Patent Publication Number: US-2022237067-A1

Title: Relay protection system risk assessment and fault positioning method and apparatus, and device and medium

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to China patent application No. 201910313700.9, filed with China National Intellectual Property Administration on Apr. 18, 2019, the disclosure of which is hereby incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     The present disclosure relates to the field of safety of power systems, and relates to a risk evaluation and fault positioning method and apparatus for a relay protection system, and a device and a medium, for example. 
     BACKGROUND 
     Relay protection is the first line of defense for safe operation of a power grid. Proposing a risk assessment and fault positioning method for a relay protection system is of great significance for timely discovering potential safety hazard of the relay protection system and improving the safe operation of the power grid. In related technologies, researches have been carried out on evaluation of relay protection statuses, and certain results have been achieved in extraction of evaluation indicators, indicator weights, evaluation methods, and other aspects, and an enterprise standard “Guidelines for the Evaluation of Relay Protection Statuses” has been made, thus realizing comprehensive evaluation for the relay protection system from different perspectives and obtaining abnormality information of the relay protection system at the same time, so that valuable information can be provided for prewarning of a relay protection risk. In order to know the degree of risk of the relay protection system and determine a sequence of investigation of different potential hazard under abnormality conditions of the relay protection system, it is in an urgent need for providing a risk assessment and fault positioning method for a relay protection system. 
     SUMMARY 
     The present disclosure provides a risk evaluation and fault positioning method and apparatus for a relay protection system, and a device and a medium, which meet the requirements for risk evaluation and fault positioning for the relay protection system. 
     The present disclosure provides a risk evaluation and fault positioning method for a relay protection system, which includes: dividing a plurality of fault events of the relay protection system into different hierarchy events, and constructing a fault tree of the relay protection system according to the different hierarchy events; transforming the different hierarchy events in the fault tree into different nodes of an initial Bayesian network, the different nodes including a root node, a leaf node and an intermediate node; endowing each node of the initial Bayesian network with a plurality of statuses; constructing a target Bayesian network according to a pre-built Bayesian network conditional probability distribution table and the plurality of statuses of each node; and determining, according to a prior probability that a root node in the target Bayesian network is in different statuses, a probability that an intermediate node in the target Bayesian network is in different statuses and a probability that a leaf node in the target Bayesian network is in different statuses to complete risk evaluation for the relay protection system; and determining, according to a status of the leaf node in the target Bayesian network, a posterior probability of a status of the root node in the target Bayesian network by using the target Bayesian network to complete fault positioning for the relay protection system. 
     The present disclosure further provides a risk evaluation and fault positioning apparatus for a relay protection system, which includes: a fault tree construction unit, configured to divide a plurality of fault events of the relay protection system into different hierarchy events, and construct a fault tree of the relay protection system according to the different hierarchy events; a Bayesian network construction unit, configured to transform the different hierarchy events in the fault tree into different nodes of an initial Bayesian network, the different nodes including a root node, a leaf node and an intermediate node; endow each node of the initial Bayesian network with a plurality of statuses; construct a target Bayesian network according to a pre-built Bayesian network conditional probability distribution table and the plurality of statuses of each node; and an evaluation and positioning unit, configured to determine, according to a prior probability that a root node in the target Bayesian network is in different statuses, a probability that an intermediate node in the target Bayesian network is in different statuses and a probability that a leaf node in the target Bayesian network is in different statuses to complete risk evaluation for the relay protection system; and determine, according to a status of the leaf node in the target Bayesian network, a posterior probability of a status of the root node in the target Bayesian network by using the target Bayesian network to complete fault positioning for the relay protection system. 
     The present disclosure further provides a device including a processor and a memory. The memory stores a computer program which, when executed by the processor, implements the method provided in any embodiment of the present disclosure. 
     The present disclosure further provides a computer storage medium storing a computer program. The computer program, when executed by a processor, implements the method provided in any embodiment of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a flow chart of a risk evaluation and fault positioning method for a relay protection system provided by an embodiment of the present disclosure. 
         FIG. 2  is an example of Bayesian network probability calculation provided by an embodiment of the present disclosure. 
         FIG. 3  is an abnormality warning fault tree of a relay protection system provided by an embodiment of the present disclosure. 
         FIG. 4  is a schematic diagram of transforming a fault tree into a Bayesian network provided by an embodiment of the present disclosure. 
         FIG. 5  is a schematic diagram of a risk evaluation and fault positioning apparatus for a relay protection system provided by an embodiment of the present disclosure. 
         FIG. 6  is a schematic structural diagram of a device provided by an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The technical solutions provided by the present disclosure are described in the following descriptions to facilitate understanding the present disclosure. 
     Referring to  FIG. 1 ,  FIG. 1  is a flow chart of a risk evaluation and fault positioning method for a relay protection system provided by an embodiment of the present disclosure, the method provided by the embodiment of the present disclosure is described below in combination with  FIG. 1 . 
     At S 1010 , a plurality of fault events of the relay protection system are divided into different hierarchy events, and a fault tree of the relay protection system is constructed according to the different hierarchy events. 
     Starting from a fault of the relay protection system, a fault cause is advanced layer by layer, and the plurality of fault events of the relay protection system are divided into a top event, a bottom event and an intermediate event. In an embodiment, an abnormality warning event occurring in the relay protection system is set to be the top event; an abnormality warning event for decomposing a fault cause to an apparatus included in the relay protection system is set to be the intermediate event. The apparatus is a relay protection apparatus, an intelligent terminal, a combination unit and the like, for example; and an abnormality warning event for decomposing a fault cause of each apparatus into each apparatus is set to be the bottom event. Thus, the fault tree of the relay protection system is constructed according to the different hierarchy events. The fault tree includes three types of hierarchy events: a top event, a bottom event, and an intermediate event. 
     At S 1020 , the different hierarchy events in the fault tree are transformed into different nodes of an initial Bayesian network, the different nodes include a root node, a leaf node and an intermediate node; each node of the initial Bayesian network is endowed with a plurality of statuses; and a target Bayesian network is constructed according to a pre-built Bayesian network conditional probability distribution table and the plurality of statuses of each node of the Bayesian network. 
     The top event, the bottom event and the intermediate event of the fault tree are respectively transformed into the leaf node, the root node and the intermediate node of the initial Bayesian network. Each node of the initial Bayesian network is then endowed with the plurality of statuses. In an embodiment, there may be three statuses: severe abnormality, abnormality and normality. 
     At this step, distribution characteristics and parameters of relay protection abnormality warning are determined by counting the same abnormality warnings occurring in the apparatuses of the same model in the same manufacturer in history, and then the probability of occurrence of the abnormality warning is then calculated according to the operation time of an apparatus to be studied and is used as the prior probability of the root node of the initial Bayesian network. The abnormality warning may not occur in a life cycle of a sample, and test data has the characteristics of random truncation. Assuming that the number of samples is n, there are a total of r samples among the n samples that have abnormality warning. For these r samples, the abnormality warning occurrence time relative to the apparatus commissioning time is t i , i.e., a difference between the abnormality warning occurrence time and the apparatus commissioning time, i=1, 2, . . . , r; a total of k samples among the n samples have no abnormality warning, where c j  is the truncation time of the samples that have no abnormality warning, i.e., a difference between the sample withdrawal time and the commissioning time, j=1, 2, . . . , k. Since an exponential distribution has a high degree of fitting for the occurrence of the abnormality warning, a frequency of occurrence of the abnormality warning, i.e., the maximum likelihood estimate of a failure rate λ, is: 
     
       
         
           
             
               
                 
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                   = 
                   
                     
                       
                         
                           
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     For abnormality warning that does not occur in history in apparatuses of the same model in the same manufacturer, the probability that the root node is in a normal state is 1, and the root node is removed from the initial Bayesian network to construct the target Bayesian network. 
     The value of a failure probability is: 
         F ( t )=1− e   −λ(t−tm)   (2);
 
     where t is the present time, and t m  is the maximum value of the apparatus commissioning time, the last full inspection time, and the last occurrence time of the same abnormality warning event. 
     The fault tree is similar to the structure of the Bayesian network. The top event, the bottom event, and the intermediate event of the fault tree correspond to the leaf node, the root node and the intermediate node of the Bayesian network. A logic gate of the fault tree may be transformed into a directed edge. The logic is illustrated by the conditional probability distribution table. The events in the fault tree only have two states: occurrence and non-occurrence. In order to reflect the difference of severities of the abnormality warning of the apparatus, a multi-status model is built for the nodes in the Bayesian network, including three statuses “severe abnormality”, “abnormal”, and “normal”. In fact, the root node still has only two statuses, i.e., “abnormality occurred” and “abnormality not occurred”. When three statuses are used for modeling, if “severe abnormality” or “abnormal” are consistent with the severity of the abnormality warning of the root node, the probability is taken as the prior probability; and if no, the probability is 0, and the probability of “normal” is a probability that no abnormality warning occurs. 
     Logic of the Bayesian network conditional probability distribution table satisfies formulas (3)-(5). 
     
       
         
           
             
               
                 
                   
                       
                   
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     where P(N=N i ) represents a probability that a node N is in a status i; P(M=M i ) represents a probability that a father node M of the node N is in the status i, i=1, 2, 3; status 1 means normal, status 2 means abnormal, and status 3 means severely abnormal. A local Bayesian network used for analyzing the failure probability of a line relay protection apparatus is taken as an example. As illustrated in  FIG. 2 , assuming that A corresponds to whether line protection TA disconnection (severe abnormality) occurs, and B corresponds to whether line protection channel warning (ordinarily abnormal) occurs, and C corresponds to the status of the line relay protection apparatus, if the prior probabilities of the line protection TA disconnection and the line protection channel warning is 0.1 and 0.2, respectively, it may be obtained that the probabilities that multiple nodes of the Bayesian network are in different statuses are illustrated in  FIG. 2 . 
     At S 1030 , it is determined, according to a prior probability that a root node in the target Bayesian network is in different statuses, a probability that an intermediate node in the target Bayesian network is in different statuses and a probability that a leaf node in the target Bayesian network is in different statuses to complete risk evaluation for the relay protection system; and it is determined, according to a status of the leaf node in the target Bayesian network, a posterior probability of a status of the root node in the target Bayesian network by using the target Bayesian network to complete fault positioning for the relay protection system. 
     If the abnormality severity of the relay protection system is higher, the risk of the relay protection system is larger, the probability of abnormality warning is larger, and the risk is also larger. 
     In an embodiment, the risk R of the relay protection system may be expressed by a product of the possibility P of occurrence of abnormality warning and the severity S; where P is reflected by the probability of abnormality warning, and S is reflected by the three statuses: “severe abnormality”, “abnormality” and “normality”. 
     In an embodiment, a probability that a node X of the Bayesian network is at a status i is: 
     
       
         
           
             
               
                 
                   
                       
                   
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     where P(X=X i ) is a probability that a node X is in a status i; y j  is a farther node of the node X, j=1, 2, . . . , m; P(y j J=y j   k     j   ) is a probability that a node y i  is in a status k j ; P(X=X i |y l =y l   k     j   , . . . , y m =y m   k     m   ) is determined according to the Bayesian network conditional probability distribution table, as illustrated in formulas (3)-(5); i=1, 2, 3, k j =1, 2, 3; state 1 means normal, status 2 means abnormal, and status 3 means severely abnormal; and k 1 , . . . , k m  is a status permutation and combination of y 1 , . . . , y m . The root node is used as the farther node, and the probability that nodes taking the root node as the father node are in different statuses is determined by using formula (6) according to the prior probability of the root node. The following steps are repeatedly executed until determining the probability that the leaf node is in different the statuses: the newly obtained node with the probability of being in different statuses is used as the father node, and the probability that the nodes taking this node as the father node are in different statuses by using formula (6). 
     In an embodiment, there are two farther nodes of the node X, i.e., y 1  and y 2 , and the probability that X is in an abnormal state is determined as: 
     
       
         
           
             
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     In the above formula, k 1  and k 2  are the status permutation and combination of y 1  and y 2 . Since values of k 1  and k 2  are in a range of {1, 2, 3}, there are 9 status permutations and combinations for k 1  and k 2 . In the above formula, it is necessary to calculate a calculation result of P(X=X 2 |y 1 =y 1   k     1   , y 2 =y 2   k     2   )P(y 1 =y 1   k     1   )P(y 2 =y 2   k     2   ) in each status permutation and combination, and the 9 calculation results obtained are added to obtain the probability that X is in the abnormal status. 
     Under a condition that a status i (i=1, 2, 3) of a leaf node T is known, the Bayesian formula is used to calculate a probability that a root node Z j  (j=1, . . . , n) is in a status s j : 
     
       
         
           
             
               
                 
                   
                     
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                       ⁡ 
                       
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                   ; 
                 
               
               
                 
                   ( 
                   7 
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     where P(Z j =Z j   s     j   |T=T i ) is a probability that the root node Z j  is in the status s j  and the status of the leaf node T is T i , i=1, 2, 3, s j =1, 2, 3; state 1 means normal, status 2 means abnormal, and status 3 means severely abnormal. The above formula is used to calculate the posterior probability of the root node Z 1  to realize the fault positioning for the relay protection system. 
     According to the embodiments of the present disclosure, the fault tree of the relay protection system is constructed and is then transformed into the Bayesian network; the prior probability of a relay protection abnormality warning root node is determined through the Bayesian network, the probability that the intermediate node is in different statuses is obtained according to the prior probability of the root node, and the posterior probability of the status of the root node is determined according to the status of the leaf node, thus realizing the risk evaluation and fault positioning for the relay protection system. 
     The risk evaluation and fault positioning method for the relay protection system provided by the present disclosure is described below through examples. The description is as follows. 
     At  10 , a fault tree of the relay protection system is constructed. 
     A single set of a 220 kV-line protection system is taken as a study object. The system includes two combination unit apparatuses, one line protection apparatus, one intelligent terminal apparatus, and one bus protection apparatus. The construction of the abnormality warning fault tree of the relay protection system is as illustrated in  FIG. 3 . Meanings of the symbols in the fault tree are as illustrated in Table 1. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Symbol 
                 Event 
               
               
                   
                   
               
             
            
               
                   
                 T 
                 Abnormality 
               
               
                   
                   
                 warning of the relay 
               
               
                   
                   
                 protection system 
               
               
                   
                 I1 
                 Abnormality 
               
               
                   
                   
                 warning of the bus 
               
               
                   
                   
                 combination unit 
               
               
                   
                 I2 
                 Abnormality 
               
               
                   
                   
                 warning of the line 
               
               
                   
                   
                 combination unit 
               
               
                   
                 I3 
                 Abnormality 
               
               
                   
                   
                 warning of line 
               
               
                   
                   
                 protection 
               
               
                   
                 I4 
                 Abnormality 
               
               
                   
                   
                 warning of the 
               
               
                   
                   
                 intelligent terminal 
               
               
                   
                 I5 
                 Abnormality 
               
               
                   
                   
                 warning of bus 
               
               
                   
                   
                 protection 
               
               
                   
                 X1 X6 
                 Abnormality of the 
               
               
                   
                   
                 combination unit 
               
               
                   
                   
                 apparatus 
               
               
                   
                 X2 X7 
                 Shutting of the 
               
               
                   
                   
                 combination unit 
               
               
                   
                   
                 apparatus 
               
               
                   
                 X3 X8 
                 Abnormality 
               
               
                   
                   
                 warning of 
               
               
                   
                   
                 combination unit 
               
               
                   
                   
                 synchronization 
               
               
                   
                 X4, X9 
                 Maintenance status 
               
               
                   
                   
                 of the combination 
               
               
                   
                   
                 unit 
               
               
                   
                 X5 
                 GOOSE 
               
               
                   
                 X10 
                 disconnection of 
               
               
                   
                   
                 combination unit 
               
               
                   
                   
                 received intelligent 
               
               
                   
                   
                 terminal 
               
               
                   
                 X11 
                 Shutting of the line 
               
               
                   
                   
                 protection apparatus 
               
               
                   
                 X12 
                 Power loss warning 
               
               
                   
                   
                 of the line 
               
               
                   
                   
                 protection apparatus 
               
               
                   
                 X13 
                 SV sampling 
               
               
                   
                   
                 abnormality of line 
               
               
                   
                   
                 protection 
               
               
                   
                 X14 
                 SV interruption of 
               
               
                   
                   
                 the line protection 
               
               
                   
                   
                 received 
               
               
                   
                   
                 combination unit 
               
               
                   
                 X15 
                 Line protection TA 
               
               
                   
                   
                 disconnection 
               
               
                   
                 X16 
                 Line protection TV 
               
               
                   
                   
                 disconnection 
               
               
                   
                 X17 
                 GOOSE 
               
               
                   
                   
                 interruption of line 
               
               
                   
                   
                 protection received 
               
               
                   
                   
                 intelligent terminal 
               
               
                   
                 X18 
                 GOOSE 
               
               
                   
                   
                 interruption of line 
               
               
                   
                   
                 protection received 
               
               
                   
                   
                 bus differential 
               
               
                   
                   
                 protection 
               
               
                   
                 X19 
                 Line protection 
               
               
                   
                   
                 channel warning 
               
               
                   
                 X20 
                 Turn-on and turn- 
               
               
                   
                   
                 off abnormality of 
               
               
                   
                   
                 line protection 
               
               
                   
                 X21 
                 Warning of 
               
               
                   
                 X25 
                 maintenance 
               
               
                   
                 X38 
                 inconsistency 
               
               
                   
                 X22 
                 Shutting of the 
               
               
                   
                   
                 intelligent terminal 
               
               
                   
                 X23 
                 GOOSE 
               
               
                   
                   
                 disconnection of 
               
               
                   
                   
                 intelligent terminal 
               
               
                   
                   
                 xx 
               
               
                   
                 X24 
                 Clock 
               
               
                   
                   
                 synchronization 
               
               
                   
                   
                 abnormality of the 
               
               
                   
                   
                 intelligent terminal 
               
               
                   
                 X26 
                 Disconnection of 
               
               
                   
                   
                 the intelligent 
               
               
                   
                   
                 terminal control 
               
               
                   
                   
                 loop 
               
               
                   
                 X27 
                 Pressure 
               
               
                   
                   
                 abnormality of the 
               
               
                   
                   
                 circuit breaker 
               
               
                   
                 X28 
                 Shutting of the bus 
               
               
                   
                   
                 protection 
               
               
                   
                   
                 apparatus 
               
               
                   
                 X29 
                 Power loss warning of 
               
               
                   
                   
                 the bus protection 
               
               
                   
                   
                 apparatus 
               
               
                   
                 X30 
                 SV sampling 
               
               
                   
                   
                 abnormality of bus 
               
               
                   
                   
                 protection xx branch 
               
               
                   
                 X31 
                 SV interruption of bus 
               
               
                   
                   
                 protection xx branch 
               
               
                   
                 X32 
                 TA interruption of bus 
               
               
                   
                   
                 protection xx branch 
               
               
                   
                 X33 
                 TA disconnection of xx 
               
               
                   
                   
                 buscouple/segmentation 
               
               
                   
                   
                 of bus protection 
               
               
                   
                 X34 
                 TV disconnection of xx 
               
               
                   
                   
                 segment of bus of bus 
               
               
                   
                   
                 protection 
               
               
                   
                 X35 
                 GOOSE interruption of 
               
               
                   
                   
                 bus protection received 
               
               
                   
                   
                 intelligent terminal 
               
               
                   
                 X36 
                 GOOSE interruption of 
               
               
                   
                   
                 bus protection received 
               
               
                   
                   
                 line protection 
               
               
                   
                 X37 
                 Turn-on and turn-off 
               
               
                   
                   
                 abnormality of bus 
               
               
                   
                   
                 protection 
               
               
                   
                 X39 
                 220 kV bus 
               
               
                   
                   
                 interconnection 
               
               
                   
                 I6 
                 Operation abnormality 
               
               
                   
                   
                 of bus protection 
               
               
                   
                 X40 
                 Non-correspondence to 
               
               
                   
                   
                 the position of the bus 
               
               
                   
                   
                 differential protection 
               
               
                   
                   
                 isolation switch 
               
               
                   
                 X41 
                 Mis-start of a failed 
               
               
                   
                   
                 contact 
               
               
                   
                 X42 
                 Non-correspondence of 
               
               
                   
                   
                 a buscouple 
               
               
                   
                   
                 segmentation contact 
               
               
                   
                   
               
            
           
         
       
     
     At  20 , a prior probability of the relay protection abnormality warning root node is determined. 
     For each apparatus, apparatuses with sufficiently reported historical abnormality warning information are selected from apparatuses of the same model in the same manufacturer, multiple abnormality warning events of the apparatuses and the occurrence time of multiple abnormality warning events are used as samples. Formula (1) is used to calculate a failure rate 2 of various abnormality warnings occurring in the apparatus, and formula (2) is used to calculate the occurrence probability of various abnormality warning at the present operation time of the apparatus. The occurrence probability and severity of various abnormality warnings in the 220 kV protection system are as illustrated in Table 2. For one abnormality warning that has not occurred in history, it will not appear in the Bayesian network. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                   
                   
                 Prior 
               
               
                   
                   
                   
                   
                 probability 
               
               
                   
                 Symbol 
                 Event 
                 Severity 
                 (×10-6) 
               
               
                   
                   
               
             
            
               
                   
                 X1  
                 Abnormality 
                 Moderate 
                 11.23 
               
               
                   
                   
                 of the 
                   
                   
               
               
                   
                   
                 combination 
                   
                   
               
               
                   
                   
                 unit 
                   
                   
               
               
                   
                   
                 apparatus 
                   
                   
               
               
                   
                 X2  
                 Shutting 
                 Severe 
                  0.54 
               
               
                   
                   
                 of the 
                   
                   
               
               
                   
                   
                 combination 
                   
                   
               
               
                   
                   
                 unit 
                   
                   
               
               
                   
                   
                 apparatus 
                   
                   
               
               
                   
                 X3  
                 Abnormality 
                 Moderate 
                  3.29 
               
               
                   
                   
                 warning of 
                   
                   
               
               
                   
                   
                 combination 
                   
                   
               
               
                   
                   
                 unit 
                   
                   
               
               
                   
                   
                 synchronization 
                   
                   
               
               
                   
                 X4  
                 Maintenance 
                 Moderate 
                  1.64 
               
               
                   
                   
                 status of the 
                   
                   
               
               
                   
                   
                 combination 
                   
                   
               
               
                   
                   
                 unit 
                   
                   
               
               
                   
                 X5  
                 GOOSE 
                 Moderate 
                 0   
               
               
                   
                   
                 disconnection 
                   
                   
               
               
                   
                   
                 of 
                   
                   
               
               
                   
                   
                 combination 
                   
                   
               
               
                   
                   
                 unit received 
                   
                   
               
               
                   
                   
                 intelligent 
                   
                   
               
               
                   
                   
                 terminal 
                   
                   
               
               
                   
                 X6  
                 Abnormality 
                 Moderate 
                  9.76 
               
               
                   
                   
                 of the 
                   
                   
               
               
                   
                   
                 combination 
                   
                   
               
               
                   
                   
                 unit 
                   
                   
               
               
                   
                   
                 apparatus 
                   
                   
               
               
                   
                 X7  
                 Shutting 
                 Severe 
                 0   
               
               
                   
                   
                 of the 
                   
                   
               
               
                   
                   
                 combination 
                   
                   
               
               
                   
                   
                 unit 
                   
                   
               
               
                   
                   
                 apparatus 
                   
                   
               
               
                   
                 X8  
                 Abnormality 
                 Moderate 
                  2.46 
               
               
                   
                   
                 warning of 
                   
                   
               
               
                   
                   
                 combination 
                   
                   
               
               
                   
                   
                 unit 
                   
                   
               
               
                   
                   
                 synchronization 
                   
                   
               
               
                   
                 X9  
                 Maintenance 
                 Moderate 
                  1.33 
               
               
                   
                   
                 status of the 
                   
                   
               
               
                   
                   
                 combination 
                   
                   
               
               
                   
                   
                 unit 
                   
                   
               
               
                   
                 X10 
                 GOOSE 
                 Moderate 
                  0.33 
               
               
                   
                   
                 disconnection 
                   
                   
               
               
                   
                   
                 of 
                   
                   
               
               
                   
                   
                 combination 
                   
                   
               
               
                   
                   
                 unit received 
                   
                   
               
               
                   
                   
                 intelligent 
                   
                   
               
               
                   
                   
                 terminal 
                   
                   
               
               
                   
                 X11 
                 Shutting of 
                 Severe 
                 0   
               
               
                   
                   
                 the line 
                   
                   
               
               
                   
                   
                 protection 
                   
                   
               
               
                   
                   
                 apparatus 
                   
                   
               
               
                   
                 X12 
                 Power loss 
                 Severe 
                 0   
               
               
                   
                   
                 warning of 
                   
                   
               
               
                   
                   
                 the line 
                   
                   
               
               
                   
                   
                 protection 
                   
                   
               
               
                   
                   
                 apparatus 
                   
                   
               
               
                   
                 X13 
                 SV sampling 
                 Severe 
                  0.71 
               
               
                   
                   
                 abnormality 
                   
                   
               
               
                   
                   
                 of line 
                   
                   
               
               
                   
                   
                 protection 
                   
                   
               
               
                   
                 X14 
                 SV 
                 Severe 
                  0.59 
               
               
                   
                   
                 interruption 
                   
                   
               
               
                   
                   
                 of the line 
                   
                   
               
               
                   
                   
                 protection 
                   
                   
               
               
                   
                   
                 received 
                   
                   
               
               
                   
                   
                 combination 
                   
                   
               
               
                   
                   
                 unit 
                   
                   
               
               
                   
                 X15 
                 Line 
                 Moderate 
                 0   
               
               
                   
                   
                 protection 
                   
                   
               
               
                   
                   
                 TA 
                   
                   
               
               
                   
                   
                 disconnection 
                   
                   
               
               
                   
                 X16 
                 Line 
                 Moderate 
                  1.78 
               
               
                   
                   
                 protection 
                   
                   
               
               
                   
                   
                 TV 
                   
                   
               
               
                   
                   
                 disconnection 
                   
                   
               
               
                   
                 X17 
                 GOOSE 
                 Moderate 
                 0   
               
               
                   
                   
                 interruption 
                   
                   
               
               
                   
                   
                 of line 
                   
                   
               
               
                   
                   
                 protection 
                   
                   
               
               
                   
                   
                 received 
                   
                   
               
               
                   
                   
                 intelligent 
                   
                   
               
               
                   
                   
                 terminal 
                   
                   
               
               
                   
                 X18 
                 GOOSE 
                 Moderate 
                 0   
               
               
                   
                   
                 interruption 
                   
                   
               
               
                   
                   
                 of line 
                   
                   
               
               
                   
                   
                 protection 
                   
                   
               
               
                   
                   
                 received bus 
                   
                   
               
               
                   
                   
                 differential 
                   
                   
               
               
                   
                   
                 protection 
                   
                   
               
               
                   
                 X19 
                 Line 
                 Moderate 
                  3.26 
               
               
                   
                   
                 protection 
                   
                   
               
               
                   
                   
                 channel 
                   
                   
               
               
                   
                   
                 warning 
                   
                   
               
               
                   
                 X20 
                 Turn-on and 
                 Moderate 
                  4.11 
               
               
                   
                   
                 turn-off 
                   
                   
               
               
                   
                   
                 abnormality 
                   
                   
               
               
                   
                   
                 of line 
                   
                   
               
               
                   
                   
                 protection 
                   
                   
               
               
                   
                 X21 
                 Warning of 
                 Moderate 
                  2.93 
               
               
                   
                   
                 maintenance 
                   
                   
               
               
                   
                   
                 inconsistency 
                   
                   
               
               
                   
                 X22 
                 Shutting of the 
                 Severe 
                 0   
               
               
                   
                   
                 intelligent 
                   
                   
               
               
                   
                   
                 terminal 
                   
                   
               
               
                   
                 X23 
                 GOOSE 
                 Moderate 
                 0   
               
               
                   
                   
                 disconnection 
                   
                   
               
               
                   
                   
                 of intelligent 
                   
                   
               
               
                   
                   
                 terminal xx 
                   
                   
               
               
                   
                 X24 
                 Clock 
                 Moderate 
                  1.11 
               
               
                   
                   
                 synchronization 
                   
                   
               
               
                   
                   
                 abnormality 
                   
                   
               
               
                   
                   
                 of the 
                   
                   
               
               
                   
                   
                 intelligent 
                   
                   
               
               
                   
                   
                 terminal 
                   
                   
               
               
                   
                 X25 
                 Warning of 
                 Moderate 
                 0   
               
               
                   
                   
                 maintenance 
                   
                   
               
               
                   
                   
                 inconsistency 
                   
                   
               
               
                   
                 X26 
                 Disconnection 
                 Severe 
                  0.66 
               
               
                   
                   
                 of the 
                   
                   
               
               
                   
                   
                 intelligent 
                   
                   
               
               
                   
                   
                 terminal 
                   
                   
               
               
                   
                   
                 control 
                   
                   
               
               
                   
                   
                 loop 
                   
                   
               
               
                   
                 X27 
                 Pressure 
                 Severe 
                 0   
               
               
                   
                   
                 abnormality 
                   
                   
               
               
                   
                   
                 of the 
                   
                   
               
               
                   
                   
                 circuit 
                   
                   
               
               
                   
                   
                 breaker 
                   
                   
               
               
                   
                 X28 
                 Shutting 
                 Severe 
                 0   
               
               
                   
                   
                 of the bus 
                   
                   
               
               
                   
                   
                 protection 
                   
                   
               
               
                   
                   
                 apparatus 
                   
                   
               
               
                   
                 X29 
                 Power loss 
                 Severe 
                 0   
               
               
                   
                   
                 warning 
                   
                   
               
               
                   
                   
                 of the bus 
                   
                   
               
               
                   
                   
                 protection 
                   
                   
               
               
                   
                   
                 apparatus 
                   
                   
               
               
                   
                 X30 
                 SV sampling 
                 Severe 
                  0.44 
               
               
                   
                   
                 abnormality 
                   
                   
               
               
                   
                   
                 of bus 
                   
                   
               
               
                   
                   
                 protection xx 
                   
                   
               
               
                   
                   
                 branch 
                   
                   
               
               
                   
                 X31 
                 SV interruption 
                 Severe 
                  0.26 
               
               
                   
                   
                 of bus 
                   
                   
               
               
                   
                   
                 protection xx 
                   
                   
               
               
                   
                   
                 branch 
                   
                   
               
               
                   
                 X32 
                 TA interruption 
                 Moderate 
                  0.59 
               
               
                   
                   
                 of bus 
                   
                   
               
               
                   
                   
                 protection xx 
                   
                   
               
               
                   
                   
                 branch 
                   
                   
               
               
                   
                 X33 
                 TA 
                 Moderate 
                 0   
               
               
                   
                   
                 disconnection 
                   
                   
               
               
                   
                   
                 of xx 
                   
                   
               
               
                   
                   
                 buscouple/ 
                   
                   
               
               
                   
                   
                 segmentation 
                   
                   
               
               
                   
                   
                 of bus 
                   
                   
               
               
                   
                   
                 protection 
                   
                   
               
               
                   
                 X34 
                 TV 
                 Moderate 
                 0   
               
               
                   
                   
                 disconnection 
                   
                   
               
               
                   
                   
                 of xx 
                   
                   
               
               
                   
                   
                 segment of 
                   
                   
               
               
                   
                   
                 bus of bus 
                   
                   
               
               
                   
                   
                 protection 
                   
                   
               
               
                   
                 X35 
                 GOOSE 
                 Moderate 
                 0   
               
               
                   
                   
                 interruption 
                   
                   
               
               
                   
                   
                 of bus 
                   
                   
               
               
                   
                   
                 protection 
                   
                   
               
               
                   
                   
                 received 
                   
                   
               
               
                   
                   
                 intelligent 
                   
                   
               
               
                   
                   
                 terminal 
                   
                   
               
               
                   
                 X36 
                 GOOSE 
                 Moderate 
                 0   
               
               
                   
                   
                 interruption 
                   
                   
               
               
                   
                   
                 of bus 
                   
                   
               
               
                   
                   
                 protection 
                   
                   
               
               
                   
                   
                 received 
                   
                   
               
               
                   
                   
                 line protection 
                   
                   
               
               
                   
                 X37 
                 Turn-on 
                 Moderate 
                  1.26 
               
               
                   
                   
                 and turn-off 
                   
                   
               
               
                   
                   
                 abnormality of 
                   
                   
               
               
                   
                   
                 bus protection 
                   
                   
               
               
                   
                 X38 
                 Warning of 
                 Moderate 
                  3.41 
               
               
                   
                   
                 maintenance 
                   
                   
               
               
                   
                   
                 inconsistency 
                   
                   
               
               
                   
                 X39 
                 220 kV bus 
                 Moderate 
                 0   
               
               
                   
                   
                 interconnection 
                   
                   
               
               
                   
                 X40 
                 Non- 
                 Moderate 
                 0   
               
               
                   
                   
                 correspondence 
                   
                   
               
               
                   
                   
                 to the 
                   
                   
               
               
                   
                   
                 position of the 
                   
                   
               
               
                   
                   
                 bus differential 
                   
                   
               
               
                   
                   
                 protection 
                   
                   
               
               
                   
                   
                 isolation 
                   
                   
               
               
                   
                   
                 switch 
                   
                   
               
               
                   
                 X41 
                 Mis-start of a 
                 Moderate 
                 0   
               
               
                   
                   
                 failed contact 
                   
                   
               
               
                   
                 X42 
                 Non- 
                 Moderate 
                 0   
               
               
                   
                   
                 correspondence 
                   
                   
               
               
                   
                   
                 of a buscouple 
                   
                   
               
               
                   
                   
                 segmentation 
                   
                   
               
               
                   
                   
                 contact 
               
               
                   
                   
               
            
           
         
       
     
     At  30 , the fault tree is transformed into the Bayesian network. 
     The prior probability of various statuses of the root node of the Bayesian network corresponding to the abnormality warning bottom event in the fault tree is determined according to the severity and occurrence rate of the various abnormality warnings in the apparatus, and the Bayesian network conditional probability distribution table is determined according to formulas (3)-(5). The fault tree is transformed into the Bayesian network, as illustrated in  FIG. 4 . 
     At  40 , the risk evaluation and fault positioning are performed on the relay protection system. 
     Starting from the prior probability of the root nodes (X 1 -X 42 ) of the Bayesian network, the probabilities of the intermediate nodes (I 1 -I 6 ) in the network in different statuses are calculated in turn, and the probability of the leaf node T in different statuses is obtained. The calculation results are as illustrated in Table 3. According to the calculation results, it is determined that the probability that the single set of 220 kV line protection system has severe abnormality is 3.2×10 −6 , and the probability of moderate abnormality is 47.49×10 −6 , thus realizing the risk evaluation for the relay protection system. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 Status 
                 I1 
                 I2 
                 I3 
                 I4 
                 I5 
                 I6 
                 T 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Severe 
                 0.54 
                 0 
                 1.3 
                 0.66 
                 0.7 
                 0 
                 3.2 
               
               
                 Moderate 
                 16.16 
                 13.88 
                 12.08 
                 0.11 
                 5.26 
                 0 
                 47.49 
               
               
                 Normal 
                 999,983.3 
                 999,986.12 
                 999,986.62 
                 999,999.23 
                 999,994.04 
                 1,000,000 
                 999,949.31 
               
               
                   
               
            
           
         
       
     
     At one moment, the 220 kV protection system has the serious abnormality. The probability that the numerators, that is, the root node and the leaf node, are both in a severely abnormal status in formula (7) is illustrated in Table 4. The denominator of formula (7), i.e., the probability that the system is in a severely abnormal status is 3.2×10 −6 . Based on this, the posterior probability that the root node has a severe abnormality under the condition that the leaf node has a severe abnormality may be calculated, as illustrated in Table 4. According to Table 4, the possibility of occurrence of different abnormality warnings may be determined, so as to determine an order of investigation. For abnormality warning with a moderate severity or a priori probability of 0 in Table 2, since the probability that the root node is in a severely abnormal status is 0, it does not appear in Table 4. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                 Node 
                 X2 
                 X13 
                 X14 
                 X26 
                 X30 
                 X31 
               
               
                   
               
             
            
               
                 Numerator (×10-6) 
                  0.54 
                  0.71 
                  0.59 
                  0.66 
                  0.44 
                  0.26 
               
               
                 of formula (7) 
                   
                   
                   
                   
                   
                   
               
               
                 Posterior 
                 16.9  
                 22.2  
                 18.4  
                 20.6  
                 13.8  
                 8.1 
               
               
                 probability (%) 
               
               
                   
               
            
           
         
       
     
     If a set of apparatus of the same model in the same manufacturer as the line protection apparatus of the 220 kV protection system (not the protection apparatus in this system) has had the X 11  apparatus shutting recently, the warning information will be added to the abnormality warning sample library of the apparatus of this model to correct the failure rate 2 of different abnormality warnings. The prior probability of other abnormality warnings remains unchanged. The prior probability of X 11  becomes 0.77×10 −6  after calculation. The node X 11  is added to the Bayesian network, as illustrated by the dotted line in  FIG. 4 , and the probabilities that the non-root nodes of the Bayesian network are in different statuses and the posterior probability of the root node under the condition that the system has the severe abnormality are re-calculated, and results are as illustrated in Table 5a and Table 5b. 
     
       
         
           
               
             
               
                 TABLE 5a 
               
             
            
               
                   
               
               
                 Probabilities that the non-root nodes are in different statuses in the Bayesian network (×10 −6 ) 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Status 
                 I1 
                 I2 
                 I3 
                 I4 
                 I5 
                 I6 
                 T 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Severe 
                 0.54 
                 0 
                 2.07 
                 0.66 
                 0.7 
                 0 
                 3.97 
               
               
                 Moderate 
                 16.16 
                 13.88 
                 12.08 
                 0.11 
                 5.26 
                 0 
                 47.49 
               
               
                 Normal 
                 999,983.3 
                 999,986.12 
                 999,985.85 
                 999,999.23 
                 999,994.04 
                 1,000,000 
                 999,948.54 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 5b 
               
             
            
               
                   
               
               
                 Posterior probability that the root node 
               
               
                 is in a severely abnormal state under the condition 
               
               
                 that the leaf node has the severe abnormality 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Node 
                 X2 
                 X13 
                 X14 
                 X26 
                 X30 
                 X31 
               
               
                   
               
               
                 Numerator (×10-6) 
                  0.54 
                  0.71 
                  0.59 
                  0.66 
                  0.44 
                  0.26 
               
               
                 of formula (7) 
                   
                   
                   
                   
                   
                   
               
               
                 Posterior 
                 16.9  
                 22.2  
                 18.4  
                 20.6  
                 13.8  
                 8.1 
               
               
                 probability (%) 
               
               
                   
               
            
           
         
       
     
     Before shutting warning of the line protection apparatus of the same model in the same manufacturer occurs, the priori probability of the abnormality warning of the root node X 11  is calculated to be 0, and this node is removed from the Bayesian network. After the shutting warning of the line protection apparatus occurs and is collected into the sample library, the priori probability of X 11  is re-calculated to be 0.77×10 −6 , and the root node X 11  is added into the Bayesian network again. The change in the prior probability of X 11  leads to an increase in the probability that a child node  13  of X 11  and the root node T of the Bayesian network are in a severely abnormal status. Under the condition that the leaf node has the severe abnormality, the posterior probability that a plurality of root nodes are in a severely abnormal status also changes. 
     Corresponding to the risk evaluation and fault positioning method for the relay protection system, the present disclosure further provides a risk evaluation and fault positioning apparatus  1000  for a relay protection system, as illustrated in  FIG. 5 , which includes: a fault tree construction unit  10001 , a Bayesian network construction unit  10002  and an evaluation and positioning unit  10003 . 
     The fault tree construction unit  10001  is configured to divide a plurality of fault events of the relay protection system into different hierarchy events, and construct a fault tree of the relay protection system according to the different hierarchy events. 
     The Bayesian network construction unit  10002  is configured to transform the different hierarchy events in the fault tree into different nodes of an initial Bayesian network, the different nodes including a root node, a leaf node and an intermediate node; endow each node of the initial Bayesian network with a plurality of statuses; construct a target Bayesian network according to a pre-built Bayesian network conditional probability distribution table and the plurality of statuses of each node. 
     The evaluation and positioning unit  10003  is configured to determine, according to a prior probability that a root node in the target Bayesian network is in different statuses, a probability that an intermediate node in the target Bayesian network is in different statuses and a probability that a leaf node in the target Bayesian network is in different statuses to complete risk evaluation for the relay protection system; and determine, according to a status of the leaf node in the target Bayesian network, a posterior probability of a status of the root node in the target Bayesian network by using the target Bayesian network to complete fault positioning for the relay protection system. 
     The present disclosure applies the fault tree and the Bayesian network to realize the risk evaluation and the fault positioning for the relay protection system. A multi-layer system of relay protection system faults is constructed by applying the cause analysis performance of the fault tree, with clear structure and clear relationships. By transforming the fault tree into the Bayesian network, modeling of the severity and probability of abnormal warnings is completed, and the probability that the relay protection system is abnormal is calculated by using a conditional probability distribution table and Bayesian formulas to realize the risk evaluation. Meanwhile, the posterior probability that various abnormalities occur under the fault condition that the relay protection system has different severe faults is proposed, thus realizing the fault positioning. The method provided herein may significantly improve the analysis and evaluation level of the relay protection system, and meets the present need for the risk evaluation and fault positioning method for the relay protection system. 
       FIG. 6  is a schematic structural diagram of a device provided by an embodiment of the present disclosure. As illustrated in  FIG. 6 , the device includes a processor  60  and a memory  61 . The number of the processor  60  in the device may be one or multiple. In  FIG. 6 , one processor  60  is taken as an example. The processor  60  and the memory  61  in the device may be connected through a bus or in other way. In  FIG. 6 , bus connection is taken as an example. 
     The memory  61  is used as a computer-readable storage medium that may be set to be storage software, a computer-executable program and a module, such as a program instruction/module corresponding to the risk evaluation and fault positioning method for the relay protection system in the embodiments of the present disclosure. The processor  60  executes at least one functional application and data processing of the device by running software programs, instructions, and modules stored in the memory  61 . 
     The memory  61  may mainly include a program storage region and a data storage region. In the memory  61 , the program storage region may store an operating system and an application program required by at least one function. The data storage region may store data created according to the use of a terminal, etc. In addition, the memory  61  may include a high-speed random access memory, and may further include a non-volatile memory, such as at least one magnetic disk storage device, a flash memory device, or other non-volatile solid-state storage devices. In some examples, the memory  61  may include a memory remotely provided with respect to the processor  60 , and these remote memories may be connected to the device through a network. Examples of the above network include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and combinations thereof. 
     The embodiments of the present disclosure also provide a storage medium including computer-executable instructions which, when executed by a processor of a computer, execute the method provided in any embodiment of the present disclosure. 
     The storage medium provided in the present embodiment and including the computer-executable instructions, and the computer-executable instructions are not limited to operations of the method described above, and may also perform related operations in the methods provided in any embodiment of the present disclosure. 
     The present disclosure can be implemented by means of software and general-purpose hardware, and can also be implemented by hardware. Based on this understanding, the technical solutions of the present disclosure can be embodied in the form of a software product, and the computer software product can be stored in a computer-readable storage medium, such as a computer floppy disk, a read-only memory (ROM), a random access memory (RAM), a flash memory (FLASH), a hard disk, an optical disk or the like, including multiple instructions to make a computer device (which can be a personal computer, server, network device, or the like) execute the method of any embodiment of the present disclosure.