Research On Identification Method Of Vulnerable Lines And Sections In Transmission Network

With the continuous expansion of power system in recent years,the power grid has to bear more potential risk of large-scale blackouts.Accident analysis shows that these largescale blackouts are often closely related to the vulnerable links in the power system,which play a key role in the generation of initial failure,the transfer of power flow and the expansion of fault range.Therefore,in order to improve the safety of power system,it’s of great importance to accurately identify the vulnerable links and conduct key monitoring.When the grid element is overloaded,searching the vulnerable sections of the overload element and performing safety analysis will help to restrain the spread of fault.Focusing on the theme of power system vulnerability,this paper studies the identification method of vulnerable lines and vulnerable sections in transmission network.In order to identify vulnerable lines,this paper takes structural vulnerability and state vulnerability as the basis of analysis.In the structural vulnerability assessment,the concept of power degree is introduced,and it is applied to the k-core decomposition of complex network to measure node importance.Then the concept of core-betweenness of the line is defined,which can reflect the importance of the line in the overall structure of the network and take electrical characteristics of the power grid into account.The rationality of structural vulnerability index is verified through the simulation of different line attack strategies for the grid.In the case of state vulnerability assessment,it is measured based on the interaction between lines during N-1 fault of the power grid.Considering that both the power grid and the Internet are typical complex networks,this paper compares the similarities between them,and the HITS algorithm for web link analysis in the Internet is applied to vulnerability assessment.Then the fault correlation network is constructed by the power flow transferring,which has considered the effects of hidden fault and power entropy meanwhile.According to the result of HITS iteration on the basis of the correlation network,the algorithm can obtain the authority and hub value of each line in the power grid,and then the state vulnerability could be evaluated comprehensively.Through the simulation of OPA cascading failure,the effectiveness of state vulnerability assessment is verified.In order to assess the vulnerability rate of the line,a fuzzy expert system is established.Considering the structural vulnerability,state vulnerability and load rate comprehensively,this paper establishes the fuzzy sets of input and output,membership functions and fuzzy rules of the system,and then the comprehensive vulnerability is analyzed by Mamdani reasoning.According to the membership degree of calculated results,the vulnerability rate is carried out,which has reference value for implementing key monitoring of vulnerable links of the power system.On the other hand,based on summarizing the concept of transmission section,the main characteristics of vulnerable section are pointed out.This paper proposes a method of subarea division to search for vulnerable sections,which takes the line vulnerability as the dominant factor.In order to follow the principle of prioritizing the vulnerable lines into regional tie lines,the power grid is partitioned based on the idea of community division of the complex network,which solves the disadvantage that traditional geographical zoning makes key lines easy to enter the region.The initial sections are obtained by cutting set search of partition graph,and then vulnerable sections can be searched after checking the power flow direction and electrical contact constraints.Simulation on IEEE39 node system verifies the effectiveness of the partition algorithm and correctness of vulnerable section searching results.Vulnerable section search can help to develop safety analysis and emergency control strategies when the power grid components are overloaded.