Research On Identification Algorithms Of Vulnerable Lines Based On Network Structure And Power Flow Transferring

With the continuous expansion of the power grid scale,the potential safety hazards of the power system are also increasing.Ensuring the safe and stable operation of the power system is of great significance to the development of various undertakings of the nation.In recent years,some cascading outages caused by vulnerable lines threaten the safe and stable operation of power system to a certain extent.Therefore,this paper identifies the vulnerable lines based on network structure and power flow transferring,and focuses on monitoring them,which can effectively prevent the occurrence of cascading failures.Firstly,a method of identifying vulnerable lines based on improved PageRank algorithm is proposed to measure the structural vulnerability of lines.On the basis of PageRank algorithm,the algorithm is improved from three aspects: system topology,load node processing and initial value optimization,which reduces the number of iterations and accelerates the convergence speed.The new England 39-bus system is used for simulation.The algorithm is used to calculate the structural importance of the line and the identification results are obtained.Two attack modes,random interruption and key attack,are designed to compare the changes of system connectivity level under the two attack modes,and verify the structural vulnerability of the selected lines.Secondly,the branch removal vulnerability is defined to measure the line breaking vulnerability in power flow transferring.The branch distribution interruption factor is modified,and the influence of the direction of power flow transfer is taken into account.The factors that are useless to the identification process,such as the reduction of line power caused by power flow transferring,are eliminated.The branch interruption vulnerability factor is obtained,and the index of branch removal vulnerability is accumulated to reflect the comprehensive impact of power flow transferring on other lines when the line is removed.Thirdly,the transferring betweenness is proposed to reflect the line's tolerance to power flow transfer or power fluctuation.The concept of power transmission distribution factor is applied to compensate for the shortage of the index of transmission medium,and the index of transmission medium is obtained.The index is combined with branch removal vulnerability to reflect the vulnerability of power flow transferring.Two kinds of attacks are still used to attack the system.The vulnerability of power flow transferring of the selected line is verified by comparing the changes of system connectivity level and load loss percentage with the disconnected line.Finally,the selected vulnerable lines are classified,and the vulnerability of the selected lines is verified by an example analysis.The identification results of the two aspects are summarized,and the selected lines are classified to distinguish the lines with single and double vulnerabilities.Taking the new England 39-bus system as a simulation example,the structural vulnerability of the line is verified by comparing the changes of the system connectivity level with the number of disconnected lines.Meanwhile,the index of power dispersion level is defined.By comparing its variation with the number of disconnected lines,it is concluded that the line selected in this paper has higher power flow transfer vulnerability than other methods.