Study On Transmission Section Search And Control Strategy For Vulnerable Lines Against Cascading Trips

In recent years, cascading tripping accidents happened more and more frequently, the process of its occurrence is mostly like that, overload line out of operation, causing a large-scale transfer of power consequently, thus resulting in power over-limit and removal of adjacent lines, eventually leading to a large-area blackout. It can be seen that, removal of overload line and the new overload of adjacent lines, as a result of unable to absorb the transfer power, play key roles in the emergence of cascading failures. Therefore, in order to achieve prevention and control of power system cascading failure, the following three-step must be implemented: identify vulnerable line, which is easy to be overload and its removal causes widespread transfer of power, search transmission section of vulnerable lines, and make online emergency control strategy.Firstly, for the purpose of searching out fragile lines, it proposed a comprehensive vulnerability index. In the basis of analyze the sensitivity of vulnerable lines as to system disturbance and the specific effects on the remaining lines on account of transfer power when the overload line out of operation, Impact Vulnerability and Transfer Vulnerability are raised to indicate capability of resist disturbance and approximate damage to power system as a result of its removal respectively, in this way, comprehensive vulnerable index to discriminate vulnerable line is obtained.Secondly, according to the relationship of the parallel line in the aspect of power transmission distribution factors, a novel algorithm of transmission section search is proposed, which is based on power transmission distribution factors. The proposed algorithm only need calculate difference coefficient of power transmission distribution factors between vulnerable line and other lines, combine with Active Power Increase Factor, then key transmission section of vulnerable line is obtained. Algorithm is simple and effective, there is no large-scale computing, such as matrix calculation, path search. Moreover, it is able to search out the lines whose power is increase and reverse.Considering the increasing scale of the grid, a new fast algorithm for transmission section searching is presented in this paper, which is based on grid partition. The algorithm combines with GN algorithm of community structure detection in complex network. On the base of grid partition, using related knowledge of graph theory to realize transmission section search. At the same time, this paper utilizes comprehensive betweenness to ensure vulnerable lines and heavy-load lines, are interval contact lines when partitioning grid. On this account, compared to traditional network partition, the proposed algorithm is able to effectively overcome previous shortcomings, which due to ignoring vulnerability and load situation of lines. It can minimize the leaking select problems to a large extent.In terms of emergency control strategy, the multi-objective particle swarm optimization algorithm is used to make strategy about power transfer. For the purpose of overcoming deficiencies that exist in previous optimization algorithm, such as large amount of calculation and too many equipment involved in adjustment.First of all, it proposes to identify sensitive lines, which is sensitive to increased injection power of nodes. Secondly, combine sensitive lines with the redefined overload lines together to constitute key line set, as the constraint of power flow in control algorithm. What's more, through integrative sensitivity of each node to exclude some optimization variables, which play a subtle effect on the optimal control,thus it is able to make preferable choice among all control nodes participate in adjustment, in this way,it can make further reduction on amount of calculation. Finally, in order to meet the require that shed the load as little as possible, and have the minimum equipment participate in the adjustment at the same time, a multi-objective particle swarm optimization algorithm is established, making advance control of cascading tripping accidents in power system,thus realize the final step of control strategy to prevent cascading trips.Finally, IEEE39-bus system is used as a standard example, to validate and analysis both the proposed index and algorithms. The application outcome adequately shows that all proposed algorithms are capable to achieve the desire result, so that providing a novel and effective research direction of prevention the re-emergence of blackouts, ensuring safe operation of the grid.