Voltage Sags Frequency Evaluation Considering the Time-varying Interval Characteristics of Bus Voltage

Prefault voltage is one of the most important factors which affect the voltage sag assessment.However,current stochastic assessment methods usually lack consideration of the prefault voltage fluctuation.Aiming at the interval time-varying characteristic of bus voltage,a mathematical model of the prefault voltage was proposed.The mathematical model consists of voltage interval magnitude matrix and time weighted factor.For the typical characteristics of the prefault voltage,the approaches were researched in detail on the basis of interval algorithm and analytical method.The proposed method has been applied to the IEEE 30-bus reliability test system and compared with the traditional method.The results validate its correctness and practicality.The interval result quantifies the influence of different voltage curve,and the expectations of the Monte-Carlo method agrees with more accuracy,adaptation and application.