中文摘要：

城市电网中存在的某些脆弱环节对城市电网大规模停电和系统失稳的发生有重要的影响。考虑电网实时运行状态，引入衡量潮流分布不均衡程度的潮流熵概念，提出将线路潮流熵变化作为脆弱线路辨识的一个指标。基于复杂网络理论，考虑电网拓扑结构特点，建立节点重要度指标；并结合线路所在电压等级和地理位置，提出脆弱度修正因子。通过综合潮流熵变化、节点电压偏移、节点重要度和修正因子提出城市电网脆弱线路辨识的方法。以长沙城市电网2011年夏大运行方式为例进行线路脆弱性分析，并进行时域仿真验证。仿真结果表明，所提方法能较好地辨识城市电网中的脆弱线路，并与电网实际运行情况相吻合，特别是能够辨识出承担功率不多但是重要的联络线路。通过对IEEE39节点系统脆弱线路的辨识，证明了所提方法的合理性和通用性。

英文摘要：

Critical lines have serious impacts on large scaled blackouts and on cascading failures in urban power grids. Considering the state of power grids, a new concept of power flow entropy based on entropy theory was introduced to quantitatively describe the unbalanced distribution of power flow. Then the paper proposed the changing of flow entropy as a vulnerability index to see the variation of load distribution due to any lines removed. Based on the complex network theory and topological characteristics, the index of node-important was defined which is corrected by factors according to the voltage grade and location of geography. Thus, the identification of vulnerable lines includes the changing of flow entropy, voltage excursion, node-important and correcting factors. Vulnerability analysis was carried out on the Changsha urban power grid, operational plan on summer, 2011, and the time-domain simulation results verified that the index this paper proposed can identify critical lines in accordance with the real systems, especially can find which line has light loads but has great impacts on vulnerability due to their special position in the power grid. Simulation on IEEE 39-bus system proves that the proposed method is reliable.