.

6. The wide area backup protection system reliability assessment method according to claim 1, characterized in that: The refusal to operate failure situation of the wide-area backup protection tripping system specifically includes: The LTU device fails to operate; the communication network from the LTU to the intelligent terminal fails; the intelligent terminal fails.

7. The wide area backup protection system reliability assessment method according to claim 1, characterized in that: The refusal to operate failure conditions of the wide area backup protection sampling system specifically include: LTU device malfunction failure; the in-station communication network is normal; the intelligent terminal is normal.

8. A wide area backup protection system reliability assessment system, characterized in that: include: A division unit, used for dividing the wide-area backup protection system into a wide-area backup protection sampling system, a wide-area power communication network, a relay protection device, and a wide-area backup protection tripping system; The first construction unit is used to analyze the refusal to operate failure situation and the malfunction failure situation of the wide-area backup protection sampling system and the wide-area backup protection tripping system based on the substation IED and the double-star network topology structure, and to construct a fault tree model according to the refusal to operate failure situation and to construct a fault tree model according to the malfunction failure situation; A second construction unit is used to establish a wide area power communication network reliability model of the wide area power communication network with a ring network and a linear network respectively, analyze the failure situation of the wide area power communication network reliability model, and establish a fault tree model of the wide area power communication network according to the failure situation; The third construction unit is used to construct a fault tree model of failure of refusal or malfunction of the hardware module according to the relationship between failure of the hardware module of the relay protection device and failure of refusal or malfunction; establish a Markov state space diagram of the software of the relay protection device, and construct a fault tree model of failure of refusal or malfunction of the software according to the Markov state space diagram; A fourth construction unit is used to construct an overall reliability fault tree model of the wide-area backup protection system according to the fault tree model of the wide-area backup protection sampling system, the fault tree model of the wide-area power communication network, the fault tree model of the relay protection device, and the fault tree model of the wide-area backup protection tripping system; The simulation unit is used to perform reliability simulation analysis on the overall reliability fault tree model by using a sequential Monte Carlo simulation method of a fault tree structure function to obtain a reliability evaluation result of the wide area backup protection system.

9. The wide area backup protection system reliability assessment system according to claim 8, characterized in that: The third building block is specifically used for: Analyze the relationship between the failure of the hardware module of the relay protection device and the failure of refusal or malfunction, obtain the failure rate of refusal to operate and the failure rate of malfunction of the relay protection device, and establish a fault tree model of the failure of refusal to operate or malfunction of the hardware module of the relay protection device; The software failure modes of the relay protection device are divided into failure due to refusal to operate and failure due to malfunction, a Markov state space diagram of the relay protection device is established, a Markov state equation is established based on the Markov state space diagram, the steady-state probability of each state is solved based on the Markov state equation, the failure rate due to refusal to operate and the failure rate due to malfunction are obtained, and a fault tree model of failure due to refusal to operate or malfunction of the software of the relay protection device is established.

10. The wide area backup protection system reliability assessment system according to claim 9, characterized in that: The Markov state space diagram specifically includes: Normal working state, hardware refusal state that cannot be self-checked, hardware refusal state that can be self-checked, hardware malfunction state that cannot be self-checked, hardware malfunction state that can be self-checked, software malfunction state, software refusal state, refusal state due to human error, malfunction state due to human error.

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