Voltage sags frequency assessment considering the coordination of protection system

Magnitude and duration are two main features used to characterize voltage sags. Many studies have been done in analyzing the factors that only impact the magnitude of the sags. As another feature of voltage sags, the duration is determined by the coordination of protection system. The faults causing the sags are usually assumed to be cleared by the primary protection system simply, the impact of protection coordination on voltage sags duration is not considered by existing studies. In order to estimate voltage sags duration more precisely, this paper firstly uses the concept of Markov state space to establish the probabilistic modeling of protection coordination according to protection configuration, and then estimates voltage sags frequency by utilizing the protection coordination probability and setting value of protection system. In addition, the proposed method was applied to the IEEE 57-bus test system, the simulation results show that the proposed method is simple and can give more accurate answers on voltage sags frequency corresponding to different duration.