首先对电压凹陷和电压短时中断各特征量及可能的影响因素进行了分析。在此基础上，对临界距离法和故障点法这两种凹陷域的评估方法做了比较和扩充。以IEEE RBTS-6可靠性测试系统为例，分别用这两种方法加以计算，并提出将两种方法相结合的思想。最后，讨论了凹陷域的影响因素。“,”The characteristic quantities of voltage sags and temporary voltage interruptions and the factors affecting the voltage sags are analysed first.Then,a comparison between the critical distance method and the fault position method,which are two methods for the voltage sag estimation,is made and the two methods are extended.By using the two methods,the IEEE RBTS-6 reliability testing system is calculated.The idea of the two methods combination is presented.Finally,the factors affecting the voltage sag areas are discussed.