中文摘要：

详细比较了高压直流输电系统可靠性评估中常用的频率和持续时间（FD）法和故障树法，分别给出了各自的优缺点。在子系统划分的基础上分别建立各子系统的状态空间图和故障树图，并加以层层组合，得到整个直流输电系统的状态空间模型和故障树模型。分别采用FD法和故障树法对一单12脉接线高压直流输电系统进行了算例对比分析，计算的可靠性指标包括双极运行、单极停运、双极停运对应的概率、频率、平均持续时间等。

英文摘要：

A detailed comparison of frequency and duration （FD） method and fault tree method in the reliability evaluation of HVDC transmission system is presneted, and the differences between these two methods are proposed. Based on the sub - system division, the state space diagram and fault tree diagram for individual components, sub - systems and the whole HVDC transmission system are established step by step. A HVDC transmission system of single 12 -pulse is used as an example to demonstrate these two methods and the reliability indices for calculation includes the probability, the frequency, the duration and so on.