中文摘要：

大电力系统可靠性评估算法包括3个基本步骤：系统状态抽取、系统状态分析和系统可靠性指标的更新。其中系统状态抽取是大电力系统可靠性评估中的重要起始环节。详细讨论了大电力系统可靠性评估的4种系统状态抽取方法，即状态枚举、状态抽样、状态转移抽样和状态持续时间抽样的基本原理，分析了它们的优缺点，并用RBTS和IEEE-RTS79可靠性测试系统进行分析研究。研究结果表明，不同的系统状态抽取方法具有不同的适用范围，并对可靠性评估的计算效率有重要影响。

英文摘要：

The algorithm of the bulk power system reliability assessment comprises three basic aspects： system state selection, system state analysis and updating of reliability indices. The system state selection is an important beginning part among these three aspects. This paper discussed in detail the basic principles of four kinds of system state selection methods, that is, state enumeration, state sampling, state transition sampling and state duration sampling. The RBTS and IEEE-RTS79 power systems were evaluated to demonstrate their advantages and disadvantages. The research results show that system state selection has significant impact on the calculation efficiency of reliability evaluation and different methods of system state selection have different application scope.