中文摘要：

电力系统的运行状态、线路与母线故障率、线路故障位置等不确定性因素对电压凹陷频次评估有重要影响。传统随机估计法分别假设电力系统运行状态、线路及母线故障率恒定，主观假设线路故障随机分布规律，不能很好地反映实际情况。综合考虑各种不确定性因素，用系统内各机组的发电计划描述系统运行状态；引入天气因子，用线路和母线的时变故障率反映其不确定性；用最大熵原理提取线路故障位置分布规律，不需任何主观假设的不足，评估结果更符合实际。考虑不同运行方式、故障类型、天气条件后，综合评估母线电压凹陷频次。假设3种不同仿真条件，对IEEE-30节点标准测试系统进行仿真分析，结果证明所得到的评估结果更符合实际，评估精度较高，具有一定的理论价值和明显的工程应用前景。

英文摘要：

There are many uncertain factors influencing the voltage sag frequency assessment at buses, such as the system operating modes, the failure rate of transmission line and buses and the fault location in transmission line. The current evaluation method usually considers that the system operating modes and the fault rate of line and bus are constant and the probability distribution rule of the fault location in transmission line is supposed. But it is not reasonable because of the uncertainty of these practical factors. Considering these influencing factors synthetically, the system operating mode is described by generator scheduling, time - yawing fault rate is considered for transmission line and bus through introducing the weather faetor in different time interval, and the probability distribution rule of fault location in line is distilled based on maximum entropy principle without any subjective assumption. In order to testify the rationality of the proposed method, the different operating modes, fault types and weather condition are considered synchronously. Three cases are used for simulation for IEEE - 30 standard testing system. The simulation results show that the results are accurate and credible, and the proposed method is with academic value and practical foreground.